GB2045373A - Trailer vehicle fluid pressure braking systems - Google Patents

Abstract

A two-line trailer vehicle fluid pressure braking system has a relay valve 8 controlled by fluid pressure in a service line 7 for controlling service brakes from a first reservoir 4 and a graduable spring brake relay valve 10 supplied from a second reservoir 5 to control spring brakes for parking and emergency purposes. The spring brake relay valve 10 has a pressure responsive piston area 22 which is connected to the first reservoir 4 so that if the pressure thereof is low, the spring brake relay valve is enabled to respond to the control line pressure at port 12 to gradually apply spring brakes such as to make up the deficiency in the service brake pressure. <IMAGE>

Description

SPECIFICATION Trailer vehicle fluid pressure braking systems This invention relates to trailer vehicle fluid pressure braking systems and relates especially to trailer vehicle systems which are provided with two line control.

Trailer vehicle two line fluid pressure braking systems have been proposed which include an emergency or supply line and a fluid pressure control line for connection respectively to towing vehicle supply and trailer control lines. The emergency or supply line provides a charging source for a'trailer service reservoir and a trailer emergency reservoir each located on the trailer vehicle and each such reservoir being protected against failure of the other by charging protection valves.The trailer vehicle further has a trailer spring brake valve which in response to predetermined supply or emergency line pressure connects the emergency reservoir to the spring brakes to maintain the spring brakes in a released condition and a trailer service relay valve operable in response to trailer control line pressure to supply pressure to service braking actuators in proportion to the control line pressure.

In order to provide adequate service braking in the event of failure of the trailer relay valve to supply the called for service brake pressure, it has further been proposed to add to such a spring brake valve a pressure responsive piston which responds to the difference between the control line pressure and the delivered pressure of the relay valve to introduce an appropriate degree of extra braking by the spring brakes.

Such a system, whilst increasing the probability of sufficient braking being produced in the event of the trailer relay valve not delivering the requisite braking pressure, can nevertheless have certain shortcomings in that application of the spring brakes to supplement a deficient service braking pressure may be delayed in coming into operation since the delivered and control pressures are required first to undergo comparisons before the spring brake valve is called into operation to provide operation of the spring brakes.

The present invention is concerned with reducing the above shortcoming and thereby increasing the viability of a proposal to provide spring braking in the event of the trailer relay valve not producing a delivered pressure which corresponds to the control line pressure.

The present invention provides a system in which the trailer spring brake valve is enabled by less than a pre-determined trailer service reservoir pressure such as to be immediately available for operation in response to control line pressure to supplement a deficient service brake force produced by a depleted service reservoir pressure.

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 of which: Figs. 1 and 2 illustrate alternative embodiments of the invention applied to two line trailer vehicle fluid pressure braking systems.

Referring to Fig. 1, the circuit arrangement shown consists of the relevant parts of the trailer braking circuit for use on a vehicle towed by a towing tractor vehicle provided with a control line and a supply or emergency line for trailer operation. In normal operation of the towing tractor vehicle, the supply line is maintained at a predetermined pressure and the control line is normally at atmospheric pressure for normal running. In order to apply the brakes, the control line pressure is increased by the tractor service braking valve or the tractor secondary braking valve to operate service braking on the trailer, making use of reservoir pressure on the trailer built up by supply line pressure through protection valves.

The trailer control line pipe coupler is denoted by reference 1 and the supply line coupler is denoted by reference 2. The supply line coupler 2 is connected to a two circuit protection valve 3 outputs of which are fed to a trailer service reservoir 4 and a trailer emergency reservoir 5.

The service line coupler is connected via a trailer variable load valve 6 which proportions the pressure on the output line 7 thereof in accordance with the loading on the vehicle and therefore applies to a service relay valve 8 a control pressure which is load dependent. The relay valve 8 derives its supply from the service reservoir 4 and produces an output to the pneumatic service chambers of dual spring and pneumatic brake actuators, only one of which is shown by reference 9. The load-dependent pressure on the line 7 is also applied to a trailer spring brake control valve 10, the contruction of which is shown in some detail.This valve has an enabling input port 11 connected to the reservoir 4, a control port 2 to which the aforementioned line 7 is connected, a reservoir supply port 1 3 to which the reservoir 5 is connected via an on/off relay valve 14 and an output port 15, the output derived at which is applied via an anticompounding valve 1 6 to the spring brake portion of the actuators such as 9. A second input of the anti-compounding valve is connected to the output of the service relay valve 8 as shown. The on/off relay valve is supplied with an on/off controlling pressure derived ordinarily from the supply line coupler 2 via a manoeuvering valve 17.

Controlling pressure to 14 of less than a given nominal pressure results in venting of the output connected to 13. Valve 1 7 is such that the coupler 2 is normally connected to the control port of 1 4 to maintain 14 open, but in order to enable the trailer vehicle to be moved with the coupler 2 disconnected, the manoeuvering valve is moved to its alternative condition in which the reservoir side of the protection valve 3 is connected directly to the on/off relay 14 to enable pressure from reservoir 5 to be applied to the spring brakes, the coupler 2 being isolated.

Referring to the spring brake control valve 10 in greater detail, it will be seen that this consists of a composite piston 20, slideable in a multi-bore cylinder, the cylinder housing a downward biassing spring 21. The valve has an upper chamber 22 separated by a seal 23 from an intermediate chamber 24 which, in turn, is separated by a further seal 25 from an intermediate chamber 26 connected to the port 1 2. Beneath the piston, a graduating region 27 is provided and extending into that region there is a lower projection 28 which forms a valve seat movable against a spring-biassed valve member 29 which is upward biassed against an inlet valve seat 30. The valve member 29 is carried by a tubular member sealingly slideable in the housing and providing access through an exhaust port 32.

In normal operation of the arrangement of Fig.

1, the supply or emergency line 2 is pressurised to a predetermined level from the braking circuit on the towing vehicle and under normal free-running conditions, the reservoirs 4 and 5 are therefore charged to this predetermined pressure via the protection valve 3. The manoeuvering valve 1 7 will be in the condition in which the coupler 2 is connected to the control port of the on/off relay valve 1 4 such that 14 provides a communication between the reservoir 5 and the supply port 13 of the spring brake relay valve 10. The normal running pressure at.the control line coupler 1 is zero and therefore zero pressure is derived from the relay valve 8 and applied to the service actuators of the trailer brakes.Additionally, the force of spring 21 and full reservoir pressure at port 11 act on piston 20 and the pressure at the supply port 13 of the trailer spring brake relay valve 10 is able to pass via the valve 29 to the output port 1 5 and valve 16 to hold the spring brakes off. When a service brake application is made on the towing vehicle, a proportional pressure is applied to the service line coupler 1 and modulated in accordance with the loading on the trailer to produce a proportional pressure in the line 7 as an input to the relay valve 8. The output of the relay valve 8 is therefore effective to control the pneumatic braking on the trailer in accordance with the tractor braking and the trailer load.The pressure appearing on the line 7 is also applied to the intermediate region 26 of the composite piston 20 and therefore tends to act upwards against the force of the spring 21, in a sense to tend to raise the piston to vent the spring brakes but the the fully charged pressure of the service reservoir 4 is such that when acting as it does above the piston 20, it prevents such venting of the spring brakes if full pressure is present at 13 from coupler 2. In the event, however, of the service reservoir 4 having less than a predetermined level of pressure, this will enable the spring brake control valve 10 and a control pressure in the line 7 can then cause upward movement of the piston 20 to enable the pressure in the graduating region 27 to be reduced sufficiently to enable the spring brakes to be partially gradually applied.Increasing pressure on the line 7 further acts to increase the graduable level of spring braking which therefore supplements the service braking available via the relay valve 8 from a depleted service reservoir.

On release of the pressure in the control line coupler 1 , the pressure in the line 7 reduces to zero, the output of the service relay valve 8 reduces to zero and the pressure under the graduating region of the piston 20 no longer assisted by control pressure at the port 12, enables the spring brake relay valve to re-open to apply full pressure from the reservoir 5 to the spring brakes. However it will be appreciated that the spring brake control valve continues to be enabled, by virtue of the reduced pressure at port 11 , for immediate action in response to pressure at port 7 to graduably apply the spring brake.

In the event of complete loss of pressure from the reservoir 4, the spring brake relay valve 10 acts in response to pressure at the control port 12 to graduate spring brake pressure in accordance with the pressure in the control line to provide full safe braking of the trailer.

In the event of a breakaway of the trailer from the tractor, the connection to the supply line coupler 2 on the trailer vehicle is vented. This results in the on/off relay valve 14 switching to a condition in which the connection from the reservoir 5 is sealed-off and the connection between the relay valve 14 and the supply port 13 is vented. The spring brakes are therefore applied.

In the event of the trailer being uncoupled, the trailer may be moved after operation of the maneouvering valve to connect the reservoir 5 to the supply port 1 3 of the trailer spring brake valve, as referred to in the foregoing.

Referring now to Fig. 2, the circuit is similar to that of Fig. 1, with the particular exception that the on/off relay valve 14 is now dispensed with and the trailer spring brake relay valve is of modified construction. In Fig. 2, the control line coupler is now denoted by reference 41 and the supply line coupler by reference 42. The supply line coupler is connected via a dual circuit protection valve 43, on the one hand to a service reservoir 44 and, on the other hand, to an emergency or spring brake reservoir 45. The control line coupler 41 is connected via a variable load valve 46 to a control line 47 for the service relay valve 48, the output of 48 being connected to the pneumatic service portion of a combined dual pneumatic spring brake actuator 49.

The line 47 is also connected to an input control port 62 of a spring brake valve 50, the details of which are shown. The circuit arrangement includes also a manoeuvering valve 57 and an anti-compounding valve connected similarly to Fig. 1, between the spring brake pressure port of the spring brake relay valve, on the one hand, and the output of the service relay valve 48, on the other hand, for providing the controlling pressure to the spring brake portion of each dual actuator such as 49.

Referring to the spring brake relay valve 50, this, again, comprises a composite piston arrangement comprising a piston 71 presenting an area 72 to the pressure at port 62 which is in excess of that presented by a lower piston portion 73. The piston portion 71 and 73 are joined to move as one and slide in respective cylinder bores 74 and 75.An upward projection from the piston portion 71 extends through an upper piston 77, slideable in a larger cylinder 78, the upward extending stem 79 being sealingly slideable in the piston 77 but having an end cap 80 by virtue of which upward movement of the piston 77 under the influence of a spring 81 is imposed upon the composite pistons 71, 73. A further spring 82 is provided between the composite piston and the upper piston 77 and the composite piston 5 provided with a downwardly projecting valve seat 84 which, when moved downwards, engages with a valve member 85 to seal-off an exhaust and unseat the valve member 85 from an inlet valve seat 86. The seat 85 is normally upward urged by a spring 87. The chamber in bore 74 between the composite piston and upper piston 77 is provided with an enabling port 88.The chamber above piston 77 in cylinder 78 is provided with a control port 89. The region beneath the piston 77 is vented. The reservoir pressure input ports and the spring brake pressure output port of the spring brake relay valve are denoted by references 90 and 91, respectively, the exhaust being denoted by reference 92.

In operation of the circuit arrangement of Fig. 2, the towing vehicle is to be considered to be the same as previousiy and designed therefore for two-line control. Under normal running conditions, the supply line coupler 42 is supplied with pressure from the towing vehicle and the reservoirs 44 and 45 are therefore charged via the protection valve 43, the reservoir 45 supplying pressure via the port 90, the unseated inlet valve of the spring brake relay valve, the output port 91, the anti-compounding valve 56 to the spring brake portion of the dual actuators such as 49 to hold the spring brakes in the fully-released condition.

Normally, zero pressure is applied from the control line coupler 41 to line 47, full reservoir pressure is applied at port 88 and piston 77 is maintained downwards deflected against its spring 81 by full reservoir pressure at port 89. A service control pressure applied at the coupler 41 is proportioned by the variable load valve 46 to provide a loaddependent pressure in the line 47 which therefore appears as a control pressure to the service relay valve 48 to control the pressure applied to the pneumatic portion of the dual actuators such as 49.The pressure in line 47 is also applied to the control input port 62 of the trailer spring brake relay valve but, in the presence of full reservoir pressure from service reservoir 44 in the port 88, the pressure at 62 has no direct effect upon the composite piston 71,73 which is therefore maintained downwardly deflected to hold the path between ports 90 and 91 fully open.

Considering now a situation where, due to a fault, the pressure in the reservoir 44 is substantially reduced, this results in a reduced pressure at the port 88 acting above the portion 71 of the dual piston. In the event now of a service brake application being made, the pressure in the control line 47 increases to act on the relay valve 48 to produce such normal service braking as is available despite the depleted service reservoir pressure. In addition, the pressure signal on the line 47, acting at the port 62 of the trailer spring brake relay valve, now has an effect upon the composite piston 71,73 and produces an upward deflection of the piston such as to graduate a reduction in the pressure acting under the piston 73 and therefore presented at the port 91 to the anti-compounding valve.The spring brakes are thus applied to an extent which is permitted by the lesser of the two pressures applied to the anticompounding valve from the relay valve 48 or the relay valve 50.

It is therefore seen that, as in the case of Fig. 1, a reduction of reservoir pressure below a predetermined level conditions the spring brake relay valve to introduce a graduable amount of spring braking dependent upon the value of the control signal such as to supplement such service braking as may nevertheless be available. In the event of a complete loss of service braking, full safe braking is made available by the spring brake control valve 50.

For release of the brakes under the above conditions where braking is provided for by the spring brake valve 50, a reduction of the control pressure on the line 47 enables the composite piston 71,73 to move downwards to increase the graduated output from the port 91 up to its maximum full reservoir pressure.

In the event of a breakaway of the combination, the emergency or supply line 42 is vented and the chamber above the additional piston 77 of the spring brake relay valve is therefore vented via the manoeuvering valve 57 and the connection to the coupler 42. This has the effect of enabling the spring 81 to lift the additional piston 77 together with the composite piston 71, 73 upwards into the position shown in the drawing whereupon the spring brakes are vented. In the event of the trailer being uncoupled from the towing vehicle and there is a need to move the trailer without recoupling to a source of pressure, the manoeuvering valve ST can be changed to its alternative condition whereby it provides a path from the reservoir 45 to the port 89 of the spring brake relay valve 50 to reset the relay valve to a condition in which the path between the input port 90 and the output port 91 is re-established to release the spring brakes and enable the trailer vehicle to be manoeuvered.

Claims (5)

1. A trailer vehicle fluid pressure braking system including a control fluid pressure input line and a supply fluid pressure input line, two independent reservoirs chargeable from the supply line, one said reservoir being connected as a supply source to a service relay valve controllable by fluid pressure in the control line to control service brakes and the other said reservoir being coupled as a supply source to an input of a graduable spring brake relay valve for controlling the application of spring brakes, said spring brake relay valve having pressure responsive means connected to the said first reservoir whereby a reduction of the pressure of said reservoir below a predetermined level can enable the spring brake relay valve to respond to a control pressure derived from the first line to graduably apply spring brakes in a sense to supplement a difficient service braking resulting from the reduced reservoir pressure.

2. A trailer vehicle fluid pressure braking system as claimed in Claim 1, wherein said spring brake relay valve has a self-lappable double valve controlling the connection between a first condition with an output port and input port or a second condition with output port and atmcsphere, said double valve being operable bypressure responsive means subject respectively to the control line pressure and the relay valve output pressure in a sense to move the double valve to the first condition and responsive to biassing means and the pressure in the first reservoir in a sense to move the double valve to the second condition.

3. A trailer vehicle fluid pressure braking system as claimed in Claim 2, wherein the input of the spring brake control valve is coupled via a connection from an on/off valve which is operable to vent the connection in the event of the pressure in the supply line falling below a given level.

4. A trailer vehicle fluid pressure braking system as claimed in Claim 2, wherein the spring brake relay valve has a pressure responsive member operable in response to a predetermined level of pressure in the supply line to override said pressure responsive means to hold said double valve in said second condition.

5. A trailer vehicle fluid pressure braking system, substantially as described herein, with reference to Fig. 1 or Fig. 2 of the accompanying drawings.