Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Reexamination Certificate
2000-03-10
2002-06-04
Pape, Joseph D. (Department: 3612)
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
C303S901000, C137S071000
Reexamination Certificate
active
06398317
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to brake systems and more particularly relates to a hydraulic automotive vehicle brake system with wheel slip control.
BACKGROUND OF THE INVENTION
A generic hydraulic brake system with a primary circuit and a secondary circuit is described in German patent application No. 43 37 133. The term ‘primary circuit’ refers to the connecting lines and channels which connect the master brake cylinder of the brake system to the wheel brakes and through which brake fluid is conducted in the direction of the wheel brakes during normal braking operations. The term ‘secondary circuit’ refers to those connecting lines and channels which are penetrated by pressure media in the case of wheel slip control.
The secondary circuit is connected to the primary circuit by way of an outlet valve on the inlet side and by way of a so-called return pump on the outlet side. The brake system is filled with a conventional brake fluid as a pressure medium. Filling is effected at the end of the vehicle assembly on the assembly line after the brake system has been installed into the vehicle in dry condition. The following procedure has proved to be quick and unproblematic to carry out. Initially, the entire system is evacuated and, in the evacuated condition, is thereafter connected to a brake fluid reservoir. The result is that brake fluid enters into the brake system and first fills the primary circuit. In order that the secondary circuit is also filled with pressure fluid, the electromagnetically operable outlet valve is opened during this process, i.e., both during evacuation and filling. This is disadvantageous inasmuch as provision must be made at the filling station to switch the normally closed outlet valve to adopt its open position.
Therefore, it has been suggested in German patent application No. 4337133 to interpose a non-return valve, which opens towards the primary circuit, between the secondary circuit and the primary circuit. This valve will open during evacuation of the system so that both circuits are evacuated. Because the valve closure member is not acted upon by a spring in the closing direction, as is disclosed in the first embodiment of the above publication, the valve remains open at the end of the evacuation process so that both the primary circuit and the secondary circuit are filled with pressure fluid during the filling process. In a second embodiment, it is emphasized as favorable that the non-return valve closes after the evacuation process. According to the application, this is said to be achieved because the valve closure member is arranged above the valve seat and urged against the valve seat by the force of gravity. In a wheel slip control operation which is induced on a roller test bench, where the outlet valve is open and the return pump is switched on, brake fluid flows into the secondary circuit.
A metal/metal seal pairing for the valve seat and the valve closure member is inappropriate because contaminants or chips may gather between the valve seat and the valve closure member and prevent complete closure of the valve. In this respect, an older application (German serial No. 19632343.6 dated Feb. 10, 1996) disclosed making at least the sealing lip of the valve closure member of a relatively soft plastic material which receives and stores the contaminants contained in the brake fluid so that reliable closure of the non-return valve is ensured. Further, it has been disclosed to load the valve closure member with a weak spring so that both circuits are evacuated during the evacuation process, similar to the second suggestion made in German patent application No. 43 37 133. Initially, only the primary circuit is filled with brake fluid during the filling process, while the secondary circuit is filled by opening the outlet valve in an induced wheel slip control operation. However, this solution, too, involves problems, especially in those cases where the secondary circuit is constituted by a channel in a so-called valve block made of steel or aluminum. Upon brake application, where pressure develops in the primary circuit, the pressure is applied to the valve closure member which, by compression of its elastically yielding sealing lip, is displaced in the direction of the secondary circuit. The volume decreases which is provided for the pressure fluid in the secondary circuit, with the result that a corresponding part of the brake fluid is displaced past the sealing lip into the primary circuit. After release of the brakes, that is, after the pressure in the primary circuit has been reduced again, the valve closure member is shifted back again, under the elastic effect of its sealing lip. The space in the secondary circuit which is available for the pressure fluid will increase, with the result that a vacuum develops therein which is not desirable. One possibility of overcoming the problem would be to increase the bias of the valve spring, which, in turn, would prevent a complete evacuation of the secondary circuit. This would necessitate a special filling process.
In another older application German patent application 196 321 58, it was suggested inserting a closure member instead of a non-return valve into the evacuation connection between primary and secondary circuits, which is made of a swellable synthetic caoutchouc and has no spring. After evacuation and filling of the brake system, the purpose of the closure member is to get swollen and interrupt the evacuation connection this way. However, the proposed solution to the above-mentioned problems involves a certain safety risk. The risk is that the swollen closure member which is durably elastic to a certain degree is directly exposed to the primary circuit and the secondary circuit and is thereby constantly subjected to deforming forces which are caused by the pressure differences between primary and secondary circuits that occur rapidly and alternatingly in the operation of the brake system. Boosted by high temperatures, the arising deformation forces can cause a viscous flow behavior of the closure member and, hence, malfunctions of the entire brake system due to leakage.
Thus, an object of the present invention is to configure a valve so that it is appropriate to eliminate the above-mentioned problems when used in the automotive vehicle brake system with wheel slip control described hereinabove.
To this end, the present invention suggests the provision of an additional device which, after filling of the brake system with brake fluid, permits automatically increasing the pilot pressure, which must be overcome for opening the spring-applied valve closure member, at least to such an extent that the valve closure member remains in the closing position at least during normal operation of the brake system.
A major advantage of the valve of the present invention is that a weak valve spring can be chosen for the purpose of evacuation of the brake system, and also the secondary circuit can reliably be evacuated this way. A ‘dry’ opening pressure for a reliable evacuation may e.g. amount to 50 millibar approximately. Because the additional device makes the opening pressure for the spring-applied closure member rise automatically after filling of the brake system with brake fluid, vacuum deposits or vacuums in the secondary circuit are prevented. However, the original spring application of the valve still exists so that at least the initial opening pressure and, thus, an unlimited operability of the brake system is ensured even if a malfunction or failure of the additional device occurs.
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Burgdorf Jochen
Volz Peter
Continental Teves AG & Co. OHG
Gutman Hilary
Pape Joseph D.
Rader & Fishman & Grauer, PLLC
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