GB2348508A

GB2348508A - Tow coupling sensor assemblies

Info

Publication number: GB2348508A
Application number: GB0007959A
Authority: GB
Inventors: Kenneth Stephen Evans
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-04-01
Filing date: 2000-04-03
Publication date: 2000-10-04
Anticipated expiration: 2020-04-03
Also published as: GB0007959D0; GB2348508B; GB9907523D0

Abstract

A system for measuring the forces on a towing coupling comprises typically a towball sensor assembly 1 and display unit 2 mounted in the towing vehicle. The force sensor is based upon a towball resiliently mounted in a material with damping properties such as an elastomer, to reduce road noise interference. The displacement of the ball, measured by capacitive or other means, is a measure of the force in up to three orthogonal directions. A processor is used to calculate towball vertical loading, fore/aft and lateral forces, and display information representing load distribution, braking, stability and tyre pressures. The addition of an accelerometer enables the system to calculate the towed vehicle gross weight. The processor program code will enable prioritisation of display information to reduce data overload to the driver, as well as enabling the ratio of the two vehicle weights to be shown.

Description

Tow Coupling Sensor Assemblies Background to Invention This invention relates to a tow coupling sensor assembly for monitoring the forces exerted on a tow coupling by a vehicle, such as a trailer or caravan, which is being towed.

The invention is more particularly, but not exclusively, concerned with measuring the forces on a vehicle tow hitch imposed by a caravan or trailer and displaying them on a read out device within the vehicle to the driver or passenger. Interpretation of the information so presented may assist whilst stationary and whilst moving along the road to establish whether the trailer is safe and within the load limits of itself and those of the car. A typical recommendation from caravan towing authorities is that the caravan gross weight should not exceed 85% of the cars kerb weight. A further use would be to provide information about the stability of the trailer whilst moving and the condition of its brakes or tyres. Additionally the information may enable the driver to change the driving conditions to improve the fuel economy of the towing vehicle. An optional audible alarm within the display unit may alert the driver should selectable limits be exceeded.

No known device is presently available to accomplish these tasks. There are simple mechanical devices, usually based on springs within concentric cylinders, which indicate by mechanical deflection the vertical load on the tow hitch. These are most often referred to as noseweight gauges. They have to be used beneath the coupling on the trailer whilst it is detached from the towing vehicle. Other devices exist to weigh a trailer by placing its wheel or wheels on sensor pads. Both these types of device are for use outside the vehicle, whilst uncoupled, and stationary.

A number of proposals have previously been made for measuring some of the information required. EP 0302437 (Pfister) discloses fore/aft and vertical towball force sensing schemes based on the use of an elastomer as a pressure transmission medium.

Pressure transducers coupled to a processor provide signals to control the brakes and alert the driver to noseweight overload, either visually or acoustically. However the combination of the two measurement directions with this method is complex, bulky, and unlikely to meet with the requirements of European directive 94/20/EC.

GB 2221047 (Cornwell) discloses a noseweight only technique using microswitches to detect the deflection of the towball against a spring, with an indication being provided to the driver by means of lights. However such an arrangement allows for the possibility of disadvantageous movement of the various parts of the coupling unless means are provided to lock them together during travel. Clearly such an arrangement is best suited to static measurements because of signal noise problems which are likely to be encountered whilst moving. Furthermore this technique cannot be conveniently extended to measurements in other planes.

WO 91/02226 (Siarr) describes an alternative noseweight only technique, utilising a sensing plate interposed between a towing ball and the vehicle attachment point.

Means for sensing the capacitance and a strain gauge are discussed in the reference.

Once again this technique cannot be conveniently extended to measurements in other planes.

GB 2275343 (Fischer) discloses a method for measuring the fore/aft and vertical loads on a fifth wheel coupling. This method uses either strain gauge techniques or measurement of the positional change of a support pin mounted elastically in a fixed support. The measurement is accomplished by means of autonomous displacement sensors at differing locations with respect to the pin. It would be impractical and costly to employ three independent sensors of this type within the confines of a conventional small vehicle tow coupling such as a tow ball.

It is an object of the present invention to provide an integrated one, two or three axis force sensing solution with inherent damping to reduce the effect of high frequency noise, together with acceleration measuring and processing means, to provide a system capable of meeting the requirements of directive 94/20/EC for determining the above mentioned safety parameters on a towing vehicle.

Summary of Invention According to the present invention there is provided a tow coupling sensor assembly for monitoring the forces exerted on a tow coupling by a vehicle being towed, the assembly comprising force sensing means with inherent damping for mounting in the vicinity of the tow coupling and for producing an output signal which varies with the forces exerted on the coupling, processing means for producing an indicator signal from said output signal, and remote indicating means responsive to said indicator signal for providing an indication of the forces exerted.

In one embodiment of the invention the arrangement consists of a tow vehicle coupling, typically a ball hitch, containing or connected to a vertical force sensor with integral damping to reduce road noise, which communicates with a remote processing and display unit within the tow vehicle. The processing unit which can be built using a microcomputer chip may be used to calculate, from the force sensor, vertical force in a convenient form for presentation. This weight may now be indicated in some form on the display unit and can indicate directly whether the weight is within limits for the towing vehicle or trailer. It will be appreciated that this parameter can be measured whilst stationary or moving.

In a second embodiment of the invention a second integrated force sensing axis is added in the fore/aft direction to the previous arrangement. Fore/aft force can be used during motion to measure the contribution from the trailer's brakes, and thus ascertain their effectiveness and alert the driver if necessary.

A third embodiment of the invention includes a fore/aft oriented accelerometer connected to the processing unit and conveniently mounted within it. The acceleration information together with that from the fore/aft force axis may be used to calculate, when moving, the gross weight of the trailer. This is accomplished by using Newton's 2nd law of motion. It is important that this calculation is only done at low speeds to avoid the influence of aerodynamic drag on the trailer. To this end it would be advantageous to include a speed sensor in the system, but alternatives are possible. A timer could be used to only allow weight calculation in the early stages of movement and thus prevent high speed operation. Another method would involve the inertial calculation of the speed from the acceleration.

In a fourth embodiment of the invention a third integrated force sensing axis is added in the lateral direction. Loss of pressure in a tyre on one side of the trailer would cause an imbalance in the lateral force measured on the tow coupling which might be used to indicate the dangerous condition to the driver. In addition variable lateral forces can be used to access the stability of the tow vehicle trailer combination whilst moving.

Typically an unstable combination will begin to slew from side to side in an oscillatory manner. A measure of periodic lateral forces on the tow coupling, within a particular low frequency band defined by the processing unit, would give early indication of this. The periodic nature of the measurement will distinguish the problem as an instability, whereas a steady force might for example be caused by a side wind or as described above by a tyre pressure imbalance.

With many items of data potentially available the software code in the processing unit will be used to decide display priority, and only indicate relevant information to the driver unless requested otherwise. In a further use of the software it will be possible to calculate and indicate the percentage ratio of the car/caravan weights.

It will be appreciated that all, or varying combinations, of these different sensing arrangements can be incorporated in a particular system realisation depending on the requirements of the driver.

One preferred force sensor design for a ball hitch comprises a ball on a vertical shaft fixed to and passing through a concentric circular rubber bush arrangement. The bush consists of a thick walled rubber or elastomer element contained within and attached to an outer metal cylindrical sleeve. Below the bush and attached to the end of the vertical shaft is an electrode in the form of a solid metal disc, sphere or other convenient shape contained within an outer housing. The outer housing has multiple isolated conducting plates within its inside surface adjacent, not touching the shaft electrode, but conforming to its general shape. The entire assembly is attached to the tow vehicle by means of the outer metal sleeve. As the force on the ball hitch varies the rubber element flexes and varies the gap, by an amount proportional to the force, between the shaft electrode and the surrounding plates. The capacitance variation between the various plates will indicate the gap dimension and hence the force applied to the ball. The geometrical design of the electrode and plates enables a measurement to be made in up to three orthogonal directions, by suitable summing and differencing of the interdependent capacitances so formed. Advantages of the rubber bush, which behaves in this invention as a spring, are its inherent damping and potential to tailor its shape to give anisotropic stiffness. A more complex alternative would be a bush as described above with an additional metal spring at least partially moulded within it, to provide addition control of the elastic rate. One further implementation would be some form of metal spring and damper unit.

In another form of the above arrangement a magnet can be attached to the bottom of the shaft and its field monitored by means of one or more magnetic field detectors such as a magnetoresistive device, so as to allow multiple axis measurement. Inductive means could also be utilised by having a multiple coil arrangement with an armature attached to the shaft and moving within the coils. Optical means would be a further method realised by interrupting a light beam, with a suitable shutter attached to the shaft, between a source and detector. In practice any transduction scheme involving a modification to the shaft, to allow the modulation of an electrically measurable effect by is movement, can be used to measure the force applied to the ball.

Brief Description of Drawings In order that the invention may be more fully understood, a preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which Figure 1 shows the positioning of the major parts on the tow vehicle; Figure 2 is an overview of the system; Figure 3 is a detailed cross section of the ball hitch sensor assembly ; Figure 4 is a top view of the ball hitch sensor assembly; Figure 5 is a block diagram of the system electronics of figure 4; and Figure 6 shows a typical design for the upper sense plate assembly Detailed Description of the Drawings A typical tow vehicle is shown on Figure 1 with a tow ball sensor assembly 1 attached to the vehicle towing bracket at the rear, and the display unit 2 mounted inside, in view of the occupants.

Figure 2 shows an overview of the system off the vehicle with the tow ball sensor assembly 1 attached by electrical cable 3 to the display unit 2. Of course, communication between 1 and 2 could be by other means such as wireless, infrared beam or fibre optics. The display unit 2 has a display screen 10 as well as a variety of controls buttons 24.

Referring to figure 3, in a preferred ball hitch sensor assembly design, a substantially cylindrical housing 17 is connected by a rigid neck 18 to a plate 19 containing a plurality of holes for attachment to a vehicle towing bracket. A typically 50mm diameter ball 11 is mounted on a shaft 15 which passes through and is secured to a rubber element 16 within the housing 17. The rubber element 16 may be cylindrical or may be segmented to change its stiffness in one or more directions, but must be attached to the housing 17 and the shaft 15. At the bottom end of shaft 15 is a disc electrode 14, which is electrically grounded and bounded above and below by an upper fixed plate 12 and a lower fixed plate 13. These plates 12 and 13 are fitted with isolated conductive surfaces so that, together with the electrode 14, they form multiple variable capacitors which change their capacitance values with any movement of the ball 11. The geometrical arrangement of the capacitors is such that it is possible to distinguish between movements along the three axes, namely vertical, lateral and fore/aft. In addition the plate 13 carries on its lower face sensor demodulation electronics to provide a suitable electrical signal to the display unit 2. The sensing arrangement and electronics is covered by a housing 4. To prevent excessive movement and damage to the sensing plates, upper and lower limit stop buffers 20 and 22 are provided. The buffer 20 prevents excess horizontal and downward motion by contact with shaft 15 and its upper shoulder. The buffer 22 prevents excessive upward motion by contact with a flange 21 on the shaft 15. A re-arrangement of the sensing means would allow the arrangement to be turned inside out so that the inner member, at present 15, would be attached rigidly to the vehicle and the outer member to the ball. This may have some operational advantage. Figure 4 shows a top view of the ball hitch sensor assembly.

Turning now to figure 5, an oscillator module 25 feeds the variable capacitors 27 whose output is converted by demodulator 26 to a signal form suitable for the display unit 2. Whilst three capacitors are shown, a larger number can improve accuracy by using differential techniques. The cable 3 connects the sensor demodulator 26 to the display unit by way of a sensor interface module 5. This further conditions the sensor signals before passing them on to a multiplexing analogue-to-digital converter 7. An accelerometer 6 also provides a signal to the converter 7 which passes on all the now digital information to a processor unit 8. The processor unit 8 separates the respective signals and after applying certain algorithms arrives at the parameters for display and alarms. Display information is passed to the display driver 9 and then on to the display screen 10. Optionally any alarm conditions can be used to sound an audio output device 28.

Figure 6 shows a possible arrangement for the upper fixed plate 12 which could be made in the form of a printed circuit board. In this arrangement printed conductor patterns 23 surround a central hole 24 which allows the shaft 15 to pass through. A similar arrangement of patterns can be used on the lower fixed plate 13.

Claims

CLAIMS 1. A tow coupling sensor assembly for monitoring the forces exerted on a tow coupling by a vehicle being towed, the assembly comprising force sensing means with inherent damping, for mounting in the vicinity of the tow coupling and for producing an output signal which varies with the forces exerted on the coupling, processing means for producing an indicator signal from said output signal, and remote indicating means responsive to said indicator signal for providing an indication of the forces exerted.
2. An assembly according to claim 1, wherein the sensing means is adapted to permit measurements to be made in as many as three mutually orthogonal directions.
3. An assembly according to claim 1 or 2, wherein the remote indicating means includes a display for providing a visual indication of the forces exerted and related parameters.
4. An assembly according to any preceding claim, wherein further sensing means are provided for sensing the forces exerted on the sensing means.
5. An assembly according to claim 4, wherein the further sensing means is an accelerometer.
6. An assembly according to any preceding claim, wherein the remote indicating means is adapted to provide an indication related to fore/aft forces exerted on the vehicle being towed.
7. An assembly according to any preceding claim, wherein the remote indicating means is adapted to provide an indication related to periodic lateral forces exerted on the tow coupling by the vehicle being towed.
8. An assembly according to any preceding claim, wherein the remote indicating means is adapted to provide an indication related to substantially steady state lateral force exerted on the tow coupling by the vehicle being towed.
9. An assembly according to any preceding claim, wherein the remote indicating means is adapted to provide an indication of that portion of the weight of the vehicle being towed bearing down on the tow coupling.
10. An assembly according to any preceding claim, wherein the remote indicating means is adapted to provide an indication of the gross weight of the vehicle being towed.
11. An assembly according to any preceding claim, wherein the remote indicating means includes a facility for communicating the ratio of the weight of the vehicle being towed to the weight of the towing vehicle.
12. An assembly according to any preceding claim, wherein the remote indicating means includes a facility for warning when vehicle parameters are considered unsafe or outside a predetermined range.
13. An assembly according to claim 12, wherein the warning facility is an audible device.
14. An assembly according to any preceding claim, wherein the remote indicating means includes a facility for prioritising and suppressing information according to importance and need, to avoid unnecessary distraction of the driver.
15. An assembly according to any preceding claim, wherein the processing means is located remotely of the coupling in the vicinity of the indicating means.
16. An assembly according to any preceding claim, wherein the sensing means includes a shaft constrained for limited movement within a housing.
17. An assembly according to claim 16, wherein the sensing means includes a discernible feature mounted on the shaft, such as an electrode.
18. An assembly according to claim 16 or 17, wherein the sensing means includes variable capacitance means having a capacitance which varies with the relative positioning of the shaft and the housing.
19. An assembly according to claim 17, wherein the discernible feature has magnetic properties.
20. An assembly according to claim 17, wherein the discernible feature is arranged to influence the properties of light from a source in the vicinity of the shaft as its position varies.
21. An assembly according to any preceding claim, wherein the sensing means is constrained for limited movement within a housing by a resilient bush providing damping of the sensing means.
22. An assembly according to claim 21, wherein the resilient bush is made of rubber.
23. An assembly according to claim 21 or 22, wherein the resilient bush incorporates a metal spring element.
24. An assembly according to claim 21,22 or 23, wherein the resilient bush is adapted to control the stiffness along a plurality of mutually transverse axes substantially independently of one another.
25. A tow coupling sensor assembly substantially as hereinbefore described with reference to the accompanying drawings.
26. A tow coupling sensor assembly for monitoring the forces exerted on a tow coupling by a vehicle being towed, the assembly comprising force sensing means for mounting in the vicinity of the tow coupling and for producing an output signal which varies with the forces exerted on the coupling, processing means for producing an indicator signal from said output signal, and remote indicating means responsive to said indicator signal for providing a warning that the ratio of the weight of the vehicle being towed to the weight of the towing vehicle has moved outside a predetermined range.
27. A tow coupling sensor assembly for monitoring the forces exerted on a tow coupling by a vehicle being towed, the assembly comprising force sensing means for mounting in the vicinity of the tow coupling and for producing an output signal which varies with the forces exerted on the coupling, the force sensing means including accelerometer means, processing means for producing an indicator signal from said output signal, and remote indicating means responsive to said indicator signal for providing an indication of the forces exerted.
28. A tow coupling sensor assembly for monitoring the forces exerted on a tow coupling by a vehicle being towed, the assembly comprising force sensing means for mounting in the vicinity of the tow coupling and for producing an output signal which varies with the forces exerted on the coupling, the force sensing means including a force sensor adapted to permit measurements to be made in three mutually transverse directions, processing means for producing an indicator signal from said output signal, and remote indicating means responsive to said indicator signal for providing an indication of the forces exerted.
29. A tow coupling sensor assembly for monitoring the forces exerted on a tow coupling by a vehicle being towed, the assembly comprising force sensing means for mounting in the vicinity of the tow coupling and for producing an output signal which varies with the forces exerted on the coupling, processing means for producing an indicator signal from said output signal, and remote indicating means responsive to said indicator signal for providing an indication of the forces exerted, wherein the force sensing means includes an elastomeric element which is adapted to control the stiffness along a plurality of mutually transverse axes substantially independently of one another.