Steering system

Abstract

To provide a steering system that allows for steering angle control in accordance with the vehicle's dynamic performance requirements demanded by the driver. [Solution] The steering ECU 14 calculates the static characteristics Csf and Csr for front wheel steering angle control based on the required vehicle dynamic performance, calculates the vehicle transient characteristics Tgy and Tyr when switching from the static characteristics Csf and Csr to the dynamic characteristics Df and Dr for front wheel steering angle control, determines whether the vehicle transient characteristics Tgy and Tyr are good or bad, calculates the vehicle transient compensation amount Hgy and Hyr if the vehicle transient characteristics Tgy and Tyr are bad, calculates the vehicle transient compensation amount Hgy and Hyr, and uses the vehicle transient compensation amount Hgy and Hyr to calculate the dynamic characteristics Df and Dr for front wheel steering angle control and control the steering operation.

Description

Technical Field

[0001] The present disclosure relates to a steering system.

Background Art

[0002] Conventionally, for example, a vehicle steering device disclosed in Patent Document 1 has been known. A conventional vehicle steering device can switchably hold a plurality of transmission ratio variable characteristics that make the transmission ratio between the steering operation angle and the steering angle of the steered wheels variable, and when the operation angle is greater than or equal to a predetermined threshold value, it is configured not to execute the switching of the transmission ratio variable characteristics.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a conventional vehicle steering device, it is selected and switched from a plurality of preset transmission ratio variable characteristics. In this case, the switched transmission ratio variable characteristics may not necessarily match the steering angle control for realizing the vehicle motion performance required by the driver, and there is room for improvement.

[0005] An object of the present disclosure is to provide a steering system capable of steering angle control in accordance with the vehicle motion performance required by a driver.

Means for Solving the Problems

[0006] The steering system of this disclosure comprises an operating device operated by a driver, a steering device that steers the steering wheels of a vehicle, and a controller that controls the steering operation of the steering wheels by the steering device according to the vehicle motion performance required by the driver. The controller calculates a static steering angle control characteristic that represents the static characteristics of steering angle control that controls the steering angle of the steering wheels in a steering operation based on the required vehicle motion performance, calculates a vehicle transient characteristic that represents the transient characteristics of the vehicle when switching from the static steering angle control characteristic to the dynamic steering angle control characteristic that represents the dynamic characteristics of steering angle control, determines whether the vehicle transient characteristics are good or bad, calculates a transient characteristic compensation amount that represents the compensation amount to improve the vehicle transient characteristics if the vehicle transient characteristics are bad, calculates a steering angle control dynamic characteristic using the transient characteristic compensation amount, and controls the steering operation based on the steering angle control dynamic characteristic. [Effects of the Invention]

[0007] According to this disclosure, if the vehicle transient characteristics based on the vehicle dynamics performance requested by the driver are poor, the steering system can calculate a transient characteristic compensation amount and control the steering operation based on the steering angle control dynamics calculated using the transient characteristic compensation amount. As a result, the steering system can achieve the vehicle dynamics performance requested by the driver while ensuring the vehicle's behavioral stability. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic diagram of the vehicle's configuration. [Figure 2] This is a diagram illustrating the setting device. [Figure 3] This is a flowchart of the program for changing the steering angle control characteristics. [Figure 4] This is a diagram to explain the transient characteristics of a vehicle. [Figure 5] This is a diagram illustrating the vehicle transient response compensation amount. [Figure 6] This diagram illustrates the difference between having and not having vehicle transient response compensation. [Modes for carrying out the invention]

[0009] Hereinafter, a steering system 10, which is an embodiment of the present disclosure, will be described in detail with reference to the drawings. In addition to the embodiments described below, the present disclosure can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art.

[0010] 1. Configuration of the steering system 10 In this embodiment, the steering system 10 is applied to the vehicle 1 shown in Figure 1. The vehicle 1 comprises a body 2, wheels 3 arranged on the front, rear, left, and right sides respectively, and a suspension unit 4. The wheels 3 consist of a right front wheel 31, a left front wheel 32, a right rear wheel 33, and a left rear wheel 34. In this embodiment, an example is given in which the right front wheel 31 and the left front wheel 32 (i.e., the left and right front wheels) are steerable wheels, as are the right rear wheel 33 and the left rear wheel 34 (i.e., the left and right rear wheels). The suspension unit 4 includes, for example, a coil spring 41 and a shock absorber 42.

[0011] Vehicle 1 is also equipped with a vehicle speed sensor 5, a yaw rate sensor 6, and an acceleration sensor 7. The vehicle speed sensor 5 detects the vehicle speed V, which is determined, for example, based on the wheel speed of the wheels 3. The yaw rate sensor 6 detects the yaw rate YR generated around the center of gravity of vehicle 1 during turning. The acceleration sensor 7, in particular, detects the lateral acceleration GY generated in the left-right direction of vehicle 1.

[0012] Furthermore, as shown in Figure 2, Vehicle 1 is equipped with a setting device 8 that can be operated by the driver to arbitrarily set the vehicle's dynamic performance. The setting device 8 includes slide bars 81 and 82 that allow the driver to continuously and finely change and adjust the vehicle's dynamic performance. The setting device 8 then outputs request information O that represents the requested content adjusted and set by slide bars 81 and 82.

[0013] Slide bar 81 is operated by sliding to continuously adjust and set the "turning performance," which is expressed by the ratio of the yaw rate YR gain and the lateral acceleration GY gain acting on the vehicle 1 during turning. Slide bar 82 is operated by sliding to continuously adjust and set the "sensitivity," which is expressed by the magnitude of the yaw rate YR gain and the magnitude of the lateral acceleration GY gain acting on the vehicle 1 during turning. Here, slide bars 81 and 82 may be, for example, so-called physical switches that can be mechanically slid by a driver, or so-called electronic switches that are displayed on a touch panel provided on the vehicle 1 and can be electronically operated by touch.

[0014] The steering system 10 includes an operating device 11 operated by the driver and a front wheel steering device 12 that steers the right front wheel 31 and the left front wheel 32. In this embodiment, the steering system 10 is a steer-by-wire type in which the mechanical connection between the operating device 11 and the front wheel steering device 12 is released. Furthermore, the steering system 10 includes a rear wheel steering device 13 that steers the right rear wheel 33 and the left rear wheel 34.

[0015] The operating device 11 mainly comprises a steering wheel 111, a steering shaft 112, a steering column 113, and a reaction force application mechanism 114. The steering wheel 111 is operated (steering) by the driver. The steering shaft 112 has the steering wheel 111 attached to its end and is rotatably supported by the steering column 113. The steering column 113 is supported by the instrument panel reinforcement (not shown). The reaction force application mechanism 114 uses a reaction force motor 115 as a driving force source to apply a reaction force Fc (strictly speaking, "reaction force torque," but hereinafter referred to as "operating reaction force Fc") to the steering wheel 111 via the steering shaft 112. The reaction force motor 115 can be exemplified by, for example, a three-phase brushless DC motor.

[0016] Further, the operation device 11 has an operation angle sensor 116 that detects the operation position of the steering wheel 111, in other words, the operation angle δ representing the amount of operation from the neutral position of the steering wheel 111. Here, when the position taken by the steering wheel 111 in the straight-ahead state of the vehicle 1 is defined as the neutral position, the operation angle sensor 116 detects the rotation angle, that is, the amount of operation, in each of the left and right directions from the neutral position as the operation angle δ. Further, the operation device 11 has an operation torque sensor 117 that detects the operation torque To applied to the steering wheel 111 by the driver.

[0017] The front-wheel side steering device 12 integrally steers each of the right front wheel 31 and the left front wheel 32 supported by the vehicle body 2 so as to be steerable by rotating the steering knuckle 43 on the front-wheel side that constitutes the suspension unit 4. The front-wheel side steering device 12 mainly has a steering actuator 121 as a main component.

[0018] The steering actuator 121 mainly includes a steering rod 122, a housing 123, and a rod movement mechanism 124. Both ends of the steering rod 122 are respectively connected to the left and right steering knuckles 43 via tie rods 125. The housing 123 is fixed to the vehicle body 2 and supports the steering rod 122 so as to be movable in the left-right direction.

[0019] The rod movement mechanism 124 uses a steering motor 126 as a driving force source to move the steering rod 122 in the left-right direction. The rod movement mechanism 124 mainly includes, for example, a ball screw mechanism constituted by a ball groove (not shown) provided on the steering rod 122 and a nut (not shown) that engages with the ball groove via a bearing ball (not shown) and is rotated by the steering motor 126.

[0020] Further, the front-wheel side steering device 12 has a steering angle sensor 127 that detects a front-wheel steering angle θf representing the steering positions of the right front wheel 31 and the left front wheel 32. Here, when the position of the steering rod 122 in the straight-ahead state of the vehicle 1 is set as the neutral position, the steering angle sensor 127 detects the amount of movement in each of the left and right directions from the neutral position as the front-wheel steering angle θf.

[0021] The rear-wheel side steering device 13 integrally steers each of the right rear wheel 33 and the left rear wheel 34 that are supported by the vehicle body 2 so as to be steerable by rotating the steering knuckle 43 on the rear-wheel side. The rear-wheel side steering device 13 mainly has a steering actuator 131 as a main component.

[0022] The steering actuator 131 mainly includes a steering rod 132, a housing 133, and a rod movement mechanism 134. Both ends of the steering rod 132 are respectively connected to the left and right steering knuckles 43 via tie rods 135. The housing 133 is fixed to the vehicle body 2 and supports the steering rod 132 so as to be movable in the left and right directions. The rod movement mechanism 134 uses a steering motor 136 as a driving force source to move the steering rod 132 in the left and right directions. The rod movement mechanism 134 can be exemplified as a case mainly including a ball screw mechanism, similar to the rod movement mechanism 124.

[0023] Further, the rear-wheel side steering device 13 has a steering angle sensor 137 that detects a rear-wheel steering angle θr representing the steering positions of the right rear wheel 33 and the left rear wheel 34. Here, when the position of the steering rod 132 in the straight-ahead state of the vehicle 1 is set as the neutral position, the steering angle sensor 137 detects the amount of movement in each of the left and right directions from the neutral position as the rear-wheel steering angle θr.

[0024] The control of the reaction motor 115 of the operating device 11, the steering motor 126 of the front wheel steering device 12, and the steering motor 136 of the rear wheel steering device 13 are performed by the steering electronic control unit 14 (hereinafter simply referred to as "steering ECU 14"), which acts as a controller. The steering ECU 14 is an electronic control unit (ECU) whose main components are a microcomputer with a CPU, ROM, RAM, and various interfaces. The steering ECU 14 acquires request information O from the setting device 8 via various interfaces and is also capable of communicating with other electronic control units (not shown) and various sensors (not shown) mounted on the vehicle 1. In Figures 1 and 2, the steering ECU is referred to as "S-ECU".

[0025] The steering ECU 14 determines the target front wheel steering angle θfd, which is the target for the front wheel steering angle θf of the right front wheel 31 and the left front wheel 32, by multiplying the acquired operating angle δ by the steering gear ratio Rgf according to Equation 1 below. Also, the steering ECU 14 determines the target rear wheel steering angle θrd, which is the target for the rear wheel steering angle θr of the right rear wheel 33 and the left rear wheel 34, by multiplying the acquired operating angle δ by the steering gear ratio Rgr according to Equation 2 below. θfd = Rgf × δ …Equation 1 θrd = Rgr × δ …Equation 2

[0026] Here, the steering ECU 14 can determine the target front wheel steering angle θfd and target rear wheel steering angle θrd by considering whether the steering direction of the right front wheel 31 and left front wheel 32 and the steering direction of the right rear wheel 33 and left rear wheel 34 are in the same direction (in phase) or whether the steering direction of the right front wheel 31 and left front wheel 32 and the steering method of the right rear wheel 33 and left rear wheel 34 are in opposite directions (out of phase) depending on the vehicle speed V. For example, the steering ECU 14 can determine the target front wheel steering angle θfd and target rear wheel steering angle θrd to be in opposite phase in the low-speed range where the vehicle speed V is less than a predetermined vehicle speed, in order to ensure good maneuverability of the vehicle 1. Also, the steering ECU 14 can determine the target front wheel steering angle θfd and target rear wheel steering angle θrd to be in phase in the medium-to-high-speed range where the vehicle speed V is above a predetermined vehicle speed, in order to ensure the behavioral stability of the vehicle 1.

[0027] 2. Processing to change the steering angle control characteristics in the steering system 10 Next, the process for changing the steering angle control characteristics in the steering system 10 will be described. As described above, the steering system 10 can determine the front wheel steering angle θf and rear wheel steering angle θr with respect to the driver's operating angle δ using the steering gear ratio Rgf and steering gear ratio Rgr. As a result, the steering system 10 can change the steering angle control characteristics that control the front wheel steering angle θf of the right front wheel 31 and left front wheel 32, and the rear wheel steering angle θr of the right rear wheel 33 and left rear wheel 34, in order to realize the vehicle motion performance set by the driver using the setting device 8, that is, to realize the gain of the yaw rate YR and the gain of the lateral acceleration GY required by the setting. For this reason, in this embodiment, the steering ECU 14 executes the steering angle control characteristic change program shown in Figure 3. The steering angle control characteristic change program will be described below.

[0028] The steering ECU 14 starts executing the steering angle control characteristic change program in step S10. In the following step S11, the steering ECU 14 inputs request information O representing the vehicle motion performance set (requested) by the driver. Specifically, the steering ECU 14 inputs request information O including the set value of the gain for lateral acceleration GY and the set value of the gain for yaw rate YR, corresponding to the operating states of the slide bars 81 and 82 operated by the driver in the setting device 8. Then, after inputting the request information O, the steering ECU 14 executes the step processing in step S12.

[0029] In step S12, the steering ECU 14 calculates the steering angle control static characteristics for the right front wheel 31 and left front wheel 32, and the right rear wheel 33 and left rear wheel 34. Specifically, the steering ECU 14 uses the following equations 3 and 4, based on a well-known linear two-wheeled automobile model, to calculate the front wheel steering angle control static characteristics Csf and the rear wheel steering angle control static characteristics Csr so as to realize the requested information O input in step S11, i.e., the steady-state characteristics requested by the driver: the steady-state gain Sgy of the lateral acceleration GY and the steady-state gain Syr of the yaw rate YR. Sgy = Ks × Csf + Ls × Csr ...Equation 3 Syr=Ms×Csf+Ns×Csr…Formula 4

[0030] Here, in equation 3, Ks represents the gain coefficient for the lateral acceleration GY of the front wheel steering angle control static characteristic, and Ls represents the gain coefficient for the lateral acceleration GY of the rear wheel steering angle control static characteristic. Also, in equation 4, Ms represents the gain coefficient for the yaw rate YR of the front wheel steering angle control static characteristic, and Ns represents the gain coefficient for the yaw rate YR of the rear wheel steering angle control static characteristic. Since it is based on a linear two-wheel model, the gain coefficients Ks, Ls, Ms, and Ns can be calculated from various vehicle parameters related to vehicle 1. Then, after calculating the front wheel steering angle control static characteristic Csf and the rear wheel steering angle control static characteristic Csr, the steering ECU 14 executes the step process of step S13.

[0031] In step S13, the steering ECU 14 calculates the vehicle transient characteristics of vehicle 1 when changing the steering angle control from static to dynamic characteristics. Specifically, the steering ECU 14 uses the following equations 5 and 6, which are based on a well-known linear two-wheeled automobile model, to calculate the vehicle transient characteristics Tgy for lateral acceleration GY and Tyr for yaw rate YR from the front wheel steering angle control static characteristics Csf and rear wheel steering angle control static characteristics Csr calculated in step S12. Tgy = Kt × Csf + Lt × Csr ... Equation 5 Tyr=Mt×Csf+Nt×Csr…Formula 6

[0032] Here, in equation 5, Kt represents the gain coefficient for the lateral acceleration GY of the front wheel steering angle control static characteristic Csf during transient conditions, and Lt represents the gain coefficient for the lateral acceleration GY of the rear wheel steering angle control static characteristic Csr during transient conditions. Also, in equation 6, Mt represents the gain coefficient for the yaw rate YR of the front wheel steering angle control static characteristic Csf during transient conditions, and Nt represents the gain coefficient for the yaw rate YR of the rear wheel steering angle control static characteristic Csr during transient conditions. Since this is based on a linear two-wheel model, the gain coefficients Kt, Lt, Mt, and Nt can be calculated from various vehicle parameters related to vehicle 1.

[0033] Incidentally, the vehicle transient characteristics Tgy and Tyr calculated according to equations 5 and 6 above tend to show a decrease in gain as the frequency increases overall, as shown in Figure 4, which illustrates the GY gain of the vehicle transient characteristic Tgy, i.e., the lateral acceleration GY during the transient. Furthermore, the example vehicle transient characteristic Tgy may show a large gain change in a specific frequency range. After calculating the vehicle transient characteristics Tgy and Tyr, the steering ECU 14 executes the step processing of step S14.

[0034] In step S14, the steering ECU 14 performs a pass / fail determination on the vehicle transient characteristics Tgy and the vehicle transient characteristics Tyr calculated in step S13 based on preset pass / fail determination conditions. As pass / fail determination conditions, for example, regarding the vehicle transient characteristics Tgy of the lateral acceleration GY, "(Condition I) The difference between the steady-state gain and the resonance gain is within X dB." and "(Condition II) The difference between the steady-state gain and the anti-resonance gain is within Y dB (Y < X)." If these are set, it is determined whether the vehicle transient characteristics Tgy calculated in step S13 satisfy Condition I and Condition II.

[0035] Specifically, when the vehicle transient characteristics Tgy calculated in step S13 are in patterns B and C shown by the solid line in FIG. 4, the steering ECU 14 determines that Condition I and Condition II are satisfied, that is, the behavior of vehicle 1 is stable and good. On the other hand, when the vehicle transient characteristics Tgy calculated in step S13 are in pattern A shown by the short dashed line, pattern D shown by the long dashed line, and pattern E shown by the dotted-dashed line in FIG. 4, the steering ECU 14 determines that at least one of Condition I and Condition II is not satisfied, that is, the behavior of vehicle 1 may become unstable and is poor. Note that for the determination of the vehicle transient characteristics Tgy and the vehicle transient characteristics Tyr, for example, it is possible to simply determine whether a plurality of representative values satisfy the pass / fail determination conditions, or to strictly determine whether the pass / fail determination conditions are satisfied by algebraic decomposition.

[0036] If the steering ECU 14 does not satisfy at least one of condition 1 and condition II, it determines "Yes" in step S14 and executes the step process in step S15, because compensation for vehicle transient characteristics is necessary to bring the vehicle dynamics closer to the vehicle dynamics requested by the driver. On the other hand, if the steering ECU 14 satisfies both condition 1 and condition II, it determines "No" in step S14 and executes the step process in step S17, because compensation for vehicle transient characteristics is not necessary to achieve the vehicle dynamics requested by the driver.

[0037] Furthermore, for the determination process in step S14, the vehicle transient characteristics Tgy and Tyr calculated in step S13 using equations 5 and 6 based on the linear two-wheel model are used. In this case, since the steering ECU 14 can calculate the vehicle transient characteristics Tgy and Tyr at any time, the determination process in step S14 can also be performed at any time.

[0038] In step S15, the steering ECU 14 calculates the vehicle transient compensation amount Hgy for lateral acceleration GY and the vehicle transient compensation amount Hyr for yaw rate YR so that the vehicle transient characteristics Tgy and Tyr satisfy conditions I and II determined in step S14. Specifically, let's assume that, for example, as a result of calculating the vehicle transient characteristic Tgy in step S13, the steering ECU 14 obtains the GY gain GYb shown by the dashed line in Figure 5, and determines in step S14 that at least one of conditions I and II is not satisfied. Then, let's assume that the steering ECU 14 determines the vehicle transient compensation amount Hgy for lateral acceleration GY in order to achieve the vehicle motion performance required by the driver, and compensates the GY gain GYb so that the GY gain GYt shown by the solid line in Figure 5 becomes the GY gain GYt.

[0039] In this case, the steering ECU 14 can determine the vehicle transient compensation amount Hgy as the time constant of an LPF calculated to suppress a known resonant frequency and resonant gain, for example, by following the assumption that the vehicle transient compensation amount Hgy is a first-order low-pass filter (LPF). Alternatively, the steering ECU 14 can calculate the vehicle transient compensation amount Hgy by L1 optimization such that the vehicle transient characteristic Tgy, i.e., the GY gain GYb in a predetermined frequency range matches the steering angle control static characteristic. After calculating the vehicle transient compensation amount Hgy and the vehicle transient compensation amount Hyr, the steering ECU 14 executes the step processing of step S16.

[0040] In step S16, the steering ECU 14 calculates the steering angle control dynamics. Specifically, the steering ECU 14 calculates the front wheel steering angle control dynamics Df and the rear wheel steering angle control dynamics Dr by using the following equations 7 and 8, which are based on a well-known linear two-wheel model of an automobile and the vehicle transient characteristic compensation amounts Hgy and Hyr calculated in step S15. Hgy = (Gf × Df + Gr × Dr) ... Equation 7 Hyr=(Yf×Df+Yr×Dr)…Formula 8

[0041] Here, in equation 7, Gf represents the gain coefficient for the lateral acceleration GY of the front wheel steering angle control dynamic characteristic Df, and Gr represents the gain coefficient for the lateral acceleration GY of the rear wheel steering angle control dynamic characteristic Dr. Also, in equation 8, Yf represents the gain coefficient for the yaw rate YR of the front wheel steering angle control dynamic characteristic Df, and Yr represents the gain coefficient for the yaw rate YR of the rear wheel steering angle control dynamic characteristic Dr. Since it is based on a linear two-wheel model, the gain coefficients Gf, Gr, Yf, and Yr can be calculated from various vehicle parameters related to vehicle 1. Then, after calculating the front wheel steering angle control dynamic characteristic Df and the rear wheel steering angle control dynamic characteristic Dr, the steering ECU 14 executes the step process of step S17.

[0042] Furthermore, by following equations 7 and 8, the steering ECU 14 can calculate and uniquely determine the front wheel steering angle control dynamic characteristics Df and rear wheel steering angle control dynamic characteristics Dr that realize the vehicle transient characteristic compensation amounts Hgy and Hyr calculated in step S15, in other words, the vehicle motion performance required (desired) by the driver. However, the determined front wheel steering angle control dynamic characteristics Df and rear wheel steering angle control dynamic characteristics Dr may be obtained as higher-order control laws that are not suitable for steering angle control in the actual vehicle 1. In this case, it is possible to convert them into control laws that are easier to handle in steering angle control in the actual vehicle 1 by performing an approximation using, for example, L1 optimization.

[0043] In step S17, the steering ECU 14 performs a switch in the steering angle control characteristics. Specifically, the steering ECU 14 switches between static and dynamic characteristics for the steering angle control of the right front wheel 31 and the left front wheel 32, and for the steering angle control of the right rear wheel 33 and the left rear wheel 34. Here, if the switch between static and dynamic characteristics for steering angle control is performed instantaneously, it may affect the stability of the vehicle 1's behavior. Therefore, the steering ECU 14 performs the switch between static and dynamic characteristics while ensuring stability, that is, it changes the steering gear ratio Rgf and the steering gear ratio Rgr.

[0044] In this case, the steering ECU 14 can change the steering gear ratio Rgf and steering gear ratio Rgr, for example, when it is determined that vehicle 1 is moving straight. Alternatively, the steering ECU 14 can gradually change the steering gear ratio Rgf and steering gear ratio Rgr, for example, in response to switching between static and dynamic characteristics. Alternatively, the steering ECU 14 can change the steering gear ratio Rgf and steering gear ratio Rgr, for example, when it is determined that vehicle 1 is stopped.

[0045] After the steering ECU 14 executes the steering angle control characteristic switching process in step S17, it temporarily terminates the execution of the steering angle control characteristic change program in the following step S18. Then, after a predetermined short period of time has elapsed, the steering ECU 14 restarts the execution of the steering angle control characteristic change program in step S10.

[0046] As can be understood from the above explanation, the steering system 10 comprises an operating device 11 operated by the driver, a front wheel steering device 12 and a rear wheel steering device 13 which are steering devices that steer the right front wheel 31 and left front wheel 32 and the right rear wheel 33 and left rear wheel 34, respectively, which are the steering wheels of the vehicle 1, and a steering ECU 14 which is a controller that controls the steering operation of the right front wheel 31 and left front wheel 32 and the right rear wheel 33 and left rear wheel 34 by the front wheel steering device 12 and the rear wheel steering device 13 according to the vehicle dynamics performance required by the driver.

[0047] The steering ECU 14 calculates the front wheel steering angle control static characteristic Csf and the rear wheel steering angle control static characteristic Csr, which represent the static characteristics of steering angle control that control the front wheel steering angles θf of the right front wheel 31 and the left front wheel 32 and the rear wheel steering angles θr of the right rear wheel 33 and the left rear wheel 34 in steering operation, based on the required vehicle dynamic performance. From the front wheel steering angle control static characteristic Csf and the rear wheel steering angle control static characteristic Csr, it calculates the vehicle transient characteristics Tgy and the vehicle transient characteristics Tyr, which represent the transient characteristics of the vehicle when switching to the front wheel steering angle control dynamic characteristic Df and the rear wheel steering angle control dynamic characteristic Dr, which represent the dynamic characteristics of steering angle control. Based on the static characteristics Csf and Csr of the front wheel steering angle control, the quality of the vehicle transient characteristics Tgy and Tyr is determined. If the vehicle transient characteristics Tgy and Tyr are poor, the vehicle transient compensation amounts Hgy and Hyr are calculated to represent the compensation amounts needed to improve the vehicle transient characteristics Tgy and Tyr. The dynamic characteristics Df and Dr of the front wheel steering angle control are then calculated using the vehicle transient compensation amounts Hgy and Hyr, and the steering operation is controlled based on the dynamic characteristics Df and Dr.

[0048] According to this, in the steering system 10, if the vehicle transient characteristics Tgy and Tyr do not meet the pass / fail judgment conditions, that is, if the vehicle transient characteristics Tgy and Tyr are poor, the steering ECU 14 can calculate the front wheel steering angle control dynamic characteristics Df and rear wheel steering angle control dynamic characteristics Dr that realize the vehicle transient characteristic compensation amount Hgy and vehicle transient characteristic compensation amount Hyr. As a result, the steering system 10 can ensure the behavioral stability of the vehicle 1 while realizing vehicle dynamic performance based on fine settings by the driver. Furthermore, it is possible to switch steering angle control characteristics while suppressing the difficulty of driving caused by the deterioration of the vehicle transient characteristics Tgy and Tyr.

[0049] Incidentally, let's consider a case where the customization of vehicle dynamics requested by the driver involves, for example, reducing the GY gain GYb of the lateral acceleration GY, as shown by the long dashed line in Figure 6. In this case, the steering ECU 14 can calculate the vehicle transient characteristic compensation amount Hgy and the front wheel steering angle control dynamic characteristics Df and rear wheel steering angle control dynamic characteristics Dr in order to achieve the GY gain GYt requested by the driver.

[0050] Furthermore, if the vehicle transient characteristic compensation amount Hgy cannot be calculated, that is, if there is no compensation for the dynamic characteristics, the steering gear ratio Rgf and steering gear ratio Rgr are usually changed statically in the steering system 10. In this case, as shown by the dashed line in Figure 6, the gain GYc, in other words, the vehicle transient characteristic Tgy, unlike the GY gains GYb and GY gains GYt, tends to increase with increasing frequency. For this reason, it becomes difficult to achieve vehicle dynamic performance based on fine settings by the driver, and it becomes difficult to switch the steering angle control characteristics while suppressing the difficulty of driving caused by the deterioration of the vehicle transient characteristic Tgy.

[0051] 3. Other variations In the embodiments described above, an example was given in which the steering system 10 employs a steer-by-wire type. However, the steering system 10 is not limited to a steer-by-wire type as long as it is possible to change the relationship between the operating angle δ and the steering angle θ. For example, an independent steering type with steering actuators on the left and right sides of the steering wheels, or a variable steering gear ratio type (so-called VGRS type) can also be employed. [Explanation of Symbols]

[0052] 1...Vehicle, 2...Body, 3...Wheels, 4...Suspension unit, 5...Vehicle speed sensor, 6...Yaw rate sensor, 7...Accelerometer, 8...Setting device, 81...Slide bar, 82...Slide bar, 10...Steering system 10, 11...Operating device, 12...Front wheel steering device (steering device), 13...Rear wheel steering device (steering device), 14...Steering electronic control unit (controller)

Claims

1. A control device operated by a driver, A steering device that steers the steering wheels of a vehicle, The system includes a controller that controls the steering operation of the steering wheels by the steering device in accordance with the vehicle dynamics performance required by the driver, The aforementioned controller, A steering system that calculates a static steering angle control characteristic representing the static characteristics of steering angle control that controls the steering angle of the steering wheels in the steering operation based on the required vehicle motion performance; calculates a vehicle transient characteristic representing the transient characteristics of the vehicle when switching from the static steering angle control characteristic to the dynamic steering angle control characteristic representing the dynamic characteristics of the steering angle control based on the static steering angle control characteristic; determines whether the vehicle transient characteristic is good or bad; calculates a vehicle transient characteristic compensation amount representing the compensation amount to improve the vehicle transient characteristic if the vehicle transient characteristic is bad; calculates the steering angle control dynamic characteristic using the vehicle transient characteristic compensation amount; and controls the steering operation based on the steering angle control dynamic characteristic.

2. The aforementioned controller The steering system according to claim 1, which determines whether the calculated transient characteristics are good or bad by determining whether or not they meet pre-set good or bad judgment conditions.

3. The required vehicle dynamics performance is, The steering system according to claim 1 or 2, comprising the yaw rate generated around the vehicle's center of gravity and the lateral acceleration generated in the vehicle.

4. The yaw rate and the transverse acceleration are, The steering system according to claim 3, which is continuously modified and required by the driver.

5. The steering device, The steering system according to claim 1, comprising a front wheel steering device for steering the left and right front wheels of the vehicle, and a rear wheel steering device for steering the left and right rear wheels of the vehicle.

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