GB1604008A

GB1604008A - Actuator cylinder in particular a brake actuator cylinder for road vehicles

Info

Publication number: GB1604008A
Application number: GB24893/78A
Authority: GB
Original assignee: Wabco Fahrzeugbremsen GmbH
Current assignee: Wabco Fahrzeugbremsen GmbH
Priority date: 1977-10-01
Filing date: 1978-05-31
Publication date: 1981-12-02
Also published as: DE2744292C3; DE2744292A1; IT1203202B; IT7869254A0; FR2404768A1; DE2744292B2; FR2404768B1

Description

(54) ACTUATOR CYLINDER, IN PARTICULAR A BRAKE ACTUATOR CYLINDER FOR ROAD VEHICLES (71) We, WABCO FAHRZEUGBREMSEN GmbH (Formerly Wabco Westinghouse GmbH), a German Company of, Am Lindener Hafen 21, 3000 Hannover 91, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to an actuator cylinder, in particular a brake-actuator cylinder for road vehicles.

A brake actuator cylinder for a road vehicle generally comprises an actuator piston carrying a tappet rod and arranged in a cylinder housing, a spring actuator on one side of the piston and, on the other side, a brake release chamber to which braking pressure medium is supplied and through which the tappet rod passes to provide an operative connection between the piston and a brake operating member.

The brake release chamber of the spring actuator cylinder is generally sealed at the piston and at the tappet rod by means of dynamic sealing rings as indicated, for example in German Patent Specification 1655742 and in German Offenlegungsschrift 1921622.

Because of the mode of operation, the full pressure of the brake system acts permanently on the brake release chamber of a spring actuator cylinder during normal vehicle travel, i.e. when the brake is released.

This means that, if a dynamic sealing ring is not tight, whether as a result of wear or other damage the brake release chamber must be constantly supplied with a pressure medium which results in longer operating times for the brake compressor.

Apart from the fact that, as a result of a pressure medium being supplied constantly there is an undesirably high pressure medium consumption, the inner surface of the cylinder must be specially treated in order to reduce the degree of wear of the sealing ring.

The present invention provides an actuator cylinder, in particular a brake-actuator cylinder for road vehicles, comprising an actuator piston carrying a tappet rod and CM-arranged in a cylinder housing; resilient actuator means for the piston and, on one side of the piston, a brake release chamber having a pressure medium inlet; a piston sealing element providing both a radiallydirected sealing surface and an axiallydirected sealing surface between the piston and the housing, and a tappet rod sealing element providing both a radially-directed sealing surface and an axially-directed sealing surface between the tappet rod and the housing.

By way of example, an embodiment of the invention will be described with reference to the accompanying drawing which shows a longitudinal section through a brake-actuator cylinder.

The spring brake-actuator cylinder shown in the drawing has a housing 1 that is closed by a cover 2 at one end. The housing 1 is divided by a spring actuator piston 3, guided in a sealed manner, into a release chamber 4 and a spring chamber 5. The spring actuator piston 3 is acted upon by a coil spring 6 which is fitted so that it is pretensioned and is supported on the base of the housing 1. The spring actuator piston 3 is also provided with a tappet rod 7 which is fastened in a central depression in the spring actuator piston 3 and, with its free end sealed off, passes through the cover 2 of the housing 1, the free end of the tappet rod 7 carrying a tappet head 8 which is brought into operative connection with corresponding brake operating rods (not shown).

The spring chamber 5 is provided with a ventilation connection 9 and the release chamber 4 is provided with a pressure medium connection 10.

A combined static and dynamic sealing ring 11 is located between the piston 3 and the housing 1. The ring 11 has a radiallydirected sealing surface 11 a, effecting a dynamic seal, and an axially-directed sealing surface I lb, effecting a static seal and serving simultaneously as a piston stop. The ring 11 is provided with an annular groove I Ic.

A sealing ring 12 is inserted in the opening of the cover 2, through which the tappet rod 7 passes. The ring 12, through a radially directed sealing surface, undertakes a dynamic sealing of the tappet rod to the housing 1 and, through an axially-directed sealing surface in conjunction with a sealing edge 8a of the tappet head 8, a static sealing operation.

The operation of the spring actuator cylinder is as follows: The Figure shows the piston 3 in the tensioned position in which the parking or auxiliary brake is released. Thus a pressure medium acts fully on the chamber 4 via the connection 10, and static sealing of the piston 3 to the housing I is effected by the axiallydirected sealing surface I I b which is pressed, against the force of the spring 6, against the stop fixed in the housing. At the same time, static sealing of the tappet rod 7 to the housing I is effected by the axially-directed sealing surface of ring 12, which cooperates with the sealing edge 8a of the tappet head 8 to seal off statically the opening in the cover 2 of the tappet rod 7.

When braking is effected using the parking or auxiliary brake the air is evacuated from the chamber 4 and the spring 6 moves the piston 3 into the braking position in which the tappet head 8 of the tappet rod 7 acts on the brake operating members (not shown) and brings about braking.

The arrangements described above make it possible, by simple means, to seal off the brake release piston 3 statically in such a manner that, even when the dynamic seals provided by the radially-directed sealing surfaces of the rings 11, 12 are not tight, the brake release pressure in the chamber 4 is maintained without constant charging. In particular, the design of the contact areas of the piston and tappet head as static seal seats and the combination of a dynamic and static sealing surface in a single element, as illustrated, can be put into practice easily and without any considerable added costs. In addition, special surface treatment to reduce wear can be omitted.

WHAT WE CLAIM IS: 1. An actuator cylinder comprising an actuator piston carrying a tappet rod and arranged in a cylinder housing; resilient actuator means for the piston and, on one side of the piston, a brake release chamber having a pressure medium inlet; a piston sealing element providing both a radiallydirected sealing surface and an axiallydirected sealing surface between the piston and the housing, and a tappet rod sealing element providing both a radially-directed sealing surface and an axially-directed sealing surface between the tappet rod and the housing.

2. An actuator cylinder according to claim 1, in which the piston sealing element is located on the piston and the axiallydirected sealing surface thereof is co-operable with a piston stop in the housing.

3. An actuator cylinder according to claim 1 or claim 2, in which the tappet rod sealing element is located on the housing and the axially-directed sealing surface thereof is co-operable with a sealing edge on the tappet rod.

4. An actuator cylinder according to any one of the preceding claims, in which the sealing elements are sealing rings.

5. An actuator cylinder according to claim 4, in which the piston sealing ring is provided with an annular groove.

6. An actuator cylinder substantially as described herein with reference to, and as illustrated by, the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. directed sealing surface, undertakes a dynamic sealing of the tappet rod to the housing 1 and, through an axially-directed sealing surface in conjunction with a sealing edge 8a of the tappet head 8, a static sealing operation. The operation of the spring actuator cylinder is as follows: The Figure shows the piston 3 in the tensioned position in which the parking or auxiliary brake is released. Thus a pressure medium acts fully on the chamber 4 via the connection 10, and static sealing of the piston 3 to the housing I is effected by the axiallydirected sealing surface I I b which is pressed, against the force of the spring 6, against the stop fixed in the housing. At the same time, static sealing of the tappet rod 7 to the housing I is effected by the axially-directed sealing surface of ring 12, which cooperates with the sealing edge 8a of the tappet head 8 to seal off statically the opening in the cover 2 of the tappet rod 7. When braking is effected using the parking or auxiliary brake the air is evacuated from the chamber 4 and the spring 6 moves the piston 3 into the braking position in which the tappet head 8 of the tappet rod 7 acts on the brake operating members (not shown) and brings about braking. The arrangements described above make it possible, by simple means, to seal off the brake release piston 3 statically in such a manner that, even when the dynamic seals provided by the radially-directed sealing surfaces of the rings 11, 12 are not tight, the brake release pressure in the chamber 4 is maintained without constant charging. In particular, the design of the contact areas of the piston and tappet head as static seal seats and the combination of a dynamic and static sealing surface in a single element, as illustrated, can be put into practice easily and without any considerable added costs. In addition, special surface treatment to reduce wear can be omitted. WHAT WE CLAIM IS:

1. An actuator cylinder comprising an actuator piston carrying a tappet rod and arranged in a cylinder housing; resilient actuator means for the piston and, on one side of the piston, a brake release chamber having a pressure medium inlet; a piston sealing element providing both a radiallydirected sealing surface and an axiallydirected sealing surface between the piston and the housing, and a tappet rod sealing element providing both a radially-directed sealing surface and an axially-directed sealing surface between the tappet rod and the housing.