Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Reexamination Certificate
1999-08-30
2001-10-02
Ryznic, John (Department: 3745)
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
Reexamination Certificate
active
06295915
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a brake booster, and more particularly, to a brake booster which is provided with a reaction disc.
DESCRIPTION OF THE PRIOR ART
A brake booster which allows an input to be reduced at the commencement of operation is known in the art which comprises a substantially tubular valve body slidably disposed within a shell, a power piston mounted on the valve body to divide the interior of the shell into a constant pressure chamber and a variable pressure chamber, a valve plunger slidably disposed on the valve body and driven back and forth by an input shaft to switchably control a flow path, an output shaft slidably mounted on the valve body and adapted to be driven back and forth in interlocked relationship with the valve body, and a reaction disc interposed between the output shaft and the valve body and having a rear end which is disposed for abutment against the valve plunger, the valve mechanism comprising an annular, first valve seat formed on the valve body, a second valve seat formed on the rear end of the valve plunger, a valve element disposed within the valve body and adapted to be seated upon the first and the second valve seat under the resilience of a poppet return spring, and a valve return spring for maintaining the valve plunger, input shaft and the valve element in their inoperative positions, an atmosphere valve being formed by a combination of the first valve seat and a first seat area on the valve element which becomes seated thereon, and a vacuum valve being formed by a combination of the second valve seat and a second seat area on the valve element which becomes seated thereon, the atmosphere valve and the vacuum valve being spaced apart axially with the diameter of the vacuum valve being reduced to the same order as the atmosphere valve (see Japanese Laid-Open Patent Application No. 113,137/1996).
With a brake booster of the kind described above, because the diameter of the vacuum valve is reduced to the same order as the atmosphere valve, the pressure responsive area which is subject to a differential pressure acting upon the valve element when the booster is actuated where the valve element is seated upon the first valve seat can be increased as compared when the vacuum valve is disposed outward of the atmosphere valve, allowing the resilience which is required of the poppet return spring to urge the valve element forwardly into abutment against the both valve seats to maintain a hermetic seal to be reduced. As a consequence of this, it is possible to reduce an input to commence the operation as the input shaft is driven forward while causing a flexure of the poppet return spring.
A brake booster is recently proposed in which a brake reaction which is transmitted to a driver upon depression of a brake pedal is reduced to enable a quick braking by a less powerful driver such as a female or aged driver, but such a booster uniformly suffers from a complex arrangement and an increased cost.
To overcome such a problem, it is contemplated to reduce the internal diameter of the valve body while maintaining the external diameter thereof in the region where it abuts the reaction disc unchanged, and simultaneously reducing the external diameter of the plunger which is received in the valve body, thereby increasing a proportion of a reaction which is transmitted from the reaction disc to the valve body while decreasing the proportion of the brake reaction which is transmitted from the reaction disc to a driver through the valve plunger.
However, with this arrangement, a deforming force of a magnitude which is increased acts in a concentrated manner upon a central portion of the reaction disc which deforms and bulges into the valve body, producing a disadvantage that the durability of the reaction disc is impaired.
To establish a higher servo ratio without impairing the durability of the reaction disc, it is contemplated to increase the external diameter of the reaction disc together with the external diameter of an abutting portion of the valve body while maintaining the internal diameter of an abutting portion of the reaction disc unchanged, thus increasing the proportion of the brake reaction which is transmitted from the reaction disc to the valve body while decreasing the proportion of the brake reaction which is transmitted from the reaction disc to a driver through the valve plunger and the input shaft.
However, referring to
FIG. 5
, if it is attempted to increase the external diameter of an abutting portion
107
G of a valve body
107
, it will be noted that a constant pressure passage
133
which provides a communication between a space located radially outward of a first valve seat
116
, which forms part of the atmosphere valve, and a constant pressure chamber A has an opening which opens into the front end face of the valve body
107
, thus standing in the way of increasing the external diameter of the abutting portion
107
beyond a value D′.
This will be discussed in further detail below. The valve body
107
is integrally molded by a casting into an enclosed space defined by a front die including a passage die
180
which projects rearward as indicated by phantom lines and a rear die including a passage die
181
which projects forward as indicated by dotted lines, and the constant pressure passage
133
which provides a communication in the axial direction and any other passage are formed by an overlap or abutment between ends of the passage die
180
of the front die and ends of the passage die
181
of the rear die.
Accordingly, if it is desired to increase the diameter of the abutting portion
107
G of the valve body
107
, it is concomitantly necessary that the location of the constant pressure passage
133
be displaced radially outward. When so arranged, the constant pressure passage die
180
′ of the passage die
180
and the constant pressure passage die
180
′ of the passage die
181
which are used to form the constant pressure passage
133
must be disposed in close contact with each other without any clearance therebetween in the radial direction (while they are depicted as spaced from each other in
FIG. 5
, it should be understood that they are in close contact with each other in practice.). This requires that the internal diameter D of a tubular terminal portion
107
A be increased.
However, when the internal diameter D of the tubular terminal portion
107
A is increased, the diameter of the valve element which is clamped within the tubular terminal portion
107
A must be increased, with consequence that a pressure responsive area which is subject to a differential pressure acting upon the valve element when the booster is inoperative increases. Consequently, a preset load on the valve return spring which is disposed between the valve body and the input shaft to maintain these members in their inoperative positions must be chosen to overcome a sum of the differential pressure acting upon the valve plunger, the differential pressure acting upon the valve element which is seated on the valve plunger and the resilience of the poppet return spring which urges the valve element forwardly, and this results in increasing an input which is required for commencing the operation.
SUMMARY OF THE INVENTION
In view of the foregoing, the invention provides a brake booster capable of establishing a servo ratio with a simple and inexpensive arrangement as compared with the prior art.
Specifically, the present invention relates to a brake booster including a substantially tubular valve body slidably disposed within a shell, a power piston mounted on the valve body to divide the interior of the shell into a constant pressure chamber and a variable pressure chamber, a valve plunger slidably mounted on the valve body and driven to move back and forth by an input shaft to switchably control a flow path, an output shaft slidably mounted on the valve body and driven back and forth in an interlocked relationship with the valve body, and a reaction disc disposed between the output shaft and the va
Bosch Braking Systems Co. Ltd.
Flynn ,Thiel, Boutell & Tanis, P.C.
Ryznic John
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