Steering control device

Abstract

A steering control device (1) includes: an absolute steering angle detection unit (53) configured to detect an absolute steering angle; and a current command value calculation unit (51) configured to calculate a current command value corresponding to a target value of motor torque output from a motor (21). The current command value calculation unit (51) is configured to perform partial release control for reducing a correction value of the current command value caused by execution of end contact mitigation control when the vehicle is being turned while executing end contact mitigation control. The current command value calculation unit (51) is configured to stop the partial release control when the current command value calculated during execution of the partial release control is a value not affected by reduction of the correction value based on the partial release control.

Description

Technical Field

[0001] The present invention relates to a steering control device. Background Art

[0002] In related art, an electric power steering system (EPS) including an actuator having an electric motor as a drive source is known as a vehicle steering system. As such an EPS, there is an EPS that acquires a steering angle of a steering wheel that is an absolute angle including a range exceeding 360° and performs various types of control based on the steering angle. As an example of such control, for example, Japanese Unexamined Patent Application Publication No. 2016-155519 (JP 2016-155519 A) discloses end contact mitigation control for mitigating the influence of so-called end contact where a rack end, which is an end of a rack shaft, contacts a rack housing.

[0003] In the EPS described in JP 2016-155519 A, a rack end position where the movement of the rack shaft is physically restricted by end contact is associated with a steering angle, and the steering angle at this position is stored as an end position corresponding angle. In the EPS, the impact of end contact is mitigated by reducing a target value of motor torque output from the motor based on a distance between the steering angle and the end position corresponding angle. Summary of the Invention

[0004] In a configuration according to related art, by performing end contact mitigation control, the movement of the rack shaft can be restricted to a virtual rack end position that is closer to a neutral steering position than an actual rack end position where the rack shaft actually contacts the rack housing. In this case, the steering angle is smaller than the steering angle when the rack shaft is at the actual rack end position. That is, a minimum turning radius when the movement of the rack shaft is restricted to the virtual rack end position is larger than a minimum turning radius based on the structure of the vehicle. Therefore, there is a concern that the small-turn performance of the vehicle deteriorates due to the execution of end contact mitigation control when the vehicle is turning.

[0005] The present invention provides a steering control device that can suppress deterioration of small-turn performance of a vehicle.

[0006] According to one aspect of the present invention, there is provided a steering control device for a steering system, the steering system including: a housing; a turning shaft accommodated in the housing such that the turning shaft can reciprocate; and an actuator that uses an electric motor as a drive source to apply a motor torque for reciprocating the turning shaft. The steering control device includes: an absolute steering angle detection unit configured to detect an absolute steering angle that is a rotation angle of a rotation shaft, the rotation angle of the rotation shaft being convertible into a turning angle of a turning wheel connected to the turning shaft and represented as an absolute angle including a range exceeding 360°; and a current command value calculation unit configured to calculate a current command value corresponding to a target value of the motor torque output from the electric motor. The steering control device is configured to control the excitation of the electric motor such that an actual current value supplied to the electric motor reaches the current command value. The current command value calculation unit is configured to store an end position corresponding angle that is an angle of an end position indicating that the movement of the turning shaft is restricted due to an end contact where the turning shaft contacts the housing and is related to the absolute steering angle. The current command value calculation unit is configured to: when an end separation angle indicating a distance of the absolute steering angle from the end position corresponding angle is equal to or less than a predetermined angle, perform an end contact relaxation control for correcting the current command value such that a decrease in the end separation angle is restricted. The current command value calculation unit is configured to: when the vehicle is attempted to be turned while performing the end contact relaxation control, perform a partial release control for reducing a correction value of the current command value caused by the execution of the end contact relaxation control. The current command value calculation unit is configured to: when the current command value calculated while performing the partial release control is a value not affected by a decrease in the correction value based on the execution of the partial release control, stop the partial release control.

[0007] With this configuration, for example, even when the movement of the turning shaft is restricted at a virtual end position due to the execution of the end contact relaxation control, when the driver attempts to turn the vehicle during driving, the partial release control is performed to reduce the correction value of the current command value. Therefore, the turning shaft can be moved to the actual end position. As a result, deterioration of the small turning performance of the vehicle can be suppressed.

[0008] With this configuration, when the current command value calculated while performing the partial release control is a value not affected by a decrease in the correction value based on the execution of the partial release control, the partial release control is stopped. That is, in a steering situation where the partial release control actually has no effect, the partial release control is stopped. Therefore, a sharp change in the current command value can be suppressed as the partial release control is stopped, and deterioration of the steering feeling can be suppressed.

[0009] In the steering control device, the current command value calculation unit may be configured to: calculate the current command value such that when the end separation angle is equal to or less than the predetermined angle, an increase in the end separation angle is not restricted by the end contact relaxation control.

[0010] With this configuration, when the end separation angle is equal to or less than a predetermined angle, the current command value is calculated such that an increase in the end separation angle is not restricted by the execution of the end contact mitigation control. Therefore, for example, when performing return steering near the end position, the motor torque is less likely to be insufficient. As a result, a sense of grip is less likely to occur, and deterioration of the steering feel can be suppressed.

[0011] In the steering control device, the current command value calculation unit may be configured to calculate a steering angle limit value that decreases as the end separation angle decreases when the end separation angle is equal to or less than a predetermined angle. The current command value calculation unit may be configured to perform end contact mitigation control by limiting the absolute value of the current command value to the steering angle limit value. The current command value calculation unit may be configured to perform partial release control by increasing the steering angle limit value. The current command value calculation unit may be configured to stop the partial release control based on a comparison result between the current command value calculated during the execution of the partial release control and a stop determination value based on the steering angle limit value that does not increase due to the execution of the partial release control.

[0012] With this configuration, the current command value calculated during the execution of the partial release control is compared with a stop determination value based on the steering angle limit value that does not increase by the execution of the partial release control. Therefore, it is possible to appropriately determine whether the current command value calculated during the execution of the partial release control is a value that is not affected by a correction value that decreases due to the execution of the partial release control.

[0013] In the steering control device, when the sign of the current command value for causing the motor to generate a motor torque for turning the turning wheel in one of the rightward and leftward directions is defined as positive and the sign of the current command value for causing the motor to generate a motor torque for turning the turning wheel in the other direction is defined as negative, the current command value calculation unit may be configured to stop the partial release control when the end separation angle becomes equal to or less than a predetermined angle by turning the turning wheel in one direction and the current command value calculated during the execution of the partial release control is less than a positive stop determination value, and to stop the partial release control when the end separation angle becomes equal to or less than a predetermined angle by turning the turning wheel in the other direction and the current command value calculated during the execution of the partial release control is greater than a negative stop determination value.

[0014] With this configuration, for example, even when the sign of the current command value is reversed by return steering, it is possible to appropriately determine whether the current command value calculated during the execution of the partial release control is a value that is not affected by a decrease in the correction value due to the execution of the partial release control.

[0015] In the steering control device, the current command value calculation unit may be configured to calculate an angular limit component that decreases as the end separation angle increases. The current command value calculation unit may be configured to calculate a steering angle limit value based on a value obtained by subtracting the angular limit component from the rated current of the motor. The current command value calculation unit may be configured to calculate the angular limit component such that the angular limit component during execution of the partial release control is smaller than the angular limit component during non-execution of the partial release control.

[0016] With this configuration, due to the end contact mitigation control, the current command value is limited to the steering angle limit value. Therefore, the correction value of the current command value obtained by executing the end contact mitigation control decreases as the steering angle limit value increases. Since the steering angle limit value is calculated based on a value obtained by subtracting the angular limit component from the rated current, the steering angle limit value increases as the angular limit component decreases. Therefore, by reducing the angular limit component, it is possible to easily execute the partial release control for reducing the correction value of the current command value.

[0017] According to the present invention, deterioration of the small turning performance of the vehicle can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Hereinafter, features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described with reference to the drawings, in which like reference numerals denote like elements, and in the drawings:

[0019] Figure 1 is a diagram schematically showing the configuration of an electric power steering system;

[0020] Figure 2 is a block diagram showing the steering control device;

[0021] Figure 3 is a block diagram showing the limit value setting unit;

[0022] Figure 4 is a flowchart showing a processing routine for adjusting the steering angle limit value executed by the steering angle limit value adjustment unit;

[0023] Figure 5 is a diagram showing the relationship between the absolute steering angle and the steering angle limit value; and

[0024] Figure 6 is a flowchart showing a processing routine for calculating the offset steering angle executed by the offset steering angle calculation unit. DETAILED DESCRIPTION

[0025] Hereinafter, a steering control device according to a first embodiment of the present invention will be described with reference to the drawings. As Figure 1As shown, an electric power steering apparatus (EPS) 2, which is a steering apparatus to be controlled by a steering control device 1, includes a steering mechanism 5 that turns turning wheels 4 based on an operation of a steering wheel 3 by a driver. The EPS 2 also includes an EPS actuator 6, which is an actuator that applies an auxiliary force for assisting a steering operation to the steering mechanism 5.

[0026] The steering mechanism 5 includes: a steering shaft 11 on which the steering wheel 3 is fixed; a rack shaft 12, which is a turning shaft connected to the steering shaft 11; a rack housing 13, which is a housing in which the rack shaft 12 is inserted so that the rack shaft 12 can reciprocate; and a rack and pinion mechanism 14 that converts a rotational motion of the steering shaft 11 into a translational motion of the rack shaft 12 in an axial direction. The steering shaft 11 has a configuration in which a column shaft 15, an intermediate shaft 16, and a pinion shaft 17 are sequentially connected from the side where the steering wheel 3 is located.

[0027] The rack shaft 12 and the pinion shaft 17 are arranged in the rack housing 13 at a predetermined crossing angle. The rack and pinion mechanism 14 has a configuration in which rack teeth 12a formed on the rack shaft 12 and pinion teeth 17a formed on the pinion shaft 17 mesh with each other. Tie rods 19 are connected to both ends of the rack shaft 12 via rack ends 18, each of the rack ends 18 being formed by a ball joint provided in a drivable manner at each shaft end. The ends of the tie rods 19 are connected to a joint (not shown), and the turning wheels 4 are assembled to the joint. Thus, in the EPS 2, the rotational motion of the steering shaft based on a steering operation is converted into a translational motion in the axial direction of the rack shaft 12 by the rack and pinion mechanism 14, and the translational motion in the axial direction is transmitted to the joint via the tie rods 19, thereby changing the steering angle of the turning wheels 4, that is, the traveling direction of the vehicle.

[0028] The position where the rack end 18 of the rack shaft 12 contacts the left end of the rack housing 13 is the position where the steering wheel 3 can be turned maximally to the right, and this position corresponds to the rack end position as the right end position. The position where the rack end 18 of the rack shaft 12 contacts the right end of the rack housing 13 is the position where the steering wheel 3 can be turned maximally to the left, and this position corresponds to the rack end position of the left end position.

[0029] The EPS actuator 6 includes a motor 21 as a drive source and a reduction gear mechanism 22 such as a worm and a worm wheel. The motor 21 is connected to the column shaft 15 via the reduction gear mechanism 22. The EPS actuator 6 applies a motor torque as an auxiliary force to the steering mechanism 5 by using the reduction gear mechanism 22 to reduce the rotation of the motor 21 and transmit the reduced rotation to the column shaft 15. According to the present embodiment, a three-phase brushless motor is employed as the motor 21.

[0030] The steering control device 1 is connected to the motor 21 and controls the operation of the motor 21. The steering control device 1 includes a central processing unit (CPU) and a memory (not shown), and the CPU executes a program stored in the memory at every predetermined calculation cycle. Accordingly, various types of control are executed.

[0031] A vehicle speed sensor 31 that detects the vehicle speed SPD of the vehicle and a torque sensor 32 that detects the steering torque Th applied to the steering shaft 11 according to the driver's steering are connected to the steering control device 1. A rotation sensor 33 that detects the rotation angle θm of the motor 21, which is a relative angle within a range of 360°, is connected to the steering control device 1. For example, the steering torque Th and the rotation angle θm are detected as positive values when the steering wheel 3 is turned to the right side and are detected as negative values when the steering wheel 3 is turned to the left side. The steering control device 1 controls the operation of the EPS actuator 6 by supplying driving force to the motor 21 based on a signal indicating the state quantity input from the sensors, that is, the operation of applying an auxiliary force to the steering mechanism 5 so that the rack shaft 12 can reciprocate.

[0032] The configuration of the steering control device 1 will be described below. As Figure 2 shown, the steering control device 1 includes a microcomputer 41 that outputs a motor control signal Sm and a drive circuit 42 that supplies driving force to the motor 21 based on the motor control signal Sm. A known PWM inverter including a plurality of switching elements (such as FETs) is used as the drive circuit 42 according to the present embodiment. The motor control signal Sm output from the microcomputer 41 defines the on-state and off-state of the switching elements. Accordingly, the switching elements are turned on and off in response to the motor control signal Sm, and the power supply mode of the motor coil for each phase is switched in each phase, thereby converting the DC (direct current) power of the in-vehicle power supply 43 into three-phase drive power and outputting it to the motor 21.

[0033] The control blocks described below are implemented by a computer program executed by the microcomputer 41, detect state quantities at every predetermined sampling cycle, and execute calculation processing assigned to the following control blocks at every predetermined calculation cycle.

[0034] The vehicle speed SPD, the steering torque Th, and the rotation angle θm of the motor 21 are input to the microcomputer 41. The phase current values Iu, Iv, and Iw of the motor 21 detected by the current sensor 44 and the power supply voltage Vb of the in-vehicle power supply 43 detected by the voltage sensor 45 are input to the microcomputer 41. A current sensor 44 is provided in the connection line 46 between the drive circuit 42 and the motor coil for each phase. A voltage sensor 45 is provided in the connection line 47 between the in-vehicle power supply 43 and the drive circuit 42. In Figure 2In this example, for the purpose of convenient description, a set of current sensors 44 for each phase and connection lines 46 for each phase in each phase are shown. The microcomputer 41 outputs a motor control signal Sm based on the input state variables.

[0035] Specifically, the microcomputer 41 includes a current command value calculation unit 51 that calculates current command values Id * and Iq * , a motor control signal generation unit 52 that outputs a motor control signal Sm based on the current command values Id * and Iq * , and an absolute steering angle detection unit 53 that detects the absolute steering angle θs.

[0036] The vehicle speed SPD, steering torque Th, power supply voltage Vb, rotation angle θm, and absolute steering angle θs are input to the current command value calculation unit 51. The current command value calculation unit 51 calculates current command values Id * and Iq * based on the input state variables. The current command values Id * and Iq * are target values of the current to be supplied to the motor 21, and are respectively the current command value on the d-axis and the current command value on the q-axis in the d / q coordinate system. Among them, the q-axis current command value Iq * represents the target value of the motor torque output from the motor 21. In this embodiment, the d-axis current command value Id * is substantially fixed to zero. For example, the current command values Id * and Iq * have positive values when assisting rightward steering, and have negative values when assisting leftward steering.

[0037] The current command values Id * and Iq * , the phase current values Iu, Iv, and Iw, and the rotation angle θm of the motor 21 are input to the motor control signal generation unit 52. The motor control signal generation unit 52 generates a motor control signal Sm by performing current feedback control in the d / q coordinate system based on the input state variables.

[0038] Specifically, the motor control signal generation unit 52 calculates the d-axis current value Id and the q-axis current value Iq by mapping the phase current values Iu, Iv, and Iw to the d / q coordinate system based on the rotation angle θm. The d-axis current value Id and the q-axis current value Iq are the actual current values of the motor 21 in the d / q coordinate system. Then, the motor control signal generation unit 52 performs current feedback control so that the d-axis current value Id follows the d-axis current command value Id * and the q-axis current value Iq follows the q-axis current command value Iq *, to generate the motor control signal Sm.

[0039] The motor control signal generating unit 52 outputs the generated motor control signal Sm to the drive circuit 42. Thus, the drive power based on the motor control signal Sm is supplied to the motor 21, and the current based on the q-axis current command value Iq is output from the motor 21. * The motor torque is applied to the steering mechanism 5.

[0040] The rotation angle θm is input to the absolute steering angle detection unit 53. Based on the rotation angle θm, the absolute steering angle detection unit 53 detects an absolute motor angle expressed as an absolute angle over a range exceeding 360°. In this embodiment, the absolute steering angle detection unit 53 integrates the rotation speed of the motor 21 with the rotation angle θm as the origin when a start switch, such as the ignition switch, is turned on for the first time after the vehicle power supply 43 has been replaced. Based on the integrated rotation speed and the rotation angle θm, the absolute steering angle detection unit 53 detects the absolute motor angle. The absolute steering angle detection unit 53 then detects the absolute steering angle θs, which indicates the steering angle of the steering shaft 11, by multiplying the absolute motor angle by a conversion factor based on the reduction gear ratio of the reduction gear mechanism 22. In the steering control device 1 according to this embodiment, the rotation of the motor 21 can be monitored and the rotation speed of the motor 21 can be integrated normally even when the start switch is off. Therefore, even when the start switch is turned on for the second or subsequent time after the vehicle power supply 43 has been replaced, the origin of the absolute steering angle θs remains the same as when the start switch was first turned on.

[0041] Since the turning angle of the turning wheel 4 changes by the rotational movement of the steering shaft 11 as described above, the absolute steering angle θs indicates the rotation angle of the rotation shaft, which can be converted into the turning angle of the turning wheel 4. When the absolute motor angle and the absolute steering angle θs are angles turned to the right from the origin, they have positive values, and when the absolute motor angle and the absolute steering angle θs are angles turned to the left from the origin, they have negative values.

[0042] The following will describe the configuration of the current command value calculation unit 51. The current command value calculation unit 51 includes an assist command value calculation unit 61 that calculates the q-axis current command value Iq * The auxiliary command value Ias of the basic component * The current command value calculation unit 51 further includes a limit value setting unit 62 and a protection processing unit 63. The limit value setting unit 62 sets the q-axis current command value Iq. * The upper limit value Ig of the absolute value of the protection processing unit 63 is the auxiliary command value Ias * The absolute value of is limited to a value equal to or smaller than the limit value Ig. The memory 64 is connected to the limit value setting unit 62.

[0043] The steering torque Th and the vehicle speed SPD are input to the assist command value calculation unit 61. The assist command value calculation unit 61 calculates an assist command value Ias based on the steering torque Th and the vehicle speed SPD * . Specifically, the assist command value calculation unit 61 calculates the assist command value Ias * to have a larger absolute value as the absolute value of the steering torque Th becomes larger and the vehicle speed SPD becomes lower. The calculated assist command value Ias * is output to the limit value setting unit 62 and the protection processing unit 63.

[0044] As will be described later, in addition to the assist command value Ias * , a limit value Ig set by the limit value setting unit 62 is also input to the protection processing unit 63. When the absolute value of the input assist command value Ias * is equal to or less than the limit value Ig, the protection processing unit 63 outputs the value of the assist command value Ias * without any change as the q-axis current command value Iq * to the motor control signal generation unit 52 and the limit value setting unit 62. On the other hand, when the absolute value of the input assist command value Ias * is greater than the limit value Ig, the protection processing unit 63 outputs, as the q-axis current command value Iq * , a value obtained by limiting the absolute value of the assist command value Ias to the limit value Ig * to the motor control signal generation unit 52 and the limit value setting unit 62.

[0045] The rated current Ir, which is the maximum current corresponding to the torque of the motor torque that can be output from the motor 21, the end position corresponding angles θs_re and θs_le, etc. are stored in the memory 64. The left end position corresponding angle θs_le is the absolute steering angle θs corresponding to the left rack end position, and the right end position corresponding angle θs_re is the absolute steering angle θs corresponding to the right rack end position. For example, the end position corresponding angles θs_re and θs_le are set by appropriate learning based on the driver's steering execution.

[0046] The configuration of the limit value setting unit 62 will be described below. The motor angular velocity ωm obtained by differentiating the rotation angle θm, the absolute steering angle θs, the vehicle speed SPD, the steering torque Th, the power supply voltage Vb, the assist command value Ias * , the q-axis current command value Iq *, the rated current Ir, and the end position corresponding angles θs_re and θs_le are input to the limit value setting unit 62. The limit value setting unit 62 sets the limit value Ig based on the input state quantities.

[0047] Specifically, as Figure 3 shown, the limit value setting unit 62 includes a steering angle limit value calculation unit 71 that calculates the steering angle limit value Ien based on the absolute steering angle θs, a voltage limit value calculation unit 72 that calculates the voltage limit value Ivb as another limit value based on the power supply voltage Vb, and a minimum value selection unit 73 that selects the smaller one of the steering angle limit value Ien and the voltage limit value Ivb.

[0048] The motor angular velocity ωm, the absolute steering angle θs, the vehicle speed SPD, the steering torque Th, the auxiliary command value Ias * , the q-axis current command value Iq * , the rated current Ir, and the end position corresponding angles θs_re and θs_le are input to the steering angle limit value calculation unit 71. As will be described later, when the end separation angle Δθ indicating the distance of the absolute steering angle θs from the end position corresponding angles θs_re and θs_le is equal to or less than a predetermined angle θ1, the steering angle limit value calculation unit 71 calculates the steering angle limit value Ien that decreases as the end separation angle Δθ decreases based on the input state quantities. The calculated steering angle limit value Ien is output to the minimum value selection unit 73.

[0049] The power supply voltage Vb is input to the voltage limit value calculation unit 72. When the absolute value of the power supply voltage Vb is equal to or less than a preset voltage threshold Vth, the voltage limit value calculation unit 72 calculates the voltage limit value Ivb that is less than the rated voltage for supplying the rated current Ir. Specifically, when the absolute value of the power supply voltage Vb is equal to or less than the voltage threshold Vth, the voltage limit value calculation unit 72 calculates the voltage limit value Ivb having an absolute value that decreases as the absolute value of the power supply voltage Vb decreases. The calculated voltage limit value Ivb is output to the minimum value selection unit 73.

[0050] The minimum value selection unit 73 selects the smaller one of the input steering angle limit value Ien and the input voltage limit value Ivb as the limit value Ig, and outputs the selected one to the protection processing unit 63. When the steering angle limit value Ien is output to the protection processing unit 63 as the limit value Ig, the absolute value of the q-axis current command value Iq * is limited to the steering angle limit value Ien. Therefore, when the end separation angle Δθ is equal to or less than the predetermined angle θ1, the q-axis current command value Iq *The absolute value of, execute end contact mitigation control for mitigating the influence of end contact. The current command value calculation unit 51 in this embodiment corrects the q-axis current command value Iq * such that the absolute value of the q-axis current command value Iq * is limited to be equal to or less than the limit value Ig. The corrected value of the q-axis current command value Iq * is the auxiliary command value Ias * which is the excess with respect to the limit value Ig, that is, the excess with respect to the steering angle limit value Ien.

[0051] When the voltage limit value Ivb is output to the protection processing unit 63 as the limit value Ig, the absolute value of the q-axis current command value Iq * is limited to the voltage limit value Ivb. Therefore, when the absolute value of the power supply voltage Vb is equal to or less than the voltage threshold Vth, execute power supply protection control for reducing the absolute value of the q-axis current command value Iq * as the absolute value of the power supply voltage Vb decreases.

[0052] When executing the end contact mitigation control, the movement of the rack shaft 12 can be restricted to a virtual rack end position that is closer to the neutral steering position than the actual rack end position where the rack shaft 12 actually contacts the rack housing 13. In this case, the absolute steering angle θs may be smaller than the absolute steering angle when the rack shaft 12 is at the actual rack end position, and the small turning performance of the vehicle may deteriorate.

[0053] Therefore, when the driver attempts to turn the vehicle while executing the end contact mitigation control, the current command value calculation unit 51 in this embodiment executes partial release control for reducing the corrected value of the q-axis current command value Iq * during the execution of the end contact mitigation control, based on the steering torque Th input to the EPS 2. As described above, since the protection processing unit 63 limits the absolute value of the q-axis current command value Iq * to be equal to or less than the limit value Ig, the corrected value of the q-axis current command value Iq * decreases as the steering angle limit value Ien, which is the limit value Ig, increases. Considering this, as will be described below, in this embodiment, when the driver attempts to turn the vehicle while executing the end contact mitigation control, the steering angle limit value calculation unit 71 calculates a larger steering angle limit value Ien compared to the steering angle limit value when not executing the partial release control, and thus executes the partial release control.

[0054] Specifically, the steering angle limit value calculation unit 71 includes an angular velocity change calculation unit 81 that calculates the angular velocity change Δωm, an offset steering angle calculation unit 82 that calculates the offset steering angle θoff, and an end separation angle calculation unit 83 that calculates the end separation angle Δθ. The steering angle limit value calculation unit 71 includes an angular limit component calculation unit 84. The angular limit component calculation unit 84 calculates the normal angular limit component Iga based on the end separation angle Δθ, and calculates the release angular limit component Iga' based on the release end separation angle Δθ' obtained by adding the offset steering angle θoff to the end separation angle Δθ. The steering angle limit value calculation unit 71 further includes an output switching unit 86. The output switching unit 86 selects one of the angular limit components Iga and Iga' and outputs the selected one to the subtractor 85, and calculates the pre-adjusted steering angle limit value Ienb by subtracting one of the angular limit components Iga and Iga' from the rated current Ir. The steering angle limit value calculation unit 71 includes a steering angle limit value adjustment unit 87. The steering angle limit value adjustment unit 87 calculates the steering angle limit value Ien based on the pre-adjusted steering angle limit value Ienb. The control blocks will be described sequentially below.

[0055] Angular velocity change calculation unit 81

[0056] The motor angular velocity ωm is input to the angular velocity change calculation unit 81. The angular velocity change calculation unit 81 calculates the angular velocity change Δωm, which is the change amount of the motor angular velocity ωm, based on the input motor angular velocity ωm. Then, the angular velocity change calculation unit 81 outputs the angular velocity change Δωm to the offset steering angle calculation unit 82. The angular velocity change calculation unit 81 in the present embodiment outputs the value obtained by performing low-pass filtering processing on the angular velocity change Δωm to the offset steering angle calculation unit 82.

[0057] Offset steering angle calculation unit 82

[0058] The vehicle speed SPD, steering torque Th, motor angular velocity ωm, angular velocity change amount Δωm, q-axis current command value Iq * 、rated current Ir, normal angular limit component Iga, and the steering angle position flag Fd, which will be described later, are input to the offset steering angle calculation unit 82. The offset steering angle calculation unit 82 determines whether the driver attempts to turn the vehicle by performing turning steering or maintaining steering while driving when performing the end contact relaxation control based on the input state quantities. When it is determined that the driver attempts to turn the vehicle when performing the end contact relaxation control, the offset steering angle calculation unit 82 starts the calculation of the offset steering angle θoff and outputs the calculated offset steering angle θoff to the adder 88. When it is determined that the driver does not attempt to turn the vehicle when performing the end contact relaxation control, the offset steering angle calculation unit 82 does not calculate the offset steering angle θoff.

[0059] The offset steering angle calculation unit 82 outputs an execution flag Fr indicating whether partial release control is being executed to the output switching unit 86. The execution flag Fr indicates that partial release control is not being executed when its value is "0", and indicates that partial release control is being executed when its value is "1". The offset steering angle calculation unit 82 sets the value of the execution flag Fr to "0" before the calculation of the offset steering angle θoff starts, and sets the value of the execution flag Fr to "1" after the calculation of the offset steering angle θoff starts. That is, when partial release control is executed, the offset steering angle calculation unit 82 calculates the offset steering angle θoff, and when partial release control is not executed, the offset steering angle θoff is not calculated.

[0060] The offset steering angle calculation unit 82 calculates the offset steering angle θoff based on the steering torque Th using the model formula represented by Expression (1).

[0061]

[0062] In the following description, for the purpose of easy description, the symbol of the target steering speed, which is the first-time differential value of "θs" * is referred to as "ωs". * This model formula defines and shows the relationship between the steering torque Th input via the steering wheel 3 and the rotation angle of the rotation axis that can be converted into the turning angle of the turning wheel 4. This model formula is represented using the elastic coefficient K obtained by modeling the specifications of the suspension or wheel alignment of a vehicle equipped with EPS 2, the viscous coefficient C obtained by modeling the friction of EPS 2, etc., and the inertia coefficient J obtained by modeling the inertia of EPS 2.

[0063] The offset steering angle calculation unit 82 in the present embodiment uses Expression (2) in which the elastic coefficient K and the inertia coefficient J are set to zero to calculate the target steering speed ωs * and defines the target steering speed ωs in consideration of a reduction in the calculation load and the steering feeling to be achieved. * .

[0064]

[0065] Then, the offset steering angle calculation unit 82 sets the value obtained by integrating the target steering speed ωs * as the offset steering angle θoff. The offset steering angle θoff calculated in this way is output to the adder 88. The determination of the intention of turning in the offset steering angle calculation unit 82, that is, the execution and stop of partial release control, will be described later.

[0066] The end separation angle calculation unit 83

[0067] The absolute steering angle θs and the end position corresponding angles θs_re and θs_le are input to an end separation angle calculation unit 83. The end separation angle calculation unit 83 calculates a left end separation angle Δθl, which is a difference between the absolute steering angle θs in the latest calculation cycle and the end position corresponding angle θs_le on the left side, and a right end separation angle Δθr, which is a difference between the absolute steering angle θs in the latest calculation cycle and the end position corresponding angle θs_re on the right side. Then, the end separation angle calculation unit 83 outputs, as an end separation angle Δθ, the smaller absolute value of the right end separation angle Δθr and the left end separation angle Δθl to an angular limit component calculation unit 84 and an adder 88.

[0068] The end separation angle calculation unit 83 sets the value of a steering angle position flag Fd indicating a position to which the steering wheel 3 is turned by comparing the absolute values of the right end separation angle Δθr and the left end separation angle Δθl with a preset end separation angle threshold Δθth. The steering angle position flag Fd is output to an offset steering angle calculation unit 82 and a steering angle limit value adjustment unit 87. The end separation angle threshold Δθth is a threshold for determining on which side (one of the right side and the left side) the steering wheel 3 is turned, and this threshold is set to a relatively large value of several hundred degrees.

[0069] Specifically, when the absolute value of the right end separation angle Δθr is less than the end separation angle threshold Δθth, the end separation angle calculation unit 83 sets the value of the steering angle position flag Fd to "1", which indicates that the steering wheel 3 is turned in the positive direction, that is, the turning wheels 4 are turned in the positive direction. When the absolute value of the left end separation angle Δθl is less than the end separation angle threshold Δθth, the end separation angle calculation unit 83 sets the value of the steering angle position flag Fd to "2", which indicates that the steering wheel 3 is turned in the negative direction, that is, the turning wheels 4 are turned in the negative direction. When the right end separation angle Δθr is equal to or greater than the end separation angle threshold Δθth and the left end separation angle Δθl is equal to or greater than the end separation angle threshold Δθth, the end separation angle calculation unit 83 sets the value of the steering angle position flag Fd to "0", which indicates that the steering wheel 3 is near the neutral position

[0070] The angular limit component calculation unit 84

[0071] The end separation angle Δθ and the vehicle speed SPD are input to the angular limit component calculation unit 84. A released end separation angle Δθ', which is obtained by adding an offset steering angle θoff and the end separation angle Δθ in an adder 88, is input to the angular limit component calculation unit 84. The released end separation angle Δθ' has a value that is larger than the end separation angle Δθ by the value of the offset steering angle θoff. The angular limit component calculation unit 84 calculates angular limit components Iga and Iga' based on the input state quantities. [[ID=X]] [[ID=Y]]

[0072] Specifically, the corner limit component calculation unit 84 includes a map that defines the relationship between the end separation angle Δθ, the vehicle speed SPD, and the normal corner limit component Iga, and with reference to this map, calculates the angle limit component Iga corresponding to the end separation angle Δθ and the vehicle speed SPD. The calculated normal corner limit component Iga is output to the offset steering angle calculation unit 82 and the output switching unit 86.

[0073] In this normal map, the corner limit component Iga is set to decrease as the end separation angle Δθ increases from the zero state, and is set to zero when the end separation angle Δθ is greater than the predetermined angle θ1. In this normal map, a region where the end separation angle Δθ is negative is also set, and when the end separation angle Δθ becomes less than zero, the corner limit component Iga increases in proportion to the decrease in the end separation angle Δθ, and after the end separation angle Δθ becomes the rated current Ir, the corner limit component Iga remains constant. The negative region in the map is assumed to be the degree of rotation of the motor 21 when the EPS 2 is elastically deformed by further performing turning steering when the rack end 18 is in contact with the rack housing 13. The predetermined angle θ1 is set to a small angle indicating the range corresponding to the near-end position angles θs_re and θs_le. That is, the angle limit component Iga is set to decrease when the absolute steering angle θs changes from the end position corresponding angles θs_re and θs_le to the neutral steering position, and to be zero when the absolute steering angle θs is closer to the neutral steering position than near the end position corresponding angles θs_re and θs_le.

[0074] In this normal map, in the region where the end separation angle Δθ is equal to or less than the predetermined angle θI, the corner limit component Iga is set to decrease as the vehicle speed SPD increases. Specifically, when the vehicle speed SPD is in the low-speed region, the corner limit component Iga is set to be greater than zero, and when the vehicle speed SPD is in the medium-speed region or the high-speed region, the corner limit component Iga is set to zero.

[0075] The corner limit component calculation unit 84 includes a release map that defines the relationship between the release end separation angle Δθ', the vehicle speed SPD, and the release angle limit component Iga', and with reference to this map, calculates the angle limit component Iga' corresponding to the release end separation angle Δθ' and the vehicle speed SPD. The calculated release angle limit component Iga' is output to the output switching unit 86.

[0076] The release mapping is set to the same mapping as the normal mapping. That is, when the vehicle speed SPD is the same and the end separation angles Δθ and Δθ’ are the same, the resulting angular limit components Iga and Iga’ are the same. As described above, since the release end separation angle Δθ’ has a value of the offset steering angle θoff larger than the end separation angle Δθ, the angular limit component calculation unit 84 calculates a release angular limit component Ig’ that is the offset steering angle θoff smaller than the normal angular limit component Ig.

[0077] Output switching unit 86

[0078] The angular limit components Iga and Iga’ and the execution flag Fr are input to the output switching unit 86. The output switching unit 86 includes a contact point P1 to which the normal angular limit component Iga is input, a contact point P2 to which the release angular limit component Iga’ is input, and a contact point P3 connected to the subtractor 85. When the execution flag Fr is “0”, the output switching unit 86 connects the contact point P1 and the contact point P3, and outputs the normal angular limit component Iga to the subtractor 85. On the other hand, when the execution flag Fr is “1”, the output switching unit 86 connects the contact point P2 and the contact point P3, and outputs the release angular limit component Iga’ to the subtractor 85.

[0079] Then, according to whether the partial release control is being executed, the value obtained by subtracting the normal angular limit component Iga or the release angular limit component Iga’ from the rated current Ir in the subtractor 85 is output as the pre-adjusted steering angle limit value Ienb to the steering angle limit value adjustment unit 87.

[0080] Steering angle limit value adjustment unit 87

[0081] The configuration of the steering angle limit value adjustment unit 87 will be described below. In the steering angle limit value adjustment unit 87, in addition to the pre-adjusted steering angle limit value Ienb, the rated current Ir, the auxiliary command value Ias * and the steering angle position flag Fd are also input. When a right turn is being executed, that is, when turning in the positive direction, the steering angle limit value adjustment unit 87 compares the auxiliary command value Ias * with the pre-adjusted steering angle limit value Ienb with a positive sign (hereinafter referred to as the positive pre-adjusted steering angle limit value Ienb). When the auxiliary command value Ias * is less than the positive pre-adjusted steering angle limit value Ienb, the steering angle limit value adjustment unit 87 sets the absolute value of the steering angle limit value Ien to the rated current Ir. On the other hand, when the auxiliary command value Ias * is equal to or greater than the positive pre-adjusted steering angle limit value Ienb, the steering angle limit value adjustment unit 87 sets the absolute value of the steering angle limit value Ien to the pre-adjusted steering angle limit value Ienb.

[0082] When performing a left turn, i.e., turning in the negative direction, the steering angle limit value adjustment unit 87 compares the auxiliary command value Ias * with a pre-adjusted steering angle limit value Ienb having a negative sign (hereinafter referred to as a negative pre-adjusted steering angle limit value Ienb). When the auxiliary command value Ias * is equal to or less than the negative pre-adjusted steering angle limit value Ienb, the steering angle limit value adjustment unit 87 sets the absolute value of the steering angle limit value Ien to the pre-adjusted steering angle limit value Ienb. On the other hand, when the auxiliary command value Ias * is greater than the negative pre-adjusted steering angle limit value Ienb, the steering angle limit value adjustment unit 87 sets the absolute value of the steering angle limit value Ien to the rated current Ir.

[0083] When turning in the positive direction, when the auxiliary command value Ias * is positive, it can be determined that a turning steering with a decreasing execution end separation angle Δθ is being performed, and when the auxiliary command value Ias * is negative, it can be determined that a return steering with an increasing execution end separation angle Δθ is being performed. Therefore, when the auxiliary command value Ias * is less than the positive pre-adjusted steering angle limit value Ienb, one of turning steering and return steering is performed, and when the auxiliary command value Ias * is equal to or greater than the positive pre-adjusted steering angle limit value Ienb, turning steering is performed. In other words, when performing a return steering when turning in the positive direction, the auxiliary command value Ias * is less than the positive pre-adjusted steering angle limit value Ienb.

[0084] Similarly, when turning in the negative direction, when the auxiliary command value Ias * is negative, it can be determined that a turning steering with a decreasing execution end separation angle Δθ is being performed, and when the auxiliary command value Ias * is positive, it can be determined that a turning steering with an increasing execution end separation angle Δθ is being performed. Therefore, when the auxiliary command value Ias * is less than or equal to the negative pre-adjusted steering angle limit value Ienb, turning steering is performed, and when the auxiliary command value Ias * is greater than the negative pre-adjusted steering angle limit value Ienb, one of turning steering and return steering is performed. In other words, when performing a return steering when turning in the negative direction, the auxiliary command value Ias * is greater than the negative pre-adjusted steering angle limit value Ienb.

[0085] That is, the steering angle limit value adjustment unit 87 in this embodiment sets the absolute value of the steering angle limit value Ien to the rated current Ir when at least performing a return steering. Therefore, when power protection control is not executed and the steering angle limit value Ien is set to the limit value Ig, the auxiliary command value Ias * is output as the q-axis current command value Iq without any change * , and even when the terminal separation angle Δθ is equal to or less than the predetermined angle θ1, correction of the q-axis current command value Iq * by terminal contact mitigation control is not performed. When power protection control is executed and the voltage limit value Ivb is set to the limit value Ig, even if the terminal separation angle Δθ is equal to or less than the predetermined angle θ1 and a return steering is performed, the q-axis current command value Iq * is restricted.

[0086] Specifically, as shown in the flowchart of Figure 4 , when various types of state quantities are acquired (step 101), the steering angle limit value adjustment unit 87 determines whether the steering angle position flag Fd is "1", that is, whether a right turn is performed (step 102). When the steering angle position flag Fd is "1" (step 102: Yes), the steering angle limit value adjustment unit 87 determines whether the auxiliary command value Ias * is less than the positive pre-adjusted steering angle limit value Ienb (step 103). When the auxiliary command value Ias * is less than the positive pre-adjusted steering angle limit value Ienb (step 103: Yes), the steering angle limit value adjustment unit 87 sets the absolute value of the steering angle limit value Ien to the rated current Ir (step 104). On the other hand, when the auxiliary command value Ias * is equal to or greater than the positive pre-adjusted steering angle limit value Ienb (step 103: No), the steering angle limit value adjustment unit 87 sets the absolute value of the steering angle limit value Ien to the pre-adjusted steering angle limit value Ienb (step 105).

[0087] When the steering angle position flag Fd is not "1" (step 102: No), the steering angle limit value adjustment unit 87 determines whether the steering angle position flag Fd is "2", that is, whether a left turn is performed (step 106). When the steering angle position flag Fd is "2" (step 106: Yes), the steering angle limit value adjustment unit 87 determines whether the auxiliary command value Ias * is equal to or less than the negative pre-adjusted steering angle limit value Ienb (step 107). When the auxiliary command value Ias *When it is equal to or less than the negative pre-adjusted steering angle limit value Ienb (Step 107: Yes), the steering angle limit value adjustment unit 87 causes the processing routine to proceed to Step 105 and sets the absolute value of the steering angle limit value Ien to the pre-adjusted steering angle limit value Ienb. On the other hand, when the assist command value Ias * is greater than the negative pre-adjusted steering angle limit value Ienb (Step 107: No), the steering angle limit value adjustment unit 104 causes the processing routine to proceed to Step 104 and sets the absolute value of the steering angle limit value Ien to the rated current Ir.

[0088] When it is determined in Step 106 that the steering angle position flag Fd is not "2", that is, when the steering angle position flag Fd is "0" and the steering wheel 3 is near the neutral position (Step 106: No), the steering angle limit value adjustment unit 87 does not perform the subsequent processing.

[0089] Therefore, as Figure 5 shown, the steering angle limit value Ien is set in consideration of the steering direction with respect to the absolute steering angle θs. In the figure, the pre-adjusted steering angle limit value Ienb is shown as a dashed line. When the assist command value Ias * is plotted in the figure, the region where the absolute value of the steering angle limit value Ien is set to the rated current Ir is hatched.

[0090] For example, assume that by turning to the right, the end separation angle Δθ becomes equal to or less than a predetermined angle θ1, and by further performing a turning steering, the absolute value of the assist command value Ias * becomes greater than a predetermined value Ias1 of the pre-adjusted steering angle limit value Ienb. In this case, the absolute value of the steering angle limit value Ien is set to the pre-adjusted steering angle limit value Ienb that is less than the predetermined value Ias1, and the absolute value of the q-axis current command value Iq * is limited to the steering angle limit value Ien. Therefore, the impact of end contact is mitigated.

[0091] Assume that by turning to the right, the end separation angle Δθ becomes equal to or less than a predetermined angle θ1, and the sign of the assist command value Ias * becomes negative, and then by performing a return steering, the absolute value of the assist command value Ias * becomes "Ias1" that is larger than the pre-adjusted steering angle limit value Ienb. At this time, in the present embodiment, when the end separation angle Δθ is equal to or less than the predetermined angle θ1 and the return steering is not performed, the absolute value of the steering angle limit value Ien is the rated current Ir, and thus the absolute value of the q-axis current command value Iq * is not limited to the predetermined value Ias1. Therefore, sufficient assist force is applied to the steering mechanism 5, and thus it is less likely to generate a sense of grip.

[0092] The determination of the turning intention performed by the offset steering angle calculation unit 82 will be described below. When the following conditions (a) to (e) for determining the intention to turn are satisfied for a predetermined time, the offset steering angle calculation unit 82 determines that the driver is attempting to turn the vehicle when executing the end contact mitigation control. The predetermined time is set to an appropriate time for determining whether the driver is performing a turning steering or maintaining the steering.

[0093] (a) The normal angle limit component Iga is greater than the current threshold Ith_st. (b) The absolute value of the steering torque Th is equal to or greater than the steering torque threshold Tth. (c) The vehicle speed SPD is within a predetermined vehicle speed range.

[0094] (d) The absolute value of the motor angular velocity ωm is equal to or less than the angular velocity threshold ωth. (e) The absolute value of the angular velocity change Δωm, which is the change amount of the motor angular velocity ωm, is less than the angular velocity change threshold Δωth.

[0095] The current threshold Ith_st is set such that when the value of the angle limit component Iga is the current threshold Ith_st and the vehicle is traveling at a low speed on a normal road surface, a predetermined auxiliary force, which is the minimum auxiliary force capable of moving the rack shaft 12 to the rack end position, is supplied from the motor 21. In other words, the absolute value of the steering angle limit value Ien obtained by subtracting the current threshold Ith_st from the rated current Ir is set to the magnitude of the predetermined auxiliary force output from the motor 21 by supplying the motor 21 with a current of the same absolute value. The current threshold Ith_st is a current value based on the rated current Ir and is set to, for example, 50% of the rated current Ir.

[0096] The steering torque threshold Tth is the steering torque required to maintain the steering of the steering wheel 3 when the vehicle is turning in a state where the rack end 18 is in contact with the rack housing 13, and is set to an appropriate value greater than zero. The predetermined vehicle speed range indicates a vehicle speed range that is equal to or greater than the lower vehicle speed Slo indicating that the vehicle is not stopped and less than the upper vehicle speed Sup indicating that the vehicle is traveling at a low speed. The lower vehicle speed Slo is set to a value slightly greater than zero, and the upper vehicle speed Sup is set to an appropriate value greater than the lower vehicle speed Slo. The angular velocity threshold ωth is the angular velocity indicating that the motor 21 has stopped and is set to a value slightly greater than zero. The angular velocity change threshold Δωth is the angular velocity change indicating that the motor 21 is neither substantially accelerating nor decelerating and is set to a value slightly greater than zero.

[0097] The q-axis current command value Iq calculated when performing the partial release control *When it is a value that is not affected by the reduction of the correction value due to the execution of the partial release control (i.e., a value that is not affected by the increase in the steering angle limit value Ien), the offset steering angle calculation unit 82 stops the calculation of the offset steering angle θoff and stops the partial release control. That is, the offset steering angle calculation unit 82 stops the partial release control in a steering situation where the partial release control actually does not work.

[0098] Specifically, the offset steering angle calculation unit 82 is based on the q-axis current command value Iq * The comparison result with the stop determination value Ith_en based on the steering angle limit value Ien that will not increase due to the execution of the partial release control is used to stop the partial release control. The offset steering angle calculation unit 82 calculates the stop determination value Ith_en by subtracting the angle limit component Iga from the rated current Ir. The stop determination value Ith_en in this embodiment is the same as the steering angle limit value Ien that will not increase due to the execution of the partial release control.

[0099] When performing a right turn, that is, a turn in the positive direction, the offset steering angle calculation unit 82 compares the q-axis current command value Iq * With the stop determination value Ith_en having a positive sign (hereinafter referred to as the positive stop determination value Ith_en). When the q-axis current command value Iq * Is less than the positive stop determination value Ith_en, that is, when the q-axis current command value Iq * Is less than the steering angle limit value Ien that will not increase due to the execution of the partial release control and the partial release control actually does not work, the offset steering angle calculation unit 82 stops the partial release control. On the other hand, when the q-axis current command value Iq * Is equal to or greater than the positive stop determination value Ith_en, that is, when the q-axis current command value Iq * Is equal to or greater than the steering angle limit value Ien that will not increase due to the execution of the partial release control and the partial release control is in effect, the offset steering angle calculation unit 82 does not stop the partial release control.

[0100] When performing a left turn, that is, a turn in the reverse direction, the offset steering angle calculation unit 82 compares the q-axis current command value Iq * With the stop determination value Ith_en having a negative sign (hereinafter referred to as the negative stop determination value Ith_en). When the q-axis current command value Iq * Is greater than the negative stop determination value Ith_en, the offset steering angle calculation unit 82 stops the partial release control. On the other hand, when the q-axis current command value Iq * Is equal to or less than the negative stop determination value Ith_en, the offset steering angle calculation unit 82 does not stop the partial release control.

[0101] The processing flow for calculating the offset steering angle θoff performed by the offset steering angle calculation unit 82 will be described below. As Figure 6 shown in the flowchart of, when various state quantities are acquired (step 201), the offset steering angle calculation unit 82 determines whether the execution flag Fr is "0", that is, whether partial release control is not executed (step 202).

[0102] When the execution flag Fr is "0" (step 202: Yes), the offset steering angle calculation unit 82 determines whether the vehicle speed SPD is equal to or greater than the lower limit vehicle speed Slo and less than the upper limit vehicle speed Sup (step 203). When the vehicle speed SPD is equal to or greater than the lower limit vehicle speed Slo and less than the upper limit vehicle speed Sup and within a predetermined vehicle speed range (step 203: Yes), the offset steering angle calculation unit 82 determines whether the angular limit component Iga is greater than the current threshold Ith_st (step 204). When the angular limit component Iga is greater than the current threshold Ith_st (step 204: Yes), the offset steering angle calculation unit 82 determines whether the absolute value of the steering torque Th is equal to or greater than the steering torque threshold Tth (step 205). When the absolute value of the steering torque Th is greater than or equal to the steering torque threshold Tth (step 205: Yes), the offset steering angle calculation unit 82 determines whether the absolute value of the motor angular velocity ωm is equal to or less than the angular velocity threshold ωTh (step 206). When the absolute value of the motor angular velocity ωm is equal to or less than the angular velocity threshold ωth (step 206: Yes), the offset steering angle calculation unit 82 determines whether the angular velocity change Δωm is less than the angular velocity change threshold Δωth (step 207). When the angular velocity change Δωm is less than the angular velocity change threshold Δωth (step 207: Yes), the offset steering angle calculation unit 82 advances the processing flow to step 208.

[0103] In step 208, after performing the determinations in steps 203 to 207, that is, after conditions (a) to (e) are satisfied, the offset steering angle calculation unit 82 increments the count value Cn of the counter indicating the elapsed time. Subsequently, the offset steering angle calculation unit 82 determines whether the count value Cn is greater than a predetermined count value Cth corresponding to a predetermined time (step 209). When the count value Cn is greater than the predetermined count value Cth (step 209: Yes), the offset steering angle calculation unit 82 starts calculating the offset steering angle θoff, sets the value of the execution flag Fr to "1" indicating that partial release control is being executed, and clears the count value Cn of the counter (steps 210, 211, and 212).

[0104] When the count value Cn is equal to or less than a predetermined count value Cth (Step 209: No), the offset steering angle calculation unit 82 does not perform subsequent processing. When the determination result of any one of Steps 203 to 207 is not positive (Steps 203 to 207: No), the offset steering angle calculation unit 82 does not perform the processing of Steps 208 to 211, advances the processing flow to Step 212, and clears the count value Cn.

[0105] On the other hand, when the value of the execution flag Fr is "1" (Step 202: No), the offset steering angle calculation unit 82 calculates a stop determination value Ith_en (Step 213), and determines whether the steering angle position flag Fd is "1" (Step 214). When the steering angle position flag Fd is "1" (Step 214: Yes), the offset steering angle calculation unit 82 determines the q-axis current command value Iq * whether it is less than a positive stop determination value Ith_en (Step 215). When the q-axis current command value Iq * is less than the positive stop determination value Ith_en (Step 215: Yes), the offset steering angle calculation unit 82 stops the calculation of the offset steering angle θoff (Step 216), and sets the value of the execution flag Fr to "0" indicating the release control of the stop part (Step 217). On the other hand, when the steering angle position flag Fd is not "1" (Step 214: No), the offset steering angle calculation unit 82 determines whether the q-axis current command value Iq * is greater than a negative stop determination value Ith_en (Step 218). When the q-axis current command value Iq * is greater than the negative stop determination value Ith_en (Step 218: Yes), the offset steering angle calculation unit 82 advances the processing routine to Steps 216 and 217.

[0106] When the q-axis current command value Iq * is equal to or greater than the positive stop determination value Ith_en (Step 215: No), or when the q-axis current command value Iq * is equal to or less than the negative stop determination value Ith_en (Step 218: No), the offset steering angle calculation unit 82 does not perform the processing of Steps 216 and 217.

[0107] The operation and advantages of this embodiment will be described below. (1) When it is determined that the driver attempts to turn the vehicle while performing the end contact mitigation control, the current command value calculation unit 51 performs a partial release control for reducing the correction value of the q-axis current command value Iq * under the end contact mitigation control based on the steering torque Th. Therefore, since the limit of the q-axis current command value Iq * for performing the end contact mitigation control is partially released, and the q-axis current command value Iq *Therefore, for example, even when the movement of the rack shaft 12 is restricted to the virtual rack end position due to the execution of the end contact relaxation control, by allowing the driver to turn the vehicle, partial release control is executed to reduce the correction value of the q-axis current command value Iq * so that the rack shaft 12 can move to the actual rack end position. As a result, deterioration of the small turning performance of the vehicle can be suppressed.

[0108] In the present embodiment, when the q-axis current command value Iq * calculated when the partial release control is executed is a value that is not affected by the reduction of the correction value due to the execution of the partial release control, the current command value calculation unit 51 stops the partial release control. Therefore, the sudden change of the q-axis current command value Iq * can be suppressed with the stop of the partial release control, and deterioration of the steering feeling can be suppressed.

[0109] (2) When the end separation angle Δθ is equal to or less than a predetermined angle θ1, the current command value calculation unit 51 calculates the q-axis current command value Iq * such that the increase of the end separation angle Δθ is not restricted by the execution of the end contact relaxation control. Specifically, when the end separation angle Δθ is equal to or less than the predetermined angle θ1, and when a return steering for increasing the end separation angle Δθ is executed, the current command value calculation unit 51 sets the absolute value of the steering angle limit value Ien to the rated current Ir. Therefore, for example, when a return steering is executed from near the rack end position, the auxiliary force applied to the steering mechanism 5 is less likely to be insufficient. As a result, the grip feeling is less likely to occur, and deterioration of the steering feeling can be suppressed.

[0110] (3) The current command value calculation unit 51 compares the q-axis current command value Iq * calculated by executing the partial release control with the stop determination value Ith_en of the steering angle limit value Ien that does not increase based on the execution of the partial release control. Therefore, it is possible to appropriately determine whether the q-axis current command value Iq * calculated when the partial release control is executed is a value that is not affected by the reduction of the correction value due to the execution of the partial release control.

[0111] (4) When the turning wheel 4 turns right and the end separation angle Δθ is equal to or less than the predetermined angle θ1, and when the q-axis current command value Iq * calculated when the partial release control is executed is less than the positive stop determination value Ith_en, the current command value calculation unit 51 stops the partial release control. When the turning wheel 4 turns left and the end separation angle Δθ is equal to or less than the predetermined angle θ1, and when the q-axis current command value Iq *When it is greater than the negative stop determination value Ith_en, the current command value calculation unit 51 stops the partial release control. Thus, for example, even when the sign of the q-axis current command value Iq * is reversed by a return turn, it is possible to appropriately determine whether the q-axis current command value Iq * calculated during the execution of the partial release control is a value that is not affected by the reduction of the correction value due to the execution of the partial release control.

[0112] (5) The current command value calculation unit 51 includes a steering angle limit value calculation unit 71. When the end separation angle Δθ is equal to or less than a predetermined angle θ1, the steering angle limit value calculation unit 71 calculates a steering angle limit value Ien that decreases as the end separation angle Δθ decreases. The current command value calculation unit 51 performs end contact relaxation control by limiting the absolute value of the q-axis current command value Iq * to the steering angle limit value Ien. Thus, as the steering angle limit value Ien increases, the correction value of the q-axis current command value Iq * for executing the end contact relaxation control decreases. The steering angle limit value calculation unit 71 includes an angle limit component calculation unit 84 that calculates a normal angle limit component Iga and a release angle limit component Iga', and calculates a value obtained by subtracting the normal angle limit component Iga or the release angle limit component Iga' from the rated current Ir as a pre-adjusted steering angle limit value Ienb. Thus, by setting the release angle limit component Iga' to be less than the normal angle limit component Iga, it is possible to easily perform partial release control for reducing the correction value of the q-axis current command value Iq * .

[0113] The above-described embodiment can be modified as follows. Unless there is a technical conflict, the above-described embodiment and the following modification examples can be combined. In the above-described embodiment, the determination condition for stopping the partial release control changes depending on the steering direction. However, the present invention is not limited thereto, and it is also possible to use a condition that the absolute value of the q-axis current command value Iq * is less than the steering angle limit value Ien that does not increase due to the execution of the partial release control as the determination condition for stopping the partial release control, and this determination condition can be constant regardless of the steering direction.

[0114] In the above-described embodiment, the steering angle limit value Ien that does not increase due to the execution of the partial release control is used as the stop determination value Ith_en. However, the present invention is not limited thereto, and as long as another value is capable of determining whether the q-axis current command value Iq * calculated during the execution of the partial release control is a value that is not affected by the reduction of the correction value due to the execution of the partial release control, this another value can be used as the stop determination value Ith_en.

[0115] In the above-described embodiment, when a right turn is executed and the auxiliary command value Ias * is less than the positive pre-adjusted steering angle limit value Ienb, the absolute value of the steering angle limit value Ien is set to the rated current Ir. However, the present invention is not limited thereto, and as long as an increase in the end separation angle Δθ is not restricted, the absolute value of the steering angle limit value Ien may also be set to a value less than the rated current Ir. Similarly, when a left turn is executed and the auxiliary command value Ias * is equal to or greater than the negative pre-adjusted steering angle limit value Ienb, the absolute value of the steering angle limit value Ien may also be set to a value less than the rated current Ir.

[0116] In the above-described embodiment, the steering angle limit value adjustment unit 87 may not be provided, and the value obtained by subtracting the normal angle limit component Iga and the release angle limit component Iga' from the rated current Ir may be used as the steering angle limit value Ien without any change.

[0117] In the above-described embodiment, the release end separation angle Δθ' is calculated by adding the offset steering angle θoff to the end separation angle Δθ. However, the present invention is not limited thereto. For example, the release absolute steering angle θs' may be calculated by subtracting the offset steering angle θoff from the absolute steering angle θs, and the value indicating the distance of the release absolute steering angle θs' from the end position corresponding angles θs_re and θs_le may be calculated as the release end separation angle Δθ'.

[0118] In the above-described embodiment, for example, the following configuration may also be adopted: that is, the angle limit component calculation unit 84 includes a normal map and a release map, and in this release map, the horizontal axis of the normal map is offset depending on the offset steering angle θoff, and the release end separation angle Δθ' is not input to the angle limit component calculation unit 84. With this configuration, since the horizontal axis in the release map is offset depending on the offset steering angle θoff, the release angle limit component Iga' smaller than the normal angle limit component Iga can also be calculated similarly to the embodiment.

[0119] In the above-described embodiment, the release angle limit component Iga' may be adjusted so that the angle limit component Iga' does not become equal to or greater than a preset limit threshold when partial release control is executed. The limit threshold is, for example, the value of the predetermined auxiliary force output from the motor 21 by supplying the same current as the limit threshold to the motor 21, and is set to the same value as the current threshold Ith_st. Therefore, even when the end contact where the rack shaft 12 contacts the rack housing 13 is generated due to the execution of the partial release control, an increase in its impact can be suppressed.

[0120] In the above-described embodiment, the target steering speed ωs is calculated using Expression (2) in a state where the elastic coefficient K and the inertia coefficient J are set to zero. * , however, the present invention is not limited thereto. For example, at least one of the elastic coefficient K and the inertia coefficient J may not be set to zero. In this case, for example, in addition to the steering torque Th, the actual absolute steering angle θs and the steering angular velocity may be used to calculate the target steering speed ωs. * . Instead of using a model formula, for example, a map indicating the relationship between the steering torque Th and the offset steering angle θoff may be set, and the offset steering angle θoff corresponding to the steering torque may be calculated with reference to this map.

[0121] In the above-described embodiment, the partial release control is performed by calculating the offset steering angle θoff based on the steering torque Th and calculating the release angle limit component Iga' smaller than the normal angle limit component Iga based on the offset steering angle θoff. However, the present invention is not limited thereto, and for example, the partial release control may be performed by calculating the release angle limit component Iga' that decreases over time since the start of the partial release control. In this case, for example, the target steering speed ωs may be calculated based on the change amount of the release angle limit component Iga'. * .

[0122] In the above-described embodiment, when the conditions (a) to (e) are continuously satisfied for a predetermined time, it is determined that the driver is attempting to turn the vehicle during the execution of the end contact mitigation control, and the partial release control is performed. However, the present invention is not limited thereto, and the conditions for starting the partial release control may be appropriately changed. For example, when the conditions (a) to (e) are satisfied, it may be determined that the driver is attempting to turn the vehicle regardless of whether the conditions are continuously satisfied for a predetermined time. For example, it may not be determined whether one of the conditions (d) and (e) is satisfied, and instead of condition (c), it may be determined whether the yaw rate of the vehicle is equal to or greater than the yaw rate threshold indicating the turning state. In addition, in conditions (d) and (e), the steering speed ωs may be used instead of the motor angular velocity ωm.

[0123] In the above-described embodiment, when it is determined that the driver is attempting to turn the vehicle during the execution of the end contact mitigation control, a large steering angle limit value Ien is calculated, and the q-axis current command value Iq is decreased by subtracting the release angle limit component Iga' smaller than the normal angle limit component Iga from the rated current Ir. * However, the present invention is not limited thereto, and for example, the correction value of the q-axis current command value Iq may be decreased by directly correcting the value of the steering angle limit value Ien so that the steering angle limit value Ien increases during the execution of the partial release control. * And the manner of executing the partial release control may be appropriately modified.

[0124] In the above-described embodiment, by monitoring the rotation of the motor 21 even when the ignition switch is turned off, the rotational speed of the motor 21 from the origin is normally integrated, and the absolute motor angle and the absolute steering angle θs are calculated. However, the present invention is not limited thereto. For example, a steering sensor that detects the steering angle as an absolute angle may be provided, and based on the steering angle detected by the steering sensor and the reduction ratio of the reduction gear mechanism 22, the rotational speed of the motor 21 from the origin may be integrated, and the absolute motor angle and the absolute steering angle θs may be calculated.

[0125] In the above-described embodiment, by limiting the auxiliary command value Ias * to the steering angle limit value Ien, the end contact mitigation control is performed. However, the present invention is not limited thereto. For example, the end contact mitigation control may also be performed by adding a steering reaction component that increases toward the rack end position (i.e., a component having a sign opposite to the sign of the auxiliary command value Ias * to the auxiliary command value Ias * . With this configuration, when it is determined that the driver attempts to turn the vehicle while the end contact mitigation control is being performed, the correction value of the q-axis current command value Iq * can be reduced by reducing the steering reaction component according to the steering torque Th.

[0126] In the above-described embodiment, the protection process of limiting the absolute value of the auxiliary command value Ias * to be equal to or less than the limit value Ig is performed on the auxiliary command value Ias * . However, the present invention is not limited thereto, and for example, the protection process may also be performed on a value obtained by correcting the auxiliary command value Ias * using a compensation value based on the torque differential value obtained by differentiating the steering torque Th.

[0127] In the above-described embodiment, the limit value setting unit 62 includes a voltage limit value calculation unit 72 that calculates the voltage limit value Ivb based on the power supply voltage Vb. However, the present invention is not limited thereto, and in addition to or instead of the voltage limit value calculation unit 72, another calculation unit that calculates another limit value based on another state quantity may be provided. A configuration may also be adopted in which the limit value setting unit 62 does not include the voltage limit value calculation unit 72 and the steering angle limit value Ien is set as the limit value Ig without any change.

[0128] In the above-described embodiment, the value obtained by subtracting the normal angle limit component Iga or the release angle limit component Iga' from the rated current Ir is used as the steering angle limit value Ien. However, the present invention is not limited to this, and the value obtained by subtracting the angle limit component Iga or the release angle limit component Iga' and the current limit amount determined by the motor angular velocity from the rated current Ir may also be used as the steering angle limit value Ien.

[0129] In the above-described embodiment, the steering control device 1 controls the type of EPS2 in which the EPS actuator 6 applies a motor torque to the column shaft 15. However, the present invention is not limited to this. For example, the steering control device 1 may also control the type of steering system that applies a motor torque to the rack shaft 12 via a ball screw nut. Not limited to EPS, the steering control device 1 may also control a steer-by-wire type steering device in which the power transmission between the steering unit operated by the driver and the turning unit that turns the turning wheels is cut off, and the torque command value or the q-axis current command value of the motor of the turning actuator provided on the turning unit may be subjected to end contact mitigation control in the same manner as in the present embodiment.

Claims

1. A steering control device (1) for a steering system (2), the steering system (2) including a housing (13), a turning shaft (12), and an actuator (6), the turning shaft (12) being accommodated in the housing (13) such that the turning shaft is capable of reciprocating movement, the actuator (6) applying a motor torque for causing the turning shaft (12) to reciprocate using a motor (21) as a drive source, the steering control device (1) being characterized by including: An absolute steering angle detection unit (53) configured to detect an absolute steering angle that is a rotation angle of a rotation shaft, the rotation angle of the rotation shaft being convertible into a turning angle of a turning wheel (4) connected to the turning shaft (12) and being represented as an absolute angle including a range exceeding 360°; and A current command value calculation unit (51) configured to calculate a current command value corresponding to a target value of the motor torque output from the motor (21), wherein, The steering control device (1) is configured to: control the excitation of the motor (21) such that an actual current value supplied to the motor (21) reaches the current command value, The current command value calculation unit (51) is configured to store an end position corresponding angle, the end position corresponding angle being an angle of an end position where the movement of the turning shaft (12) is restricted due to an end contact where the turning shaft (12) contacts the housing (13) and being related to the absolute steering angle, The current command value calculation unit (51) is configured to: when an end separation angle indicating a distance of the absolute steering angle from the end position corresponding angle is equal to or less than a predetermined angle, perform end contact mitigation control for correcting the current command value such that a decrease in the end separation angle is restricted, The current command value calculation unit (51) is configured to: when the vehicle is being turned while the end contact mitigation control is being executed, perform partial release control for reducing a correction value of the current command value caused by the execution of the end contact mitigation control, and The current command value calculation unit (51) is configured to: when the current command value calculated while the partial release control is being executed is a value not affected by reducing the correction value based on the execution of the partial release control, stop the partial release control.

2. The steering control device (1) according to claim 1, characterized in that, The current command value calculation unit (51) is configured to: calculate the current command value such that when the end separation angle is equal to or less than the predetermined angle, an increase in the end separation angle is not restricted by the end contact mitigation control.

3. The steering control device (1) according to claim 1 or 2, characterized in that: The current command value calculation unit (51) is configured to calculate a steering angle limit value, and when the end separation angle is equal to or less than the predetermined angle, the steering angle limit value decreases as the end separation angle decreases; The current command value calculation unit (51) is configured to perform the end contact mitigation control by limiting an absolute value of the current command value to the steering angle limit value; The current command value calculation unit (51) is configured to perform the partial release control by increasing the steering angle limit value; and the current command value calculation unit (51) is configured to: stop the partial release control based on a comparison result between the current command value calculated when performing the partial release control and a stop determination value based on a steering angle limit value that does not increase due to the execution of the partial release control.

4. The steering control device (1) according to claim 3, characterized in that, When the sign of the current command value for causing the motor (21) to generate a motor torque for turning the turning wheel (4) in one of the rightward and leftward directions is defined as positive and the sign of the current command value for causing the motor (21) to generate a motor torque for turning the turning wheel (4) in the other direction is defined as negative, the current command value calculation unit (51) is configured to: stop the partial release control when the end separation angle becomes equal to or less than the predetermined angle by turning the turning wheel (4) in the one direction and the current command value calculated when performing the partial release control is less than the positive stop determination value, and stop the partial release control when the end separation angle becomes equal to or less than the predetermined angle by turning the turning wheel (4) in the other direction and the current command value calculated when performing the partial release control is greater than the negative stop determination value.

5. The steering control device (1) according to claim 3 or 4, characterized in that: the current command value calculation unit (51) is configured to calculate an angle limit component that decreases as the end separation angle increases; the current command value calculation unit (51) is configured to calculate the steering angle limit value based on a value obtained by subtracting the angle limit component from the rated current of the motor (21); and the current command value calculation unit (51) is configured to: calculate the angle limit component such that the angle limit component during the execution of the partial release control is smaller than the angle limit component during non-execution of the partial release control.

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