GB2145485A

GB2145485A - Releasing spring-applied parking brake by service brake pressure

Info

Publication number: GB2145485A
Application number: GB08322737A
Authority: GB
Inventors: Ivor Henry Bull; John Dale Coleman
Original assignee: Westinghouse Brake and Signal Co Ltd
Current assignee: Siemens Mobility Ltd
Priority date: 1983-08-24
Filing date: 1983-08-24
Publication date: 1985-03-27
Also published as: IN161159B; ZA846466B; GB2145485B; GB8322737D0

Abstract

In a vehicle brake system, particularly for a railway vehicle, the parking brake (1) is released by an effective service brake (2) application by distributor (13) which causes fluid pressure from reservoir (10) to be applied via step-up relay (7) and two-way valve (4) in opposition to the force exerted by the parking brake spring. Subsequently, build-up of service brake pressure closes switch (17) whereupon valve 4 is switched over and parking brake (1) is maintained released for normal running by fluid pressure derived from a main pressure reservoir (5). The two-way valve (4) is held switched over by an electrical self-maintaining circuit, including relay (16, 18), in the normal running position thereafter. The system avoids excessive compounding of the brake forces while allowing release of the parking brake automatically when the service brake is applied. <IMAGE>

Description

SPECIFICATION Vehicle brake system The invention relates to a vehicle brake system.

In a vehicle, particularly a railway vehicle, fitted with air brakes a mechanically applied form of brake i.e. one which is not applied by the air pressure used to operate the service brakes, is required to hold a parked that is "dead" vehicle. This is normally provided by a spring applied parking brake which, under norml running conditions, is held off by air pressure from the service brake air pressure system. In order that this shall not leave the vehicle without brakes, when the air compressor is started and the air pressure backs-off the parking brake, an interlock is arranged between the service brakes and the parking brake so that the service brakes have to be applied to release the parking brake.

The parking brake and service brake system usually employ separate actuators but acting on the rigging and brake blocks or pads.

Consequently when service brake is applied to release the parking brake the rigging etc. is subjected to double loading. This need not be a problem if all the components are amply strong enough to withstand the extra loading but in the type of lighter rail vehicle being designed nowadays this is not always the case.

The invention seeks to overcome this problem of double loading in the type of brake system described whilst retaining the operating characteristic whereby the parking brake is released by a service brake application.

According to the present invention there is provided a vehicle brake system having a parking brake interlocked with a service brake such that the parking brake is released by a service brake application wherein the parking brake has a pressure inlet in opposition to the brake force to which pressure is connected for brake release through a two-way valve means which in the normal running position occupies a first position providing communication with a pressure supply line and alternatively a second position providing communication with service brake cylinder pressure.

The invention and how it may be carried into practice will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of part of a two-pipe air brake system showing the interrelationship of pneumatic and electrical components, and Figure 2 is a circuit diagram of the corresponding electrical system.

The parking brake of a railway vehicle must be fail-safe so that it will hold stationary an uncoupled, unattended (a so-called "dead") vehicle. The parking brake is thus spring applied and arranged to be held-off by, say, the service brake air pressure supply on an air-braked vehicle. A straight forward air supply to parking brake connection is not safe, although it works satisfactorily in normal running by holding-off the parking brake and when the vehicle is braked to a standstill and "killed" so that the parking brake leaks on gradually as service brake air pressure decays, when the vehicle systems are first started up a transient condition arises when the parking brake is released before full service brake is available. This is avoided by interlocking the parking brake and service brake.In one example admission of air to the parking brake cylinder is controlled by a magnet valve, open when energised, the electrical portion of which is connected in a stick circuit, so that once made it holds a normal running condition until the electrical supply is disconnected, as by "killing" the vehicle for example. Also in the stick circuit is a pressure switch the pneumtic portion of which is fed from a service brake cylinder. By this arrangement the parking brake can only be released by an application of the service brake which is only possible when full service brake air pressure has been reached.

The result of such an arrangement may be excessively high loading of the brake actuator linkages due to compound service brake and parking brake applications. In the presently proposed arrangement that part of the loading due to the parking brake is reduced in proportion to the service brake cylinder pressure during the initial application to release step.

How this is achieved will now be described with reference to the accompanying drawings.

Referring now to Fig. 1 electrical connections are shown as thin, solid black lines and pneumatic supplies and connections by broad, hatched lines. The parking brake actuator is represented at 1 and the corresponding service brake cylinder actuator at 2. The parking brake actuator 1 comprises a spring applied mechanism which is capable of being "backed-off" by opposing air pressure carried by pneumtic line 3 connected to two-way valve means 4 which receives its pressure supply, when in a first position shown by the dotted line (a), from a main reservoir 5 via pipe 6, or when in a second position shown by solid line (b), from the output of a relay valve 7 via a connection 8.This relay valve 7 draws air pressure supply via a connection 9 from auxiliary reservoir 10 and operates to step-up the pressure present at its input on a branch 11 from the service brake line 1 2 connecting service brake distributor valve 1 3 to the service brake actuator cylinders of which cylinder 2 is one. A pressure operated switch 14 is also connected to receive service brake actuator pressure and, for the purposes of illustration, is shown in the drawing connected to brake cylinder 2, the switch is set to operate at a pressure in the order of 3.0 bar.

The brake system of which this forms part is of the conventional railway two-pipe type which normally includes such items as main reservoir 5, auxiliary reservoir 10 and distributor 1 3. If a basic description of such a system reference is directed to appropriate published works such as ''Introduction to Railway Braking" by H.R. Broadbent.

Turning now to the associated electrical system as shown in Figs. 1 and 2, in which like parts have like references, the positive or current supply line is denoted by the symbol + V and the current return or earth line by Ov. Overall electrical energistion of the parking brake circuit is controlled by closure of a set of contacts 1 5 operated by the armature of relay 20 arranged to be energised by key operated switch or equivalent, shown in Fig.

2. In series with contacts 1 5, but in parallel with each other, are stick relay contacts 1 6 and contacts 1 7 of pressure switch 14.

Then in series with this but again in parallel with each other are the operating coil 18 of the stick relay and the energising coil 1 9 of the parking brake magnet valve 4.

When the vehicle is parked, i.e. is left in a "dead" condition the brake system is unpressurised so that the parking brake has applied itself to hold the vehicle stationary. Also the electrical system is de-energised so that contacts 15, 1 6 and 1 7 are open and magnet valve 4 assume position (b) as shown in Fig.

1. In preparation for moving such a vehicle a driver enters the cab and energises the electrical system using the key operated switch which results in contacts 1 5 closing. Amongst other things he is now able to start the motors, which also power air compressors which begin charging up the brake system pressurising reservoirs 5 and 10.

In due course when the driver wishes to move the vehicle he will make a service brake application whereupon the distributor 1 3 will admit pressure into lines 11 and 12, the latter connecting with service brake cylinder 2. As the service brake pressure in connection 11 builds up towards the selected level, up to a maximum of 3.5 bar, the relay valve 7 responds by feeding a correspondingly steppedup pressure derived from auxiliary reservoir 10 into the parking brake 1 via line 3, up to the maximum available auxiliary reservoir pressure of usually 7 bar in a 2-pipe system.

Thus, as service brake cylinder pressure rises the parking brake is backed-off by a proportional amount reducing the effort exerted on the brake rigging by the parking brake as that exerted by the service brake increases. The maximum force ever exerted by a compound brake application is consequently greatly decreased.

When the brake cylinder pressure reaches 3.0 bar the contacts 1 7 close energising both the stick relay coil 1 8 and magnet valve coil 1 9. The magnet valve operates and switches the two-way valve into position (a) connecting the parking brake actuator directly with the main reservoir 5 which remains charged for as long as the compressor remains operating.

The energised stick relay 1 8 closes its normally open contacts 1 6 and effectively maintains itself and magnet valve 1 9 in the energised state for as long as electricl power remains connected.

If the vehicle is subsequently parked again it is brought to a standstill by full service brake application and then the compressors are stopped and electrical disconnected. Although the magnet valve 1 9 is thereby deenergised and valve 4 returned to position (b) the parking brake does not immediately take effect because of the air pressure retained in the brake system maintaining the service brake. As this pressure leaks away the opposing force holding back the parking brake diminishes permitting it to gradually deploy with increasing effort.

Claims

CLAIMS 1. A vehicle brake system having a parking brake interlocked with a service brake such that the parking brake is released by a service brake application wherein the parking brake has a pressure inlet in opposition to the brake force to which pressure is connected for brake release through a two-way valve means which in the normal running position occupies a first position providing communication with a pressure supply line and alternatively a second position providing communication with service brake cylinder pressure. 2. A brake system as claimed in Claim 1 wherein the two-way valve means is operated under the control of a signal indicative of brake cylinder pressure. 3. A brake system as claimed in Claim 2 wherein the two-way valve means is connected in a self-maintaining circuit arranged to hold the valve in the first, normal running position. CLAIMS

1. A vehicle brake system having a parking brake interlocked with a service brake such that the parking brake is released by a service brake application comprising a parking brake and a fluid pressure operated service brake, the parking brake having a pressure inlet connected to apply fluid pressure at the inlet in opposition to the brake force, a connection to said inlet through a two-way valve means which oppupies a first position for normal running of a vehicle in which it provides a communication with a source of substantially constant fluid pressure, and alternatively occupies a second position in which it provides a communication with a source of fluid pressure derived from a service brake.

2. A brake system according to claim 1 wherein a second position of the two-way valve there is provided communication with the outlet of a relay valve operatively responsive to service brake fluid pressure.

3. A brake system according to claim 1 or claim 2 wherein the two-way valve is operated to change from the second position to the first position in response to service brake fluid pressure in excess of a predetermined threshold value.

4. A brake system according to any one of claims 1 to 3 wherein the two-way valve is operated to the first position for normal running by an electrical signal.

5. A brake system according to claim 4 wherein the electrical signal to operate the two-way valve is produced by the operation of a fluid pressure responsive switch in response to service brake fluid pressure in excess of a predetermined threshold value.

6. A brake system according to claim 4 or 5 wherein an electrical operating portion of the two-way valve is connected in a selfmaintaining circuit arranged to hold the valve in the first position.

7. A brake system according to claim 6 wherein the self-maintaining circuit comprises a stick relay.

8. A brake system according to claim 7 comprising a first circuit branch including contacts of the stick relay connected in parallel with the contacts of a fluid pressure responsive switch operatively connected to receive service brake cylinder pressure, a second branch comprising an operating coil of the stick relay connected in parallel with an operating coil of the two-way valve, the first branch is connected to a source of electrical potential and the second branch is connected in series with the first branch and a reference potential.

9. A brake system substantially as hereinbefore described with reference to the accompanying drawings.