Steering system

Abstract

To improve practicability of a steer-by-wire type steering system.SOLUTION: A steer-by-wire type steering system includes an operation member 80 operated by a driver, a wheel turning device 12 for turning wheels according to the operation of the operation member, a reaction force application device 84 for applying operation reaction force to the operation member, and controllers 16 and 18, wherein the controller is configured to determine operation reaction force TqC to be applied, and to control the reaction force application device on the basis of the determined operation reaction force, and to determine operation reaction force including vehicle behavior-based components TqC-GY and TqC-γ depending on at least one of lateral acceleration GY generated in the vehicle and a yaw rate γ of the vehicle. The lateral acceleration and the yaw rate are indices of a vehicle turning behavior, and accordingly the operation reaction force including the component based on the indices is appropriate according to the vehicle turning behavior.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a steer-by-wire type steering system, and more particularly to reaction force control thereof. [Background technology]

[0002] A steering system is a system that steers the wheels, and the vehicle turns by steering the wheels. The turning behavior of the vehicle can be understood from changes in behavior indicators such as yaw rate and lateral acceleration. In view of this, for example, the technology described in the following patent document uses yaw rate for wheel steering control. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Application No. 2016-101837 Summary of the Invention [Problem to be solved by the invention]

[0004] The technology described in the above patent document relates to a so-called electric power steering system, and is a technology for controlling a force for assisting the steering of wheels. Recently, a system different from a power steering system, specifically, a steer-by-wire type steering system (hereinafter, sometimes referred to as a "steer-by-wire system") in which an operating member such as a steering wheel and a steering device for steering the wheels are not mechanically connected, and the steering device realizes steering of the wheels according to the operation of the operating member without depending on the operating force applied to the operating member by the driver, has been actively developed. In the steer-by-wire system, since the steering device and the operating member are not connected, it is necessary to give the driver a steering operation feeling by some means. As a specific means, for example, a reaction force imparting device is provided that imparts a reaction force against the operation of the driver (hereinafter, sometimes referred to as an "operation reaction force") to the operating member by an electric motor or the like. The present inventor has found that the practicality of the steer-by-wire system can be improved by utilizing the above-mentioned behavior index for controlling this operation reaction force. Based on the founding, the present invention aims to provide a highly practical steer-by-wire type steering system. [Means for solving the problem]

[0005] In order to solve the above problems, the steering system of the present invention comprises: A steer-by-wire type steering system mounted on a vehicle, The steering system includes an operating member operated by a driver, a steering device that steers wheels in response to the operation of the operating member, a reaction force imparting device that imparts an operation reaction force to the operating member, and a controller that controls the steering system, The controller: The reaction force applying device is configured to determine the reaction force to be applied and to control the reaction force applying device based on the determined reaction force; and A vehicle behavior dependent component that is dependent on at least one of a lateral acceleration occurring in the vehicle and a yaw rate of the vehicle. and the components other than the vehicle behavior dependent components. The operation reaction force is determined by and a contribution degree of the vehicle behavior dependent component in the operation reaction force is changeable. Furthermore, the steering system Each of the steering devices is the steering device, and the vehicle is provided with two steering devices that independently steer one of the left and right wheels, The controller: In a one-wheel steering situation in which one of the left and right wheels is steered by only one of the two steering devices, the contribution of the vehicle behavior dependent component is increased. It is composed. Effect of the Invention

[0006] The lateral acceleration and yaw rate are indicators of the turning behavior of the vehicle, and the operation reaction force including the vehicle behavior dependent component based on these indicators is appropriate according to the turning behavior of the vehicle. Therefore, according to the present invention, a practical steer-by-wire system can be constructed.

[0007] The present invention can be applied to a system in which the left and right wheels are steered by a single steering device, and also to a system equipped with two steering devices, each of which independently steers one of the left and right wheels, i.e., a left and right independent steering system.

[0008] Both the lateral acceleration and the yaw rate are behavior indicators that indicate the turning behavior of the vehicle, and the vehicle behavior-dependent component may be a component based on only one of the lateral acceleration and the yaw rate, or may be a vehicle behavior-dependent component based on both the lateral acceleration and the yaw rate. The latter can be considered as a combination of the lateral acceleration-dependent component based on the lateral acceleration and the yaw rate-dependent component based on the yaw rate. Both the lateral acceleration and the yaw rate can be estimated based on the operation amount of the operating member and the traveling speed of the vehicle (hereinafter sometimes referred to as "vehicle speed"). From the viewpoint of applying an operation reaction force that takes into account the actual turning behavior of the vehicle, it is preferable that the lateral acceleration and the yaw rate on which the vehicle behavior-dependent component is determined are the lateral acceleration and the yaw rate actually detected by the lateral acceleration sensor and the yaw rate sensor mounted on the vehicle. Considering that it is preferable to increase the operation reaction force as the turning behavior of the vehicle becomes larger (stronger), it is preferable to set the vehicle behavior-dependent component to be larger as the lateral acceleration and the yaw rate become larger.

[0009] The operation reaction force may include components other than the vehicle behavior dependent components. Specifically, the other components may include a vehicle speed / turning amount dependent component that is dependent on the vehicle speed and the amount of steering of the wheels (which may be considered as the "steered angle" or "toe angle of the wheels"), a steering load dependent component that is dependent on the load of the steering device, an operation speed dependent component that is dependent on the operation speed of the operating member, and various other components.

[0010] If the force for steering the wheels is defined as the steering force, the vehicle speed-based steering amount dependent component can be considered to be, for example, a component corresponding to the steering force for opposing the self-aligning torque acting on the wheels. In order to maintain or increase the amount of steering of the wheels, it is necessary to overcome the self-aligning torque, and in order to make the driver aware of the self-aligning torque, it is desirable to set the vehicle speed-based steering amount dependent component to be larger the higher the vehicle speed and the larger the steering amount.

[0011] The above-mentioned steering load dependent component can be considered to be, for example, a component corresponding to the steering force that the steering device actually exerts to steer the wheels. For example, in a steering operation when the vehicle speed is quite low, such as a stationary steering operation, the influence of the frictional force between the road surface and the tires is large, a considerable steering force is required, and the load on the steering device is quite large. The steering load dependent component can be considered to be a component that makes the driver feel such a load on the steering device. Therefore, it is desirable to set the steering load dependent component so that it is larger as the load on the steering device is larger. Note that, when the steering device has an electric motor as a drive source, the load on the steering device can be considered to be roughly proportional to the current supplied to the electric motor, and the steering load dependent component can be determined depending on the current supplied.

[0012] The operation-velocity-dependent component can function, for example, as a component for restricting abrupt operation of the operating member. Simply put, it functions as a damper against the operation. In order to ensure this function, it is desirable to set the operation-velocity-dependent component so that it becomes larger as the operating speed of the operating member increases.

[0013] The operation reaction force to be applied may be determined by weighting and adding up each of the above-mentioned components. The weighting coefficient is, in other words, a gain. In other words, the gain can be considered as the contribution of each component to the operation reaction force. The present steer-by-wire system may be configured to change this contribution. By changing the contribution of each component, for example, it becomes possible to optimize the operation reaction force according to the situation in which the vehicle is placed. In addition, to supplement the contribution degree, the change of the contribution degree is a concept that includes making the contribution degree 0 or increasing it from 0. In other words, making the contribution degree of some of the multiple components 0 to eliminate the part from the operation reaction force, and increasing the contribution degree of some of the components from 0 to include the part in the operation reaction force are also included in the change of the contribution degree. In addition, the contribution degree of each of the multiple components is relative, and increasing the contribution degree of one component means decreasing the contribution degree of the other components.

[0014] As a specific example of the change in the contribution degree, in the above-mentioned left and right wheel independent steering type steer-by-wire system, for example, in a one-wheel steering situation in which one of the left and right wheels is steered by only one of the two steering devices, the contribution degree of the vehicle behavior dependent component may be increased. In the case where the other of the two steering devices fails, one of the left and right wheels cannot be steered by the other. In such a one-wheel steering situation, the steering amount of the wheel steered by the other steering device may deviate from the steering amount of the wheel steered by one steering device, and if the other steering device does not operate, it is considered that no load is generated on the other steering device. In such a case, it is predicted that the above-mentioned vehicle speed steering amount dependent component and steering load dependent component will not be of appropriate magnitude. In consideration of such a situation, by increasing the contribution of the vehicle behavior dependent component in a one-wheel turning situation, in other words, by decreasing the contribution of the vehicle speed turning amount dependent component and the turning load dependent component, it becomes possible to apply an appropriate operation reaction force even in a one-wheel turning situation.

[0015] In addition, in a one-wheel steering situation, sudden wheel steering is not preferable. Therefore, in order to suppress sudden wheel steering, that is, to suppress sudden operation of the operating member, the contribution of the operation speed dependent component may be increased. [Brief description of the drawings]

[0016] [Figure 1] 1 is a schematic diagram showing an overall configuration of a vehicle equipped with a steering system according to an embodiment of the present invention; [Diagram 2] 1 is a perspective view showing a wheel arrangement module in which a wheel steering device constituting a steering system of an embodiment is incorporated; FIG. [Diagram 3] FIG. 2 is a block diagram showing functions related to control of the steering system according to the embodiment. [Figure 4] 5 is a graph showing map data for determining a steering gear ratio, and a table for explaining a change in the contribution of each component of an operation reaction force. [Diagram 5] 4 is a graph showing map data for determining each component of an operation reaction force. [Figure 6] 5 is a flowchart of a target steering angle determination program and a wheel steering program executed for performing steering control. [Figure 7] 1 is a program for controlling an actuation reaction force executed to perform actuation reaction force control. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] A steer-by-wire type steering system according to an embodiment of the present invention will be described in detail below with reference to the drawings. In addition to the following embodiment, the present invention can be embodied in various forms including the form described in the above [Mode of the invention], and various modifications and improvements based on the knowledge of those skilled in the art.

[0018] [A] Overall configuration of the vehicle equipped with the steering system The steering system of the embodiment is mounted on a vehicle having left and right front wheels 10FL, 10FR and left and right rear wheels 10RL, 10RR, as shown in Fig. 1. The left and right front wheels 10FL, 10FR are drive wheels and steerable wheels. When it is not necessary to distinguish between the left and right front wheels 10FL, 10FR, they will be collectively referred to as front wheels 10F, and when it is not necessary to distinguish between the left and right rear wheels 10RL, 10RR, they will be collectively referred to as rear wheels 10R. When it is not necessary to distinguish between the front wheels 10F and the rear wheels 10R, they will be collectively referred to simply as wheels 10.

[0019] This steering system is a so-called steer-by-wire type, left and right wheel independent steering system, and is configured to include a pair of wheel steering devices (hereinafter sometimes simply referred to as "steering devices") 12 provided for two front wheels 10F respectively to steer the two front wheels 10F independently of each other, an operation device 14 for receiving an operation by the driver, a pair of steering electronic control units (hereinafter sometimes abbreviated as "steering ECU" and shown as "S-ECU" in the figure) 16 for controlling the pair of wheel steering devices 12 respectively, and an operation electronic control unit (hereinafter sometimes abbreviated as "operation ECU" and shown as "O-ECU" in the figure) 18 for controlling the operation device 14 and integrating the steering ECU 16. The configuration and control of this steering system will be described in detail later, but the two steering ECUs 16 and the operation ECU 18 can be considered to constitute a controller of the steering system.

[0020] The vehicle is also equipped with a vehicle drive system including a pair of wheel drive units 20 that are provided on the two front wheels 10F and rotated by electric motors. The vehicle drive system includes an accelerator pedal 22 as an accelerator operation member operated by the driver, and an accelerator operation amount ε Aand a vehicle drive electronic control unit (hereinafter sometimes abbreviated as "drive ECU" and shown as "A-ECU" in the figure) 26 that controls the operation of the pair of wheel drive units 20 based on the accelerator operation amount detected by the accelerator operation amount sensor 24. The vehicle drive system has a general configuration and performs general control, so a description of the configuration and control of the vehicle drive system will be omitted.

[0021] Furthermore, the vehicle is provided with a hydraulic brake system. The brake system includes a brake pedal 30 as a brake operation member operated by the driver, a master cylinder 32 connected to the brake pedal 30, a hydraulic fluid supply device 34 having a hydraulic pressure source such as a pump for pressurizing hydraulic fluid, four brake devices 36 provided on the four wheels 10 for braking the wheels by the pressure of the hydraulic fluid from the hydraulic fluid supply device 34, and a brake electronic control unit (hereinafter sometimes referred to as a "brake ECU" and represented as "B-ECU" in the figure) 38 for controlling the operation of the hydraulic fluid supply device 34. The brake system is a so-called brake-by-wire type system, and the brake ECU 38 detects a brake operation amount ε, which is the operation amount of the brake pedal 30 detected by a brake operation amount sensor 40, and detects the brake operation amount ε, which is the operation amount of the brake pedal 30 detected by a brake operation amount sensor 40. B Based on this, the pressure of the hydraulic fluid supplied from the hydraulic fluid supply device 34 to the brake device 36 of each wheel 10 is controlled, thereby controlling the braking force applied to the vehicle. Since the brake system has a general configuration and is controlled in a general manner, a description of the configuration and control of the brake system will be omitted.

[0022] The vehicle is provided with a CAN (car area network or controllable area network) 42, to which two steering ECUs 16, an operation ECU 18, a drive ECU 26, and a brake ECU 38 are connected. These ECUs 16, 18, 26, and 38 communicate with each other via the CAN 42 and execute the control that each should perform. Incidentally, each of these ECUs 16, 18, 26, and 38 is configured to include a computer having a CPU, ROM, RAM, etc., and a driver (drive circuit) for driving components (e.g., electric motor, valve, pump, etc.) based on instructions from the computer. Note that in this vehicle, the lateral acceleration G acting on the vehicle body is Y A lateral acceleration sensor 44 for detecting the lateral acceleration of the vehicle, a yaw rate sensor 46 for detecting the yaw rate γ of the vehicle, and a wheel rotation speed (hereinafter sometimes referred to as the "wheel speed") v W The lateral acceleration sensor 46, the yaw rate sensor 46, and the wheel speed sensor 48 are also connected to the CAN 42.

[0023] Incidentally, the vehicle speed v, which is the traveling speed of the vehicle, is determined by the brake ECU 38. More specifically, the wheel speed v of each of the front wheels 10F is W is grasped by the drive ECU 26 based on the rotation speed of the electric motor which is the drive source of the wheel drive unit 20, and the information is sent to the brake ECU 38 via the CAN 42. On the other hand, the wheel speed v W is detected by the wheel speed sensor 48, and the information is sent to the brake ECU 38 via the CAN 42. The brake ECU 38 determines the vehicle speed v based on the information.

[0024] [B] Steering system hardware configuration (a) Hardware configuration of wheel steering device Each of the pair of wheel turning devices 12 of the vehicle steering system of this embodiment is incorporated in a wheel arrangement module 50. One of the pair of wheel drive units 20 of the vehicle drive system described above and one of the four brake devices 36 of the brake system are also incorporated in the wheel arrangement module 50. The wheel arrangement module (hereinafter may be simply abbreviated as "module") 50 is a module for arranging a wheel 10b on which a tire 10a is mounted on a vehicle body, as shown in FIG. 2. The wheel 10b itself can be considered as a wheel, but in this embodiment, for convenience, the wheel 10b on which the tire 10a is mounted will be referred to as the wheel 10.

[0025] The wheel turning device 12 of the steering system will be described while explaining the configuration of the module 50. The wheel drive unit 20 described above disposed in the module 50 has a housing 20a, an electric motor as a drive source built into the housing 20a, a reducer for reducing the rotation of the electric motor (both not shown), and an axle hub (hidden in the figure) to which the wheel 10b is attached. The wheel drive unit 20 is disposed inside the rim of the wheel 10b, and is a so-called in-wheel motor unit. The wheel drive unit 20 has a well-known structure, and therefore a description of the structure will be omitted.

[0026] This module 50 is configured to include a McPherson type suspension device (also called a "McPherson strut type"). In this suspension device, the housing 20a of the wheel drive unit 20 functions as a carrier that rotatably holds the wheel, and more specifically, the housing 20a functions as a steering knuckle in the wheel turning device 12, and is allowed to move up and down relative to the vehicle body. Therefore, the suspension device is configured to include a lower arm 52 which is a suspension arm, the housing 20a of the wheel drive unit 20, a shock absorber 54, and a suspension spring 56.

[0027] Since the suspension device itself has a general structure, to briefly explain, lower arm 52 has a shape called an L arm, with a base end divided into two parts in the vehicle front-rear direction, and the base end is supported by a side member (not shown) of the vehicle body so as to be rotatable about arm rotation axis LL via a first bush 58 and a second bush 60. Housing 20a of wheel drive unit 20 is rotatably connected at its lower part to the tip end of lower arm 52 via an arm connecting ball joint 62 (hereinafter sometimes referred to as "first joint 62") which is a first joint.

[0028] The lower end of the shock absorber 54 is fixedly supported by the housing 20a of the wheel drive unit 20, and the upper end is supported by the upper part of the tire housing of the vehicle body via an upper support 64. The upper end of the suspension spring 56 is also supported by the upper part of the tire housing of the vehicle body via the upper support 64, and the lower end of the suspension spring 56 is supported by a lower support 54a provided in a flange shape on the shock absorber 54. In other words, the suspension spring 56 and the shock absorber 54 are disposed in parallel with each other between the lower arm 52 and the vehicle body.

[0029] As described above, the module 50 has the brake device 36, which is a disc brake device including a disc rotor 66 that is attached to the axle hub together with the wheel 10b and rotates together with the wheel 10, and a brake caliper 68 that is held in the housing 20a of the wheel drive unit 20 so as to straddle the disc rotor 66. Although a detailed explanation will be omitted, the brake caliper 68 has brake pads as friction members and a hydraulic cylinder, and the brake device 36 is configured to generate a braking force for stopping the rotation of the wheel 10 by pressing the brake pads against the disc rotor 66 depending on the pressure of the hydraulic fluid supplied from the hydraulic fluid supply device 34 to the hydraulic cylinder.

[0030] The wheel turning device 12 is a single-wheel independent steering device for steering only one of a pair of left and right front wheels 10F independently of the other, and generally comprises a housing 20a of the wheel drive unit 20 which functions as a steering knuckle as described above (hereinafter, when treated as a component of the wheel turning device 12, it may be referred to as the "steering knuckle 20a"), a steering actuator 70 arranged on the lower arm 52 at a position close to the base end of the lower arm 52, and a tie rod 72 which connects the steering actuator 70 and the steering knuckle 20a.

[0031] The steering actuator 70 includes a steering motor 70a, which is an electric motor serving as a drive source, a reduction gear 70b that reduces the speed of rotation of the steering motor 70a, and an actuator arm 70c that is rotated by the rotation of the steering motor 70a via the reduction gear 70b and functions as a pitman arm. The base end of the tie rod 72 is connected to the actuator arm 70c via a rod base end connecting ball joint 74 (hereinafter sometimes referred to as the "second joint 74"), which is a second joint, and the tip end of the tie rod 72 is connected to a knuckle arm 20b of the steering knuckle 20a via a rod tip end ball joint 76 (hereinafter sometimes referred to as the "third joint 76"), which is a third joint.

[0032] In this wheel steering device 12, the line connecting the centre of the upper support 64 and the centre of the first joint 62 is the kingpin axis KP. By operating the steering motor 70a, the actuator arm 70c of the steering actuator 70 rotates about the actuator axis AL, as shown by the thick arrow in the figure. This rotation is transmitted by the tie rod 72, and the steering knuckle 20a is rotated about the kingpin axis KP. In other words, the front wheels 10F are steered, as shown by the thick arrow in the figure. Due to this structure, the wheel steering device 12 is provided with a motion conversion mechanism 78, which includes the actuator arm 70c, the tie rod 72, the knuckle arm 20b etc., and converts the rotational motion of the steering motor 70a into a steering motion of the front wheels 10F.

[0033] In the wheel turning device 12, the turning actuator 70 is disposed in the lower arm 52. This allows the module 50 to be easily assembled onto the vehicle body. Simply put, the suspension device, brake device and wheel turning device can be mounted onto the vehicle by simply attaching the base end of the lower arm 52 to a side member of the vehicle body and attaching the upper support 64 to an upper portion of the tire housing of the vehicle body. In other words, this module 50 is a module that excels in ease of mounting onto a vehicle.

[0034] To briefly explain the rear wheels 10R, each of the rear wheels 10R is held on the vehicle body via a trailing arm type suspension device. Although a brake device 36 is provided for each of the rear wheels 10F, the wheel drive unit 20 and the wheel steering device 12 are not provided for each of the rear wheels 10R because they are neither drive wheels nor steerable wheels.

[0035] (b) Hardware configuration of the operation device 1, the operation device 14 has a general structure in a steer-by-wire type steering system, and is configured to include a steering wheel 80 as a steering operation member steered by a driver, a steering sensor 82 for detecting a steering operation angle (hereinafter, may be simply referred to as an "operation angle") δ, which is the rotation angle of the steering wheel 80, as an operation amount from a straight-ahead state position of the steering operation member, and a reaction force imparting device 84 for imparting an operation reaction force, which is a reaction force against the operation of the steering wheel 80 by the driver, to the steering wheel 80. The reaction force imparting device 84 includes a reaction force motor 84a, which is an electric motor as a force source, and a reducer 84b for transmitting the force of the reaction force motor 84a to the steering wheel 80.

[0036] [C] Steering system control (a) Functional configuration related to control The control of the steering system is executed by the above-mentioned operation ECU 18 and two steering ECUs 16. The operation ECU 18 is configured to include a computer including a CPU, ROM, RAM, etc., and a driver (drive circuit) for the reaction force motor 84a, and similarly, the steering ECU 16 is configured to include a computer including a CPU, ROM, RAM, etc., and a driver (drive circuit) for the steering motor 70a. Below, the functions of the operation ECU 18 and the steering ECU 16 will be explained with reference to the block diagram of Fig. 3, which shows them in schematic form.

[0037] i) Steering control First, a description will be given of the steering control, which is a control related to the steering of the wheels 10. Roughly speaking, in this steering system, the operation ECU 18 calculates a target steering angle θ, which is a steering angle θ of the wheels 10 to be realized, based on a steering operation angle δ. * Each of the two steering ECUs 16 determines the target steering angle θ * Based on this, the actual steering angle θ of the corresponding wheel 10 (hereinafter sometimes referred to as the "actual steering angle θ") is calculated based on the target steering angle θ *The operation of steering motor 70a of steering actuator 70 is controlled so as to satisfy the following. Note that steering angle θ is a rotational phase of wheel 10 about kingpin axis KP based on the attitude of the vehicle traveling straight ahead, and is a type of steering amount.

[0038] This steering system employs a so-called variable gear ratio system (VGRS), and the operation ECU 18 has a gear ratio determination section 100 that determines a steering gear ratio β, which is the ratio of the steering angle θ of the wheels 10 to the operation angle δ, in relation to steering control. This gear ratio determination section 100 determines the steering gear ratio β based on the vehicle speed v and in accordance with map data as shown in the graph of FIG. 4(a). Incidentally, as can be seen from the graph, in consideration of the running stability of the vehicle, the steering gear ratio β is set so that it generally becomes smaller as the vehicle speed v becomes higher. The operation ECU 18 has a target steering angle determination section 102 that determines the target steering angle θ in accordance with the following equation, based on the operation angle δ detected by the steering sensor 82 and the steering gear ratio β determined by the gear ratio determination section 100: * Determine. θ * =β×δ

[0039] This steering system does not have a steering angle sensor that directly detects the steering angle θ of the wheels 10. Therefore, the motor rotation angle θ of the steering motor 70a is M and the steering angle θ of the wheels 10 are in a constant proportional relationship. M In order to obtain the steering angle θ based on the above, the steering ECU 16 has a steering angle conversion section 104. The steering motor 70a has a motor rotation angle sensor 70d, and the steering angle conversion section 104 converts the motor rotation angle θ M The actual steering angle θ is determined based on the above.

[0040] The steering ECU 16 has a steering torque determination section 106, and the steering torque determination section 106 determines the target steering angle θ *Based on the actual steering angle θ determined by the steering angle conversion unit 104, the steering torque Tq is calculated as the steering force required to steer the wheels 10. S To explain in detail, the steering torque determination unit 106 determines the target steering angle θ * The steering angle deviation Δθ, which is the deviation of the actual steering force θ relative to the steering angle θ, is specified, and the steering torque Tq is calculated according to the following formula in order to perform steering control using a PID feedback control method based on the steering angle deviation Δθ. S Determine. Tq S =K P ×Δθ+K I ×∫Δθdt+K D ×dΔθ / dt The first, second, and third terms on the right side of the above equation are the proportional term, integral term, and differential term, respectively. P ,K I ,K D are the proportional term gain, the integral term gain, and the differential term gain, respectively. Note that information on the actual steering angle θ specified by the steering angle conversion unit 104 is transmitted to the operation ECU 18.

[0041] The steering ECU 16 has a steering current control unit 108, and since the steering motor 70a is a three-phase DC brushless motor, the steering current control unit 108 is configured to include an inverter that is a drive circuit (driver) of the steering motor 70a. The steering current control unit 108 determines the steering torque Tq determined by the steering torque determination unit 106. S Based on this, the steering current I S Determine the steering current I S is supplied from the inverter to the steering motor 70a.

[0042] In addition, the steering ECU 16 receives the steering current I S The steering wheel has a current sensor 110 for detecting the steering current I SThis information is transmitted to operation ECU 18 to be used for controlling the operation reaction force, which will be described later. Furthermore, steering ECU 16 has a self-diagnosis section 111 for diagnosing the operating state of wheel turning device 12, and as will be described in detail later, the diagnosis information, specifically, failure information DEF which is information to the effect that wheel turning device 12 has a failure, is also transmitted to operation ECU 18.

[0043] ii) Operation reaction force control Next, the operation reaction force control, that is, the control of applying an operation reaction force to the steering wheel 80, which is an operating member, so as to give the driver a feeling of operation in response to the steering operation, will be described. This operation reaction force control is performed by the operation ECU 18. Roughly speaking, the operation ECU 18 controls a reaction torque Tq C is determined by adding up multiple components, and the reaction torque Tq C Based on this, a current (hereinafter sometimes referred to as a "reaction current") I C supplies.

[0044] As the above-mentioned multiple components, a vehicle speed / steered angle dependent component Tq determined based on the vehicle speed v and the steering angle θ of the wheel 10 C-v θ and a steering load dependent component Tq determined based on the load of the steering device 12 C-IS and an operation speed dependent component Tq determined based on the operation speed dδ of the steering wheel 80. C-d δ and a vehicle behavior dependent component determined based on the vehicle behavior are set. More specifically, the vehicle behavior dependent component is a lateral acceleration G acting on the vehicle body. Y Lateral acceleration dependent component Tq determined based on C-GY and a yaw rate dependent component Tq determined based on the yaw rate γ of the vehicle. C- γ is set.

[0045] Vehicle speed / steering angle dependent component Tq C-v θ can be considered as a component corresponding to the steering force for countering the self-aligning torque acting on the wheel 10. C-IScan be considered as a component corresponding to the steering force actually exerted by the wheel steering device 12 to steer the wheels 10. C-d δ can be considered as a component for limiting the sudden operation of the steering wheel 80. The lateral acceleration dependent component Tq C-GY , yaw rate dependent component Tq C- Each of γ can be considered as a component of the operation reaction force that takes into account the actual turning behavior of the vehicle.

[0046] The operation ECU 18 calculates the vehicle speed / steering angle dependent component Tq C-v The vehicle speed / steered angle dependent component determining unit 112 determines θ. C-v The steering angle θ of the wheels 10 on which the determination of θ is based is the actual steering angle θ of the right wheel 10 sent as information from each of the two steering ECUs 16. R and the actual steering angle θ of the left wheel 10 L The average steering angle θ AVE and the average steering angle θ AVE In order to obtain the steering angle in accordance with the following equation, the operation ECU 18 has a steering angle averaging unit 114. θ AVE =(θ R +θ L ) / 2 The vehicle speed / steered angle dependent component determining unit 112 determines the average steering angle θ AVE Based on the vehicle speed v sent as information from the brake ECU 38, the average steering angle θ AVE According to the function shown in the following equation, which has the parameters of and the vehicle speed v, the vehicle speed steering angle dependent component Tq C-v Determine θ. Tq C-v θ=f(θ AVE ,v) This function f(θ AVE , v) is the average steering angle θ AVE The larger the vehicle speed v, the higher the Tq C-v This is a function set so that θ becomes large.

[0047] The operation ECU 18 also calculates the steering load dependent component Tq C-ISThe load of the wheel turning device 12 is generally determined by the turning current I S The steering load dependent component determination unit 116 determines the steering current I S Strictly speaking, the steering load dependent component Tq C-IS The steering current I based on which the determination S is the steering current I on the right wheel 10 side sent as information from each of the two steering ECUs 16. S - R and the steering current I S - L The average steering current I S - AVE and the average steering current I S - AVE In order to calculate the load average in accordance with the following equation, the operation ECU 18 has a load average unit 118. I S - AVE =(I S - R +I S - L ) / 2 The steering load dependent component determining unit 116 determines the average steering current I S - AVE Based on the above, the steering load dependent component Tq C-IS As can be seen from the graph, the steering load dependent component Tq C-IS is the average steering current I S - AVE The larger is the larger it is determined to be.

[0048] The operation ECU 18 further includes an operation speed dependent component Tq C-d The operation velocity dependent component determiner 120 determines the operation velocity dδ of the steering wheel 80 based on the operation angle δ detected by the steering sensor 82, and determines the operation velocity dependent component Tq based on the operation velocity dδ and in accordance with map data as shown in the graph of FIG. C-dAs can be seen from the graph, the operation speed dependent component Tq C-d δ is determined so as to increase as the operation speed dδ increases.

[0049] The operation ECU 18 has a vehicle behavior dependent component determination unit 122 that determines a vehicle behavior dependent component, and the vehicle behavior dependent component determination unit 122 has a lateral acceleration dependent component determination unit 124 and a yaw rate dependent component determination unit 126. The lateral acceleration dependent component determination unit 124 determines the lateral acceleration G Y Based on the above, the lateral acceleration dependent component Tq is calculated according to the map data shown in the graph of FIG. 5(c). C-GY The yaw rate dependent component determiner 126 determines the yaw rate dependent component Tq based on the yaw rate γ detected by the yaw rate sensor 46 and in accordance with map data as shown in the graph of FIG. C- Determine γ. As can be seen from the graph, the lateral acceleration dependent component Tq C-GY is the lateral acceleration G Y The higher the value, the larger the yaw rate dependent component Tq C- γ is determined so as to be larger as the yaw rate γ is higher.

[0050] The operation ECU 18 has an adder 128, which adds up the determined components Tq C-v θ,Tq C-IS ,Tq C-d δ,Tq C-GY ,Tq C- γ is added, but each component Tq C-v θ,Tq C-IS ,Tq C-d δ,Tq C-GY ,Tq C- γ is added after taking into account the contribution degree, in other words, weighting is performed. For this reason, the operation ECU 18 has a gain setting multiplication unit 130. C-v θ,Tq C-IS ,Tq C-d δ,Tq C-GY ,Tq C- The contribution of γ is, respectively, the vehicle speed steering angle dependent component determination gain K vθ, steering load dependent component determination gain K IS ,Operation speed dependent component decision gain K d δ, lateral acceleration dependent component determination gain K GY , and is defined by the yaw rate dependent component determination gain Kγ. In the gain setting multiplication unit 130, the multipliers 132 to 140 multiply each component Tq determined by each component determination unit 112, 116, 120, 124, and 126 by C-v θ,Tq C-IS ,Tq C-d δ,Tq C-GY ,Tq C- γ, each component decision gain K v θ,K IS ,K d δ,K GY ,Kγ is multiplied, and each multiplied component Tq C-v θ,Tq C-IS ,Tq C-d δ,Tq C-GY ,Tq C- γ is output to the adder 128. The component Tq C-v θ,Tq C-IS ,Tq C-d δ,Tq C-GY ,Tq C- γ is added by an adder 128 to obtain the reaction torque Tq C The processing by the multipliers 132 to 140 and the adder 128 is expressed by the following equation: Tq C =K v θ×Tq C-v θ+K IS ×Tq C-IS +K d δ×Tq C-d δ+K GY ×Tq C-GY +Kγ×Tq C- Gamma

[0051] The operation ECU 18 has a reaction force current control unit 142. Since the reaction force motor 84a is a three-phase DC brushless motor, the reaction force current control unit 142 includes an inverter that is a drive circuit (driver) of the reaction force motor 84a. The reaction force current control unit 142 determines the reaction force torque TqC Based on this, the reaction current I C Determine the reaction current I C is supplied from the inverter to the reaction motor 84a.

[0052] In this steering system, the reaction torque Tq C In determining the above, each component Tq C-v θ,Tq C-IS ,Tq C-d δ,Tq C-GY ,Tq C- The contribution of γ can be changed. To explain in detail, each component decision gain K v θ,K IS ,K d δ,K GY ,Kγ, high gain K v θ- H ,K IS - H ,K d δ- H ,K GY - H ,Kγ- H and low gain K v θ- L ,K IS - L ,K d δ- L ,K GY - L ,Kγ- L The high gain K is set in a two-wheel steering state in which both the two wheel steering devices 12 are normal and both the left and right wheels 10 are properly steered, and in a one-wheel steering state in which one of the two wheel steering devices 12 fails and one of the left and right wheels 10 is not properly steered. v θ- H ,K IS - H ,K d δ- H ,K GY - H ,Kγ- H and low gain K v θ- L ,K IS - L ,K d δ- L ,K GY -L ,Kγ- L Between each component, the gain K v θ,K IS ,K d δ,K GY , Kγ are switched.

[0053] To explain in more detail, the vehicle speed steering angle dependent component Tq C-v θ, steering load dependent component Tq C-IS are the actual steering angles θ of the left and right wheels 10, and the steering current I S In a single-wheel steering situation where one of the two wheel steering devices 12 is defective, the actual steering angle θ of one of the left and right wheels 10 and the steering current I S It may not be possible to accurately grasp the vehicle speed and steering angle dependent component Tq C-v θ, steering load dependent component Tq C-IS Therefore, in the case of one wheel turning, the vehicle speed turning angle dependent component Tq C-v θ, steering load dependent component Tq C-IS The contribution of the lateral acceleration-dependent component Tq is set low, and the reaction force corresponding to the actual turning behavior of the vehicle is obtained. C-GY , yaw rate dependent component Tq C- The contribution of γ is set high, and the steering speed dependent component Tq is set high to limit sudden steering operations. C-d The contribution of δ is set high.

[0054] Specifically, as shown in the table of FIG. 4(b), in the two-wheel steering situation, the vehicle speed / steering angle dependent component determination gain K v θ, steering load dependent component determination gain K IS , respectively, high gain K v θ- H ,K IS - H , the gain K d δ, lateral acceleration dependent component determination gain K GY , yaw rate dependent component determination gain Kγ, respectively, low gain K d δ- L ,K GY - L ,Kγ-L On the other hand, in the case of one-wheel steering, the vehicle speed / steering angle dependent component determination gain K v θ, steering load dependent component determination gain K IS , respectively, low gain K v θ- L ,K IS - L , the gain K d δ, lateral acceleration dependent component determination gain K GY , yaw rate dependent component determination gain Kγ, respectively, high gain K d δ- H ,K GY - H ,Kγ- H Set to.

[0055] The gain setting multiplication unit 130 judges whether the state is a two-wheel steering state or a one-wheel steering state based on the failure information DEF transmitted from the self-diagnosis unit 111 of each steering ECU 16, and based on that judgment, calculates each component determination gain K v θ,K IS ,K d δ,K GY , Kγ is changed.

[0056] In addition, in this steering system, for example, low gain K v θ- L ,K IS - L ,K d δ- L ,K GY - L ,Kγ- L By setting to 0, the vehicle speed / steering angle dependent component Tq C-v θ, steering load dependent component Tq C-IS Only the reaction torque Tq C In the single wheel steering situation, the operation speed dependent component Tq C-d δ, lateral acceleration dependent component Tq C-GY , yaw rate dependent component Tq C- Reaction torque Tq of γ alone C In addition, a lateral acceleration dependent component Tq may be added as a vehicle behavior dependent component. C-GY , yaw rate dependent component TqC- Only one of γ may be used.

[0057] (b) Control flow The above-mentioned steering control and actuation reaction force control may be performed by electronic circuits such as ASIC designed according to the functional blocks of Fig. 3, but in this steering system, the steering control is performed by the computers of the operation ECU 18 and the steering ECU 16 repeatedly executing at short time intervals (for example, several meters to several tens of milliseconds) a target steering angle determination program and a wheel steering program, the flowcharts of which are shown in Fig. 6, and the actuation reaction force control is performed by the computer of the operation ECU 18 repeatedly executing at short time intervals (for example, several meters to several tens of milliseconds) an actuation reaction force control program, the flowchart of which is shown in Fig. 7. The flow of the steering control and actuation reaction force control according to these programs will be explained below with reference to those flowcharts.

[0058] i) Steering control In the process according to the target steering angle determination program executed in the operation ECU 18, first, in step 1 (hereinafter sometimes referred to as "S1"; the same applies to the other steps), the vehicle speed v is acquired based on information transmitted from the brake ECU 38, and in S2, the steering gear ratio β is determined based on the vehicle speed v with reference to the map data shown in FIG. 4(a). In the following S3, the steering operation angle δ is detected by the steering sensor 82, and in S4, the target steering angle θ of each wheel 10 is determined based on the operation angle δ and the steering gear ratio β. * The determined target steering angle θ * The information about is transmitted to each steering ECU 16 in S5.

[0059] In the process according to the wheel steering program executed in each steering ECU 16, first, in S11, a target steering angle θ of the wheels 10 to be steered is calculated based on information transmitted from the operation ECU 18. * On the other hand, in S12, the motor rotation angle θ detected by the motor rotation angle sensor 70d is acquired.M Based on the above, the actual steering angle θ of the wheels 10 is obtained. Then, in S13, the target steering angles θ * and the actual steering angle θ, a steering angle deviation Δθ is determined.

[0060] Next, in S14, the steering torque Tq to be applied to the wheels 10 is calculated based on the steering angle deviation Δθ according to a feedback control method. S In the next step S15, the steering torque Tq S Based on this, the steering current I to be supplied to the steering motor 70a is S is determined, and in S16, the steering current I S Based on the acquired actual steering angle θ and the determined steering current I S This information is sent to the operation ECU 18 in S17.

[0061] ii) Operation reaction force control In the process according to the operation reaction force control program executed in the operation ECU 18, first, in S21, the vehicle speed v and the actual steering angle θ are acquired based on the information transmitted from the brake ECU 38 and the information transmitted from each steering ECU 16. Since the information on the actual steering angle θ is transmitted for each of the left and right wheels 10, in S21, as described above, the actual steering angle θ is calculated as the average steering angle θ, which is the average of the actual steering angles θ of the left and right wheels 10. AVE Then, in S22, the vehicle speed v and the average steering angle θ AVE Based on the above, the vehicle speed / steering angle dependent component Tq C-v θ is determined.

[0062] Next, in S23, based on the information transmitted from each steering ECU 16, the steering current I S is obtained. The steering current I S The information on the steering current I S are the steering currents I SThe average steering current I S-AVE Then, in S24, the average steering current I S-AVE Based on the map data shown in Fig. 5(a), the steering load dependent component Tq C-IS is determined.

[0063] In the next step S25, the steering angle δ of the steering wheel 80 is detected by the steering sensor 82, and the operation speed dδ is determined based on the operation angle. Then, in step S26, the operation speed dependent component Tq C-d δ is determined.

[0064] In S27, the lateral acceleration G detected by the lateral acceleration sensor 44 Y is obtained, and in S28, the lateral acceleration G Y Based on the above, the lateral acceleration dependent component Tq is calculated according to the map data shown in FIG. C-GY In S29, the yaw rate γ detected by the yaw rate sensor 46 is acquired, and in S30, the yaw rate dependent component Tq is calculated based on the yaw rate γ and in accordance with the map data shown in FIG. C- γ is determined.

[0065] In the next step S31, it is determined whether the steering system is in the above-mentioned two-wheel steering state or one-wheel steering state, depending on whether or not the failure information DEF is transmitted from the self-diagnosis unit 111 of either of the two steering ECUs 16. If it is determined that the steering system is in the two-wheel steering state, in step S32, the vehicle speed-turning angle dependent component determination gain K v θ is high gain K v θ- H , the steering load dependent component determining gain K IS High gain K IS - H , the gain K d δ is low gain K d δ- L , the lateral acceleration dependent component determination gain K GY Low gain K GY- L The yaw rate dependent component decision gain Kγ is low gain Kγ- L On the other hand, if it is determined that the vehicle is in a one-wheel steering state, the vehicle speed / steer angle dependent component determination gain K v θ is low gain K v θ- L , the steering load dependent component determining gain K IS Low gain K IS - L , the gain K d δ is high gain K d δ- H , the lateral acceleration dependent component determination gain K GY High gain K GY - H The yaw rate dependent component decision gain Kγ is high gain Kγ- H are set to, respectively.

[0066] The above-specified component decision gain K v θ,K IS ,K d δ,K GY ,Kγ and each of the components Tq determined above C-v θ,Tq C-IS ,Tq C-d δ,Tq C-GY ,Tq C- Based on γ, in S34, the reaction torque Tq C The reaction torque Tq is determined. C Based on this, in S35, the reaction current I to be supplied to the reaction motor 84a is C is determined, and in S36, the reaction current I C Based on this, a current is supplied to the reaction force motor 84a. [Explanation of symbols]

[0067] 10: Wheel 12: Wheel turning device 14: Operation device 16: Turning electronic control unit (turning ECU) [controller] 18: Operation electronic control unit (operation ECU) [controller] 42: CAN 44: Lateral acceleration sensor 46: Yaw rate sensor 70: Turning actuator 70a: Turning motor [electric motor] [drive source] 70d: Motor rotation angle sensor 80: Steering wheel [steering operation member] 82: Steering sensor 84: Reaction force imparting device 84a: Reaction force motor 110: Current sensor 111: Self-diagnosis unit 112: Vehicle speed / turning angle dependent component determination unit 114: Turning angle averaging unit 116: Turning load dependent component determination unit 118: Load averaging unit 120: Operation speed dependent component determination unit 122: Vehicle behavior dependent component determination unit 124: Lateral acceleration dependent component determination unit 126: Yaw rate dependent component determination unit 128: Adder 130: Gain setting multiplication section 132-140: Multiplier 142: Reaction force current control section G Y : Lateral acceleration γ: Yaw rate δ: Steering angle [amount of steering] dδ: Steering speed θ: Turning angle [amount of steering] / actual turning angle θ R : Actual steering angle of the right wheel θ L : Actual steering angle of the left wheel θ AVE :Average steering angle Tq C : Reaction torque [operation reaction force] Tq C-v θ: Vehicle speed steering angle dependent component Tq C-IS : Steering load dependent component Tq C-d δ: Operation speed dependent component Tq C-GY :Lateral acceleration dependent component Tq C- γ: Yaw rate dependent component I S :Steering current I S-R : Right wheel steering current I S-L : Left wheel steering current I S-AVE :Average steering current I C : Reaction current K v θ: Vehicle speed / steering angle dependent component determination gain K IS : Steering load dependent component determination gain K d δ: Gain K depending on the operation speed GY : Lateral acceleration dependent component determination gain Kγ: Yaw rate dependent component determination gain K v θ- H ,K IS - H, K d δ- H , K GY - H , Kγ- H : High gain K v θ- L , K IS - L , K d δ- L , K GY - L , Kγ- L : Low gain DEF: Defect information

Claims

1. A steer-by-wire type steering system mounted on a vehicle, The steering system includes an operating member operated by a driver, a steering device that steers wheels in response to the operation of the operating member, a reaction force imparting device that imparts an operation reaction force to the operating member, and a controller that controls the steering system, The controller: The reaction force applying device is configured to determine the reaction force to be applied and to control the reaction force applying device based on the determined reaction force; and The control system is configured to determine the operation reaction force including a vehicle behavior dependent component that is dependent on at least one of a lateral acceleration occurring in the vehicle and a yaw rate of the vehicle, and a component other than the vehicle behavior dependent component, and is configured to be able to change the contribution of the vehicle behavior dependent component in the operation reaction force, Furthermore, the steering system Each of the steering devices is the steering device, and the vehicle is provided with two steering devices for independently steering one of the left and right wheels, The controller: A steering system configured to increase the contribution of the vehicle behavior dependent component in a one-wheel steering situation in which one of the left and right wheels is steered by only one of the two steering devices.

2. The controller:

2. The steering system according to claim 1, configured to determine the operation reaction force including at least one of a vehicle speed-turning amount-dependent component that depends on the traveling speed of the vehicle and the steering amount of the wheels, and a steering load-dependent component that depends on the load of the steering device, as a component other than the vehicle behavior-dependent component.

3. the components other than the vehicle behavior dependent component include an operation speed dependent component that is dependent on the operation speed of the operation member, The controller: The steering system according to claim 1 , wherein the steering system is configured to increase the contribution of the operation speed dependent component in the one-wheel steering situation.

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