GB2122748A - Vehicle axle load measuring device - Google Patents

Abstract

A leaf spring suspension unit (19) of a vehicle supports an axle (12). A forward bolt (14) of the suspension unit for supporting the unit on a chassis (13) is a load measuring bolt incorporating strain gauges which form part of a load measuring device (11). The degree of bending of the bolt is a measure of the load on the axle, and the bending is detected by the strain gauges mounted on an inwardly facing surface of a cavity in the bolt. Each leaf spring suspension unit can be provided with a load measuring bolt, the outputs of which can be stored and combined for displaying the total load at (25). <IMAGE>

Description

SPECIFICATION Vehicle axle load measuring device DESCRIPTION OF INVENTION The invention relates to a measurement device that has prime but not exclusive application to measurement of the load applied to a vehicle axle.

Regulations exist which relate to the maximum load which may be applied to axles of some vehicles, such as goods vehicles, and it is therefore be desirable for a reliable means to be provided which can give an accurate measurement of the load applied to an axle.

In the past the weight of a vehicle, but not necessarily the load applied to a particular axle, has been measured by means of a weighbridge. It is also known to measure the applied load by measuring the relative positions of a vehicle body and the axle caused by the weight of the load, change in the relative position being due to compression of the suspension means. However since the characteristics of the suspension means, which are often leaf springs, change through use and age, such a means of measurement of applied load may become unreliable.

Whereas the present invention is to be principally applied to the loading on an axle, it will be appreciated that whilst some vehicles may not have axles as such, a measurement must still be provided of the load carried by each wheel or pair of wheels on respective sides of the vehicle. The term axle is intended to cover any means for rotatably supporting a wheel or wheels, which supporting means also carries a load supporting chassis or assembly.

It is an object of the present invention to provide a new or improved device for indicating the load applied to an axle of a vehicle.

According to the present invention, we provide a device adapted to measure the load applied to an axle af a vehicle, said device comprising a means having an output indicative of a force applied thereto, said means being mounted intermediate said axle and load carrying means supported by said axle.

It is another object of the present invention to provide a vehicle having a new or improved axle load indicating means.

According to a second aspect of the present invention, we provide a vehicle comprising an axle and a load carrying means supported by said axle, wherein a device is provided adapted to measure the load applied to said axle, said device comprising a means having an output indicative of a force applied thereto, the means being mounted intermediate said axle and a load carrying means.

Preferably said device includes a display means adapted to indicate the load applied to said axle.

Conveniently, said means may comprise a strain gauge secured to or forming part of a vehicle suspension means through which part forces are applied indicative of the load supported by said axle.

In vehicles which have their load supporting chassis supported by the axle through the intermediary of springs, said strain gauge may be applied to the part by means of which one end of said spring is connected to or supported by the axle or the load supporting chassis.

In the case of vehicles in which axles support the load carrying chassis through the intermediary of leaf springs, such part may comprise a bolt connecting one end of the leaf spring with the chassis. Preferably said bolt may comprise a "load measuring bolt" which is a bolt having one or more axial holes therethrough, which holes have strain gauges bonded thereto. Thus in a typical arrangement such a load measuring bolt may take the place of a conventional bolt by means of which a leaf spring is secured to the chassis.

Said strain gauge may be connected in a bridge circuit and is adapted to cause an electrical current to flow when a force is applied through the bolt. The force and therefore the electrical current is indicative of the load carried by the axle. The current may be calibrated in a manner to relay a signal indicative of the load applied to an axle to a display means.

Preferably, storage means may be incorporated in circuitry associated with the strain gauge and display means to enable the subtraction of the chassis weight borne by a particular axle or all axles of the vehicle, in order to enable the device to give a reading of the load carried by the vehicle in addition to the load borne by the or each axle. It will be appreciated that in, for example, a vehicle in which an axle supports a load carrying chassis through leaf springs it is conventional that a pair of such leaf springs are provided in spaced relationship, each end of each spring being secured to the chassis. It is envisaged that each spring so provided will incorporate, in its means for securing the spring to the chassis, a single load indicating means and preferably said load indicating means comprises a "load measuring bolt" securing the "fixed end" of the spring to the chassis.It is conventional for the other end of the spring to be secured to the chassis through the intermediary of a shackle or a sliding slipper, and it is also envisaged that instead of or in addition to the load indicating bolt at the fixed end of the spring, a further load indicating bolt may be provided in the shackle or said sliding slipper may incorporate a load cell adapted to provide an output indicative of the force applied to the slipper from the end of the spring sliding therein.

Where load measuring bolts or load cells are used at both ends of each suspension means, the total load on an axle is applied through the bolts.

However it is more economical to substitute one bolt by the load measuring bolt, in which case the bolt measures a proportion of the load on the axle.

Means is provided for calculating the total load from this proportion.

The device of the present invention operates quite independently of the resilience of the suspension means and thus overcomes problems associated with the above mentioned known device.

In one of the preferred embodiments of the present invention in which a spring is secured to a chassis through the intermediary of a load measuring bolt, such load measuring bolt takes the place of a conventional bolt, thus the device may be introduced in a very simple manner into the assembly of new vehicles in addition to being equally applicable to existing vehicles in that it simply entails the removal of the bolt which holds the spring to the chassis and the introduction of the load measuring bolt.

The device does not therefore entail the designing of new mounting elements nor does it involve costly dismantling and rebuilding of a vehicle.

An example of a device in accordance with the invention will now be described, with reference to the accompanying drawing, wherein FIGURE 1 is a side view of a suspension unit; and FIGURE 2 is a block diagram showing components of the device.

Figure 1 shows a portion of a vehicle and, in particular, a suspension means comprising a unit 10 of a kind commonly fitted on road vehicles. The suspension unit is mounted on a chassis 13 (a portion of which is shown), which chassis supports a load carrying means comprising a vehicle body (not shown in the drawings). An axle 12, shown in cross-section, is in turn mounted on the suspension unit and one or more other suspension units of the vehicle. Wheels on the axle (not shown) are mounted adjacent the ends of the axle so that load is transmitted from the vehicle body to the axle via the suspension units on which the axle is mounted. The suspension unit tends to absorb the shock when one or more wheels on the axle pass over a bump on a road.

The suspension unit 10 comprises a leaf spring 19 which extends between a forward bolt 14 and a rearward bolt 1 5. The forward bolt is mounted on the chassis 13 with respective end portions thereof in fixed engagement with the chassis. The rearward bolt forms part of a shackle arrangement 1 7 and is pivotable about a shackle bolt 1 6 of the shackle, which shackle bolt is mounted on the chassis in the same manner as the forward bolt.

The leaf spring comprises several layers, the topmost of which is wrapped at respective ends around the forward and rearward bolts at respective positions between the fixed ends thereof.

The axle 12 is mounted on the leaf spring 19 intermediate of the bolts 14 and 1 5. The axle can be mounted either above or below the leaf spring and, in the illustrated example, is shown mounted below the leaf spring and attached thereto by means of U-clips 20. In a typical arrangement a Uclip engages the axle on either side of the leaf spring and stems of the clips extend away from the axle with free ends thereof linked by crosspieces on the opposite side of the leaf spring.

In the suspension unit 10, the forward bolt 14 is a load measuring bolt which forms part of a load measuring device 11. The bolt is formed of a material such as steel which is resiliently bendable when subjected to a load so that the bolt tends to bend between its fixed ends in response to the component of the load of the vehicle body which the bolt transmits to the axle. Thus the degree of bending of the bolt is a measure of the load on the axle. Bending of the bolt is detected by means of strain gauges mounted on an inwardly facing surface of a cavity in the bolt.

A load measuring bolt typically contains four strain gauges and can be adapted to be sensitive to bending relative to two or more different axes.

The strain gauges are mounted in a cavity in the form of an aperture which extends coaxially with the bolt, the aperture being sealed at either end against the ingress of particles. The strain gauges are of a form which undergo a change in the electrical properties of an associated circuit when there is a change in the strain on the bolt. The electrical signals from the strain gauges in a bolt are passed to a monitor 21 which can store the signals. The strain gauges and the monitor form a measuring means.

Figure 2 shows a block diagram for a device in use on a two-axle four-wheel vehicle. A pair of monitors each receive two input signals from strain gauges which are mounted in bolts adjacent respective wheels on each axle. A signal from each monitor which is a measure of the total load on each axle is relayed to a display unit 22 which may for convenience of use be mounted in the vehicle, for example on the dash board. A pair of display components 23 of the display unit give a visual reading of the load on each axle in a digital form. Signals from the display components can be passed to a summing component 24 which in turn passes a signal to a further display component 25 which is a measure of the total load on the axles of the vehicle.

Whereas various bolts of a suspension unit in a vehicle may be substituted for load measuring bolts, it has been found that the forward bolt 14 is the most convenient for this purpose. Each monitor comprises microprocessor means capable of deducing the load on an axle from a measurement of the strain on bolts adjacent respective wheels on the axle. The axle 12 is a variable horizontal distance from the forward bolt 14 for different vehicle loads and the monitors are programmed to compensate for this when measuring the load. It will be apparent that, where the load has been evenly distributed on a vehicle body, one load measuring bolt may be sufficient to measure the load on an axle.

When the load measuring device 11 has been mounted on a vehicle by substitution of bolts of the suspension units of the vehicle for load measuring bolts, and by attachment of the monitors 21 and display unit 22 of the device to the vehicle, the monitors may be calibrated by carrying out an external measurement of the load on each axle of the vehicle. Alternatively, calibration of the monitors may be effected by a calculation based on the known dimensions and parameters of the vehicle. The device may then be used for measuring the load on each axle as the vehicle is loaded.

Claims (8)

1. A device adapted to measure the load applied to an axle, said device comprising a means having an output indicative of a force applied thereto, said means being mounted intermediate said axle and load carrying means supported by said axle.

2. A device according to Claim 1 wherein said means comprises a strain gauge.

3. A device according to either preceding claim wherein the means is secured to or forms part of a suspension means.

4. A device according to Claim 3 wherein said part comprises a bolt.

5. A device according to Claim 3 or Claim 4 wherein the suspension means comprises a leaf spring on which an axle is mounted, and the bolt connects one end of the leaf spring to a vehicle chassis.

6. A vehicle comprising an axle and a load carrying means supported by said axle, wherein a device is provided adapted to measure the load applied to said axle, said device comprising a means having an output indicative of a force applied thereto, the means being mounted intermediate said axle and a load carrying means.

7. A device substantially as hereinbefore described with reference to and as shown in the accompanying drawing.

8. Any novel feature or novel combination of features disclosed herein and/or shown in the accompanying drawing.