Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Reexamination Certificate
1999-12-29
2001-02-06
Butler, Douglas C. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
C188S358000, C303S003000, C303S010000, C303S013000, C303S116100, C303S119100, C303S050000, C303S014000, C303S113200, C303SDIG001
Reexamination Certificate
active
06183050
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates in general to a vehicle brake systems and in particular to a brake system having a pilot-operated boost valve located remotely from a master cylinder.
Vehicles are commonly slowed and stopped with hydraulic brake systems. These systems vary in complexity but a base brake system typically includes a brake pedal, a tandem master cylinder, fluid conduits arranged in two similar but separate brake circuits, and wheel brakes in each circuit. The driver of the vehicle operates a brake pedal which is connected to the master cylinder. When the brake pedal is depressed, the master cylinder generates hydraulic forces in both brake circuits by pressurizing brake fluid. The pressurized fluid travels through the fluid conduit in both circuits to actuate brake cylinders at the wheels to slow the vehicle.
Base brake systems typically use a brake booster which act during braking to provide a force to the master cylinder which assists the pedal force created by the driver. The booster can be vacuum or hydraulically operated. A typical hydraulic booster senses the movement of the brake pedal and generates pressurized fluid which is introduced into the master cylinder. The fluid from the booster assists the pedal force acting on the pistons of the master cylinder which generate pressurized fluid in the conduit in fluid communication with the wheel brakes. Thus, the pressures generated by the master cylinder are increased. Hydraulic boosters are commonly located adjacent the master cylinder piston and use a boost valve to control the pressurized fluid applied to the booster. Typically the boost valve is connected with the booster in the master cylinder assembly and mechanically coupled to the brake pedal for proper operation. Although this placement of the booster adjacent the master cylinder has been satisfactory in the past, it would be desirable to locate the booster remotely from the master cylinder because the tighter packaging constraints in the engine compartment of modem vehicles.
Braking a vehicle in a controlled manner under adverse conditions requires precise application of the brakes by the driver. Under these conditions, a driver can easily apply excessive braking pressure thus causing one or more wheels to lock, resulting in excessive slippage between the wheel and road surface. Such wheel lock-up conditions can lead to greater stopping distances and possible loss of directional control.
Advances in braking technology have led to the introduction of Anti-lock Braking Systems (ABS). An ABS system monitors wheel rotational behavior and selectively applies and relieves brake pressure in the corresponding wheel brakes in order to maintain the wheel speed within a selected slip range to achieve maximum braking force. While such systems are typically adapted to control the braking of each, braked wheel of the vehicle, some systems have been developed for controlling the braking of only a portion of the plurality of braked wheels.
Electronically controlled ABS valves, comprising apply valves and dump valves, are located between the master cylinder and the wheel brakes. The ABS valves regulate the pressure between the master cylinder and the wheel brakes. Typically, when activated, these ABS valves operate in three pressure control modes: pressure apply, pressure dump and pressure hold. The apply valves allow pressurized brake fluid into respective ones of the wheel brakes to increase pressure during the apply mode, and the dump valves relieve brake fluid from their associated wheel brakes during the dump mode. Wheel brake pressure is held constant during the hold mode by closing both the apply valves and the dump valves.
To achieve maximum braking forces while maintaining vehicle stability, it is desirable to achieve optimum slip levels at the wheels of both the front and rear axles. During vehicle deceleration different braking forces are required at the front and rear axles to reach the desired slip levels. Therefore, the brake pressures should be proportioned between the front and rear brakes to achieve the highest braking forces at each axle. ABS systems with such ability, known as Dynamic Rear Proportioning (DRP) systems, use the ABS valves to separately control the braking pressures on the front and rear wheels to dynamically achieve optimum braking performance at the front and rear axles under the then current conditions.
A further development in braking technology has led to the introduction of Traction Control (TC) systems. Typically, valves have been added to existing ABS systems to provide a brake system which controls wheel speed during acceleration. Excessive wheel speed during vehicle acceleration leads to wheel slippage and a loss of traction. An electronic control system senses this condition and automatically applies braking pressure to the wheel cylinders of the slipping wheel to reduce the slippage and increase the traction available. In order to achieve optimal vehicle acceleration, pressurized brake fluid is made available to the wheel cylinders even if the master cylinder is not actuated by the driver.
During vehicle motion such as cornering, dynamic forces are generated which can reduce vehicle stability. A Vehicle Stability Control (VSC) brake system improves the stability of the vehicle by counteracting these forces through selective brake actuation. These forces and other vehicle parameters are detected by sensors which signal an electronic control unit. The electronic control unit automatically operates pressure control devices to regulate the amount of hydraulic pressure applied to specific individual wheel brakes. In order to achieve optimal vehicle stability, braking pressures greater than the master cylinder pressure must quickly be available at all times.
SUMMARY OF THE INVENTION
This invention relates to an improved vehicle braking system. The vehicle braking system includes a master cylinder for generating pressurized fluid. A wheel brake is in fluid communication with the master cylinder. The brake system further includes a first valve for regulating the flow of fluid between the master cylinder and the wheel brake. The brake system also includes a pedal travel simulator including a housing having a bore formed therein. A piston is slidably disposed in the bore. The piston and the housing generally defining a fluid chamber which is in fluid communication with the master cylinder. The pedal travel simulator further includes a spring which biases the piston in a direction so as to contract the fluid chamber. The brake system further includes a source of pressurized fluid, such as a pump and high pressure accumulator. A boost valve can be located remotely from the master cylinder. The boost valve is in fluid communication with the source of pressurized fluid and the wheel brake. The boost valve is preferably mechanically actuated by the spring of the pedal travel simulator to supply pressurized fluid from the source of pressurized fluid to the wheel brake at a pressure ratio greater than fluid pressure generated by the master cylinder.
In a specific embodiment of a boost valve, in accordance with the present invention, the boost valve includes a valve body having first and second valve chambers. A sleeve member is fixed relative to the valve body. The sleeve member has a first end having a bore formed therein. A poppet valve assembly is movable relative to the sleeve member between a first position and a second position. The poppet valve has first and second ends. The boost valve further include a first valve member defined by the first end of the poppet valve assembly and the cooperation of the second end of a reaction spool engaged with a spring of a pedal travel simulator. A second valve member is defined by the cooperation of the first end of the sleeve member and the second end of the poppet valve assembly. When the poppet valve assembly is in its first position, the first valve member allows the flow of fluid between the bore of the reaction spool and the first valve chamber, and the second valve memb
Butler Douglas C.
Kelsey-Hayes Company
MacMillan Sobanski & Todd LLC
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