GB1561647A - Trailer braking systems - Google Patents

Description

(54) IMPROVEMENTS RELATING TO TRAILER BRAKING SYSTEMS (71) We, CLAYTON DEWANDRE COMPANY LIMITED, a British Company, of P O BOX No. 9, Titanic Works, Lincoln, LN5 7JL; 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 air braking systems for trailers and particularly to twoline trailer braking systems, of the kind which comprise between a tractor and a trailer an Emergency line, providing a constant air supply from the tractor vehicle through a relay emergency valve on the trailer to a trailer-mounted reservoir, and a Service line which, when activated by a hand or foot valve on the tractor, actuates the relay emergency valve to direct air pressure from the trailer reservoir to the trailer brakes, the relay emergency valve also initiating application of the trailer brakes in the event of a trailer breakaway or other disconnection.

The object of the present invention is to improve a system of the above character by the provision of secondary braking on the trailer operable from the service brake control in the event of a failure of the trailer service braking system.

According to the invention the trailer brake actuators are of the dual or triple diaphragm type, one diaphragm of each actuator being responsive in the normal manner to trailer service braking pressure delivered by the relay emergency valve, whilst another or secondary diaphragm is rendered responsive to Service line pressure by a trailer secondary brake valve in the event of a failure in the trailer service line downstream of the relay emergency valve.

Reference will now be made to the accompanying drawings which illustrate by way of example one embodiment of the invention and wherein Figure 1 shows diagrammatically the improved trailer braking system and Figure 2 is an axial section through the trailer residual brake valve.

Referring first to Figure 1 it will be seen that the improved trailer braking system comprises basically a conventional two-pipe line system, the Emergency line E and coupling 1 providing a constant air supply through a relay emergency valve 2 of known construction to the trailer reservoir 3 whilst the Service line S and coupling 4 provide a control pressure created by a hand or foot valve on the tractor for actuating the relay valve 2 to conduct air pressure from the trailer reservoir to the brake actuators 5.For the purpose of the invention, brake actuators of the dual diaphragm type are used, that is, actuators comprising service and secondary chambers for actuating respectively service diaphragms 6 and secondary diaphragms 7 which have a common non-compounding output 8 to the brakes or brake linkages, the trailer service line S1 from the relay emergency valve being connected to the service chambers of the actuators. The Service line is branched upstream of the relay emergency valve, the branch line Sll leading to a secondary brake valve 9.This valve is shown in detail in Figure 2 and comprises a housing 10 defining in its lower part an inlet port 11, for connection to the Service line Sll, and an outlet port 12 for connection by lines 13 to the secondary chambers of the brake actuators, a hollow spring-loaded tappet valve 14 coacting with a fixed seating 15 to control air flow between the ports 11 and 12 and the bore 16 of the tappet valve constituting an exhaust passage opening at its lower end to atmosphere past a check valve 17. The upper part of the housing defines a chamber in which is mounted a stepped differential piston 18 having a downwardly-directed stem 19 which, when the piston is depressed, engages the tappet valve 14 and moves it off its seating 15.

A transfer passage 20 leads from the inlet port 11 to the space 21 above the piston and conducts Service line pressure to the upper smaller area of the piston whilst a further port 22 in the housing is connected by line 23 to the trailer service line S1 between the relay emergency valve and the service chambers of the brake actuators and conducts the pressure in said line to the lower larger area of the piston 18. The piston 18 is also loaded by spring 24 towards its lowered position and the valve operates in the following manner: In the "brakes off" condition the differ ential piston 18 is held by its loading spring 24 in the lowered position in which the tappet valve 14 is held open and the exhaust passage 16 therein is closed off by the piston stem 19.

When service braking is effected, air pressure will be conducted to the relay emergency valve to effect application of trailer service brakes in the usual manner and will also be conducted via the inlet port 11 and transfer passage 20 of the residual brake valve to the space 21 above the differential piston 18. The air pressure conducted via the relay emerg- ency valve to the trailer service line S1 is also conducted via line 23 and port 22 to the space beneath the differential piston 18 thereby lifting the piston against the action of spring 24 and allowing the tappet valve 14 to close on to its seating.Thus, air pressure will only build up in the service diaphragm chambers and any initial air directed to the secondary diaphragm chambers will be exhausted, thereby ensuring that the components move under every braking application, a desirable safety feature on braking systems.

Should a service diaphragm fail or any other failure occur between the relay emergency valve 2 and the brake actuators 5, for example, a reservoir connection failure, then effective secondary braking effort is available under the driver's control as follows: Control pressure from the Service line will as previously stated be directed on brake application to the inlet port 11 of the secondary brake valve 9 and by the transfer passage 20 to the top of the differential piston 18. This pressure will effectively hold the tappet valve 14 in the open position, allowing continuous supply of air through the valve to the secondary chambers of the actuators 5, there being no pressure build up beneath the piston 18 to oppose such valve movement.

Thus, successive braking applications can be made directly from the Service line through the open secondary brake valve.

The two differing diameter portions of the piston 18 are each provided with a ring seal 18a, 18b respectively, a peripheral groove 25 between the two seals being vented to atmosphere via an axial passage 26 in the piston communicating with the exhaust passage 16 in the tappet valve.

In the preferred arrangement a pressure protection valve 26 is installed in the Emergency line E between its coupling 1 and the relay emergency valve 2, the valve 26 including a valve element responsive to Emergency line pressure and allowing pressure build up from the tractor supply to the trailer reservoir during normal running, but being set to dose at a pressure of, for example, 60 p.s.i.

which is below the normal setting of a low pressure warning switch incorporated in the system. This pressure protection valve achieves two desirable results, namely: (a) it provides a warning to the driver that a failure has occurred; and (b) it retains sufficient pressure in the tractor system effectively to supply the trailer brake actuators as above des cribed.

A non return valve 27 is inserted in a bypass around the pressure protection valve 26 to allow normal actuation of the emergency breakaway system, that is, it allows the Emergency line to exhaust to atmosphere thus atomatically applying the trailer brakes via the relay emergency valve 2. In addition, a failure in the Service line is automatically safe-guarded by the present system when the Emergency line is allowed to exhaust through the failed Service line via a conventional dump valve.

Although reference is made to the use of dual diaphragm actuators it will be understood that such actuators may be substituted by any equivalent dual brake actuator means, and the phrase "dual diaphragm actuators" is to be read as embracing such equivalent means.

WHAT WE CLAIM IS: 1. A two-line air braking system of the kind herein defined wherein the trailer brake actuators are of the dual or triple diaphragm type, one diaphragm of each actuator being responsive in the normal manner to trailer service braking pressure delivered by the relay emergency valve, whilst another or secondary diaphragm is rendered responsive to Service line pressure by a trailer secondary brake valve in the event of a failure in the trailer service line downstream of the relay emergency valve.

2. A braking system as claimed in Claim 1, wherein said secondary brake valve is interposed in a line between the Service line upstream of the relay emergency valve and the secondary diaphragms of the brake actuators, flow of air through the secondary brake valve being controlled by a valve element which is actuated by means responsive to pressure in the trailer service line.

3. A braking system as claimed in Claim 2, wherein the valve element actuating means comprises a differential piston responsive on one side to direct Service line pressure and on the other side to said trailer service line pressure and operable, in the event of loss of pressure in the trailer service line, to move said valve element off its seating to connect the Service line to the secondary diaphragms of the brake actuators.

4. A braking system as claimed in any of Claims 1-3, including a pressure protection valve in the Emergency line upstream of the relay emergency valve.

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

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. ential piston 18 is held by its loading spring 24 in the lowered position in which the tappet valve 14 is held open and the exhaust passage 16 therein is closed off by the piston stem 19. When service braking is effected, air pressure will be conducted to the relay emergency valve to effect application of trailer service brakes in the usual manner and will also be conducted via the inlet port 11 and transfer passage 20 of the residual brake valve to the space 21 above the differential piston 18. The air pressure conducted via the relay emerg- ency valve to the trailer service line S1 is also conducted via line 23 and port 22 to the space beneath the differential piston 18 thereby lifting the piston against the action of spring 24 and allowing the tappet valve 14 to close on to its seating.Thus, air pressure will only build up in the service diaphragm chambers and any initial air directed to the secondary diaphragm chambers will be exhausted, thereby ensuring that the components move under every braking application, a desirable safety feature on braking systems. Should a service diaphragm fail or any other failure occur between the relay emergency valve 2 and the brake actuators 5, for example, a reservoir connection failure, then effective secondary braking effort is available under the driver's control as follows: Control pressure from the Service line will as previously stated be directed on brake application to the inlet port 11 of the secondary brake valve 9 and by the transfer passage 20 to the top of the differential piston 18. This pressure will effectively hold the tappet valve 14 in the open position, allowing continuous supply of air through the valve to the secondary chambers of the actuators 5, there being no pressure build up beneath the piston 18 to oppose such valve movement. Thus, successive braking applications can be made directly from the Service line through the open secondary brake valve. The two differing diameter portions of the piston 18 are each provided with a ring seal 18a, 18b respectively, a peripheral groove 25 between the two seals being vented to atmosphere via an axial passage 26 in the piston communicating with the exhaust passage 16 in the tappet valve. In the preferred arrangement a pressure protection valve 26 is installed in the Emergency line E between its coupling 1 and the relay emergency valve 2, the valve 26 including a valve element responsive to Emergency line pressure and allowing pressure build up from the tractor supply to the trailer reservoir during normal running, but being set to dose at a pressure of, for example, 60 p.s.i. which is below the normal setting of a low pressure warning switch incorporated in the system. This pressure protection valve achieves two desirable results, namely: (a) it provides a warning to the driver that a failure has occurred; and (b) it retains sufficient pressure in the tractor system effectively to supply the trailer brake actuators as above des cribed. A non return valve 27 is inserted in a bypass around the pressure protection valve 26 to allow normal actuation of the emergency breakaway system, that is, it allows the Emergency line to exhaust to atmosphere thus atomatically applying the trailer brakes via the relay emergency valve 2. In addition, a failure in the Service line is automatically safe-guarded by the present system when the Emergency line is allowed to exhaust through the failed Service line via a conventional dump valve. Although reference is made to the use of dual diaphragm actuators it will be understood that such actuators may be substituted by any equivalent dual brake actuator means, and the phrase "dual diaphragm actuators" is to be read as embracing such equivalent means. WHAT WE CLAIM IS:

1. A two-line air braking system of the kind herein defined wherein the trailer brake actuators are of the dual or triple diaphragm type, one diaphragm of each actuator being responsive in the normal manner to trailer service braking pressure delivered by the relay emergency valve, whilst another or secondary diaphragm is rendered responsive to Service line pressure by a trailer secondary brake valve in the event of a failure in the trailer service line downstream of the relay emergency valve.

2. A braking system as claimed in Claim 1, wherein said secondary brake valve is interposed in a line between the Service line upstream of the relay emergency valve and the secondary diaphragms of the brake actuators, flow of air through the secondary brake valve being controlled by a valve element which is actuated by means responsive to pressure in the trailer service line.

3. A braking system as claimed in Claim 2, wherein the valve element actuating means comprises a differential piston responsive on one side to direct Service line pressure and on the other side to said trailer service line pressure and operable, in the event of loss of pressure in the trailer service line, to move said valve element off its seating to connect the Service line to the secondary diaphragms of the brake actuators.

4. A braking system as claimed in any of Claims 1-3, including a pressure protection valve in the Emergency line upstream of the relay emergency valve.

5. A braking system as claimed in Claim

4, including a non-return in a by-pass around the pressure protection valve.

6. A two-line trailer air braking system substantially as herein described with reference to the accompanying drawings.