Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Reexamination Certificate
1999-07-07
2001-12-04
Look, Edward K. (Department: 3745)
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
Reexamination Certificate
active
06324958
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an automatic brake booster as used in a brake of an automobile or the like, and more particularly, to an improvement of a valve mechanism thereof.
DESCRIPTION OF THE PRIOR ART
An automatic brake booster is known in the art including a valve body slidably disposed within a shell, a power piston mounted on the valve body, a constant and a variable pressure chamber defined across the power piston and a valve mechanism disposed within the valve body for switchingly controlling a flow path therein; the valve mechanism comprising a first valve seat formed on the valve body and facing rearward, a sleeve slidably fitted into the valve body and urged rearward by a spring, a second valve seat formed on the sleeve and facing rearward, a valve element urged forward by a poppet return spring to be seated on the first and the second valve seat, drive means for displacing the sleeve forward to switch the flow path, a valve plunger sidably disposed in the sleeve and coupled to an input shaft for driving the sleeve forward as the input shaft is driven forward to switch the flow path, and a seal member interposed between the sleeve and the valve plunger to maintain a hermetic seal between the members; the valve element comprising a rolling part located at a rear portion thereof and which is folded radially outward to be connected to the valve body, and a first and a second seat area disposed forwardly of the rolling part and which are adapted to be seated on the first and the second valve seat, respectively (see Japanese Laid-Open Patent Application No. 2243 of 1997).
In a conventional automatic brake booster as mentioned above, the drive means generally comprises a solenoid. However, in the disclosed valve mechanism, the effective diameter of the second valve seat (atmosphere valve seat) is chosen to be larger than the effective diameter of the seal member and the effective diameter of the rolling part of the valve element is chosen to be larger than the effective diameter of the second valve seat, whereby in the inoperative condition of the booster where the valve element is seated on the second valve seat and is removed from the first valve seat, the differential pressure acting upon the sleeve causes the latter to be urged forwardly, and the valve element itself, which is seated on the second valve seat formed on the sleeve, is urged forwardly due to the differential pressure thereacross. This required that a load to which the spring urging the sleeve rearward is charged or preset be chosen high in consideration of the differential pressure across the sleeve, the differential pressure across the valve element and the force exerted by the poppet return spring which urges the valve element forward. To displace the sleeve forward against the resilience of the spring, it has been necessary that the solenoid could supply a magnetic force of an increased magnitude. This in turn requires a solenoid of an increased size and an increased weight, involves a high heating value, and results in an increased cost, all of which are disadvantageous.
SUMMARY OF THE INVENTION
In view of the foregoing, the invention provides a valve mechanism for an automatic brake booster which allows the use of a solenoid of a reduced magnetic force as compared with the prior art.
Specifically, according to a first aspect of the invention, there is provided an automatic brake booster of the same type as mentioned above, but in which the effective diameter of the rolling part of the valve element is chosen to be equal to the effective diameter of the seal member and the effective diameter of the second valve seat is chosen to be equal to or less than the initially mentioned effective diameter.
According to the first aspect of the invention, in the inoperative condition of the booster where the valve element is seated on the second valve seat formed on the sleeve and is removed from the first valve seat formed on the valve body, the differential pressure which urges the sleeve and the valve element forward is cancelled out by a differential pressure of an equivalent magnitude which urges them rearward. Thus the sleeve and the valve element are no longer urged by any differential pressure.
Accordingly, as compared with the prior art practice in which a high load, to which the spring is charged, is chosen in consideration of the differential pressure which urges the sleeve and the valve element forward, the load to which the spring must be charged can be reduced, allowing the use of a solenoid which is reduced in size and weight as well as a heating value involved and which is thus of a reduced cost in comparison to the prior art.
According to a second aspect of the invention, there is provided an automatic brake booster of the same type as mentioned above, but in which the effective diameter of the seal member is chosen to be larger than the effective diameter of the second valve seat and less than the effective diameter of the rolling part of the valve element.
According to the second aspect of the invention, no differential pressure acts on the sleeve in the inoperative condition of the booster where the valve element is seated on the second valve seat formed on the sleeve and is removed from the first valve seat formed on the valve body. As a consequence, in comparison to the prior art practice as mentioned above, the load to which the spring must be charged can be reduced by an amount corresponding to the differential pressure acting on the sleeve. This again allows the use of a solenoid which is reduced in size, weight, heating value involved and cost in comparison to the prior art.
Above and other objects, features and advantages of the invention will become apparent from the following description of several embodiments thereof with reference to the drawings.
REFERENCES:
patent: 4667568 (1987-05-01), Morimoto
patent: 5651300 (1997-07-01), Ikeda et al.
patent: 5857399 (1999-01-01), Tsubouchi et al.
patent: 5907990 (1999-06-01), Satoh
patent: 9-2243 (1997-01-01), None
patent: 9-2243-A (1997-01-01), None
Bosch Braking Systems Co. Ltd.
Flynn ,Thiel, Boutell & Tanis, P.C.
Leslie Michael
Look Edward K.
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