Fluid-pressure and analogous brake systems – Speed-controlled – With failure responsive means
Reexamination Certificate
1999-11-09
2001-08-21
Oberleitner, Robert J. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
With failure responsive means
C303S122110, C303S113400, C303S155000
Reexamination Certificate
active
06276765
ABSTRACT:
The present invention relates generally to a power assisted braking system for a vehicle and more particularly to methods and apparatus for optimal control and improved time response for a secondary or back-up braking system.
BACKGROUND OF THE INVENTION
The time-honored skid avoidance technique of “pumping” a brake pedal to control a skid situation has largely been displaced by anti-lock braking systems. Many known anti-lock devices operate by cyclically increasing and decreasing a braking force exerted on the wheels so that a slipping wheel having a tendency to lock is permitted to re-accelerate back to a spoed corresponding to the speed of the vehicle. This is typically achieved by control valves alternately allowing fluid to flow out of and then into a brake cylinder to first lower and then raise the brake pressure in the brake system.
Typically anti-lock or anti-skid braking systems utilize a so-called pump-back scheme or a replenishing scheme during a reapply or build operational sequence to maintain a desired level of hydraulic fluid in a brake system. In a pump-back scheme, the same hydraulic fluid is re-supplied from a local accumulator to the brake pad actuators while in a replenish scheme hydraulic fluid comes from a separate source such as either a hydraulic accumulator or a separate pump and motor.
Most of such anti-lock braking systems are further capable of operating in a traction control function. A traction control function is established by detecting conditions where the rotational speed of a first powered wheel substantially exceeds that of a second powered wheel. To provide a power balance in the operation of a vehicle, a braking force is applied to the powered wheel rotating at a higher speed to effectively transferring driving torque back to that wheel with better traction. Many anti-lock systems having such a traction control feature employ a motor and hydraulic pump or pumps which operate independent of the service braking system. Such a braiding system is disclosed in U.S. Pat. No. 5,709,438 wherein a traction control motor and hydraulic pump are called into action to provide a back-up power assisted braking feature in the event of a malfunction of the primary braking system. Such malfunctions may occur simply because the engine is not operating to drive the primary power braking source, ruptured or failed brake lines, broken power steering pump drive belts, or for a variety of other reasons. This prior patent provides back-up anti-skid braking in but a single mode. This prior patent represents the point of departure for the present invention.
It is desirable to provide a braking control system of the type disclosed in the above mentioned U.S. Patent having a back-up feature which modulates pressure to the service brakes in the event of loss of the primary brake power source. It is also desirable to provide a “wake-up” mode of operation which allows secondary or back-up power assisted braking with the ignition off.
SUMMARY OF THE INVENTION
The present invention provides solutions to the above problems by providing a braking control which uses brake pedal input and vehicle wheel speeds or hydraulic pressure available in a primary braking system to activate a secondary or back-up braking in either a static or dynamic control mode.
In general, the invention provides a power assisted braking system for a vehicle having anti-skid capability with primary and secondary pressurized fluid sources and includes an operator actuable pedal for developing an input force to command the application of braking force hydraulic pressure as well as one or more pressure transducers for measuring the actual hydraulic pressure applied during braking. The vehicle velocity is determined and the vehicle deceleration computed. The primary brake system is operable in a normal mode utilizing a primary source of hydraulic fluid pressure to provide normal power assisted braking. There is an arrangement for detecting a malfunction in the primary braking system fluid source which is effective to substitute the secondary fluid source for the primary fluid source to provide continued back-up power assisted braking. The system is operable in a first back-up mode upon detecting a malfunction of the primary braking system, a command for braking, and a first vehicle speed input to provide anti-skid braking wherein pedal input force is compared with measured vehicle deceleration to generate braking pressure build and decay commands for operating the brake system. The system is operable in a second back-up mode upon detecting a malfunction of the primary braking system, a demand for braking, and a second vehicle speed input to provide anti-skid braking wherein pedal input force is compared with calculated vehicle deceleration to generate braking pressure build and decay commands for operating the brake system.
Also in general and in one form of the invention, a power assisted braking system for a vehicle has a primary power source and an electrically driven back-up power source for supplying pressurized hydraulic fluid for braking. The system includes a wake-up circuit having means for sensing depression of the vehicle brake pedal whereby input force is created, and means responsive to the brake pedal sensing means indicating depression has occurred for enabling the back-up power source to provide power assisted braking even when the vehicle ignition is in the off position. The wake-up circuit may include an arrangement to test for adequate hydraulic pressure either when the brake pedal is depressed or the ignition is turned to the on position and to enable the back-up power source when the hydraulic pressure is not adequate.
Still further in general and in one form of the invention, back-up power assisted braking includes a pump operable upon detection of a malfunction of the normal power assisted braking and at least one transducer for sensing the hydraulic pressure applied to the brake actuators and providing a signal indicative thereof. During back-up power assisted braking, if the sensed hydraulic pressure exceeds a prescribed value, the supply of hydraulic fluid to or from the actuators is blocked and the back-up pump turned off to maintain the braking pressure at the actuators near the prescribed value.
REFERENCES:
patent: 4258819 (1981-03-01), Baptiste, Sr.
patent: 5013094 (1991-05-01), Nishii et al.
patent: 5393131 (1995-02-01), Nomura et al.
patent: 5868473 (1999-02-01), Kato et al.
patent: 5954406 (1999-09-01), Sawada
patent: 6007164 (1999-12-01), Sakai et al.
patent: 6092880 (2000-07-01), Towers et al.
Albert Timothy Jay
Goodzey Gregory Paul
Towers Kenneth Scott
Comstock Warren
McCormick Jr. Leo H
Oberleitner Robert J.
Robert Bosch Corporation
Sy Mariano
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