Steering control device

Abstract

To provide a steering control device capable of reducing a calculation load.SOLUTION: A steering control device includes a limitation axial force calculation unit 82 for calculating limitation axial force. The limitation axial force calculation unit 82 includes a steering angle holding unit 91, a reference angle calculation unit 93, a final difference calculation unit 94, and a pre-limitation axial force calculation unit 95. The steering angle holding unit 91 holds a steering angle when the turning operation of turning wheels is limited. When the turning operation of the turning wheels is limited, the reference angle calculation unit 93 calculates a reference angle by executing limitation processing to limit the steering angle held by the steering angle holding unit 91 to a virtual end angle. When the turning operation of the turning wheels is not limited, the reference angle calculation unit 93 calculates the reference angle by executing the limitation processing to limit a current steering angle to the virtual end angle. The final difference calculation unit calculates a final difference between the reference angle and the current steering angle. The pre-limitation axial force calculation unit 95 calculates pre-limitation axial force according to the value of the final difference.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] Steer-by-wire steering devices that separate power transmission between the steering wheel and the steered wheels are known. This steering device includes a reaction motor, a turning motor, and a control device. The reaction motor generates a steering reaction force that is applied to the steering shaft. The turning motor generates a steering force that steers the steered wheels. When the vehicle is traveling, the control device controls the reaction motor to generate a steering reaction force and controls the turning motor to turn the steered wheels.

[0003] For example, the steering control device of Patent Document 1 calculates a normal reaction force based on the steering angle of the steering wheel, the turning angle of the steered wheels, and the vehicle speed. The steering control device also calculates an end contact reaction force based on the steering angle and the turning angle. The end contact reaction force is a reaction force that gives the driver an end contact feeling of the steering mechanism. The steering control device calculates a final steering reaction force from the normal reaction force and the end contact reaction force. The steering control device controls the supply of electricity to the reaction motor so that the reaction motor generates the final steering reaction force.

[0004] However, there is a risk of vibration occurring because the direction of the normal reaction force, which increases as the absolute value of the steering angle or turning angle increases, is opposite to the direction of the end contact reaction force, which increases as the difference between the absolute value of the turning angle and the upper threshold value increases. Therefore, the steering control device of Patent Document 1 corrects at least one of the normal reaction force and the end contact reaction force in a direction that relatively decreases the absolute value of the normal reaction force when the direction of the normal reaction force is opposite to the direction of the end contact reaction force. This makes it possible to suppress vibration, even if the direction of the normal reaction force is opposite to the direction of the end contact reaction force. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-133534 Summary of the Invention [Problem to be solved by the invention]

[0006] The steering control device of Patent Document 1 calculates the normal reaction force and the end contact reaction force separately, and performs processing to correct at least one of the normal reaction force and the end contact reaction force according to the direction of these calculated reaction forces. Calculating multiple reaction forces in this way, and further performing processing to reconcile the multiple reaction forces, is one factor that hinders reduction in the calculation load of the steering control device. A reduction in the calculation load is required for conventional steering control devices, including the device of Patent Document 1. [Means for solving the problem]

[0007] A steering control device that solves the above problem is a steering control device that controls a reaction force motor that generates a steering reaction force applied to a steering wheel, the power transmission of which is separated from the steering shaft that steers the steered wheels, based on a command value calculated in accordance with the steering state. The steering control device has a basic axial force calculation unit, a limiting axial force calculation unit, and a final axial force calculation unit. The basic axial force calculation unit calculates a basic axial force including an axial force that reflects at least the force acting on the steered shaft via the steered wheels when the steering wheel is operated within a predetermined operation range. The limiting axial force calculation unit calculates a limiting axial force that is an axial force for virtually limiting the operation of the steering wheel. The final axial force calculation unit calculates a final axial force that is the final axial force to be reflected in the command value based on the basic axial force and the limiting axial force. The limiting axial force calculation unit has a steering angle holding unit, a reference angle calculation unit, a final difference calculation unit, and an axial force calculation unit. The steering angle holding unit When the steered wheels hit an obstacle,When the steering operation of the steered wheels is restricted, the steering angle at the time of restriction is held. A reference angle calculation unit calculates a reference angle by executing a limiting process to limit the steering angle held by the steering angle holding unit when the steering operation of the steered wheels is restricted, or to a virtual end angle corresponding to the limit position of a virtual operation range of the steering wheel when the steering operation of the steered wheels is not restricted. A final difference calculation unit calculates a final difference, which is the final difference between the reference angle and the current steering angle. An axial force calculation unit calculates the limiting axial force according to the value of the final difference.

[0008] According to this configuration, when the steering operation of the steered wheels is restricted, a limiting axial force is calculated according to the difference between the steering angle at that time and the current steering angle. This limiting axial force is reflected in the final axial force and, ultimately, in the command value, so that a driving force for virtually restricting the operation of the steering wheel is applied to the steering mechanism of the vehicle. Therefore, the driver can recognize the situation in which the steering operation of the steered wheels is restricted through the feedback via the steering wheel.

[0009] Furthermore, if the steering operation of the steered wheels is not restricted, when the steering wheel is operated beyond the virtual end angle, a limiting axial force is calculated according to the difference between the current steering angle and the virtual end angle. This limiting axial force is reflected in the final axial force and, ultimately, in the command value, so that a driving force for virtually limiting the operation of the steering wheel is applied to the steering mechanism of the vehicle. Therefore, the driver can recognize, through the feedback via the steering wheel, that they are about to operate the steering wheel beyond the limit position of its virtual operation range.

[0010] Here, it is conceivable to separately calculate a limiting axial force for limiting further steering wheel operation when the steering operation of the steered wheels is limited, and a limiting axial force for limiting steering beyond the virtual end angle of the steering wheel. In this case, there is a concern that, for example, a process for arbitrating the values ​​of the two limiting axial forces will be required from the viewpoint of providing an appropriate steering feel to the driver.

[0011] In this regard, with the above configuration, either the limiting axial force for limiting further operation of the steering wheel when the steering operation of the steered wheels is restricted or the limiting axial force for limiting steering beyond the virtual end angle of the steering wheel is calculated based on the difference between the reference angle calculated depending on whether the steering operation of the steered wheels is restricted and the current steering angle. In other words, a common part is used to calculate the limiting axial force for limiting further operation of the steering wheel when the steering operation of the steered wheels is restricted, and the limiting axial force for limiting steering beyond the virtual end angle of the steering wheel. This eliminates the need for a process to reconcile the two limiting axial forces. This reduces the computational load compared to when the two limiting axial forces are calculated separately.

[0012] In the above steering control device, the final difference calculation unit may correct the calculated value of the final difference so as to decrease it when the steering operation of the steered wheels is restricted. When the steered wheels attempt to turn further while their steering operation is restricted, the reaction force increases gradually as the tires elastically deform. According to the above configuration, the calculated final difference value is corrected to decrease, so that the steering reaction force can be increased more gradually. This makes it possible to apply a steering reaction force to the steering wheel that more closely resembles the actual state in which the steering operation of the steered wheels is restricted.

[0013] In the above steering control device, when the steering operation of the steered wheels is restricted and the rotational position of the steering wheel has reached the limit position of its virtual operation range, the final difference calculation unit may use the larger of the final difference calculated as the steering operation of the steered wheels being restricted, and the final difference calculated as the rotational position of the steering wheel having reached the limit position of its virtual operation range.

[0014] With this configuration, a steering reaction force can be applied to the steering wheel according to the larger of the final difference calculated as the steering operation of the steered wheels being restricted and the final difference calculated as the rotational position of the steering wheel reaching the limit position of its virtual operating range.

[0015] The above steering control device may have a gain calculation unit that calculates a damping gain for the limiting axial force in accordance with the value of the final difference calculated by the final difference calculation unit, and a multiplier that calculates a damping axial force to be reflected in the limiting axial force by multiplying the gain calculated by the gain calculation unit by the steering angular velocity.

[0016] The larger the gradient of the change in the limiting axial force relative to the final difference, the more likely it is that the value of the limiting axial force will fluctuate in response to changes in the value of the final difference. With the above configuration, the damping axial force is reflected in the limiting axial force, making it possible to stabilize the value of the limiting axial force relative to the final difference.

[0017] The steering control device may further include a difference calculation unit that calculates, when the steering operation of the steered wheels is restricted, a difference between the steering angle of the steered wheels when the steering operation of the steered wheels is restricted and the current steering angle. When the steering operation of the steered wheels is restricted, the reference angle calculation unit may correct the steering angle held by the steering angle holding unit in accordance with the difference calculated by the difference calculation unit, and execute the restriction process on the corrected steering angle to calculate the reference angle.

[0018] Even when the steering operation of the steered wheels is restricted, there is a risk that the steered wheels may turn, even if only slightly. With the above configuration, the steering angle held by the steering angle holding unit is corrected according to the amount of rotation of the shaft linked to the steering operation of the steered wheels. The reference angle is calculated based on this corrected steering angle. Therefore, even when the steered wheels turn while the steering operation of the steered wheels is restricted, a more appropriate steering reaction force can be applied to the steering wheel. [Effects of the Invention]

[0019] According to the steering control device of the present invention, the calculation load can be reduced. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a configuration diagram of a steer-by-wire steering device in which an embodiment of a steering control device is mounted. [Figure 2] FIG. 2 is a block diagram of a control device according to an embodiment. [Figure 3] FIG. 2 is a block diagram of a steering reaction force command value calculation unit according to an embodiment. [Figure 4] FIG. 2 is a control block diagram of a limit axial force calculation unit according to an embodiment. [Figure 5] 10 is a graph showing the relationship between the final difference and the pre-limiting axial force according to an embodiment. [Figure 6] 10 is a graph illustrating a relationship between a final difference and a gain according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0021] An embodiment of a steering control device will be described below. As shown in Figure 1, a vehicle steering device 10 has a steering shaft 12 connected to a steering wheel 11. Steering device 10 also has a steered shaft 14 extending in the vehicle width direction (left-right direction in Figure 1). Left and right steered wheels 16 are connected to both ends of steered shaft 14 via tie rods 15, 15, respectively. The linear movement of steered shaft 14 controls the steering angle θ of steered wheels 16. w The steering shaft 12 and the steered shaft 14 constitute a steering mechanism of the vehicle.

[0022] The steering device 10 has a configuration for generating a steering reaction force, which includes a reaction force motor 31, a speed reduction mechanism 32, a rotation angle sensor 33, and a torque sensor 34. Incidentally, the steering reaction force is a force that acts in the opposite direction to the direction of operation of the steering wheel 11 by the driver. By applying the steering reaction force to the steering wheel 11, it is possible to give the driver an appropriate sense of response.

[0023] The reaction motor 31 is a source of generating a steering reaction force. For example, a three-phase brushless motor is used as the reaction motor 31. The rotation shaft of the reaction motor 31 is connected to the steering shaft 12 via a reduction mechanism 32. The torque of the reaction motor 31 is applied to the steering shaft 12 as a steering reaction force. The torque of the reaction motor 31 is a driving force applied to the steering shaft 12.

[0024] The rotation angle sensor 33 is provided on the reaction motor 31. The rotation angle sensor 33 detects the rotation angle θ of the reaction motor 31. a The rotation angle θ of the reaction motor 31 is detected. a is the steering angle θ s The reaction force motor 31 and the steering shaft 12 are linked via a speed reducer 32. Therefore, the rotation angle θ of the reaction force motor 31 a and the steering angle θ, which is the rotation angle of the steering shaft 12 and thus the rotation angle of the steering wheel 11. s Therefore, the rotation angle θ of the reaction force motor 31 a Based on the steering angle θ s can be obtained.

[0025] The torque sensor 34 detects the steering torque T h Detects the steering torque T h is the torque applied to the steering shaft 12 through the rotation of the steering wheel 11. The torque sensor 34 detects the steering torque T applied to the steering shaft 12 based on the amount of twist of a torsion bar provided midway along the steering shaft 12. hThe torque sensor 34 is provided on the steering shaft 12 between the speed reduction mechanism 32 and the steering wheel 11.

[0026] The steering device 10 has a steering motor 41, a reduction mechanism 42, and a rotation angle sensor 43 as components for generating a steering force that is the power for steering the steered wheels 16. Steering motor 41 is a source of steering force. A three-phase brushless motor, for example, is used as steering motor 41. The rotating shaft of steering motor 41 is connected to pinion shaft 44 via speed reducer 42. Pinion teeth 44a of pinion shaft 44 mesh with rack teeth 14b of steering shaft 14. The torque of steering motor 41 is applied as a steering force to steering shaft 14 via pinion shaft 44. The torque of steering motor 41 is a driving force applied to steering shaft 14. In response to the rotation of steering motor 41, steering shaft 14 moves along the vehicle width direction, which is the left-right direction in FIG. 1.

[0027] The rotation angle sensor 43 is provided on the steering motor 41. The rotation angle sensor 43 detects the rotation angle θ of the steering motor 41. b Detect. Incidentally, steering device 10 has pinion shaft 13. Pinion shaft 13 is arranged so as to intersect with steered shaft 14. Pinion teeth 13a of pinion shaft 13 mesh with rack teeth 14a of steered shaft 14. The reason for providing pinion shaft 13 is to support steered shaft 14 together with pinion shaft 44 inside a housing (not shown). In other words, by a support mechanism (not shown) provided in steering device 10, steered shaft 14 is supported so as to be movable along its axial direction and is pressed toward pinion shafts 13, 44. In this way, steered shaft 14 is supported inside the housing. However, another support mechanism for supporting steered shaft 14 in the housing may be provided without using pinion shaft 13.

[0028] The steering device 10 has a control device 50. The control device 50 can be configured by a processing circuit including: 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 various processes; or 3) a combination thereof. The processor includes a CPU (Central Processing Unit). The processor also includes memory such as RAM and ROM. The memory stores program code or instructions configured to cause the CPU to execute processes. The memory, i.e., a non-transitory computer-readable medium, includes any available medium that can be accessed by a general-purpose or special-purpose computer. The control device 50 corresponds to a steering control device.

[0029] Control device 50 controls reaction force motor 31 and steering motor 41 based on the detection results of various sensors mounted on the vehicle. In addition to the above-mentioned rotation angle sensor 33, torque sensor 34 and rotation angle sensor 43, the sensors include a vehicle speed sensor 501. Vehicle speed sensor 501 detects vehicle speed V.

[0030] The control device 50 controls the reaction motor 31 to generate the steering torque T h The control device 50 executes reaction force control to generate a steering reaction force according to the steering torque T h and vehicle speed V, and calculates a target steering reaction force based on the calculated target steering reaction force. Control device 50 supplies to reaction motor 31 a current required to generate a steering reaction force according to the steering reaction force command value.

[0031] The control device 50 executes steering control to steer the steered wheels 16 in accordance with the steering state through control of the steering motor 41. The control device 50 controls the rotation angle θ of the steering motor 41 detected by the rotation angle sensor 43. b The pinion angle θ, which is the actual rotation angle of the pinion shaft 44, is calculated based on the p This pinion angle θ p is the steering angle θ of the steered wheels 16 wThe control device 50 also detects the rotation angle θ of the reaction force motor 31 detected by the rotation angle sensor 33. a Based on the steering angle θ s The calculated steering angle θ s Based on the pinion angle θ p The control device 50 then calculates the target pinion angle, which is the target value of the target pinion angle θ p The deviation between the two is calculated, and the power supply to the steering motor 41 is controlled so as to eliminate the deviation.

[0032] <Control device configuration> Next, the configuration of the control device 50 will be described. As shown in FIG. 2, the control device 50 has a reaction force control section 50a that performs reaction force control, and a steering control section 50b that performs steering control.

[0033] The reaction force control unit 50 a includes a steering angle calculation unit 51 , a steering reaction force command value calculation unit 52 , and an electric current control unit 53 . The steering angle calculation unit 51 calculates the rotation angle θ of the reaction force motor 31 detected through the rotation angle sensor 33. a The steering angle θ of the steering wheel 11 is s Calculate the following.

[0034] The steering reaction force command value calculation unit 52 calculates the steering torque T h and the steering reaction force command value T based on the vehicle speed V. * The steering reaction force command value calculation unit 52 calculates the steering torque T h The larger the absolute value of the steering reaction force command value T * The steering reaction force command value calculation unit 52 will be described in detail later.

[0035] The power supply control unit 53 controls the steering reaction force command value T * Specifically, the power supply control unit 53 supplies power according to the steering reaction force command value T *The current control unit 53 calculates a current command value for the reaction motor 31 based on the current I. The current control unit 53 also detects the actual current I generated in the power supply path through a current sensor 54 provided in the power supply path for the reaction motor 31. a The value of this current I a is the value of the actual current supplied to the reaction force motor 31. The current control unit 53 then calculates the current command value and the actual current I a The deviation from the steering reaction force command value T is calculated and the power supply to the reaction force motor 31 is controlled so as to eliminate the deviation. * It is possible to give the driver a sense of appropriate response according to the road reaction force.

[0036] The steering control unit 50b has 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. The pinion angle calculation unit 61 calculates the rotation angle θ of the steering motor 41 detected through the rotation angle sensor 43. b The pinion angle θ, which is the actual rotation angle of the pinion shaft 44, is calculated based on the p The steering motor 41 and the pinion shaft 44 are linked via a speed reducer 42. Therefore, the rotation angle θ of the steering motor 41 is calculated. b and pinion angle θ p There is a correlation between the rotation angle θ of the steering motor 41 and the rotation angle θ of the steering motor 41. b From pinion angle θ p Furthermore, the pinion shaft 44 is meshed with the steered shaft 14. Therefore, the pinion angle θ p There is also a correlation between the pinion angle θ and the amount of movement of the steering shaft 14. p is the steering angle θ of the steered wheels 16 w This is a value that reflects the

[0037] The target pinion angle calculation unit 62 calculates the steering angle θ calculated by the steering angle calculation unit 51. s Based on the target pinion angle θ p *In this embodiment, the target pinion angle calculation unit 62 calculates the target pinion angle θ p * steering angle θ s That is, the steering angle θ s and steering angle θ w The steering angle ratio is 1:1.

[0038] Incidentally, the target pinion angle calculation unit 62 calculates the target pinion angle θ p * steering angle θ s That is, the target pinion angle calculation unit 62 may set the steering angle θ to a value different from the target pinion angle θ in accordance with the vehicle running state, such as the vehicle speed V. s steering angle θ w A steering angle ratio is set, and a target pinion angle θ p * The target pinion angle calculation unit 62 calculates the steering angle θ s steering angle θ w The steering angle θ becomes larger as the vehicle speed V increases. s steering angle θ w The target pinion angle θ p * The target pinion angle calculation unit 62 calculates the steering angle θ s The correction angle for the steering angle θ is calculated. s By adding to the target pinion angle θ according to the steering angle ratio p * Calculate the following.

[0039] The pinion angle feedback control unit 63 receives the target pinion angle θ calculated by the target pinion angle calculation unit 62. p * , and the actual pinion angle θ calculated by the pinion angle calculation unit 61 p The pinion angle feedback control unit 63 receives the actual pinion angle θ p The target pinion angle θ p *The pinion angle θ p Through feedback control, the pinion angle command value T p * Calculate the following.

[0040] The power supply control unit 64 determines the pinion angle command value T p * Specifically, the power supply control unit 64 supplies the steering motor 41 with electric power according to the pinion angle command value T p * Further, the current control unit 64 detects an actual current I generated in the power supply path to the steering motor 41 through a current sensor 65 provided in the power supply path to the steering motor 41. b The value of this current I b is the value of the actual current supplied to the steering motor 41. The current control unit 64 then compares the current command value with the actual current I b The deviation from the value of the pinion angle command value T is calculated, and the power supply to the steering motor 41 is controlled so as to eliminate the deviation. p * It rotates by an angle according to

[0041] <Configuration of steering reaction force command value calculation unit> Next, the configuration of the steering reaction force command value calculation unit 52 will be described. As shown in FIG. 3, the steering reaction force command value calculation unit 52 has a target steering reaction force calculation unit 71, an axial force calculation unit 72, and a subtractor 73.

[0042] The target steering reaction force calculation unit 71 calculates the steering torque T h and target steering reaction force T1 based on vehicle speed V * Calculate the target steering reaction force T1 * is a target value of the torque that acts in the opposite direction to the steering direction of the steering wheel 11 and that should be generated through the reaction force motor 31. The target steering reaction force calculation unit 71 calculates the steering torque T h The larger the absolute value of the target steering reaction force T1, and the slower the vehicle speed V, the larger the absolute value of the target steering reaction force T1 * Calculate the following.

[0043] The axial force calculation unit 72 calculates the pinion angle θ p , the current I of the steering motor 41 b The axial force acting on the steered shaft 14 through the steered wheels 16 is calculated based on the value of the steering angle θ and the vehicle speed V, and the calculated axial force is converted into a torque equivalent value (steering reaction force according to the axial force) T2 * Calculate the following.

[0044] The subtractor 73 subtracts the target steering reaction force T1 calculated by the target steering reaction force calculation unit 71. * The torque conversion value T2 calculated by the axial force calculation unit 72 from * By subtracting the steering reaction force command value T * Calculate the following.

[0045] <Configuration of axial force calculation unit> Next, the configuration of the axial force calculation unit 72 will be described in detail. The axial force calculation unit 72 has a basic axial force calculation unit 81, a limit axial force calculation unit 82, an adder 83, and a converter 84.

[0046] The basic axial force calculation unit 81 calculates a basic axial force F1, which is a basic axial force acting on the steered shaft 14 via the steered wheels 16. The basic axial force F1 is one of the following three axial forces (A1) to (A3).

[0047] (A1) Angular axial force The angular axial force is, for example, the pinion angle θ p The basic axial force calculation unit 81 calculates the axial force according to the pinion angle θ p The basic axial force calculation unit 81 calculates the angular axial force based on the pinion angle θ p The larger the absolute value of θ and the slower the vehicle speed V, the larger the calculated angular axial force. p The absolute value of the angular axial force increases linearly with the increase in the absolute value of the pinion angle θ p The angular axial force is an axial force that does not reflect the road surface condition or the force acting on the steered shaft 14 via the steered wheels 16.

[0048] (A2) Current axial force The current axial force is the current I of the steering motor 41. b The basic axial force calculation unit 81 calculates the axial force according to the value of the current I b The current axial force is calculated based on the value of the current I of the steering motor 41. b The value of the target pinion angle θ p * and the actual pinion angle θ p That is, the current I of the steering motor 41 changes depending on the difference between b The value of the current I of the steering motor 41 reflects the actual road surface condition acting on the steering wheels 16. b The basic axial force calculation unit 81 calculates an axial force that reflects the influence of the road surface condition based on the value of the basic axial force. The basic axial force calculation unit 81 calculates a gain, which is a coefficient corresponding to the vehicle speed V, by multiplying the current I of the steering motor 41 by the b The current axial force is calculated by multiplying the value of the current axial force by the road surface condition or the force acting on the steered shaft 14 via the steered wheels 16.

[0049] (A3) Mixed axial force The mixed axial force is an axial force in which the angular axial force and the current axial force are mixed at a predetermined ratio. The basic axial force calculation unit 81 sets distribution ratios for the angular axial force and the current axial force individually according to various state variables that reflect the vehicle behavior, road surface condition, or steering state. The basic axial force calculation unit 81 calculates the mixed axial force by adding up the values ​​obtained by multiplying the angular axial force and the current axial force by the distribution ratios that are individually set for each.

[0050] The limit axial force calculation unit 82 calculates a limit axial force F2 for virtually limiting the operation range of the steering wheel 11. The limit axial force F2 is at least one of the following two axial forces (B1) and (B2).

[0051] (B1) End axial force The end axial force is calculated based on the viewpoint of abruptly increasing the torque generated by reaction motor 31 in the direction opposite to the steering direction when the operating position of steering wheel 11 approaches the limit position of its operating range, or when steered shaft 14 approaches the limit position of its physical movable range. The limit position of the operating range of steering wheel 11 is determined, for example, by the length of the spiral cable provided on steering wheel 11. The limit position of the physical movable range of steered shaft 14 refers to the position where the rack end, which is the end of steered shaft 14, hits a housing (not shown), so-called end contact occurs, and the movable range of steered shaft 14 is physically restricted. The limit axial force calculation unit 82 calculates the limit axial force based on, for example, pinion angle θ p Or steering angle θ s The end axial force is calculated based on the above.

[0052] (B2) Curb axial force The curbstone axial force is an axial force that notifies the driver through a steering reaction force that the steered wheels 16 are hitting an obstacle such as a curb, for example, when the vehicle starts from a stopped state. The curbstone axial force is calculated based on the viewpoint of rapidly increasing the torque generated by the reaction motor 31 in the direction opposite to the steering direction in order to restrict further turning steering or turning back steering when the steered wheels 16 are hitting an obstacle. The limiting axial force calculation unit 82 determines whether the steered wheels 16 are hitting an obstacle such as a curbstone. When it is determined that the steered wheels 16 are hitting an obstacle such as a curbstone, the limiting axial force calculation unit 82 calculates a limiting axial force by, for example, increasing the steering angle θ s The curb axial force is calculated based on the above.

[0053] The adder 83 calculates the final axial force F3 by adding the basic axial force F1 calculated by the basic axial force calculation unit 81 and the limit axial force F2 calculated by the limit axial force calculation unit 82. The final axial force F3 is calculated based on the steering reaction force command value T * The adder 83 corresponds to the final axial force calculation unit.

[0054] The converter 84 converts the final axial force F3 calculated by the adder 83 into torque to obtain a torque conversion value T2 * Calculate the following. Here, it is conceivable to adopt a configuration in which the limit axial force calculation unit 82 separately calculates both the limit axial force F2 as the end axial force and the limit axial force F2 as the curb axial force. However, if this configuration is adopted, arbitration processing between the end axial force and the curb axial force may be necessary. Depending on product specifications, for example, to prevent an excessive value of the final axial force F3 from being calculated, it is conceivable to select the axial force with the larger absolute value of either the end axial force or the curb axial force as the limit axial force F2. Furthermore, in order to provide the driver with a more appropriate steering feel, it is conceivable to adjust the value of at least one of the basic axial force F1 and the limit axial force F2 depending on the steering state or the vehicle running state.

[0055] However, it is required to reduce the calculation load on the control device 50. In this regard, the fact that the limit axial force calculation unit 82 calculates both the end axial force and the curb axial force separately, and furthermore, that it executes arbitration processing between the end axial force and the curb axial force, is one factor that hinders reduction of the calculation load on the limit axial force calculation unit 82. There is also a concern that the calculation load on the limit axial force calculation unit 82 will increase.

[0056] Therefore, in this embodiment, the limit axial force calculation unit 82 has the following configuration. As shown in FIG. 4, the limit axial force calculation unit 82 has a determination unit 90, a steering angle holding unit 91, a difference calculation unit 92, a reference angle calculation unit 93, a final difference calculation unit 94, a pre-limit axial force calculation unit 95, a gain calculation unit 96, a differentiator 97, a multiplier 98, and an adder 99.

[0057] The determination unit 90 determines whether the steered wheels 16 have hit an obstacle such as a curb. For example, when all of the following four determination conditions (C1) to (C4) are met, the determination unit 90 determines that the steered wheels 16 have hit an obstacle such as a curb.

[0058] (C1)│Δθ p (=│θ p* -θ p │)│>θ pth (C2)│I b │>I th (C3)│ω p │<ω th (C4)│V│ <V th In the judgment condition C1, "θ p * " is the target pinion angle calculated by the target pinion angle calculation unit 62. "θ p " is the pinion angle calculated by the pinion angle calculation unit 61. "Δθ p " is the target pinion angle θ p * From the actual pinion angle θ p The angle difference is obtained by subtracting θ pth " is the angle difference threshold. pth is set based on the following viewpoint: When the steered wheels 16 hit an obstacle, it is difficult to steer the steered wheels 16 toward the further turning side or the return side. In this state, when the steering wheel 11 is steered toward the further turning side or the return side, the target pinion angle θ p * increases, whereas the steering angle θ w , and thus the pinion angle θ p Therefore, when the steered wheels 16 are in contact with an obstacle, the more the steered wheels 16 are attempted to be steered, the more the target pinion angle θ p * and pinion angle θ p Therefore, the difference between the angle Δθ p The larger the absolute value of the angle difference Δθ, the higher the probability that the steered wheels 16 have hit an obstacle. p is a value indicating the degree of likelihood that the steered wheels 16 are hitting an obstacle. pth is set by experiment or simulation, taking into consideration tolerances due to noise from the rotation angle sensor 43 and the like.

[0059] In the judgment condition C2, "I b " is the current I of the steering motor 41 b The value of "I th " is the current threshold. Current threshold I th is set based on the following viewpoint: In other words, when the steered wheels 16 are in contact with an obstacle, the more the steered wheels 16 are tried to be steered, the more the current I b Therefore, the absolute value of the current I of the steering motor 41 increases. b The larger the absolute value of I, the higher the probability that the steered wheels 16 have hit an obstacle. b The value of I also indicates the degree of likelihood that the steered wheels 16 are hitting an obstacle. th is set by experiment or simulation.

[0060] In the judgment condition C3, "ω p " is the pinion angular velocity, and the pinion angle θ p It can be obtained by differentiating "ω th " is the angular velocity threshold. th is set based on the following viewpoint: In other words, it is difficult to steer the steerable wheels 16 when the steerable wheels 16 are hitting an obstacle. Therefore, the steering speed of the steerable wheels 16, and therefore the pinion angular velocity ω p The smaller the absolute value of the pinion angular velocity ω, the higher the probability that the steered wheels 16 have hit an obstacle. p is also a value indicating the degree of likelihood that the steered wheels 16 are hitting an obstacle. th is set by experiment or simulation, taking into consideration tolerances due to noise from the rotation angle sensor 43 and the like.

[0061] In the determination condition C4, "V" is the vehicle speed detected by the vehicle speed sensor 501. th" is a vehicle speed threshold value that serves as a reference for determining whether the vehicle is traveling at a low speed. th is set based on the vehicle speed V in the low speed range (0 km / h to less than 40 km / h), and is set to, for example, "40 km / h." th is set from the viewpoint of determining whether the steered wheels 16 are hitting an obstacle, and whether the driving state is appropriate to notify the driver that the steered wheels 16 are hitting an obstacle by suddenly changing the steering reaction force.

[0062] The determination unit 90 sets the value of flag F according to the determination result of whether or not the steered wheels 16 have hit an obstacle. When it is determined that the steered wheels 16 have not hit an obstacle, that is, when at least one of the four determination conditions C1 to C4 is not met, the determination unit 90 sets the value of flag F to "0." When it is determined that the steered wheels 16 have hit an obstacle, that is, when all four determination conditions C1 to C4 are met, the determination unit 90 sets the value of flag F to "1."

[0063] The steering angle holding unit 91 determines the value of the flag F set by the determination unit 90 and the steering angle θ calculated by the steering angle calculation unit 51. s When the determination unit 90 determines that the steered wheels 16 have hit an obstacle, that is, when the value of the flag F set by the determination unit 90 is "1," the steering angle holding unit 91 takes in the steering angle θ at that time as shown in the following equation (D1). s The steering angle θ when the curb is detected s This is because the steering angle θ s 1 is the curb axial force generation start position, and the steering angle θ s Steering angle θ based on 1 s When the determination unit 90 does not determine that the steered wheels 16 are hitting an obstacle, that is, when the value of the flag F set by the determination unit 90 is "0", the steering angle holding unit 91 holds the steering angle θ sThe steering angle holding unit 91 does not hold the steering angle θ s The steering angle θ when the curb is not detected s 1 to the reference angle calculation unit 93. That is, when the value of the flag F is "0", the steering angle θ s 1 is the steering angle θ at that time s is the same value as

[0064] θ s 1=θ s …(D1) The difference calculation unit 92 calculates the value of the flag F set by the determination unit 90 and the pinion angle θ calculated by the pinion angle calculation unit 61. p Pinion angle θ p is the steering angle θ of the steered wheels 16 w When the value of flag F set by determination unit 90 is "1", difference calculation unit 92 calculates the steering angle θ at that time as shown in the following equation (D2). w The steering angle θ when the curb is detected w The difference calculation unit 92 holds the pinion angle θ p Based on the steering angle θ w can be calculated.

[0065] θ w 1=θ w …(D2) When the value of the flag F set by the determination unit 90 is "1", the difference calculation unit 92 calculates the steering angle θ at the time of the curb determination as shown in the following equation (D3): w 1 and the current steering angle θ w The difference Δθ w This is calculated based on the steering angle θ w Steering angle θ based on 1 w The curb axial force generation start position, that is, the steering angle θ at the time of curb determination, is determined by the amount of change in s It is intended to update 1.

[0066] Δθ w =θ w -θ w 1 …(D3) When the value of the flag F set by the determination unit 90 is "0", the difference calculation unit 92 calculates the steering angle θ w When the value of flag F is "0", the difference calculation unit 92 does not hold the value of the difference Δθ based on the above equation (D3). w does not calculate.

[0067] The reference angle calculation unit 93 calculates the steering angle θ when the curb is determined or when the curb is not determined from the steering angle holding unit 91. s 1. The difference Δθ calculated by the difference calculation unit 92 w , and the virtual end angle θ stored in the memory device of the control device 50. e The virtual end angle θ e The steering angle θ corresponding to the limit position of the virtual operation range of the steering wheel 11 is s , or the pinion angle θ corresponding to the limit position of the imaginary movable range of the steering shaft 14 p Virtual end angle θ e is the steering angle θ when the rotation position of the steering wheel 11 reaches the limit position of its virtual operation range. s or the pinion angle θ when the steering shaft 14 reaches the limit position of its movable range. p is set based on the neighborhood values ​​of

[0068] The limit axial force calculation unit 82 calculates the virtual end angle θ e For example, the calculation unit may have a calculation unit that calculates the virtual end angle θ with a smaller absolute value as the vehicle speed V increases. e Calculate the following.

[0069] The reference angle calculation unit 93 calculates the steering angle θ at the time of curb determination as shown in the following equation (D4). s When 1 is captured, the captured steering angle θ s Difference Δθ to 1 w By adding hold Calculate the reference angle θ hold is the steering angle θ when the curb is detected s 1 is the steering angle θ when the curb is detected w Steering angle θ based on 1 wThe value is updated by the amount of change in

[0070] θ hold =θ s 1+Δθ w …(D4) Incidentally, the reference angle calculation unit 93 calculates the steering angle θ s When 1 is captured, the captured steering angle θ s 1 as the reference angle θ hold This is because when the steered wheels 16 are not in contact with an obstacle and the curb is not determined, the difference Δθ w is not calculated, that is, the difference Δθ w This is because the value of becomes "0".

[0071] The reference angle calculation unit 93 calculates the virtual end angle θ as shown in the following equation (D5). e Based on the reference angle θ hold By performing the limiting process for the final reference angle θ hold 1. This is because the position of the steering wheel 11 or the position of the steered shaft 14 is calculated based on the virtual end angle θ e The intention is to generate a curb axial force starting from the point where the curb axial force reaches ...

[0072] θ hold 1=GRD(θ hold ,θ e ) …(D5) The reference angle calculation unit 93 calculates the reference angle θ hold and the virtual end angle θ e The reference angle calculation unit 93 compares the values ​​of the reference angle θ hold The value of the virtual end angle θ e If the value of θ exceeds the reference angle hold The value of the virtual end angle θ e The reference angle calculation unit 93 limits the reference angle θ hold The value of the virtual end angle θ e If the value is less than or equal to the reference angle θ calculated using equation (D4), hold However, the final reference angle θ hold It is calculated as 1.

[0073] The final difference calculation unit 94 calculates the final reference angle θ hold 1, and the steering angle θ calculated by the steering angle calculation unit 51 s The final difference calculation unit 94 also takes in the virtual end angle θ stored in the storage device of the control device 50. e , and the value of flag F set by the determination unit 90. The final difference calculation unit 94 calculates the final reference angle θ as shown in the following equation (D6): hold 1 and the current steering angle θ s The difference Δθ between

[0074] Δθ=θ s -θ hold 1 …(D6) The final difference calculation unit 94 calculates the final reference angle θ by correcting the value of the difference Δθ according to the following three situations (E1) to (E3), for example: hold 1 and the current steering angle θ s The final difference Δθ1 is calculated.

[0075] (E1) Without curb detection If it is not determined that the steered wheels 16 have hit an obstacle, i.e., if the value of flag F is "0", the final difference calculation unit 94 sets the difference Δθ calculated using the previous equation (D6) as the final difference Δθ1 as shown in the following equation (D7).

[0076] Δθ1=Δθ …(D7) (E2) When curb detection is enabled When it is determined that the steered wheels 16 have hit an obstacle, i.e., when the value of flag F is "1," the final difference calculation unit 94 corrects the difference Δθ calculated using the above-mentioned equation (D6) to a smaller value. For example, the final difference calculation unit 94 corrects the value of the difference Δθ to, for example, "½" or "⅓." The final difference calculation unit 94 sets the corrected difference Δθ2 as the final difference Δθ1, as shown in the following equation (D8). This is intended to reproduce the gradual increase in reaction force accompanying elastic deformation of the tires when the steered wheels 16 attempt to turn after hitting an obstacle.

[0077] Δθ1=Δθ2 …(D8) (E3) When curb detection and end detection are enabled The final difference calculation unit 94 calculates, for example, the virtual end angle θ e and steering angle θ s Through a comparison with the reference value, an end determination is made to determine whether the rotational position of the steering wheel 11 has reached the limit position of the virtual operation range.

[0078] When it is determined that the steered wheels 16 have hit an obstacle and that the rotational position of the steering wheel 11 has reached the limit position of its virtual operation range, the final difference calculation unit 94 executes the following processing.

[0079] That is, the final difference calculation unit 94 corrects the difference Δθ calculated using the above equation (D6) to a smaller value. The final difference calculation unit 94 corrects the value of the difference Δθ, for example, to a value of "½" or "⅓." The final difference calculation unit 94 provisionally sets the corrected difference Δθ2 as the first final difference Δθ1, as shown in the following equation (D9):

[0080] Δθ1=Δθ2 …(D9) Further, the final difference calculation unit 94 calculates the steering angle θ as shown in the following equation (D10). s and virtual end angle θ e The difference between these values ​​is calculated, and the calculated difference value is temporarily set as the second final difference Δθ1.

[0081] Δθ1=θ s -θ e …(D10) The final difference calculation unit 94 selects the larger of the first final difference Δθ1 calculated using the above equation (D9) and the second final difference Δθ1 calculated using the above equation (D10).

[0082] The pre-limit axial force calculation unit 95 calculates the pre-limit axial force F21 based on the final difference Δθ1 calculated by the final difference calculation unit 94. The pre-limit axial force calculation unit 95 calculates the pre-limit axial force F21 using a limit axial force map stored in the storage device of the control device 50.

[0083] As shown in the graph of FIG. 5, the limit axial force map M1 is a two-dimensional map with the horizontal axis representing the final difference Δθ1 and the vertical axis representing the pre-limit axial force F21. The limit axial force map M1 has the following characteristics. That is, as shown by the characteristic line L1, the pre-limit axial force F21 is set to a larger value as the value of the final difference Δθ1 increases. However, as the value of the final difference Δθ1 increases, the slope, which is the rate of change of the pre-limit axial force F21 relative to the final difference Δθ1, gradually increases. That is, the characteristic line L1 is a curve with a positive, gradually increasing slope.

[0084] Incidentally, when it is determined that the steered wheels 16 are hitting an obstacle (situations E2 and E3), the difference Δθ calculated using equation (D6) is corrected to a smaller value. The relationship between the final difference Δθ1 and the pre-limit axial force F21 at this time is shown by the characteristic line L2. The characteristic line L2 shows the relationship between the final difference Δθ1 and the pre-limit axial force F21 when it is assumed that the value of the difference Δθ calculated using equation (D6) is not reduced. The characteristic line L2 is a curve with a positive, gradually increasing slope. However, the slope of the characteristic line L2 is generally smaller than the slope of the characteristic line L1. In other words, when it is determined that the steered wheels 16 are hitting an obstacle, the pre-limit axial force calculation unit 95 calculates the pre-limit axial force F21 using a limit axial force map M1 in which the slope of the characteristic line is made gentler by extending the characteristic line L1 along the horizontal axis.

[0085] The pre-limiting axial force calculation unit 95 corresponds to an axial force calculation unit that calculates a limiting axial force (pre-limiting axial force F21) for virtually limiting the operation of the steering wheel 11 according to the value of the final difference Δθ1.

[0086] The gain calculation unit 96 calculates a gain G for damping in accordance with the final difference Δθ1 calculated by the final difference calculation unit 94. The gain calculation unit 96 calculates the gain G using a gain map M2 stored in the storage device of the control device 50.

[0087] As shown in the graph of FIG. 6, the gain map M2 is a map with the horizontal axis representing the final difference Δθ1 and the vertical axis representing the gain G. The gain map M2 has the following characteristics. That is, as the value of the final difference Δθ1 increases, the value of the pre-limiting axial force F21 is set to a larger value. However, as the value of the final difference Δθ1 increases, the slope, which is the rate of change in the gain G relative to the final difference Δθ1, gradually increases.

[0088] The differentiator 97 calculates the steering angle θ s The steering angle θ s By differentiating the steering angular velocity ω s Calculate the following. The multiplier 98 multiplies the gain G calculated by the gain calculation unit 96 and the steering angular velocity ω calculated by the differentiator 97 by s The damping axial force F22 is calculated by multiplying this by Δθ1. The reason for calculating the damping axial force is as follows. That is, the larger the gradient of the change in the pre-limiting axial force F21 relative to the final difference Δθ1, the more likely it is that the value of the pre-limiting axial force F21 will oscillatorily change with changes in the value of the final difference Δθ1. For this reason, the damping axial force F22 is calculated to stabilize the value of the pre-limiting axial force F21 relative to the final difference Δθ1.

[0089] The adder 99 calculates the final limit axial force F2 by adding the pre-limit axial force F21 calculated by the pre-limit axial force calculation unit 95 and the damping axial force F22 calculated by the multiplier 98.

[0090] <Operation of the embodiment> Next, the operation of this embodiment will be described. When the operation position of the steering wheel 11 has not reached a position near the limit position of its operation range, or when the steered shaft 14 has not reached a position near the limit position of its physical movable range, the limit axial force calculation unit 82 does not basically calculate the limit axial force F2. Also, when the limit axial force calculation unit 82 does not determine that the steered wheels 16 are hitting an obstacle, the limit axial force calculation unit 82 does not basically calculate the limit axial force F2. Therefore, the basic axial force F1 calculated by the basic axial force calculation unit 81 becomes the final axial force F3. In this case, the torque conversion value T2 obtained by converting this final axial force F3 into torque is * is the steering reaction force command value T * By reflecting the steering reaction force in the steering wheel 11, it becomes possible to apply a steering reaction force corresponding to the vehicle behavior or road surface condition to the steering wheel 11. The driver can grasp the vehicle behavior or road surface condition by feeling the steering reaction force via the steering wheel 11 as a response.

[0091] When the operation position of the steering wheel 11 reaches the limit position of its operation range, or when the steered shaft 14 reaches the limit position of its physical movable range, the limit axial force calculation unit 82 calculates the limit axial force F2 as the end axial force according to the final difference Δθ1. Therefore, the value obtained by adding the limit axial force F2 as the end axial force to the basic axial force F1 becomes the final axial force F3. In this case, the torque equivalent value T2 obtained by converting the final axial force F3 into torque is * is the steering reaction force command value T * Therefore, the driver must turn the steering wheel at a constant angle of θ s It becomes difficult to operate steering wheel 11 in a direction in which the absolute value of θ becomes larger. Therefore, by feeling a sense of hitting a dead end as a steering reaction force (response), the driver can recognize that steering wheel 11 has reached the limit position of its virtual operation range, or that steered shaft 14 has approached the limit position of its physical movable range.

[0092] When further turning or turning is performed while the steered wheels 16 are in contact with an obstacle, the limit axial force calculation unit 82 calculates a limit axial force F2 as a curb axial force according to the final difference Δθ1. Therefore, the value obtained by adding the limit axial force F2 as a curb axial force to the basic axial force F1 becomes the final axial force F3. In this case, the torque conversion value T2 obtained by converting the final axial force F3 into torque is * is the steering reaction force command value T * The steering reaction force increases rapidly as a result of the steering reaction force being reflected in the steering wheel 11. This makes it difficult for the driver to perform further steering or turning. Therefore, the driver can recognize that the steered wheels 16 are hitting an obstacle such as a curb by feeling a sense of hitting an obstacle as the steering reaction force. Incidentally, the limiting axial force F2 as the curb axial force increases more gradually with an increase in the final difference Δθ1 than the limiting axial force F2 as the end axial force. This allows the driver to feel a response through the steering wheel 11 that is closer to the actual situation of trying to steer the steered wheels 16 further after they have hit an obstacle.

[0093] <Effects of the embodiment> Therefore, according to this embodiment, the following effects can be obtained. (1) A reference angle θ calculated depending on whether the steering operation of the steered wheels 16 is restricted or not hold and the current steering angle θ s Depending on the difference between these, either the limit axial force F2 as a curb axial force or the limit axial force F2 as an end axial force is calculated. The limit axial force F2 as a curb axial force is an axial force that limits further operation of the steering wheel 11 in a situation where the steering operation of the steered wheels 16 is restricted. The end axial force is an axial force that limits steering that exceeds the virtual end angle of the steering wheel 11. In other words, the part that calculates the limit axial force F2 as a curb axial force and the limit axial force F2 as an end axial force is shared. Therefore, there is no need for processing to reconcile the curb axial force and the end axial force. This reduces the calculation load compared to when the curb axial force and the end axial force are calculated separately.

[0094] (2) When the steered wheels 16 attempt to turn further while the steering operation of the steered wheels 16 is restricted, the reaction force increases gradually as the tires elastically deform. When the steering operation of the steered wheels 16 is restricted, the value of the final difference Δθ1 calculated by the final difference calculation unit 94 is corrected and decreased. This makes it possible to increase the steering reaction force more gradually. Therefore, it is possible to apply to the steering wheel 11 a steering reaction force that more closely resembles the actual state in which the steering operation of the steered wheels 16 is restricted.

[0095] (3) When the steering operation of the steered wheels 16 is restricted and the rotational position of the steering wheel 11 has reached the limit position of its virtual operation range, the final difference calculation unit 94 uses the larger of the two final differences Δθ1 calculated for each case. This makes it possible to apply a steering reaction force to the steering wheel 11 according to the larger final difference Δθ1.

[0096] (4) The greater the gradient of the change in the limiting axial force F2 relative to the final difference Δθ1, the more likely it is that the pre-limiting axial force F21 and, consequently, the value of the limiting axial force F2 will fluctuate in response to changes in the value of the final difference Δθ1. In this regard, by incorporating the damping axial force F22 into the pre-limiting axial force F21, it is possible to stabilize the pre-limiting axial force F21 relative to the final difference Δθ1 and, consequently, the value of the final limiting axial force F2.

[0097] (5) Even if the steering operation of the steered wheels 16 is restricted, there is a risk that the steered wheels 16 may be turned, even if only slightly. s is corrected in accordance with the amount of steering of the steered wheels 16. s Based on the reference angle θ hold Therefore, even if the steered wheels 16 are turned while the steering operation of the steered wheels 16 is restricted, a more appropriate steering reaction force can be applied to the steering wheel 11.

[0098] <Other embodiments> This embodiment may be modified as follows. The limiting axial force calculation unit 82 may be configured without the difference calculation unit 92. In this case, the reference angle calculation unit 93 calculates the steering angle θ s 1 is the reference angle θ hold This becomes:

[0099] The limit axial force calculation unit 82 may have a configuration in which the gain calculation unit 96, the differentiator 97, the multiplier 98, and the adder 99 are omitted. In this case, the pre-limit axial force F21 calculated by the pre-limit axial force calculation unit 95 becomes the final limit axial force F2 as is. The pre-limit axial force calculation unit 95 corresponds to an axial force calculation unit that calculates the pre-limit axial force F21 as the final limit axial force F2 according to the value of the final difference Δθ1.

[0100] The final difference calculation unit 94 determines the curb by the reference angle θ hold and the current steering angle θ s It is not necessary to perform a correction to decrease the value of the difference Δθ between the The steering device 10 may be provided with a clutch. In this case, as shown by the two-dot chain line in FIG. 1 , the steering shaft 12 and the pinion shaft 13 are connected via a clutch 21. An electromagnetic clutch that connects and disconnects power by turning on and off current to an exciting coil is used as the clutch 21. The control device 50 executes an on / off control that switches the on / off state of the clutch 21. When the clutch 21 is disconnected, the power transmission between the steering wheel 11 and the steered wheels 16 is mechanically disconnected. When the clutch 21 is connected, the power transmission between the steering wheel 11 and the steered wheels 16 is mechanically connected.

[0101] The left and right steerable wheels 16 may be steerable independently of each other. In this case, the control device 50 steers the steerable wheels 16 by controlling the steering motors provided in the respective steerable wheels 16. [Explanation of symbols]

[0102] 11...Steering wheel 12...Steering shaft that constitutes the steering mechanism 14...Steering shaft constituting the steering mechanism 16...Steering wheel 31...Reaction motor 41...Steering motor 50...Control device (steering control device) 81...Basic axial force calculation section 82...Limited axial force calculation section 83...Adder (final axial force calculation unit) 91...Steering angle holding section 92...Difference calculation section 93...Reference angle calculation section 94...Final difference calculation section 95...Pre-limiting axial force calculation unit (axial force calculation unit) 96...Gain calculation section 98...Multiplier

Claims

1. A steering control device that controls a reaction motor that generates a steering reaction force applied to a steering wheel, the power transmission of which is separated from a steering shaft that steers steered wheels, based on a command value calculated in accordance with a steering state, a basic axial force calculation unit that calculates a basic axial force including an axial force that reflects at least a force acting on the steered shaft via the steered wheels when the steering wheel is operated within a predetermined operation range; a limiting axial force calculation unit that calculates a limiting axial force, which is an axial force for virtually limiting the operation of the steering wheel; a final axial force calculation unit that calculates a final axial force that is a final axial force to be reflected in the command value based on the basic axial force and the limiting axial force, the limiting axial force calculation unit is a steering angle holding unit that holds the steering angle at the time of the restriction when the steering operation of the steered wheels is restricted due to the steered wheels hitting an obstacle; a reference angle calculation unit that calculates a reference angle by executing a limiting process to limit the steering angle held by the steering angle holding unit when the steering operation of the steered wheels is limited, or the current steering angle when the steering operation of the steered wheels is not limited, to a virtual end angle corresponding to a limit position of a virtual operation range of the steering wheel; a final difference calculation unit that calculates a final difference between the reference angle and the current steering angle; an axial force calculation unit that calculates the limiting axial force in accordance with the value of the final difference.

2. 2. The steering control device according to claim 1, wherein the final difference calculation unit corrects the calculated final difference value so as to decrease it when the steering operation of the steered wheels is restricted.

3. 3. The steering control device according to claim 1, wherein, when the steering operation of the steered wheels is restricted and the rotational position of the steering wheel has reached a limit position of its virtual operation range, the final difference calculation unit uses the larger of the final difference calculated as the steering operation of the steered wheels is restricted, and the final difference calculated as the rotational position of the steering wheel has reached the limit position of its virtual operation range.

4. a gain calculation unit that calculates a damping gain for the limiting axial force in accordance with the value of the final difference calculated by the final difference calculation unit; A multiplier that calculates an axial force for damping to be reflected in the limiting axial force by multiplying the gain calculated by the gain calculation unit by the steering angular velocity.

5. a difference calculation unit that calculates, when the turning operation of the steered wheels is restricted, a difference between a turning angle of the steered wheels when the turning operation of the steered wheels is restricted and a current turning angle, 5. The steering control device according to claim 1, wherein when the steering operation of the steered wheels is restricted, the reference angle calculation unit corrects the steering angle held by the steering angle holding unit in accordance with the difference value calculated by the difference calculation unit, and calculates the reference angle by executing the restriction process on the corrected steering angle.

Images