JPS632773A - Rear wheel steering method - Google Patents

Abstract

PURPOSE:To dissolve weak-kneed feeling of a driver at the early stage of turning and make small a turning radius at a time of low speed travel by steering rear wheels so that the smaller a vehicle speed or the larger front wheel steering angles, the larger the toe-out amount of the rear wheels becomes, at a low speed time when the vehicle speed is below a predetermined value. CONSTITUTION:In a 4WS which controls the rear wheel steering angles of a vehicle according to a vehicle speed and front wheel steering angles gammaf, the rear wheels 18L, 18R of the vehicle are controlled respectively to the toe-outs of steering angles thetarl, thetarr at a low speed time when the vehicle speed is below a predetermined value. The smaller the vehicle speed or the larger front wheel steering angles, the larger the toe-in amount is made to become. At the early stage of turning, each cornering force due to the toe-outed rear wheels is canceled, and a driver is able to feel the same turning traverse acceleration as in a 2 WS, and steering instability due to weak-kneed feeling is dissolved. While turning, at the rear wheels, a load is on a rear wheels' turning outer wheel, thus making small a turning radius as a 4WS and enabling the improvement of turning-roundability.

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention [Field of Industrial Application] The present invention relates to a rear wheel steering method for controlling a rear wheel steering angle of a vehicle in accordance with vehicle speed and a front wheel steering angle.

[Prior Art] Conventionally, a so-called four-wheel steering method has been proposed in which the front wheels are steered and the rear wheels are also steered when a vehicle turns (for example, Japanese Patent Laid-Open No. 52-61024).

The above four-wheel steering method, as shown in Japanese Patent Laid-Open No. 55-91457, for example, adjusts the rear wheel steering angle so that the front and rear wheels are in opposite phases when driving at low speeds, and so that the front and rear wheels are in the same phase when driving at high speeds. It's in control.

Therefore, when traveling at low speeds, the turning radius can be reduced, improving retrospective performance. Also, when driving at high speeds, the tendency to take pictures of your butt is eliminated, allowing you to adjust the direction of the vehicle to the desired course.

[Problems to be Solved by the Invention] However, the following problems occurred during low-speed running in the conventional example, and the problem was still not satisfactory.

This is because the driver can only recognize the turning of the vehicle when he/she feels the acceleration (jumping) in the lateral direction of the vehicle due to the turn at the beginning of the turn when driving at low speed. If the phases are opposite, the driver will not experience the above-mentioned bumpy feeling. For this reason, the driver feels that his/her back is crushed, and the steering stability may be impaired due to a difference in driving feeling.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a rear wheel steering method that eliminates the feeling of hip crushing and improves steering stability.

Structure of the Invention [Means for Solving the Problems] In order to achieve the above object, the present invention has taken the following steps as a means for solving the problems. That is, the present invention provides a rear wheel steering method for controlling a rear wheel steering angle of a vehicle according to a vehicle speed and a front wheel steering angle, as illustrated in FIG. (Pl), and the rear wheel steering method is characterized in that the rear wheels of the vehicle are controlled to toe out (P2) according to the vehicle speed and the front wheel steering angle.

[Operation] When the vehicle attempts to turn at a low speed below a predetermined speed, the rear wheels of the vehicle toe out. For this reason, the initial stage of vehicle turning (
Before the load transfer between the left and right wheels occurs, the cornering force generated by the slip angle of the rear left wheel and the cornering force generated by the slip angle of the rear left wheel hit each other in opposite directions and moisten each other, similar to a conventional two-wheel steered vehicle. You will feel the acceleration of the vehicle in the lateral direction as it turns. Therefore, the driver does not feel the back fracture.

In addition, during the middle to late stages of vehicle turning (from when the load transfer between the left and right wheels begins until it ends), the load is applied to the outer turning wheel (rear wheel), and the cornering force due to the slip angle of the outer turning wheel becomes dominant. As a result, it is possible to obtain turning performance similar to that of a conventional four-wheel steering vehicle in which the front and rear wheels are in opposite phases.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a schematic diagram of a vehicle employing a rear wheel steering method according to a first embodiment of the present invention.

As shown in the figure, the steering wheel 10 is interlocked with a steering column shaft 12, and a front wheel steering angle sensor 14 detects the rotation angle of the steering column shaft 12. That is, the front wheel steering angle sensor 14 detects the steering angle θf of the front wheels (not shown). A vehicle speed sensor 16 for detecting vehicle speed V is provided on an instrument panel (not shown).

Further, a wheel support member 20L is fixed to the rear left wheel 18L. A first arm 2 is provided at the axial center of the wheel support member 2OL.
One end of the second arm 24L is connected to the second arm 24L, and one end of the second arm 24L is connected to a portion away from the shaft center. 2nd arm 24L
The other end is connected to the rear left wheel steering angle drive device 26L,
The second arm 24L is moved in the left-right direction in FIG. 2, so that the rear left wheel 18L can turn. The rear left wheel steering angle drive device 26L is provided with a rear left wheel steering angle sensor 28L that detects the steering angle Arl of the rear left wheel.

The rear right wheel 18R side has the same configuration as the rear left wheel 181- side, and the same parts are given the same numbers.
Furthermore, R is added instead of L.

Next, the configuration of the rear left wheel steering angle drive device 26L will be described in detail according to FIGS. 3A and 3B.

FIG. 3(A) is a partially cutaway front view of the rear left wheel steering angle drive device 26L, FIG. 3(B) is a sectional view taken along the line A-A of FIG. 3(A>,
It is.

As shown in the figure, a worm 34 is fitted onto the rotating shaft 32 of the motor 30, and the worm 34 is fixed to the rotating shaft 32 by a pin 36. The tip of the rotating shaft 32 is pivotally supported by a radial bearing 40 fixed to the housing 38. The housing 38 is fixed to the vehicle body 46 with bolts 44 via a bracket 42. The worm 34 meshes with a worm wheel 48. An eccentric cam 50, a pillow ball inner cylinder 51, and an eccentric cam 54 are superimposed on the worm wheel 48, and a shaft 56 passes through these and is tightened with a nut 58. The shaft 56 includes a worm wheel 48, an eccentric cam 50, and an eccentric cam 5.
It is off the center C of 4.

A pillowball outer cylinder 52 is fitted onto the pillowball inner cylinder 51, and a second arm 24 is attached to the peripheral surface of the pillowball outer cylinder 52.
L is welded. The eccentric cam 54 is pivotally supported by an angular contact bearing 62, and the eccentric cam 50 is pivotally supported by an angular contact bearing 62. A bearing nut 64 is screwed into the opening at one end of the housing 38, and a cap 66 is fitted onto the opening at the other end. An O-ring 68 is provided on the inner peripheral surface of the housing 38 in correspondence with the peripheral surface of the cap 66.

Therefore, when the motor 30 is turned on and the worm 34 is rotated, the worm wheel 48, eccentric cam 50, pillow ball inner cylinder 51, and eccentric cam 54 rotate around the central axis C. This causes the second arm 24L to move in the direction of arrow X. Further, the tip of the second arm 241- moves in the vertical direction around the pillow ball inner cylinder 51, so that the roll steer is variable.

This amount of movement is detected by a rear left wheel steering angle sensor 28L that is fixed to the housing 38 in correspondence with the end surface of the worm wheel 48. For example, the rear left wheel steering angle sensor 28L is a light emitter/receiver, and a reflective paper having reflective parts provided at regular intervals is attached to the end face of the worm foil 48. As an example, magnets are embedded at regular intervals in the end face of the worm wheel 48, and the rear right wheel steering angle sensor 28
The rotation angle of the worm wheel 48 is detected by detecting a change in impedance by L, and the amount of movement of the second arm 24L in the direction of the arrow X is detected.

The rear right wheel steering angle drive device 26R has the same configuration as the rear left wheel steering angle drive device 26L.

Returning to Figure 2 again, the above rear left wheel 18L and rear right wheel 18R
An electronic control device 70 is provided to control the steering angle of the vehicle.

The electronic control unit 70 is a well-known CPLJ72. ROM74
．． It is composed of a RAM 76, an input port 8, an output port 80, etc., and the above-mentioned parts are connected by a common bus 82. The electronic control device 70 includes the front wheel steering angle sensor 14 and the vehicle speed sensor 16 described above. Input the detection signals of the rear left wheel steering angle sensor 28L and the rear right wheel steering angle sensor 28R to the port door 8.
A control signal is output from the output port 80 to the rear left wheel steering angle drive device 26L and the rear right wheel steering angle drive device 26R.

Next, the rear wheel steering routine executed by the electronic control unit 70 will be explained based on the flowchart of FIG. 4.

When the process is started, it is executed from step 100.

In step 100, the front wheel steering angle θf detected by the front wheel steering angle sensor 14 and the vehicle speed ■ detected by the vehicle speed sensor 16 are read. In the following step 110, it is determined whether the vehicle speed V is less than or equal to a predetermined speed VO. If "YES" in step 110, that is, if the vehicle speed V is lower than the predetermined speed vO, the process moves to step 120.

In step 120, the toe amount is calculated from the product of the absolute value of the front wheel steering angle θf read in step 100 and a predetermined function f(v). The toe amount T here is obtained by subtracting the front part from the rear part a of the dimension between the center lines of the road surface of the rear left and right wheels 18L and 18R, and takes a negative value in a toe-out state. The function f (v) has a relationship as shown in FIG. 5, for example, and has a negative value when the vehicle speed V is less than VO, and becomes smaller as the vehicle speed ■ decreases. In other words, at this time, the toe suspension - "is", the rear left and right wheels 18L and 18R are in a toe-out state, and the vehicle speed is V.
The smaller the front wheel steering angle θr is, the larger the toe-out amount becomes.

An upper limit is set so that the absolute value of the toe suspension does not exceed a maximum of 0.1 L (where L is the diameter of the rear wheel).

In the following step 130, the rear right wheel steering angle θr' and the rear right wheel steering angle θr1 that can take the above calculated toe ff1T are calculated using the following equation.

θrr=jan-1(T/2L) θrl=-tan-goose (T/2L) This is the diameter of the rear wheel.

On the other hand, if the determination in step 110 is "NO", the process moves to step 140, and the rear left and right wheel steering angle θ"1. The function Q (V) has a relationship as shown in Fig. 6, and takes a positive value when the vehicle speed V is 70 or more.In other words, the rear left and right wheel steering angle θrr, θ'1 is It is set to face in the same direction as the front wheel steering angle θf.

If step 130 or step 140 is executed, the process moves to step 150. In step 150, the rear left wheel steering angle Ar+ detected by the rear left wheel steering angle sensor 28L and the rear right wheel steering angle Arr detected by the rear right wheel steering angle sensor 28R are read. In the subsequent step 160, the read rear left and right wheel steering angle A r is calculated from the calculated rear left and right wheel steering angles θrr and θr1.
The control values X and Y are obtained by subtracting r and r1, respectively. In the subsequent step 170, the control value X calculated above is output to the rear left wheel steering angle drive device 26R, and the rear right wheel 18R is set to the rear right wheel steering angle θrr calculated above. In the following step 180,
The control value Y calculated in step 160 is output to the rear left wheel steering angle drive device 26L, and the rear left wheel 18L is set to the rear left wheel steering angle θr1 calculated above. After completing step 180, the process is “
"Return" and this routine ends once.

In the rear wheel steering routine configured as described above, when turning at a low speed where rYEsJ is determined in step 110, the rear left and right wheels 18R, 18
Rear left and right wheel steering angle θrr such that L is in a toe-out state,
θr1 is calculated, and steps 150 to 180
The actual steering angles of the rear left and right wheels 18R and 18L are θrr and θr.
The rear left and right wheel steering angle drive devices 28R and 28L are driven so that the angle becomes 1. That is, when turning at a low speed, the left and right rear wheels 18R and 18L are brought into a toe-out state, as shown in No. 7 on the left.

On the other hand, during a high-speed turn where rNOJ is determined in step 110, in step 140 the rear left and right wheels 18R, 18
1i left and right wheel steering angle θrr such that L is in the same phase as the front wheels,
θr1 is calculated, and steps 150 to 180
The steering angles of the rear left and right wheels 18R and '18L are the above θrr and θr.
The rear left and right wheel steering angle drive devices 28R and 28L are driven so that the angle becomes 1. That is, during high-speed turning, the rear left and right wheels 18R, 18L are kept in the same phase as the front wheels, as shown in the seventh right.

The configuration of the first embodiment of the present invention has been described in detail above, and in this embodiment, when turning at low speed, the rear left and right wheels 18L.

18R is in a toe-out state.

For this reason, at the beginning of a vehicle turn (before load transfer between the left and right wheels occurs), the cornering force generated by the slip angle of the rear left wheel 18L and the cornering force generated by the slip angle of the rear right wheel 18R cancel each other in opposite directions. Similar to conventional two-wheel steered vehicles, the vehicle experiences a sense of acceleration as it turns. Therefore, the driver does not feel the membrane frame, and the driving stability is excellent.

In addition, during the middle to first transition period of the vehicle turning (from the time when the load transfer between the left and right wheels begins until the end), the outer turning wheel of the rear wheel (
18R or 18L) is applied to the rotating outer ring (18R or 18L).
The cornering force due to the slip angle (8R or 18L) becomes dominant, and as a result, it is possible to obtain turning performance similar to that of a conventional four-wheel steering vehicle in which the front and rear wheels are in opposite phases. In addition, in this embodiment, as the vehicle speed V becomes lower and the front wheel steering angle θ becomes larger, the toe amount in the toe-out state (toe-out amount) is increased. The turning effect is made more suitable for driving conditions.

Further, since the load shift between the left and right wheels due to the turning of the vehicle starts earlier than the roll of the vehicle, this embodiment is more effective than steering by roll steering.

Furthermore, in this embodiment, since the front and rear wheels are in the same phase when turning at high speeds, there is no tendency for the rear end to be photographed when changing lanes while driving at high speeds, resulting in excellent steering stability. .

Next, a second embodiment of the present invention will be described. This embodiment differs from the first embodiment in the rear wheel steering routine executed by the electronic control unit 7o, and the hardware configuration is completely the same.

The rear wheel steering routine will be explained below based on the flowchart of FIG.

Steps 200, 230, 250° 260 of this routine
．． 270 and 280 are steps 100, 130, 150, 160, 170 and 18 in FIG. 4 of the first embodiment, respectively.
This is the same process as 0, so the explanation will be omitted. step 200
After executing, the process moves to step 220. Step 22
0, the toe amount T is calculated from the product of the absolute value of the front wheel steering angle θf read in step 200 and a predetermined function h (v). The function h(v) has a relationship as shown in FIG. 9, and takes a negative value when the vehicle speed V is less than vO, and takes a positive value when it is greater than VO. That is, the toe amount T is set so that the rear wheels are in a toe-out state when the vehicle speed V is less than or equal to VO, and are in a toe-in state when the vehicle speed is greater than VO. Note that the upper limit is set so that the absolute value of the toe amount (lower toe amount) does not exceed a maximum of 0.1·L. Then, similar to the first embodiment,
After step 230, the rear left and right wheels 18R, 1
The rear left and right wheel steering angle drive devices 28R, 2, and 8L are driven so that the steering wheel 8L can take the above-described toe-iT position.

That is, in this embodiment, as shown in FIG. 10, the rear left and right wheels 18L and 18R are in a toe-out state during low-speed turns, and the rear left and right wheels 181 and 18R are in a toe-in state during high-speed turns. For this reason, when attempting to turn at low speed, it is possible to obtain maneuvering stability similar to the effect of the first embodiment. Furthermore, when attempting to turn at high speed, it is possible to eliminate the poor turning performance of conventional four-wheel steering vehicles at the beginning of high-speed turns. That is, one of the vehicles
Because the variable wheels are toe-in, at the beginning of the vehicle turn (before the 'H' heavy movement of the left and right wheels occurs), the cornering force generated by the slip angle of the rear left wheel and the cornering force generated by the slip angle of the rear right wheel are combined. cancel each other out in opposite directions, making it possible to obtain a turning performance similar to that of a conventional two-wheel steering vehicle. A load is applied to the outer turning wheel, and the cornering force due to the slip angle of the outer turning wheel becomes dominant.As a result, it is possible to obtain the same steering stability as a conventional four-wheel steering vehicle in which the front and rear wheels are in the same phase.

Next, a third embodiment of the present invention will be described. The difference between this embodiment and the first embodiment lies in the processing of step 140 (FIG. 4) of the rear wheel steering routine executed by the electronic control unit 70, and the other steps and hardware configuration are completely the same. I'll go.

Hereinafter, the rear wheel steering routine of this embodiment will be explained based on the flowchart of FIG. 11. Step 3 of this routine
00,310,320,330°350.360,37
0.380 are steps 100, 110, 120, 130, 150, 160, 1 in FIG. 4 of the first embodiment, respectively.
This is the same process as 70.180, so the explanation will be omitted. If it is determined in step 310 that the speed is higher than the predetermined speed ■O, the process moves to step 340. Step 340
Then, the rear left wheel steering angle θr1 and the rear right wheel steering angle θrr are set to the value O', and the process moves to step 150.

That is, in this embodiment, as shown in FIG. 12, the rear left and right wheels 18L and 18R are in a 1--out state during a low-speed turn, and the rear left and right wheels 181 and 18R are in a state where there is no change in toe amount during a high-speed turn. It's been like that. Therefore, when trying to turn at low speed, the same steering stability as the first embodiment can be achieved, and when trying to turn at high speed, conventional two-wheel steering can be achieved. It has maneuverability similar to that of a car.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-mentioned embodiments in any way, and can be modified in various forms without departing from the gist of the present invention.

Effects of the Invention As described above in detail, the rear wheel steering method of the present invention controls the rear wheel steering angle of the vehicle according to the vehicle speed and the front wheel steering angle. When the speed is low, the rear wheels of the vehicle are controlled to toe out according to the vehicle speed and the front wheel steering angle. For this purpose, the conventional 4
Similar to wheel-steering vehicles, it is possible to reduce the turning radius when driving at low speeds and improve turning performance, but it also
The membrane frame eliminates the feeling felt by the driver at the beginning of a turn in a wheel-steering vehicle, improving handling stability. Note that the above-mentioned steering performance is far more effective than that achieved by roll steering.

[Brief explanation of the drawing]

Fig. 1 is a flowchart showing the procedure of the present invention, Figs. 2 to 7 show a first embodiment of the invention, Fig. 2 is a schematic configuration diagram of the vehicle, and Fig. 3 (A) is a rear view of the vehicle. Partially cutaway front view of the left wheel steering angle drive device, Fig. 3 (B) is A of Fig. 3 (A>
- A sectional view, FIG. 4 is a flowchart showing the rear wheel steering routine executed by the electronic control device, and FIG. 5 is the function f.
6 is a graph showing rg: I number Ω(V), FIG. 7 is a schematic diagram explaining the details of rear wheel steering, and FIGS. 8 to 10 are graphs showing rg:I number Ω(V). 2 examples are shown,
Fig. 8 is a flowchart showing the rear wheel steering routine executed with the electronic control installed, Fig. 9 is a graph showing the function h (v), and Fig. 10 is Na1 explaining the rear wheel steering content.
8 schematic diagram, FIGS. 11 and 12 show a third embodiment of the present invention, FIG. 11 is a flowchart showing a rear wheel steering routine executed by the electronic control il' II device, and FIG. FIG. 3 is a schematic diagram illustrating the details of wheel steering. 14...Front wheel steering angle sensor 16...Vehicle speed sensor 18L...Rear left wheel 18R...Rear stone wheel 26L...Rear left wheel steering angle drive device 26R...Rear right wheel steering angle drive device 28L. ...Rear left wheel steering angle sensor 28R...Rear right wheel steering angle sensor 70...Electronic control device

Claims (1)

[Scope of Claims] 1. In a rear wheel steering method for controlling a rear wheel steering angle of a vehicle according to a vehicle speed and a front wheel steering angle, when the vehicle speed is a low speed below a predetermined value, the rear wheels of the vehicle are controlled. A rear wheel steering method characterized by controlling toe-out according to vehicle speed and front wheel steering angle. 2 The toe-out control described above becomes more effective as the vehicle speed decreases and/or
Alternatively, the rear wheel steering method according to claim 1, wherein the larger the front wheel steering angle, the larger the toe-out amount.