GB2221047A

GB2221047A - A coupling load sensor

Info

Publication number: GB2221047A
Application number: GB8913753A
Authority: GB
Inventors: Michael Ian Cornwell
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-06-15
Filing date: 1989-06-15
Publication date: 1990-01-24
Anticipated expiration: 2009-06-15
Also published as: GB2221047B; GB8913753D0; GB8814231D0

Abstract

A coupling load sensor formed as a trailer coupling has means for detecting if the vertical load applied to the coupling by the trailer exceeds a predetermined threshold. A coupling body (12) has a slidable pin (22) resiliently biased by a spring (28) and surmounted by a coupling ball (27). The spring (28) is compressed by the load applied by a trailer and the degree of compression of the spring (28) is indicative of the trailer load. This may be represented purely visibly at the coupling by a reference mark (29, 30, 31) referred against a movable index (23) on the pin (22), or may be indicated by means of microswitches (54, 55) engaged by an actuator (53) to cause illumination of warning lamps (59, 60, 61) in a dashboard panel (58). In an alternative (Fig 3), the load is detected by strain gauges mounted on the upper and lower surfaces of the drawer bar of a trailer. <IMAGE>

Description

A COUPLING LOAD SENSOR The present invention relates generally to a coupling load sensor and particularly to a sensor for detecting and indicating the static load applied by a trailer vehicle to a coupling by which it is coupled to a towing vehicle.

It is widely known that the static, vertical, load applied by a trailer drawn onto the towing coupling by which it is interconnected with a towing vehicle must not exceed certain limits not only for safety reasons and so as not to cause excessive deflection of the vehicle suspension, but also to avoid excessive tyre wear. This is of particular importance with trailers such as caravans the weight distribution of which may vary from time to time due to variations in the distribution of the contents of the caravan. Although reference will be made hereinafter to caravans as exemplary trailers it will be appreciated that no loss of generality is introduced thereby and that the present invention is equally applicable to any form of trailer.

Apparatus exists for performing a loading test on the draw bar of a trailer such as a caravan prior to coupling it to a towing vehicle, such apparatus comprising a stand with a load indicator scale onto which the draw bar of the trailer may be placed in order to provide an indication of the static vertically downward load of the draw bar prior to coupling it to the towing hitch of a towing vehicle.

Such known devices have a number of disadvantages in practice. First they are inconvenient to use because the trailer has to be manoeuvred by hand into a position where the load detecting stand is positioned under the draw bar, which latter must then be lowered onto the load detecting stand to provide an indication of the static load exerted thereby. Further, a change in the load distribution within the trailer (particularly in the case of a caravan which may be coupled and uncoupled several times during a holiday and occupied whilst uncoupled) may not necessarily come to the attention of the intending driver so that he may not be aware or may not recollect the need to make use of the load tester prior to coupling.For example, a caravan with an appropriate load distribution at the commencement of a journey may be tested for the trip to determine that it is within safe limits, but may fall outside those limits due to redistribution of the caravan contents during use without this being brought to the driver's notice.

Moreover, the fact that the coupling load is outside safe limits would not necessarily immediately be apparent, but may be critical in an emergency situation when, for example, the effect on the towing vehicle's steering and the road holding of the towing vehicle may be detrimentally affected. This might only come to the notice of the driver in an emergency situation when the road holding and behaviour of the vehicle may be unexpectedly poor. Even if not of dangerous proportions the loading may result in an increased rate of wear of the towing vehicle tyres.

Another disadvantage of the known load-testing stand is the necessity for this to be carried about with the trailer, and the possibility that even if its use is remembered, it may be mislaid or lost.

The present invention seeks to provide-means by which the static load exerted by a trailer on the towing coupling of a towing vehicle can be detected upon coupling of the trailer, with means being provided to indicate whether or not the load falls within predetermined safety limits.

According to one aspect of the present invention, therefore, a coupling load sensor for use on trailer connection apparatus for coupling a trailer to a towing vehicle is provided with means for detecting the static load between the trailer and the towing vehicle at the point of interconnection thereof, including means for providing an indication representative thereof. This indication may be no more than an alerting signal, if the trailer load falls outside predetermined limit values, or may be a graduated indication of the position within a scale of the instantaneous load. The load detection may take place automatically and result in an alerting signal only if it falls outside the predetermined range, may be arranged to give a permanent readout indicative of the load test result or may be energised or activated only periodically at the command of the driver.It will be appreciated that since the contents of a trailer may shift whilst travelling, to result in an increased or a decreased load (or even a negative load in some cases), a permanent indication visible from the driving seat may give more reassurance.

In one embodiment of the invention the load detector is located on a towing hitch fitted to the towing vehicle. Such load detector may be provided with indicator means for providing a direct indication at the coupling of the load applied by the trailer to the towing vehicle so that the trailer load can be indicated at the moment of coupling. Alternatively, however, the load indicator means may be located within the vehicle passenger compartment at a point remote from the coupling so that the driver may be alerted to the loading conditions on the hitch.The load detector may be permanently sensitive so that the driver is alerted should any change to the loading conditions be experienced during a journey, or may be sensitive only when activated on the assumption that, once the trailer has been connected and tested, the possibility of weight distribution change during a journey is sufficiently low as to require no permanent monitoring.

Various different embodiments of the invention may be produced making use of different physical phenomena to produce the necessary indication. In a simple embodiment of the invention, for example, the load indicator means may be mechanically actuated by relative displacement of two parts of a towing coupling, in such a configuration the two parts may be resiliently biased towards a first position and displaceable by the load exerted by the trailer, against the resilient biasing. Indication of the load may be provided simply by reference to the relative positions of the two relatively movable components one or both of which may be suitably marked for this purpose to provide a reading scale, or by means of electrical or electronic switching means actuated by the relative movement of the two components.

Alternatively, however, the indication may be effected hydraulically. Again, two relatively movable parts of a towing hitch may be employed to cause displacement of an hydraulic fluid, or alternatively pressure measurement of a body of fluid may be effected without significant displacement of the fluid.

Further embodiments may provide indication by pneumatic means, again sensitive to relative displacement of two or more relatively movable parts of a towing coupling. A more sophisticated embodiment may make use of electrical measurement of deformation of a single component of a towing coupling. For example a plurality of strain gauges may be mounted on a monolithic towing coupling component to detect deformations to which the towing coupling is subjected when a trailer load is applied.

In another aspect of the present invention the load detector means may be located on a draw bar of the trailer rather than on a towing coupling of the towing vehicle. Any of the above-mentioned physical phenomena may be used for providing a corresponding indication of the loading on the towing coupling by analogy. The electrical embodiment referred to above may be most conveniently applied to a trailer draw bar since strain gauges are most conveniently used to detect bending moments and the draw bar of a trailer has a convenient configuration and is orientated so as to be subjected to bending moments, making it particularly suitable for this purpose.

If embodiments of the invention are provided with relatively movable components there may be provided means for locking such relatively movable components into an immovable configuration so that no slackness in the towing coupling due to movement of the relatively movable components during driving is experienced.

According to another aspect of the present invention a towing coupling for a towing vehicle is provided with a trailer vehicle load sensor for providing an indication of the magnitude of the downward load applied by the draw bar thereof to the towing coupling when connected.

Such a trailer vehicle load sensor may operate to detect the trailer load by determining the displacement of an elastic component from its natural position or length. Such elastic component may be a spring which biases a first towing coupling component connectible to a trailer to a first position with respect to a second towing coupling component which is connectible to a towing vehicle.

Various embodiments of the present invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side view of a towing coupling formed as a first embodiment of the invention; Figure 2 is a rear view of the towing coupling illustrated in Figure 1; Figure 3 is a schematic side view of a draw bar of a trailer formed as a second embodiment of the present invention; Figure 4 is a circuit diagram illustrating the basic components of a strain gauge circuit suitable for use in the embodiment of Figure 3; Figure 5 is a rear view similar to that of Figure 2, of a further embodiment of the invention; and Figure 6 is another circuit diagram of an electrical circuit suitable for use with the embodiment of Figure 5.

Referring now to the drawings, and particularly to Figures 1 and 2 thereof a towing coupling formed as an embodiment of the invention is generally indicated with the reference numeral 11. This coupling comprises a main body 12 having two parallel side walls 13, 14 defining an elongate open sided chamber 15 between two opposite projecting terminal flanges 16, 17.

Extending transversely from the body 12 are two ears 18, l9 having respective holes 20, 21 by means of which the towing coupling may be secured by fixing elements such as bolts to a mounting plate in a conventional manner. When so fixed the elongate chamber 15 is orientated with its longitudinal axis substantially vertically.

Extending through the elongate chamber 15 and passing through aligned apertures in the two opposite end flanges 16, 17 is a shouldered pin 22. The aperture in the upper terminal flange 16 is larger than that in the lower terminal flange 17 and receives an upper portion 24 of the pin 22, which has a larger diameter than the main part of the pin 22 and which joins it at a shoulder 23. The lower part of the pin 22 projects below the lower terminal flange 17 and receives a nut 25 which limits the upward axial sliding movement of the pin 22 with respect to the body 12 within the aligned apertures in the terminal flanges 16, 17.

At the upper end of the upper portion 24 of the pin 22 is a neck 26 surmounted by a spherical coupling ball 27 the dimensions of which match those conventionally used for towing couplings, namely 50 mm. Surrounding the pin 22 within the chamber 15 is a compression coil spring 28 the upper end of which engages against the should-23 and the lower end of which rests on the upper surface of the lower terminal flange 17. The spring 28 urges the pin 22 upwardly so that the nut 25 is pressed against the lower face of the lower terminal flange 17 when in its relaxed or unstressed position.

The side wall 13 of the casing 12 is provided with three indicator marks 29, 30, 31 which are visible from both the front and side of the coupling and which are positioned, in relation to the spring rating of the coil spring 28 to provide an indication of the downward load applied to the pin 22 when a trailer coupling is connected to the ball 27. In such circumstances the downward load causes compression of the spring 28 so that the shoulder 23 moves downwardly towards the three marks 29, 30, 31, coming to rest when the upward force of the compressed spring matches the downward force applied by the trailer load.By referring the position of the shoulder 23 against the three marks 29, 30, 31 the user can readily ascertain whether the trailer load is light, (when the shoulder 23 is in the vicinity of the mark 29), normal (when the shoulder 23 is in the vicinity of the mark 30) or heavy (when the shoulder 23 is in the vicinity of the mark 31). The position of the mark 31 represents the maximum permissible trailer load and if the shoulder 23 should be displaced below that position the user will be aware that the towing vehicle is overloaded and the weight distribution in the trailer must be rearranged or the load on the trailer reduced so that the load on the towing coupling is not excessive.

In use of the towing coupling illustrated in Figures 1 and 2, as the vehicle moves over uneven ground (and at relatively high speed even the arterial road surface may be considered as not being entirely smooth, the forces on the coupling will vary so that the pin 22 may slide up and down to absorb the shocks. It may be considered, however, that such relative displacement between the trailer and the towing vehicle is disadvantageous, in which case means may be provided for locking the pin 22 in relation to the body 12 to prevent such motion. This may be achieved, for example, by means of a wedge suitably shaped to fit under the projecting flange between the upper part 24 of the pin 22 and the neck 26 or by tightening the nut 25 to take up any exposed thread. This latter arrangement, however, is less likely to be satisfactory since the time taken to tighten a nut, and the requirement for tools is likely to be unacceptable. A suitable pivoted wedging or toggle arrangement is therefore likely to be found most satisfactory.

Figures 3 and 4 illustrate an alternative embodiment in which an indication of the trailer static load can be provided without modification of a conventional coupling hitch as would be fitted to a towing vehicle.

in this embodiment a draw bar 32 of a trailer, typically a caravan, is provided with two strain gauges 33, 34 positioned one above and one below the draw bar 32. As is conventional, the draw bar 32 may be provided with a cup-type connection 35 which, in use, fits over the ball of a conventional ball hitch, and may further be provided with a telescopic leg 36 with a castor wheel 37 for taking the load off the trailer when it is not coupled to a towing vehicle.

As can be seen in Figure 4 the two strain gauges 33, 34 are connected in a bridge circuit with a fixed resistor 38 and a variable resistor 39 which can be adjusted to provide calibration of the circuit. The two strain gauges 33, 34 effectively act as variable resistors respectively increasing and decreasing in resistance in response to the application of a bending load to the draw bar 32 which causes one (the lower strain gauge 34) to extend and the other (the upper strain gauge 33) to contract. The bridge circuit is supplied by the vehicle battery 40 which feeds the nodes 41, 42 of the bridge and the detection circuit is connected across nodes 43, 44 of the bridge.The detection circuit may simply comprise an amplifier 45 and threshold detector 46 which produces a single output when a certain out-of-balance current is generated due to variations in the resistance of the strain gauges 33, 34. The output from the threshold circuit 46 is applied to a warning lamp 47 positioned, for example, on the dashboard of the vehicle. The circuit apart from the strain gauges 33 and 34 may all be mounted on the towing vehicle, for connection to the strain gauges 33 and 34 typically through the normal electrical coupling which is made to interconnect the electrical circuit of the towing vehicle with the lights on the trailer.Thus, when the trailer is connected and the electrical circuit completed a monitoring action is automatically effected at all times that the circuit is live so that, when the driver intends to move off, the warning lamp 47 will be illuminated to provide a warning that the trailer is exerting an overluad. The trailer load may be permanently monitored since no relative displacement of the coupling components is necessary in this case so that the whole circuit may remain permanently active without detriment to the driving characteristics of the vehicle/trailer combination.

In order to avoid unwanted flashing of the lamp 47 due to short term instantaneous overloads, for example if the vehicle should go over a bump the circuit may include a delay or integrating component which prevents illumination of the lamp until the overload has been detected for a continuous period of, say, 1.5 seconds.

Referring now to Figures 5 and 6, the alternative embodiment shown has a physical structure similar to that of the embodiment of Figures 1 and 2, and in Figures 5 and 6 those components fulfilling the same or equivalent functions as corresponding components in the embodiment of Figures 1 and 2 have been identified with the same reference numerals. In this embodiment the pin 22 is guided within bushes 50, 51 in the flanges 16, 17 and, unlike the embodiment of Figures 1 and 2, carries an actuator member 53 secured by a clamping screw 52 to an upper part of the pin 22 immediately beneath the flange 16 when the spring 28 is at its maximum extension.The body 12 carries an upper microswitch 54 and a lower microswitch 55 having respective actuating members 56j 57 engageable by the actuator 53 as the pin 28 slides with respect to the flanges 16, 17 upon exertion of a downward load on the ball 27. The positions of the switches 54, 55 is such that the switch 54 is closed when the downward load on the ball 27 is within a normal or safe range, and open when the actuator member 53 is, as illustrated in Figure 5, located above this position, thereby indicating that the load is lighter than a safe or normal range.

Figure 6 illustrates a circuit diagram incorporating the switches 54, 55 and a display panel for mounting on the vehicle dashboard. The display panel is generally indicated with the reference numeral 58 by the broken outline. The panel includes three light emitting diodes 59, 60, 61 connected in parallel via a resistor 62, push button test switch 63 to the vehicle supply indicated by the terminal 64.The three parallel lines containing the light emitting diodes 59, 60, 61 are identified with the reference numerals 69, 70, 71 and are connected, as shown in Figure 6, to the poles of the two microswitches 54, 55 such that the normally open contacts of the microswitch 54 are connected to the lines 69, 70 and the normally closed contacts are connected between the lines 69 and one of the normally open contacts of the switch 55, the other of which is connected to the line 71 whilst the normally closed contacts of the switch 55 are connected to the microswitch 54 and vehicle earth.

When the spring 28 is at its maximum extension as illustrated in Figure 5 both switches 54, 55 are open and the circuit is configured as illustrated in Figure 6 with a current path from the vehicle supply through the test switch 63 and the light emitting diode 59 along the line 69 through the two microswitches 54, 55 to earth. If the test switch 63 is closed, therefore, the light emitting diode 59 will illuminate to indicate that the ball 27 is high, namely the load is less then a normal or safe range.

When a normal load is applied to the ball 27 the spring 28 is compressed to appoint where the actuator 53 engages the actuating member 56 of the switch 54 causing the normally open contacts to close, opening the circuit connected to the line 69 and closing that to the line 70 so that now, when the test switch 63 is pushed, the circuit is completed through the light emitting diode 60 which thus illuminates to indicate that the load is safe. If an excess load is applied to the ball 27 the spring 28 will be compressed to a point where the actuator 53 also engages the switch actuating member 57 causing the switch 55 to commute, opening the circuit from the switch 54 and closing the circuit from the line 71 so that, now, if the test switch 63 is pushed the light emitting diode 61 will illuminate to indicate an excess load or "low" position of the ball 27. An alarm tap 72 is taken from the line 70 to an audible indicator energised if there is an open circuit between the tap 72 and the vehicle earth indicating that the switches 54, 55 are either in the position illustrated in Figure 5, namely with neither switch actuated, or in a condition with both switches actuated.

Claims

1. A coupling load sensor for use on trailer connection apparatus for coupling a trailer to a towing vehicle, in which there are provided means for detecting the static load applied by the trailer to the towing vehicle at the point of interconnection thereof, and means for providing an indication representative thereof.

2. A coupling load sensor as claimed in Claim 1, in which the load detector is located on a towing hitch fitted to the towing vehicle.

3. A coupling load sensor as claimed in Claim 1 or Claim 2, in which the load indicator means provides a directindication, at the coupling, of the load applied by the trailer to the towing vehicle.

4. A coupling load sensor as claimed in Claim 1, in which the load indicator means are located within the vehicle passenger compartment at a point remote from the coupling.

5. A coupling load sensor as claimed in any preceding Claim, in which the load indicator means provides an indication of whether the load on the towing vehicle coupling hitch exceeds a predetermined threshold value.

6. A coupling load sensor as claimed in any preceding Claim, in which the load indicator means is mechanically actuated by relative displacement of two parts of a towing coupling.

7. A coupling load sensor as claimed in any preceding Claim, in which the indication provided by the indicator means is generated hydraulically.

8. A coupling load sensor as claimed in any of Claims 1 to 6, in which the indication provided by the indicator means is generated pneumatically.

9. A coupling load sensor as claimed in any of Claims 1 to 6, in which the means for detecting the static load comprise strain gauges on a monolithic towing coupling component.

10. A coupling load sensor as claimed in Claim 1, in which the load detector means are located on a draw bar of the trailer.

11. A coupling load sensor as claimed in Claim 20, in which the said load detector means are electrically or electronically activated.

12. A coupling load sensor as claimed in Claim 10 or Claim 11, in which the load detector means comprise a strain gauge system and associated sensing network.

13. A coupling load sensor as claimed in any of Claims 10 to 12, in which there is provided an hydraulic indication of the detected load, such as by pressure measurement in an hydraulic fluid without causing displacement thereof.

14. A coupling load sensor as claimed in any preceding Claim, in which a locking device is provided to prevent displacement of relatively movable coupling parts when the vehicle is in motion.

15. Trailer coupling apparatus incorporating or having associated therewith a coupling load sensor as claimed in any preceding Claim.

16. Trailer coupling apparatus as claimed in Claim 15, comprising a body attachable to a towing vehicle, a trailer coupling member mounted to the body and relatively movable with respect thereto in the direction of the load applied by a trailer connected to the coupling member, resilient biasing means urging the trailer coupling member in a direction opposite that of the said applied load, and position gauging means operable to produce an output signal when the trailer coupling member is in a predetermined relative position with respect to the said body.

17. A towing coupling for a towing vehicle having a trailer vehicle load sensor for providing an indication of the magnitude of the downward load applied by the draw bar thereof to the towing coupling.

18. A towing coupling as claimed in Claim 17, in which the trailer vehicle load sensor operates to detect the trailer load by determining the displacement of an elastic component from its natural position or length.

19. A towing coupling as claimed in Claim 18, in which the elastic component is a spring which biases a first towing coupling component connectable to a trailer to a first position with respect to a second towing coupling component which is connectable to a towing vehicle.

20. A towing coupling substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.