GB2178180A

GB2178180A - Onboard vehicle weighing system

Info

Publication number: GB2178180A
Application number: GB08616065A
Authority: GB
Inventors: Philip Wilson Turner
Original assignee: SEC DEP FOR TRANSPORT
Current assignee: SEC DEP FOR TRANSPORT
Priority date: 1985-07-04
Filing date: 1986-07-01
Publication date: 1987-02-04
Also published as: GB2178180B; GB8616065D0; GB8517021D0

Abstract

The member (3) which locates a vehicle axle (6) relative to a vehicle spring (1) is in the form of a shear beam load cell having at least one web (35) to each side of which is attached at least one strain gauge (8). <IMAGE>

Description

SPECIFICATION Vehicle onboard axle weighing system with shear beam load cell The present invention relates to vehicle weighing systems, particularly where such a system is built into a vehicle and may be used to monitor vehicle weight continuously.

A known method of weighing a vehicle, whether to determine the all-up weight of the vehicle, or the weight of the payload carried by the vehicle, has been to position that vehicle on a weighbridge, where the weighbridge has formed part of a road surface, a runway surface or railway track.

There is, however, an increasing demand for vehicles to be equipped with on-board weighing equipment, to determine vehicle weight, payload weight and the weight of each axle which may also provide a continuous reading of these weights during loading or unloading operations. The provision of an on-board weighing system in a payload carrying vehicle will, among other benefits, allow the vehicle operator to ensure that the vehicle and each of its axles is operated within the weight limits for the vehicle and its axles and, for road going vehicles, within the weight limit of the road.

The use of strain gauges to measure the deflections generated by the forces acting on vehicle structures is well known. However the application of strain gauges to provide information on the deflection of the axles of a vehicle, from which information the weight of the vehicle and its payload may be derived, is not straightforward due to the multiplicity of load paths through the suspension between the wheel or wheels on an axle and the vehicle body, the presence of friction in the suspension system and the presence of parasitic strains in the axle caused by forces not associated with the weight of the vehicle and payload acting on the axle.

On board systems for accurately measuring the weight of vehicles have, in the past, required the use of load cells, or other additional structure, included in the vehicle suspension system. For example in UK Patent No 1506377 and US Patent No 3743041 pairs of spaced parallel beams have been interposed between leaf springs and vehicle axles. Strain gauges on one or both of the beams are used to indicate strain in the beams as they move relative to one another under load. The strain gauge outputs are calibrated to give a direct reading of load. The incorporation of extra items inevitably increases the tare weight of the vehicles and reduces the useful load which they can carry.

According to the present invention an on board vehicle weighing system includes a member connecting a vehicle spring to an axle and providing location of the axle relative to the spring, the member being in the form of a shear beam load cell having at least one web lying in the centre plane thereof to act as a strain transformer for at least one strain sensing element placed at each side of the web.

It will be realised that, as location of the axle relative to the spring is essential, use of the invention involves, at worst, a minimal increase in vehicle weight.

In one embodiment of the invention the shear beam load cell is substantially in the form of a truncated isosceles triangular section having a web at each junction of upwardly directed sides of the triangle to a base of the triangle, the axle being located by the base of the triangle, the spring being located across the open top of the triangle.

In another embodiment of the invention the shear beam load cell is substantially in the form of a C providing a cantilevered location for the axle on the spring, the cantilever including a web lying in the centre plane of the cantilever on the neutral axis. Preferrably the open end of the C faces forward pn the vehicle so that the action of the braking torque when the vehicle is moving forwards is opposed by the action of the vehicle weight on the cantilever.

In a vehicle weighing system having shear beam load cells with integral shear webs to which strain gauges are fixed, the strain gauges are preferrably arranged in pairs on each side of a web and with their outputs so connected as to nullify all outputs except those derived from the action of the vehicle weight on the shear beam load cell.

Embodiments of the invention will now be described with reference to the accompanying drawings in which: Figure 1 shows a first type of shear beam load cell connecting a vehicle spring to an axle, and Figure 2 shows a second type of shear beam load cell connecting a vehicle spring to an axle.

Similar features appearing in both figures are accorded to the same reference numeral.

In Fig. 1 the attachment of a vehicle axle to a spring via a truncated triangularly shaped shear beam load cell is shown in part cross section.

The multi-leaf spring 1 is attached by shackle bolts 2 passing through plate 21 to the shear beam load cell 3. The shear beam load cell is of truncated isosceles triangular cross section with the base 31 of the triangle lying horizontal and the sides 32 of the triangle extending upwards to meet a closing plate 4 and reinforcing plate 5 beneath the spring.

The shear beam load cell extends the width of the spring, as do the closing plate and the reinforcing plate. Channels 33 in the base of the shear beam load cell and spigots (ndt shown) between the closing plate, the load cell arms, the reinforcing plate and the lower leaf of the spring provide for accurate location of the load cell on-the spring.

The axle 6 is attached to the base 31 of the load cell by U-bolts 7 of which one only is shown, the U-bolts being spaced apart from the centre line of the load cell along the axis of the axle. The axle is located on the load cell base by a circular segment 34 cut from the inner surface of the base of the load cell to-operate with the axle which is circular in cross section.

The shear beam load cell 3 has two web sections 35 on the centre line of the load cell.

Strain gauges 8 are bonded to the web, to measure the strains induced in the sections A-C and B-C. The web sections 35 act as strain transformers for the strain gauges. Placing the strain gauges as shown in Fig. 1 on each web, with each strain gauge lying at 45 degrees to the vertical allows connection of the strain gauge outputs to a monitoring circuit, such as a bridge circuit (not shown) in such a way as to provide cancellation for signals resulting from strains other than those arising from forces vertically on the section A-B, these including the weight of the vehicle and its load acting on the axle through the load cell.

In Fig. 2 the attachment of a vehicle axle to a spring via a cantilever beam load cell is shown in part cross section. The multi-leaf spring 1 is attached by shackle bolts 2 passing through plate 21 to the shear beam load cell 13. The cantilever beam load cell is of substantially C shaped cross section arranged to lie with the open mouth of the C facing in the forward direction of travel of the vehicle.

A reinforcing plate 5 is interposed between the top of load cell and the lower leaf of the spring. The load cell extends the width of the spring, as does the reinforcing plate. Channels 133, one in the base 131 of the load cell and one in the forward end of the aupper arm 132 of the load cell and spigots (not shown) between the upper arm of the load cell, the reinforcing plate and the lower leaf of the spring provide accurate location of the load cell on the spring.

The axle 6 is attached to the load cell by Ubolts 7 of which one only is show, the U bolts being spaced apart from the centre line of the load cell along the axis of the axle. The axle is located on the load cell base by a circular segment 134 cut from the inner surface of the base of the load cell to co-operate with the axle which is circular in cross section.

The shear beam load cell 13 has a single web 135 on the centre line of the load cell.

Strain gauges are bonded one on each side of the web to measure the strain induced in the section G-F. The web section 135 acts as a strain transformer. The major forces acting on the cantilever beam load cell are the braking torque and the vehicle weight which are opposed.

Claims

1. An on board vehicle weighing system including a member connecting a vehicle spring to an axle, and providing location of the axle relative to the spring, the member being in the form of a shear beam load cell member having at least one web lying in the centre plane thereof to act as a strain transformer for at least one strain sensing element placed at each side of the web.

2. A weighing system as claimed in Claim 1 wherein the load cell member is substantially in the form of a truncated isosceles triangular section having a web at each junction of upwardly directed sides of the triangle to a base of the triangle, the axle being located by the base of the triangle and the spring being located across an open top of the triangle.

3. A weighing system as claimed in Claim 1 wherein the load cell member is substantially in the form of a C providing a cantilevered location for the axle on the spring, the cantilever including a web lying in the centre plane and on the neutral axis of the cantilever.

4. A weighing system as claimed in Claim 3 wherein an open end of the C faces forward on the vehicle.

5. A weighing system as claimed in any one of Claims 1 to 4 wherein the strain sensing elements are strain gaugs.

6. A weighing system as claimed in Claim 5 wherein the strain gauges are arranged in pairs on each side of each web.

7. A weighing system as claimed in Claim 6 wherein the strain gauges have their outputs so connected as to nullify all outputs except those derived from the action of the vehicle weight on the shear beam load cell.

8. An on board vehicle weighing system substantially as herein described with reference to Fig. 1 or to Fig. 2 of the accompanying drawings.

9. A vehicle having an on board weighing system as claimed in any one of Claims 1 to 8.