Power plants – Pressure fluid source and motor – Pulsator
Patent
1993-08-05
1994-11-01
Look, Edward K.
Power plants
Pressure fluid source and motor
Pulsator
60577, 60578, 60589, F15B 700
Patent
active
053598547
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to an actuating unit for a hydraulic brake system which includes a pneumatic brake power booster and a master brake cylinder connected down-stream of the pneumatic brake power booster. The piston of the master brake cylinder confines a hydraulic pressure chamber and is coupled to an annular piston of larger diameter. The annular piston confines a filling chamber which can be connected to the pressure chamber.
A similar actuating unit is disclosed in German patent number 33 17 996. The annular piston of this actuating unit is hollow and is composed of a cylindrical inner wall and a cylindrical outer wall which are connected at one end and which confine an open annular chamber. The cylindrical outer wall of the annular piston is adapted to move through sealing elements arranged in the master cylinder housing into a filling chamber of annular cross-section at the end of the master brake cylinder close to the brake power booster. The filling chamber is arranged radially outward and coaxially relative to the first pressure chamber of the master brake cylinder. The first pressure chamber is bounded by a bottom that forms the primary piston and closes the cylindrical inner wall.
Less favorable aspects of the prior art actuating unit are its considerable axial length and its complicated structure. Another shortcoming of the prior art is that the pressure fluid volume, which on actuation is displaced by the annular piston through a complicated valve into a supply reservoir, is displaced over the entire stroke of the master brake cylinder. Thus, in the event of a slow actuation, the pressure fluid volume flows through the throttle bores provided in the valve into the supply reservoir so that no filling effect is achieved and the actuating travel is not shortened. On the other hand, in the event of a quick actuation, dynamic pressure develops in the filling chamber so that a sealing cup sealing the primary piston is flooded and the pressure in the primary pressure chamber increases until the valve is opened by the dynamic pressure. In this case, however, filling is undefined and depends on the pressure in the filling chamber. In addition, the slowly progressing release action of the actuating unit of the prior art is a disadvantage. The release action progresses slowly because both the primary chamber and the filling chamber are replenished solely through the previously mentioned throttle bores.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide an actuating unit for hydraulic brake systems which operates with a precisely defined change-over pressure and lost travel independent of the speed of actuation. Further, the present invention ensures that the displacement of the filling volume by the annular piston does not require an entire stroke of the master cylinder.
This object is achieved by the present invention in that the annular piston uncouples from the primary piston when the hydraulic pressure acting on it reaches a predetermined amount. The pressure acting upon the annular piston is the pressure prevailing in the pressure chamber of the master brake cylinder. Thus, the filling stage is activated only until a defined pressure is reached, and thereafter is terminated. Therefore, the entire actuating unit can become smaller and hence less expensive.
Another favorable improvement of the present invention over the prior art is that the annular piston, after being uncoupled, slides on the piston and cooperates with a stop. This feature limits the maximum possible stroke of the annular piston, which becomes important in the event of failure of the hydraulic circuit connected to the pressure chamber.
Another favorable embodiment of this invention is that the filling chamber serves as a supply chamber for the hydraulic pressure chamber bounded by the piston. This measure eliminates the lost travel, which has to be covered in the pressure chamber of the master brake cylinder on actuation, so that tolerances can be diminish
REFERENCES:
patent: 2041164 (1936-05-01), Carroll
patent: 2185264 (1940-01-01), Mistral
patent: 2298314 (1942-10-01), Sauzedde
patent: 2396536 (1946-03-01), Sauzedde
patent: 2768502 (1956-10-01), Sherman et al.
patent: 3150493 (1964-09-01), Rike
patent: 3412556 (1968-11-01), Rike et al.
patent: 4662688 (1987-05-01), Reinartz
Schiel Lothar
Wagner Wilfried
Alfred Teves GmbH
Lewis J. Gordon
Look Edward K.
Lopez F. Daniel
Seitter Robert P.
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