JP5217901B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering apparatus.

  2. Description of the Related Art Conventionally, power steering apparatuses for vehicles include an electric power steering apparatus (EPS) using a motor as a drive source. In such EPS, various proposals have been made to realize a better steering feeling by utilizing the high controllability.

  For example, Patent Document 1 discloses a configuration in which various compensation control characteristics are changed based on a change rate (assist gradient) of a basic assist component with respect to a change in steering torque. That is, normally, EPS executes the application of assist force according to the steering torque detected based on the torsion angle of the torsion bar provided on the steering shaft, but the change in the assist gradient means that the spring of the torsion bar is changed. Equivalent to changing the constant. And the said structure is a structure which implement | achieves a favorable steering feeling by optimizing the characteristic of the various compensation control according to the change of such basic steering characteristics.

  By the way, as one of the compensation controls to which the characteristic change based on the assist gradient is applied, the vibration of the steering system caused by the application of reverse input stress from the road surface or the like through the steered wheels (for example, the resonance of the rack shaft or the suspension). There is a vibration suppression control for suppressing).

  That is, the vibration (reverse input vibration) caused by the application of reverse input stress to the steered wheels called so-called flutter, shimmy, etc. is, for example, the absolute value or change amount of the input steering torque, such as in a straight traveling state. When the assist force applied to the steering system is small, that is, when the assist gradient is relatively small, it is likely to be manifested. As vibration suppression control, a method of calculating a compensation component based on the steering torque differential value (torque differential control) is generally used, but tends to become excessive during normal steering when the assist gradient is large. In some cases, such as a so-called “disengagement feeling” may cause a situation where the user feels excessive assistance, and the steering feeling may be impaired.

Therefore, the larger the assist gradient value, the smaller the calculated compensation component (more positively, the compensation component is calculated only when the assist gradient value is relatively small). Like), the characteristic of the said vibration suppression control is changed. As a result, the occurrence of excessive assist during normal steering is avoided, and the occurrence of reverse input vibration during straight traveling is effectively suppressed to maintain good steering feeling.
JP 2006-131191 A

  However, in actuality, even during normal steering, the assist gradient may have a small value, such as when driving straight ahead, such as lane change or reverse steering. For example, as shown in FIG. 9, when hysteresis is set in the assist characteristic, in a situation where so-called reverse steering is performed across the steering neutral position (the steering angle generated by the steering operation is zero, that is, the steering angle θs = 0). Are points P1 and P2 at which the steering torque τ becomes “0”. That is, in the conventional technique, the steering angle θs is not always maintained in the vicinity of zero as in the straight traveling state, and the compensation component for suppressing the reverse input vibration is calculated even during normal steering. The assist force is given. As a result, there is a problem in that the continuity of the steering feeling is lost and the driver feels uncomfortable. In this respect, there is still room for improvement.

  The present invention has been made to solve the above-described problems, and its purpose is to more reliably avoid the occurrence of vibration due to reverse input during straight traveling while avoiding excessive assist during normal steering. An object of the present invention is to provide an electric power steering device that can suppress and realize a good steering feeling without a feeling of slipping out.

  In order to solve the above-described problems, the invention according to claim 1 is directed to a steering force assisting device that applies an assist force for assisting a steering operation to a steering system using a motor as a drive source, and the steering force assisting device. Control means for controlling the operation, and the control means calculates a basic component of the assist force to be generated by the steering force assisting device based on a steering torque, and is generated by applying reverse input stress through the steered wheels. The compensation control for suppressing the vibration of the steering system is executed, and based on the assist gradient that is the ratio of the change in the basic component to the change in the steering torque, the larger the assist gradient value, the more the calculation is performed. An electric power steering apparatus that changes the characteristics of the compensation control so that a compensation component is reduced, wherein the control means is configured to perform the steering operation. The larger sly steering angle, that the compensation component is the operation to change the properties of the compensation control so as to reduce, and the gist.

  In other words, the vibration caused by the application of reverse input stress through the steered wheels tends to be manifested when the assist gradient is relatively small as in straight traveling, but the assist gradient is also observed during straight traveling during normal steering. It may take such a small value.

  In this regard, as in the above configuration, not only when the assist gradient is small, but also when the steering angle generated by the steering operation is small, for example, when indicating the vicinity of the steering neutral indicating that the vehicle is running straight, By changing the compensation control characteristic so that the calculated compensation component becomes smaller, it is possible to more reliably avoid the occurrence of excessive assist during normal steering. As a result, the continuity of the steering feeling is lost due to the application of such an excessive assist force, and thus it is possible to effectively prevent the occurrence of a situation that makes the driver feel uncomfortable.

The gist of the invention described in claim 2 is that the control means executes the compensation control based on a differential value of the steering torque.
That is, regardless of the calculation method, excessive compensation components are not desirable, but in particular, the compensation components calculated based on the steering torque differential value tend to cause excessive assist as the assist gradient increases. Therefore, a more remarkable effect can be obtained by applying the invention of claim 1 to the configuration as described above.

  According to the present invention, it is possible to more reliably avoid the occurrence of excessive assist during normal steering, and suppress the occurrence of vibration due to reverse input during straight traveling, thereby realizing a good steering feeling without feeling of coming off. It is possible to provide an electric power steering device capable of achieving the above.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of the EPS 1 of the present embodiment. As shown in the figure, a steering shaft 3 to which a steering wheel (steering) 2 is fixed is connected to a rack 5 via a rack and pinion mechanism 4. It is converted into a reciprocating linear motion of the rack 5 by the and pinion mechanism 4. The rudder angle of the steered wheels 6 is changed by the reciprocating linear motion of the rack 5.

  Further, the EPS 1 includes an EPS actuator 10 as a steering force assisting device that applies an assist force for assisting a steering operation to the steering system, and an ECU 11 as a control unit that controls the operation of the EPS actuator 10. .

  The EPS actuator 10 of the present embodiment is a so-called rack-type EPS actuator in which a motor 12 that is a driving source thereof is arranged coaxially with the rack 5, and an assist torque generated by the motor 12 is a ball screw mechanism (not shown). Is transmitted to the rack 5 via. In addition, the motor 12 of this embodiment is a brushless motor, and rotates by receiving supply of three-phase (U, V, W) driving power from the ECU 11. And ECU11 as a motor control apparatus controls the assist force given to a steering system by controlling the assist torque which this motor 12 generate | occur | produces (power assist control).

  In the present embodiment, a torque sensor 14, a vehicle speed sensor 15, and a steering angle sensor 16 are connected to the ECU 11. In the present embodiment, the torque sensor 14 employs a so-called twin resolver type torque sensor that detects a torsion angle of a torsion bar provided in the middle of the steering shaft 3 with a pair of angle sensors (resolvers). The ECU 11 operates the EPS actuator 10 based on the steering torque τ (τ_na) and the vehicle speed V detected by the torque sensor 14, the vehicle speed sensor 15, and the steering angle sensor 16 and the steering angle θs, that is, the power. Execute assist control.

Next, the electrical configuration of the EPS of this embodiment will be described.
FIG. 2 is a control block diagram of the EPS of this embodiment. As shown in the figure, the ECU 11 includes a microcomputer 17 as motor control signal output means for outputting a motor control signal, and a drive circuit 18 for supplying three-phase drive power to the motor 12 based on the motor control signal. ing.

  In the present embodiment, the ECU 11 is connected to a current sensor 20 for detecting an actual current value I supplied to the motor 12 and a rotation angle sensor 21 for detecting a motor rotation angle θm. Then, the microcomputer 17 controls the drive circuit 18 based on the vehicle state quantities and the actual current value I of the motor 12 and the motor rotation angle θm detected based on the output signals of the current sensor 20 and the rotation angle sensor 21. A motor control signal to be output is generated.

  More specifically, the microcomputer 17 calculates the target value of the assist force applied to the steering system, that is, the current command value calculation unit 22 that calculates the current command value Iq * corresponding to the target assist force, and the current command value calculation unit 22. And a motor control signal output unit 23 that outputs a motor control signal based on the current command value Iq *.

  The current command value Iq * output from the current command value calculation unit 22 is output to the motor control signal output unit 23 together with the actual current value I detected by the current sensor 20 and the motor rotation angle θm detected by the rotation angle sensor 21. Entered. The motor control signal output unit 23 calculates a motor control signal by executing feedback control so that the actual current value I follows the current command value Iq * corresponding to the target assist force.

  Specifically, in the present embodiment, a brushless motor that rotates by supplying three-phase (U, V, W) driving power is used as the motor 12. Then, the motor control signal output unit 23 converts the phase current values (Iu, Iv, Iw) of the motor 12 detected as the actual current value I into d, q axis current values in the d / q coordinate system (d / q The current feedback control is performed by performing conversion.

  That is, the current command value Iq * is input to the motor control signal output unit 23 as a q-axis current command value, and the motor control signal output unit 23 outputs the phase current based on the motor rotation angle θm detected by the rotation angle sensor 21. The value (Iu, Iv, Iw) is d / q converted. The motor control signal output unit 23 calculates the d and q axis voltage command values based on the d and q axis current values and the q axis current command value. Then, the phase voltage command values (Vu *, Vv *, Vw *) are calculated by performing d / q inverse conversion on the d and q axis voltage command values, and a motor control signal is generated based on the phase voltage command values. To do.

  In the ECU 11 of the present embodiment, the microcomputer 17 outputs the motor control signal generated as described above to the drive circuit 18, and the drive circuit 18 supplies the three-phase drive power based on the motor control signal to the motor 12. Is configured to control the operation of the EPS actuator 10.

Next, details of the current command value calculation by the current command value calculation unit 22 will be described.
The current command value calculation unit 22 of the present embodiment includes a basic assist control unit 25 that calculates a basic assist control amount Ias *, which is a basic component of the current command value Iq * indicating the target assist force, and a steered wheel as a compensation component thereof. And a vibration suppression control unit 26 for calculating a vibration suppression compensation amount Ivr * for suppressing the vibration of the steering system caused by the application of reverse input stress to 6.

  In the present embodiment, the steering torque τ_na as a detection signal output from the torque sensor 14 is first input to the phase compensation control unit 27. Then, the steering torque τ and the vehicle speed V after the phase compensation processing is performed in the phase compensation control unit 27 are input to the basic assist control unit 25.

  The basic assist control unit 25 calculates the basic assist control amount Ias * having a larger absolute value as the absolute value of the steering torque τ is larger and the vehicle speed V is smaller (see FIG. 3). In particular, with respect to the relationship with the steering torque τ, the assist gradient Rag, which is the ratio of the change in the basic assist control amount Ias * to the change in the steering torque τ, increases as the steering torque τ increases. Yes.

  Here, the microcomputer 17 of the present embodiment has a function of changing the characteristics of each compensation control based on the assist gradient Rag whose value changes according to the steering torque τ detected as described above. (Assist gradient compensation control).

  Specifically, in the present embodiment, the basic assist control unit 25 outputs an assist gradient Rag to the phase compensation control unit 27. Then, the phase compensation control unit 27 of the present embodiment changes the filter constant based on the input assist gradient Rag so that the gain of the filter characteristic is reduced according to the increase of the assist gradient Rag. It has a configuration (see FIG. 4).

  That is, the change in the assist gradient Rag is equivalent to the change in the spring constant of the torsion bar provided in the middle of the steering shaft 3, and as the assist gradient Rag increases, vibration tends to occur. However, by changing the characteristics of the phase compensation control as described above, specifically, by suppressing the gain of the filter characteristics in the phase compensation processing to a low level, it is possible to suppress the increase in vibration associated with the increase of the assist gradient Rag. Yes.

  On the other hand, in the present embodiment, the vibration suppression control unit 26 receives a differential value of the steering torque τ (steering torque differential value dτ). And the vibration suppression control part 26 performs the vibration suppression control based on the steering torque differential value dτ. That is, the assist force is applied in a direction that reduces torsion of the torsion bar, but the compensation component based on the steering torque differential value dτ acts in a direction that strengthens the movement. That is, the torsion bar torsion caused by the application of reverse input stress to the steered wheels 6 also acts in a direction to cancel this. And thereby, the vibration which generate | occur | produces in a steering system resulting from the application of reverse input stress with respect to the steered wheel 6, such as what is called a flutter and shimmy can be suppressed.

  Specifically, the vibration suppression control unit 26 of the present embodiment is provided with a basic control amount calculation unit 28 that calculates a basic control amount ε that is the basis of the vibration suppression compensation amount Ivr * based on the steering torque differential value dτ. It has been. The basic control amount calculation unit 28 calculates a larger basic control amount ε as the input steering torque differential value dτ (the absolute value thereof) increases (see FIG. 5).

  In the present embodiment, the vibration suppression control unit 26 is input with the vehicle torque V, the assist gradient Rag, and the steering angle θs together with the steering torque differential value dτ. And the vibration suppression control part 26 changes the characteristic of the vibration suppression control which the said vibration suppression control part 26 performs based on these each state quantity input.

  Specifically, the vibration suppression control unit 26 is provided with a vehicle speed gain calculation unit 29, an assist gradient gain calculation unit 30, and a steering angle gain calculation unit 31 corresponding to each of these state quantities. Then, the vibration suppression control unit 26 suppresses vibration by using the multiplier 32 to multiply the basic control variable ε by the vehicle speed gain Kv, the assist gradient gain Kag, and the steering angle gain Kan calculated by each gain calculation unit. The compensation amount is output as Ivr *.

  Specifically, the vehicle speed gain calculation unit 29 is configured to calculate a vehicle speed gain Kv having a larger value as the vehicle speed increases (see FIG. 6). Further, as shown in FIG. 7, the assist gradient gain calculation unit 30 calculates the assist gradient gain Kag having a smaller value, that is, finally, as the value (absolute value) of the input assist gradient Rag is larger. The assist gradient gain Kag is calculated so that the vibration suppression compensation amount Ivr * as the compensation component becomes small. As shown in FIG. 8, the rudder angle gain calculation unit 31 finally calculates the rudder angle gain Kan having a smaller value as the value (absolute value) of the input steering angle θs increases. The steering angle gain Kan is calculated so that the vibration suppression compensation amount Ivr * as the compensation component becomes small.

  More specifically, the assist gradient gain calculation unit 30 is configured to calculate “0” as the assist gradient gain Kag when the value (absolute value) of the input assist gradient Rag is equal to or greater than a predetermined threshold value α. ing. Then, the steering angle gain calculation unit 31 also sets the steering angle gain Kan as “the steering angle gain Kan” when the input value (absolute value) of the steering angle θs is equal to or larger than the predetermined angle θ0 set near the steering neutral position. It is configured to calculate “0”.

  That is, vibration (reverse input vibration) caused by application of reverse input stress to the steered wheels 6 is easily manifested when the assist gradient Rag is relatively small as in straight traveling, and is based on the steering torque differential value dτ. The calculated basic control amount ε tends to become excessive as the assist gradient Rag increases. Therefore, as described above, the larger the assist gradient Rag value (absolute value), the smaller the assist gradient gain Kag multiplied by the basic control amount ε, thereby causing excessive assist during normal steering. While avoiding, it is possible to effectively suppress the occurrence of reverse input vibration during straight traveling.

  However, as described above, in actuality, even during normal steering, the assist gradient Rag may have a small value as when traveling straight ahead (see FIG. 9). In such a case, an excessive assist force is applied to the steering system by outputting the vibration suppression compensation amount Ivr * in a state where it is not sufficiently reduced. There is a risk that the continuity of the ring will be lost, and the driver may feel uncomfortable.

  In this respect, as described above, the larger the value (absolute value) of the input assist gradient Rag, the smaller the value of the steering angle gain Kan multiplied by the basic control amount ε, and the value of the steering angle θs. Is equal to or greater than a predetermined angle θ0 set in the vicinity of the steering neutral position, the steering angle gain Kan is set to “0”. In other words, the output of the vibration suppression compensation amount Ivr * is specialized in a state indicating that the vehicle is in a straight traveling state, that is, when the steering angle (steering angle θs) of the steering wheel 2 is near the steering neutral position. It is possible to suppress the occurrence of reverse input vibration during straight traveling while reliably avoiding the occurrence of excessive assist during normal steering.

  As shown in FIG. 2, the vibration suppression compensation amount Ivr * calculated by the vibration suppression control unit 26 in this way is superimposed on the basic assist control amount Ias * in the adder 33. The current command value calculation unit 22 is configured to output the value added by the adder 33 to the motor control signal output unit 23 as the current command value Iq *.

As described above, according to the present embodiment, the following operations and effects can be obtained.
The vibration suppression control unit 26 includes an assist gradient gain calculation unit 30 that calculates an assist gradient gain Kag based on the assist gradient Rag and a steering angle gain calculation unit 31 that calculates a steering angle gain Kan based on the steering angle θs. The assist gradient gain calculation unit 30 calculates an assist gradient gain Kag having a smaller value as the assist gradient Rag value (absolute value) increases, and the steering angle gain calculation unit 31 calculates the steering angle θs value (absolute value). ) Is larger, the steering angle gain Kan having a smaller value is calculated. Then, the vibration suppression control unit 26 calculates the vibration suppression compensation amount Ivr * by multiplying the assist gradient gain Kag and the steering angle gain Kan by the basic control amount ε calculated based on the steering torque differential value dτ.

  That is, vibration (reverse input vibration) caused by application of reverse input stress to the steered wheels 6 is easily manifested when the assist gradient Rag is relatively small as in straight traveling, and is based on the steering torque differential value dτ. The calculated basic control amount ε tends to become excessive as the assist gradient Rag increases. Further, even during normal steering, the assist gradient Rag may have a small value as when traveling straight ahead.

  In this respect, as in the above-described configuration, not only when the assist gradient Rag is small but also when the steering angle θs is small, that is, when the steering angle of the steering wheel 2 indicating that the vehicle is in the straight traveling state is in the vicinity of the steering neutral. By generating the vibration suppression compensation amount Ivr *, the occurrence of excessive assist during normal steering can be avoided more reliably. As a result, it is possible to effectively suppress the occurrence of a situation in which the continuity of the steering feeling is lost due to the application of an excessive assist force, and thus the driver feels uncomfortable, such as a feeling of slipping.

In addition, you may change this embodiment as follows.
In the present embodiment, the basic control amount calculation unit 28 calculates the basic control amount ε that is the basis of the vibration suppression compensation amount Ivr * based on the steering torque differential value dτ. However, the present invention is not limited thereto, and the present invention may be applied to a configuration in which vibration suppression control is executed by other methods using other than the steering torque differential value dτ.

  In the present embodiment, the assist gradient gain calculation unit 30 calculates the assist gradient gain Kag having a smaller value as the assist gradient Rag value (absolute value) is larger (see FIG. 7), and the steering angle gain calculation unit. No. 31 calculates the steering angle gain Kan having a smaller value as the value (absolute value) of the input steering angle θs is larger (see FIG. 8). However, the present invention is not limited to this, and the assist gradient gain Kag and the steering angle gain Kan always change continuously according to changes in the corresponding assist gradient Rag and steering angle θs as shown in the corresponding drawings. It doesn't have to be. For example, it may be changed stepwise on a step, or may be configured to be turned on / off at a predetermined threshold (for example, “α” or “θ0”).

The schematic block diagram of an electric power steering device (EPS). The control block diagram of EPS in this embodiment. Explanatory drawing which shows the outline | summary of a basic assist control calculation and an assist gradient. Explanatory drawing which shows the aspect of the assist gradient compensation control about a phase compensation process. Explanatory drawing which shows the relationship between a steering torque differential value and a basic control amount. Explanatory drawing which shows the relationship between a vehicle speed and a vehicle speed gain. Explanatory drawing which shows the relationship between an assist gradient and an assist gradient gain. Explanatory drawing which shows the relationship between a steering angle and a steering angle gain. Explanatory drawing which shows an example in case an assist gradient takes a small value at the time of normal steering.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus (EPS), 2 ... Steering, 6 ... Steering wheel, 10 ... EPS actuator, 11 ... ECU, 12 ... Motor, 14 ... Torque sensor, 16 ... Steering angle sensor, 17 ... Microcomputer, 18 ... Drive Circuit, 22 ... Current command value calculation unit, 23 ... Motor control signal output unit, 25 ... Basic assist control unit, 26 ... Vibration suppression control unit, 27 ... Phase compensation control unit, 28 ... Basic control amount calculation unit, 29 ... Vehicle speed Gain calculating unit, 30 Assist gradient gain calculating unit, 31 Steering angle gain calculating unit, 32 Multiplier, 33 Adder, τ, τ_na Steering torque, V Vehicle speed, dτ Steering torque differential value, Rag Assist gradient, α ... threshold, θs ... steering angle, θ0 ... predetermined angle, Iq * ... current command value, Ias * ... basic assist control amount, Ivr * ... vibration suppression compensation amount, ε ... basic control amount, Kag ... assist gradient gain, Kan: Rudder angle gain, Kv: Vehicle speed gain.

Claims (2)

A steering force assisting device for applying an assisting force for assisting a steering operation to a steering system using a motor as a drive source; and a control means for controlling the operation of the steering force assisting device, wherein the control means adjusts the steering torque. And calculating a basic component of the assist force to be generated by the steering force assisting device, executing compensation control for suppressing vibration of the steering system caused by application of reverse input stress through the steered wheels, and Based on the assist gradient that is the ratio of the change in the basic component to the change in the electric power steering device, the characteristic of the compensation control is changed so that the calculated compensation component becomes smaller as the value of the assist gradient is larger Because
The control means changes the characteristic of the compensation control so that the calculated compensation component becomes smaller as the steering angle generated by the steering operation increases.
An electric power steering device. The electric power steering apparatus according to claim 1, wherein
The control means performs the compensation control based on a differential value of the steering torque;
An electric power steering device.

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