JPH0352385B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a steering system for a vehicle such as a four-wheeled vehicle.

The applicant has already steered not only the front wheels of a vehicle but also the rear wheels depending on certain conditions such as vehicle speed and front wheel steering angle, greatly improving maneuverability and steering response of the vehicle. A variety of vehicle steering devices have been proposed (Japanese Patent Application No. 57-134888 (see Japanese Patent Application Laid-open No. 59-26368), etc.) that are designed to improve performance.

Incidentally, in general, the coefficient of friction between the road surface and the tires greatly affects the running performance of a vehicle. Especially if it is small, it becomes difficult for the vehicle's running direction to follow the steering wheel operation. In this case, the above-mentioned disadvantages can be effectively eliminated by controlling the rear wheels to steer in a direction that reduces such influence.

Therefore, an object of the present invention is to prevent the vehicle running from being adversely affected by the coefficient of friction between the road surface and the tires, and to make it difficult to operate the steering wheel even on a road with a small coefficient of friction, such as an icy road. To provide a steering device for a vehicle that can improve stable running and turning performance without any problems.

To achieve the above object, the present invention provides a vehicle steering system capable of variable control of the steering ratio between front wheels and rear wheels, including a friction coefficient detection means for detecting a friction coefficient between a road surface and a tire, and a friction coefficient detection means for detecting a friction coefficient between a road surface and a tire. In response to the detection result, when the friction coefficient becomes larger or smaller than the reference setting value, outputs control information to additionally steer the rear wheels by a predetermined steering angle in a direction where the influence of the friction coefficient is reduced. The present invention is characterized in that it includes a calculation means for controlling the steering of the rear wheels based on the control information.

Further, the friction coefficient detection means may be constituted by friction coefficient derivation means that predicts and derives the friction coefficient between the road surface and the tires based on preset data by detecting factors indicating the driving condition. preferable.

Below, preferred embodiments that further embody the present invention will be described in detail with reference to the drawings.

First, in order to clarify the present invention, a schematic configuration of a vehicle steering system will be explained based on FIG. This figure is a schematic plan view showing the basic structure of a vehicle equipped with a steering device according to the present invention. In the figure, reference numeral 1 denotes a steering handle, and the steering shaft 2 of this handle 1 is connected to a steering gear mechanism, for example, a rack-and-pinion type, installed in a gear box 3, and the steering rotation of the handle 1 is transmitted to a tie rod 4 in the width direction of the vehicle body. Convert to motion. Both ends of this tie rod 4 are connected to knuckle arms 6, 6 that support the front wheels 5, 5, and the displacement of the tie rod 4 in the vehicle width direction is controlled by the function of the knuckle arms 6, 6, which are rotatably supported in the left and right directions. The front wheels 5, 5 are steered in the steering direction of the steering wheel 1.

On the other hand, 7 is a rear wheel side gearbox, and a shaft 8a extending rearward from a rear wheel steering servo actuator 8 is connected to a direction changing means such as a rack and pinion type built in this gearbox 7. Furthermore, the tie rod 9, which passes through the gearbox 7 in a movable manner in the width direction of the vehicle body, has a knuckle arm 10 at both ends.
10 are rotatably connected, and this knuckle arm 1
0 and 10 support the rear wheels 11 and 11. As a result, similar to the steering of the rear wheels, the tie rod 9 is displaced in the width direction of the vehicle body by the rotation of the shaft 8a, and the rear wheels 11, 11 are further steered in a predetermined direction.

On the other hand, the vehicle is equipped with an on-board computer 12, and this computer 12 includes, for example, a lateral acceleration sensor (or yaw rate sensor) 13 that detects the acceleration of the vehicle in the lateral direction, and a front wheel turning angle that detects the turning angle of the front wheels. The sensor 14 receives a detection signal from a vehicle speed sensor (not shown), etc., and supplies a corresponding control signal to the rear wheel steering servo actuator 8 to perform necessary rear wheel steering, for example, at high speeds. Steering control is performed in the phase direction, and in the opposite phase direction at low speeds.

Next, the configuration and functions of the main parts of the present invention will be specifically explained with reference to FIGS. 2 to 4. Second
The figure is a functional block diagram of the rear wheel steering system, FIG. 3 is a diagram for explaining the principle, and FIG. 4 is a characteristic diagram for explaining the principle.

First, in FIG. 2, various sensors such as the lateral acceleration sensor 13 shown in FIG. 1 or the front wheel steering angle sensor 14 shown in FIG. At this point, arithmetic processing is performed based on the data set in advance to obtain rear wheel steering information _d0 corresponding to the detection result. This information d ₀ is given to the servo actuator 8, which causes the shaft 8a to rotate through operations such as digital-to-analog conversion, amplification, and motor drive.
1 and 11 are steered. The above configuration and functions have already been proposed by the applicant and are the basic technology of the present invention.

On the other hand, in the computer 12, the front wheel actual steering angle (δ ₀ ), which is a factor indicating the driving state detected by the front wheel steering angle sensor 14, is determined by a plurality of friction coefficients (μ1), which differ depending on the conversion process. (μ2), (μ3)…(μn
)
Predicted lateral acceleration data (α1), (α2), corresponding to
(α3)…(αn) respectively. The principle of this conversion will be explained with reference to FIGS. 3 and 4. As shown in FIG. becomes as shown. In addition, the relationship between the lateral force (F) and the sideslip angle (β) is expressed by the fourth
It is shown as shown in the figure. In addition, the friction coefficient is (μ1)>
If (μ2) > (μ3) >…> (μn) and the sideslip angle (β) does not change, the smaller the friction coefficient, the smaller the lateral force (F). On the other hand, the relationship between the front wheel steering angle (δ) and sideslip angle (β) is expressed by β = f
Since it is expressed as (u)·δ, the front wheel steering angle (δ) and sideslip angle (β) are approximately proportional. Further, lateral force (F) and lateral acceleration (α) are approximately proportional. Therefore, in Fig. 4, the sideslip angle (β) is expressed as the actual front wheel steering angle (δ ₀ ).
Also, the lateral force (F) can be replaced with the lateral acceleration (α). Therefore, from the detected actual front wheel steering angle (δ ₀ ), each friction coefficient (μ1), (μ2), (μ3)...
Predicted lateral acceleration data (α1) corresponding to (μn),
(α2), (α3), ... (αn) can be obtained.

On the other hand, the magnitude of the actual lateral acceleration, which is a factor indicating the running state of the vehicle, can be detected from the lateral acceleration sensor 13 as actually measured lateral acceleration data (α ₀ ). Then, this measured lateral acceleration data (α ₀ ) and the predicted lateral acceleration data (α1), (α2)...(αn) are compared and processed as a friction coefficient derivation means to find the predicted lateral acceleration data that most closely approximates (α ₀ ). If you select (α1), (α2)…(αn), the corresponding friction coefficients (μ1), (μ2)…
(μn) can be derived and the actual coefficient of friction can be predicted. As described above, the friction coefficient detection means is configured by the front wheel turning angle 14, the lateral acceleration 13, the conversion process (d), and the comparison process (e). In addition, as the friction coefficient detection means, a friction coefficient detection sensor or the like which is brought into contact with the road surface and directly detects the friction coefficient may be used.

The derived friction coefficient is processed as control data d1 by a calculation means, which will be described in detail later, based on preset data, and the control data d1 is
Obtain the required control information d2 corresponding to . and,
This control information d2 is added or subtracted from the rear wheel steering information d ₀ by the addition/subtraction processing C, which is a control means, and the information (d ₀ +d2) is sent to the servo actuator 8.
or (d ₀ −d2).

Next, the calculation processing will be specifically explained. This calculation process is performed when the friction coefficient of the road surface is small, such as on an icy road, that is, when it is smaller than the reference setting value.For example, when changing lanes on a straight road, the rear wheel steering information d ₀ is used. Generates control information d2 for additionally steering the front wheels in the steering direction (in the same phase direction) by a predetermined amount of steering angle in response to the steering state of the rear wheels steered according to the above. do. The magnitude of this additional turning angle is selected to be such that the steering angle of the entire rear wheels prevents the vehicle body from wobbling, and is set and stored as data. On the other hand,
Even if the coefficient of friction is small, when attempting to pass a sharp corner such as a hairpin at a certain vehicle speed or higher, contrary to the above, the front wheels are steered relative to the rear wheels. Control information d2 is generated to additionally steer the steering wheel by a predetermined steering angle in a direction opposite to the steering direction (opposite phase direction), and the size of this additional steering angle is determined when the front wheels are turned at a corner. Select a size that will not lose grip. In addition, whether the rear wheels are steered in the steering direction of the front wheels in this way,
Alternatively, the driver can arbitrarily select whether to steer the vehicle in the opposite direction using an external manual selection means 15. Further, the magnitude of the rear wheel turning angle that is additionally turned can also be controlled by various factors indicating the vehicle speed and other driving conditions.

Therefore, when the vehicle is turning, that is, when the front wheels are being steered, the computer 12 predicts the friction coefficient of the road surface and additionally controls the steering angle of the rear wheels. The rear wheel steering angle is set to be the most suitable for the road, and each process in the computer 12 is executed according to a control program (software) stored in the memory in advance. Note that the computer 12 may be replaced by an electrical circuit or the like having the same function.

In this way, the running of the vehicle according to the present invention is not adversely affected by the coefficient of friction between the road surface and the tires due to differences in road surface temperature, road surface material, road surface conditions due to water, etc., and stable running and turning can be achieved. Performance can be improved.

[Brief explanation of drawings]

Fig. 1 is a schematic plan view showing the basic structure of a vehicle equipped with a steering system according to the present invention, Fig. 2 is a functional block diagram of the rear wheel steering system, Fig. 3 is a diagram explaining the principle, and Fig. 4 is the principle. It is a characteristic diagram for explanation. In the drawing, 11 and 11 are rear wheels, 12 is an on-board computer, 13 is a lateral acceleration sensor, 14 is a front wheel steering angle sensor, A and F are data, B and G are arithmetic processing, C is addition and subtraction processing, and Ni ... is conversion processing, e is comparison processing, d ₀ is rear wheel steering information, and d2 is control information.

Claims (1)

[Scope of Claims] 1. In a vehicle steering device capable of variable control of the steering ratio between front wheels and rear wheels, a friction coefficient detection means for detecting a friction coefficient between a road surface and the tires, and a friction coefficient detection means corresponding to the detection result from the detection means. calculation means for outputting control information for additionally steering the rear wheels by a predetermined steering angle in a direction in which the influence of the friction coefficient decreases when the friction coefficient becomes larger or smaller than a reference setting value; A steering device for a vehicle, comprising a control means for controlling steering of rear wheels based on the control information. 2. In claim 1, the friction coefficient detection means predicts and derives the friction coefficient between the road surface and the tires based on preset data by detecting factors indicating the driving state. A vehicle steering device comprising a deriving means.