GB2246864A

GB2246864A - Load sensing arrangement

Info

Publication number: GB2246864A
Application number: GB9110034A
Authority: GB
Inventors: David Anthony Troman; Michael John Mechan; Gary Michael Bishop
Original assignee: JC Bamford Excavators Ltd
Current assignee: JC Bamford Excavators Ltd
Priority date: 1990-07-11
Filing date: 1991-05-09
Publication date: 1992-02-12
Anticipated expiration: 2011-05-09
Also published as: GB9015284D0; GB2246864B; GB9110034D0

Abstract

A load sensing arrangement comprises first and second members connected together by a pin (30) for relative movement about the axis (31) of the pin, the pin having an internal hollow (38), at least two strain gauge means (S1-S4) spaced longitudinally along the pin (30) and each being secured to a side wall (49) of the pin, an electronic circuit (39) located within the internal hollow of the pin longitudinally between the two strain gauge means (S1, S2;S3,S4), each strain gauge means being electrically connected to the electronic circuit (39) which includes an amplifier to amplify signals produced by the strain gauge means, and means to provide a signal from the electronic circuit (39) to a remote indicating means which at least indicates when the load transmitted from the first to the second member through the pin (30), sensed by the strain gauge means, reaches a threshold value. As described the first and second members are the body and rear axle of a fork-lift vehicle and the arrangement responds to a drop in the rear axle load, indicating that the vehicle is about to tip forward on its front wheels. The pin couples plates (63, 64) on the body to a lug (60) on the axle. The arrangement is stated to be insensitive to torque on the pin resulting from travel of the vehicle. <IMAGE>

Description

Title: "Load sensing arrangement" Description of Invention This invention relates to a load sensing arrangement and more particularly but not exclusively, to a load sensing arrangement for sensing a load transmitted between a body of a vehicle and an axle carried thereby.

Arrangements have been proposed, for example in British Patent 1528741 in which a strain gauge is carried by a pin which connects an axle with a vehicle body.

This invention provides an improved load sensing arrangement.

According to one aspect of the invention we provide a load sensing arrangement comprising first and second members connected together by a pin for relative movement about the axis of the pin, the pin having an internal hollow, at least two strain gauge means spaced longitudinally along the pin and each being secured to a side wall of the pin and there being an electronic circuit located within the internal hollow of the pin, longitudinally between the two strain gauge means, each strain gauge means being electrically connected to the electronic circuit which includes an amplifier to amplify signals produced by the strain gauge means, means to provide a signal from the electronic circuit to a remote indicating means which at least indicates when the load transmitted from the first to the second member through the pin, sensed by the strain gauge means, reaches a threshold value.

Thus the amplifier of the electronic circuit amplifies the very small level signal from the strain gauge means before transmitting the signal to the remote indicating means and is protected inside the hollow of the pin. Thus the pin and electronic circuit can conveniently be provided as a single component to facilitate assembly and maintenance.

The means which provide the signal from the electronic circuit to the remote indicating means may comprise one or more electrical conductors, and electrical connection may be made between the electronic circuit and the or each conductor by means including a plug and socket type connector, at an end of the pin.

Further conductors e.g. to carry power to the electronic circuit may be electrically connected to the electronic circuit via means including the pplug and socket connector.

The hollow of the pin may thus open to one end of the pin, which opening may be closed by the plug or socket of the connector.

If desired, the hollow of the pin may open to the other end of the pin also to facilitate manufacturing of the pin, which other opening may be closed in use by an appropriate cap.

The electronic circuit may be provided on a printed circuit board, from which a respective electrical lead extends to each of the strain gauge means and further electrical leads may extend from the circuit board to the plug or socket of the connector at the one end of the pin.

Means may be provided to prevent rotation of the pin relative to the first or second member. Such means may comprise a location element secured to the first or second member, which engages in a recess provided in the outer surface of the pin, the recess providing an engagement surface which co-operates with an engagement surface of the location element to prevent rotation of the pin, and to locate the pin axially relative to the first and second members.

The strain gauge means may be secured to the side wall of the pin in respective further recesses in the outer surface of the pin'so that the strain gauge means are protected as the second or first member rotates relative to the pin.

Openings may be provided from each of the further recesses through the side wall of the pin to the hollow, through which openings the respective electrical leads may extend between the electronic circuit and the strain gauge means.

In this case, preferably the strain gauge means are sealed in their respective recesses by suitable sealant to prevent the ingress of dirt etc. through the respective opening from the recess to the hollow of the pin where such dirt could contaminate the electronic circuit.

Preferably though, the strain gauge means are each located within the hollow of the pin. The strain gauge means may thus each be secured to the inside surface of the side wall of the pin, and the respective electrical leads between the strain gauge means and the electronic circuit may thus extend along the hollow of the pin.

The invention has been devised particularly but not exclusively for use in sensing a load transmitted from a body to an axle of a load carrying vehicle of the kind, hereinafter referred to as being "of the kind specified" having a working arm mounted at one end on the body of the vehicle, and the arm carrying at its other end a working implement such as a pair of forks, or a bucket, for examples only.

It will be appreciated that where such an arm extends outwardly of the vehicle, for example forwardly of the vehicle, if the arm is loaded to an extent which exceeds the lifting capacity of the vehicle, there would be a tendency for the vehicle to tip. In a vehicle having two pairs of wheels, and the working arm extending forwardly, the rear wheels could be raised from the ground as the vehicle tips, thus endangering the operator of the vehicle. The problem particularly arises where the working arm is telescopic and the working implement is loaded, with the working implement near to the vehicle body, and then the arm is telescoped outwardly to move the loaded working implement away from the body.

The load sensing arrangement of the present invention can be used to provide a warning to an operator of a vehicle of the kind specified that the vehicle is about to tip. The strain gauge means may sense when the load transmitted from the body to the rear axle of the vehicle decreases below a threshold value, or alternatively the strain gauge means may be used to sense when the load transmitted from the body to the front axle exceeds a threshold value.

Preferably the remote indicating means gives to the operator a constant visual indication of the load being sensed, and a visual and/or audible warning is provided to the operator when the load sensed approaches the threshold value.

When the load sensing arrangement is applied to a vehicle of the kind specified, the first member may comprise a body of the vehicle and the second member an axle thereof, the axle being connected to the body via the pin of the load sensing arrangement, which pin may be provided in a position such that a central axis of the pin coincides with a longitudinal central axis of the vehicle such that the axle may oscillate relative to the body of the vehicle as the vehicle travels over uneven ground. The average load sensed by strain gauge means at each end of the pin may be used to provide the signal to the remote indicating means but preferably each strain gauge means comprises two pairs of strain gauges which may be connected electronically in a bridge as is well known in the art.

The axle may comprise a central lug with an opening therein to receive the pin, and the body may comprise a pair of yokes again with openings for the pin, which yokes in use lie either side of the lug and are connected to the lug via the pin.

Each strain gauge means may be located in each of the regions adjacent the interface between the yokes and the lugs, where maximum bending of the pin occurs.

Preferably though, the strain gauge means are located along the pin in positions where the pin is subjected to minimum bending.

Where the strain gauge means each comprises two pairs of strain gauges, the pairs of strain gauges of each strain gauge means may be located at opposite ends of a diameter of the pin, the diameter being contained within a plane which is generally perpendicular to the direction of applied load, the strain gauges each sensing movement transverse to the plane, so that the strain gauges each sense the shear forces to which the pin is subjected.

According to a second aspect of the invention we provide a pin for a load sensing arrangement according to the first aspect of the invention.

According to a third aspect of the invention we provide a vehicle of the kind specified including a load sensing arrangement in accordance with the first aspect of the invention.

The load sensing arrangement is preferably provided at the connection between a rear axle of the vehicle and the body thereof, to sense a decrease in load transmitted from the body of the vehicle to the axle below a threshold value, which would indicate that the vehicle is about to tip about the front wheel axis of rotation of the vehicle.

The invention will now be described with reference to the accompanying drawings in which: FIGURE 1 is a side view of a vehicle including a load sensing arrangement in accordance with the invention; FIGURE 2 is an illustrative rear view of the vehicle of Figure 1 to an enlarged scale, with parts of the body of the vehicle omitted for clarity; FIGURE 3 is an exploded perspective view of part of a load sensing arrangement in accordance with the invention, FIGURE 3a is a side sectional view through an assembled pin of the part of the load sensing arrangement shown in figure 3.

Referring to the drawings, a load handling vehicle 10 comprises a body 11, a front pair of wheels 12 and a rear pair of wheels 13, the front wheels 12 being carried by a first axle 36, and the rear wheels 13 being carried by a second axle 14.

The body 11 has mounted upon it a working arm 15 which is mounted adjacent one end on a mounting 16 of the body 11 of the vehicle, and extends forwardly outwardly of the body 11, the other end 17 of the arm 15 carrying a working implement which in the present instance is a pair of forks 18. The working arm 15 can be raised and lowered about an axis 20 by means of a pair of hydraulic actuators 21, only one of which can be seen in the drawing, although in another arrangement, a single actuator only, may perform this task. The working implement 18 can be moved relative to the arm 15 about a further axis 22 by means of a further hydraulic actuator 23 to enable the forks 18 to be loaded, and unloaded.

The arm 15 is telescopic, comprising an outer part 24 which is attached to the mounting 16, and an inner telescopically movable part 25 which carries the working implement 18. The arm 15 can be telescoped inwardly and outwardly by means of one or more hydraulic actuators located within the working arm 15.

The vehicle 10 further comprises an operator's cab 26 comprising part of the body 11 of the vehicle 10, there being within the operator's cab 26, an indicating means 27 the purpose of which will become apparent hereinafter.

The rear axle 14 is connected to the body 11 by a pin 30, a central axis 31 of the pin coinciding with a longitudinal axis of the vehicle 10. Thus the axle 14 can oscillate about the axis 31 relative to the body 11 of the vehicle, as the vehicle travels over ground 32, to accommodate any bumps in the ground. If desired, dampers (not shown) may be provided between the axle 14 and the body 11. The rear axle 14 carries the wheels 13 which are each movable relative to the axle 14 about a respective vertical axis 33,34, under the control of hydraulic actuators (not shown) whereby the vehicle 11 can be steered by movement of a steering wheel 35 within the operator's cab 26.

It will be appreciated that if the forks 18 are loaded to an extent which exceeds the load carrying capacity of the vehicle 10, there would be a tendency of the vehicle to tip about an axis 36 of the front wheels 12 thus lifting the rear wheels 13 from the ground 32. For example, if the forks 18 were loaded with the working arm 15 in an inwardly telescoped condition, and then the arm 15 were lifted and the arm telescoped outwardly to move the forks 18 further away from the body 11, a point could be reached where the vehicle 10 would tip about axis 36.

To provide a warning to an operator of this impending condition, a load sensing arrangement is provided which signals the indicating device 27 within the operator's cab 26.

The load sensing arrangement is shown in detail in Figures 3 and 3a.

It can be seen that the pin 30 has an internal hollow 38 which in this example, extends for the length of the pin 30 and opens at either end.

Within the hollow 38 an electronic circuit 39 is received, the circuit comprising a flexible printed circuit board from which a plurality of electrical leads 40 to 43 extend to respective strain gauge pairs S1 to S4. Hence four strain gauge pairs S1 to S4 are provided on the pin 30, two at or adjacent each end, the strain gauge pairs S1, S2, being arranged at an opposite side of a diametric plane P of the pin 30 to strain gauge pairs S3,S4. The electronic circuit 39 is located longitudinally between strain gauge pairs S1,S3 and S2,S4.

The leads 40 to 43 provide electrical connections to the strain gauge pairs S1 to S4. Thus any signals from the strain gauge pairs S1 to S4 are passed to the electronic circuit 39 via the leads 40 to 43.

The circuit 39 comprises an amplifier which amplifies the very low level signals from the strain gauge pairs S1 to S4 and then passes a signal via a further electrical conductor to the remote indicating means 27 within the operator's cab 26, via a plug and socket connector, the socket comprising a first part 46 which carries terminals which are electrically connected via further leads 4SL 45h, to the circuit board 39, and a second part 47 into which the first part 46 is a screw fit, the second part 47 in use being glued or otherwise secured in the opening of the hollow 38 at one end 48 of the pin 30.

At the opposite end 50 of the pin 30, a cap 51 is provided, which is a screw fit in the end 50 of the pin, to close the other end opening of the hollow 38. If desired, the above described screw fits may alternatively be any other suitable form of connection. Thus, the electronic circuit 39 is received within the hollow 38, and is protected in the hollow, with the hollow 38 being closed at both ends 48 and 59 by the socket of the electrical connector 40, 47 and the cap 51 respectively.

As mentioned above, the circuit board 39 is flexible. The board 39 can thus conveniently be secured in the hollow 38 of the pin 30 to the inside of the side wall 49 of the hollow 38 of the pin 30.

The strain gauge pairs S1 to S4 may also be secured to the inside of the side wall 49 of the hollow 38 of the pin 30.

The pin 30 is fixed relative to the body 11 of the vehicle so as to prevent rotation of the pin 38 about the axis 31. This is achieved by there being a recess R provided in the outer surface 46 of the pin 30, in which a location element 52 is received. The location element 52 is secured relative to the body 11 in any desired manner, and a flat inside surface 53 of the recess R provides an engagement surface which abuts with the corresponding engagement surface 54 of the location plate 52. Thus the plate 52 not only prevents rotation of the pin 30, but also locates the pin 30 axially of the body 11 of the vehicle.

The axle 14 of the vehicle comprises a lug 60 which has an opening 61 through it to receive the pin 30. Preferably the opening 61 carries a hardened insert 62 which provides a bearing material for the pin 30.

The body 11 of the vehicle carries a pair of yoke plates 63, 64 which each also have openings 65,66, respectively to receive the pin 30. When the plug 60, pin 30 and yoke plates 63,64, are assembled, the strain gauge pairs S1 to S4 may be located at regions adjacent the interfaces between the yoke plates 63,64 and the end surfaces 67 of the lug 60.

The strain gauge pairs S1 to S4 each comprise a first plurality of strain elements arranged in generally parallel fashion, extending transverse to the diametric plane P in this example at an angle of 45C to the plane P, and a second plurality of strain gauge elements, arranged in generally parallel fashion, extending transverse to the plane P, at an angle of 45" to the plane, but oppositely to the elements of the first plurality. The plane P itself is arranged generally perpendicularly to the direction of applied load on the pin 30 so that the gauge pairs S1 to S4 actually sense shear accross plane P, where minimum bending of the pin 30 occurs.

It will be appreciated that as the vehicle 10 travels, the wheels 13 which are driven, can exert a torque on the pin 30. The electronic circuit 39 may be arranged to average the readings from the four strain gauge pairs S1 to S4 provided on the pin 30 so as to counteract any false signals due to any such torque forces.

Alternatively, and preferably, the strain gauge pairs S1, S3 and S2, S4, are arranged in respective bridges, as is well known in the art.

In each case, preferably the indicating means 27 provides a continuous indication to an operator of the vehicle 10 of the load sensed by the load sensing arrangement. When the load transmitted from the body 11 to the axle 14 decreases below a threshold value, indicating that the vehicle is nearly at tipping point, preferably the indicating means 27 provides an audible warning, in addition to a visual warning by the load sensed being indicated in a red region 28 of the indicating means 27. If desired, the signal from the load sensing arrangement may also be used to prevent any further movement of the loaded working implement 18 outwardly of the vehicle, or raising of the arm, both of which conditions could accentuate the risk of tipping.

Various modifications are possible without departing from the scope of the invention. For example in place of the load sensing arrangement being provided at the connection between the rear axle 14 and the body 11, to sense tipping of the vehicle, if desired the load sensing arrangement may be provided on the vehicle between the body 11 and the front and/or rear axle 14 of the vehicle to sense the actual load of the vehicle transmitted to the ground 42,.

The load sensing arrangement may be provided on other types of vehicle to the load carrying vehicle 10 described, for example to an excavating type of vehicle, or any other vehicle which comprises a working arm which extends outwardly of the body 11 of the vehicle 10 and which carries a working implement to carry a load.

If desired, four strain gauge pairs S1 to S4 need not be provided on the pin 30, but less than four or more than four strain gauge pairs may be provided as desired, provided there are at least two strain gauge pairs longitudinally spaced along the pin 30.

The hollow 38 need not open to either end of the pin 30, although this arrangement is preferred for ease of manufacturing and assembly.

Instead of the socket 46/47 being provided by the pin 30, to enable the electrical connection between the electronic circuit 39 and the remote indicating means 27, if desired, a plug of a plug and socket connector may be provided on the pin.

If desired, yokes may be provided by the axle 14 and a lug by the body 11 instead of the lug 60 being provided on the axle 14 and yoke plates 63,64, on the body 11 as described.

If desired, the pin 30 may be mounted in cantilever fashion with there only being one yoke plate.

As described, the strain gauge pairs S1 to S4 are provided inside the side wall 49 of the pin 30. If desired, the gauge pairs S1 to S4 may be provided on the outside of side wall 49 of the pin 30, for example in protective recesses.

In this case, openings would need to be provided through the side wall 49, for leads to make electrical connections from the strain gauge pairs S1 to S4 to the electronic circuit 39.

The features disclosed in the foregoing description, or the accompanying drawings, expressed in their specific forms or in the terms or means for performing the desired function, or a method or process for attaining the disclosed result, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

1. A load sensing arrangement comprising first and second members connected together by a pin for relative movement about the axis of the pin, the pin having an internal hollow, at least two strain gauge means spaced longitudinally along the pin and each being secured to a side wall of the pin and there being an electronic circuit located within the internal hollow of the pin, longitudinally between the two strain gauge means, each strain gauge means being electrically connected to the electronic circuit which includes an amplifier to amplify signals produced by the strain gauge means, means to provide a signal from the electronic circuit to a remote indicating means which at least indicates when the load transmitted from the first to the second member through the pin, sensed by the strain gauge means, reaches a threshold value.

2. An arrangement according to claim 1 wherein the means which provide the signal from the electronic circuit to the remote indicating means comprises one or more electrical conductors.

3. An arrangement according to claim 2 wherein electrical connection is made between the electronic circuit and the or each conductor by means including a plug and socket type connector, at an end of the pin.

4. An arrangement according to claim 3 wherein further conductors to carry power to the electronic circuit are electrically connected to the electronic circuit via means including the plug and socket connector.

5. An arrangement according to claim 3 or claim 4 whereinthe hollow of the pin opens to one end of the pin, the opening being closed by the plug or socket of the connector.

6. An arrangement according to claim 5 whereinthe hollow of the pin opens to the other end of the pin and is closed, in use, by a cap.

7. An arrangement according to any one of the preceding claims wherein the electronic circuit is provided on a printed circuit board, from which a respective electrical lead extends to each of the strain gauge means.

8. An arrangement according to claim 7 where appendant to claim 3 wherein further electrical leads extend from the circuit board to the plug or socket of the connector at the one end of the pin.

9. An arrangement according to any one of the preceding claims wherein means are provided to prevent rotation of the pin relative to the first or second member.

10. An arrangement according to claim 9 wherein the means which prevent rotation of the pin comprise a location element secured to the first or second member, which engages in a recess provided in the outer surface of the pin, the recess providing an engagement surface which co-operates with an engagement surface of the location element to prevent rotation of the pin, and to locate the pin axially relative to the first and second members.

11. An arrangement according to claim 10 wherein the strain gauge means are secured to the side wall of the pin in respective further recesses in the outer surface of the pin so that the strain gauge means are protected as the second or first member rotates relative to the pin.

12. An arrangement according to claim 11 wherein openings are provided from each of the further recesses through the side wall of the pin to the hollow, through which openings electrical leads extend between the electronic circuit and respective strain gauge means.

13. An arrangement according to claim 12 wherein the strain gauge means are sealed in their respective recesses by sealant to prevent the ingress of dirt through the respective opening from the recess to the hollow of the pin.

14. An arrangement according to any one of claims 1 to 10 wherein the strain gauge means are each located within the hollow of the pin.

15. An arrangement according to claim 14 wherein the strain gauge means are each secured to the inside surface of the side wall of the pin, and respective electrical leads between the strain gauge means and the electronic circuit extend along the hollow of the pin.

16. An arrangement according to any one of the preceding claims wherein the load sensed is that transmitted from a body to an axle of a load carrying vehicle of the kind specified.

17. An arrangement according to claim 16 wherein the vehicle has two pairs of wheels, and the working arm extends forwardly of the vehicle, the working arm being telescopic and thus able to move the loaded working implement towards and away from the body.

18. An arrangement according to claim 17 wherein the pairs of wheels are carried on respective front and rear axles, the strain gauge means sensing when the load transmitted from the body to a rear axle of the vehicle decreases below a threshold value, or when the load transmitted from the body to the front axle exceeds a threshold value.

19. An arrangement according to any one of the preceding claims wherein the remote indicating means gives to the operator a constant visual indication of the load being sensed, and a visual and/or audible warning when the load sensed approaches the threshold value.

20. An arrangement according to any one of claims 16 to 19 where appendant to claim 16 wherein the first member comprises a body of the vehicle and the second member an axle thereof, the axle being connected to the body via the pin of the load sensing arrangement, which pin is provided in a position such that a central axis of the pin coincides with a longitudinal central axis of the vehicle such that the axle may oscillate relative to the body of the vehicle as the vehicle travels over uneven ground.

21. An arrangement according to any one of the preceding claims wherein each strain gauge means comprises two pairs of strain gauges connected electronically in a bridge.

22. An arrangement according to claim 20 or claikm 21 where append ant to claim 20 wherein the axle comprises a central lug with an opening therein to receive the pin, and the body comprises a pair of yokes with openings for the pin, which yokes in use lie either side of the lug and are connected to the lug via the pin.

23. An arrangement according to claim 22 wherein each strain gauge means is located in each of the regions adjacent the interface between the yokes and the lugs, where maximum bending of the pin occurs.

24. An arrangement according to claim 22 wherein the strain gauge means are located along the pin in positions where the pin is subjected to minimum bending.

25. A load sensing arrangement substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

26. A pin for a load sensing arrangement according to any one of the preceding claims.

27. A pin for a load sensing arrangement substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

28. A vehicle of the kind specified including a load sensing arrangement in accordance with any one of claims 1 to 25.

29. A vehicle according to claim 28 wherein the load sensing arrangement is provided at the connection between a rear axle of the vehicle and the body thereof, to sense a decrease in load transmitted from the body of the vehicle to the axle below a threshold value, which would indicate that the vehicle is about to tip about the front wheel axis of rotation of the vehicle.

30. A vehicle substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

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