JP5991273B2 - Electric power steering control device - Google Patents

Description

  The present invention relates to a failure detection technique for an electric power steering apparatus.

  As a power steering device for a vehicle, an electric power steering (EPS) device that assists a steering torque generated by a driver's steering operation with a motor is known.

  Conventionally, various techniques for detecting failures of various sensors (steering angle sensors, current sensors, etc.) included in the EPS apparatus have been proposed (for example, Patent Documents 1 and 2).

JP 2007-261548 A JP 2011-088521 A JP-A-7-087770

  The EPS device controls driving of a motor based on signals from a torque sensor that detects steering torque, a vehicle speed sensor that detects vehicle speed, and the like, and provides auxiliary steering force. At that time, the EPS device performs drive control of the motor so that the actual motor current value detected by the current sensor follows the target current determined based on the steering torque and the vehicle speed.

  Here, when detecting a short-circuit failure of the current sensor, generally, a detection value of the current sensor and a detection value of the torque sensor are used. As a result, for example, a case where a counter electromotive force is generated in the motor due to high-speed steering and the detected value of the current sensor indicates approximately 0 [A] is excluded, so that the current sensor can be accurately failed. Can be detected.

  However, when the torque sensor breaks down, for example, the motor driving current is controlled by estimating the steering torque based on the detected values of the steering angle sensor, the rotation angle sensor of the motor, etc., and an auxiliary steering force is applied. is there. In such a case, since the detection value of the torque sensor cannot be used, it is impossible to accurately detect a short-circuit failure of the current sensor.

  In view of the above problems, an object of the present invention is to provide an electric power steering control device capable of detecting a short-circuit failure of a current sensor that detects a motor current without using a detection value of a torque sensor.

In order to achieve the above object, in one embodiment, the present electric power steering control device comprises:
A steering torque detecting means for detecting a steering torque input from the steering handle to the steering shaft;
A steering angle sensor for detecting a steering angle at the steering handle;
A motor provided in the steering mechanism for generating steering assist torque;
Motor current detecting means for detecting current flowing in the motor;
A motor drive circuit configured to form a bridge circuit with a plurality of switching elements to drive the motor ;
Before SL in accordance with the steering torque or the steering angle, and the target current determining means for determining a target current of the motor,
Target current limiting means for determining a limited target current that limits the target current so as to satisfy a predetermined condition ;
By the current detected by the previous SL motor current detecting means performs PWM driving of each said switching element of the motor drive circuit so as to follow the limited target current, and motor control means for controlling said motor,
A failure detection means for detecting a failure of the motor current detection means,
The target current limiting means, as the predetermined condition, the duty ratio of the PWM driving when the motor current detecting means is normal to determine the limited target current to be equal to or less than the predetermined ratio,
The failure detection means is in a situation where at least the target current determination means determines the target current based on the steering angle, and the duty ratio of the PWM drive currently performed exceeds the predetermined ratio. A failure of the motor current detection means is detected.

  According to the present embodiment, it is possible to provide an electric power steering control device capable of detecting a short-circuit failure of a current sensor that detects a motor current without using a detection value of a torque sensor.

It is a block diagram of electric power steering control device 1 concerning a 1st embodiment. It is a figure (target current restriction map) explaining the restriction | limiting of the target current by the target current limiting means 51b which concerns on 1st Embodiment. It is a figure explaining the duty ratio of PWM drive of the motor drive circuit 53 by the switching element drive circuit 52 at the time of failure of the current sensor 54 (shunt resistor 54a) according to the first embodiment. It is a block diagram of electric power steering control device 1 concerning a 2nd embodiment. It is a figure explaining the relationship between steering angular velocity (omega) and estimated steering angular velocity (omega) e at the time of the failure of the current sensor 54 (shunt resistance 54a) which concerns on 2nd Embodiment.

  Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings.

[First Embodiment]
FIG. 1 is a block diagram of an electric power steering (EPS) control device 1 according to the present embodiment.

  The EPS control apparatus 1 according to the present embodiment controls an automobile EPS apparatus. The EPS device reduces the driver's steering operation by generating an assist torque by the motor 6 in accordance with a steering torque generated on a steering shaft (not shown) by a driver's operation of a steering handle (not shown). . The assist torque by the motor 6 may be applied to the steering shaft (column assist), may be applied to a pinion portion of a rack and pinion mechanism (not shown) (pinion assist), or applied to the rack portion. (Rack assist).

  The EPS control device 1 includes a torque sensor (steering torque detection means) 2, a vehicle speed sensor 3, a steering angle sensor (steering angular velocity detection means) 4, an ECU (Electric Control Unit) 5, a motor 6, a battery 7, and the like.

  The torque sensor 2 detects the steering torque input to the steering shaft by the driver operating the steering wheel, and outputs a steering torque signal to the ECU 5 (microcomputer 51). The torque sensor 2 is provided on the steering shaft, and for example, a steering torque detection method such as a magnetic induction method, a Hall IC method, or a twin resolver method may be used.

  The vehicle speed sensor 3 detects the vehicle speed of the vehicle on which the EPS control device 1 is mounted, and outputs a vehicle speed signal to the ECU 5 (microcomputer 51).

  The steering angle sensor 4 detects the steering angle of the steering wheel and outputs a steering angle signal to the ECU 5 (microcomputer 51). Further, it is possible to calculate the steering angular velocity by differentiating the detected steering angle (calculating the rate of change of the steering angle detected at predetermined intervals), and the steering angle sensor 4 is a steering angular velocity detecting means. Function as.

  The motor 6 is a DC motor with a brush, and is an auxiliary steering force generating means for assisting the driver to operate the steering handle in the EPS device as described above. The motor 6 is supplied with electric power from the battery 7 and is driven by a motor drive circuit 53 described later.

  The battery 7 is an in-vehicle power source. For example, the battery 7 may be a lead storage battery having a terminal voltage of about 12V to 14V. The battery 7 supplies electric power to the ECU 5. The battery 7 supplies power to the motor 6 via the ECU 5 (motor drive circuit 53).

  The ECU 5 is an in-vehicle control unit. The ECU 5 receives power supply from the battery 7 and supplies power to the motor 6. The ECU 5 receives a steering torque signal, a vehicle speed signal, and a steering angle signal from the torque sensor 2, the vehicle speed sensor 3, and the steering angle sensor 4, respectively. The ECU 5 performs drive control of the motor 6 based on a steering torque signal, a vehicle speed signal, a steering angle signal, and the like.

  The ECU 5 includes a microcomputer (target current determining means, target current limiting means, motor control means, failure detection means) 51, switching element drive circuit 52, motor drive circuit 53, current sensor (motor current detection means) 54, motor voltage detection circuit. 55 etc. are included.

  The motor drive circuit 53 is configured as an H-bridge circuit by four switching elements, for example, MOSFET (Metal Oxide Semiconductor Field Effect Transistor). Switching elements 53a and 53c are connected in series to one branch of the H-bridge circuit, and switching elements 53b and 53d are connected in series to the other branch. A connection point between the switching elements 53 a and 53 c is connected to one terminal of the motor 6, and a connection point between the switching elements 53 b and 53 d is connected to the other terminal of the motor 6. Switching elements 53 a and 53 b are connected to the positive terminal of battery 7. The switching elements 53c and 53d are grounded via a shunt resistor 54a. When the switching elements 53a and 53d are on and the switching elements 53b and 53c are off, a current flows from the battery 7 to the motor 6 through the switching element 53a from top to bottom in the drawing (hereinafter, in this case, the motor 6 Will rotate to the right). When the switching elements 53b and 53c are on and the switching elements 53a and 53d are off, a current flows from the battery 7 to the motor 6 via the switching element 53b from the bottom to the top in the drawing (hereinafter, in this case) It is assumed that the motor 6 rotates in the left direction).

  The switching element drive circuit 52 is a PWM (Pulse Width Modulation) control circuit, and outputs a gate drive signal to each of the switching elements 53 a to 53 d of the motor drive circuit 53. The switching element driving circuit 52 is driven and controlled by a microcomputer 51 (motor control means 51c) described later. The switching element driving circuit 52 selects the direction of the auxiliary torque generated by the motor 6 by selecting the driving direction of the motor 6, and the magnitude of the auxiliary torque generated by the motor 6 by PWM driving the switching elements 53 a to 53 d. To control.

  The current sensor 54 detects the current flowing through the motor 6. The current sensor 54 includes a shunt resistor 54a and a motor current detection circuit 54b.

  The shunt resistor 54a is provided for detecting the current as a voltage.

  The motor current detection circuit 54b detects the voltage across the shunt resistor 54a, detects the motor current value based on the voltage across the shunt resistor and the resistance value of the shunt resistor, and outputs the detected current value to the microcomputer 51.

  The motor voltage detection circuit 55 detects the voltage across the motor 6 and outputs it to the microcomputer 51.

  The microcomputer 51 calculates a voltage command value that is a control amount of the motor 6 based on the steering torque signal, the vehicle speed signal, and the like, converts the voltage command value into a duty ratio of PWM drive, a switching element drive circuit 52, a motor drive This is a processing device that controls the motor 6 via a circuit 53. The microcomputer 51 includes a CPU that executes a program for performing a specific process for controlling the motor 6, a ROM that stores the program, a RAM that temporarily stores data, and the like.

  The microcomputer 51 includes target current determining means 51a, target current limiting means 51b, motor control means 51c, and failure detection means 51d. The target current determining means 51a, the target current limiting means 51b, the motor control means 51c, and the failure detection means 51d are configured by executing corresponding programs on the CPU.

  The target current determining means 51a determines the target current (including the current direction) of the motor 6 according to the steering torque signal and the vehicle speed signal. The assist force that the motor 6 should give changes according to the steering torque, and the steering force that the driver should input from the steering wheel also changes depending on the vehicle speed. Therefore, for example, a map for determining a target current (including the direction of the current) for the steering torque (including the direction of the steering torque) for each vehicle speed range may be set in advance, and the target current may be determined based on the map. . The determined target current is input to the target current limiting means 51b.

  The target current limiting unit 51b performs limitation so that the target current determined by the target current determining unit 51a satisfies a predetermined condition. Specific details and methods will be described later. The limited target current is input to the motor control means 51c. In the following, the target current limited by the target current limiting unit 51b is referred to as “limited target current”, and the target current determined by the target current determining unit is simply referred to as “target current”.

  The motor control means 51c applies PWM to each switching element of the motor drive circuit 53 via the switching element drive circuit 52 so that the motor current (detected current value) detected by the current sensor 54 follows the limit target current. Drive to control the motor 6. Specifically, the motor control unit 51c is configured as, for example, a PI (Proportional Integral) controller, performs PI control on the difference between the limited target current and the detected current value, and sets the voltage as the control amount of the motor 6 Calculate the command value. The motor control unit 51 c converts the voltage command value into a duty ratio (hereinafter simply referred to as a duty ratio) of the PWM drive, and outputs the duty ratio to the switching element drive circuit 52. The duty ratio is also output to failure detection means 51d described later.

  The switching element drive circuit 52 drives and controls the motor drive circuit 53 with the duty ratio input from the motor control means 51c. For example, when the motor 6 is driven in the right direction, the switching element 53a is PWM-driven with the duty ratio, and the switching element 53d is continuously turned on and the switching elements 53b and 53c are turned off. When the motor 6 is driven in the left direction, the switching element 53b is PWM-driven with the duty ratio, and the switching element 53c is continuously turned on and the switching elements 53a and 53d are turned off.

  The failure detection means 51d detects a failure of the current sensor 54. In the present embodiment, the failure detection means 51d detects a short-circuit failure of the shunt resistor 54a included in the current sensor 54. Although details will be described later, a short circuit failure of the shunt resistor 54a is detected based on the duty ratio input from the motor control means 51c.

  Next, specific target current limitation by the target current limiting means 51b will be described.

  Here, FIG. 2 is a diagram for explaining the limitation of the target current by the target current limiting means 51b, and represents a target current limit map. In the figure, the vertical axis represents the current (torque) of the motor 6, and the horizontal axis represents the rotational speed of the motor 6.

  Referring to FIG. 2, a line segment 110 is a characteristic line of the motor 6 corresponding to the duty ratio of 95%. That is, the line represents the relationship between the rotational speed of the motor 6 and the current when the motor 6 is driven with a voltage command value corresponding to a duty ratio of 95%. In the DC motor, the rotational speed decreases as the torque increases, and the current increases in proportion to the torque. Therefore, the characteristic line of the motor 6 corresponding to the duty ratio of 95% is a straight line that falls to the right.

  Further, since the rotation speed is proportional to the voltage applied to the motor 6, the characteristic line of the motor 6 when the voltage applied to the motor 6 is changed becomes a line segment parallel to the line segment 110. Therefore, a line segment parallel to the line segment 110 located on the left side of the line segment 110 corresponds to a case where the motor 6 is driven with a voltage command value corresponding to a duty ratio smaller than 95%. That is, the light black portion 100 is a set of characteristic lines of the motor 6 when the motor 6 is driven with a duty ratio of 0% to 95%. A line segment 120 indicates a characteristic line of the motor 6 corresponding to a duty ratio of 100%, and a hatched portion 120 is a set of characteristic lines of the motor 6 when the motor 6 is driven at a duty ratio of 95% to 100%. It will be.

  A line segment with a constant current (torque) at the upper end of the light black portion 100 and the upper end of the shaded portion 110 corresponds to the rated current (rated torque) of the motor 6. Since the motor 6 is overloaded when driven at a rated current and a rated torque or higher, the motor 6 is driven at a rated current and a rated torque or lower.

  In the present embodiment, the target current limiting means 51b is configured so that the duty ratio when the current sensor 54 (shunt resistor 54a) is normal is equal to or less than a predetermined ratio (95%) by setting the target current within the thin ink portion 100. The target current is limited so that

  Specifically, first, based on the target current determined by the target current determining means 51 a and the voltage across the motor 6 input from the motor voltage detection circuit 55, the relationship between the target current and the rotational speed is included in the thin ink portion 100. Determine whether or not. As described above, since the rotation speed is proportional to the voltage across the motor 6, the rotation speed of the motor 6 is calculated from the voltage across the motor 6. Here, when the relationship between the target current and the rotation speed is included in the thin ink portion 100, the target current determined by the target current determining means 51a is output as it is to the motor control means 51c as the limited target current. On the other hand, when the relationship between the target current and the rotation speed is not included in the light black portion 100, the limited target current obtained by limiting the target current determined by the target current determining means 51a to the value on the line segment 110 is given to the motor control means 51c. Output.

  Next, the duty ratio of the PWM drive when the current sensor 54 (shunt resistor 54a) fails will be described.

  Here, FIG. 3 is a diagram for explaining the duty ratio of the PWM drive of the motor drive circuit 53 by the switching element drive circuit 52 when the current sensor 54 (shunt resistor 54a) fails. FIG. 3A shows an example of the transition of the duty ratio with respect to time when the current sensor 54 (shunt resistor 54a) is normal. For comparison, the transition of the steering angular speed of the steering wheel with respect to time is also shown. Yes. FIG. 3B shows an example of the change of the duty ratio with respect to time when the current sensor 54 (shunt resistor 54a) fails. For comparison, the change of the steering wheel steering angular velocity with respect to time is also shown. Has been. 3A and 3B, the duty ratio 95% line 200 is indicated by a one-dot chain line.

  Referring to FIG. 3 (a), the duty ratio increases as the steering angular speed increases due to the operation of the steering wheel. However, as described above, the target current is limited by the target current limiting means 51b, so the duty ratio is 95%. The trend is as follows.

  On the other hand, referring to FIG. 3B, the duty ratio changes in a state of 100% after the failure of the current sensor 54 occurs.

  As described above, the motor control unit 51c calculates the voltage command value so that the motor current (detected current value) detected by the current sensor 54 follows the limited target current, and converts the voltage command value into a duty ratio. . When the current sensor 54 fails, that is, when the shunt resistor 54a is short-circuited, the voltage across the shunt resistor 54a is detected as 0 [V] by the motor current detection circuit 54b, and the detected current value is 0. [A] is continuously input to the microcomputer 51. Therefore, when the current sensor 54 fails, the motor control unit 51c increases the duty ratio in order to make the detected current value continuously input as 0 [A] follow the limit target current, and finally, The duty ratio continuously changes at 100%.

  Therefore, as described above, the target current limiting unit 51b limits the target current so that the duty ratio is equal to or less than a predetermined ratio (95%) when the current sensor 54 is normal, and thus the duty ratio is a predetermined ratio (95 %), A failure of the current sensor 54 can be detected.

  That is, the failure detection unit 51d detects a failure of the current sensor 54 when the duty ratio input from the motor control unit 51c exceeds a predetermined ratio (95%).

  Thereby, failure of the current sensor 54 can be detected without using the torque sensor 2.

  In particular, when the torque sensor 2 fails, the target current of the motor 6 may be determined based on the steering angle signal from the steering angle sensor 4 and the motor 6 may be controlled. In this case, it is possible to detect a failure of the current sensor 54 without using the torque sensor 2, and it is preferable to stop applying the auxiliary steering force by the motor 6 after detecting the failure. Thereby, the self-steering at the time of failure of the current sensor 54 (shunt resistor 54a) can be prevented.

  Further, as described above, after the failure of the current sensor 54 occurs, the duty ratio changes at 100%. Therefore, if the target current limiting unit 51b limits the target current so that the duty ratio when the current sensor 54 is normal is within a predetermined ratio even smaller than 100%, the failure detecting unit 51d detects the failure. be able to. Thereby, since the duty ratio is limited to a predetermined ratio (for example, 95%) that does not affect the performance of the EPS device, both the performance of the EPS device and the failure detection of the current sensor not using the torque sensor are compatible. It becomes possible.

[Second Embodiment]
Next, a second embodiment will be described.

  The EPS control apparatus 1 according to the present embodiment includes a steering angular velocity detected by the steering angle sensor 4 and an estimated steering angular velocity calculated from the current and voltage of the motor 6 detected by the current sensor 54 and the motor voltage detection circuit 55. , The point of detecting a failure of the current sensor 54 is mainly different from the first embodiment. Hereinafter, the same components as those in the first embodiment are denoted by the same reference numerals, and different portions will be mainly described.

  FIG. 4 is a block diagram of the EPS control apparatus 1 according to the present embodiment.

  In the present embodiment, the target current determining unit 51a determines the target current (including the direction of the current) of the motor 6 according to the steering torque signal and the vehicle speed signal, as in the first embodiment. The target current is output to the motor control means 51c.

  The motor control unit 51c PWM-drives each switching element of the motor drive circuit 53 via the switching element drive circuit 52 so that the motor current (detected current value) detected by the current sensor 54 follows the target current. The motor 6 is controlled. Specifically, as in the first embodiment, the motor control unit 51c is configured as a PI controller, for example, and performs PI control on the difference between the target current and the detected current value to control the motor 6. The voltage command value as a quantity is calculated. The motor control unit 51 c converts the voltage command value into a duty ratio (hereinafter simply referred to as a duty ratio) of the PWM drive, and outputs the duty ratio to the switching element drive circuit 52.

  The failure detection means 51d is configured to control the steering wheel based on the current of the motor 6 (detected current value Im) input from the current sensor 54 and the voltage of the motor 6 (detected voltage value Vm) input from the motor voltage detection circuit 55. An estimated value (estimated steering angle ωe) of the steering angular velocity is calculated. The estimated steering angle ωe can be calculated by the following equation (1) based on the induced voltage of the motor 6.

ωe = (Vm−Rm × Im) / Ke / Rr (1)
Rm is the resistance between the terminals of the motor 6, Ke is the counter electromotive force constant of the motor 6, and Rr is the reduction ratio of the reduction gear that transmits the driving force of the motor 6 to the steering mechanism.

  In addition, the steering angle of the steering wheel is input from the steering angle sensor 4 to the failure detection means 51d, and the failure detection means 51d differentiates the steering angle (the rate of time change of the steering angle detected at predetermined intervals). By calculating), the steering angular velocity ω is obtained.

  The estimated steering angular velocity ωe calculated by the above formula (1) shows a value close to the steering angular velocity ω when a short failure has not occurred in the current sensor 54 (shunt resistor 54a) (normal time).

  However, when a short-circuit failure occurs in the current sensor 54 (shunt resistor 54a), the detected current value Im is continuously input as 0 [A], so that the estimated steering angular velocity ωe and the steering angular velocity ω are greatly different. It will be.

  Therefore, the failure detection means 51d detects the current sensor 54 (shunt resistor 54a) when the difference between the estimated steering angular velocity ωe and the steering angular velocity ω based on the steering angle detected by the steering angle sensor 4 exceeds a predetermined threshold. Detect failure.

  Here, FIG. 5 is a diagram for explaining the relationship between the steering angular velocity ω and the estimated steering angular velocity ωe when the current sensor 54 (shunt resistor 54a) according to the present embodiment fails. FIG. 5A shows an example of transition of the steering angular velocity ω and the estimated steering angular velocity ωe with time when the current sensor 54 (shunt resistor 54a) is normal. FIG. 5B shows an example of the transition of the steering angular velocity ω and the estimated steering angular velocity ωe with time when the current sensor 54 (shunt resistor 54a) fails. 5 (a) and 5 (b), the steering angular velocity ω shows a change with time with a thick solid line, and the estimated steering angular velocity ωe shows a change with time with a thin solid line.

  Referring to FIG. 5 (a), when the current sensor 54 is normal, the steering angular velocity ω and the estimated steering angular velocity ωe show values that are somewhat close to each other, and show a similar transition with time.

  On the other hand, referring to FIG. 5 (b), after the failure of the current sensor 54, the estimated steering angular velocity ωe is significantly different from the steering angular velocity ω.

  Therefore, the failure detection means 51d determines that the difference between the estimated steering angular velocity ωe based on the detected current value Im detected by the current sensor 54 and the steering angular velocity ω based on the steering angle detected by the steering angle sensor 4 has a predetermined threshold value. If it exceeds, a failure of the current sensor 54 (shunt resistor 54a) can be detected.

  As described above, the EPS control device 1 (failure detection unit 51d) according to the present embodiment can detect a failure of the current sensor 54 without using the torque sensor 2 as in the first embodiment.

  As mentioned above, although the form for implementing this invention was explained in full detail, this invention is not limited to this specific embodiment, In the range of the summary of this invention described in the claim, various Can be modified or changed.

DESCRIPTION OF SYMBOLS 1 Electric power steering control apparatus 2 Torque sensor (steering torque detection means)
3 Steering angle sensor (steering angular velocity detection means)
51 microcomputer 51a target current determination means 51b target current limiting means 51c motor control means 51d failure detection means 53 motor drive circuit 53a switching element 53b switching element 53c switching element 53d switching element 54 current sensor (motor current detection means)
55 Motor voltage detection circuit (motor voltage detection means)

Claims (1)

A steering torque detecting means for detecting a steering torque input from the steering handle to the steering shaft;
Steering angle detection means for detecting a steering angle at the steering handle;
A motor provided in the steering mechanism for generating steering assist torque;
Motor current detecting means for detecting current flowing in the motor;
A motor drive circuit configured to form a bridge circuit with a plurality of switching elements to drive the motor ;
Before SL in accordance with the steering torque or the steering angle, and the target current determining means for determining a target current of the motor,
Target current limiting means for determining a limited target current that limits the target current so as to satisfy a predetermined condition ;
By the current detected by the previous SL motor current detecting means performs PWM driving of each said switching element of the motor drive circuit so as to follow the limited target current, and motor control means for controlling said motor,
A failure detection means for detecting a failure of the motor current detection means,
The target current limiting means, as the predetermined condition, the duty ratio of the PWM driving when the motor current detecting means is normal to determine the limited target current to be equal to or less than the predetermined ratio,
The failure detection means is in a situation where at least the target current determination means determines the target current based on the steering angle, and the duty ratio of the PWM drive currently performed exceeds the predetermined ratio. Detecting a failure of the motor current detection means,
Electric power steering control device.

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