JPH0514940Y2 - - Google Patents

Description

[Detailed description of the invention] (Industrial application field) This invention steers the rear wheel steering angle of a rear wheel steered vehicle from a non-steered state to a steered state, or from a steered state to a non-steered state. The present invention relates to a rear wheel steering control device having a characteristic time constant.

(Prior Art) Conventional rear wheel steering control devices include, for example, Japanese Patent Application Laid-Open No. 61-27766, which was previously filed by the present applicant, or Japanese Patent Application Laid-Open No. 59-1987, which was filed by Toyo Kogyo Co., Ltd.
There is one disclosed in Publication No. 81264.

(Problem to be solved by the invention) However, in such conventional rear wheel steering angle control devices, the former device (Japanese Patent Application Laid-Open No. 61-27766) is unable to control the front wheel steering angle below a constant value or above a constant vehicle speed value. The rear wheels are not steered under at least one of the following conditions, and the latter (Japanese Unexamined Patent Publication No. 59-81264)
This device determines the rear wheel steering angle as a function of vehicle speed and front wheel steering angle, and steers the rear wheels. Therefore, for example, when a vehicle equipped with the former device accelerates in the middle of a curve, the The rear wheel steering angle suddenly returns to normal, and the vehicle's behavior changes even though the steering wheel is not operated. Vehicles equipped with the latter device also have a one-to-one relationship between the front and rear steering angles and the vehicle speed in order to reduce the side slip angle of the tires while turning, so they cannot turn while keeping the front wheel steering angle constant. However, when accelerating suddenly, the rear wheels would suddenly roll back. Therefore, in order to prevent the rear wheels from suddenly returning when suddenly accelerating during a turn, the above problem can be solved by setting the above relationship as a function that does not change the front/rear steering angle ratio much with respect to the vehicle speed. The original purpose of reducing the side slip angle of the tires is not achieved when the vehicle is turning, and the same goes for the steering angle; when the steering wheel angle is suddenly returned, the rear wheels are suddenly steered and the vehicle moves unnaturally. If the above relationship is set to avoid this problem, this problem is solved, but the original purpose of reducing the side slip angle of the tire during cornering cannot be achieved.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides a rear wheel steering angle that changes the rear wheel steering angle to a preset value based on the front wheel steering angle and the vehicle speed. The control device is provided with a time constant setting means for suppressing changes in the rear wheel steering angle with respect to changes in the front wheel steering angle and vehicle speed, and the time constant setting means is provided with a time constant T for suppressing changes in the rear wheel steering angle with respect to changes in the vehicle speed. ₁ is set to be larger than the time constant T ₂ that suppresses a change in the rear wheel steering angle with respect to a change in the front wheel steering angle.

(Function) In the rear wheel steering angle control device of the present invention,
When changing the rear wheel steering angle to a preset value based on the front wheel steering angle and the vehicle speed, the time constant setting means provides a time constant _T1 to suppress changes in the rear wheel steering angle with respect to changes in vehicle speed, A time constant T ₂ smaller than the time constant T ₁ is provided to suppress changes in the rear wheel steering angle relative to changes in the front wheel steering angle.

It goes without saying that during steady turning, the original purpose of four-wheel steering, such as reducing the side slip angle of the tires, is achieved.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

In the figure, 1 is the steering wheel of the vehicle, 2 is a sensor for detecting its steering angle, 3 is a controller, and 4 is a steering wheel of the vehicle.
is an electric steering wheel for the front wheels, 5 is its motor, 6 is an encoder, 7 is a side rod, 8 is a knuckle arm, 9 is a side rod, 10 is a knuckle arm, 11 and 12 are front wheels, 13 is an electric steering wheel for the rear wheels, 14 is the motor, 15 is the encoder, 16 is the side rod, 17 is the knuckle arm, 18 is the side rod, 19 is the knuckle arm, 20, 21 are the rear wheels, 30 is the sensor for detecting vehicle speed, 31 is the sensor connection part, δ _F is the front wheel rudder angle,
δ _R is the rear wheel steering angle.

That is, the device shown in FIG.
2 and rear wheels 20, 21 are steered by electric steering wheels 4, 13, respectively, and these electric steering wheels 4, 13 are driven by motors 5, 14. Controlled by controller 3.

2 is a cross-sectional view of the electric steering 4, 13. A shaft 24 is inserted into the housing 26, both ends of which are connected to the left and right side rods 9, 18 and 7, 16.
A ball screw 23 is screwed into the shaft 4. The ball screw 23 is rotated by the output gear 22 of the motor 5, 14, thereby moving a shaft 24 in the axial direction. At this time, a spline 25 is provided between the shaft 24 and a housing 26 to prevent the shaft 24 from rotating.

When the shaft 24 is moved by the rotation of the motors 5 and 14 in this manner, the knuckle arms 8, 10, 17, and 19 of each wheel connected to the side rods are rotated, and the steering of the wheels 11, 12, 20, and 21 is controlled. It will be done. It goes without saying that this device can also be constructed as a hydraulically driven type.

Figure 3 shows a control logic diagram of the present invention, in which the abscissa represents the vehicle speed V and the ordinate represents the front wheel steering angle δ _F
It is a coordinate system with . In the figure, A is a small turning area in which the rear wheels are in a steered state, and B is an area in which the rear wheels are in a non-steered state.

In the present invention, in a vehicle having a mechanism that steers the rear wheels according to the front wheel steering angle and vehicle speed, the rear wheel steering state A is changed from the rear wheel steering state A to the non-steered state B, or from the rear wheel non-steering state B to the rear wheel steered state. When at least one state transition to A is performed, the rear wheels are steered with time constants T ₁ and T ₂ of T ₁ >T ₂ set by the time constant setting means.

That is, by setting the time constant T ₁ , it is possible to suppress sudden changes in the rear wheels due to increases or decreases in vehicle speed, and by setting the time constant T ₂ , it is possible to suppress sudden changes in the rear wheels due to sudden turning of the front wheels. Since it is easier to feel discomfort when the rear wheel steering angle changes even when the steering wheel is not operated, the discomfort can be effectively reduced by setting T ₁ > T ₂ .

Furthermore, Fig. 4 shows the relationship between the vehicle speed V and the steering angle ratio Rr/Fr of the front and rear wheels in the device of JP-A No. 59-81264, which does not include the concept of time. The rear wheel steering angle may change suddenly due to acceleration or sudden turning of the front wheels.

On the other hand, according to the present invention, since the time constants T ₁ and T ₂ are provided when the state transition is performed, the rear wheel steering angle does not suddenly change, which eliminates the sense of discomfort.

Furthermore, although the method for determining the time constants T ₁ and T ₂ is not mentioned in the above embodiment, when the vehicle C turns a curve to avoid the obstacle D, as shown in FIG. If the rear wheels are steered with a certain time constant after the vehicle is turned, a strange feeling will occur. Therefore, in order to eliminate this discomfort, the time constant T ₁ is set to gradually decrease as the vehicle speed changes, as shown in Figure 6a, and the time constant T1 is set to become smaller as shown in Figure 6b. ₂ may be set to decrease in accordance with the speed of change of the steering angle of the front wheels.

FIG. 7 shows a control flowchart of the controller 3 of the device of the present invention. The symbols are explained below.

V: Vehicle V _O : Specified vehicle speed δ _F : Front wheel steering angle δ _FO : Specified front wheel steering angle T: Time constant T ₁ : Time constant depending on vehicle speed T ₂ : Time constant depending on front wheel steering angle FLAG=1: Rear wheel steering state FLAG = 0: Rear wheel non-steering state VFLAG = 1: V≦V _O VFLAG = 0: V > V _O DFLAG = 1: δ _F ≧V _O DFLAG = 0: δ _F < δ _FO δ _F > δ _FO and V Rear wheel steering when ≦V _O (effect of the invention) As explained above, in the rear wheel steering angle control device of the present invention, the change in the front wheel steering angle and the change in the rear wheel steering angle in response to a change in vehicle speed are controlled by the time constant T. ₁ and _T2 , it eliminates sudden movement of the rear wheels due to sudden steering or sudden acceleration, eliminating the driver's discomfort. Furthermore, since the driver feels a great deal of discomfort when the rear wheels are steered even though he or she is not performing any steering operations, setting the time constant T ₁ to be larger than the time constant T ₂ effectively counteracts this. Can be suppressed.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a vehicle to which the device of the present invention is applied;
Fig. 2 is a sectional view of the electric steering section, Fig. 3 is a control logic diagram of the present invention, Fig. 4 is a diagram showing the relationship between vehicle speed and steering angle ratio, and Fig. 5 shows the running state of the vehicle. 6A and 6B are time constant characteristic diagrams, and FIG. 7 is a flowchart of the device of the present invention. 1... Steering wheel, 3... Controller, 4... Electric steering, 5... Motor, 6... Encoder, 11, 12... Front wheel, 1
3...Electric steering, 14...Motor, 1
5... Encoder, 20, 21... Rear wheel, δ _F ...
Front wheel steering angle, δ _R ...Rear wheel steering angle, T...Time constant, T ₁
...Time constant due to vehicle speed, T ₂ ...Time constant due to front wheel steering angle.

Claims (1)

[Scope of Claim for Utility Model Registration] 1. In a rear wheel steering angle control device that changes the rear wheel steering angle to a preset value based on the front wheel steering angle and vehicle speed, A time constant setting means for suppressing a change in the steering angle is provided, and the time constant setting means sets a time constant _T1 for suppressing a change in the rear wheel steering angle in response to a change in vehicle speed to suppress a change in the rear wheel steering angle in response to a change in the front wheel steering angle. A rear wheel steering angle control device characterized in that the time constant T2 is set larger than the time constant _T2 . 2. A utility model characterized in that the time constant T ₁ is set to become smaller as the vehicle speed change increases, and the time constant T ₂ is set to become smaller as the front wheel steering angle change speed increases. A rear wheel steering angle control device for a vehicle according to claim 1.