Steering control device

Abstract

To provide a steering control device capable of further highly precisely transmitting road surface reaction force to a steering wheel.SOLUTION: A steering control device that controls a steer-by-wire type steering device executes processes relating to: a control for current supply to a reaction force motor; and a control for current supply to a turning motor. A reaction force control unit includes a process of calculating a reaction force torque command value that is a control quantity for controlling the current supply to the reaction force motor. A turning control unit includes a turning control quantity calculating process of calculating a turning torque command value that is a control quantity for controlling the current supply to the turning motor. The reaction force control unit includes a process of reflecting, on the reaction force torque command value, a frequency signal applied to a turning wheel to a road surface. The frequency signal applied to the turning wheel from the road surface is a signal obtained from the turning torque command value calculated by the turning control unit.SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

[0002] Steer-by-wire steering devices have been installed in vehicles in the past. These steer-by-wire steering devices apply a steering reaction force to the steering wheel, allowing the driver to grasp the state of the steered wheels. Patent Document 1, for example, describes a steering control device as a technology for applying a steering reaction force to the steering wheel.

[0003] In the above-mentioned Patent Document 1, a predetermined frequency component of the current of the motor that steers the steered wheels is reflected in the steering reaction force applied to the steering wheel. The current flowing through the motor reflects the road reaction force. Therefore, the above-mentioned steering control device can transmit the road reaction force to the steering wheel. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-142704 Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, when transmitting a road reaction force to the steering wheel, other methods can be considered in addition to reflecting a predetermined frequency component of the current of the motor that steers the steered wheels. When other methods are considered, for example, from the viewpoint of transmitting the road reaction force to the steering wheel with higher accuracy, there is still room for improvement in the selection of parameters to be reflected in the steering reaction force applied to the steering wheel. [Means for solving the problem]

[0006] The steering control device that can solve the above problem controls a steer-by-wire type steering device having a structure in which the power transmission paths between a steering unit that is steered by the steering wheel of the vehicle and a steering unit that operates to move the steering shaft to which the steered wheels of the vehicle are connected are separated. The steering unit has a steering side motor that generates a steering reaction force on the steering wheel, and the steering unit has a steering side motor that generates a steering force that moves the steering axis, and the steering control device is configured to execute processing related to control of supply of current to the steering side motor and processing related to control of supply of current to the steering side motor, the processing related to control of supply of current to the steering side motor includes a reaction force control amount calculation processing that calculates a reaction force control amount that is a control amount for controlling the supply of current to the steering side motor, and the processing related to control of supply of current to the turning side motor includes a turning control amount calculation processing that calculates a turning control amount that is a control amount for controlling the supply of current to the turning side motor, the reaction force control amount calculation processing includes processing that reflects a frequency signal imparted to the steered wheels from a road surface in the reaction force control amount, and the frequency signal imparted to the steered wheels from the road surface is a signal obtained from the turning control amount in the turning control amount calculation processing.

[0007] According to the above configuration, the turning control amount is a control amount for controlling the supply of current to the turning-side motor. In other words, the current output from the turning-side motor changes as a result of reflecting the turning control amount after the turning control amount is calculated. When considering the time series from when the turning control amount is calculated to when the current in the turning-side motor based on the turning control amount is detected, the turning control amount is a parameter that exists earlier in the time series. This makes it possible to reflect a parameter that exists earlier in the time series in the reaction force control amount as a frequency signal imparted to the steered wheels by the road surface. Therefore, compared to when a parameter that exists later in the time series is reflected in the reaction force control amount as a frequency signal imparted to the steered wheels by the road surface, it is possible to reduce the temporal deviation from the actual road reaction force. This is effective from the perspective of transmitting the road reaction force to the steering wheel with higher accuracy.

[0008] In the above steering control device, it is preferable that the frequency signal applied to the steered wheel from the road surface is a frequency component within a predetermined range of frequency components possessed by the steering control amount, and the reaction force control amount calculation process includes a component extraction process that extracts the frequency components within the predetermined range from the steering control amount.

[0009] According to the above configuration, it is possible to optimize the road reaction force transmitted to the steering wheel. For example, the component extraction process may be embodied by being adapted to extract a component that reflects the condition of the road surface.

[0010] In the above steering control device, it is preferable that the steering control amount calculation process includes steering feedback process which calculates a steering control amount for controlling a steering converted angle to a target steering angle by feedback control, the steering converted angle being information that can be acquired by the steering unit, the steering feedback process includes process which calculates a proportional output value of a proportional element, the proportional output value being a value obtained by multiplying a difference between the target steering angle and the steering converted angle by a proportional gain, and the frequency signal applied to the steered wheels from the road surface is a signal obtained from at least the proportional output value of the steering control amount.

[0011] According to the above configuration, the steering control amount is a signal obtained from the proportional output value while being calculated through steering feedback processing. When the steering feedback processing includes a proportional element, the proportional element is the dominant element in the steering control amount. In other words, focusing on the proportional output value is effective in optimizing the road reaction force transmitted to the steering wheel. Therefore, the road reaction force can be transmitted to the steering wheel with higher accuracy.

[0012] In the above steering control device, it is preferable that the steering feedback processing includes processing for calculating a differential output value of a differential element in addition to processing for calculating the proportional output value, and the differential output value is a value obtained by multiplying a first-order time differential value of a difference between the target steering angle and the steering converted angle by a differential gain.

[0013] According to the above configuration, the steering control amount is a signal obtained from the proportional output value and the differential output value while being calculated through steering feedback processing. Even if the steering feedback processing includes a differential element in addition to a proportional element, the proportional output value remains the dominant element of the steering control amount. In other words, regardless of the specifications of the steering feedback processing, focusing on the proportional output value is effective in optimizing the road reaction force transmitted to the steering wheel. [Effects of the Invention]

[0014] According to the present invention, road reaction force can be transmitted to the steering wheel with higher accuracy. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a diagram showing a configuration of a vehicle steering system according to an embodiment; [Figure 2] FIG. 2 is a block diagram showing the functions of the steering control device of FIG. 1. [Figure 3] FIG. 3 is a block diagram showing the functions of a pinion angle feedback control unit in FIG. 2. [Figure 4] FIG. 3 is a block diagram showing the functions of an axial force calculation unit in FIG. 2. [Figure 5] FIG. 3 is a block diagram showing the functions of a target steering reaction force calculation unit in FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

[0016] A steering control device according to an embodiment will be described below. As shown in FIG. 1, vehicle steering system 2 includes a steering control device 1. Vehicle steering system 2 includes a steering unit 4 and a steering unit 6. Steering unit 4 is steered by a driver via a steering wheel 3 of the vehicle, which is a steering member. Steering unit 6 steers left and right steered wheels 5 of the vehicle in accordance with the steering input to steering unit 4 by the driver. Vehicle steering system 2 has a structure in which, for example, the power transmission paths between steering unit 4 and steering unit 6 are always separated. The power transmission paths between steering actuator 12, which will be described later, and steering actuator 31, which will be described later, are always separated. In other words, vehicle steering system 2 includes a steer-by-wire type steering device.

[0017] The steering unit 4 includes a steering shaft 11 and a steering actuator 12. The steering shaft 11 is connected to the steering wheel 3. The steering actuator 12 includes a reaction motor 13 and a steering-side reduction gear mechanism 14. The reaction motor 13 is a steering-side motor that applies a steering reaction force, which is a force that resists steering, to the steering wheel 3 via the steering shaft 11. The reaction motor 13 is connected to the steering shaft 11 via the steering-side reduction gear mechanism 14, which is made up of, for example, a worm and wheel. The reaction motor 13 is, for example, a three-phase brushless motor.

[0018] The steering unit 6 includes a pinion shaft 21, a rack shaft 22 as a steering shaft, and a rack housing 23. The pinion shaft 21 and the rack shaft 22 are connected with each other at a predetermined cross angle. A rack-and-pinion mechanism 24 is formed by meshing pinion teeth 21a formed on the pinion shaft 21 with rack teeth 22a formed on the rack shaft 22. The pinion shaft 21 corresponds to a rotation axis that can be converted into a steering angle θi, which is the steering position of the steered wheels 5. The rack housing 23 accommodates the rack-and-pinion mechanism 24.

[0019] One end of the pinion shaft 21 opposite to the end connected to the rack shaft 22 protrudes from a rack housing 23. Both ends of the rack shaft 22 protrude from both axial ends of the rack housing 23. Tie rods 26 are connected to both ends of the rack shaft 22 via rack ends 25 made up of ball joints. The ends of the tie rods 26 are connected to knuckles (not shown) to which the left and right steered wheels 5 are respectively attached.

[0020] The steering unit 6 includes a steering actuator 31. The steering actuator 31 includes a steering motor 32, a transmission mechanism 33, and a conversion mechanism 34. The steering motor 32 is a steering-side motor that applies a steering force to the rack shaft 22 to turn the steerable wheels 5 via the transmission mechanism 33 and the conversion mechanism 34. The steering motor 32 transmits rotation to the conversion mechanism 34 via the transmission mechanism 33, which is, for example, a belt transmission mechanism. The transmission mechanism 33 converts the rotation of the steering motor 32 into reciprocating motion of the rack shaft 22 via the conversion mechanism 34, which is, for example, a ball screw mechanism. The steering motor 32 may be, for example, a three-phase brushless motor.

[0021] In vehicle steering system 2, steering actuator 31 applies motor torque as a steering force to rack shaft 22 in response to steering by the driver, thereby changing the steering angle θi of steered wheels 5. At this time, steering actuator 12 applies a steering reaction force that resists the steering by the driver to steering wheel 3. As a result, in vehicle steering system 2, the steering reaction force, which is the motor torque applied from steering actuator 12, changes the steering torque Th required to steer steering wheel 3.

[0022] The reason for providing the pinion shaft 21 is to support the rack shaft 22 together with the pinion shaft 21 inside the rack housing 23. The rack shaft 22 is supported movably along its axial direction and is pressed toward the pinion shaft 21 by a support mechanism (not shown) provided in the vehicle steering system 2. In this way, the rack shaft 22 is supported inside the rack housing 23. However, another support mechanism may be provided to support the rack shaft 22 in the rack housing 23 without using the pinion shaft 21.

[0023] <Electrical configuration of the steering system> 1, the reaction force motor 13 and the steering motor 32 are connected to the steering control device 1. The steering control device 1 controls the operation of each of the motors 13, 32.

[0024] Detection results of various sensors are input to the steering control device 1. The various sensors include, for example, a torque sensor 41, a steering side rotation angle sensor 42, a turning side rotation angle sensor 43, and a vehicle speed sensor 44.

[0025] Torque sensor 41 is provided on steering shaft 11 between steering wheel 3 and steering-side reduction mechanism 14. Torque sensor 41 detects steering torque Th, which is a value indicating the torque applied to steering shaft 11 by the driver's steering. Steering torque Th is detected in relation to the torsion of a torsion bar 41a provided on steering shaft 11 between steering wheel 3 and steering-side reduction mechanism 14, midway along steering shaft 11. Steering-side rotation angle sensor 42 is provided on reaction motor 13. Steering-side rotation angle sensor 42 detects rotation angle θa, which is the angle of the rotation shaft of reaction motor 13, within a range of 360 degrees. Turning-side rotation angle sensor 43 is provided on steering motor 32. Steering-side rotation angle sensor 43 detects rotation angle θb, which is the angle of the rotation shaft of steering motor 32, within a range of 360 degrees. Vehicle speed sensor 44 detects vehicle speed V, which is the traveling speed of the vehicle.

[0026] <Functions of the steering control device> As shown in FIG. 2, steering control device 1 has reaction force control unit 50 and steering control unit 60. Reaction force control unit 50 controls steering wheel 3, which is the object to be controlled. Reaction force control unit 50 controls the drive of steering actuator 12, more specifically the supply of current to reaction force motor 13, in order to control the steering reaction force, which is the control variable of the object to be controlled. Steering control unit 60 controls rack shaft 22, which is the object to be controlled. Steering control unit 60 controls the drive of steering actuator 31, more specifically the supply of current to steering motor 32, in order to control the steering force, which is the control variable of the object to be controlled. Reaction force control unit 50 and steering control unit 60 transmit and receive information to and from each other via a local network such as serial communication, for example. Reaction force control unit 50 is combined with steering unit 4 to form a reaction force system RS. Steering control unit 60 is combined with steering unit 6 to form a steering system TS.

[0027] The reaction force control unit 50 is equipped with a central processing unit (hereinafter referred to as "CPU") and a memory. The reaction force control unit 50 performs various processes by having the CPU execute programs stored in the memory at predetermined calculation cycles. The turning control unit 60 is equipped with a central processing unit (hereinafter referred to as "CPU") and a memory. The turning control unit 60 performs various processes by having the CPU execute programs stored in the memory at predetermined calculation cycles. The CPU and memory constitute a microcomputer, which is a processing circuit. The memory includes computer-readable media such as RAM (Random Access Memory) and ROM (Read Only Memory). However, it is one example that various processes are realized by software. The processing circuits of the reaction force control unit 50 and the turning control unit 60 may be configured to realize at least a part of their processes by hardware circuits such as logic circuits.

[0028] Fig. 2 shows part of the processing executed by reaction force control unit 50 and steering control unit 60. The processing shown in Fig. 2 is part of the processing realized by a CPU executing a program stored in memory, and is described for each type of processing realized.

[0029] The reaction force control unit 50 has a current sensor 54. The current sensor 54 detects an actual current value Ia obtained from the current value of each phase of the reaction force motor 13 flowing through a connecting wire between the reaction force control unit 50 and the motor coil of each phase of the reaction force motor 13. The current sensor 54 acquires, as a current, the voltage drop across a shunt resistor connected to the source side of each switching element in an inverter (not shown) provided corresponding to the reaction force motor 13. For ease of explanation, FIG. 2 shows the connecting wires and current sensors for each phase collectively.

[0030] The steering control unit 60 has a current sensor 65. The current sensor 65 detects an actual current value Ib obtained from the value of a current for each phase of the steering motor 32 flowing through a connecting wire between the steering control unit 60 and the motor coil for each phase of the steering motor 32. The current sensor 65 obtains, as a current, a voltage drop across a shunt resistor connected to the source side of each switching element in an inverter (not shown) provided corresponding to the steering motor 32. For ease of explanation, in FIG. 2, the connecting wires for each phase and the current sensors for each phase are shown as one unit.

[0031] <About the reaction force control unit> As shown in Fig. 2, reaction force control unit 50 receives as input steering torque Th, vehicle speed V, rotation angle θa, proportional output value Ttp, and actual current value Ib. Proportional output value Ttp is a component calculated in steering control unit 60. Actual current value Ib is a component obtained from steering control unit 60. Reaction force control unit 50 controls the power supply to reaction force motor 13 based on steering torque Th, vehicle speed V, rotation angle θa, proportional output value Ttp, and actual current value Ib.

[0032] The reaction force control unit 50 includes a steering angle calculation unit 51 , a reaction force control amount calculation unit 52 , and an electric current control unit 53 . Steering angle calculation unit 51 calculates steering angle θs by inputting rotation angle θa. Steering angle calculation unit 51 converts rotation angle θa into an integrated angle including a range exceeding 360°, for example, by counting the number of rotations of reaction force motor 13 from a steering neutral position, which is the rotation position of steering wheel 3 when the vehicle is traveling straight. Steering angle calculation unit 51 calculates steering angle θs by multiplying the integrated angle obtained by conversion by a conversion coefficient based on the rotational speed ratio of steering-side reduction gear mechanism 14. Steering angle θs obtained in this way is output to steering control unit 60.

[0033] The reaction force control amount calculation unit 52 receives the steering torque Th, the vehicle speed V, the proportional output value Ttp, the actual current value Ib, and the steering angle θs. The reaction force control amount calculation unit 52 executes a reaction force control amount calculation process to calculate a reaction force torque command value Ts* based on the steering torque Th, the vehicle speed V, the proportional output value Ttp, the actual current value Ib, and the steering angle θs. The reaction force torque command value Ts* is a reaction force control amount that is a target for the steering reaction force of the steering wheel 3 to be generated by the reaction force motor 13.

[0034] The energization control unit 53 receives the reaction torque command value Ts*, the actual current value Ia, and the rotation angle θa. The energization control unit 53 calculates a steering current command value based on the reaction torque command value Ts*. The steering current command value is a target value of the torque to be generated by the reaction motor 13. The energization control unit 53 calculates a converted steering current value based on the input actual current value Ia and the rotation angle θa. The converted steering current value is a converted value obtained by converting the actual current value Ia into a current value on the dq coordinate. The energization control unit 53 controls the power supply to the reaction motor 13 by performing feedback control of the converted steering current value so that the converted steering current value follows the steering current command value. This causes the reaction motor 13 to generate torque corresponding to the reaction torque command value Ts*. In other words, it is possible to provide the driver with an appropriate sense of control corresponding to the road reaction force.

[0035] <About the steering control unit> 2, steering control unit 60 receives as input vehicle speed V, rotation angle θb, and steering angle θs to control the power supply to steering motor 32. Steering angle θs is a component calculated in reaction force control unit 50.

[0036] The steering control unit 60 has a pinion angle calculation unit 61, a steering angle ratio variable control unit 62, a pinion angle feedback control unit ("pinion angle F / B control unit" in the drawing) 63, and an energization control unit 64.

[0037] Pinion angle calculation unit 61 calculates pinion angle θp by inputting rotation angle θb. Pinion angle calculation unit 61 converts rotation angle θb into an integrated angle that includes a range exceeding 360°, for example, by counting the number of rotations of steering motor 32 from a rack neutral position, which is the position of rack shaft 22 when the vehicle is traveling straight. Pinion angle calculation unit 61 calculates pinion angle θp, which is the actual rotation angle of pinion shaft 21, by multiplying the integrated angle obtained by conversion by a conversion coefficient that is based on the rotational speed ratio of transmission mechanism 33, the lead of conversion mechanism 34, and the rotational speed ratio of rack and pinion mechanism 24. Turning motor 32 and pinion shaft 21 are linked. For this reason, there is a one-to-one correspondence between the integrated value of rotation angle θb of turning motor 32 and pinion angle θp. This correspondence can be used to find pinion angle θp from rotation angle θb of turning motor 32. Furthermore, pinion shaft 21 is meshed with rack shaft 22. Therefore, there is also a one-to-one correspondence between pinion angle θp and the amount of movement of rack shaft 22. And there is also a one-to-one correspondence between pinion angle θp and steering angle θi of steered wheels 5. Pinion angle θp is an example of information that can be acquired by steering actuator 31 and is also an example of a steering converted angle.

[0038] The steering angle ratio variable control unit 62 receives the vehicle speed V and the steering angle θs as input. The steering angle ratio variable control unit 62 calculates the target pinion angle θp* by adding the adjustment amount θvg to the steering angle θs. The target pinion angle θp* is a target steering angle that is a target for the pinion angle θp obtained as a result of steering the steered wheels 5. The adjustment amount θvg is a manipulation amount for changing the steering angle ratio of the target pinion angle θp* to the steering angle θs. The adjustment amount θvg is obtained by reflecting the gear ratio VG. The gear ratio VG is a steering angle variable value obtained, for example, by subtracting "1" from a value that indicates the relationship between the steering angle θs as the denominator and the target pinion angle θp* as the numerator. The value that indicates the relationship between the steering angle θs as the denominator and the target pinion angle θp* as the numerator is an index that indicates the ratio of the change in the target pinion angle θp* to the change in the steering angle θs. Such an index is called, for example, a transmission ratio or a steering angle ratio, and defines the relationship between the steering angle θs and the pinion angle θp, that is, the relationship between the steering angle θs and the steered angle θi. In other words, the gear ratio VG is a value that indicates the difference from the case where the steering angle θs and the target pinion angle θp* correspond 1:1.

[0039] Pinion angle feedback control unit 63 receives as input target pinion angle θp* and pinion angle θp. Pinion angle feedback control unit 63 executes steering control amount calculation processing to calculate steering torque command value Tp* based on target pinion angle θp* and pinion angle θp. Turning torque command value Tp* is a steering control amount that serves as a target for the turning force of steered wheels 5 to be generated via turning motor 32. Pinion angle feedback control unit 63 calculates turning torque command value Tp* by executing feedback control of pinion angle θp so as to make pinion angle θp follow target pinion angle θp*. Feedback control of pinion angle θp that is executed so as to make pinion angle θp follow target pinion angle θp* is an example of steering feedback processing.

[0040] More specifically, as shown in FIG. 3, the pinion angle feedback control unit 63 has an angle deviation calculation unit 71, a proportional element calculation unit 72, a differential element calculation unit 73, and an addition processing unit 74.

[0041] The target pinion angle θp* and the pinion angle θp are input to the angle deviation calculation unit 71. The angle deviation calculation unit 71 calculates the angle deviation Δθp obtained by subtracting the pinion angle θp from the target pinion angle θp*.

[0042] The proportional element calculation unit 72 receives the angular deviation Δθp. The proportional element calculation unit 72 calculates a proportional output value Ttp, which is a value proportional to the angular deviation Δθp. More specifically, the proportional element calculation unit 72 calculates the proportional output value Ttp by multiplying the angular deviation Δθp by a proportional gain Kp via a proportional gain multiplication unit 75. The proportional output value Ttp thus obtained is output to the reaction force control unit 50.

[0043] The differential element calculation unit 73 receives the angle deviation Δθp. The differential element calculation unit 73 calculates a differential output value Ttd, which is a value proportional to the first-order time differential value of the angle deviation Δθp. More specifically, the differential element calculation unit 73 calculates an angle deviation differential value dtθp obtained by first-order time differentiation of the angle deviation Δθp through a differential processing unit 76. The differential element calculation unit 73 then calculates the differential output value Ttd by multiplying the angle deviation differential value dtθp by a differential gain Kd through a differential gain multiplication processing unit 77.

[0044] The proportional output value Ttp and the differential output value Ttd are input to the addition processing unit 74. The addition processing unit 74 calculates the PD output value Ttpd by adding the proportional output value Ttp and the differential output value Ttd.

[0045] The compensation element calculation unit 78 calculates a compensation output value Ttc, which is a control amount other than the PD output value Ttpd, for controlling the pinion angle θp to the target pinion angle θp*. The compensation output value Ttc is, for example, a damping output value for controlling the angle deviation derivative value dtθp.

[0046] The PD output value Ttpd and the compensation output value Ttc are input to the addition processing unit 79. The addition processing unit 79 calculates the turning torque command value Tp* obtained by adding the PD output value Ttpd and the compensation output value Ttc.

[0047] Energization control unit 64 receives as input steering torque command value Tp*, actual current value Ib, and rotation angle θb. Energization control unit 64 calculates a steering current command value based on steering torque command value Tp*. The steering current command value is a target value for torque to be generated in steering motor 32. Energization control unit 64 calculates a converted steering current value based on actual current value Ib and rotation angle θb. The converted steering current value is a converted value obtained by converting actual current value Ib into a current value on the dq coordinate. Energization control unit 64 controls the power supply to steering motor 32 by executing feedback control of the converted steering current value so that the converted steering current value follows the turning current command value. This causes steering motor 32 to generate torque according to steering torque command value Tp*. In other words, it is possible to rotate steered wheels 5 by an angle according to the steering force.

[0048] <Details of the reaction force control amount calculation unit> As shown in FIG. 2, the reaction force control amount calculation section 52 of the reaction force control section 50 has an axial force calculation section 55, a target steering reaction force calculation section 56, and a reflection processing section 57.

[0049] The axial force calculation unit 55 receives the vehicle speed V, the steering angle θs, and the actual current value Ib as input. The axial force calculation unit 55 calculates the axial force component F based on the vehicle speed V, the steering angle θs, and the actual current value Ib. The axial force component F corresponds to a calculated axial force that is an estimate of the axial force acting on the rack shaft 22 through the steered wheels 5.

[0050] The target steering reaction force calculation unit 56 receives the steering torque Th, the vehicle speed V, the steering angle θs, and the proportional output value Ttp. The target steering reaction force calculation unit 56 calculates a steering reaction force component Tb* based on the steering torque Th, the vehicle speed V, the steering angle θs, and the proportional output value Ttp. The steering reaction force component Tb* corresponds to the motor torque for rotating the steering wheel 3 in the steering direction of the driver, i.e., the assist force for assisting the steering of the steering wheel 3 by the driver.

[0051] The reflection processing unit 57 receives the axial force component F and the steering reaction force component Tb*. The reflection processing unit 57 calculates a reaction torque command value Ts* by subtracting the axial force component F from the steering reaction force component Tb*.

[0052] <About the axial force calculation unit> As shown in FIG. 4, the axial force calculation unit 55 has an angle axial force calculation unit 81, a current axial force calculation unit 82, a distribution ratio calculation unit 83, and an addition processing unit 84.

[0053] The angular axial force calculation unit 81 receives the vehicle speed V and the steering angle θs. The angular axial force calculation unit 81 calculates the angular axial force Fr based on the vehicle speed V and the steering angle θs. The angular axial force Fr is an ideal value of the axial force defined by an arbitrarily set vehicle model. The angular axial force Fr is calculated in the dimension of torque (N·m). The angular axial force Fr is calculated as an axial force that does not reflect road surface information such as minute irregularities that do not affect the lateral behavior of the vehicle or steps that affect the lateral behavior of the vehicle. The angular axial force calculation unit 81 calculates the angular axial force Fr using, for example, an angular axial force map that defines the relationship between the vehicle speed V, the steering angle θs, and the angular axial force Fr. The angular axial force Fr is set so that its absolute value increases as the absolute value of the steering angle θs increases. The angular axial force Fr is also set so that its absolute value increases as the vehicle speed V increases.

[0054] Current axial force calculation unit 82 receives input of actual current value Ib. Based on actual current value Ib, current axial force calculation unit 82 calculates current axial force Fi. Current axial force Fi is an axial force that actually acts on rack shaft 22, which operates to steer steered wheels 5, i.e., an estimated value of the axial force actually transmitted to rack shaft 22. Current axial force Fi is calculated in the dimension of torque (N m). Current axial force Fi is calculated as a road surface reaction force, which is an axial force that reflects the road surface information. Current axial force calculation unit 82 calculates current axial force Fi using, for example, a current axial force map that defines the relationship between actual current value Ib and current axial force Fi. The current axial force Fi is set so that its absolute value increases as the absolute value of actual current value Ib increases, assuming that the torque applied to rack shaft 22 by steering motor 32 is balanced with the torque corresponding to the force applied to rack shaft 22 via steered wheels 5.

[0055] The distribution ratio calculation unit 83 receives the vehicle speed V. The distribution ratio calculation unit 83 calculates the distribution ratio Di based on the vehicle speed V. The distribution ratio Di is a distribution ratio of the current axial force Fi when the axial force component F is obtained by distributing the angular axial force Fr and the current axial force Fi. In other words, the distribution ratio Di indicates a reflection state of the current axial force Fi to the axial force component F, and indicates a reflection state of the current axial force Fi to the steering reaction force component Tb*, i.e., the reaction torque command value Ts*. The distribution ratio calculation unit 83 calculates the distribution ratio Di using, for example, a distribution ratio map that defines the relationship between the vehicle speed V and the distribution ratio Di. The distribution ratio Di is "1 (100%)" when the vehicle speed V is low, including when the vehicle is stopped. In other words, this indicates that at low speeds, only the current axial force Fi is distributed to the axial force component F, i.e., the angle axial force Fr is not distributed. The distribution ratio includes the concept of "0 (zero)" in which only either the angular axial force Fr or the current axial force Fi is distributed to the axial force component F, for example.

[0056] The allocation ratio conversion processing unit 87 receives the allocation ratio Di. The allocation ratio conversion processing unit 87 calculates the allocation ratio Dr by subtracting the allocation ratio Di from a predetermined reference value "1". The allocation ratio Dr is the allocation ratio of the angular axial force Fr when the axial force component F is obtained by allocating the angular axial force Fr and the current axial force Fi. In other words, the allocation ratio Dr indicates the reflection state of the angular axial force Fr to the axial force component F, and indicates the reflection state of the angular axial force Fr to the steering reaction force component Tb*, i.e., the reaction torque command value Ts*. The sum of the allocation ratio Dr and the allocation ratio Di is set to, for example, the reference value "1", i.e., the combined allocation ratio is set to "100%".

[0057] Each distribution ratio Di, Dr is reflected in the corresponding axial force Fi, Fr. More specifically, the distribution ratio reflection processing unit 85 calculates the final angular axial force Frm by multiplying the angular axial force Fr by the distribution ratio Dr. The distribution ratio reflection processing unit 86 calculates the final current axial force Fim by multiplying the current axial force Fi by the distribution ratio Di.

[0058] The addition processing unit 84 receives the angular axial force Frm and the current axial force Fim and calculates the axial force component F obtained by adding the angular axial force Frm and the current axial force Fim. <About the target steering reaction force calculation unit> As shown in FIG. 5, the target steering reaction force calculation unit 56 has a basic control amount calculation unit 91, a road information control amount calculation unit 92, and a subtraction processing unit 93.

[0059] The basic control amount calculation unit 91 receives the steering torque Th and the vehicle speed V. The basic control amount calculation unit 91 calculates a basic control amount Ib* based on the steering torque Th and the vehicle speed V. The basic control amount Ib* is a control amount calculated in relation to the steering of the steering wheel 3. The basic control amount Ib* is a basic component of the steering reaction force component Tb* and is set so that the steering of the steering wheel 3 exhibits desired characteristics. The basic control amount calculation unit 91 calculates the basic control amount Ib* using, for example, an assist map that defines the relationship between the steering torque Th, the vehicle speed V, and the basic control amount Ib*. The basic control amount Ib* is set so that the larger the absolute value of the steering torque Th, the larger its absolute value becomes, and the smaller the vehicle speed V, the larger its absolute value becomes.

[0060] The road information control amount calculation unit 92 receives the proportional output value Ttp. The road information control amount calculation unit 92 calculates the road information control amount If* based on the proportional output value Ttp. The road information control amount If* is calculated as a road surface reaction force, which is an axial force that reflects a predetermined range of frequency components of the road surface information. The predetermined range of frequency components of the road surface information are, for example, components that represent vibrations caused by unevenness on the road surface, having intermediate frequencies between low and high frequencies, excluding low and high frequency vibrations.

[0061] More specifically, the proportional output value Ttp is input to a band-pass filter 101 as a variable including vibration components of the steered wheels 5 due to road surface reaction force. The band-pass filter 101 executes component extraction processing to extract an extracted frequency signal Tfr, which is a frequency component within a predetermined range, from the proportional output value Ttp. The band-pass filter 101 has filter characteristics, i.e., a transfer function, adapted to extract signals in a frequency band caused by road surface irregularities, for example. The road information control amount calculation unit 92 calculates a road information control amount If* by multiplying the extracted frequency signal Tfr by a filter gain Kf via a filter gain multiplication processing unit 102. The road information control amount If* is calculated in the dimension of torque (N m), similar to the axial forces Fi and Fr.

[0062] The basic control amount Ib* and the road information control amount If* are input to the subtraction processing unit 93. The subtraction processing unit 93 calculates the steering reaction force component Tb* by subtracting the road information control amount If* from the basic control amount Ib*.

[0063] <Operation of this embodiment> As shown in Fig. 2, turning torque command value Tp* is a control variable for controlling the supply of current to turning motor 32. In other words, the current that is the output of turning motor 32 changes as a result of reflecting turning torque command value Tp* after turning torque command value Tp* is calculated. When considering the time series from when turning torque command value Tp* is calculated to when the current in turning motor 32 based on turning torque command value Tp* is detected, turning torque command value Tp* is a parameter that exists earlier in the time series. For example, while turning torque command value Tp* and the current detected in turning motor 32 are values ​​that correspond to each other, turning torque command value Tp* is a parameter that can be obtained earlier in the time series than the current detected in turning motor 32.

[0064] In response to this, as shown in FIG. 5, road information control amount calculation section 92 calculates road information control amount If* based on proportional output value Ttp included in turning torque command value Tp*.

[0065] This makes it possible to reflect the proportional output value Ttp, which is a parameter calculated earlier in the time series, in the reaction torque command value Ts* as a frequency signal imparted to the steered wheels 5 from the road surface.

[0066] <Effects of this embodiment> (1-1) It becomes possible to reflect the proportional output value Ttp, which is a parameter calculated earlier in the time series, in the reaction torque command value Ts* as a frequency signal imparted to the steered wheels 5 by the road surface. For example, compared to when the current detected by the turning motor 32 is reflected in the reaction torque command value Ts* as a frequency signal imparted to the steered wheels 5 by the road surface, it is possible to reduce the temporal deviation from the actual road reaction force. This is effective from the viewpoint of transmitting the road reaction force to the steering wheel 3 with higher accuracy.

[0067] (1-2) Road information control amount calculation unit 92 includes band-pass filter 101 for calculating extracted frequency signal Tfr from proportional output value Ttp included in steering torque command value Tp*. Band-pass filter 101 is adapted to extract signals in a frequency band caused by unevenness of the road surface. This makes it possible to optimize the road surface reaction force transmitted to steering wheel 3.

[0068] (1-3) Steering control unit 60 includes pinion angle feedback control unit 63 which calculates steering torque command value Tp* by feedback control. Pinion angle feedback control unit 63 includes proportional element calculation unit 72. The frequency signal imparted to steered wheels 5 from the road surface, which is input to road information control amount calculation unit 92, is set to proportional output value Ttp included in steering torque command value Tp*. As a result, steering torque command value Tp* is a signal obtained from proportional output value Ttp while being calculated via pinion angle feedback control unit 63. When pinion angle feedback control unit 63 includes proportional element calculation unit 72, proportional element calculation unit 72 is a dominant element in steering torque command value Tp*. In other words, focusing on proportional output value Ttp is effective in optimizing the road surface reaction force transmitted to steering wheel 3. Therefore, the road surface reaction force can be transmitted to steering wheel 3 with higher accuracy.

[0069] (1-4) When road information control amount calculation unit 92 inputs proportional output value Ttp included in steering torque command value Tp*, the characteristics of so-called P control are reflected in reaction torque command value Ts*. Therefore, this embodiment is effective in transmitting road surface reaction force to steering wheel 3, particularly in improving the accuracy of the static characteristics of the road surface reaction force.

[0070] (1-5) Pinion angle feedback control unit 63 includes derivative element calculation unit 73 in addition to proportional element calculation unit 72. As a result, turning torque command value Tp* is a signal obtained from proportional output value Ttp and derivative output value Ttd while being calculated through pinion angle feedback control unit 63. Even in the case where pinion angle feedback control unit 63 includes derivative element calculation unit 73 in addition to proportional element calculation unit 72, proportional output value Ttp remains the dominant element in turning torque command value Tp*. In other words, regardless of the specifications of pinion angle feedback control unit 63, focusing on proportional output value Ttp is effective in optimizing the road surface reaction force transmitted to steering wheel 3.

[0071] <Other embodiments> The above embodiment may be modified as follows: In addition, the following other embodiments may be combined with each other within the scope of technical compatibility.

[0072] The pinion angle feedback control unit 63 does not necessarily have to include the differential element calculation unit 73 or the compensation element calculation unit 78. In the pinion angle feedback control unit 63, the compensation element calculation unit 78 may be an integral element calculation unit that calculates an integral output value, which is a value obtained by integrating the angle deviation Δθp. In other words, the pinion angle feedback control unit 63 may be configured to perform PID control.

[0073] Pinion angle feedback control unit 63 may be configured to execute open-loop control in addition to feedback control. In this case, steering torque command value Tp* is obtained as the sum of a feedback control amount obtained through feedback control and a feedforward control amount obtained through open-loop control.

[0074] The road information control amount calculation unit 92 may be configured to calculate the road information control amount If* by inputting the turning torque command value Tp* or the PD output value Ttpd. Even in this case, the effect corresponding to (1-1) above can be achieved. Furthermore, in the other embodiments described herein, the differential output value Ttd can also be reflected in the reaction torque command value Ts*, so that the characteristics of so-called D control are reflected in the reaction torque command value Ts*. Therefore, the other embodiments described herein are effective in improving the accuracy of not only the static characteristics but also the dynamic characteristics of transmitting the road reaction force to the steering wheel 3. This allows the road reaction force to be transmitted to the steering wheel 3 with high accuracy, even when the steering wheel 3 is suddenly steered.

[0075] Road information control amount calculation unit 92 may calculate road information control amount If* by inputting the turning current command value or a proportional element obtained in the process of calculating the turning current command value. Even in this case, the time divergence from the actual road reaction force can be reduced compared to, for example, a case where the current detected by turning motor 32 is reflected in reaction torque command value Ts* as a frequency signal applied to steered wheels 5 from the road surface.

[0076] The road information control amount calculation unit 92 may be configured to have a high-pass filter or a low-pass filter instead of the band-pass filter 101 depending on the signal of the target frequency band of the road surface.

[0077] In the road information control amount calculation unit 92, the band-pass filter 101 may be a composite filter in which a low-pass filter and a high-pass filter are connected in series, as long as the band-pass filter 101 has the same function.

[0078] The road information control amount calculation unit 92 may perform map calculation of the road information control amount If* as long as it has the same function as the band pass filter 101. The map calculation only needs to define the relationship between the proportional output value Ttp and the road information control amount If*. In this case, the road information control amount calculation unit 92 may not include the filter gain multiplication unit 102.

[0079] Road information control amount calculation unit 92 may be the processing of axial force calculation unit 55. Furthermore, road information control amount calculation unit 92 may be realized as the processing of steering control unit 60. Similarly, for example, current axial force calculation unit 82 may be realized as the processing of steering control unit 60. In the other embodiments described herein, the road information control amount If* and current axial force Fi obtained through the processing in steering control unit 60 may each be output to reaction force control unit 50.

[0080] The axial force calculation unit 55 may calculate a vehicle state quantity axial force that can be calculated based on the vehicle speed V, lateral acceleration, and yaw rate, instead of the current axial force Fi. Also, the axial force calculation unit 55 may calculate a tire axial force that is obtained in consideration of the tire force acting on the steered wheels 5, instead of the current axial force Fi. The vehicle state quantity axial force and the tire axial force can also be used by being added to the angle axial force Fr and the current axial force Fi.

[0081] The angle axial force calculation unit 81 may be configured to input the pinion angle θp or the target pinion angle θp* instead of the steering angle θs. The current axial force calculation unit 82 only needs to use at least the actual current value Ib, and may use other elements in combination, such as the vehicle speed V. Furthermore, the actual current value Ib input to the current axial force calculation unit 82 may be a processed actual current value Ib obtained by processing it, for example, by filtering it with a low-pass filter or by performing predetermined compensation.

[0082] Current axial force calculation unit 82 may be configured to input proportional output value Ttp, PD output value Ttpd, or turning torque command value Tp*. Current axial force calculation unit 82 may calculate current axial force Fi based on proportional output value Ttp, PD output value Ttpd, or turning torque command value Tp*. For example, depending on how the map calculation used to calculate current axial force Fi is designed, if current axial force Fi also serves as road information control variable If*, road information control variable calculation unit 92 may be eliminated.

[0083] The distribution ratio calculation unit 83 only needs to use at least the vehicle speed V, and may use the pinion angle θp, the target pinion angle θp*, or the steering angle θs, or may use a combination of other elements.

[0084] The sum of the distribution ratios Dr and Di may be set to a value less than the reference value "1" or greater than the reference value "1". The basic control amount calculation unit 91 may be configured to input the steering angle θs instead of the steering torque Th when calculating the basic control amount Ib*. Also, the basic control amount calculation unit 91 does not have to use the vehicle speed V, and may use a combination of other elements.

[0085] The target steering reaction force calculation unit 56 may calculate, as the steering reaction force component Tb*, a value calculated by executing torque feedback control that causes the steering torque Th to follow a target steering torque calculated based on the steering torque Th.

[0086] The steering angle calculation unit 51 may calculate the steering angle θs by taking into account the amount of torsion of the steering shaft 11 that corresponds to the steering torque Th. The steering angle θs may be a detection value of a steering angle sensor that directly detects the rotation angle of the steering shaft 11. The steering angle sensor may be provided, for example, on the steering shaft 11 between the steering wheel 3 and the torque sensor 41.

[0087] The steering actuator 12 does not necessarily have to include the steering-side reduction mechanism 14. The reaction motor 13 is not limited to a three-phase brushless motor. For example, it may be a DC motor with brushes. The other embodiments described herein can be similarly applied to the steering motor 32.

[0088] The pinion angle θp may be obtained by converting a detected value of the movement amount of the rack shaft 22. In this case, the control amount and the like related to the pinion angle θp are converted using the detected value of the movement amount of the rack shaft 22.

[0089] Although steering unit 6 transmits the rotation of steering motor 32 to conversion mechanism 34 via transmission mechanism 33, the present invention is not limited to this. For example, steering unit 6 may be configured so that the rotation of steering motor 32 is transmitted to conversion mechanism 34 via a gear mechanism. Also, steering unit 6 may be configured so that steering motor 32 directly rotates conversion mechanism 34. Furthermore, steering unit 6 may be configured to include a second rack-and-pinion mechanism, and so that the rotation of steering motor 32 is converted into reciprocating motion of rack shaft 22 by the second rack-and-pinion mechanism.

[0090] The steering unit 6 is not limited to a configuration in which the right steered wheels 5 and the left steered wheels 5 are linked together. In other words, the right steered wheels 5 and the left steered wheels 5 may be independently controlled.

[0091] The vehicle steering system 2 has a linkless structure in which the power transmission path between the steering unit 4 and the turning unit 6 is always separated, but this is not limited to this. For example, the vehicle steering system 2 may have a structure in which the steering unit 4 and the turning unit 6 can be mechanically separated by a clutch. [Explanation of symbols]

[0092] 1...Steering control device 2...Vehicle steering system 3...Steering wheel 4...Steering unit 5...Steering wheel 6...Steering unit 13...Reaction motor (steering side motor) 22...Rack shaft (steering shaft) 32...Steering motor (steering side motor) 50...Reaction force control unit 52...Reaction force control amount calculation unit 56...Target steering reaction force calculation unit 60...Steering control unit 63...Pinion angle feedback control unit 71...Angle deviation calculation unit 72...Proportional element calculation section 73...Differential element calculation unit 92...Road information control amount calculation unit 101...Bandpass filter

Claims

1. A steering control device that controls a steer-by-wire type steering device having a structure in which a power transmission path between a steering unit steered by a steering wheel of a vehicle and a steering unit that operates to move a steering shaft to which steered wheels of the vehicle are connected is separated, the steering unit has a steering-side motor that generates a steering reaction force on the steering wheel, and the turning unit has a turning-side motor that generates a steering force that moves the turning shaft, the steering control device is configured to execute a process related to control of supply of current to the steering-side motor and a process related to control of supply of current to the steered-side motor, the processing related to the control of the supply of current to the steering-side motor includes a reaction force control amount calculation processing for calculating a reaction force control amount which is a control amount for controlling the supply of current to the steering-side motor, the processing related to control of supply of current to the turning-side motor includes a turning control amount calculation processing of calculating a turning control amount which is a control amount for controlling supply of current to the turning-side motor, the reaction force control amount calculation process includes a process of reflecting a frequency signal imparted to the steered wheels from a road surface in the reaction force control amount, A steering control device wherein the frequency signal applied to the steered wheels from a road surface is a signal obtained from the steering control amount in the steering control amount calculation process.

2. the frequency signal applied to the steered wheels from a road surface is a frequency component within a predetermined range of frequency components of the steering control amount, 2. The steering control device according to claim 1, wherein the reaction force control amount calculation process includes a component extraction process for extracting frequency components within the predetermined range from the steering control amount.

3. The steering control device according to claim 2 , wherein the component extraction process is adapted to extract a component that reflects the state of the road surface.

4. the steering control amount calculation process includes a steering feedback process that calculates a steering control amount for controlling the steering converted angle to a target steering angle by feedback control, The steering converted angle is information that can be acquired by the steering unit, the steering feedback processing includes processing for calculating a proportional output value of a proportional element, the proportional output value is a value obtained by multiplying a difference between the target turning angle and the turning converted angle by a proportional gain, 2. A steering control device according to claim 1, wherein the frequency signal applied to the steered wheels from the road surface is a signal obtained from at least the proportional output value of the steering control amount.

5. the steering feedback processing includes a processing for calculating a differential output value of a differential element in addition to a processing for calculating the proportional output value, 5. The steering control device according to claim 4, wherein the differential output value is a value obtained by multiplying a first-order time differential value of the difference between the target steering angle and the steering converted angle by a differential gain.

Images