Fluid-pressure and analogous brake systems – Speed-controlled – Braking pressure demand or braking force desire
Reexamination Certificate
1998-01-30
2001-04-10
Graham, Matthew C. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Braking pressure demand or braking force desire
C303S119200, C303S113400
Reexamination Certificate
active
06213572
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates in general to an electronically controlled hydraulic brake actuation system for automobiles, and more specifically to a brake by wire system in which the vehicle wheel brakes are not normally hydraulically connected to the brake pedal. In such a system, brake pedal feel (pedal travel versus pedal force characteristics) is normally independent of wheel brake characteristics.
In conventional hydraulic vehicle brake systems, the force used to pressurize hydraulic fluid to operate the vehicle brakes comes from the vehicle operator pressing on the vehicle brake pedal to actuate the master cylinder of the brake systems. Normally, the resultant movement of the brake pedal linkage to the master cylinder is also used to actuate a vacuum or hydraulic boost system to provide an assisting for which aids the force provided by the vehicle operator in actuating the master cylinder and thus operate the vehicle brakes.
In certain recent advanced vehicle brake systems, such as so-called brake-by-wire brake systems, it is known to supply all of the force to operate the vehicle brakes from mechanical devices such as pumps or electrical linear actuators. When the mechanical device is a pump, the pressure generated by the pump and applied to the wheel brake will frequently be regulated by valves interposed between the pump and the wheel brakes. An example of such a brake-by-wire system is described in German Patent Application DE 44 13 579 A1.
In some known brake-by-wire systems, the vehicle brake pedal is connected to sensors providing signals used to control the operation of these mechanical devices supplying the force for operating the vehicle brakes. Such sensors typically measure the amount of movement of the brake pedal, the force with which the operator steps on the brake pedal, or both. Since the brake pedal does not actuate the vehicle brakes, it is common to provide a pedal simulator (also known as a compliance unit) to provide a simulated load on the brake pedal which provides a reaction force to the operation of the brake pedal similar to that experienced during the operation of a brake pedal in a conventional brake system. By providing a simulated load on the brake pedal similar to that experienced during the operation of a brake pedal in a conventional brake system, the transition from conventional brake systems to advanced brake systems having a pedal simulator is eased, since the driver of a vehicle with such an advanced brake system will enjoy a “normal” pedal feel. An additional purpose of the simulated load on a brake pedal is to provide a reaction force to the operation of the brake pedal to enable the use of a pedal force sensor as an input to the control of the operation of the mechanical devices supplying the force for operating the vehicle brakes.
SUMMARY OF THE INVENTION
This invention relates to an electro-hydraulic brake-by-wire system including a hydraulic pump and a plurality of valves to achieve a demanded braking force, and to achieve a desired brake pedal feel. The brake system includes a plurality of wheel brakes, a reservoir of hydraulic fluid, and a pump for selectively pumping hydraulic fluid from the reservoir and supplying pressurized hydraulic fluid to the wheel brakes for applying a braking force. The pump acts as a source of pressurized hydraulic fluid to the wheel brakes during normal brake apply, as well as during advanced braking functions as Antilock Braking (ABS), Traction Control (TC), or Vehicle Stability Control (VSC). An apply valve is associated with each of the wheel brakes for selectively permitting flow of pressurized hydraulic fluid from the pump to the associated wheel brake. A dump valve is associated with each of the wheel brakes for selectively permitting flow of pressurized hydraulic fluid from the associated wheel brake to the reservoir. A master cylinder is operated by a brake pedal for pressurizing hydraulic fluid. An isolation valve is associated with each of the wheel brakes for selectively preventing flow of pressurized hydraulic fluid from the master cylinder to the associated wheel brake. A sensor senses the position of the brake pedal and generates a pedal position signal representative of the position of the brake pedal. An electronic control unit receives the pedal position signal, which signal is utilized to determine a brake demand. The electronic control unit controls the operation of the pump, and the apply, dump, and isolation valves associated with each wheel brake to achieve a desired braking force at each wheel brake based on the brake demand and to regulate pressure generated by the master cylinder to achieve a predetermined relationship between the pressure generated by the master cylinder and the position of the brake pedal, whereby a desired pedal feel is achieved.
REFERENCES:
patent: 4462642 (1984-07-01), Leiber
patent: 5443309 (1995-08-01), Beck
patent: 5511862 (1996-04-01), Fujioka
patent: 5542755 (1996-08-01), Staib et al.
patent: 5709438 (1998-01-01), Isakson et al.
patent: 5730509 (1998-03-01), Eith et al.
patent: 5836334 (1998-11-01), Mittwollen et al.
patent: 4127578 (1993-02-01), None
patent: 44 13 579 A1 (1995-10-01), None
“Electrohydraulic Brake System—The First Approach to Brake-By-Wire Technology” by Jonner et al., SAE Technical Paper Series #960991, copyright 1996 Society of Automotive Engineers, Inc.
“Intelligent Braking for Current and Future Vehicles” by Schenk et al., SAE Technical Paper Series #950762, copyright 1995 Society of Automotive Engineers, Inc.
Linkner, Jr. Herbert L.
Tackett Wendell D.
Graham Matthew C.
Kelsey-Hayes Company
MacMillan Sobanski & Todd LLC
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