JPH0571431B2 - - 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. 59-26363), etc.) that are capable of improving performance.

By the way, the amount of cornering power that acts on the tires of each wheel when a vehicle turns is generally expressed as the rate of increase in lateral force with respect to changes in the tire's sideslip angle, and is determined by factors such as tire air pressure, ground contact load, and road surface conditions. It varies depending on various conditions.

In other words, when the tire air pressure decreases or the ground load increases due to loaded cargo, cornering power decreases, and especially when the cornering power of the rear tires decreases, the vehicle body tends to shake its tail during turns. This reduces turning performance and makes it difficult for the driver to operate the steering wheel stably. On the other hand, if the cornering power of the rear tires increases, on the other hand, the vehicle will have a stronger tendency to understeer, and for example, it will become difficult to turn the head while cornering at medium speeds, reducing turning performance and forcing the driver to control the steering wheel. It needs to be larger than normal. In this case, if the rear wheels are steered in a direction that reduces such adverse effects, the adverse effects can be effectively eliminated.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a vehicle steering system that allows stable steering operation at all times even when cornering, without causing any adverse effects on vehicle running due to fluctuations in cornering power, and that improves cornering performance. It is in.

In order to achieve the above object, the present invention is applied to a steering system for a vehicle that can variably control the steering angle of the rear wheels according to certain conditions, and its main components include factors indicating the running state of the vehicle; For example, a derivation means for predicting and deriving the cornering power of the tire by detecting the steering angle of the steering wheel, the lateral acceleration, etc.;
processing means for outputting control information for controlling the steering of the rear wheels in response to the derivation result from the derivation means; For example, when the cornering power becomes larger or smaller than a reference setting value, the rear wheels are controlled in a direction in which the cornering power is corrected to the reference setting value by predicting the cornering power. It is characterized by being able to be steered.

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 change 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 sensor that detects the turning angle of the front wheels. 14. Receives a detection signal from a vehicle speed sensor (not shown), etc. that detects the vehicle speed, and supplies a corresponding control signal to the rear wheel steering servo actuator 8 to perform necessary rear wheel steering, for example, in the same phase direction at high speeds. At low speeds, steering control is performed in the opposite phase direction.

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 operation, and FIG. 4 is a characteristic diagram for explaining the principle.

As shown in FIG. 2, the computer 12 constitutes a deriving means, a processing means, and a control means.

The deriving means derives the cornering power of the tire by detecting factors indicating the driving condition, and is composed of a conversion process (d) and a comparison process (e).

The processing means outputs control information for steering the rear wheels in a direction in which the cornering power is corrected to the basic set value in accordance with the derivation result from the derivation means, and performs arithmetic processing on preset data. It consists of

The control means receives control information d2 from the processing means.
This system controls the steering of the rear wheels by means of preset data, arithmetic processing (b), and addition processing (c).

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. In step 1, arithmetic processing is performed based on the data set in advance to obtain rear wheel steering information corresponding to the detection result. This information do is given to the servo actuator 8, which causes the shaft 8a to rotate by, for example, digital-to-analog conversion, amplification, motor drive, etc., or by the operation of mechanical means such as a hydraulic cylinder.
Turn 1. 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 δo, which is a factor indicating the driving state detected by the front wheel steering angle sensor 14, is calculated by converting the actual front wheel steering angle δo to a plurality of cornering powers C1, C2, C3, which differ depending on the conversion process...
... are respectively converted to Cn. To explain the principle of this conversion, the relationship between the tire's sideslip angle β and the lateral angle F is generally shown in FIG. 4. As mentioned above, the cornering power C is C in the same figure.
It can be determined by =△F/△β. On the other hand, the relationship between the front wheel steering angle δ and the sideslip angle β is expressed as β=f(u)・δ, where f(u) is the function for the vehicle speed u, so the front wheel actual steering angle δo and the sideslip angle β are approximately proportional to each other. . Further, the lateral force F and the lateral acceleration α are approximately proportional.
Therefore, in FIG. 4, the sideslip angle β can be replaced with the front wheel actual steering angle δo, and the lateral force F can be replaced with the lateral acceleration α. Therefore, each cornering power C1,
C2...Change in lateral acceleration corresponding to Cn △α,
Furthermore, predicted lateral acceleration data α1, α2...αn
can be found.

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 actual measurement value acceleration data α ₀ . Then, this measured lateral acceleration data α ₀ and the predicted lateral acceleration data α1, α2 . _. . αn are compared and the predicted lateral acceleration data α 1 , α2 .
If αn is selected, the corresponding cornering power C
1, C2...Cn can be derived, and the actual cornering power can be predicted.

The derived cornering power is used as control data d1 and is subjected to arithmetic processing, which will be described in detail later, based on preset data to obtain required control information d2 corresponding to the control data d1. Then, this control information d2 is added or subtracted from the rear wheel steering information do by addition/subtraction processing C, and the information (do+d2) or (do-
d2).

Next, the calculation processing will be specifically explained. This arithmetic processing is performed according to the rear wheel steering information do when the tire air pressure decreases or the ground contact load increases due to loaded cargo, etc., and the cornering power becomes smaller than the set value. With respect to the rear wheel steering state, the front wheels are additionally steered by a predetermined steering angle in the steering direction (same phase direction). In other words, as shown in FIG. 3, the rear wheels 11, 11 are shown by solid lines, while the rear wheels 11a, 1 are shown by imaginary lines.
Control information d2 for causing steering to 1a is generated. 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, if the cornering power becomes larger than the set value, the rear wheel steering information do
With respect to the rear wheel steering state based on , the front wheels are additionally steered by a predetermined steering angle in a direction opposite to the front wheel steering direction (opposite phase direction). In other words, control information d for steering the rear wheels 11, 11 shown by solid lines to the rear wheels 11b, 11b shown by imaginary lines as shown in FIG.
2, and the magnitude of this steering angle is set to a magnitude that allows a normal turning trajectory to be obtained based on the steering wheel operation.

In addition, as mentioned at the beginning, the magnitude of cornering power fluctuates in relation to tire air pressure and ground load, so by directly detecting these, each detection result was sent to the computer 12 and calculated as described above. It is also possible to generate control information in parallel with the cornering power prediction results to improve control reliability.

Therefore, the computer 12 predicts the cornering power of the tires while the vehicle is turning, that is, when the front wheels are being steered, and adjusts the driving conditions by additionally controlling the steering angle of the rear wheels. The rear wheel steering angle can be set to the most suitable rear wheel steering angle, 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.

As described above, the front and rear wheel steering system for a vehicle according to the present invention can prevent vehicle running from being adversely affected by changes in tire cornering power due to changes in tire air pressure, ground contact load, road surface conditions, etc., even when cornering. Always perform stable steering operation,
It is possible to improve the turning performance of the vehicle.

[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 an explanatory diagram of the operation, and Fig. 4 is the principle. It is a characteristic diagram for explanation. In addition, in the drawing, 11, 11, 11a, 11a, 1
1b and 11b are rear wheels, 12 is an on-board computer,
13 is a lateral acceleration sensor, 14 is a front wheel steering angle sensor, A, F are data, B, G are arithmetic processing, C is addition/subtraction processing, D... is conversion processing, E is comparison processing,
do is rear wheel steering information, and d2 is control information.

Claims (1)

[Scope of Claims] 1. In a vehicle steering system capable of variably controlling the steering angle of rear wheels according to certain conditions, a derivation means for deriving cornering power of a tire by detecting a factor indicating a driving state. and processing means for outputting control information for steering the rear wheels in a direction in which the cornering power is corrected to the reference setting value in accordance with the derivation result from the derivation means; 1. A steering device for a vehicle, comprising: a control means for controlling steering of wheels. 2. The processing means outputs control information for steering the rear wheels by a predetermined steering angle in the steering direction (same phase direction) of the front wheels when the cornering power becomes smaller than a reference setting value. A vehicle steering device according to claim 1. 3. The processing means outputs control information for steering the rear wheels by a predetermined steering angle in a direction opposite to the steering direction of the front wheels (opposite phase direction) when the cornering power becomes larger than a reference setting value. A vehicle steering system according to claim 1, characterized in that: