Control system for four-wheel steering vehicles

Abstract

To provide a control device of a four-wheel steering vehicle capable of properly performing four-wheel steering regardless vehicle speed or steering speed.SOLUTION: A control device of a four-wheel steering vehicle includes a steering wheel 5, a front wheel steering device 3 steering a front wheel 1, and a rear wheel steering device 4 steering a rear wheel 2, and operates the front wheel steering device 3 and the rear wheel steering device 4 on the basis of an operation state of the steering wheel 5. A first steering operating the steering wheel 5 in a predetermined direction, and a second steering operating the steering wheel 5 in a direction opposite to the first steering are continuously carried out. When the rear wheel 2 is steered in a direction opposite to a steering direction of the front wheel 1, an absolute value of the steering angle speed of the front wheel 1 steered corresponding to the first steering is higher than a first threshold value, and an absolute value of the steering angle speed of the front wheel 1 steered corresponding to the second steering is higher than a second threshold value, the steering of the rear wheel 2 corresponding to the second steering is limited (step S4).SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] This invention relates to a control device for a vehicle (four-wheel steering vehicle) capable of steering both the front and rear wheels.

Background Art

[0002] Patent Document 1 describes a steering control device for a vehicle (four-wheel steering vehicle) equipped with a four-wheel steering mechanism. The four-wheel steering vehicle described in this Patent Document 1 includes a front-wheel steering device, a rear-wheel steering device, and a VGRS device (variable gear ratio steering device), etc. The VGRS device is an auxiliary steering device for realizing so-called active steering, and performs correction of the steering angle or automatic control of the steering angle so that the steering angle of the front wheel matches the target steering angle. Also, it is possible to change the steering gear ratio of the steering device by this VGRS device. And the steering control device described in this Patent Document 1 controls the steering angle of the rear wheel so that the rear wheel steers in the same phase (the same steering direction) or the opposite phase (the opposite steering direction) with respect to the steering direction of the front wheel based on the running conditions of the vehicle. Also, it detects a state in which the vehicle should be moved laterally, and determines the target movement distance in the lateral direction. And when it detects a state in which the vehicle should be moved laterally, for a period determined based on the target movement distance, the rear wheel is steered in the opposite phase with respect to the front wheel, and the timing for steering the rear wheel in the same phase as the front wheel is delayed.

[0003] Furthermore, Patent Document 2 describes a steering assist control device for a four-wheel steering vehicle. The steering assist control device described in Patent Document 2 has an electric power steering device and a steering angle changing device. The steering angle changing device steers the front wheels relatively and auxiliaryly with respect to the rotation of the steering wheel. The steering angle changing device also functions as a variable gear ratio steering device (VGRS device) that increases or decreases the steering gear ratio or steering transmission ratio, or as a steering transmission ratio changing device. The steering assist control device described in Patent Document 2 changes the steering control law of the rear wheels according to the driving conditions. Specifically, when the curvature of the road is large, the steering control law of the rear wheels is set to the standard first control law, and when the curvature of the road is small, the steering control law of the rear wheels is set to a second control law that is different from the first control law. In this way, the assist characteristics of the steering assist device are changed in accordance with the change in steering characteristics due to the change in the steering control law of the rear wheels.

[0004] Patent Document 3 describes a steer-by-wire steering system and a vehicle steering control device that controls the steering system. The steer-by-wire steering system described in Patent Document 3 includes a steering angle detection device that detects the rotation angle (steering angle) of the steering wheel, a reaction force actuator that applies steering reaction torque to the steering wheel, a steering mechanism that steers the steering wheels in response to steering torque, a steering actuator that applies steering torque to the steering mechanism, and a steering angle detection device that detects the steering angle of the steering wheels. The vehicle steering control device described in Patent Document 3 electrically controls the reaction force actuator and steering actuator in the above-mentioned steering system. Specifically, when the steering mode is manual steering mode, the vehicle steering control device sets the steering gear ratio to a preset standard steering gear ratio and controls the steering angle of the steering wheels based on the steering angle detected by the steering angle detection device. Furthermore, when the steering mode is set to automatic steering mode, the system calculates the target steering angle of the steering wheels, sets the steering gear ratio to the automatic steering gear ratio which is smaller than the standard steering gear ratio, and controls the steering angle of the steering wheels to match the target steering angle. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2009-280102 [Patent Document 2] Japanese Patent Publication No. 2013-129262 [Patent Document 3] Japanese Patent Publication No. 2022-41538 [Overview of the project] [Problems that the invention aims to solve]

[0006] In a four-wheel steering vehicle equipped with a rear-wheel steering system as described in Patent Documents 1 and 2 above, generally, at low speeds, the rear wheels are steered in the opposite direction (opposite phase) to the front wheels. This action generates a yaw moment in the direction of the vehicle's turn, thereby reducing the vehicle's turning radius. On the other hand, at high speeds, the rear wheels are steered in the same direction (in phase) as the front wheels. This action reduces the vehicle's yawing during steering, thereby improving the vehicle's handling stability.

[0007] By applying a variable gear ratio steering system or a steer-by-wire steering system to a four-wheel steering vehicle as described above, and setting a low steering gear ratio, it is possible to construct a four-wheel steering vehicle that enables agile steering. However, in the motion system of such a four-wheel steering vehicle with a low steering gear ratio, resonance may occur when the vehicle is steered at a predetermined frequency (steering speed, steering direction), potentially causing the vehicle's behavior to become unstable. For example, as shown in the time chart in Figure 1, when driving at low speed, if the vehicle is steered in a predetermined direction from time t1 to time t2 (first steering), and then continuously steered in the opposite direction to the first steering from time t2 to time t3 (second steering), the rear wheels will be steered in opposite phase to the steering direction of the front wheels. In this case, for example, in a four-wheel steering vehicle with a typical steering gear ratio of around "15", the front and rear wheels are steered at a standard steering angular velocity according to the waveforms (frequencies) of the first and second steering inputs, resulting in a standard magnitude of lateral acceleration. In contrast, in a four-wheel steering vehicle with a steering gear ratio lowered to around "5", the front and rear wheels are steered at approximately three times the standard steering angular velocity. As a result, resonance may occur in the later stages of the second steering input (around time t3), potentially causing excessive lateral acceleration. Such excessive lateral acceleration can reduce the ride comfort and handling stability of a four-wheel steering vehicle. However, when steering at high speeds, if the front and rear wheels are steered in phase, the above-mentioned resonance problem does not occur.

[0008] This invention was conceived in response to the above-mentioned technical problems, and aims to provide a control device for a four-wheel steering vehicle that can appropriately steer the front and rear wheels regardless of vehicle speed or steering speed. [Means for solving the problem]

[0009] To achieve the above objective, this invention provides a steering device operated by the driver and a front wheel steering device that steers the front wheels. , in conjunction with the steering action of the front wheels, the rear Rear-wheel steering system that turns the wheels In a four-wheel steering vehicle that comprises and constitutes a motion system that generates resonance at a predetermined frequency,Based on the operating state of the aforementioned steering device, the front wheel steering device and the rear wheel steering device are operated. ru, yon A control device for a wheel-steering vehicle, comprising a controller that controls the front wheel steering device and the rear wheel steering device, wherein the controller controls the steering device The steering angle is maintained in a steered state for a predetermined period of time or longer. A first steering system that is operated in a fixed direction, and the steering device is the first steering system The opposite direction If the steering angle exceeds the steering angle in the aforementioned steering state, The second steering maneuver is performed in succession. Before The present invention is characterized in that, when steering the rear wheels in the opposite direction to the steering direction of the front wheels, if the absolute value of the steering angular velocity of the front wheels or the rear wheels steered in response to the first steering is higher than a predetermined first threshold, and the absolute value of the steering angular velocity of the front wheels or the rear wheels steered in response to the second steering is higher than a predetermined second threshold, the steering of the rear wheels corresponding to the second steering is restricted.

[0010] Furthermore, the controller in this invention may be configured to limit the steering of the rear wheels by fixing the steering angle of the rear wheels to 0 or within a predetermined angle range.

[0011] Furthermore, the controller in this invention may be configured to limit the steering of the rear wheels by suppressing the amount of steering of the rear wheels (for example, the amount of change in the steering angle).

[0012] Furthermore, the controller in this invention is The steering state is the same as the steering Rudder speed is tending to decrease or It is acceptable for the value to be 0.

[0013] Furthermore, the controller in this invention may be configured to change the magnitudes of the first threshold and the second threshold according to the vehicle speed of the four-wheel steering vehicle.

[0014] Furthermore, the controller in this invention may be configured to decrease the magnitudes of the first threshold and the second threshold as the vehicle speed increases. [Effects of the Invention]

[0015] The vehicle control device of this invention controls a four-wheel steering vehicle capable of steering a rear wheel in addition to steering a front wheel, and controls a front wheel steering device and a rear wheel steering device with the four-wheel steering vehicle as a control target. During low-speed driving, the front wheels and the rear wheels are steered in opposite directions (reverse phase) to each other. On the other hand, during high-speed driving, the front wheels and the rear wheels are steered in the same direction (in-phase) to each other. However, as described above, for example, by applying a variable gear ratio steering device or a steer-by-wire type steering device, etc., in a four-wheel steering vehicle where a lower steering gear ratio than normal is set to enable sensitive steering, when the front wheels and the rear wheels are steered in reverse phase, resonance is likely to occur. When such resonance occurs, excessive lateral acceleration may occur, and there is a possibility that the behavior of the vehicle may be disturbed. Therefore, in the control device of the four-wheel steering vehicle of this invention, when the first steering and the second steering with different steering directions are continuously performed, if the absolute value of the steering angular velocity by the first steering and the second steering is higher than a predetermined threshold value, the steering of the rear wheel by the second steering is restricted. For example, the steering angle of the rear wheel can be suppressed. Therefore, even when steering that may cause resonance as described above is performed, by restricting the steering of the rear wheel, the occurrence of resonance can be suppressed, and four-wheel steering can be appropriately performed.

[0016] The above-described restriction of the steering of the rear wheel can be easily implemented specifically by fixing the steering angle of the rear wheel to 0 or near 0, or within a predetermined angle range. Alternatively, it can be easily implemented by suppressing the steering amount of the rear wheel (for example, the change amount of the steering angle).

[0017] Also In the present invention, the first steering is steering when the steering device is operated in a predetermined direction from a state in which the steering speed is decreasing or remains at zero for a predetermined time or longer, and therefore steering from a steered state after the steering is performed The steering angle if it continues for a predetermined time or more, that is , the steering maneuvers performed and the subsequent other maneuvers if the time interval between the steers The gap becomes long , subsequent other operations the steering is newly set as the first steering, and the control is executed again. Therefore, the situation of steering that may cause resonance as described above can be appropriately determined, and the control can be executed accurately.

[0018] Then, each threshold value for the steering angular velocity for determining a steering state in which resonance as described above may occur is increased or decreased according to the vehicle speed. For example, the magnitudes of the first threshold value and the second threshold value are changed and set so that they become smaller as the vehicle speed is higher. Therefore, control can be executed accurately according to the vehicle speed.

[0019] Therefore, according to the control device for a four-wheel steering vehicle of this invention, regardless of the vehicle speed and the speed of steering, generation of resonance can be suppressed and four-wheel steering of the front wheels and the rear wheels can be appropriately performed.

Brief Description of the Drawings

[0020] [Figure 1] FIG. 1 is a time chart for explaining a problem of the prior art (a situation in which resonance occurs and excessive lateral acceleration is generated due to fast steering during low-speed driving). [Figure 2] FIG. 2 is a block diagram schematically showing a schematic configuration of a four-wheel steering vehicle to be controlled by the control device for a four-wheel steering vehicle of this invention. [Figure 3] FIG. 3 is a flowchart for explaining an example of control executed by the control device for a four-wheel steering vehicle of this invention. [Figure 4] FIG. 4 is a time chart for explaining the content of the control shown in the flowchart of FIG. 3 (an example of fixing the steering angle of the rear wheels in the vicinity of 0 in the second steering), and the operation and effect when the control is executed. [Figure 5] FIG. 5 is a time chart for explaining the content of the control shown in the flowchart of FIG. 3 (an example of suppressing the control amount of the steering angle of the rear wheels in the second steering), and the operation and effect when the control is executed. [Figure 6] FIG. 6 is a diagram showing an image of a threshold value for the steering angular velocity for determining a steering state in which resonance may occur (an example of a map for changing the threshold value according to the vehicle speed).

Mode for Carrying Out the Invention

[0021] Embodiments of this invention will be described with reference to the drawings. Note that the embodiments shown below are merely examples of how this invention can be implemented and do not limit the invention.

[0022] Figure 2 shows a schematic configuration of the vehicle Ve that is the target of control in this embodiment of the present invention. The vehicle Ve shown in Figure 2 is a so-called "four-wheel steering vehicle" that is capable of steering both the front wheels 1 and the rear wheels 2. To this end, the vehicle Ve is equipped with a front wheel steering device 3 for steering the front wheels 1 and a rear wheel steering device 4 for steering the rear wheels 2.

[0023] The front wheel steering system 3 steers the front wheels 1 according to the operating state of the "control device" operated by the driver. In the example shown in Figure 2, the front wheel steering system 3 includes a steering wheel 5, an electric actuator 6, a steering gearbox 7, and a VGRS device 8. The electric actuator 6 assists steering by the steering wheel 5, making the front wheel steering system 3 function as a so-called power steering device. The VGRS device 8 is, in other words, a "variable gear ratio steering device," which allows the steering gear ratio of the front wheel steering system 3 to be changed. The front wheel steering system 3 then steers the front wheels 1 according to the steering state (steering angle, or steering direction and amount) of the steering wheel 5, which corresponds to the "control device" in this embodiment of the invention.

[0024] The rear-wheel steering system 4 steers the rear wheels 2 in conjunction with the steering operation of the front wheels 1 by the front-wheel steering system 3 described above. In the example shown in Figure 2, the rear-wheel steering system 4 has an electric actuator 9. The rear-wheel steering system 4 is a type of "steer-by-wire steering system" and steers the rear wheels 2 based on the steering state of the steering wheel 5 and the driving state of the vehicle Ve by operating the electric actuator 9 with an electrical signal from the controller 11, which will be described later.

[0025] In this embodiment of the invention, the vehicle Ve to be controlled can, for example, be configured as a "four-wheel steering vehicle" as described in Patent Document 1 or Patent Document 2. In that case, a detailed description of the vehicle Ve configuration is as described in the specifications of Patent Document 1 or Patent Document 2.

[0026] Furthermore, although not shown in Figure 2, the vehicle Ve actually includes a power source such as an engine, motor, or hybrid drive unit, as well as a power transmission system that transmits the output torque of the power source to the drive wheels. The control device for a four-wheel steering vehicle in this embodiment of the invention can control any vehicle Ve with any drive system.

[0027] Furthermore, the vehicle Ve is equipped with a detection unit 10 and a controller (ECU) 11 to control the front wheel steering system 3 and the rear wheel steering system 4 based on the steering state of the steering wheel 5 and the driving state of the vehicle Ve.

[0028] The detection unit 10 is a device or apparatus for acquiring various data and information necessary for controlling the vehicle Ve, and includes, for example, a power supply unit, a microcomputer, sensors, and an input / output interface. In particular, the detection unit 10 in this embodiment of the invention detects various data for controlling the front wheel steering device 3 and the rear wheel steering device 4. For example, the detection unit 10 has various sensors and devices such as a vehicle speed sensor 10a for detecting vehicle speed, an acceleration sensor 10b for detecting the acceleration of the vehicle Ve, a steering angle sensor 10c for detecting the steering angle of the steering wheel 5 or the rotation angle of the steering shaft (not shown), a steering angle sensor 10d for detecting the steering angles of the front wheel 1 and the rear wheel 2, respectively, and a timer 10e for detecting control time (for example, the steering time of the steering wheel 5 and the steering hold time during which steering is maintained). The detection unit 10 is electrically connected to a controller 11, which will be described later, and outputs electrical signals, etc., corresponding to the detected values ​​or calculated values ​​of the various sensors, devices, etc. as detection data to the controller 11.

[0029] The controller 11 is an electronic control device mainly composed of a microcomputer, and in this embodiment of the invention, the controller 11 controls the vehicle Ve, and in particular controls the front wheel steering device 3 and the rear wheel steering device 4. Various data detected or calculated by the detection unit 10 are input to the controller 11. The controller 11 performs calculations using the input data and pre-stored data and calculation formulas. The controller 11 then outputs the calculation result as a control command signal and is configured to control the vehicle Ve as described above. Although Figure 2 shows an example in which one controller 11 is provided, multiple controllers 11 may be provided for each device or equipment to be controlled, or for each control content.

[0030] As described above, the control device for a four-wheel steering vehicle in this embodiment of the invention aims to suppress the occurrence of resonance and the lateral acceleration or yaw rate of the vehicle Ve that increases due to resonance, even when steering is performed continuously in different directions and the front wheels 1 and rear wheels 2 are steered in opposite phases. To this end, the controller 11 of the vehicle Ve in this embodiment of the invention is configured to perform the control shown in the flowchart of Figure 3 below, for example.

[0031] In the flowchart of Figure 3, first, in step S1, it is determined whether the rear wheels 2 are steered in opposite phases relative to the front wheels 1, or whether the vehicle speed is below the low-speed threshold, as preconditions for control. In this embodiment of the invention, vehicle Ve, like a conventional "four-wheel steering vehicle," steers the front wheels 1 and rear wheels 2 in opposite directions (opposite phases) when traveling at low speed (i.e., when the vehicle speed is below the low-speed threshold). On the other hand, when traveling at high speed (i.e., when the vehicle speed is above the low-speed threshold), steers the front wheels 1 and rear wheels 2 in the same direction (in phase). The control shown in the flowchart of Figure 3 is performed to suppress the occurrence of resonance when the front wheels 1 and rear wheels 2 are steered in opposite phases. Therefore, if the situation is not such that the rear wheel 2 is steered in opposite phase to the front wheel 1, or if the vehicle speed is above the low-speed threshold (i.e., the front wheel 1 and rear wheel 2 are steered in the same phase), and the result in "No" in step S1, the routine shown in the flowchart of Figure 3 is terminated without executing the control of the subsequent steps.

[0032] On the other hand, if the situation is such that the rear wheel 2 is steered in opposite phases to the front wheel 1, or the vehicle speed is below the low-speed threshold (i.e., the front wheel 1 and rear wheel 2 are steered in opposite phases to each other), and the result in a "Yes" in step S1, then proceed to the next step S2.

[0033] In step S2, a determination is made as to whether the first steering maneuver should be performed. In the four-wheel steering control in this embodiment of the invention, steering in either a predetermined direction, that is, steering the vehicle Ve to the right or to the left, is defined as the first steering maneuver, and steering in the opposite direction to the first steering maneuver, performed immediately after the first steering maneuver, is defined as the second steering maneuver. The first and second steering maneuvers are to be performed consecutively within a predetermined time. Therefore, if the second steering maneuver is not performed within a predetermined time after the first steering maneuver has been performed, the first steering maneuver performed after the predetermined time has elapsed will again be the first steering maneuver. Specifically, if, after the first steering maneuver has been performed, a steering hold state in which the steering speed of the first steering maneuver tends to decrease or becomes zero continues for a predetermined time or longer, the first steering maneuver in which the steering wheel 5 is operated in either direction after that steering hold state will again be the first steering maneuver.

[0034] Therefore, in step S2, in order to determine whether the first steering maneuver has been performed, it is determined whether the current steering maneuver is from a steering state that has been maintained for a predetermined time or longer, and whether the absolute value of the steering angular velocity of the front wheel 1 that is turned in response to that steering maneuver is higher than a predetermined threshold A. If the current steering maneuver is from a steering state that has been maintained for a predetermined time or longer, and the absolute value of the steering angular velocity of the front wheel 1 is higher than threshold A, it is determined that the first steering maneuver has been performed. Threshold A is a threshold corresponding to the "first threshold" in this embodiment of the invention. Furthermore, threshold A and the predetermined time are set in advance based on, for example, the results of driving experiments with an actual vehicle or simulations. Alternatively, the absolute value of the steering angular velocity of the rear wheel 2 may be compared with threshold A instead of the steering angular velocity of the front wheel 1. Alternatively, the steering angular velocity of the front wheel 1 or the steering angular velocity of the rear wheel 2 may be estimated from the steering speed or steering angular velocity of the steering wheel 5, and the estimated value may be compared with threshold A. Therefore, if the current steering is not a steering maneuver that has been maintained for a predetermined time or longer, or if the absolute value of the steering angular velocity of the front wheel 1 (or rear wheel 2) is less than or equal to threshold A, and the result is determined to be "No" in step S2, the routine shown in the flowchart of Figure 3 is terminated without executing the control of the subsequent steps.

[0035] On the other hand, if the steering in this case is determined to be performed from a steering state that has been maintained for a predetermined time or longer, and the absolute value of the steering angular velocity of the front wheel 1 (or rear wheel 2) is higher than threshold A, that is, if the first steering operation is determined to have been performed, and the result is "Yes" in step S2, then proceed to the next step S3.

[0036] In step S3, a determination is made as to whether a second steering maneuver has been performed. Specifically, it is determined whether the current steering maneuver occurred within a predetermined time from the first steering maneuver (i.e., not from a steering state that has continued for a predetermined time or longer), whether the steering maneuver is in the opposite direction to the first steering maneuver, and whether the absolute value of the steering angular velocity of the front wheel 1 that is turned in response to that maneuver is higher than a predetermined threshold B (second threshold). If the current steering maneuver occurred within a predetermined time from the first steering maneuver, is in the opposite direction to the first steering maneuver, and the absolute value of the steering angular velocity of the front wheel 1 is higher than threshold B, then it is determined that a second steering maneuver has been performed. In this case as well, instead of comparing the steering angular velocity of the front wheel 1, the absolute value of the steering angular velocity of the rear wheel 2 may be compared with threshold B. Threshold B is a threshold corresponding to the "second threshold" in this embodiment of the invention. Furthermore, threshold B is set in advance, similar to threshold A above, based on, for example, the results of driving experiments with actual vehicles or simulations. Therefore, if the current steering is determined to be "No" in step S3 because it is either steering from a steering state that has continued for a predetermined time or longer since the first steering, or steering in the same direction as the first steering, or the absolute value of the steering angular velocity of the front wheel 1 (or rear wheel 2) is less than or equal to threshold B, then the routine shown in the flowchart of Figure 3 is terminated without executing the control of the subsequent steps.

[0037] On the other hand, if the current steering is performed within a predetermined time from the first steering, is in the opposite direction to the first steering, and the absolute value of the steering angular velocity of the front wheel 1 (or rear wheel 2) is higher than threshold B, that is, if it is determined that the second steering has been performed, and the result is "Yes" in step S3, then proceed to the next step S4.

[0038] In step S4, the steering of the rear wheel 2 is restricted. For example, as shown in the time chart in Figure 4, the steering of the rear wheel 2 is restricted by fixing the steering angle of the rear wheel 2 to 0 or near 0. The time chart in Figure 4 shows an example of control when the vehicle Ve is traveling at a low speed below the low speed threshold. When the first steering is performed during the period from time t11 to time t12, the front wheel 1 and the rear wheel 2 are steered in response to that first steering. In this case, the front wheel 1 and the rear wheel 2 are steered in opposite phases to each other. The first steering is such that the absolute value of the steering angular velocity of the front wheel 1, which is steered in response to that first steering, exceeds the threshold A. If the steering direction reverses at time t12, and steering in the opposite direction to the first steering is performed consecutively (i.e., within a predetermined time), the period from time t12 to time 14, when the steering directions of the front wheel 1 and rear wheel 2 reverse, is considered the second steering, with time t13 in between, when the steering angles of the front wheel 1 and rear wheel 2 become 0 (return to the origin). This second steering is a steering operation in which the absolute value of the steering angular velocity of the front wheel 1, which is steered in response to the second steering, exceeds threshold B. Therefore, since the conditions for determining whether both the first and second steering are performed are met, the steering of the rear wheel 2 in the second steering is restricted. In the example shown in the time chart of Figure 4, from time t13 onward, the steering angle of the rear wheel 2 in the second steering is fixed at 0 or near 0. As shown in the image on the far right of Figure 4, when the steering angle of the rear wheel 2 is fixed near 0, the value of the steering angle is fixed near 0 either before or after the steering direction of the rear wheel 2 reverses. In addition to fixing the steering angle of the rear wheel 2 to 0 or near 0, the steering of the rear wheel 2 may also be restricted by fixing the value of the steering angle of the rear wheel 2 within an arbitrary, predetermined angle range. In this case, the predetermined angle range is set in advance to an appropriate value that yields an effect of restricting the steering of the rear wheel 2, for example, based on the results of actual vehicle driving experiments or simulations.

[0039] As described above, by fixing the steering angle of the rear wheel 2 in the second steering operation to 0, near 0, or within a predetermined angular range, the lateral acceleration acting on the vehicle Ve decreases after time t13 compared to when the steering of the rear wheel 2 is not restricted. Therefore, the occurrence of resonance as described above can be avoided, and the behavior of the vehicle Ve can be stabilized.

[0040] Furthermore, in step S4, for example, as shown in the time chart of Figure 5, the steering of the rear wheels 2 may be restricted by suppressing the control amount of the rear wheels 2, that is, by suppressing the amount of steering of the rear wheels 2 or the amount of change in the steering angle of the rear wheels 2. The time chart of Figure 5 shows an example of control when the vehicle Ve is traveling at a low speed below the low speed determination threshold, similar to the time chart of Figure 4 above. When the first steering is performed during the period from time t21 to time t22, the front wheels 1 and rear wheels 2 are steered in response to the first steering. In this case, the front wheels 1 and rear wheels 2 are steered in opposite phases to each other. The first steering is such that the absolute value of the steering angular velocity of the front wheels 1 steered in response to the first steering exceeds the threshold A. If the steering direction reverses at time t22, and steering in the opposite direction to the first steering is performed consecutively (i.e., within a predetermined time), the period from time t22 to time t24, when the steering directions of the front wheel 1 and rear wheel 2 reverse, with time t23 in between, when the steering angles of the front wheel 1 and rear wheel 2 become 0 (return to the origin), constitutes the second steering. This second steering is a steering operation in which the absolute value of the steering angular velocity of the front wheel 1, which is steered in response to the second steering, exceeds threshold B. Therefore, since the conditions for determining whether both the first and second steering are performed are met, the steering of the rear wheel 2 in the second steering is restricted. In the example shown in the time chart of Figure 5, the amount of change in the steering angle of the rear wheel 2 in the second steering is suppressed from time t23 onward.

[0041] Similarly, in this case, the change in the steering angle of the rear wheel 2 during the second steering maneuver is suppressed, resulting in a reduction in the lateral acceleration acting on the vehicle Ve from time t23 onward compared to when the steering of the rear wheel 2 is not restricted. Therefore, the occurrence of resonance as described above can be avoided, and the behavior of the vehicle Ve can be stabilized.

[0042] As described above, once the steering of the rear wheel 2 in the second steering input is restricted in step S4, the routine shown in the flowchart of Figure 3 is then terminated.

[0043] In the control example described above, thresholds A and B for steering angular velocity are both set as preset values ​​to determine the state of the first and second steering operations. In contrast, in the control device for a four-wheel steering vehicle in this embodiment of the present invention, thresholds A and B may be changed according to the vehicle speed. For example, as shown in Figure 6, thresholds A and B may be changed and set so that they decrease as the vehicle speed increases. The lateral acceleration of the vehicle Ve caused by steering changes depending on the vehicle speed. When the front wheels 1 and rear wheels 2 are steered in opposite phases, the lateral acceleration of the vehicle Ve caused by steering increases as the vehicle speed increases. Therefore, by applying a map as shown in Figure 6, the threshold is reduced as the vehicle speed increases, i.e., as the likelihood of a large lateral acceleration increases, making it easier to execute the control described above (control that limits the steering of the rear wheels 2 in the second steering operation). This avoids restricting the steering of the rear wheels 2 more than necessary, and allows for appropriate control in accordance with the driving state of the vehicle Ve.

[0044] As described above, in the control device for a four-wheel steering vehicle according to the embodiment of this invention, even when the first steering and second steering operations, which may cause resonance, are performed consecutively, the occurrence of resonance can be suppressed by limiting the steering of the rear wheels 2 during the second steering operation. Therefore, according to the control device for a four-wheel steering vehicle according to the embodiment of this invention, the occurrence of resonance can be suppressed and four-wheel steering of the front wheels 1 and rear wheels 2 can be performed appropriately, regardless of the vehicle speed or steering state. [Explanation of symbols]

[0045] 1 Front wheel 2 Rear wheels 3. Front wheel steering system 4. Rear-wheel steering system 5. Steering wheel (control device) 6 Electric Actuator 7 Steering gearbox 8 VGRS equipment 9 Electric Actuator 10 Detection unit 10a Vehicle speed sensor (detection unit) 10b Accelerometer (of the detection unit) 10c (Detection unit) Steering angle sensor 10d (Detection unit) Steering angle sensor 10e (Detection unit) timer 11. Controller (ECU) Vehicle (four-wheel steering vehicle)

Claims

1. A control device for a four-wheel steering vehicle comprising a steering device operated by a driver, a front-wheel steering device for steering the front wheels, and a rear-wheel steering device for steering the rear wheels in conjunction with the steering of the front wheels, and having a motion system that generates resonance at a predetermined frequency, wherein the control device for the four-wheel steering vehicle operates the front-wheel steering device and the rear-wheel steering device based on the operating state of the steering device, The system includes a controller that controls the front wheel steering system and the rear wheel steering system, The aforementioned controller, When the steering device is operated in a predetermined direction from a state in which the steering angle is maintained for a predetermined period of time or longer, a first steering maneuver is performed, and the steering device is operated in a second steering maneuver in the opposite direction to the first steering maneuver, exceeding the steering angle in the state in which the steering angle was maintained, the rear wheels are steered in the opposite direction to the steering direction of the front wheels, If the absolute value of the steering angular velocity of the front wheel or the rear wheel steered in response to the first steering input is higher than a predetermined first threshold, and the absolute value of the steering angular velocity of the front wheel or the rear wheel steered in response to the second steering input is higher than a predetermined second threshold, then the steering of the rear wheel in response to the second steering input is restricted. A control device for a four-wheel steering vehicle, characterized by the following features.

2. A control device for a four-wheel steering vehicle according to claim 1, The aforementioned controller, The steering angle of the rear wheels is fixed to 0 or within a predetermined angle range, thereby restricting the steering of the rear wheels. A control device for a four-wheel steering vehicle, characterized by the following features.

3. A control device for a four-wheel steering vehicle according to claim 1, The aforementioned controller, The amount of steering of the rear wheels is suppressed, thereby limiting the steering of the rear wheels. A control device for a four-wheel steering vehicle, characterized by the following features.

4. A control device for a four-wheel steering vehicle according to any one of claims 1 to 3, The steering state is when the steering speed is decreasing or zero. A control device for a four-wheel steering vehicle, characterized by the following features.

5. A control device for a four-wheel steering vehicle according to any one of claims 1 to 3, The aforementioned controller, The magnitudes of the first threshold and the second threshold are changed according to the vehicle speed of the four-wheel steering vehicle. A control device for a four-wheel steering vehicle, characterized by the following features.

6. A control device for a four-wheel steering vehicle according to claim 5, The aforementioned controller, The higher the vehicle speed, the smaller the magnitudes of the first threshold and the second threshold. A control device for a four-wheel steering vehicle, characterized by the following features.

7. A control device for a four-wheel steering vehicle according to claim 4, The aforementioned controller, The magnitudes of the first threshold and the second threshold are changed according to the vehicle speed of the four-wheel steering vehicle. A control device for a four-wheel steering vehicle, characterized by the following features.

8. A control device for a four-wheel steering vehicle according to claim 7, The aforementioned controller, The higher the vehicle speed, the smaller the magnitudes of the first threshold and the second threshold. A control device for a four-wheel steering vehicle, characterized by the following features.

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