GB2168119A

GB2168119A - A master cylinder

Info

Publication number: GB2168119A
Application number: GB08524437A
Authority: GB
Inventors: Rudiger Eckhart; Robert Muckelbauer
Original assignee: FAG Kugelfischer Georg Schaefer KGaA; Kugelfischer Georg Schaefer and Co
Current assignee: IHO Holding GmbH and Co KG
Priority date: 1984-10-04
Filing date: 1985-10-03
Publication date: 1986-06-11
Also published as: FR2571445A1; IT1185983B; GB8524437D0; IT8522347A0

Abstract

In order to reduce the space required for installing the master cylinder (1) of a hydraulic system and for reducing the number of seals in the cylinde, a protective cap (9) constructed as a bellows simultaneously forms a secondary seal by being sealingly joined at one end to the cylinder and at the other end to a piston rod (6) of a piston (3) in the cylinder. In a further development of the invention, the bellows (9) is surrounded by a guard (18) which limits the return motion of the piston (3) and the piston rod (6) respectively. <IMAGE>

Description

SPECIFICATION A master cylinder This invention relates to a master cylinder for an hydraulic brake, hydraulic clutch or other hydraulic system such as those used in vehicles or power-driven craft, the cylinder having a piston and comprising at least one pressure chamber sealed by a primary seal, at least one follower chamber sealed by a secondary seal and a protective cap constructed as a bellows.

Such a master cylinder is known from published German Patent Application No.

1,530,757. However, a disadvantage of the design shown therein is the large space required for the master cylinder and the reservoir mounted on its casing, as well as that for the secondary sealing member which is required for sealing the follower chamber and which, as a result of wear or fouling, can cause the system to leak.

It is accordingly an aim of the present invention to devise a master cylinder in such a way as to reduce not only the space required for its installation but also its seals.

With this aim in view, the invention is directed to a master cylinder of the construction set forth in the opening paragraph of the specification wherein the protective cap is sealingly joined to the cylinder casing and to a piston rod of the piston and simultaneously forms the secondary seal.

By virtue of the fact that the protective cap is constructed as a bellows and simultaneously forms the secondary seal, it is now possible to dispense not only with a conventional secondary seal slidingly arranged in the casing bore but also with the complicated piston construction which is necessary when a conventional secondary seal is used. Moreover, the space within the protective cap can serve additionally as a reservoir with the result that the conventional reservoirs mounted on the casing may be of smaller size or may, for some applications, be omitted entirely. Further, a master cylinder provided with a swivably-joined operating rod can now be fitted with a spherical or part-spherical piston so that the piston and the rod are a one-piece component.

In a further development of the master cylinder described above, the bellows is surrounded by a guard which limits return motion of the piston and the piston rod respectively.

The benefit of such a construction can be appreciated by considering the form of master cylinder shown in German Patent No. 840,800 where a locking washer is arranged in the cylinder bore to serve as a stop for the piston.

This demands space in a direction axially of the cylinder which cannot therefore be utilised.

In addition, difficulties occur when fluid entering the bellows under high pressure (of up to 8 bars) inflates the bellows and increases the risk of the bellows becoming leaky or torn at its seating on the cylinder. Moreover, since the bellows is freely accessible, it can easily be damaged from outside. All these drawbacks are overcome by arranging a guard around the bellows, the guard serving also to limit return motion of the piston and piston rod respectively.

Examples of master cylinders in accordance with the invention are illustrated in the accompanying drawings, in which Figure 1 is a section through one form of master cylinder; Figure 2 is a section through a master cylinder fitted with a spherical piston; and Figure 3 is a section through a third form of master cylinder.

The master cylinder shown in Fig. 1 comprises a casing 1 arranged to be swivably attached by its mounting lug 1' to a vehicle. A restoring spring 2 arranged in the casing bore abuts at one end against the casing base and at its other end against a piston 3. The latter carries a primary sealing member 4 and a centrally-mounted suction valve 5. A piston rod 6 is fastened to the piston 3 and is axially guided by a guide bush 7 joined by ribs to the casing 1. A stop plate 8 is arranged in the vicinity of the ribs, and the piston rests, in its normal position, against this stop plate. A protective cap 9 constructed as a bellows is sealingly fastened at one end to the casing 1 and at the other end to the piston rod 6. The cap 9 simultaneously forms a secondary seal and is provided at each of its two ends-for the purpose of strengthening the seals there-with a springy ring 10.The casing 1 also includes an inlet junction 11 for a reservoir 11' and a delivery junction 12 for a delivery duct leading to a slave, or wheel, cylinder.

In the normal position, the junction 11 is in communication, through a groove 13 machined into the casing, with both the space 14 surrounded by the protective cap 9 and with the pressure chamber 15.

The method of operation of the master cylinder shown in Fig. 1 is as follows: The piston rod 6 and the piston 3 are pushed, on actuation of the brake or clutch pedal of the vehicle, against the bias of the restoring spring 2 to the left-hand side. As a result, the primary sealing member 4 seals, as soon as it has passed the extent of the groove 13, the pressure chamber 15 against the space 14 which is filled with pressure medium. Since the suction valve 5 is shut, pressure can now build up and be ducted through the delivery junction 12 to the slave or wheel cylinder. As soon as the braking or clutching operation is terminated, the restoring spring 2 pushes the piston 3 and the piston rod 6 to the righthand side until the piston 3 rests again against the stop plate 8.If need be, an equalisation of the pressure in the space 14 and the pressure chamber 15 is effected through the suction valve 5. In contrast to the state of the art, a separate secondary seal is not required, the reason being that the pressure medium-filled space 14 is sealed by the protective cap 9 constructed as a bellows. The advantage of this arrangement is that the volume of the pressure medium (brake fluid or the like) to be kept for safety's sake in the reservoir can be reduced, with the consequence that the size of the reservoir can be reduced and the master cylinder therefore occupies a smaller space. The reservoir 11' may, for some applications, be omitted altogether.

Fig. 2 illustrates a master cylinder where the reservoir 11' is, in fact, omitted. Its method of operation is the same as that of the master cylinder illustrated in Fig. 1. A difference between them however is that the master cylinder according to Fig. 2 is fitted with a socalled spherical or part-spherical piston.

Whereas the master cylinder illustrated in Fig.

1 is arranged to counter-balance the deflection of the rod 6-brought about by the brake or clutch pedal-by a swivel motion which is rendered possible by the mounting lug 1' of its casing, the master cylinder illustrated in Fig. 2 is secured immovably by two mounting lugs 16 to the vehicle. The rod deflection is, in this construction, counter-balanced by the piston 3 which, at its rear, is spherically shaped and which, in its normal position, rests against a concavely-shaped stop plate 17.

Advantageously, all the components of the master cylinder other than the piston rod 6 and the restoring spring 2 are made of a synthetic plastics material. The protective cap 9 formed as a bellows, the suction valve 5, the primary sealing member 4 and the stop plate 8 are made, for example, of a synthetic elastomer, while the guide bush 7 and the stop plate 17 are ultrasonically welded to the casing 1.

A third form of master cylinder is shown in Fig. 3. As in Figs. 1 and 2, the cylinder casing 1 encloses a piston 3 which is axially displaceable by means of the piston rod 6, while a bellows 9 is sealingly joined at its ends to the cylinder casing 1 and the piston rod 4. The bellows is filled with pressure fluid, again as in Figs. 1 and 2. In this instance, however, the bellows is surrounded by a guard 18 which abuts against the casing 1 and is secured, together with the latter, to a vehicle 19. The guard 18 is made of sheet metal or of a strong synthetic plastics material and thus prevents or reduces mechanical damage to the bellows from outside and, in addition, bulging and tearing of the elastomeric bellows when high pressure is produced within the bellows. In addition, return motion of the piston and piston rod respectively is limited by the guard 18, the piston rod 4 having a stop plate 20 mounted thereon which rests against the base of the guard 6 as shown in Fig. 3. As a result, the stop plate 8 in Fig. 1 becomes superfluous so that less components are required in a direction axially of the cylinder.

Claims

1. A master cylinder for an hydraulic brake, hydraulic clutch or other hydraulic system, the cylinder having a piston and comprising at least one pressure chamber sealed by a primary seal, at least one follower chamber sealed by a secondary seal and a protective cap constructed as a bellows, in which the protective cap is sealingly joined to the cylinder casing and to a piston rod of the piston and simultaneously forms the secondary seal.

2. A master cylinder according to claim 1, in which the space surrounded by the protective cap serves as a reservoir.

3. A master cylinder according to claim 1 or claim 2, in which the bellows is surrounded by a guard which limits return motion of the piston and the piston rod respectively.

4. A master cylinder for an hydraulic system substantially as described herein with reference to Fig. 1, Fig. 2 or Fig. 3 of the accompanying drawings.