Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Reexamination Certificate
2000-03-28
2001-07-31
Oberleitner, Robert J. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
C060S591000, C060S592000
Reexamination Certificate
active
06267456
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to brake systems for wheeled motor vehicles, and more specifically it relates to a brake master cylinder and pedal feel emulator for a brake-by-wire system.
2. Background Information
Hydraulic-operated service brakes of a motor vehicle comprise a hydraulic master cylinder that is coupled via hydraulic brake lines to hydraulic wheel brakes at individual wheels. When a plunger of the master cylinder is depressed by a brake pedal to apply the wheel brakes, resistance is encountered. That resistance is typically due to a combination of the actual brake applications at the wheels and the force of a return spring acting on the pedal. Consequently, an operator of the vehicle expects to sense that resistance as a normal incident of driving.
A brake-by-wire system that utilizes a pedal to depress the master cylinder plunger performs the service brake function by selectively applying one of hydraulic brakes and brake-by-wire controlled brakes. Hydraulic brakes generally apply friction forces directly from the master cylinder to the wheels to dissipate energy as heat. Hydraulic brakes are typically used as a backup to brake-by wire controlled braking. Brake-by-wire controlled brakes generally are capable of applying friction forces to the wheels independent of the master cylinder displacement. Whether hydraulic or brake-by-wire controlled brakes are applied is determined by an electronic controller. Because flow of hydraulic fluid from the master cylinder to the wheel brakes is isolated from the friction brakes in brake-by-wire controlled braking when the controller determines that brake-by-wire controlled braking is to be applied, it may be considered desirable to associate an emulator with the master cylinder so that the feel sensed by the operator depressing the brake pedal is similar, and ideally identical, to the feel sensed when the hydraulic brakes are applied in a non-brake-by-wire braking system.
U.S. Pat. Nos. 5,729,979 and 5,927,825 disclose pedal feel emulators associated with master brake cylinders in brake-by-wire systems. Additional U.S. patents developed by a preliminary novelty search include: U.S. Pat. Nos. 4,526,003; 4,655,511; 5,253,929; 5,378,052; 5,421,643; 5,567,021; and 5,749,633.
SUMMARY OF THE INVENTION
The present invention relates to a novel association of a pedal feel emulator with a hydraulic brake master cylinder via hydraulic fluid paths that do not include an electric-actuated valve that is present at least in certain known brake systems. It is believed that the ability to eliminate such an electric-actuated valve is beneficial to overall system reliability. The association may be achieved by intimate integration of the emulator with the master cylinder, although generic principles of the invention contemplate a discrete emulator that can be mounted in a vehicle remote from the master cylinder.
One general aspect of the invention relates to a brake system for braking road-engaging wheels of a motor vehicle. The brake system comprises a brake master cylinder comprising a plunger adapted to be depressed within a bore of a master cylinder housing by operation of a brake pedal to brake the vehicle wheels. The bore comprises a first cylinder space within which a first piston, that divides the first cylinder space into a distal zone distal to a distal face of the first piston and a proximal zone proximal to a proximal face of the first piston, is displaced distally when the plunger is depressed. The bore further comprises a second cylinder space within which a second piston, that divides the second cylinder space into a distal zone distal to a distal face of the second piston and a proximal zone proximal to a proximal face of the second piston, is displaceable. A third piston that is disposed within the bore to isolate the distal zone of the first cylinder space from the proximal zone of the second cylinder space, and in response to distal displacement of the first piston, is displaced distally to impart distal displacement to the second piston when hydraulic-operated brakes for the vehicle wheels are applied.
A first reservoir port provides open fluid communication between the proximal zone of the first cylinder space and a hydraulic fluid reservoir, and a second reservoir port provides open fluid communication between the proximal zone of the second cylinder space and the hydraulic fluid reservoir. A first wheel brake port communicates the distal zone of the first cylinder space through a first normally open solenoid valve to at least a first hydraulic-operated brake for at least a first of the vehicle wheels, and a second wheel brake port communicates the distal zone of the second cylinder space through a second normally open solenoid valve to at least a second hydraulic-operated brake for at least a second of the vehicle wheels. Those two solenoid valves are open for hydraulic braking, but they are operated closed when brake-by-wire controlled braking is occurring.
In response to depression of the plunger coincident with disallowance of operation of the hydraulic-operated brakes caused by blockage of hydraulic fluid flow out of the master cylinder via the wheel brake ports, an emulator is effective to emulate resistance force encountered by depression of the plunger when the absence of such blockage causes the hydraulic-operated brakes to be applied.
The emulator comprises an emulator housing comprising an emulator cylinder space within which an emulator piston, that divides the emulator cylinder space into a distal zone distal to a distal face of the emulator piston and a proximal zone proximal to a proximal face of the emulator piston, is displaceable. The emulator further comprises a resiliently compressible element disposed in one of the zones of the emulator cylinder space for creating resistance force on the emulator piston in response to a change in volume of that one zone that occurs in response to displacement of the emulator piston within the emulator cylinder space. A first of the zones of the emulator cylinder space has open fluid communication with the distal zone of the first cylinder space, and a second of the zones of the emulator cylinder space has selective communication with the second reservoir port to allow open communication of the second zone of the emulator cylinder space with the second reservoir port, and hence cause the emulator piston to be displaced within the emulator cylinder space to compress the resiliently compressible element in consequence of depression of the plunger coincident with blockage of hydraulic fluid flow from the master cylinder via the wheel brake ports disallowing operation of the hydraulic-operated brakes, and to disallow communication of the second zone of the emulator cylinder space with the second reservoir port, and hence cause the emulator piston not to be displaced in consequence of depression of the plunger coincident with absence of such blockage.
Another general aspect of the invention relates to the master cylinder and emulator just described.
Still another aspect of the invention relates to the combination of a master cylinder and a pedal feel emulator for a motor vehicle that has multiple road-engaging wheels that are braked in consequence of a brake pedal depressing a plunger within a bore of a hydraulic master cylinder to cause a selected one of hydraulic brakes and brake-by-wire controlled brakes to be applied.
The master cylinder bore comprises a first cylinder space within which a first piston, that divides the first cylinder space into a distal zone distal to a distal face of the first piston and a proximal zone proximal to a proximal face of the first piston, is displaced distally when the a plunger is depressed, and a second cylinder space within which a second piston, that divides the second cylinder space into a distal zone distal to a distal face of the second piston and a proximal zone proximal to a proximal face of the second piston, is displaceable.
A third piston is disposed within the bore to
Brown Gregory P.
Coughlin William J.
Ford Global Technologies Inc.
Kramer Devon
Oberleitner Robert J.
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