Rear-wheel steering device

Abstract

To provide a rear-wheel steering device that realizes well-balanced rear-wheel steering control that is able to reduce a sense of incongruity based on an operation sound and is able to properly exhibit the response performance of rear-wheel steering.SOLUTION: A rear wheel steering device includes: a rear-wheel steering mechanism capable of setting a control speed of a rear-wheel steering actuator according to a speed of a vehicle; an acquisition unit that acquires traveling operation input information of the vehicle; a correction unit that corrects the control speed, based on the traveling operation input information; and a drive control unit that drives the rear-wheel steering actuator based on a correction result corrected by switching between a case of limiting the control speed and a case of not limiting the control speed.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to rear wheel steering devices. [Background technology]

[0002] Conventionally, vehicles that allow steering of the rear wheels by a rear-wheel steering device in addition to steering of the front wheels by a front-wheel steering device have been put into practical use. The rear-wheel steering device is capable of steering the rear wheels according to the steering angle of the front wheels by an actuator constituted by, for example, a motor, a planetary gear, etc., and the front and rear wheels are steered in the same phase or in opposite phases according to the running state of the vehicle. Steering the rear wheels in addition to the front wheels can contribute to stabilizing the running posture and improving cornering performance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6945799 [Patent Document 2] JP 2019-214311 A Summary of the Invention [Problem to be solved by the invention]

[0004] In a rear wheel steering device, the higher the control speed of the actuator, the better the rear wheel steering performance and the higher the response performance can be obtained. On the other hand, increasing the control speed increases the operating noise, which can cause the vehicle to be less quiet, causing the occupants to feel uncomfortable. In other words, in a rear wheel steering device, if the control speed is slowed down with an emphasis on reducing the operating noise, there are cases in which sufficient response performance cannot be obtained. In addition, if the control speed is increased with an emphasis on responsiveness, there is a problem in that the quietness is insufficient and the occupants feel uncomfortable.

[0005] Therefore, one of the problems that the embodiment of the present invention aims to solve is to provide a rear wheel steering device that can realize well-balanced rear wheel steering control by reducing the discomfort felt by occupants due to operating noise and by appropriately demonstrating the response performance of the rear wheel steering. [Means for solving the problem]

[0006] A rear wheel steering device as an example of the present disclosure includes a rear wheel steering mechanism capable of setting a control speed of the rear wheel steering actuator in accordance with the vehicle speed, an acquisition unit that acquires driving operation input information of the vehicle, a correction unit that corrects the control speed of the rear wheel steering actuator set in accordance with the vehicle speed based on the driving operation input information, and a drive control unit that drives the rear wheel steering actuator by switching between operating sound suppression priority control that limits the control speed or performance priority control that does not limit the control speed based on the correction result of the correction unit.

[0007] According to the above configuration, for example, the control speed of the rear wheel steering actuator is corrected in accordance with the vehicle driving operation (driving operation input information), and switching (distinguishing between) operation sound suppression priority control, which limits the control speed, and performance priority control, which does not limit the control speed, is performed, making it possible to perform a balanced operation sound suppression priority control and performance priority control in accordance with the driving operation state. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is an exemplary schematic diagram showing a vehicle equipped with a rear wheel steering device according to an embodiment. [Diagram 2] FIG. 2 is an exemplary schematic block diagram showing the configuration of the rear wheel steering device according to the embodiment. [Diagram 3] FIG. 3 is an exemplary schematic control map showing the relationship between the control speed and the speed in a case where emphasis is placed on suppression of operating noise and a case where emphasis is placed on performance in the rear wheel steering device according to the embodiment. [Figure 4]FIG. 4 is an exemplary schematic explanatory diagram showing a procedure for limiting and adjusting the control speed of rear-wheel steering in response to a driver input and calculation of a target rear-wheel angle after the limiting and adjusting in a rear-wheel steering device according to the embodiment. [Diagram 5] FIG. 5 is an exemplary schematic explanatory diagram showing a rear wheel steering holding function when slalom running is performed in the rear wheel steering device according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, embodiments and modifications of the present disclosure will be described with reference to the drawings. The configurations of the embodiments and modifications described below, as well as the actions and effects brought about by the configurations, are merely examples and are not limited to the contents described below.

[0010] FIG. 1 is an exemplary schematic diagram showing a vehicle 12 equipped with a rear wheel steering device 10 according to an embodiment.

[0011] The vehicle 12 is equipped with a four-wheel steering system including a front-wheel steering mechanism 14 and a rear-wheel steering mechanism 16. A pair of left and right front wheels 18 can be steered by the front-wheel steering mechanism 14. In addition, a pair of left and right rear wheels 20 can be steered by the rear-wheel steering mechanism 16.

[0012] The front wheels 18 are steered by moving the steering rod 14a in accordance with the steering angle of the steering wheel 22. The rotation of the steering wheel 22 steered by the driver is transmitted to the front wheel steering mechanism 14 via the steering column 22a, and the steering rod 14a moves linearly in the axial direction. This linear movement is transmitted via the tie rod 14b, and the direction of the front wheels 18 changes accordingly. A steering angle sensor is provided on the steering column 22a, which rotates integrally with the steering wheel 22.

[0013] The rear wheel steering mechanism 16 is attached across the wheel side members and vehicle body side members of the suspension mechanism supporting the left and right rear wheels 20. Left and right wheel supports 16b are pivotally connected to a cross member 16a on the vehicle body side. The left and right wheel supports 16b are respectively connected to a steering link 16c pivotally provided on the cross member 16a via left and right tie rods 16d. The rear wheel steering mechanism 16 is driven by a rear wheel steering actuator 24 included in the rear wheel steering device 10. Of a first connecting portion 24a and a second connecting portion 24b provided on both ends of the rear wheel steering actuator 24, the first connecting portion 24a is connected to a first connected portion 16e that is a part of the cross member 16a, and the second connecting portion 24b is connected to a second connected portion 16f that is one end of the steering link 16c. The rear wheels 20 are steered by swinging the steering link 16c by extension and contraction of the rod 24c that is integrally configured with the second connecting portion 24b of the rear wheel steering actuator 24. The rod 24c is extended and contracted relative to the rear wheel steering actuator 24 by linear movement by, for example, the motor M and the planetary gear G that configure the rear wheel steering actuator 24. The rear wheel steering mechanism 16 can steer the rear wheels 20 in the same phase or in the opposite phase relative to the front wheels 18 according to the running state of the vehicle 12. In addition, the response speed of the rear wheel steering mechanism 16 can be controlled by controlling the drive speed of the motor M. The vehicle 12, which is provided with the front wheel steering mechanism 14 and the rear wheel steering mechanism 16, can achieve a more stable running posture and improved cornering performance than a vehicle provided with only the front wheel steering mechanism 14.

[0014] The rear wheel steering mechanism 16 configured as described above can improve the rear wheel steering performance and obtain high response performance as the control speed of the rear wheel steering actuator 24 is increased. On the other hand, increasing the control speed of the rear wheel steering actuator 24 increases the operating noise, for example, the teeth rattle of the planetary gear, which may cause a decrease in quietness of the vehicle 12 and may cause the passengers to feel uncomfortable. In general, when the vehicle 12 is traveling at a low speed, the steering amount of the rear wheels 20 tends to be large, and the operating sound of the rear wheel steering actuator 24 becomes more noticeable. Conversely, when traveling at a high speed, the steering amount of the rear wheels 20 tends to be small and road noise tends to be large, making the operating sound of the rear wheel steering actuator 24 less noticeable. Therefore, during low-speed traveling where sounds such as road noise are less likely to be generated, the control speed of the rear wheel steering actuator 24 may be limited to suppress the generation of operating sounds, and control that emphasizes quietness may be performed. On the other hand, when driving at high speeds where road noise and other sounds are likely to be generated, the operating sounds of the rear wheel steering actuator 24 are less noticeable due to road noise and other sounds, so the limit on the control speed of the rear wheel steering actuator 24 may be lifted and control may be performed that emphasizes the response performance of the rear wheel steering performance.

[0015] However, when the control speed is uniformly limited for each vehicle speed as described above, there are cases where the performance is not satisfactory in the low to medium speed range depending on the operation input for driving by the driver. For example, when returning to straight driving after turning right or left at an intersection, the steering wheel 22 may be quickly steered to the neutral position. In this case, the front wheel steering mechanism 14 directly connected to the steering wheel 22 moves the front wheels 18 in almost the same phase, but the rear wheel steering mechanism 16 is driven by steer-by-wire, so the steering of the rear wheels 20 is delayed. As a result, the steering wheel may be off-center for a certain period of time. In this case, a self-aligning torque acts on the front wheels 18 by the amount that the rear wheels 20 are steered, and the front wheels 18 are steered by the same amount to try to go straight, but the vehicle may become so-called crab-walking and swerve.

[0016] Also, even in slalom driving with fast steering of the steering wheel 22, the steering angle (rear wheel angle) of the rear wheels 20 lags behind the steering angle (front wheel angle) of the front wheels 18. As a result, a delay in the yaw rate occurs, which may result in an error from the ideal driving line.

[0017] Therefore, the rear wheel steering device 10 of this embodiment does not simply control the rear wheel steering mechanism 16 in response to the vehicle speed, but rather controls the rear wheel steering mechanism 16 in consideration of driving operation input information of the vehicle 12. In other words, the above-mentioned problems are eliminated by adding a correction to the control speed of the rear wheel steering actuator 24 taking into consideration the driving operation status of the driver.

[0018] FIG. 2 is an exemplary schematic block diagram showing the configuration of the rear wheel steering device 10. The rear wheel steering device 10 includes a rear wheel steering control unit 28, a storage unit 30, and the like, in addition to the above-mentioned rear wheel steering mechanism 16. The rear wheel steering control unit 28 controls the rear wheel steering mechanism 16 based on the detection results of various sensors 26 mounted on the vehicle 12. The storage unit 30 also stores a map and the like that the rear wheel steering control unit 28 refers to when setting the control speed of the rear wheel steering actuator 24. The map may be, for example, one that defines the relationship between the control speed of the rear wheel steering actuator 24 and the vehicle speed, one that defines the relationship between the control speed of the rear wheel steering actuator 24 and the steering speed of the steering wheel 22, one that defines the relationship between the control speed of the rear wheel steering actuator 24 and the acceleration / deceleration of the vehicle 12, one that defines the relationship between the control speed of the rear wheel steering actuator 24 and the control speed of the rear wheel steering actuator 24 when the steering wheel 22 is returned to the neutral direction, and the like. These maps may be determined in advance, for example, by testing or the like. The above-described map is an example, and the storage unit 30 may hold maps showing correspondences with other driving operation input information.

[0019] The various sensors 26 supply driving operation input information indicating the driving operation status of the driver to the rear wheel steering control unit 28. The vehicle speed sensor 26a detects the amount of rotation or the number of rotations per unit time by, for example, a Hall element provided near the front wheels 18 or the rear wheels 20, and outputs the vehicle speed. The yaw rate sensor 26b detects the yaw rate (the rate of change of the rotation angle in the yaw direction (turning direction)) of the vehicle 12. The acceleration sensor 26c detects the acceleration in the front-rear direction or the left-right direction of the vehicle 12. The steering angle sensor 26d is, for example, a sensor that detects the steering amount of the steering wheel 22, and is configured using, for example, a Hall element. Information regarding the steering direction and steering speed of the steering wheel 22 can also be obtained based on the signal output by the steering angle sensor 26d. The accelerator pedal sensor 26e outputs information regarding the amount and speed of depression of the accelerator pedal, and can be used to detect sudden acceleration of the vehicle 12. The brake pedal sensor 26f outputs information regarding the depression amount and depression speed of the brake pedal, and can be used to detect sudden deceleration of the vehicle 12. Note that the sensor 26 shown in Fig. 2 is just one example, and any sensor that outputs driving operation input information indicating the driving operation status of the driver may be used, and the output results may be sequentially provided to the rear wheel steering control unit 28.

[0020] The rear wheel steering control unit 28 includes an acquisition unit 28a, a control speed setting unit 28b, a correction unit 28c, a drive control unit 28d, and the like.

[0021] The acquisition unit 28a acquires the detection results of the various sensors 26, that is, the driving operation input information of the vehicle 12. The acquisition unit 28a acquires, for example, steering speed information of the front wheel steering of the vehicle 12 from the steering angle sensor 26d as the driving operation input information. The acquisition unit 28a also acquires acceleration / deceleration information of the vehicle 12 from the acceleration sensor 26c, the accelerator pedal sensor 26e, the brake pedal sensor 26f, etc. as the driving operation input information. The acquisition unit 28a also acquires steering direction information of the front wheel steering of the vehicle 12 from the steering angle sensor 26d, the yaw rate sensor 26b, etc. as the driving operation input information. The acquisition unit 28a also acquires reversal operation information indicating that the front wheel steering of the vehicle 12 has been reversed at a predetermined speed or faster, that is, that the vehicle has traveled in a slalom manner, from the steering angle sensor 26d, the yaw rate sensor 26b, etc. as the driving operation input information.

[0022] The control speed setting unit 28b can set the basic control speed (basic control speed) of the rear wheel steering actuator 24 based on the vehicle speed of the vehicle 12 obtained from the vehicle speed sensor 26a by referring to a map stored in the memory unit 30 that defines the relationship between the control speed of the rear wheel steering actuator 24 and the vehicle speed.

[0023] Further, the correction unit 28c corrects the basic control speed of the rear wheel steering actuator 24, which is set by the control speed setting unit 28b in accordance with the vehicle speed, based on the driving operation input information acquired by the acquisition unit 28a from the various sensors 26. The correction by the correction unit 28c will be described in detail later.

[0024] Based on the correction result of the correction unit 28c, the drive control unit 28d switches (distinguishes) between operating noise suppression priority control, which limits the control speed of the rear wheel steering actuator 24, and performance priority control, which does not limit the control speed, and generates a drive command to drive the rear wheel steering actuator 24, and outputs it to the rear wheel steering actuator 24.

[0025] In addition, the switching between the operation sound suppression priority control and the performance priority control may be performed by the correction unit 28c generating a switching signal for instructing the switching between the operation sound suppression priority control and the performance priority control and supplying it to the drive control unit 28d, and the drive control unit 28d performing the switching process based on the switching signal. In another embodiment, the drive control unit 28d may acquire a correction result (correction content) from the correction unit 28c, for example, correction information required for the control switching obtained by referring to various control maps stored in the storage unit 30, and generate a switching signal in the drive control unit 28d based on the correction information to perform the switching between the operation sound suppression priority control and the performance priority control. In the following description, an example will be shown in which the correction unit 28c generates a switching signal instructing the switching between the operation sound suppression priority control and the performance priority control, and the drive control unit 28d performs the control switching process of the rear wheel steering actuator 24 based on the switching signal.

[0026] The details of rear wheel steering control by the rear wheel steering device 10 configured as described above will be described. For example, a sense of discomfort such as swerving when returning to straight driving after turning right or left at an intersection becomes apparent when the control of the rear wheels 20 is delayed with respect to the input of the steering wheel 22. That is, the sooner the steering wheel 22 is steered, the more likely this is to occur. On the other hand, in a scene where the steering is fast, it can be considered that the driver is operating the steering wheel 22 that much more quickly and that the behavior of the vehicle 12 is also changing rapidly. In such a case, it can be said that the operating sound of the rear wheel steering actuator 24 is difficult for the driver to recognize even when the vehicle speed is low. That is, it can be considered that the operating sound is not noticeable.

[0027] Therefore, the correction unit 28c corrects the control speed (basic control speed) determined by the control speed setting unit 28b based on the vehicle speed, based on the driving operation input information (driver's driving operation status) of the vehicle 12. The correction unit 28c corrects the control speed of the rear wheel steering actuator 24 based on, for example, the steering speed of the steering wheel 22, the acceleration / deceleration of the vehicle 12, and whether the steering direction of the steering wheel 22 is a neutral return direction or a non-neutral direction (increased turning direction), and realizes this by operating sound suppression priority control that limits the control speed of the rear wheel steering actuator 24 or performance priority control that does not limit the control speed. In other words, in a situation where performance is important (a situation where sound is not easily noticeable), even when the vehicle speed is low, the limit on the control speed is temporarily relaxed (operating sound is allowed to occur in a situation where it is not easily noticeable), thereby improving the performance of the vehicle 12 and simultaneously achieving measures against operating sound.

[0028] An individual example of the correction by the correction unit 28c will be specifically described. First, the correction according to the steering speed of the steering wheel 22 will be described. The rear wheel steering control unit 28 basically controls the rear wheel steering actuator 24 at a control speed according to the vehicle speed set by the control speed setting unit 28b, but in addition to this, the correction unit 28 adjusts (corrects) the limit of the control speed of the rear wheel steering actuator 24 according to the steering speed of the steering wheel 22. That is, when the steering wheel 22 is moved quickly, the correction unit 28c generates a switching signal for switching to control that prioritizes the behavior of the vehicle 12, and releases the limit of the control speed of the rear wheel steering actuator 24. That is, the generation of operating noise is permitted, but in a scene where the steering wheel 22 is moved quickly, the behavior of the vehicle 12 is also moving violently, so that the operating noise is less noticeable, and therefore, a performance-priority control that prioritizes the response performance of the vehicle 12 is executed. That is, it is possible to reduce the discomfort due to the operating noise while obtaining the response performance of the vehicle 12. On the other hand, when the steering wheel 22 is operated slowly, the behavior of the vehicle 12 also changes slowly, and the operating sound of the rear wheel steering actuator 24 becomes noticeable when the rear wheel steering actuator 24 is operated. Therefore, when the steering wheel 22 is operated slowly, the correction unit 28c generates a switching signal for switching to control that prioritizes reduction of the operating sound, and limits the control speed of the rear wheel steering actuator 24 according to the operation speed of the steering wheel 22 and the vehicle speed, thereby executing the operating sound suppression priority control. In other words, the discomfort caused by the operating sound can be reduced.

[0029] Next, a correction according to acceleration / deceleration will be described in the case where the behavior of the vehicle 12 changes significantly due to the acceleration / deceleration state of the vehicle 12, for example, the operation of the accelerator pedal or the brake pedal. While the vehicle 12 is traveling, the rear wheel steering control unit 28 basically controls the rear wheel steering actuator 24 at a control speed according to the vehicle speed set by the control speed setting unit 28b. In addition, the rear wheel steering control unit 28 adjusts (corrects) the limit of the control speed of the rear wheel steering actuator 24 according to the acceleration / deceleration of the vehicle 12 (accelerator pedal operation or brake pedal operation). That is, when the vehicle 12 is rapidly accelerated or decelerated, the correction unit 28c generates a switching signal for switching to control that prioritizes the behavior of the vehicle 12, and releases the limit of the control speed of the rear wheel steering actuator 24. That is, the generation of operating noise is permitted, but when the vehicle 12 is rapidly accelerated or decelerated, the behavior of the vehicle 12 also changes drastically, so that the operating noise is less noticeable. Therefore, a performance-priority control that prioritizes the response performance of the vehicle 12 is executed. That is, it is possible to reduce the discomfort caused by the operating noise while obtaining the response performance of the vehicle 12. On the other hand, when sudden acceleration is not occurring, the behavior of the vehicle 12 changes slowly, and the operating sound of the rear wheel steering actuator 24 becomes noticeable when the rear wheel steering actuator 24 is operated. Therefore, when sudden acceleration is not occurring, the correction unit 28c generates a switching signal for switching to control that prioritizes reduction of the operating sound, and executes operating sound suppression priority control that limits the control speed of the rear wheel steering actuator 24 according to the vehicle speed to reduce the operating sound. In other words, it is possible to reduce the discomfort caused by the operating sound.

[0030] FIG. 3 is an exemplary schematic control map showing the relationship between the control speed and the speed when emphasis is placed on suppression of operating noise in the rear wheel steering device 10 and when emphasis is placed on performance. In FIG. 3, the horizontal axis is vehicle speed. The vertical axis is the reference control speed of the rear wheel steering actuator 24. Map A shown by the dashed line indicates emphasis on suppression of operating noise, and when control is performed at or below map A, the operating noise can be considered to be at a level that is not noticeable. On the other hand, map B shown by the solid line takes into consideration the performance of the vehicle 12, and is the control speed of the rear wheel steering actuator 24 that is required when it is desired to fully utilize the performance of the vehicle 12. A control speed variable region E between maps A and B is a region where performance decreases if emphasis is placed on suppression of operating noise, and where the generation of operating noise becomes noticeable if emphasis is placed on performance. Therefore, by setting (correcting) the control speed within the control speed variable region E according to the driving style of the vehicle 12 (travel operation input information for driving) and the vehicle speed, as described above, it becomes possible to control the rear wheel steering while balancing between prioritizing the suppression of operational noise of the rear wheel steering actuator 24 and prioritizing the performance of the vehicle 12. In other words, the above-mentioned operational noise suppression priority control is control that prioritizes operational noise suppression while minimizing performance degradation, and performance priority control is control that prioritizes performance while minimizing degradation of the operational noise suppression effect.

[0031] Next, a correction will be described for returning the steering wheel 22 to the neutral direction, such as returning to straight driving after turning right or left at an intersection, or returning from a turning state to a straight state after making a U-turn. In general, the steering speed of the steering wheel 22 to return to the neutral direction (steering to the center position) is faster than that of steering to a non-neutral direction for turning. When steering to return to the neutral direction, if the rear wheel steering actuator 24 is limited at the same control speed as the steering wheel 22 is turned based on the vehicle speed, the control speed is severely limited. In this case, the front wheels 18 return in response to the steering of the steering wheel 22, but the rear wheels 20 return with a delay because the speed is limited. In this case, the vehicle 12 tries to go straight. In other words, the front wheels 18 want to return to a straight driving position, but the front wheels 18 turn in the opposite direction to the extent that the rear wheels 20 are turned, resulting in a state in which the vehicle 12 goes diagonally. Therefore, the correction unit 28c refers to a dedicated map when the steering wheel 22 is returned to the neutral direction. The dedicated map in this case makes it easier for the rear wheels 20 to return to the center when the steering wheel 22 is returned to the neutral direction. In other words, when the steering wheel 22 is returned to the neutral direction, the correction unit 28c generates a switching signal for switching control so as to prioritize the behavior of the vehicle 12 over the case of turning the steering wheel 22 further (steering to a non-neutral direction) and release the limit on the control speed of the rear wheel steering actuator 24. In other words, the performance priority control is executed. For example, the correction control of the control speed is not executed. As a result, it is possible to suppress the occurrence of skewing (steering wheel off-center), which is likely to occur when turning right or left at an intersection and returning to straight driving. In this case, the occurrence of operating noise is permitted, but when the steering wheel 22 is returned to the neutral direction, the steering speed is fast and the behavior of the vehicle 12 changes drastically, so the operating noise is less noticeable. Therefore, it is possible to reduce the discomfort caused by the operating noise while obtaining the response performance of the vehicle 12. On the other hand, when the steering wheel 22 is turned further, the steering speed is slower than when the steering wheel is returned to the neutral direction, and the behavior of the vehicle 12 tends to change more slowly. In other words, the operating sound of the rear wheel steering actuator 24 becomes more noticeable when the rear wheel steering actuator 24 operates.Therefore, in this case, a switching signal is generated to switch the control so as to limit the control speed of the rear wheel steering actuator 24 according to the vehicle speed. In other words, an operation noise suppression priority control that reduces the operation noise is executed. As a result, the discomfort caused by the operation noise can be reduced.

[0032] Fig. 4 is a diagram for explaining the above-mentioned control in summary, and is an exemplary and schematic explanatory diagram showing a procedure for limiting and adjusting the control speed of the rear wheel steering according to the driver's input and a calculation of the target rear wheel angle after the limiting and adjusting in the rear wheel steering device 10. Note that Fig. 4 shows a case where steering speed information of the front wheel steering (steering wheel 22) of the vehicle 12 is used as driving operation input information.

[0033] First, in a first step, the rear wheel steering control unit 28 (correction unit 28c) compares a control speed set in a map (map A in FIG. 3) that prioritizes suppression of operating noise based on the vehicle speed of the vehicle 12 with a control speed set in a variable control speed map based on the steering angle during driving, and adopts the larger control speed. For example, when the steering wheel 22 is steered quickly, the control speed of the rear wheel steering actuator 24 is adopted to the release side (the side that moves faster). Note that in the first step, when the acceleration information of the vehicle 12 is referred to as the driving operation input information and the acceleration / deceleration is large, the control speed of the rear wheel steering actuator 24 is adopted to the release side (the side that moves faster). Note that when the steering wheel 22 indicates steering to the neutral direction as the driving operation input information, the side that moves the rear wheel steering actuator 24 faster (the release side) is adopted.

[0034] Next, in the second step, the control speed adopted in the first step is compared with the control speed set in the performance-oriented map (map B in FIG. 3) based on the vehicle speed of the vehicle 12, and the smaller value is adopted. In this case, the performance-oriented map B becomes the upper limit value, but if the control speed adopted in the first step is below the line of the performance-oriented map B, the value obtained by prioritizing the suppression of operating noise adopted in the first step is adopted. Also, if the control speed set in the performance-oriented map B based on the vehicle speed is smaller, this value is the upper limit value, so the performance-oriented control speed is adopted. At this stage, the control speed of the rear wheel steering actuator 24 based on the current driving operation input information of the vehicle 12 is determined. In other words, the correction unit 28c generates information (switching signal) for switching between the operating sound suppression priority control that limits the control speed and the performance priority control that does not limit the control speed by determining the control speed of the rear wheel steering actuator 24 based on the driving operation input information.

[0035] Then, the rear wheel steering control unit 28 (drive control unit 28d) calculates a final target rear wheel angle (after limitation) by limiting the amount of change (late limit) based on the control speed (switching signal) determined by the correction unit 28c with respect to the target angle (target rear wheel angle) of the rear wheels 20 that are originally intended to proceed based on the steering of the steering wheel 22. In other words, the rear wheel steering actuator 24 is controlled based on the target rear wheel angle after limitation. As a result, a well-balanced rear wheel steering control can be realized that can simultaneously reduce the discomfort felt by the driver (passenger) due to the operating sound and appropriately exhibit the response performance of the rear wheel steering.

[0036] Regarding the delay in the yaw rate during slalom driving (driving in which the vehicle 12 performs a front wheel steering reversal operation at a predetermined speed or faster), in a fast slalom, the vehicle 12 is in a situation where it is turning violently to the left and right. Therefore, it can be said that there is no longer any advantage to enhancing the yaw response of the rear wheels 20 when the steering wheel 22 is input too quickly. Therefore, when the steering wheel 22 is being switched at a speed faster than a certain level, the current position is maintained until the target angle of the rear wheels 20 matches the actual rear wheel angle. In other words, the correction unit 28c maximizes the limit on the control speed of the rear wheel steering actuator 24 and temporarily stops the rear wheel steering control.

[0037] Here, consider a case where the control speed of the rear wheels 20 is limited with an emphasis on suppressing operating noise during slalom driving. In this case, as shown in Fig. 5, a delay occurs on the rear wheels 20 side with respect to the reversal (e.g., from left to right) of the front wheel angle SA of the front wheels 18 based on the steering of the steering wheel 22 during slalom driving. For example, the actual rear wheel angle SC (delayed target rear wheel angle) becomes the target rear wheel angle SB in the case where there is no delay or control speed limit for the front wheel angle SA. In this case, the rear wheels 20 continue to turn further to the left at the target rear wheel angle SB (e.g., left) when the front wheels 18 are steered left until the target rear wheel angle SB is reached, causing a delay in the yaw rate.

[0038] Therefore, for example, when the steering angle sensor 26d or the like detects slalom driving (point P in the figure), that is, when a fast turn is detected, the correction unit 28c generates a switching signal to switch to control for correcting the limit of the control speed of the rear wheel steering actuator 24 to the maximum (for example, control speed = 0), and maintains the current rear wheel angle (from point P1 in the figure). That is, further turning of the rear wheels 20 to the left is stopped. As a result, an increase in the yaw rate in the direction opposite to the direction of the front wheels 18 can be prevented. Also, the correction unit 28c corrects the limit of the control speed of the rear wheel steering actuator 24 to the maximum (switching to operation sound suppression priority control), thereby making it possible to avoid the generation of operation sound.

[0039] Then, when the target rear wheel angle SB coincides with the actual rear wheel angle SC (point P2 in the figure), that is, when the target rear wheel angle SB returns to the position of the actual rear wheel angle SC after the steering wheel 22 is steered in the opposite direction, the correction unit 28c resumes control of the rear wheel steering actuator 24 so as to resume control of the rear wheels 20. As a result, an increase in the yaw rate in the direction opposite to the direction of the front wheels 18 can be prevented.

[0040] In this manner, in a configuration in which the control speed of the rear wheel steering actuator 24 is corrected, it is possible to reduce deviation from the ideal driving line that may occur due to a delay in the yaw rate when slalom driving is performed, and it is possible to obtain appropriate response performance of the vehicle 12. In addition, at that time, the control speed of the rear wheel steering actuator 24 temporarily becomes 0, so the generation of operating noise is avoided. As a result, it is possible to contribute to reducing the discomfort caused by the operating noise.

[0041] As described above, according to this embodiment, the rear wheel steering device 10 includes the rear wheel steering mechanism 16 capable of setting the control speed of the rear wheel steering actuator 24 according to the vehicle speed of the vehicle 12, an acquisition unit 28a that acquires driving operation input information of the vehicle 12, a correction unit 28c that corrects the control speed of the rear wheel steering actuator 24 set according to the vehicle speed based on the driving operation input information, and a drive control unit 28d that switches between operation sound suppression priority control that limits the control speed and performance priority control that does not limit the control speed based on the correction result of the correction unit 28c, and drives the rear wheel steering actuator 24. According to this configuration, for example, the control speed of the rear wheel steering actuator 24 is corrected according to the driving operation (driving operation input information) of the vehicle 12, and switching (distinguishing between) operation sound suppression priority control that limits the control speed and performance priority control that does not limit the control speed is performed, making it possible to perform a well-balanced operation sound suppression priority control and performance priority control according to the driving operation state.

[0042] In the above embodiment, the acquisition unit 28a may acquire steering speed information of the front wheel steering of the vehicle 12 as the driving operation input information, and the correction unit 28c may correct the control speed according to the steering speed information. With this configuration, it is possible to switch (distinguish) between operation sound suppression priority control that limits the control speed in response to a behavior change such as sudden steering of the vehicle 12 and performance priority control that does not limit the control speed, thereby making it possible to perform a well-balanced operation sound suppression priority control and performance priority control according to the driving operation state.

[0043] In the above embodiment, the acquisition unit 28a may acquire acceleration / deceleration information of the vehicle 12 as the driving operation input information, and the correction unit 28c may correct the control speed according to the acceleration / deceleration information. With this configuration, it is possible to switch (distinguish) between operation sound suppression priority control that limits the control speed in response to behavior changes such as sudden acceleration or deceleration of the vehicle 12 and performance priority control that does not limit the control speed, thereby making it possible to perform a well-balanced operation sound suppression priority control and performance priority control according to the driving operation state.

[0044] In the above embodiment, the acquisition unit 28a may acquire steering direction information of the front wheel steering of the vehicle 12 as the driving operation input information, and the correction unit 28c may execute correction control to limit the control speed when the steering direction information indicates steering to a neutral steering direction, and may not execute correction control of the control speed when the steering direction information indicates steering to a non-neutral steering direction. With this configuration, switching (distinguishing between) between operation sound suppression priority control that limits the control speed and performance priority control that does not limit the control speed is performed in response to a behavior change when the vehicle 12 returns from a turning state to a straight driving state, making it possible to perform a well-balanced operation sound suppression priority control and performance priority control according to the driving operation state.

[0045] Also, in the above embodiment, the acquisition unit 28a acquires, as the driving operation input information, reversal operation information indicating that a reversal operation of the front wheel steering of the vehicle 12 was performed at a predetermined speed or faster, and when the reversal operation information is acquired, the correction unit 28c may maximize the limit on the control speed to hold the current rear wheel steering angle until the target steering angle of the rear wheels 20 by the rear wheel steering matches the actual steering angle of the rear wheels 20, and release the maximum limit on the control speed after they match. According to this configuration, in a configuration in which the control speed of the rear wheel steering actuator 24 is corrected, when slalom driving is performed, it is possible to reduce deviation from the ideal driving line that may occur due to a delay in the yaw rate.

[0046] Furthermore, when the correction unit 28c sets the control speed based on the driving operation input information, the correction unit 28c may set the control speed in a first step and a second step. In the first step, the control speed set in a map prioritizing suppression of operating noise based on the vehicle speed of the vehicle 12 is compared with the control speed set in a variable control speed map based on the steering angle during driving, and the larger control speed is adopted. In the second step, the control speed adopted in the first step is compared with the control speed set in a map prioritizing performance based on the vehicle speed of the vehicle 12, and the smaller value is adopted to determine the control speed of the rear wheel steering actuator 24 based on the current driving operation input information of the vehicle 12. With this configuration, an appropriate control speed of the rear wheel steering actuator 24 can be easily determined.

[0047] 4, the correction unit 28c generates a switching signal instructing switching between operational sound suppression priority control and performance priority control, and the drive control unit 28d performs control switching processing for the rear wheel steering actuator 24 based on the switching signal. In other embodiments, the drive control unit 28d may acquire a correction result (correction content) from the correction unit 28c, for example, correction information required for control switching obtained by referring to various control maps stored in the storage unit 30. Then, the drive control unit 28d may generate a control switching signal based on the acquired correction information and determine whether to control with operational sound suppression priority control or performance priority control, thereby obtaining a similar effect.

[0048] 1 shows an example in which the rear wheel steering actuator 24 is configured with a motor M and a planetary gear G, but the configuration of the rear wheel steering actuator 24 is not limited to this. For example, the actuator 24 may be configured by combining a motor M with a belt, and the same effect can be obtained.

[0049] Although the embodiment and the modified examples of the present disclosure have been described above, the above-mentioned embodiment and the modified examples are merely examples and are not intended to limit the scope of the invention. The above-mentioned novel embodiment and modified examples can be implemented in various forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. The above-mentioned embodiment and modified examples are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0050] 10...rear wheel steering device, 12...vehicle, 14...front wheel steering mechanism, 16...rear wheel steering mechanism, 18...front wheel, 20...rear wheel, 22...steering wheel, 24...rear wheel steering actuator, 26...sensor, 28...rear wheel steering control unit, 28a...acquisition unit, 28b...control speed setting unit, 28c...correction unit, 28d...drive control unit.

Claims

1. a rear wheel steering mechanism capable of setting a control speed of a rear wheel steering actuator in accordance with a vehicle speed; An acquisition unit that acquires driving operation input information of the vehicle; a correction unit that corrects the control speed of the rear wheel steering actuator, which is set in accordance with the vehicle speed, based on the driving operation input information; a drive control unit that switches between an operating noise suppression priority control that limits the control speed and a performance priority control that does not limit the control speed based on a correction result of the correction unit, and drives the rear wheel steering actuator; A rear wheel steering device equipped with

2. The acquisition unit acquires steering speed information of front wheel steering of the vehicle as the driving operation input information, The rear wheel steering device according to claim 1 , wherein the correction unit corrects the control speed in accordance with the steering speed information.

3. The acquisition unit acquires acceleration / deceleration information of the vehicle as the driving operation input information, The rear wheel steering device according to claim 1 , wherein the correction unit corrects the control speed in accordance with the acceleration / deceleration information.

4. The acquisition unit acquires steering direction information of front wheel steering of the vehicle as the driving operation input information, 2. The rear wheel steering device according to claim 1, wherein the correction unit executes correction control to limit the control speed when the steering direction information indicates steering toward a neutral steering direction, and does not execute correction control of the control speed when the steering direction information indicates steering toward a non-neutral steering direction.

5. The acquisition unit acquires, as the driving operation input information, reversal operation information indicating that a reversal operation of the front wheel steering of the vehicle has been performed at a predetermined speed or faster, 2. The rear wheel steering device according to claim 1, wherein, when the reversal operation information is acquired, the correction unit maximizes the limit on the control speed to hold the current rear wheel steering angle until a target steering angle of the rear wheels due to rear wheel steering matches an actual steering angle of the rear wheels, and releases the maximum limit on the control speed after the target steering angle matches an actual steering angle of the rear wheels.

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