JPH03157270A - Rear wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To make stability during reversing of a vehicle compatible with utility during forward running thereof by a method wherein one rear wheel steering characteristic can be selected from a plurality of rear wheel steering characteristics by a manual switch only during forward running. CONSTITUTION:A rear wheel steering device 4 of a four-wheel steering device comprises a steering ratio varying means 21, a power steering means 22, a rear wheel steering shaft 23, and a neutral position return means 24. Rear wheels are steered by a control means 32 in response to a front wheel steering angle according to a given steering ratio. During forward running, the control means 32 controls steering of rear wheels based on a plurality of rear wheel steering characteristics decided according to a given condition during forward running and controlled based on a single rear wheel steering characteristic decided according to a given condition during reversing. Only when forward running is detected, a single rear wheel steering characteristic can be selected from a plurality of rear wheel steering characteristics through operation of a manual switch 35.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a rear wheel steering device for a vehicle that steers the rear wheels according to predetermined conditions.

(Prior Art) Conventionally, in a four-wheel steering device that can variably control the steering angle of the rear wheels, a steering angle ratio of one or two or more preset (or rear wheel steering angle) information, a manual switching means that selects this steering angle ratio (or rear wheel steering angle) information and changes the desired steering angle ratio (or rear wheel steering angle), and detects the vehicle speed and manually sets the steering angle ratio (or rear wheel steering angle) information. Vehicles that are equipped with an alarm generating means that issues an alarm when the vehicle speed exceeds a certain level are known.

(Problem to be solved by the invention) However, with such manual switching means,
If you make it possible to select any steering angle information, there will be no major problem when driving forward, but if the steering angle information is changed when reversing, the toe angle will change, and the change in toe angle will affect the vehicle behavior. It occurs noticeably. Therefore, if such a change is allowed when traveling backwards, the driver may not be able to follow the change in characteristics.

The present invention provides a rear wheel steering device for a vehicle that can achieve both safety when the vehicle is traveling backwards and convenience when the vehicle is traveling forward.

(Means for Solving the Problems) The present invention steers the rear wheels according to predetermined conditions, and when traveling forward, it steers the rear wheels based on a plurality of rear wheel steering characteristics determined according to the predetermined conditions. Rear wheel steering control means for steering rear wheels based on a single rear wheel steering characteristic determined according to predetermined conditions during driving; forward travel detection means for detecting forward travel; and forward travel detection means for detecting forward travel. The vehicle is characterized in that it includes a manual switch that receives the output and selects one rear wheel steering characteristic from the plurality of rear wheel steering characteristics only when traveling forward.

(Function) During forward travel, the rear wheel steering control means controls the steering of the rear wheels based on one rear wheel steering characteristic selected from a plurality of rear wheel steering characteristics by a manual switch. When traveling backwards, the rear wheel steering control means controls the steering of the rear wheels based on a single rear wheel steering characteristic.

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

In FIG. 1 showing the overall configuration of the present invention, the four-wheel steering device includes a front wheel steering device 2 that steers left and right front wheels IL and IR.
and a rear wheel steering device 4 that steers the left and right rear wheels 3L and 3R.

The front wheel steering device 2 extends in the vehicle width direction, and both ends thereof are arranged on the left and right sides.
Pair of tie rods IIL, IIR and knuckle arm 12
A front wheel steering shaft 13 is connected to a pair of left and right front wheels IL and IR via L and 12R, and a binion 15 is provided at one end and engages with a rack portion 14 formed on the front wheel steering shaft 13. , a steering shaft 17 with a steering wheel 16 provided at the end thereof, and the front wheel steering shaft 1 is controlled by operating the steering wheel 16.
3 in the vehicle width direction to steer the front wheels IL and IR.

The rear wheel steering device 4 is configured to steer the rear wheels according to the front wheel steering angle according to a predetermined steering ratio (rear wheel steering angle/front wheel steering angle) and to change the steering ratio according to the vehicle speed. .

The rear wheel steering device 4 includes a variable steering ratio means 21, a power steering means 22, a rear wheel steering shaft 23, and a neutral position return means 24.

The rear wheel steering shaft 23 extends in the vehicle width direction, and both ends thereof are connected to a pair of left and right rear wheels 3L, 3R via a pair of left and right tie rods 25L, 25R and knuckle arms 26L, 26R. The rear wheels 3L and 3R are steered by stroke displacement of the wheel steering shaft 23 in the vehicle width direction.

The neutral position return means 24 includes a centering spring 24a disposed as shown in the figure in a compressed state, and the centering spring 24a constantly moves the rear wheel steering shaft 23 to the neutral position.
The straight forward position of the rear wheels 3L and 3R) is energized.

The stroke displacement of the rear wheel steering shaft 23 in the vehicle width direction is performed by the variable steering ratio means 21 and the power steering means 22.

The steering ratio variable means 21 is for changing the steering ratio when steering the rear wheels 3L and 3R, and is for changing the steering ratio when steering the rear wheels 3L and 3R.
and a rack portion 18. formed on the front wheel steering shaft 13.
Binion 19 meshed with rack portion 18, Binion 1
A front wheel steering angle is inputted via a transmission shaft 20 which rotates together with the front wheel steering angle, and the output shaft 21a is stroked in the vehicle width direction in accordance with the inputted front wheel steering angle.

Also, the output shaft 21a for the input front wheel steering angle is
The ratio of the variable positions (corresponding to the ratio of the rear wheel steering angle to the front wheel steering angle, referred to as a steering ratio) is configured to change according to the amount of rotation of the stepping motor 30. The amount of rotation of the stepping motor 30 is appropriately controlled by the #+I8 means 32 based on the vehicle speed signal output from the vehicle speed sensor 31, and the actual amount of rotation of the stepping motor 30 is detected by the steering ratio sensor 33. It is configured to be feedback-controlled by the detection signal.

In addition, the control means 32 controls a plurality of rear wheel steering characteristics (A in FIG. 2,
B, C), when driving backward, a single rear wheel steering characteristic (second
It functions as a rear wheel steering control means that steers the rear wheels 3L and 3R based on the forward motion (see D in the figure), and receives the output of the inhibitor switch 34, which serves as a forward travel detection means that detects forward travel, and is displayed on the instrument panel, etc. The disposed manual switch 35 allows one rear wheel steering characteristic to be selected from the plurality of rear wheel steering characteristics only when the vehicle is traveling forward. In other words, when traveling backwards, the rear wheel steering characteristics are always constant. In addition, A of the rear wheel steering characteristics,
B and C indicate the normal characteristics, sporty characteristics, and low μ road characteristics (μ: coefficient of friction), respectively.

The rear wheels 3L,
3R steering is performed.

That is, the power steering means 22 includes a piston 41 fixed to the rear wheel steering shaft 23, a cylinder 42 that accommodates the piston 41, an engine-driven hydraulic pump 43 that supplies hydraulic pressure to the cylinder 42, and a cylinder 42 that accommodates the piston 41. The control valve 45 controls the supply of hydraulic pressure from the hydraulic pump 43 to the cylinder 42 and the discharge of hydraulic pressure from the cylinder 42 to the tank 44, and the displacement of the output shaft 21a of the variable steering ratio means 21 is controlled by the control valve 45. The control valve 45 is transmitted to the spool 45a of the valve 45, and the control valve 45 controls the cylinder 4 by the displacement of the spool 45a.
The supply and discharge of hydraulic pressure to the left and right oil chambers 42a and 42b in the cylinder 2 is controlled, and the hydraulic pressure (rear wheel steering force) in the cylinder 42 is used to shift the rear wheel steering shaft by an amount corresponding to the displacement amount of the output shaft 21a. 23 in the vehicle width direction to steer the rear wheels 3L and 3R.

In fact, the control valve 45 is connected to the spool 45a.
is housed in the valve housing 45b so as to be displaceable in the vehicle width direction, and the valve housing 45b is fixed to the rear wheel steering shaft 23 so as to be displaced in the vehicle width direction together with the rear wheel steering shaft 23,
When the spool 45a is displaced, for example, to the right from the illustrated neutral position, hydraulic pressure is supplied from the hydraulic pump 43 to the left bending chamber 42a of the cylinder 42, and the rear wheel steering is performed via the piston 41 fixed to the rear wheel steering shaft 23. The shaft 23 is displaced to the right,
Along with this, the valve housing 45b is also displaced to the right, and when the position of the sprue 45a with respect to the housing 45b returns to the approximately neutral position, the supply of hydraulic pressure to the left bending chamber 42a of the cylinder 42 is stopped, and from this state, the spool 45
When a is displaced to the right, the rear wheel steering shaft 23 is displaced to the right by the amount of displacement of the spool 45a in the same manner as described above. Of course, when the spool 45a is displaced to the left, hydraulic pressure is supplied to the oil chamber 42b of the cylinder 42, and the rear wheel steering shaft 23 is displaced to the left by the amount of leftward displacement of the spool 45a.

The structure of the steering ratio variable means 21 itself is not directly related to the present invention, and the structure is also disclosed in, for example, Japanese Patent Laid-Open No. 61-10.
It is described in Japanese Patent Application No. 8070, etc., and is already well known, so a detailed explanation thereof will be omitted.

The rear wheel steering device 4 is equipped with a power steering means 22 that generates a steering force using hydraulic pressure. A valve means 51 is provided for dissipating the rear wheel steering force (hydraulic pressure within the cylinder 42) in the power steering means 22.

The valve means 51 is provided on a drain passage 52 that directly communicates between the discharge side of the hydraulic pump 43, the control valve 45, and the tank 44 in order to return oil discharged from the hydraulic pump 43 to the tank 44. and an electromagnetic normally closed valve 5 that closes when no power is applied, arranged in parallel.
3 and an electromagnetic normal oven valve 54 that is open when no current is applied. In addition, the above normal oven valve 5
An orifice 55 is provided in the drain passage 52a on the fourth side. In addition, in the figure, 56 is a filter.

Both valves 53 and 54 are controlled by the control means 32 to which various information (not shown) necessary for controlling them is input.

That is, during normal rear wheel steering, the normal close valve 53 is de-energized and the normal oven valve 54 is de-energized.
Control is performed by energizing only one of the two valves 53 and 54 to close both valves 53 and 54, generating a rear wheel steering force based on the hydraulic pressure discharged from the hydraulic pump 43, and causing the rear wheels to be steered by the steering force.

Further, when a predetermined abnormality occurs in the rear wheel steering device 4, the normally closed valve 53 is energized, and the normal oven valve 54 is energized, and both valves 53.
54 is opened, thereby discharging the hydraulic pressure discharged from the hydraulic pump 43 directly into the tank 44 via the drain passage 52,
By doing so, the rear wheel steering force in the power steering means 22 is eliminated, and the neutral position return means 24
The rear wheel steering shaft 23 is returned to the neutral position by the urging force of
Control is performed to set the state to 2WS. In addition, both valves 53
．． When 54 is opened, the oil discharged from the hydraulic pump 43 is discharged into the tank 43 through these valves 53 and 54 due to the large resistance in the area of the control valve 45.

Further, when the ignition switch is turned off, the power supply to both valves 53 and 54 is stopped, and as a result, the normally closed valve 53 is closed, but the normally oven valve 54 is opened.

Next, control by the control means 32 will be explained.

In FIG. 3, when the vehicle starts, it is determined whether or not the vehicle is traveling backwards based on a signal from the inhibitor switch 34 (step SL).

If it is not when driving backwards, it is when driving forwards and the rear wheel 3L
, 3R, the rear wheel steering characteristics selected by the manual switch 35 are read (step S2).

First, it is determined whether the normal characteristic is selected (step S3). If it has been selected, the process moves to step S4, selects the normal characteristic shown by characteristic A in FIG. 2, performs rear wheel steering control based on the characteristic A, and returns. , the process moves to step S5.

In step S5, it is determined whether or not the characteristic is sporty. If the characteristic is sporty, characteristic B in FIG.
(step 58), while if no sporty characteristic is selected;
Proceeding to step S7, the remaining characteristic, characteristic C in FIG. 2, that is, the low μ road characteristic (μ: coefficient of friction) is selected, and the process returns.

Further, if it is determined in step Sl that the vehicle is traveling backwards, the process moves to step S8, the characteristic shown in FIG. 2 is selected, and the process returns.

Therefore, with the above configuration, when traveling forward, the control means 32 controls the rear wheel 3L based on one rear wheel steering characteristic selected from the three rear wheel steering characteristics A, B, and C by the manual switch 35. , 3R are steered. On the other hand, when the vehicle is traveling backwards, the control means 32 controls the steering of the rear wheels 3L and 3R based on a single rear wheel steering characteristic.

Therefore, when driving forward, it is possible to select the rear wheel steering characteristics using the manual switch 35, and while it is convenient to be able to control steering according to the rear wheel steering characteristics according to the driver's request, when the rear wheels are driving, the rear wheel steering characteristics are always the same. Since the steering is controlled based on the rear wheel steering characteristics, there is no problem in which the driver cannot follow changes in the characteristics and become unable to drive.

(Effects of the Invention) As described above, the present invention makes it possible to select one rear wheel steering characteristic from a plurality of rear wheel steering characteristics using a manual switch only when driving forward. This is controlled by the wheel steering characteristics, making it possible to achieve both safety when the vehicle is traveling backwards and convenience when the vehicle is traveling forward.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention. Fig. 1 is an overall configuration diagram of a four-wheel steering system for a vehicle, and Fig. 2 shows rear wheel steering characteristics (three) when driving forward and rear wheel steering characteristics when driving backward. FIG. 3 is a flowchart showing the flow of processing in which the rear wheel steering characteristics are set by the control means. 3L, 3R... Rear wheel 32... Control means (rear wheel steering control means) 34.
...Inhibitor switch (forward travel detection means) 35 ...Manual switch

Claims (1)

[Claims] (1) In a device that steers the rear wheels according to predetermined conditions, when driving forward, the rear wheel steering characteristics are determined according to the predetermined conditions, and when driving backward, the steering characteristics are determined according to the predetermined conditions. a rear wheel steering control means for steering the rear wheels based on a single rear wheel steering characteristic; a forward travel detection means for detecting forward travel;
A rear wheel steering device for a vehicle, comprising a manual switch that allows one rear wheel steering characteristic to be selected from the plurality of rear wheel steering characteristics.