Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Patent
1994-11-21
1997-09-09
Nguyen, Hoang
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
91376R, F15B 910
Patent
active
056644752
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to pneumatic servos of the type which are used to provide assistance with braking of motor vehicles.
BACKGROUND OF THE INVENTION
Such servos 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 an axial control rod subjected to the action of a return spring located in an annular space between the control rod and a rear tubular part of the movable wall structure, projecting out of the casing, the three-way valve being located in this rear tubular part.
These servos are usually located in the engine compartment of the vehicle, on its bulkhead, so that the rod for controlling the servo 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 servo, 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 servo 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 servo in which the intake for air at atmospheric pressure is situated in the engine compartment of the vehicle.
SUMMARY OF THE DRAWINGS
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 servo at the beginning of its actuation phase.
Then again, studies conducted by the Applicant have shown that the noise generated by the operation of a servo has two main sources. The first lies in the three-way valve itself, which offers the air only a small passage cross-section. The second lies in the spring for returning the control rod, which spring presents an obstacle to the passage of the air.
The prior documents tried to minimize the first source of noise, with the drawbacks mentioned above, and neglected the second source of noise, or did not know how or were not able to solve the problem posed by this second source of noise.
The object of the present invention is therefore to propose a servo the operation of which is totally silent, implementing means which are simple, reliable and inexpensive, and which do not influence the response time of the servo.
To this end, the invention proposes a servo of the type recalled above, in which means are provided for dividing the annular space into a housing for the return spring and an annular volume for the circulation of moving air upstream of the three-way valve.
Other objects, characteristics and advantages of the present invention will emerge more clearly from the description which follows of one embodiment given by way of illustration with reference to the appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side view, in longitudinal section, representing the rear central part o
REFERENCES:
patent: 4368661 (1983-01-01), Ohmi et al.
patent: 4450688 (1984-05-01), Boehm
patent: 4667568 (1987-05-01), Morimoto
patent: 5031507 (1991-07-01), Bornemann et al.
patent: 5161454 (1992-11-01), Frasier
patent: 5249505 (1993-10-01), Hewitt
Gautier Jean Pierre
Perez Revilla Miguel
Tripier Bernard
Verbo Ulysse
AlliedSignal Europe Services Techniques
McCormick Jr. Leo H.
Nguyen Hoang
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