GB1572439A

GB1572439A - Trailer braking systems

Info

Publication number: GB1572439A
Application number: GB2007276A
Authority: GB
Original assignee: Clayton Dewandre Co Ltd
Current assignee: Wabco Automotive UK Ltd
Priority date: 1976-05-14
Filing date: 1976-05-14
Publication date: 1980-07-30
Also published as: DE2720632C2; DE2720632A1; FR2392854A1; FR2392854B1

Description

(54) IMPROVEMENTS RELATING TO TRAILER BRAKING SYSTEMS (71) We, CLAYTON DEWANDRE COMPANY LIMITED, a British Com- pany, of 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 trailer braking systems of the kind incorporating springapplied fluid pressure-released brake actuators, and has for its object the provision of an improved system of this kind.

According to the invention the improved trailer braking system comprises a trailermounted reservoir adapted to be charged through a supply line from a towing vehicle, a trailer valve responsive to the pressure in said supply line and operative while a predetermined pressure is maintained in said line to connect the reservoir to the fluid pressure chambers of the actuators to hold the actuators in the inoperative condition, and on loss of pressure in said supply line to connect said fluid pressure chambers to exhaust to effect application of the brakes, a manually-actuated "Park" control valve operable to actuate said trailer valve to effect application of the brakes, a "Manoeuvre" control valve operable to connect the trailer valve to the reservoir after disconnection of the trailer from the towing vehicle to to actuate the trailer valve to conduct fluid pressure to the fluid pressure chamber of the actuators and effect release of the brakes, and means preventing actuation of said Manoeuvre control valve when the Park control valve is in the operative position to effect application of the brakes.

An important advantage of the improved system is that it does not necessitate any modification of the braking system on the towing vehicle other than the provision of a supply of pressure fluid from that vehicle if not already provided, but the invention does have particular but not exclusive aPPlication to trailers adapted to be used with towing vehicles having the conventional two-line braking connections, namely, an Emergency or trailer supply line which conducts pressure fluid from the towing vehicle to a reservoir on the trailer via a non-return valve immediately ahead of the reservoir, and a Service line which when the service brakes on the towing vehicle are actuated simultaneously delivers a control signal to a relay valve on the trailer and by which reservoir pressure is conducted to the trailer service brakes to actuate them, and such an embodiment of the invention will now be described in more detail and with reference to the accompanying drawings, wherein: Fig. 1 is a diagrammatic layout of the system; Fig. 2 is a cross sectional view of the trailer valve; Fig. 3 is a cross sectional view of the Park control valve; and Fig. 4 is a cross sectional view of the Manoeuvre control valve.

Referring first to Fig. 1 which shows the invention applied to a single axle semitrailer compressed air braking system, said system is of the conventional two-line type, that is, it comprises an Emergency or supply line 1 which is always pressurised and conducts air from the towing vehicle to a trailer-mounted reservoir 2 via a non-return valve 3, and a Service line 4 which is a control or trigger line and, when the towing vehicle service brakes are actuated, conducts pressure simultaneously to a relay valve 5 which relays air from the reservoir 2 and via line 6 to the service diaphragm chambers 7 of the brake actuators.

A line connection 8 is taken from the Emergency line 1 ahead of the reservoir and branched, one branch 9 leading via a double check valve 10 to a trailer valve 11 and the other branch 12 via a further double check valve 13 to an air lock chamber in a Manoeuvre control valve 14. There is also provided a two-way manually-operable Park control valve 15, said three valves 11, 14, 15 each having an inlet port connected to the reservoir by lines 16, 17, 18 respectively.

The trailer valve includes an outlet port connected by line 19 to the air chambers 20 of the spring brake actuators and a control port connected by line 21 to an outlet port of the Park control valve 15, the latter port also having a connection via line 22, the double check valve 13 and a further line 22a to a control port of the Manoeuvre control valve 14.

The above-mentioned valves will now be described in more detail.

Referring particularly to Fig. 2, trailer valve 11 is basically a relay valve in that it comprises an upper relay piston 23 responsive to Emergency line pressure delivered via the branch line 9, double check valve 10 and a line 24 and which transmits an effort through a captive spring 25 to a lower reaction piston 26, the latter piston having a stem 27 which, when the piston is depressed, first engages a spring-loaded tappet valve element 28 to close off an exhaust passage 29 therein and then displaces the tappet valve element from its seating 30 to establish a communication between the inlet port 31 and the outlet port 32.

As the air pressure builds up in line 19 and air chambers 20 of the spring brake actuators the lower reaction piston effort gradually increases to balance the graduated spring load and in doing so the upward movement of the piston allows the valve element to assume a lapped position at a predetermined delivery pressure. This pressure holds the springs in the spring brakes units in the compressed position thus fully releasing the parking brakes.

The control port 33 of the trailer valve leads into an annular chamber or cylinder in which a control annulus integral with the lower reaction piston is operably situated.

When pressure is directed to this annulus (for example during parking action when the trailer is coupled to the tractor) the area is large enough to produce an effort which will overbalance the graduated spring effort allowing tappet valve element 28 to close and the exhaust valve element to unseat thus venting line 19, which vents the air chambers to atmosphere allowing the springs to apply the brakes.

The Park control valve 15 is a hand lever-actuated two-way valve and as shown in Fig. 3 comprises a hollow lever-actuated valve-operated plunger 35 which in the "Park" position of the lever 36 indicated in broken lines holds a spring-loaded disc valve member 37 off its seating 38 to interconnect the inlet port 39 and the outlet port 40 and in the "Off" position of the lever as shown allows the disc valve member to close on to its seating and seal off the inlet port whilst connecting the outlet port to exhaust via the bore of the plunger and a cross passage 41.

The Manoeuvre control valve 14 shown in Figure 4 comprises a finger-operated button 42 which when actuated depresses a piston 43 having a stem 44 operable to move a spring-loaded disc valve member 45 off its seating 46 to connect an inlet port 47 to an outlet port 48 which has a line connection 49 via the double check valve 10 with a chamber 50 in the trailer valve above the relay piston 23. The Maneouvre control valve is used to release the spring brakes after disconnection of the trailer from the towing vehicle and to avoid the necessity of keeping a finger on the control button when maneouvring the trailer, the valve incorporates an automatic hold-on feature.For this purpose a passage 51 is provided in the valve body connecting the outlet port 48 to a chamber 52 above the piston 43, the arrangement being such that as soon as reservoir pressure is established in the outlet port 48 by depression of the button, said pressure is transmitted to an upper surface of the piston/stem structure to hold it in the depressed position. The control port 53 of the Manoeuvre control valve leads into an air lock chamber 54 beneath the piston 43 so that when the Park control valve is set to a "Park" position and reservoir pressure is established in said air lock chamber, the piston/stem structure is lifted to and held in the "off" or inoperative position. It therefore requires the Park control valve lever to be moved to the "off" position before the brakes can be released by depressing the manoeuvre valve button.

The system operates in the following manner: For normal parking with the trailer remaining connected to the towing vehicle, the driver applies the brakes to the towing vehicle, then dismounts and moves the Park control valve lever to the "Park" position.

Reservoir air is thus conducted via line 21 to the underside of the reaction piston 26 in the trailer valve, the reaction area being greater than the relay piston area so that the piston assembly 23, 26 rises and the air chambers of the spring brake actuators are vented to apply the brakes. It will be noted that the air interlock prevents actuation of the Manoeuvre control valve in this condition. Return of the Park control valve to "Off" position vents the chamber 34 beneath the trailer valve reaction piston and the valve is set to re-admit reservoir air to the spring brake actuators to release the brakes.

To de-couple and manoeuvre the trailer, the brakes are applied on the towing vehi cle, the Park control valve is set to "Park" and the trailer then uncoupled. Although this action cuts the Emergency line connection to the air lock chamber 54 of the Manoeuvre control valve this chamber remains pressurised by reservoir pressure via the Park control valve and lines 22, 22a so that the Manoeuvre control valve cannot be actuated. Only when the Park control valve lever is set to "Off" can the Manoeuvre control valve button be depressed to pass reservoir air via lines 49, 24 to the relay chamber 34 of the trailer valve to set the latter to release the brakes, the Manoeuvre control valve remaining automatically locked on and permitting manoeuvring of the trailer without constant manual effort on the control button.

The brakes are re-applied and the Maneouvre control valve automatically moved to the 'Off" position by resetting the Park control valve lever to "Park". It is to be noted that only the action of moving the said lever to "Park" can reset the Manoeuvre control valve to the "Off" position, since the button will be held in the "On" position by the air lock-on thus preventing manual actuation.

The action of recoupling the trailer should not, for reasons of safety, automatically cancel the parking brake, but recoupling will normally be effected with the Park control valve in the "Park" position and only on setting this valve to the "Off" position will the trailer valve release the brakes. Recoupling to the Emergency line pressurises the air lock chamber 54 of the Manoeuvre control valve so ensuring that this valve is at the rest or "Off" position and cannot in any way prevent automatic braking in the event of trailer breakaway which action would result in loss of pressure above the trailer valve relay piston and consequential setting of the valve to vent the spring brake air chambers and so apply the brakes.

Thus it will be seen that with the incorporation of the features of the embodiment as described there is provided a trailer braking system embodying spring-applied fluid pressure-released brake actuators which not only satisfies the requirements of automatic application of the trailer brakes on breakaway of the trailer from the towing vehicle, or upon rupture of the pressure fluid supply line to the trailer braking system, but also ensures safety in the operation of coupling and uncoupling the trailer and towing vehicle.

WHAT WE CLAIM IS: 1. A trailer braking system of the kind referred to comprising a trailer-mounted reservoir adapted to be charged through a supply line from a towing vehicle, a trailer valve responsive to the pressure in said supply line and operative while a predetermined pressure is maintained in said line to connect the reservoir to the fluid pressure chambers of the actuators to hold the actuators in the inoperative condition, and on loss of pressure in said supply line to connect said fluid pressure chambers to exhaust to effect application of the brakes, a manually-actuated "Park" control valve operable to actuate said trailer valve to effect application of the brakes, a "Manoeuvre" control valve operable to connect the trailer valve to the reservoir after disconnection of the trailer from the towing vehicle to to actuate the trailer valve to conduct fluid pressure to the fluid pressure chamber of the actuators and effect release of the brakes, and means preventing actuation of said Manoeuvre control valve when the Park control valve is in the operative position to effect application of the brakes.

2. A trailer braking system as claimed in Claim 1, wherein the trailer valve includes a relay piston which is responsive to supply line pressure and which transmits an effort through a captive spring to a reaction piston, the Park control valve being operable to conduct fluid under reservoir pressure to an area of the reaction piston larger than the area of the relay piston responsive to supply line pressure thereby to move the reaction piston - relay piston assembly against the supply line pressure to vent the fluid pressure chamber of the actuators.

3. A trailer braking system as claimed in Claim 1 or 2, wherein the Manoeuvre control valve includes a manually-operable piston which when depressed actuates a valve for conducting air under reservoir pressure to a relay piston chamber of the trailer valve, the Park control valve when in its operative position admitting fluid under reservoir pressure to a line leading to a fluid lock chamber beneath the manuallyoperable piston of the Manoeuvre control valve thereby to urge said piston to and hold it in its inoperative position.

4. A trailer braking system as claimed in Claim 3, wherein the body of the Manoeuvre control valve includes a passage whereby when fluid under reservoir pressure is being directed to the trailer valve such fluid is also conducted to the upper side of said manually-operable piston to hold it in the depressed position.

5. A trailer braking system constructed and adapted to operate substantially as herein described with reference to the accompanying drawings.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. cle, the Park control valve is set to "Park" and the trailer then uncoupled. Although this action cuts the Emergency line connection to the air lock chamber 54 of the Manoeuvre control valve this chamber remains pressurised by reservoir pressure via the Park control valve and lines 22, 22a so that the Manoeuvre control valve cannot be actuated. Only when the Park control valve lever is set to "Off" can the Manoeuvre control valve button be depressed to pass reservoir air via lines 49, 24 to the relay chamber 34 of the trailer valve to set the latter to release the brakes, the Manoeuvre control valve remaining automatically locked on and permitting manoeuvring of the trailer without constant manual effort on the control button. The brakes are re-applied and the Maneouvre control valve automatically moved to the 'Off" position by resetting the Park control valve lever to "Park". It is to be noted that only the action of moving the said lever to "Park" can reset the Manoeuvre control valve to the "Off" position, since the button will be held in the "On" position by the air lock-on thus preventing manual actuation. The action of recoupling the trailer should not, for reasons of safety, automatically cancel the parking brake, but recoupling will normally be effected with the Park control valve in the "Park" position and only on setting this valve to the "Off" position will the trailer valve release the brakes. Recoupling to the Emergency line pressurises the air lock chamber 54 of the Manoeuvre control valve so ensuring that this valve is at the rest or "Off" position and cannot in any way prevent automatic braking in the event of trailer breakaway which action would result in loss of pressure above the trailer valve relay piston and consequential setting of the valve to vent the spring brake air chambers and so apply the brakes. Thus it will be seen that with the incorporation of the features of the embodiment as described there is provided a trailer braking system embodying spring-applied fluid pressure-released brake actuators which not only satisfies the requirements of automatic application of the trailer brakes on breakaway of the trailer from the towing vehicle, or upon rupture of the pressure fluid supply line to the trailer braking system, but also ensures safety in the operation of coupling and uncoupling the trailer and towing vehicle. WHAT WE CLAIM IS:

1. A trailer braking system of the kind referred to comprising a trailer-mounted reservoir adapted to be charged through a supply line from a towing vehicle, a trailer valve responsive to the pressure in said supply line and operative while a predetermined pressure is maintained in said line to connect the reservoir to the fluid pressure chambers of the actuators to hold the actuators in the inoperative condition, and on loss of pressure in said supply line to connect said fluid pressure chambers to exhaust to effect application of the brakes, a manually-actuated "Park" control valve operable to actuate said trailer valve to effect application of the brakes, a "Manoeuvre" control valve operable to connect the trailer valve to the reservoir after disconnection of the trailer from the towing vehicle to to actuate the trailer valve to conduct fluid pressure to the fluid pressure chamber of the actuators and effect release of the brakes, and means preventing actuation of said Manoeuvre control valve when the Park control valve is in the operative position to effect application of the brakes.