Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1994-04-26
1995-05-02
Graham, Matthew C.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
3031132, B60T 834, B60T 848, B60T 842, B60K 2816
Patent
active
054113261
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention is concerned with a slip-controlled hydraulic brake system for controlling fluid pressure in a wheel cylinder of a driven wheel of an automotive vehicle, during normal braking, brake slip control and traction slip control.
A brake system of this type is described by German Patent DE-38 32 023 A1. During brake slip control, this system operates on the back-flow principle, which involves pressure fluid flow from the outlet of a pump to a brake conduit in fluid communication with an inlet valve of a wheel brake and from an outlet valve of the wheel brake to the inlet of the pump. The pump of this system is a self-priming pump, which is also used for traction slip control. The pump takes in pressure fluid, through the master cylinder, from the pressure fluid reservoir, and feeds the pressure fluid into the wheel cylinder. The direct feed to the wheel cylinder results in the benefit that no additional high-pressure accumulator is required.
However, in systems of that type, especially at low temperatures due to the high viscosity of the pressure fluid, the response time of traction slip control is longer than the response time for systems having a high-pressure accumulator. A reason for the increased response time is because long-length conduits and a plurality of valves are provided between the pump and the pressure fluid reservoir, thereby constricting the volume flow and resulting in take-in losses.
SUMMARY OF THE INVENTION
The problem underlying the present invention resides in providing, in a brake system of the aforedescribed type, during traction slip control, a rapid loading of the wheel cylinder, avoiding the need for a high-pressure accumulator.
This problem is solved by providing a low-pressure accumulator on the intake side of a pump and regulating pressure fluid flow between the low-pressure accumulator and the intake side of the pump. A brake slip control intake channel and a traction slip control intake channel permit pressure fluid flow between the intake side of the pump and the low-pressure accumulator. The brake slip control intake channel is closed as long as the pressure fluid volume stored within the low-pressure accumulator is less than a predetermined standby volume. The traction slip control intake channel is independently opened and closed by a traction slip control loading valve, regardless of the pressure fluid volume stored within the low-pressure accumulator.
Because a stand-by volume is made available by the low-pressure accumulator to the pump during traction-slip control, no intake losses occur toward the intake side of the pump in view of the short-length traction-slip control intake channel. In addition, the static pressure in the low-pressure accumulator has a positive effect on the initial rating of the pump.
According to an embodiment of the present invention, the low-pressure accumulator is disposed in a housing bore and includes an axially displaceable piston, which is sealed against the housing bore. The piston separates a pressure-fluid containing axial section of the housing bore, serving as a reservoir, from a pressure fluid-free axial section of the housing bore, which is open to atmospheric pressure. Disposed in the brake slip control intake channel is a valve, for example a travel-controlled valve, which is switched depending on the position of the piston. This embodiment obviates the need for a costly electronic system provided with sensors and conduits.
According to another aspect of the present invention, the axially displaceable piston of the low-pressure accumulator is loaded by a compression spring toward the reservoir. Within a central bore of the piston is a second compression spring, which applies pressure to a plunger axially protruding from the central bore of the piston into the reservoir. The end of the plunger serves as a valve body and cooperates with a valve seat formed on the housing of the low-pressure accumulator, for controlling pressure fluid flow through the brake slip control intake channel
REFERENCES:
patent: 5152586 (1992-10-01), Burgdorf
patent: 5174636 (1992-12-01), Burgdorf et al.
patent: 5288142 (1994-02-01), Burgdorf
Graham Matthew C.
ITT Automotive Europe GmbH
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