Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Patent
1993-07-30
1995-06-20
Look, Edward K.
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
91376R, F15B 910
Patent
active
054253020
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 conventionally comprise a piston comprising a back tubular part and a skirt and which, with the aid of an unrolling membrane, defines a front chamber connected permanently to a source of partial vacuum and a back chamber connected selectively to the front chamber or to the atmosphere via a valve means actuated by a control rod capable of bearing, through the intermediary of the front face of a plunger, against a first face of a reaction disk securely attached through a second face to a thrust rod.
Such boosters, as illustrated for example by document EP-A-0,101,658, have various disadvantages. Thus for example, in normal operation, that is to say in boost phase, the plunger controls the valve means, the latter comprising a valve interacting through an active part with a first valve seat formed on the plunger and with a second valve seat formed on the piston, so as to admit a certain quantity of air into the back chamber, as a function of the force exerted by the driver of the vehicle on the control rod. The difference in the pressures exerted on the two faces of the skirt of the piston then creates a boost force, itself also a function of the force exerted on the control rod.
A moment arrives however when the control force, otherwise termed input force, is strong enough for the pressure in the back chamber to be equal to the atmospheric pressure. The booster is then in saturation phase, that is to say the difference in pressure between back chamber and front chamber has reached its maximum. Whatever the force exerted by the driver on the control rod, this pressure difference can no longer increase and the boost force remains constant, and any additional input force results in the same increase in the output force on the thrust rod. There is therefore an abrupt transition between the boost phase and the saturation phase, during which the boost force, which was increasing linearly with the input force, becomes constant. This transition from one phase to the other is perceived by the driver as an abrupt rise in the force to be exerted in order to obtain in the saturation phase the same increase in the output force as during the boost phase.
The object of the present invention is consequently to provide a booster whose operation does not exhibit any abrupt transition from the boost phase to the saturation phase.
According to the present invention, the piston bears against the reaction disk through a resilient annular front face.
According to advantageous features of the invention, this annular front face is resiliently deformable between a rest position and an active position, which is obtained when the thrust rod exerts on the reaction disk a force greater than a predetermined value. Advantageously, an intermediate resilient member is disposed between the annular front face of the piston and the plunger, this intermediate resilient member coming into contact with the plunger and the annular front face of the piston when the latter is in its active position.
According to other particularly advantageous features, the annular front face of the piston and the intermediate resilient member comprise radial sectors, so that the transition from the boost phase to the saturation phase is adjustable.
The invention will now be described by way of example with reference to the accompanying drawings in which:
FIG. 1 is a side view, in longitudinal section, showing the back central part of a pneumatic brake-booster of the type known, for example, from the above-mentioned document,
FIG. 2 is a curve showing diagrammatically the development of the force Fs exerted on the thrust rod at the booster output as a function of the force Fe exerted on the control rod at the booster input,
FIG. 3 is a side view in longitudinal section, showing the back central part of a pneumatic brake-booster according to one embodiment of the invention,
FIG. 4 is a curve showing dia
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patent: 5054370 (1991-10-01), Osterday et al.
patent: 5146837 (1992-09-01), Inoue
patent: 5261313 (1993-11-01), Yared
Castel Philippe
Le Normand Pascal
Levrai Roland
Bendix Europe Services Techniques
Look Edward K.
McCormick Jr. Leo H.
Nguyen Hoang
Palguta Larry J.
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