JPH0361174A - Rear-wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To improve a small sharp turn of a vehicle by operating a front-wheel steering speed and correcting a rear-wheel steered angle to an inphase side at the time of low-speed quick steering based on the operation result in a device in which rear wheels are steered to an antiphase side to front wheels to a front-wheel steered angle at the time of a low speed. CONSTITUTION:In a four-wheel steering vehicle, following units are provided: a front-wheel steering device 3 steering front wheels 2 corresponding to the operation of a steering wheel 1, a rear-wheel steering device 5 steering rear wheels 4 corresponding to the steering of the front wheels 2, a power steering mechanism 6 assisting the steering force of the front-wheel steering device 3, and a 4WS control unit 7 changing a rear-wheel steering characteristic from an in-phase side to an antiphase side to the front wheels corresponding to a vehicle speed and a front-wheel steered angle. Moreover the 4WS control unit 7 is composed so as to control the rear wheel steering device 5 so that the rear wheels 4 are steered to the antiphase side to the front wheels 2 to the front-wheel steered angle at the time of a low speed, and also a rear-wheel steered angle is corrected in the in-phase side at the time of low-speed quick steering corresponding to a front-wheel steering speed.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention aims to improve the turning ability by, for example, steering the rear wheels in a phase opposite to the front wheels at low speeds with respect to the steering angle of the front wheels. The present invention relates to a rear wheel steering system for a vehicle such as a vehicle speed sensitive electronically controlled 4WS.

(Prior Art) Conventionally, as the rear wheel steering device of the above-mentioned vehicle, for example,
There is an apparatus described in JP-A-60-1-93771.

That is, a front wheel steering mechanism that steers the front wheels, a hydraulically assisted rear wheel steering mechanism that steers the rear wheels, a steering mechanism linked to the above-mentioned front wheel steering mechanism, vehicle speed, front wheel steering angle θ, and a steering ratio changing device that changes the steering ratio (θ/θ,) in accordance with the above-mentioned vehicle speed, for example,
km/h, set the rear wheel steering angle θ1 to 0 (2WS), and set the rear wheel steering angle θ1 to 20
At low vehicle speeds of less than 50 km/h, the rear wheel steering characteristics are changed to the opposite phase side with respect to the front wheels, and at high vehicle speeds of 50 km/h or more, the rear wheel steering characteristics are changed to the same phase side with respect to the front wheels. This is a four-wheel steering device for a vehicle.

However, such conventional devices have the following problems.

For example, when the above-mentioned 4WS vehicle is parked on the road shoulder and the steering wheel is turned sharply from this parking position to the opposite road shoulder to suddenly start, the rear wheels are steered at a relatively large angle to the opposite phase side due to the above-mentioned rear wheel steering characteristic. Therefore, there is a problem in that the rear part of the vehicle body largely protrudes toward the road shoulder during the above-mentioned sudden start (during sudden steering at low speed).

(Object of the Invention) The present invention provides a rear wheel of a vehicle that can improve maneuverability by suppressing the protrusion of the rear part of the vehicle body during low-speed sudden steering such as when suddenly starting from a parking position. The purpose is to provide a steering system.

(Structure of the Invention) The present invention is a rear wheel steering device for a vehicle configured to steer the rear wheels in a phase opposite to the front wheels at low speeds with respect to the steering angle of the front wheels, the output of a front wheel steering angle sensor. A rear wheel steering device for a vehicle, comprising a calculation means for calculating a front wheel turning speed based on the calculation means, and a correction means for correcting a rear wheel turning angle to the same phase side during low speed sudden steering based on the calculation result of the calculation means. characterized by something.

(Effects of the Invention) According to the present invention, during low-speed sudden steering, for example, when starting suddenly from a roadside parking position, the above-mentioned correction means corrects the rear wheel turning angle to the in-phase side based on the calculation result of the above-mentioned calculation means. Therefore, it is possible to suppress the protrusion of the rear part of the vehicle body when suddenly starting from a parking position such as in a double-barreled parking position, thereby improving maneuverability.

(Example) An embodiment of the present invention will be described in detail below based on the drawings.

The drawing shows a four-wheel steering system for a vehicle, and in FIG. a rear wheel steering device 5 that steers the rear wheels 4, 4 in response to the steering of the vehicle; a power steering mechanism 6 that assists the steering force of the front wheel steering device 3;
The 4WS control unit 7 changes the rear wheel steering characteristic (see FIG. 3) from the in-phase side to the opposite-phase side with respect to the front wheels 2, 2 in response to the steering angle θ.

The front wheel steering device 3 described above includes a rack shaft 8 extending in the vehicle width direction.
A so-called relay rod, left and right tie rods 10.10 and knuckle arms 14, 1 connected to both ends of this rack shaft 8 via ball joints 9.9, respectively.
1, and a steering shaft having a pinion 13 attached to its tip end that meshes with the rack 12 of the above-mentioned rack shaft 8]
4, and when the steering shaft 14 is rotationally driven via the steering wheel 1, the rack shaft 8 slides left and right to steer the front wheels 2.2 in the left and right directions around the kingpin. It consists of

On the other hand, the above-mentioned rear wheel steering device 5 has a knuckle 15, 1.5, a knuckle arm 16° 16, a tie rod 17. ], 7. A rear wheel steering rod 19 connected via a ball joint 18, 18, a motor 20 serving as an operating section for slidingly displacing this rear wheel steering rod 19 in the vehicle width direction, and driving of this motor 20. A reduction gear mechanism 21 is provided that transmits force to the rear wheel steering rod 19 described above.

The above-mentioned rear wheel steering rod 19 is provided with the following functions: when the clutch 22 is turned off when a failure occurs in the rear wheel steering device 5,
A neutral position biasing means 23 is installed as a fail-safe mechanism for biasing the rear wheels 4.4 to the neutral position (2WS state of the rear wheel steering system).

As shown in FIG. 2, this neutral position biasing means 23 includes a locking holder 24.24 fixed to a predetermined portion of the rear wheel steering rod 19 for 1ulF, and both of these locking holders 24.24.
A slideable retainer 25, 25 loosely fitted to the rear wheel steering rod 19, a centering spring 26 stretched between the left and right retainers 25, 25, and a stopper tube 27 fixed to the rear steering control box. When the rear wheels 4, 4 are in the neutral position, the left and right retainers 25, 25 maintain contact with the stopper tubes 27, and the rear wheel steering rod 19 slides to either the left or right. rear wheel 4,
4 is steered, the retainer 25 on the reverse steering direction side is separated from the stopper tube 27, and due to the compression reaction force of the centering spring 26, the above-mentioned rear wheel steering rod 1
-9 is set to the neutral position with a spring (j force).

- A rotary encoder 28 for detecting the rotation angle of the motor 2o is attached to one side of the motor 20, while a brake 3° is installed between the motor rotation shaft 29 and the clutch 22 on the other side of the motor 2o. The brake 30 is operated when the rear wheels 4, 4 are steered at a predetermined angle, and the motor 2o is stopped to reduce the load on the motor 20.

A plurality of reduction gears and a ball screw 32 are provided between the output shaft 31 of the clutch 22 and the rear wheel steering rod 19.
A deceleration mechanism 21 including a deceleration mechanism 21 is provided, and the rotational force of the motor 20 is converted into a slide driving force by the ball screw 32 to drive the rear wheel steering rod 19.

For the above-mentioned deceleration, a gear sensor 33 is disposed near the wheel mechanism 21 to detect the amount of operation of the mechanism 21.

By the way, the above-mentioned 4WS control unit 7 is CP
Equipped with U40, ROM34, and RAM35, the above-mentioned CPU
Reference numeral 40 indicates a steering angle signal from a wheel steering angle sensor 36 that detects the amount of operation of the steering wheel 1, and a steering angle from a front wheel steering angle sensor 37 that detects the front wheel steering angle according to the amount of operation of the front wheel rack shaft 8. signal, a vehicle speed signal from a first vehicle speed sensor 38 that detects the vehicle speed according to the rotational speed of the front wheels 2, 2, and a vehicle speed signal from the second vehicle speed sensor 39 that detects the vehicle speed according to the rotational speed of the thrust shaft (propeller shaft). ROM 3 based on the vehicle speed signal and the feedback signals from the rotary encoder 28 and gear sensor 33.
The motor 20, the brake 30, and the clutch 22 are controlled according to the program stored in the RAM 35.
are vehicle speed data that changes the rear wheel steering characteristic to the in-phase side with respect to the front wheels 2, 2, vehicle speed data that changes the same characteristic to the opposite phase side, vehicle speed data that makes the rear wheel steering angle zero (2WS), and Necessary data of α such as data corresponding to the set value θ of the wheel turning angle and data corresponding to the set value θ9 of the front wheel turning speed are stored.

Here, the above-mentioned CPU 40 is the above-mentioned steering angle sensor 36.3.
a calculation means for calculating the front wheel turning speed θ, based on the output from 7; and a calculation means for calculating the front wheel turning speed θ, based on the calculation result of this calculation means, during low speed sudden steering, for example, when the vehicle speed is 10 km/h or less. , is the set value θ°. It also serves as a correction means for correcting the rear wheel turning angle θ1 to the in-phase side when the angle is larger, and the above correction is performed by the following equation. That is, θ, = -f (V) θF 01F where 01 is the rear wheel steering angle f (V) is the steering ratio θ that changes with vehicle speed (V), and the front wheel steering angle is a correction constant θ. , represents the front wheel turning speed K e'', and represents the correction term.

Note that the normal 4WS control that does not require the above-mentioned correction term (Kθ°, ) has the steering ratio characteristic shown in FIG.

The operation of the four-wheel steering system for a vehicle configured as described above will be described and explained with reference to the flowchart shown in FIG.

When the ignition switch is turned on in the first step 41, the CPU 40 turns on the RAM 3 in the next second step 42.
A flag is set in a predetermined area of 5 (F=1).

Next, in a third step 43, the CPU 40 controls the vehicle speed sensor 3.
The current vehicle speed (V) from 8.38 is compared with a set value stored in advance in the RAM 35, for example], Okm/l], and when V>10 km/h, the process moves to the next fourth step 44.

In this fourth step 44, the CPU 40
Knock down the flag set in the designated area of 35 (F=0).

Next, in a fifth step 45, the CPU 40 controls the steering angle sensor 3.
Based on the signals from 6 and 37, the current front wheel steering angle θ is detected.

Next, in a sixth step 46, the CPU 40 determines the rear wheel steering angle (θ==f(V)θF) based on the above-mentioned front wheel steering angle θF, and adjusts the rear wheel steering angle to the rear wheel 4 via the rear wheel steering device 5. , 4.

Such normal 4WS control has a steering ratio characteristic as shown in FIG.

By the way, in the third step 43 mentioned above, the CPU 40
When it is determined that the speed is <10 km/h, the process moves to the next seventh step 47.

In this seventh step 47, the CPU 4o determines whether or not a flag is set in a predetermined area of the RAM 35 (F-↓), and when F=Q, the process proceeds to the fourth step 44 described above; When this happens, the process moves to the next eighth step 48.

In this eighth step 48, the CPU 4o controls the steering angle sensor 36.
, 37, detects the current front wheel steering angle θ, and detects the above-mentioned front wheel steering angle θ.

The front wheel steering speed θ is calculated by differentiating θ with respect to a predetermined unit time.
, is calculated.

Next, in the ninth step 49, the CPU 40 compares the absolute value (Iθ, 1) of the current front wheel steering angle θ with the set value θ stored in advance in the RAM 35, and when θF l<θN, The process moves to the fifth step 45 described above, while the process moves to the next tenth step 50 when θ, >θ.

1 In this tenth step 50, the CPU 40 calculates the current front wheel turning speed θ□ and the set value θ゛ stored in advance in the RAM 35.
Compared with, α θ°F〈θ°. When , the process moves to the fifth step 45 described above, while when θ,>θ6, that is, during low-speed sudden steering such as a sudden start from a parking position (when transitioning to a large steering angle), the process moves to the next 11th step 5.
Move to 1.

At this 10th step 50, the CPU 40 determines the double front wheel steering speed θ9. Based on this, the rear wheel turning angle θ1 is corrected to the in-phase side.

That is, the above-mentioned rear wheel steering angle θ1 becomes θR=-f(■)θF+θF, and the rear wheel steering device 5 turns the rear wheel 4 according to 01 in the above equation.
.

In this way, during low-speed sudden steering, for example when starting suddenly from a parking position on the roadside, the correction means (eleventh step 51 under the control of the CPU 40) is executed based on the calculation result of the above-mentioned calculation means (the eighth step 48 under the control of the CPU 40). Since the rear wheel steering angle θ1 is corrected to the in-phase side, it suppresses the protrusion of the rear of the vehicle body when suddenly starting from a parking position as described above, assists the driver's driving sense, and improves maneuverability. There is an effect that can be done.

Note that such correction processing for the in-phase side is performed only once at the time of sudden start, and after that, normal 4WS control is performed.

In the correspondence between the structure of the present invention and the embodiments described above, the calculation means of the present invention corresponds to the eighth step 48 controlled by the CPU 40 in the embodiment, and similarly, the correction means corresponds to the 11th step 48 controlled by the CPU 40 in the embodiment. Step 5
] However, the present invention is not limited to the configuration of the above-described embodiment.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, FIG. 1 is a system diagram showing a four-wheel steering system of a vehicle, FIG. 2 is a system diagram showing a rear wheel steering system of a vehicle, and FIG. 3 is a system diagram showing a steering ratio characteristic. The explanatory diagram, FIG. 4, is a flowchart. 2... Front wheel 4... Rear wheel 5... Rear wheel steering device 36.37... Rudder angle sensor 40... CPU 48... Eighth step (calculating means)

Claims (1)

[Claims] (1) A rear wheel steering device for a vehicle configured to steer the rear wheels in a phase opposite to the front wheels at low speeds with respect to the steering angle of the front wheels, the device steering the front wheels based on the output of a front wheel steering angle sensor. A rear wheel steering device for a vehicle, comprising a calculation means for calculating a speed, and a correction means for correcting a rear wheel turning angle to the same phase side during low speed sudden steering based on the calculation result of the calculation means.