Fluid pressure boosting device and brake system employing...

Power plants – Pressure fluid source and motor – Pulsator

Reexamination Certificate

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Details

C091S373000

Reexamination Certificate

active

06467267

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a fluid pressure boosting device, which boosts operating force exerted on an operating means with working fluid pressure, controlled by a control valve, into predetermined magnitude to output the boosted force and a brake system employing the fluid pressure boosting device. More particularly, the present invention relates to a fluid pressure boosting device which can set the input stroke into various values without being affected by the operation of a working unit of a master cylinder and the like operated with the output of the fluid pressure boosting device and can control the output of the fluid pressure boosting device during its operation regardless of the operating force exerted on the operating means and a brake system employing the fluid pressure boosting device.
For example, in a conventional brake system of an automobile, a brake fluid pressure boosting device has been employed which intensifies pedal pressure on a brake pedal by fluid pressure of hydraulic fluid into predetermined magnitude to develop large brake fluid pressures. The brake fluid pressure boosting device functions to obtain large braking force from small pedal pressure on the brake pedal, thereby securing the braking action and reducing the fatigue of a driver.
In the conventional brake fluid pressure boosting device, a control valve is actuated by an input based on the pedal pressure on the brake pedal to develop working fluid pressure of hydraulic fluid and the developed working fluid pressure is introduced into a power chamber, thereby intensifying the input at a predetermined ratio to output intensified pressure. A piston of a master cylinder is moved by the output of the brake fluid pressure boosting device so that the master cylinder outputs master cylinder pressure. The master cylinder pressure is introduced as braking pressure of hydraulic fluid into wheel cylinders, thus carrying out the braking action.
By the way, conventional brake systems employ various brake controls such as for controlling the braking force during the braking operation, for example, Anti-Lock Control (ABS), Brake Assist Control to be typically used for starting or stopping in the middle of a slope, and Regenerative Brake Coordination Control to be performed for controlling the braking pressure produced by a service braking system when a regenerative brake system is used to develop braking pressure during the braking operation by the service brake system, and automatic brake controls, for example, a brake control for controlling the distance from another vehicle, a brake control for avoiding a collision with an obstacle object, and Traction Control (TRC).
Most of such brake controls are normally conducted in a brake circuit between the master cylinder and the wheel cylinders. However, when the brake control is conducted in the brake circuit after the master cylinder, it is required to prevent the input stroke of the hydraulic boosting from being affected by such brake controls, for instance, for obtaining better operational feeling.
However, in a brake system in which a conventional brake fluid pressure boosting device and a brake master cylinder are combined, the stroke of a piston of the master cylinder is fixed by the relation between the master cylinder and wheel cylinders so that the stroke of an input shaft of the brake fluid pressure boosting device, i.e. the pedal stroke of a brake pedal, depends on the stroke of the piston of the master cylinder. That is, the stroke for input is affected by the brake controls conducted in the brake circuit after the master cylinder. In the combination between the conventional brake fluid pressure boosting device and the brake master cylinder, the aforementioned requirement can not be securely and sufficiently satisfied.
For changing the stroke characteristic of the brake pedal as the input side to obtain better operational feeling, the brake master cylinder and the brake circuit after the brake master cylinder are also affected so that some change on the output side, for instance a size change on the master cylinder, should be required. By the change on the output side, the output characteristic of the brake system is affected. This means that the overall change on the brake system is required, i.e. large-scale change is required.
It is further desired that the input side is affected as little as possible by brake circuit which may differ according to the type or size of vehicle.
If the input side and the output side are just separated from each other to produce outputs regardless of the travel of the input side, the input side does not travel so that the stroke of the input side can not be ensured.
For this, it has been conventionally proposed that a stroke simulator is provided on the brake circuit after the master cylinder to prevent the travel of the input side from being affected by the brake control after the master cylinder and to ensure the stroke of the input side.
However, to add specially the stroke simulator, many parts such as a stroke cylinder and an electromagnetic switching valve used for the stroke simulator are required, making the structure complex and increasing the cost.
There is still a problem that brakes must be securely operated in case of a fluid pressure source failure even when a stroke simulator is provided.
In an anti-lock control system, it is desired that when a braked wheel or braked wheels are in locking tendency, the braking force is controlled to cancel the locking tendency of the wheel(s). Further, in a regenerative coordination brake system composed of a combination of a service brake system and a regenerative brake system, when the regenerative brake system is operated during the operation of the brake fluid pressure boosting device, the braking force produced by the brake fluid pressure boosting device should be reduced for the braking force produced by the regenerative brake system. In this case, it is desired to reduce the output of the brake fluid pressure boosting device to a value obtained by subtracting the output of the regenerative brake system from the output of the fluid pressure boosting device. In a brake system composed of a combination of a service brake system and a brake assist system, it is desired to facilitate starting at a slope by controlling the cancellation of braking operation and also desired to increase the output of the brake fluid pressure boosting device to intensify the braking force produced by the brake fluid pressure boosting device in such case that brake assist operation is needed, for example, a case that a driver can not depress a brake pedal enough during the operation of the brake fluid pressure boosting device so as not to develop predetermined braking force.
As mentioned above, when the brake control is performed during the operation, the brake pedal is not affected even when the stroke simulator is provided.
Further, in a brake system for controlling the distance from a front vehicle, it is desired to hold the distance constant by automatically actuating brakes when the distance becomes short during running. In a brake system for avoiding a collision, it is desired to avoid a collision with an obstacle object by automatically actuating brakes when there is a possibility of collision with the obstacle object. Furthermore, in a traction control system, it is desired to cancel a slipping tendency to ensure the secure starting by automatically braking driving wheels when the driving wheel(s) is in slipping tendency at the starting.
As mentioned above, it is desired that the brake pedal is not affected when the automatic braking is conducted even when the stroke simulator is provided.
Further, it is desired that such a system for controlling the braking force during braking operation or controlling the automatic braking can be manufactured with a simple structure.
Moreover, it is desired that the input-stroke characteristic, the input-brake pressure characteristic, or the stroke-brake pressure characteristic is allowed to be changed according

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