JPH03178880A - Rear wheel steering device of vehicle - Google Patents

Abstract

PURPOSE:To prevent uneven wearing of a tire while ensuring running stability of a vehicle by providing a means for steering a rear wheel in a toe-in direction only in the case that the vehicle is during turning motion further with acceleration of the vehicle in its deceleration direction in not less than a predetermined value. CONSTITUTION:A control of rear wheel steering is started simultaneously with stepping in an accelerator pedal. First a steering angle signal thetaH and an acceleration signal alpha are read. Next, whether the steering angle thetaH is 0 or not, that is, whether a vehicle is during turning motion or not is discriminated, further in the case of the vehicle during turning, acceleration alpha acts in a deceleration direction, further whether its absolute value is in not less than a predetermined value alpha0 or not, that is, whether acceleration in the deceleration direction in not less than the predetermined value alpha0 acts or not on the vehicle is discriminated. In the case of the acceleration in the deceleration direction in not less than the predetermined value alpha0 acting on the vehicle, the vehicle is judged during deceleration turning motion by a control unit 40, and a control target value of a rear wheel toe-angle is determined from the steering angle thetaH and the acceleration based on a map.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a rear wheel steering device for a vehicle.

(Prior Art) A rear wheel steering device is known as a steering device for improving turning performance of a vehicle at low speeds or improving running stability at high speeds. The rear wheel steering device steers the rear wheels to the opposite phase or the same phase as the front wheels, or steers the rear wheels in a toe-in direction or a toe-out direction, depending on the driving condition of the vehicle. For example, Japanese Unexamined Patent Publication No. 193780/1983 discloses a method for changing the toe angle of the rear wheels in the toe-in direction as the vehicle speed increases, so that the vehicle can run over a wide range of vehicle speeds. A rear wheel steering device with improved stability is disclosed.

(Problems to be Solved by the Invention) When the vehicle is traveling straight, the running stability of the vehicle is ensured even when traveling at high speed. Furthermore, even if the vehicle is making a turning motion, the running stability of the vehicle will not be significantly compromised if the vehicle is accelerating or traveling in a erratic manner. Taking these points into consideration, it is considered that there is a relatively low need to control the torque angle of the rear wheels in the toe-in direction while the vehicle is traveling straight or accelerating or turning at a constant speed in order to ensure running stability of the vehicle. However,
・The rear wheel steering device disclosed in Japanese Patent Application Laid-open No. 193780/1980 allows the rear wheels to be steered even when driving straight, or when accelerating or turning at a constant speed. The torque angle of the engine is controlled in the toe-in direction, and in order to pursue such excessive running stability, there is a problem in that unnecessary load is applied to the engine and the engine, causing uneven tire wear.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a rear wheel steering device for a vehicle that can prevent uneven tire wear while ensuring running stability of the vehicle.

(Means for Solving the Problems) In order to solve the above problems, the present invention includes means for detecting the running state of the vehicle, and means for steering the rear wheels in the toe-in direction according to the running state of the vehicle. A rear wheel steering system for a vehicle, comprising: a means for detecting a turning motion of the vehicle; a means for detecting an acceleration of the vehicle; and a means for detecting a turning motion of the vehicle; and means for steering the rear wheels in the toe-in direction only in the above cases.
゛Providing a vehicle rear wheel steering device.

(Function) In the present invention, as described above, by means of the means for detecting rotational motion of the vehicle and the means for detecting the acceleration of the vehicle, the lI
The torque angle of the rear wheels is controlled in the toe-in direction only when it is detected that the vehicle is turning at a deceleration rate with an acceleration of J'T.

(Example) The present invention will be described in detail below based on the accompanying drawings.

In Figure 1, 1R is the right front wheel, IL is the left front wheel, 2R is the right rear wheel, and 2L is the left rear wheel.The left and right front wheels IR and LL are connected to the front wheel steering mechanism A, and the left and right rear wheels are connected to the front wheel steering mechanism A. 2R and 2L are connected to rear wheel steering mechanism B.

The front wheel steering mechanism A includes a pair of left and right knuckle arms: 3R, 3L and a tie rod 4R14L, and a relay rod 5 that connects the pair of left and right tie rods 4R14L.

A steering mechanism C is connected to this front wheel steering mechanism A, and the steering mechanism C is of a rack and pinion type in the embodiment, and when the steering wheel 6 is turned to the right, the relay rod 5 is 1, and the left and right front wheels IR and IL are steered to the right by an amount corresponding to the amount of operation displacement of the handle 6, that is, the steering angle. Similarly, when the steering wheel 6 is operated to turn to the left, the left and right front wheels IR1IL are steered to the left according to the amount of displacement of this operation.

Further, like the front wheel steering mechanism A, the rear wheel steering mechanism B also includes a pair of left and right knuckle arms 10R, IOL and tie rods IIR, IIL, as well as a coupling mechanism that connects the tie rods 4R14L.

As shown in detail in FIG. 2, the above-mentioned coupling mechanism is arranged between the left and right rear wheels 2R12L, each with a pivot center 2 relative to the vehicle body.
It has a pair of rocking pieces 2OR12OL attached so as to be swingable in the left-right direction about 0R' and 2OL'. Of the pair of rocking pieces 2OR120L, the right rocking piece 20R is connected to the inner end in the vehicle width direction of the right relay rod 21R, and the outer end of the right relay rod 21R is connected to the right tie rod IIR. . Similarly, the left swing piece 2OL is connected to the inner end in the vehicle width direction of the left relay rod 21L, and the outer end of the left relay rod 21L is connected to the left tie rod IIL. Further, the pair of swinging pieces 20R120L are each connected to a pair of left and right connecting rods 22R122L, and the inner ends of the pair of left and right connecting rods 22R, 22L are both connected to a ball nut 23.

The pole nut 23 is supported so as to be axially displaceable with respect to the vehicle body, and is attached with its axis directed in the longitudinal direction of the vehicle body. A threaded rod 24 is inserted into the inside of the pole nut 23, and the outer peripheral surface of the threaded rod 24 and the pole nut 23
A large number of balls 25 are movably disposed between the inner circumferential surface of the ball and the inner circumferential surface of the ball.

Incidentally, a threaded groove in which the ball 25 rolls is formed on the inner circumferential surface of the pole nut 23 and the outer circumferential surface of the threaded rod 21, but since such a structure is known, it is shown in a simplified manner in the drawing. As a result, the pole nut 23 is displaced in the longitudinal direction of the vehicle body in accordance with the forward and reverse rotation of the threaded rod 24, and the left and right relays 21R and 21L approach or separate from each other in the vehicle width direction. Now, when the pole nut 23 is displaced to the rear of the vehicle body, the right relay rod 21R is displaced to the right in FIG. 2, and at 2, the right rear wheel 2R is steered in the toe-in direction.

Similarly, the left relay rod 21L is displaced to the left in FIG. 2, and the left rear wheel 2L is also steered in the toe-in direction.

The means for driving the rear wheel steering mechanism B described in L, that is, the drive mechanism E for steering the left and right rear wheels 2R12L will be explained. The drive mechanism E includes a step motor 30, which is fixed to the vehicle body, and whose output shaft 30a is connected to the threaded rod 24. Therefore, in accordance with the forward and reverse rotation of the step motor 30, the pole nut 23 is displaced in the longitudinal direction of the vehicle body, and due to the displacement of the pole nut 23, the left and right rear wheels 2R12L are simultaneously steered in the toe-in or toe-out direction. .

Furthermore, 40 is a control unit configured by a microcomputer, and the control unit 40 basically includes a CPU, ROM, and RAM, and also has a built-in control circuit 41 that controls the rotation of the step motor 30. . 42 is a steering angle sensor that detects the steering wheel angle; 43 is an acceleration sensor that detects the acceleration of the vehicle; signals from these sensors 42 and 43, that is, a steering angle signal θ8 and an acceleration signal α, are sent to the control unit 40. is input. Further, a control signal is output from the control unit 40 to the step motor 30.

Next, the details of rear wheel steering control will be explained. The toe angle of the rear wheels is a predetermined reference toe angle T. Then, the toe-in direction is controlled according to the driving state of the vehicle, that is, the steering wheel angle and the acceleration in the deceleration direction. FIG. 3 is an example of a map for rear wheel steering that defines the correlation between the control target value of the rear wheel toe angle in the toe-in direction, the steering wheel steering angle, and the acceleration in the deceleration direction. In Fig. 3, the control target value is expressed in mm.
To explain with reference to the figure, for example, if the control target value is +6 mm
In the case of , the angle that increases the difference between A and B in the diagram by 6 mm,
The toe angle of the rear wheel is the standard toe angle T. This means steering the rear wheels 2R12L so as to change from toe-in direction.

Furthermore, even with the same steering angle, the control target value is set to a larger value as the acceleration in the deceleration direction increases, which makes it possible to effectively suppress spin during deceleration turns, that is, to ensure running stability during deceleration turns. It is being

Control of rear wheel steering is performed based on the flow shown in FIG.

In addition, in FIG. 5, S means a control step. Rear wheel steering control starts at the same time as the accelerator pedal is depressed. First, the steering angle signal θ8 and the acceleration signal α are read (St, 32).

Next, it is determined whether the steering angle θ8 is not 0, that is, whether the vehicle is turning or not (S3). If the vehicle is turning, it is determined that the acceleration α is acting in the deceleration direction and that the vehicle is turning. The absolute value is the predetermined value α.

In other words, whether or not the predetermined value α is greater than or equal to the vehicle value.

It is determined whether or not the above acceleration in the deceleration direction is working (S4). A predetermined value α is applied to the vehicle. When the above acceleration in the deceleration direction is acting, the control unit 40 determines that the vehicle is decelerating and turning, and based on the map in FIG. S5 to determine the control target value f(θ□・α) of the rear wheel toe angle to
), and outputs a control signal corresponding to the control target value f(θ9·α) to the step motor 30 (S6). As a result, the toe angle of the rear wheels becomes the reference toe angle T by an angle corresponding to the control target value f(θ, ·α). The rear wheels 2R12L are steered so as to change from the toe-in direction to the toe-in direction. When the vehicle is not turning, a predetermined value α is applied to the vehicle. If the above acceleration in the deceleration direction is not working, the process returns to step S1 and the control continues (S3.84).

Although the present invention has been described in detail above, it goes without saying that the present invention is not limited to the above-mentioned embodiments, and that various modifications can be made within the scope of the invention described in the claims.

(Effects) As described above, in the present invention, when it is detected by the vehicle turning motion detection means and the vehicle acceleration detection means that the vehicle is decelerating and turning with a predetermined acceleration, only, the toe angle of the rear wheels is controlled in the toe-in direction.

Therefore, running stability is ensured during deceleration and turns when the vehicle tends to run unstable, thereby ensuring the running stability of the vehicle and limiting rear wheel toe-in control to the minimum necessary range. Therefore, uneven tire wear is prevented.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram of a rear wheel steering device according to an embodiment of the present invention, and FIG. 2 is a detailed diagram of the main parts of FIG. 1. Fig. 3 is an example of a map for rear wheel steering that defines the correlation between the control target value of the rear wheel toe angle in the toe-in direction, the steering wheel steering angle, and the acceleration in the deceleration direction, and Fig. 4 shows the toe-in control target value. FIG. 3 is an explanatory diagram of settings. FIG. 5 is a flowchart showing an example of control. 2R, 2L... Rear wheel, 30... Step motor, 40... Control unit, 42... Rudder angle sensor, 43... Acceleration sensor. Figure 1 Figure 3

Claims (1)

[Claims] A rear wheel steering device for a vehicle, which includes a means for detecting a running state of the vehicle, and a means for steering a rear wheel in a toe-in direction according to the running state of the vehicle, the means for detecting a turning motion of the vehicle; and means for steering the rear wheels in the toe-in direction only when the vehicle is in a turning motion and the acceleration in the deceleration direction of the vehicle is equal to or greater than a predetermined value. Rear wheel steering device for vehicles.