Power plants – Pressure fluid source and motor – Pulsator
Patent
1996-05-08
1998-02-10
Lopez, F. Daniel
Power plants
Pressure fluid source and motor
Pulsator
60588, 92182, F15B 708
Patent
active
057156816
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an hydraulic master cylinder, primarily for a vehicle brake or clutch actuating system, being of the general kind comprising a relatively movable cylinder body and piston, and sealing means between relatively slidable surfaces thereof operable to permit pressurisation of hydraulic fluid in a pressure chamber during relative movement of the body and piston in one direction for actuation of the system, and recuperation of fluid into the chamber via a recuperation port during reverse relative movement of the body and piston. The majority of master cylinders for use in vehicles have a piston movable within a fixed cylinder by action on a driver-operated pedal.
Conventional master cylinders are usually provided with flexible pressure seals, of rubber or similar material for example, which are satisfactory under most conditions of use. However, in the case of heavy duty cylinders in which very high actuating pressures arise, such as those used on off-highway vehicles for example, it has been found that excessively rapid wear of the pressure seal can occur, particularly when the cylinder incorporates a radial recuperation port which is traversed by the seal during the reciprocal movement of the piston.
An object of the present invention is to provide an hydraulic master cylinder of the aforesaid general kind in which the aforesaid problem is alleviated or avoided.
According to the invention, an hydraulic master cylinder of the aforesaid general kind is provided with sealing means in the form of a pressure seal assembly having a first seal part of relatively hard material slidable against one of the cooperating surfaces, and a relatively resilient second seal part arranged to act between one of the cooperating surfaces and the first seal part in order to provide a fluid-tight pressure seal during pressurisation of fluid in the chamber.
Preferably, the second seal part lies generally radially within the first seal part and the surface co-acting with the second seal part is conveniently shaped so as to cause resilient deformation of the second seal part during relative movement of the cylinder body and piston in said one direction, whereby the second seal seals against said co-acting surface and causes radial deformation of the first seal part against its adjacent cooperating surface to enhance sealing thereof.
The pressure chamber may conveniently be provided with a generally radial recuperation port which is traversed by the seal assembly during working relative movement of the body and piston, radial and/or axial recuperation passages in the piston permitting fluid flow around the seal assembly between the pressure chamber and the recuperation port during reverse relative movement of the body and piston following a pressure stroke.
The invention will now be described, by way of example, with reference to the accompanying drawings, in which:
FIG. 1 is a longitudinal cross-section of one form of the hydraulic master cylinder of the invention;
FIGS. 2-4 are similar enlarged sectional views of the encircled part of FIG. 1, illustrating the master cylinder in different operational conditions, and
FIG. 5 is a view similar to FIG. 1 illustrating an alternative embodiment of the master cylinder of the invention.
The master cylinder of FIG. 1 has a cylinder body 1 with a longitudinal bore 2 within which slides a pressure piston 3, the forward end 4 of which defines, with the bore and an end wall 5 of the cylinder, a pressure chamber 6. Actuating force is applied to the piston by way of a force input rod 7 connected, in use, to a driver's foot pedal for example (not shown), the piston being urged towards its illustrated rest position by a return spring 8 which holds the piston and rod against a washer 9 which cooperates with a circlip or the like 9A to serve as a backstop. A convoluted boot 10 surrounding the rod and engaging around a grooved boss 11 of the body 1 seals the open end of the cylinder against the ingress of foreign material. The body 1 is provided with a radially extending mounting f
REFERENCES:
patent: 2561009 (1951-07-01), Byers et al.
patent: 3141303 (1964-07-01), Baldwin
patent: 3656414 (1972-04-01), Muller
patent: 4866938 (1989-09-01), Keegan et al.
Lopez F. Daniel
Lucas Industries plc
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