Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Patent
1996-01-16
1997-08-19
Nguyen, Hoang
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
913691, F15B 910
Patent
active
056576803
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to pneumatic boosters of the type used to boost the braking of motor vehicles.
Such boosters are well known in motor car technology and conventionally include a casing having an axis of symmetry, the casing being divided in leaktight fashion by a moving wall structure into a front chamber permanently connected to a source of low pressure, and a rear chamber connected selectively to the front chamber or to a source of high pressure by a three-way valve means actuated by a control rod capable of bearing, via the front face of a plunger, on the rear face of a push rod secured to a reaction disk, the plunger sliding in a bore of the moving wall, the three-way valve including a valve element located in a tubular rear part of the moving wall and interacting via a first region of an annular front face with a first annular valve seat formed on the plunger and, via a second region of the annular front face, with a second annular valve seat formed on the moving wall, the first valve seat being concentric with the second valve seat and of smaller diameter, the annular front face of the valve element being urged toward the annular valve seats by a valve spring and being reinforced by a rigid annular insert.
Furthermore, the control rod is returned to its rear position of rest by a rod spring, bearing on a spring plate secured to the rear tubular part, this position of rest being defined by a limit stop member secured to the moving wall, against which one shoulder of the plunger bears.
The mass-production of these boosters requires manufacturing tolerances to be envisaged, particularly for the bore in the moving wall in which the plunger slides and for the plunger itself, so that it can slide freely in this bore, as well as for the valve spring and for the limit stop member.
As a result of the combination of these factors, the plunger does not slide in the bore of the moving wall while remaining perfectly parallel to itself. The axes of the bore and of the plunger may thus form an angle which may reach 1 to 2 degrees, depending on the friction and rotational torques to which the plunger and control rod are subjected. Correspondingly, the planes in which the first and second annular valve seats are formed may form an angle of the same value between them as the plunger moves.
It follows that the sealing between the annular front face of the valve element and at least one of the annular valve seats is not accomplished under the best of conditions. When the booster is operating, for a given force on the control rod theoretically resulting in a position of equilibrium, it may happen that, depending on the respective configurations of the valve seats, the booster exhibits a leak between the source of high pressure and the front chamber or the rear chamber of the booster, and that the output force of the booster therefore does not correspond to that which is expected as a function of the input force.
A known solution for solving this problem consists in increasing the preload at rest and/or the stiffness of the valve spring. This solution does, however, exhibit the drawback of substantially increasing the hysteresis of the booster.
Another solution known, for example, from the document FR-A-2,560,135 consists in providing the annular front face of the valve element with concentric projections, each of which is in the form of a torus cut through transversely relative to its axis of rotation, the respective axes of rotation coinciding with the longitudinal axis of the valve element. Such a solution exhibits various drawbacks: the dead travel of the booster is increased substantially, the booster jump, which constitutes one of the more important parameters in the operation of boosters, can no longer be controlled satisfactorily, and the parasitic friction induced by the particular shape of the front face of the valve element also contribute to increasing the hysteresis of the booster.
Document U.S. Pat. No. A-4,399,736, which corresponds to the preamble of the main claim, also makes known a solution
REFERENCES:
patent: 4005638 (1977-02-01), Takeuchi
patent: 4399736 (1983-08-01), Schubert
patent: 5564325 (1996-10-01), Satoh
Gautier Jean Pierre
Verbo Ulysse
AlliedSignal Europe Services Techniques
McCormick Jr. Leo H.
Nguyen Hoang
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