Steering control system

Abstract

The present invention provides a steering control device that can suppress unintended changes in steering feel by the driver. [Solution] The steering control device controls a steering system in which power transmission between the vehicle's steering wheels and the steering wheel is separated. The steering system includes a reaction force motor that generates a steering reaction force applied to the steering wheel. The steering control device includes a processing circuit configured to calculate a reaction force torque command value for controlling the reaction force motor based on the vehicle speed and the steering state of the steering wheel. The processing circuit is configured to perform processing to suppress changes in the reaction force torque command value due to changes in vehicle speed when the steering state of the steering wheel is maintained.

Description

[Technical Field]

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

[0002] Conventionally, steering systems using the so-called steer-by-wire system, which separates power transmission between the steering wheel and the steering wheels, are known. The steering system comprises a reaction motor and a steering motor. The reaction motor generates a steering reaction force applied to the steering shaft. The steering motor generates a steering force that turns the steering wheels. The control device of the steering system generates the steering reaction force via the reaction motor and steers the steering wheels via the steering motor. Improved steering performance is required for the steering system.

[0003] For example, the steering control device described in Patent Document 1 changes the steering angle ratio according to the vehicle speed by controlling the steering motor. The steering angle ratio is the ratio of the steering angle of the steering wheel to the steering angle of the steering wheel. However, if the steering wheel is kept at a constant steering angle with respect to its neutral position, the steering control device makes the change in the steering angle ratio with respect to the change in vehicle speed zero. For example, if the steering control device determines that the steering state of the steering wheel is a maintained steering state, it fixes the vehicle speed to the value of the vehicle speed immediately before it was determined that the steering state was maintained. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-53017 [Overview of the project] [Problems that the invention aims to solve]

[0005] According to the steering control device described in Patent Document 1, when the steering wheel is in a steering-hold state, the steering angle ratio does not change with respect to changes in vehicle speed, and therefore the steering angle of the steering wheels does not change with changes in vehicle speed. Consequently, even if the vehicle speed changes while the steering wheel is in a steering-hold state, unintended vehicle behavior by the driver can be suppressed.

[0006] However, the steering control device described in Patent Document 1 has the following concerns. Specifically, the steering control device generates a steering reaction force in the reaction force motor based on the steering torque and vehicle speed. Therefore, if the vehicle speed changes while the steering wheel is in a steering position, the change in steering reaction force may cause discomfort to the driver. [Means for solving the problem]

[0007] A steering control device capable of solving the above problems is configured to control a steering device in which power transmission between the vehicle's steering wheels and the steering wheel is separated. The steering device includes a reaction motor configured to generate a steering reaction force applied to the steering wheel. The steering control device includes a processing circuit configured to calculate a reaction torque command value for controlling the reaction motor based on the vehicle speed and the steering state of the steering wheel. The processing circuit is configured to perform processing to suppress changes in the reaction torque command value due to changes in the vehicle speed when the steering state of the steering wheel is maintained.

[0008] With this configuration, when the steering wheel is in a steered position, changes in the reaction torque command value due to changes in vehicle speed are suppressed. Therefore, even if the vehicle speed changes while the steering wheel is steered, the steering reaction force does not change significantly. Since changes in steering feel that are not intended by the driver due to vehicle deceleration or acceleration are suppressed, it is possible to reduce the feeling of discomfort to the driver.

[0009] In the steering control device described above, the processing circuit may be configured to fix the vehicle speed value used in calculating the reaction force torque command value when the steering state of the steering wheel is in a steered state.

[0010] In this configuration, when the steering wheel is in a steered position, the vehicle speed value used to calculate the reaction torque command value is fixed. This prevents the reaction torque command value from changing in response to actual changes in vehicle speed.

[0011] In the steering control device described above, the processing circuit may be configured to determine whether the steering state of the steering wheel is a steered state based on a state variable that reflects the steering state of the steering wheel. In this case, if the processing circuit determines that the steering state of the steering wheel is a steered state, it may be configured to fix the value of the vehicle speed used in calculating the reaction force torque command value to the value of the vehicle speed immediately before it was determined that the steering state of the steering wheel was a steered state.

[0012] In this configuration, when it is determined that the steering wheel is in a steered state, the vehicle speed value used to calculate the reaction torque command value is fixed to the vehicle speed value immediately before it is determined that the steering wheel is in a steered state. This prevents the reaction torque command value from changing in response to actual changes in vehicle speed.

[0013] In the steering control device described above, the processing circuit may be configured to determine whether the steering state of the steering wheel is a steered state based on a state variable that reflects the steering state of the steering wheel. In this case, if the processing circuit determines that the steering state of the steering wheel is a steered state, it may be configured to fix the value of the vehicle speed used in calculating the reaction force torque command value to the value of the vehicle speed at the time it was determined that the steering state of the steering wheel was a steered state.

[0014] In this configuration, if the steering wheel is determined to be in a steered state, the vehicle speed value used to calculate the reaction torque command value is fixed to the vehicle speed value at the time the steering wheel was determined to be in a steered state. This prevents the reaction torque command value from changing in response to actual changes in vehicle speed.

[0015] In the steering control device described above, the processing circuit may be configured to determine whether the steering state of the steering wheel is a steered state based on a state variable that reflects the steering state of the steering wheel. Furthermore, if the processing circuit determines that the steering state of the steering wheel is a steered state, it may be configured to determine whether the current value of the vehicle speed at the time the steering state of the steering wheel was determined to be a steered state is the same as the previous value of the vehicle speed. In this case, the processing circuit may be configured to fix the value of the vehicle speed used in calculating the reaction force torque command value to the previous value of the vehicle speed only if the current value of the vehicle speed is different from the previous value of the vehicle speed.

[0016] In this configuration, if the steering wheel is determined to be in a steered state, the vehicle speed value used to calculate the reaction torque command value is fixed to the previous value only if the current vehicle speed at the time the steering wheel was determined to be in a steered state differs from the previous vehicle speed value. This prevents the reaction torque command value from changing in response to actual changes in vehicle speed.

[0017] In the steering control device described above, the processing circuit may be configured to gradually change the value of the vehicle speed used in calculating the reaction force torque command value from a fixed value of the vehicle speed to the actual vehicle speed when the steering wheel is released from its steered state.

[0018] With this configuration, the reaction torque command value gradually changes from a value corresponding to a fixed vehicle speed to a value corresponding to the actual vehicle speed. Therefore, it is possible to suppress a sudden change in steering reaction force when the steering wheel is released from its steered state.

[0019] In the steering control device described above, the processing circuit may be configured to perform the following: a first process of calculating an assist torque command value, which is a torque in the same direction as the steering direction of the steering wheel, based on the steering state of the steering wheel; a second process of calculating the axial force acting on the steering shaft that steers the steering wheel, based on the steering state of the steering wheel, and converting the calculated axial force into a torque for the steering wheel to calculate the axial force torque; and a third process of calculating the reaction force command value by subtracting the axial force torque from the assist torque command value.

[0020] The first process may include a fourth process of calculating a basic assist torque that forms the basis for calculating the assist torque command value using an assist torque map based on the steering state of the steering wheel; a fifth process of calculating a compensation torque for the basic assist torque based on the steering state of the steering wheel; and a sixth process of calculating the assist torque command value by adding the basic assist torque and the compensation torque. The assist torque map may be a three-dimensional map that defines the relationship between the steering torque and the basic assist torque according to the vehicle speed.

[0021] With this configuration, when the steering wheel is in a steered position, the vehicle speed value used to calculate the basic assist torque and, consequently, the reaction torque command value is fixed. Therefore, the basic assist torque and, consequently, the reaction torque command value can be kept unchanged in response to actual changes in vehicle speed. Consequently, even if the vehicle speed changes while the steering wheel is steered, the steering reaction force does not change significantly. [Effects of the Invention]

[0022] According to the present invention, it is possible to suppress changes in steering feel that are not intended by the driver of the vehicle. [Brief explanation of the drawing]

[0023] [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 graph showing an assist torque map according to one embodiment. [Figure 6] This is a block diagram of a correction processing unit according to one embodiment. [Modes for carrying out the invention]

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] As the steering shaft 22 moves axially, the steering angle θ of the steering wheel 6 changes. wThe 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] The vehicle speed sensor 41 detects the vehicle speed V. The vehicle speed V is a state variable that reflects the running state of the vehicle. The torque sensor 42 is provided on the steering shaft 11. The torque sensor 42 is located on the steering wheel 5 side with respect to the connection portion of the speed reducer 13 in the steering shaft 11. The torque sensor 42 detects the steering torque T h applied to the steering shaft 11. h The steering torque T h is calculated based on the amount of twist of the torsion bar 42a provided on the steering shaft 11. The steering torque T h 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

[0035] 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.

[0036] 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.

[0037] The steering control device 1B performs steering control. Steering control is a control that steers the steering wheels 6 according to the steering state of the steering wheel 5. The steering control device 1B controls the operation of the steering motor 31. The steering control device 1B controls the operation of the steering motor 31 using the detection result of the second rotation angle sensor 44. The steering control device 1B controls the power supply to the steering motor 31 so that the steering wheels 6 are steered according to the steering state of the steering wheel 5.

[0038] <Configuration of reaction force control device 1A> Next, the configuration of the reaction force control device 1A will be described. 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] <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.

[0043] 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.

[0044] 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 angle w It is the ratio of .

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] <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.

[0050] The assist torque command value calculation unit 81 takes in the steering torque T detected through the torque sensor 42 h and the vehicle speed V detected through the vehicle speed sensor 41. The assist torque command value calculation unit 81 calculates an assist torque command value T1 based on the steering torque T h and the vehicle speed V. 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 larger the absolute value of the steering torque T h and the slower the vehicle speed V, the larger the absolute value of the assist torque command value T1 becomes.

[0051] The axial force calculation unit 82 takes in the pinion angle θ calculated by the pinion angle calculation unit 61 p the value of the current I of the steering motor 31 detected through the current sensor 65 b 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 and calculates the axial force acting on the steering shaft 22 based on these values. The axial force is an angular axial force, a current axial force, or a mixed 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.

[0052] 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 the 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 pinion angle θ pAs the absolute value of [] increases and the vehicle speed V decreases, the absolute value of the angular axial force increases.

[0053] The current axial force is the axial force corresponding to the current I of the steering motor 31 b and is the axial force that reflects the road surface condition. The axial force calculation unit 82 calculates, for example, the current axial force by multiplying the value of the current I of the steering motor 31 b by a gain. The gain is a coefficient corresponding to the vehicle speed V. The combined axial force is the 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 that reflect the vehicle behavior, the steering state, or the road surface condition.

[0054] 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.

[0055] <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.

[0056] The basic control unit 81A calculates a basic assist torque T11 based on the steering torque T h and the vehicle speed V. The basic assist torque T11 is the torque that serves as a basis for generating a steering reaction force of an appropriate magnitude corresponding to the steering torque T h and the vehicle speed V. Also, the basic assist torque T11 is the torque that serves as a basis for calculating the assist torque command value T1.

[0057] As shown in Figure 5, the basic control unit 81A calculates the basic assist torque T11 using, for example, the assist torque map M1 stored in memory. The assist torque map M1 is the steering torque T h This is a three-dimensional map that defines the relationship between the steering torque T11 and the basic assist torque T11 according to the vehicle speed V. The assist torque map M1 has the following characteristics: that is, steering torque T h The larger the absolute value of V, and the slower the vehicle speed V, the larger the absolute value of the basic assist torque T11. The basic control unit 81A switches the characteristics of the assist torque map M1 according to the vehicle speed V.

[0058] 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.

[0059] The adder 81C calculates the assist torque command value T1 by adding the basic assist torque T11 and the compensation torque T12. <Regarding changes in vehicle speed while steering is maintained> The steering control device 1 configured in this way has the following concerns. Specifically, the steering control device 1 has steering torque T h Based on the vehicle speed V, a steering reaction force is generated in the reaction force motor 12. For example, the assist torque command value calculation unit 81 calculates the steering torque T h The assist torque command value T1 is calculated based on the vehicle speed V. Therefore, for example, if the vehicle speed V changes while the steering wheel 5 is in a steering-hold state, the assist torque command value T1 changes, and consequently the steering reaction force changes.s Even when the steering is held in place, the steering reaction force changes in accordance with the change in vehicle speed V. Therefore, this may cause discomfort to the driver due to an unintended change in steering feel.

[0060] Examples of discomfort include a feeling of steering slippage or a feeling of being pushed back. Steering slippage is a steering feel in which the steering reaction force transmitted through the steering wheel 5 is no longer felt as feedback, and may occur, for example, when the vehicle is decelerating. A feeling of being pushed back is a steering feel in which the steering wheel 5 is pushed back in the opposite direction to the current steering direction, and may occur, for example, when the vehicle is accelerating.

[0061] Therefore, in this embodiment, in order to suppress changes in steering feel that are not intended by the driver, the steering control device 1 is configured as follows. <Correction Processing Unit> As shown in Figure 4, the assist torque command value calculation unit 81 has a correction processing unit 90. The correction processing unit 90 takes in the vehicle speed V detected by the vehicle speed sensor 41 and corrects the taken vehicle speed V according to the steering state of the steering wheel 5. The corrected vehicle speed V is the corrected vehicle speed Vc. The basic control unit 81A takes in the steering torque T detected by the torque sensor 42. h The corrected vehicle speed V calculated by the correction processing unit 90 c The basic control unit 81A uses the assist torque map M1 shown in Figure 5 to input the steering torque T. h and corrected vehicle speed V c The basic assist torque T11 is calculated based on this.

[0062] As shown in Figure 6, the correction processing unit 90 includes a differentiator 91, a steering determination unit 92, and a corrected vehicle speed calculation unit 93. The differentiator 91 processes the steering angle θ calculated by the steering angle calculation unit 51. s The steering angular velocity ω is calculated by differentiating it with respect to time.

[0063] The steering determination unit 92 receives the vehicle speed V detected by the vehicle speed sensor 41 and the steering angular velocity ω calculated by the differentiator 91. Based on the vehicle speed V and the steering angular velocity ω, the steering determination unit 92 determines whether the steering state of the steering wheel 5 is maintained at a constant steering angle θs. Steering refers to the steering angle θ in order to keep the vehicle in a straight-ahead or turning state. s The goal is to hold the steering wheel 5 in a way that prevents it from changing. The steering determination unit 92 sets the value of flag F0 according to the determination result of whether the steering state of the steering wheel 5 is in a steered state.

[0064] The steering determination unit 92 calculates a steering angular velocity threshold value according to the vehicle speed V. The steering determination unit 92 calculates the steering angular velocity threshold value using, for example, a threshold map stored in memory. The threshold map is, for example, a two-dimensional map that defines the relationship between the vehicle speed V and the steering angular velocity threshold value, and has the following characteristics: That is, the steering angular velocity threshold value is set to a smaller value as the vehicle speed V increases.

[0065] The steering determination unit 92 determines whether the steering state of the steering wheel 5 is in a steered state by comparing the absolute value of the steering angular velocity ω with the steering angular velocity threshold. If the absolute value of the steering angular velocity ω is less than the steering angular velocity threshold, the steering determination unit 92 determines that the steering state of the steering wheel 5 is in a steered state and sets the value of flag F0 to "1". If the absolute value of the steering angular velocity ω is greater than or equal to the steering angular velocity threshold, the steering determination unit 92 determines that the steering state of the steering wheel 5 is not in a steered state and sets the value of flag F0 to "0".

[0066] The corrected vehicle speed calculation unit 93 uses the vehicle speed V detected by the vehicle speed sensor 41 and the steering angle θ calculated by the steering angle calculation unit 51. s The system takes in the steering angular velocity ω calculated by the differentiator 91 and the value of flag F0 set by the steering determination unit 92. The corrected vehicle speed calculation unit 93 takes the vehicle speed V and the steering angle θ. sCorrected vehicle speed V by correcting the value of vehicle speed V based on the steering angular velocity ω and the value of flag F0. c The calculation is performed. Correcting the value of vehicle speed V includes fixing the value of vehicle speed V.

[0067] The corrected vehicle speed calculation unit 93 calculates the corrected vehicle speed V based on the value of flag F0 at a predetermined calculation cycle. c The corrected vehicle speed V is calculated and the corrected vehicle speed V is calculated. c It maintains the corrected vehicle speed V. However, the corrected vehicle speed calculation unit 93 maintains the corrected vehicle speed V. c Each time the calculation is performed, the held corrected vehicle speed V c The corrected vehicle speed V held in the corrected vehicle speed calculation unit 93 is updated. c This is the corrected vehicle speed V calculated by the corrected vehicle speed calculation unit 93. c This is the previous value relative to the current value. The previous value is the corrected vehicle speed V from one calculation cycle ago. c That is the case.

[0068] The corrected vehicle speed calculation unit 93 calculates the vehicle speed V detected by the vehicle speed sensor 41 and the held corrected vehicle speed V based on the value of flag F0. c Correct the vehicle speed V by either the previous value or the current value. c The current value is used for calculation. When the value of flag F0 is "0", the corrected vehicle speed calculation unit 93 uses the vehicle speed V detected by the vehicle speed sensor 41 as the corrected vehicle speed V. c The current value is used for the calculation. When the value of flag F0 is "1", the corrected vehicle speed calculation unit 93 calculates the held corrected vehicle speed V c Corrected vehicle speed V based on the previous value c This value will be used for the calculation.

[0069] The steering wheel 5 maintains a constant steering angle θ. s If the steering is not maintained, the value of flag F0 remains at "0". During the period when the value of flag F0 is set to "0", the vehicle speed V detected by the vehicle speed sensor 41 is always corrected vehicle speed V c This value is used in the calculation. In other words, during the period when the value of flag F0 is set to "0", the corrected vehicle speed V is used as the vehicle speed V used in the calculation of the basic assist torque T11. c The value is not fixed.

[0070] The steering wheel 5 maintains a constant steering angle θ. s If the steering state is maintained, the value of flag F0 remains at "1". During the period when the value of flag F0 is set to "1", the held corrected vehicle speed V c The previous value is always corrected vehicle speed V c This value is used in the calculation. That is, during the period when the value of flag F0 is set to "1", the corrected vehicle speed V is used as the vehicle speed V used in the calculation of the basic assist torque T11. c The value of is fixed.

[0071] The steering wheel 5 maintains a constant steering angle θ. s When the steering hold is released, the value of flag F0 switches from "1" to "0". Therefore, the corrected vehicle speed V used in the calculation of the basic assist torque T11 is... c The value of is the retained corrected vehicle speed V c The value switches from the previous value to the vehicle speed V detected by the vehicle speed sensor 41. That is, the corrected vehicle speed V is used as the vehicle speed V used in the calculation of the basic assist torque T11. c The fixed state of the value is released.

[0072] However, the steering wheel 5 is at a constant steering angle θ. s When the steering hold is released, the corrected vehicle speed V held in the corrected vehicle speed calculation unit 93 is released. c There is a risk that the previous value of and the vehicle speed V value detected by the vehicle speed sensor 41 may diverge. Therefore, the corrected vehicle speed calculation unit 93 may execute a first gradual change process or a second gradual change process when the value of flag F0 switches from "1" to "0".

[0073] The first gradual change process is performed using the corrected vehicle speed V held in the corrected vehicle speed calculation unit 93. c From the previous value, the corrected vehicle speed V is calculated up to the value of the vehicle speed V detected by the vehicle speed sensor 41. c This process gradually changes the value of over time.

[0074] The second gradual change process involves adjusting the corrected vehicle speed V held in the corrected vehicle speed calculation unit 93 according to the steering angular velocity ω. c From the previous value, the corrected vehicle speed V is calculated up to the value of the vehicle speed V detected by the vehicle speed sensor 41. c This process gradually changes the value of over time. For example, the faster the steering angular velocity ω, the more the corrected vehicle speed V held in the corrected vehicle speed calculation unit 93 changes. c The time it takes for the value of the corrected vehicle speed V to change from the previous value to the value of the vehicle speed V detected by the vehicle speed sensor 41 becomes shorter. This is because the faster the steering angular velocity ω, the shorter the time it takes for the corrected vehicle speed V to change. c This is based on the objective of quickly restoring the value to the true vehicle speed V detected by the vehicle speed sensor 41.

[0075] <Effect of this embodiment> Next, the operation of this embodiment will be described. When the vehicle is running with the steering wheel 5 held down, the value of flag F0 is set to "1". Therefore, the held corrected vehicle speed V c The previous value is always the corrected vehicle speed V c This is the current value. In other words, during the period when the value of flag F0 is set to "1", the corrected vehicle speed V is used as the vehicle speed V used in the calculation of the basic assist torque T11. c The value of is the retained corrected vehicle speed V c It will be fixed to the previous value.

[0076] Therefore, regardless of the actual vehicle speed V detected by the vehicle speed sensor 41, the corrected vehicle speed V is the final vehicle speed V used in the calculation of the basic assist torque T11 and, consequently, the assist torque command value T1. c The value of does not change. Therefore, even if the vehicle starts to decelerate or accelerate while the steering wheel 5 is steered, the basic assist torque T11, and consequently the assist torque command value T1, does not change.

[0077] In particular, the steering wheel 5 has a constant steering angle θ. sWhen a vehicle is turning while steered, if the steering reaction force changes, the driver of the vehicle is likely to feel uncomfortable due to the unintended change in steering feel. In this respect, according to this embodiment, the steering wheel 5 maintains a constant steering angle θ. s When a vehicle is turning with the steering wheel held in place, the steering reaction force does not change significantly even if the vehicle begins to decelerate or accelerate. In other words, unintended changes in steering feel due to the vehicle's deceleration or acceleration are suppressed, thus reducing the likelihood of the driver feeling uncomfortable. This discomfort can manifest as, for example, a feeling of the steering wheel slipping or being pushed back.

[0078] <Effects of this embodiment> This embodiment provides the following effects. (1) The steering control device 1 controls the steering device 2, which separates the power transmission between the vehicle's steering wheels 6 and the steering wheel 5. The steering device 2 includes a reaction force motor 12 that generates a steering reaction force applied to the steering wheel 5. Based on the vehicle speed V and the steering state of the steering wheel 5, the steering control device 1 controls the reaction force torque command value T for controlling the reaction force motor 12. * The system includes a processing circuit that calculates the steering angular velocity ω, which is a state variable that reflects the steering state of the steering wheel 5. The reaction force control device 1A corresponds to the processing circuit. When the steering state of the steering wheel 5 is maintained, the processing circuit calculates the reaction force torque command value T due to the change in vehicle speed V. * Execute a process to suppress the change.

[0079] In this configuration, when the steering state of the steering wheel 5 is maintained, the reaction torque command value T due to the change in vehicle speed V is... * This suppresses the change in steering feel. As a result, even if the vehicle speed V changes while the steering wheel 5 is steered, the steering reaction force does not change significantly. Because changes in steering feel that the driver did not intend due to the vehicle's deceleration or acceleration are suppressed, it is possible to prevent the driver from feeling uncomfortable.

[0080] (2) When the steering state of the steering wheel 5 is maintained, the processing circuit controls the reaction force torque command value T* The value of the vehicle speed V used in the calculation is fixed. With this configuration, when the steering state of the steering wheel 5 is in a steered state, the reaction force torque command value T * The value of the vehicle speed V used in the calculation is fixed. This means that the reaction torque command value T will not change in response to the actual change in vehicle speed V. * It is possible to prevent it from changing.

[0081] (3) The processing circuit determines whether the steering state of the steering wheel 5 is a steered state based on a state variable that reflects the steering state of the steering wheel 5. The state variable is, for example, the steering angular velocity. If the processing circuit determines that the steering state of the steering wheel 5 is a steered state, the reaction force torque command value T * The value of vehicle speed V used in the calculation is fixed to the value of vehicle speed V immediately before it is determined that the steering state of the steering wheel 5 is in a steered state.

[0082] According to this configuration, when the steering state of the steering wheel 5 is maintained, the reaction force torque command value T * The value of vehicle speed V used in the calculation is fixed to the value of vehicle speed V immediately before it is determined that the steering state of the steering wheel 5 is in a steered state. As a result, the reaction torque command value T is affected by the actual change in vehicle speed V. * It is possible to prevent it from changing.

[0083] (4) When the steering wheel 5 is released from its steered state, the processing circuit controls the reaction torque command value T * The value of the vehicle speed V used in the calculation is gradually changed from a fixed value of vehicle speed V to the actual vehicle speed V. With this configuration, the reaction force torque command value T * The steering reaction force gradually changes from a value corresponding to a fixed vehicle speed V to a value corresponding to the actual vehicle speed V. Therefore, when the steering wheel 5 is released from its steered state, a sudden change in steering reaction force can be suppressed.

[0084] (5) The processing circuit is configured to perform a first process, a second process, and a third process. The first process is a process that calculates an assist torque command value T1, which is a torque in the same direction as the steering direction of the steering wheel 5, based on the steering state of the steering wheel 5. Steering torque T h This is a state variable that reflects the steering state of the steering wheel 5. The second process calculates the axial force acting on the steering shaft 22 that steers the steering wheel 6 based on the steering state of the steering wheel 6, and then converts the calculated axial force into a torque for the steering wheel 5 to calculate the axial force torque T2. Pinion angle θ p and the current I of the steering motor 31 b The value of is a state variable that reflects the steering state of the steering wheel 6. The third process is to subtract the axial force torque T2 from the assist torque command value T1 to obtain the reaction force torque command value T * This is a process that performs calculations.

[0085] The first process includes the fourth process, the fifth process, and the sixth process. The first process is a process that calculates the basic assist torque T11 which is the basis for calculating the assist torque command value T1 using the assist torque map M1 based on the steering state of the steering wheel 5. Steering torque T h This is a state variable that reflects the steering state of the steering wheel 5. The fifth process is to calculate the compensation torque T12 for the basic assist torque T11 based on the steering state of the steering wheel 5. Steering angle θ s This is a state variable that reflects the steering state of the steering wheel 5. The sixth process is to calculate the assist torque command value T1 by adding the basic assist torque T11 and the compensation torque T12.

[0086] The assist torque map M1 controls the steering torque T h This is a three-dimensional map that defines the relationship between the basic assist torque T11 and the reaction torque command value T11 according to the vehicle speed V. According to this configuration, when the steering state of the steering wheel 5 is in a steered state, the basic assist torque T11, and consequently the reaction torque command value T11, *The vehicle speed V used in the calculation is fixed. Therefore, the basic assist torque T11, and consequently the reaction torque command value T, are affected by changes in the actual vehicle speed V. * This allows the steering force to remain unchanged. Therefore, even if the vehicle speed V changes while the steering wheel 5 is steered, the steering reaction force will not change significantly.

[0087] <Other Embodiments> This embodiment may be implemented with the following modifications. • When the vehicle is moving straight, the correction processing unit 90 does not need to fix the value of the vehicle speed V used for the basic assist torque T11. In this case, the steering determination unit 92, for example, the steering angle θ s Based on this, it is determined whether the rotational position of the steering wheel 5 is outside the neutral position. The steering determination unit 92 determines the steering angle θ s The absolute value of is compared with the steering angle threshold, and the steering angle θ s When the absolute value of is greater than the steering angle threshold, it is determined that the steering wheel 5 is steered to a position away from the neutral position. The steering angle threshold is a criterion for determining whether the vehicle is moving straight, and corresponds to the steering angle θ of the neutral position of the steering wheel 5. s It is set based on this.

[0088] The steering determination unit 92 determines that the steering state of the steering wheel 5 is in a steered state when both of the following two conditions B1 and B2 are met, and sets the value of flag F0 to "1". Conversely, the steering determination unit 92 determines that the steering state of the steering wheel 5 is not in a steered state when at least one of the following two conditions B1 and B2 is not met, and sets the value of flag F0 to "0".

[0089] B1. The rotational position of the steering wheel 5 is outside the neutral position. B2. The absolute value of the steering angular velocity ω is less than the steering angular velocity threshold. When the vehicle is moving straight, the steering wheel 5 is basically held in the neutral position. Therefore, the value of flag F0 is set to "0". Consequently, the vehicle speed V detected by the vehicle speed sensor 41 is always corrected vehicle speed V c It is calculated as follows: In other words, when the vehicle is moving straight, the vehicle speed V detected by the vehicle speed sensor 41 is used as the vehicle speed V used in the calculation of the basic assist torque T11.

[0090] However, when the steering wheel 5 is held in the neutral position, regardless of the value of the vehicle speed V, the steering torque T h The absolute value of is "0 Nm," which corresponds to the neutral position of the steering wheel 5. Also, when the steering wheel 5 is held in the neutral position, the steering angle θ remains constant regardless of the vehicle speed V. s The absolute value of is "0°", which corresponds to the neutral position of the steering wheel 5. Therefore, when the steering wheel 5 is held in the neutral position, the basic assist torque T11, and consequently the steering reaction force, hardly changes regardless of the vehicle speed V. Consequently, even if the vehicle speed V changes due to deceleration or acceleration of the vehicle, the driver will not feel any discomfort in the steering feel.

[0091] The correction processing unit 90 may fix the value of vehicle speed V used for the basic assist torque T11 not only when the steering wheel 5 is steered, but also when the value of vehicle speed V detected by the vehicle speed sensor 41 is abnormal. The vehicle speed V is, for example, the corrected vehicle speed V held in the corrected vehicle speed calculation unit 93. c It is fixed to the previous value. In this way, it is possible to suppress the continued execution of reaction force control based on an abnormal vehicle speed V.

[0092] • If the correction processing unit 90 determines that the steering state of the steering wheel 5 is in a steered state, the reaction force torque command value T * The value of the vehicle speed V used in the calculation may be fixed to the value of the vehicle speed V at the time it is determined that the steering state of the steering wheel 5 is in a steered state. Even in this case, the reaction torque command value T will not change in response to the actual change in vehicle speed V.* It is possible to prevent it from changing.

[0093] The correction processing unit 90 may, if it determines that the steering state of the steering wheel 5 is in a steered state, further determine whether the current value of the vehicle speed V at the time it was determined that the steering state of the steering wheel 5 is in a steered state is the same as the previous value of the vehicle speed V. In this case, the correction processing unit 90 will only determine the reaction force torque command value T if the current value of the vehicle speed V is different from the previous value of the vehicle speed V. * The value of the vehicle speed V used in the calculation may be fixed to the previous value of the vehicle speed V. Even in this case, the reaction torque command value T will not change in the actual vehicle speed V. * It is possible to prevent it from changing.

[0094] The correction processing unit 90 may fix the basic assist torque T11 when the steering state of the steering wheel 5 is in a steered state. In this case, the correction processing unit 90 is provided on the calculation path between the basic control unit 81A and the adder 81C. However, the corrected vehicle speed calculation unit 93 functions as a corrected assist torque calculation unit. The corrected assist torque calculation unit takes in the basic assist torque T11 calculated by the basic control unit 81A and the value of flag F0 set by the steered determination unit 92.

[0095] The correction assist torque calculation unit calculates the correction basic assist torque at a predetermined calculation cycle based on the value of flag F0, and holds the calculated correction basic assist torque. However, the correction assist torque calculation unit updates the held correction basic assist torque each time the correction basic assist torque is calculated. In other words, the correction basic assist torque held by the correction assist torque calculation unit is the previous value relative to the current value of the correction basic assist torque calculated by the correction assist torque calculation unit.

[0096] The Correction Assist Torque Calculation Unit calculates either the basic assist torque T11 calculated by the basic control unit 81A or the previously held value of the Correction Basic Assist Torque as the current value of the Correction Basic Assist Torque, based on the value of flag F0. When the value of flag F0 is "0", the Correction Assist Torque Calculation Unit calculates the basic assist torque T11 calculated by the basic control unit 81A as the current value of the Correction Basic Assist Torque. When the value of flag F0 is "1", the Correction Assist Torque Calculation Unit calculates the previously held value of the Correction Basic Assist Torque as the current value of the Correction Basic Assist Torque.

[0097] Even in this way, the assist torque command value T1, and consequently the reaction torque command value T, will change in accordance with the actual vehicle speed V. * It is possible to suppress changes in this. In addition, similar to the basic assist torque T11, the correction processing unit 90 may fix the assist torque command value T1 when the steering state of the steering wheel 5 is in a steered state. In this case, the correction processing unit 90 is provided, for example, on the calculation path between the assist torque command value calculation unit 81 and the subtractor 83. [Explanation of symbols]

[0098] 1... Steering control device 1A…Reaction force control device (processing circuit) 2… Steering gear 5… Steering wheel 6… Steering wheel 12… Reaction motor

Claims

1. A steering control device configured to control a steering system in which power transmission between the steering wheels of a vehicle and the steering wheel is separated, wherein the steering system includes a reaction motor configured to generate a steering reaction force applied to the steering wheel, The system includes a processing circuit configured to calculate a reaction torque command value for controlling the reaction motor based on the vehicle speed and the steering state of the steering wheel. The processing circuit is configured to perform processing to suppress changes in the reaction force torque command value due to changes in the vehicle speed when the steering state of the steering wheel is maintained.

2. The steering control device according to claim 1, wherein the processing circuit is configured to fix the value of the vehicle speed used in calculating the reaction force torque command value when the steering state of the steering wheel is in a steered state.

3. The processing circuit is configured to determine whether the steering state of the steering wheel is a maintained state, based on a state variable that reflects the steering state of the steering wheel. The steering control device according to claim 1, wherein the processing circuit is configured to fix the value of the vehicle speed used in calculating the reaction force torque command value to the value of the vehicle speed immediately before it is determined that the steering state of the steering wheel is in a steered state, when it is determined that the steering state of the steering wheel is in a steered state.

4. The processing circuit is configured to determine whether the steering state of the steering wheel is a maintained state, based on a state variable that reflects the steering state of the steering wheel. The steering control device according to claim 1, wherein the processing circuit is configured to fix the value of the vehicle speed used in calculating the reaction force torque command value to the value of the vehicle speed at the time it was determined that the steering state of the steering wheel was in a steered state, when it is determined that the steering state of the steering wheel is in a steered state.

5. The processing circuit is configured to determine whether the steering state of the steering wheel is a maintained state, based on a state variable that reflects the steering state of the steering wheel. If the processing circuit determines that the steering state of the steering wheel is in a steered state, it further determines whether the current value of the vehicle speed at the time the steering state of the steering wheel was determined to be in a steered state is the same as the previous value of the vehicle speed. The steering control device according to claim 1, wherein the processing circuit is configured to fix the value of the vehicle speed used in calculating the reaction force torque command value to the previous value of the vehicle speed only when the current value of the vehicle speed is different from the previous value of the vehicle speed.

6. The steering control device according to any one of claims 2 to 4, wherein the processing circuit is configured to gradually change the value of the vehicle speed used in calculating the reaction force torque command value from a fixed value of the vehicle speed to the actual vehicle speed when the steering wheel is released from its steered state.

7. The processing circuit includes a first process that calculates an assist torque command value, which is a torque in the same direction as the steering direction of the steering wheel, based on the steering state of the steering wheel, A second process calculates the axial force acting on the steering shaft that steers the steering wheel based on the steering state of the steering wheel, and converts the calculated axial force into a torque applied to the steering wheel to calculate the axial torque. The system is configured to perform a third process, which involves calculating the reaction torque command value by subtracting the axial force torque from the assist torque command value, The first process is, A fourth process that calculates a basic assist torque, which is the basis for calculating the assist torque command value, based on the steering state of the steering wheel, using an assist torque map. A fifth process that calculates a compensation torque for the basic assist torque based on the steering state of the steering wheel, A sixth process is included in which the assist torque command value is calculated by adding the basic assist torque and the compensation torque, The steering control device according to claim 2 or 3, wherein the assist torque map is a three-dimensional map that defines the relationship between steering torque and the basic assist torque according to the vehicle speed.

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