GB2330813A

GB2330813A - An apparatus for testing stabilisers for towing devices

Info

Publication number: GB2330813A
Application number: GB9722932A
Authority: GB
Inventors: Jonathan Ward
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-10-31
Filing date: 1997-10-31
Publication date: 1999-05-05
Anticipated expiration: 2017-10-31
Also published as: GB9722932D0; GB2330813B

Abstract

An apparatus for testing the pressure of caravan stabilisers by exerting a strain on the stabiliser to cause movement thereof and having means (40) for measuring a parameter associated with the strain, such as the degree of rotation or an electrical parameter. In one embodiment a torque wrench indicator (40) is used to measure the extent of rotation of a dummy ball (42) held within a towball hitch stabiliser. The wrench has a receptacle (44) for receiving the neck (43) of the dummy ball in a non-rotatable manner and an arm (45) extending laterally therefrom. A pointer (48) is rotatably mounted to the receptacle and lies over a scale (50) provided on the arm (45). Movement of the arm to its limit causes a deflection of the pointer which can be measured on the scale to obtain a reading which corresponds to the limit pressure of the stabiliser.

Description

Title: An apparatus for testing stabilisers for towing devices DESCRIPTION The present invention relates to an apparatus for testing stabilisers for towing devices, such as caravans.

Caravans, trailers and the like may be towed by attachment to the rear of the vehicle by means of a tow bar. This allows satisfactory attachment of a caravan or the like to the vehicle but does not prevent snaking (horizontal movement) or pitching (vertical movement) of the caravan during towing. This is clearly dangerous since the caravan may sway to and fro or up and down behind the vehicle whilst being towed, particularly when travelling at high speeds and/or around sharp corners. This is not only hazardous for drivers passing by or travelling behind the towed caravan but may also result in the caravan toppling over causing damage to the van and possibly injury to the occupants.

Stabilisers have been produced for attachment to a towed device which endeavour to alleviate this problem. The stabilisers, which are fastened to the towbar of a car and attached to the front of the caravan, contain friction pads which act to reduce the transverse movement of the van. The stabilisers must allow a degree of movement between the caravan and the car to enable the caravan to travel around corners whilst being able to prevent unwanted swaying of the caravan for example, during windy conditions or when another vehicle passes by. Hence, the stabilisers are required to work within a particular pressure range recommended by the manufacturers of the stabilisers.

There are two main types of stabiliser available for reducing the lateral movement of caravans. Firstly, there is the leaf spring stabiliser which is connected to the tow ball of the tow bar and is attached to the caravan by means of a lever, around 24 inches in length, which is made of sprung steel. For example, that manufactured by Scott Halley Limited. The lever is attached to a base plate of a device having two friction discs which are sandwiched between the base plate and a cover plate with a central plate being provided between the two discs. These discs are tightened to a specific pressure (between 60 to 90 Ibs/in2, preferably 751bs at the end of the lever, or any other prescribed pressure to resist any transverse movement of the caravan caused by, for example, passing traffic. Vertical movement of the caravan which is caused by road undulations is resisted by a sprung bar used in the connection.

The second type of stabiliser is a towball hitch type such as that manufactured by Alko. The stabiliser comprises a hitching couple incorporating two small friction discs formed to the shape of a tow ball. These discs are pressed over and locked onto the tow ball and act to resist both transverse and vertical movement of the caravan.

The ball should be held within given pressure range, as instructed by the handbook accompanying the stabiliser, for example, 110 lbs/in2.

The manufacturers of such stabilisers recommend that the pressure is regularly checked and maintained within a specified range since the friction pads become worn through use, causing a corresponding drop in the pressure. However, prior hereto, it has not been possible to test the pressure of the stabilisers to ensure that replacement or tightening of the pads is not required except by using the sophisticated and expensive techniques employed by the manufacturers of such equipment.

It is an object of the present invention to provide a means for testing the pressure of a stabiliser which is cheap and easy to use.

It is a further object of the present invention to provide a means for testing the pressure of a stabiliser which is lightweight and portable.

Accordingly, the present invention provides an apparatus for testing the pressure of a stabiliser comprising means for exerting a strain on the stabiliser to cause movement of the stabiliser and means for measuring a parameter associated with said strain whereby the pressure can be determined from said measured parameter.

In one preferred embodiment of the present invention, the apparatus measures the limit pressure of the stabiliser, being provided with means for exerting a strain on the stabiliser to cause movement of the stabiliser to its limit extent.

In the context of this disclosure, the term "limit pressure" is the maximum pressure or force which may be resisted by the stabiliser.

A second preferred embodiment of the present invention, the apparatus continuously measures the working pressure of the stabiliser.

A number of different parameters may be utilised in the apparatus of the present invention. Preferably, the degree of rotation of the stabiliser is used to provide a reading corresponding to the limit pressure of the stabiliser. Preferably, this is achieved by providing an extension for increasing the length of the stabiliser to reduce the load which has to be exerted to move the same. Preferably, a calibrated scale is provided to give a pressure reading corresponding to the distance travelled by the extension.

Preferably, the extension is a length of non-resilient material for attachment to the stabiliser. For example, the extension may be attached to the free end of a lever of a leaf spring stabiliser which is normally attached to the caravan. It is preferable that a spring balance is attached at the end of the extension, being provided with a scale to measure the distance moved by the apparatus thereby providing the working pressure of the stabiliser. A receptacle is preferably provided at the end of the extension opposite the spring balance for attachment to the end of the lever of the stabiliser. Preferably, the spring balance is provided with a handle for movement of the extension.

It is to be appreciated that if the pressure of the stabiliser is to be calculated whilst the stabiliser is detached from a vehicle, the end of the stabiliser which is normally attached to the vehicle should be retained, for example within a housing, to prevent movement thereof.

The extension may also be used for reading the pressure of a towball hitch type stabiliser, for example by inserting a dummy ball (i.e., a replica of a normal towball but without any attachments) into the stabiliser and locking the ball in place between the friction discs. Preferably, the dummy ball has a ball-shaped head having a neck extending downwardly therefrom. It is preferable that the dummy ball is comprised of mild steel and preferably is 50mom in diameter, being the standard size of a towball. The extension is provided with means for attachment to the neck of the dummy ball thereby enabling the limit pressure of the stabiliser to be obtained by movement of the arm and obtaining a reading on the scale of the spring balance.

It is to be appreciated that the extension may be provided in a variety of different lengths depending upon the amount of force which an individual is able to apply to the apparatus.

Alternatively, a torque wrench indicator may be provided for measuring the extent of rotation of the stabiliser. Preferably, the torque wrench comprises a receptacle for receiving the neck of the dummy ball in a nonrotatable manner. For example, the neck of the ball and the cavity of the receptacle may be hexagonal in cross section to prevent rotation of the ball relative to the receptacle. The receptacle is provided with an arm for rotation of the receptacle and a scale for measuring the degree of movement of the arm.

Preferably, the arm is fixedly attached to the receptacle and is preferably provided with a handle at the free end thereof. Preferably, a pointer, in the form of a second arm, is rotatably attached to the receptacle above the first arm and extends substantially parallel thereto. The first arm is preferably provided with a scale across an upper region thereof over which the free end of the pointer lies. Preferably, the scale is in the shape of a semicircle in plan view. It is preferable that the scale is provided with means to prevent excessive movement of the pointer. For example, the straight edge of the semicircle may be continuous with a bar which is parallel thereto for forming a slot to constrain the lateral and longitudinal movement of the pointer.

The torque wrench may alternatively have a ratchet mechanism settable to a desired torque for obtaining the pressure of the stabiliser by alteration of the torque of the wrench.

Preferably, the torque wrench indicator is made of a strong material, such as a reinforced metal to withstand the strain exerted thereon during use. The indicator may also be adapted to fit onto the end of a leaf spring stabiliser, for example, by the provision of a suitable socket on the stabiliser for receiving the dummy ball or providing a suitable extension from the stabiliser for engagement with the receptacle of the torque wrench.

Alternatively, an electrical parameter associated with the strain exerted on the stabiliser may be measured to determine the pressure of the stabiliser.

The pressure of the stabiliser may be obtained by reading a change in voltage or the flow of current between the friction discs of the stabiliser. For example, a dummy ball may be provided with a pair of load cell terminals and transducer, the cells being energised by suitable means, such as a battery. The pressure required to move the stabiliser is read by an increase or decrease in the voltage across the terminals. Preferably, the change in voltage is connected to electronic means which provide an analogue or digital read out of the pressure of the stabiliser. It is to be appreciated that this type of apparatus may be a permanent feature of a stabiliser to continuously monitor the pressure of a stabiliser.

The apparatus of the present invention may alternatively comprise an electrically would coil linking the frictions pads for obtaining a pressure by means of a piezo-electrical effect. The strain exerted on the stabiliser causes electricity to be produced to provide an electrical output proportional to the pressure of the stabiliser.

The apparatus may again form a permanent feature of the stabiliser to provide a continuous reading of the pressure. Preferably, the apparatus is linked to the electrical power supply of the vehicle such that the pressure may be monitored from inside the vehicle, for example, being displayed by means of a LCD unit.

For a better understanding of the present invention and to show more clearly how it may be carried into effect, reference will now be made to the accompanying drawings in which Figure 1 is a perspective diagram of a conventional leaf spring stabiliser detached from a caravan; Figure 2 is a perspective view of a conventional towball hitch stabiliser fitted to a caravan; Figure 3 is a schematic diagram of an apparatus for testing the pressure of a stabiliser according to one embodiment of the present invention; Figure 4 is schematic diagram of the apparatus of Figure 3 shown attached to a leaf spring stabiliser; and Figure 5 is a schematic diagram of an apparatus for testing the pressure of a stabiliser according to another embodiment of the present invention.

Referring to Figure 1 of the accompanying drawings, a conventional leaf spring stabiliser for attachment between a vehicle and a caravan is illustrated. The stabiliser has a lever 3 of sprung steel which is attached at one end to a base plate 7a.

A central plate 8 and a cover plate 7b are also provided, the central plate being provided with a member 4 having a bore therethrough for mounting onto a towbar of the vehicle. The opposite end 6 of the lever 3 may be secured within a latch (not shown) provided on a caravan or other device to be towed. The central plate 8 is sandwiched between two friction discs 5 provided between the central plate and each outer plate 7a, 7b. The discs are tightened to a specified pressure around the central plate 8 to allow the required degree of lateral movement of the lever 3.

Figure 2 of the accompanying drawings illustrates a second type of stabiliser, known as the towball hitch stabiliser. This type of stabiliser is permanently fitted inside the hitching couple 10 of a caravan 12. Two small friction discs 14 are provided within the hitch and are moulded into a shape such that they surround the towball by means of a scissor action. The towball is inserted into the base of the couple (see arrow A) and the handle 9 is moved downwards (see arrow B) to lock the ball within the hitch. The friction discs resist both transverse and vertical movement of the caravan.

The pressure range of the aforementioned stabilisers is important to ensure that the caravan is free to turn corners but is restricted against unwanted snaking. The present invention provides an apparatus for checking the pressure of the stabiliser by measuring the maximum distance the stabiliser will move when a force is applied thereto. The distance depends upon the force applied and the resistance to movement exerted by the stabiliser corresponding to the pressure being applied by the stabiliser.

The apparatus may be calibrated using known forces, pressures and distances to provide a scale which will give the exact pressure reading of the stabiliser.

Figures 3 and 4 of the accompanying drawings show one embodiment of an apparatus according to the present invention for measuring the pressure of a leaf spring stabiliser. The apparatus comprises an extension arm 24 having a receptacle 22 for fitting onto the end of the lever 3 of the stabiliser. The opposite end of the arm is provided with a spring balance 26 having a scale 27 and handle 30.

In use, the end of the lever 3 which is normally attached to a caravan is fitted into the receptacle 22. The extension arm acts to increase the length of the lever thereby reducing the load which is required to move the stabiliser to ascertain the pressure. The lever is pulled by means of the handle 30 (shown by arrow P in Figure 4) until it is not possible to move it any further due to the lever reaching the boundary of its extent of movement. The amount of movement is then converted into the amount pressure which has to be applied to the lever to move it a certain distance, through mechanical advantage, by reading the scale 27 on the spring balance by multiplying by a factor of the extension length to produce an actual reading of the pressure or a pre-set pressure. Hence, the pressure at which the stabiliser is acting can be obtained easily and using a reduced amount of effort.

The aforementioned apparatus may be used to test the stabiliser whilst it is still attached to the back of a vehicle or the stabiliser may be removed therefrom. In the latter case, the end of the lever 4 which is normally attached to the tow bar of the car should be retained within a housing 32 to restrict the movement thereof. It is to be appreciated that the extension arm of the apparatus should be comprised of a nonresilient material such that all movement is imparted by the range of movement of the lever of the stabiliser.

The extension may also be used to read the pressure of a towball hitch type stabiliser by inserting a dummy towball (i.e, a replica of a normal towball) into the stabiliser between the friction discs 14 and locking the ball in place. The extension arm may be provided with means for attaching it to the dummy ball such that the pressure of the stabiliser can be read as described above in relation to the leaf spring stabiliser.

Figure 5 of the accompanying drawings show an alternative embodiment of the apparatus of the present invention. The apparatus comprises a dummy ball 42 and a torque wrench indicator 40 having a receptacle 44 for receiving the dummy ball. The dummy ball is comprised of a mild steel and has a diameter of 50mm, corresponding to the standard size of a conventional towball. The tow ball may be made of any other suitable material, such as stainless steel, aluminum or a rigid plastics material.

The neck 43 of the dummy ball is dimensioned such as to fit snugly within the receptacle 44 with the neck and receptacle being shaped to prevent rotation of the dummy ball. An arm 45 extends substantially perpendicularly from one side of the base of the receptacle and terminates with a handle 46. A pointer 48 is rotatably attached to the receptacle and extends therefrom slightly above and parallel to the arm 45 with the end of the pointer lying over scales 50 attached to the arm 45.

In operation, the dummy ball 42 is fastened within the towball hitch stabiliser and the receptacle 44 is placed around the neck of the ball. The arm 45 of the torque indicator is then held by the handle 46 and rotated as far as possible. The pointer remains in the same position due to it being rotatably attached to the receptacle whilst the receptacle and arm move with the movement of the dummy ball 42 relative to the stabiliser. Hence, all movement that occurs is as a result of the movement between the dummy ball and friction pads of the stabiliser. The extent of movement is measured by the position of the pointer 48 over the scales 50 which is altered due to the scales being attached to the extension arm 45. Thus, the deflection of the pointer will be proportional to the pressure at which the stabiliser is working and hence, can be used to determine whether the stabiliser is working within the recommended pressure range.

Alternatively, the apparatus of the present invention may comprise a torque wrench having a ratchet mechanism and settable to a desired torque, whereby incremental pressures can be applied via the ratchet to obtain the pressure of the stabiliser. For example, the receptacle of the torque wrench receives the dummy ball and the wrench set to a torque corresponding to a pressure of 801bs. If the pressure of the stabiliser is greater than 801bs the torque wrench will not give. The pressure of the torque wrench may then be increased to, for example, lOOlbs. If the torque wrench does not give on the application of pressure thereto, the torque pressure of the stabiliser must be between 80-lOOlbs.

The torque wrench indicator may also be adapted to fit onto the end of a leaf spring type stabiliser, for example, by the provision of a suitable socket. It is also to be appreciated that electronic means may be provided within the apparatus to provide a digital reading of the pressure of the stabiliser.

A further apparatus for testing the pressure of a stabiliser comprises load cell terminals which are attached to a dummy ball fitted in a towball hitch stabiliser or to a clamp fitted to a part of the leaf spring stabiliser, the load cells terminals being energised by means of a battery. The pressure required to move the stabiliser is registered by an increase or decrease in the voltage across the terminals which, when computed to an analogue or digital read out provides the pressure of the stabiliser.

Alternatively, a piezo electrical effect involving the compression of an electrically wound coil may be used to obtain a pressure value. The mechanical strain applied by the stabiliser causes electricity to be produced thereby providing an electrical output which is proportional to the pressure of the stabiliser. These types of apparatus are particularly useful because they can provide a continuous reading of the stabiliser pressure. The electricity produced may be connected to the electrical power supply of the vehicle such that the pressure of the stabiliser may be continually monitored within the vehicle, for example by means of a liquid crystal display unit.

Yet a further embodiment of the present invention provides a compression spring fitted or connected to either the arm of the towball hitch stabiliser or the discs of the leaf spring stabiliser which indicates the working pressure of the stabiliser.

The apparatus of the present invention provides a convenient and effective means for checking the pressure of a caravan stabiliser to ensure that it is still working within the recommended pressure range. The stabiliser may be checked whilst it is still attached to the caravan which is particularly important for the towball hitch type stabiliser which cannot be easily removed from the caravan. Alternatively, the stabiliser may be tested in a workshop where any necessary maintenance of the device can be carried out. Thus, this will allow caravan owners to be aware of the efficiency of their stabiliser thereby enabling the stabiliser to be replaced or serviced when required, for example by replacement of the friction discs. This will greatly reduce the number of towed vehicles on the roads which are fitted with deficient stabilisers. The testing apparatus may be installed as a permanent feature of the stabiliser for continuously checking the pressure or comprise a hand-held device for testing the pressure of the stabilisers at regular intervals.

Claims

CLAIMS 1. An apparatus for testing the pressure of a stabiliser comprising means for exerting a strain on the stabiliser to cause movement of the stabiliser and means for measuring a parameter associated with said strain whereby the pressure can be determined from said measured parameter.
2. An apparatus as claimed in claim 1, wherein the apparatus measures the limit pressure of the stabiliser, being provided with means for exerting a strain on the stabiliser to cause movement of the stabiliser to its limit extent.
3. An apparatus as claimed in claim 1, wherein the pressure of the stabiliser is continuously monitored.
4. An apparatus as claimed in claim 1 or 2, wherein the parameter to be measured is the degree of rotation of the stabiliser.
5. An apparatus as claimed in claim 4, wherein an extension is provided for increasing the length of the stabiliser thereby reducing the load which has to be exerted to move the same.
6. An apparatus as claimed in claim 4 or 5, wherein a calibrated scale is provided to give a pressure reading from the distance travelled by the extension.
7. An apparatus as claimed in claim 5 or 6, wherein the extension is of a nonresilient material.
8. An apparatus as claimed in claim 5, 6 or 7, wherein a spring balance is attached to an end of the stabiliser.
9. An apparatus as claimed in claim 8, wherein the spring balance is provided with a handle.
10. An apparatus as claimed in any one of claims 5 to 9, wherein the extension is attached to the end of a sprung lever of a leaf spring type stabiliser.
11. An apparatus as claimed in claim 10, wherein a receptacle is provided at the end of the extension opposite to the spring balance for attachment to the end of the stabiliser.
12. An apparatus as claimed in claim 10 or 11, wherein the end of the stabiliser which is normally attached to a vehicle is retained within a housing to prevent movement thereof.-
13. An apparatus as claimed in any one of claims 5 to 9, wherein the extension is attached to a dummy ball held within a towball hitch type stabiliser.
14. An apparatus as claimed in claim 13, wherein the dummy ball is a replica of a standard towball without attachments for insertion in the hitch type stabiliser.
15. An apparatus as claimed in 14, wherein the dummy ball has a ball-shaped head and a neck extending downwardly therefrom.
16. An apparatus as claimed in claim 13, 14 or 15, wherein the dummy ball is comprised of mild steel.
17 An apparatus as claimed in claim 15 or 16, wherein the head is 50mm in diameter.
18. An apparatus as claimed in any one of claims 13 to 17, wherein the extension is provided with means for attachment to the neck of the dummy ball.
19. An apparatus as claimed in claim 4, wherein a torque wrench indicator is provided for measuring the degree of rotation of the stabiliser.
20. An apparatus as claimed in claim 19, wherein the torque wrench comprises a receptacle for receiving a dummy ball having an arm extending laterally therefrom for causing rotation of the receptacle.
21. An apparatus as claimed in claim 20, wherein the torque wrench has a ratchet mechanism for obtaining the pressure of the stabiliser by alteration of the torque of the wrench.
22. An apparatus as claimed in claim 20, wherein the receptacle receives the dummy ball in a non-rotatable manner and is provided with a scale for measuring the degree of rotation of the arm.
23. An apparatus as claimed in claim 20, 21 or 22 wherein the dummy ball is a replica of a standard towball without attachments for insertion in the hitch type stabiliser.
24. An apparatus as claimed in claim 23, wherein the dummy ball has a ballshaped head and a neck extending downwardly therefrom.
25. An apparatus as claimed in any one of claims 20 to 24, wherein the dummy ball is comprised of mild steel, stainless steel, aluminium or a rigid plastics material.
26. An apparatus as claimed in claim 24 or 25, wherein the head is 50mm in diameter.
27. An apparatus as claimed in any one of claims 24 to 26, wherein the neck of the dummy ball and cavity of the receptacle are hexagonal in cross section to prevent rotation relative to one another.
28. An apparatus as claimed in any one of claims 22 to 27, wherein the scale is provided across an upper region of the arm.
29. An apparatus as claimed in claim 28, wherein the scale is a semicircle in plan view.
30. An apparatus as claimed in any one of claims 22 to 29, wherein a pointer, in the form of a second arm, is rotatably attached and extends laterally from the receptacle of the torque wrench.
31. An apparatus as claimed in claim 30, wherein the pointer extends from the receptacle above and substantially parallel to the arm, the free end of the pointer lying over the scale provided on the arm.
32. An apparatus as claimed in claim 31, wherein the scale is provided with means to constrain excessive lateral and longitudinal movement of the pointer.
33. An apparatus as claimed in claim 19, wherein the torque wrench indicator is adapted to be attached to a leaf spring type stabiliser.
34. An apparatus as claimed in claim 1, 2 or 3, wherein an electrical parameter associated with strain exerted on the stabiliser is measured to determine the pressure of the stabiliser.
35. An apparatus as claimed in claim 34, wherein the pressure is obtained by reading a change of voltage or the flow of current between frictions discs of a stabiliser.
36. An apparatus as claimed in claim 35, wherein the change in voltage is measured by the provision of load cell terminals and a transducer between the friction pads of the stabiliser.
37. An apparatus as claimed in claim 35 or 36, wherein the change in voltage is connected to electronic means to provide an analogue or digital read out of the pressure of the stabiliser.
38. An apparatus as claimed in 34, wherein an electrically wound coil links the friction discs of the stabiliser for obtaining the pressure by means of a piezo-electrical effect.
39. An apparatus as claimed in any one of claims 34 to 38, wherein the electrical parameter is connected to the electrical power supply of a vehicle having means for displaying the pressure reading inside the vehicle.
40. An apparatus as claimed in claim 39, wherein the pressure reading is displayed by a liquid crystal display unit.
41. An apparatus substantially as hereinbefore described and with reference to Figures 3 and 4 or 5 of the accompanying drawings.