GB2199383A - Emergency brake control arrangement - Google Patents

Abstract

An emergency brake control arrangement for a railway vehicle provides for an emergency brake application of fluid pressure to an emergency relay valve for an emergency brake application should the relay valve fail to operate to design specification. For example, if the emergency relay valve leaks it is unlikely to supply sufficient pressure to the brake actuator for an emergency application. During an emergency brake application the normal brake control is set to full service application. Normally the service brake pressure is isolated from the brake cylinders by an isolating valve. The invention provides a by-pass path controlled by a valve responsive to emergency relay valve output pressure which, in the event that the emergency pressure is below a threshold valve, opens to supply full service brake pressure in place of the emergency supply thereby ensuring that at least full service braking is achieved. <IMAGE>

Description

EMERGENCY BRAKE CONTROL ARRANGEMENT The invention relates to an emergency brake control arrangement for a pneumatically operated vehicle brake system, particularly for the brake system of a railway vehicle.

In a typical fluid pressure operated brake system on a railway vehicle a compressor is connected to a supply of fluid under pressure to a brake pipe extending the length of the train. A second pipe provides working fluid to the brake system and, by varying its pressure, the brake pipe is used to control operation of the brake system. On each vehicle fluid pressure storage reservoirs are connected to be charged from the second pipe and to act as a source of fluid pressure for supplying brake actuator cylinders under the control of valves responsive to reductions in pressure in the brake pipe.

One such reservoir is reserved as a source of fluid pressure for emergency brake actuation. An emergency brake application is brought about by a rapid or total decompression of the brake pipe which activates emergency relay valves to connect the emergency reservoirs to the brake actuator cylinders.

The purpose of reserving a reservoir of fluid pressure for emergency use only is that its pressure shall not be depleted by the requirements of the braking equipment during service brake applications so that full pressure is, theoretically at least, always available for an emergency application. However, should a leak occur in individual storage reservoirs or in an emergency relay valve, the stored pressure may leak away and leave the reservoir at least partially exhausted and unable to contribute significantly when an emergency brake application is called for. An object of the present invention is to provide a safety brake valve which will come into operation automatically in such an event to provide some level of emergency braking effort in substitution.

According to the present invention there is provided an emergency brake control arrangement for a pneumatically operated vehicle brake system comprising selector valve means for supplying to an outlet communicating with the vehicle brake actuator cylinder fluid at pressure from a first source for service brake applications or from a second source in response to an emergency indication, and bypass means for connecting the first source to the outlet in the event that the fluid pressure of the second source is lower than a predetermined threshold value.

The invention and how it may be carried to practice will now be described with reference to an embodiment illustrated in the accompanying drawings, in which: Fig 1 shows a schematic diagram of a pneumatic brake system for a railway vehicle, and Fig 2 shows a section through the safety brake unit of the system of Fig 1.

In the system illustrated in Fig 1 the main reservoir pipe 1 receives fluid under pressure from a compressor (not shown) and supplies pressurised fluid to all vehicles in the train. In the driving cab the pipe 1 is also connected to a valve controlled mechanically by a driver's brake controller 2. The train's brakes are controlled by the driver moving the handle 3 of the controller 2 to an appropriate brake demand position which generates a brake controlling signal in one of two ways. In the system being described the brakes are normally controlled by means of an electrical signal carried by a train wire 4, the signal on this wire is provided by a train wire signal generator 5 which is connected with the controller 2 by an electrical connection 6. The second way of controlling the brakes is via a brake pipe 7.The fluid pressure in brake pipe 7 may be varied by a valve in controller 2, which is also operated by the handle 3 to vent pressure in the brake pipe 7 to bring about a brake application or to recharge the pipe to release the brakes. The controller 2 is interconnected with a brake pipe unit 8 and an emergency reservoir 9.

The construction and operation of train wire signal generators and brake pipe units such as those at 5 and 8 are well known in the art and will not be further described here as they are merely incidental to the invention.

The pneumatically operated friction brake system about to be described may form part of an overall braking system including a dynamic brake, the dynamic brake control unit is generally indicated at 10. This also forms no part of the invention and will not be further described. Suffice to say that it provides a signal on line 11 which has the effect of "backing-off" pneumatic brake effort according to the amount of braking effort contributed by the dynamic brake.

As previously mentioned the brake system may be controlled by electric signals carried by train wire 4 or pneumatically by pressure variations in the brake pipe 7. Normally the brake system is controlled electrically by signals on the train wire 4, which is also connected with the dynamic brake control unit 10.

A branch of the train wire 4 is connected to a brake control electronic block 12 which decodes the signal and controls operation of a digital electro-pneumatic brake unit 14. The unit 14 receives working fluid under pressure at an inlet 16 connected with a first auxiliary reservoir 18, and a load weighted pneumatic signal at input port 20 from a pneumatic load signal line 22. The unit 14 provides a variable pressure pneumatic output at port 24 which is connected to the brake actuating cylinders (not shown) through a double check valve 26 and a safety brake unit 28, which is to be further described below with reference to Fig 2.

For operation in the alternative pneumatic control mode the brake pipe 7 is connected to the inlet 30 of a pneumatic brake unit 32 which also receives working fluid under pressure at a further input 34 connected with the first auxiliary reservoir 18. The output of pneumatic brake unit 32 at port 36 is connected to the pilot pressure input 38 of a variable load valve 40.

Load valve 40 is also connected to receive pressure from the load weighted signal pipe 22, and to receive working fluid from the auxiliary reservoir 18 at ports 42 and 44 respectively. Load weighed pneumatic pressure for the brake actuating cylinders is produced by load valve 40 at output 46 which is connected through the double check valve 26 and the safety brake unit 28 to the brake actuating cylinders.

Thus, whether the vehicle brake system is originally controlled electrically or pneumatically brake cylinder actuating pressure is supplied through the double check valve 26 and safety brake unit 28.

The construction and operation of the latter will now be described with reference to Fig 2.

The safety brake unit 28 comprises a plurality of valves interconnected by passage-ways and ducts formed in a pipe bracket or manifold member 48. The bracket 48 is formed with a plurality of internal passage-ways and a number of external communication ports A-E which are connected- as follows: inlet port A is connected to the double check valve 26 to receive brake actuating pressure, the brake cylinders are connected to receive brake actuating pressure from an outlet port B, a further inlet port C is connected with a second auxiliary reservoir 50, a fourth inlet port D is connected with the load weighed signal pipe 22, and the brake pipe 7 is connected to provide an input to a fifth port E.

The inlet port A is normally connected with the outlet port B through a spool valve 52 in order to supply brake actuating pneumatic pressure directly to the brake cylinders. The spool valve 52 comprises a valve body 54 having a valve chamber 56 which houses an axially movable spool valve member 58. The chamber 56 has an inlet port 60 towards the right in the drawing connected with the inlet port A, an outlet port 62 leads from a central region of the chamber 56 to the outlet port B. A second inlet port 64 is located towards the left of the chamber 56. The spool valve member 58 is coupled with a pressure differential diaphragm operating means 66 so as to be positioned in the chamber 56 according to the pressure difference across its diaphragm. A bias spring 68 urges the member 58 towards the diaphragm.

One side of the diaphragm of the valve operating means 66 is vented to atmosphere and the opposite side is connected via a communication 70 with the chamber 72 of a safety valve 74. The chamber 72 is connected with the brake pipe inlet port E. The safety valve 74 also houses an electrically operable magnet valve 76 which when energised closes off an exhaust port 78 through which the chamber 72 of the safety valve may be vented to atmosphere.

The safety brake unit of Fig 2 is called upon to connect pressure from the second auxiliary reservoir 50 with the brake cylinder outlet B, in the event of a emergency, to bring about an emergency application of the brakes. The inlet port C provides this emergency brake actuating pressure through an emergency relay valve 80, operation of which is piloted by a pilot pressure provided by a load shut off valve 82 in response to the load weighted pressure signal appearing at inlet-port D.

The emergency relay valve 80 comprises a valve assembly 84 which is biased to close off a communication between an inlet port 86, connected with the inlet port C, and an outlet port 88 which supplies the emergency fluid pressure path through pipe bracket 48. The valve 84 is operated by a pressure differential responsive diaphragm operating means 90 which is exposed on one side to a pilot pressure supplied via port 92 which is connected through the pipe bracket 48 with a pilot pressure output 94 in the load cut-off valve 82.

The inlet port C is also connected with a pressure inlet port 96 in the valve 82, and this inlet port is connected with the pilot output port 94 through a variable valve 98 operated by pressure differential valve operating means 100 responsive to the load weighed signal appearing at inlet port D.

The outlet port 88 of relay valve 80 communicates with a passageway 102 in the bracket 48. This passageway 102 branches and one branch leads via a one-way check valve 104, mounted on the outside of bracket 48, to the second inlet port 64 of the spool valve 52. The second branch of passageway 102 leads to a second spool valve 106. The second spool valve 106 is virtually identical with the first spool valve 42 except that it utilises only one input to the spool valve chamber.

The second branch from passageway 102 carrying emergency actuating pressure from the relay valve 80 is connected to a pressure chamber on one side of pressure differential valve operating means 108 coupled with the valve member 100 of the second spool valve. The service brake pressure port A is connected with an input port 112 towards the left of the spool valve chamber, and the outlet 114 towards the centre of the valve- chamber is connected with a passageway 116 in the pipe bracket 48 which leads into a duct feeding the brake cylinder output port B. The spool valve 110 is biased by spring 118 which pressure in the pressurised chamber of the valve operating means 108 must overcome to close off a communication through the chamber between the inlet 112 and the outlet 114.

Operation of the safety brake unit of Fig 2 is as follows. During normal service brake operation the brake pipe 7 is pressurised and a relatively high, although variable pressure, if pneumatic control is being utilised, appears at inlet port E. This exerts a pressure on the valve operating means 66 of the first spool valve 52 biasing the member 58 towards the right against the pressure of spring 68. This closes off inlet port 64 and opens communication between inlet port 60 and the outlet 62. This allows service brake actuating pressure at inlet port A to pass through the valve chamber of spool valve 2 to the outlet duct E.

The second auxiliary reservoir 50 is charged to maximum pressure and this appears at inlet port C, but the valve 84 is closed and the relay valve outlet 88 is vented to atmosphere. Therefore, there is no operating pressure in duct 102 and the check valve 104 is closed and no operating pressure is exerted on the valve operating means 108 of the second spool valve 106 other than that provided by spring 118. Because there is no pressure difference between fluid pressure appearing at the inlet 112 and at the outlet 114 of the second spool valve this, at this stage, effectively plays no part in the operation of the safety break unit.

An emergency indication may arise in one of two ways; firstly, the pressure in brake pipe 7 may be subject to a sudden drop by the driver moving the control handle 3 (see Fig 1) to the emergency position which operates brake pipe unit 8 to "dump" pressure from brake pipe 7, secondly, an electrical emergency signal may be generated on the train wire 4 which causes de-energisation of the magnet valve 76 which immediately opens to vent the chamber 72 to atmosphere.

Either way the pressure exerted on the valve operating means 66 of the first spool valve 52 is relatively suddenly removed and the operating diaphragm moves the spool valve member 58 towards the left closing the communication between inlet port 60 and outlet port 62 and establishing an alternative communication from the inlet port 64. This port 64 leads back through the one-way valve 104 to the emergency actuating pressure outlet of relay valve 80. Thus, the emergency pressure output of relay valve 80 is connected through the first spool valve 52 to the brake actuating output B.

Providing the pressure in duct 102 of the emergency output is sufficient to overcome the bias of spring 118 in the second spool valve 106 the bypass path through the second spool valve remains closed.

However, if the pressure in duct 102 is too low the bypass path will be opened. During an emergency brake application the low pressure prevailing in the brake pipe 7 causes the pneumatic brake unit 32 to generate a full service brake pressure output. If the driver has called for an emergency brake application by moving his brake control handle 3 he will have had to move it through the full service brake application demand point causing the train wire 4 to carry a signal also calling for full serv-ice brake application so that the electro pneumatic brake unit 14 will call for a full service brake application. Therefore, during an emergency brake application full service brake pressure is available at inlet port A in the pipe bracket 48.

However, this is normally prevented from reaching the brake cylinder output B due to the first spool valve 52 closing off the communication from inlet port 60 and the second spool valve 106 closing off the bypass loop via its inlet port 112 and outlet port 114.

If, as the result of a leak or failure, emergency output pressure is not available at the output port 88 of the relay valve 80 the pressure acting on the valve operating means 108 at a pressure determined by the force exerted by brake 118 will be too low to maintain the spool valve member 110 in a position which closes off the bypass loop. At that pressure the valve member 110 will move towards the left in Fig 2 and open the bypass loop allowing service brake pressure from inlet A to pass through the second spool valve into the communication 116 leading to the brake cylinder outlet B.

To sumnarise, during nor,fiai service brake applications service brake pressure is conducted between ports A and B through the first spool valve 52.

In the event of an emergency brake application the spool valve 52 is moved to a second postion to supply emergency brake actuating pressure to the outlet B and to close off the service brake pressure inlet A.

Providing full emergency pressure is available from the relay valve 80 the second spool valve 106 remains in a cut-off position. However, if the emergency brake pressure falls below a predetermined threshold level set by spring 118 the second spool valve is moved to a second positon to open a bypass loop connecting the service brake inlet A with the outlet B, thus providing a supplementary source of pressure to actuate the brake cylinders. As a result the brakes controlled from the safety brake unit are able to contribute a substantial level of braking effort in an emergency even though the normal emergency brake actuating control means may have failed either completely or to provide a sufficient of output pressure.

Claims (12)

1. An emergency brake control arrangement for a

pneumatically operated vehicle brake system comprising selector valve means for supplying to an outlet communicating with a vehicle brake actuator cylinder fluid at pressure from a first source or from a second source in response to an emergency indication, and by-pass means for connecting the first source to the outlet in the event that the fluid pressure of the second source is lower than a predetermined threshold value.

2. An emergency brake control arrangement as claimed in Claim 1 wherein the first source provides service brake fluid pressure and the second source provides emergency brake fluid pressure.

3. An emergency brake control arrangement as claimed in either Claim l-or claim 2 wherein the selector valve comprises a valve having a first inlet connected to the source of service brake fluid pressure, a second inlet connected to an emergency fluid pressure reservoir and means for alternatively connecting the first or second inlet to the outlet according to the presence or absence of an emergency indication and the by-pass means comprises a second valve in parallel with the selector valve, said second valve having an inlet connected to the source of service brake fluid pressure according to the level of emergency reservoir fluid pressure.

4. An emergency brake control arrangement as claimed in Claim 3 wherein the second valve comprises a spool valve operation of which is controlled by a pressure differential responsive valve operating means.

5. An emergency brake control arrangement as claimed in Claim 4 wherein the valve operating means comprises a diaphragm coupled to operate the spool valve and exposed on one side to the emergency fluid pressure source in a sense to close the by-pass path when the emergency fluid pressure exceeds a predetermined level.

6. An emergency brake control arrangement as claimed in Claim 5 wherein the said predetermined level is determined by the pressure exerted by a bias spring.

7. An emergency brake control arrangement as claimed -in any preceeding claim wherein a communication between the selector valve and the second source of fluid pressure includes check valve means operative to prevent reverse flow of fluid from the selector valve outlet towards the emergency source.

8. An emergency brake control arrangement as claimed in any one of Claims 3 to 7 wherein the selector valve and the second valve in the by-pass path are of substantially indentical constructions excepting that the selector valve has a second inlet for connection with the outlet alternatively with the first inlet according to operation of the valve.

9. An emergency brake control arrangement as claimed in any preceeding claim wherein the emergency indication is provided by a reduction in fluid pressure in a control brake pipe by means of operation of a mechanical valve to vent the pipe or by re-energisation of a magnet valve by an electrical signal.

10. An emergency brake control arrangement as claimed in any preceeding claim wherein the second source of fluid pressure comprises a reservoir of fluid which is controlled by a pilot pressure.

11. An emergency brake control arrangement as claimed in Claim 10 wherein the said pilot pressure is governed by a load responsive valve in accordance with the total weight of the vehicle.

12. An emergency brake control arrangement substantially as hereinfore described with reference to the accompanying drawings.