Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Reexamination Certificate
2000-06-06
2001-11-06
Butler, Douglas C. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
C303S116100, C303SDIG001, C303S115400
Reexamination Certificate
active
06312062
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an automotive brake fluid pressure control device that can perform automatic braking functions such as traction control and vehicle stability control.
For economical reasons, the most popular automotive antilock brake control systems are what is known as the circulation type, which has a wheel brake fluid pressure control valve unit including a discharge valve and provided in a main fluid line extending from a master cylinder to each wheel brake, a fluid reservoir for temporarily storing brake fluid discharged through the discharge valve, and a power pump for sucking fluid in the reservoir and returning it into the main fluid line.
Various braking systems have been proposed which are versions of the circulation type and can perform automatic braking such as traction control and vehicle stability control.
One of them is disclosed in Japanese patent publication 64-74153, which includes a main line, a fluid supply line and an on-off valve adapted to connect the fluid supply line to the main line only during traction control, and a pump provided in the fluid supply line for applying brake fluid to the wheel brake during traction control. The on-off valve opens only during traction control and otherwise kept shut. While the on-off valve is closed, there is no spare fluid in the fluid supply line. Thus, when traction control starts, brake fluid has to be sucked to the pump from the master cylinder reservoir through the master cylinder, brake piping, and the on-off valve. Thus, high suction resistance makes it impossible to apply brake fluid to the wheel brake quickly upon start of the traction control.
Japanese Patent Publication 5-116607 disclosed an improved brake fluid pressure control system, which was proposed to solve these problems.
This unit is basically a circulation type antilock brake control system with the following elements added: that is, a fluid supply line branching from the main fluid line at its point between the master cylinder and a fluid return point at which the line from the pump outlet merges: a discharged fluid reservoir provided at the end of the fluid supply line: an on-off valve for checking fluid flow from the fluid supply line to the discharged fluid reservoir during traction control: an intermediate fluid reservoir provided in the fluid supply line for supplying fluid during traction control.
The applicant of the present invention also proposed a system having a similar intermediate reservoir in unexamined Japanese patent publication 8-108838. In either of these systems, fluid can be more smoothly supplied to the pump inlet from the intermediate reservoir during automatic braking control than with a system without an intermediate reservoir. But since these reservoirs are both nonactive ones and thus fluid is sucked under the atmospheric pressure, it is difficult to smoothly supply fluid to the pump inlet so that the drake pressure can be increased with sufficient quickness necessary for vehicle stability control particularly when the ambient temperature is low and the fluid viscosity is high.
Japanese patent publication 4-231241 proposes to use a power-driven active pressure accumulator instead of the above-described (passive) fluid reservoir. Although such an active accumulator greatly improves the responsiveness and the fluid supply capability, such a system is naturally very costly because the accumulator needs an actuator and an actuator circuit.
Unexamined Japanese patent publication 11-59377 proposes a system having a means for storing fluid at a higher-than-atmopheric pressure. This system needs a sealing mechanism for maintaining the higher-than-atmopheric pressure.
One problem with this system is that failure of the sealing mechanism leads to leakage of fluid. This considerably increases the brake pedal stroke.
Also, it is practically impossible to completely prevent leak of brake fluid stored at a higher-than-atmospheric pressure. Thus, fluid tends to be lost gradually. One solution to this problem is the provision of means for restoring fluid during braking. But when this means is activated, the brake pedal stroke increases.
An object of the invention is to provide a brake fluid pressure control unit that has improved reliability and improved pedal feeling.
SUMMARY OF THE INVENTION
According to the invention, there is provided a brake fluid pressure control device for use in an automotive brake system including a master cylinder, a wheel brake, and a main fluid line connecting the master cylinder to the wheel brake, the device having an automatic braking function and comprising: a power pump having an inlet port connected to the main fluid line at a first point by a first fluid line, and a discharge port connected to the main fluid line at a second point between the first point and the wheel brake through a second fluid line; a fluid reservoir comprising a housing, a slider slidably mounted in the housing to liquid-tightly partition the interior of the housing into a first chamber and a second chamber, the second chamber communicating with the master cylinder, and a biasing element biasing the slider toward the first chamber; an on-off valve provided in the main fluid line between the first point and the second point; a changeover valve movable between a first position at which the inlet port and discharge port of the pump communicate with the first chamber of the reservoir and the main fluid line, respectively, and a second position at which the inlet and discharge ports of the pump communicate with the second and first chambers of the reservoirs, respectively; a control unit for closing the on-off valve and moving the changeover valve to the first position during an automatic braking mode to supply brake fluid to the pump, and otherwise opening the on-off valve and moving the changeover valve to the second position.
According to this invention, there is also provided a brake fluid pressure control device which comprises, instead of the changeover valve in the abovesaid device, a valve for opening the passage in the fluid reservoir when the slider has moved by a predetermined distance toward the second chamber, and otherwise closing the passage; an on-off valve provided in the fluid supply line between the fluid reservoir and the inlet port of the pump; a bypass line branching from the main fluid line at a third point between the first point and the first on-off valve and merging with the fluid supply line at a point between the fluid reservoir and the second on-off valve, the bypass line being provided with a check valve for allowing a fluid flow from the main fluid line toward the first chamber of the fluid reservoir and preventing a fluid flow from the fluid supply line toward the main fluid line; a pressure-responsive valve provided in the main fluid line between the first and third points for allowing a fluid flow from the master cylinder toward the wheel brake at all times, and restricting a fluid flow toward the master cylinder while the master cylinder pressure is higher than a predetermined level; and a control unit for opening the second on-off valve and closing the first on-off valve during the automatic braking mode to communicate the first chamber with the inlet port of the pump, and otherwise closing the second on-off valve and opening the first on-off valve to communicate the discharge port of the pump with the wheel brake.
According to this invention, there is also provided a brake fluid pressure control device wherein the pressure-responsive valve is a proportional pressure-reducing valve having an outlet port and an inlet port and adapted to transmit fluid pressure applied to the inlet port to the outlet port after reducing the pressure at a predetermined ratio, the outlet and inlet ports communicating with the master cylinder and the third point, respectively.
Other features and objects of the present invention will become apparent from the following description made with reference to the accompanying drawings, in which:
REFERENCES:
patent: 5368374 (1994-11-01), Fu
Butler Douglas C.
Greenblum & Bernstein P.L.C.
Sumitomo (SEI) Brake Systems, Inc.
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