Power plants – Pressure fluid source and motor – Pulsator
Reexamination Certificate
1999-12-21
2002-01-08
Ryznic, John E. (Department: 3745)
Power plants
Pressure fluid source and motor
Pulsator
C092S256000, C092S128000
Reexamination Certificate
active
06336329
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a master cylinder for a hydraulically operated clutch or brake of a vehicle. It is customary in the field of automotive technology that a device that functions by the application of a force is operated by means of hydraulic forces. Required for this purpose are so-called master cylinders, also called working cylinders, that serve to convert a mechanical force into a hydraulic force. The master cylinder is connected through a pressure conduit to the device that is to be hydraulically operated, e.g., a slave cylinder.
The invention further relates to a hydraulic cylinder, particularly a master cylinder for hydraulic systems of motor vehicles, with a cylinder housing comprising a cylinder compartment and with a piston that is guided for axial movement inside the cylinder compartment and sealed against the cylinder wall. The piston has a cup-shaped bushing that is closed against the cylinder compartment. Arranged inside the bushing is an insert body containing an essentially spherical cavity to accommodate a spherical head that is integrally connected as a single part with a swiveling piston rod that extends to the outside of the cylinder housing.
The working cylinder comprises a housing that is made of a polymer material and contains a pressure compartment formed (e.g., bored) as a cylindrical blind hole. The pressure compartment is connected to a supply port and a pressure port and accommodates an axially movable piston. A guide sleeve is arranged inside the housing at an axial distance from the pressure compartment and surrounds the piston when the latter is in a neutral position. A piston rod is attached by a swivel joint to the piston and connects to a manually operated pedal device.
A working cylinder of the kind mentioned at the beginning is known from DE 38 16 608 A1. Inserted in the housing of the known working cylinder is a short guide sleeve of a length that is less than 30% of the lengthwise dimension of the piston. For additional support of the piston in its neutral position, the known working cylinder is further provided with a holder element called “sheet-metal cup” that surrounds the piston on the outside. The known working cylinder has a total of three seals for the piston and the guide sleeve. A primary seal is on the outside fitted into the housing and has a sealing lip towards the inside that lies against the outside surface of the piston. A disk is placed ahead of the primary seal in the direction of the guide sleeve. The disk is provided with radial channels distributed over its circumference on the side that faces towards the back of the primary seal. The channels allow the pressure medium to be replenished when the piston is in its neutral position and if there is a pressure differential between the reservoir and the pressure compartment of the working cylinder.
Starting from the supply port, there is a fluid-flow connection through a cylindrical gap formed on the guide sleeve by a radially stepped-off section that extends to the back of the primary seal and continues into a radial channel of the intermediate disk before the pressure medium enters the pressure compartment through axial openings of the piston. Because the radial channels of the disk correspond with the axial openings of the piston, it is imperative for the disk to be installed in its correct orientation. If the disk is installed incorrectly, i.e., with the radial channels facing in the direction of the guide sleeve, the self-regulated in-flow of pressure medium through the supply port from the reservoir is blocked. A grooved ring seal, inserted at the edge of the guide sleeve, has an inner sealing lip lying against the piston. Furthermore, a seal ring for sealing a cylindrical gap between the guide sleeve and the housing wall is inserted into a ring groove of the guide sleeve and lies against the housing wall.
A hydraulic cylinder of the kind mentioned above is further known from DE 196 20 580 A1. This hydraulic cylinder, configured as a master cylinder, comprises a piston that is composed of more than one part. A cup-shaped bushing that is closed towards the pressure compartment contains an insert body with a spherical cavity to accommodate the head of a piston rod. The insert body is held in place by a radially inward-facing flange that is formed on the bushing after the insert body has been installed. This type of construction takes several assembly steps for the completion of the piston.
Known from DE 196 08 132 A1 is a hydraulic cylinder, particularly a master cylinder for hydraulic systems of motor vehicles, where the cylinder itself has a spherical cavity into which the spherical head of the piston rod is inserted under pressure. The opening of the spherical cavity is at a distance from the piston wall so as to allow the spherical head to be pushed into place. To prevent the spherical head from leaving the cavity when the piston is pulled against an end stop in the cylinder housing, a retaining ring is pushed into place between the cylinder wall and the opening area of the cavity.
A piston of this type of construction is expensive to manufacture because the spherical cavity is formed directly into the piston and also because a ring-shaped space has to be provided between the piston wall and the spherical cavity. Furthermore, a snug fit of the spherical head in the cavity is not assured because the inserted ring only fills the ring-shaped space but has no pre-tensioning effect on the exterior wall of the cavity, as there is no place provided where a forced deformation could be applied to the end portion of the cavity.
A further embodiment of the same document, in which the piston is configured in an essentially known way as a dual piston for two hydraulic circuits, shows the spherical head engaged in only a hemispherical recess of the piston, so that under a pulling force the piston rod lifts off from the recess. Therefore it is only due to a spring in the cylinder compartment that the piston is returned to its initial position.
Further known from DE 44 05 581 A1 is a master cylinder with a bearing element deep inside the piston. The bearing element, which has a spherical cavity in which the spherical head of the piston rod is inserted, is positioned at such a depth inside the piston that disassembly is impossible once the bearing element has been pushed into place inside the piston. Here, too, the manufacture of the piston is very expensive because the interior space of the piston has to be finished in a very expensive process, particularly due to the need for a groove located far back inside the piston that is engaged by noses of the bearing element. Also, the end portion of the spherical cavity of the bearing element does not have a defined area where it is elastically deformable and, consequently, the dimensional tolerances, too, have to meet exacting requirements.
OBJECT OF THE INVENTION
Therefore, in view of the disadvantages of the known device, the present invention has the object of providing a master cylinder that is optimized with regard to the design of its components and provides a highly effective fluid-flow connection when there is a pressure difference between the reservoir of the pressure medium and the pressure compartment. Another requirement is for the working cylinder to be manufacturable in a functionally safe, simple assembly process. A further object of the invention is to avoid the drawbacks of the known solutions and to provide a hydraulic cylinder, particularly a master cylinder, that is cost-effective as well as uncomplicated to produce and assemble. Also required is that the individual components can be completed separately without the need for other subsequent work operations. In addition, the hydraulic cylinder is to be suitable for mass production.
SUMMARY OF THE INVENTION
In hydraulic cylinders according to the invention, the stated object is attained through the following improvements:
a) The master cylinder comprises a guide sleeve that extends axially out of the housing and surrounds the piston wh
Adler Dieter
Eckert Wilfried
Prosch Gerhard
Wilhelm Sigurd
Darby & Darby
Ina Walzlager Schaffler oHG
Ryznic John E.
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