GB2069644A - Emergency pneumatic braking system - Google Patents

Abstract

In a fluid pressure braking system which has at least one service 3,4, and secondary 5 reservoirs and service 6 and spring brake 12 control valves the supply to the secondary spring brake control valve 12 is via a fluid pressure connection through respective pressure responsive cut-off valves 9,10 which remain open only so long as a viable service reservoir pressure is present to cause the spring brake to be applied in the event of unsafe service brake pressure being present in the service reservoir 3 or 4. <IMAGE>

Description

SPECIFICATION Fluid pressure operable braking systems This invention relates to fluid pressure operable braking systems and relates especially but not exclusively to braking systems including spring brakes for providing secondary braking for a vehicle.

Fluid pressure operable braking systems are known which provide service braking of a vehicle including a two-circuit service brake control valve with independent reservoirs for each circuit thereby providing discrete circuits, failure of only one of which does not affect the operation of the other. Typically, one circuit may be used to operate front wheel brakes of the vehicle and the other circuit may be used to operate rear wheel brakes of the vehicle but provision of double actuators can enable independent front service brakes to be provided.

In spite of the provision of such dual circuits, there is an albeit remote possibility of failure of an air compressor supply to the reservoirs which can leave a vehicle without brakes after a number of brake applications and releases have depleted the separate reservoirs.

The present invention provides a fluid pressure-operable braking system including at least one service brake fluid pressure supply reservoir for supplying a service brake circuit, a further supply reservoir for a secondary and/or parking brake control valve operable to control a secondary and/or parking brake regardless of the operation of the service brake circuit and valve means operable in response to a discharged value of the service supply reservoir to apply said secondary and/ or parking brake.

Preferably, the secondary and/or parking brake is a spring brake and fluid pressure from the further reservoir is normally applied via the secondary brake control valve to hold the spring brakes off.

One advantageous feature of such a system can be that in recharging a brake system where secondary and/or parking brakes are provided by spring brakes is that the spring brakes can be arranged to be not normally releaseable until the apparatus has established that more than a predetermined pressure (corresponding to said discharged value) of the service supply reservoir has been reached.

In order to enable a vehicle fitted with such a system to be driven despite such a discharged value of the service brake supply reservoir, manually operable valve means may be provided for connecting the spring brake reservoir directly to the spring brake control reservoir. Alternatively, in order to enable a vehicle fitted with such a system to be driven despite such a discharged value of the service brake supply reservoir, manually operable valve means may be provided for connecting a further reservoir directly to the control valve.

Preferably, the manually operable valve is responsive to recovery of supply pressure from the service reservoir to enable it to be automatically reset.

In order that the invention may be more clearly understood and readily carried into effect, the same will be further described by way of example with reference to the accompanying drawings in which: Figure 1 illustrates the relevant parts of a braking system in accordance with one embodiment of the invention and Figure 2 illustrates a modification which may be applied to the system of Fig. 1.

In Fig. 1, a compressor, which is now shown, supplies compressed air via a wet-tank denoted by reference 1 and a multi-circuit protection valve 2 to charge a first rear brake service reservoir 3, a second front service brake reservoir 4 and a further spring brake reservoir 5. The service reservoirs 3 and 4 constitute pressure sources for a dual service brake foot valve 6 operation of which provides graduable fluid pressure on output lines 7 and 8 to the front and rear axle brake actuators respectively. Connections from the front and rear service reservoirs 3 and 4 are also made to control inputs for respective so-called cut off or synchro-valves 9 and 10.The valves 9 and 10 are valves known as SV-1 valves manufactured by Bendix Corporation Automotive Air Brake Company in the U.S.A. but they may be any suitable such valve which operates to provide a connection between an input port and an output port when the pressure at a respective control port is above a predetermined value. In the case of valves 9 and 10, these are connected effectively in series, the input to the valve 10 being derived from the output of the spring/secondary brake reservoir 5 and the input to the valve 9 being derived from the output of the valve 10. It may therefore be noted that collapse of control pressure to one or other of valves 9 and 10 will interrupt the output from the valve 9.

The output from the valve 9 is applied via a manoeuvering valve 11 to the supply port to a secondary and/or parking spring brake control valve 12, the output of which is connected to a relay valve 13, the supply to which is derived directly from the reservoir 5.

The manoeuvering valve 11 is a valve which is so-designed that in the normal running position, it provides a connection from the synchro-valve 9 to the spring brake control valve 12, but on manual operation of a plunger provided on the valve 11, it may be moved to its alternative condition in which a direct connection is provided between the spring brake reservoir 5 and the spring brake control valve 1 2. Such valves are manufactured by a number of commercial suppliers and preferably the valve 11 is one which is of a form which resets to its normal running condition when the pressure presented to it from the valve 9 recovers to an acceptable operating pressure.

Referring now to the operation of the circuit of Fig. 1, the compressor, which is not shown, is driven by the engine of the vehicle and supplied compressed air via the wet-tank 1 and protection valves 2 to charge reservoirs 3, 4 and 5 to a prescribed value determined by the system governor which is now shown.

Operation of the dual circuit foot valve 6 by the vehicle driver can apply the normal service brakes in the usual way and, by virtue of the pressure in reservoirs 3 and 4 being at a level which maintains the synchro-valves 9 and 10 in the actuated condition, fluid pressure is applied from the reservoir 5 via the valves 10 and 9 in series, and the valve 11 to the spring brake control valve 12. Assuming the spring brake control valve 1 2 is in the brake release condition, this maintains a full pressure to the relay valve 1 3 to apply full release pressure to the output line 14 for application to the vehicle spring brakes.

In the vent of fluid pressure in one or other of reservoirs 3 and 4 collapsing below a given level due to a failure downstream of the protection valve 2, the respective valve 9 or 10 switches to its unactuated condition thereby venting the line which is connected between the synchro-valve 9 and the manoeuvering valve 11. Accordingly, with the manoeuvering valve 11 in the normal running condition, the spring brakes are vented thereby preventing the driver from proceeding without taking remedial action.

If the driver wishes to proceed with caution, he is still able to operate the vehicle by actuating the plunger of the manoeuvering valve 11 to thereby connect the reservoir 5 directly to the spring brake control valve 1 2.

Assuming that only one service brake circuit has failed subsequent service braking will then be available only by virtue of the other of the two service brake circuits.

In the event of the compressor failing, in the absence of a low pressure warning device, a driver will be unaware of such failure until the service brakes fail to operate. This may not occur until a number of application and release operations have been made such as to sufficiently deplete the service reservoirs 3 and 4. After such an event, the spring brakes will again be applied due to reduction of control pressure to valve 9 and 10 below the set values thereof thereby venting the line between valve 9 and the manoeuvering valve 11. Again, the driver may operate the manoeuvering valve 11 to provide a direct connection between the secondary brake reservoir 5 and the spring brake valve 1 2 which, if placed in the release position, will enable the spring brakes to be released and the vehicle can thereby be moved under spring brake capability only.

A further feature of the cicuit of Fig. 1 is that the spring brakes are not normally releaseable on recharging of the system from rest until at least predetermine pressures corresponding to the settings of valve 9 and 10 have been attained in both the service reservoirs 3 and 4 respectively.

Referring to Fig. 2, this shows the addition of a of a further reservoir 1 5 to the system as described above the reference to Fig. 1, and with the modification that the direct connection for control pressure to relay valve 1 3 via the manoeuvering valve 11 is derived either from the secondary reservoir 5 or from the further reservoir 1 5 via a double check valve 16. The protection valves are designed such as to give the reservoir 1 5, (which may be of small capacity), preference in charging whereby after starting the engine, a rapid recharge of pressure into the reservoir 1 5 is achieved to permit rapid release of the spring brakes by a driver requiring hastily to move the vehicle. Such a system may be of particular interest in fire appliances or, alternatively, in vehicles which are stored in warehouses and wherein rapid moving of the vehicle is required to be guaranteed in the event of the unfortunate occurrence of a fire.

In an alternative manner used in Fig. 2 of connections of the further reservoir 1 5 this reservoir may be connected via a check valve directly to the wet-tank 1.

In yet another alternative to the arrangement of Fig. 2 the reservoir 1 5 may be dispensed with an a connection for alternative pressure input via the valve 11 may be made direct to the wet-tank 1.

Claims (9)

1. A fluid pressure-operable braking system including at least one service brake fluid pressure supply reservoir for supplying a service brake circuit, a further supply reservoir for a secondary and/or parking brake control valve operable to control a secondary and/or parking brake regardless of the operation of the service brake cicuit and valve means operable in response to a discharged value of the service supply reservoir to apply said secondary and/or parking brake.

2. A fluid pressure operable braking system as claimed in Claim 1 including a second service brake fluid pressure supply reservoir for supplying a second service brake circuit said valve means being operable in response to a discharged value of either service supply reservoir to apply said secondary and/or parking brake.

3. A fluid pressure operable braking system as claimed in Claim 1 or Claim 2 the secondary and/or brake control value being a spring brake control valve and said valve means comprising cut-off valve means operable to cut-off supply pressure from the further reservoir to the spring brake control valve.

4. A fluid pressure operable braking system as claimed in Claim 2 and 3, the cut-off valve means comprising two cut-off valves in series and controlled respectively by the pressures of the first and second reservoirs.

5. A fluid pressure operable braking system as claimed in Claim 3 or 4 including a mnoeuvering valve operable to bypass mid cut-off valve means to permit release of the spring brake with sufficient pressure present in the further reservoir.

6. A fluid pressure operable braking system as claimed in Claims 3, 4 and 5 wherein said further reservoir is a preferentially chargeable reservoir in relation to the first or first and second reservoirs.

7. A fluid pressure operable braking system as claimed in Claims 3, 4, 5 or 6 wherein said further reservoir is of low capacity relative to the first or first and second reservoirs.

8. A fluid pressure operable braking system as claimed in Claim 6 when the further reservoir comprises two reservoirs one of which is of relatively low capacity and preferentially chargeable and the outputs from which are applied to the spring brake control valve via a double check valve.

9. A fluid pressure operable braking system substantially as described herein with reference to Fig. 1 or Fig. 2 of the accompanying drawings.