Steering control system

Abstract

To provide a steering control device that can appropriately adjust the return speed of a steering wheel when the hand is released from the steering wheel. 【Solution means】The steering control device executes a first process for calculating a basic torque that is the basis for calculating a reaction torque command value, and a target steering return torque T for compensating the return characteristics of the steering wheel. re * And a second process. The second process includes a third process and a fourth process. The third process calculates a target steering angular velocity ω based on the steering state of the steering wheel, and performs feedback control to make the actual steering angular velocity ω follow the target steering angular velocity ω, and calculates a basic feedback return torque T. * Is a process of calculating. The fourth process is a process of calculating a torque gain G that multiplies the basic feedback return torque T based on the steering torque T and the axial force gradient γ. The axial force gradient γ reflects the axial force acting on the steering shaft. * Is a process of calculating. The fourth process is a process of calculating a torque gain G that multiplies the basic feedback return torque T based on the steering torque T and the axial force gradient γ. The axial force gradient γ reflects the axial force acting on the steering shaft. FB Is a process of calculating. The fourth process is a process of calculating a torque gain G that multiplies the basic feedback return torque T based on the steering torque T and the axial force gradient γ. The axial force gradient γ reflects the axial force acting on the steering shaft. h Is a process of calculating. The fourth process is a process of calculating a torque gain G that multiplies the basic feedback return torque T based on the steering torque T and the axial force gradient γ. The axial force gradient γ reflects the axial force acting on the steering shaft. FB Is a process of calculating. The fourth process is a process of calculating a torque gain G that multiplies the basic feedback return torque T based on the steering torque T and the axial force gradient γ. The axial force gradient γ reflects the axial force acting on the steering shaft. T Is a process of calculating. The fourth process is a process of calculating a torque gain G that multiplies the basic feedback return torque T based on the steering torque T and the axial force gradient γ. The axial force gradient γ reflects the axial force acting on the steering shaft.

Description

[Technical Field]

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

[0002] Conventionally, steering control devices that perform steering return control are known. Steering return control is a control that assists steering the steering wheel when returning it to the neutral position. For example, the steering control device described in Patent Document 1 controls an electric power steering device. The steering control device adds a return control amount to assist with steering back steering to the basic assist control amount for assisting with steering inward.

[0003] The steering control system calculates the basic assist control amount based on steering torque and vehicle speed. It also calculates the target steering angular velocity based on steering angle and steering torque, and performs feedback control of the steering angular velocity to calculate the return control amount so that the actual steering angular velocity follows the target steering angular velocity. The steering control system corrects the target steering angular velocity according to the steering torque. This allows the actual steering angular velocity to follow the target steering angular velocity at an appropriate speed. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2017-24449 [Overview of the project] [Problems that the invention aims to solve]

[0005] The steering control device described in Patent Document 1 has the following concerns. For example, when the driver of a vehicle releases their hands from the steering wheel, the return speed of the steering wheel depends on the axial force acting on the steering shaft. Furthermore, the axial force depends on the vehicle speed. Therefore, depending on the vehicle speed, the return speed of the steering wheel may become unstable. The return speed is the steering angular velocity when the steering wheel returns to the neutral position. [Means for solving the problem]

[0006] A steering control device capable of solving the above problems is configured to control the steering device of a vehicle. The steering device includes a motor configured to generate torque to be applied to the steering wheel. The steering control device includes a processing circuit configured to calculate a torque command value for controlling the motor based on the steering state of the steering wheel. The processing circuit is configured to perform a first process and a second process. The first process is to calculate a basic torque that forms the basis for calculating the torque command value based on the steering state of the steering wheel. The second process is to calculate a steering return torque to compensate for the return characteristics of the steering wheel according to the steering state of the steering wheel. The second process includes a third process and a fourth process. The third process is to calculate a target steering angular velocity based on the steering state of the steering wheel, and to calculate a basic return torque by performing feedback control to make the actual steering angular velocity follow the target steering angular velocity. The fourth process involves calculating a torque gain multiplied by the basic return torque, based on the steering torque and a state variable that reflects the axial force acting on the steering shaft of the vehicle.

[0007] For example, when a vehicle driver releases their hands from the steering wheel, the steering wheel's return speed depends on the axial force acting on the steering shaft. Furthermore, the axial force depends on the vehicle speed. According to the steering control device described above, the torque gain is calculated considering a state variable that reflects the axial force. Therefore, by reflecting the steering return torque obtained by multiplying the basic return torque by the torque gain in the torque command value, the steering wheel's return speed when the driver releases their hands from the steering wheel can be appropriately adjusted.

[0008] In the steering control device described above, the processing circuit may be configured to calculate the torque gain using a torque gain map that defines the relationship between the steering torque and the torque gain according to the state variable.

[0009] With this configuration, torque gain can be easily obtained by using a torque gain map. In the steering control device described above, the value of the torque gain may decrease as the absolute value of the steering torque increases, and the value of the torque gain may increase as the value of the state variable increases.

[0010] In this configuration, the larger the absolute value of the steering torque, the smaller the value of the torque gain. Therefore, when the driver applies steering torque in the direction of turning the steering wheel, the value of the torque gain, and consequently the steering return torque, decreases. Consequently, the feeling of resistance to steering can be reduced. Conversely, when the driver applies steering torque in the direction of turning the steering wheel back, the value of the torque gain, and consequently the steering return torque, increases. Therefore, the steering load on the steering wheel can be reduced.

[0011] In the steering control device described above, the torque gain change characteristics with respect to the change in the absolute value of the steering torque may have multiple characteristics with different slopes. In this case, the processing circuit may be configured to select one of the multiple characteristics according to the state variable.

[0012] With this configuration, the torque gain change characteristics in response to changes in the absolute value of steering torque can be changed to one of several characteristics depending on the state variable. In the steering control device described above, the state variable may be the axial force gradient, which is the rate of change of the axial force.

[0013] With this configuration, the characteristic of the torque gain change in response to a change in the absolute value of the steering torque can be changed according to the axial force gradient. [Effects of the Invention]

[0014] According to the steering control device of the present invention, the return speed of the steering wheel can be appropriately adjusted when the hands are released from the steering wheel. [Brief explanation of the drawing]

[0015] [Figure 1] This is a diagram showing the configuration of a steering system equipped with one embodiment of the steering control device. [Figure 2] This is a block diagram of a reaction force control device and steering control device according to one embodiment. [Figure 3] This is a block diagram of a reaction force torque command value calculation unit according to one embodiment. [Figure 4] This is a block diagram of an assist torque command value calculation unit according to one embodiment. [Figure 5] This is a block diagram of a steering return control unit according to one embodiment. [Figure 6] This is a graph showing a torque gain map according to one embodiment. [Figure 7] This graph shows the change in steering wheel return speed in the comparative example. [Figure 8] This graph shows the change in steering wheel return speed in the comparative example. [Figure 9] This is a graph showing the change in the return speed of the steering wheel according to one embodiment. [Modes for carrying out the invention]

[0016] The following describes one embodiment of a steering control device. <Overall configuration of the steering control system> As shown in Figure 1, the steering control device 1 controls a steer-by-wire type steering device 2. The steering device 2 has a steering mechanism 3 and a steering mechanism 4. The steering mechanism 3 is a mechanism that is steered by the driver via the steering wheel 5. The steering mechanism 4 is a mechanism that steers the steering wheels 6 of the 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 control device 1B. The reaction force control device 1A controls the steering mechanism 3. The steering control device 1B controls the steering mechanism 4.

[0017] Depending on the product specifications, the reaction force control device 1A and the steering control device 1B may be integrated into a single steering control device 1. In this case, the reaction force control device 1A corresponds to the reaction force control unit, and the steering control device 1B corresponds to the steering control unit.

[0018] The steering mechanism 3 includes a steering shaft 11, a reaction motor 12, and a reduction gear 13. The steering wheel 5 is rotatably connected to the steering shaft 11. The reaction motor 12 is the source of the steering reaction force applied to the steering shaft 11. The steering reaction force is a force in the opposite direction to the steering direction of the steering wheel 5. The reaction motor 12 is, for example, a three-phase brushless motor. The reduction gear 13 reduces the rotation of the reaction motor 12 and transmits the reduced rotation to the steering shaft 11.

[0019] The steering mechanism 4 includes a pinion shaft 21, a steering shaft 22, and a housing 23. The housing 23 rotatably supports the pinion shaft 21. The housing 23 also reciprocates the steering shaft 22. Power transmission between the steering shaft 22 and the steering wheel 5 is isolated. The pinion shaft 21 is positioned 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, which are ball joints. The ends of the tie rods 25 are connected to knuckles (not shown) to which the steering wheel 6 is assembled.

[0020] The steering mechanism 4 comprises a steering motor 31, a transmission mechanism 32, and a conversion mechanism 33. The steering motor 31 is the source of the steering force applied to the steering shaft 22. The steering force is the force that causes the steering wheel 6 to turn. The steering motor 31 is, for example, a three-phase brushless motor. The transmission mechanism 32 is, for example, a belt drive 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 axial motion of the steering shaft 22.

[0021] As the steering shaft 22 moves axially, the steering angle θ of the steering wheel 6 changes. w The pinion teeth 21a of the pinion shaft 21 mesh with the rack teeth 22a of the steering shaft 22, and therefore rotate in conjunction with the movement of the steering shaft 22. The pinion shaft 21 is a shaft that rotates in conjunction with the steering action of the steering wheel 6.

[0022] The reaction force control device 1A and the steering control device 1B each have a processing circuit that includes one of the following three configurations A1, A2, and A3. The processing circuit of the reaction force control device 1A is the first processing circuit, and the processing circuit of the steering control device 1B is the second processing circuit.

[0023] A1. One or more processors that operate according to a computer program, which is software. A processor includes a CPU (Central Processing Unit) and memory. A2. One or more dedicated hardware circuits, such as application-specific integrated circuits (ASICs), that perform at least some of the various processes. An ASIC includes a CPU and memory.

[0024] A3. A circuit combining configurations A1 and A2. Memory is a medium readable by a computer that stores programs describing processes or instructions for the computer. In this embodiment, the computer is the CPU. Memory includes RAM (Random Access Memory) and ROM (Read Only Memory). The CPU performs various controls by executing the programs stored in memory at predetermined calculation cycles.

[0025] The reaction force control device 1A and the steering control device 1B each acquire detection results from on-board sensors. The reaction force control device 1A acquires detection results from, for example, the vehicle speed sensor 41, the torque sensor 42, and the first rotation angle sensor 43. The steering control device 1B acquires detection results from, for example, the second rotation angle sensor 44.

[0026] The vehicle speed sensor 41 detects the vehicle speed V. The vehicle speed V is a state variable that reflects the vehicle's driving state. The torque sensor 42 is located on the steering shaft 11. The torque sensor 42 is positioned on the steering wheel 5 side relative to the connection portion of the reduction gear 13 on the steering shaft 11. The torque sensor 42 measures the steering torque T applied to the steering shaft 11. h It detects the steering torque T. h This is calculated based on the amount of twist of the torsion bar 42a provided on the steering shaft 11. Steering torque T hFor example, it becomes a positive value when the steering wheel 5 is steered to the right with respect to the neutral position, and becomes a negative value when the steering wheel 5 is steered to the left with respect to the neutral position. The neutral position is the rotational position of the steering wheel 5 corresponding to the straight-ahead state of the vehicle. The steering torque T h is a state variable that reflects the steering state of the steering wheel 5.

[0027] The first rotation angle sensor 43 is provided on the reaction force motor 12. The first rotation angle sensor 43 detects the rotation angle θ a of the reaction force motor 12. The second rotation angle sensor 44 is provided on the steering motor 31. The second rotation angle sensor 44 detects the rotation angle θ b of the steering motor 31.

[0028] The reaction force control device 1A executes reaction force control. The reaction force control is control for generating a steering reaction force corresponding to the steering torque T h in the reaction force motor 12. 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 first 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. ​​​​​​​​​​As shown in Figure 2, the reaction force control device 1A includes a steering angle calculation unit 51, a reaction force torque command value calculation unit 52, and an energization control unit 53.

[0031] The steering angle calculation unit 51 calculates the rotation angle θ of the reaction motor 12 detected through the first rotation angle sensor 43. a Based on this, the steering angle θ of the steering wheel 5 s The steering angle θ is calculated. s This is the rotation angle of the steering wheel 5 relative to the neutral position of the steering wheel 5. Steering angle θ s This is a state variable that reflects the steering state of the steering wheel 5.

[0032] The reaction torque command value calculation unit 52 calculates the steering torque T h And the reaction torque command value T based on the vehicle speed V. * The reaction force torque command value T is calculated. * This is the target value of the steering reaction force generated by the reaction force motor 12. The steering reaction force is the torque in the opposite direction to the steering direction of the steering wheel 5. Steering torque T h The larger the absolute value of T, and the slower the vehicle speed V, the larger the reaction force torque command value T. * The absolute value of becomes larger.

[0033] The energization control unit 53 controls the reaction force torque command value T. * The power supplied to the reaction motor 12 corresponds to the reaction torque command value T. Specifically, the power supply control unit 53 supplies power to the reaction torque command value T. * Based on this, the current command value for the reaction motor 12 is calculated. The power supply control unit 53, through the current sensor 54 provided in the power supply path to the reaction motor 12, receives the current I generated in the power supply path. a The value of current I is detected. a The value of is the value of the current supplied to the reaction motor 12. The energization control unit 53 controls the current command value and current I a The deviation from the value is calculated, and the power supply to the reaction motor 12 is controlled to eliminate the deviation. As a result, the reaction motor 12 controls the reaction torque command value T * It generates torque corresponding to the value.

[0034] <Configuration of steering control device 1B> Next, the configuration of the steering control device 1B will be described. As shown in Figure 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.

[0035] The pinion angle calculation unit 61 calculates the rotation angle θ of the steering motor 31 detected through the first rotation angle sensor 43. b Based on this, the pinion angle θ p The calculation is performed. Pinion angle θ p This is the rotation angle of the pinion shaft 21, and corresponds to the actual angle of the pinion shaft 21. The steering motor 31 and the pinion shaft 21 are linked via the transmission mechanism 32, the conversion mechanism 33, and the steering shaft 22. Therefore, the rotation angle θ of the steering motor 31 b and pinion angle θ p There is a correlation between this and the rotation angle θ of the steering motor 31. b From the pinion angle θ p The pinion shaft 21 is meshed with the steering shaft 22. Therefore, the pinion angle θ can be determined. p There is also a correlation between this and the amount of movement of the steering shaft 22. That is, the pinion angle θ p The steering angle θ of the steering wheel 6. w In other words, it is a state variable that reflects the steering state of the steering wheel 6.

[0036] 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 * The target pinion angle θ is calculated. p * The pinion angle θ is p This is the target angle. The target pinion angle calculation unit 62 calculates the target pinion angle θ so that the steering angle ratio set according to the product specifications is realized. p * The rudder angle ratio is calculated as the steering angle θ. s The steering angle θ relative to this anglew It is the ratio of .

[0037] The target pinion angle calculation unit 62 sets the steering angle ratio according to the vehicle's driving conditions, such as the vehicle speed V, and sets the target pinion angle θ according to this set steering angle ratio. p * The target pinion angle calculation unit 62 calculates the steering angle θ as the vehicle speed V decreases. s The steering angle θ relative to this angle w The target pinion angle θ increases as much as possible. p * The target pinion angle calculation unit 62 calculates the steering angle θ as the vehicle speed V increases. s The steering angle θ relative to this angle w To make it smaller, the target pinion angle θ p * The target pinion angle calculation unit 62 calculates the steering angle θ in order to achieve the steering angle ratio set according to the vehicle's driving state. s The correction angle is calculated for the steering angle θ, and this calculated correction angle is used as the steering angle θ. s By adding this, the target pinion angle θ corresponds to the steering angle ratio. p * Perform the calculation.

[0038] Depending on the product specifications, the target pinion angle calculation unit 62 will calculate the target pinion angle θ such that the steering angle ratio is "1:1" regardless of the vehicle's driving conditions. p * You may also perform the calculation in this way.

[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 pinion angle θ calculated by the pinion angle calculation unit 61 p The pinion angle feedback control unit 63 takes in the pinion angle θ. p The target pinion angle θ p * To follow this, the pinion angle θ p Through feedback control, the steering torque command value T p *The steering torque command value T is calculated. p * This is a command value for the torque generated by the steering motor 31, and is the target value for the steering force.

[0040] The energization control unit 64 controls the steering torque command value T p * The power supply control unit 64 supplies power to the steering motor 31 according to the steering torque command value T. p * Based on this, the current command value for the steering motor 31 is calculated. The power supply control unit 64, through a current sensor 65 provided in the power supply path to the steering motor 31, receives the current I generated in the power supply path. b The value of current I is detected. b The value of is the value of the current supplied to the steering motor 31. The energization control unit 64 controls the current command value and current I b The deviation from the value is calculated, and the power supply to the steering motor 31 is controlled to eliminate the deviation. As a result, the steering motor 31 controls the steering torque command value T p * It generates torque corresponding to the value.

[0041] <Configuration of the reaction force torque command value calculation unit 52> Next, the configuration of the reaction force torque command value calculation unit 52 will be described in detail. As shown in Figure 3, the reaction torque command value calculation unit 52 includes an assist torque command value calculation unit 81, an axial force calculation unit 82, and a subtractor 83.

[0042] The assist torque command value calculation unit 81 calculates the steering torque T detected through the torque sensor 42. h The vehicle speed V detected through the vehicle speed sensor 41 is acquired. The assist torque command value calculation unit 81 calculates the steering torque T hBased on the steering torque T and vehicle speed V, an assist torque command value T1 is calculated. The assist torque command value T1 corresponds to the target value of the assist torque when the steering device 2 is an electric power steering device. The assist torque is a force for assisting the steering of the steering wheel 5. The assist torque command value T1 is a torque in the same direction as the steering direction of the steering wheel 5. The absolute value of the steering torque T h The larger the absolute value of the steering torque T and the slower the vehicle speed V, the larger the absolute value of the assist torque command value T1 becomes.

[0043] The axial force calculation unit 82 takes in the pinion angle θ calculated by the pinion angle calculation unit 61 p and the current I of the steering motor 31 detected through the current sensor 65 b and the vehicle speed V detected through the vehicle speed sensor 41 and the steering angle θ calculated by the steering angle calculation unit 51 s The axial force calculation unit 82 takes in the pinion angle θ p the value of the current I of the steering motor 31 b and the steering angle θ s Based on these, the axial force acting on the steering shaft 22 is calculated. The axial force is an angular axial force, a current axial force, or a combined axial force. The axial force calculation unit 82 calculates an axial force torque T2 by converting the calculated axial force into a torque with respect to the steering shaft 11.

[0044] The angular axial force is, for example, an ideal axial force corresponding to the pinion angle θ p and does not reflect the road surface condition. The axial force calculation unit 82 calculates the angular axial force using, for example, an axial force map stored in a memory. The axial force map is a two-dimensional map that defines the relationship between the pinion angle θ p and the angular axial force according to the vehicle speed V. The axial force map has the following characteristics. That is, the larger the absolute value of the pinion angle θ p and the slower the vehicle speed V, the larger the absolute value of the angular axial force becomes.

[0045] The current axial force is the current I of the steering motor 31 bThe axial force corresponding to the value, which reflects the road surface condition. The axial force calculation unit 82, for example, multiplies the value of the current I of the steering motor 31 by a gain to calculate the current axial force. The gain is a coefficient corresponding to the vehicle speed V. The combined axial force is an axial force in which the angular axial force and the current axial force are mixed at a predetermined ratio. The ratio is a distribution ratio individually set for the angular axial force and the current axial force according to various state variables reflecting the vehicle behavior, the steering state, or the road surface condition. b The subtractor 83 takes in the assist torque command value T1 calculated by the assist torque command value calculation unit 81 and the axial force torque T2 calculated by the axial force calculation unit 82. The subtractor 83 calculates the reaction force torque command value T by subtracting the axial force torque T2 from the assist torque command value T1.

[0046] *

[0047] <Configuration of the assist torque command value calculation unit 81> Next, the configuration of the assist torque command value calculation unit 81 will be described in detail. As shown in FIG. 4, the assist torque command value calculation unit 81 includes a basic control unit 81A, a compensation control unit 81B, and an adder 81C.

[0048] The basic control unit 81A calculates a basic assist torque T11 based on the steering torque T and the vehicle speed V. The basic assist torque T11 is a torque that serves as a basis for generating a steering reaction force of an appropriate magnitude according to the steering torque T and the vehicle speed V. Also, the basic assist torque T11 is a torque that serves as a basis for calculating the assist torque command value T1. h h

[0049] The basic control unit 81A calculates the basic assist torque T11 using, for example, an assist torque map stored in a memory. The assist torque map is a three-dimensional map that defines the relationship between the steering torque T and the basic assist torque T11 according to the vehicle speed V. The assist torque map has the following characteristics. That is, the steering torque T h and the basic assist torque T11​​​​h The larger the absolute value of T11, and the slower the vehicle speed V, the larger the absolute value of the basic assist torque T11.

[0050] The compensation control unit 81B performs various compensation controls according to the steering state of the steering wheel 5. Compensation control is a control that aims to achieve a better steering feel and includes, for example, steering return control. Steering return control is a control that compensates for the return characteristics of the steering wheel 5 and appropriately returns the steering wheel 5 to the neutral position. The compensation control unit 81B controls the steering angle θ. s Based on this, the compensation torque T12 is calculated. The compensation torque T12 includes the steering return torque. The steering return torque is the torque used to compensate for the return characteristic of the steering wheel 5 to the neutral position.

[0051] The adder 81C calculates the assist torque command value T1 by adding the basic assist torque T11 and the compensation torque T12. <Configuration of Compensation Control Unit 81B> Next, the configuration of the compensation control unit 81B will be described.

[0052] As shown in Figure 5, the compensation control unit 81B includes a steering return control unit 90. The steering return control unit 90 includes a target steering speed calculation unit 91, a vehicle speed gain calculation unit 92, a differentiator 93, a feedback calculation unit 94, an axial force gradient calculation unit 95, and a steering return torque calculation unit 96.

[0053] The target steering speed calculation unit 91 calculates the steering angle θ calculated by the steering angle calculation unit 51. s The target steering speed calculation unit 91 takes in the steering angle θ. s Depending on the target steering angular velocity ω * Calculate the target steering angular velocity ω. * This is the target value of the steering angular velocity ω when the steering wheel 5 is returned to the neutral position. The target steering velocity calculation unit 91 uses the angular velocity map stored in memory to calculate the target steering angular velocity ω *The angular velocity map may be calculated, for example, by steering angle θ. s and target steering angular velocity ω * This is a two-dimensional map that defines the relationship between the target steering angular velocity ω. * The absolute value of is the steering angle θ s It increases as the absolute value of increases. However, the target steering angular velocity ω * The sign of the symbol corresponds to the steering angle θ. s It is the opposite of the sign of .

[0054] The vehicle speed gain calculation unit 92 receives the vehicle speed V detected by the vehicle speed sensor 41. The vehicle speed gain calculation unit 92 calculates the vehicle speed gain G according to the vehicle speed V. V The vehicle speed gain calculation unit 92 uses the vehicle speed gain map stored in memory to calculate the vehicle speed gain G. V The following calculations may be performed: The vehicle speed gain map is, for example, the vehicle speed V and the vehicle speed gain G. V This is a two-dimensional map that defines the relationship between [the two elements].

[0055] The differentiator 93 receives the steering angle θ calculated by the steering angle calculation unit 51. s It takes in the steering angle θ. Differentiator 93 takes the steering angle θ s The steering angular velocity ω is calculated by differentiating it with respect to time. The feedback calculation unit 94 includes a basic feedback return torque calculation unit 94A and a multiplier 94B.

[0056] The basic feedback return torque calculation unit 94A calculates the target steering angular velocity ω calculated by the target steering speed calculation unit 91. * The steering angular velocity ω calculated by the differentiator 93 is taken in. The basic feedback return torque calculation unit 94A performs feedback control of the steering angular velocity ω, thereby calculating the basic feedback return torque T FB The following is calculated. Feedback control of steering angular velocity ω is performed using the target steering angular velocity ω * The deviation between the steering angular velocity ω and the basic feedback return torque T is calculated, and the calculated deviation is eliminated. FB This is a control that calculates the basic feedback return torque T. FB The target steering angular velocity ω* This is the basic torque used to compensate for the difference between the steering angular velocity ω and the actual steering angular velocity ω. The multiplier 94B is the basic feedback return torque T calculated by the basic feedback return torque calculation unit 94A. FB The vehicle speed gain G calculated by the vehicle speed gain calculation unit 92 V It incorporates and.

[0057] The multiplier 94B is the basic feedback return torque T FB Vehicle speed gain G V By multiplying by the target feedback return torque T, FB * Perform the calculation. The axial force gradient calculation unit 95 receives, for example, the axial force AF calculated by the axial force calculation unit 82. The axial force AF is an angular axial force, an electric axial force, or a mixed axial force. The axial force gradient calculation unit 95 calculates the axial force gradient γ based on the axial force AF. The axial force gradient γ is, for example, the target pinion angle θ p * This refers to the slope, which is the rate of change in axial force AF with respect to the change in the target pinion angle θ. The axial force gradient calculation unit 95 calculates, for example, the unit change amount of axial force AF to the target pinion angle θ. p * The axial force gradient γ is calculated by dividing by the unit change rate. The unit change rate of axial force AF is the current value of axial force AF minus the previous value. Target pinion angle θ p * The unit change is the target pinion angle θ. p * This value is obtained by subtracting the previous value from the current value. The previous value is the value from one calculation cycle ago.

[0058] The axial force gradient calculation unit 95 calculates the target pinion angle θ. p * Instead, steering angle θ s The axial force gradient γ may be calculated using [a specific method / tool]. The steering return torque calculation unit 96 includes a torque gain calculation unit 96A and a multiplier 96B. The torque gain calculation unit 96A calculates the steering torque T detected by the torque sensor 42. hThe axial force gradient γ calculated by the axial force gradient calculation unit 95 is taken in. The torque gain calculation unit 96A calculates the torque gain G based on the steering torque Th and the axial force gradient γ. T The multiplier 96B calculates the target feedback return torque T calculated by the feedback calculation unit 94. FB * The torque gain G calculated by the torque gain calculation unit 96A T It incorporates the target feedback return torque T. The multiplier 96B is the target feedback return torque T. FB * Torque gain G T By multiplying by the target steering return torque T, re * Perform the calculation.

[0059] <Torque Gain Map M1> The torque gain calculation unit 96A calculates the torque gain G using, for example, the torque gain map M1 stored in memory. T Perform the calculation.

[0060] As shown in Figure 6, the torque gain map M1 is the steering torque T h and Torque Gain G T This is a three-dimensional map that defines the relationship with the axial force gradient γ. The torque gain map M1 is axial force gradient sensitive. That is, steering torque T h Torque gain G in response to changes T The characteristics of the change vary according to the axial force gradient γ. Steering torque T h Torque gain G in response to changes T The change characteristics may have multiple characteristics. These multiple characteristics may include, for example, the first to fourth characteristics.

[0061] The first characteristic is shown by the first characteristic line L1 in Figure 6. The first characteristic is the default characteristic. In the first characteristic, the steering torque T h Depending on the change in the absolute value of, the torque gain G T The value of changes as follows: that is, torque gain G T The value of the steering torque T starts from "0".h The absolute value of increases, and the first set value T th1 It is maintained at "1" until it reaches a certain value. Steering torque T h The absolute value of is the first setting value T th1 After reaching the steering torque T h As the absolute value of increases, the torque gain G T The value of decreases gradually and linearly. Eventually, the steering torque T h The absolute value of is the second setting value T th2 At the timing when it reaches, the torque gain G T The value of is "0". Second setting value T th2 This is the first setting value T th1 Larger than that. Steering torque T h The absolute value of is the second setting value T th2 If the above conditions are met, the steering torque T h Regardless of the absolute value of, the torque gain G T The value will be "0".

[0062] The second characteristic is shown by the second characteristic line L2 in Figure 6. In the second characteristic, the steering torque T h Depending on the change in the absolute value of, the torque gain G T The value of changes as follows: That is, starting from "0", the steering torque T h As the absolute value of increases, the torque gain G T The value of starts at "1" and gradually decreases linearly. Eventually, the steering torque T h The absolute value of is the third setting value T th3 At the timing when it reaches, the torque gain G T The value of is "0". Third setting value T th3 This is the second setting value T th2 Larger than that. Steering torque T h The absolute value of is the third setting value T th3 If the above conditions are met, the steering torque T h Regardless of the absolute value of, the torque gain G T The value will be "0".

[0063] Furthermore, the slope of the second characteristic curve L2 is smaller than the slope of the first characteristic curve L1. However, the slope of the second characteristic curve L2 is less than the steering torque T.h The absolute value of is "0" to the third setting value T th3 This is the slope over the period until it reaches [a certain value]. The slope of the first characteristic curve L1 is the steering torque T h The absolute value of is the first setting value T th1 From the second setting value T th2 This is the slope over the period until it reaches [a certain point]. The slope is the steering torque T h Torque gain G in response to changes T This is the rate of change.

[0064] The third characteristic is shown by the third characteristic line L3 in Figure 6. In the third characteristic, the steering torque T h Depending on the change in the absolute value of, the torque gain G T The value of changes as follows: That is, starting from "0", the steering torque T h As the absolute value of increases, the torque gain G T The value of starts at "1" and gradually decreases exponentially. Eventually, the steering torque T h The absolute value of is the fourth setting value T th4 At the timing when it reaches, the torque gain G T The value of this becomes "0". The fourth setting value T th4 This is the second setting value T th2 Larger than the third setting value T th3 Smaller than. Steering torque T h The absolute value of is the fourth setting value T th4 If the above conditions are met, the steering torque T h Regardless of the absolute value of, the torque gain G T The value will be "0".

[0065] The fourth characteristic is shown by the fourth characteristic line L4 in Figure 6. In the fourth characteristic, the steering torque T h Depending on the change in the absolute value of, the torque gain G T The value of changes as follows: That is, starting from "0", the steering torque T h As the absolute value of increases, the torque gain G T The value of starts at a value less than "1" and gradually decreases exponentially. Eventually, the steering torque T h The absolute value of is the fourth setting value Tth4 At the timing when it reaches, the torque gain G T The value of is "0". Steering torque T h The absolute value of is the fourth setting value T th4 If the above conditions are met, the steering torque T h Regardless of the absolute value of, the torque gain G T The value of is "0". However, steering torque T h The absolute value of is from "0" to the fourth setting value T th4 During the period until it reaches this point, the torque gain G shown by the third characteristic curve L3 is T The value of is the torque gain G shown by the second characteristic curve L2. T It is less than the value of [the specified value].

[0066] Steering Torque T h Torque gain G with respect to change in absolute value T The characteristics of the change change in the following order as the value of the axial force gradient γ decreases: for example, the first characteristic, the second characteristic, the third characteristic, and the fourth characteristic.

[0067] <Effect of this embodiment> Next, the operation of this embodiment will be described. For example, if the first characteristic is selected from among the multiple characteristics of the torque gain map M1, the steering torque T h Torque gain G in response to changes in the absolute value of T The value of changes as follows: steering torque T h The absolute value of is the first setting value T th1 After reaching this point, the torque gain G increases as the absolute value of the steering torque Th increases. T The value gradually decreases, and the second set value T th2 It becomes "0" when it reaches this point. Torque gain G T When the value becomes "0", the target steering return torque T re * The value also becomes "0". In other words, the execution of steering return control is canceled.

[0068] Therefore, for example, when the driver of a vehicle turns the steering wheel 5 in the direction of steering torque Th When applying the target steering return torque T re * By reducing this value, the feeling of steering obstruction from the steering wheel 5 can be reduced. The turning direction is the direction away from the neutral position of the steering wheel 5. Therefore, the steering feel during turning can be improved.

[0069] Furthermore, the driver of the vehicle can turn the steering wheel 5 back to the steering torque T. h When applying the target steering return torque T re * By increasing the value of , the steering load on the steering wheel 5 can be reduced. The counter-steering direction is towards the neutral position of the steering wheel 5. Therefore, the steering feel during counter-steering can be improved.

[0070] Furthermore, the steering wheel 5 is set to a constant steering angle θ. s When the steering is maintained and the driver of the vehicle releases their hands from the steering wheel 5, the steering torque T h As the absolute value of decreases, the torque gain G along the first characteristic curve L1 increases. T The value of changes. Therefore, the target steering return torque T re * The value of steering torque T h As the absolute value of decreases, it changes along the first characteristic curve L1. That is, during hands-free driving, the target steering return torque T re * The value of can be controlled to change along the shape of the first characteristic curve L1.

[0071] Furthermore, if any one of the second to fourth characteristics shown by the second to fourth characteristic lines L2 to L4 is selected from among the multiple characteristics of the torque gain map M1, the steering torque T h Torque gain G with respect to change in absolute value T The trend of change in the first characteristic is the same as that of the second to fourth characteristics. The reason why the second to fourth characteristics differ from the first characteristic is mainly due to the steering torque Th Torque gain G with respect to change in absolute value T This is the slope, which is the rate of change. Therefore, even if only one of the second to fourth characteristics is selected, the same action and effect as when only the first characteristic is selected can be obtained.

[0072] However, the return speed of the steering wheel 5 during hands-free driving depends, for example, on the axial force acting on the steering shaft 22. Furthermore, the axial force depends on the vehicle speed V. Therefore, if the torque gain map M1 has only one of the first to fourth characteristics, the intended return characteristics of the steering wheel 5 may not be obtained due to changes in the vehicle speed V. For example, there is concern that the return speed of the steering wheel 5 may become unstable depending on the vehicle speed V. The return speed is the steering angular velocity ω when the steering wheel 5 returns to the neutral position.

[0073] For example, consider the case where the torque gain map M1 has only the second characteristic shown by the second characteristic line L2. In this case, as shown in region S1 of Figure 7, if you release your hands from the steering wheel 5 when the vehicle speed V is in the low speed range of about 20 km / h, the steering angular velocity ω may fluctuate greatly when the steering wheel 5 begins to return to the neutral position. This is because the value of the axial force gradient γ decreases as the vehicle speed V decreases, and the target steering return torque T re * This is because the steering wheel 5 returns to the neutral position depending on the torque gain G. In particular, in the second characteristic, T The value of, and consequently the target steering return torque T re * The value of becomes larger compared to the first to third characteristics. Therefore, when you release your hands from the steering wheel 5, the target steering return torque T re * The value of changes rapidly, which may cause a large fluctuation in the steering angular velocity ω.

[0074] Furthermore, consider the case where the torque gain map M1 has only the fourth characteristic shown by the fourth characteristic line L4. In this case, as shown in region S2 of Figure 8, if you release your hands from the steering wheel 5 when the vehicle speed V is in the medium speed range of about 30 km / h, the steering angular velocity ω may become too fast when the steering wheel 5 begins to return to the neutral position. This is because the value of the axial force gradient γ increases as the vehicle speed V increases, and the target steering return torque T re * This is because the steering wheel 5 returns to the neutral position without relying on it.

[0075] To suppress the return speed of the steering wheel 5, the target steering return torque T re * It can also be considered to use it as a brake. However, in the fourth characteristic, torque gain G T The value of, and consequently the target steering return torque T re * The value of becomes smaller compared to the first to third characteristics. Also, in the fourth characteristic, the steering torque T h Torque gain G with respect to the decrease in the absolute value of T The rate of increase is smaller compared to the first to third characteristics. In other words, the braking is delayed in relation to the return speed of the steering wheel 5. Therefore, it is difficult to appropriately control the return speed of the steering wheel 5.

[0076] In this respect, according to this embodiment, the steering torque T h Torque gain G with respect to change in absolute value T The characteristic change of the first to fourth characteristic is represented, for example, by the first to fourth characteristic lines L1 to L4 in Figure 6, depending on the value of the axial force gradient γ.

[0077] For example, when the vehicle speed V is in the low-speed range, that is, when the value of the axial force gradient γ is small, the characteristics of the torque gain map M1 switch to the third characteristic shown by the third characteristic line L3, or the fourth characteristic shown by the fourth characteristic line L4. Therefore, when the driver of the vehicle releases their hands from the steering wheel 5, the steering torque T hAs the absolute value of decreases, the torque gain G T The value of, and consequently the target steering return torque T re * The value of starts at "0" and gradually increases exponentially.

[0078] Therefore, as shown in Figure 9, the steering angular velocity ω when the steering wheel 5 returns to the neutral position does not increase abruptly but changes gradually. Furthermore, fluctuations in the steering angular velocity ω when the steering wheel 5 returns to the neutral position are also suppressed. In particular, in the fourth characteristic shown by the fourth characteristic curve in Figure 6, the torque gain G T The upper limit is set to a value less than "1". Therefore, the steering angular velocity ω when the steering wheel 5 returns to the neutral position can be appropriately limited. Incidentally, the torque gain G T The lower limit is "0".

[0079] Furthermore, when the vehicle speed V is in the medium to high speed range, that is, when the value of the axial force gradient γ is large, the characteristics of the torque gain map M1 switch to either the first characteristic shown by the first characteristic line L1 or the second characteristic shown by the second characteristic line L2. Therefore, when the driver of the vehicle releases their hands from the steering wheel 5, the steering torque T h As the absolute value of decreases, the torque gain G T The value of, and consequently the target steering return torque T re * The value of increases gradually in a linear fashion, starting from "0".

[0080] However, in the first and second characteristics, the steering torque T h Torque gain G is calculated according to the absolute value of T The value of is greater than in the cases of the third and fourth characteristics. Also, in the first and second characteristics, the steering torque T h Torque gain G with respect to the decrease in the absolute value of T The rate of increase is greater than in the cases of the third and fourth characteristics.

[0081] The steering angular velocity ω when the steering wheel 5 returns to the neutral position is the target steering angular velocity ω, depending on the vehicle speed V and, consequently, the axial force gradient γ. * If the speed exceeds this, the target steering return torque T re * This acts as a brake on the steering wheel 5. That is, the target steering return torque T. re * As the value of changes along the shape of the first characteristic curve L1 or the second characteristic curve L2, the actual steering angular velocity ω becomes the target steering angular velocity ω * This is limited. Therefore, when the vehicle speed V is high and the value of the axial force gradient γ is large, the steering torque T h As the absolute value of decreases, the torque gain G T The value of, and consequently the target steering return torque T re * It is preferable to rapidly increase the value of .

[0082] <Effects of the Embodiment> This embodiment provides the following effects. (1) The steering control device 1 controls the vehicle's steering system 2. The steering system 2 includes a motor that generates torque applied to the steering wheel 5. The reaction force motor 12 corresponds to a motor. The steering control device 1 includes a processing circuit that calculates a torque command value for controlling the motor based on the steering state of the steering wheel 5. The reaction force control device 1A corresponds to a processing circuit and controls the reaction force torque command value T * This corresponds to the torque command value. Steering torque T h This is a state variable that reflects the steering state of the steering wheel 5.

[0083] The processing circuit performs a first process and a second process. The first process calculates the basic torque that forms the basis for calculating the torque command value, based on the steering state of the steering wheel 5. The basic assist torque T11 corresponds to the basic torque. The second process calculates the steering return torque to compensate for the return characteristics of the steering wheel 5, according to the steering state of the steering wheel 5. Target steering return torque Tre * This corresponds to the steering return torque.

[0084] The second process includes the third and fourth processes. The third process determines the target steering angular velocity ω based on the steering state of the steering wheel 5. * The actual steering angular velocity ω is calculated to be the target steering angular velocity ω * This process calculates the basic return torque by executing feedback control that follows the target feedback return torque T. FB * This corresponds to the basic return torque. The fourth process is the steering torque T h Based on this and a state variable that reflects the axial force acting on the vehicle's steering shaft 22, the torque gain G is multiplied by the basic return torque. T This is a process that calculates the axial force gradient γ, which corresponds to a state variable that reflects the axial force.

[0085] For example, when the driver of a vehicle releases their hands from the steering wheel 5, the return speed of the steering wheel 5 depends on the axial force acting on the steering shaft 22. Furthermore, the axial force depends on the vehicle speed V. According to the steering control device 1 of this embodiment, the torque gain G is determined by considering the state variable that reflects the axial force. T This is calculated. Therefore, the torque gain G is added to the basic return torque. T By reflecting the steering return torque obtained by multiplying by the value in the torque command value, the return speed of the steering wheel 5 when the hands are released from the steering wheel 5 can be appropriately adjusted.

[0086] (2) The processing circuit controls the steering torque T according to the state variable. h and Torque Gain G T Using the torque gain map M1 which defines the relationship with the torque gain G T This calculates the torque gain G. With this configuration, by using the torque gain map M1, the torque gain G T It can be easily obtained.

[0087] (3) Steering torque T hThe larger the absolute value of G, the greater the torque gain. T The value of becomes smaller, and the larger the value of the state variable, the greater the torque gain G. T The value of becomes larger. The axial force gradient γ corresponds to a state variable that reflects the axial force. According to this configuration, the steering torque T h The larger the absolute value of G, the greater the torque gain. T The value of becomes smaller. Therefore, the driver turns the steering wheel 5 in the direction of steering torque T. h When this is applied, the torque gain G T Consequently, the value of the steering return torque decreases. Therefore, the feeling of resistance to steering the steering wheel 5 can be reduced. Also, the driver can turn the steering wheel 5 in the return direction and apply steering torque T. h When this is applied, the torque gain G T Consequently, the steering return torque value increases. This reduces the steering load on the steering wheel 5.

[0088] (4) Steering torque T h Torque gain G with respect to change in absolute value T The change characteristics have multiple characteristics with different slopes. The processing circuit selects one of these characteristics depending on the state variable. According to this configuration, the steering torque T h Torque gain G with respect to change in absolute value T The change characteristics can be changed to one of several characteristics depending on the state variable.

[0089] (5) The state variable is the axial force gradient γ, which is the rate of change of the axial force. With this configuration, the steering torque T h Torque gain G with respect to change in absolute value T The characteristics of this change can be modified according to the axial force gradient γ.

[0090] <Other Embodiments> This embodiment may be implemented with the following modifications. The torque gain map M1 may have at least two characteristics from the first to fourth characteristics shown by the first to fourth characteristic lines L1 to L4 in Figure 6. The two characteristics may be a pair of the first characteristic and the third or fourth characteristic. Alternatively, the two characteristics may be a pair of the second characteristic and the third or fourth characteristic. The torque gain map M1 may have five or more characteristics.

[0091] The torque gain map M1 may be vehicle speed-sensitive or current-sensitive. In this case, a configuration can be adopted in which the axial force gradient calculation unit 95 is omitted as the steering return torque calculation unit 96. When the torque gain map M1 is vehicle speed-sensitive, the steering torque T h Torque gain G in response to changes T The characteristics of the change vary depending on the vehicle speed V. When the torque gain map M1 is current-sensitive, the steering torque T h Torque gain G in response to changes T The characteristic change is the current I of the steering motor 31. b It changes according to the values ​​of the vehicle speed V and the current I of the steering motor 31. b The value of is a state variable that reflects the axial force acting on the steering shaft 22.

[0092] The characteristics of the torque gain map M1 may be tuned, for example, according to the characteristics of the vehicle or the steering system 2. In this way, the return characteristics of the steering wheel 5 can be obtained according to the characteristics of the vehicle or the steering system 2.

[0093] The steering device 2 may be an electric power steering device. In this case, the steering wheel 5 and the vehicle's steering wheels 6 are connected in a way that allows power transmission. Specifically, the steering shaft 11 and the pinion shaft 21 are connected integrally so as to be rotatable. The reaction motor 12 or steering motor 31 functions as a drive source for the electric power steering device. The reaction motor 12 or steering motor 31 functions as an assist motor that generates an assist force. The steering control device 1 calculates an assist torque command value according to the steering state of the steering wheel 5 and causes the assist motor to generate an assist force according to the assist torque command value. Steering torque T h This is a state variable that reflects the steering state of the steering wheel 5. [Explanation of symbols]

[0094] 1... Steering control device 1A…Reaction force control device (processing circuit) 2… Steering gear 5… Steering wheel 12… Reaction motor (motor) M1... Torque Gain Map

Claims

1. A steering control device configured to control the steering system of a vehicle, wherein the steering system includes a motor configured to generate torque to be applied to the steering wheel, The system includes a processing circuit configured to calculate a torque command value for controlling the motor based on the steering state of the steering wheel, The processing circuit includes a first process that calculates a basic torque that forms the basis for calculating the torque command value based on the steering state of the steering wheel, The system is configured to perform a second process that calculates a steering return torque to compensate for the return characteristics of the steering wheel, depending on the steering state of the steering wheel. The second process involves a third process which calculates a target steering angular velocity based on the steering state of the steering wheel, performs feedback control to make the actual steering angular velocity follow the target steering angular velocity, and calculates a basic return torque. A steering control device including a fourth process that calculates a torque gain multiplied by the basic return torque based on the steering torque and a state variable that reflects the axial force acting on the steering shaft of the vehicle.

2. The steering control device according to claim 1, wherein the processing circuit is configured to calculate the torque gain using a torque gain map that defines the relationship between the steering torque and the torque gain according to the state variable.

3. The steering control device according to claim 1 or claim 2, wherein the value of the torque gain decreases as the absolute value of the steering torque increases, and the value of the torque gain increases as the value of the state variable increases.

4. The characteristics of the change in torque gain with respect to the change in the absolute value of the steering torque have multiple characteristics with different slopes. The steering control device according to claim 1 or 2, wherein the processing circuit is configured to select one of a plurality of characteristics according to the state variable.

5. The steering control device according to claim 1 or claim 2, wherein the state variable is the axial force gradient, which is the rate of change of the axial force.

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