JP2012201333A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device which suppresses vibration without delay and provides improved steering feelings.SOLUTION: An ECU 23 includes: a microcomputer 41 which outputs a motor control signal; and a drive circuit 42 which supplies drive power to a motor 21 on the basis of the motor control signal. The microcomputer 41 includes a motor control signal output section 44 including: an F/B control section 57 which calculates a voltage command value V* by multiplying a current deviation ΔI by an F/B gain K; and a PWM conversion section 58 which generates the motor control signal on the basis of the voltage command value V*. The motor control signal output section 44 includes an F/B gain calculation part 61 which changes a value of the F/B gain K into low response value when a vehicle is in a straight moving state.

Description

  The present invention relates to an electric power steering apparatus.

  2. Description of the Related Art Conventionally, power steering devices for vehicles include electric power steering devices (EPS) using a motor as a drive source. Usually, in such EPS, the power assist is based on steering torque transmitted to a steering system. Control is performed. In recent years, it has become common to improve steering feeling by executing various compensation controls utilizing the high degree of freedom of control.

  For example, Patent Document 1 discloses a basic component that is a basic component of an assist force that calculates a compensation control amount according to a torque differential value obtained by differentiating a steering torque detected by a torque sensor and applies the compensation control amount to a steering system. An EPS is disclosed in which disturbances such as brake vibration generated by a brake operation, for example, are suppressed by being superimposed on the assist control amount.

JP 2004-276804 A

  By the way, in general, the torque sensor detects the steering torque based on the twist of the torsion bar. Therefore, the vibration cannot be detected unless the torsion bar is twisted by the vibration due to the disturbance. Later in time. In this regard, in the configuration of Patent Document 1 described above, the time delay is reduced by calculating the compensation control amount based on the torque differential value obtained by differentiating the steering torque and advancing the phase. There is no denying that there will be a delay. Further, if the compensation control amount is increased in order to increase the vibration suppression effect, there is a possibility that the steering feeling is lowered, for example, the feeling of responsiveness is reduced. In this respect, there is still room for improvement.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide an electric power steering apparatus that can suppress vibration without delay and has excellent steering feeling.

  In order to achieve the above object, the invention according to claim 1 is directed to a steering force assisting device that applies an assisting force for assisting a steering operation to a steering system using a motor as a driving source, and supply of driving power to the motor. Control means for controlling the operation of the steering force assisting device, the control means calculates a target assist force to be generated by the steering force assisting device based on a steering torque transmitted to the steering system, and In the electric power steering apparatus that executes feedback control so that the actual current value follows the current command value corresponding to the target assist force, the feedback control is based on a deviation between the current command value and the actual current value and a feedback gain. By applying a voltage to the motor, the actual current value follows the current command value. There, the control unit, when the vehicle is running straight is summarized in that to change the gain of the feedback control to reduce the responsiveness of the feedback control.

  That is, when the feedback control response is low, the value of the voltage applied to the motor is small with respect to the current deviation (absolute value thereof). In other words, since the change in the voltage applied to the motor is slow, even if an induced voltage is generated by the motor rotating (vibrating in the rotational direction) due to the influence of brake vibration, the induced voltage can be canceled immediately. become unable. As a result, when a current based on the induced voltage is generated, a force (brake) that impedes rotation of the motor acts on the motor, so that vibration transmitted to the steering by the motor is suppressed. In this case, since vibration is suppressed by generating an induced voltage in the motor, the vibration is suppressed without delay unlike the case of adding a compensation control amount based on the detected steering torque.

  However, when the vehicle turns due to the driver's steering, if the feedback control response is low, the assist force is not immediately applied to the steering system, resulting in a decrease in steering feeling. Therefore, when the vehicle is in a straight traveling state as in the above configuration, it is possible to suppress the brake vibration transmitted to the steering without delay by reducing the responsiveness of the feedback control and to promptly assist during steering. An excellent steering feeling can be realized by applying force.

  ADVANTAGE OF THE INVENTION According to this invention, a vibration can be suppressed without delay and the electric power steering apparatus excellent in steering feeling can be provided.

The schematic block diagram of an electric power steering device (EPS). The control block diagram of ECU. The flowchart which shows the process sequence of F / B gain variable calculation. The schematic block diagram of the map used for the calculation of F / B gain of another example.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the drawings.
As shown in FIG. 1, in an electric power steering apparatus (EPS) 1, a steering shaft 3 to which a steering 2 is fixed is connected to a rack shaft 5 via a rack and pinion mechanism 4. Thereby, the rotation of the steering shaft 3 accompanying the steering operation is converted into a reciprocating linear motion of the rack shaft 5 by the rack and pinion mechanism 4. The steering shaft 3 is formed by connecting a column shaft 8, an intermediate shaft 9, and a pinion shaft 10. The reciprocating linear motion of the rack shaft 5 accompanying the rotation of the steering shaft 3 is transmitted to a knuckle (not shown) via tie rods 11 connected to both ends of the rack shaft 5, whereby the steered angle of the steered wheels 12. That is, the traveling direction of the vehicle is changed.

  The EPS 1 is an EPS actuator 22 serving as a steering force assisting device that applies an assist force for assisting a steering operation to the steering system using the motor 21 as a driving source, and a control unit that controls the operation of the EPS actuator 22. ECU23.

  The EPS actuator 22 is configured as a so-called column type EPS actuator in which a motor 21 as a driving source thereof is drivingly connected to the column shaft 8 via a speed reduction mechanism 25. Note that a brushed DC motor is employed as the motor 21 of the present embodiment. The EPS actuator 22 is configured to apply the motor torque as an assist force to the steering system by decelerating and transmitting the rotation of the motor 21 to the column shaft 8.

  On the other hand, a vehicle speed sensor 31, a torque sensor 32, and a steering sensor (steering angle sensor) 33 are connected to the ECU 23. In the present embodiment, a torsion bar 34 is provided in the middle of the column shaft 8, and the torque sensor 32 is configured to detect the steering torque T based on the twist of the torsion bar 34. The ECU 23 is configured to control the operation of the EPS actuator 22 by supplying driving power to the motor 21 based on these state quantities (power assist control).

Next, the electrical configuration of the EPS of this embodiment will be described.
As shown in FIG. 2, the ECU 23 includes a microcomputer 41 that outputs a motor control signal, and a drive circuit 42 that supplies drive power to the motor 21 based on the motor control signal.

  The drive circuit 42 is formed by connecting a plurality (four) of switching elements (MOSFETs) in a bridge shape, and each pair of switching elements positioned diagonally is turned on / off according to the rotation direction of the motor 21. Thus, a known configuration for outputting drive power based on the applied voltage is provided. Each control block shown below is realized by a computer program executed by the microcomputer 41. The microcomputer 41 detects each state quantity at a predetermined sampling cycle (detection cycle), and generates a motor control signal by executing each calculation process shown in the following control blocks at each predetermined cycle. .

  The microcomputer 41 includes a current command value calculation unit 43 that calculates a target value of power supply to the motor 21, that is, a current command value I * corresponding to the target assist force, and a current command value I calculated by the current command value calculation unit 43. And a motor control signal output unit 44 that outputs a motor control signal based on *.

  The current command value calculation unit 43 is provided with a basic assist control unit 51, and the vehicle speed SPD and the steering torque T are input to the basic assist control unit 51. In the present embodiment, the steering torque T ′ after the low-pass filter processing in the stabilization filter 52 is input to the current command value calculation unit 43. Then, the basic assist control unit 51 calculates a basic assist control amount Ias * as a basic control component corresponding to the target assist force based on the steering torque T ′ and the vehicle speed SPD. Specifically, the basic assist control unit 51 calculates the basic assist control amount Ias * having a larger value (absolute value) as the steering torque T ′ (absolute value thereof) is larger and the vehicle speed SPD is slower. It is configured as follows.

  The current command value calculation unit 43 is provided with a disturbance suppression control unit 53, and a torque differential value dT obtained by differentiating the steering torque T is input to the disturbance suppression control unit 53. The disturbance suppression control unit 53 calculates a disturbance suppression control amount Iti * as a compensation component to be added to the basic assist control amount Ias * based on the torque differential value dT. Specifically, the disturbance suppression control unit 53 increases the basic assist control amount Ias * (absolute value) calculated by the basic assist control unit 51 as the input torque differential value dT (absolute value) increases. The disturbance suppression control amount Iti * having a value that increases is calculated. Note that, by superimposing the disturbance suppression control amount Iti * on the basic assist control amount Ias *, for example, there is an effect of suppressing disturbance such as brake vibration caused by a brake operation.

  The basic assist control amount Ias * and the disturbance suppression control amount Iti * calculated in this way are input to the adder 54. Then, the current command value calculation unit 43 outputs a value based on the added value of the basic assist control amount Ias * and the disturbance suppression control amount Iti * to the motor control signal output unit 44 as the current command value I *.

  On the other hand, the motor control signal output unit 44 receives the current command value I * output from the current command value calculation unit 43 and the actual current value I of the motor 21 detected by the current sensor 55. The motor control signal output unit 44 generates a motor control signal by executing feedback control (PI control) so that the actual current value I follows the current command value I *, and outputs the motor control signal to the drive circuit 42. It is the composition to do.

  In the motor control signal output unit 44, the current command value I * and the actual current value I are input to the subtractor 56, and the current deviation ΔI calculated in the subtractor 56 is input to the F / B (feedback) control unit 57. The Then, the F / B control unit 57 executes the feedback control based on the current deviation ΔI and the F / B gain (PI gain) K.

  Specifically, the F / B control unit 57 calculates the voltage command value V * by multiplying the current deviation ΔI by the F / B gain K. That is, as the F / B gain K increases, the value of the voltage command value V * with respect to the current deviation ΔI increases and the responsiveness of the feedback control increases. On the other hand, the smaller the F / B gain K, the smaller the voltage command value V * with respect to the current deviation ΔI, and the lower the feedback control response. The voltage command value V * calculated by the F / B control unit 57 is input to the PWM conversion unit 58, and the PWM conversion unit 58 generates a motor control signal based on the voltage command value V *.

  The motor control signal generated in this way is output from the microcomputer 41 to the drive circuit 42, and the drive power based on the motor control signal is supplied to the motor 21 by the drive circuit 42. A motor torque corresponding to the driving power (energization current amount) is applied to the steering system as an assist force.

(Feedback gain variable control)
Next, an aspect of F / B gain variable control in the EPS of the present embodiment will be described.
As described above, although it is possible to suppress the brake vibration and the like by superimposing the disturbance suppression control amount Iti * based on the torque differential value dT on the basic assist control amount Ias *, there is a delay in the effect. can not deny. Further, if the disturbance suppression control amount Iti * is increased in order to increase the vibration suppression effect, there is a possibility that the steering feeling will be lowered instead, for example, the feeling of response is reduced.

  Here, when the responsiveness of the feedback control is low, the value of the voltage command value V * relative to the current deviation ΔI (absolute value thereof) becomes small. That is, since the change in the voltage applied to the motor 21 is slow, even if an induced voltage is generated by the motor 21 rotating (vibrating in the rotation direction) due to the influence of disturbance such as brake vibration, the induced voltage is immediately generated. Cannot be countered. As a result, since a current based on the induced voltage is generated, a force (brake) that impedes the rotation is applied to the motor 21, so that vibration transmitted to the steering 2 (the steering shaft 3) by the motor 21 is generated. It will be suppressed. However, when the vehicle turns due to the driver's steering, if the feedback control response is low, the assist force is not quickly applied, and the steering feeling is reduced.

  In consideration of this point, the motor control signal output unit 44 is provided with an F / B gain calculation unit 61 that calculates the F / B gain K used in feedback control by the F / B control unit 57. Then, the F / B gain calculation unit 61 determines whether or not the vehicle is in a straight traveling state. If it is determined that the vehicle is in a straight traveling state, the F / B gain K is set to reduce the responsiveness of the feedback control. Change the value to a smaller value.

  More specifically, the steering torque T detected by the torque sensor 32 and the steering speed ωs that is a differential value of the steering angle θs detected by the steering sensor 33 are input to the F / B gain calculator 61. The F / B gain calculation unit 61 determines that the vehicle is traveling straight when the steering torque T is substantially zero and the steering speed ωs is substantially zero. When the F / B gain calculation unit 61 determines that the vehicle is in the straight traveling state, the F / B gain calculating unit 61 sets the value of the F / B gain K to the low response value K1, and when it is determined that the vehicle is not in the straight traveling state, The value of the F / B gain K is set to a high response value K2 that is larger than the low response value K1. Accordingly, when the vehicle is in a straight traveling state, the value of the F / B gain K becomes the low response value K1, so that the responsiveness of the feedback control executed by the F / B control unit 57 is reduced, and the brake vibration or the like Is to be suppressed.

Next, the processing procedure of the F / B gain variable calculation by the F / B gain calculation unit of the present embodiment will be described with reference to the flowchart of FIG.
When the F / B gain calculation unit 61 acquires the steering torque T and the steering speed ωs as sensor values (step 101), it determines whether or not the absolute value of the steering torque T is smaller than the predetermined torque Tth (step 102). . The predetermined torque Tth is set to a value slightly larger than zero in consideration of noise and the like. Subsequently, when the absolute value of the steering torque T is smaller than the predetermined torque Tth (step 102: YES), it is determined whether or not the steering speed ωs is smaller than the predetermined steering speed ωth (step 103). The predetermined steering speed ωth is set to a value slightly larger than zero in consideration of noise and the like. Then, when the steering speed ωs is smaller than the predetermined steering speed ωth (step 103: YES), the F / B gain calculation unit 61 determines that the vehicle is in a straight traveling state and determines the value of the F / B gain K. Is set to the low response value K1 (step 104).

On the other hand, when the absolute value of the steering torque T is equal to or greater than the predetermined torque Tth (step 102: NO) and when the steering speed ωs is equal to or greater than the predetermined steering speed ωth (step 103: NO) ), It is determined that the vehicle is not in a straight traveling state, and the value of the F / B gain K is set to the high response value K2 (step 105).
As described above, according to the present embodiment, the following operational effects can be achieved.

  (1) When the F / B gain calculation unit 61 determines that the vehicle is in the straight traveling state, the F / B gain calculation unit 61 sets the value of the F / B gain K to the low response value K1 and determines that the vehicle is not in the straight traveling state. The value of the F / B gain K is set to the high response value K2.

  According to the above configuration, when the vehicle is in a straight traveling state, the response of feedback control becomes low. Therefore, even if an induced voltage is generated in the motor 21 due to the influence of brake vibration or the like, the induced voltage is canceled immediately. Therefore, vibration transmitted to the steering shaft 3 by the motor 21 can be reduced. In this way, the vibration is suppressed by the generation of the induced voltage in the motor 21. Therefore, unlike the case where the compensation control amount based on the detected steering torque is added, the vibration can be suppressed without delay. Further, when it is determined that the vehicle is not in a straight traveling state, that is, when the vehicle is in a turning state, the responsiveness of the feedback control is increased, so that the assist force can be quickly applied to the steering system, and excellent steering is achieved. Feeling can be realized.

  (2) Since the F / B gain calculation unit 61 determines whether or not the vehicle is in a straight traveling state based on the steering torque T and the steering speed ωs, for example, the vehicle is held in a turning state. Even when it is determined that the vehicle is in the straight traveling state only by the steering speed ωs such as the situation, it can be determined whether or not the vehicle is in the straight traveling state without erroneous determination. As a result, even in a situation where the vehicle is steered in a turning state, the assist force can be quickly applied, and a more excellent steering feeling can be realized.

In addition, the said embodiment can also be implemented in the following aspects which changed this suitably.
In the above embodiment, the F / B gain calculation unit 61 sets the value of the F / B gain K according to the magnitude comparison between the steering torque T and the steering speed ωs and the threshold value (the predetermined steering torque T and the predetermined steering speed ωth). The low response value K1 or the high response value K2 was changed. However, the present invention is not limited to this, and a map in which the steering torque T, the steering speed ωs, and the F / B gain K are associated with each other is provided in the F / B gain calculation unit 61, and the map is input by referring to the map. The F / B gain K corresponding to the steering torque T and the steering speed ωs may be calculated. For example, as shown in FIG. 4, such a map can be set so that the value of the F / B gain K increases as the steering torque T increases and the steering speed ωs increases.

  In the above embodiment, the F / B gain calculation unit 61 calculates different values of the F / B gain K according to the traveling state of the vehicle. However, the present invention is not limited to this. For example, the F / B gain calculation unit 61 outputs a constant F / B gain K, and multiplies the F / B gain K by a coefficient that changes according to the traveling state of the vehicle. Accordingly, the value of the F / B gain used for the feedback control of the F / B control unit 57 may be changed.

  In the above-described embodiment, it is determined whether or not the vehicle is traveling straight on the basis of the steering torque T and the steering speed ωs. However, the present invention is not limited to this, and various methods can be adopted. For example, in the above embodiment, the condition that the steering angle θs is substantially zero may be added. Further, the determination may be made based on the vehicle speed SPD, the yaw rate, or the like.

  In the above embodiment, when the steering torque T is smaller than the predetermined torque Tth and the steering speed ωs is smaller than the predetermined steering speed ωth, the value of the F / B gain K is immediately changed. However, the value of the F / B gain K may be changed to the low response value K1 when the above condition is satisfied for a predetermined time. Similarly, the value of the F / B gain K is changed to the high response value K2 when the steering torque T is equal to or higher than the predetermined torque Tth or when the steering speed ωs is equal to or higher than the predetermined steering speed ωth for a predetermined time. It may be.

  In the above embodiment, the current command value I * is calculated by superimposing the disturbance suppression control amount Iti * based on the torque differential value dT on the basic assist control amount Ias *. However, the present invention is not limited to this, and the disturbance suppression control amount Iti * May not be superimposed, and the current command value I * may be calculated by superimposing another compensation control amount on the basic assist control amount Ias *.

  In the above embodiment, the present invention is embodied in a column assist type EPS, but may be applied to other types of EPS such as a so-called rack assist type. Further, a brushless motor may be adopted as the motor 21 that is a drive source of the EPS actuator 22.

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus, 21 ... Motor, 22 ... EPS actuator, 23 ... ECU, 41 ... Microcomputer, 42 ... Drive circuit, 43 ... Current command value calculating part, 44 ... Motor control signal output part, 57 ... F / B Control unit 61: F / B gain calculation unit I: Actual current value, I * current command value, ΔI: Current deviation, K: F / B gain, SPD: Vehicle speed, T: Steering torque, V *: Voltage command Value, ωs ... steering speed.

Claims (1)

A steering force assisting device for applying an assisting force for assisting a steering operation to a steering system using a motor as a driving source, and a control means for controlling the operation of the steering force assisting device through supply of driving power to the motor; The control means calculates a target assist force to be generated by the steering force assisting device based on a steering torque transmitted to the steering system, and causes an actual current value to follow a current command value corresponding to the target assist force. In an electric power steering apparatus that executes feedback control as much as possible,
In the feedback control, by applying a voltage based on a deviation and a feedback gain between the current command value and the actual current value to the motor, the actual current value is made to follow the current command value,
When the vehicle is in a straight traveling state, the control means changes the gain of the feedback control to reduce the responsiveness of the feedback control.

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