Motors: expansible chamber type – Working member position feedback to motive fluid control – Plural input signal means for single motor valve
Patent
1998-07-24
2000-04-04
Lopez, F. Daniel
Motors: expansible chamber type
Working member position feedback to motive fluid control
Plural input signal means for single motor valve
91376R, F15B 910, F15B 1316
Patent
active
060447494
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to pneumatic boosters of the type used to boost braking in motor vehicles.
BACKGROUND OF THE INVENTION
Boosters of this kind are well known in the field of motor vehicles and in the conventional way comprise a casing having an axis of symmetry and divided in leaktight fashion by at least one moving wall structure into a front chamber permanently connected to a low-pressure source and a rear chamber selectively connected to the front chamber or to a high-pressure source by a three-way valve means actuated by an operating rod secured to a plunger, subjected to the action of a return spring and capable of sliding in a bore formed in a pneumatic piston, secured to the moving wall and a tubular rear part of which can slide in leaktight fashion in an opening in the rear wall of the casing, the three-way valve comprising a valve element arranged in the tubular rear part of the moving wall and interacting with a first valve seat formed on the plunger and with a second valve seat formed on the pneumatic piston, the rear position of rest of the plunger being defined by a stop formed at the front end of a sleeve arranged in the tubular rear part of the pneumatic piston.
A great many documents illustrate this type of booster, these including, for example, the document EP-A-0,233,026. For a long time attempts have been made to improve the performance of such boosters, and in particular to reduce the attack force and the response time so as to obtain rapid actuation of the brakes when the brake pedal is operated, and also to reduce the return time so that the driver can precisely gage his braking action.
The improvement in the response time can conventionally be obtained by increasing the cross section through which air can pass at the first annular valve seat, formed on the plunger, generally by increasing its diameter. By contrast, if the return time of the booster is to be reduced, that necessitates reducing the diameter of the second annular valve seat formed on the pneumatic piston. These two improvements are thus contradictory because, in this design of booster, the valve seats are located in more or less the same plane and the diameter of the first valve seat is limited, among other things, by the diameter of the second valve seat.
SUMMARY OF THE INVENTION
The present invention falls within this context and its object is to provide a booster of the type recalled hereinabove, in which a reduction in the attack force, and in the response and return times can be obtained simultaneously using means that are simple to employ and reliable and which in addition involve modifying only a minimum number of the components of a conventional booster so that maximum use can be made of components already in production so that the cost of the booster will not increase. Such a booster needs in addition to be able to be actuated automatically in a simple way in order to meet the current desires of motor manufacturers.
To this end, the present invention makes provision for the plunger to comprise a cylindrical rear part capable of sliding over the front end of the sleeve, and for the return spring for the operating rod to be arranged between the pneumatic piston and the plunger.
As a preference, the valve element is formed in a flexible component in the form of a circular duct that is symmetric with respect to the axis of symmetry of the booster, the opening of which valve element points backward, and which with a holding piece forms a compensation chamber in permanent communication with the rear chamber of the booster.
Provision can then be made for a compression spring to be arranged in the compensation chamber in order to urge the valve element forward toward the first and second valve seats.
Advantageously, the plunger may slide in leaktight fashion in the bore of the pneumatic piston and comprise a passage allowing the high pressure to act permanently on the front face of the plunger.
According to one embodiment, the sleeve is secured to the tubular rear part of the pneumatic piston by snap-
REFERENCES:
patent: 4643075 (1987-02-01), Wagner
patent: 4794844 (1989-01-01), Taft
patent: 4905571 (1990-03-01), DeHoff et al.
BoschSistemas de Frenado S.L.
Constock Warren
Lopez F. Daniel
McCormick, Jr. Leo H
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