Steering control device and steering control method

Abstract

A steering control device (1) comprises: a target turning corresponding-value computation unit configured so as to compute a target turning corresponding value, which is a target value of a convertible value that can be converted into the turning angle (θi) of turning wheels (3); and a control signal generation unit configured so as to generate a control signal that causes a turning unit (5) to operate on the basis of the target turning corresponding value. The target turning corresponding-value computation unit is configured so as to execute: a low-sensitivity determination process for determining whether or not a low-sensitivity condition is satisfied which makes the amount of change in the turning angle (θi) smaller than the amount of change in the operation amount (θl) of an operating lever (11); an ordinary computation process for computing the target turning corresponding value on the basis of the operation amount if the low-sensitivity condition is not satisfied; and a low-sensitivity computation process for computing, on the basis of the operation amount if the low-sensitivity condition is satisfied, a target turning corresponding value having an absolute value smaller than the target turning corresponding value computed by the ordinary computation process.

Description

[Technical Field]

[0001] The present disclosure relates to a steering control device and a steering control method. [Background technology]

[0002] Conventionally, there is a steer-by-wire steering device in which the power transmission path between an operation unit to which a steering wheel is connected and a steering unit that steers the steered wheels is separated. For example, as described in Patent Document 1, a steering control device that controls such a steering device changes the angle ratio of the steering angle of the steered wheels to the steering angle of the steering wheel depending on the driving conditions of the vehicle.

[0003] Patent Document 2 discloses a vehicle that employs a joystick in addition to or instead of a steering wheel as an operating member operated by the driver. When a joystick is used as the operating member, it is possible to reduce the amount of operation required to steer the steered wheels compared to when a steering wheel is used as the operating member, thereby improving convenience for the driver. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-30837 [Patent Document 2] Japanese Patent Application Publication No. 8-34353 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, when a joystick is used as an operating member, reducing the amount of operation required to steer the steered wheels increases the amount of change in the steering angle relative to the amount of operation. In other words, even if the amount of operation of the joystick is small, the steering angle of the steered wheels changes significantly. This makes it difficult to fine-tune the steering angle of the steered wheels. [Means for solving the problem]

[0006] One aspect of the present disclosure provides a steering control device for controlling a steering device of a vehicle. The steering device has a structure in which power transmission paths are separated between an operation unit having an operation lever and a steering unit configured to steer steered wheels. The steering control device includes a target steering corresponding value calculation unit configured to calculate a target steering corresponding value, which is a target value of a convertible value that can be converted into a steering angle of the steered wheels, and a control signal generation unit configured to generate a control signal for operating the steering unit based on the target steering corresponding value. The target steering corresponding value calculation unit is configured to execute a low-sensitivity determination process for determining whether a low-sensitivity condition is met that reduces the amount of change in the steering angle relative to a change in an operation amount of the operation lever; a normal calculation process for calculating the target steering corresponding value based on the operation amount when the low-sensitivity condition is not met; and a low-sensitivity calculation process for calculating the target steering corresponding value based on the operation amount, the target steering corresponding value having an absolute value smaller than that calculated by the normal calculation process when the low-sensitivity condition is met.

[0007] Another aspect of the present disclosure provides a steering control method for controlling a steering device of a vehicle. The steering device has a structure in which power transmission paths are separated between an operation unit having an operation lever and a steering unit configured to steer steered wheels. The steering control method includes: calculating a target steering corresponding value, which is a target value of a convertible value that can be converted into a steering angle of the steered wheels, and generating a control signal for operating the steering unit based on the target steering corresponding value. The calculating the target steering corresponding value includes executing a low-sensitivity determination process for determining whether a low-sensitivity condition is met that reduces a change in the steering angle relative to a change in an operation amount of the operation lever; a normal calculation process for calculating the target steering corresponding value based on the operation amount when the low-sensitivity condition is not met; and a low-sensitivity calculation process for calculating the target steering corresponding value, based on the operation amount, having an absolute value smaller than that of the target steering corresponding value calculated by the normal calculation process when the low-sensitivity condition is met. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic configuration diagram of a steering device according to an embodiment and a steering control device that controls the steering device; [Figure 2] FIG. 2 is a block diagram of the steering control device of FIG. 1. [Figure 3] 3A is a diagram showing an example of a normal map that the steering control device of FIG. 1 has, and FIG. 3B is a diagram showing an example of a low-sensitivity map that the steering control device of FIG. [Figure 4] 1. FIG. 4 is a flowchart showing an example of a processing procedure for calculating a target steering-corresponding angle by a target steering-corresponding angle calculation unit of the steering control device of FIG. [Figure 5] 10 is a flowchart showing an example of a processing procedure for guard processing by a guard processing unit of the steering control device of FIG. [Figure 6] 10 is a flowchart showing an example of a processing procedure for calculating an upper limit speed by a guard processing unit of the steering control device of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] An embodiment of a steering control device will be described below with reference to the drawings. (Overall composition) As shown in Fig. 1, a steering control device 1 controls a steer-by-wire steering device 2. The steering device 2 changes the traveling direction of the vehicle by steering steered wheels 3 in response to an operation by the driver. The steering device 2 includes an operation unit 4 that is operated by the driver, and a steering unit 5 that steers the steered wheels 3. The steering device 2 has a structure in which the power transmission paths between the operation unit 4 and the steering unit 5 are mechanically separated.

[0010] The operation unit 4 includes an operating lever 11 operated by the driver and a base 12 that supports the operating lever 11 so that it can tilt. In this embodiment, the base 12 supports the operating lever 11 so that it can tilt laterally, i.e., in the left-right direction, of the vehicle, and the operating lever 11 tilts in the left-right direction when operated by the driver. In other words, the amount of operation by the driver is represented by the tilt angle of the operating lever 11 (hereinafter referred to as the lever tilt angle θl). In other embodiments, the base 12 may support the operating lever 11 so that it can tilt in the front-rear direction of the vehicle.

[0011] In the illustrated example, the operation unit 4 is equipped with a tilt angle sensor 13 that detects the lever tilt angle θl. The lever tilt angle θl is detected as a positive value when the operating lever 11 is tilted to the right and a negative value when the operating lever 11 is tilted to the left, but the opposite may also be true.

[0012] The operation unit 4 further includes a sensitivity switch 14 that is operated by the driver. As will be described later, the sensitivity switch 14 is used to change the angle ratio α of the steering angle θi of the steered wheels 3 to the lever inclination angle θl of the operation lever 11 in accordance with the driver's will. The angle ratio α is a value obtained by dividing the steering angle θi by the lever inclination angle θl (α=θi / θl). A switch signal Ss indicating the on / off state of the sensitivity switch 14 is output from the sensitivity switch 14 to the steering control device 1. The sensitivity switch 14 of this embodiment is a type of switch that continuously switches between on and off states when pressed once by the driver. The sensitivity switch 14 is located on the operation lever 11, for example, but is not limited to this. It may also be located in any position that can be operated by the driver, such as on the base 12 or near the driver's seat.

[0013] The steering unit 5 includes a pinion shaft 21, a rack shaft 22 connected to the pinion shaft 21, a rack housing 23 that accommodates the rack shaft 22 so that it can reciprocate, and a rack-and-pinion mechanism 24 that has the pinion shaft 21 and the rack shaft 22. The rack-and-pinion mechanism 24 is configured such that pinion teeth 21a formed on the pinion shaft 21 mesh with rack teeth 22a formed on the rack shaft 22. As a result, the pinion shaft 21 rotates in response to the reciprocating motion of the rack shaft 22. Tie rods 26 are connected to both ends of the rack shaft 22 via ball joints 25. The ends of the tie rods 26 are connected to a knuckle (not shown) to which the steered wheels 3 are assembled.

[0014] Furthermore, steering unit 5 is equipped with steering actuator 31 that applies a steering force to rack shaft 22 that steers steerable wheels 3. In the example shown, steering actuator 31 is equipped with steering motor 32 and a power transmission mechanism 33 that transmits the torque of steering motor 32 to rack shaft 22. Power transmission mechanism 33 is equipped with a belt mechanism 34 and a ball screw mechanism 35. Steering actuator 31 transmits the rotation of steering motor 32 to ball screw mechanism 35 via belt mechanism 34, and applies the steering force to steerable wheels 3 by converting it into reciprocating motion of rack shaft 22 by ball screw mechanism 35.

[0015] In the steering device 2 configured in this manner, a steering force is applied from the steering actuator 31 in response to the driver's operation of the control lever 11. This causes the rack shaft 22 to reciprocate, changing the steering angle θi of the steered wheels 3. In other words, the steering actuator 31 steers the steered wheels 3 in response to the driver's operation.

[0016] The steering control device 1 is connected to the steering motor 32 and controls the operation of the steering motor 32. The steering control device 1 is also connected to the alarm 37 and controls the operation of the alarm 37. The alarm 37 may be a device that outputs a physical quantity that can be recognized by the driver through the five senses, such as a display panel or a speaker.

[0017] The steering control device 1 receives input of detection results from various sensors. These sensors include, for example, the inclination angle sensor 13, vehicle speed sensor 41, rotation angle sensor 42, and acceleration sensor 43. The vehicle speed sensor 41 detects the vehicle speed V, which is the traveling speed of the vehicle. The rotation angle sensor 42 detects the rotation angle θt of the rotation shaft of the steering motor 32 as a relative angle within a range of 360°. In this embodiment, the acceleration sensor 43 detects the lateral acceleration GY and vertical acceleration GZ of the vehicle. The vertical acceleration GZ is detected as an upward acceleration with a positive value and a downward acceleration with a negative value, but the opposite may also be true. In another embodiment, the acceleration sensor may detect the longitudinal acceleration of the vehicle in addition to the lateral acceleration GY and vertical acceleration GZ. In another embodiment, a lateral acceleration sensor that detects the lateral acceleration GY and a vertical acceleration sensor that detects the vertical acceleration GZ may be connected separately to the steering control device 1.

[0018] A switch signal Ss from the sensitivity switch 14 is input to the steering control device 1. Furthermore, a position signal Sp is input to the steering control device 1 from a position sensor 44 that detects the shift position of a shift lever (not shown). The shift positions include, for example, a parking position P for parking the vehicle, a reverse position R for moving the vehicle backward, and a drive position D for moving the vehicle forward. Then, the steering control device 1 controls the operation of the steering motor 32 based on the input state variables.

[0019] (Steering control device 1) The configuration of the steering control device 1 will be described in detail below. As shown in FIG. 2, the steering control device 1 includes a microcomputer 51 that outputs a control signal Mt, and a drive circuit 52 that supplies power to the steering motor 32 based on the control signal Mt.

[0020] The microcomputer 51, which is a processing circuit, can be configured as (1) one or more processors that operate according to a computer program (software), (2) one or more dedicated hardware circuits such as an application-specific integrated circuit (ASIC) that executes at least some of the various processes, or (3) a combination thereof. The processor includes a CPU and memory such as RAM and ROM, and the memory stores program code or instructions configured to cause the CPU to execute processes. Memory, i.e., non-transitory computer-readable medium, includes any available medium that can be accessed by a general-purpose or dedicated computer. Various controls by the microcomputer 51 are performed by the CPU executing programs stored in the memory at predetermined calculation cycles.

[0021] A typical PWM inverter having a plurality of switching elements such as FETs, IGBTs, etc. is employed for the drive circuit 52. The control signal Mt is a gate on / off signal that defines the on / off state of each switching element.

[0022] When microcomputer 51 outputs control signal Mt to drive circuit 52, power according to control signal Mt is supplied from the on-board power supply to steering motor 32. This causes steering motor 32 to rotate and, as described above, a steering force is applied to steered wheels 3. In this way, steering control device 1 controls the motor torque generated by steering motor 32 through the supply of power to steering motor 32, and steers steered wheels 3.

[0023] (Microcomputer 51) The configuration of the microcomputer 51 will be described in detail below. The microcomputer 51 outputs a control signal Mt by having the following control blocks execute calculation processes at predetermined calculation cycles. The vehicle speed V, lever tilt angle θl, rotation angle θt, lateral acceleration GY, vertical acceleration GZ, switch signal Ss, and position signal Sp are input to the microcomputer 51. The microcomputer 51 generates and outputs the control signal Mt based on these state variables.

[0024] In detail, microcomputer 51 includes a steering response angle calculation unit 61 that calculates the steering response angle θp, a target steering response angle calculation unit 62 that calculates a target steering response angle θp* that is a target value of the steering response angle θp, and a control signal generation unit 63 that generates a control signal Mt.

[0025] Rotation angle θt of steering motor 32 is input to steering response angle calculation unit 61. For example, steering response angle calculation unit 61 counts the number of rotations of steering motor 32 from the midpoint and calculates an integrated angle by integrating rotation angle θt with the midpoint set as zero degrees. Then, steering response angle calculation unit 61 calculates steering response angle θp by multiplying this integrated angle by a conversion coefficient based on the reduction ratio of belt mechanism 34, the lead of ball screw mechanism 35, and the rotational speed ratio of rack and pinion mechanism 24. In other words, steering response angle θp corresponds to the pinion angle, which is the rotation angle of pinion shaft 21, and the midpoint is the rotation angle of pinion shaft 21 when the vehicle is traveling straight. As described above, pinion shaft 21 rotates in response to the reciprocating motion of rack shaft 22, and therefore the rotation angle of pinion shaft 21, i.e., steering corresponding angle θp, corresponds to a steering corresponding value that is an actual value of a convertible value that can be converted into steering angle θi of steered wheels 3, and steering corresponding angle calculation unit 61 corresponds to a steering corresponding value calculation unit. The steering corresponding angle θp calculated by steering corresponding angle calculation unit 61 is output to control signal generation unit 63.

[0026] Vehicle speed V, lever tilt angle θl, lateral acceleration GY, vertical acceleration GZ, switch signal Ss, and position signal Sp are input to target turning corresponding angle calculation unit 62. Target turning corresponding angle calculation unit 62 calculates target turning corresponding angle θp*, which is a target value of the turning corresponding angle θp, based on these state variables. In other words, the target turning corresponding angle θp* corresponds to a target turning corresponding value, which is a target value of a convertible value that can be converted into the turning angle θi of the steered wheels 3, and target turning corresponding angle calculation unit 62 corresponds to a target turning corresponding value calculation unit. The calculation process of target turning corresponding angle θp* by target turning corresponding angle calculation unit 62 will be described later. Target turning corresponding angle θp* is output to control signal generation unit 63.

[0027] The vehicle speed V, lever tilt angle θl, steering response angle θp, target steering response angle θp*, and a mode signal Sm, which will be described later, are input to the control signal generation unit 63. The control signal generation unit 63 generates a control signal Mt based on these state variables.

[0028] More specifically, the control signal generating unit 63 includes a subtractor 71, a guard processing unit 72, and a feedback control unit 73. In the following description, the term feedback may be abbreviated as "F / B."

[0029] The turning corresponding angle θp and the target turning corresponding angle θp* are input to the subtractor 71. The subtractor 71 calculates the difference Δθp by subtracting the turning corresponding angle θp from the target turning corresponding angle θp*. The difference Δθp is output to the guard processing unit 72.

[0030] In addition to the difference Δθp, the guard processing unit 72 is input with the vehicle speed V, the lever tilt angle θl, and the mode signal Sm. Based on these state variables, the guard processing unit 72 calculates the difference Δθpg by limiting the difference Δθp to a difference upper limit value Δθlim or less. The difference upper limit value Δθlim is a value that is set according to the upper limit speed of the steering speed of the steered wheels 3. The guard processing of the difference Δθp by the guard processing unit 72 will be described later. The difference Δθpg after the guard processing is output to the F / B control unit 73.

[0031] The difference Δθpg after guard processing is input to F / B control section 73. F / B control section 73 calculates the target steering torque by performing F / B calculation based on the difference Δθpg. As an example, a PID control calculation is used for the F / B calculation, but the F / B calculation is not limited to this and may be a PI control calculation or the like. Then, F / B control section 73 generates a control signal Mt by using any known technology so as to cause steering motor 32 to generate the target steering torque.

[0032] As described above, difference Δθpg used in the F / B calculation is limited to not more than difference upper limit value Δθlim corresponding to the upper limit speed. Therefore, when power is supplied from drive circuit 52 to steering motor 32 in accordance with control signal Mt, steered wheels 3 are steered to a steering angle θi corresponding to target steering-related angle θp* at a steering speed not more than the upper limit speed. In other words, control signal generation unit 63 generates control signal Mt so as to keep the steering speed of steered wheels 3 not more than the upper limit speed.

[0033] (Target steering angle calculation unit 62) Next, the calculation process of the target turning-corresponding angle θp* by the target turning-corresponding angle calculation unit 62 will be described in detail.

[0034] Target turning corresponding angle calculation unit 62 executes a low-sensitivity determination process for determining whether a low-sensitivity condition is satisfied, and a prohibition determination process for determining whether a prohibition condition is satisfied. As will be described later, the low-sensitivity condition is a condition for determining whether the vehicle is in a situation where the amount of change in the turning angle θi relative to the amount of change in the lever tilt angle θl should be reduced, i.e., the angle ratio α should be reduced. The prohibition condition is a condition for determining whether the vehicle is in a situation where reducing the amount of change in the turning angle θi relative to the lever tilt angle θl should be prohibited, i.e., the angle ratio α should be prohibited.

[0035] When the low-sensitivity condition is not satisfied or the prohibition condition is satisfied, target steering corresponding angle calculation unit 62 executes normal calculation processing to calculate target steering corresponding angle θp* based on lever tilt angle θl and vehicle speed V. On the other hand, when the low-sensitivity condition is satisfied and the prohibition condition is not satisfied, target steering corresponding angle calculation unit 62 executes low-sensitivity calculation processing to calculate target steering corresponding angle θp* having an absolute value smaller than the target steering corresponding angle θp* calculated by the normal calculation processing, based on lever tilt angle θl and vehicle speed V. In other words, when the prohibition condition is satisfied, target steering corresponding angle calculation unit 62 does not execute low-sensitivity calculation processing but executes normal calculation processing to calculate target turning corresponding angle θp* even when the low-sensitivity condition is satisfied. Note that hereinafter, the state in which target steering corresponding angle calculation unit 62 calculates target turning corresponding angle θp* by normal calculation processing may be referred to as a normal mode, and the state in which target turning corresponding angle θp* is calculated by low-sensitivity calculation processing may be referred to as a low-sensitivity mode.

[0036] More specifically, the target steering-corresponding angle calculation unit 62 includes a memory 62a, which stores a normal map 81 that is normal calculation information and a low-sensitivity map 82 that is low-sensitivity calculation information.

[0037] 3A and 3B, the normal map 81 and the low-sensitivity map 82 show the relationship between the lever tilt angle θl, the vehicle speed V, and the target steering-corresponding angle θp*. In other words, the normal map 81 and the low-sensitivity map 82 are three-dimensional maps showing the relationship between the lever tilt angle θl and the vehicle speed V and the target steering-corresponding angle θp*. In the example shown, in both the normal map 81 and the low-sensitivity map 82, when the lever tilt angle θl is zero degrees, the target steering-corresponding angle θp* is zero degrees. In both the normal map 81 and the low-sensitivity map 82, the absolute value of the target steering-corresponding angle θp* increases as the absolute value of the lever tilt angle θl increases. In addition, in both the normal map 81 and the low-sensitivity map 82, the absolute value of the target steering-corresponding angle θp* increases as the vehicle speed V decreases. The amount of change in the absolute value of the target steering corresponding angle θp* with respect to the amount of change in the lever tilt angle θl and vehicle speed V in the low-sensitivity map 82 is set to be smaller than the amount of change in the absolute value of the target steering corresponding angle θp* with respect to the amount of change in the lever tilt angle θl and vehicle speed V in the normal map 81. As a result, the absolute value of the target steering corresponding angle θp* in the low-sensitivity map 82 is smaller than the absolute value of the target steering corresponding angle θp* in the normal map 81 at any lever tilt angle θl and vehicle speed V, except when the absolute value of the target steering corresponding angle θp* in the normal map 81 is zero.

[0038] In normal calculation processing, target steering corresponding angle calculation unit 62 calculates target steering corresponding angle θp* corresponding to lever tilt angle θl and vehicle speed V by referring to normal map 81. On the other hand, in low-sensitivity calculation processing, target steering corresponding angle calculation unit 62 calculates target steering corresponding angle θp* corresponding to lever tilt angle θl and vehicle speed V by referring to low-sensitivity map 82. In other words, target steering corresponding angle calculation unit 62 switches the maps used between normal calculation processing and low-sensitivity calculation processing. As a result, in low-sensitivity calculation processing, target steering corresponding angle calculation unit 62 calculates target steering corresponding angle θp* having a smaller absolute value than the target steering corresponding angle θp* calculated by normal calculation processing.

[0039] When the prohibition condition is not satisfied but the low-sensitivity condition is satisfied, target turning corresponding angle calculation unit 62 outputs a mode signal Sm indicating that the low-sensitivity mode is in effect to guard processing unit 72 and the annunciator 37. In other words, target turning corresponding angle calculation unit 62 executes annunciator processing. This mode signal Sm is configured to cause the annunciator 37 to perform an annunciator operation that indicates that target turning corresponding angle calculation unit 62 is in the low-sensitivity mode. On the other hand, when the prohibition condition is satisfied or the low-sensitivity condition is not satisfied, target turning corresponding angle calculation unit 62 outputs a mode signal Sm indicating that the normal mode is in effect to guard processing unit 72 and the annunciator 37. This mode signal Sm is configured to cause the annunciator 37 to perform an annunciator operation that indicates that target turning corresponding angle calculation unit 62 is in the normal mode. In other words, target turning corresponding angle calculation unit 62 corresponds to an annunciator control unit.

[0040] Next, the low sensitivity condition and the prohibition condition will be described. The target turning corresponding angle calculation unit 62 determines that the low sensitivity condition is met when at least one of the following conditions is met.

[0041] (a1) The vehicle speed V is equal to or greater than the high speed determination threshold Vth, and the absolute value of the lever tilt angle θl is equal to or less than the straight-travel determination threshold θlth. (a2) The vehicle speed V is equal to or greater than the high-speed determination threshold Vth, and the absolute value of the lateral acceleration GY is equal to or less than the turning determination threshold GYth.

[0042] (a3) The vehicle speed V is equal to or greater than the high-speed determination threshold Vth, and the vertical acceleration GZ is equal to or less than the inclination determination threshold GZth. (a4) The sensitivity switch 14 is in the on state.

[0043] (a5) The shift lever is in the reverse position R. The high-speed determination threshold Vth is a vehicle speed V at which it can be determined that the vehicle is traveling at high speed, and is set in advance. The straight-line determination threshold θlth is a lever tilt angle θl at which it can be determined that the operating lever 11 is not tilted, and is set in advance. The turning determination threshold GYth is a lateral acceleration GY at which it can be determined that the vehicle is not turning significantly, and is set in advance. The tilt determination threshold GZth is a vertical acceleration GZ at which it can be determined that the vehicle is traveling on a canted road, and is set in advance to a negative value.

[0044] As in (a1) to (a3), the low sensitivity conditions include conditions based on the results of comparison of threshold values ​​of driving parameters that indicate the vehicle's driving state. In (a1) to (a3), the driving parameters are vehicle speed V, lateral acceleration GY, and vertical acceleration GZ. As in (a4), the low sensitivity conditions include conditions based on the on / off state of sensitivity switch 14. As in (a5), the low sensitivity conditions include a condition that the vehicle is moving backward.

[0045] The target steering corresponding angle calculation unit 62 determines that the prohibition condition is met when the following condition is met: (b1) The operating speed ωl of the operating lever 11 is equal to or greater than the sudden operation determination threshold ωlth.

[0046] The sudden operation determination threshold ωlth is a preset operation speed ωl at which it can be determined that the driver is suddenly operating the operation lever 11. The target steering response angle calculation unit 62 of this embodiment calculates the operation speed ωl by differentiating the lever tilt angle θl. In other embodiments, a speed sensor may be provided in the operation unit 4, and the operation speed ωl may be input from the speed sensor.

[0047] Next, an example of a processing procedure in which the target turning-corresponding angle calculation unit 62 calculates the target turning-corresponding angle θp* will be described with reference to the flowchart shown in FIG. As shown in the figure, when target steering corresponding angle calculation unit 62 acquires various state variables (step 101), it calculates the operation speed ωl of operating lever 11 (step 102). Next, target steering corresponding angle calculation unit 62 determines whether the operation speed ωl is equal to or greater than abrupt operation determination threshold ωlth (step 103). If the operation speed ωl is equal to or greater than abrupt operation determination threshold ωlth (step 103: YES), it calculates target steering corresponding angle θp* using normal map 81 (step 104). Then, it outputs mode signal Sm indicating that the mode is normal (step 105), and ends the processing. The processing of step 103 corresponds to prohibition determination processing, the processing of step 104 corresponds to normal calculation processing, and the processing of step 105 corresponds to notification processing.

[0048] On the other hand, if the operation speed ωl is less than the sudden operation determination threshold ωlth (step 103: NO), target turning corresponding angle calculation unit 62 determines whether or not sensitivity switch 14 is in the ON state (step 106). If sensitivity switch 14 is in the ON state (step 106: YES), target turning corresponding angle θp* is calculated using low-sensitivity map 82 (step 107). Then, mode signal Sm indicating the low-sensitivity mode is output (step 108), and the processing ends. The processing of step 107 corresponds to low-sensitivity calculation processing, and the processing of step 108 corresponds to notification processing.

[0049] If sensitivity switch 14 is in the OFF state (step 106: NO), target turning corresponding angle calculation unit 62 determines whether or not position signal Sp indicates reverse position R (step 109). If position signal Sp indicates reverse position R (step 109: YES), the process proceeds to steps 107 and 108, where the corresponding processing is performed.

[0050] If the position signal Sp is not the reverse position R (step 109: NO), the target steering corresponding angle calculation unit 62 determines whether the vehicle speed V is equal to or greater than the high speed determination threshold Vth (step 110). If the vehicle speed V is equal to or greater than the high speed determination threshold Vth (step 110: YES), the target steering corresponding angle calculation unit 62 determines whether the absolute value of the lever tilt angle θl is equal to or less than the straight-line determination threshold θlth (step 111). If the absolute value of the lever tilt angle θl is greater than the straight-line determination threshold θlth (step 111: NO), the target steering corresponding angle calculation unit 62 determines whether the absolute value of the lateral acceleration GY is equal to or less than the turning determination threshold GYth (step 112). If the absolute value of the lateral acceleration GY is greater than the turning determination threshold GYth (step 112: NO), the target steering corresponding angle calculation unit 62 determines whether the vertical acceleration GZ is equal to or less than the negative tilt determination threshold GZth (step 113). If the vertical acceleration GZ is greater than the negative tilt determination threshold GZth (step 113: NO), the target steering corresponding angle calculation unit 62 proceeds to steps 104 and 105 and performs the corresponding processing. If the vehicle speed V is less than the high speed determination threshold Vth (step 110: NO), the process similarly proceeds to steps 104 and 105, and the corresponding processing is performed.

[0051] If the absolute value of the lever tilt angle θl is equal to or less than the straight-ahead determination threshold θlth (step 111: YES), target steering-corresponding angle calculation unit 62 proceeds to steps 107 and 108 and performs the corresponding processing. Also, if the absolute value of the lateral acceleration GY is equal to or less than the turning determination threshold GYth (step 112: YES), or if the vertical acceleration GZ is equal to or less than the negative tilt determination threshold GZth (step 113: YES), target steering-corresponding angle calculation unit 62 similarly proceeds to steps 107 and 108 and performs the corresponding processing. The processing of steps 109 to 113 corresponds to the low-sensitivity determination processing.

[0052] (Guard processing unit 72) Next, the guard processing of the difference Δθp by the guard processing unit 72 will be described. 2, the guard processing unit 72 executes an upper limit speed calculation process to set an upper limit speed of the steered wheels 3. The guard processing unit 72 also executes a difference upper limit value calculation process to calculate a difference upper limit value Δθlim according to the upper limit speed, and a guard process to limit the difference Δθp based on a comparison of the magnitude between the difference Δθp and the difference upper limit value Δθlim.

[0053] In the upper limit speed calculation process, the guard processing unit 72 of this embodiment calculates the upper limit speed in accordance with the running state of the vehicle and the operation state of the operation lever 11. More specifically, even if the lever tilt angle θl remains constant, a change in the mode of target turning-corresponding angle calculation unit 62 may cause the target turning-corresponding angle θp* to change. Taking such a situation into consideration, the guard processing unit 72 separately calculates a transition upper limit speed, which is the upper limit speed when transitioning from the normal mode to the low-sensitivity mode, and a return upper limit speed, which is the upper limit speed when returning from the low-sensitivity mode to the normal mode, based on the vehicle speed V. In other words, the transition upper limit speed and the return upper limit speed are set separately. The guard processing unit 72 determines whether the mode has switched from the normal mode to the low-sensitivity mode or from the low-sensitivity mode to the normal mode, based on the mode signal Sm.

[0054] The guard processing unit 72 calculates an upper limit steering speed, which is the upper limit speed when performing a steering operation, and an upper limit steering speed, which is the upper limit speed when performing a steering-back operation, separately based on the vehicle speed V. That is, the upper limit steering speed and the upper limit steering speed are set separately. A steering operation is an operation that increases the absolute value of the lever tilt angle θl, and a steering-back operation is an operation that decreases the absolute value of the lever tilt angle θl. The guard processing unit 72 of this embodiment determines whether a steering operation or a steering-back operation is being performed based on the amount of change in the absolute value of the lever tilt angle θl. In other embodiments, the guard processing unit 72 may determine whether a steering operation or a steering-back operation is being performed based on the amount of change in the absolute value of the steering response angle θp.

[0055] Furthermore, the guard processing unit 72 calculates a general upper limit speed, which is the upper limit speed in cases other than those mentioned above. When it is determined that the normal mode has been switched to the low-sensitivity mode, the guard processing unit 72 calculates the transition upper limit speed based on the vehicle speed V. In this embodiment, the guard processing unit 72 calculates the transition upper limit speed so that the transition upper limit speed decreases as the vehicle speed V increases, but the guard processing unit 72 may also calculate the transition upper limit speed so that the transition upper limit speed increases as the vehicle speed V increases. For example, the guard processing unit 72 is provided with a map or a function formula that indicates the relationship between the vehicle speed V and the transition upper limit speed, and calculates the transition upper limit speed according to the vehicle speed V by referring to the map or the function formula.

[0056] When it is determined that the low-sensitivity mode has been switched to the normal mode, the guard processing unit 72 calculates the upper return speed based on the vehicle speed V. In this embodiment, the guard processing unit 72 calculates the upper return speed so that the higher the vehicle speed V, the lower the upper return speed. However, the guard processing unit 72 may also calculate the upper return speed so that the higher the vehicle speed V, the higher the upper return speed. Furthermore, when the vehicle speed V is the same, the guard processing unit 72 may set the upper return speed to a value higher or lower than the transition upper speed. Then, similar to the case of calculating the transition upper speed, the guard processing unit 72 calculates the upper return speed using a map or a function formula.

[0057] When it is determined that a steering operation is being performed, the guard processing unit 72 calculates the steering upper limit speed based on the vehicle speed V. In this embodiment, the guard processing unit 72 calculates the steering upper limit speed so that the higher the vehicle speed V, the lower the steering upper limit speed; however, the guard processing unit 72 may calculate the steering upper limit speed so that the higher the vehicle speed V, the higher the steering upper limit speed. As in the case of calculating the transition upper limit speed, the guard processing unit 72 calculates the steering upper limit speed using a map or a function formula.

[0058] When it is determined that a steering-back operation is being performed, the guard processing unit 72 calculates a steering-back upper limit speed based on the vehicle speed V. In this embodiment, the guard processing unit 72 calculates the steering-back upper limit speed so that the higher the vehicle speed V, the lower the steering-back upper limit speed. However, the guard processing unit 72 may also calculate the steering-back upper limit speed so that the higher the vehicle speed V, the higher the steering-back upper limit speed. Furthermore, when the vehicle speed V is the same, the guard processing unit 72 may set the steering-back upper limit speed to a value higher or lower than the steering upper limit speed. The guard processing unit 72 calculates the steering-back upper limit speed in the same way as when calculating the transition upper limit speed.

[0059] When it is determined that the mode of target steering corresponding angle calculation unit 62 is maintained and that neither a turning operation nor a returning operation is being performed, guard processing unit 72 calculates a general upper limit speed based on vehicle speed V. In this embodiment, guard processing unit 72 sets a lower general upper limit speed as vehicle speed V increases, but it may also set a higher general upper limit speed as vehicle speed V increases. In the same way as when calculating the transition upper limit speed, guard processing unit 72 calculates the general upper limit speed.

[0060] Then, in the difference upper limit value calculation process, the guard processing unit 72 calculates a difference upper limit value Δθlim corresponding to the calculated upper limit speed, i.e., the transition upper limit speed, the return upper limit speed, the steering upper limit speed, the return upper limit speed, or the general-purpose upper limit speed. For example, the guard processing unit 72 has a map or a function formula that indicates the relationship between the upper limit speed and the difference upper limit value Δθlim, and calculates the difference upper limit value Δθlim corresponding to the calculated upper limit speed by referring to the map or the function formula.

[0061] In guard processing, the guard processing unit 72 compares the absolute value of the input difference Δθp with the calculated difference upper limit value Δθlim to determine which is larger. If the absolute value of the difference Δθp is equal to or smaller than the difference upper limit value Δθlim, the guard processing unit 72 outputs the input difference Δθp as is as the difference Δθpg after guard processing to the F / B control unit 73. On the other hand, if the absolute value of the difference Δθp is larger than the difference upper limit value Δθlim, the guard processing unit 72 maintains the sign of the input difference Δθp and outputs a value obtained by making the absolute value equal to the difference upper limit value Δθlim as the difference Δθpg after guard processing to the F / B control unit 73.

[0062] In the present embodiment, when the normal mode is changed to the low-sensitivity mode while a steering operation or a steering-back operation is being performed, the guard processing unit 72 performs guard processing using the difference upper limit value Δθlim corresponding to the transition upper limit speed. However, in other embodiments, in such cases, the guard processing may be performed using the difference upper limit value Δθlim corresponding to the steering upper limit speed or the steering-back upper limit speed. Furthermore, in the present embodiment, when the low-sensitivity mode is changed to the normal mode while a steering operation or a steering-back operation is being performed, the guard processing is performed using the difference upper limit value Δθlim corresponding to the return upper limit speed. However, in other embodiments, in such cases, the guard processing may be performed using the difference upper limit value Δθlim corresponding to the steering upper limit speed or the steering-back upper limit speed.

[0063] Next, an example of a procedure for the guard processing unit 72 to perform guard processing on the difference Δθp will be described with reference to the flowcharts shown in FIGS. As shown in Fig. 5, when the guard processing unit 72 acquires various state variables (step 201), it calculates the upper limit speed (step 202). The calculation of the upper limit speed is performed according to the flowchart shown in Fig. 6. The processing in step 202 corresponds to the upper limit speed calculation processing.

[0064] 6, the guard processing unit 72 determines whether the mode has changed from the normal mode to the low-sensitivity mode based on the mode signal Sm (step 301). If the mode has changed from the normal mode to the low-sensitivity mode (step 301: YES), the guard processing unit 72 calculates the transition upper limit speed based on the vehicle speed V (step 302).

[0065] If the mode has not changed from the normal mode to the low sensitivity mode (step 301: NO), the guard processing unit 72 determines whether the mode has changed from the low sensitivity mode to the normal mode (step 303).If the mode has changed from the low sensitivity mode to the normal mode (step 303: YES), the guard processing unit 72 calculates the upper recovery speed limit based on the vehicle speed V (step 304).

[0066] If the low sensitivity mode has not been changed to the normal mode (step 303: NO), the guard processing unit 72 determines whether or not a steering operation is being performed based on a change in the absolute value of the lever tilt angle θl (step 305). If a steering operation is being performed (step 305: YES), the guard processing unit 72 calculates an upper steering speed limit based on the vehicle speed V (step 306).

[0067] If a steering operation is not being performed (step 305: NO), the guard processing unit 72 determines whether a steering-back operation is being performed (step 307). If a steering-back operation is being performed (step 307: YES), the guard processing unit 72 calculates a steering-back upper limit speed based on the vehicle speed V (step 308). On the other hand, if a steering-back operation is not being performed (step 307: NO), the guard processing unit 72 calculates a general-purpose upper limit speed based on the vehicle speed V (step 309).

[0068] 5, after calculating the upper limit speed in step 202, the guard processing unit 72 calculates a difference upper limit value Δθlim according to the calculated upper limit speed (step 203). The processing in step 203 corresponds to the difference upper limit value calculation processing.

[0069] Next, it is determined whether the absolute value of the difference Δθp acquired in step 201 is equal to or less than the difference upper limit value Δθlim (step 204). If the absolute value of the difference Δθp is equal to or less than the difference upper limit value Δθlim (step 204: YES), the difference Δθp is output as is as the difference Δθpg after the guard processing (step 205), and the processing ends. On the other hand, if the absolute value of the difference Δθp is greater than the difference upper limit value Δθlim (step 204: NO), the sign of the acquired difference Δθp is maintained, and a value obtained by making the absolute value equal to the difference upper limit value Δθlim is output as the difference Δθpg after the guard processing (step 206), and the processing ends. The processing of steps 205 and 206 corresponds to the guard processing.

[0070] Next, the operation and effects of this embodiment will be described. (1) When the low-sensitivity condition is met, target steering-corresponding angle calculation unit 62 executes low-sensitivity calculation processing to calculate, based on lever tilt angle θl, a target steering-corresponding angle θp* having an absolute value smaller than the target steering-corresponding angle θp* calculated by normal calculation processing. Therefore, when the low-sensitivity condition is met, target steering-corresponding angle θp* is calculated to be smaller than normal. This reduces angle ratio α, making it easier to fine-tune the steering angle θi of steered wheels 3. By making fine adjustments to steering angle θi easier in this way, it is possible to easily perform operations to prevent deviation from the lane when traveling straight or operations when traveling on a gently curving canted road, for example.

[0071] (2) The target steering angle calculation unit 62 determines whether the low sensitivity condition is met based on the result of comparing the threshold value with the driving parameter indicating the vehicle driving state, and can therefore reduce the angle ratio α appropriately depending on the vehicle driving state.

[0072] (3) Steering device 2 has sensitivity switch 14 that is operated by the driver. Target steering-corresponding angle calculation unit 62 determines whether the low-sensitivity condition is met based on the on / off state of sensitivity switch 14. Therefore, angle ratio α can be reduced in accordance with the driver's intention.

[0073] (4) The target steering angle calculation unit 62 determines that the low sensitivity condition is met when the vehicle is moving backward. As a result, the angle ratio α becomes smaller while the vehicle is moving backward, so that the behavior of the vehicle is less likely to become unstable while moving backward.

[0074] (5) Target steering corresponding angle calculation unit 62 further executes prohibition determination processing to determine whether or not the prohibition condition is satisfied, and if the prohibition condition is satisfied, it executes normal calculation processing without executing low-sensitivity calculation processing even if the low-sensitivity condition is satisfied. Therefore, if the prohibition condition is satisfied, angle ratio α does not become small, and steered wheels 3 can be steered to a large extent. This allows steered wheels 3 to be steered smoothly, for example, when avoiding an obstacle ahead of the vehicle.

[0075] (6) Target steering angle calculation unit 62 determines whether the prohibition condition is met based on whether the operation speed ωl of control lever 11 is equal to or greater than sudden operation determination threshold ωlth. In many cases, a quick operation is performed when avoiding an obstacle. Therefore, for example, when avoiding an obstacle, it is possible to appropriately prohibit the angle ratio α from being reduced.

[0076] (7) Target steering corresponding angle calculation unit 62 includes memory 62a. Memory 62a stores a normal map 81 and a low-sensitivity map 82 that indicate the relationship between lever tilt angle θl and target steering corresponding angle θp*. The amount of change in the absolute value of target steering corresponding angle θp* with respect to changes in lever tilt angle θl and vehicle speed V in the low-sensitivity map 82 is set to be smaller than that in the normal map 81. The normal calculation process is a process that calculates the target steering corresponding angle θp* based on the lever tilt angle θl using the normal map 81. The low-sensitivity calculation process is a process that calculates the target steering corresponding angle θp* based on the lever tilt angle θl using the low-sensitivity map 82. In other words, target steering corresponding angle calculation unit 62 switches the maps used between the normal calculation process and the low-sensitivity calculation process. This allows target steering corresponding angle calculation unit 62 to easily calculate, in low-sensitivity mode, a target steering corresponding angle θp* with an absolute value smaller than the target steering corresponding angle θp* calculated by the normal calculation process.

[0077] (8) The control signal generator 63 generates a control signal Mt that controls the steering speed of the steered wheels 3 to be equal to or lower than the upper limit speed. This suppresses abrupt changes in the steering angle θi, thereby suppressing disturbances in the vehicle behavior.

[0078] (9) The control signal generating unit 63 includes a subtractor 71 that calculates the difference between the steering-corresponding angle θp and the target steering-corresponding angle θp*, a guard processing unit 72 that limits the absolute value of the difference Δθp to equal to or less than the difference upper limit value Δθlim that corresponds to the upper limit speed, and an F / B control unit 73 that generates a control signal Mt based on the difference after the guard processing. According to the above configuration, it is only necessary to limit the absolute value of the difference Δθp to equal to or less than the difference upper limit value Δθlim, so that the calculation load for keeping the steering speed of the steered wheels 3 equal to or less than the upper limit speed can be reduced compared to, for example, when speed F / B control is executed.

[0079] (10) The guard processing unit 72 executes an upper limit speed calculation process to calculate an upper limit speed based on the vehicle speed V. Here, even if the steering speed is the same, the likelihood of the vehicle's behavior becoming unstable varies depending on the vehicle speed V. In other words, the higher the vehicle speed V, the more likely the vehicle's behavior becomes unstable. In this regard, with the above configuration, an appropriate upper limit speed can be set depending on the vehicle speed V.

[0080] (11) The guard processing unit 72 sets the transition upper limit speed and the return upper limit speed separately. Therefore, the steering of the steered wheels 3 caused by the target steering angle calculation unit 62 switching to the normal mode or the low-sensitivity mode can be performed at an appropriate steering speed.

[0081] (12) The guard processing unit 72 sets the upper limit steering speed and the upper limit steering speed separately, so that the steered wheels 3 can be turned at an appropriate steering speed depending on whether the steering operation is being performed or not.

[0082] (13) An annunciator 37 is connected to the steering control device 1. When the target steering corresponding angle calculation unit 62 is in the low sensitivity mode, the target steering corresponding angle calculation unit 62 notifies the fact through the annunciator 37. Therefore, the driver can easily recognize whether the low sensitivity mode is in effect, i.e., whether the angle ratio α is small or not.

[0083] This embodiment can be modified as follows: This embodiment and the following modifications can be combined and implemented within the scope of technical compatibility. Although the guard processing unit 72 separately calculates the steering upper limit speed and the steering return upper limit speed, it may calculate a single upper limit speed as the upper limit speed when the control lever 11 is operated without distinguishing between steering operation and steering return operation. Also, although the guard processing unit 72 separately sets the transition upper limit speed and the return upper limit speed, it may calculate a single upper limit speed as the upper limit speed when the mode is changed. Furthermore, it may calculate only the general-purpose upper limit speed as the upper limit speed regardless of the running state of the vehicle and the operation state of the control lever 11.

[0084] At least one of the transition upper limit speed, return upper limit speed, steering upper limit speed, return upper limit speed, and general-purpose upper limit speed may be a preset fixed value instead of being a value calculated by the guard processing unit 72 based on the vehicle speed V.

[0085] The control signal generating unit 63 generates the control signal Mt such that the turning speed of the steered wheels 3 is equal to or lower than the upper limit speed by limiting the absolute value of the difference Δθp to the upper limit difference value Δθlim or lower. However, this is not limiting, and the control signal Mt may be generated such that the turning speed of the steered wheels 3 is equal to or lower than the upper limit speed by executing speed feedback control. Furthermore, the control signal generating unit 63 may generate the control signal Mt without taking the turning speed of the steered wheels 3 into consideration.

[0086] The microcomputer 51 does not have to include the steering-corresponding angle calculation unit 61. In this case, for example, the steering-corresponding angle θp, which is the rotation angle, may be input from a sensor that detects the rotation angle of the pinion shaft 21. The sensor may detect the rotation angle of the pinion shaft 21 as an absolute angle exceeding the range of 360°.

[0087] By switching between the maps used in the normal calculation processing and the low-sensitivity calculation processing, target steering corresponding angle calculation unit 62 calculates a target steering corresponding angle θp* having an absolute value smaller than the target steering corresponding angle θp* calculated by the normal calculation processing when the low-sensitivity condition is met. However, this is not limiting, and for example, the target steering corresponding angle θp* may be calculated using normal map 81 in the normal calculation processing, and the target steering corresponding angle θp* calculated using the normal map 81 may be corrected in the low-sensitivity calculation processing to calculate a target steering corresponding angle θp* having an absolute value smaller than the target steering corresponding angle θp*. As a method of correction, for example, a predetermined value may be subtracted from the target steering corresponding angle θp* calculated using the normal map 81, or the target steering corresponding angle θp* calculated using the normal map 81 may be multiplied by a gain smaller than "1".

[0088] Although target steering corresponding angle calculation unit 62 has a single low-sensitivity map 82, this is not limiting and two or more low-sensitivity maps may be provided. For example, in the case where a first low-sensitivity map and a second low-sensitivity map are provided, the second low-sensitivity map may be set so that the absolute value of target steering corresponding angle θp* with respect to lever tilt angle θl is smaller than that of the first low-sensitivity map. Target steering corresponding angle calculation unit 62 may be configured to calculate target steering corresponding angle θp* using the first low-sensitivity map when, for example, only one of (a1) to (a5) holds, and to calculate target steering corresponding angle θp* using the second low-sensitivity map when two or more of (a1) to (a5) hold.

[0089] A dead zone may be set in the normal map 81 and the low-sensitivity map 82. Specifically, a range may be set near zero degrees of the lever tilt angle θl within which the target steering-corresponding angle θp* remains zero degrees even if the absolute value of the lever tilt angle θl increases. Furthermore, the normal map 81 and the low-sensitivity map 82 may be two-dimensional maps that indicate the relationship between the target steering-corresponding angle θp* and the lever tilt angle θl. In other words, the normal calculation process and the low-sensitivity calculation process may be processes that calculate the target steering-corresponding angle θp* based only on the lever tilt angle θl. Furthermore, the normal calculation information and the low-sensitivity calculation information may not be maps but may be, for example, functional expressions.

[0090] Although the target steering corresponding angle calculation unit 62 judges the conditions (a1) to (a5) to determine whether the low sensitivity condition is satisfied, it may judge only one of these conditions. Also, it may use other conditions to determine whether the low sensitivity condition is satisfied.

[0091] The conditions (a1) to (a5) can be changed as appropriate. For example, in the condition (a2), in addition to determining whether the absolute value of the lateral acceleration GY is equal to or less than the turning determination threshold GYth, it is also possible to determine whether the absolute value of the vehicle's yaw rate is equal to or less than the turning determination threshold GYth. Furthermore, the high speed determination thresholds Vth in (a1) to (a3) ​​may be different values.

[0092] Although the target turning response angle calculation unit 62 judges the condition (b1) to determine whether the prohibition condition is satisfied, other conditions may be used in addition to or instead of this. Such other conditions may be, for example, input of a signal indicating that the driver has performed a sudden braking operation. Furthermore, the target turning response angle calculation unit 62 does not have to judge whether the prohibition condition is satisfied.

[0093] The processing procedure by target steering corresponding angle calculation unit 62 is not limited to the procedure shown in Fig. 4 and can be changed as appropriate. For example, after various state variables are acquired (step 101), target steering corresponding angle θp* may be calculated (step 104) immediately using normal map 81, and if the low-sensitivity condition is met, the calculated target steering corresponding angle θp* may be changed to a value based on low-sensitivity map 82. Similarly, the processing procedure by guard processing unit 72 is not limited to the procedure shown in Figs. 5 and 6 and can be changed as appropriate.

[0094] In the above embodiment, the convertible value that can be converted into the steering angle θi of the steered wheels 3 is the rotation angle of the pinion shaft 21. However, this is not limited to this. For example, the convertible value may be the stroke amount of the rack shaft 22 or the steering angle θi itself.

[0095] The sensitivity switch 14 may be a type of switch that is switched to the on state only while the driver is pressing it. The sensitivity switch 14 may also be a dial-type multi-stage switch that can be switched to three or more states. Such a multi-stage switch is preferably used when the target steering-corresponding angle calculation unit 62 has multiple low-sensitivity maps. Furthermore, the steering device 2 does not necessarily have to have the sensitivity switch 14.

[0096] The microcomputer 51 may be provided with a separate notification control unit that determines whether the low-sensitivity condition or the prohibition condition is met, similar to the target steering corresponding angle calculation unit 62, and this notification control unit may notify the fact that the low-sensitivity mode is being used via the annunciator 37. Also, the microcomputer 51 may not necessarily notify the fact that the low-sensitivity mode is being used.

[0097] Although the operating lever 11 is tiltably supported on the base 12, the present invention is not limited to this and may be supported, for example, slidably with respect to the base 12. In this case, the amount of operation by the driver is represented by the amount of sliding of the operating lever 11. The operating lever 11 may be used to control the driving / braking of the vehicle in addition to controlling the steering angle θi of the steered wheels 3.

[0098] The operation unit 4 may be equipped with a motor and / or a spring that applies a reaction force to the operation lever 11 in response to the driver's operation. In a configuration in which a reaction force is applied by a motor, the lever inclination angle θl may be detected based on the rotation angle of the motor. Furthermore, the operation unit 4 may be equipped with a steering wheel operated by the driver in addition to the operation lever 11. The steering device 2 has a linkless structure in which power transmission between the operation unit 4 and the steering unit 5 is separated, but this is not limited to this. If a steering wheel is provided, the steering device 2 may be equipped with a structure in which power transmission between the operation unit 4 and the steering unit 5 can be separated by a clutch.

[0099] In the above embodiment, steering actuator 31 transmits the rotation of steering motor 32 to ball screw mechanism 35 via belt mechanism 34, but this is not limiting, and steering actuator 31 may be configured, for example, so that the rotation of steering motor 32 is transmitted to ball screw mechanism 35 via a gear mechanism. Also, steering actuator 31 may be configured so that steering motor 32 directly rotates ball screw mechanism 35. Furthermore, steering unit 5 may be configured to include a second rack-and-pinion mechanism, and steering actuator 31 may be configured so that the rotation of steering motor 32 is converted into reciprocating motion of rack shaft 22 by the second rack-and-pinion mechanism, thereby applying a steering force to steering unit 5.

[0100] Next, the technical ideas that can be understood from the above-described embodiment and modifications will be described below. (i) The low sensitivity condition may include a straight-ahead condition including that the vehicle speed, which is the travel parameter, is equal to or greater than a high-speed determination threshold, and the absolute value of the operation amount is equal to or less than a straight-ahead determination operation amount.

[0101] (b) The low sensitivity condition may include a turning condition in which the vehicle speed, which is the driving parameter, is equal to or greater than a high speed determination threshold, and the absolute value of the yaw rate or lateral acceleration of the vehicle, which is the driving parameter, is equal to or less than a turning determination threshold.

[0102] (c) The vertical acceleration of the vehicle may be detected with upward acceleration being a positive value and downward acceleration being a negative value, and the low sensitivity condition may include a slope condition in which the vehicle speed, which is the driving parameter, is equal to or greater than a high speed determination threshold, and the vertical acceleration, which is the driving parameter, is equal to or less than a negative slope determination threshold.

Claims

1. A steering control device that controls a steering device of a vehicle, the steering device has a structure in which a power transmission path between an operation unit having an operation lever and a steering unit configured to steer steered wheels is separated, The steering control device includes: a target steering corresponding value calculation unit configured to calculate a target steering corresponding value which is a target value of a convertible value which can be converted into a steering angle of the steered wheels; a control signal generating unit configured to generate a control signal for operating the steering unit based on the target steering corresponding value, The target steering corresponding value calculation unit a low-sensitivity determination process for determining whether a low-sensitivity condition is satisfied that reduces the amount of change in the steering angle relative to the amount of change in the operation amount of the operating lever; a normal calculation process for calculating the target steering corresponding value based on the operation amount when the low sensitivity condition is not satisfied; a low-sensitivity calculation process for calculating, when the low-sensitivity condition is established, the target steering corresponding value having an absolute value smaller than that of the target steering corresponding value calculated by the normal calculation process, based on the operation amount; The target steering corresponding value calculation unit further executing a prohibition determination process for determining whether a prohibition condition is satisfied that prohibits the amount of change in the steering angle relative to the amount of change in the operation amount from being reduced; A steering control device configured to execute the normal calculation process without executing the low-sensitivity calculation process when the prohibition condition is satisfied, even when the low-sensitivity condition is satisfied.

2. The steering control device according to claim 1, A steering control device, wherein the low sensitivity condition includes a condition based on a result of comparing a driving parameter indicating the driving state of the vehicle with a threshold value.

3. The steering control device according to claim 1 or 2, the steering device has a sensitivity switch configured to be operated by a driver; A steering control device, wherein the low sensitivity condition includes a condition based on an on / off state of the sensitivity switch.

4. The steering control device according to any one of claims 1 to 3, A steering control device, wherein the low sensitivity condition includes a condition in which the vehicle is moving backward.

5. The steering control device according to any one of claims 1 to 4, The prohibition condition includes a condition that the operation speed of the operation lever is greater than an abrupt operation determination threshold.

6. The steering control device according to any one of claims 1 to 5, The target steering corresponding value calculation unit includes a memory, the memory stores normal calculation information and low-sensitivity calculation information indicating a relationship between the operation amount and the target steering corresponding value, a change amount in the absolute value of the target steering corresponding value with respect to a change amount in the operation amount in the low-sensitivity calculation information is set to be smaller than that in the normal calculation information, the normal calculation processing is processing for calculating the target steering corresponding value based on the operation amount using the normal calculation information, A steering control device, wherein the low-sensitivity calculation process is a process of calculating the target steering corresponding value based on the operation amount using the low-sensitivity calculation information.

7. The steering control device according to any one of claims 1 to 6, A steering control device, wherein the control signal generation unit is configured to generate the control signal that controls the steering speed of the steered wheels to be equal to or lower than an upper limit speed.

8. The steering control device according to claim 7, The control signal generation unit a subtractor configured to calculate a difference between a steering corresponding value, which is an actual value of the convertible value, and the target steering corresponding value; a guard processing unit configured to execute a guard process for limiting the absolute value of the difference to a difference upper limit value corresponding to the upper speed limit; a feedback control unit configured to generate the control signal based on the difference after the guard processing.

9. The steering control device according to claim 8, A steering control device, wherein the guard processing unit is configured to further execute upper limit speed calculation processing for calculating the upper limit speed based on a vehicle speed.

10. The steering control device according to any one of claims 7 to 9, modes of the target steering corresponding value calculation unit include a normal mode in which the target steering corresponding value is calculated by executing the normal calculation processing, and a low-sensitivity mode in which the target steering corresponding value is calculated by executing the low-sensitivity calculation processing, the upper limit speed includes a transition upper limit speed that is the upper limit speed when transitioning from the normal mode to the low sensitivity mode, and a return upper limit speed that is the upper limit speed when returning from the low sensitivity mode to the normal mode, A steering control device, wherein the transition upper limit speed and the return upper limit speed are set individually.

11. The steering control device according to any one of claims 7 to 10, the upper limit speed includes a turning upper limit speed, which is the upper limit speed when a turning operation is performed to increase the absolute value of the operation amount, and a return upper limit speed, which is the upper limit speed when a return operation is performed to decrease the absolute value of the operation amount, A steering control device, wherein the upper limit steering speed and the upper limit steering speed are set individually.

12. A steering control device according to any one of claims 1 to 11, An alarm is connected to the steering control device, The steering control device further includes a notification control unit configured to notify the user through the alarm when the mode of the target steering corresponding value calculation unit is a low-sensitivity mode in which the target steering corresponding value is calculated by executing the low-sensitivity calculation process.

13. A steering control method for controlling a steering device of a vehicle, comprising: the steering device has a structure in which a power transmission path between an operation unit having an operation lever and a steering unit configured to steer steered wheels is separated, The steering control method includes: Calculating a target steering corresponding value which is a target value of a convertible value which can be converted into a steering angle of the steered wheels; generating a control signal for operating the steering unit based on the target steering corresponding value, Calculating the target steering corresponding value a low-sensitivity determination process for determining whether a low-sensitivity condition is satisfied that reduces the amount of change in the steering angle relative to the amount of change in the operation amount of the operating lever; a normal calculation process for calculating the target steering corresponding value based on the operation amount when the low sensitivity condition is not satisfied; a low-sensitivity calculation process for calculating, when the low-sensitivity condition is satisfied, the target steering corresponding value having an absolute value smaller than the target steering corresponding value calculated by the normal calculation process, based on the operation amount; Calculating the target steering corresponding value further executing a prohibition determination process for determining whether a prohibition condition is satisfied that prohibits the amount of change in the steering angle from being reduced relative to the amount of change in the operation amount, When the prohibition condition is satisfied, the normal calculation process is executed without executing the low-sensitivity calculation process even when the low-sensitivity condition is satisfied.

14. (delete)

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