Turning control device, turning control method, and steering device

Abstract

This control device is provided in a vehicle having a steering wheel that receives steering by a driver and a motor that imparts a turning force to a wheel that is mechanically separated from the steering wheel, and controls a turning angle of the wheel by controlling the motor on the basis of the steering by the driver. The control device acquires a first physical quantity related to a steering amount of the steering wheel and a second physical quantity related to a traveling state of the vehicle. When the vehicle starts in a state where the steering wheel has been steered to a predetermined steering amount or more while the vehicle is in a stopped state, the control device drives the motor so that the wheel moves to a position based on the steering amount of the steering wheel. In a case where the traveling state of the vehicle is a first state, the control device reduces a driving force of the motor as compared with a case where the traveling state of the vehicle is a second state in which the vehicle travels more gently than in the first state.

Description

Steering control device, steering control method, steering device

[0001] The present invention relates to a steering control device, a steering control method, and a steering device.

[0002] The steering device disclosed in Patent Document 1 includes a steering shaft that is separated from the steering wheel and that steers the steerable wheels of a vehicle and that generates a steering force that is a torque applied to the steering shaft to turn the steerable wheels, and a control device that controls the steering motor to make an angle that can be converted into a steering angle of the steerable wheels follow a target angle calculated in accordance with the steering state of the steering wheel, and that executes a correction process to correct the target angle so that the maximum steering force that the steering motor can generate and the axial force generated in the steering shaft are within an angle range defined so that a balance of forces can be maintained.The control device described in Patent Document 1 corrects the target angle in an extremely low speed range immediately after starting, in accordance with the axial force characteristics of the vehicle immediately after starting, and in an extremely low speed range immediately before stopping, in accordance with the axial force characteristics of the vehicle immediately before stopping.

[0003] Japanese Patent Application Laid-Open No. 2022-49972

[0004] In the steering device described in Patent Document 1, when the steering wheel is steered while the vehicle is stopped, resulting in a large steering angle, there is a risk that the movement of the steered wheels will be sudden and not smooth when the vehicle suddenly starts, for example. The present invention aims to provide a steering control device etc. that can smooth the movement of the steered wheels even when the vehicle suddenly starts in a state where the steering amount is large while the vehicle is stopped.

[0005] With this object in mind, the present invention provides a steering control device that is provided in a vehicle having a steering member that accepts steering by a driver and a motor that applies a steering force to steered wheels that are mechanically separated from the steering member, and that controls the steering angle of the steered wheels by controlling the motor based on the steering of the driver. The steering control device acquires a first physical quantity related to the steering amount of the steering member and a second physical quantity related to the traveling state of the vehicle, and when the vehicle starts off in a state in which the steering member is steered by a predetermined steering amount or more while the vehicle is stopped, drives the motor so that the steered wheels move to a position based on the steering amount of the steering member, and when the traveling state of the vehicle is in a first state, reduces the driving force of the motor compared to when the vehicle is in a second state in which the vehicle travels more slowly than in the first state. Viewed from another perspective, the present invention is a steering control method for controlling the steering angle of steered wheels in a vehicle having a steering member that accepts steering by a driver, and a motor that applies a steering force to steered wheels that are mechanically separated from the steering member, the steering control method acquiring a first physical quantity related to the steering amount of the steering member and a second physical quantity related to a traveling state of the vehicle, and when the vehicle starts moving in a state in which the steering member is steered by a predetermined steering amount or more while the vehicle is stopped, driving the motor so that the steered wheels move to a position based on the steering amount of the steering member, and when the traveling state of the vehicle is in a first state, reducing the driving force of the motor compared to when the traveling state of the vehicle is in a second state in which the vehicle travels more slowly than in the first state.Also, from another perspective, the present invention is a steering device comprising: a steering member that accepts steering by a driver of a vehicle; a motor that applies a steering force to steered wheels that are mechanically separated from the steering member; and a control device that controls the steering angle of the steered wheels by controlling the motor based on the steering of the driver, wherein the control device acquires a first physical quantity related to the steering amount of the steering member and a second physical quantity related to a traveling state of the vehicle, and when the vehicle starts off in a state in which the steering member is steered by a predetermined steering amount or more while the vehicle is stopped, drives the motor to move the steered wheels to a position based on the steering of the steering member, and when the traveling state of the vehicle is in a first state, reduces the driving force of the motor compared to when the vehicle is in a second state in which the vehicle travels more slowly than in the first state.

[0006] According to the present invention, the movement of the steered wheels can be made smooth even when the vehicle is suddenly started in a state where the steering amount is large while the vehicle is stopped.

[0007] FIG. 1 is a diagram showing a schematic configuration of a steering device according to a first embodiment. FIG. 2 is a diagram showing an example of a schematic configuration of a control device according to the first embodiment. FIG. 3 is a diagram showing an example of a schematic configuration of a target rack speed calculation unit and a rack speed F / B control unit. FIG. 4 is a diagram showing an example of a correlation between a target displacement amount, a vehicle speed, and a limit value. FIG. 5 is a diagram showing an example of an operation of the steering device. FIG. 6 is a diagram showing an example of a schematic configuration of a control device according to a second embodiment. FIG. 7 is a diagram showing an example of a correlation between the sign of an actual rack speed, a target displacement amount, a vehicle speed, and a limit value.

[0008] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. <First Embodiment> Fig. 1 is a diagram showing a schematic configuration of a steering device 100 according to a first embodiment. Fig. 2 is a diagram showing an example of a schematic configuration of a control device 10. The steering device 100 is a steering device for arbitrarily changing the direction of travel of a vehicle 1, and in this embodiment, a configuration applied to an automobile as an example of a vehicle 1 is illustrated. The steering device 100 is a steer-by-wire electric power steering device in which a steering wheel 101 (described later) and wheels 150 are mechanically separated.

[0009] The steering device 100 includes a wheel-shaped steering wheel 101 (hereinafter referred to as the "steering wheel 101") that is operated by the driver to change the direction of travel of the vehicle 1, a steering angle sensor 131 that detects the steering angle θs of the steering wheel 101, and a reaction force device 132 that applies a steering reaction force to the driver via the steering wheel 101.

[0010] The steering device 100 also includes tie rods 104 connected to left and right wheels (e.g., front wheels) 150, which serve as steered wheels, respectively, and a rack shaft 105 connected to the tie rods 104. The steering device 100 also includes a pinion shaft 106 having a pinion 106a formed at its lower end, which constitutes a rack-pinion mechanism together with rack teeth 105a formed on the rack shaft 105.

[0011] The steering device 100 also includes a steering gear box 107 that houses the pinion shaft 106. Rack teeth 105a formed in the center of a rack shaft 105 are fitted inside the steering gear box 107, and both ends of the rack shaft 105 protrude from the steering gear box 107. Each end of the rack shaft 105 is provided with a protruding portion 105b that is larger in outer shape than the openings of both end faces 107a of the steering gear box 107 in the left-right direction as viewed in FIG. 1. The protruding portion 105b abuts against the left-right end faces 107a of the steering gear box 107, thereby restricting the amount of movement of the rack shaft 105.

[0012] The steering device 100 also includes a motor 110 supported by a steering gearbox 107, and a speed reduction mechanism 111 that reduces the driving force of the motor 110 and transmits it to the pinion shaft 106. The speed reduction mechanism 111 is composed of, for example, a worm wheel (not shown) fixed to the pinion shaft 106 and a worm gear (not shown) fixed to the output shaft of the motor 110. The motor 110 applies a rotational driving force to the pinion shaft 106, thereby applying a steering force to the rack shaft 105 to steer the wheels 150. The motor 110 can be, for example, a three-phase brushless motor having a resolver 120 that outputs a rotation angle signal linked to a motor rotation angle θm, which is the rotation angle of the motor 110.

[0013] The steering device 100 also includes a control device 10 that controls the operation of the motor 110 and the reaction device 132. In the steering device 100, when the driver steers the steering wheel 101, the wheels 150 are steered while maintaining a balance between the driving force generated by the motor 110 and the axial force acting on the rack shaft 105 (hereinafter, sometimes referred to as the "rack axial force"). Therefore, if the maximum driving force that the motor 110 can generate is less than the rack axial force generated when steering the wheels 150 to a steering angle corresponding to the steering angle of the steering wheel 101, it becomes difficult to steer the wheels 150 to a steering angle corresponding to the steering of the steering wheel 101. In particular, when the steering wheel 101 is steered while the vehicle 1 is stopped, in other words, when the steering wheel 101 is turned while stationary, the rack axial force becomes large. Therefore, it is preferable that the maximum driving force of the motor 110 be large. On the other hand, increasing the maximum driving force of the motor 110 increases the size of the motor 110. Therefore, in the steering device 100, taking into consideration that the steering device is a steer-by-wire type device, the motor 110 is made smaller by making the maximum driving force of the motor 110 lower than the maximum rack axial force, and the control device 10 controls the driving of the motor 110 so that no uncomfortable steering feeling occurs due to the attempt to make the motor 110 smaller. The control device 10 will be described in detail below.

[0014] The steering device 100 includes a control device 10 that controls the operation of the motor 110 and the reaction device 132. The control device 10 is an arithmetic and logic operation circuit including a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like.

[0015] The control device 10 receives an output signal from the steering angle sensor 131 and a rotation angle signal from the resolver 120. In addition, the control device 10 receives an output signal from a vehicle speed detection unit 170 that detects the vehicle speed Vc, which is the moving speed of the vehicle 1, via a network (CAN) that communicates with various devices mounted on the vehicle 1.

[0016] The control device 10 includes an actual displacement amount calculation unit 20 that calculates an actual displacement amount Da, which is the actual displacement amount of the rack shaft 105, and an actual rack speed calculation unit 25 that calculates an actual rack speed Rva, which is the actual moving speed of the rack shaft 105. The control device 10 also includes a target displacement amount calculation unit 30 that calculates a target displacement amount Dt, which is a target displacement amount of the rack shaft 105, and a target rack speed calculation unit 40 that calculates a target rack speed Rvt, which is a target value for the moving speed of the rack shaft 105. The control device 10 also includes a rack speed F / B control unit 50 that outputs a torque command value Tt, and a motor drive control unit 60 that generates a signal for driving the motor 110. The control device 10 also includes a motor drive unit 70 that controls the driving of the motor 110, and a motor current detection unit 80 that detects an actual current Im that actually flows through the motor 110.

[0017] Here, the state in which the steering wheel 101 is located in the neutral position (in other words, the state in which the steering angle θs is 0) is defined as the neutral state of the steering device 100, and the steering angle θs when the steering wheel 101 is rotated to the right from the neutral position is defined as a positive value. Also, the steering angle θs when the steering wheel 101 is rotated to the left from the neutral position is defined as a negative value. Also, the position of the rack shaft 105 when the steering wheel 101 is located in the neutral position is defined as the neutral position, and the amount of displacement of the rack shaft 105 from the neutral position is simply referred to as the amount of displacement of the rack shaft 105. The direction of displacement of the rack shaft 105 that rotates the wheels 150 to the right is defined as a positive value, and the direction of displacement of the rack shaft 105 that rotates the wheels 150 to the left is defined as a negative value.

[0018] The actual displacement amount calculation unit 20 calculates the actual displacement amount Da based on the motor rotation angle θm in consideration of the fact that the output shaft of the motor 110, the pinion shaft 106, the rack shaft 105, etc. are mechanically coupled to each other, and therefore there is a correlation between the motor rotation angle θm and the actual displacement amount Da of the rack shaft 105. Note that the actual displacement amount calculation unit 20 may calculate the actual displacement amount Da based on an output value from a sensor that detects the displacement amount of the rack shaft 105, or may calculate the actual displacement amount Da based on an output value from a sensor that detects the rotation angle of the pinion shaft 106.

[0019] The actual rack speed calculation unit 25 calculates the actual rack speed Rva based on the motor rotation angle θm. Note that the actual rack speed calculation unit 25 may calculate the actual rack speed Rva by differentiating the actual displacement amount Da calculated by the actual displacement amount calculation unit 20.

[0020] The target displacement amount calculation unit 30 calculates the target displacement amount Dt based on the steering angle θs. For example, the target displacement amount calculation unit 30 multiplies the steering angle θs by a predetermined coefficient K to obtain the target displacement amount Dt (Dt = θs × K). Here, there is a one-to-one correspondence between the steering angle of the wheels 150 and the displacement amount of the rack shaft 105, and there is also a one-to-one correspondence between the displacement amount of the rack shaft 105 and the rotation angle of the pinion shaft 106. In addition, there is a predetermined ratio between the steering angle θs and the displacement amount of the rack shaft 105. Therefore, there is an example in which the coefficient K is 1 / predetermined ratio.

[0021] Note that the steering device 100 is a steer-by-wire system and can freely change the predetermined ratio, so it is possible to change the predetermined ratio according to the vehicle speed Vc. For example, when the vehicle speed Vc is low, the predetermined ratio may be set small so that the wheels 150 can be steered to a large extent with little steering wheel operation, and when the vehicle speed Vc is high, the predetermined ratio may be set large so that the wheels 150 can be steered to a small extent with much steering wheel operation. In other words, the coefficient K may be set small when the vehicle speed Vc is low, and large when the vehicle speed Vc is high.

[0022] Fig. 3 is a diagram showing an example of a schematic configuration of the target rack speed calculation unit 40 and the rack speed F / B control unit 50. Fig. 4 is a diagram showing an example of the correlation between the target displacement amount Dt, the vehicle speed Vc, and the limit value L. The target rack speed calculation unit 40 has a deviation calculation unit 41 that calculates the deviation ΔD between the target displacement amount Dt and the actual displacement amount Da, and a F / B processing unit 42 that performs feedback (hereinafter sometimes referred to as "F / B") processing so that the deviation ΔD becomes zero and outputs a tentative target rack speed Rvp that is a tentative value of the target rack speed Rvt. The F / B processing unit 42 performs feedback control so that the target displacement amount Dt and the actual displacement amount Da coincide with each other, and can, for example, perform proportional processing using a proportional element on the deviation ΔD calculated by the deviation calculation unit 41.

[0023] The target rack speed calculation unit 40 also has a limit value setting unit 43 that sets a limit value L for limiting the final target rack speed Rvt, and a limit unit 44 that limits the target rack speed Rvt using the limit value L. The limit value setting unit 43 sets the limit value L using the target displacement amount Dt and the vehicle speed Vc. The limit value setting unit 43 calculates the limit value L by substituting the target displacement amount Dt and the vehicle speed Vc into a map that shows the correspondence between the target displacement amount Dt, the vehicle speed Vc, and the limit value L, as shown in FIG. 4, which has been created in advance based on empirical rules and stored in ROM.

[0024] In the map shown in Fig. 4, when the target displacement amount Dt is within a predetermined range, the limit value L is set to 1, and when the target displacement amount Dt exceeds the predetermined range, the limit value L is set to decrease as the absolute value of the target displacement amount Dt increases. Also, in the map shown in Fig. 4, when the target displacement amount Dt exceeds the predetermined range, the degree to which the limit value L decreases is set to be greater when the vehicle speed Vc is at vehicle speed Vb than when the vehicle speed Vc is at vehicle speed Va. The vehicle speed Va is a speed within the extremely low speed range, and the vehicle speed Vb is a speed outside the extremely low speed range. An example of a speed within the extremely low speed range is a speed of 5 km / h or less.

[0025] The limiting unit 44 outputs the value obtained by multiplying the tentative target rack speed Rvp by the limiting value L as the target rack speed Rvt (Rvt=Rvp×L).

[0026] By the limit value setting unit 43 and limiting unit 44 configured as described above, when the target displacement amount Dt is within a predetermined range, the tentative target rack speed Rvp becomes the target rack speed Rvt. On the other hand, when the target displacement amount Dt is outside the predetermined range, the limit value L becomes smaller as the absolute value of the target displacement amount Dt increases, and therefore the target rack speed Rvt becomes smaller as the absolute value of the target displacement amount Dt increases. Also, when the target displacement amount Dt is outside the predetermined range, the limit value L is smaller when the vehicle speed Vc is outside the extremely low speed range than when it is within the extremely low speed range, and therefore the target rack speed Rvt is smaller when the vehicle speed Vc is outside the extremely low speed range than when it is within the extremely low speed range.

[0027] The rack speed F / B control unit 50 has a deviation calculation unit 51 that calculates the deviation ΔRv between the target rack speed Rvt and the actual rack speed Rva, and a F / B processing unit 52 that performs F / B processing so that the deviation ΔRv becomes zero and outputs a torque command value Tt. The F / B processing unit 52 performs feedback control so that the target rack speed Rvt and the actual rack speed Rva match. An example of the F / B processing unit 52 is PI control. That is, the F / B processing unit 52 performs proportional processing using a proportional element on the deviation ΔRv calculated by the deviation calculation unit 51, performs integral processing using an integral element, and adds these values ​​together in an addition calculation unit.

[0028] 2, the motor drive control unit 60 includes an F / B control unit that performs feedback control based on the deviation between the torque command value Tt and the actual current Im supplied to the motor 110, which is detected by the motor current detection unit 80, and a signal generation unit that generates a signal for PWM driving the motor 110. For example, the F / B control unit performs proportional processing using a proportional element and integral processing using an integral element on the deviation between the torque command value Tt and the actual current Im, and adds these values ​​together in an addition operation unit. The signal generation unit generates a PWM signal for PWM driving the motor 110 based on the output value from the F / B control unit, and outputs the generated PWM signal.

[0029] The motor drive unit 70 (see FIG. 2) is a so-called inverter, and includes, for example, six independent transistors (FETs) as switching elements, with three of the six transistors connected between the positive line of the power supply and the electric coil of each phase, and the other three transistors connected between the electric coil of each phase and the negative (ground) line of the power supply. The drive of the motor 110 is controlled by driving the gates of two selected transistors from the six to cause these transistors to perform a switching operation.

[0030] 2, motor current detection unit 80 detects the value of actual current Im flowing through motor 110 from the voltage generated across a shunt resistor connected to motor drive unit 70. Motor drive control unit 60, motor drive unit 70, and motor current detection unit 80 configured as described above cause motor 110 to rotate by an angle corresponding to torque command value Tt.

[0031] (Operation of Steering Device 100) Figure 5 is a diagram showing an example of the operation of the steering device 100 (see Figure 1). As shown in Figure 5(a), when the vehicle 1 (see Figure 1) is stopped (in other words, when the vehicle speed Vc is 0), if the steering wheel 101 (see Figure 1) is turned clockwise from the neutral position (in other words, a position where the steering angle θs is 0) to the maximum steering angle θsmax as shown in Figure 5(b), the target displacement amount Dt of the rack shaft 105 changes to the maximum displacement amount Dtmax as shown by the two-dot chain line in Figure 5(d). If the rack shaft 105 is displaced to the target displacement amount Dt, the rack axial force will be as shown by the two-dot chain line in Figure 5(c).

[0032] As described above, in the steering device 100, the driving force that the motor 110 (see FIG. 1) can generate is less than the maximum rack axial force indicated by the two-dot chain line in FIG. 5C, so the rack shaft 105 cannot be displaced to the maximum displacement amount Dtmax. As a result, the actual displacement amount Da of the rack shaft 105 is the displacement amount indicated by the solid line in FIG. 5D, which is smaller than the maximum displacement amount Dtmax. In addition, the wheels 150 do not reach the maximum steering angle.

[0033] Thereafter, if the vehicle 1 starts moving at a speed within the extremely low speed range in a state where the steering angle θs is the maximum steering angle θsmax but the actual displacement amount Da of the rack shaft 105 has not yet reached the maximum displacement amount Dtmax, the actual displacement amount Da will gradually approach the target displacement amount Dt as shown by the dashed line in Figure 5(e) as the rack axial force gradually decreases.

[0034] On the other hand, if the vehicle 1 starts (e.g., suddenly starts) at a speed outside the extremely low speed range while the steering angle θs is at its maximum and the actual displacement Da is not equal to the maximum displacement Dtmax, and if the target rack speed Rvt (see FIG. 2) is not limited, the actual displacement Da will suddenly approach the target displacement Dt as shown by the two-dot chain line in FIG. 5E as the rack axial force suddenly decreases. Therefore, if the limiting configuration is not implemented, the actual rack speed Rva (see FIG. 2) will be higher when the vehicle 1 starts at a speed outside the extremely low speed range than when the vehicle 1 starts at a speed within the extremely low speed range. As a result, the steering speed of the wheels 150 will also be higher, resulting in less smooth movement of the wheels 150. Furthermore, the noise generated when the protruding portion 105b (see FIG. 1) of the rack shaft 105 hits the end face 107a (see FIG. 1) of the steering gear box 107 will be louder.

[0035] In contrast, in the steering device 100, the target rack speed Rvt is limited using the limit value L. For example, as shown in FIG. 4, when the vehicle 1 is traveling at a speed outside the extremely low speed range and the target displacement amount Dt is the maximum displacement amount Dtmax, the limit value L is 0.2, so the target rack speed Rvt is 0.2 times the tentative target rack speed Rvp (see FIG. 3). Therefore, the actual rack speed Rva also decreases, and the steering speed of the wheels 150 also decreases, resulting in smoother movement of the wheels 150. As a result, for example, even if the vehicle 1 suddenly starts moving in a state where the steering amount is large while the vehicle 1 is stopped, the movement of the wheels 150 becomes smoother. In addition, the noise generated when the protruding portion 105b of the rack shaft 105 hits the end face 107a of the steering gear box 107 is reduced.

[0036] If the range in which the motor 110 can displace the rack shaft 105 when the steering wheel 101 is steered while the vehicle 1 is stopped, in other words, when the steering wheel 101 is turned while the vehicle is stationary, is referred to as the "displaceable range," then the above-mentioned predetermined range can be, for example, the same as the "displaceable range." Alternatively, the predetermined range can be, for example, a range that is wider than the displaceable range and narrower than the maximum amount of displacement by which the rack shaft 105 can be displaced. Furthermore, the steering amount of the steering wheel 101 that corresponds to the predetermined range may also be referred to as the "predetermined steering amount."

[0037] As described above, control device 10 is an example of a steering control device that is provided in vehicle 1 having steering wheel 101 (an example of a steering member) that accepts steering by a driver and motor 110 that applies a steering force to wheels 150 (an example of steered wheels) that are mechanically separated from steering wheel 101, and that controls the steering angle of wheels 150 by controlling motor 110 based on the steering by the driver. Control device 10 acquires target displacement amount Dt as an example of a first physical quantity related to the steering amount of steering wheel 101 (e.g., steering angle θs), and vehicle speed Vc as an example of a second physical quantity related to the traveling state of vehicle 1. When vehicle 1 starts moving with steering wheel 101 steered by a predetermined steering amount or more while vehicle 1 is stopped, control device 10 controls the driving force of motor 110 as described below to drive motor 110 so that wheels 150 move to a position based on the steering amount of steering wheel 101. That is, when the traveling state of the vehicle 1 is in the first state, the control device 10 reduces the driving force of the motor 110 compared to when the vehicle 1 is in the second state in which the vehicle 1 travels more slowly than in the first state.

[0038] According to the control device 10 configured as described above, when the vehicle 1 starts moving with the steering wheel 101 steered by a predetermined steering amount or more, the driving force of the motor 110 is reduced when the traveling state of the vehicle 1 is in the first state compared to when the traveling state of the vehicle 1 is in the second state, thereby reducing the movement speed of the rack shaft 105. Therefore, the control device 10 can reduce the steering speed of the wheels 150 when the traveling state of the vehicle 1 is in the first state, thereby smoothing the movement of the wheels 150. As a result, even if the vehicle 1 suddenly starts moving with a large steering amount while the vehicle 1 is stopped, the movement of the wheels 150 can be smoothed. Furthermore, according to the control device 10, since the movement speed of the rack shaft 105 is reduced when the traveling state of the vehicle 1 is in the first state, even if the protruding portion 105b of the rack shaft 105 hits the end face 107a of the steering gear box 107, the impact noise is reduced.

[0039] Here, as described above, the case where the traveling state of the vehicle 1 is in the first state can be exemplified as the case where the vehicle 1 is traveling at a speed outside the extremely low speed range, and the case where the traveling state of the vehicle 1 is in the second state can be exemplified as the case where the vehicle 1 is traveling at a speed within the extremely low speed range. Alternatively, the case where the traveling state of the vehicle 1 is in the first state can be exemplified as the case where the acceleration of the vehicle 1 is greater than a predetermined acceleration, and the case where the traveling state of the vehicle 1 is in the second state can be exemplified as the case where the acceleration of the vehicle 1 is equal to or less than the predetermined acceleration.

[0040] Furthermore, the control device 10 reduces the driving force of the motor 110 so that the steering speed of the wheels 150 when the vehicle 1 starts moving with the steering wheel 101 steered by more than a predetermined steering amount while the vehicle 1 is stopped is smaller than the steering speed of the wheels 150 when the vehicle 1 starts moving with the steering wheel 101 steered by less than the predetermined steering amount while the vehicle 1 is stopped. In other words, as shown in the map in FIG. 4 , the limit value L is set to 1 when the target displacement amount Dt corresponding to the steering angle θs of the steering wheel 101 is within a predetermined range, and when the target displacement amount Dt exceeds the predetermined range, the limit value L is set to decrease as the absolute value of the target displacement amount Dt increases. As a result, the steering speed of the wheels 150 decreases when the steering wheel 101 is steered by more than the predetermined steering amount while the vehicle 1 is stopped, which tends to increase the difference between the target displacement amount Dt and the actual displacement amount Da. As a result, the control device 10 can accurately reduce the steering speed of the wheels 150, thereby smoothing the movement of the wheels 150.

[0041] Furthermore, the control device 10 determines a torque command value Tt for the motor 110 so that the deviation (e.g., deviation ΔRv) between a target value (e.g., target rack speed Rvt) of the movement speed of the rack shaft 105 (an example of a transmission member) that transmits the driving force of the motor 110 to the steering of the wheels 150 and the actual movement speed (e.g., actual rack speed Rva) becomes 0 (zero). Then, the control device 10 sets a smaller torque command value Tt when the traveling state of the vehicle 1 is in the first state than when the traveling state of the vehicle 1 is in the second state. As a result, the movement speed of the rack shaft 105 is reduced when the traveling state of the vehicle 1 is in the first state, thereby enabling smooth movement of the wheels 150 with high reliability.

[0042] Furthermore, the control device 10 decreases the target value of the movement speed of the rack shaft 105 (for example, the target rack speed Rvt) as the steering amount of the steering wheel 101 increases. As a result, in a state where the steering amount of the steering wheel 101 is large while the vehicle 1 is stopped, which tends to increase the difference between the target displacement amount Dt and the actual displacement amount Da, the movement speed of the rack shaft 105 decreases, so the steering speed of the wheels 150 can be reduced with high accuracy, and the movement of the wheels 150 can be made smoother.

[0043] Furthermore, when the traveling state of the vehicle 1 is in the first state, the control device 10 gradually reduces the moving speed of the wheels 150 more than when the traveling state is in the second state. In other words, the rack speed F / B control unit 50 performs PI control F / B processing so that the deviation ΔRv between the target rack speed Rvt and the actual rack speed Rva becomes 0. As a result, even if the protruding portion 105b of the rack shaft 105 hits the end face 107a of the steering gear box 107, the actual rack speed Rva immediately before the hit will be small, and the sound produced when the hit occurs will be quieter.

[0044] Furthermore, because the control device 10 has the above-described configuration, it is possible to prevent an uncomfortable steering feeling even if the maximum driving force of the motor 110 is set lower than the maximum rack axial force that would be generated in the rack shaft 105 if the steering wheel 101 were steered to the maximum steering angle θsmax while the vehicle 1 is stopped and the wheels 150 were steered to the maximum steering angle. As a result, the maximum driving force of the motor 110 can be reduced, allowing for a reduction in the size of the motor 110. Furthermore, even if the steering wheel 101 is steered to the maximum steering angle θsmax while the vehicle 1 is stopped, the wheels 150 are not steered to the maximum steering angle. Therefore, compared to a configuration in which the wheels 150 are steered to the maximum steering angle, wear debris on the wheels 150 can be suppressed and the wear speed of the wheels 150 can be slowed.

[0045] The steering control method performed by control device 10 is a method of controlling the steering angle of wheels 150 in vehicle 1, which has steering wheel 101 that accepts steering by the driver, and motor 110 that applies a steering force to wheels 150 that are mechanically separated from steering wheel 101. The steering control method performed by control device 10 acquires a target displacement amount Dt related to the steering amount of steering wheel 101 and a vehicle speed Vc related to the traveling state of vehicle 1, and when vehicle 1 starts in a state in which steering wheel 101 is steered by a predetermined steering amount or more while vehicle 1 is stopped, drives motor 110 so that wheels 150 move to a position based on the steering amount of steering wheel 101, but reduces the driving force of motor 110 when the traveling state of vehicle 1 is in a first state compared to when it is in a second state.

[0046] Furthermore, the processing performed by the control device 10 described above can be realized by the cooperation of software and hardware resources. In this case, the CPU of the control device 10 executes a program that realizes each function of the device, thereby realizing each function. For example, a non-transitory computer-readable recording medium on which a program is recorded is provided to the control device 10, and the CPU of the control device 10 reads the program stored on the recording medium. Alternatively, the CPU of the control device 10 downloads the program via a network. In these cases, the program read from the recording medium or the downloaded program itself realizes the functions of the above-described embodiments, and the program itself and the recording medium on which it is recorded constitute the present invention.

[0047] The program that realizes the functions of the control device 10 executes the functions of acquiring a target displacement amount Dt related to the steering amount of the steering wheel 101 and a vehicle speed Vc related to the traveling state of the vehicle 1, and of driving the motor 110 so that the wheels 150 move to a position based on the steering amount of the steering wheel 101 when the vehicle 1 starts moving with the steering wheel 101 steered by more than a predetermined steering amount while the vehicle 1 is stopped, and of reducing the driving force of the motor 110 when the traveling state of the vehicle 1 is in a first state compared to when the traveling state is in a second state.

[0048] <Second embodiment> Fig. 6 is a diagram showing an example of a schematic configuration of a control device 210 according to the second embodiment. The control device 210 according to the second embodiment differs from the control device 10 according to the first embodiment in that it has a target rack speed calculation unit 240 that corresponds to the target rack speed calculation unit 40. Below, the control device 210 according to the second embodiment will be described in terms of differences from the control device 10 according to the first embodiment. The same components in the first and second embodiments are designated by the same reference numerals, and detailed description thereof will be omitted.

[0049] The target rack speed calculation unit 240 differs from the target rack speed calculation unit 40 according to the first embodiment in that it has a limit value setting unit 243 equivalent to the limit value setting unit 43 and also has an extraction unit 245 that extracts the sign of the actual rack speed Rva. The limit value setting unit 243 uses the target displacement amount Dt and the vehicle speed Vc and sets the limit value L2 by considering whether the direction of the target displacement amount Dt is the same as the displacement direction of the rack shaft 105 (see FIG. 1). This is because the speed is limited when the rack shaft 105 moves toward the end and is not limited when the rack shaft 105 returns to the neutral position, so that resistance to movement of the wheels 150 (see FIG. 1) is not applied when the rack shaft 105 returns.

[0050] The extraction unit 245 extracts a plus value when the sign of the actual rack speed Rva is plus, and extracts a minus value when the sign of the actual rack speed Rva is minus.

[0051] 7 is a diagram showing an example of the correlation between the sign of the actual rack speed Rva, the target displacement amount Dt, the vehicle speed Vc, and the limit value L2. The limit value setting unit 243 sets the limit value L2 using the sign of the actual rack speed Rva, the target displacement amount Dt, and the vehicle speed Vc extracted by the extraction unit 245. The limit value setting unit 243 calculates the limit value L2 by substituting the sign of the actual rack speed Rva, the target displacement amount Dt, and the vehicle speed Vc into a map, as shown in FIG. 7, which is created in advance based on empirical rules and stored in ROM and shows the correspondence between the sign of the actual rack speed Rva, the target displacement amount Dt, the vehicle speed Vc, and the limit value L2.

[0052] 7 differs from the map shown in FIG. 4 in that the sign of the actual rack speed Rva is set on the vertical axis. As a result, the limit value L2 becomes a value in the first quadrant when the sign of the target displacement amount Dt and the sign of the actual rack speed Rva are positive, and becomes a value in the second quadrant when the sign of the target displacement amount Dt and the sign of the actual rack speed Rva are negative. Furthermore, the limit value L2 becomes a value in the third quadrant when the sign of the target displacement amount Dt and the sign of the actual rack speed Rva are negative, and becomes a value in the fourth quadrant when the sign of the target displacement amount Dt is positive and the sign of the actual rack speed Rva is negative.

[0053] 7, in the first and third quadrants where the sign of the target displacement amount Dt and the sign of the actual rack speed Rva are the same, the limit value L2 is 1 when the target displacement amount Dt is within a predetermined range, and when the target displacement amount Dt exceeds the predetermined range, the limit value L decreases as the absolute value of the target displacement amount Dt increases, similar to the map shown in Fig. 4. Also, in the map shown in Fig. 7, similar to the map shown in Fig. 4, the degree to which the limit value L2 decreases when the target displacement amount Dt exceeds the predetermined range is set to be greater for vehicle speed Vb than for vehicle speed Va.

[0054] 4, the map shown in Fig. 7 differs from the map shown in Fig. 4 in that in the second and fourth quadrants where the sign of the target displacement amount Dt and the sign of the actual rack speed Rva are different, the limit value L2 is 1 even if the target displacement amount Dt exceeds the predetermined range. As a result, when the rack shaft 105 returns to the neutral position, the limit value L2 is set to 1, and no limit is imposed.

[0055] Therefore, in the control device 210 according to the second embodiment configured as described above, when the rack shaft 105 moves toward the end, the limit value L2 becomes smaller than 1, and the target rack speed Rvt is limited, just as in the control device 10 according to the first embodiment. As a result, the steering speed of the wheels 150 also decreases, resulting in smoother movement of the wheels 150. In addition, the noise generated when the protruding portion 105b (see FIG. 1) of the rack shaft 105 hits the end face 107a (see FIG. 1) of the steering gear box 107 is reduced.

[0056] On the other hand, when the rack shaft 105 returns to the neutral position, the limit value L2 becomes 1, and the target rack speed is not limited. As a result, no resistance force is applied to the wheel 150 when it returns to the neutral position, which prevents the steering feel from deteriorating.

[0057] As described above, when the steering wheel 101 (see Figure 1) is steered by more than a predetermined steering amount, the control device 210 changes the driving force of the motor 110 (see Figure 1) depending on whether the vehicle 1 starts off with the steering wheel 101 turned back toward the neutral position while the vehicle 1 (see Figure 1) is stopped, or whether the vehicle 1 starts off with the steering wheel 101 turned further.

[0058] Furthermore, when the vehicle 1 starts moving with the steering wheel 101 turned back to the neutral position while the vehicle 1 is stopped, even if the steering wheel 101 is turned by a predetermined steering amount or more, the driving force of the motor 110 is not changed whether the traveling state of the vehicle 1 is the first state or the second state. As a result, no resistance is applied to the movement of the wheels 150 when returning to the neutral position regardless of the traveling state of the vehicle 1, and therefore, deterioration of the steering feeling can be suppressed.

[0059] Furthermore, it is determined whether the steering wheel 101 is being turned further or turned back based on the sign of the actual rack speed Rva, which is an example of a third physical quantity related to the steering speed of the wheels 150, and the target displacement amount Dt. This makes it possible to easily and accurately determine whether the steering wheel 101 is being turned further or turned back.

[0060] 1...vehicle, 10, 210...controller (an example of a steering control device), 20...actual displacement amount calculation unit, 25...actual rack speed calculation unit, 30...target displacement amount calculation unit, 40...target rack speed calculation unit, 50...rack speed F / B control unit, 60...motor drive control unit, 70...motor drive unit, 80...motor current detection unit, 100...steering device, 101...steering wheel (an example of a steering member), 105...rack shaft (an example of a transmission member), 110...motor, 150...wheel (an example of a steered wheel)

Claims

1. A steering control device that is provided to a vehicle having a steering member that accepts steering by a driver and a motor that applies a steering force to steered wheels that are mechanically separated from the steering member, and that controls the steering angle of the steered wheels by controlling the motor based on the steering of the driver, wherein the steering control device obtains a first physical quantity related to the steering amount of the steering member and a second physical quantity related to the traveling state of the vehicle, and when the vehicle starts moving with the steering member steered by more than a predetermined steering amount while the vehicle is stopped, drives the motor to move the steered wheels to a position based on the steering amount of the steering member, and when the traveling state of the vehicle is in a first state, reduces the driving force of the motor compared to when the vehicle is in a second state in which the vehicle travels more slowly than in the first state.

2. A steering control device as claimed in claim 1, wherein the driving force of the motor is reduced so that the steering speed of the steered wheels when the vehicle starts moving with the steering member steered by more than the predetermined steering amount while the vehicle is stopped is smaller than the steering speed of the steered wheels when the vehicle starts moving with the steering member steered by less than the predetermined steering amount while the vehicle is stopped.

3. A steering control device as claimed in claim 1, wherein a torque command value for the motor is determined so that the deviation between a target value of the movement speed of a transmission member that transmits the driving force of the motor to the steering of the steered wheels and the actual movement speed becomes zero, and when the traveling state of the vehicle is in the first state, the torque command value is made smaller than when the vehicle is in the second state.

4. A steering control device according to claim 3, wherein the target value of the movement speed of the transmission member is set smaller as the steering amount of the steering member increases.

5. A steering control device according to claim 1, wherein when the traveling state of the vehicle is in the first state, the moving speed of the steered wheels is gradually reduced compared to when the traveling state of the vehicle is in the second state.

6. A steering control device as claimed in claim 1, wherein, when the steering member is steered by more than the predetermined steering amount, the driving force of the motor is changed when the vehicle starts moving with the steering member turned back towards the neutral position while the vehicle is stopped, and when the vehicle starts moving with the steering member turned further.

7. A steering control device as claimed in claim 1, wherein when the vehicle starts moving with the steering member turned back to the neutral position while the vehicle is stopped, the driving force of the motor is not changed depending on whether the traveling state of the vehicle is in the first state or the second state, even if the steering member is steered by more than the predetermined steering amount.

8. A steering control device according to claim 6 or 7, wherein a determination is made as to whether the steering member is being turned further or turned back based on a third physical quantity related to the turning speed of the steered wheels and the first physical quantity.

9. A steering control method for controlling the steering angle of steered wheels in a vehicle having a steering member that accepts steering by a driver and a motor that applies a steering force to steered wheels that are mechanically separated from the steering member, the steering control method comprising: obtaining a first physical quantity related to the steering amount of the steering member and a second physical quantity related to the traveling state of the vehicle; and when the vehicle starts moving with the steering member steered by more than a predetermined steering amount while the vehicle is stopped, driving the motor so that the steered wheels move to a position based on the steering amount of the steering member; and when the traveling state of the vehicle is in a first state, reducing the driving force of the motor compared to when the vehicle is in a second state in which the vehicle travels more slowly than in the first state.

10. A steering device comprising: a steering member that accepts steering by a vehicle driver; a motor that applies a steering force to steered wheels that are mechanically separated from the steering member; and a control device that controls the steering angle of the steered wheels by controlling the motor based on the steering of the driver, wherein the control device obtains a first physical quantity related to the steering amount of the steering member and a second physical quantity related to the traveling state of the vehicle, and when the vehicle starts moving with the steering member steered by a predetermined steering amount or more while the vehicle is stopped, drives the motor to move the steered wheels to a position based on the steering of the steering member, and when the traveling state of the vehicle is in a first state, reduces the driving force of the motor compared to when the vehicle is in a second state in which the vehicle travels more slowly than in the first state.

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