JP6505526B2 - Control device of electric power steering device - Google Patents

Description

  The present invention relates to a control device used in an electric power steering apparatus (EPS: Electric Power Steering) that assists (steering assists) a steering operation by a driving force of an electric motor.

  Conventionally, there is known an electric power steering apparatus mounted on a vehicle such as an automobile and configured to transmit the driving force of the electric motor to the steering mechanism as a steering assist force.

  In control of the electric power steering apparatus, a target current value is set according to a steering torque applied to a steering wheel (steering wheel) and a vehicle speed. In addition, when the steering wheel is returned to the neutral position after being cut into one (when the steering wheel is returned), the motor rotational speed is estimated from the voltage and current value between the terminals of the electric motor in order to improve the return performance. The steering wheel return current value is set according to the motor rotational speed. Specifically, the range including the zero for the motor rotational speed is set as the dead zone, and the steering wheel return current value is set to zero for the motor rotational speed in the dead zone, and for the motor rotational speed outside the dead zone. As the motor rotational speed is higher, the steering wheel return current value is set to a larger value. Then, the electric motor is feedback-controlled based on the target current value or the sum of the target current value and the steering wheel return current value. Thereby, a steering assist force corresponding to the steering state is applied to the steering mechanism.

JP 2001-171532 A

  However, the estimation accuracy of the motor rotational speed largely depends on the individual difference and the temperature of the winding resistance of the motor. In order to absorb the variation in the estimation accuracy, it is necessary to provide a wide dead zone where the steering wheel return current value is set to zero. When the dead zone is wide, when the motor rotational speed is low, the steering wheel return current is not supplied to the electric motor and the steering wheel return is not assisted.

  Therefore, when the steering wheel is returned at a low motor rotational speed, the self alignment torque may lose mechanical friction and the steering wheel may not return to the neutral position.

  In addition, when the rotation of the steering wheel is stopped by the hand while the driver releases the steering wheel from the steering wheel and the steering wheel is returned, the self alignment torque becomes mechanical friction even if the hand is released again from the steering wheel thereafter. Losing may cause the handle to stick in its position (handle return does not resume).

  Furthermore, when the driver slowly operates the steering wheel to the left and right, mechanical friction is felt, and the steering torque is not lost even when the steering wheel is in the neutral position, so there is a problem that the neutral position of the steering wheel is difficult to understand.

  An object of the present invention is to provide a control device of an electric power steering device, which can realize a good steering wheel return and can improve the steering feeling near the steering angle midpoint.

  In order to achieve the above object, a control device according to the present invention is a control device used in an electric power steering apparatus that assists steering by transmitting a driving force of an electric motor to a steering mechanism, and acquires a steering torque. Driving force of the electric motor in a direction corresponding to the steering torque based on the torque acquisition means, the steering angle acquisition means for acquiring the steering angle with respect to the steering angle midpoint, and the steering torque acquired by A basic assist current value setting means for setting a basic assist current value to be generated, a steering angular velocity calculation means for calculating a steering angular velocity based on a steering angle acquired by the steering angle acquisition means, a rudder calculated by the steering angular velocity calculation means A hysteresis is added to the steering angle acquired by the steering angle acquisition means based on the angular velocity, and the steering is performed based on the steering angle to which the hysteresis is applied. Current value setting means for middle point return setting the current value for middle point return which generates driving force of the motor, and basic assist current value set by the basic assist current value setting means and current value setting means for middle point return And a motor control means for controlling the electric motor on the basis of the addition value with the current value for midpoint return to be set.

  According to this configuration, the basic assist current value is set based on the steering torque. The current of the basic assist current value flows to the electric motor, whereby the electric motor generates a driving force in a direction corresponding to the steering torque. Further, the steering angular velocity is calculated from the steering angle with respect to the steering angle midpoint, and based on the steering angular velocity, hysteresis is given to the actual steering angle (actual steering angle) with respect to the steering angle midpoint. The steering angle to which the hysteresis is applied changes late with respect to the time change of the actual steering angle. Then, the midpoint return current value is set based on the steering angle (the hysteresis application steering angle) to which the hysteresis is applied. When a current having a midpoint return current value flows to the electric motor, the electric motor generates a driving force in the direction to reduce the steering angle.

  The electric motor is controlled based on the addition value of the basic assist current value and the midpoint return current value. Thereby, when the steering wheel (for example, the steering wheel) operated for steering of the vehicle is returned to the neutral position (steering-angle middle point) from the state where it is cut into one side or the other side to the neutral position Even if the steering torque is not applied to the steering wheel, the driving force according to the midpoint return current value is transmitted to the steering mechanism. Therefore, at the time of steering wheel return, a driving force corresponding to the current value for midpoint return is added to the self alignment torque, so that the steering wheel returns to the neutral position without losing mechanical friction.

  In addition, even if the rotation of the steering wheel is stopped by hand in the middle of the steering wheel return in the released state, the driving force according to the current value for return to middle point is transmitted to the steering mechanism, so the hand is released again from the steering wheel When it is done, the steering wheel begins to return to the neutral position again. Therefore, it is possible to prevent the occurrence of the sticking phenomenon due to the handgrip of the rotation of the handle during the return of the handle in the released state.

  Furthermore, since the driving force in the direction to reduce the steering angle, that is, the driving force in the direction to move the steering wheel toward the neutral position is transmitted to the steering mechanism, the driver is given a feeling of being in the neutral position be able to.

  Therefore, a favorable steering wheel return can be realized, and the steering feeling near the steering angle midpoint can be improved.

  Also, for example, when a range including a zero for the steering angle is set as a dead zone, and the current value for mid point return is set to zero with respect to the steering angle within the dead zone, the actual steering angle The steering angle to which the hysteresis is applied does not enter the dead zone even if the angle decreases to near the corner middle point, and the current value for middle point return is set to a value other than zero. Therefore, even when the actual steering angle decreases near the middle of the steering angle when the steering wheel is returned, the driving force in the direction in which the steering wheel is directed to the neutral position is transmitted from the electric motor to the steering mechanism. Thus, the steering wheel return can be further improved.

  The steering angle with respect to the steering angle middle point is zero (steering angle middle point) when the steering wheel is at the neutral position, and takes a positive value when the member is on one side with respect to the neutral position. This is a steering angle that takes a negative value when the member is located on the other side with respect to the neutral position, that is, an absolute steering angle.

  The control device determines, based on the steering torque acquired by the torque acquiring means, whether or not the steering wheel operated for steering the vehicle (the steering wheel to which the driver's steering torque is applied) is released. Midpoint return current value limiting means that limits the midpoint return current value set by the midpoint return current value setting means when it is determined by the hand release determination means and the hand release determination means that it is determined to be in the left state And may be included.

  As a result, in the release state, the midpoint return current value is suppressed, so it is possible to suppress the occurrence of vehicle flow due to the driving force according to the midpoint return current value.

  The hand release determination means may determine whether or not the vehicle is in the released state based on the steering angular velocity calculated by the steering angular velocity calculation means in addition to the steering torque acquired by the torque acquisition means.

  According to the present invention, it is possible to realize a good steering wheel return, and to improve the steering feeling near the middle of the steering angle.

1 is a block diagram schematically showing the configuration of an electric power steering apparatus according to an embodiment of the present invention. It is a figure which shows a steering torque-basic assist current value characteristic. It is a block diagram which shows the structure of the electric current value setting part for handle return. It is a figure which shows the time change of the steering angle to which hysteresis was provided. It is a graph which shows the change of the steering torque when changing a steering angle (steering angle). It is a graph which shows the time change of the steering angle (steering angle) at the time of steering wheel return.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings.

<Electric power steering device>

  FIG. 1 is a block diagram schematically showing the configuration of an electric power steering apparatus 1 according to an embodiment of the present invention.

  The electric power steering apparatus 1 is mounted on a vehicle such as an automobile, and is configured to assist (steering assist) the steering wheel operation by the driver by transmitting the driving force generated by the electric motor M to the steering mechanism 2. ing. The electric power steering apparatus 1 is provided with a steering wheel (steering wheel) 3 and a steering shaft 4 in addition to the electric motor M and the steering mechanism 2.

  The steering mechanism 2 is configured to include, for example, a rack and pinion type steering gear.

  The steering wheel 3 is disposed in front of the driver's seat in the vehicle compartment.

  The steering shaft 4 is provided to pass through the inside of the vehicle interior. The lower end of the steering shaft 4 is connected to the steering mechanism 2. When the steering mechanism 2 is configured to include a rack and pinion type steering gear, the lower end portion of the steering shaft 4 is coupled to the pinion of the steering gear so as to be relatively non-rotatable. The upper end of the steering shaft 4 is connected to the steering wheel 3.

  Further, the electric power steering apparatus 1 includes an ECU (Electronic Control Unit) 5 for controlling the electric motor M.

  The torque sensor 6 and the steering angle sensor 7 are connected to the ECU 5. The torque sensor 6 is provided, for example, in association with a torsion bar interposed at an intermediate portion of the steering shaft 4, detects the magnitude and direction of torsion occurring in the torsion bar as a steering torque, and corresponds to the steering torque Output a detection signal. The steering angle sensor 7 outputs, for example, a detection signal according to the steering angle (absolute steering angle) of the steering wheel 3 with respect to the midpoint of the steering angle of the steering wheel 3 recognized by itself. The steering angle detected by the steering angle sensor 7 takes, for example, a positive value when the steering wheel 3 is turned to the right from the steering angle midpoint, and takes a negative value when the steering wheel 3 is turned to the left. Further, vehicle information such as the vehicle speed, the wheel speeds of the respective wheels, the yaw rate of the vehicle, and the lateral G (lateral acceleration) generated in the vehicle are input to the ECU 5.

  The ECU 5 includes a microcomputer (micro controller) configured to include a CPU and a memory, and a motor drive circuit 11 that drives the electric motor M based on a control signal from the microcomputer.

  Motor drive circuit 11 is formed of, for example, an H bridge circuit. The voltage of the power supply (battery) 12 of the vehicle is applied to the motor drive circuit 11.

  The ECU 5 substantially includes the assist calculation unit 13. The assist calculation unit 13 is realized by program processing by a microcomputer as a function of the microcomputer.

  The assist calculation unit 13 sets a target assist current value of the electric motor M by calculation. Specifically, the assist calculation unit 13 includes a basic assist current value setting unit 15 and a steering wheel return current value setting unit 16 in order to set a target assist current value. The assist calculation unit 13 adds the basic assist current value set by the basic assist current value setting unit 15 and the steering wheel return current value set by the steering wheel return current value setting unit 16, and the added value is used as a target assist. Set to the current value. Then, the assist calculation unit 13 outputs a control signal (for example, a PWM (Pulse Width Modulation) control signal) corresponding to the difference between the target assist current value and the current (motor current) actually flowing through the electric motor M to the motor drive circuit 11. Give to. Thus, a drive current corresponding to the target assist current value is supplied from the motor drive circuit 11 to the electric motor M.

  The basic assist current value setting unit 15 and the steering wheel return current value setting unit 16 will be described later.

  The vehicle on which the electric power steering apparatus 1 is mounted is provided with an ECU different from the ECU 5. The ECU substantially includes, for example, a steering angle midpoint learning unit 14 realized by program processing by a microcomputer. Have.

  Since the steering angle midpoint recognized by the steering angle sensor 7 does not necessarily coincide with the actual steering angle midpoint of the vehicle, the steering angle midpoint learning unit 14 keeps the vehicle running while the start switch of the vehicle is turned on. The steering angle midpoint, which is the steering angle at the time of straight-ahead traveling (the neutral position of the steering wheel), is stored in the memory, and the stored steering angle midpoint is learned. In order to learn the steering angle midpoint, the steering angle midpoint learning unit 14 determines whether the vehicle is traveling straight. When the vehicle is traveling straight, the wheel speed of each wheel is greater than 0 and the wheel speeds of the left and right wheels are almost equal (while cornering, the wheel speed of the outer wheel is greater than the wheel speed of the inner wheel) ). In addition, in the straight running state of the vehicle, the yaw rate becomes equal to or less than a predetermined value, and the lateral G becomes equal to or less than a predetermined value. When the wheel speeds of the respective wheels are greater than 0 and the difference between the wheel speeds of the left and right wheels, the yaw rate and the lateral G are respectively equal to or less than predetermined values, the vehicle is traveling straight ahead I will judge. Then, when it is determined that the vehicle is traveling straight, the steering angle is acquired from the detection signal of the steering angle sensor 7, and the steering angle is stored (learned) in the memory as the steering angle midpoint.

  For example, each time the steering angle midpoint learning unit 14 learns the steering angle midpoint, the steering angle midpoint learning unit 14 inputs information on the learned steering angle midpoint to the steering angle sensor 7. The steering angle sensor 7 inputs information on the steering angle midpoint to the assist computing unit 13 together with information on the detected steering angle. In addition to the signal from the steering angle sensor 7, a signal representing a detection signal of the torque sensor 6 and a vehicle speed is input to the assist calculation unit 13. Further, the steering angle midpoint learning unit 14 performs assist computation of steering angle midpoint reliability information indicating whether the steering angle midpoint input from the steering angle sensor 7 to the assist computing unit 13 is a value having reliability. Input to section 13. For example, when the newly learned steering angle falls within the range of ± 10 ° with respect to the steering angle stored in the memory as the steering angle middle point, the steering angle input from the steering angle sensor 7 to the assist calculation unit 13 The steering angle midpoint reliability information indicating that the midpoint is a value having reliability is input from the steering angle midpoint learning unit 14 to the assist computing unit 13.

<Basic assist current value setting unit>

  FIG. 2 is a graph showing steering torque-basic assist current value characteristics.

  The basic assist current value setting unit 15 sets a basic assist current value according to the vehicle speed and the steering torque in accordance with the basic assist map stored in the memory.

  Specifically, the basic assist map defines the basic characteristics of the basic assist current value with respect to the steering torque, and is prepared for each of a plurality of vehicle speed ranges. The steering torque takes a positive value, for example, when the right direction torque (torque for right direction steering) is applied to the steering wheel 3, and the left direction torque (torque for left direction steering) is applied to the steering wheel 3 Takes a negative value when input. In each basic assist map, a dead zone in which the basic assist current value with respect to the steering torque is zero is provided. Then, each basic assist map has a positive sign for the basic assist current value when the steering torque outside the dead zone is a positive value, and with the increase of the absolute value of the steering torque, The absolute value is generated so as to increase monotonously from zero to a predetermined upper limit value. In each basic assist map, when the steering torque outside the dead zone is a negative value, the basic assist current value takes a negative sign, and with the increase of the absolute value of the steering torque, The absolute value is generated so as to increase monotonously from zero to a predetermined upper limit value. The rate of increase of the absolute value of the basic assist current value to the absolute value of the steering torque outside the dead zone (slope of the map) differs for each predetermined vehicle speed range, the rate of increase is small in the high speed range, and increases in the low speed range The proportion of is being increased. The basic assist current value setting unit 15 selects one of a plurality of basic assist maps according to the vehicle speed, and according to the selected basic assist map, a basic according to the steering torque acquired from the detection signal of the torque sensor 6 Set the assist current value.

<Current value setting unit for steering wheel return>

  FIG. 3 is a block diagram showing the configuration of the steering wheel return current value setting unit 16. FIG. 4 is a diagram showing a time change of the steering angle to which the hysteresis is applied.

  The steering wheel return current value setting unit 16 includes a subtracting unit 31, a hysteresis giving unit 32, a steering wheel return basic current value setting unit 33, an output / limit unit 34, a steering speed calculation unit 35, a hand release judgment unit 36 and a fail safe judgment unit. It has 37.

  Subtraction unit 31 subtracts the steering angle midpoint from the steering angle (relative steering angle) acquired from the detection signal of steering angle sensor 7 to obtain a steering angle (absolute steering angle) based on the steering angle midpoint. calculate. The absolute steering angle takes, for example, a positive value when the steering wheel 3 is turned to the right from the neutral position and a negative value when the steering wheel 3 is turned to the left.

  The hysteresis applying unit 32 applies hysteresis to the absolute steering angle calculated by the subtracting unit 31. The time change of the absolute steering angle calculated by the subtraction part 31 is shown by the dashed-two dotted line by FIG. The steering angle to which the hysteresis is applied by the hysteresis applying unit 32 (hysteresis applying steering angle; hereinafter, unless otherwise specified, simply referred to as “steering angle”) is calculated by the subtracting unit 31 as shown by a solid line in FIG. Changes late with respect to the time change of the absolute steering angle.

  The steering wheel return basic current value setting unit 33 sets the steering wheel return basic current value according to the vehicle speed and the steering angle in accordance with the steering wheel return basic current value map stored in the memory.

  Specifically, the steering wheel return basic current value map defines the characteristics of the steering wheel return basic current value with respect to the steering angle, and is prepared for each of a plurality of vehicle speed ranges. Each steering wheel return basic current value map is provided with a dead zone in which the steering wheel return basic current value with respect to the steering angle is zero. When the steering angle outside the dead zone is a positive value, each steering wheel return basic current value map has a negative sign with the steering wheel return basic current value, and the absolute value of the steering angle increases. The absolute value of the steering wheel return basic current value is monotonously increased from zero to a predetermined upper limit value. In addition, in the basic current value map for steering wheel return, when the steering angle outside the dead zone is a negative value, the basic current value for steering wheel return takes a positive sign, and along with the increase of the absolute value of the steering angle. The absolute value of the steering wheel return basic current value is monotonously increased from zero to a predetermined upper limit value. The rate of increase of the absolute value of the basic current value for steering wheel return to the absolute value of the steering angle outside the dead zone (slope of the map) differs for each predetermined vehicle speed range, the rate of increase is small in the high speed range, and in the low speed range The rate of increase is being increased. The steering wheel return basic current value setting unit 33 selects one of the plurality of steering wheel return basic current value maps according to the vehicle speed, and the steering wheel according to the steering angle according to the selected steering wheel return basic current value map. Set the basic current value for return.

  The steering wheel return basic current value setting unit 33 sets the steering wheel return basic current value in the increasing direction with respect to the steering wheel return basic current value set according to the steering wheel return basic current value map. A relatively large restriction may be applied to the current value, and the restriction added to the basic current value for steering wheel return may be made smaller (not added) when the basic steering current value for steering wheel return is in the decreasing direction. By setting such a rate limiter, it is possible to suppress a sudden change in steering torque due to a sudden change in the basic current value for steering wheel return, and to suppress an unnecessary current due to the basic current value for steering wheel return Can quickly suppress the current.

  The output / limitation unit 34 outputs the steering wheel return basic current value set by the steering wheel return basic current value setting unit 33 as it is as the steering wheel return current value, or limits the steering wheel return basic current value. This value is output as the steering wheel return current value. The concept of "restriction" includes the case of stopping the output of the steering wheel return current value, in other words, the case of setting the steering wheel return current value to zero.

  The steering speed calculator 35 calculates the steering speed by time-differentiating the absolute steering angle calculated by the subtractor 31. The steering speed calculated by the steering speed calculation unit 35 is supplied to the hysteresis applying unit 32 and the release judgment unit 36. In the hysteresis applying unit 32, hysteresis may be applied to the absolute steering angle calculated by the subtracting unit 31 according to the vehicle speed and / or the steering angle, or in addition to the vehicle speed and / or the steering angle, or Alternatively, instead of the steering angle, hysteresis may be given to the absolute steering angle calculated by the subtraction unit 31 according to the steering speed. When the hysteresis according to the steering speed is given, for example, the amount of hysteresis according to the steering angle at that time is set by using the fact that the steering angular velocity is close to 0 or the left and right (positive and negative) switching is triggered. The hysteresis of the hysteresis amount may be added to the absolute steering angle calculated by the subtraction unit 31.

  The release judgment unit 36 determines whether or not the driver's hand is released from the steering wheel 3 based on the steering torque, the basic current value for steering wheel return, and the steering speed. Specifically, the release judgment unit 36 determines that the driver's hand is released from the steering wheel 3 when the following four conditions (1) to (4) are satisfied.

(1) The absolute value of the steering torque is equal to or less than a predetermined value.
(2) The absolute value of the steering wheel return basic current value is a value that causes the vehicle flow.
(3) The absolute value of the steering angular velocity is equal to or less than a predetermined value.
(4) The condition in which the conditions (1) to (3) are satisfied continues the vehicle flow for an acceptable time.

  The determination result by the release judgment unit 36 is given to the output / limit unit 34. When the result of the judgment by the release judgment unit 36 shows that the output / limitation unit 34 is in the release state, the steering wheel return current value that does not cause a vehicle flow by adding a restriction to the steering wheel return basic current value. Output This makes it possible to suppress the flow of the vehicle in the released state.

  The fail-safe determination unit 37 determines whether the steering angle midpoint has reliability based on the steering angle midpoint reliability information input from the steering angle midpoint learning unit 14. Further, the fail safe determination unit 37 determines whether or not any system abnormality has occurred in the electric power steering apparatus 1. Then, the failsafe determination unit 37 determines that it is necessary to execute failsafe when the steering angle midpoint does not have reliability or when a system abnormality occurs.

  The determination result by the failsafe determination unit 37 is given to the output / limitation unit 34. The output / limitation unit 34 stops the output of the steering wheel return current value when the determination result by the failsafe determination unit 37 is the result that it is necessary to execute the failsafe.

  When the output / limitation unit 34 limits the basic electric current value for steering wheel return, the absolute value of the basic electric current steering wheel return value may be gradually reduced as time passes.

<Function effect>

  As described above, the basic assist current value is set based on the steering torque. When the current of the basic assist current value flows to the electric motor M, the electric motor M generates a driving force in the direction according to the steering torque. Further, the steering angular velocity is calculated from the absolute steering angle calculated by the subtracting unit 31, and hysteresis is given to the absolute steering angle calculated by the subtracting unit 31 based on the steering angular velocity. Then, the steering wheel return current value is set based on the steering angle to which the hysteresis is applied. When the current for the steering wheel return current flows to the electric motor M, the electric motor M generates a driving force in the direction to reduce the steering angle.

  The electric motor M is controlled based on the addition value of the basic assist current value and the steering wheel return current value. As a result, when returning from the state where the steering wheel 3 is cut in one side or the other side to the neutral position to the neutral position (the steering angle middle point), the steering wheel is returned even when no steering torque is applied to the steering wheel 3 A driving force corresponding to the return current value is transmitted to the steering mechanism 2. Therefore, when the steering wheel is returned, a driving force corresponding to the current value for steering wheel return is added to the self alignment torque, so that the steering wheel 3 returns to the neutral position without losing mechanical friction.

  In addition, even if the rotation of the steering wheel 3 is stopped by hand in the middle of the steering wheel return in the released state, the driving force corresponding to the steering wheel return current value is transmitted to the steering mechanism 2. When released again, the handle 3 begins to return towards the neutral position again. Therefore, it is possible to prevent the occurrence of the sticking phenomenon due to the hand-held rotation of the handle 3 in the middle of the handle return in the released state.

  Furthermore, since the driving force in the direction to reduce the steering angle, that is, the driving force in the direction to move the steering wheel 3 toward the neutral position is transmitted to the steering mechanism 2, the steering wheel 3 senses that the steering wheel 3 is at the neutral position Can be given to Therefore, a favorable steering wheel return can be realized, and the steering feeling near the steering angle midpoint can be improved.

  Although the driving force in the direction to reduce the steering angle is also transmitted to the steering mechanism 2 when the steering wheel 3 is cut, when the steering torque applied to the steering wheel 3 is thereby increased, the basic set according to the steering torque The assist current value increases, and the driving force of the electric motor M according to the basic assist current value increases. Therefore, there is no possibility that the steering feeling at the time of turning of the steering wheel 3 will be deteriorated.

  In addition, the steering angle used to set the basic electric current value for steering wheel return (electric steering wheel return electric current value) changes with a delay relative to the time change of the actual absolute steering angle (actual steering angle). It is a steering angle with hysteresis applied to the corner. Therefore, even if the actual steering angle falls near the middle of the steering angle when the steering wheel returns, the steering angle (hysteresis attachment steering angle) does not enter the dead zone, and the absolute value of the steering wheel return basic current value is larger than 0 Set to Therefore, even when the actual steering angle decreases near the middle of the steering angle when the steering wheel returns, the driving force in the direction in which the steering wheel 3 is directed to the neutral position is transmitted from the electric motor M to the steering mechanism 2. Thus, the steering wheel return can be further improved.

  FIG. 5 is a graph showing a change in steering torque when the steering angle (steering angle) is changed.

  In a vehicle on which the electric power steering apparatus 1 is mounted, the steering wheel 3 is operated in a range of about 60 ° (deg) on the right and about 60 ° (deg) on the left from the neutral position (steering angle middle point) The value of the steering torque at was measured. The measurement result is shown by a solid line in FIG.

  On the other hand, in a vehicle equipped with the configuration described in the background art section, that is, the electric power steering apparatus of the conventional configuration in which the steering wheel return current value is set according to the motor rotational speed, The steering torque value at each steering angle was measured by operating in the range of about 60 ° on the left side. The measurement result is shown by the broken line in FIG.

  As understood by comparing these results, in the electric power steering apparatus 1, the steering angle when the steering torque is 0 is closer to the steering angle midpoint than in the electric power steering apparatus of the conventional configuration. From this, it was confirmed that the electric power steering apparatus 1 can give the driver the feeling that the steering wheel 3 is in the neutral position.

  FIG. 6 is a graph showing the time change of the steering angle (steering angle) when the steering wheel is returned.

  In a vehicle on which the electric power steering apparatus 1 is mounted, the time of the steering angle at the time of steering wheel return in the released state from the state where the steering wheel 3 is cut about 360 ° (deg) to the right during traveling at a predetermined speed I examined the change. The measurement result is shown by a solid line in FIG.

  On the other hand, in a vehicle equipped with the configuration described in the background art section, that is, the electric power steering apparatus of the conventional configuration in which the steering wheel return current value is set according to the motor rotational speed; The time change of the steering angle at the time of the steering wheel return in the hand released state from the state where the steering wheel 3 was cut into about 360 degrees on the right side was investigated. The measurement result is shown by the broken line in FIG.

  From these results, it is understood that in the electric power steering apparatus 1, the steering wheel 3 returns to a position closer to the neutral position in the released state than in the electric power steering apparatus of the conventional configuration.

<Modification>

  As mentioned above, although one Embodiment of this invention was described, this invention can also be implemented with another form.

  For example, in the above-described embodiment, although the release state is determined when the conditions (1) to (4) are satisfied, the condition (3) may be removed from the determination condition.

  In addition, various design changes can be made to the above-described configuration within the scope of the matters described in the claims.

1 electric power steering device 2 steering mechanism 5 ECU (control device)
6 Torque sensor (torque acquisition means)
7 Steering angle sensor (steering angle acquisition means)
11 Motor drive circuit (motor control means)
13 Assist calculation unit (motor control means)
15 Basic assist current value setting unit (Basic assist current value setting unit)
16 Steering wheel return current value setting unit (midpoint return current value setting means)
M electric motor

Claims (1)

A control device for use in an electric power steering apparatus that assists steering by transmitting a driving force of an electric motor to a steering mechanism,
Torque acquisition means for acquiring steering torque;
Steering angle acquisition means for acquiring a steering angle with respect to a steering angle midpoint;
Basic assist current value setting means for setting a basic assist current value for causing the driving force of the electric motor to be generated in the direction according to the steering torque based on the steering torque acquired by the steering torque acquisition means;
Steering angular velocity computing means for computing a steering angular velocity based on the steering angle acquired by the steering angle acquiring means;
A hysteresis is added to the steering angle acquired by the steering angle acquisition means based on the steering angular velocity calculated by the steering angular velocity calculation means, and the driving force of the electric motor is based on the steering angle to which the hysteresis is added. Current value setting means for middle point return which sets the current value for middle point return which generates
The basic assist current value set by the basic assist current value setting means and the middle point return current value set by the middle point return current value setting means are added, and the electric motor is calculated based on the sum value. And motor control means for controlling

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