Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Patent
1996-05-21
1998-09-01
Look, Edward K.
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
F15B 910
Patent
active
057995591
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a pneumatic rake booster for a motor vehicle, using first and second sources of air pressure delivering first and second respective and different pressures, this booster comprising: a rigid casing; at least one moving partition dividing the rigid casing into at least two chambers in leaktight fashion, the first of which chambers is connected to the first source; a pneumatic piston linked to the moving partition and exhibiting an at least partially cylindrical wall sliding in the casing in leaktight fashion; a plunger mounted so that it can slide inside the pneumatic piston; a threeway valve operated by the plunger in order selectively to connect the second chamber to either one of the two sources and selectively subject the moving partition to a pressure difference, the valve comprising a tubular shut-off member and two annular seats including a first seat linked to the plunger and a second seat outside the first seat and linked to the piston, the shut-off member exhibiting an active face which can move axially when acted upon by the plunger and which is capable of interacting with each one of the two seats; and a compensation volume delimited in leaktight fashion between an internal face of the wall of the piston and the shut-off member, permanently communicating with the second chamber through a passage made in the pneumatic piston and isolated from the first chamber by the active face of the shut-off member being applied against the second seat.
A device of this type is especially described in the patent U.S. Pat. No. 5,233,907, well known to experts in this field.
This prior device offers the advantage of achieving balancing of the valve by virtue of a permanent inlet, into the compensation volume, of the pressure let into or prevailing in the second chamber of the booster, which avoids the booster exhibiting operating characteristics which depend on the pressure in the second chamber.
However, despite its widely acclaimed benefit, this prior device requires, in order to produce it, the use of a supplementary piston disk serving to delimit the compensation volume and assumes that orifices will be made in the active face of the valve, facing the two seats, something which limits the possibility of bringing the two seats closer together.
The object of the invention is to provide a booster which has performance levels at least very close to those of this prior booster, but which has a substantially simpler structure.
To this end, the booster of the invention is essentially characterized in that the active face of the valve, facing the two seats, exhibits a continuous and leaktight surface and in that the passage between the compensation volume and the second chamber is pierced directly in the cylindrical wall of the pneumatic piston.
For preference, the passage between the compensation volume and the second chamber consists of an axial piercing of a portion of greater thickness of the cylindrical wall of the pneumatic piston.
Further characteristics and advantages of the invention will emerge clearly from the description thereof given hereafter by way of non-limiting indication with reference to the appended drawings, in which:
FIG. 1 is a diagrammatic sectional view of a pneumatically boosted braking system using a very conventional booster, predating the aforementioned patent U.S. Pat. No. 5,233,907; and
FIG. 2 is a part sectioned view of a booster in accordance with the invention.
Insofar as the invention relates merely to an improvement made to pneumatically boosted braking systems, and as the overall make-up and operation of the latter are well known to those skilled in the art, these systems will be recalled rapidly here merely to allow complete understanding of the improvement that the invention represents.
Schematically, a system of this type comprises a booster 1 and a master cylinder 2.
The booster itself comprises a rigid casing 3 divided into two chambers 3a and 3b in leaktight fashion by a moving partition 4 capable of driving a pneumatic piston 5 at least par
REFERENCES:
patent: 5233907 (1993-08-01), Gautier
Carre Jean Jacques
Gautier Jean Pierre
Verbo Ulysse
Bosch Systems de Freinage
Karimi Bijan N.
Look Edward K.
McCormick Jr. Leo H.
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