Power plants – Pressure fluid source and motor – Pulsator
Reexamination Certificate
1999-11-17
2001-11-20
Ryznic, John E. (Department: 3745)
Power plants
Pressure fluid source and motor
Pulsator
Reexamination Certificate
active
06318082
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a master cylinder, and it is suitable for the use in a clutch actuating device, a braking device, or the like of an automobile.
FIG. 5
is a longitudinal sectional view showing a master cylinder relating to the present invention. In this master cylinder
1
, a primary pressure chamber
6
and a secondary pressure chamber
7
are configured by a freely slidable primary piston
4
and a freely slidable secondary piston
5
In a cylinder hole
3
of a cylinder housing
2
. In the cylinder housing
2
, connecting passages
8
,
9
are pieced at side wall portions corresponding to the respective pistons
4
,
5
. The respective connecting passages
8
,
9
are open at the inner surface of the cylinder housing
2
, and near the opening portions, cup seals
10
,
11
are fitted, and by the cup seals
10
,
11
, the opening portions are sealed. In the respective pistons
4
,
5
, a plurality of communicating holes
12
,
13
arranged in the circumferential direction are pieced along the radial direction. Both pressure chambers
6
,
7
are connected to two lines of oil hydraulic circuits in an automobile through the respective ports
14
,
15
.
Both pistons
4
,
5
are urged to the right in the figure by return springs
16
,
17
respectively; and to the rear end portion of the primary piston
4
, an unillustrated push rod is connected. Then, during the operation, when the pistons
4
,
5
advance and move to the left so that the communicating holes
12
,
13
may pass the cup seals
10
,
11
, pressure is created in the pressure chambers
6
,
7
. The initial portion of the strokes of the pistons
4
,
5
until this pressure is created are ineffective. Accordingly, it is preferable that sizes of the communicating holes
12
,
13
measured along the axial direction of the cylinder housing
2
are as short as possible. For that, it is necessary to decrease diameters of the holes. During the return stroke, when the pistons
4
,
5
move to the right so that the communicating holes
12
,
13
may pass the cup seals
10
,
11
, the pressure chambers
6
,
7
are refilled with liquid oil from an unillustrated overhead reservoir. Accordingly, it is preferable that the resistance of flow of the communicating holes
12
,
13
is as small as possible. For that, it is necessary to enlarge the diameters of the communicating holes
12
,
13
, or to increase the number of the holes.
However, in the above master cylinder
1
, the communicating holes
12
,
13
are pierced in the radial direction with respect to the pistons
4
,
5
, and it is impossible to deal with the situation only by enlarging the diameters of the communicating holes
12
,
13
, since the ineffective portion of the piston strokes are thereby enlarged. Alternatively, if the number of communicating holes
12
,
13
is increased, the time and labor for perforating or deburring during the perforating, are increased so that the cost may be raised, and therefore, there is a limit in increasing the number of holes further and if variations in the position of a plurality of holes are caused in the axial direction, the ineffective portion of the piston strokes becomes larger. In order to prevent this, it is necessary to improve the accuracy in the work, and there has been a problem of raising of the cost.
OBJECT AND SUMMARY OF THE INVENTION
In order to solve the above problems, it is an object of the present invention to provide a master cylinder, wherein the processing of a communicating hole of a piston becomes unnecessary and the manufacturing cost of a piston can be reduced, and/or wherein, the resistance of flow in the communicating passage between the pressure chamber and the reservoir can be reduced and the ineffective portion of the stroke can also be reduced.
In order to achieve the objective, the present invention provides a master cylinder comprising a cylinder housing which has a connecting passage connected to a reservoir, and a piston which is freely slidable in a cylinder hole of the cylinder housing, the piston configuring a pressure chamber. The pressure chamber and the reservoir communicate through the connecting passage and a communicating hole provided on the piston exterior. The piston includes reduced outside diameter portion formed by a radially inward step surface on the periphery of the piston. A sleeve is fitted onto the periphery of the reduced outside diameter portion of the piston. A radial passage groove is formed between a radial portion of the step surface and an end surface of the sleeve opposite to the step surface and, and an axial passage groove which exists between an inner surface of the sleeve and a peripheral surface of the reduced outside diameter portion of the piston and intersects the radial passage groove so that the communicating hole is by defined the radial passage groove and the axial passage groove.
Furthermore, in the present invention, the size of the continuous length in the circumferential direction of the radial passage groove is preferably larger than the depth of the axial passage groove is preferably smaller than, the radial size, i.e., the size of the step of the step surface.
The present invention has the following effects.
That is, since the present invention is composed as mentioned above, the processing of a communicating hole of the piston becomes unnecessary and the work cost of the piston can be reduced, and further, the resistance of flow in the communicating passage between the pressure chamber and the reservoir is reduced and the ineffective stroke length can also be reduced. Furthermore, since the size of the continuous length in the circumferential direction of the radial passage groove is set larger and the size of the depth of the axial passage groove is set smaller than the size of the step of the step surface, the sectional area of the passage of the communicating hole is held and the resistance of flow of the passage can be reduced.
REFERENCES:
patent: 3593267 (1971-07-01), Klein
patent: 4745751 (1988-05-01), Gaiser
patent: 4939901 (1990-07-01), Saalbach et al.
patent: 5878575 (1999-03-01), Kreh et al.
Alston & Bird LLP
Bosch Braking Systems Co. Ltd.
Ryznic John E.
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