JPH0825482B2 - Vehicle rear wheel steering system - Google Patents

Description

TECHNICAL FIELD The present invention relates to a rear wheel steering system for a vehicle.

(Prior Art) Conventionally, as a rear wheel steering device of a vehicle, for example, Japanese Patent Application Laid-Open
As disclosed in Japanese Patent Publication No. 61-200064, a toe control device including a hydraulic cylinder or the like for independently toe-controlling the left and right rear wheels and a control means for controlling the operation of the toe control device At this time, by steering only the rear wheels on the outside of the turn in the toe-in direction, or the left and right rear wheels in the same phase as the turning direction, that is, the rear wheels on the inside of the turn in the toe-out direction and the rear wheels on the outside of the turn in the toe-in direction. By steering, lateral G at high speed
It is known to reduce the cutting action due to (lateral acceleration) to improve running stability.

(Problems to be solved by the invention) However, in the above-mentioned conventional one, since the rear wheels are always steered in the toe-in direction during the steering of the front wheels, there is a dislike for the understeer characteristic to become too strong, and the turning ability is significantly reduced. There was a problem of doing.

The present invention has been made in view of the above problems, and an object of the present invention is to improve the toe control control of the rear wheels in the conventional rear wheel steering device to improve the stability of the vehicle immediately after steering. The driving stability of the vehicle is ensured, the understeer characteristic is prevented from becoming strong immediately after steering, and the turning ability can be improved.

(Means for Solving Problems) In order to achieve the above object, a solution means of the present invention is to provide a rear wheel steering system for a vehicle equipped with a toe control device for independently controlling the left and right rear wheels. During steering, immediately after the steering, only the rear wheels on the outside of the turn are steered in the toe-in direction, and then only the rear wheels on the inside of the turn are steered in the toe-in direction. It comes.

(Operation) With the above configuration, in the present invention, when steering the front wheels,
The toe control device operates under the control of the control means,
Immediately after steering when the vehicle tends to become unstable, only the rear wheels on the outside of the turn are steered in the toe-in direction, so traveling stability can be improved. Further, immediately after the operation, it is possible to prevent only the rear wheel on the inside of the turn from being steered in the toe-in direction and the understeer characteristic becoming too strong.

Moreover, when shifting from a state immediately after steering to a state after steering during such front wheel steering, the rear wheel on the inside of the turn is toe-in steering from the state of zero toe displacement, and the rear wheel on the outside of the toe is toe-in. Since only the steering state is changed to the state where the toe displacement is zero, and neither the left or right rear wheel is changed between the toe-in steering state and the toe-out steering state, a rear wheel steering response delay occurs. There is no such thing.

(Example) Hereinafter, the Example of this invention is described based on drawing.

FIG. 1 shows a rear wheel steering system for a vehicle according to an embodiment of the present invention, in which 1L and 1R are left and right rear wheels.
L and 1R are supported by the vehicle body via the wheel support member 2 and the pair of front and rear lateral links 3a and 3b, respectively. Further, 4L and 4R are a pair of left and right hydraulic cylinders arranged between the rear lateral link 3b and the vehicle body.

As shown in detail in FIG. 2, the hydraulic cylinders 4L and 4R have the piston 6 inside the piston fitting portion 5a of the cylinder body 5.
Has a hydraulic chamber 7 and a spring chamber 8 which are slidably inserted by a predetermined stroke and partitioned by the piston 6. The cylinder body 5 is attached to the vehicle body, while the piston 6 is connected to one end of a rear lateral link 3b inserted from the spring chamber 8 side. Further, the spring chamber 8 is provided with a spring 9 that compresses and urges the piston 6 toward the end of the piston fitting portion 5a on the hydraulic chamber 7 side. When pressure oil is not supplied to the hydraulic chamber 7 and the piston 6 is positioned at the end of the piston fitting portion 5a on the hydraulic chamber 7 side due to the biasing force of the spring 9, the rear wheel
1L and 1R are in a state where the toe displacement is zero, and the supply of the pressure oil to the hydraulic chamber 7 causes the piston 6 to move the spring chamber 8 in the piston fitting portion 5a.
The rear wheels 1L and 1R are steered in the toe-in direction as they move to the side.

Further, an oil pump 10 for steering the rear wheels is provided in each of the hydraulic chambers 7 of the pair of hydraulic cylinders 4L, 4R.
11c, the oil pump 10 is driven by the engine output transmitted via the pulley 14 together with the front wheel steering oil pump 13 that supplies pressure oil to the front wheel steering hydraulic cylinder 12. Has become. In the hydraulic passage 16 which branches from the hydraulic supply passage 11a and communicates with the reserve tank 15, the hydraulic cylinders 4L, 4R are connected from the oil pump 10 to the hydraulic passage 16.
A variable orifice 17 for adjusting the hydraulic pressure discharged toward the hydraulic pressure supply passage 11b, 11c is provided.
The on-off valves 18 and 19 are provided in each of them. The variable orifice 17 is in a fully opened state (that is, there is no restriction to the passage surface passage) when the operating portion 17a is not operated (that is, when not energized), and the opening / closing valves 18 and 19 are Is also in the closed state when the operation parts 18a and 19a are not operated (not energized).

Further, hydraulic pressure discharge passages 20a, 20b for discharging the pressure oil in the hydraulic chambers 7 of the hydraulic cylinders 4L, 4R to the reserve tank 15.
On-off valves 21 and 22 are provided in each of them, and both of the on-off valves 21 and 22 are in an open state when the operating parts 21a and 22a are not operated (when not energized). With the above hydraulic cylinders 4L, 4R and the hydraulic circuit connected to them, the left and right rear wheels 1L, 1R
Toe control device 2 for independent toe control of R
3 are configured.

Further, the toe control device 23 includes the variable orifice 17 and the operating portions 17a, 18 of the on-off valves 18, 19, 21, 22.
Controller 24 as control means for a, 19a, 21a, 22a
The operation is controlled by inputting an ON / OFF switching signal of energization from the vehicle. The controller 24 includes a vehicle speed sensor 25 for detecting a vehicle speed and a steering wheel steering angle for detecting a steering angle of a steering wheel. The signal from the sensor 26 is input.

The operation control (toe control control) of the toe control device 23 by the controller 24 is performed based on the flowchart shown in FIG. That is, first, after having been read a steering angle and a vehicle speed of the steering wheel in step S _1, the steering wheel is determined whether or not it is steered in step S _2, when the YES go to Step S _3, the NO If so, the process returns to step S ₁ . Step S
₃ , the lateral G (lateral acceleration) μ is 0.2 or less from the steering angle of the steering wheel and the vehicle speed based on the lateral G calculation map stored in advance in FIG. 4 (that is, non-control in FIG. 4). It is determined whether or not it is in the area A). If YES, the process returns, and if NO, the process goes to step S ₄ , and as in step S ₃ , the lateral G calculation map is used to determine the lateral G.
It is determined whether or not μ is 0.5 or more (that is, the second control area B _{2 in} FIG. 4).

If the determination in step S ₄ is YES, then step S
_While it is determined whether or not the steering wheel is steered to the left in step ₅ , when the determination in step S ₄ is NO (that is, when the lateral Gμ is in the first control area B ₁ in FIG. 4), the step In S ₆ , it is determined whether the steering wheel is steered to the left. When the determination in step S ₅ is NO and when the determination in step S ₆ is YES, the process goes to step S ₇ , respectively, and when the determination in step S ₅ is YES and the determination in step S ₆ is NO. If so, step S ₈
go to.

In step S _7, and controls the variable orifice 17 as a hydraulic discharged from the oil pump 10 becomes a predetermined pressure, the opening and closing valve 19 is open movement, the opening and closing valve 22 by closing operation, the hydraulic cylinder 4R A predetermined amount of pressure oil is supplied to the hydraulic chamber 7 to steer only the right rear wheel 1R in the toe-in direction. Further, in step S _8, the oil pump 1
The variable orifice 17 is controlled so that the hydraulic pressure discharged from 0 becomes a predetermined pressure, and the opening / closing valve 18 is opened and the opening / closing valve 21 is closed, so that the hydraulic chamber 7 of the hydraulic cylinder 4L has a predetermined pressure. Supply pressure oil and steer only the left rear wheel 1L in the toe-in direction.

Next, the operation of the above-described embodiment will be described. When the front wheels are not steered and are in a straight traveling state (when the lateral G is in the non-control area A in FIG. 4), the controller 24 turns on the power. Signal is not output at all, the variable orifice 17 is fully open, the open / close valves 18 and 19 are closed, and the open / close valve 2
1,22 are open. Therefore, the pressure oil is not supplied to the hydraulic chambers 7 of the hydraulic cylinders 4L and 4R, and the piston 6 is located at the end of the piston fitting insertion portion 5a on the side of the hydraulic chamber 7, whereby the left and right rear wheels 1L are , 1R is maintained in a state where the toe displacement is zero as shown in FIG. 5 (a).

On the other hand, when the front wheels are steered and the vehicle is apt to become unstable immediately after the steering (at this time, the lateral G is 0.2 or more and 0.5 or less, that is, the fourth G
(Corresponding to being in the first control area B ₁ in the figure),
In the case of left steering, the controller 24 outputs an energization ON signal to the variable orifice 17 and the on-off valves 19 and 22, and
In the case of right steering, the controller 24 outputs a signal indicating that the energization is ON to the variable orifice 17 and the on-off valves 18 and 21. As a result, the variable orifice 17 controls the hydraulic pressure discharged from the oil pump 10 to a predetermined pressure due to its passage area throttling action, and the opening / closing valve 19 or 18 is opened to open the opening / closing valve 22.
Or, 21 closes the hydraulic cylinder 4R or
Pressure oil is supplied to the 4 L hydraulic chamber 7, and the piston 6 moves from the hydraulic chamber 7 side end to the spring chamber 8 side in the piston fitting insertion portion 5a, so that the rear wheel on the outside of the turning (in the case of left steering turning) Only the rear wheel 1R on the right side corresponds, and the rear wheel 1L on the left side corresponds in the case of a right steering turn), as shown in FIG. 5 (b) is steered in the toe-in direction. As a result, running stability immediately after steering can be improved.

Also, during steering immediately after steering (at this time, the lateral G is 0.5
That is, the above corresponds to the case of being in the second control area B ₂ in FIG. 4). Contrary to the case immediately after the above steering, in the case of left steering, the variable orifice 17 and the opening / closing valves 18, 21 A signal to turn ON the power is output to the controller 24, and in the case of right steering
A signal to turn on the energization is output to, so that only the rear wheels inside the turn (the left rear wheel 1L corresponds to the left steering turn, the right rear wheel 1R corresponds to the right steering turn), The steering is performed in the toe-in direction as shown in FIG. Therefore, even in a vehicle having an understeer characteristic, it is possible to effectively prevent the understeer characteristic from becoming too strong during steering, and it is possible to improve the turning performance.

Moreover, when shifting from a state immediately after steering to a state after steering during such front wheel steering, the rear wheel on the inside of the turn is toe-in steering from the state of zero toe displacement, and the rear wheel on the outside of the toe is toe-in. Only the steering state is changed to a state where the toe displacement is zero, and neither the left or right rear wheel 1L or 1R is changed between the toe-in steering state and the toe-out steering state. There is no delay, and it is possible to secure good responsiveness to prevent the occurrence of strong understeer characteristics immediately after steering.

In the above embodiment, the toe control device 23 for toe-controlling the left and right rear wheels 1L, 1R is described as being constituted by the hydraulic cylinders 4L, 4R and the hydraulic circuit.However, the present invention uses an electric motor or the like. It can be similarly applied to the case of using other toe control devices such as those constructed. In short, in the control of the toe control device, when steering the front wheels, it is necessary to steer only the rear wheels on the outside of the turn in the toe-in direction immediately after the steering, and then steer only the rear wheels on the inside of the turn in the toe-in direction.

(Advantages of the Invention) As described above, according to the vehicle rear wheel steering system of the present invention, when the front wheels are steered, only the rear wheels on the outside of the turn are steered in the toe-in direction immediately after the steering where the vehicle tends to be unstable, and By steering only the rear wheels on the inside of the turn in the toe-in direction, it is possible to ensure running stability immediately after steering, and it is possible to effectively and effectively prevent a strong understeer characteristic. It is possible to improve the turning ability.

[Brief description of drawings]

The drawings show an embodiment of the present invention. FIG. 1 is a schematic overall configuration diagram of a rear wheel steering system of a vehicle, FIG. 2 is a vertical sectional side view of a hydraulic cylinder, and FIG. 3 is a flow chart diagram of toe control control. FIG. 4 is a diagram showing a lateral G calculation map,
FIG. 5 is an explanatory diagram for explaining steering of the rear wheels. 1L, 1R …… rear wheel, 23 …… toe control device, 24 ……
controller.

Claims (1)

[Claims] 1. A rear wheel steering system for a vehicle, comprising a toe control device for independently controlling the left and right rear wheels, wherein only the rear wheels on the outside of the turning direction in the toe-in direction when the front wheels are steered. A rear wheel steering system for a vehicle, comprising: a control unit that controls the operation of the toe control device so that only the rear wheel inside the turn is steered in the toe-in direction.