GB1582213A - Combined pressure-medium-operated and spring-loaded brake cylinder - Google Patents

Abstract

In the combined pressure medium and spring loaded brake cylinder, a partition wall (1) divides the pressure medium brake cylinder (4) from the spring loaded brake cylinder (5). A piston rod (17) coupled to the piston (12) of the spring loaded brake cylinder (5) displaceably passes through a bore (18) in the partition wall (1). Two sealing rings (18' and 19), which seal off the piston rod (17) are located in the bore (18). A venting duct (20) to the atmosphere running in the partition wall (1) opens into that section (18a) of the bore (18) which is located between the sealing rings (18' and 19). In the event of leakages from the sealing rings (18', 19) an outflow of the compressed air passing through the leakage to the atmosphere is thereby achieved. <IMAGE>

Description

(54) COMBINED PRESSURE-MEDIUM-OPERATED AND SPRING-LOADED BRAKE CYLINDER (71) We, KNORR-BREMSE GmbH, of 8 Munchen 40, Moosacher Strasse 80, Federal Republic of Germany, and a German company, 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: This invention relates to a brake cylinder comprising: a first chamber in which a first piston is movable for operating a brake mechanism when pressure medium is supplied to the chamber; a second chamber in which a springloaded second piston is movable in one direction by the spring, said second piston being movable in an opposite direction against the spring loading when pressure medium is supplied to the second chamber; a partition separating said first and second chambers; a passage formed in said partition and intercommunicating said first and second chambers; a connecting element taken through said passage and operable to transmit movement of said second piston in said one direction to said first piston for operating the brake mechanism in the event of a failure in the supply of pressure medium to the first and second chambers; and a sealing arrangement for sealing the movement of said connecting element in said passage.

In brake cylinders of the above type, usually the first chamber is used for service braking when the chamber is subjected to the action of pressure medium, whereas the spring-loaded second piston in the second chamber is retained in its release position when the second chamber is subjected to the action of pressure medium and the second piston only becomes effective when there is a failure or a reduction in the pressure level of the pressure medium supply. In such event, the second piston causes the operation of the brake mechanism via the connecting element extending through the passage in the partition. In the known arrangements, special valve devices are provided in the connections of the pressure medium supply to the first and second chambers for monitoring the pressure levels of the supply.

Thus, when the brake mechanism is released, the first chamber is maintained pressureless via an external valve, whereas the second chamber is maintained subjected to the action of the pressure medium. Due to the differing pressure levels now prevailing in the first and second chambers, the connecting element must extend through the partition in substantially sealed manner, for which purpose there are inserted in the partition packings which coact with the connecting element. Therefore, inevitably a more or less considerable degree of loss of fluidtightness in service has to be envisaged.If, then, in the event of breakdown, the external venting valve is not opened, or is only inadequately opened, there will build-up pressure in the first chamber due to leakage of pressure medium from the second chamber through the partition and past the ineffective packing, whereby undesired braking may occur. Since such a breakdown may not be immediately recognised in every case, this may give rise to.

considerable damage.

It is an object of the invention to provide a brake cylinder which is improved over the known arrangements whereby the risk of overflow of pressure medium from the second chamber to the first chamber is avoided or at least substantially minimised.

According to the invention there is provided a brake cylinder comprising; a first chamber in which a first piston is movable for operating a brake mechanism when pressure medium is supplied to the chamber; a second chamber in which a spring-loaded second piston is movable in one direction by the spring, said second piston being movable in an opposite direction against the spring loading when pressure medium is supplied to the second chamber; a partition separating said first and second chambers; a passage formed in said partition and intercommunicating said first and second chambers; a connecting element taken through said passage and operable to transmit movement of said second piston in said one direction to said first piston for operating the brake mechanism in the event of a failure in the supply of pressure medium to the first and second chambers;; two spaced seals provided in said passage and engaging with said connecting element in order to seal the first and second chambers from each other during movement of the connecting element in said passage; and a discharge duct communicating with a space defined in said passage between said seals for discharging pressure medium from said space in the event of a faulty sealing operation developing in one of said seals whereby the respective chamber is able to leak pressure medium to said space for subsequent discharge through said discharge duct.

One embodiment of brake cylinder according to the invention will now be described in detail, by way of example only, with reference to the accompanying drawing which illustrates the brake cylinder schematically and partly in section.

Referring now to the drawing, there is shown a combined pressure-medium -operated and spring-loaded brake cylinder for operating a brake mechanism. The brake cylinder effectively has two parts, namely a pressure medium brake cylinder 4 and a spring-loaded brake cylinder 5, which are separated from each other by a partition 1. The cylinder 4 has a housing 2 which defines a first chamber within which a first piston 6 is moveable. The piston 6 subdivides the housing 2 into a pressure chamber 8 adjacent the partition 1 into which pressure medium may be supplied via a pressure medium connection 7, and an external air chamber 9.

The piston 6 is connected to a tubular piston rod 10 which projects through the chamber 9 into the ambient atmosphere. A relatively weak spring 11 surrounds the piston rod 10 and urges the piston 6, to the right as seen in the drawing, into the release position as shown. Upon admission of pressure medium through connection 7, the piston 6 moves against the action of the spring 11 in order to operate a brake mechanism (not shown) connected to the connecting rod 10.

The brake cylinder 5 has a housing 3 which defines a second chamber in which a second, spring-loaded piston 12 is movable. The piston 12 subdivides the second chamber into a cylinder chamber 14 adjacent the partition 1 into which pressure medium may be admitted via the pipe connection 13, and a spring chamber 15. In the spring chamber 15 there is arranged a relatively strong loading spring 16 which urges the piston 12 to move in one direction towards the partition.l.

A connecting element is taken through a passage or bore 18 formed in the partition 1, the connecting element being operable to transmit movement of the second piston 12 towards the partition 1 to the first piston 6 to enable operation of the brake mechanism (not shown) in the event of a failure in the supply of pressure medium to the first and second chambers in housings 2 and 3. In the illustrated embodiment, the connecting element comprises a tubular piston rod 17 which is connected to the second piston 12 and extends towards the first piston 6. However, many other arrangements of connecting element are possible e.g. the connecting element may comprise a connecting rod connected to the first piston 6 and extending towards the second piston 12.

Two spaced annular seals 18' arid 19 are provided in the bore 18 and engage with the external surface of the piston rod 17 is in order to seal the chambers 8 and 14 from each other during movement of the rod 17 in the bore 18.

The seals 18' and 19 are axially spaced from each other and define in the bore 18 an annular space 18a. The annular space 1 8a communicates with a discharge duct in the form of a venting duct 20 which extends radially outwardly of annular space 1 8a and through the partition 1 to atmosphere.

In normal operation, pressure medium is supplied to chambers 8 and 14 to enable operation of a brake mechanism, in which case the first piston 6 moves to the left under the action of the pressure medium, whereas the second piston 12 remains in the position as illustrated or is moved to the right under the action of the spring loading provided by spring 16. In the event of a failure in the supply of pressure medium to the chambers 8 and 14, although the first piston 6 will no longer be biased by the action of pressure medium to operate the brake, the second piston 12 is able to move to the left under the action of the spring 16 and this movement is transmitted via the piston rod 17 to the first piston 6 which can then maintain the operation of the brake mechanism.

Although not shown, the supply of pressure medium to the chambers 8 and 14 will be controlled by suitable valves so that the chamber 14 will normally be maintained pressurised (even in the event of small leakages via packing 19 when the latter is faulty) in the release mode of the brake cylinder when pressure medium is no longer supplied to chamber 8. This then enables the first piston 6 to move to the right under the action of the spring 11 so as to terminate the operation of the brake mechanism.

If one of the seals or packings 18' or 19 should become damaged or carry out faulty sealing operation, then upon the respective adjacent chamber 8 or 14 being subjected to the action of pressure medium, this pressure medium will be able to come into communication with the annular space 1 8a via the faulty seal. However, assuming the remaining seal to remain effective, this leakage of pressure medium will not pass to the other of the chambers since it passes from the annular space 1 8a to the venting duct 20 and thence to atmosphere. Accordingly, undesired actuation of the brake mechanism will be prevented even in the case of faulty sealing actions developing for the movement of the piston rod 17 through the partition 1.

Usually, the pressure medium operating the brake cylinder will be compressed air, in which case discharge of the compressed air to atmosphere via venting duct 20 will be satisfactory.

However, if other pressure mediums shouldbe envisaged for operating the brake cylinder, the venting duct may comprise a discharge duct leading to a supply and return tank.

Furthermore, even if both seals 18' arid 19 should become defective, at least the greater part of any leakage of pressure medium from one of the chambers 8 and 14 will be discharged to atmosphere via annular space 1 8a and duct 20 rather than pass to the other of the chambers.

WHAT WE CLAIM IS: 1. A brake cylinder comprising: a first chamber in which a first piston is movable for operating a brake mechanism when pressure medium is supplied to the chamber; a second chamber in which a spring-loaded second piston is movable in one direction by the spring, said second piston being movable in an opposite direction against the spring loading when pressure medium is supplied to the second chamber; a partition separating said first and second chambers; a passage formed in said partition and intercommunicating said first and second chambers; a connecting element taken through said passage and operable to transmit movement of said second piston in said one direction to said first piston for operating the brake mechanism in the event of a failure in the supply of pressure medium to the first and second chambers;; two spaced seals provided in said passage and engaging with said connecting element in order to seal the first and second chambers from each other during movement of the connecting element in said passage; and a discharge duct communicating with a space defined in said passage between said seals for discharging pressure medium from said space in the event of a faulty sealing operation developing in one of said seals whereby the respective chamber is able to leak pressure medium to said space for subsequent discharge through said discharge duct.

2. A brake cylinder according to claim 1, in which the discharge duct communicates said space with atmosphere.

3. A brake cylinder according to claim 1 or 2, in which the connecting element comprises a piston rod connected to one of said pistons.

4. A brake cylinder according to claim 3, in which said piston rod is connected to said second piston.

5. A brake cylinder according to claim 3 or 4, in which said two seals are annular seals axially spaced with respect to said connecting rod.

6. A brake cylinder according to claim 1 and substantially as hereinbefore described with reference to and as shown in the accompanying drawing.

7. A brake mechanism including a brake cylinder according to any one of the preceding

Claims (1)

1. claims.