GB2399608A

GB2399608A - System for controlling the air brakes of a towed vehicle

Info

Publication number: GB2399608A
Application number: GB0305951A
Authority: GB
Inventors: Terence William Bland
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-03-15
Filing date: 2003-03-15
Publication date: 2004-09-22
Anticipated expiration: 2023-03-15
Also published as: GB0305951D0; GB2399608B

Abstract

A system for controlling the air brakes of a towed vehicle from the braking system of a towing vehicle, where both vehicles are of the type having spring-actuated air release parking brakes and pressure-actuated operating brakes, and the towing vehicle includes a compressed air reservoir 4 for supplying the parking brakes thereof. The system comprises supply means for selectively supplying compressed air from the reservoir 4 to parking brakes of the towed vehicle to effect release thereof, and connecting means for connecting the air supply for the operating brakes of the towing vehicle to the operating brakes of the towed vehicle whereby the brakes may be operated together, and is characterised in that the supply means comprise valve means 9 which can be operated to supply compressed air to release the towed vehicle parking brakes only when the towing vehicle parking brakes are released. Preferably the towed vehicle is a non-articulated truck, eg. a dump truck.

Description

SYSTEM FOR CONTROLLING THE AIR BRAKES OF A TOWED VEHICLE

Field of the Invention

This invention relates to a braking system for a breakdown towing vehicle for con- trolling braking of the towed vehicle, particularly a truck or other vehicle provided with air brakes.

Background to the Invention

While trailer vehicles are required to have braking systems operable from the tractor vehicle, rigid (i.e. non-articulated) trucks or lorries provided with air braking sys- tems present a problem when broken down and requiring to be towed, because it is gen erally not possible to operate the brakes from the towing vehicle. Further, the parking brake system, which operates separately from the foot-brake system, typically involves mechanical spring-actuated brakes which, during normal operation of the vehicle, are held disengaged from the brake drums by pneumatic pressure to provide a fail-safe system in which loss of air pressure causes application of the brakes. By contrast, the foot-brake system used for normal braking in operation of the vehicle requires the application of pneumatic pressure to apply the brakes.

However, in the event of a breakdown, it is necessary to apply air pressure to the spring-brake system to release the brakes to permit the vehicle to be towed. In addition, it Is necessary to disconnect the gearbox from the driven wheels for towing, to prevent the gearbox from being driven by the wheels during towing, because the gearbox- lubricating pump, normally driven from the engine, no longer operates, and so damage to the unlubricated gearbox could result. This requires work to be done underneath the broken down vehicle, and since the result of the work leaves the towed vehicle without brakes, there is a considerable risk to the person doing the work, since the towing and towed vehicles are together dependent on the towing vehicle's brakes, because once the spring brakes have been released by application of air pressure, there is no way of re- applying them, other than to disconnect the air supply. This situation also applies during the towing operation, where the combined weight of the vehicles has to be controlled, especially on hills, solely by the towing vehicles own braking system. It is not uncommon for accidents to take place in both such circumstances, sometimes with fatalities occurring.

Specfcabon BLANDJW P11 1 5 GBA 2003-03-1 4 doc - 2

Summary of the Invention

A system for controlling the air brakes of a towed vehicle from the braking system of a towing vehicle, both vehicles being of the type having spring- actuated air release park- ing brakes and pressure-actuated operating brakes, and the towing vehicle including a compressed air reservoir for supplying the parking brakes thereof, the system comprising supply means for selectively supplying compressed air from the reservoir to the parking brakes of the towed vehicle to effect release thereof, and connecting means for connect- ing the air supply for the operating brakes of the towing vehicle to the operating brakes of the towed vehicle whereby the brakes may be operated together, characterized in that the supply means comprise valve means which can be operated to supply compressed air to release the towed vehicle parking brakes only when the towing vehicle parking brakes are released.

Preferably, the valve means comprise a relay valve connected between the reser- voir and the parking brakes of the towed vehicle and operable between a first state, wherein air can flow from the reservoir to the said parking brakes, and a second state, wherein the path from the reservoir is closed and the air in the said parking brakes is vented to atmosphere. The relay valve is preferably caused to operate in the first state thereof by air pressure in a control line connected to the towing vehicle's parking brake pressure line, a manually operable release valve being connected in the control line, said release valve being operable to close off the pressure from the parking brake pressure line and thereby cause the relay valve to move to the second state thereof.

Preferably, the relay valve is connected via a flexible line to the rear parking brakes of the towed vehicle, the front brakes being disconnected from the rear brakes so as to be inoperative. In addition, the operating brake system supply is connected via a second flexible line to the rear operating brakes of the towed vehicle, the front brakes again being disconnected to permit this to happen and to render then inoperative. It is conventional for the towing of large commercial vehicles to be effected by lifting the front wheels off the ground, and thus the permanent application of the front spring brakes, and the absence of any braking control over these wheels, will have no effect on the recovery operation.

Specticatwn BLANDTWP1115 GBA2003-03-14 doc - 3 Typically, the operational braking supply to the rear brakes on the towed vehicle will be connected via an existing load sensing valve connected between the front brakes and the rear brakes. The two ports leading to the front brakes will usually both be dis- connected and then coupled to the service line from the towing vehicle via a tee piece so that there is no risk of leakage from an unconnected port. Similarly, both ports on the spring brake control valve in the towed vehicle will be connected via a tee piece to an ex- tension pipe connected to the said supply means of the towing vehicle. This is preferably done via a special self-sealing coupling mounted on the towing vehicle, separate from the normal service and emergency couplings.

The system of the invention provides a straightforward way of obtaining full brak ing control of a towed broken down vehicle from the cab of the towing vehicle under all conditions, leading to greater operating safety, both on the move and while preparing to tow.

Brief Description of the Drawings

In the drawings, which illustrate diagrammatically exemplary embodiments of the invention: Figure 1 shows the modifications to the parking brake system of the towing vehi- cle; Figure 2 shows the manner of connection to the rear brakes of the towed vehicle; and Figure 3 shows the relationship between typical towed and towing vehicles.

Detailed Description of the illustrated Embodiments Referring first to Figure 1, the towing vehicle is provided in conventional manner with airrelease spring brakes to serve as parking and emergency brakes. The braking system includes a brake control valve 1 having an inlet 2 connected through a non-return valve 3 to a spring brake air reservoir 4. The valve 1 has two outlet lines, one 5 leading to the towing vehicle's spring brakes and the other 6 leading to a connector (not shown) for a flexible hose whereby air can be supplied to a trailer vehicle's emergency braking system.

Spec'ficaton BLAND1WP1115 GBA2003-03-14 doc - 4 The reservoir 4 is provided, in accordance with the invention, with a tapping 7 for a line 8 supplying air to a relay valve 9 via a protection valve 10 whose function is to close the line in the event of a pipe fracture or the like downstream. The relay valve 9 is con- trollable by air pressure on a control line 11 to allow air pressure from the reservoir to be supplied to a self-sealing coupling 12 on the towing vehicle to which a hose 13 can be connected to supply air to the spring brakes of a towed vehicle, as hereinafter described.

The relay valve 9 is configured so that, when no air pressure is on the control line 11, the connection between the reservoir 4 and the coupling 12 is interrupted, and the connec- tion to the coupling is opened to the atmosphere.

The control line 1 1 is connected via a release valve 14 to a tee connection in the brake control line leading from the port 5 on the brake control valve 1 to the towing ve hicle's spring brakes, so that pressure is only present at the release valve when the towing vehicle's spring parking brakes have been released. The release valve 14 is configured so that, when pushed, and only when the towing vehicle's brakes have been released, it ap plies air pressure to the relay valve 9, thereby pressurising the line 13 to release the towed vehicle's spring brakes. When the release valve knob is lifted, the air pressure is released from the control line 11, causing the relay valve to close off the air pressure and to vent the line 13 to atmosphere, thereby applying the emergency or parking brakes of the towed vehicle.

Figure 2 shows the connections to the towed vehicle's rear-wheel braking system.

A first flexible hose 20, conventionally coloured yellow, leads from the towing vehicle's operating or foot-brake system and is therefore supplied with compressed air when the towing vehicle's brakes are applied via the foot-brake control. The towed vehicle's brak ing system conventionally includes a load-sensing valve 21, which is linked to the vehicle's air suspension system to vary the braking force applied to the wheels according to the load which the vehicle is carrying. The load-sensing valve 21 has a pair of ports 22 for connection to the front brakes of the vehicle, and when a breakdown has occurred, it will be necessary for the operator to disconnect these pipes and to replace them with a pair of pipes 23 which in turn connect to the hose 20 via a tee connector 24. Although it might be possible to connect to only one of the ports 22, damage to the brakes at the front of Specfcaton BLANDTWP111 5.GBA2003-0314 doc - 5 the vehicle could cause leakage leading to brake failure, so the double connection ensures that this cannot occur. Application of air pressure to the load-sensing valve 21 distributes air to the brake cylinders 25 on the (in the example illustrated) four rear wheels, applying the brakes. Thus, with this connection made, it is possible for normal braking of the towed vehicle to be synchronised with that of the towing vehicle, giving the driver of the towing vehicle safe control of the two vehicles together.

However, this connection alone would not enable the vehicles to be moved, be- cause air pressure is required to be applied to release the spring brakes of the towed ve- hicle. This is achieved by the air supply on the line 13 from the towing vehicle. The line 13 is connected to two test ports 26 on the towed vehicle's spring brake control valve 27 using two short pipes 28 and a tee-piece adaptor 29. When compressed air is supplied to the spring brake control valve 27 via the line 13 from the towing vehicle, this directs the air to a second valve 30 having a connection 31 to the load-sensing valve 21. The second valve 30 is an anti-compound valve which ensures that both braking systems cannot be actuated at the same time. The air is supplied to each of the spring brake release cylin- ders 32 on the four wheels to release the spring brakes.

In use, the driver of the towing vehicle applies the towing vehicle's parking brakes and then pulls the knob on the release valve 14 (Figure 1) to ensure that the line coupling 12 is not pressurised. He then makes the connections to the towed vehicle's operating braking system and to the spring brake system, as described with reference to Figure 2, and as shown schematically in Figure 3, where the towing vehicle is indicated by reference numeral 33 and the towed vehicle by 34. When ready to tow, the parking brake on the towing or recovery vehicle 33 is released, and the recovery vehicle then takes the strain of the load of the towed vehicle 34. The driver can then press the knob on the release valve 14 to pressurise the line 13, releasing the parking brakes on the towed vehicle. It will be appreciated that, in the event of an emergency as a result of loss of normal brak- ing, the driver of the recovery vehicle can simply lift the knob on the release valve 14 to cause emergency application of the spring brakes on the towed vehicle.

Speaficaton BLANDTWP1115 GBA2003-03-14 doc - 6

Claims

1. A system for controlling the air brakes of a towed vehicle from the brak- ing system of a towing vehicle, both vehicles being of the type having spring-actuated air release parking brakes and pressure-actuated operating brakes, and the towing vehicle including a compressed air reservoir for supplying the parking brakes thereof, the system comprising supply means for selectively supplying compressed air from the reservoir to the parking brakes of the towed vehicle to effect release thereof, and connecting means for connecting the air supply for the operating brakes of the towing vehicle to the operat- ing brakes of the towed vehicle whereby the brakes may be operated together, character ised in that the supply means comprise valve means which can be operated to supply compressed air to release the towed vehicle parking brakes only when the towing vehicle parking brakes are released.

2. A system according to Claim 1, wherein the valve means comprise a relay valve connected between the reservoir and the parking brakes of the towed vehicle and operable between a first state, wherein air can flow from the reservoir to the said parking À À brakes, and a second state, wherein the path from the reservoir is closed and the air in the said parking brakes is vented to atmosphere. À.. À

3. A system according to Claim 2, wherein relay valve is preferably caused to operate in the first state thereof by air pressure in a control line connected to the towing vehicle's parking brake pressure line, a manually operable release valve being connected in the control line, said release valve being operable to close off,the pressure from the parking brake pressure line and.thereby cause the relay valve to move to the second state thereof.

4. A system according to CJaim 2 or 3, wherein the relay valve is connected via a flexible line to the rear parking brakes of the towed vehicle, the front brakes being disconnected from the rear brakes so as to be inoperative.

5. A system according to Claim 4, wherein the operating brake system supply is connected via a second flexible line to the rear operating brakes of the towed vehi- cle.

Spec'ficabon BLANDJWP1115 GBA2004-03-15 doc - 7

6. A system according to any preceding claim, wherein the operational brak- ing supply to the rear brakes on the towed vehicle is connected via an existing load sens- ing valve connected between the front brakes and the rear brakes.

7. A system for controlling the air brakes of a towed vehicle from the brak ding system of a towing vehicle, substantially as described with reference to, and/or as shown in, the drawings. À

I Àe À À À À. À À À Àe Àe À. À Àe- Àe A.

Specification BLANDTWP1115 GBA2004-03-15 doc