Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Patent
1996-12-11
2000-05-30
Ryznic, John E.
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
913692, B60T 13569, B60T 1357
Patent
active
060678917
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to pneumatic boosters, or servo actuators, of the kind which are used to provide braking assistance for automobile vehicles.
BACKGROUND OF THE INVENTION
Such boosters are well known in automobile technology and comprise in general an envelope having an axis of symmetry, separated sealingly by at least one movable partition structure into a front chamber connected permanently to a source of low pressure, and a rear chamber connected selectively to the front chamber or to a source of hitch pressure by a three way valve means actuated by a control rod capable of bearing, through the intermediary of the front face of a plunger, on the rear face of a thrust rod which is solid with a reaction disc, the plunger sliding in a bore in the movable partition, the three way valve comprising a valve member disposed in a tubular rear part of the movable partition and co-operating through an annular front face with a first valve seat formed on the plunger and with a second valve seat formed on the movable partition, a space being arranged between the two valve seats and communicating with at least one radial passage formed in the movable partition and opening out into the rear chamber, at least one axial passage being formed in the movable partition and openings into the front chamber, the annular front face of the valve member being urged in the direction of the valve seats by a valve spring.
Very many documents illustrate this type of booster, like for example the document GB-A-2 095 778. For a long time, improvements have been sought in the performance of the boosters, and in particular reductions in the response time, such as to obtain rapid actuation of the brakes when a force is applied to the brake pedal and also the return time, so that the driver will be able to control precisely the amount of his braking action.
Improvement of the response time is obtained by increasing the cross sectional area of the air flow passage at the level of the first annular valve seat, and generally by increasing its diameter. On the other hand, when a reduction in the return time of the booster is sought, this requires a reduction in the diameter of the second annular valve seat. These two improvements are thus in contradiction since in this design of booster, the valve seats are disposed substantially in the same plane and the diameter of the first valve seat is limited by, amongst other parameters, the diameter of the second valve seat.
SUMMARY OF THE INVENTION
The present invention is situated in this context and has as object to provide a booster of the kind referred to above, in which a reduction is obtained both in the response time and the return time, by means which are simple to implement and reliable, and moreover while modifying only a minimum of the components of a conventional booster so as to use a maximum of parts which are already in production and thus avoid increasing the cost of the booster.
To this end, the present invention provides that the second valve seat formed on the movable partition is formed by bringing together at least two circular arcs which are concentric, coplanar and of different radiuses.
Preferably, the second valve seat formed on the movable partition comprises at least a first circular arc substantially in an angular sector where the space communicates directly with the radial passage and at least a second circular arc substantially in an angular sector where the axial passage is formed which opens out into the front chamber.
Advantageously, the radius of the first circular arc is greater than the radius of the second circular arc.
In accordance with an advantageous embodiment the axial passage which opens out into the front chamber is partially formed by an axial groove formed in the rear tubular part of the movable partition.
Other objects, features and advantages of the present invention will appear more clearly from the following description of an embodiment thereof, given by way of illustration, with reference to the accompanying drawings.
BRIEF DESCRI
REFERENCES:
patent: 4803912 (1989-02-01), Nishii
Gautier Jean Pierre
Verbo Ulysse
Bosch Systems de Freinage
McCormick Jr. Leo H.
Ryznic John E.
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