GB2151321A - Braking system, method of braking and rail vehicle incorporating the braking system - Google Patents

Abstract

A rail vehicle, primarily for use in mines, has a spring-applied track brake (14) and an hydraulic cylinder (16) for withdrawing the brake from the track. A valve (21) controlled by a pilot valve (25) connects the chamber (17) of the cylinder (16) with an accumulator (22) so that fluid can be discharged rapidly from the cylinder without reducing the pressure in the cylinder to atmospheric pressure to lightly apply the brake element (14) to the track 10. To apply full spring brake force the accumulator is exhausted to a low pressure reservoir (20) through a duct (23) and restrictor (24) or through the pilot valve (25) and a restrictor (26). The duct (23) or restrictor (26) may be omitted. <IMAGE>

Description

SPECIFICATION Braking device, method of braking and vehicle incorporating the device One aspect of the present invention relates to a braking device of the kind, hereinafter called the kind specified, comprising a brake element movable between a first position in which the brake element co-operates with a member to establish a braking force and a second position in which the brake element is substantially clear of said member, a spring for urging the brake element from the second position to the first position and a pressure chamber so arranged that the pressure of fluid in the chamber urges the brake element from the first position towards the second position.

When a vehicle equipped with a braking device of the kind specified is out of use, the brake element is held by the spring in its first position. When the vehicle is required to travel, the brake element is held by pressure in the chamber in its second position. In an emergency, the pressure in the chamber can be dropped to atmospheric pressure to allow the spring to overcome the fluid pressure and to move the brake element to its first position.

When a braking device of the kind specified is also used in a vehicle for normal service braking, this also is achieved by dropping the pressure in the chamber to atmospheric pressure.

Braking devices of the kind specified are commonly used in railway vehicles. An example of such a braking device is disclosed in G.B. 1,109,046. Known braking devices of the kind specified have the disadvantage that the magnitude of the braking force, by which we mean in the case of a braking device used in a vehicle, a force which decelerates the vehicle, is determined by the residual force exerted by in the spring when the brake element has moved to its first position and is therefore usually constant.

In railway systems used in mine workings, it is common for a train of vehicles to comprise a single vehicle having a braking device of the kind specified and a number of other vehicles without brakes. The number of vehicles in a train is varied according to requirements. Thus, a train may comprise a relatively large number of vehicles, each bearing a heavy load, or two or three lightly loaded or unloaded vehicles. In each case, braking is required to be effected by the same braking device on the single, braked vehicle.

Clearly, the same braking force is not ideal in each case.

In GB 1,450,100, there are disclosed two force-generating devices suitable for operating a brake of a vehicle. The first of these devices comprises a gas spring for urging the brake to the "on" condition and a two-stage piston and cylinder unit which can be pressurised to hold the the brake in the "off" condition.

When a sudden stop is desired, both stages of the piston and cylinder unit are exhausted rapidly. Thus, the braking force rises substantially instantaneously to a value which is then maintained. If the device is used to achieved a "slow stop", then the speed of movement of a piston rod of the piston and cylinder unit is limited so that the rate of flow of fluid from the piston and cylinder unit is relatively slow and is controlled and the change in condition of the vehicle brake occurs relatively slowly.

Operation in this manner may be suitable for normal service braking but is not suitable for emergency braking, where it is essential that the vehicle brake assumes its "on" condition without any significant delay.

In GB 1,379,501, there is disclosed a vehicle braking system having a coiled spring for applying the brakes and a pneumatic piston and cylinder unit for holding the brakes in the "off" condition. The piston and cylinder unit is charged through a valve which normally operates as a non-return valve. However, this valve can be opened by fluid pressure to permit the piston and cylinder unit to be exhausted, when the brakes are to be applied. The valve is so arranged that it is closed by the action of a spring before the pressure in the piston and cylinder unit drops to atmospheric pressure. As the valve closes, it will restrict flow of air from the piston and cylinder unit progressively and restriction will be promoted by the pressure drop across the valve, which will increase as the valve closes.

Thus, the speed at which the piston moves to permit application of the brake is restricted and controlled so that the brake will not be applied instantaneously. If the brake has achieved the "on" condition by the time the non-return valve closes, then there will be no significant, further movement of the piston, even when the pressure in the piston and cylinder unit is permitted to drop further and such pressure drop will occur substantially instantaneously. However, if the brake has not achieved the "on" condition by the time the valve closes, subsequent movement of the piston will occur even more slowly and there will be a significant delay before the brake achieves the "on" condition.

According to a first aspect of the invention, there is provided a method of braking movement of a body wherein a brake element is urged towards an operative position by a spring and is urged away from the operative position by pressure of a fluid in a pressure chamber, prior to braking the fluid pressure overrides the spring and maintains the brake element out of the operative position, when braking commences fluid is permitted to leave the pressure chamber at a high rate and the spring moves the brake element substantially instantaneously to its operative position, the fluid pressure in the pressure chamber is maintained substantially above atmospheric pressure throughout a period which begins with movement of the brake element into its operative position, the brake element remaining in its operative position throughout said period, and the pressure in the pressure chamber falls during said period.

It will be understood that, as the pressure in the chamber falls, the force to which the brake element is subjected rises and, provided other circumstances remain unchanged, the braking force will increase. In a method according to the first aspect of the invention, there is a first stage, during which there is expelled from the pressure chamber substantially immediately a sufficient volume of the fluid to allow the brake element to move substantially immediately to its operative position and then a second stage, during which the pressure in the pressure chamber decreases but the volume of the pressure chamber remains substantially constant because the brake element remains in its operative position.This can be contrasted with the method disclosed in GB 1,379,501, where movement of the piston to a position corresponding to the "on" condition of the brake is impeded by gradual closing of the valve so that the movement will not be completed substantially instantaneously and, if the movement is completed by the time the valve closes, then the pressure will drop substantially immediately to atmospheric pressure, at which it will then remain. Similarly, in the "slow stop" procedure described in GB 1,450,100, the rate of flow of fluid is restricted during a first stage of application of the brake so that the pistons move only slowly and there is a delay before the brake assumes the "on" condition.

The present invention provides a method wherein the brake achieves the "on" condition without any significant delay but the braking force is initially low and increases over a period commencing when the brake assumes the "on" condition.

The duration of the period during which pressure in the pressure chamber falls may be such that a single, lightly loaded vehicle, can usually be braked to rest within that period.

Typically, the period would be in the region of five seconds. A train comprising a relatively large number of heavily laden vehicles, only one of which is provided with braking means, would not normally be brought to rest within a period of five seconds but, once the pressure in the pressure chamber has fallen to a minimum value, the train would be subjected to maximum braking force. Braking of small, lightly loaded trains and of long, heavily laden trains, which is more appropriate than the braking hitherto achieved can thus be achieved without adjustment of braking means according to the size of train and load.

It will be understood that braking devices of the kind specified are generally relied upon to fail safe and that adjustment of braking devices in accordance with train size or load by an operator would conflict with the principle of fail safe brakes.

According to a second aspect of the invention, there is provided a braking device of the kind specified comprising an accumulator, a valve for controlling flow of fluid from the pressure chamber to the accumulator along a duct which permits relatively unrestricted flow, when the valve is open, and wherein there communicates with the accumulator a relatively restricted passage, through which fluid can leave the accumulator other than to the pressure chamber. By an accumulator, we mean a device which can receive and accommodate various amounts of a fluid and maintain that fluid under a pressure higher than atmosphere pressure.

There is also provided in accordance with the invention a railway vehicle having a braking device according to the second aspect of the invention, with the brake element thereof arranged for engagement, when in its first position, with a rail of a track on which the vehicle runs. Examples of vehicles embodying braking devices in accordance with the invention will now be described, with reference to the accompanying drawing, wherein: Figure 1 shows a diagrammatic representation of a part of a first vehicle and a part of a track on which the vehicle runs; Figure 2 is a diagram of a part of an hydraulic circuit of the first vehicle; Figure 3 is a representation, similar to Fig.

1 of a part of a second vehicle and a part of the track; Figure 4 is a diagrammatic representation of a cross-section of the second vehicle on the line IV-IV of Fig. 3, with the vehicle in normal, running condition; Figure 5 is a representation, similar to Fig.

4, illustrating a first stage of braking of the vehicle; and Figure 6 is a representation, similar to Fig.

4, illustrating a second stage of braking of the vehicle.

The vehicle illustrated in Fig. 1 is a railway vehicle and runs on a track comprising parallel rails, one of which is indicated at 1 0. The vehicle comprises a chassis 11 supported from the track by running wheels 1 2. The chassis carries a body 1 3. The vehicle may be a bogie vehicle, the chassis 11 being comprised by one bogie and a suspension system may be interposed between the wheels and the chassis.

A braking device is mounted on the chassis 11. The braking device comprises a brake element 1 4 which is guided by guides 1 5 for vertical reciprocation on the chassis towards and away from an upwardly facing surface of the rail 1 0. The brake element can move between a first position, in which it bears on the rail, and a second position, which is illustrated in the drawing, and in which the brake element is clear of the rail. When the braking device is used in a railway system in a mine working, there will be considerable movement of the brake element between its first and second positions, in order that the brake element will normally remain clear of the track rail, even when the rail is uneven.In other circumstances, the movement of the brake element between the first and second positions may be slight, to reduce the pressure under which the brake element engages a further member substantially to zero, rather than to move the brake element clear of the other member. This would be appropriate in a case where the brake element engages a wheel or a disc which rotates with a wheel, rather than a track rail.

The braking device further comprises an hydraulic piston and cylinder unit 16, one element of which, the cylinder in the example illustrated, is fixed with respect to the chassis 11 and the other element of which is fixed with respect to the brake element 1 4. Between the piston and one end of the cylinder, there is defined a pressure chamber 1 7. The brake element is urged away from the track rail 10 by any super atmospheric pressure maintained in the chamber 1 7. The brake element is urged towards the track rail by a spring 1 8 which acts effectively between the chassis 11 and the brake element. In the example illustrated, the spring is accommodated in the piston and cylinder unit 1 6 and acts between the piston and one end of the cylinder.

As shown in Fig. 2, a pump 1 9 is provided for supplying hydraulic fluid under pressure from a reservoir 20 to the pressure chamber 17. The pressjre chamber is also connected, via a valve 21, with an accumulator 22. A duct 23 containing an adjustable constriction 24 leads from the accumulator to the reservoir 20.

When the vehicle is out of use, the pump 1 9 is de-energised, the pressure in the chamber 1 7 is at least approximately equal to atmospheric pressure and the brake element 1 4 is held in firm engagement with the track 10 by the spring 18. When the vehicle is brought into operation, the chamber 1 7 is pressurised by the pump 1 9 to move the brake element to its second position clear of the track rail. When the vehicle is required to travel freely along the track, the valve 21 remains closed so that flow of hydraulic fluid from the chamber 1 7 to the accumulator is prevented.

If a braking force is required to be established by engagement of the brake element 1 4 with the track rail 10 during use of the vehicle, the valve 21 is opened. This valve is selected to permit flow of hydraulic fluid at a relatively high rate from the chamber 1 7 to the accumulator 22 without a large pressure drop across the valve. Accordingly, when the valve is opened hydraulic fluid is immediately expelled from the chamber 1 7 into the accumulator.The brake element 14 is moved from its second position to its first position in a short interval of time by the action of the spring 1 8. The accumulator 22 is of a size such that it can readily accommodate the volume of fluid which is expelled from the chamber 1 7 when the brake element moves from its second position to its first position.

The accumulator 22 maintains a super atmospheric pressure in the hydraulic fluid present in the accumulator. A corresponding pressure will be maintained in the chamber 17, whilst the valve 21 remains open. The pressure in the chamber 1 7 relieves the brake element 14 of a part of the load exerted by the spring 18. The pressure in the accumulator and therefore the pressure in the chamber 1 7 is dependent on the volume of hydraulic fluid in the accumulator.

Immediately the valve 21 opens and a super atmospheric pressure is established in the accumulator 22, flow of hydraulic fluid from the accumulator to the reservoir 20 through the variable restriction 24 commences. The pressure in the accumulator reaches a maximum value when the brake element 1 4 reaches its first position but, during the immediately following period, the pressure in the accumulator gradually falls as fluid escapes from the accumulator.During that period, the pressure in the chamber 1 7 falls gradually to atmospheric pressure and the force exerted on the brake element 1 4 by the piston and cylinder unit 1 6 gradually increases to a maximum valve corresponding to the residual stress in the spring 1 8. Typically, the force exerted on the brake element when it moves into its first position is one half the maximum force exerted by the unit 1 6 on the brake element when the pressure in the accumulator 22 has fallen to atmospheric pressure.

If the vehicle illustrated in the drawing is used alone and is not heavily laden, or is included in a train of unladen or lightly loaded vehicles, the vehicle or train may be braked to rest during the period in which the pressure in chamber 1 7 falls gradually. If the vehicle is used in a train of heavily laden vehicles, other vehicles of the train being unbraked, the braking force available will be generally be insufficient to bring the train to rest during the period in which the pressure in chamber 1 7 falls. In such cases, the relatively large braking force available after the pressure in chamber 1 7 has reached atmospheric pressure will be effective to brake the train rapidly to rest.

In no case, does the braking device generate the maximum braking force immediately the brake is applied. It will be seen that the braking device provides a braking force which is matched, at least to some degree, to the inertia of the vehicle or train being braked.

For operating the valve 21, there is provided a pilot valve 25 through which hydraulic fluid can flow from an operating cylinder of the valve 21 to the reservoir 20. As shown, the operating cylinder of the valve 21 is supplied with hydraulic fluid under pressure from the pump 19, via the chamber 1 7. Flow from the pump 1 9 to that end of the operating cylinder of the valve 21 which is connected with the pilot valve 25 is via a restrictor 26.

The duration of the period during which the force exerted on the brake element 14 by the unit 16 rises to its maximum value can be varied by adjustment of the restrictor 24.

It will be understood that a duplicate of the braking device illustrated in the accompanying drawing would normally be provided at the other side of the vehicle to act on the other track rail. It will be appreciated that a braking device in accordance with the invention may be applied to a vehicle which is suspended from an overhead rail and to a vehicle which does not run on a track. In the former case, the piston and cylinder unit of each braking device may be arranged generally as disclosed in G.B. 1,109,046. In the latter case, the brake element of the braking device may be arranged to act on a member which moves relative to a chassis of the vehicle when the vehicle is in motion. In the arrangement disclosed in GB 1,109,046, a rail is gripped between two brake shoes. Such gripping of a rail may also be used in the case of groundmounted rails.In such cases, one shoe may engage an upwardly facing surface of a rail whilst a further shoe engages a downwardly facing surface of the rail. The piston and cylinder unit comprising a spring may then be arranged to act between the brake shoes, rather than between one of the shoes and a chassis of the vehicle.

As can be seen from Fig. 1, when the valve 21 is open and flow of fluid from the pressure chamber 1 7 to the accumulator 22 has substantially ceased, fluid can flow from the accumulator to the reservoir 20 via the duct 23 and also via the restrictor 26 and the valve 25. In some cases, the duct 23 and restrictor 24 may be omitted, flow from the accumulator to the reservoir taking place only via the valve 21, restrictor 26 and valve 25. The restrictor 26 may be variable and may be omitted in certain cases.

Certain parts of the vehicle illustrated in Figs. 3 to 6 correspond to parts of the vehicle herein before described. Such corresponding parts are identified in Figs. 3 to 6 by corresponding references numerals with the prefix 1 and the preceding description is deemed to apply, except for differences hereinafter mentioned.

The running wheels 11 2 of the vehicle shown in Fig. 3 are not carried directly on the chassis 111. The chassis supports directly the body 11 3 and is rigidly connected with a pair of load-bearing members, one at each side of the vehicle, and one of which is shown at 1 30. The running wheels at each side of the vehicle are mounted on a respective beam 131 which extends between the wheels. Each wheel may be mounted by means of a respective stub-axle on the adjacent beam. Alternatively, the beams at opposite sides of the vehicle may be connected together by axles, each carrying two running wheels.

For transferring to the beam 1 31 the downward load received from the chassis 111, there is provided an intermediate member which is arranged for upwards and downwards movement relative to the beam 131 and relative to the load bearing member 1 30.

The intermediate member includes an upper portion 133 which overlies the beam 131 and extends therefrom in a direction laterally outwardly of the vehicle. The load bearing member 1 30 includes a similar, upper portion 1 34 which projects laterally outwardly of the vehicle over the portion 1 33. A piston and cylinder unit 1 35 is interposed between the portions 1 33 and 1 34 to transfer between these portions a vertically directed force having a magnitude which is dependent upon the pressure maintained in a pressure chamber defined by the piston and cylinder unit.During normal running of the vehicle, the pressure in this chamber is maintained at a sufficiently high value to ensure that the piston and cylinder unit is fully extended, even when the body 1 3 bears the maximum payload carried by the vehicle, in use. The weight of the payload and of the body 11 3 is transferred by the chassis to the member 130, via piston and cylinder unit 1 35 to the intermediate member and thence to the beam 131 which is supported by the running wheels.

On a lower part 1 36 of the member 130, there is provided a brake pad 1 37 which overlies the rail 11 0. During normal running of the vehicle, this brake pad is held clear of the rail. A further brake pad 1 38 is provided on a lower part 1 39 of the intermediate member to lie below a top flange 1 40 of the rail. During normal running of the vehicle, the brake pad 1 38 is clear of the rail.

The vehicle illustrated in Fig. 3 has an hydraulic circuit similar to that shown in Fig.

2, with the piston and cylinder unit 1 35 substituted for the unit defining the pressure chamber 1 7. A coiled compression spring 141, which is equivalent to the spring 18, is interposed between the lower part 1 36 of the load bearing member and the upper part 1 33 of the intermediate member. During normal running of the vehicle, the spring 141 is maintained in a compressed condition by the pressure in the piston and cylinder unit 1 35.

During a first stage of application of the vehicle brakes, fluid is permitted to leave the piston and cylinder unit 1 35 at a high rate, by opening of a valve corresponding to the valve 21. The fluid flows into an accumulator.

Transfer of fluid from the piston and cylinder unit to the accumulator permits the piston and cylinder unit to contract so that the load bearing member 1 30 descends relative to the beam 131 until the brake pad 137 engages the upper face of the rail 11 0. Downward movement of the member 1 30 is then arrested by the rail so that contraction of the piston and cylinder unit is interrupted. The member 1 30 is moved downwardly by the action of gravity on this member, the chassis 111, the body 113 and any payload. The residual, super-atmospheric pressure in the piston and cylinder unit 1 35 ensures that a proportion of the load is transferred to the beam 131 via the portion 133 of the intermediate member.

As the pressure in the accumulator falls, gradually, there is a further flow of fluid from the piston and cylinder unit 1 35 and this unit contracts further, allowing the spring 141 to raise the intermediate member relative to the load bearing member 1 30 until the brake pad 1 38 engages the underside of the rail flange 1 40. The brake pad 1 38 is then urged against the underside of the rail by a force exerted by the spring 141.As can be seen from Fig. 6, upward movement of the intermediate member by the spring relieves the beam 1 31 of downward loading applied via the intermediate member so that the weight of the vehicle and of any payload is transferred to the track by the brake pad 1 38 and a corresponding brake pad at the opposite side of the vehicle. It will be noted that, when application of the vehicle brakes is complete, the downward load of the vehicle and any payload, which is exerted by the brake pad 1 37 on the rail 110, is augmented by the force exerted by the spring 141 on the lower part 1 36 of the load bearing member. The spring 141 can be selected to provide a required relation between the force exerted by the spring and the combined weight of the vehicle and a predetermined payload.

It will be appreciated that application if the brake element 1 4 of the vehicle shown in Fig.

1 to the rail 10 and application of the brake pad 1 37 of the vehicle shown in Fig. 3 to the rail 110 do not occur instantaneously as the valve is opened to permit transfer of hydraulic fluid from the piston and cylinder unit to the accumulator. Nevertheless, this stage of operation of the braking devices is completed quickly, the fluid flowing at a high rate to the reservoir. Generally, the first stage of application of the brakes will be completed within a period of one second. We prefer that this stage be completed within a period of 0.5 second and a delay as short as 0.3 seconds is generally achieved in the vehicles illustrated in the drawings.The second stage of application of the brakes, that is the increase in the pressure exerted by the brake element 1 4 on the rail to a maximum value and, in the case of the vehicle shown in Fig. 3, engagement of the brake pad 1 38 with the rail and increase in the respective pressures under which the brake pads engage the rail to respective maximum values, occurs more slowly. In general, the second stage occupies a period of at least 0.5 seconds and preferably a period in excess of one second. The degree to which flow of hydraulic fluid during the second stage of operation is restricted can be selected to provide a second stage of operation having a duration which is at least approximately selected. Generally, the second stage of operation would be completed within a period of 5 seconds from the end of the first stage of application of the brake.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, or a class or group of substances or compositions, as appropriate, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims (11)

1. A method of braking movement of a body wherein a brake element is urged towards an operative position by a spring and is urged away from the operative position by pressure of a fluid in a pressure chamber, prior to braking the fluid pressure overrides the spring and maintains the brake element out of the operative position, when braking commences fluid is permitted to leave the pressure chamber at a high rate and the spring moves the brake element substantially instantaneously to its operative position, the fluid pressure in the pressure chamber is maintained substantially above atmospheric pressure throughout a period which begins with movement of the brake element into its operative position, the brake element remaining in its operative position throughout said period, and the pressure in the pressure chamber falls during said period.

2. A method according to Claim 1 wherein the fluid pressure in the pressure chamber drops in a stepless manner during said period.

3. A method according to Claim 1 wherein, prior to said period, fluid flows from the pressure chamber into an accumulator and wherein the fluid flows out of the accumulator throughout said period.

4. A braking device of the kind specified comprising an accumulator, a valve for controlling flow of fluid from the pressure chamber to the accumulator along a duct which permits relatively unrestricted flow, when the valve is open, and wherein there communicates with the accumulator a relatively restricted passage, through which fluid can leave the accumulator other than to the pressure chamber.

5. A device according to Claim 4 wherein the accumulator is arranged to maintain in fluid present in the accumulator a pressure, the magnitude of which depends upon the volume of fluid in the accumulator.

6. A railway vehicle having a braking device according to Claim 4 or Claim 5 with the brake element thereof arranged for engagement, when in its first position, with a rail of a track on which the vehicle runs.

7. A railway vehicle according to Claim 6 having first and second brake elements arranged for engagement with oppositely facing surfaces of the rail, the spring being arranged to urge both of the brake elements into engagement with the rail and the arrangement being such that the brake elements can be held out of contact with the rail by the maintenance of a sufficiently high pressure in the pressure chamber.

8. A railway vehicle comprising a body for supporting a payload, a carrier carrying one or more running wheels, a load bearing member equipped with a brake element for engaging a rail of a track on which the the vehicle runs and exerting thereon a load applied to the load bearing member from the body, an intermediate member movable upwardly and downwardly into and out of engagement with the wheel carrier and a fluid-pressure device operatively interposed between the load bearing member and the intermediate member for transferring the downward load from the load bearing member to the intermediate member and thereby transferring the load to the wheel support and relieving the brake element of the load.

9. A braking device having an hydraulic circuit substantially as herein described with reference to and as shown in Fig. 2 of the accompanying drawing.

10. A rail vehicle having a braking device substantially as herein described with reference to Figs. 1 and 2 of the accompanying drawings.

11. A rail vehicle having a braking device substantially as herein described with reference to Figs. 3 to 6 of the accompanying drawings.

1 2. Any novel feature or novel combination of features disclosed herein or in the accompanying drawings.