GB2178546A - Vehicle load-measuring system - Google Patents

Abstract

A vehicle load-measuring system which comprises a linkage (16) connected between the chassis (10) and each end of each road axle (12, 14) each linkage driving the slider of a potentiometer or like transducer which provides an electrical output representative of vehicle load to a display and/or recording unit. Processing circuitry receiving the electrical outputs includes zeroing devices and a switching means enabling front axle load, rear axle load and total load to be indicated and/or displayed. <IMAGE>

Description

SPECIFICATION Vehicle load measuring system Field of the invention.

This invention relates to a system for measuring the load being carried by a vehicle, more especially, in the case of a vehicle having a load-carrying platform, for enabling load distribution and total load to be checked and monitored on board the vehicle.

The invention.

According to the invention, a vehicle load measuring system comprises a movement responsive transducer to produce an electrical output, means responsive to relative displacement of the vehicle chassis and at least one of the wheel axles, as when the vehicle is loaded or off-loaded, in order to produce said movement, and an electrical processing circuit in which said transducer is connected and which responds to the output of the transducer to produce an electrical signal for actuating an electrical display device and/or recording means, to indicate and/or record a value indicative of the vehicle chassis displacement and thereby the load carried thereon.

The means responsive to chassis/axle displacement preferably comprises mechanical devices at the front wheel axle and at the rear wheel axle or axles, most preferably one such device at each end of each said axle.

The processing circuitry preferably includes a switch whereby either the chassis/front axle displacement can be measured, to indicate load at the front of the vehicle, or the chassis/rear axle displacement can be measured to indicate load at the rear of the vehicle, or the chassis/axle displacements can be summed to indicate total load.

The chassis/axle displacement is desirably measured relative to the chassis/axle position in the no-load condition. Whilst mechanical calibration is possible, most preferably the processing circuitry includes electrical means for setting the indicating device such as a meter or recording means to zero, in the noload condition.

In the case of a vehicle having mechanical devices responsive to chassis/wheel axle displacement at each end of each axle, the calibration means may conveniently include, for each axle, a device for adding a compensating output to the sum of the outputs of the two transducers associated with the axle, whereby the meter or equivalent device reads zero for that axle in the no-load condition. A similar device is also preferably provided for zeroing the measurement of total load.

In addition, the calibration means may also comprise, for each axle and the total load measurement, a variable gain amplifier for setting the scale of the display meters or recording means so that a given loading is currently indicated or displayed. This scale calibration will be carried out with the aid of a conventional weighbridge. All the calibration devices will normally be preset when a system which incorporates the invention is installed in a vehicle.

Where the processing unit supplies its output signal(s) to a recorder intended to operate continuously while the vehicle is in use, an averaging or smoothing circuit may be provided to eliminate all but very slow variations in signal, so as to eliminate spurious signal variation which would otherwise arise as the vehicle moves over an uneven road surface.

An existing recording device such as a vehicle tachograph, may be used for recording the load as hereinbefore mentioned, or a separate special purpose recorder, specifically designed for the purpose of load measurement, may be provided on board the vehicle.

In the latter case, a suitable recording unit may include a switch for front, rear and total load indication, a load display, a calender clock which may also include a display, and a chart recorder which provides a graphical indication of all three load measurements (front, rear and total).

A preferred mechanical device for operating the transducer comprises a pair of hinged links, which are also individually pivotally connected one to the vehicle chassis and one to the wheel axle. The links will be relatively pivoted due to relative displacement of the chassis and axle (as will occur when a vehicle is loaded or off-loaded), and this relative pivoting can be used to drive the slider of a rotary potentiometer to control the current flowing therethrough or the potential developed thereacross, to provide the required electrical output.

Alternatively, however, the conventional telescopic strut, e.g. Macpherson strut, of the vehicle suspension may provide a simpler method of mounting and operating the transducer. Thus, the fixed resistance of a linear potentiometer may be carried by the first part of the strut, and the linearly displaceable slider may be carried by the second part of the strut which telescopes relative to the first part when relative displacement of the chassis/ road axle occurs. This alternative and possibly simpler method of mounting and operating the transducer may only be practicable where the level of accuracy of measurement is not too great, owing to the usual practice of resiliently mounting upper and/or lower ends of the suspension strut.

Preferably security locking means is provided which will prevent the unit mounted in the cab from being tampered with particularly where the unit includes a recording means for recording the load place or is linked to a tachograph or similar recording unit. A simple security seal may be sufficient which will reveal if unauthorised access has occurred. Al ternatively the unit may include a recording device which records unauthorised access in a permanent manner.

Brief description of the drawings.

The invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic representation of a vehicle chassis structure embodying the invention; Figure 1A shows a detail of Fig. 1 to an enlarged scale; Figure 2 shows the face of sn on-board control/display unit; Figure 3 is a circuit diagram Figure 4 shows an embodiment of measurement recorder; and Figure 5 shows a transducer device alternative to that shown in Fig. 1A.

Description of drawings.

Referring first to Figs. 1 and 1 A, a vehicle chassis 10 is depicted in Fig. 1, together with associated front and rear road axles 12 and 14. At the end of each road axle is fitted a mechanical linkage 16 for driving a mechanica I/electrical transducer. Thus, in the case of the vehicle chassis depicted in Fig. 1, there are in total four such devices 16, two at the front and two at the rear.

Fig. 1A shows one such device 16. It comprises two links 18, 18A with ends which are hinged together at 20. The links are individually pivoted at their other ends 22, 22A to the chassis 10 and to the road axle 12 (or 14), respectively. The rotary hinge 20 between the two links incorporates a rotary potentiometer.

When the load carrying platform of the vehicle is loaded or off-loaded, relative displacement occurs between the chassis 10 and the road axles 12, 14, resulting in relative pivoting of the links 18, 18A at each of the devices 16, which is in turn accompanied by movement of the slider of the corresponding rotary potentiometer in the rotary joint 20.

The four potentiometers, which may for example be powered from a constant current source, provide respective voltage outputs proportionately related to the applied load at the respective points of the vehicle chassis, i.e. at the ends of the front and rear road wheel axles.

The potentiometer outputs are fed through processing circuitry (to be later described) in order to provide one or more signal outputs for operating a meter and/or display device.

Fig. 2 shows one such control/display unit 22. This unit incorporates a switch 24 with respective positions enabling a reading to be displayed on the analogue meter 26, corresponding to the load at the front or the load at the rear, or the total load. The meter 26 includes markings 28 designating maximum safe front, rear and total ioadings, as well as a danger zone marking 30 for indicating overloading. The display scale of the meter 26, having the aforesaid markings, is selected to suit the type of lorry or other vehicle in which the system is installed.

Fig. 3 is a diagram illustrating the processing circuitry for the outputs of the rotary potentiometers hitherto described. The two front outputs, and likewise the two rear outputs, are designated dl, d2. The outputs d, and d2 are summed (for the front and for the rear separately) and a compensating voltage is added from a potentiometer 32. This is preset, for calibration purposes, so that the output meter 26 (Fig. 2) reads zero under no-load conditions, for both the front and the rear axles. The resultant signal is fed to a variable gain amplifier 34 of less than unity gain, which is preset so that a correct meter reading is given for a known load, e.g. known by taking the loaded vehicle to a conventional weighbridge. This again applies to both the front load reading and the rear load reading, taken separately.

The two outputs of the amplifiers 34, in addition to being supplied individually to the meter 30 via the switch 24, are also summed, together with a compensating voltage from a potentiometer 36, (for setting the zero), in a further amplifier 38 having variable gain for meter calibration (scale-setting) in respect of the total load measurement.

The reference 40 denotes an operational amplifier preferably provided in the input circuit of the meter, more particularly if a digital display device and/or graphical recorder is used instead of the anaologue meter 26.

One possible embodiment of such a display device/recorder is shown in Fig. 4. This unit comprises a casing 42 equipped with the switch 24 and a digital display 44. The unit incorporates a calender clock providing a display 46. Reference 48 denotes a "record" switch. When this switch is operated, print head 50 is fed with one or more load measurement signals to produce a time-related graphical recording at the chart recorder 52 within the casing 42.

Instead of the specially designed recorder of Fig. 4, a standard tachograph/recorder in the vehicle may be modified to take in the load measurement signals produced by the invention and to incorporate a record of load in the tachograph record.

In either case, when a continuous record is required, it is preferable to exclude the fluctuations in the signals produced by normal movement of the vehicle suspension as the vehicle travels along an uneven road. Referring back to Fig. 3, the low pass filter circuits 54 indicated therein are sufficient to provide the necessary averaging or smoothing of the load measurement signals.

In some cases, where a requirement for very high accuracy of load measurement is not a pre-requisite, it is possible to replace the mechanical linkage devices 16 of Figs. 1 and 1A by a device as illustrated in Fig. 5.

In this figure, reference 60 generally denotes a telescopic suspension strut of the vehicle, e.g. a Macpherson strut. A linear potentiometer device 62 is connected between the two parts of the telescopic strut. In practice, jubilee clips 64 or the like enable a potentiometer casing 66 to be fixed to one part of the strut and a rod 68 for driving the potentiometer slider, to be fixed to the other part. This simpler method of operating the mechanical/electrical transducer may be subject to small errors in view of the resilient mountings usually employed for Macpherson struts.

The above described arrangement may be subject to various modifications within the scope of the invention hereinbefore defined.

Claims (6)

1. A vehicle load measuring system comprising a movement responsive transducer to produce an electrical output, means responsive to relative displacement of the vehicle chassis and at least one of the wheel axles, as when the vehicle is loaded or off-loaded, in order to produce said movement, and an electrical processing circuit in which said transducer is connected and which responds to the output of the transducer to produce an electrical signal for actuating an electrical display device and/or recording means, to indicate and/or record a value indicative of the vehicle chassis displacement and thereby the load carried thereon.

2. A system according to claim 1, wherein said chassis displacement-responsive means comprises mechanical devices at the front wheel axle and at the rear wheel axle or axles, most preferably one such device at each end of each said axle.

3. A system according to claim 2, wherein the processing circuit includes a switch whereby either the chassis/front axle displacement can be measured, to indicate load at the front of the vehicle, or the chassis/rear axle displacement can be measured to indicate load at the rear of the vehicle, or the chassis/axle displacements can be summed to indicate total load.

4. A system according to claim 1 or claim 2 or claim 3, wherein the chasis displacementresponsive means is operative relative to the chassis/axle position in the no-load condition.

5. A system according to claim 4, wherein the processing circuit includes electrical means for setting the indicating device such as a meter or recording means to zero, in the noload condition.

6. A system according to claim 2, wherein the calibration means includes a device for adding a compensating output to the sum of the outputs of the two transducers associated with each axle.

6. A system according to claim 5 when appendant to claim 2, wherein the calibration means includes, for each axle, a device for adding a compensating output to the sum of the outputs of the two transducers associated with the axle, whereby the meter or equivalent device reads zero for that axle in the no-load condition.

7. A system according to claim 6, also including a device provided for zeroing the measurement of the total load.

8. A system according to claim 5 or claim 6 or claim 7, wherein the calibration means also includes, for each axle and the total load measurement, a variable gain amplifier for setting the scale of the display meters or recording means so that a given loading is currently indicated or displayed.

9. A system according to any of claims 1 to 8, wherein the processing circuit supplies its output signal(s) to a recorder intended to operate continuously while the vehicle is in use.

10. A system according to claim 9, wherein the processing circuit includes an averaging or smoothing circuit to eliminate all but very slow variations in signal, so as to eliminate spurious signal variation which would otherwise arise as the vehicle moves over an uneven road surface.

11. A system according to claim 10, wherein the recording unit includes a switch for front, rear and total load indication, a load display, a calendar clock which may also include a display, and a chart recorder which provides a graphical indication of all three load measurements (front, rear and total).

12. A system according to claim 2 or any claim appendant thereto, wherein the transducer is operative by one or more mechanical devices which comprises a pair of hinged links, which are also individually pivotally connected one to the vehicle chassis and one to the wheel axle.

13. A system according to claim 12, wherein the links are relatively pivoted due to relative displacement between the chassis and axle, and such relative pivoting movement drives the slider of a rotary potentiometer which provides a required electrical output.

14. A system according to claim 2 or any claim appendant thereto, wherein the transducer is operative by one or more telescopic struts, e.g. Macpherson struts, forming part of the vehicle suspension arrangement.

15. A system according to claim 14, wherein the telescopic struts drive the slider of a linear potentiometer which provides a required electrical output.

16. A system according to any of claims 1 to 15, wherein the display and/or recording unit is mounted in the vehicle cab and a security locking device is provided therefor.

17. A vehicle load measuring system substantially as hereinbefore described with reference to the accompanying drawings.

CLAIMS Amendments to the claims have been filed, and have the following effect: Claims 1 and 6 above have been deleted or textually amended.

New or textually amended claims have been filed as foliows:

1. A vehicle load measuring system comprising, for each axle, at least one movement responsive transducer to produce an electrical output, means responsive to relative displacement of the vehicle chassis and each of the wheel axles, as when the vehicle is loaded or off-loaded, in order to produce said movement to which the respective transducers are responsive, and an electrical processing circuit in which said transducers are connected and which responds to the output of the transducers to produce an electrical signal for actuating an electrical display device and/or recording means, to indicate and/or record a value indicative of the vehicle chassis displacement at each axle and thereby the load carried thereon, the processing circuit incorporating a calibration means which includes, for each axle, a device for adding a compensating output to the output of the at least one transducer associated with the axle, whereby the display device or recording means indicates zero for that axle in the no-load condition.