Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Patent
1995-11-13
1999-03-09
Nguyen, Hoang
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
F15B 910
Patent
active
058786465
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to pneumatic boosters of the type of those used to boost the braking in motor vehicles.
Such boosters conventionally include a casing having an axis of symmetry, divided in leaktight fashion by a movable wall structure into a front chamber permanently connected to a source of partial vacuum, and a rear chamber connected selectively to the front chamber or to the outside atmosphere by a three-way valve actuated by a plunger sliding in a bore of the moving wall and secured to an axial control rod, the three-way valve being located in a rear tubular part of the moving wall structure projecting outside of the casing and including a valve element interacting via a first annular surface with a first valve seat formed on the plunger and via a second annular surface with a second valve seat formed on the moving wall.
These boosters are usually located in the engine compartment of the vehicle, on its bulkhead, so that the rod for controlling the booster projects into the passenger compartment so that it can be actuated by the driver. It follows that the rear central part of the movable wall, including the three-way valve, also projects into the passenger compartment.
As a result, when the driver actuates the brake pedal connected to the control rod of the booster, the latter sucks air at atmospheric pressure in from the passenger compartment of the vehicle. The air set in motion by the operation of the booster therefore generates noises which are wholly transmitted into the passenger compartment of the vehicle.
Attempts have been made to provide various solutions to this problem. For example, document FR-A-2,551,009 provides means for guiding the air in the immediate surroundings of the three-way valve, upstream and downstream of the latter.
Document FR-A-2,516,880 provides a silencer device made from crosslinked foam, located inside the rear central part of the movable wall structure, this device including an outer surface applied against the inner surface of this rear central part, and the inside of which is formed with uninterrupted passage openings pointing in the direction of the control rod to give a passage for the flow of air through the device.
Document DE-A-3,924,672 for its part provides a booster in which the intake for air at atmospheric pressure is situated in the engine compartment of the vehicle.
However, these prior solutions still present devices which are imperfect, or economically inapplicable because they are too complicated. What is more, for the purpose of reducing the operating noise, these systems introduce into the path of the air, obstacles to its movement which increase the response time of the booster at the beginning of its actuation phase.
The object of the present invention is therefore to propose a booster the operation of which is silent, implementing means which are simple, reliable and inexpensive, and which do not adversely influence the response time of the booster.
To this end, the invention provides a booster of the type recalled above, in which the second annular surface is situated in a transverse plane forwards of the transverse plane in which the first annular surface is situated, the first and second annular surfaces being joined together by a surface of the valve element situated facing a surface of the plunger, the first annular surface and the surface of the valve element defining, together with the first valve seat formed on the plunger, a valve passage, the cross-section(s) of which is a non-linear function of the distance between the first valve seat and the first annular surface lower than or equal to the linear function of this distance.
According to preferred embodiments, the surface of the valve element is cylindrical or frustoconical and defines, together with the valve seat formed on the plunger, a valve passage, the cross-section of which is constant or substantially constant for any value of the distance between the first valve seat and the first annular surface.
Thus, since the passage cross-section offered to the air towards
REFERENCES:
patent: 4005638 (1977-02-01), Takeuchi
patent: 4643075 (1987-02-01), Wagner
patent: 4729288 (1988-03-01), Thioux
patent: 5263399 (1993-11-01), Flory et al.
Bosch Systems de Freinage
Comstock Warren
McCormick Jr. Leo H.
Nguyen Hoang
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