JPH03153463A - Rear-wheel steering system for vehicle - Google Patents

Abstract

PURPOSE:To improve the travel safety and controllability of a vehicle at high speed by providing a regulating means which controls rear wheels for steering only at a range where a steering ratio comes to the same phase side when a shift position is in a high gear speed, in a device which changes the steering ratio according to a car speed. CONSTITUTION:A rear-wheel steering system steers both rear-wheels 3L, 3R according to car speed in conformity with a steering ratio characteristic, and it is provided with a steering ratio variable means 21, a power steering means 22, a rear-wheel steering shaft 23 and a neutral position resetting means 24. The steering ratio variable means 21 is provided with a stepping motor 30 controlled by a control means 32 in accordance with each output of a car speed sensor 31, a steering ratio sensor 33, and a shift position detecting means 34. In addition, it steers and controls these rear- wheels at the control means 32 so as to make the steering ratio come to the opposite phase at time of low speed and to the same phase side at time of high speed respectively, but in this case, when it is so detected that the shift position is in a high gear speed, steering control for these rear wheels are made so as to be allowed only at a range where the steering ratio comes to the same phase side by a regulating means 32b.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a rear wheel steering device for a vehicle that changes the steering ratio, which is the ratio of the rear wheel steering angle to the front wheel steering angle, in accordance with the vehicle speed. .

(Prior Art) Conventionally, as described in, for example, Japanese Unexamined Patent Application Publication No. 59-26365, vehicle speed is detected by a vehicle speed sensor, and steering is performed based on the ratio of the rear wheel steering angle to the front wheel steering angle according to the detected vehicle speed. It is known to have a rear wheel steering control means that changes the ratio and controls the steering of the rear wheels so that the steering ratio is on the opposite phase side at low speeds and on the same phase side at high speeds.

(Problem to be Solved by the Invention) However, in the case of such control based on vehicle speed, when braking suddenly at high speed or when the vehicle speed sensor that detects vehicle speed fails, etc., even though the actual vehicle speed is high, If the vehicle speed is determined to be 0, the rear wheels are steered so that the steering ratio is on the opposite phase side, and the vehicle may become unstable. Therefore, conventionally,
To determine the failure of the vehicle speed sensor, two vehicle speed sensors are installed, and a failure of the vehicle speed sensor is determined by determining a discrepancy between them. Also, the shift position is detected in consideration of the case where two vehicle speed sensors fail. An inhibitor switch is installed to determine failure based on the relationship between the shift position and vehicle speed, and brake lock during sudden braking is determined by detecting deceleration when the brake switch is turned on. is a complex and expensive system.

The present invention provides a rear wheel steering device for a vehicle that easily and inexpensively prevents the steering ratio from going to the opposite phase side in the event of a failure of the vehicle speed detection means at high speeds or sudden braking.

(Means for Solving the Problems) In order to achieve the above object, the present invention controls steering of the rear wheels only within a range where the steering ratio is on the same phase side when the vehicle is in a high speed gear.

A specific solution for this purpose is to change the steering ratio, which is the ratio of the rear wheel steering angle to the front wheel steering angle, according to the vehicle speed,
Assuming that the vehicle has a rear wheel steering control means for controlling the rear wheels so that the steering ratio is on the opposite phase side at low speeds and on the same phase side at high speeds, there is provided a vehicle speed sensor for detecting vehicle speed. , a shift position detection means for detecting a shift position of the transmission, and receiving an output from the shift position detection means and controlling the rear wheel steering control means when the shift position is in a high gear, so that the steering ratio is on the same phase side. and a regulating means for controlling the steering of the rear wheels only within a range where

(Function) When the regulating means determines that the shift position is in the high gear based on the signal from the shift position detecting means, the rear wheel steering control means receives the signal from the regulating means and adjusts the output of the vehicle speed detecting means. Even if it is determined that the speed is lower, the steering of the rear wheels is controlled only within a range where the steering ratio is on the same phase side.

(Example) Embodiments of the present invention will now be described in detail 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 left and right rear wheels 3L and 3R. Be prepared.

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 ILL, 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. It consists of a steering shaft 17 with a steering wheel 16 provided at its end, and the front wheel steering shaft 13 is controlled by operating the steering wheel 16.
The front wheels IL and IR are deflected 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 3L and 3R according to the vehicle speed according to a predetermined steering ratio characteristic (see FIG. 2).

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 24H 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 configured to change 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.

Further, the output shaft 21 for the input front wheel steering angle,
The ratio of the displacement amount of a (corresponding to the steering ratio) is configured to change according to the rotation amount of the stepping motor 30. The amount of rotation of the stepping motor 30 is appropriately controlled by a control means 32 based on a vehicle speed signal output from a vehicle speed sensor 31, and the actual amount of rotation of the stepping motor 30 is detected by a steering ratio sensor 33. It is configured to be feedback-controlled by signals.

In order to perform such control, the control means 32 changes the steering ratio according to the vehicle speed and turns off the rear wheel steering control means 32a that controls the steering of the rear wheels 3L and 3R.

The control means 32 also controls the vehicle speed when it is determined that the vehicle is in a high speed gear (for example, 3rd or 4.5th gear in the case of a 5th gear) based on a signal from an inhibitor switch 34 serving as a shift position detection means. Even if it is determined that the speed is low based on the signal from the sensor 31, the rear wheel steering control means 32a is controlled to control the rear wheels 3L and 3R so that the steering ratio is in the same phase based on the characteristic B shown in FIG. Regulation means 3 for controlling steering only in the range where
2b. Note that if it is determined that the gear is in a low gear (1st or 2nd gear, Re gear), the regulation by the regulating means 32b is released, and the rear wheel steering control means 32a operates according to the characteristic A shown in FIG. Based on this, the rear wheels 3L and 3R are steered so that the steering ratio is on the opposite phase side at low speeds and the same phase side at high speeds.

In the case of characteristic B in Fig. 2, the steering ratio approaches the opposite phase side in the low speed range in the high speed gear (for example, 5th gear).
This is to ensure turning performance when driving at low speeds, and the reason why the steering ratio increases in the positive direction on the positive phase side when the vehicle speed is around O is that the vehicle speed sensor This is because the vehicle speed is immediately determined to be 0 in the event of a failure such as a disconnection of the 31, or in the case of brake lock during sudden braking, so the control is performed to ensure stability in such cases.

The power steering means 22 adjusts the rear wheel
L and 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 signal is transmitted to the spool 45a of the control valve 45, and the control valve 45 is moved to 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.

That is, in the control valve 45, the sprue 45a is accommodated 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 neutral position shown in the drawing, hydraulic pressure is supplied from the hydraulic pump 43 to the left oil chamber 42a of the cylinder 42, and the rear wheel steering shaft 23 is affixed to the piston 41. When the wheel steering shaft 23 is displaced to the right, the valve housing 45b is also displaced to the right, and the position of the spool 45a relative to the housing 45b returns to the substantially neutral position, the oil pressure in the left oil chamber 42a of the cylinder 42 is reduced. The supply of spool 45 is stopped, and from that state the supply of spool 45 is stopped.
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 right bending 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
Since it is already well known as described in Japanese Patent No. 8070, etc., 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, and the power steering means 22 further includes a hydraulic pump 4.
A valve means 51 is provided for draining the hydraulic pressure discharged from the cylinder 3 to eliminate 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 passage 52a on the fourth side, and the passage 52a is drained into the tank 44 through a passage 52b. In addition, normally closed valve 5
Nothing is provided in the third side passage 52C. In addition, in the figure, 56 is a filter.

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

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 to close both valves 53 and 54 by energizing only the hydraulic pump 43, generate a rear wheel steering force based on the hydraulic pressure discharged from the hydraulic pump 43, and use the steering force to steer the rear wheels 3L and 3R. Ru.

In addition, in the event of a failure such as when a predetermined abnormality occurs in the rear wheel steering device 4, the normally closed valve 53 is energized, the normal oven valve 54 is deenergized, and both valves 53 and 54 are opened. The hydraulic pressure discharged from the hydraulic pump 43 is directly transferred to the tank 44 via the drain passage 52.
to be discharged.

By doing so, the rear wheel steering force in the power steering means 22 is eliminated, and the neutral position return means 2
Control is performed to return the rear wheel steering shaft 23 to the neutral position by the biasing force of 4, and to bring it into the 2WS state. In addition, both valves 5
3.54 is opened, the oil discharged from the hydraulic pump 43 passes through the control valves 53 and 54 to the tank 43 due to the large resistance of the control valve 450.
is discharged.

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 normal oven valve 54 is opened, resulting in the 2WS state.

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

In FIG. 3, when starting, a shift position is input by a signal from the inhibitor switch 34 (step S1), and then the shift position is set to 1st gear, 2nd gear, or R.
It is determined whether the gear is e (ie, low gear) (step S2).

If the shift position is 1st gear, 2nd gear, or Re gear, the actual vehicle speed is not so high, so even if the steering ratio goes to the opposite phase side due to a failure of the vehicle speed sensor 31 or sudden braking, it will not have much effect. Or, rather, in order to obtain small turning characteristics in the low speed range, based on characteristic A shown in Figure 2, the steering ratio is set to the opposite phase side at low speeds and the same phase at high speeds. Rear wheel 3L
, 3R steering control is performed (step S3), and the process returns.

On the other hand, if it is not 1st gear, 2nd gear, or Re gear, 3.4,
Since the vehicle is in high gear (5th gear) and the actual vehicle speed is considered to be high, based on characteristic B shown in Figure 2, the rear wheels are 3L, 3R
Rear wheel steering control is performed to control steering only within a range where the steering ratios are on the same phase side (step S4), and the process returns.

Therefore, when the shift position is in the high speed gear, the steering ratio is never on the opposite phase side, but always on the same phase side, and the running stability of the vehicle is reliably ensured.

In the above embodiment, the shift positions are 3rd gear, 4th gear, and 5th gear.
Although it is determined that the stage is a high speed stage when the stage is a high speed stage, the second stage, the third stage, the fourth stage, and the fifth stage may be set as the high speed stage, or other combinations may be used.

(Effects of the Invention) As described above, in the present invention, when the regulation means determines the high speed gear based on the signal of the shift position detection means,
Since the rear wheels are controlled only within the same phase range,
i'+J function is a simple and inexpensive way to prevent the steering ratio from going to the opposite phase side even when the actual vehicle speed is high, in the event of a vehicle speed sensor failure or sudden braking. Driving stability and maneuverability can be improved.

[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, FIG. 2 is a diagram showing rear wheel steering characteristics, and FIG. 3 is a diagram showing rear wheel steering characteristics set by a control means. FIG. 3 is a flowchart showing the flow of processing performed. 3L, 3R... Rear wheel 31... Vehicle speed sensor 32... Control means 32a... Rear wheel steering control means 32b... Regulation means 34...Inhibitor switch (shift position detection means) (vehicle speed detection means) 3L, 3R...Rear wheel 31...Vehicle speed sensor (vehicle speed detection means) 32
... Control means 32a ... Rear wheel steering control means 32 b ... Regulation means 34 ... Inhibitor switch (shift position detection means) Fig. 3

Claims (1)

[Claims] (1) The steering ratio, which is the ratio of the front wheel steering angle to the rear wheel steering angle, is changed according to the vehicle speed, and the steering ratio is set to the opposite phase side at low speeds and to the same phase side at high speeds. A vehicle having a rear wheel steering control means for controlling the steering of the rear wheels, comprising: a vehicle speed sensor for detecting vehicle speed; a shift position detection means for detecting a shift position of the transmission; and a shift position detecting means receiving an output of the shift position detecting means. and regulating means for controlling the rear wheel steering control means to control the steering of the rear wheels only within a range where the steering ratios are on the same phase side when the rear wheels are in a high speed gear. Steering device.