JP4612508B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering device that reduces the steering force of a driver by directly applying electric motor power to a steering system.

  The electric power steering device assists the steering force of the driver by directly using the driving force of the electric motor. In general, an electric power steering apparatus detects a current flowing through an electric motor by an electric motor current detecting unit, and feedback-controls the electric motor based on the detected current and a target current set based on a steering torque or the like. Further, when the failure of the motor current detection means is detected, the electric power steering device corrects the target current set based on the steering torque or the like, and feed-forward-controls the motor based on the corrected target current.

  For example, Patent Document 1 by the applicant of the present application discloses an electric power steering apparatus that performs feedback control during normal operation and performs feedforward control when a motor current detector fails. The electric power steering apparatus includes an electric motor for adding an auxiliary torque to the steering system and an electric motor current detector for detecting an electric motor current that actually flows through the electric motor, and a steering torque for detecting the steering torque of the steering system. A detector is provided. The electric power steering apparatus includes a target current setting unit that sets a target current to be supplied to the electric motor based on at least the steering torque. Furthermore, the electric power steering apparatus includes a first drive control signal generation unit that generates a first drive control signal for driving and controlling the motor based on a deviation between the target current and the motor current for feedback control, For feedforward control, a second drive control signal generation unit is provided that generates a second drive control signal for driving and controlling the electric motor based on the target current. In addition, the electric power steering apparatus includes a failure detection unit that detects a failure of a detector such as an electric motor current detector. When the failure detector does not detect a failure of the electric motor current detector, the first drive control is performed. When the failure detector detects a failure of the motor current detector by switching to the signal, a motor operation control mode switching unit that switches to the second drive control signal and controls the operation of the motor is provided. That is, this electric power steering device performs feedback control based on the first drive control signal when the motor current detector is normal, and performs feedforward control based on the second drive control signal when the motor current detector fails.

  Incidentally, the electric power steering apparatus drives the motor by PWM (Pulse Width Modulation) by a bridge circuit composed of four FETs (Field Effect Transistor). The electric motors are connected in series between two FETs on opposite sides of the bridge circuit. The electric power steering device applies a motor voltage from the bridge circuit to the motor, and causes the motor current to flow to drive the motor in the normal direction or the reverse direction. This motor current also flows through the FET. Then, the electric power steering device converts the rotational torque of the electric motor into a thrust with a ball screw, acts on the rack shaft, and assists the linear movement of the rack shaft in the vehicle width direction. Note that the motor voltage is not all consumed as a motor current for rotating the motor. That is, as can be seen from the relational expression of the motor voltage, the motor current, and the rotation speed of the motor shown in Equation (1) of Equation 1, the motor voltage is only for rotating the motor (IM / RM component of Equation (1)). In addition, it is also consumed as a back electromotive force component (K · N component of equation (1)) due to rotation of the electric motor.

VM = IM · RM + K · N (1)
VM: Motor voltage IM: Motor current RM: Motor resistance value K: Induced voltage coefficient N: Motor rotation speed

In the steering system, the maximum turning angle is set so that the steered wheel does not come into contact with the tire house or the like. For this reason, the steering system is provided with stoppers on the left and right sides to restrict the movement of the rack shaft in the vehicle width direction. For example, when the driver steers the steering wheel in the right direction, in the steering system, the rack shaft linearly moves in the right direction, and the steered wheels are steered in the right direction. Further, when the driver increases the steering amount of the steering wheel, in the steering system, the rack shaft hits the stopper (hereinafter referred to as “rack abutment”), the linear movement of the rack shaft is restricted, and the steering wheel is turned. The rudder also stops.
Japanese Patent Laid-Open No. 11-49002 (FIGS. 2 and 3 etc.)

  By the way, at the time of rack abutment, the electric power steering device stops the rotation of the electric motor acting on the rack shaft by stopping the movement of the rack shaft. At that time, the rotation speed of the electric motor suddenly becomes 0, but the electric motor voltage substantially maintains the voltage value at the time of rack contact due to the control delay. Therefore, as can be seen from the above equation (1), the back electromotive force component (K · N component of equation (1)) is 0, but the motor voltage VM is almost unchanged, so the motor current IM is instantaneously excessive. (See FIG. 6). As a result, an overcurrent (for example, a current of about 120 A) flows as an instantaneous current in the FET of the bridge circuit, and the FET may be destroyed. Incidentally, the electric power steering apparatus capable of performing feedback control and feedforward control is based on the drive current controlled by the first drive control signal in the case of feedback control or the second drive control signal in the case of feedforward control. The increased current flows to the motor and FET as an instantaneous current. However, in the case of feedback control, this electric power steering device can limit the current by feedback control based on the motor current detected by the motor current detection means, so that the rate of increase of the current that is increased as the instantaneous current can be reduced. It can be kept low. Therefore, an excessive motor current as an instantaneous current does not flow through the motor, and an instantaneous current that destroys the FET does not flow through the FET. For example, in the case of feedback control, if the increase rate is increased by 20% with respect to the drive current by the first drive control signal, the instantaneous current is 100 A or less even if a drive current of 80 A is passed through the motor. However, this electric power steering device generates a second drive control signal that is larger than the target current signal in consideration of the back electromotive force component (K · N component) of Equation (1) in advance during feedforward control. . In addition, since the motor current detecting means is out of order, current limitation cannot be performed by feedback control based on the motor current, and therefore the rate of increase of current that is increased as instantaneous current cannot be kept low. Therefore, in the electric power steering device, when the back electromotive force component (K · N component of the equation (1)) becomes 0, an excessive motor current instantaneously flows due to a large motor voltage and a large increase rate, and the FET also instantaneously Overcurrent flows as current. For example, in the case of feedforward control, assuming that the increase rate is 40% of the drive current by the second drive control signal and the increment from the target current by the back electromotive force component is 20 A, a drive current of 100 A was passed through the motor. As a result, the instantaneous current is 140A. As a result, in this electric power steering apparatus, in the case of feedforward control, there is a possibility that the FET is destroyed by an excessive instantaneous current.

  Accordingly, an object of the present invention is to provide an electric power steering device that prevents the field effect transistor from being destroyed during feedforward control.

An electric power steering apparatus according to the present invention that has solved the above problems, an electric motor that adds an auxiliary steering torque to a steering system, a steering torque sensor that detects a steering torque acting on the steering system, and outputs a steering torque signal; A motor current detection unit that detects a motor current flowing through the motor and outputs a motor current signal, a failure detection unit that detects a failure of the motor current detection unit, and supplies the motor based on at least the steering torque signal A target current setting unit that sets a target current and outputs a target current signal, and generates a first drive control signal for driving the motor based on a deviation between the target current signal and the motor current signal A first drive control signal generator for outputting, and a current value corresponding to a back electromotive force of the motor in the target current of the target current signal Based on the added current value, a second drive control signal generation unit that generates and outputs a second drive control signal for driving the motor, and the failure detection unit detects that the motor current detection unit is normal. A control mode for switching to the first drive control signal when the failure detection unit detects that the motor current detection means has failed, and switching to the second drive control signal to control the motor. A switching unit, an electric motor drive unit for driving the electric motor in a normal rotation direction or a reverse rotation based on a drive control signal from the control mode switching unit, a limiting unit for limiting the maximum value of the second drive control signal, and An assist prohibiting unit that determines whether or not steering assist is prohibited based on at least the steering torque signal and determines prohibition of addition of auxiliary steering torque by the electric motor; For example, the restriction unit compares the drive current and the predetermined current of the second driving control signal, wherein when the driving current is large and outputs the predetermined current as the second driving control signal, the assist prohibition section When a failure is detected based on whether or not a failure is detected by the failure detection unit, the assist prohibition unit determines prohibition of addition of the auxiliary steering torque, and the steering torque signal for starting prohibition of the assist is determined. The addition of the auxiliary steering torque is prohibited by making the absolute value smaller than when no failure is detected .

According to this electric power steering device, even if the rotation of the motor suddenly becomes zero in the case of feedforward control, the drive current of the second drive control signal is limited to a predetermined current or less by the limiting unit. The electric current driven by the electric current flows through the maximum current limited instantaneous current. As a result, an excessively large instantaneous current that does not destroy the FET flows. The predetermined current may be the maximum value of the drive current that is set so that the instantaneous current is less than or equal to the current value that does not destroy the FET even if the drive current by the second drive control signal is increased as the instantaneous current. That's fine. In the present embodiment, the predetermined current is set to 80A. Note that limiting the maximum value of the second drive control signal means that the drive current that flows to the motor that is driven and controlled based on the second drive control signal is less than or equal to a predetermined value, and that the maximum value of the instantaneous current that flows to the motor or FET is It is to limit. The predetermined value is the maximum value of the drive current that is set so that the instantaneous current is less than or equal to the current value that does not destroy the FET even if the drive current by the second drive control signal is increased as the instantaneous current. I just need it. (For example, the maximum value of the second drive control signal is set in consideration of the rate of increase in instantaneous current so that the maximum value of the instantaneous current is less than or equal to the current value guaranteed by the FET manufacturer. ). By the way, the rate of increase when instantaneous current is generated is determined by the characteristics of the motor and the like, so it is necessary to know in advance through experiments or the like.

Alternatively, the electric power steering device detects a steering torque that acts on the steering system and outputs a steering torque signal, and an electric motor current that flows through the electric motor. A motor current detecting means for detecting and outputting a motor current signal; a fault detecting unit for detecting a fault in the motor current detecting means; and a target current to be supplied to the motor based on at least the steering torque signal; A target current setting unit that outputs a current signal, and a first drive control signal that generates and outputs a first drive control signal for driving the motor based on a deviation between the target current signal and the motor current signal And a current value obtained by adding a current value corresponding to a back electromotive force of the motor to the target current of the target current signal. A second drive control signal generation unit that generates and outputs a second drive control signal for driving the electric motor, and when the failure detection unit detects the motor current detection means as normal, A control mode switching unit that switches to the second drive control signal and controls the motor when the failure detection unit detects that the motor current detection means is failed; Based on a drive control signal from a mode switching unit, an electric motor drive unit for driving the electric motor in forward rotation or reverse rotation, a limiting unit for limiting the maximum value of the second drive control signal, and at least the steering torque signal An assist prohibiting unit that determines whether or not the steering assist is prohibited based on the motor and determines whether to prohibit the addition of the auxiliary steering torque by the electric motor. Parts, to pulse width modulation driving a field-effect transistor of the bridge circuit, comprising a pulse width modulation signal generation unit for generating and outputting a pulse width modulation signal based on the drive control signal from the control mode switching unit The limiting unit compares the duty ratio of the pulse width modulation signal with a predetermined ratio when the failure detection unit detects the motor current detection unit as a failure, and when the duty ratio is large, The predetermined ratio is output as the pulse width modulation signal, and the assist prohibition unit prohibits the assist prohibition unit from adding the auxiliary steering torque when a failure is detected based on whether or not the failure detection unit detects a failure. And adding the auxiliary steering torque by making the absolute value of the steering torque signal for starting prohibition of assist smaller than when no failure is detected. It is characterized by prohibiting. According to this electric power steering apparatus, at the time of feedforward control, the motor is PWM driven only at a duty ratio less than or equal to a predetermined ratio by the limiting unit, and therefore only the motor voltage generated at or below this predetermined ratio is applied to the motor. Therefore, in the case of feedforward control, the electric power steering device passes only a driving current equal to or less than (the motor voltage generated at a predetermined ratio / the resistance value of the motor) even if the rotation of the motor suddenly becomes zero. Therefore, only an instantaneous current whose maximum value is limited flows through the motor. As a result, an excessively large instantaneous current that does not destroy the FET flows. Note that the predetermined ratio is equal to or less than the maximum value of the drive current set so that the instantaneous current is not more than the current value that does not destroy the FET even if the drive current by the second drive control signal is increased as the instantaneous current. On the basis of the motor voltage to be set, the power supply voltage applied to the bridge circuit is taken into consideration. In this embodiment, the predetermined ratio is set to 50%, and when the power supply voltage applied to the bridge circuit is 12V, a motor voltage of a maximum of 6V is continuously applied to the motor.

Electric power steering apparatus according to claim 1 of the present invention, when the feed forward control, in consideration of the counter electromotive force caused by the rotation of the motor, adds a predetermined current value corresponding to the counter electromotive force to the target current, the Two drive control signals are generated. In the electric power steering apparatus, the steering feeling during normal steering during feedforward control is the same as the steering feeling during feedback control. In addition, since the drive current of the second drive control signal is limited to a predetermined current or less by the limiting unit, even if the rotation of the motor suddenly becomes zero in the case of feedforward control, the instantaneous current whose maximum value is limited to the motor I only flow. As a result, an excessively large instantaneous current that does not destroy the FET flows.
Further, even when the motor current detecting means fails, the prohibition of assist can be determined, and when the motor current failure means fails, the absolute value of the steering torque signal that starts prohibiting the assist To make it easier to prohibit the addition of auxiliary steering torque. For this reason, fail-and-safe can be performed more reliably.

The electric power steering apparatus according to claim 2 of the present invention adds a predetermined current value corresponding to the counter electromotive force to the target current in consideration of the counter electromotive force due to the rotation of the motor during the feedforward control, Two drive control signals are generated. In the electric power steering apparatus, the steering feeling during normal steering during feedforward control is the same as the steering feeling during feedback control. Further , since the electric motor is PWM-driven with a duty ratio less than or equal to a predetermined ratio by the limiting unit at the time of feedforward control, only the electric motor voltage generated at or below the predetermined ratio is applied to the electric motor. Therefore, in the case of feedforward control, the electric power steering device passes only a driving current equal to or less than (the motor voltage generated at a predetermined ratio / the resistance value of the motor) even if the rotation of the motor suddenly becomes zero. Therefore, only the instantaneous current limited to the maximum value flows through the motor.
As a result, an excessively large instantaneous current that does not destroy the FET flows.
Further, even when the motor current detecting means fails, the prohibition of assist can be determined, and when the motor current failure means fails, the absolute value of the steering torque signal that starts prohibiting the assist To make it easier to prohibit the addition of auxiliary steering torque. For this reason, fail-and-safe can be performed more reliably.

  The best mode for carrying out an electric power steering apparatus according to the present invention (hereinafter referred to as “embodiment”) will be described below with reference to the drawings.

  In the electric power steering apparatus according to the present invention, by limiting the maximum value of the second drive control signal by the limiting unit, the rotation of the motor suddenly becomes 0 during the feedforward control, and instantaneously depends on the second drive control signal. Even if the drive current increases, the maximum value of this instantaneous current can be limited. Therefore, an instantaneous current whose maximum value is limited by the drive current limited to the maximum value or less flows in all the FETs of the bridge circuit that drives the electric motor. In the present invention, the means for limiting the maximum value of the second drive control signal is used to set the drive current of the second drive control signal to a predetermined current or less or the PWM signal generated based on the second drive control signal. There is no particular limitation such as setting the duty ratio to a predetermined ratio or less.

  The electric power steering apparatus according to the present embodiment includes a feedback control unit that generates a first drive control signal and a feedforward control unit that generates a second drive control signal. The two drive control signals are switched by the control mode switching unit to control the electric motor. In the electric power steering apparatus, the PWM signal generation unit generates an electric motor control signal based on the first drive control signal or the second drive control signal, and PWM drives the electric motor by a bridge circuit based on the electric motor control signal. . In the present embodiment, the limiting unit according to the present invention is arranged downstream of the feedforward control unit, and the driving current of the second drive control signal is set to a predetermined current or less, and the limiting according to the present invention. A second embodiment will be described in which a part is arranged at the subsequent stage of the PWM signal generation unit so that the duty ratio of the PWM signal is not more than a predetermined ratio.

  First, the overall configuration of the electric power steering apparatus 1 will be described with reference to FIG.

  The electric power steering device 1 is provided in a steering system S from the steering wheel 3 to the steering wheels W and W, and assists the steering force by the manual steering force generation means 2. For this purpose, the electric power steering apparatus 1 generates an electric motor voltage VM by the control apparatus 20 and drives the electric motor 8 by the electric motor voltage VM to generate an auxiliary steering torque (auxiliary steering force). Reduces the manual steering force caused by. In the present embodiment, the electric motor 8 corresponds to the electric motor described in the claims.

  In the manual steering force generating means 2, a pinion 7 a of a rack and pinion mechanism 7 provided in the steering gear box 6 is connected to a steering shaft 4 provided integrally with the steering wheel 3 via a connecting shaft 5. The connecting shaft 5 includes universal joints 5a and 5b at both ends. In the rack and pinion mechanism 7, rack teeth 7b that mesh with the pinion 7a are formed on the rack shaft 9, and the rotation of the pinion 7a is caused in the lateral direction (vehicle width direction) of the rack shaft 9 by meshing the pinion 7a and the rack teeth 7b. Reciprocating motion. Furthermore, left and right front wheels W, W as steering wheels are coupled to the rack shaft 9 via tie rods 10, 10 at both ends thereof. The manual steering force generating means 2 includes stoppers (not shown) for restricting the movement of the rack shaft 9 on the left and right sides in order to define the maximum turning angle of the steered wheels W, W.

  In the electric power steering apparatus 1, the electric motor 8 is disposed coaxially with the rack shaft 9 in order to generate an auxiliary steering force (auxiliary torque). Then, the electric power steering apparatus 1 converts the rotation of the electric motor 8 into a thrust through a ball screw mechanism 11 provided coaxially with the rack shaft 9, and this thrust is applied to the rack shaft 9 (ball screw shaft 11a). . Incidentally, when the movement of the rack shaft 9 is restricted by the stopper (not shown), the rotation of the electric motor 8 is stopped.

  The control device 20 receives the detection signals V, T, IMO, and VMO from the vehicle speed sensor VS, the steering torque sensor TS, the motor current detection means 21, and the motor voltage detection means 22. Then, the control device 20 determines the magnitude and direction of the motor current IM that flows to the motor 8 based on the detection signals V, T, IMO, and VMO for feedback control, and sends a first drive control signal to the control mode switching unit 38. C1 is output (see FIGS. 2 and 5). Further, the control device 20 determines the magnitude and direction of the motor current IM that flows to the motor 8 based on the detection signals V and T for feedforward control, and outputs the second drive control signal C2 to the control mode switching unit 38. (See FIGS. 2 and 5). Then, the control device 20 switches the first drive control signal C1 and the second drive control signal C2 by the control mode switching unit 38 based on whether the motor current detection means 21 is abnormal / normal, and the drive control signals C1 and C2 Based on this, the motor voltage VM is applied from the motor drive unit 40 to the motor 8 (see FIGS. 2 and 5). In the present embodiment, the steering torque sensor TS corresponds to the steering torque sensor described in the claims, and the motor current detection means 21 corresponds to the motor current detection means described in the claims.

The control device 20A of the first embodiment, a drive current limiting unit 37 in the subsequent stage of the feedforward control unit 36, a predetermined current MI driving current of the second driving control signal C2 in the drive current limit unit 37 The maximum value of the instantaneous current when the rotation of the electric motor suddenly becomes 0 is limited (see FIG. 2). Further, the control device 20B of the second embodiment includes a duty ratio limiting unit 44 subsequent to the PWM signal generating unit 41, and when the motor current detection means 21 is out of order, the duty ratio limiting unit 44 performs the duty of the PWM signal. The ratio is limited to a predetermined ratio MD or less, and the maximum value of the instantaneous current when the rotation of the motor suddenly becomes 0 is limited (see FIG. 5).

  The vehicle speed sensor VS detects the vehicle speed as the number of pulses per unit time, and transmits an analog electric signal corresponding to the detected number of pulses as the vehicle speed signal V to the control device 20. The vehicle speed sensor VS is not provided only for transmitting the vehicle speed signal V to the electric power steering apparatus 1, but also transmits the vehicle speed signal V to other systems.

  The steering torque sensor TS is disposed in the steering gear box 6 and detects the magnitude and direction of the manual steering torque by the driver. Then, the steering torque sensor TS transmits an analog electric signal corresponding to the detected manual steering torque to the control device 20 as the steering torque signal T. The steering torque signal T includes information on the steering torque indicating the magnitude and the torque direction indicating the direction of the torque. The torque direction is represented by a plus value / minus value of the steering torque. The negative value indicates that the steering torque direction is the left direction.

  The motor current detection means 21 includes a resistor or a Hall element connected in series with the motor 8 and detects the magnitude and direction of the motor current IM that actually flows through the motor 8. Then, the motor current detection means 21 feeds back (negative feedback) the motor current signal IMO corresponding to the motor current IM to the control device 20.

  The motor voltage detection means 22 detects the voltages at both ends of the motor 8, and detects the magnitude and direction of the motor voltage VM that is actually applied to the motor 8. The motor voltage detection means 22 transmits a motor voltage signal VMO corresponding to the motor voltage VM to the control device 20.

Next, the control device 20A according to the first embodiment will be described with reference to FIG. The control device 20A includes an electric motor speed calculation unit 30, a sensor abnormality detection unit 31, an abnormality display unit 32, a steering torque correction unit 33, a target current setting unit 34, a feedback control unit 35, a feedforward control unit 36, and a drive current limiting unit 37. The control mode switching unit 38, the assist prohibiting unit 39, and the motor driving unit 40 are configured. The electric motor drive unit 40 includes a PWM signal generation unit 41, a gate drive circuit unit 42, and an electric motor drive circuit 43. The control device 20A includes at least two CPUs (Central Processing Units) that perform various operations and processes, and further includes an input signal conversion unit, a signal generation unit, a storage unit, a power supply circuit, an electric motor drive circuit, and the like. In the present embodiment, the sensor abnormality detection unit 31 corresponds to the failure detection unit described in the claims, the target current setting unit 34 corresponds to the target current setting unit described in the claims, and feedback. The controller 35 corresponds to the first drive control signal generator described in the claims, the feedforward controller 36 corresponds to the second drive control signal generator described in the claims, and the drive current limiter 37 corresponds to the limiting unit described in claim 1 of the claims, the control mode switching unit 38 corresponds to the control mode switching unit described in the claims, and the motor drive unit 40 corresponds to the claims. It corresponds to the motor drive section described.

  The motor speed calculation unit 30 receives the motor current signal IMO from the motor current detection means 21 and the motor voltage signal VMO from the motor voltage detection means 22, calculates the actual rotation speed of the motor 8, and outputs the motor rotation speed signal RS. Is output to the sensor abnormality detection unit 31 and the like. The motor speed calculation unit 30 calculates the rotation speed of the motor from the motor current signal IMO and the motor voltage signal VMO based on the above equation (1) (note that the resistance value and the induced voltage coefficient of the motor are constants). . Incidentally, although the motor rotation speed signal RS is used for damping correction when correcting the target current, the detailed description thereof is omitted in the present embodiment.

  The sensor abnormality detector 31 includes a vehicle speed signal V from the vehicle speed sensor VS, a motor current signal IMO from the motor current detector 21, a motor voltage signal VMO from the motor voltage detector 22, and a motor rotation speed from the motor speed calculator 30. When the signal RS is input, the abnormal signal SA is output to the control mode switching unit 38 and the assist prohibiting unit 39, and the abnormal sensor type information SS is output to the target current setting unit 34 and the abnormal display unit 32. The sensor abnormality detection unit 31 monitors the vehicle speed signal V, the electric motor current signal IMO, the electric motor voltage signal VMO, the electric motor rotation speed signal RS, and the like, and if the signal exceeds the preset signal value range for each signal, When it is not detected or when the signal change is not normal, the operation of each sensor is determined to be abnormal. Then, the sensor abnormality detection unit 31 determines abnormality / normality of the motor current detection means 21 from the motor current signal IMO, and outputs an abnormality signal SA. The abnormality signal SA is set to 1 as the logic level when the motor current detection means 21 is abnormal, and is set to 0 as the logic level when it is normal. Further, the sensor abnormality detection unit 31 determines abnormality / normality of the vehicle speed sensor VS, the detection means 21 and 22 and the motor speed calculation unit 30 from each signal, and outputs abnormality sensor type information SS. In the abnormal sensor type information SS, logical levels are respectively set for the vehicle speed sensor VS, each of the detection means 21 and 22, and the motor speed calculation unit 30, and 1 is set for each logical level when abnormal, and 0 is set when normal. The The sensor abnormality detection unit 31 stores the abnormality signal SA and the abnormality sensor type information SS in a nonvolatile memory (not shown), and the abnormality signal SA and the abnormality sensor type information SS even when the control device 20A is restarted. Holding.

  The abnormality display unit 32 receives the abnormal sensor type information SS from the sensor abnormality detection unit 31, and outputs a sensor abnormality signal to a visual display (not shown) or an audible output device (not shown) provided on the vehicle. Output. This sensor abnormality signal is displayed as abnormal information for each sensor when the visual indicator or audible output device can output the abnormality / normality of each sensor individually based on the abnormal sensor type information SS. If the output device or the audible output device outputs abnormality / normality of the electric power steering apparatus 1, the abnormality information of the electric power steering apparatus 1 is used.

  The steering torque correction unit 33 receives the steering torque signal T from the steering torque sensor TS, and outputs a correction steering torque signal TH to the target current setting unit 34. For this purpose, the steering torque correcting unit 33 includes a proportional unit 33a, a differentiating unit 33b, and an adding unit 33c. The proportional unit 33a multiplies the steering torque signal T by a coefficient in order to linearly represent the change in the steering torque signal T, and outputs the result to the adding unit 33c as a proportional term. In order to improve the responsiveness of the steering torque signal T, the differentiating unit 33b performs time differentiation on the steering torque signal T and outputs it to the adding unit 33c as a differential term. Incidentally, when the driver is operating the steering wheel 3 in the right direction, the differential term becomes a positive value when the driver's operating torque is strengthened, becomes zero when the steering torque is constant, and the steering torque becomes weaker. When it is set, it becomes a negative value. Further, when the driver is operating the steering wheel 3 in the left direction, the differential term becomes a negative value when the driver's operating torque is strengthened, becomes zero when the steering torque is constant, and weakens the steering torque. It is a positive value when The adding unit 33c adds the proportional term from the proportional unit 33a and the differential term from the differentiating unit 33b, and outputs the result as a corrected steering torque signal TH. The corrected steering torque signal TH includes information on the corrected steering torque indicating the magnitude and the torque direction indicating the direction of the torque. The torque direction is expressed by a plus / minus value of the corrected steering torque, and the plus value is corrected steering. The torque direction is the right direction, and a negative value indicates the corrected steering torque direction is the left direction. Incidentally, if necessary, an integral unit may be provided to calculate the integral term of the steering torque signal T, and the integral term may be added by the adder 33c.

  The target current setting unit 34 receives the corrected steering torque signal TH from the steering torque correction unit 33, the vehicle speed signal V from the vehicle speed sensor VS, and the abnormal sensor type information SS from the sensor abnormality detection unit 31, and the feedback control unit 35 The target current signal IT is output to the feedforward control unit 36. The target current signal IT includes a target current indicating the magnitude of the current desired to flow through the motor 8 and current direction information indicating the direction of the current desired to flow through the motor 8. The current direction is a plus / minus value of the target current. A positive value indicates that the assist direction is in the right direction, and a negative value indicates that the assist direction is in the left direction. The target current setting unit 34 includes storage means such as a ROM (Read Only Memory), and stores data corresponding to the corrected steering torque signal TH, the vehicle speed signal V, and the target current signal IT set in advance based on experimental values or design values. I remember it. Then, when the vehicle speed sensor VS is normal in the abnormal sensor type information SS, the target current setting unit 34 reads the corresponding target current signal IT using the corrected steering torque signal TH and the vehicle speed signal V as addresses. FIG. 3 shows an example of a correction steering torque signal and vehicle speed signal-target current signal conversion table. As shown in FIG. 3, the target current signal IT is associated with 0 when the corrected steering torque signal TH is close to 0, and increases as the corrected steering torque signal TH increases when the corrected steering torque signal TH exceeds a predetermined corrected steering torque signal (absolute value). Is associated with the value to be Further, the inclination of the target current signal IT with respect to the corrected steering torque signal TH varies depending on the vehicle speed signal V. The inclination is associated with a large value (absolute value) in the case of a low speed with a large road reaction force, and a small value (in the case of a high speed) with respect to the vehicle speed signal V. (Absolute value) is associated. That is, as the vehicle speed increases, the increment (absolute value) of the target current signal IT with respect to the corrected steering torque signal TH decreases. The target current signal IT is set to be equal to or less than the maximum target current because the maximum current that can be passed through the power FETs 43a to 43d of the electric motor 8 and the bridge circuit 43 is defined.

  In addition, when the vehicle speed sensor VS is abnormal in the abnormal sensor type information SS, the target current setting unit 34 responds with the vehicle speed signal V as the maximum vehicle speed and the corrected steering torque signal TH and the vehicle speed signal V as addresses from a fail-and-safe viewpoint. The target current signal IT to be read is read. That is, the vehicle speed is set to the maximum vehicle speed, the target current signal IT is reduced, the auxiliary steering torque is reduced from the normal time, and the driver is made aware of the abnormality of the electric power steering device 1.

  The feedback control unit 35 receives the target current signal IT from the target current setting unit 34 and the motor current signal IMO from the motor current detection means 21 and outputs the first drive control signal C1 to the control mode switching unit 38. The feedback control unit 35 generates a first drive control signal C1 that is PID (Proportional Integral Differential) controlled so that the deviation between the target current signal IT and the motor current signal IMO approaches zero. For this purpose, the feedback controller 35 includes a deviation calculator 35a and a PID controller 35b. The deviation calculator 35a has a subtractor or a soft control subtraction function, and subtracts the motor current signal IMO from the target current signal IT to calculate a deviation signal ΔIM (= IT−IMO). The PID control unit 35b performs P (proportional), I (integral) and D (differential) control on the deviation signal ΔIM from the deviation calculating unit 35a, and supplies the deviation signal ΔIM to 0 so that the deviation signal ΔIM approaches zero. A first drive control signal C1 for controlling the current is generated. The first drive control signal C1 includes a drive current indicating the magnitude of the current supplied to the electric motor 8 and current direction information indicating the direction of the current supplied to the electric motor 8, and the current direction is a plus value / It is represented by a negative value, with a positive value indicating that the assist direction is rightward and a negative value is indicating that the assist direction is leftward.

The feedforward control unit 36 receives the target current signal IT from the target current setting unit 34 and outputs the second drive control signal C2 to the drive current limiting unit 37. The feedforward control unit 36 takes into account the consumption of the motor voltage VM due to the back electromotive force component (K · N component of the equation (1)) due to the rotation of the electric motor 8 shown in the above equation (1). A larger value is generated as the second drive control signal C2. That is, when the target current signal IT is used as it is as the second drive control signal C2, a counter electromotive force is generated by the rotation of the motor 8, so that the motor current IM flowing through the motor 8 is smaller than the target current signal IT. Therefore, in consideration of the counter electromotive force due to the rotation of the electric motor 8, a predetermined current value corresponding to the counter electromotive force is added to the target current signal IT to generate the second drive control signal C2. For this purpose, the feedforward control unit 36 includes a back electromotive force setting unit 36a and an addition unit 36b. Counter electromotive force setting unit 36a includes a storage means such as a ROM, and outputs the Oh RugyakuOkoshi power current CC to the adder 36b with a predetermined current value. The back electromotive force current CC is determined in consideration of the characteristics of the electric motor 8 and the like. The adder 36b includes an adder or a soft control addition function, and adds the back electromotive force current CC to the target current of the target current signal IT to generate the second drive control signal C2. The second drive control signal C2 includes a drive current indicating the magnitude of the current supplied to the electric motor 8 and current direction information indicating the direction of the current supplied to the electric motor 8. The current direction is a plus value / It is represented by a negative value, with a positive value indicating that the assist direction is rightward and a negative value is indicating that the assist direction is leftward.

  The drive current limiting unit 37 receives the second drive control signal C2 from the feedforward control unit 36, and the second drive control in which the control mode switching unit 38 limits the drive current of the second drive control signal C2 to the maximum value. The signal C2 is output. The drive current limiting unit 37 causes the motor drive circuit 43 to increase instantaneously when the rotation of the motor suddenly becomes zero during feedforward control where control based on the motor current signal IMO cannot be performed, and the drive current generated by the second drive control signal C2 increases instantaneously. In order to prevent an excessive current that destroys the power FETs 43a to 43d from flowing through the power FETs 43a to 43d as an instantaneous current, the drive current of the second drive control signal C2 is set to a predetermined current MI or less. That is, when the rotation of the electric motor 8 stops suddenly at the time of rack contact or the like, the rotation speed of the electric motor 8 becomes zero. However, in the case of the feed forward control, the first output from the feed forward control unit 36 due to the influence of the control delay. The electric motor voltage VM based on the drive current of the 2 drive control signal C2 is maintained at the voltage value at the time of rack contact. Therefore, as can be seen from the above equation (1), the motor current IM becomes instantaneously excessive. Since an excessive current (120 A or more) flows as an instantaneous current also in the power FETs 43a to 43d, the power FETs 43a to 43d may be destroyed. Therefore, the drive current of the second drive control signal C2 is always set to the predetermined current MI or less, and the maximum value of the instantaneous current flowing through the power FETs 43a to 43d is limited. The predetermined current MI is set as the maximum value of the drive current that is set so that the instantaneous current is less than or equal to the current value that does not absolutely destroy the power FETs 43a to 43d due to the characteristics of the power FETs 43a to 43d. 80A. Incidentally, the predetermined current MI grasps how much the drive current of the second drive control signal C2 increases when the rotation speed of the electric motor 8 suddenly becomes 0, and this increase rate and It is set in consideration of the current value that destroys the power FETs 43a to 43d. The predetermined current MI is also a current value that does not cause any abnormality in the electric motor 8. In addition, since the steering torque by the driver is reduced by rack abutting with the lapse of time after the rack abutment, the target current of the target current signal IT becomes small and the drive current of the second drive control signal C2 is also small. Therefore, the motor voltage VM is also reduced.

  Therefore, the drive current limiting unit 37 includes a predetermined current setting unit 37a and a drive current comparison unit 37b. The predetermined current setting unit 37a includes storage means such as a ROM, and outputs a predetermined current MI to the drive current comparison unit 37b. The drive current comparison unit 37b compares the predetermined current MI with the drive current of the second drive control signal C2 from the feedforward control unit 36. Then, when the drive current of the second drive control signal C2 from the feedforward control unit 36 is larger than the predetermined current MI, the drive current comparison unit 37b generates the second drive control signal C2 using the predetermined current MI as the drive current. And output to the control mode switching unit 38. On the other hand, when the drive current of the second drive control signal C2 from the feedforward control unit 36 is equal to or less than the predetermined current MI, the drive current comparison unit 37b receives the second drive control signal C2 from the feedforward control unit 36 as it is. The data is output to the control mode switching unit 38.

  The control mode switching unit 38 receives the first drive control signal C1 from the feedback control unit 35, the second drive control signal C2 from the drive current limiting unit 37, and the abnormality signal SA from the sensor abnormality detection unit 31, and drives the motor. The drive control signal CS is output to the PWM signal generation unit 41 of the unit 40. The control mode switching unit 38 switches the control of the motor 8 to feedback control when the motor current detection means 21 is normal, and to feedforward control when the motor current detection means 21 is abnormal. Therefore, when the logic level of the abnormal signal SA is 0, the control mode switching unit 38 uses the first drive control signal C1 from the feedback control unit 35 as the drive control signal CS, and the logic level of the abnormal signal SA is 1. In this case, the second drive control signal C2 from the drive current limiting unit 37 is used as the drive control signal CS, and the drive control signal CS is output to the PWM signal generating unit 41. The drive control signal CS includes a drive current indicating the magnitude of the current supplied to the electric motor 8 and current direction information indicating the direction of the current supplied to the electric motor 8, and the current direction is expressed by a plus / minus value of the drive current. In the plus value, the assist direction is the right direction, and in the negative value, the assist direction is the left direction.

  The assist prohibition unit 39 includes a steering torque signal T from the steering torque sensor TS, an electric motor current signal IMO from the electric motor current detection means 21, an abnormal signal SA from the sensor abnormality detection unit 31, and a drive control signal from the control mode switching unit 38. CS is input, and an assist prohibit signal SB is output to the gate drive circuit unit 42. The assist prohibition unit 39 monitors whether or not the main CPU of the control device 20A is operating normally. When the motor current detecting means 21 is normal, the relationship between the steering torque signal T and the motor current signal IMO. The relationship between the steering torque signal T and the drive control signal CS is determined. When the motor current detection means 21 is abnormal, the relationship between the steering torque signal T and the drive control signal CS is determined. The assist prohibition unit 39 is controlled by a CPU different from the main CPU of the control device 20A. When the abnormal signal SA is 0 (the motor current detection means 21 is normal), the assist prohibition unit 39 displays a map M1 (see FIG. 4A) and a map M2 (see FIG. 4B). Based on the map M3 (see FIG. 4 (c)), the assist prohibition determination is made when the assist prohibition determination is made based on the abnormal signal SA of 1 (the motor current detection means 21 is abnormal).

  First, the case where the motor current detection means 21 is normal will be described. The assist prohibition unit 39 includes storage means such as a ROM, and a map M1 indicating the relationship between the steering torque signal T and the motor current signal IMO set in advance based on experimental values or design values (see FIG. 4A). In addition, a map M2 (see FIG. 4B) showing the relationship between the steering torque signal T and the drive control signal CS is stored. In the map M1, the horizontal axis represents the steering torque signal T, and the vertical axis represents the motor current signal IMO. The plus region of the steering torque signal T (the right region of the origin (0) of the horizontal axis) corresponds to the case where the manual steering torque in the right turn direction is input to the steering wheel 3, and the minus region (horizontal side of the steering torque signal T) The left region of the axis origin (0) corresponds to the case where a manual steering torque in the left turning direction is input to the steering wheel 3. The plus region of motor current signal IMO (upper region of origin (0) on the vertical axis) corresponds to the case where current in the right-turn direction flows through motor 8, and the negative region of motor current signal IMO (the origin of vertical axis) The lower region (0) corresponds to the case where a current in the left turn direction flows through the electric motor 8. The assist prohibition areas M1a, M1a and M1b, M1b of the map M1 are areas where the motor current signal IMO is undesirable with respect to the steering torque signal T, and are areas where the main CPU of the control device 20A can be determined to be abnormal. . Note that the assist prohibition areas M1a and M1a are conditions that can be satisfied during actual traveling in consideration of damping control and inertia control for the motor 8. Therefore, even if this area is less than 100 mS, assistance is provided. This is a region that is not prohibited (that is, assistance is prohibited if the assist prohibited regions M1a and M1a enter 100 mS or more). Further, the assist prohibition areas M1b and M1b are areas that cannot be entered even if damping control or inertia control is taken into consideration. In the map M2, the horizontal axis represents the steering torque signal T, and the vertical axis represents the drive control signal CS. The plus region of the steering torque signal T (the right region of the origin (0) of the horizontal axis) corresponds to the case where the manual steering torque in the right turn direction is input to the steering wheel 3, and the minus region (horizontal side of the steering torque signal T) The left region of the axis origin (0) corresponds to the case where a manual steering torque in the left turning direction is input to the steering wheel 3. Further, the plus region of the drive control signal CS (the upper region of the origin (0) on the vertical axis) corresponds to the case where the electric motor 8 outputs the torque in the right turn direction, and the negative region (the vertical axis of the drive control signal CS). The lower area of the origin (0) corresponds to the case where the electric motor 8 outputs torque in the left turn direction. The assist prohibition regions M2a and M2a of the map M2 are regions where the drive control signal CS is undesirable with respect to the steering torque signal T, and are regions where the main CPU of the control device 20A can be determined to be abnormal. Therefore, the assist prohibition unit 39 searches the map M1 and the map M2, and the relationship between the steering torque signal T and the motor current signal IMO is 100 mS or more in the assist prohibition regions M1a and M1a of the map M1, and the assist prohibition region of the map M1. When the area of M1b, M1b is 1 mS or more, or when the relationship between the steering torque signal T and the drive control signal CS is in the area of the assist prohibition areas M2a, M2a of the map M2, 1 is set as the logic level of the assist prohibition signal SB. In other cases, 0 is set as the logic level of the assist prohibition signal SB, and it is output to the gate drive circuit unit 42. The setting of the logic level of the assist prohibition signal SB is not limited to the above setting, and is set according to the configuration of the logic circuit of the gate drive circuit unit 42 and the like. Incidentally, the determination conditions based on the map M1 and the map M2 are stricter than the determination conditions based on the map M1, and when the motor current detection means 21 is normal, the assist is prohibited under the determination conditions of the map M1.

  Next, the case where the motor current detection means 21 is abnormal will be described. When the motor current detection means 21 is abnormal, the determination condition in the map M1 based on the motor current signal IMO cannot be used. Therefore, assist prohibition determination is performed using a map M3 (see FIG. 4C) in which the determination condition of the map M2 based on the drive control signal CS is strict. When the main CPU of the control device 20A is normal, normally, the drive control signal CS has a current corresponding to the current supplied to the motor 8 in order to assist in the same direction as the direction in which the manual steering torque is applied. The direction to which manual steering torque is added is set as the direction. For example, when the driver operates the steering wheel 3 in the right direction, the drive control signal CS is set with a current direction indicating the direction of the current supplied to the electric motor 8 for generating the auxiliary steering torque in the right direction. However, even when the main CPU of the control device 20A is normal, the drive control is performed in order to assist in the opposite direction to the direction in which the manual steering torque is applied by the action of the differentiation unit 33b of the steering torque correction unit 33. In the signal CS, the current direction with respect to the current supplied to the electric motor 8 may be set in the opposite direction to the normal time. For example, when the driver operates the steering wheel 3 in the right direction but weakens the manual steering torque, the differential term by the differential unit 33b becomes a negative value, and the magnitude of the steering torque in the corrected steering torque signal TH is It may be negative (leftward). At that time, although the direction of the steering torque signal T is rightward, the current direction of the drive control signal CS with respect to the current supplied to the motor 8 is leftward (see point a in FIG. 4C). However, when the main CPU of the control device 20A is abnormal, the current direction and the drive current of the drive control signal CS set based on the steering torque signal T are clearly abnormal values ((c in FIG. 4). ) Refer to point b in the figure). Therefore, the assist prohibition unit 39 includes storage means such as a ROM, and a map M3 (a diagram (c) in FIG. 4) showing a relationship between the steering torque signal T and the drive control signal CS set in advance based on experimental values or design values. Reference) is stored. In the map M3, instead of the assist prohibition areas M2a and M2a of the map M2, areas M3a and M3a are set as assist prohibition areas. The assist prohibition areas M3a and M3a are areas where the drive control signal CS is undesirable with respect to the steering torque signal T, and are areas where the main CPU of the control device 20A can be determined to be abnormal. The assist prohibition areas M3a and M3a prohibit the assist from the steering torque signals T3 and -T3 whose absolute values are smaller than the steering torque signals T2 and -T2 which start prohibition of the assist prohibition areas M2a and M2a of the map M2. (That is, the map M3 is a stricter determination condition than the determination condition of the map M2). Therefore, the assist prohibition unit 39 searches the map M3, and when the relationship between the steering torque signal T and the drive control signal CS is in the assist prohibition regions M3a and M3a of the map M3, the assist prohibition signal SB is set as the logic level of the assist prohibition signal SB. When 1 is set and the area other than the assist prohibition areas Ma and Ma is set, 0 is set as the logic level of the assist prohibition signal SB and the logic level is output to the gate drive circuit unit 42. The setting of the logic level of the assist prohibition signal SB is not limited to the above setting, and is set according to the configuration of the logic circuit of the gate drive circuit unit 42 and the like.

  The PWM signal generation unit 41 receives the drive control signal CS from the control mode switching unit 38 and outputs an electric motor control signal MS to the gate drive circuit unit 42. The PWM signal generation unit 41 generates a PWM signal, an on signal, and an off signal corresponding to the direction and current value of the motor current supplied to the motor 8 based on the drive control signal CS. The PWM signal is input to the gate G1 of the power FET 43a or the gate G2 of the power FET 43b of the motor drive circuit 43, and is a signal for PWM driving the power FET 43a or the power FET 43b according to the magnitude of the drive current of the drive control signal CS. Note that whether the PWM signal is input to the gate G1 or the gate G2 depends on the polarity (current direction) of the drive current of the drive control signal CS. When a PWM signal is input to the gate G1, an on signal is input to the gate G4 of the power FET 43d, and the power FET 43d is turned on. On the other hand, when a PWM signal is input to the gate G2, an ON signal is input to the gate G3 of the power FET 43c, and the power FET 43c is driven ON. Further, an OFF signal is input to the gate to which no PWM signal is input, of the gate G1 or the gate G2, and the power FET 43a or the power FET 43b is turned OFF. At this time, when an off signal is input to the gate G1, an off signal is also input to the gate G4 of the power FET 43d, and the power FET 43d is also turned off. On the other hand, when an off signal is input to the gate G2, an off signal is also input to the gate G3 of the power FET 43c, and the power FET 43c is also turned off. The motor control signal MS is composed of a PWM signal output to the gates G1 to G4, an ON signal, and an OFF signal, and is logically determined by the gate drive circuit unit 42.

  The gate drive circuit unit 42 receives the motor control signal MS from the PWM signal generation unit 41 and the assist prohibition signal SB from the assist prohibition unit 39, and controls the motor to drive the gates G1 to G4 of the motor drive circuit 43. The signal MS is output. The gate drive circuit unit 42 prohibits the generation of the auxiliary steering torque by the electric motor 8 when the logic level of the assist prohibition signal SB is 1. That is, the gate drive circuit unit 42 prohibits the assist by the electric motor 8 when the main CPU of the control device 20A is abnormal. For this purpose, the gate drive circuit unit 42 includes a logic circuit including four NOT circuits and four AND circuits (not shown). Then, the gate drive circuit unit 42 inverts and outputs the assist prohibition signal SB to each of four AND circuits using four NOT circuits. Further, the gate drive circuit unit 42 receives the signals of the motor control signal MS for the gates G1 to G4 of the motor drive circuit 43 and the inverted outputs of the NOT circuit, respectively, in the four AND circuits, and drives the motor from the four AND circuits. The motor control signal MS is output to the gates G1 to G4 of the circuit 43. The gate drive circuit unit 42 outputs all off signals as the motor control signal MS when the assist prohibition signal SB has a logic level of 1, and outputs a PWM signal as the motor control signal MS when the assist prohibition signal SB has a logic level of 0. The motor control signal MS from the generation unit 41 is output as it is.

  The motor drive circuit 43 receives the motor control signal MS logically determined from the gate drive circuit unit 42, applies the motor voltage VM to the motor 8 based on the motor control signal MS, and outputs the motor current IM to the motor 8. To do. The motor drive circuit 43 is configured by a bridge circuit including switching elements of four power FETs 43a, 43b, 43c, and 43d, and a voltage of 12 V is supplied from the power supply voltage. Further, in the motor drive circuit 43, the motor 8 is connected in series between the power FET 43a and the power FET 43d and in series between the power FET 43b and the power FET 43c. The power FETs 43a and 43b are turned on when a PWM signal or an OFF signal is input to each of the gates G1 and G2 and a PWM signal is input and the logic level is 1. The power FETs 43c and 43d are turned on when an ON signal or an OFF signal is input to each of the gates G3 and G4 and an ON signal is input. When the motor control signal MS is input to each of the gates G1, G2, G3, and G4 of the power FETs 43a, 43b, 43c, and 43d, the motor drive circuit 43 supplies the motor voltage to the motor 8 based on the motor control signal MS. Apply VM. Then, an electric motor current IM flows through the electric motor 8, and the electric motor 8 is driven forward or backward to generate an auxiliary steering torque proportional to the electric motor current IM. The motor voltage VM applied to the motor 8 is determined by the duty ratio of the PWM signal. The motor current IM flowing through the motor 8 corresponds to the motor voltage VM. For example, when the duty ratio of the PWM signal is 70% (that is, 7 (logic level 1): 3 (logic level 0)), 12V × (7/10) = 8.4V becomes the motor voltage VM, and the motor 8 This means that 8.4 V is continuously applied.

  The control by the control device 20A in the electric power steering device 1 will now be described with reference to FIGS. Here, a case where the control device 20A controls the motor 8 by feedback control when the motor current detection means 21 is normal and a case where the motor current detection means 21 controls the motor 8 by feedforward control when the motor current detection means 21 is abnormal will be described.

  Regardless of whether the motor current detection means 21 is abnormal or normal, the control device 20A generates a corrected steering torque signal TH based on the steering torque signal T by the steering torque correction unit 33. Then, in the control device 20A, the target current setting unit 34 sets the target current signal IT based on the corrected steering torque signal TH and the vehicle speed signal V. Further, in the control device 20A, the feedback control unit 35 generates the first drive control signal C1 based on the deviation ΔIM between the target current signal IT and the motor current signal IMO. In addition, the control device 20A generates the second drive control signal C2 by the feedforward control unit 36 based on the target current signal IT. Further, the control device 20A limits the drive current of the second drive control signal C2 from the feedforward control 36 to the predetermined current MI or less by the drive current limiting unit 37.

  In addition, the control device 20A monitors each signal from various sensors by the sensor abnormality detection unit 31, and determines whether the various sensors are abnormal / normal. In particular, the sensor abnormality detection means 31 sets the logic level of the abnormality signal SA to 0 when the motor current detection means 21 is normal, and sets the logic level of the abnormality signal SA to 1 when the motor current detection means 21 is abnormal. To the control mode switching unit 38.

  When the logic level of the abnormality signal SA is 0, the control device 20A outputs the first drive control signal C1 as the drive control signal CS to the motor drive unit 40 by the control mode switching unit 38, and feedback-controls the motor 8. The motor drive unit 40 generates a motor control signal MS based on the first drive control signal C1 in consideration of the motor current signal IMO actually flowing to the motor 8, and the motor drive circuit 43 generates a motor control signal MS based on the motor control signal MS. An electric motor voltage VM is applied to the electric motor 8. Then, a motor current IM flows through the motor 8, and an auxiliary steering torque corresponding to the motor current IM is generated. Incidentally, even if the rotation of the electric motor 8 suddenly stops due to rack abutment, the control device 20A performs the feedback control by the electric motor current signal IMO, so that the current can be limited. Therefore, although the motor current IM in which the drive current by the first drive control signal C1 is increased flows as an instantaneous current, the motor 8 does not flow an excessive current that destroys the power FETs 43a to 43d.

  The control device 20A determines that the assist prohibition unit 39 has a relationship between the steering torque signal T and the motor current signal IMO of 100 mS or more in the assist prohibition regions M1a and M1a of the map M1 or 1 mS or more in the assist prohibition regions M1b and M1b. Alternatively, when the relationship between the steering torque signal T and the drive control signal CS is within the assist prohibition areas M2a and M2a of the map M2 (see FIG. 4), the main CPU determines that it is abnormal. At that time, the control device 20A outputs 1 as the logic level of the assist prohibition signal SB from the assist prohibition unit 39 to the gate drive circuit unit 42. Then, the control device 20A generates a motor control signal MS that is all turned off in the gate drive circuit unit 42, and stops application of the motor voltage VM from the motor drive circuit 43 to the motor 8 based on the motor control signal MS. To do. Then, the supply of the motor current IM to the motor 8 is stopped, and no auxiliary steering torque is generated.

  When the logic level of the abnormal signal SA is 1, the control device 20A outputs the second drive control signal C2 as the drive control signal CS to the motor drive unit 40 by the control mode switching unit 38, and feedforward controls the motor 8. The motor drive unit 40 generates a motor control signal MS based on the second drive control signal C2 limited to a predetermined current MI or less, and applies the motor voltage VM from the motor drive circuit 43 to the motor 8 based on the motor control signal MS. To do. Then, in the case of the feedforward control, the electric motor current IM that is equal to or smaller than the predetermined current MI flows to the electric motor 8 and an auxiliary steering torque corresponding to the electric motor current IM is generated. Further, even when the rotation of the electric motor 8 suddenly stops due to the rack butting and the back electromotive force component of the equation (1) (K · N component in the equation (1)) becomes 0, the control device 20A At the time of feedforward control, the drive current based on the second drive control signal C2 is set to be equal to or less than the predetermined current MI. Can do. Accordingly, the motor current IM flows as a limited instantaneous current in the motor 8, and an excessive instantaneous current that does not cause destruction does not flow in the power FETs 43a to 43d. For example, if the rate of increase in instantaneous current is increased by 40%, the drive current based on the second drive control signal C2 is limited to 80 A or less, so the instantaneous current is limited to 112 A or less in the motor 8. Incidentally, during the feedforward control, the drive current based on the second drive control signal C2 is limited to a predetermined current MI or less, but the steering feeling during normal steering (when the steering torque T is small) is not different from that during feedback control.

  When the relationship between the steering torque signal T and the drive control signal CS is within the assist prohibition areas M3a and M3a of the map M3 (see FIG. 4 (c)), the control device 20A performs main processing. CPU is determined to be abnormal. At that time, the control device 20A outputs 1 as the logic level of the assist prohibition signal SB from the assist prohibition unit 39 to the gate drive circuit unit 42. Then, the control device 20A generates a motor control signal MS that is all turned off in the gate drive circuit unit 42, and stops application of the motor voltage VM from the motor drive circuit 43 to the motor 8 based on the motor control signal MS. To do. Then, the supply of the motor current IM to the motor 8 is stopped, and no auxiliary steering torque is generated.

  According to the electric power steering apparatus 1 including the control device 20A, the electric motor current IM flowing through the electric motor 8 can be limited by feedback of the electric motor current signal IMO from the electric motor current detecting means 21 during feedback control. In addition, the electric power steering apparatus 1 sets the drive current by the second drive control signal C <b> 2 that is caused to flow to the electric motor 8 by the drive current limiting unit 37 during the feedforward control to a predetermined current MI or less. Therefore, the electric power steering device 1 limits the maximum value of the instantaneous current even when the rotation of the electric motor 8 suddenly stops and the rotation speed becomes zero, and the electric motor 8 does not flow an excessive electric motor current IM. The FET 43a to 43d is not supplied with an excessively high instantaneous current that would destroy the FETs 43a to 43d.

Next, the control device 20B of the second embodiment will be described with reference to FIG. Note that the control device 20B differs from the control device 20A of the first embodiment only in the means for limiting the maximum value of the second drive control signal C2, and is otherwise the same as the control device 20A. Therefore, in the description of the control device 20B, the same components as those of the control device 20A are denoted by the same reference numerals, and detailed description of the same components is omitted. The control device 20B includes an electric motor speed calculation unit 30, a sensor abnormality detection unit 31, an abnormality display unit 32, a steering torque correction unit 33, a target current setting unit 34, a feedback control unit 35, a feedforward control unit 36, and a control mode switching unit 38. The assist prohibition unit 39 and the electric motor drive unit 40 are configured. The electric motor drive unit 40 includes a PWM signal generation unit 41, a gate drive circuit unit 42, an electric motor drive circuit 43, and a duty ratio limiting unit 44. That is, the control device B limits the maximum value of the second drive control signal C2 by the duty ratio limiting unit 44 instead of the drive current limiting unit 37 (see FIG. 2) of the control device 20A. The control device 20B includes at least two CPUs that perform various calculations and processes, and further includes input signal conversion means, signal generation means, storage means, a power supply circuit, an electric motor drive circuit, and the like. In the present embodiment, the duty ratio limiting unit 44 corresponds to the limiting unit described in claim 2 of the claims.

  In the control device 20B, the feedforward control unit 36 directly outputs the second drive control signal C2 to the control mode switching unit 38. In the control device 20 </ b> B, the abnormality signal SA is also output from the sensor abnormality detection unit 31 to the control mode switching unit 38 and the duty ratio limiting unit 44.

  The duty ratio limiting unit 44 receives the motor control signal MS from the PWM signal generation unit 41 and the abnormality signal SA from the sensor abnormality detection unit 31, and the gate drive circuit unit 42 has a predetermined ratio to the PWM signal of the motor control signal MS. An electric motor control signal MS subjected to duty ratio restriction is output. The duty ratio limiting unit 44 prevents the motor current IM from becoming excessive during feed-forward control that cannot be controlled based on the motor current signal IMO, and causing an excessive current to flow through the power FETs 43a to 43d of the motor drive circuit 43 as an instantaneous current. For this reason, the duty ratio of the PWM signal of the motor control signal MS is set to a predetermined ratio MD or less. That is, when the rotation of the electric motor 8 stops suddenly at the time of rack contact or the like, the rotation speed of the electric motor 8 becomes zero. However, in the case of the feed forward control, the first output from the feed forward control unit 36 is caused by the control delay. The electric motor voltage VM based on the drive current of the 2 drive control signal C2 is maintained at the voltage value at the time of rack contact. Therefore, as can be seen from the equation (1), the motor current IM instantaneously becomes excessive. Since an excessive current (120 A or more) flows as an instantaneous current also in the power FETs 43a to 43d, the power FETs 43a to 43d may be destroyed. Therefore, in the case of feedforward control, the duty ratio of the PWM signal of the motor control signal MS input to the gate G1 or the gate G2 is set to a predetermined ratio MD or less, and the maximum value is limited to the motor 8 below the predetermined ratio MD. The motor voltage VM is applied. Therefore, the maximum value of the instantaneous current that is increased at an increase rate due to the characteristics of the electric motor 8 is also limited, and only the limited instantaneous current flows through the power FETs 43a to 43d. The predetermined ratio MD is the maximum of the drive current that is set so that the instantaneous current never becomes less than the current value that does not destroy the power FETs 43a to 43d even if the drive current by the second drive control signal C2 is increased as the instantaneous current. It is set to be equal to or less than the duty ratio of the PWM signal based on the motor voltage VM to be equal to or less than the value, and is set to 50% in the present embodiment (that is, the motor 8 is continuously 6V (= 12V × (5/10)) Only the following motor voltage VM is applied): Incidentally, the predetermined ratio MD knows how much the drive current of the second drive control signal C2 increases when the rotational speed of the electric motor 8 suddenly becomes 0, and this increase rate, It is set in consideration of the power supply voltage value of the motor drive circuit 43 and the current value that destroys the power FETs 43a to 43d. The predetermined ratio MD is also a duty ratio that does not cause any abnormality in the electric motor 8. Since the steering torque by the driver is reduced by rack abutting with the lapse of time after the rack abutment, the target current of the target current signal IT becomes small, and the drive current of the second drive control signal C2 becomes small. Therefore, the duty ratio of the PWM signal of the motor control signal MS is also reduced.

  Therefore, the duty ratio limiting unit 44 includes a predetermined ratio setting unit 44a and a duty ratio comparison unit 44b. The predetermined ratio setting unit 44a includes storage means such as a ROM, and outputs the predetermined ratio MD to the duty ratio comparison unit 44b. Only the signals (PWM signal and OFF signal) input to the gate G1 and the gate G2 in the motor control signal MS from the PWM signal generation unit 41 are input to the duty ratio comparison unit 44b. Therefore, the signals (ON signal and OFF signal) input to the gate G3 and the gate G4 in the motor control signal MS from the PWM signal generation unit 41 are directly input from the PWM signal generation unit 41 to the gate drive circuit unit 42. The The duty ratio comparison unit 44b outputs the off signal for the gate G1 or the gate G2 of the motor control signal MS from the PWM signal generation unit 41 to the gate drive circuit unit 42 as it is regardless of the logic level of the abnormal signal SA. Then, when the logic level of the abnormal signal SA is 0 (that is, in the case of feedback control), the duty ratio comparison unit 44b uses the PWM signal for the gate G1 or the gate G2 of the motor control signal MS from the PWM signal generation unit 41 as it is. Output to the gate drive circuit unit 42. Further, when the logic level of the abnormal signal SA is 1 (that is, in the case of feedforward control), the duty ratio comparison unit 44b outputs the PWM signal for the gate G1 or the gate G2 of the motor control signal MS from the PWM signal generation unit 41. The duty ratio is compared with the predetermined ratio MD. When the duty ratio of the PWM signal from the PWM signal generation unit 41 is greater than the predetermined ratio MD, the duty ratio comparison unit 44b generates a PWM signal using the predetermined ratio MD as the duty ratio of the PWM signal, and the gate drive circuit To the unit 42. On the other hand, when the duty ratio of the PWM signal from the PWM signal generation unit 41 is equal to or less than the predetermined ratio MD, the duty ratio comparison unit 44b outputs the PWM signal from the PWM signal generation unit 41 to the gate drive circuit unit 42 as it is. .

  Then, with reference to FIG. 1 and FIG. 5, the control by the control apparatus 20B in the electric power steering apparatus 1 is demonstrated. Here, a case where the control device 20B controls the motor 8 by feedback control when the motor current detection means 21 is normal and a case where the motor current detection means 21 controls the motor 8 by feedforward control when the motor current detection means 21 is abnormal will be described. In addition, about description which the control apparatus 20B performs the same control as above-described control apparatus 20A, the description of the control is abbreviate | omitted.

  Regardless of whether the motor current detection means 21 is abnormal or normal, the control device 20B generates a corrected steering torque signal TH based on the steering torque signal T by the steering torque correction unit 33. In the control device 20B, the target current setting unit 34 sets the target current signal IT based on the corrected steering torque signal TH and the vehicle speed signal V. Further, in the control device 20B, the feedback control unit 35 generates the first drive control signal C1 based on the deviation ΔIM between the target current signal IT and the motor current signal IMO. In addition, the control device 20B generates the second drive control signal C2 by the feedforward control unit 36 based on the target current signal IT. When the logic level of the abnormal signal SA is 0, the control device 20B outputs the first drive control signal C1 as the drive control signal CS to the motor drive unit 40 by the control mode switching unit 38, and feedback-controls the motor 8. . When the logic level of the abnormal signal SA is 1, the control device 20B outputs the second drive control signal C2 to the motor drive unit 40 as the drive control signal CS by the control mode switching unit 38, and feedforward controls the motor 8. To do. Subsequently, the control device 20B generates a motor control signal MS based on the drive control signal CS in the PWM signal generation unit 41, and outputs signals for the gate G1 and the gate G2 in the motor control signal MS to the duty ratio limiting unit 44. Then, signals for the gate G3 and the gate G4 in the motor control signal MS are output to the gate drive circuit unit 42.

  When the logic level of the abnormal signal SA is 0, the control device 20B causes the duty ratio limiting unit 44 to output signals (PWM signal and OFF signal) for the gate G1 and the gate G2 in the motor control signal MS from the PWM signal generation unit 41. The data is output to the gate drive circuit unit 42 as it is. The control device 20B performs feedback control of the electric motor 8 based on the electric motor control signal MS logically determined by the gate drive circuit unit 42. The control device 20B generates the motor control signal MS by the first drive control signal C1 in consideration of the motor current signal IMO actually flowing to the motor 8 by the PWM signal generation unit 41, and the motor control signal MS Based on this, the motor voltage VM is applied from the motor drive circuit 43 to the motor 8. Then, a motor current IM flows through the motor 8, and an auxiliary steering torque corresponding to the motor current IM is generated. Incidentally, even if the rotation of the electric motor 8 suddenly stops due to rack abutment, the control device 20B performs the feedback control by the electric motor current signal IMO, so that the current can be limited. Therefore, although the motor current IM in which the drive current by the first drive control signal C1 is increased flows as an instantaneous current, the motor 8 does not have an excessive current that destroys the power FETs 43a to 43d.

  When the logic level of the abnormal signal SA is 1, the control device 20B determines that the duty ratio of the PWM signal with respect to the gate G1 or the gate G2 in the motor control signal MS from the PWM signal generation unit 41 is the predetermined ratio MD. While being limited to the following, the signal is output to the gate drive circuit unit 42, and the OFF signal for the gate G1 or the gate G2 in the motor control signal MS is output to the gate drive circuit unit 42 as it is. Then, the control device 20B performs feedforward control of the electric motor 8 based on the electric motor control signal MS logically determined by the gate drive circuit unit 42. Since the duty ratio limiting unit 44 limits the duty ratio of the PWM signal to a predetermined ratio MD or less, the control device 20B limits the duty ratio of the PWM signal from the motor drive circuit 43 to the motor 8 to generate the motor voltage generated by the PWM signal whose duty ratio is limited. Apply VM. Then, in the case of the feedforward control, the motor current IM whose maximum value is limited flows to the motor 8 by the motor voltage VM limited to a predetermined ratio MD or less, and the auxiliary steering corresponding to the motor current IM is performed. Torque is generated. Further, even when the rotation of the electric motor 8 suddenly stops due to the rack butting and the back electromotive force component of the equation (1) (K · N component in the equation (1)) becomes 0, the control device 20B At the time of feedforward control, the motor voltage VM limited to a predetermined ratio MD or less is applied to the motor 8 to limit the maximum value of the drive current that flows to the motor 8. Therefore, the maximum value of the instantaneous current that is instantaneously increased at an increase rate due to the characteristics of the electric motor 8 is also limited. Accordingly, the motor current IM flows as a limited instantaneous current in the motor 8, and an excessive instantaneous current that does not cause destruction does not flow in the power FETs 43a to 43d.

  According to the electric power steering device 1 including the control device 20B, the electric motor current IM flowing through the electric motor 8 can be limited by feedback of the electric motor current signal IMO from the electric motor current detecting means 21 during feedback control. Further, during the feedforward control, the electric power steering device 1 limits the maximum value of the motor voltage VM by the PWM signal that is limited to a predetermined ratio MD or less by the duty ratio limiting unit 44. Therefore, the electric power steering apparatus 1 is limited in the maximum value of the instantaneous current even when the rotation of the electric motor 8 suddenly stops and the rotational speed becomes zero, and an excessive electric motor current IM does not flow through the electric motor 8. The FET 43a-43d does not flow an excessively large instantaneous current that would destroy it. Incidentally, the duty ratio of the PWM signal is limited to a predetermined ratio MD or less during the feedforward control, but the steering feeling during normal steering (when the steering torque T is small) is the same as during feedback control.

As described above, the present invention is not limited to the above-described embodiment, and can be implemented in various forms. For example, although the second driving control signal drive current limit unit 37 or the duty ratio limit unit 44 as a means for limiting the maximum value of C2, not limited to these means.

1 is an overall configuration diagram of an electric power steering apparatus according to an embodiment. It is a block block diagram of the control apparatus which concerns on 1st Embodiment. 3 is a conversion table of a corrected steering torque signal and a vehicle speed signal-target current signal of the target current setting unit of FIG. 3 is a map showing an assist prohibition region of the assist prohibition unit in FIG. 2, (a) is a characteristic diagram of a steering torque signal-motor current signal used when the motor current detection means is normal, and (b) is a motor current detection means FIG. 4C is a characteristic diagram of a steering torque signal-drive control signal used when the motor is normal, and FIG. 5C is a characteristic diagram of a steering torque signal-drive control signal used when the motor current detecting means is abnormal. It is a block block diagram of the control apparatus which concerns on 2nd Embodiment. FIG. 6 is a characteristic diagram of time-motor current during feedforward control in a conventional electric power steering apparatus, and shows a case where there is a rack abutment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus 8 ... Electric motor 20, 20A, 20B ... Control apparatus 21 ... Electric motor current detection means 31 ... Sensor abnormality detection part (failure detection part)
34 ... target current setting unit 35 ... feedback control unit (first drive control signal generation unit)
36... Feedforward control unit (second drive control signal generation unit)
37... Drive current limiter (limiter)
38 ... Control mode switching unit 40 ... Motor drive unit 41 ... PWM signal generation unit (pulse width modulation signal generation unit)
44: Duty ratio limiter (limiter)
S ... Steering system TS ... Steering torque sensor

Claims (3)

An electric motor for adding auxiliary steering torque to the steering system;
A steering torque sensor for detecting a steering torque acting on the steering system and outputting a steering torque signal;
Motor current detection means for detecting a motor current flowing in the motor and outputting a motor current signal;
A failure detection unit for detecting a failure of the motor current detection means;
A target current setting unit configured to set a target current to be supplied to the electric motor based on at least the steering torque signal and to output a target current signal;
A first drive control signal generator for generating and outputting a first drive control signal for driving the electric motor based on a deviation between the target current signal and the electric motor current signal;
Generating and outputting a second drive control signal for driving the motor based on a current value obtained by adding a current value corresponding to a back electromotive force of the motor to the target current of the target current signal; A drive control signal generator;
When the failure detection unit detects the motor current detection unit as normal, the failure detection unit switches to the first drive control signal, and when the failure detection unit detects the motor current detection unit as a failure, A control mode switching unit for controlling the electric motor by switching to a second drive control signal;
Based on a drive control signal from the control mode switching unit, an electric motor drive unit that drives the electric motor in normal rotation or reverse rotation, and
A limiting unit that limits the maximum value of the second drive control signal;
And an assist prohibiting unit that determines whether or not steering assist is prohibited based on at least the steering torque signal and determines prohibition of addition of auxiliary steering torque by the electric motor ,
The restriction unit is
Comparing the drive current of the second drive control signal with a predetermined current;
When the drive current is large, the predetermined current is output as the second drive control signal,
The assist prohibition unit is
When a failure is detected by the presence or absence of failure detection of the failure detection unit,
The assist prohibition unit determines prohibition of addition of the auxiliary steering torque, and the absolute value of the steering torque signal for starting prohibition of the assist is made smaller than when no failure is detected, and the addition of the auxiliary steering torque is performed. Ban
An electric power steering device. An electric motor for adding auxiliary steering torque to the steering system;
A steering torque sensor for detecting a steering torque acting on the steering system and outputting a steering torque signal;
Motor current detection means for detecting a motor current flowing in the motor and outputting a motor current signal;
A failure detection unit for detecting a failure of the motor current detection means;
A target current setting unit configured to set a target current to be supplied to the electric motor based on at least the steering torque signal and to output a target current signal;
A first drive control signal generator for generating and outputting a first drive control signal for driving the electric motor based on a deviation between the target current signal and the electric motor current signal;
Generating and outputting a second drive control signal for driving the motor based on a current value obtained by adding a current value corresponding to a back electromotive force of the motor to the target current of the target current signal; A drive control signal generator;
When the failure detection unit detects the motor current detection unit as normal, the failure detection unit switches to the first drive control signal, and when the failure detection unit detects the motor current detection unit as a failure, A control mode switching unit for controlling the electric motor by switching to a second drive control signal;
Based on a drive control signal from the control mode switching unit, an electric motor drive unit that drives the electric motor in normal rotation or reverse rotation, and
A limiting unit that limits the maximum value of the second drive control signal;
And an assist prohibiting unit that determines whether or not steering assist is prohibited based on at least the steering torque signal and determines prohibition of addition of auxiliary steering torque by the electric motor,
The electric motor drive unit is
The field effect transistor of the bridge circuit to the pulse width modulation driving, has a pulse width modulation signal generation unit for generating and outputting a pulse width modulation signal based on the drive control signal from the control mode switching unit,
The restriction unit is
When the failure detection unit detects the motor current detection means as a failure,
Compare the duty ratio of the pulse width modulation signal with a predetermined ratio,
When the duty ratio is large, the predetermined ratio is output as the pulse width modulation signal,
The assist prohibition unit is
When a failure is detected by the presence or absence of failure detection of the failure detection unit,
The assist prohibition unit determines prohibition of addition of the auxiliary steering torque, and the absolute value of the steering torque signal for starting prohibition of the assist is made smaller than when no failure is detected, and the addition of the auxiliary steering torque is performed. An electric power steering device characterized by prohibiting Furthermore, a vehicle speed sensor that detects the vehicle speed and outputs a vehicle speed signal is provided.
The target current signal output by the target current setting unit is:
As the vehicle speed signal is high, the increment of the target current signal to the steering torque signal is small and the maximum value of the target current signal, to claim 1 or claim 2, characterized in that does not depend on the vehicle speed signal The electric power steering apparatus as described.

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