JPH04345515A - Rear wheel steering device for vehicle - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear wheel steering device for a vehicle, and more particularly to a rear wheel steering device for a four-wheel steering type vehicle.

0002

BACKGROUND OF THE INVENTION Some rear wheel steering devices for four-wheel steering vehicles that steer both the front wheels and the rear wheels simultaneously steer the left and right rear wheels, as shown in Japanese Patent Application Laid-open No. 193780/1983. There is something that steers the vehicle in the toe-in direction. This conventional vehicle rear wheel steering system variably controls the toe of the left and right rear wheels in response to the vehicle speed, setting the optimal toe for the vehicle speed from extremely low speeds to high speeds, ensuring driving stability at all vehicle speeds. is improving.

0003

However, the conventional vehicle rear wheel steering system described above merely variably controls the toe of the left and right rear wheels in response to the vehicle speed. Therefore, when braking to decelerate while turning,
Simply performing toe control in response to vehicle speed has the problem of decreasing vehicle stability.

The present invention has been made to solve the above-mentioned problems of the prior art, and provides a rear wheel steering system for a vehicle that can ensure running stability of the vehicle when decelerating in a turning state. is intended to provide.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a rear wheel steering system for a vehicle in which the left and right rear wheels are respectively steered in the toe-in direction during deceleration. toe-in control means for starting rear wheel toe-in control when the start threshold is exceeded;
The present invention is characterized by comprising a threshold value changing means that sets the toe-in control start threshold value of the toe-in control means smaller as the amount of steering angle of the steering wheel becomes larger.

In the rear wheel steering system of the present invention configured as described above, when the vehicle decelerates while turning, the toe-in control means performs toe-in control on the left and right rear wheels, and furthermore, when starting this toe-in control, Since the threshold value of the deceleration of the vehicle is set by the threshold value changing means to be smaller as the amount of steering angle of the steering wheel increases, running stability of the vehicle can be quickly ensured in accordance with the amount of steering angle of the steering wheel.

Further, in the present invention, the threshold value changing means sets the threshold value smaller as the vehicle speed increases. Therefore, the running stability of the vehicle can be quickly ensured in accordance with the vehicle speed.

[0008]

[Embodiment] An embodiment of the present invention will be described below with reference to FIGS. 1 to 5.
Explain with reference to. FIG. 1 is an overall schematic diagram showing a rear wheel steering device of a vehicle according to the present invention, FIG. 2 is a detailed view of the main parts of FIG. 1, FIG. 3 is a flowchart showing toe-in control by the rear wheel steering device of a vehicle according to the present invention, and FIG. is a map showing the relationship between the deceleration threshold for starting toe-in control, the steering angle of the steering wheel, and the vehicle speed;
FIG. 5 is a map showing the relationship between the toe-in correction angle, the steering angle of the steering wheel, and the deceleration of the vehicle.

In FIG. 1, 1R is a right front wheel, 1L is a left front wheel, 2R is a right rear wheel, and 2L is a left rear wheel. These left and right front wheels 1R, 1L are connected by a front wheel steering mechanism A,
Further, the left and right rear wheels 2R and 2L are connected by a 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 4R.
, 4L, and a relay rod 5 connecting these left and right pair of tie rods 4R, 4L. A rack and pinion type steering mechanism C is connected to this front wheel steering mechanism A. According to this steering mechanism C, when the steering wheel 6 is turned to the right,
The relay rod 5 is displaced to the left in FIG. 1, and the left and right front wheels 1R and 1L are steered to the right by an amount corresponding to the steering angle of the steering wheel. Similarly, if you turn the handle 6 to the left,
The left and right front wheels 1R and 1L are steered to the left in accordance with this operational displacement amount.

Similarly to the front wheel steering mechanism A, the rear wheel steering mechanism B also includes a pair of left and right knuckle arms 1, respectively.
In addition to having 0R and 10L and tie rods 11R and 11L, it also has a connecting mechanism D that connects these pair of left and right tie rods 11R and 11L. Next, the connection mechanism D will be explained with reference to FIG. The coupling mechanism D has a pair of swinging pieces 20R and 20L that are attached to the vehicle body between the left and right rear wheels 2R and 2L so as to be swingable in the left-right direction. 20 in the diagram
R' and 20L' indicate the rocking centers of the rocking pieces 20R and 20L. This pair of rocking pieces 20R and 20L are the right rocking piece 2
0R 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 11R. Similarly, the left swing piece 20L 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 11L. The pair of rocking pieces 20R, 2
0L is further connected to a pair of left and right connecting rods 22R, 22L, and the pair of left and right connecting rods 22R,
22L is connected to the ball nut 23 at its inner end.

The ball nut 23 is supported so as to be axially displaceable with respect to the vehicle body, and is attached with its axis facing in the longitudinal direction of the vehicle body. A threaded rod 24 is inserted into the ball nut 23, and a number of balls 25 are rotatably arranged between the outer peripheral surface of the threaded rod 24 and the inner peripheral surface of the ball nut 23. Here, threaded grooves in which the balls 25 roll are formed on the inner circumferential surface of the ball nut 23 and the outer circumferential surface of the threaded rod 24, but since this structure is known, it is simplified in the drawing. . As a result, the ball 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 relay rods 21R and 21L are moved toward or away from each other in the vehicle width direction. Now, when the ball nut 23 is displaced in a predetermined constant direction, the right relay rod 21R is displaced to the right in FIG. 2, and the right rear wheel 2R is towed in. Similarly, the left relay rod 21L is displaced to the left, and the left rear wheel 2L is also towed in.

Referring to FIG. 2, the drive means E for steering the left and right rear wheels 2R and 2L, which is means for driving the rear wheel steering mechanism B, will be described. This driving means E is constituted by a step motor 30, and this step motor 3
0 is fixed to the vehicle body, and its output shaft 30a is connected to the threaded rod 24. For this reason, the step motor 30
The ball nut 23 is displaced in the longitudinal direction of the vehicle body in accordance with the forward and reverse rotation of the vehicle, and the displacement of the ball nut 23 causes the left and right rear wheels 2R, 2L to be simultaneously steered in the toe-in or toe-out direction.

In FIGS. 1 and 2, reference numeral 40 denotes a control unit constituted by a microcomputer, and this control unit 40 includes a CPU, ROM, and RAM, and also includes a control means 41 for changing the rotational speed of the step motor 30. Built-in. This control unit 40 includes
Signals from sensors S1 to S5 are input. S1 is a vehicle speed sensor, S2 is a throttle position sensor, S3 is a brake switch, S4 is a steering wheel angle sensor, and S5
indicate the respective encoders.

Next, details of rear wheel toe control according to the present invention will be explained with reference to FIGS. 3 to 5. In the present invention, when turning and braking, the toe angle of the rear wheels is further controlled in the toe-in direction from the toe angle (T1), which is a control target value based on the vehicle speed, in order to ensure vehicle stability. Ru. At this time, when the deceleration of the vehicle exceeds a predetermined threshold value (αTR≧0), toe-in direction control is started. In the present invention, the value of the vehicle deceleration threshold (αTR) for starting this toe-in control is changed depending on the steering angle (θH) of the steering wheel and the vehicle speed. That is, the larger the steering angle (θH) of the steering wheel is, the smaller the vehicle deceleration threshold (αTR) is set, and the larger the vehicle speed is, the smaller the vehicle deceleration threshold (αTR) is set.

Specifically, as shown in FIG.
At step 10, the vehicle speed (V) is input, and at step P11, the steering angle (θH) of the steering wheel is input. Next, in P12, it is determined whether the flag F=1. Flag F=1 means that toe-in control based on braking is being performed. If F=0 now, the process proceeds to P13, where it is determined whether the vehicle speed (V) exceeds 50 km/H. If the vehicle speed (V) exceeds 50 km/h, the process proceeds to P14, where it is determined whether the brake switch S3 is turned on, that is, whether the brake pedal is depressed. When the brake pedal is depressed, first, in P15, the vehicle speed (V) is changed from the deceleration (α≧
0), and then in P16 the steering angle of the steering wheel (θ
The toe-in control start threshold (αTR) is determined from H ). This threshold (αTR) is read from the map shown in FIG. This map shows the relationship between the deceleration threshold for starting toe-in control, the steering angle of the steering wheel, and the vehicle speed,
The larger the steering angle (θH) of the steering wheel is, the smaller the vehicle deceleration threshold (αTR) is set, and the vehicle speed (V1 >
The larger the value (V2>V3>V4) is, the smaller the vehicle deceleration threshold (αTR) is set. In P17, if the vehicle deceleration (α≧0) is larger than the toe-in control start threshold (αTR≧0), in P18 A(
For example, a target value T2 of 6 mm) is set. Here, the value of the correction angle A in the toe-in direction is read from the map shown in FIG. FIG. 5 is a map showing the relationship between the toe-in correction angle, the steering angle of the steering wheel, and the deceleration of the vehicle.
The larger α2 > α3 ≧0), the larger the value. The toe-in control speed during this braking, that is, the rotation of the step motor 30 is quickly rotated at a speed of 50 msec. This quickly ensures driving stability when braking while turning. In this toe-in control, the flag F=1 is set at P19 until the braking is released, and this toe-in state is continued. Note that when the vehicle speed is 50 km/h or less and the braking is released, the flag F is reset.

Toe-in control based on this braking is not performed unless the brake pedal is depressed, and the control target value T1 based on the vehicle speed is set as is (P20, P21). Here, in P21, the control in the toe-out direction accompanying the release of the brake is performed relatively slowly, with the rotational speed of the step motor 30 being set to 1 sec, thereby ensuring running stability. Further, in P22, the flag F=0 is set. Note that in FIG. 3, T2 indicates a control target value that takes into account braking.

[0017]

[Effects of the Invention] As explained above, in the present invention,
When decelerating while turning, the threshold for vehicle deceleration when starting toe-in control is set smaller as the steering angle of the steering wheel increases. Stability can be ensured.

Further, in the present invention, the threshold value is set to be smaller as the vehicle speed increases, so that the running stability of the vehicle can be ensured in accordance with the vehicle speed.

[Brief explanation of drawings]

FIG. 1 is an overall schematic diagram showing a rear wheel steering device of a vehicle according to the present invention.

[Figure 2] Detailed view of the main parts of Figure 1

FIG. 3 is a flowchart showing toe-in control by the rear wheel steering device of the vehicle according to the present invention.

[Figure 4] Map showing the relationship between the deceleration threshold for starting toe-in control, steering angle of the steering wheel, and vehicle speed

[Figure 5] Map showing the relationship between toe-in correction angle, steering angle of the steering wheel, and vehicle deceleration

[Explanation of symbols]

2R Right rear wheel 2L Left rear wheel B Rear wheel steering mechanism D Connection mechanism E Rear wheel drive mechanism 23 Ball nut 30 Step motor 40 Control unit 41 Step motor rotational speed control means S1 Vehicle speed sensor S2 Throttle position sensor S3 Brake switch S4 Handle Rudder angle sensor S5 encoder

Claims (2)

[Claims] Claim 1: A rear wheel steering system for a vehicle in which the left and right rear wheels are respectively steered in a toe-in direction during deceleration, which performs toe-in control of the rear wheels when the deceleration of the vehicle becomes greater than a toe-in control start threshold. Rear wheel steering of a vehicle characterized by comprising: toe-in control means for starting the toe-in control; and threshold value changing means for setting the toe-in control start threshold value of the toe-in control means smaller as the amount of steering angle of the steering wheel becomes larger. Device. 2. The rear wheel steering system for a vehicle according to claim 1, wherein the threshold value changing means sets the threshold value smaller as the vehicle speed increases.