Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Reexamination Certificate
1999-06-24
2001-03-13
Schwartz, Christopher P. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
C303S010000, C417S470000, C417S549000
Reexamination Certificate
active
06199962
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates in general to vehicular brake systems. More specifically, this invention relates to a hydraulic control unit having a self-priming pump for use in a vehicular brake system.
Conventional vehicular brake systems having anti-lock brake, traction control and/or vehicle stability control functions employ a hydraulic control unit. A typical hydraulic control unit used in these types of brake systems includes a housing having multiple fluid control valves or isolation valves for modulating the flow of fluid to a plurality of wheel brakes during designated braking events. The housing further includes multiple fluid control valves or dump valves for modulating hydraulic flow from the wheel brakes during designated braking events. During these designated braking events, a pump, disposed in the housing, transfers fluid from a master cylinder to the wheel brakes, and vice versa. The pump includes a pair of opposing pistons and sleeves. Each pair of pistons and sleeves defines a single variable-volume chamber. Each variable-volume chamber includes an inlet in fluid communication with the master cylinder and at least one of the dump valves. Each variable-volume chamber further includes an outlet in fluid communication with the master cylinder and at least one of the isolation valves.
Pump efficiency is defined by the flow rate of the fluid transferred from the variable-volume chambers divided by the flow rate capacity of the pump. The flow rate capacity of the pump is defined by the pump cycle rate multiplied by the combined volumes of the variable-volume chambers.
It is a noted concern that the pump efficiency is reduced when the temperature of the fluid decreases and/or when the pump cycle rate is increased. The reduction in the pump efficiency is significantly due to the drag placed on the fluid supplied to the variable-volume chambers, which in turn places a limit on the flow rate of the fluid supplied to the variable-volume chambers. The drag placed on the fluid supplied to the pump becomes more pronounced when additional components are placed in the fluid flow path of a given variable-volume chamber in advance of the inlet of the variable-volume chamber.
Accordingly, there is a need for a hydraulic control unit having a pump capable of operating efficiently at low ambient temperatures and/or at an increased pump rate.
It is also known that during braking events in which the pump draws fluid from the master cylinder while an operator is applying force to the brake pedal that the brake pedal may “shutter” or exhibit a stepped displacement. The stepped displacement of the brake pedal is a result of the pump displacing fluid from the master cylinder in an intermittent manner. In other words, the pump does not draw fluid from the master cylinder in a continuous manner, rather the pump only draws fluid from the master cylinder when moving from a top-dead-center position to a bottom-dead-center position. Consequently, the pump causes the brake pedal to shutter when the pump draws fluid from the master cylinder and the operator is applying force to the brake pedal.
Accordingly, there is a further need for a hydraulic control unit having a pump that reduces shuttering of a brake pedal associated with braking events in which the pump draws fluid from a master cylinder while an operator is applying force to the brake pedal.
SUMMARY OF THE INVENTION
This invention concerns a hydraulic control unit (HCU) for use in vehicular brake systems. The HCU comprises a housing having a cavity. An eccentric drive means presenting a drive axis is rotatably disposed in the cavity. A sleeve extends from the cavity substantially perpendicular to the drive axis. A first end of a piston is slidably disposed in the sleeve for movement between a bottom-dead-center position and a top-dead-center-position. A second end of the piston extends from the sleeve and engages the drive means. The drive means moves the piston from the bottom-dead-center position to the top-dead-center position during designated braking events. A biasing means moves the piston from the top-dead-center position to the bottom-dead-center position.
The piston and the sleeve form a pump. The pump includes a first variable-volume chamber defined by the piston and the sleeve adjacent to the first end of the piston. A first check valve is placed in fluid communication with the first variable-volume chamber and is adapted for placement in fluid communication with at least one wheel brake. The first check valve prevents fluid from flowing from the corresponding wheel brakes to the first variable-volume chamber while allowing fluid to flow from the first variable-volume chamber to corresponding wheel brakes. Fluid is transferred from the first variable-volume chamber to the corresponding wheel brakes when the piston moves from the bottom-dead-center position to the top-dead-center position.
The piston includes an axial fluid passage for transferring fluid to the first variable-volume chamber. A second check valve is connected to the first end of the piston and is in fluid communication with the fluid passage and the first variable-volume chamber. The second check valve prevents fluid from flowing from the first variable-volume chamber to the fluid passage while allowing fluid to flow from the fluid passage to the first variable-volume chamber.
The pump further includes a constant-volume chamber defined by the piston and the sleeve between the first and second ends of the piston. The constant-volume chamber is connected in fluid communication with the fluid passage and an inlet channel formed in the sleeve. The inlet channel is adapted for placement in fluid communication with a fluid supply source, such as a master cylinder. Fluid is transferred from the fluid supply source to the first variable-volume chamber through the inlet channel and the fluid passage when the piston moves from the top-dead-center position to the bottom-dead-center position.
The pump further includes a second variable-volume chamber defined by the piston and the sleeve adjacent the constant-volume chamber. The second variable-volume chamber is connected in fluid communication with the fluid passage. Fluid is transferred to the second variable-volume chamber from the inlet channel through the fluid passage when the piston moves from the bottom-dead-center position to the top-dead-center position. Fluid is transferred from the second variable-volume chamber through the fluid passage to the first variable-volume chamber when the piston moves from the top-dead-center position to the bottom-dead-center position. Accordingly, the second variable-volume chamber acts to prime the first variable-volume chamber.
Preferably, the constant-volume chamber is formed between the first and second variable-volume chambers. Alternatively, the orientation of the constant-volume chamber and the second variable-volume chamber may be reversed. In the preferred embodiment, the fluid flow characteristics of the fluid transferred from the second variable-volume chamber through the fluid passage assists in the transfer of fluid from the fluid supply source through the constant-volume chamber to the first variable-volume chamber.
This invention increases pump efficiency, in that fluid is supplied to the first variable-volume chamber from both the inlet channel and the second variable-volume chamber when the piston moves from the top-dead-center position to the bottom-dead-center position. In the preferred embodiment, pump efficiency is further increased by fluid being drawn from the constant-volume chamber by the fluid transferred from the second variable-volume chamber to the first variable-volume chamber. Most notably, the pump efficiency is significantly increased when the fluid is at low operating temperatures and/or when the pump cycle rate is increased.
Accordingly, this invention provides a hydraulic control unit for use in a vehicular brake system having a self-priming pump capable of operating efficiently at low ambient temperatures and/or an increa
Dokas David M.
Ganzel Blaise J.
Kelsey-Hayes Company
MacMillan Sobanski & Todd LLC
Schwartz Christopher P.
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