Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Patent
1993-05-04
1994-11-29
Look, Edward K.
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
91376R, B60T 1357
Patent
active
053679415
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to pneumatic boosters, and more particularly those of the type used in order to boost the braking of motor vehicles.
Boosters of this type comprise in conventional mariner a piston formed by a hub and by a skirt and which, with the aid of an unrolling membrane, defines a front chamber permanently connected to a partial vacuum source and a back chamber connected selectively to the front chamber when a first valve passage is opened or to the atmosphere when a second valve passage is opened, the first and second valve passages being formed by first valve means cooperating with second valve means, and being actuated by a control rod capable of bearing, through the intermediary of a plunger, against one of the faces of a reaction disc securely attached to a push rod.
Such boosters, as disclosed for example by Document EP-A-0,004,477, have some disadvantages. Thus, in order for the control rod not to have too long a dead travel, the valve means has necessarily to be designed in such a manner that the "shutter lift" between the valve shutter and the second valve seat is as low as possible. It therefore follows that, during braking, the chamber is reduced, as is the passage offered to the air from the back chamber towards the front cheer during brake release. The operation of these boosters is therefore accompanied by air suction noises, which may become annoying, all the more so as the structure of the piston hub, having a single radial passage towards the back chamber and a single axial passage towards the front chamber, additionally induces considerable turbulence in the moving air.
Another disadvantage due to these reduced and turbulent air passages resides in the fact that the air is greatly slowed down in its various movements between the atmosphere, the back chamber and the front chamber, and therefore that the boosters have long response times. Yet another disadvantage of known boosters resides in the fact that the annular shutter valve member has the general shape of a tulip with an external bead for its mounting, in association with the shutter valve member support, in the tubular hub of the piston assembly, the active part of the shutter valve member being connected to this mounting bead by a thin web which flares towards the outside so as to connect to the mounting bead. In such an arrangement, the intermediate web member of the shutter valve member is subjected, during the useful life of the booster, to very numerous flexural and compressive actions which in the long term can induce a fatigue, in this place, of the elastomer material constituting the shutter valve member. Moreover, in operation, this intermediate web part of the shutter valve member is subjected to a pressure differential between the atmosphere permanently prevailing inside the tubular hub, around the input rod, and the vacuum permanently prevailing in the annular chamber surrounding this intermediate web part of the shutter valve member and permanently connected to the front chamber, or partial vacuum chamber of the booster. This pressure differential, apart from contributing to the fatigue of the intermediate web part, induces on the active part of the shutter valve member an axial force which is added to the force of the valve spring and which the valve plunger must overcome during each brake release phase in order to disengage the active part of the shutter valve member from the first shutter valve seating formed in the hub and to re-establish the communication between the back working chamber of the booster and the partial vacuum chamber, which necessitates an overdimensioning of the input rod return spring, this manifesting itself particularly in the need for the driver to supply a substantial force in order to operate the booster, said force being known in the arts [sic] by the term "attack force".
Document DE-A-3,836,609 also discloses a pneumatic booster, corresponding to the preamble of the main claim, in which booster some of the abovementioned disadvantages are avoided: it does not contain an
REFERENCES:
patent: 3081744 (1963-03-01), Brooks et al.
patent: 4598548 (1986-07-01), Wagner
patent: 5096267 (1992-03-01), Volz
Gautier Jean Pierre
Verbo Ulysse
AlliedSignal Europe Services Techniques
Look Edward K.
Palguta Larry J.
Ryznic John
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