GB2395019A

GB2395019A - Spring brake testing device

Info

Publication number: GB2395019A
Application number: GB0222992A
Authority: GB
Inventors: Anthony Richard Mayne
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-10-04
Filing date: 2002-10-04
Publication date: 2004-05-12
Also published as: GB0222992D0

Abstract

A spring brake testing device for measuring the force of a power spring in a spring brake actuator of an air brake assembly is described. The device incorporates a fluid driven ram 10 having a forward extension 20 adapted to engage with the power spring of a spring brake, a power means acting via the ram to draw against the power spring, and a fluid pressure detector to detect the drawing force applied thereby. In particular, the device is compact and portable, incorporating a portable power source. A method of testing and a testing regime for spring brake actuators are also described.

Description

( SPRING BRAKE TESTING DEVICE

The invention relates to a spring brake testing device for measuring the spring 5 load applied by a power spring in a spring brake actuator, and thereby for testing the performance thereof and/or identifying weakness or failure thereof.

The invention also relates to a method for measuring the load applied by a power spring inner spring brake actuator and to a method of determining the performance and/or identifying failure or weakness thereof.

Spring brakes are in common use as part of the air brake system used on trucks, buses, agricultural vehicles and other large vehicles and trailers. Such braking systems normally include a primary service brake system adapted to apply and release the brakes in response to a supply of compressed air, by 15 which means the brakes are applied in normal use. Generally, this primary air-brake system is designed for short term application in use, in particular when vehicle systems are operating. Accordingly, it is often necessary to provide a secondary brake, in particular as a parking brake, which can be applied over a longer period and/or when the vehicle systems are not 20 otherwise operating.

Conveniently, the parking brake is incorporated into the air brake system. The system includes a spring brake actuator which uses spring pressure to apply the brakes. Depending on the particular configuration of braking system, this 25 might be by deliberate actuation by a user, by automatic actuation when air pressure in the main brake chamber is released below the predetermined pressure under control of the operator, or automatically as a result of failure of the main brake system. An example of such a braking system is illustrated in US Patent 4860640.

( In such systems a large spring is used to store energy, the spring being retained in compression when the brakes are not applied, but being able to exert the large force required to apply the brakes when the vehicle is parked etc. There is a general desire to be able to monitor the force which this power spring is capable of applying to ensure that it remains effective in applying the brake. This is in part because the performance of any spring retained for long periods in compression can be expected to deteriorate over time, and in part 10 because failure is frequently partial, perhaps by loss of one or more coils, so that in each case the brake is still apparently applied but not to full safety specifications.

As a consequence, mere observation of the application of the brake might be 15 insufficient and it is desirable to be able to obtain some more quantitative measurement of the condition of the spring. Ideally, this should involve measurement in situ. Disassembly of brakes systems is likely to be time consuming if not impossible.

20 Traditional in situ measurements have involved the use of a rolling road to assess brake effectiveness. This is an involved process, and consequently is likely only to be practical as part of a major overhaul regime.

International Patent Application number PCT/US94/09269 describes a 25 possible system for measuring the force applied by the power spring in a spring brake which takes advantage of the caged bolt frequently supplied with such assemblies to enable the brake to be taken off manually. In accordance with this system, the caged bolt has a threaded shank, and the spring is drawn back into a more compressed state by drawing this caged bolt through a 30 threaded caging nut. r

l A strain gage positioned between the caging nut and the spring housing gives a indication of the force required to draw the spring. The system thus allows measurement of forces within the spring without the need for a rolling road or 5 like arrangement, or the need to disassemble the braking system. I Nevertheless, drawing the caged bolt through the thread on the caging nut is a laborious and physically demanding process.

It is an object of the present invention to provide an alternative system for in 10 situ measurement of the spring force of the power spring in a spring brake of an air brake assembly which mitigates some or all of the above disadvantages.

It is a particular object of the present invention to provide a measuring device which permits the rapid testing in situ of such spring brakes, and thus allows 15 for the development of a more regular maintenance and detection regime than has been hitherto possible.

Thus according to the invention in a broadest aspect there is provided a spring brake testing device for measuring the force of a power spring in a spring 20 brake actuator of an air brake assembly comprising a fluid driven (and in particular a hydraulic) ram, having a forward extension adapted to engage with the power spring of a spring brake, a power means acting via the ram to draw against the power spring, and a fluid pressure detector to detect the drawing force applied thereby.

In a typical arrangement, the power spring of the spring brake is disposed within the brake housing acting between a housing end wall and a spring plate.

The spring plate typically acts against a diaphragm portion separating the spring brake unit from an air brake unit, so that the power spring remains in 30 compression when air pressure is at a predetermined level within the brake

( housing, but extends to apply a force to the spring plate and hence to apply the brake when air pressure in the housing is reduced.

In accordance with the invention, a forward extension of the fluid driven ram j 5 engages mechanically with a power spring in the extended configuration and draws it back towards a more compressive state. The pressure detector detects the force applied by the ram, in particular by measuring the fluid pressure change within the ram system as the spring is drawn and hence measures a force representative of the force applied by the spring, and indicative of the 10 condition of the spring.

A rapid and simple measurement is enabled of the condition of the spring in admirable manner. In particular, the device may be made portable, incorporating a portable power means with a suitable portable power source, 15 so that measurement of spring condition using the device can be made part of the routine inspection regime for a vehicle rather than part of a more major maintenance programme.

Engagement of the forward extension of the fluid driven ram to the power 20 spring may be by any suitable method enabling the hydraulic ram to draw the power spring back in the manner required by the invention. In particular such connection may be direct or indirect. For example, the forward extension of the ram may itself be provided with means to engage directly upon the power spring. A more practical arrangement in many instances will exploit the existing means already provided with most typical brake arrangements to allow the spring brake to be removed mechanically at a user's option. In this embodiment, the testing device is provided for use with such spring brake, 30 having means to mechanically remove from the spring from an applied

( position, the forward extension of the ram being adapted to engage mechanically with such means and therefore to be put into indirect mechanical engagement with the spring.

5 In particular, the means to remove the power spring from an applied position comprises a caged bolt, and the forward extension of the hydraulic ram is engaged to or adapted to engage with an upward extension of such a caged bolt. In this embodiment, the caged bolt may be integral to or provided for use with the brake assembly, or may be integral to or provided for use with the 10 testing device.

Engagement between the forward extension of the ram and the spring/any intermediate connecting member may be through a permanent fixing, or through a removable fixing, for example a snap fit connection, an interference 15 fit, a threaded fit etc. Power means may comprise a fluid drive such as a pump for urging the fluid driving the ram, for example in the form of an electrical pump. The power means may be driven by a suitable power source, for example an electrical 20 power source, and in particular a portable power source such as a battery. The fluid drive and/or power source are conveniently associated together with the testing device in compact and portable manner, in particular comprising a portable electric motor pump and electrical power source.

25 In the alternative a separate and remote power means may be provided to drive the ram, which may be of any suitable form, including electrical, mechanical, electro-mechanical, hydraulic, pneumatic etc. The fluid pressure detector is able to detect the pressure in the fluid driving the 30 ram, and consequently indicate the applied force. Conveniently, the fluid

( pressure detector comprises or is provided in association with suitable display means to display this pressure in the form of a meaningful result.

The display means may comprise an alphanumeric display, a dial display or 5 the like calibrated to display pressures and/or forces in appropriate units. The displayed result may then be compared against standard reference results predetermined for the brake spring under test to give an indication of its functional condition.

10 Additionally or alternatively the display means may be adapted to display the result as one of a small number of predetermined conditions by comparison with pre-stored values. For example, the display means may comprise a pass/fail indicator, a good/poor/fail indicator or the like. Such indicators may comprise an alphanumeric display, a series of coloured lights, audible alarms 15 etc. In accordance with a further aspect of the invention there is provided a method for measuring the force of a power spring in a spring brake actuator of an air brake assembly for test purposes, comprising engaging the power spring with 20 a ram extension of a hydraulic ram, actuating the ram to draw the power spring into a more compressed state, detecting the fluid pressure within the ram to detect the drawing force applied thereby.

In particular, the method further comprises comparing the drawing force so 25 measured with predetermined parameters for the spring brake and test, and using that comparison as the basis for a decision as to the serviceability of the brake. The comparison step of the method may be carried out manually by a user, or 30 automatically by a test system comprising the steps of passing the detected

( drawing force or a result derived therefrom to a suitable comparative device, comparing this with a predetermined specification range, and on the basis of

that comparison displaying a result indicative of the condition of the spring and the test.

In a further embodiment of the method, the hydraulic ram is actuated by a portable power source, in particular as part of a self-contained system, for example comprising a portable fluid drive such as an electrical pump to urge the driving fluid under the action of a portable electrical power source.

Further preferred features of the method will be understood by an analogy with the foregoing.

In accordance with a further aspect of the invention, a maintenance regime for 15 a vehicle brake system comprises the use of the above described device or the application of the above described method to the brakes on a vehicle at a predetermined regular interval, and the replacement of any springs whose performance falls below predetermined service parameters.

20 The invention will now describe by way of example with reference to the accompanying figure, which illustrates a testing device in accordance with the invention. The test device and the illustrated embodiment is designed for use with brakes 25 of the type described in US Patent 4860640 brake systems of this type are provided with a drawing bolt which can be received in a suitable recess in the power spring chamber to enable an applied power spring to be mechanically drawn into a non applied configuration. This is a particularly common prior art design. However, it will be understood by those skilled in the art that the 30 invention is not limited to such a brake design, and that other mechanical

( arrangements to effect a coupling between the hydraulic ram and the power spring (whether directly or indirectly) to enable it to be drawn back from its applied state will be appropriate for other brake designs to give effect to the principles of the invention.

The testing device in accordance with the invention comprises a hydraulic ram (10). The ram (10) comprises a hydraulic cylinder (12) of 40 mm diameter containing suitable hydraulic fluid (14). Slidingly mounted within the cylinder (14) is a piston (16) on suitable bearings (18) in conventional manner.

A forward extension (20) of the piston (16) projects through an opening (22) in a forward face (24) of the cylinder casing (12) which is sealed with an O-

ring (26).

15 In the particular embodiment shown engagement is effected to a power spring of a spring brake of the type shown in US 4860640 via an engagement portion (29) of a bolt (28). Bolt (28) is releasably engaged in a receiving cavity (30) in the forward extension (20) of the ram piston by means of the screw threading (32).

Although the illustrated embodiment exploits the drawing bolt system conventionally employed by the example brake, it does not in this particular instance use the provided bolt itself. This is because the bolt provided with the brake is threaded for use with a threaded caging nut whereby a drawing 25 force is applied, whereas in accordance with the present invention it is important that the drawing force is applied directly by the action of the hydraulic ram. Accordingly, in this embodiment, a special shortened bolt is provided to be used instead of the conventional caged bolt. The forward extension (20) of the ram is also suitably sized and shaped to be partially 30 received within the bolt recess of the brake to effect drawing of the power

( spring. Other connecting arrangements to ensure a connection between the piston (16) and the power spring of a brake under test will be appropriate for other brake designs.

5 In the embodiment, the arrangement is intended to be portable and hand held for use by a single user. Although power components are illustrated merely schematically in Figure 1, it will be understood that these will be appropriately associated within a suitable housing in convenient and compact manner together with the piston arrangement.

The power means comprise an electric motor (34) acting to pump the hydraulic fluid via the pump reservoir (36) and diaphragm reservoir (37). The electrical power source is provided by a 12 volt dry cell (38).

15 In use the engaging portion (29) of the bolt engages with a spring of a spring brake initially in its applied state. The power system is actuated to draw the hydraulic ram, and hence to draw the spring into a more compressed state.

The resultant necessary hydraulic pressure is measured by the pressure dial gauge (40). This dial gives an indication of the force required to draw the 20 spring from its applied state, and accordingly an indication of the condition of the spring. The gauge may be calibrated with predetermined tolerance ranges to indicate the condition of the spring, or alternatively a reading may be taken and compared with predetermined reference tables.

25 In this way, an early indication of degraded performance or incipient failure of a spring can be obtained, such as might be caused for example by degradation over time of spring condition, or by partial failure of one or two coils. This means that springs which continue to apply the brake, and thus would pass a simple yes no visual inspection, but which do so with an inadequate below

specification braking force, and thus could present a safety hazard, can be

detected early.

The simple portable arrangement allows springs to be tested regularly and 5 routinely, and allows early identification of such safety problems in admirable manner.

Claims

1. A spring brake testing device for measuring the force of a power spring 5 in a spring brake actuator of an air brake assembly comprising a fluid driven ram having a forward extension adapted to engage with the power spring of a spring brake, a power means acting via the ram to draw against the power spring, and a fluid pressure detector to detect the drawing force applied thereby.

2. A spring brake testing device in accordance with claim I wherein the fluid driven ram is a hydraulic ram.

3. A spring brake testing device in accordance with claim I or claim 2 15 adapted as a portable device and incorporating a portable power means with a suitable portable power source.

4. A spring brake testing device in accordance with any preceding claim wherein the forward extension of the ram is provided with means to 20 engage directly upon the power spring.

5. A spring brake testing device in accordance with any one of claims I to 3 for use with a spring brake having means provided to mechanically remove the spring from an applied position, wherein the forward 25 extension of the ram is adapted to engage mechanically with such means and therefore to be put into indirect mechanical engagement with the spring.

12 l (I. A spring brake testing device in accordance with claim 5 wherein the means to remove the power spring from an applied position comprises a caged bolt, and the forward extension of the hydraulic ram is engaged to or adapted to engage with an upward extension of such a caged bolt.

7. A spring brake testing device in accordance with any preceding claim wherein the power means comprises a fluid drive in the form of an electrical pump for urging the fluid driving the ram.

1() 8. A spring brake testing device in accordance with claim 7 wherein the power source is an electrical power source.

). A spring brake testing device in accordance with any preceding claim wherein the fluid pressure detector comprises or is provided in 15 association with suitable display means to display a meaningful result representative of the pressure in the fluid driving the ram, and consequently indicative of the applied force.

1(). A spring brake testing device in accordance with any claim 9 wherein the 20 display means is adapted to display a result as one of a small number of predetermined conditions by comparison with pre-stored values, for example comprising a pass/fail indicator, a good/poor/fail indicator or the like.

25 11. A method of measuring the force of a power spring in a spring brake actuator of an air brake assembly for test purposes, comprising engaging the power spring with a ram extension of a hydraulic ram, actuating the ram to draw the power spring into a more compressed state, detecting the fluid pressure within the ram to detect the drawing force applied thereby.

12. The method of claim I I further comprising comparing the drawing force so measured with predetermined parameters for the spring brake and test, and using that comparison as the basis for a decision as to the 5 serviceability of the brake.

13. The method of claim I I or 12 wherein the comparison step is carried out automatically by a test system, which system performs the steps of passing the detected drawing force or a result derived therefrom to a I () suitable comparative device, comparing this with a predetermined specification range, and on the basis of that comparison displaying a

result indicative of the condition of the spring.

14. The method of one of claims 11 to 13 wherein the hydraulic ram is 15 actuated by a portable power source as part of a self-contained system, comprising a portable electrical pump to urge the driving fluid under the action of a portable electrical power source.

15. A maintenance regime for a vehicle brake system comprises the use of 20 the above described device or the application of the above described method to the brakes on a vehicle at a predetermined regular interval, and the replacement of any springs whose performance falls below predetermined service parameters.

25 1(. A device method or maintenance regime as hereinbefore described with particular reference to the accompanying drawings.