GB2033514A

GB2033514A - Braking system for the control of fail-safe brakes

Info

Publication number: GB2033514A
Application number: GB7934841A
Authority: GB
Original assignee: Massey Ferguson Perkins Ltd
Current assignee: Perkins Engines Group Ltd
Priority date: 1978-10-10
Filing date: 1979-10-08
Publication date: 1980-05-21
Also published as: FR2438567A1; IT1124594B; ES484920A1; GB2033514B; DE2940836A1; IT7926338A0; FR2438567B1; DE2940836C2

Abstract

A braking system for the control of a fail-safe brake 16, particularly for use on a trailer, includes a source 10 of pressurised fluid connected with a braking effect control valve 12 which is in turn connected via conduits 14a, 14, 15 with first 23 and second 26 fluid pressure operated actuators so that both actuators are subject to an equal level of fluid pressure from the valve 12 at all times. A spacing 30 is provided to apply the brake 16 in the absence of a brake releasing force. The first actuator 23 is arranged to generate a brake releasing force to render the spring 30 ineffective to apply the brake at conduit pressures at and above a first level thus allowing release of the brake. The second actuator 26 is arranged to apply the brake at conduit pressures above a second higher level. The control valve 12 is arranged on activation of the system to raise the pressure in the conduits to a level between the first and second levels to release the brake, and, on receipt of a braking command input signal Y, to raise the pressure in the conduits to a level above the second level proportional to the value of the braking command input signal thus applying the brake. An alternative construction in which the first and second actuators are combined into a single compound actuator 40 (Fig. 2, not shown) is also disclosed. <IMAGE>

Description

SPECIFICATION Braking system for the control of fail-safe brakes This invention relates to braking systems for the control of fail-safe brakes and particularly, though not exclusively, to such systems for use in braking trailers.

The term fail-safe brake as used throughout this specification refers to a brake which, in the absence of the application of a brake releasing force, is automatically applied by a brake applying means such as a spring or a fluid pressure from an accumulator.

There is a requirement for a trailer braking system which enables an agricultural tractor to be provided with an efficient and fail-safe trailer braking facility.

It is an object of the present invention to provide a braking system which is suitable for use on trailers and meets the above requirements.

According to a first aspect of the present invention there is provided a braking system for the control of a fail-safe brake, the system including a source of pressurised fluid, a braking effort control valve connected to said source and having a braking command input signal receiving means and an output port, brake applying means arranged to apply the brake in the absence of a brake releasing force, first and second fluid pressure operated actuator means both connected to the output port of said control valve via conduit means so as to be subject to an equal level of fluid pressure at all times, said first actuator means being arranged to generate a brake releasing force to render the brake applying means ineffective at conduit means pressures at and above a first level thus allowing release of the brake, said second actuator means being arranged to apply the brake at conduit means pressures at or above a second higher level, said control valve being arranged on activation of system to raise the pressure in said conduit means to a level between said first and second levels to release the brake, and, on receipt of a braking command input signal, to raise the pressure in said conduit means to a level above said second level proportional to the value of said braking command input signal thus applying the brake.

Preferably the brake applying means comprises first spring means whose brake applying action is rendered ineffective by said first actuator means in the form of a first fluid pressure operated piston at conduit means pressures at or above said first level.

Preferably also said second actuator means comprises a second fluid pressure operated piston biased against movement in a brake applying direction by second spring means at conduit means pressures below said second level.

In one construction said first and second actuator means are arranged to act on opposite end portions of a pivotable beam to pivot the beam in opposite directions to release and apply the brake respectively, the beam being arranged to be connected with the brake and the brake applying means at locations intermediate the end portions.

Preferably the beam is supported intermediate the end portions so that the first actuator means, when releasing the brake against the action of the brake applying means, pivots about a first fulcrum to bring the associated end portion of the beam into contact with a stop, the second actuator means being arranged, when applying the brake to pivot the beam in the opposite direction using the stop as a second fulcrum.

In another construction said first and second actuator means are combined into a single compound actuator in which said pistons operate in a common chamber connected to said control valve outlet via said conduit means.

Preferably said first piston is in sealed sliding contact with the walls of said common chamber and is subjected on one side to conduit means pressure and on the other side to the brake applying force of said first spring means, the area of said one side of said first piston being such that the brake releasing force applied to said first piston by said conduit means pressure renders said first spring means ineffective to apply the brake at conduit means pressures at or above said first level, said second piston being positioned on said one side of said first piston and being operatively connected with linkage means connected with said brake, said second piston being biased in a brake releasing direction towards said one side by said second spring means to ensure release of the brake at conduit means pressures at or above said first level, the effective area of said second piston exposed to said conduit means pressure in said chamber being such that at conduit means pressures at or above said second level said second piston is displaced in the brake applying direction against the action of said second spring means to apply the brake via the linkage means, and said first piston being arranged to abut and displace said second piston at conduit means pressures below said first level to give a braking effect via said linkage means.

A hand or parking brake provision may be included in the system by providing a hand or parking brake control which is arranged when moved to an operative position to give a signal to said control valve which lowers said conduit means pressure to a level below said first level thus applying the brake.

The invention also provides a tractor and trailer combination fitted with a braking system in accordance with the first aspect of the invention for the control of a fail-safe brake on the trailer wherein the braking command input signal receiving means is connected with a service brake control member mounted on the tractor which controls the application of the fail-safe trailer and brake and fluid pressure operated brakes on the tractor, said control valve supplying both said tractor and trailer brakes with applying pressure proportional to the movement of said service brake control member.

Alternatively, in a further form of tractor and trailer combination the input signal receiving means may be connected with a separate braking system on the tractor so that the control valve receives braking command input signals proportional to the level of braking being applied by the tractor braking signal resulting in a proportional braking effect being applied by the fail-safe brake on the trailer.

Preferably when used in a tractor and trailer combination the control valve includes timing means to ensure that the fail-safe brake is applied before the tractor brakes.

Two embodiments of the present invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings in which: Figure 1 shows a braking system embodying the present invention as applied to an agricultural tractor and trailer combination in which separate first and second actuator means operate on opposite end portions of a pivotable beam, and Figure 2 shows part of a further form of system for use in an agricultural tractor and trailer combination in which a single compound actuator is employed.

Referring to Fig. 1 the braking system comprises a source of hydraulic pressure in the form of a pump 10 which draws fluid from a sump 11. The pump delivers pressurised fluid to a control valve 1 2 via a line 1 3. The control valve in turn delivers the pressurised fluid at various pressure levels to the remainder of the braking system via an output port connected to lines 14a, 14 and 15 and fluid is returned to the sump 11 from the control valve 12 via a return line 32. The pump 10, sump 11 and valve 1 2 are all conveniently mounted on the tractor.

The trailer fitted with the braking system is provided with wheel brakes, one of which is shown diagrammatically at 1 6 in the accompanying drawings. Any appropriate type of brake may be employed, the illustrated brake being of the drum type and being of the failsafe spring-applied type as explained below.

The brakes are operated by a rod 1 7 which is connected at 1 8 with a pivotable beam 1 9.

The beam 19 is supported at 20 by a pin 21 carried by the beam which extends through an elongated slot 22 in the support 20.

A first actuator means in the form of a hydraulic piston and cylinder assembly 23 acts on the end portion 24 of the beam 1 9.

This piston and cylinder assembly is fed with pressurised fluid via line 14. The other end portion 25 of the beam 1 9 is acted upon by a second actuator means in the form of a further piston and cylinder aassembly 26 connected with line 1 5. A strong compression spring 27 acts between the piston 28 and cylinder 29 of the assembly 26 to prevent substantial displacement of the piston within the cylinder at pressure levels below a preselected value.

Brake applying means in the form of a tension spring 30 which acts on the beam 1 9 are provided for applying brake 16. This spring causes the beam to pivot in a clockwise sense about a fulcrum provided by the connection 31 of the piston 28 with the beam thus pulling the rod 1 7 in the direction of the arrow X.

The control valve 1 2 receives a braking command input signal Y from a master cylinder (not shown) mounted on the tractor and connected with a pedal or pedals which control the tractor and trailer brakes. This signal causes the control valve to supply pressurised fluid to lines 14 and 1 5 at a level proportional to the braking pressure generated by the master cylinder. The valve 1 2 also supplies pressure, proportional to the master cylinder pressure, to the brakes on the tractor via line 34, a timing device being prefereably included in the valve 1 2 to ensure that the trailer brakes are applied fractionally before the tractor brakes to reduce the likelihood of jack-knifing.

Alternatively, the control valve 1 2 may only control the brakes of the trailer and its braking command input signal Y may be a mechanical, fluid pressure or other signal proportional to the braking force being applied by the tractor brakes to give proportional trailer braking.

The control valve 1 2 may also be arranged to receive a further braking command input Z from a hand or parking brake lever (not shown) mounted on the trailer or tractor. This command input is arranged to reduce the level of pressure in the trailer braking system so that the brake can be applied by the spring 30.

The system operates as follows: The part of the system mounted on the trailer is connected with that part carried on the tractor by a quick-attach type of connector in part 14a of line 14 and, where a hand brake lever is mounted on the trailer, by a releasable connection in the signal path from the hand brake lever to the control valve 1 2.

If the pump 10 is not operating either due to failure or to the tractor engine being switched off, the lines 14 and 1 5 are not pressurised so that the brake is applied by the spring 30 which pivots the beam 1 9 about the fulcrum provided by the connection 31 to pull the rod 1 7 in the direction of the arrow X. The brakes are also automatically applied in this manner should there by a failure in the braking system which results in the system being incapable of applying the brakes.

If the tractor engine is not started so that the pump 10 provides pressurised fluid to the control valve this pressurised fluid will, assum ing that the system is provided with a hand brake control and that this is operating to give the control valve the input signal Z for the application of the brakes in a parking mode, be either vented back to the sump or a line 33 may be provided to divert the pump flow to other circuits (e.g. for the operation of other auxiliary equipment on the tractor) when it is not required for braking.

If the hand brake lever is now released this allows the control valve 1 2 to supply pressurised fluid to the lines 14 and 1 5 at a first pressure level of say 1 50 psi. This pressure is fed to both piston and cylinder assemblies 23 and 26. The compression spring 27 is arrranged to be sufficiently strong to prevent this pressure level from causing the piston 28 to move relative to the cylinder 29 of the assembly. This level of pressure is however arranged to be sufficient when applied to the assembly 23 to ensure that the spring 30 is rendered ineffective to apply the brakes and causes the beam 1 9 to be pivotted about the fulcrum provided by the connection 31 into contact with a stop 32 to fully release the brakes.During this brake releasing movement of the beam 1 9 under the action of assembly 23 the pin 21 moves along the slot 22.

Thus at pressure levels in the lines 1 4 and 1 5 at or above a first level of say 1 50 psi the spring 30 is prevented from applying the brakes and the brakes are held in a fully released condition by assembly 23.

When the tractor driver wishes to apply the tractor and trailer brakes during use of the trailer he depresses the brake pedal(s) on the tractor to produce a braking command input signal Y proportional to the desired braking effect. This input signal is fed to the control valve 1 2 which in turn supplies the lines 14 and 1 5 and the tractor braking circuit with a high pressure proportional to the desired braking effect. The system is arranged so that the pressure supplied to lines 14 and 1 5 in response to an input signal Y is always at or above some predetermined second pressure level of say 225 psi up to a maximum of say 1 800 psi depending on the value of signal Y.

When the pressures above this second level are supplied to lines 14 and 15, piston and cylinder assembly 23 maintains the end portion 24 of the beam 1 9 against the stop 32 and the piston and cylinder assembly 26 is enabled to extend since the higher levels of pressure are capable of overcoming the strong compression spring 27. Thus the beam 1 9 is pivoted by the piston and cylinder assembly 26 using the stop 32 as a second fulcrum.

This pivoting of the beam 1 9 pulls the rod 1 7 again in the direction of the arrow X thus applying the brakes and giving a braking effect proportional to the value of signal Y.

When the brake pedal(s) is released the pressure in the braking circuits is vented back to the sum via line 32 and the output of the pump can then flow to other circuits via line 33. As stated above should the braking system suffer a hydraulic failure spring 30 will apply the brakes automatically as the level of pressure in assembly 23 falls below the first level of 1 50 psi. It will thus be appreciated that the present invention provides a simple and efficient braking system which is particularly suitable for use on a trailer, which is fail-safe and which enables the trailer to be braked with a braking effect proportional to that of the towing vehicle.The system can also be provided with a hand or parking brake function and can also be arranged so that when the brakes are applied during use of the trailer the piston and cylinder assembly 26 and the spring 30 applying moments to the beam 1 9 in the same sense about the stop 32 to give a good braking effect.

Various modifications to the system described above are possible. For example, if the hand brake lever were to be mounted on the tractor at a location adjacent the driver's seat the driver would then have the ability to apply the trailer brakes, using the hand brake lever, without applying the brakes on the tractor.

This could be a distinct safety advantage in certain circumstances such as, for example, when descending a hill.

Also, means may be provided for manually releasing the trailer brakes to override the spring 30. Such a facility would be advantageous since it would allow the trailer to be manoeuvred when disconnected from the tractor and would allow the tractor and trailer combination to be tow started. This facility could be easily provided by providing a handle 35 on the end of the beam 1 9 which could be used to move the beam against the spring 30 to release the brake. A ratchet 36 or similar retaining means could also be provided to hold the beam 1 9 in the brake releasing position, this retaining means preferably being arranged to automatically release the beam 1 9 when the braking system is next reactivated.

Fig. 2 shows part of a further form of braking system in which the functions of piston and cylinder assemblies 23 and 26 are combined into a single compound actuator 40. The remainder of the system not shown in Fig. 2 is identical to that shown in Fig. 1 and functions in the same manner.

Brake operating rod 1 7 is connected at 41 to a beam 42 which is pivotted at 43 on the trailer. Actuator 40 is pivotally mounted at 44 on the trailer and comprises a housing 45 with an internal chamber 46 within which a first brake applying spring 47, first piston 48, second piston 49 and second spring 50 are housed.

The second piston is connected with the beam 42 by a rod 51 which slides through a seal 52 in the housing. Line 14a delivers pressurised fluid from control vale 1 2 and a second seal 53 engages the first piston 48 to prevent fluid entering that part of chamber 46 which houses the spring 47. A vent 54 en sures that the piston 48 is free to slide within the chamber 46.

When line 1 4a is supplying pressure at a level below the first level of, say, 1 50 psi, the spring 47 is free to press on first piston 48 which in turn contacts second piston 49 and pushes rod 51 away from the housing 45 against the action of second spring 50 thus applying the brakes via beam 42 and rod 1 7.

The area of the side 48a of piston 48 exposed to the pressure level in chamber 46 is arranged to be such that at chamber pressures of 1 50 psi and over the piston 48 has been displaced upwardly as viewed in Fig. 2 against spring 47 by a sufficient amount to ensure that the spring 47 can no longer apply any braking force to the beam 42 via rod 51.

At chamber pressures below a second level of say 225 psi the second piston 49 is maintained in contact with the piston 48 by spring 50 so that as the piston 48 rises so the rod 51 is drawn into the housing 45 thus releasing the brakes. As previously stated the brakes are arranged to be fully released at chamber pressures of 1 50 psi and over.

The surface of piston 49 which contacts piston 48 is provided with grooves or other formations indicated by dotted line 55 which ensure that the chamber pressure is fully effective on this surface of piston 49.

The effective area of piston 49 exposed to the pressure in chamber 46 and the characteristics of spring 50 are chosen such that at chamber pressures at or above 225 psi the chamber pressure commences to displace the piston 49 downwardly away from the piston 48 to apply the brake.

As will be appreciated the level of pressure in chamber 46 rises above the second level of 225 psi in response to a braking signal Y as described above in relation to Fig. 1 Again the pressure in chamber 46 can rise, depending on the value of the signal Y, up to a maximum of say 1 800 psi thus giving a large range of braking pressure and thus good precise control of the applied braking effect.

The beam 42 is provided with a handle 56 which has a similar function to the handle 35 of Fig. 1. The beam 42 also carries an abutment in the form of a pin 57 which can be engaged by a spring loaded latch 58 to hold the brakes in the released condition. As will be seen as pressure builds up in chamber 46 to release the brakes when the system is next activated the frictional contact between pin 57 and surfae 58a of the latch caused by the effect of spring 47 is progressively reduced until eventually the latch 58 is retracted to the right by spring 59 to disengaged pin 57 and thus allow the system to function normally.

An important feature of the present invention is the subjection of both the first and second actuator means to an equal level of fluid pressure at all times. This greatly simplifies the construction of the system and actuator means and in particular when using the system in a tractor and trailer combination enables, for example, the pump and control valve to be mounted on the tractor and the remainder of the system to be mounted on the trailer and connected with that part of the system on the tractor by a single fluid pressure line.

It will also be appreciated that although the invention has been described with reference to a tractor drawn trailer it is also suitable for numerous other uses and could in fact be used, with suitable adaption, as the braking system for a towing vehicle such as, for example, the traction unit of an articulated lorry.

Also, although the invention has been described as a hydraulic system the operating fluid can be of different types and, for example, the system could operate using air with appropriately adjusted pressure levels etc.

Claims

1. A braking system for the control of a fail-safe brake, the system including a source of pressurised fluid, a braking effort control valve connected to said source and having a braking command input signal receiving means and an output port, brake applying means arranged to apply the brake in the absence of a brake releasing force, first and second fluid pressure operated actuator means both connected to the output port of said control valve via conduit means so as to be subject to an equal level of fluid pressure at all times, said first actuator means being arranged to generate a brake releasing force to render the brake applying means ineffective at conduit means pressures at and above a first level thus allowing release of the brake, said second actuator means being arranged to apply the brake at conduit means pressures above a second higher level, said control valve being arranged on activation of system to raise the pressure in said conduit means to a level between said first and second levels to release the brake, and, on receipt of a braking command input signal, to raise the pressure in said conduit means to a level above said second level proportional to the value of said braking command input signal thus applying the brake.

2. A braking system according to claim 1 wherein the brake applying means comprises first spring means whose brake applying action is rendered ineffective by said first actuator means in the form of a first fluid pressure operated piston at conduit means pressures at or above said first level.

3. A braking system according to claim 1 or claim 2 wherein said second actuator means comprises a second fluid pressure operated piston biased against movement in a brake applying direction by second spring means at conduit means pressures below said second level.

4. A braking system according to any one of claims 1 to 3 wherein said first and second actuator means are arranged to act on opposite end portions of a pivotable beam to pivot the beam in opposite directions to release and apply the brake respectively, the beam being arranged to be connected with the brake and the brake applying means at locations intermediate the end portions.

5. A braking system according to claim 4 wherein the beam is supported intermediate the end portions so that the first actuator means, when releasing the brake against the action of the brake applying means, pivots about a first fulcrum to bring the associated end portion of the beam into contact with a stop, the second actuator means being arranged, when applying the brake, to pivot the beam in the opposite direction using the stop as a second fulcrum.

6. A braking system according to claims 1, 2 and 3 wherein said first and second actuator means are combined into a single compound actuator in which said pistons operate in a common chamber connected to said control valve outlet via said conduit means.

7. A braking system according to claim 6 wherein said first piston is in sealed sliding contact with the walls of said common chamber and is subjected on one side to conduit means pressure and on the other side to the brake applying force of said first spring means, the area of said one side of said first piston being such that the brake releasing force applied to said first piston by said conduit means pressure renders said first spring means ineffective to apply the brake at conduit means pressures at or above said first level, said second piston being positioned on said one side of said first piston and being operatively connected with linkage means connected with said brake, said second piston being biased in a brake releasing direction towards said one side by said second spring means to ensure release of the brake at conduit means pressures at or above said first level, the effective area of said second piston exposed to said conduit means pressure in said chamber being such that at conduit means pressures at or above said second level said second piston is displaced in the brake applying direction against the action of said second spring means to apply the brake via the linkage means, and said first piston being arranged to abut and displace said second piston at conduit means pressures below said first level to give a braking effect via said linkage means.

8. A braking system according to any one of claims 1 to 7 having a hand or parking brake provision wherein a hand or parking brake control is arranged when moved to an operative position to give a signal to said control valve which lowers said conduit means pressure to a level below said first level thus applying the brake.

9. A braking system for the control of a fail-safe brake, the system being constructed and arranged substantially as hereinbefore described with reference to and as shown in Fig.

1 or Fig. 2 of the accompanying drawings.

10. A tractor and trailer combination fitted with a braking system according to any one of claims 1 to 9 for the control of a fail-safe brake on the trailer wherein the braking command input signal receiving means is connected with a service brake control member mounted on the tractor which controls the application of the fail-safe trailer brake and fluid pressure operated brakes on the tractor, said control valve supplying both said tractor and trailer brakes with applying pressure proportional to the movement of said service brake control member.

11. A tractor and trailer combination fitted with a braking system according to any one of claims 1 to 9 for the control of a fail-safe brake on the trailer wherein the braking command input signal receiving means is connected with a separate braking system on the tractor so that the control valve receives braking command input signals proportional to the level of braking being applied by the tractor braking signal resulting in a proportional braking effect being applied by the fail-safe brake on the trailer.

1 2. A tractor and trailer combination according to claim 10 or claim 11 wherein the control valve includes timing means to ensure that the fail-safe brake is applied before the tractor brakes.

1 3. A tractor and trailer combination according to any one of claims 10 to 1 2 wherein the control valve is mounted on the tractor and the first and second actuator means and brake applying means are mounted on the trailer, the portions of the system for the control of the fail-safe brake which are mounted on the tractor and trailer respectively being interconnected by a single fluid pressure carrying conduit.