JPH0350077A - Four-wheel steering gear - Google Patents

Abstract

PURPOSE:To secure the neutral returnability of rear wheels and prevent the sudden change of a steering angle characteristic by using a neutral return mechanism for lowering the spring constant of a neutral resetting spring mechanism when the rear wheel steering angle exceeds the specified value. CONSTITUTION:When the steering angle is more than the first specified value, a negative-phase control valve 150, responding to the steering operation of a steering wheel 10, generates such oil pressure as to steer rear wheels 82L, 82R in the negative- phase direction to front wheels 1L, 1R. When the steering angle becomes more than the second specified value larger than the first specified value, a neutral return mecha nism 53 for lowering the spring constant of a neutral resetting spring mechanism is used to lower the increase rate of oil pressure output against the increase of the steering angle so as to generate the oil pressure corresponding to the spring constant variable characteristic of the neutral return mechanism 53, thus securing the neutral returnability of the rear wheels 82L, 82R, as well as the increase rate of the rear wheel steering angle in relation to the increase rate of the rear wheel steering angle in relation to the increase of the steering angle is kept approximately constant while reducing the steering output necessary for large steering angle steering. A stable steering characteristic can be thus secured.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an improvement of a four-wheel steering device that steers front wheels and rear wheels.

(Prior art) Conventionally, in four-wheel steering systems, stability during vehicle turns is improved by steering the rear wheels in the same phase as the front wheels, and the rear wheels are steered slowly in the opposite phase direction from the front wheels. It is known that the turning radius of a vehicle can be reduced by this.

On the other hand, as long as the rear wheels are steered, it is necessary to reliably return the rear wheels to the neutral position, and conventionally it has been common practice to provide a spring for returning the rear wheels to the neutral position. by the way,
If the spring constant for returning to neutral is set to a large value, the ability to return to neutral is reliably improved, but if the spring constant is set to be large, there is a problem in that the steering output required to steer the rear wheels increases. In the case of anti-phase steering, the generated steering angle is generally larger than that of in-phase steering, so the above-mentioned problem often becomes a particular problem.

As a means to solve such problems,
As shown in Japanese Patent No. 69070, it is known to use a neutral return mechanism incorporating a variable spring constant mechanism. This uses a spring mechanism with a spring that is given a preload, so that when the steering angle of the rear wheels exceeds a predetermined amount, the spring constant exerted by the spring mechanism decreases. This improves return performance and reduces the steering output required for large rudder angle steering.

(Problem to be Solved by the Invention) However, since the conventional example described above is simply a mechanism in which the spring constant of the neutral return mechanism is varied, the steering output is adjusted at a constant ratio according to the steering angle of the steering wheel. As the spring constant increases, the rate of increase in the rear wheel steering angle relative to the increase in the steering wheel steering angle suddenly increases from the point where the spring constant decreases, giving the driver a sense of discomfort and causing safety problems. There is.

(Means for Solving the Problems) The present invention was devised to solve the above problems, and includes a hydraulic actuator provided to steer the rear wheels, and a spring that biases the rear wheels to a neutral position. A neutral return mechanism is provided between the hydraulic power source and the hydraulic actuator and is configured to reduce the spring constant exerted by the spring mechanism when the steering angle of the rear wheels exceeds a predetermined amount. a reverse phase control valve that is activated in response to a steering operation and is provided to generate a hydraulic output that steers the rear wheels in a direction opposite to the front wheels when the steering angle of the steering wheel exceeds a first predetermined value; and the reverse phase control valve has a second predetermined value in which the steering angle of the steering wheel is larger than the first predetermined value so as to generate a hydraulic pressure corresponding to the spring constant variable characteristic of the neutral return mechanism. The four-wheel steering device is characterized in that the four-wheel steering device is configured such that when the value exceeds the value, the rate of increase in the hydraulic output with respect to the increase in the steering angle of the steering wheel decreases.

(Function) According to the present invention, the hydraulic output is activated in response to the steering operation of the steering wheel, and when the steering angle of the steering wheel exceeds a first predetermined value, the hydraulic output is generated to steer the rear wheels in a direction opposite to that of the front wheels. A reverse phase control valve provided to
In order to generate hydraulic pressure corresponding to the spring constant variable characteristic of the neutral return mechanism, when the steering angle of the steering wheel exceeds a second predetermined value that is larger than the first predetermined value, the hydraulic output is adjusted as the steering angle of the steering wheel increases. Since the increase rate is configured to decrease, when the steering angle of the rear wheels exceeds a predetermined amount, the neutral return mechanism is configured to reduce the spring constant exerted by the neutral return spring mechanism. Stable steering characteristics are achieved by ensuring the ability of the wheels to return to neutral and reducing the steering output necessary for large steering angle steering, while keeping the ratio of increase in rear wheel steering angle to an increase in steering wheel steering angle almost constant. is ensured.

(Example) Hereinafter, an example of the present invention will be described in detail based on the accompanying drawings.

1 to 12 show an embodiment of the present invention.

1 and 2 are schematic configuration diagrams of this four-wheel steering system.

The left and right front wheels IL and IR are knuckle 2L.

It is rotatably supported by 2R. Also, knuckle 2L
, 2R are connected to the left and right ends of the piston rod 5 of the power steering device 4 via tie rods 3L and 3R. The piston rod 5 is provided by passing through the cylinder 6, and has left and right pressure chambers 7L inside the cylinder 6.
, 7H. Further, the piston rod 5 has a rack that meshes with a pinion gear in the steering gear box 9. A first steering shaft 12 receives steering human power from the steering wheel 10 through a column shaft 11, and a second steering shaft 1 is connected to a steering gear box 9.
A variable gear ratio mechanism 14 is interposed between the two. Therefore, the steering force from the steering wheel 10 is
The signal is transmitted to the steering gear box 9 via the variable gear ratio mechanism 14. Further, a power steering valve, which is known per se, is provided between the second steering shaft 13 and the pinion gear, and controls the supply of hydraulic pressure to the pressure chambers 7L and 7R. Note that the oil pump 15 for the power steering device 4 is driven by the engine 16.
A type is used in which the discharge flow rate decreases as the engine speed increases after the engine speed reaches a predetermined value or higher.

Claims (1)

[Claims] a hydraulic actuator provided to steer the rear wheels;
A neutral return mechanism includes a spring mechanism that urges the rear wheels to a neutral position, and is configured such that the spring constant exerted by the spring mechanism decreases when the steering angle of the rear wheels exceeds a predetermined amount, a hydraulic source, and the hydraulic pressure. and an actuator, which is actuated in response to a steering operation of a steering wheel, and outputs a hydraulic output to steer the rear wheels in a direction opposite to the front wheels when the steering angle of the steering wheel exceeds a first predetermined value. and a reverse phase control valve provided to generate hydraulic pressure in accordance with the first variable spring constant characteristic of the neutral return mechanism. A four-wheel steering device characterized in that the four-wheel steering device is configured such that when the value reaches a second predetermined value, which is larger than the predetermined value of