Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Patent
1994-12-27
1997-05-20
Lopez, F. Daniel
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
F15B 910
Patent
active
056303505
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to pneumatic servos of the type of those which are used to provide assistance with braking of motor vehicles.
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 a plunger sliding in a bore of the movable wall and secured to 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 and including a shutter 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 movable wall.
These servos are usually located in the engine compartment of the vehicle, on its bulkhead, so that the control rod of 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. 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 main source of noise generated by the operation of a servo is the three-way valve itself, which forces the moving air through a winding path generating whistling noises which may become troublesome.
The object of the present invention is therefore to propose a servo, the operation of which is silent, implementing means which are simple, reliable and inexpensive, and which do not worsen the response time of the servo.
To this end, the invention proposes a servo of the type recalled above, in which the first and second annular surfaces are in different transverse planes, the first and second annular surfaces being joined together by a surface of frustoconical overall shape for guiding the moving air downstream of the first valve seat when it is moved away from the first annular surface.
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 in which:
FIG. 1 is a side view, in longitudinal section, representing the rear central part of a pneumatic servo for assisting with b
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patent: 4770082 (1988-09-01), Kawasumi
patent: 4777865 (1988-10-01), Gautier
patent: 5233904 (1993-08-01), Gautier et al.
patent: 5249505 (1993-10-01), Hewitt
Monteillet Jean Claude
Verbo Ulysse
AlliedSignal Europe Services Techniques
Lopez F. Daniel
McCormick Jr. Leo H.
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