Steering Controls

Abstract

The steering control device (1) includes an ECU. The ECU is configured to: when an end separation angle indicating a distance of an absolute steering angle from an end position corresponding angle is equal to or less than a predetermined angle, perform end contact relaxation control for correcting a current command value so that a reduction in the end separation angle is limited, and when a vehicle intends to turn while traveling when the end contact relaxation control is performed, perform partial release control for reducing a correction value of the current command value caused by performing the end contact relaxation control based on a steering torque input to a steering system.

Description

Technical Field

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

[0002] In the related art, an electric power steering system (EPS) including an actuator with a motor as a driving source is called a vehicle steering system. As such an EPS, there is an EPS that obtains a steering angle of a steering wheel (which 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 performing end contact mitigation control for mitigating the influence of so-called end contact in which a rack end as an end of a rack shaft contacts a rack housing.

[0003] In the EPS described in JP 2016-155519 A, the rack end position where the movement of the rack shaft is physically restricted by the end contact is related to the steering angle, and the angle is stored as the end position corresponding angle. In the EPS, the influence of the end contact is mitigated by reducing the target value of the motor torque output from the motor based on the distance of the steering angle from the end position corresponding angle. Summary of the invention

[0004] In a configuration according to the related art, by executing end contact easing control, the movement of the rack shaft can be limited 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, the minimum steering radius when the movement of the rack shaft is limited to the virtual rack end position is larger than the minimum steering radius based on the structure of the vehicle. Therefore, there is a concern that the small steering performance of the vehicle will deteriorate due to the execution of end contact easing control when the vehicle is turning while driving.

[0005] The present invention provides a steering control device that can suppress the degradation of the small turning performance of a vehicle.

[0006] According to one aspect of the present invention, a steering control device for a steering system is provided, the steering system comprising: a housing; a steering shaft, which is accommodated in the housing so that the steering shaft can reciprocate; and an actuator, which uses a motor as a driving source to apply a motor torque for causing the steering shaft to reciprocate, the steering control device including an electronic control unit ECU. The ECU is configured to: detect an absolute steering angle, which is a rotation angle of a rotating shaft that can be converted into a steering angle of a steering wheel connected to a steering shaft and is expressed as an absolute angle including a range exceeding 360; calculate a current command value corresponding to a target value of a motor torque output from a motor; control the excitation of the motor so that an actual current value supplied to the motor reaches the current command value; store an end position corresponding angle, which is an angle indicating an end position at which movement of the steering shaft is restricted due to end contact of the steering shaft with a housing and is related to the absolute steering angle; when an end separation angle indicating a distance from the end position corresponding angle to the absolute steering angle is equal to or less than a predetermined angle, perform an end contact easing control for correcting the current command value so that a reduction in the end separation angle is restricted; and when the vehicle intends to steer while driving when the end contact easing control is performed, perform a partial release control for reducing a correction value of the current command value caused by performing the end contact easing control based on the steering torque input to the steering system.

[0007] With this configuration, when the driver intends to steer the vehicle while driving when the end contact easing control is executed, the correction value for correcting the current command value is reduced by executing the partial release control. Therefore, the restriction of the current command value is partially released when the end contact easing control is executed, and the current command value is increased. Therefore, for example, even when the movement of the steering shaft is restricted to the virtual end position by executing the end contact easing control and the driver intends to steer the vehicle while driving, the partial release control is executed and the current command value is increased. Therefore, the steering shaft can be moved to the actual end position. As a result, the reduction in the small steering performance of the vehicle can be suppressed. With this configuration, since the correction value is reduced based on the steering torque, that is, the current command value is increased, it is possible to prevent the driver from feeling uncomfortable due to the execution of the partial release control.

[0008] In a steering control device, the ECU 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; perform end contact relaxation control by limiting the absolute value of a current command value to the steering angle limit value; calculate an angle limit component that decreases as the end separation angle increases, and calculate the steering angle limit value based on a value obtained by subtracting the angle limit component from the rated current of the motor; and calculate the angle limit component so that when partial release control is performed, the angle limit component is reduced compared to a case where partial release control is not performed.

[0009] With this configuration, since the end contact relaxation control is performed so that the current command value is limited to a value equal to or less than the steering angle limit value, the correction value of the current command value due to the execution of the end contact relaxation control decreases as the steering angle limit value increases. Since the steering angle limit value is calculated based on the value obtained by subtracting the angle limit component from the rated current, the steering angle limit value increases as the angle limit component decreases. Therefore, by reducing the angle limit component, partial release control for reducing the correction value of the current command value can be easily performed.

[0010] In a steering control device, the ECU may be configured to: when performing partial release control, calculate a target steering speed based on the steering torque using a model formula for relating the steering torque to the rotation angle; calculate an offset steering angle based on a value obtained by integrating the target steering speed; and reduce an angle limiting component based on the offset steering angle.

[0011] With this configuration, the offset steering angle reaches a value close to the rotation angle of the rotation shaft caused when the steering torque is input to the model indicated by the model formula. Therefore, by reducing the angle limit component based on the offset steering angle, the current command value can be appropriately increased so that a steering feel corresponding to the model is achieved.

[0012] In the steering control device, the ECU may be configured to calculate the steering angle limit value so that the steering angle limit value does not become equal to or greater than a preset limit threshold value when the partial release control is performed.

[0013] With this configuration, an excessive increase in the current command value due to execution of the partial release control can be suppressed. Therefore, for example, when end contact of the steering shaft with the housing occurs while the partial release control is executed, an increase in the influence of the end contact can be suppressed.

[0014] According to the present invention, it is possible to suppress the deterioration of the small turning performance of the vehicle. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which like symbols represent like elements, and in which:

[0016] Figure 1 is a diagram schematically showing the configuration of an electric power steering system;

[0017] Figure 2 is a block diagram showing a steering control device;

[0018] Figure 3 is a block diagram showing a limit value setting unit;

[0019] Figure 4 is a flowchart showing a processing routine associated with calculation of an offset steering angle performed by an offset steering angle calculation unit;

[0020] Figure 5 is a block diagram showing an angle limit component calculation unit; and

[0021] Figure 6 is a graph showing an example of changes in the q-axis current command value in the partial release control. DETAILED DESCRIPTION

[0022] Hereinafter, a steering control device according to a first embodiment of the present invention will be described with reference to the accompanying drawings. Figure 1 As shown, an electric power steering system (EPS) 2 as a steering system to be controlled by a steering control device 1 includes a steering mechanism 5 that steers a steering wheel 4 based on a driver's operation of a steering wheel 3. The EPS 2 also includes an EPS actuator 6 that applies an auxiliary force to the steering mechanism 5 for assisting the steering operation.

[0023] The steering mechanism 5 includes a steering shaft 11 to which the steering wheel 3 is fixed, a rack shaft 12 which is a steering shaft connected to the steering shaft 11, a rack housing 13 which is a housing into which the rack shaft 12 is inserted so that the rack shaft 12 can reciprocate, and a rack and pinion mechanism 14 which converts the rotational motion of the steering shaft 11 into the translational motion of the rack shaft 12. 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.

[0024] 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 are meshed with each other. The tie rod 19 is rotatably connected to both ends of the rack shaft 12 via rack ends 18, each of which is formed by a spherical joint provided at each shaft end. The end of the tie rod 19 is connected to a joint (not shown), and the steering wheel 4 is assembled to the joint. Therefore, in the EPS 2, the rotational movement of the steering shaft 11 based on the steering operation is converted into a translational movement in the axial direction of the rack shaft 12 through the rack and pinion mechanism 14, and the translational movement in the axial direction is transmitted to the joint via the tie rod 19, thereby changing the steering angle of the steering wheel 4, that is, the driving direction of the vehicle.

[0025] 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 steered to the right most, and this position corresponds to the rack end position which is 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 steered to the left most, and this position corresponds to the rack end position which is the left end position.

[0026] The EPS actuator 6 includes a motor 21 as a driving 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 reducing the rotational motion of the motor 21 using the reduction gear mechanism 22 and transmitting the reduced rotation to the column shaft 15. According to the present embodiment, a three-phase brushless motor is used as the motor 21.

[0027] 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 an electronic control unit (ECU) not shown. The ECU includes a central processing unit (CPU) not shown and a memory, and the CPU executes a program stored in the memory at each predetermined calculation cycle. Thus, various types of control are performed.

[0028] A vehicle speed sensor 31 that detects a vehicle speed SPD of the vehicle and a torque sensor 32 that detects a 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 a rotation angle θm of the motor 21 as 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 steered to the right, and are detected as negative values ​​when the steering wheel 3 is steered to the left. A yaw rate sensor 34 that detects a yaw rate γ of the vehicle is connected to the steering control device 1. The steering control device 1 controls the operation of the EPS actuator 6 by supplying a driving force to the motor 21 based on a signal indicating a state quantity input from the sensor, that is, an assist force applied to the steering mechanism 5 so that the rack shaft 12 can move to reciprocate.

[0029] The configuration of the steering control device 1 will be described below. Figure 2As shown, the steering control device 1 includes a microcomputer 41 that outputs a motor control signal Sm and a drive circuit 42 that supplies drive power 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 element. Therefore, the switching element is turned on and off in response to the motor control signal Sm, and the power supply mode to the motor coil of each phase is switched in each phase, thereby converting the DC (direct current) power of the vehicle power supply 43 into three-phase drive power and outputting it to the motor 21.

[0030] The control blocks to be described below are realized by a computer program executed by the microcomputer 41 , detect the state quantity at each predetermined sampling cycle, and execute calculation processing assigned to the following control blocks at each predetermined calculation cycle.

[0031] 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 vehicle power supply 43 detected by the voltage sensor 45 are also input to the microcomputer 41. The current sensor 44 is provided in the connection line 46 between the drive circuit 42 and the motor coil of each phase. The voltage sensor 45 is provided in the connection line 47 between the vehicle power supply 43 and the drive circuit 42. Figure 2 , for the purpose of convenience of description, one set of each current sensor 44 in each phase and each connection line 46 in each phase is shown. The microcomputer 41 outputs a motor control signal Sm based on the input state quantity.

[0032] 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.

[0033] The vehicle speed SPD, the steering torque Th, the power supply voltage Vb, the rotation angle θm, and the absolute steering angle θs are input to the current command value calculation unit 51. The current command value calculation unit 51 calculates the current command values ​​Id* and Iq* based on the input state quantity. The current command values ​​Id* and Iq* are target values ​​of the current to be supplied to the motor 21, and are the current command value on the d-axis and the current command value on the q-axis in the d / q coordinate system, respectively. 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 basically fixed to zero. For example, the current command values ​​Id* and Iq* have positive values ​​when assisting steering to the right, and have negative values ​​when assisting steering to the left.

[0034] Current command values ​​Id* and Iq*, phase current values ​​Iu, Iv and Iw, and rotation angle θm of motor 21 are input to motor control signal generating unit 52. Motor control signal generating unit 52 generates motor control signal Sm by performing current feedback control in d / q coordinate system based on the input state quantity.

[0035] Specifically, the motor control signal generating unit 52 calculates the d-axis current value Id and the q-axis current value Iq, which are actual current values ​​of the motor 21 in the d / q coordinate system, by mapping the phase current values ​​Iu, Iv, and Iw onto the d / q coordinate system based on the rotation angle θm. Then, the motor control signal generating unit 52 generates the motor control signal Sm by performing 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*.

[0036] The motor control signal generating unit 52 outputs the generated motor control signal Sm to the drive circuit 42. Therefore, the drive power based on the motor control signal Sm is supplied to the motor 21, and the motor torque based on the q-axis current command value Iq* is output from the motor 21, thereby applying the assist force to the steering mechanism 5.

[0037] The rotation angle θm is input to the absolute steering angle detection unit 53. The absolute steering angle detection unit 53 detects an absolute motor angle expressed as an absolute angle (including a range exceeding 360°) based on the rotation angle θm. The absolute steering angle detection unit 53 in the present embodiment integrates the rotation speed of the motor 21 with the rotation angle θm as the origin when the start switch (such as the ignition switch) is turned on for the first time after the vehicle-mounted power supply 43 has been replaced, for example, and detects the absolute motor angle based on the integrated rotation speed and the rotation angle θm. Then, the absolute steering angle detection unit 53 detects the absolute steering angle θs indicating 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 the present embodiment, the rotation of the motor 21 is monitored even when the start switch is turned off, and the rotation speed of the motor 21 is normally integrated. Therefore, even when the start switch is turned on for the second time or later after the in-vehicle power supply 43 has been replaced, the origin of the absolute steering angle θs is the same as the origin set when the start switch was turned on for the first time.

[0038] As described above, since the steering angle of the steering wheel 4 changes by the rotation of the steering shaft 11, the absolute steering angle θs indicates the rotation angle of the rotation shaft that can be converted into the steering angle of the steering wheel 4. The absolute motor angle and the absolute steering angle θs have positive values ​​when they are angles steering in the right direction from the origin, and have negative values ​​when they are angles steering in the left direction from the origin.

[0039] The configuration of the current command value calculation unit 51 will be described below. The current command value calculation unit 51 includes an auxiliary command value calculation unit 61 that calculates an auxiliary command value Ias* as a basic component of the q-axis current command value Iq*. The current command value calculation unit 51 also includes a limit value setting unit 62 that sets a limit value Ig as an upper limit of the absolute value of the q-axis current command value Iq*, and an upper limit protection processing unit 63 that limits the absolute value of the auxiliary command value Ias* to a value equal to or less than the limit value Ig. A memory 64 is connected to the limit value setting unit 62.

[0040] 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 the assist command value Ias based on the steering torque Th and the vehicle speed SPD. * Specifically, when the absolute value of the steering torque Th becomes larger and the vehicle speed SPD becomes lower, the assist command value calculation unit 61 calculates the assist command value Ias* to a larger absolute value. The calculated assist command value Ias* is output to the upper limit protection processing unit 63.

[0041] As will be described later, in addition to the assist command value Ias*, the limit value Ig set by the limit value setting unit 62 is input to the upper limit 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 upper limit protection processing unit 63 outputs the value of the assist command value Ias* as the q-axis current command value Iq* to the motor control signal generating unit 52 without any change. On the other hand, when the absolute value of the input assist command value Ias* is greater than the limit value Ig, the upper limit protection processing unit 63 outputs a value obtained by limiting the absolute value of the assist command value Ias* to the limit value Ig to the motor control signal generating unit 52 as the q-axis current command value Iq*.

[0042] The rated current Ir as the maximum current corresponding to the torque preset as 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 end position corresponding angle θs_le on the left side is the absolute steering angle θs corresponding to the left rack end position, and the end position corresponding angle θs_re on the right side 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 performed based on the steering of the driver.

[0043] The following will describe the configuration of the limit value setting unit 62. The motor angular velocity ωm (which is 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 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 quantity.

[0044] Specifically, Figure 3 As shown, the limit value setting unit 62 includes a steering angle limit value calculation unit 71 that calculates a steering angle limit value Ien based on the absolute steering angle θs, a voltage limit value calculation unit 72 that calculates a 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.

[0045] The motor angular velocity ωm, the absolute steering angle θs, the vehicle speed SPD, the steering torque Th, 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, 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 quantity 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 calculated steering angle limit value Ien is output to the minimum value selection unit 73.

[0046] 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 the preset voltage threshold value Vth, the voltage limit value calculation unit 72 calculates a 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 value Vth, the voltage limit value calculation unit 72 calculates a 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.

[0047] The minimum value selection unit 73 selects the smaller of the input steering angle limit value Ien and the input voltage limit value Ivb as the limit value Ig, and outputs the selected smaller one to the upper limit protection processing unit 63. When the steering angle limit value Ien is output to the upper limit 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 end contact mitigation control for mitigating the influence of the end contact is performed by reducing the absolute value of the q-axis current command value Iq* as the end separation angle Δθ decreases. In the present embodiment, the current command value calculation unit 51 corrects the q-axis current command value Iq* so that the absolute value of the q-axis current command value Iq* is limited to a value equal to or less than the limit value Ig. The correction value of the q-axis current command value Iq* is a value at which the assist command value Ias* exceeds the limit value Ig, that is, a value that exceeds the steering angle limit value Ien.

[0048] When the voltage limit value Ivb is output as the limit value Ig to the protection processing unit 63, 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 value Vth, 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 is performed.

[0049] Here, by performing the end contact relaxation control, the movement of the rack shaft 12 can be restricted at a virtual rack end position that is closer to the neutral steering position than the actual rack end position where the rack shaft 12 is actually in contact with 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 located at the actual rack end position, and the small turning performance of the vehicle may be deteriorated.

[0050] Therefore, when the driver intends to steer the vehicle while traveling when the end contact relaxation control is executed, the current command value calculation unit 51 in the present embodiment performs a partial release control for reducing the correction value of the q-axis current command value Iq in the end contact relaxation control based on the steering torque Th input to the EPS 2. As described above, since the upper limit 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 correction value of the q-axis current command value Iq* decreases as the steering angle limit value Ien, which is the limit value Ig, increases. In view of this, as described below, in the present embodiment, when the driver intends to steer the vehicle while traveling when the end contact relaxation control is executed, the steering angle limit value calculation unit 71 calculates a steering angle limit value Ien that is larger than the steering angle limit value when the partial release control is not executed, and thus executes the partial release control.

[0051] Specifically, the steering angle limit value calculation unit 71 includes an angular velocity change calculation unit 81 that calculates an angular velocity change Δωm, an offset steering angle calculation unit 82 that calculates an offset steering angle θoff, and an end separation angle calculation unit 83 that calculates an end separation angle Δθ. The steering angle limit value calculation unit 71 includes an angle limit component calculation unit 84 that calculates a normal angle limit component Iga based on the end separation angle Δθ, and calculates a release angle limit component Iga" based on a 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 also includes an output switching unit 86 that selects one of the angle limit components Iga and Iga" and outputs the selected one to a subtractor 85, and calculates the steering angle limit value Ien by subtracting one of the angle limit components Iga and Iga" from the rated current Ir. The control blocks will be described sequentially below.

[0052] Angular velocity change calculation unit 81

[0053] 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 as the amount of change in 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 this embodiment outputs a value obtained by performing a low-pass filter process on the angular velocity change Δωm to the offset steering angle calculation unit 82.

[0054] Offset steering angle calculation unit 82

[0055] The vehicle speed SPD, the steering torque Th, the motor angular velocity ωm, the angular velocity change Δωm, and the normal angle limit component Iga to be described later are input to the offset steering angle calculation unit 82. The offset steering angle calculation unit 82 determines whether the driver has an intention to steer the vehicle while traveling by performing steering or holding steering when the end contact relaxation control is performed based on the input state quantity. When it is determined that the driver intends to steer the vehicle while traveling when the end contact relaxation control is performed, the offset steering angle calculation unit 82 starts calculation of the offset steering angle θoff and outputs the calculated offset steering angle θoff to the adder 87. When it is determined that the driver does not intend to steer the vehicle while traveling when the end contact relaxation control is performed, the offset steering angle calculation unit 82 does not calculate the offset steering angle θoff.

[0056] The offset steering angle calculation unit 82 outputs an execution flag F indicating whether the partial release control is being executed to the output switching unit 86. The execution flag F indicates that the partial release control is not being executed when its value is "0", and indicates that the 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 F to "0" before the calculation of the offset steering angle θoff is started, and sets the value of the execution flag F to "1" after the calculation of the offset steering angle θoff is started.

[0057] The method of calculating the offset steering angle θoff will be described in detail below. The offset steering angle calculation unit 82 calculates the offset steering angle θoff using a model formula indicated by Expression (1) based on the steering torque Th.

[0058]

[0059] In the following description, for the purpose of convenience of description, the symbol of the target steering speed which is the first time differential value of "θs*" is referred to as "ωs*". The 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 shaft which can be converted into the steering angle of the steering wheel 4. The model formula is expressed using an elastic coefficient K obtained by modeling the specifications such as the suspension or wheel alignment of the vehicle on which the EPS 2 is installed, a viscosity coefficient C obtained by modeling the friction of the EPS 2, and the inertia coefficient J obtained by modeling the inertia of the EPS 2.

[0060] The offset steering angle calculation unit 82 in the present embodiment calculates the target steering speed ωs* using expression (2) in which the elastic coefficient K and the inertia coefficient J are set to zero, and defines the target steering speed ωs* in consideration of the reduction in calculation load and the steering feel to be achieved.

[0061]

[0062] 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 87.

[0063] The determination of the intention to steer will be described below. When the following conditions (a) to (e) for determining the intention to steer are satisfied for a predetermined time, the offset steering angle calculation unit 82 determines that the driver intends to steer the vehicle while driving when performing the end contact mitigation control. The predetermined time is set to be an appropriate time for determining that the driver performs steering or maintains steering.

[0064] (a) Normal angle limit component Iga is greater than current threshold Ith1.

[0065] (b) The absolute value of the steering torque Th is equal to or greater than the steering torque threshold value Tth.

[0066] (c) The vehicle speed SPD is within a predetermined vehicle speed range.

[0067] (d) The absolute value of the motor angular velocity ωm is equal to or smaller than the angular velocity threshold ωth.

[0068] (e) The absolute value of the angular velocity change Δωm, which is the amount of change in the motor angular velocity ωm, is smaller than the angular velocity change threshold Δωth.

[0069] The current threshold value Ith1 is set so that when the value of the angle limit component Iga is the current threshold value Ith1 and the vehicle is traveling at a low speed on a normal road surface, a predetermined assist force as a minimum assist 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 value Ith1 from the rated current Ir is set to be the magnitude of the predetermined assist force output from the motor 21 by supplying the motor 21 with a current of the same absolute value. The current threshold value Ith1 is a current value based on the rated current Ir, and is set to, for example, 50% of the rated current Ir.

[0070] The steering torque threshold value Tth is the steering torque required to maintain the steering of the steering wheel 3 when the vehicle is turning while traveling 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 limit vehicle speed Slo indicating that the vehicle is not stopped and is less than the upper limit vehicle speed Sup indicating that the vehicle is traveling at a low speed. The lower limit vehicle speed Slo is set to a value slightly greater than zero, and the upper limit vehicle speed Sup is set to an appropriate value greater than the lower limit vehicle speed Slo. The angular velocity threshold value ωth is the angular velocity indicating that the motor 21 is stopped, and is set to a value slightly greater than zero. The angular velocity change threshold value Δωth ​​is an angular velocity change indicating that the motor 21 is substantially neither accelerated nor decelerated, and is set to a value slightly greater than zero.

[0071] When the normal angle limit component Iga is smaller than the current threshold value Ith1, the offset steering angle calculation unit 82 stops calculating the offset steering angle θoff, for example, by allowing the driver to perform return steering when calculating the offset steering angle θoff (i.e., when performing the partial release control). That is, the partial release control is stopped.

[0072] The following will describe the processing flow of calculating the offset steering angle θoff performed by the offset steering angle calculation unit 82. Figure 4 As shown in the flowchart of , when various state quantities are acquired (step 101), the offset steering angle calculation unit 82 determines whether the execution flag F is "0", that is, whether the partial release control is not executed (step 102).

[0073] When the execution flag F is "0" (step 102: 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 103). 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 is within the predetermined vehicle speed range (step 103: yes), the offset steering angle calculation unit 82 determines whether the angle limit component Iga is greater than the current threshold value Ith1 (step 104). When the angle limit component Ig is greater than the current threshold value Ith1 (step 104: 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 value Tth (step 105). When the absolute value of the steering torque Th is greater than or equal to the steering torque threshold value Tth (step 105: 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 value ωTh (step 106). When the absolute value of the motor angular velocity ωm is equal to or less than the angular velocity threshold value ωth (step 106: Yes), the offset steering angle calculation unit 82 determines whether the angular velocity change Δωm is less than the angular velocity change threshold value Δωth ​​(step 107). When the angular velocity change Δωm is less than the angular velocity change threshold value Δωth ​​(step 107: Yes), the offset steering angle calculation unit 82 causes the processing flow to proceed to step 108.

[0074] In step 108, the offset steering angle calculation unit 82 increments the count value Cn of the counter indicating the elapsed time after executing the determination in steps 103 to 107, that is, after conditions (a) to (e) are satisfied. 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 109). When the count value Cn is greater than the predetermined count value Cth (step 109: yes), the offset steering angle calculation unit 82 starts calculation of the offset steering angle θoff (step 110), sets the value of the execution flag F to "1" indicating that the partial release control is being executed, and clears the count value Cn of the counter (steps 111 and 112).

[0075] When the count value Cn is equal to or less than the predetermined count value Cth (step 109: No), the offset steering angle calculation unit 82 does not perform the subsequent processing. When the determination result of any one of steps 103 to 107 is not affirmative (steps 103 to 107: No), the offset steering angle calculation unit 82 does not perform the processing of steps 108 to 111, advances the processing flow to step 112, and clears the count value Cn.

[0076] On the other hand, when the value of the execution flag F is "1" (step 102: No), the offset steering angle calculation unit 82 determines whether the angle limit component Iga calculated based on the end separation angle Δθ is less than the current threshold value Ith1 (step 113). When the angle limit component Iga is less than the current threshold value Ith1 (step 113: Yes), the offset steering angle calculation unit 82 stops the calculation of the offset steering angle θoff (step 114), and sets the value of the execution flag F to "0" indicating the stop of the partial release control (step 115). When the angle limit component Iga is equal to or greater than the current threshold value Ith1 (step 113: No), the offset steering angle calculation unit 82 does not perform subsequent processing.

[0077] End separation angle calculation unit 83

[0078] like Figure 3 As shown in FIG. 1 , the absolute steering angle θs and the end position corresponding angles θs_re and θs_le are input to the end separation angle calculation unit 83. The end separation angle calculation unit 83 calculates the 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 the 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 the smaller absolute value of the calculated difference as the end separation angle Δθ to the angle limit component calculation unit 84 and the adder 87.

[0079] Angle limit component calculation unit 84

[0080] The end separation angle Δθ and the vehicle speed SPD are input to the angle limiting component calculation unit 84. The release end separation angle Δθ' obtained by adding the offset steering angle θoff and the end separation angle Δθ in the adder 87 is input to the angle limiting component calculation unit 84. The release end separation angle Δθ' has a value that is greater than the end separation angle Δθ by the value of the offset steering angle Δoff. The angle limiting component calculation unit 84 calculates the angle limiting components Iga and Iga" based on the input state quantity.

[0081] Specifically, Figure 5 As shown, the angle limit component calculation unit 84 includes a map calculation unit 91 that calculates the normal angle limit component Iga and the release angle limit component Iga′ and a lower limit protection processing unit 92 that defines a lower limit value of the absolute value of the release angle limit component Iga′.

[0082] The mapping calculation unit 91 includes a normal mapping in which the relationship between the end separation angle Δθ and the vehicle speed SPD and the normal angle limit component Iga is defined, and refers to the mapping to calculate the angle limit component Iga corresponding to the end separation angle Δθ and the vehicle speed SPD. The calculated normal angle limit component Iga is output to the offset steering angle calculation unit 82 and the output switching unit 86.

[0083] In this normal map, the angle 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 is less than zero, the angle 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 angle limit component Iga remains constant. The negative region in the map is assumed to be the degree to which the motor 21 rotates when the EPS 2 is elastically deformed by performing more 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 a range close to the end position corresponding angles θs_re and θs_le. That is, the angle limit component Iga is set to decrease when the absolute steering angle θs transitions from the end position corresponding angles θs_re and θs_le to the neutral steering position, and is set to 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.

[0084] In this normal mapping, in the region where the end separation angle Δθ is equal to or less than the predetermined angle θ1, the angle 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 angle 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 angle limit component Iga is set to zero.

[0085] The map calculation unit 91 includes a release map in which the relationship between the release end separation angle Δθ' and the vehicle speed SPD and the release angle limit component Iga' is defined, and calculates the release angle limit component Iga' corresponding to the release end separation angle Δθ' and the vehicle speed SPD with reference to the map. The calculated release angle limit component Iga' is output to the lower limit protection processing unit 92.

[0086] The release map is set to the same map as the normal map. That is, when the vehicle speed SPD is the same and the end separation angle Δθ and the release end separation angle Δθ' are the same, the angle limit component Iga and the release angle limit component Iga' calculated as a result are the same. As described above, since the release end separation angle Δθ' rather than the end separation angle Δθ has a larger value than the offset steering angle θoff, the map calculation unit 91 calculates the release steering angle limit value Ien' which is smaller than the normal steering angle limit value Ien by the offset steering angle θoff.

[0087] The lower limit protection processing unit 92 adjusts the release angle limit component Iga' when executing the partial release control so that the steering angle limit value Ien will not be equal to or greater than the preset limit threshold value Ith2. The limit threshold value Ith2 is set to a value at which a predetermined assist force is applied from the motor 21 by supplying the same current as the limit threshold value Ith2 to the motor 21, and is set to the same value as the current threshold value Ith1. The lower limit protection processing unit 92 adjusts the angle limit component Iga' based on the comparison result between the angle limit component Iga' and the current threshold value Ith1.

[0088] Specifically, when the absolute value of the input release angle limit component Iga' is equal to or greater than the preset current threshold value Ith1, the lower limit protection processing unit 92 outputs the value of the angle limit component Iga' as the angle limit component Iga" to the output switching unit 86 without any change. On the other hand, when the absolute value of the input release angle limit component Iga' is less than the current threshold value Ith1, the lower limit protection processing unit 92 outputs the value obtained by changing the absolute value of the angle limit component Iga' to the current threshold value Ith1 as the angle limit component Iga" to the output switching unit 86.

[0089] Therefore, since the angle limiting component Iga" output to the output switching unit 86 is equal to or greater than the current threshold Ith1, when the angle limiting component Iga" is subtracted from the rated current Ir, that is, when partial release control is performed, the steering angle limiting value Ien will not be equal to or greater than the limiting threshold Ith2.

[0090] Output switching unit 86

[0091] like Figure 3 As shown, the angle limit components Iga, Iga” and the execution flag F are input to the output switching unit 86. The output switching unit 86 includes a contact point P1 to which the normal angle limit component Iga is input, a contact point P2 to which the release angle limit component Iga” is input, and a contact point P3 connected to the subtractor 85. When the execution flag F is "0", the output switching unit 86 connects the contact point P1 and the contact point P3, and outputs the normal angle limit component Iga to the subtractor 85. On the other hand, when the execution flag F is "1", the output switching unit 86 connects the contact point P2 and the contact point P3, and outputs the release angle limit component Iga” to the subtractor 85.

[0092] Then, a value obtained by subtracting the normal angle limit component Iga or the release angle limit component Iga" from the rated current Ir depending on whether the partial release control is being performed is output from the subtractor 85 to the minimum value selection unit 73 as the steering angle limit value Ien.

[0093] The operation of this embodiment will be described below. It is assumed that the driver steers the steering wheel 3 to the right when the vehicle power supply 43 is normal and the power supply protection control is not executed. Figure 6 As shown, when the end separation angle Δθ is equal to or less than the predetermined angle θ1, the steering angle limit value Ien having a value less than the rated current Ir is calculated. When the steering angle limit value Ien is less than the current threshold value Ith1, the steering of the steering wheel 4 can be stopped at a virtual rack end position located before the actual rack end position according to the road surface state and the like.

[0094] Here, when the driver continues to perform the right-side steering and it is determined that the driver has the intention to steer the vehicle, the steering angle limit value Ien is increased and the correction value of the q-axis current command value Iq* is decreased by performing the partial release control. That is, since the absolute value of the q-axis current command value Iq* increases as indicated by the alternating long and short dashed lines in the drawing, the rack shaft 12 can be moved to the actual rack end position. At this time, since the steering angle limit value Ien is not equal to or greater than the limit threshold value Ith2 as described above, the strong contact of the rack shaft 12 with the rack housing 13 is suppressed.

[0095] Advantages in this embodiment will be described below. When it is determined that the driver intends to steer the vehicle while driving when performing the end contact easing 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* caused by the execution of the end contact easing control based on the steering torque Th. Therefore, the restriction of the q-axis current command value Iq* caused by the execution of the end contact easing control is partially released, so the q-axis current command value Iq* increases. Therefore, for example, even in the case where the movement of the rack shaft 12 is limited to the virtual rack end position due to the execution of the end contact easing control, the partial release control is performed by allowing the driver to steer the vehicle while driving to increase the q-axis current command value Iq*, and thus the rack shaft 12 can move to the actual rack end position. As a result, the reduction in the small steering performance of the vehicle can be suppressed. In this embodiment, since the correction value is reduced based on the steering torque Th, that is, the q-axis current command value Iq* increases, it is possible to prevent the driver from feeling uncomfortable due to the execution of the partial release control.

[0096] The current command value calculation unit 51 includes a steering angle limit value calculation unit 71, which calculates a steering angle limit value Ien that decreases as the end separation angle Δθ decreases when the end separation angle Δθ is equal to or less than a predetermined angle θ1. The current command value calculation unit 51 performs end contact easing control by limiting the absolute value of the q-axis current command value Iq* to the steering angle limit value Ien. Therefore, the correction value of the q-axis current command value Iq* caused by the execution of the end contact easing control decreases as the steering angle limit value Ien increases. The steering angle limit value calculation unit 71 includes an angle limit component calculation unit 84, which 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 the steering angle limit value Ien. Therefore, by setting the release angle limit component Iga" to be smaller 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*.

[0097] When performing partial release control, the steering angle limit value calculation unit 71 calculates the target steering speed ωs* based on the steering torque Th using expression (2), and calculates the offset steering angle θoff based on the value obtained by integrating the target steering speed ωs*. The steering angle limit value calculation unit 71 calculates a release angle limit component Iga'' that is smaller than the normal angle limit component Iga based on the offset steering angle θoff. Specifically, the steering angle limit value calculation unit 71 calculates the release angle 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. Here, the offset steering angle θoff has a value close to the absolute steering angle θs, which is generated when the steering torque Th is input to the model represented by the model formula, that is, the model of EPS 2 represented by the viscosity coefficient C in this embodiment. Therefore, by calculating the release angle limit component Iga'' based on the offset steering angle θoff, the q-axis current command value Iq* can be appropriately increased to achieve a steering feel corresponding to the model of EPS 2.

[0098] Since the steering angle limit value calculation unit 71 calculates the steering angle limit value Ien when the partial release control is executed so that the steering angle limit value Ien will not be equal to or greater than the limit threshold value Ith, it is possible to suppress an excessive increase in the q-axis current command value Iq* due to the execution of the partial release control. Therefore, for example, even when an end contact occurs in which the rack shaft 12 contacts the rack housing 13, an increase in the influence of the end contact due to the execution of the partial release control can be suppressed.

[0099] When the normal angle limit component Iga is less than the current threshold value Ith1, the steering angle limit value calculation unit 71 stops the partial release control. Therefore, for example, as in the case where the partial release control is stopped in a state where the normal angle limit component Iga is equal to or greater than the current threshold value Ith1, a sharp change in the steering angle limit value Ien (i.e., the q-axis current command value Iq*) can be prevented, and deterioration of the steering feel can be suppressed.

[0100] The above embodiment may be modified as follows. Unless a technical conflict occurs, the above embodiment and the following modified example may be combined. In the 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, and 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 a value indicating the distance of the 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'.

[0101] In the above embodiment, for example, a configuration may be implemented in which the map calculation unit 91 includes a normal map and a release map in which the horizontal axis of the normal map is shifted depending on the offset steering angle θoff and the release-end separation angle Δθ′ is not input to the map calculation unit 91. With this configuration, since the horizontal axis in the release map is shifted depending on the offset steering angle θoff, the release angle limit component Iga′ that is smaller than the normal angle limit component Iga can also be calculated similarly to the embodiment.

[0102] In the above embodiment, when the normal angle limit component Iga becomes less than the current threshold value Ith1 due to the execution of the partial release control after the partial release control is executed, the partial release control is stopped. However, the present invention is not limited to this, and when the angle limit component Iga is equal to or greater than the current threshold value Ith1, for example, when one of the conditions (a) to (e) is not satisfied, the partial release control may be stopped.

[0103] In the above embodiment, when the partial release control is performed, the steering angle limit value Ien may be equal to or greater than the limit threshold value Ith2. In the above 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, but the present invention is not limited thereto, and 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 target steering speed ωs* may be calculated using the actual absolute steering angle θs and the steering angular velocity. Instead of using the model formula, a map indicating the relationship between the steering torque Th and the offset steering angle θoff may be set, for example, and the offset steering angle θoff corresponding to the steering torque may be calculated with reference to the map.

[0104] In the above embodiment, when conditions (a) to (e) are continuously satisfied for a predetermined time, it is determined that the driver intends to turn the vehicle while driving when executing the end contact easing control, and the release control is performed, but the present invention is not limited to this, and the starting conditions for the partial release control can be appropriately changed. For example, when conditions (a) to (e) are satisfied, it can be determined that the driver intends to turn the vehicle while driving, regardless of whether the conditions are continuously satisfied for a predetermined time. For example, it may not be determined whether one of conditions (d) and (e) is satisfied, and it may be determined whether the yaw rate of the vehicle is equal to or greater than the yaw rate threshold indicating the steering state, instead of condition (c). In addition, under conditions (d) and (e), the steering speed ωs may be used instead of the motor angular speed ωm.

[0105] In the above embodiment, when it is determined that the driver intends to steer the vehicle while driving when executing end contact easing control, a large steering angle limit value Ien is calculated, and the correction value of the q-axis current command value Iq* is reduced by subtracting a release angle limit component Iga" that is smaller than the normal angle limit component Iga from the rated current Ir. However, the present invention is not limited to this, and the correction value of the q-axis current command value Iq* can be reduced by directly correcting the value of the steering angle limit value Ien so that the steering angle limit value Ien increases when executing partial release control, and the manner of executing partial release control can be appropriately modified.

[0106] In the embodiment, the rotation speed of the motor 21 from the origin is normally integrated by monitoring the rotation of the motor 21 even when the ignition switch is turned off, and the absolute motor angle and the absolute steering angle θs are calculated. However, the present invention is not limited to this, and for example, a steering sensor that detects the steering angle as an absolute angle may be provided, and the rotation speed of the motor 21 from the origin may be integrated based on the steering angle detected by the steering sensor and the reduction ratio of the reduction gear mechanism 22, and the absolute motor angle and the absolute steering angle θs may be calculated.

[0107] In the above embodiment, the end contact relaxation control is performed by limiting the assist command value Ias* to the steering angle limit value Ien, but the present invention is not limited thereto, and for example, the end contact relaxation control may be performed by adding a steering reaction component (i.e., a component having a sign opposite to that of the assist command value Ias*) that increases toward the rack end position to the assist command value Ias*. With this configuration, when it is determined that the driver intends to steer the vehicle while traveling when the end contact relaxation control is performed, the correction value of the q-axis current command value Iq* may be reduced by reducing the steering reaction component according to the steering torque Th.

[0108] In the above embodiment, a protection process is performed on the auxiliary command value Ias* to limit the absolute value of the auxiliary command value Ias* to a value equal to or less than the limit value Ig, but the present invention is not limited to this, and for example, a protection process may be performed on a value obtained by correcting the auxiliary command value Ias* using a compensation value based on a torque differential value obtained by differentiating the steering torque Th.

[0109] In the 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, but the present invention is not limited thereto, and another calculation unit that calculates another limit value based on another state amount may be provided in addition to or in place of the voltage limit value calculation unit 72. It is also possible to adopt a configuration 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 to the limit value Ig without any change.

[0110] In the above embodiment, the value obtained by subtracting the normal angle limitation component Iga or the release angle limitation component Iga" from the rated current Ir is used as the steering angle limitation value Ien, but the present invention is not limited to this. The value obtained by subtracting the angle limitation component Iga or the release angle limitation component Iga" and the current limitation amount determined by the motor angular velocity from the rated current Ir may be used as the steering angle limitation value Ien.

[0111] In the embodiment, the steering control device 1 controls the EPS 2 of the type in which the EPS actuator 6 applies a motor torque to the column shaft 15, but the present invention is not limited to this, and for example, the steering control device 1 may also control a steering system of the type in which a motor torque is applied to the rack shaft 12 via a ball screw nut. Not limited to EPS, the steering control device 1 may also control a steering device of a steer-by-wire type in which the power transmission between the steering unit operated by the driver and the steering unit that steers the steering wheel is cut off, and end contact relaxation control may be performed on the torque command value or the q-axis current command value of the motor of the steering actuator provided on the steering unit as in the present embodiment.

[0112] The following is an additional description of the technical ideas that can be understood from the above embodiments and the above modified examples: a steering control device, wherein, when performing partial release control, a steering angle limit value calculation unit calculates a release angle limit component based on a release end separation angle obtained by adding an offset steering angle to an end separation angle.

Claims

1. A steering control device (1) for a steering system (2), the steering system (2) comprising a housing (13), a steering shaft (12) and an actuator (6), the steering shaft (12) being accommodated in the housing (13) so that the steering shaft (12) can reciprocate, the actuator (6) using a motor (21) as a driving source to apply a motor torque for causing the steering shaft (12) to reciprocate, the steering control device (1) being characterized in that it comprises an electronic control unit ECU, wherein: The ECU is configured to: detecting an absolute steering angle, which is a rotation angle of a rotation shaft of the motor (21) that can be converted into a steering angle of a steering wheel (4) connected to the steering shaft (12) and is expressed as an absolute angle including a range exceeding 360°; calculating a current command value corresponding to a target value of the motor torque output from the motor (21); controlling the excitation of the motor (21) so that the actual current value supplied to the motor (21) reaches the current command value; storing an end position corresponding angle, the end position corresponding angle being an angle indicating an end position at which movement of the steering shaft (12) is restricted due to end contact of the steering shaft (12) with the housing (13) and being related to the absolute steering angle; when an end separation angle indicating a distance of the absolute steering angle from the end position corresponding angle is equal to or smaller than a predetermined angle, performing an end contact relaxation control for correcting the current command value so that a decrease in the end separation angle is restricted; determining whether the vehicle intends to turn while traveling when executing the end contact mitigation control; When it is determined that the vehicle intends to turn while traveling when the end contact relaxation control is executed, based on the steering torque input to the steering system (2), a partial release control for reducing the correction value of the current command value caused by executing the end contact relaxation control is executed; calculating a steering angle limit value that decreases as the end separation angle decreases when the end separation angle is equal to or less than the predetermined angle; executing the end contact relaxation control by limiting the absolute value of the current command value to the steering angle limit value; calculating an angle limit component that decreases as the end separation angle increases, and calculating the steering angle limit value based on a value obtained by subtracting the angle limit component from a rated current of the motor (21); as well as The angle limit component is calculated so that the angle limit component is reduced when the partial release control is executed compared to a case where the partial release control is not executed.

2. The steering control device (1) according to claim 1, characterized in that: The ECU is configured to: when executing the partial release control, using a model formula for relating the steering torque to the rotation angle, and calculating a target steering speed based on the steering torque; calculating an offset steering angle based on a value obtained by integrating the target steering speed; as well as The angle limit component is reduced based on the offset steering angle.

3. The steering control device (1) according to claim 1 or 2, characterized in that: The ECU is configured to calculate the steering angle limit value so that the steering angle limit value does not become equal to or greater than a preset limit threshold value when the partial release control is performed.

Images