GB2178178A

GB2178178A - Vehicle on-board axle weighing systems

Info

Publication number: GB2178178A
Application number: GB08517218A
Authority: GB
Inventors: Philip Wilson Turner
Original assignee: SEC DEP FOR TRANSPORT
Current assignee: SEC DEP FOR TRANSPORT
Priority date: 1985-07-06
Filing date: 1985-07-06
Publication date: 1987-02-04
Also published as: GB8517218D0

Abstract

An on-board vehicle weighing system includes at least one strain gauge (7, 8) for sensing shear strain of an axle (2). The strain gauge is attached to the axle between a spring attachment point (9) and a wheel attachment point (10). <IMAGE>

Description

SPECIFICATION Vehicle on-board axle weighing systems 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 payload carrying vehicles to be equipped with on-board weighing equipment, to determine vehicle weight, axle weight and payload weight, which may also provide a continuous reading of vehicle weight and axle 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 limit for the vehicle and its axle 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.

The object of the invention is to provide a location, and, where necessary relative positions and interconnections for a strain gauge or gauges on an axle so that information about the axle strain due to the vehicle and payload weight alone acting on the axle is sensed by the strain. gauge or gauges, without modification of the attachment of the axle to the vehicle.

According to the present invention there is provided an on board vehicle weighing system including at least one strain gauge for sensing the shear strain of at least one axle on the vehicle, the strain gauge being attached to the axle between a spring attachment point and a wheel attachment point on the front or rear of the axle.

Where a pair of strain gauges are fixed at one position on the axle they may be arranged at right angles, with both gauges at 45 degrees to the long axis of the axle.

A pair of strain gauges may be fixed on the front and on the rear of the axle.

Where the axle is supported by a wheel or wheels at each end a strain gauge or strain gauges may be placed between the spring attachment point and the wheel attachment point on the front or rear of said axle, at both ends of said axle.

The strain gauge or gauges may be fixed on mechanical strain amplifiers which are in turn fixed on the axle.

The output of the strain gauges may be monitored by a bridge network, the bridge network being so connected as to nullify all signals from the strain gauges not produced by the shear strain of the axle.

An embodiment of the invention will now be described with particular reference to the drawings, in which: Figure 1 shows schematically a commercial vehicle axle and spring assembly.

Figure 2 shows a cross-section on the axis of Fig. 1, Figure 3 shows the connection of strain gauges into a superimposed bridge network, and Figures 4A and 4B show embodiments of strain amplifiers attachable to the axle of Fig.

1.

The wheels and tyres 1, axle 2 and springs 3 of a conventionally suspended commercial vehicle rear axle are shown in Fig. 1. The wheels and tyres are shown sectioned for clarity. The contact patch 4 of each tyre and the forward and rear spring shackles 5, 6 are the extremities of the load path between the road and vehicle body (not shown), the load being transferred by the axle 2. The vertical men force Fv indicated by an arrow acting on each wheel and tyre pair due to the weight of the vehicle is sensed by strain gauges 7 placed at the rear of the axle and 8 placed on the front of the axle between axle-spring attachments 9 and an axle hub 10. The vertical shear force and resultant mean vertical shear strain are independent of bending and twisting moments in the axle at this position.

The axle cross-section 20 shown in Fig. 2 depicts only the outer circumference of the axle at the position of the strain gauge attachment 7, 8 of Fig. 1. The internal construction of the axle need not be considered. The forward side of the axle is to the right hand side of the Figure. The numerals 21, 22, 23, 24 denote strain gauge elements placed at the near end of the axle and the numerals 25, 26, 27, 28 denote strain gauge elements placed at the far end of the axle. Connection and relative position of each strain gauge element pair 21 and 22, 23 and 24, 25 and 26, 27 and 28 is shown in Fig. 3 where the connections of the strain gauge elements is shown in the superimposed bridge form 30 required to nullify unwanted strain gauge outputs.The elements in a pair of elements 21, and 22, for example are arranged normally, with both- elements lying at 45 degrees to the long axis of the axle. The layout of strain gauge element pairs is more clearly shown in Figs. 4A and 4B which show strain gauge elements, 41 and 42, 51 and 52, mounted on strain amplifiers 40, 50 attached in turn to an axle 60. The excitation 31 and outputs connections 32 is also shown in Fig. 3. AC excitation and synchronous detection is used.

The strain amplifiers shown have pedestals 43, 53 conforming to the axle shape for bonding purposes leading to substantially square sectioned blocks 44, 54 with rectangular hollowed sections 45, 55 in the centre.

The bottom 46, 56 of each rectangular hollowed section is in the form of a thin web.

The linek A-B represents the long axis of the axle, the shear forces caused by the weight of the vehicle being applied normal to this axis, parallel to the web 56 of each strain amplifier.

The shear strain present in the axle between the pedestals 53 of the amplifier (dimension b) appears across the web width alone (dimension a) giving an effective strain amplification of b/a for sensing by the gauge elements.

Strain amplifier 50 has a thin leg 57 linking the pedestal to the block 54 to decouple bending strain from the strain amplifier.

Claims

1. An on-board vehicle weighing system including at least one strain gauge for sensing the shear strain of at least one axle on the vehicle, the strain gauge being attached to the axle between a spring attachment point and a wheel attachment point on the front or rear of the axle.

2. A weighing system as claimed in Claim 1 having a pair of strain gauges fixed at one position on the axle.

3. A weighing system as claimed in Claim 2 wherein the gauges are arranged at right angles with both gauges at 45 degrees to a long axis of the axle.

4. A weighing system as claimed in Claim 2 or in Claim 3 having a pair of strain gauges fixed on a front and a pair of strain gauges fixed on a back of the axle.

5. A weighing system as claimed in Claim 4 having pairs of strain gauges fixed on the front and the back of the axle at each of the two ends of the axle.

6. A weighing system as claimed in any one of Claims 1 to 5 wherein each gauge is fixed on a mechanical strain amplifier which is in turn fixed to the axle.

7. A weighing system as claimed in any one of Claims 1 to 6 wherein the strain guage output is monitored by a bridge network.

8. A weighing system as claimed in Claim 7 wherein the bridge network is so connected as to nullify all strain gauge outputs not pro duced by shear strain of the axle.

9. A weighing system substantially as herein described with reference to the accompanying drawings..

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