JPH0134185B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a four-wheel steering system for a vehicle that steers the rear wheels in response to the steering of the front wheels. This relates to a system that allows lane changes to be made with good responsiveness in the area.

(Prior Art) Various types of four-wheel steering devices for vehicles of this type have been known. For example, JP-A-55-
In the system disclosed in Publication No. 91457, the rear wheels are in opposite phase to the front wheels in a low vehicle speed range, and are in the same phase as the front wheels in a medium and high vehicle speed range. Furthermore, in the system disclosed in Japanese Patent Application Laid-Open No. 56-167562, the steering ratio is zero in the low vehicle speed range, and the rear wheels are in the same phase as the front wheels in the medium and high vehicle speed ranges. In other words, in both medium and high vehicle speed ranges, the rear wheels are in the same phase as the front wheels to facilitate lane changes and the like.

(Problem to be Solved by the Invention) By the way, when changing lanes in a medium to high vehicle speed range, in order to improve the response, it is usually necessary to
It is necessary to generate a large lateral acceleration (hereinafter referred to as lateral G). Now, if we look in detail at the process by which this lateral G is generated, starting from the start of the steering operation, first, a slip angle is generated in the front wheels due to the steering operation, and then a lateral force (cornering force) is generated in the front wheels. Yaw rate occurs. Therefore, a slip angle is subsequently generated in the rear wheel, which causes a lateral force to be generated in the rear wheel and a lateral G.

However, in the conventional system described above, since the rear wheels are steered in the same phase at the same time as the front wheels start turning, the amount of yaw rate generated is small, and moreover, this yaw rate occurs at the same time as the front wheels start turning. slightly later than that. For this reason, the lateral G cannot be increased, and as a result, the improvement in responsiveness during lane changes and the like is not as noticeable as compared to a normal two-wheel steered vehicle.

The present invention has been made in view of the above points, and at the beginning of front wheel steering, the rear wheels are steered in the opposite phase to the front wheel steering direction, and then the rear wheels are steered in the front wheel steering direction. By steering in the same phase, the amount of yaw rate generated is increased and the timing of its occurrence is brought forward, resulting in a large lateral G, which is useful when changing lanes at medium to high vehicle speeds. The purpose is to significantly improve responsiveness.

In this case, especially when the front wheels are steered relatively significantly in a high vehicle speed range, the driver is requesting a quick lane change, so the responsiveness of the lane change should be further increased than in the middle vehicle speed range. is desirable. From this point of view, an object of the present invention, in addition to the above-mentioned object, is to vary the delay time from when the front wheels start turning to when the rear wheels start turning in the same phase as the front wheels, so that the In situations where a quick lane change is required, by setting this delay time shorter than when required at medium vehicle speeds, lateral force is generated on the rear wheels more quickly and in a shorter time than at medium vehicle speeds. It also enables quick lane changes, which is especially required at high vehicle speeds.

(Means for Solving the Problem) In order to achieve the above object, the configuration of the present invention includes a steering device that steers the front wheels, a rear wheel steering device that steers the rear wheels, and a steering device that steers the front wheels and a rear wheel steering device that steers the rear wheels. At the beginning of the front wheel turning in the area, the rear wheels are steered in the opposite phase to the front wheel turning direction, and then, after a predetermined delay time from the start of front wheel turning, the rear wheels are turned to the same phase as the front wheel turning direction. A control device is provided to control the operation of the rear wheel steering device so as to steer the vehicle. Furthermore, the predetermined delay time is set to be shorter when the vehicle is traveling at high speed than when traveling at medium speed, at least when the front wheels are steered relatively largely.

(Function) With the above configuration, in the present invention, when the front wheels are steered at medium to high vehicle speeds, the rear wheels are first steered in a phase opposite to the front wheels. As a result, the amount of yaw rate generated increases and the timing of its occurrence becomes earlier.

Thereafter, when a predetermined delay time has elapsed from the start of steering of the front wheels, the rear wheels are steered in the same phase as the front wheels at this point. As a result, as the above-mentioned large yaw rate occurs, the slip angle of the rear wheels becomes large, and a large lateral force acts on the rear wheels, which generates a large lateral G and allows the vehicle to change lanes with good response. It turns out.

In particular, when the front wheels are steered relatively significantly in a high vehicle speed range and a faster lane change is required, the rear wheels are steered to the same phase as the front wheels earlier than when required in a medium speed range. Ru. This ensures that a large yaw rate is generated by steering the rear wheels to the opposite phase in the previous stage, and lateral force is generated on the rear wheels earlier, resulting in even more responsiveness than at medium vehicle speeds. A good lane change takes place.

(Effects of the Invention) As explained above, according to the four-wheel steering system for a vehicle of the present invention, in the middle to high vehicle speed range, at the beginning of front wheel steering, the rear wheels are steered in the opposite phase, After that, the rear wheels are steered in the same phase after a predetermined delay time after the start of steering of the front wheels, which promotes the generation of a large yaw rate, making it possible to generate lateral acceleration earlier and to increase the amount of generation. It is possible to improve the responsiveness of the vehicle when driving, etc. Furthermore, in situations where the driver requests a quick lane change in a high vehicle speed range, the delay from the start of front wheel turning until the rear wheels begin to be steered in the same phase as the front wheels is longer than in the middle vehicle speed range. Since it is set shorter than that, it is possible to generate a large yaw rate while generating lateral force on the rear wheels at an early stage, making it possible to change lanes with even better responsiveness.

(Example) Hereinafter, an example of the present invention will be described based on the drawings.

FIG. 1 shows the overall configuration of a four-wheel steering system for a vehicle showing a first embodiment of the present invention, in which 1 indicates left and right front wheels 2.
A steering device for steering a and 2b,
The steering device 1 includes a steering wheel 3, a rack and pinion mechanism 4, and left and right tie rods 5, 5.
and left and right knuckle arms 6, 6.

Reference numeral 7 denotes a rear wheel steering device for steering left and right rear wheels 8a, 8b.
and a rod 11 extending in the lateral direction of the vehicle body and connected via tie rods 10, 10. The rod 11 has a rack 12 formed on the rod 11.
The pinion 13 is moved in the lateral direction of the vehicle by the rotation of a pinion 13 that meshes with the pinion 13, and the pinion 13 is rotated by a pinion drive pulse motor 16 via a transmission mechanism 15 consisting of a pinion shaft 14 and a pair of bevel gears 15a and 15b. possible to be connected. Further, a power cylinder 17 is connected to the rod 11, which uses the rod 11 as an operating rod. The power cylinder 17 has a left-turning hydraulic chamber 17b and a right-turning hydraulic chamber 17c, which are partitioned in the lateral direction of the vehicle body by a piston 17a fixed to the rod 11.
and each hydraulic chamber 17b, 17
c through hydraulic passages 17d and 17e, respectively,
It communicates with a control valve 18 that controls the oil supply direction and oil pressure to the power cylinder 17, and a hydraulic pump 21 is connected to the control valve 18 via an oil supply passage 19 and an oil return passage 20. The control valve 18 detects the rotational direction of the pinion shaft 14 and communicates the oil supply passage 19 with the left rotation hydraulic chamber 17b when the rear wheels 8a, 8b are steered to the left (counterclockwise in the figure). At the same time, the right turning hydraulic chamber 17c is communicated with the oil return path 20, while the communication state is reversed to the above when the rear wheels 8a, 8b are steered to the right (clockwise in the figure).
At the same time, the hydraulic pressure from the hydraulic pump 21 is applied to the pinion shaft 1.
It reduces the pressure to the pressure according to the rotational force of 4,
When the pinion 13 moves the rod 11 in the lateral direction of the vehicle body, pressure oil is supplied to the power cylinder 17 to assist the rod 11 in the lateral direction of the vehicle body.

Furthermore, 22 is a vehicle speed sensor that detects vehicle speed;
3 is a front wheel steering angle sensor that detects the steering amount of the steering wheel 3 and detects the front wheel steering angle; 24 is a rear wheel steering angle sensor that detects the displacement position of the rod 11 of the rear wheel steering device 7 and detects the rear wheel steering angle. A vehicle speed signal, a front wheel turning angle signal, and a rear wheel turning angle signal from each of the above-mentioned sensors 22 to 24 are input to a controller 25, respectively.

The controller 25 constitutes a control device that controls the operation of the motor 26 for driving the hydraulic pump 21 and the pulse motor 16. The controller 25 has a control device that controls the operation of the motor 26 and the pulse motor 16 for driving the hydraulic pump 21. As shown in FIG. In contrast to the gradual increase characteristic of the front wheel steering angle shown by the thin line, when the front wheel turning angle is relatively large, the time at the start of front wheel turning is as shown by the thick solid line and the thick dashed-dotted line. During the predetermined delay times Δt1 and Δt2 from
After the passage of , a characteristic is stored in advance in which the rear wheel steering angle is zero and gradually increases in the same phase as the front wheel steering angle increases.

Therefore, the predetermined delay time Δt2 for the rear wheel turning angle characteristic in the high vehicle speed range, indicated by the dashed line, is set shorter than the predetermined delay time Δt1 for the rear wheel turning angle characteristic in the medium vehicle speed range, indicated by the solid line. .

Then, the controller 25 selects the rear wheel steering characteristic of the solid line or the dashed line based on the vehicle speed signal from the vehicle speed sensor 22, and also selects the rear wheel steering characteristic based on the front wheel steering angle signal from the front wheel steering angle sensor 23. The start of front wheel turning in a high vehicle speed range is determined and detected, and upon this detection, feedback control is performed based on the rear wheel turning angle signal from the rear wheel turning angle sensor 24, and the selected rear wheel turning angle characteristics shown in FIG. 2 are performed. By controlling the operation of both motors 16 and 26 so that the rear wheels 8a and 8b are steered to opposite phases during a predetermined delay time Δt1 or Δt2, and after this delay time has passed, they are steered to the same phase. The rear wheel steering device 7 is configured to operate and control the rear wheel steering device 7 so as to do so.

Therefore, in the above embodiment, when starting front wheel steering in a medium to high vehicle speed range, during the initial predetermined delay time Δt1 or Δt2, the selection of the pulse motor 16 and the hydraulic pump drive motor 26 by the controller 25 is limited. As a result of the operation control based on the rear wheel steering angle characteristics, the rear wheels 8a, 8b are steered in the opposite phase to the front wheels 2a, 2b, so the slip angles of the rear wheels 8a, 8b become negative values, and accordingly Accordingly, the amount of yaw rate generated increases and the timing of generation becomes earlier.

In this state, a predetermined delay time Δt1 or Δt2
After passing this point, the controller 25 controls the operation of the pulse motor 16 and the hydraulic pump drive motor 26, so that the rear wheels 8a and 8b are rotated from zero steering angle to the same phase as the front wheels as the front wheel steering angle increases. Since the rear wheels 8a and 8b are steered, the slip angles of the rear wheels 8a and 8b increase to a positive value as the yaw rate increases.
A large lateral force acts on a and 8b. the result,
A large lateral G is generated quickly, and the vehicle changes lanes with good response.

In particular, when the steering angle of the front wheels is relatively large, the predetermined delay time Δt2 of the rear wheel steering characteristic in the high vehicle speed range is longer than the predetermined delay time Δt1 of the rear wheel steering characteristic in the medium vehicle speed range, as shown in Fig. 2. is also set short, so when the driver steers the front wheels relatively significantly in order to quickly change lanes at high vehicle speeds, the wheels will shift to the same phase earlier due to the shorter delay time Δt2 compared to when the vehicle is at medium speeds. Since the wheels are steered, a large yaw rate can be generated by anti-phase control during this delay time Δt2, and lateral force can be generated early on the rear wheels by the time the wheels are steered to the same phase as the front wheels. This allows for more responsive lane changes.

Further, FIG. 3 shows a second embodiment of the present invention, and in the above embodiment, the rotational movement of the pinion 13 by the pulse motor 16 is used as the drive source of the rear wheel steering device 7.
Instead of using a combination of the separately provided hydraulic pump 21 and the operation of the power cylinder 17, the rear wheel steering device is driven by using the hydraulic power source of the power steering device provided in advance. .

That is, in FIG. 3, 30 is a hydraulic pump of the power steering device 31, 32 is a pressure oil distribution device that distributes the pressure oil of the hydraulic pump 30 to the steering device 31 and the rear wheel steering device 7', and 33 is a rear wheel steering device. The power cylinder 34 of the device 7' is a control valve that controls the pressure oil supply direction and oil pressure to the power cylinder 33. The controller 35 has the rear wheel steering angle characteristics shown in FIG. 2 stored therein in advance, and when the front wheels are steered in a medium or high vehicle speed range, the rear wheel steering angle characteristics selected as shown in FIG. 2 above are used. The control valve 34 is configured to operate and control the control valve 34 so that the control valve 34 is operated. still,
The power cylinder 33 is provided with return springs 36a and 36b that urge the rod 11 to a neutral position when hydraulic pressure is not applied. The rest of the configuration is the same as that of the above embodiment, and the same parts are given the same reference numerals and the explanation thereof will be omitted. Therefore, in this embodiment, the same operation as in the above embodiment can be performed by controlling the operation of the control valve 34 by the controller 35 based on the selected rear wheel steering characteristic shown in FIG. When starting front wheel steering in a high vehicle speed range, a large lateral G is generated to enable a responsive lane change, and when a quick lane change is required in a high vehicle speed range, the rear wheels are It is possible to generate lateral force earlier than in the case of medium vehicle speeds and perform lane changes with better responsiveness.

Note that the set time Δt for steering the rear wheels 8a and 8b in opposite phases is set to be relatively large at both medium and high vehicle speeds when the steering angle of the front wheels is small. In addition, the maximum steering angle a for steering the rear wheels 8a and 8b in opposite phases is determined by the need to generate an appropriately large lateral G.
It is set variably depending on the vehicle speed and the front wheel turning angle (or steering angle); for example, it is set to a larger value when the front wheel turning angle is small at medium vehicle speeds, and when the front wheel turning angle is small at high vehicle speeds. When the front wheel turning angle is large, it is set to be small at both medium and high vehicle speeds.

Further, in the first embodiment, the rear wheel turning angle sensor 24 is provided to perform feedback control of the steering control of the rear wheels 8a and 8b, but the rear wheel turning angle sensor 24 is not originally necessary in the present invention. However, it is more preferable to provide this because the steering control of the rear wheels 8a, 8b can be performed with higher accuracy.

[Brief explanation of drawings]

The drawings show embodiments of the present invention; FIG. 1 is an overall schematic configuration diagram showing the first embodiment, FIG. 2 is a diagram showing rear wheel steering angle characteristics, and FIG. 3 is an overall schematic diagram showing the second embodiment. FIG. DESCRIPTION OF SYMBOLS 1... Steering device, 7, 7'... Rear wheel steering device, 13... Pinion, 17... Power cylinder, 22... Vehicle speed sensor, 23... Front wheel steering angle sensor, 25... Controller, 33... ...Power cylinder, 34...Control valve, 35...
...Controller (control device).

Claims (1)

[Claims] 1 A steering device that steers the front wheels, a rear wheel steering device that steers the rear wheels, and a steering device that steers the rear wheels in the opposite phase to the front wheel steering direction at the beginning of front wheel steering in medium and high speed ranges. and a control device that controls the operation of the rear wheel steering device so that the rear wheel steering device is steered in the same phase as the front wheel turning direction after a predetermined delay time from the start of turning the front wheels, and the predetermined delay time is A four-wheel steering system for a vehicle, characterized in that when at least the front wheels are steered relatively largely, the steering length is set to be shorter when traveling at high speeds than when traveling at medium speeds.