GB2256718A

GB2256718A - Load-measuring method and apparatus for vehicles

Info

Publication number: GB2256718A
Application number: GB9211358A
Authority: GB
Inventors: Stanley Dobson
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-06-10
Filing date: 1992-05-29
Publication date: 1992-12-16
Also published as: GB9211358D0

Abstract

The load being carried by a vehicle is measured by providing a transducer (10) and associated readout on the vehicle. The transducer (10) is activated to measure the movement between the vehicle chassis (12) and a point on the vehicle (16) which moves relative to the vehicle chassis (12) in accordance with the load induced deflection of the vehicle suspension of at least one ground engaging wheel. The transducer output is converted to a load read-out corresponding to the load which would be expected to produce the measured load induced movement at the point relative to the chassis. <IMAGE>

Description

LOAD MEASURING METHOD AND APPARATUS FOR VEHICLES This invention relates to a method and apparatus for measuring the load carried by a vehicle. The invention has particular application for road-going commercial vehicles.

Measurement of the load carried by trucks is conventionally carried out using weighbridges. For large scale operations, such as a large quarry, the provision of a weighbridge may provide a convenient and cost effective means for measuring the loads taken from the quarry and ensuring that vehicles are not overloaded. However, for smaller operations, or in temporary construction sites, the provision of a weighbridge may not be economically justifiable. Certain local authorities provide public weighbridges, but these may not always be conveniently located and may entail a considerable detour from the normal route of the vehicle.

Overloading of vehicles may result in danger, both to the driver and to other road users and pedestrians and may damage vehicles. Also, overloading is illegal and can result in considerable fines being levied when incidents of overloading are detected. Underloading, while not presenting any danger, is uneconomic.

It is an object of the present invention to provide a method and apparatus for measuring the load carried by a vehicle, which apparatus may be fitted to the vehicle.

According to one aspect of the present invention there is provided a method of measuring the load being carried by a vehicle comprising: providing a transducer and associated read-out means on the vehicle; activating the transducer to measure the movement between the vehicle chassis and a point on the vehicle which moves relative to the vehicle chassis in accordance with the load-induced deflection of the vehicle suspension of at least one ground engaging wheel; and converting the transducer output to a load read-out corresponding to the load which would be expected to produce the measured load-induced movement of said point relative to the chassis.

According to another aspect of the present invention there is provided a vehicle having a chassis, a plurality of ground engaging wheels mounted to the chassis via suspension means, at least one transducer for measuring movement between the chassis and a point on the vehicle which moves relative to the chassis in accordance with the load-induced deflection of the suspension of at least one ground engaging wheel, and read-out means linked to the transducer, the transducer and read-out means being calibrated to provide a load read-out determined by the measured load-induced movement of said point relative to the chassis.

According to a further aspect of the present invention there is provided apparatus for retro-fitting to a vehicle for measuring the load carried by the vehicle comprising: a transducer for mounting on the vehicle for measuring movement between a vehicle chassis and a point on the vehicle which moves relative to the chassis in accordance with the load-induced deflection of the vehicle suspension of at least one ground engaging wheel; and read-out means linked to the transducer, the transducer and read-out means being calibrated to provide a load read-out determined by the measured load-induced movement of said point on the vehicle relative to the chassis.

In use, a transducer may be provided for each individual wheel of a vehicle, or for selected wheels of the vehicle. Where two or more wheels are provided with a common mounting, such as a fixed axle or a bogie, a single transducer may be used if the combined movement of the wheels may be measured with reference to a single point.

In certain circumstances, it may not be possible to mount a transducer to measure the movement at, for example, a mid-point of an axle and in these circumstances two transducers may be provided, the outputs of the transducers being averaged to provide a load read-out.

Preferably, the transducer is fixed to the vehicle chassis and has a connecting portion in contact with the point on the vehicle which is subject to movement. In certain vehicles it may be more appropriate to mount the transducer on another part of the vehicle structure and in unitary construction vans, for example, the transducer may be mounted on the vehicle body.

The transducer is preferably a linear displacement transducer, though angular displacement transducers may also be utilised.

The read-out means are conveniently in the form of a digital read-out and may be located at a convenient location on the exterior of the vehicle or in the vehicle cab.

A sufficient number of transducers may be provided for determining the total load carried by a vehicle or may be used to measure individual axle, bogie or wheel loads.

This feature may be used to detect incorrectly located loads and to indicate the optimum location of, for example, a heavy small volume load on a trailer.

The method and apparatus are utilised while the vehicle is stationary, so that spurious readings caused by dynamic suspension deflection will not affect measurement. When not in use, the transducers may be retracted to minimise wear on the apparatus due to vibration.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic cut away view of the transducer of apparatus for measuring the load carried by a vehicle shown mounted on the underside of a vehicle; Figure 2 is a schematic illustration of apparatus for measuring the load carried by a vehicle including the transducer of Figure 1; and Figure 3 is a plan view of a vehicle chassis indicating suitable locations for the transducer of Figure 1.

Reference is first made to Figure 1 of the drawings, which shows a transducer 10 forming part of apparatus for measuring the load carried by a vehicle in accordance with an embodiment of the present invention. The transducer is of the linear variable differential transformer type, such as sold by Lucas Schaevitz of Slough, Berks, England. The transducer 10 is fixed to a cross member 12 of the vehicle chassis and has a connecting rod 14 shown extended and in contact with an upper face of the differential housing 16 of the vehicle rear axle 18. The transducer 10 is thus able to measure movement of the axle 18 relative to the chassis, where the degree of movement represents the load-induced deflection of the vehicle suspension of the pair of wheels associated with the axle 18.As the reading is taken at the centre of the axle 18, parking the vehicle on an incline and off-centre loading will not affect the measured movement.

The transducer 10 is an electro-mechanical device that produces an electrical output proportional to the displacement of a separate moveable core and consists of a primary coil 20 and two secondary coils 22, 24 symmetrically spaced on a cylindrical housing 26. A free-moving rod-shaped magnetic core 28 inside the coil assembly provides a path for the magnetic flux linking the coils.

When the primary coil 20 is energised by an external AC source, voltages are induced in the two secondary coils 22, 24. These coils 22, 24 are connected series opposing so the two voltages are of opposite polarity. Therefore, the net output of the transducer is the difference between these voltages, which is zero when the core is at the centre or null position. When the core is moved from the null position, the induced voltage in the coil toward which the core 28 is moved increases, while the induced voltage in the opposite coil decreases. This action produces a differential voltage output that varies linearly with changes in core position. The phase of this output voltage changes abruptly by 1800 as the core is moved from one side of null to the other.

A connecting rod 14 is fixed to the lower end of the core 28 and when the transducer is in use, extends into contact with the differential casing 16. An upper connecting rod 30 may be provided extending from the upper end of the core 28 and may engage means to retract the core 28 and connecting rod 14 when the transducer 10 is not in use. Any appropriate pneumatic, hydraulic or spring means may be utilised to retract and extend the connecting rod 14.

Figure 2 is a schematic illustration of load measuring apparatus including the transducer 10.

Excitation, amplification and demodulation for operating the transducer 10 is provided by an analogue signal conditioner 32 which provides an analogue DC output to feed a digital transducer read-out 34. Suitable analogue signal conditioners and digital transducer read-out are available from Lucas Schaevitz. The read-out 34 may receive summed signals from a plurality of transducers to provide an indication of the total load carried by a vehicle, or may provide read-outs for individual transducers to indicate the load being carried by a particular wheel or axle.

Reference is now also made to Figure 3 of the drawings which shows a truck chassis 36 and front and rear axles 38, 18. A single transducer 10a is provided for the the rear axle 18, whereas two transducers 10a, lOb are provided for the front axle 38, due to space restrictions at the centre of the front axle. The read-outs from the transducers lOb, lOc are averaged to provide a read-out corresponding to the deflection at the centre of the axle.

The transducers 10 may be individually calibrated using a conventional weighbridge, and may require calibrating over the life of the vehicle to compensate for suspension settling, wear and the like. If suspension deflection in a vehicle type is known to be linear or consistently proportional to load, minimal calibration will be required. Most conveniently, vehicles are manufactured with the load measuring facility though apparatus may be readily retro-fitted to an existing vehicle.

Calibration of the transducers allows non linearities, such as are introduced by "helper" springs, t6 be taken into account. Also, to limit the degree of displacement which the transducer is required to measure the datum for readings may start at, for example 5 tonnes.

Thus, the present invention provides a convenient means for measuring the load on a vehicle to assist drivers, vehicle loaders, regulatory authorities and the like in ensuring that vehicles are safely and legally loaded, without requiring use of a weighbridge.

It will be obvious to those of skill in the art that the above described apparatus is merely exemplary of the present invention and that various modifications and improvements may be made without departing from the scope of the invention; although the apparatus is only shown in use in conjunction with fixed axles, the apparatus may also be utilised on lift axles, to be activated when the axle is in the lowered, load-bearing position.

Claims

1. A vehicle having a chassis, a plurality of ground engaging wheels mounted to the chassis via suspension means, at least one transducer for measuring movement between the chassis and a point on the vehicle which moves relative to the chassis in accordance with the load-induced deflection of the suspension of at least one ground engaging wheel, and read-out means linked to the transducer, the transducer and read-out means being calibrated to provide a load read-out determined by the measured load-induced movement of said point relative to the chassis.

2. The vehicle of claim 1 wherein the transducer is fixed to the vehicle chassis and has a connecting portion in contact with the point on the vehicle which is subject to movement.

3. The vehicle of claim 1 or claim 2 wherein the transducer is a linear displacement transducer.

4. The vehicle of claim 1 or claim 2 wherein the transducer is an angular displacement transducer.

5. The vehicle of any one of the preceding claims wherein a sufficient number of transducers are provided to determine the total load carried by the vehicle.

6. The vehicle of any one of the preceding claims wherein transducers are provided to measure the movement of an individual axle, bogie or wheel and thus to determine the loading thereon.

7. The vehicle of any one of the preceding claims wherein the transducer may be retracted to an out-of-use position.

8. The vehicle of any one of the preceding claims wherein the transducer measures the load induced deflection of the suspension at the centre of an axle, such that parking the vehicle on an incline or off-centre loading will not affect the measured movement.

9. Apparatus for retro-fitting to a vehicle for measuring the load carried by the vehicle comprising: a transducer for mounting on the vehicle for measuring movement between a vehicle chassis and a point on the vehicle which moves relative to the chassis in accordance with the load-induced deflection of the vehicle suspension of at least one ground engaging wheel; and read-out means linked to the transducer, the transducer and read-out means being calibrated to provide a load read-out determined by the measured load-induced movement of said point on the vehicle relative to the chassis.

10. A method of measuring the load being carried by a vehicle comprising: providing a transducer and associated read-out means on the vehicle; activating the transducer to measure the movement between the vehicle chassis and a point on the vehicle which moves relative to the vehicle chassis in accordance with the load-induced deflection of the vehicle suspension of at least one ground engaging wheel; and converting the transducer output to a load read-out corresponding to the load which would be expected to produce the measured load-induced movement of said point relative to the chassis.

11. The vehicle substantially described herein and illustrated in the accompanying drawings.

12. Apparatus for retro-fitting to a vehicle for measuring the load carried by the vehicle substantially as described herein and as shown in the accompanying drawings.