JPS63162372A - Rear wheel steering device for automobile - Google Patents

Abstract

PURPOSE:To enable controlling the steering angle of rear wheels optimally at all times by judging a running mode and controlling said angle via the selection of the characteristics of front and rear wheel steering angle ratios optimum for the judged running mode from a plurality of the characteristics as preliminarily set up. CONSTITUTION:A front wheel steering angle sensor 1, a speed sensor 2 and a rear wheel steering angle sensor 3 are provided, and output signals from said sensors are inputted to a control unit 4. In the running mode judgement part 41 of the control unit 4, a running mode (i.e. running condition at street, in suburbs and mountain, on freeway and so on) is judged from a mean steering amount and a mean speed within the preliminarily determined sampling time. And according to the result of the judgement, a plurality of the preliminarily determined characteristics of front and rear wheel steering angle ratios are selected and the theoretical steering angle of rear wheels in this case is determined from a front wheel steering angle and an automobile speed on the basis of the selected ratios, thereby driving and controlling an actuator 6 for steering the rear wheels via a drive circuit 5.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a rear wheel steering device for an automobile.

Conventional Technology Various types of automobiles have been developed in which the rear wheels are simultaneously steered when the front wheels are steered by turning the steering wheel. It has already been published in official bulletins, etc.

Problems to be Solved by the Invention Conventional devices such as those described above generally set a front and rear wheel steering angle ratio characteristic in which the ratio of the rear wheel steering angle to the front wheel steering angle changes depending on the vehicle speed. Rear wheel steering is normally performed using ratio characteristics, so no matter what kind of road the vehicle is traveling on, that is, regardless of the driving mode, the rear wheel steering angle is determined only by the vehicle speed and the front wheel steering angle.

However, if the driving mode changes, for example when driving in an urban area with relatively narrow road widths and many sharp turns, or when driving on a mountain road that meanderes in a large zigzag pattern, the rear wheel steering characteristics may be less favorable. The problem is that the conventional rear wheel steering system as described above cannot obtain optimum steering characteristics for all driving modes.

The main purpose of the present invention is to address the problems of the conventional rear wheel steering device as described above.

Means for Solving the Problems In the present invention, a control unit determines an ideal rear wheel steering angle based on a preset front and rear wheel steering angle ratio characteristic based on a front wheel steering angle and a vehicle speed, and issues an output signal. In a rear wheel steering system of an automobile, in which an actuator is actuated by the output signal to steer the rear wheels, the driving mode is determined and a plurality of preset front and rear wheel steering angle ratio characteristics are determined. A driving mode determination section is provided that selects front and rear wheel steering angle ratio characteristics suitable for the determined driving mode, and based on the selected front and rear wheel steering angle ratio characteristics, the control unit determines the ideal rear wheel steering from the front wheel steering angle and vehicle speed. The present invention is characterized in that it is configured to determine the angle and generate an output signal to operate the actuator.

Function In the above, when the driving mode determination section determines that the vehicle is in city driving mode, it selects a front and rear wheel steering angle ratio characteristic that emphasizes turning performance, and when determining that it is highway driving mode, it selects a steering angle ratio characteristic that emphasizes stability. We selected the front and rear wheel steering angle ratio characteristics with emphasis,
When it is determined that the vehicle is in mountain road driving mode, the front and rear wheel steering angle ratio characteristics are selected to ensure turning performance at extremely low speeds and to ensure stability without significantly reducing turning performance at higher vehicle speeds. Rear wheel steering angle (including steering direction) control is always performed automatically using the front and rear wheel steering angle ratio characteristics that are most suitable for the driving mode.

Example Embodiments of the present invention will be described below with reference to the accompanying drawings.

In FIG. 1, reference numeral 1 denotes a front wheel steering angle sensor that detects the steering angle of a front wheel (not shown) that is steered by a rotational operation of a steering wheel (not shown) and generates a front wheel steering angle signal a;
2 is a vehicle speed sensor that detects the vehicle speed and issues a vehicle speed signal, and 3 is a rear wheel steering angle sensor that detects the steering angle of the rear wheels 12 and issues a rear wheel steering angle signal C, which will be described later. The three signals a, b and C are input to the control unit 4.

The control unit 4 has a driving mode determination section 41, and for example, the front wheel steering angle signal a from the front wheel steering angle sensor 1 and the vehicle speed signal from the vehicle speed sensor 2 are used to determine the average steering amount during a preset sampling period. (For example, the number of steering operations per minute) and the average vehicle speed determine the driving mode, for example, as shown in Figure 2, whether it is city driving, suburban driving, mountain road driving, or expressway driving. etc., and selects the optimal front and rear wheel steering angle ratio characteristics for the driving mode from among a plurality of preset front and rear wheel steering angle ratio characteristics, which will be described later, in response to a determination command from the driving mode determining unit 41. Based on the selected front and rear wheel steering angle ratio characteristics, the ideal rear wheel steering angle at that time is determined from the front wheel steering angle signal a of the front wheel steering angle sensor 1 and the vehicle speed signal S of the vehicle speed sensor 2, and an output signal d is determined. is generated, and the rear wheel steering actuator, for example, the electric motor 6, is operated in the forward or reverse direction via the drive circuit 5.

When the electric motor 6 rotates, the pinion gear 8 rotates via the reduction gear mechanism 7 consisting of a cylindrical worm 7a, a worm wheel 7b, etc., and the rack shaft 9 meshing with the pinion gear 8 is moved in the axial direction. Due to the axial movement of the tie rod 10. Knuckle arm 11
The rear wheel 12 is steered to the left or right via the rear wheel steering angle sensor 3, and the steered angle of the rear wheel 12 is inputted to the control unit 4 as the rear wheel steering angle signal C of the rear wheel steering angle sensor 3, and is subjected to feedback control thereby. The rear wheels are then steered to a steering angle that matches the ideal steering angle determined by the control unit 4.

In addition to the determination based on the average vehicle speed and average maneuver amount as illustrated in Fig. 2 above, the driving mode can be determined based on (a) vehicle speed and engine rotation speed, (I) vehicle speed and braking frequency, and (c) vehicle speed and electric power. Any one of the current value of the steering device, (d) vehicle speed and steering force, and (e) vehicle speed and engine boost pressure, or a combination of two or more of (a) to (b). The determination may be made based on the following.

For example, as shown in FIG. 3, the control unit 4 includes front and rear wheel steering with a wide reverse phase steering range in which the reverse rotation is steered in the opposite direction to the front wheels, emphasizing turning performance in the city driving mode. Ratio characteristics ■: In mountain road driving mode, the vehicle is steered in a slightly opposite phase to improve turning performance only in extremely low speed ranges, and in higher speed ranges, the rear wheels are steered in the same direction as the front wheels to give priority to stability. In highway driving mode, the rear wheels are steered in the same phase to emphasize stability. In suburban driving mode, the rear wheels are steered in the same phase, and the front and rear wheel steering angle ratio is lower than in highway driving mode, and in mountain road driving mode. The optimal front and rear wheel steering angle ratio characteristics for each driving mode are set in advance, such as the higher characteristic ■, and when the driving mode determining section 41 determines that the driving mode is, for example, mountain road driving mode, the above-mentioned By selecting the characteristic II and controlling the rear wheel steering angle based on the characteristic H, the optimum rear wheel steering angle can always be achieved in various driving modes.

In the illustrated embodiment, an electric motor is used as the rear wheel steering actuator, and the electric motor steers the rear wheels through a reduction gear mechanism, pinion gear, rack shaft, etc. when the electric motor rotates at night. However, the actuator for rear wheel steering and the mechanism for transmitting the steering force from the actuator to the rear wheels are other than those in the illustrated embodiment, for example, a mechanism for steering the rear wheels with the hydraulic pressure of a hydraulic actuator, etc. Any configuration can be adopted.

Effects of the Invention As described above, according to the present invention, by extremely simple measures, the steering angle of the rear wheels (including the steering direction) can be controlled with the optimum front and rear wheel steering angle ratio characteristics for each of various driving modes. As a result, it is possible to significantly improve turning performance and stability, and to prevent the vehicle from becoming unstable especially in transient conditions, making it possible to maximize the benefits of rear wheel steering, which has a great practical effect. It is something that can be brought about.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing an example of a driving mode determination method, and FIG. 3 is a diagram showing an example of front and rear wheel steering angle ratio characteristics in each driving mode. . 1... Front wheel steering angle sensor, 2... Vehicle speed sensor, 3...
・Rear wheel steering angle sensor, 4...Control unit, 4
DESCRIPTION OF SYMBOLS 1... Driving mode determination part, 6... Electric motor, 12
···Rear wheel. ”2

Claims (3)

[Claims] (1) Ideal steering for the rear wheels based on the front and rear wheel steering angle ratio characteristics that are preset from the front wheel steering angle signal of the front wheel steering angle sensor that detects the front wheel steering angle and the vehicle speed signal of the vehicle speed sensor that detects the vehicle speed. In a rear wheel steering system for an automobile, which consists of a control unit that determines the angle and issues an output signal, and an actuator that is activated by the output signal of the control unit and steers the rear wheels, a driving mode is determined and the driving mode is determined in advance. A driving mode determining unit is provided that selects a front and rear wheel steering angle ratio characteristic suitable for the driving mode from among a plurality of set front and rear wheel steering angle ratio characteristics, and the front and rear wheel steering angle ratio selected by the driving mode determining unit is A rear wheel steering device for an automobile, characterized in that a control unit is configured to determine an ideal rear wheel steering angle from the front wheel steering angle signal and the vehicle speed signal based on the characteristics, and to issue an output signal for operating an actuator. (2) The driving mode determination unit determines whether the driving mode is city driving mode, mountain road driving mode, suburban driving mode, expressway driving mode, etc. from the average vehicle speed and average steering amount within a preset sampling time. 2. A rear wheel steering device for an automobile according to claim 1, wherein said vehicle is configured to determine a driving mode of said vehicle. (3) The driving mode determination unit selects one or more of vehicle speed and engine rotation speed, vehicle speed and braking frequency, vehicle speed and electric power steering device current value, vehicle speed and steering force, and vehicle speed and engine boost pressure. The rear wheel steering device for an automobile according to claim 1, wherein the driving mode is determined based on the combination.