JP2011131629A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device in a simple constitution, which easily optimizes hysteresis characteristics at alternative control based on a steering angle. <P>SOLUTION: An alternative assist control unit 30 includes a basic control amount calculation part 32 and a hysteresis control amount calculation part 33, and outputs an alternative assist control amount Isb* by adding a hysteresis control amount ε_hy to a basic control amount ε_bs based on a steering angle. The alternative assist control unit 30 includes a first hysteresis width calculation part 35 that calculates a first hysteresis width ε_hy1 decreasing according to an increase in a vehicle speed V and a second hysteresis width calculation part 36 that calculates a second hysteresis width ε_hy2 increasing according to an increase in a steering angle θs and an increase in a vehicle speed V. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus.

  Conventionally, there is an electric power steering device (EPS) using a motor as a drive source as a power steering device for a vehicle, and in such an EPS, a torque sensor is usually provided in the middle of a steering shaft. The assist force applied to the steering system is controlled based on the detected steering torque.

  Some EPSs perform power assist control based on a steering angle generated in steering. As a mode of power assist control using such a steering angle (steering speed), in addition to various compensation controls executed to compensate for the basic component of the power assist control, a control target value (target) that serves as the basic component. Alternative control for calculating (assist force) itself can be mentioned.

  Specifically, the compensation control using the steering angle (steering speed) includes, for example, so-called steering return control that improves the return to the steering neutral position (steering returnability) (for example, Patent Document 1). reference). Further, for example, Patent Document 2 discloses an alternative control based on the steering angle (and the steering speed). By using the steering angle for power assist control in this way, it is possible to achieve excellent steering feeling, or to continue applying assist force to the steering system even after an abnormality occurs in the torque sensor. become.

  By the way, conventionally, in a power steering device, it is known that a good steering feeling can be obtained by optimizing the hysteresis characteristic of the axial force against the steering torque (the axial reaction force acting on the rack shaft during the steering operation). It has been. For example, Patent Document 3 discloses a configuration in which the hysteresis is increased based on the magnitude of steering torque detected by a torque sensor. In Patent Document 4, a target steering torque is calculated by adding a hysteresis component corresponding to the steering speed to a basic component based on the steering angle, and feedback control is performed so that the actual steering torque follows the target steering torque. Is executed to calculate a current command value corresponding to the target assist force.

  That is, normally, the axial force generated during the steering operation increases as the steering angle increases, and thus the steering torque also increases. Therefore, for example, by applying the configuration of Patent Document 3, butterfly-like hysteresis characteristics can be obtained (see FIGS. 5 and 6 of the same document). In the alternative control based on the steering angle, the hysteresis characteristic can be controlled by adding the same hysteresis component according to the steering direction to the basic component of the target assist force based on the steering angle. .

JP 2006-137359 A JP 2004-338562 A JP-A-9-156526 JP 2002-104220 A

  However, in practice, the axial force generated during the steering operation cannot be uniquely determined only by the magnitude of the steering angle. For this reason, in the case of alternative control based on the steering angle, it becomes a problem how to optimize the hysteresis characteristic.

  In other words, the actual axial force at the time of detection is naturally reflected in the steering torque detected by the torque sensor. Therefore, in the hysteresis control using the detected value, the hysteresis characteristic is automatically optimized. However, in the alternative control based on the steering angle, the actual axial force cannot be reflected in the hysteresis control. For this reason, conventionally, calibration data for optimizing the hysteresis characteristics has been required, and it takes a lot of time and labor to collect the data, and a large capacity memory is required even at the mounting stage. In this respect, there was still room for improvement.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an electric power steering apparatus capable of optimizing hysteresis characteristics at the time of alternative control based on a steering angle with a simple configuration and easily. Is to provide.

  In order to solve the above problems, the invention according to claim 1 is a steering force assisting device for applying an assisting force to a steering system using a motor as a drive source, and a steering angle detecting means for detecting a steering angle generated in the steering. And control means for controlling the operation of the steering force assisting device based on the steering angle, wherein the control means is a hysteresis component corresponding to a steering direction with respect to a basic component of the target assist force based on the steering angle. In the electric power steering apparatus to which is added, the control means includes, as the hysteresis component, a first hysteresis component that decreases as the vehicle speed increases, and a second hysteresis component that increases as the steering angle increases and the vehicle speed increases. The gist is to calculate.

  That is, the following two elements that constitute the axial reaction force (axial force) generated on the rack shaft in accordance with the steering operation, the “road friction force” based on the grip force of the steered wheel, and the rolling force generated on the steered wheel during traveling. The “road resistance” acting in the direction of restoring the rudder angle to the neutral state has a contradictory tendency in relation to the vehicle speed. However, as in the above configuration, the first hysteresis component corresponding to the road surface friction force that decreases as the vehicle speed increases, and the second hysteresis component that corresponds to the road surface resistance force that increases as the steering angle increases and the vehicle speed increases. Are independently calculated, it becomes easy to collect conformity data regarding the hysteresis characteristics. In the mounting stage, the required memory capacity can be kept small. In particular, in consideration of the relationship between the vehicle speed and the road surface resistance force, for those having a configuration in which the absolute value of the basic control amount is increased as the vehicle speed is higher, the second hysteresis component can be easily adjusted. The hysteresis can be expanded in accordance with the assist force that increases as the vehicle speed increases. Therefore, according to the above configuration, it is possible to optimize the hysteresis characteristic during the alternative control based on the steering angle with a simple and easy configuration.

The gist of the invention described in claim 2 is that the control means reduces the hysteresis component when the steering angle is in a small steering angle region corresponding to steering neutral.
According to the above configuration, in the vicinity of the neutral steering position, the assist force can be reduced and the steering return performance can be improved. In addition, it is possible to suppress the “stabilization” of the steering and enhance the so-called steering rigidity feeling, thereby ensuring “moderate steering feeling”.

  The gist of the invention described in claim 3 is that the control means limits the target assist force based on the steering angle so as not to exceed the upper limit value, and varies the upper limit value according to the vehicle speed. .

  That is, in the region in the vicinity of the maximum steering angle corresponding to the so-called steering end, the increase in the axial force corresponding to the increase in the steering angle tends to slow down due to the influence of the wheel alignment (caster angle etc.) of the vehicle. . Therefore, according to the above configuration, it is possible to suppress the excessive assist that occurs in the region in the vicinity of the maximum steering angle, thereby causing a problem that causes the excessive assist, that is, a so-called “disengagement feeling” that suddenly becomes less responsive. And the collision to the steering end due to the occurrence of the occurrence of the above can be suppressed. In the low vehicle speed region, the second hysteresis component corresponding to the “road resistance” that increases according to the vehicle speed has a small value. Therefore, with the above configuration, by reducing the guard process according to the vehicle speed, it is possible to appropriately suppress the excessive assist in the maximum steering angle region by the guard process.

  The invention according to claim 4 includes a torque sensor that detects a steering torque transmitted through a steering shaft, and an abnormality determination unit that determines abnormality of the torque sensor, and the control unit includes: When normal, the operation of the steering force assisting device is controlled based on the steering torque, and when an abnormality occurs in the torque sensor, the assist force corresponding to the steering angle is generated. The gist is to control the operation of the steering force assisting device.

  According to the above configuration, the assist force can be stably applied to the steering system even when the torque sensor is abnormal with a simple configuration.

  According to the present invention, it is possible to provide an electric power steering apparatus capable of optimizing the hysteresis characteristic at the time of alternative control based on the steering angle in a simple and easy configuration.

The schematic block diagram of an electric power steering device (EPS). The control block diagram of EPS. Explanatory drawing which shows the relationship between a steering angle, vehicle speed, and basic control amount. Explanatory drawing which shows the relationship between a vehicle speed and a 1st hiss width. Explanatory drawing which shows the relationship between the vehicle speed and the multiplication coefficient used for the calculation of the 2nd hysteresis width. Explanatory drawing which shows the hysteresis characteristic acquired by the 1st hiss width and the 2nd hiss width. Explanatory drawing which shows the relationship between a steering angle (its absolute value) and a steering angle gain. Explanatory drawing which shows the hysteresis characteristic acquired by rudder angle gain. Explanatory drawing which shows the hysteresis characteristic obtained by execution of a guard process. Explanatory drawing which shows the relationship between a vehicle speed and the upper limit of a guard process.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the drawings.
As shown in FIG. 1, in the electric power steering apparatus (EPS) 1 of the present embodiment, 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. The rotation of the steering shaft 3 accompanying the operation is converted into a reciprocating linear motion of the rack shaft 5 by the rack and pinion mechanism 4. The steering shaft 3 of this embodiment is formed by connecting a column shaft 3a, an intermediate shaft 3b, and a pinion shaft 3c. Then, the 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 6 connected to both ends of the rack shaft 5, whereby the steering angle of the steered wheels 7, That is, the traveling direction of the vehicle is changed.

  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 configured as a so-called column-type EPS actuator in which a motor 12 that is a drive source is drivingly connected to a column shaft 3 a via a speed reduction mechanism 13. In the present embodiment, the motor 12 is a DC motor with a brush. The EPS actuator 10 is configured to apply the motor torque as an assist force to the steering system by decelerating and transmitting the rotation of the motor 12 to the column shaft 3a.

  On the other hand, the ECU 11 is connected with a torque sensor 14, a vehicle speed sensor 15, and a steering sensor (steering angle sensor) 16 constituting a steering angle detecting means. The ECU 11 detects the steering torque τ, the vehicle speed V, and the steering angle θs based on the output signals of these sensors.

  More specifically, in the present embodiment, the torsion bar 17 is provided in the middle of the column shaft 3a, more specifically, on the steering 2 side with respect to the speed reduction mechanism 13 constituting the EPS actuator 10. The torque sensor 14 of the present embodiment outputs sensor signals Sa and Sb that can detect the steering torque τ transmitted through the steering shaft 3 based on the twist of the torsion bar 17. It is configured with.

  Such a torque sensor has two magnetic detection elements (not shown) on the outer periphery of a sensor core (not shown) that generates a magnetic flux change based on torsion of the torsion bar 17, as disclosed in, for example, Japanese Patent Laid-Open No. 2003-149062. In the present embodiment, the Hall IC can be formed as the sensor elements 14a and 14b.

  That is, when the torsion bar 17 is twisted by torque input to the steering shaft 3 that is the rotating shaft, the magnetic flux passing through the sensor elements 14a and 14b changes. The torque sensor 14 according to the present embodiment is configured to output the output voltages of the sensor elements 14a and 14b, which fluctuate with the change of the magnetic flux, to the ECU 11 as sensor signals Sa and Sb, respectively.

  The steering sensor 16 according to the present embodiment includes a rotor 18 fixed to the column shaft 3a on the steering 2 side of the torque sensor 14, and a sensor element (Hall IC) that detects a change in magnetic flux accompanying the rotation of the rotor 18. ) 19 and a magnetic rotation angle sensor.

  Then, the ECU 11 calculates a target assist force based on each detected state quantity, and through the supply of drive power to the motor 12 that is the drive source in order to cause the EPS actuator 10 to generate the target assist force. The operation of the EPS actuator 10, that is, the assist force applied to the steering system is controlled (power assist control).

Next, the aspect of the power assist control by EPS of this embodiment is demonstrated.
As shown in FIG. 2, the ECU 11 includes a microcomputer 21 that outputs a motor control signal, and a drive circuit 22 that supplies drive power to the motor 12 that is a drive source of the EPS actuator 10 based on the motor control signal. ing.

  Each control block shown below is realized by a computer program executed by the microcomputer 21. The microcomputer 21 detects each state quantity at a predetermined sampling period, and generates a motor control signal by executing each arithmetic processing shown in the following control blocks at every predetermined period.

  More specifically, the microcomputer 21 is calculated by a current command value calculation unit 25 that calculates a current command value I * corresponding to a target value of power supply to the motor 12, that is, a target assist force, and a current command value calculation unit 25. And a motor control signal output unit 26 that outputs a motor control signal based on the current command value I *.

  The current command value calculation unit 25 is provided with a basic assist control unit 27, and the vehicle speed V and the steering torque τ are input to the basic assist control unit 27. The basic assist control unit 27 calculates a basic assist control amount Ias * that is a basic component of the target assist force.

  Here, in this embodiment, the steering torque τ that is the basis of the target assist force is based on the sensor signals Sa and Sb output from the torque sensor 14 in the steering torque detector 28 provided in the microcomputer 21. Detected. The basic assist control unit 27 of the present embodiment is a value to which a larger assist force should be applied as the steering torque τ (absolute value) output from the steering torque detection unit 28 is larger and the vehicle speed V is smaller. The basic assist control amount Ias * having the above is calculated.

  Furthermore, in the present embodiment, the steering torque detection unit 28 is provided with a function as an abnormality determination unit that determines abnormality of the torque sensor 14 based on the sensor signals Sa and Sb output from the torque sensor 14. An abnormality determination signal Str indicating the determination result is input to the current command value calculation unit 25. The current command value calculation unit 25 indicates that the input abnormality determination signal Str is normal, that is, when the torque sensor 14 is operating normally, the basic assist control amount Ias. A value based on * is output to the motor control signal output unit 26 as a current command value I * corresponding to the target assist force.

  On the other hand, the motor control signal output unit 26 receives the current command value I * output from the current command value calculation unit 25 and the actual current value I of the motor 12 detected by the current sensor 29. That is, the motor control signal output unit 26 of the present embodiment generates a motor control signal by executing current feedback control so that the actual current value I follows the current command value I * corresponding to the target assist force. In this embodiment, the motor control signal generated in this way is output from the microcomputer 21 to the drive circuit 22, and the drive power based on the motor control signal is supplied to the motor 12 by the drive circuit 22. Thus, an assist force corresponding to the target assist force is applied to the steering system.

  In addition, the current command value calculation unit 25 according to the present embodiment is generated in the steering 2 together with the basic assist control unit 27 that calculates the basic assist control amount Ias * based on the steering torque τ (and the vehicle speed V) as described above. An alternative assist control unit 30 is provided for calculating an alternative assist control amount Isb * based on the steering angle θs. When any abnormality occurs in the torque sensor 14, the alternative assist control unit 30 calculates to execute the alternative assist control based on the steering angle θs instead of the normal assist control based on the steering torque τ. The substitute assist control amount Isb * is used as a control component corresponding to the target assist force in the substitute assist control.

  Specifically, the current command value calculation unit 25 of the present embodiment is provided with a switching control unit 31, and the alternative assist control amount Isb * calculated in the alternative assist control unit 30 is the basic assist control unit. The basic assist control amount Ias * calculated in 27 and the abnormality determination signal Str output from the steering torque detector 28 are input to the switching controller 31. When the input abnormality determination signal Str indicates that the torque sensor 14 is abnormal, the switching control unit 31 sets the alternative assist control amount Isb * in place of the basic assist control amount Ias *. By outputting, alternative assist control based on the steering angle θs is executed.

(Hysteresis control during alternative assist control based on steering angle)
Next, the configuration of the alternative assist control unit in the present embodiment and the mode of hysteresis control during the alternative assist control based on the steering angle will be described.

  As shown in FIG. 2, the alternative assist control unit 30 of the present embodiment calculates a basic control amount ε_bs, which is a basic component of the target assist force based on the steering angle θs, and calculates a hysteresis component for the basic control amount ε_bs. The above-mentioned alternative assist control amount Isb * is calculated by adding the hysteresis control amount ε_hy.

  More specifically, in the present embodiment, the alternative assist control unit 30 is provided with a basic control amount calculation unit 32 and a hysteresis control amount calculation unit 33. These calculation units have a steering angle θs and a steering angle θs, respectively. The vehicle speed V is input. Based on the steering angle θs and the vehicle speed V, the basic control amount calculator 32 calculates the basic control amount ε_bs, and the hysteresis control amount calculator 33 calculates the hysteresis control amount ε_hy.

  Specifically, in the hysteresis control amount calculation unit 33 of the present embodiment, these basic control amount ε_bs and hysteresis control amount ε_hy (ε_hy ′) are input to the additional calculation unit 34. Further, a steering speed ωs is input to the additional calculation unit 34, and the additional calculation unit 34 specifies a steering direction based on the steering speed ωs. Then, the addition calculation unit 34 adds the hysteresis control amount ε_hy to the basic control amount ε_bs according to the steering direction.

  More specifically, when the steering direction is the “+” direction (corresponding to right steering in this embodiment), the addition calculation unit 34 adds (adds) the hysteresis control amount ε_hy to the “+” direction. When the steering direction is the “−” direction (also corresponding to the left steering), the hysteresis control amount ε_hy is added (subtracted) in the “−” direction. Then, the alternative assist control unit 30 according to the present embodiment switches the above-mentioned switching using the total control amount ε_cm (ε_cm ′) obtained by adding the hysteresis control amount ε_hy to the basic control amount ε_bs as the alternative assist control amount Isb *. By outputting to the control unit 31, the hysteresis characteristic in the alternative control based on the steering angle θs is controlled.

  More specifically, as shown in FIG. 3, the basic control amount calculation unit 32 has a basic control having a larger absolute value as the detected absolute value of the steering angle θs is larger and as the vehicle speed V is faster. The quantity ε_bs is calculated. Specifically, in the present embodiment, the basic control amount ε_bs is set to be proportional to the steering angle θs. Then, the basic control amount calculation unit 32 of the present embodiment executes the calculation of the basic control amount ε_bs by changing the inclination α according to the vehicle speed V.

  On the other hand, as shown in FIG. 2, the hysteresis control amount calculator 33 of the present embodiment is provided with a first hysteresis width calculator 35 and a second hysteresis width calculator 36. As shown in FIG. 4, the first hysteresis width calculator 35 calculates a first hysteresis width ε_hy1 as a first hysteresis component that decreases as the vehicle speed V increases. In the present embodiment, the first hysteresis width ε_hy1 is set to decrease in an approximately inverse proportion to the increase in the vehicle speed V. Further, as shown in FIG. 5, the second hysteresis width calculator 36 calculates a multiplication coefficient β that increases as the vehicle speed V increases, and multiplies the steering coefficient θs (absolute value) by the multiplication coefficient β. Then, a second hysteresis width ε_hy2 is calculated as a second hysteresis component that increases as the steering angle θs increases and the vehicle speed V increases (ε_hy2 = | θs | × β). In the present embodiment, the multiplication coefficient β is set to be “zero” (β = 0) in a low speed region (V ≦ V1) equal to or lower than the predetermined speed V1. Then, the hysteresis control amount calculator 33 calculates the hysteresis control amount ε_hy by adding the first hysteresis width ε_hy1 and the second hysteresis width ε_hy2 in the adder 37.

  Then, the alternative assist control unit 30 according to the present embodiment adds the hysteresis control amount ε_hy (ε_hy ′) to the basic control amount ε_bs in the additional calculation unit 34, as shown in FIG. As the (absolute value) increases, a substitute assist control amount Isb * is calculated so that a so-called butterfly-like hysteresis characteristic in which the magnitude of the hysteresis (his width) becomes large is obtained.

  In FIG. 6, the basic control amount ε_bs as a basic component based on the steering angle θs can be represented by a straight line L. The first hysteresis width ε_hy1 as the first hysteresis component is a region in the enclosure M indicated by the broken line, and the second hysteresis width ε_hy2 as the second hysteresis component is between the enclosure M and the enclosure N indicated by the solid line. It is expressed in the area (hatched part).

  That is, the axial reaction force (axial force) generated in the rack shaft 5 with the steering operation is based on the frictional force generated between the steered wheel 7 and the road surface based on the grip force of the steered wheel 7, and the steered wheel 7 during traveling. The two main components are road resistance force (force corresponding to self-aligning torque) acting in the direction to restore the turning angle generated in the step to the neutral state. The former road surface friction force decreases as the vehicle speed V increases, while the latter road surface resistance force corresponding to the latter self-aligning torque increases as the rudder angle increases and the vehicle speed V increases. Become. That is, the two components of the axial force generated by the steering operation, the “road surface friction force” and the “road surface resistance force” have contradictory tendencies in relation to the vehicle speed V.

  Based on this point, in the present embodiment, the first hiss width ε_hy1 corresponding to the road friction force that decreases as the vehicle speed V increases, and the road surface resistance force that increases as the steering angle θs increases and the vehicle speed V increases. 2 His width ε_hy2 is calculated independently. That is, by calculating these independently, it becomes easy to collect the conforming data, and it is possible to reduce the memory capacity required in the mounting stage. In this embodiment, the hysteresis characteristic can be easily optimized with a simple configuration.

  In the present embodiment, the hysteresis control amount calculation unit 33 is provided with a steering angle gain calculation unit 38, and the steering angle gain calculation unit 38 is based on the steering angle θs (absolute value thereof). The gain Kθ (0 ≦ Kθ ≦ 1) is calculated.

  Specifically, as shown in FIG. 7, when the detected steering angle θs is in the small steering angle region corresponding to the steering neutral (| θs | ≦ θ1), the steering angle gain calculation unit 38 As the steering angle θs (absolute value) decreases, a smaller value of the steering angle gain Kθ is calculated. The steering angle gain calculation unit 38 calculates “1” as the steering angle gain Kθ when the steering angle θs is not in the small steering angle region (| θs |> θ1). When the steering angle θs indicates steering neutrality (θs = 0), “1” is calculated as the steering angle gain Kθ.

  As shown in FIG. 2, in the present embodiment, the steering angle gain Kθ output from the steering angle gain calculation unit 38 is input to the multiplier 39 together with the hysteresis control amount ε_hy. Then, the hysteresis control amount calculation unit 33 according to the present embodiment outputs the hysteresis control amount ε_hy ′ after being corrected by multiplying the additional calculation unit 34 by the steering angle gain Kθ.

  That is, as shown in FIG. 8, when the steering angle θs is in the small steering angle region by performing the correction using the steering angle gain Kθ, the correction is performed as the steering angle θs approaches the steering neutral position. As the subsequent hysteresis control amount ε_hy ′ decreases, the assist force applied to the steering system decreases. In addition, the dashed-two dotted line in the figure has shown transition of the assist force when not correct | amending by steering angle gain K (theta). And in this embodiment, while improving the steering return property by this, it is possible to ensure "moderate steering feeling" by suppressing the "stabilization" of the steering wheel 2 and enhancing the so-called steering rigidity feeling. It has become.

  Further, as shown in FIG. 2, the hysteresis control amount calculation unit 33 of the present embodiment is provided with a guard processing unit 40, and the additional calculation unit 34 adds the hysteresis control amount ε_hy to the basic control amount ε_bs. The total amount of control ε_cm obtained by this is subjected to guard processing by the guard processing unit 40. Specifically, the guard processing unit 40 limits the absolute value of the total control amount ε_cm so as not to exceed the upper limit value (εth). Then, the hysteresis control amount calculation unit 33 outputs the summed control amount ε_cm ′ after the guard processing to the switching control unit 31 as the alternative assist control amount Isb *.

  That is, in the region in the vicinity of the maximum steering angle corresponding to the so-called steering end, the increase in the axial force according to the increase in the steering angle θs as described above is generally slowed down due to the influence of the wheel alignment (caster angle etc.) of the vehicle. Tend to. In view of this point, in the present embodiment, by limiting the combined control amount ε_cm that becomes the alternative assist control amount Isb * by the guard process, the steering angle θs is in the maximum steering angle region as shown in FIG. The excessive assist that occurs in the case is suppressed. As a result, in a region near the maximum steering angle, the so-called “disengagement” in which the response is suddenly lightened, and the collision with the steering end due to the so-called “disengagement feeling” are suppressed.

  More specifically, the guard processing unit 40 according to the present embodiment takes into account the influence of the second hiss width ε_hy2 calculated corresponding to the “road resistance” corresponding to the self-aligning torque. As shown, the upper limit value εth in the guard process is varied according to the vehicle speed V. Specifically, when the detected vehicle speed V is equal to or lower than the predetermined value V2, the guard processing unit 40 reduces the upper limit value εth as the vehicle speed V decreases. That is, as described above, the “road resistance” increases according to the vehicle speed V. In the present embodiment, in the low vehicle speed region where the second hysteresis width ε_hy2 corresponding to this “road resistance” becomes small, the maximum steering by execution of the guard processing is reduced by reducing the upper limit value εth of the guard processing. The assist force is appropriately reduced in the corner region.

As described above, according to the present embodiment, the following operations and effects can be obtained.
(1) The alternative assist control unit 30 includes a basic control amount calculation unit 32 and a hysteresis control amount calculation unit 33. By adding the hysteresis control amount ε_hy to the basic control amount ε_bs based on the steering angle, the alternative assist control amount Output Isb *. Then, a first hysteresis width calculator 35 that calculates a first hysteresis width ε_hy1 that decreases as the vehicle speed V increases, and a second hysteresis width ε_hy2 that increases as the steering angle θs increases and the vehicle speed V increases. A width calculation unit 36.

  That is, the following two elements constituting the axial reaction force (axial force) generated in the rack shaft 5 in accordance with the steering operation, the “road friction force” based on the grip force of the steered wheels 7, and the steered wheels 7 when traveling. The “road surface resistance force” acting in the direction of restoring the generated turning angle to the neutral state has a contradictory tendency in relation to the vehicle speed V. However, as in the above configuration, the first hiss width ε_hy1 corresponding to the road surface friction force that decreases as the vehicle speed V increases, and the second surface force that increases as the steering angle θs increases and the vehicle speed V increases. By calculating the hysteresis widths ε_hy2 independently of each other, it becomes easy to collect conformity data regarding the hysteresis characteristics. In the mounting stage, the required memory capacity can be kept small. Therefore, according to the above configuration, it is possible to optimize the hysteresis characteristic during the alternative control based on the steering angle with a simple and easy configuration.

  (2) The basic control amount calculation unit 32 calculates the basic control amount ε_bs having a larger absolute value as the absolute value of the detected steering angle θs increases, and at the same time, as the vehicle speed V increases, The absolute value of the basic control amount ε_bs is increased.

  That is, when the vehicle travels, the road resistance corresponding to the self-aligning torque increases as the vehicle speed V increases. Therefore, according to the above configuration, a more appropriate assist force can be applied regardless of the vehicle speed V. The hysteresis characteristic can be easily optimized by expanding the hysteresis in accordance with the assist force that increases as the vehicle speed V increases by the second hysteresis width ε_hy2.

  (3) The hysteresis control amount calculator 33 includes a steering angle gain calculator 38 that calculates a steering angle gain Kθ (0 ≦ Kθ ≦ 1) based on the steering angle θs (absolute value thereof). Then, by multiplying the steering angle gain Kθ by the hysteresis control amount ε_hy, when the steering angle θs is in the small steering angle region corresponding to the steering neutrality (| θs | ≦ θ1), the steering angle θs becomes the steering neutral. As the position gets closer, the corrected hysteresis control amount ε_hy ′ is reduced.

  According to the above configuration, in the vicinity of the neutral steering position, the assist force can be reduced and the steering return performance can be improved. In addition, it is possible to suppress the “fluctuation” of the steering wheel 2 and enhance a so-called steering rigidity feeling, thereby ensuring a “moderate steering feeling”.

  (4) The hysteresis control amount calculation unit 33 includes a guard processing unit 40, and the guard processing unit 40 adds the hysteresis control amount ε_hy to the basic control amount ε_bs (the absolute value of ε_cm). Is restricted so as not to exceed the upper limit (εth). Then, the guard processing unit 40 varies the upper limit value εth in the guard processing according to the vehicle speed V.

  That is, in the region in the vicinity of the maximum steering angle corresponding to the so-called steering end, the increase in the axial force corresponding to the increase in the steering angle θs tends to slow down due to the influence of the vehicle wheel alignment (caster angle, etc.). is there. Therefore, according to the above configuration, it is possible to suppress the excessive assist that occurs in the region in the vicinity of the maximum steering angle, thereby causing a problem that causes the excessive assist, that is, a so-called “disengagement feeling” that suddenly becomes less responsive. And the collision to the steering end due to the occurrence of the occurrence of the above can be suppressed. In the low vehicle speed region, the second hysteresis width ε_hy2 corresponding to the “road resistance” that increases with the vehicle speed V is a small value. Accordingly, by reducing the upper limit value εth of the guard process according to the vehicle speed as in the above configuration, it is possible to appropriately reduce the assist force in the maximum steering angle region by executing the guard process.

In addition, you may change the said embodiment as follows.
In the above embodiment, the present invention is embodied in a so-called column type EPS 1, but the present invention may be applied to a so-called pinion type or rack assist type EPS.

In the above embodiment, the present invention is embodied in EPS 1 using a brushed DC motor as a drive source, but may be applied to EPS using a brushless motor as a drive source.
In the above embodiment, the present invention is embodied in the alternative assist control after the abnormality of the torque sensor, but may be applied to a configuration in which an assist force based on the steering angle θs is always applied to the steering system.

  In the above-described embodiment, the second hysteresis width calculation unit 36 calculates the multiplication coefficient β that increases as the vehicle speed V increases, and multiplies the steering coefficient θs (the absolute value thereof) by the multiplication coefficient β. The second hysteresis width ε_hy2 as a second hysteresis component that increases with the increase of θs and the increase of the vehicle speed V is calculated (ε_hy2 = | θs | × β). However, the configuration is not limited to this, and the second hysteresis component may be directly calculated from the steering angle θs and the vehicle speed V by map calculation or the like.

  In the above embodiment, by multiplying the steering angle gain Kθ by the hysteresis control amount ε_hy, when the steering angle θs is in the small steering angle region corresponding to the steering neutral (| θs | ≦ θ1), the steering angle θs As the value approaches the steering neutral position, the corrected hysteresis control amount ε_hy ′ is reduced. However, the present invention is not limited to this, and a configuration may be adopted in which a reduction component for reducing the hysteresis control amount ε_hy is calculated and added to the hysteresis control amount ε_hy.

  In the above embodiment, the basic control amount calculation unit 32 calculates the basic control amount ε_bs having a larger absolute value as the absolute value of the detected steering angle θs is larger, and the vehicle speed V is faster. The absolute value of the basic control amount ε_bs is increased. However, the present invention is not limited to this, and the present invention may be applied to a configuration in which the basic control amount ε_bs is calculated based on only the steering angle θs or a combination with a state quantity other than the vehicle speed V.

  In the above embodiment, when the steering angle θs is in the small steering angle region corresponding to the steering neutral (| θs | ≦ θ1), the hysteresis control after the correction is performed as the steering angle θs approaches the steering neutral position. The amount ε_hy ′ was reduced. However, the present invention is not limited to this. For example, the reduction may be uniformly reduced over the entire small steering angle region, or may be reduced stepwise in a stepwise manner.

Next, technical ideas that can be grasped from the above embodiments will be described together with effects.
(A) In the electric power steering apparatus according to claim 1, the control means calculates a multiplication coefficient that increases as the vehicle speed increases, and multiplies the steering coefficient by the multiplication angle to obtain a second hysteresis. An electric power steering device characterized by calculating a component. Thereby, the memory capacity for storing the matching data can be suppressed.

  (B) The electric power steering apparatus according to claim 2, wherein the control means reduces the hysteresis component as the steering angle decreases in the small steering angle region. apparatus. Thereby, the fluctuation | variation of assist force can be suppressed and a favorable steering feeling can be ensured.

  (C) In the electric power steering apparatus according to (b) or claim 2, the control means sets the hysteresis component to be added to the basic component to zero when the steering angle is zero. An electric power steering apparatus characterized by the above. Thereby, the steering return property can be further improved.

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering device (EPS), 2 ... Steering, 3 ... Steering shaft, 3a ... Column shaft, 5 ... Rack shaft, 7 ... Steering wheel, 10 ... EPS actuator, 11 ... ECU, 12 ... Motor, 14 ... Torque DESCRIPTION OF SYMBOLS 15 ... Vehicle speed sensor 16 ... Steering sensor 21 ... Microcomputer 22 ... Drive circuit 25 ... Current command value calculation part 26 ... Motor control signal output part 27 ... Basic assist control part 28 ... Steering torque detection part , 30 ... alternative assist control unit, 31 ... switching control unit, 32 ... basic control amount calculation unit, 33 ... hysteresis control amount calculation unit, 34 ... additional calculation unit, 35 ... first hysteresis width calculation unit, 36 ... second hysteresis Width calculating unit 37 ... adder 38 ... steering angle gain calculating unit 39 ... multiplier 40 ... guard processing unit I * ... current command value Ias * ... basic assist control amount , Τ ... steering torque, Sa, Sb ... sensor signal, Str ... abnormality detection signal, Isb ** ... alternative assist control amount, θs ... steering angle, V ... vehicle speed, ε_bs ... basic control amount, ε_hy, ε_hy '... hysteresis control Amount, ε_hy1 ... first hysteresis width, ε_hy2 ... second hysteresis width, ε_cm, ε_cm '... total control amount, εth ... upper limit value, Kθ ... steering angle gain.

Claims (4)

A steering force assisting device for applying an assisting force to the steering system using a motor as a drive source, a steering angle detecting means for detecting a steering angle generated in the steering, and controlling the operation of the steering force assisting device based on the steering angle. An electric power steering apparatus that adds a hysteresis component according to a steering direction to a basic component of a target assist force based on the steering angle,
The control means, as the hysteresis component,
A first hysteresis component that decreases as the vehicle speed increases;
A second hysteresis component that increases as the steering angle increases and the vehicle speed increases;
An electric power steering device characterized by calculating The electric power steering apparatus according to claim 1, wherein
The electric power steering apparatus according to claim 1, wherein the control means reduces the hysteresis component when the steering angle is in a small steering angle region corresponding to steering neutral. In the electric power steering device according to claim 1 or 2,
The control means limits the target assist force based on the steering angle so as not to exceed an upper limit value, and varies the upper limit value according to the vehicle speed;
An electric power steering device. In the electric power steering device according to any one of claims 1 to 3,
A torque sensor for detecting a steering torque transmitted via the steering shaft; and an abnormality determining means for determining an abnormality of the torque sensor;
The control means controls the operation of the steering force assisting device based on the steering torque when the torque sensor is normal, and responds to the steering angle when an abnormality occurs in the torque sensor. And controlling the operation of the steering force assisting device to generate the assist force.

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