Expansible chamber devices – Cylinder detail – Nonmetallic piston contacting portion
Reexamination Certificate
2000-05-01
2001-09-18
Ryznic, John E. (Department: 3745)
Expansible chamber devices
Cylinder detail
Nonmetallic piston contacting portion
C092S187000, C092S248000, C060S588000
Reexamination Certificate
active
06289790
ABSTRACT:
International patent application Ser. No. PCT/FR99/01355, publication No. WO99/64758
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a device for the hydraulic control of a clutch, especially for motor vehicles, comprising at least one emitter or receiver cylinder having a piston.
More particularly, the invention relates to a hydraulic control device for a motor vehicle clutch including at least one control cylinder, of the type in which the cylinder comprises a substantially tubular cylinder body in which there slides axially a piston which, through a front transverse face, bounds a hydraulic chamber, and which is in cooperation through a rear transverse face with a piston rod, wherein an aperture for connection of a pipe or a duct is open into the hydraulic chamber, and wherein the cylinder body is made of mouldable material such as plastics material.
Such a device is described for example in the document DE-U-2951 6488.
2. Description of the Related Art
In the latter, the piston is part of an assembly which includes a metallic piston skirt.
More precisely, the piston skirt has at its front end a projecting element on which the piston is formed by applied moulding. The skirt serves as a receptacle for two half shells which are so configured as to receive the head of the rod of the piston.
In addition, the piston carries a piston seal which is adapted to cooperate with a metallic guide sleeve mounted in the internal bore of the cylinder body and bounding the hydraulic chamber, while the cylinder body carries a secondary seal which is adapted to cooperate with the piston skirt. The cylinder body is for this purpose stepped internally in diameter, so that it has, at its rear end, an enlarged cross section whereby it can contain the secondary seal within it. A securing skirt is mounted in this larger section so as to retain the secondary seal.
Such a solution, which calls for a large number of components, is relatively costly and necessitates the presence of a dynamic piston seal carried by the piston and cooperating with the guide sleeve fixed to the cylinder body.
An object of the present invention is to overcome these drawbacks in a simple and inexpensive way.
SUMMARY OF THE INVENTION
According to the invention, a hydraulic control device of the type described above is characterized in that the piston is so configured as to receive the head of the piston rod, in that the piston is surrounded by the piston skirt, in that the piston seal is interposed operatively between the outer periphery of the piston and the inner periphery of the piston skirt, and in that the piston skirt penetrates into the hydraulic chamber.
Thanks to the invention, the guide sleeve of the prior art is eliminated, and the piston skirt penetrates into the hydraulic chamber. The piston and the piston skirt are concentric and coaxial components, and they constitute a unit in the form of a sub-assembly which can be handled and transported.
It should be noted that the manufacturing cost of the outer surface of the piston skirt is less than the manufacturing cost of the inner surface of the guide sleeve in the prior art, the said outer surface being in cooperation with the secondary seal of the dynamic type. The immobilizing skirt is elongated axially and is a good guide for the piston skirt. The internal bore of the said skirt extends the internal bore of the cylinder body.
The piston seal has a simplified form, and acts statically between the piston and the piston skirt. In one embodiment, the piston seal consists of an O-ring seal.
The piston skirt has a simple and inexpensive tubular form. This skirt does not have a base portion.
Preferably, the piston is of plastics material such that the seating for the head of the piston rod can easily be formed by moulding.
Preferably, the cylinder body has an abutment which serves to centre the spring which acts between the base of the body of the cylinder and the piston.
The front face of the piston is arranged to come into contact with this abutment.
Thus the piston skirt only undergoes weak forces when the piston is in its retracted position.
In one embodiment, the piston has a posterior axial fixing groove into which at least one deformation of the piston skirt penetrates.
The deformation of the skirt, which constitutes a projecting element, penetrates, for example by insertion, into the groove in such a way that the piston skirt is fixed axially to the piston. For example the piston skirt has lugs or pegs penetrating into the groove of the piston.
The skirt can then be snap-fitted on the piston.
In another version, the piston skirt is secured on the piston by applied moulding.
In a further version, the skirt is secured on the piston by adhesive bonding.
It is of course possible to reverse the structures, with the piston having, for example, projecting elements that penetrate into apertures formed in the piston skirt.
In another version, the piston skirt comes into abutment on a shoulder of the front and/or rear face of the piston.
It will be noted that the piston seal plays a part in the axial retention of the piston skirt on the piston, and that the constitution of the piston in plastics material facilitates assembly of the piston skirt with the piston.
In another version, an additional plastics member is associated with the piston for trapping the piston skirt and holding it in position.
This additional member may for example be ultrasonically welded on the piston so as to retain the piston skirt.
In a further version, the welding operation is carried out locally by indirect application of heat with the aid of at least one energy source of the laser type.
The supplementary member may be attached by conical telescopic engagement on the piston in order to trap the piston skirt in position locally.
Thus in these embodiments, the piston skirt is sandwiched locally between the piston, which is preferably of a plastics material, and the additional member which is of plastics material.
In the case where the control cylinder is an emitter cylinder, the piston skirt has at least one anterior hole which puts the hydraulic chamber into communication with a reservoir associated with the emitter cylinder.
Preferably several holes are provided to ensure a higher flow of fluid, and to enable any orientation to be avoided during assembly, with a view always to having a passage in the upper part of the piston.
The position of the passage hole or holes is determined according to the action of the piston skirt which is movable from one side to the other of a secondary seal, such as a lip seal. It will be appreciated that no burr is formed at the outer periphery of the piston skirt, and this facilitates sliding of the latter within the cylinder body.
Preferably, the securing skirt has at least two posterior abutments, such as lugs or pegs, which are diametrically opposed to each other so as to cooperate with the piston skirt and limit the displacement of the latter.
Thus the tolerance of the dead travel of the piston skirt is determined by the aggregate of the tolerances of three components.
It is easily possible to incorporate an integral reservoir with the emitter cylinder.
This working cylinder can be formed by means of a bellows, or a sealed membrane which is able to be unrolled, interposed operatively between the cylinder body and the piston rod.
The membrane or the bellows has at each end a bead for fastening them on the fixed part (that is to say the cylinder body) and on the movable part (that is to say the piston rod).
Fastening members are secured, for example by snap-fitting, on the fixed part and the moving part respectively in order to retain the beads.
Thus it is possible to return leaked fluid back into the working reservoir, and the reservoir is defined by a flexible and elastic element consisting of the bellows or membrane, which are typically of elastomeric material such as rubber.
In addition, filling of the hydraulic control device for the clutch may not have been carried out before it is fitted on the motor vehicle, filling the
Liniak Berenato Longacre & White
Ryznic John E.
Valeo
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