Steering control device

Abstract

A steering control device (1) controls a steering device (2). The steering device includes a turning shaft (22) and a turning motor (31). The steering control device executes processing for controlling the turning motor and processing for correcting a target angle (θp *) of an angle (θp) that can be converted into a turning angle of a turning wheel. The processing for correcting the target angle includes processing for calculating a restriction value (θL1) with respect to the target angle so that, when, in a stopped state or an extremely low speed region, the target angle increases toward a limit value of the angle region in which the maximum turning force that the turning motor can generate and the axial force generated in the turning shaft can maintain the balance of forces, the degree of increase in the target angle becomes gentler as the target angle approaches the limit value. The restriction value is represented by a function including an intercept (a0) that changes according to a vehicle speed (V) on a coordinate plane of the target angle and the restriction value.

Description

Steering control device

[0001] The present disclosure relates to a steering control device.

[0002] Conventionally, there is a so-called steer-by-wire type steering device that separates the power transmission between the steering wheel and the steering wheel. For example, the steering device described in Patent Document 1 has a reaction force motor that is a source of the steering reaction force applied to the steering shaft, and a steering motor that is a source of the steering force that steers the steering wheel. When the vehicle is running, the control device of the steering device generates a steering reaction force through power supply control for the reaction force motor, and steers the steering wheel through power supply control for the steering motor.

[0003] Japanese Patent Application Laid-Open No. 2014-133521

[0004] In a conventional general steer-by-wire type steering device including that of Patent Document 1, when the steering wheel is operated by a driver, the steering wheel steers while maintaining the balance between the steering force generated by the steering motor and the axial force generated in the steering shaft.

[0005] However, when an axial force exceeding the maximum steering force that can be generated by the steering motor is generated, it becomes difficult to maintain the balance between the steering force generated by the steering motor and the axial force acting on the steering shaft depending on the axial force characteristics of the vehicle. For this reason, there is a possibility that it may be difficult to smoothly steer the steering wheel according to the steering state of the steering wheel.

[0006] A steering control device according to one aspect of the present disclosure is configured to control a steering device in which the power transmission between the steered wheels of a vehicle and the steering wheel is separated. The steering device includes a steering shaft that steers the steered wheels and a steering motor configured to generate a steering force applied to the steering shaft. The steering control device has a steering control unit. The steering control unit performs a process of controlling the steering motor so that an angle convertible to the steering angle of the steered wheels follows a target angle calculated according to the steering state of the steering wheel, and a process of correcting the target angle so that the maximum steering force that can be generated by the steering motor and the axial force generated in the steering shaft become angles within an angular region where the balance of forces can be maintained. The process of correcting the target angle includes a process of calculating a limit value for the target angle so that when the target angle increases toward the limit value of the angular region in a stopped state or at an extremely low speed range, the degree of increase of the target angle gradually becomes gentle as the target angle approaches the limit value. The limit value is represented by a function including a section that changes according to the vehicle speed on the coordinate plane of the target angle and the limit value.

[0007] It is a configuration diagram of a steering device in which an embodiment of a steering control device is mounted. FIG. 2 is a block diagram of the steering control device of FIG. 1. FIG. 3 is a block diagram of the correction processing unit of FIG. 2. FIG. 4 is a block diagram of the limit value calculation unit of FIG. 3. FIG. 5 is a graph defining the relationship between the vehicle speed and the section. FIG. 6 is a graph defining the relationship between the target pinion angle at the time of stopping and the first limit value. FIG. 7 is a graph defining the relationship between the target pinion angle during traveling and the first limit value. FIG. 8 is a diagram for explaining the correction process of the target pinion angle. The graph of (a) shows the change over time of the vehicle speed, the graph of (b) shows the change over time of the steering angle, and the graph of (c) shows the change over time of the target pinion angle. FIG. 9 is a diagram for explaining the offset process of the target pinion angle. The graph of (a) shows the change over time of the vehicle speed, the graph of (b) shows the change over time of the steering angle, and the graph of (c) shows the change over time of the target pinion angle.

[0008] The steering control device 1 according to an embodiment will be described. <Overall configuration> As shown in FIG. 1, the control target of the steering control device 1 is a steer-by-wire type steering device 2. The steering device 2 has a steering mechanism 3 and a steering gear mechanism 4. The steering mechanism 3 is a mechanism part that is steered by a driver via a steering wheel 5. The steering gear mechanism 4 is a mechanism part that steers the steering wheels 6 of a vehicle in response to the steering of the steering wheel 5. The steering control device 1 includes a reaction force control device 1A and a steering gear control device 1B. The control target of the reaction force control device 1A is the steering mechanism 3. The reaction force control device 1A executes reaction force control. The reaction force control device 1A corresponds to a reaction force control unit. The control target of the steering gear control device 1B is the steering gear mechanism 4. The steering gear control device 1B executes steering gear control. The steering gear control device 1B corresponds to a steering gear control unit.

[0009] The steering mechanism 3 has a steering shaft 11, a reaction force motor 12, and a speed reducer 13. The steering wheel 5 is integrally rotatably connected to the steering shaft 11. The reaction force motor 12 is a source of the steering reaction force applied to the steering shaft 11. The steering reaction force is a force in a direction opposite to the steering direction of the steering wheel 5. The reaction force motor 12 is, for example, a three-phase brushless motor. The speed reducer 13 reduces the rotation of the reaction force motor 12 and transmits the reduced rotation to the steering shaft 11.

[0010] The steering gear mechanism 4 has a pinion shaft 21, a steering shaft 22, and a housing 23. The housing 23 rotatably supports the pinion shaft 21. Further, the housing 23 reciprocally accommodates the steering shaft 22. The power transmission between the steering shaft 22 and the steering wheel 5 is separated. The pinion shaft 21 is provided so as to intersect the steering shaft 22. The pinion teeth 21a of the pinion shaft 21 mesh with the rack teeth 22a of the steering shaft 22. Tie rods 25 are connected to both ends of the steering shaft 22 via rack ends 24 each formed of a ball joint. The tip of each tie rod 25 is connected to a knuckle (not shown) to which the steering wheel 6 is assembled.

[0011] The steering mechanism 4 includes a steering motor 31, a transmission mechanism 32, and a conversion mechanism 33. The steering motor 31 is a source of the steering force applied to the steering shaft 22. The steering force is a force for steering the steering wheel 6. The steering motor 31 is, for example, a three-phase brushless motor. The transmission mechanism 32 is, for example, a belt transmission mechanism. The transmission mechanism 32 transmits the rotation of the steering motor 31 to the conversion mechanism 33. The conversion mechanism 33 is, for example, a ball screw mechanism. The conversion mechanism 33 converts the rotation transmitted via the transmission mechanism 32 into the axial movement of the steering shaft 22.

[0012] When the steering shaft 22 moves axially, the steering angle θ of the steering wheel 6 ｗ is changed. Since the pinion teeth 21a of the pinion shaft 21 mesh with the rack teeth 22a of the steering shaft 22, the pinion shaft 21 rotates in conjunction with the movement of the steering shaft 22. The pinion shaft 21 is a shaft that rotates in conjunction with the steering operation of the steering wheel 6.

[0013] The reaction force control device 1A controls the operation of the reaction force motor 12. The reaction force control device 1A has a processing circuit including any one of the following three configurations A1, A2, and A3. A1. One or more processors that operate according to a computer program which is software. The processor includes a CPU (central processing unit) and a memory.

[0014] A2. One or more dedicated hardware circuits such as an application-specific integrated circuit (ASIC) that executes at least some of various processes. The ASIC includes a CPU and a memory.

[0015] A3. A hardware circuit combining configurations A1 and A2. The memory is a computer-readable medium that stores a program describing processes or instructions for the computer. In the present embodiment, the computer is a CPU. The memory includes a RAM (random access memory) and a ROM (read only memory). The CPU executes various controls by executing the program stored in the memory at a defined operation cycle.

[0016] The reaction force control device 1A captures the detection results of in-vehicle sensors. The sensors include a vehicle speed sensor 41, a torque sensor 42, and a rotation angle sensor 43. The vehicle speed sensor 41 detects the vehicle speed V. The vehicle speed V is a state variable that reflects the running state of the vehicle. The torque sensor 42 is provided on the steering shaft 11. The torque sensor 42 is located on the steering wheel 5 side with respect to the connection portion of the reduction gear 13 in the steering shaft 11. The torque sensor 42 detects the steering torque T ｈ applied to the steering shaft 11. The steering torque T ｈ is calculated based on the amount of twist of the torsion bar 42a provided on the steering shaft 11. The steering torque T ｈ is a state variable that reflects the steering state of the steering wheel 5. The rotation angle sensor 43 is provided on the reaction force motor 12. The rotation angle sensor 43 detects the rotation angle θ ａ of the reaction force motor 12.

[0017] The steering torque T ｈ , and the rotation angle θ ａ of the reaction force motor 12 are, for example, positive values when the steering wheel 5 is steered to the right, and negative values when the steering wheel 5 is steered to the left.

[0018] The reaction force control device 1A controls the operation of the reaction force motor 12 using the detection results of the vehicle speed sensor 41, the torque sensor 42, and the rotation angle sensor 43. The reaction force control device 1A controls the power supply to the reaction force motor 12 so as to generate a steering reaction force corresponding to the steering torque T ｈ in the reaction force motor 12.

[0019] The steering control device 1B controls the operation of the steering motor 31. Similar to the reaction force control device 1A, the steering control device 1B has a processing circuit including any one of the three previous configurations A1, A2, and A3.

[0020] The steering control device 1B captures the detection results of in-vehicle sensors. The sensors include a rotation angle sensor 44. The rotation angle sensor 44 is provided on the steering motor 31. The rotation angle sensor 44 detects the rotation angle θ ｂ of the steering motor 31. The rotation angle θ ｂ of the steering motor 31 is, for example, a positive value when the steering wheel 5 is steered to the right, and a negative value when the steering wheel 5 is steered to the left.

[0021] The steering control device 1B uses the detection results of the rotation angle sensor 44 to control the operation of the steering motor 31. The steering control device 1B controls the power supply to the steering motor 31 so that the steered wheels 6 are steered according to the steering state of the steering wheel 5.

[0022] <Configuration of the reaction force control device 1A> Next, the configuration of the reaction force control device 1A will be described. As shown in FIG. 2, the reaction force control device 1A includes a steering angle calculation unit 51, a reaction force torque command value calculation unit 52, and a power supply control unit 53.

[0023] The steering angle calculation unit 51 calculates the steering angle θ ａ of the steering wheel 5 based on the rotation angle θ ｓ of the reaction force motor 12 detected through the rotation angle sensor 43. The steering angle θ ｓ is the rotation angle of the steering wheel 5 with respect to the neutral position of the steering wheel 5. The neutral position is the rotation position of the steering wheel 5 corresponding to the straight-ahead state of the vehicle.

[0024] The reaction force torque command value calculation unit 52 calculates a reaction force torque command value T ｈ based on the steering torque T ＊ and the vehicle speed V. The reaction force torque command value T ＊ is the target value of the steering reaction force to be generated in the reaction force motor 12. The steering reaction force is a torque in the direction opposite to the steering direction of the steering wheel 5. The larger the absolute value of the steering torque T ｈ , and the slower the vehicle speed V, the larger the absolute value of the reaction force torque command value T ＊ .

[0025] The power supply control unit 53 is the reaction force torque command value T＊ Supply power corresponding to the reaction force motor 12. Specifically, the energization control unit 53 calculates a current command value for the reaction force motor 12 based on the reaction torque command value T ＊ The energization control unit 53 detects the value of the current I generated in the power supply path through the current sensor 54 provided in the power supply path for the reaction force motor 12. The value of the current I ａ is the value of the current supplied to the reaction force motor 12. The energization control unit 53 obtains the deviation between the current command value and the value of the current I ａ and controls the power supply to the reaction force motor 12 so as to eliminate the deviation. As a result, the reaction force motor 12 generates a torque corresponding to the reaction torque command value T ａ ＊

[0026] <Configuration of the steering control device 1B> Next, the configuration of the steering control device 1B will be described. As shown in FIG. 2, the steering control device 1B includes a pinion angle calculation unit 61, a target pinion angle calculation unit 62, a pinion angle feedback control unit 63, and an energization control unit 64

[0027] The pinion angle calculation unit 61 calculates the pinion angle θ ｂ based on the rotation angle θ of the steering motor 31 detected through the rotation angle sensor 43. The pinion angle θ ｐ is the rotation angle of the pinion shaft 21 and corresponds to the actual angle, which is the actual angle of the pinion shaft 21. The steering motor 31 and the pinion shaft 21 are interlocked via a transmission mechanism 32, a conversion mechanism 33, and a steering shaft 22. Therefore, there is a correlation between the rotation angle θ ｐ of the steering motor 31 and the pinion angle θ ｂ Using this correlation, the pinion angle θ ｐ can be obtained from the rotation angle θ ｂ of the steering motor 31. The pinion shaft 21 is meshed with the steering shaft 22. Therefore, there is also a correlation between the pinion angle θ ｐ and the movement amount of the steering shaft 22. That is, the pinion angle θ ｐ is a state variable that reflects the steering angle θ ｐ of the steering wheel 6, that is, the steering state of the steering wheel 6 ｗ ​​​

[0028] The target pinion angle calculation unit 62 calculates a target pinion angle θ ｓ based on the steering angle θ ｐ ＊ calculated by the steering angle calculation unit 51. The target pinion angle θ ｐ ＊ is the target angle of the pinion angle θ ｐ The target pinion angle calculation unit 62 calculates the target pinion angle θ ｐ ＊ so that a steering angle ratio set according to product specifications or the like is achieved. The steering angle ratio is the ratio of the steering angle θ ｓ to the steering angle θ ｗ of the steering wheel.

[0029] The target pinion angle calculation unit 62, for example, sets a steering angle ratio according to the running state of the vehicle such as the vehicle speed V, and calculates the target pinion angle θ ｐ ＊ according to the set steering angle ratio. The target pinion angle calculation unit 62 calculates the target pinion angle θ ｓ so that the steering angle θ ｗ of the steering wheel increases as the vehicle speed V decreases. The target pinion angle calculation unit 62 calculates the target pinion angle θ ｐ ＊ so that the steering angle θ ｓ of the steering wheel decreases as the vehicle speed V increases. The target pinion angle calculation unit 62 calculates a correction angle for the steering angle θ ｗ in order to achieve the steering angle ratio set according to the running state of the vehicle, and adds the calculated correction angle to the steering angle θ ｐ ＊ to calculate the target pinion angle θ ｓ ｓ corresponding to the steering angle ratio. ｐ ＊ ｐ ＊

[0030] Note that depending on product specifications or the like, the target pinion angle calculation unit 62 may calculate the target pinion angle θ ｐ ＊ so that the steering angle ratio becomes "1:1" regardless of the running state of the vehicle.

[0031] The pinion angle feedback control unit 63 takes in the target pinion angle θ calculated by the target pinion angle calculation unit 62 ｐ ＊ , and the pinion angle θ calculated by the pinion angle calculation unit 61 ｐ . The pinion angle feedback control unit 63 calculates the steering torque command value T ｐ through feedback control of the pinion angle θ ｐ ＊ so that it follows the target pinion angle θ ｐ . The steering torque command value T ｐ ＊ is a command value for the torque generated by the steering motor 31 and is the target value of the steering force. ｐ ＊

[0032] The energization control unit 64 supplies power corresponding to the steering torque command value T ｐ ＊ to the steering motor 31. Specifically, the energization control unit 64 calculates a current command value for the steering motor 31 based on the steering torque command value T ｐ ＊ . The energization control unit 64 detects the value of the current I ｂ that occurs in the power supply path through the current sensor 65 provided in the power supply path for the steering motor 31. The value of the current I ｂ is the value of the current supplied to the steering motor 31. The energization control unit 64 obtains the deviation between the current command value and the value of the current I ｂ and controls the power supply to the steering motor 31 so as to eliminate the deviation. Thereby, the steering motor 31 generates a torque corresponding to the steering torque command value T ｐ ＊ .

[0033] <Regarding insufficient steering force> Here, in the steer-by-wire type steering device 2, when the steering wheel 5 is operated by the driver, the steering force generated by the steering motor 31 and the axial force acting on the steering shaft 22 steer while maintaining the balance of forces.

[0034] ​However, if an axial force exceeding the maximum output of steering motor 31 is generated, it becomes difficult to maintain a balance between the steering force generated by steering motor 31 and the axial force acting on steering shaft 22. The maximum output of steering motor 31 is the maximum steering force that steering motor 31 can generate. This may make it difficult to smoothly steer steered wheels 6 in accordance with the steering state of steering wheel 5.

[0035] For example, when the steered wheels 6 are steered while the vehicle is stopped, i.e., when stationary steering is performed, a larger axial force is likely to be generated. This may make it difficult to steer the steered wheels 6 to the end position or from the end position toward the neutral position. The end position is the limit position of the physical range of movement of the steered wheels 6. The neutral position is the position of the steered wheels 6 that corresponds to the straight-ahead state of the vehicle.

[0036] Therefore, in this embodiment, in order to prevent the generation of an axial force exceeding the maximum output of the steering motor 31 and to steer the steered wheels 6 more smoothly, the following configuration is adopted as the steering control device 1B.

[0037] <Correction processing unit 66> As shown in Figure 2, turning control device 1B has correction processing unit 66. Correction processing unit 66 is provided on the calculation path between target pinion angle calculation unit 62 and pinion angle feedback control unit 63.

[0038] The correction processing unit 66 calculates the target pinion angle θ calculated by the target pinion angle calculation unit 62. ｐ ＊ Specifically, correction processing section 66 corrects target pinion angle θ that allows the balance between the maximum output of steering motor 31 and the axial force to be maintained. ｐ ＊ The target pinion angle θ is set to an angle within the maximum steering range defined as the range ｐ ＊ The final target pinion angle θ is supplied to the pinion angle feedback control unit 63. ｐ ＊ is the angle within the maximum steering range.

[0039] 3, the correction processing unit 66 includes a limit value calculation unit 71, a determination unit 72, a switching processing unit 73, a limit processing unit 74, and an offset processing unit 75. The limit value calculation unit 71 calculates the target pinion angle θ calculated by the target pinion angle calculation unit 62. ｐ ＊ and the vehicle speed V detected by the vehicle speed sensor 41. The limit value calculation unit 71 calculates the target pinion angle θ ｐ ＊ and the target pinion angle θ based on the vehicle speed V. ｐ ＊ The first limit value θ Ｌ１ Calculate the target pinion angle θ ｐ ＊ The range of change of the first limit value θ Ｌ１ The first limit value θ Ｌ１ is a target pinion angle θ that can maintain a balance between the maximum output and axial force of the steering motor 31 in accordance with the axial force characteristics of the vehicle when, for example, the vehicle speed V is within an extremely low speed range. ｐ ＊ The extremely low speed range is, for example, a speed range below 5 km / h.

[0040] Incidentally, the axial force when the steered wheels 6 are steered while the vehicle is stopped, or the axial force when the steered wheels 6 are steered when the vehicle speed V is within the extremely low speed range, is significantly larger than the axial force when the steered wheels 6 are steered when the vehicle speed V exceeds the extremely low speed range. In other words, the axial force when the steered wheels 6 are steered when the vehicle speed V exceeds the extremely low speed range is significantly smaller than the axial force when the steered wheels 6 are steered when the vehicle speed is within the extremely low speed range.

[0041] The determination unit 72 determines the first limit value θ calculated by the limit value calculation unit 71. Ｌ１The determination unit 72 determines whether the vehicle speed state signal S1 should be enabled or disabled. The determination unit 72 receives a vehicle speed state signal S1. The vehicle speed state signal S1 is an electrical signal indicating the state of the vehicle speed V detected through the vehicle speed sensor 41. The vehicle speed V is a state variable that reflects the traveling state of the vehicle. The vehicle speed state signal S1 is generated, for example, by an abnormality determination unit mounted on the vehicle. If no abnormality or malfunction of the vehicle speed sensor 41 is detected, the abnormality determination unit generates a vehicle speed state signal S1 indicating that the vehicle speed V is normal. If an abnormality or malfunction of the vehicle speed sensor 41 is detected, the abnormality determination unit generates a vehicle speed state signal S1 indicating that the vehicle speed V is abnormal.

[0042] The determination unit 72 sets the value of flag F1 based on the vehicle speed state signal S1. The determination unit 72 determines whether the vehicle speed V is normal or not based on the vehicle speed state signal S1. If the vehicle speed V is normal, the determination unit 72 sets the value of flag F1 to "1." If the vehicle speed V is abnormal, the determination unit 72 sets the value of flag F1 to "0."

[0043] The switching processing unit 73 is configured to change the first limit value θ calculated by the limit value calculation unit 71. Ｌ１ and a second limit value θ, which is a fixed value stored in the storage device of the steering control device 1B. Ｌ２ The second limit value θ Ｌ２ is, for example, a target pinion angle θ that can maintain a balance between the maximum output of the steering motor 32 and the axial force in accordance with the axial force characteristics of the vehicle. ｐ ＊ That is, the second limit value θ Ｌ２ is a target pinion angle θ at which the steered wheels 6 can be steered by the steering motor 31 while the vehicle is running. ｐ ＊ is the maximum value in the range.

[0044] The switching processing unit 73 determines the first limit value θ in accordance with the value of the flag F1 set by the determination unit 72. Ｌ１ and the second limit value θ Ｌ２ One of the two is the final limit value θ Ｌ３ That is, the switching processing unit 73 selects the final limit value θ Ｌ３ the first limit value θ Ｌ１and the second limit value θ Ｌ２ When the value of the flag F1 is "1", that is, when the vehicle speed V is normal, the switching processing unit 73 switches between the final limit value θ Ｌ３ The first limit value θ Ｌ１ When the value of the flag F is "0", that is, when the vehicle speed V is abnormal, the switching processing unit 73 selects the final limit value θ Ｌ３ The second limit value θ Ｌ２ Select .

[0045] The limiting processing unit 74 limits the target pinion angle θ calculated by the target pinion angle calculation unit 62. ｐ ＊ and the final limit value θ selected by the switching processing unit 73. Ｌ３ The limiting processing unit 74 takes in the final limiting value θ Ｌ３ Based on the target pinion angle θ ｐ ＊ That is, the limiting processing unit 74 performs limiting processing on the target pinion angle θ ｐ ＊ Absolute value of and final limit value θ Ｌ３ The limiting processor 74 compares the target pinion angle θ ｐ ＊ The absolute value of the final limit value θ Ｌ３ If it exceeds the target pinion angle θ ｐ ＊ The absolute value of the final limit value θ Ｌ３ The limited target pinion angle θ ｐ ＊ is the target pinion angle θ after limiting processing ｐ ＊ In response to this, the limiting processing unit 74 limits the target pinion angle θ ｐ ＊ The absolute value of the final limit value θ Ｌ３ If the target pinion angle θ is ｐ ＊ In this case, the absolute value of the target pinion angle θ calculated by the target pinion angle calculation unit 62 is not limited. ｐ ＊ is the target pinion angle θ after limiting processing. ｐ ＊ This becomes:

[0046] The offset processing unit 75 calculates the target pinion angle θ after the limiting process. ｐ ＊ and the offset request signal S2. The offset processing unit 75 calculates the target pinion angle θ after the limiting process. ｐ ＊ The offset processing is performed for the target pinion angle θ ｐ ＊ The offset processing unit 75, for example, adjusts the target pinion angle θ after the limiting process. ｐ ＊ The difference between the current value and the previous value is the target pinion angle θ after limiting processing. ｐ ＊ The offset processing unit 75 subtracts or adds the offset value from the current value, and gradually changes the offset value toward "0" over time at a predetermined timing.

[0047] The offset request signal S2 is an electrical signal that indicates a change in the state of the vehicle speed V, and is also an electrical signal that requests the offset processing unit 75 to execute offset processing. The offset request signal S2 is generated, for example, by the switching processing unit 73. The switching processing unit 73 controls the final limit value θ Ｌ３ the first limit value θ Ｌ１ to the second limit value θ Ｌ２ When switching to the final limit value θ Ｌ３ The second limit value θ Ｌ２ to the first limit value θ Ｌ１ When switching to the offset request signal S2, the offset request signal S2 is generated.

[0048] When the offset processing is performed, the offset processing unit 75 calculates the target pinion angle θ after the offset processing. ｐ ＊ The final target pinion angle θ ｐ ＊ When the offset processing is not performed, the offset processing unit 75 supplies the target pinion angle θ after the limiting processing to the pinion angle feedback control unit 63. ｐ ＊ The final target pinion angle θ ｐ ＊to the pinion angle feedback control unit 63.

[0049] <Limit Value Calculation Unit 71> Next, the configuration of the limit value calculation unit 71 will be described in detail. As shown in Fig. 4, the limit value calculation unit 71 has a function processing unit 71A. The function processing unit 71A calculates the first limit value θ based on the concept of a spline curve. Ｌ１ That is, the function processing unit 71A calculates the first limit value θ Ｌ１ As shown in the following equation (1), the function is expressed by, for example, a seventh-order polynomial.

[0050] y = a ７ x ７ +a ６ x ６ +a ５ x ５ +a ４ x ４ +a ３ x ３ +a ２ x ２ +a １ x + a ０ …(1) However, “a １ ~a ７ " is a coefficient of each term, and is set so as to obtain a predetermined curve shape that is desirable when the vehicle is stopped. ０ " is the intercept. Intercept a ０ is set each time according to the vehicle speed V.

[0051] The function processing unit 71A calculates the target pinion angle θ by substituting “x” in the formula (1). ｐ ＊ The value of “y” calculated by substituting Ｌ１ The first limit value θ Ｌ１ is the target pinion angle θ ｐ ＊ The shape of the curve is determined by the constraints of the function. For example, four parameters B1 to B4 are set as constraints at the start and end points of the curve.

[0052] B1. Position (X ｓ , X ｅ ) B2. Angular velocity (ω ｓ , ωｅ ) B3. Angular acceleration (α ｓ , α ｅ ) B4. Angular jerk (j ｓ , j ｅ ) However, "X ｓ " is the position of the starting point. ｅ " is the position of the end point. "ω ｓ " is the target pinion angular velocity at the starting point. "ω ｅ " is the target pinion angular velocity at the end point. "α ｓ " is the target pinion angular acceleration at the starting point. "α ｅ " is the target pinion angular acceleration at the end point. ｓ " is the target pinion angular jerk at the start point. ｅ " is the target pinion angular jerk at the end point. Jerk is also called jerk.

[0053] The limit value calculation unit 71 has an intercept calculation unit 71B. The intercept calculation unit 71B calculates an intercept a according to the vehicle speed V. ０ The intercept a for the change in vehicle speed V is calculated. ０ The change characteristics of are as follows:

[0054] As shown in FIG. 5, as the vehicle speed V increases from "0", the intercept a ０ The value of increases linearly and gradually. ｔｈ After reaching the intercept α ０ is maintained at a constant value regardless of the vehicle speed V.

[0055] Vehicle speed threshold V ｔｈ is the vehicle speed that is the reference for determining whether the vehicle is stationary or moving. ｔｈ is, for example, a speed in the extremely low speed range. That is, the vehicle speed threshold V ｔｈ A vehicle speed range below the threshold vehicle speed V is a first vehicle speed range in which the vehicle is considered to be in a stopped state. ｔｈ The above vehicle speed range is a second vehicle speed range in which the vehicle is considered to be in a traveling state.

[0056] Intercept a ０ is the target pinion angle θｐ ＊ Target pinion angle θ at which the restriction of ｐ ＊ The intercept a when the vehicle speed V is "0" is ０ is the first intercept a ０１ The first intercept a ０１ is a value greater than "0" and is set to the target pinion angle θ when the vehicle is stopped. ｐ ＊ Target pinion angle θ at which the restriction of ｐ ＊ The vehicle speed V is the vehicle speed threshold V ｔｈ Intercept a when greater than or equal to ０ is the second intercept a ０２ The second intercept a ０２ is the target pinion angle θ when the vehicle is running. ｐ ＊ Target pinion angle θ at which the restriction of ｐ ＊ is the value.

[0057] <First limit value θ Ｌ１ Next, the change characteristics of the target pinion angle θ ｐ ＊ The first limit value θ for changes in Ｌ１ Explain the characteristics of the change.

[0058] As shown in FIG. 6, when the vehicle is stopped, that is, when the vehicle speed V is "0", the target pinion angle θ ｐ ＊ The first limit value θ for changes in Ｌ１ The change characteristic of the target pinion angle θ is shown by a first characteristic line L1. The first characteristic line L1 has a curved shape based on the above formula (1). The starting point P0 of the first characteristic line L1 is ｐ ＊ and the first limit value θ Ｌ１ The origin of the coordinate system is the target pinion angle θ ｐ ＊ As the absolute value of increases from the origin, the first limit value θ Ｌ１ However, the slope of the first characteristic line L1 gradually increases in accordance with the target pinion angle θ ｐ ＊The slope gradually decreases as the absolute value of the target pinion angle θ increases. ｐ ＊ A first limit value θ for the increase in the absolute value of Ｌ１ This is the percentage increase.

[0059] Target pinion angle θ ｐ ＊ The absolute value of the first limit value θ ｐ１ When the first limit value θ Ｌ１ is the second limit value θ ｐ２ The first limit value θ ｐ１ is the maximum value within the maximum steering range. The maximum steering range is the steering angle θ at which the steered wheels 6 can be steered by the steering motor 31 while the vehicle is running. ｗ Target pinion angle θ corresponding to the maximum range of ｐ ＊ That is, the first limit value θ ｐ１ is a target pinion angle θ at which the steered wheels 6 can be steered by the steering motor 31 while the vehicle is running. ｐ ＊ is the maximum value in the range.

[0060] Second limit value θ ｐ２ is the maximum value within the steering range. The steering range is the maximum steering angle θ at which the steered wheels 6 can be turned by the steering motor 31 when the vehicle is stopped. ｗ Target pinion angle θ corresponding to the maximum range of ｐ ＊ That is, the second limit value θ ｐ２ is the target pinion angle θ at which the steered wheels 6 can be steered by the steering motor 31 when the vehicle is stopped. ｐ ＊ The second limit value θ is the maximum value within the range. ｐ２ is the first limit value θ ｐ１ is smaller than.

[0061] As shown in FIG. 7, in the first vehicle speed range where the vehicle is considered to be in a stopped state, the target pinion angle θ ｐ ＊ The first limit value θ for changes in Ｌ１The change characteristic of changes in accordance with the vehicle speed V. Specifically, the starting point P0 of the first characteristic line L1 moves along the straight line L2 according to the vehicle speed V. The movement of the starting point P0 is due to the change in the intercept a ０ moves, that is, the intercept a ０ The line L2 is a line that passes through the origin and has a slope of "1". The line L2 is expressed by the following equation (2).

[0062] y = x (2) When the vehicle speed V is, for example, from 0 km / h to the first vehicle speed V １ When the change occurs, the starting point P0 of the first characteristic line L1 moves from the origin to the first point (θ ｐ２ , θ ｐ２ ) to move to the target pinion angle θ ｐ ＊ The limit of the target pinion angle θ ｐ ＊ is the second limit value θ ｐ２ The timing starts when the target pinion angle θ ｐ ＊ is the second limit value θ ｐ２ If it is less than the target pinion angle θ ｐ ＊ This is because the starting point P0 of the first characteristic line L1 is located at the first point (θ ｐ２ , θ ｐ２ ) to move to the target pinion angle θ ｐ ＊ is the second limit value θ ｐ２ If it is less than the first limit value θ Ｌ１ This is because the first vehicle speed V １ is, for example, greater than 0 km / h and is equal to or less than the vehicle speed threshold V ｔｈ The speed is as follows:

[0063] When the vehicle speed V is, for example, 0 km / h to a second vehicle speed V ２ When the change occurs, the starting point P0 of the first characteristic line L1 moves from the origin to the second point (θ ｐ１ , θ ｐ１ ) to move to the target pinion angle θ ｐ ＊ The limit of the target pinion angle θ ｐ ＊ is the first limit value θ ｐ１The timing starts when the target pinion angle θ ｐ ＊ is the first limit value θ ｐ１ If it is less than the target pinion angle θ ｐ ＊ This is because the starting point P0 of the first characteristic line L1 is located at a distance from the origin to the second point (θ ｐ１ , θ ｐ１ ) to move to the target pinion angle θ ｐ ＊ is the first limit value θ ｐ１ If it is less than the first limit value θ Ｌ１ This is because the second vehicle speed V ２ is, for example, the first vehicle speed V １ exceeds the vehicle speed threshold V ｔｈ The second vehicle speed V ２ is the vehicle speed threshold V ｔｈ It may be the same speed.

[0064] <Target pinion angle θ due to limiting process ｐ ＊ Next, the target pinion angle θ ｐ ＊ 8(a) and 8(b), when the vehicle speed V is "0" and the steering wheel 5 is turned to the right or left from the neutral position, the steering angle θ ｓ The absolute value of gradually increases linearly, and eventually reaches the maximum steering angle θ ｓｍａｘ (time T1). ｓｍａｘ indicates the limit position of the imaginary operation range of the steering wheel 5.

[0065] As shown in FIG. 8(c), the steering angle θ ｓ As the absolute value of increases, the target pinion angle θ ｐ ＊ As shown by the dashed line in FIG. 8(c), the absolute value of the target pinion angle θ ｐ ＊ If the limiting process for the steering angle θ ｓ The absolute value of the maximum steering angle θ ｓｍａｘ When the target pinion angle θ ｐ ＊The absolute value of the first limit value θ ｐ１ (time T1).

[0066] However, in this embodiment, the target pinion angle θ ｐ ＊ The limiting process is performed in accordance with the characteristic line L1 when the vehicle speed V is "0" shown in FIG. 6. Therefore, as shown by the solid line in FIG. 8(c), the target pinion angle θ ｐ ＊ The limit of the target pinion angle θ ｐ ＊ The absolute value of the second limit value θ ｐ２ The limiting process starts when the steering angle θ ｓ As the absolute value of increases, the target pinion angle θ ｐ ＊ The absolute value of the target pinion angle θ gradually increases in a curved line. ｐ ＊ The absolute value of the steering angle θ ｓ The absolute value of the maximum steering angle θ ｓｍａｘ When the second limit value θ ｐ２ (time T1).

[0067] As shown in FIGS. 8(b) and 8(c), after that, the steering angle θ ｓ The absolute value of the maximum steering angle θ ｓｍａｘ When the target pinion angle θ ｐ ＊ The absolute value of the second limit value θ ｐ２ is maintained.

[0068] As shown in FIGS. 8(a) and 8(c), the target pinion angle θ ｐ ＊ The absolute value of the second limit value θ ｐ２ When the vehicle speed V starts to increase in the state limited to the target pinion angle θ ｐ ＊ is limited in accordance with the characteristic line L1 when the vehicle speed V exceeds "0" shown in FIG. 7. Therefore, the target pinion angle θ ｐ ＊ The absolute value of increases gradually in a curve as the vehicle speed V increases, and eventually reaches the first limit value θ ｐ１ (time T3). In this embodiment, the target pinion angle θｐ ＊ The absolute value of the vehicle speed V is the second vehicle speed V ２ When the first limit value θ ｐ１ reaches.

[0069] As shown in FIGS. 8(a), (b), and (c), after that, the steering angle θ ｓ The absolute value of the maximum steering angle θ ｓｍａｘ and the vehicle speed V is maintained at a second vehicle speed V ２ If the target pinion angle θ ｐ ＊ The absolute value of the first limit value θ ｐ１ is kept limited to

[0070] As shown in FIGS. 8(a) and 8(c), the target pinion angle θ ｐ ＊ The absolute value of the first limit value θ ｐ１ When the vehicle speed V starts to decrease in the state limited to the target pinion angle θ ｐ ＊ is limited in accordance with the characteristic line L1 when the vehicle speed V exceeds "0" shown in FIG. 7. Therefore, the target pinion angle θ ｐ ＊ The absolute value of the target pinion angle θ gradually decreases in a curved manner as the vehicle speed V decreases. ｐ ＊ The absolute value of the second limit value θ ｐ２ (time T5).

[0071] As shown by the dashed line in FIG. 8(c), the target pinion angle θ ｐ ＊ If the limiting process for the steering angle θ is not executed, even if the vehicle speed V starts to decrease, ｓ The absolute value of the maximum steering angle θ ｓｍａｘ As long as the target pinion angle θ ｐ ＊ The absolute value of the first limit value θ ｐ１ is maintained.

[0072] As shown in FIGS. 8(b) and 8(c), when the steering wheel 5 is subsequently turned back while the vehicle speed V is 0 km / h, the steering angle θ ｓThe absolute value of the steering angle θ decreases linearly. ｓ As the absolute value of decreases, the target pinion angle θ ｐ ＊ The absolute value of the target pinion angle θ also gradually decreases (time T6). ｐ ＊ is limited in accordance with the characteristic line L1 when the vehicle speed V is "0" shown in FIG. 6. Therefore, the target pinion angle θ ｐ ＊ The absolute value of the second limit value θ ｐ２ to the second limit value θ ｐ２ The target pinion angle θ gradually decreases in a curved line to a value close to the target value. ｐ ＊ The absolute value of the second limit value θ ｐ２ After the steering angle θ ｓ As the absolute value of decreases, the target pinion angle θ ｐ ＊ The absolute value of decreases linearly and gradually.

[0073] In this way, when the vehicle speed V is within the first vehicle speed range, the target pinion angle θ ｐ ＊ The absolute value of the target pinion angle θ is limited to a steerable range. This is because the axial force when steering the steered wheels 6 when the vehicle speed V is within the first vehicle speed range is significantly larger than the axial force when steering the steered wheels 6 when the vehicle speed V is within the second vehicle speed range. For this reason, the absolute value of the target pinion angle θ ｐ ＊ By limiting the absolute value of θ to within the steerable range, it is possible to avoid a situation in which the steering force is insufficient, and therefore the steered wheels 6 can be steered smoothly.

[0074] The first vehicle speed range is a vehicle speed range in which the vehicle is considered to be stopped, and is, for example, a vehicle speed range of 0 km / h or more (vehicle speed threshold V ｔｈ The second vehicle speed range is a vehicle speed range in which the vehicle is considered to be traveling, and is, for example, a vehicle speed range less than a vehicle speed threshold V ｔｈ This is the vehicle speed range.

[0075] When the vehicle speed V is within the second vehicle speed range, the target pinion angle θ ｐ＊ The absolute value of the target pinion angle θ is not limited. This is because the axial force when the steered wheels 6 are steered when the vehicle speed V is within the second vehicle speed range is considerably smaller than the axial force when the steered wheels 6 are steered when the vehicle speed V is within the first vehicle speed range. Therefore, the absolute value of the target pinion angle θ ｐ ＊ If the absolute value of is within the maximum steering range, the steering force is not insufficient and the steered wheels 6 can be smoothly steered in accordance with the steering state of the steering wheel 5.

[0076] In addition, the vehicle that was stopped is turned at a steering angle of θ ｓ The absolute value of the maximum steering angle θ ｓｍａｘ or maximum steering angle θ ｓｍａｘ When the vehicle starts running while the target pinion angle θ ｐ ＊ The absolute value of the second limit value θ ｐ２ to the first limit value θ ｐ１ That is, the target pinion angle θ ｐ ＊ , and thus the steering angle θ ｗ Therefore, the driver of the vehicle can easily change the target pinion angle θ ｐ ＊ In addition, the driver of the vehicle is less likely to feel uncomfortable.

[0077] <When an abnormal vehicle speed occurs while the vehicle is stopped> Next, an example of when an abnormal vehicle speed occurs while the vehicle is stopped will be described. As shown in Figures 9(a) and 9(b), when the vehicle speed V is "0" and the steering wheel 5 is turned to the right or left from the neutral position, the steering angle θ ｓ The absolute value of gradually increases linearly, and eventually reaches the maximum steering angle θ ｓｍａｘ (time T11).

[0078] As shown in FIG. 9(c), the steering angle θ ｓ As the absolute value of increases, the target pinion angle θ ｐ ＊ As shown by the dashed line in FIG. 9C, the absolute value of the target pinion angle θ ｐ ＊If the limiting process for the steering angle θ ｓ The absolute value of the maximum steering angle θ ｓｍａｘ When the target pinion angle θ ｐ ＊ The absolute value of the first limit value θ ｐ１ (time T1).

[0079] However, in this embodiment, the target pinion angle θ ｐ ＊ The limiting process is performed in accordance with the characteristic line L1 when the vehicle speed V is "0" shown in FIG. 6. Therefore, as shown by the solid line in FIG. 9(c), the target pinion angle θ ｐ ＊ The limit of the target pinion angle θ ｐ ＊ The absolute value of the second limit value θ ｐ２ The limiting process starts when the steering angle θ ｓ As the absolute value of increases, the target pinion angle θ ｐ ＊ The absolute value of the target pinion angle θ gradually increases in a curved line. ｐ ＊ The absolute value of the steering angle θ ｓ The absolute value of the maximum steering angle θ ｓｍａｘ When the second limit value θ ｐ２ (time T12).

[0080] As shown in FIGS. 9(b) and 9(c), after that, the steering angle θ ｓ The absolute value of the maximum steering angle θ ｓｍａｘ When the target pinion angle θ ｐ ＊ The absolute value of the second limit value θ ｐ２ is maintained.

[0081] As shown in FIGS. 9(a) and 9(c), the target pinion angle θ ｐ ＊ The absolute value of the second limit value θ ｐ２ When an abnormality occurs in the vehicle speed V while the vehicle speed V is limited to the target pinion angle θ ｐ ＊ The limiting process for the final limit value θ Ｌ３ is the first limit value θＬ１ to the second limit value θ Ｌ２ The second limit value θ Ｌ２ is, for example, the maximum value within the maximum steering range, and is smaller than the first limit value θ ｐ１ The target pinion angle θ calculated by the target pinion angle calculation unit 62 is the same value as ｐ ＊ is the second limit value θ Ｌ２ is limited to.

[0082] However, the switching processing unit 73 does not change the final limit value θ Ｌ３ Therefore, the offset processing unit 75 generates an offset request signal S2 in response to the switching of the target pinion angle θ after the limiting process. ｐ ＊ The offset processing unit 75 performs offset processing on the target pinion angle θ after the limiting processing. ｐ ＊ The difference between the current value and the previous value is the target pinion angle θ after limiting processing. ｐ ＊ Offset value θ for ｏｆｓ The current value is set as, for example, the second limit value θ Ｌ２ The second limit value θ Ｌ２ is the first limit value θ ｐ１ The previous value is, for example, equal to the second limit value θ ｐ２ The offset processing unit 75 calculates an offset value θ from the current value. ｏｆｓ Therefore, the target pinion angle θ ｐ ＊ is the previous value of the second limit value θ ｐ２ is maintained.

[0083] As shown in FIGS. 9B and 9C, when the steering wheel 5 is subsequently turned back while the vehicle speed V is 0 km / h, the steering angle θ ｓ The absolute value of the steering angle θ decreases linearly. ｓ As the absolute value of decreases, the target pinion angle θ ｐ ＊ The absolute value of the offset value θ ｏｆｓis gradually decreased toward "0". Eventually, the second limit value θ ｐ２ is the second limit value θ Ｌ２ In the example of FIG. 9C, the target pinion angle θ ｐ ＊ Before the absolute value of ｐ２ is the second limit value θ Ｌ２ This coincides with (time 14).

[0084] In this way, when an abnormality occurs in the vehicle speed V while the vehicle is stopped, the target pinion angle θ ｐ ＊ Therefore, the limiting process for the target pinion angle θ ｐ ＊ The range of possible absolute values ​​of θ is expanded from the steering range to the maximum steering range. Therefore, the turning performance of the vehicle while traveling is ensured. In addition, with the release of the limiting process, the final limiting value θ Ｌ３ is the first limit value θ Ｌ１ to the second limit value θ Ｌ２ When the limit value is changed to , the final limit value θ Ｌ３ is the second limit value θ Ｌ２ When the steering of the steering wheel 5 is started, the final limit value θ Ｌ３ is the true value of the second limit value θ Ｌ２ and finally approaches the second limit value θ Ｌ２ Therefore, the target pinion angle θ ｐ ＊ , and thus the steering angle θ ｗ Therefore, the driver of the vehicle is prevented from feeling uncomfortable.

[0085] <Effects of the embodiment> This embodiment provides the following effects: (1) Steering control device 1 controls steering device 2 in which power transmission is separated between steerable wheels 6 of a vehicle and steering wheel 11. Steering device 2 includes steering shaft 22 that steers steerable wheels 6, and steering motor 31 that generates a steering force that is applied to steering shaft 22. Steering control device 1 includes steering control device 1B.

[0086] The steering control device 1B is configured to ｐis the target pinion angle θ ｐ ＊ The process for controlling the steering motor 31 is executed so that the pinion angle θ follows the ｐ is the steering angle θ of the steered wheels 6 ｗ The target pinion angle θ ｐ ＊ is the pinion angle θ calculated according to the steering state of the steering wheel 11. ｐ Further, steering control device 1B adjusts target pinion angle θ so that the maximum steering force that steering motor 31 can generate and the axial force generated in steering shaft 22 are within an angle range in which the forces can be balanced. ｐ ＊ The angular region is the maximum steering range or the steering possible range.

[0087] Target pinion angle θ ｐ ＊ The process of correcting the target pinion angle θ ｐ ＊ When the target pinion angle θ increases toward the limit of the angle range where the aforementioned force balance can be maintained, ｐ ＊ As the target pinion angle θ approaches the limit value, ｐ ＊ The target pinion angle θ ｐ ＊ The first limit value θ Ｌ１ The limit value is a first limit value θ ｐ１ The first limit value θ Ｌ１ is the target pinion angle θ ｐ ＊ and the first limit value θ Ｌ１ On the coordinate plane, the intercept a changes depending on the vehicle speed V. ０ It is expressed as a function including

[0088] According to this configuration, the target pinion angle θ ｐ ＊is corrected so that the maximum steering force that can be generated by the steering motor 31 and the axial force generated in the steering shaft 22 are within an angle range in which the forces can be balanced. ｐ ＊ However, it is possible to prevent deviation from an angle region in which a balance can be maintained between the steering force of steering motor 31 and the axial force generated in steering shaft 22. In other words, it is possible to prevent the generation of an axial force that exceeds the maximum steering force that can be generated by steering motor 31. Therefore, steered wheels 6 can be smoothly steered in accordance with the steering state of steering wheel 11.

[0089] However, the target pinion angle θ ｐ ＊ The driver may feel uncomfortable with the vehicle behavior resulting from the correction of the target pinion angle θ. In particular, when the vehicle is stopped or in an extremely low speed range, the steered wheels 6 are likely to be turned to a greater extent. For this reason, when the vehicle is stopped or in an extremely low speed range, the target pinion angle θ ｐ ＊ There is a concern that the driver may feel uncomfortable with the vehicle behavior resulting from the correction.

[0090] In this regard, according to the steering control device 1 of the present embodiment, when the vehicle is stopped or in an extremely low speed range, the target pinion angle θ ｐ ＊ When the target pinion angle θ increases toward the limit value of the angle region where the balance between the steering force of the steering motor 31 and the axial force can be maintained, ｐ ＊ As the target pinion angle θ approaches the limit value, ｐ ＊ The target pinion angle θ ｐ ＊ is limited. Target pinion angle θ ｐ ＊ By gradually changing the vehicle speed to the limit value, it is possible to reduce the sense of discomfort felt by the driver with respect to the vehicle behavior.

[0091] In addition, the first limit value θ Ｌ１ The function used to calculate is an intercept a that changes depending on the vehicle speed V. ０ Therefore, the first limit value θ Ｌ１changes depending on the vehicle speed V. Therefore, the target pinion angle θ ｐ ＊ can be appropriately limited in accordance with the vehicle speed V. Furthermore, the first limit value θ Ｌ１ is calculated using a function. Therefore, for example, the first limit value θ Ｌ１ Compared to the case where the first limit value θ Ｌ１ This ensures continuity.

[0092] In the case of map calculation, there is a concern that the points may break apart. Also, if the number of planes of the three-dimensional map is not increased, the first limit value θ when the vehicle speed V changes will be Ｌ１ In addition, increasing the number of planes in the three-dimensional map increases the computation load. Ｌ１ By calculating the above, it is possible to reduce the calculation load.

[0093] (2) The extremely low speed range is a vehicle speed range in which the vehicle is considered to be in a stopped state. With this configuration, it is possible to suppress a lack of steering force when the vehicle is turned stationary. (3) When an abnormality occurs in the vehicle speed V, the steering control device 1B adjusts the first limit value θ Ｌ１ Instead, the second limit value θ Ｌ２ Using the target pinion angle θ ｐ ＊ The second limit value θ Ｌ２ is a fixed value that is set based on the limit value of the angle range in which the above-mentioned balance of forces can be maintained. ｐ ＊ The limit value that limits Ｌ１ to the second limit value θ Ｌ２ By switching to the target pinion angle θ ｐ ＊ This increases the range in which the vehicle can turn, ensuring the vehicle's turning performance while in motion.

[0094] (4) When an abnormality occurs in the vehicle speed V, the steering control device 1B executes offset processing. The offset processing is performed by adjusting the target pinion angle θ ｐ ＊ The difference between the current value and the previous value is the target pinion angle θｐ ＊ Offset value θ for ｏｆｓ and the target pinion angle θ ｐ ＊ The offset value θ from the current value ｏｆｓ According to this configuration, the target pinion angle θ ｐ ＊ The limit value that limits Ｌ１ to the second limit value θ Ｌ２ Therefore, when the target pinion angle θ ｐ ＊ This also suppresses sudden changes in

[0095] Other Embodiments This embodiment may be modified as follows: The offset processing unit 75 executes the offset processing based on the offset request signal S2, but the offset processing unit 75 may also be modified as follows: That is, the offset processing unit 75 acquires the vehicle speed V and determines whether the vehicle speed V is normal based on the acquired vehicle speed V.

[0096] The order of the function may be changed depending on the number of parameters to be considered. For example, the first limit value θ Ｌ１ If the jerk is not taken into consideration when calculating the first limit value θ, the function may be a fifth-order polynomial, as shown in the following equation (3). Ｌ１ Depending on the number of parameters to be considered in the calculation of (1), the order of the function can be set to seventh or fifth order.

[0097] y = a ５ x ５ +a ４ x ４ +a ３ x ３ +a ２ x ２ +a １ x + a ０ ...(3) ・Intercept a ０ is a target pinion angle θ depending on the vehicle speed V. ｐ ＊ and the first limit value θ Ｌ１ The first limit value θ Ｌ１may vary along the coordinate axis on which is plotted the value of the parameter . The coordinate axis is the vertical axis in FIG.

[0098] - The reaction force control device 1A and the turning control device 1B may be configured as a single control device. - In this embodiment, a so-called linkless structure in which power transmission between the steering shaft 11 and the steered wheels 6 is separated is adopted as the vehicle steering device 2, but a structure in which power transmission between the steering shaft 11 and the steered wheels 6 can be separated by a clutch may also be adopted. When the clutch is disengaged, power transmission between the steering wheel 11 and the steered wheels 6 is disconnected. When the clutch is engaged, power transmission between the steering wheel 11 and the steered wheels 6 is connected.

Claims

A steering control device configured to control a steering device in which power transmission between steered wheels of a vehicle and a steering wheel is separated, the steering device including a steering shaft that steers the steered wheels, and a steering motor configured to generate a steering force to be applied to the steering shaft, A steering control unit is provided, a process of controlling the steering motor so that an angle that can be converted into a steering angle of the steered wheels follows a target angle calculated in accordance with a steering state of the steering wheel; and a process of correcting the target angle so that a maximum steering force that can be generated by the steering motor and an axial force generated in the steering shaft become an angle within an angle range in which a balance of the forces can be maintained, the process of correcting the target angle includes a process of calculating a limit value for the target angle so that, when the target angle increases toward a limit value of the angle region in a stopped state or in an extremely low speed range, the rate of increase of the target angle becomes gentler as the target angle approaches the limit value; A steering control device in which the limit value is expressed as a function including an intercept that changes according to vehicle speed on a coordinate plane between the target angle and the limit value.

2. The steering control device according to claim 1, wherein the extremely low speed range is a vehicle speed range in which the vehicle is considered to be in a stopped state. 　 the limit value is set as a first limit value, and the steering control unit is configured to limit the target angle by using a second limit value instead of the first limit value when an abnormality occurs in the vehicle speed, 3. The steering control device according to claim 1, wherein the second limit value is a fixed value that is set based on the limit value of the angle region. 　 the steering control unit is configured to execute offset processing when an abnormality occurs in the vehicle speed, 4. The steering control device according to claim 3, wherein the offset process includes a process of setting a difference between a current value and a previous value of the target angle as an offset value for the target angle, and subtracting the offset value from the current value of the target angle.

3. The steering control device according to claim 1, wherein the function is expressed by a seventh-order polynomial or a fifth-order polynomial.

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