Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Reexamination Certificate
1999-03-16
2001-10-23
Graham, Matthew C. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
C303S113400, C303S155000
Reexamination Certificate
active
06305758
ABSTRACT:
TECHNICAL FIELD
This invention relates to an electro-hydraulic actuator for a motor vehicle brake-by-wire brake system.
BACKGROUND OF THE INVENTION
A traditional motor vehicle brake system includes a plurality of fluid pressure actuated wheel brakes, a master cylinder, and a brake pedal linked to a piston assembly in the master cylinder. To apply the wheel brakes, an operator pushes on the brake pedal and linearly strokes the piston assembly to create a high fluid pressure in the wheel brakes through a plurality of hydraulic channels. Before the wheel brakes become applied, fluid expelled by the piston assembly must first take up compliance in the wheel brakes and in the hydraulic channels. To maximize response, the piston assembly typically has a relatively large effective area in order to rapidly expel a substantial volume of fluid at relatively low fluid pressure at the onset of pedal travel. To attain high fluid pressure to apply the wheel brakes without requiring that the operator apply an uncomfortably high pedal force, the traditional motor vehicle brake system also typically includes a booster which supplements the pedal force applied by the operator.
A brake-by-wire brake system is distinguished from traditional motor vehicle brake systems by the addition of an electro-hydraulic actuator having a piston which performs the function of the master cylinder piston assembly but which is driven through a speed reducer by an electric motor under the control of an electronic control module (ECM) on the motor vehicle. The electrohydraulic actuator piston has a relatively large effective area for rapid response. However, to attain high fluid pressure for wheel brake application with a piston having a large effective area, the electric motor must have a relatively high torque capacity. Such high capacity electric motors are relatively expensive and represent a significant fraction of the cost of a brake-by-wire brake system. An electro-hydraulic actuator according to this invention for a brake-by-wire brake system is an improvement over prior electro-hydraulic actuators having comparable performance characteristics in that the electro-hydraulic actuator according to this invention includes a more economical electric motor of reduced torque capacity.
SUMMARY OF THE INVENTION
This invention is a new and improved electro-hydraulic actuator for a motor vehicle brake-by-wire brake system including a housing, a piston bore in the housing, a T-shaped piston in the piston bore, and an electric motor connected to the piston through a speed reducer. The T-shaped piston includes a disc-shaped head supported in the piston bore for back and forth linear translation and a tubular stem perpendicular to the head slidable in and out of the piston bore through a sealed guide in the bottom of the piston bore. The side of the piston head opposite the stem, referred to herein as the “top side ”, constitutes a large effective area of the piston for rapidly expelling a relatively large volume of fluid from the piston bore in a low pressure interval of operation the actuator. When the fluid pressure in the piston bore exceeds a transition pressure, a transition valve opens a bypass passage to the piston bore behind the piston head so that the same fluid pressure reacts against the other side of the piston head, referred to herein as the “bottom side”. A high pressure interval of operation of the electro-hydraulic actuator then ensues in which the effective area of the piston is reduced to the area of the cross-sectional profile of the stem so that high fluid pressure is produced in the piston bore with less output torque from the electric motor.
REFERENCES:
patent: 5042885 (1991-08-01), Villec
patent: 5147117 (1992-09-01), Quinn
patent: 5163744 (1992-11-01), Tiernay et al.
patent: 5927825 (1999-07-01), Schenk et al.
patent: 6105737 (2000-08-01), Weigert et al.
Hageman John Benjamin
Schenk Donald Edward
Shaw Schuyler Scott
Delphi Technologies Inc.
Graham Matthew C.
Sigler Robert M.
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