WO1998038481A1

WO1998038481A1 - Method and apparatus for measuring mass load

Info

Publication number: WO1998038481A1
Application number: PCT/US1998/003880
Authority: WO
Inventors: David Lechtman
Original assignee: Amalgamated Consulting Engineers Of South Africa (Proprietary) Limited; Handelman, Joseph, H.
Priority date: 1997-02-26
Filing date: 1998-02-26
Publication date: 1998-09-03
Also published as: ZA981632B; AU6342098A

Abstract

An apparatus and method for measuring a mass load of a vehicle. The apparatus includes a fluid chamber (14), placed between an axle support (40) and a suspension element (38) of the vehicle, which is in fluid communication with a differential pressure sensor (18) through a damping device (26). A reference fluid chamber (22) provides temperature compensation. The pressure reading is indicative of the weight of the vehicle.

Description

METHOD AND APPARATUS FOR MEASURING MASS LOAD

THIS INVENTION relates to load measurement. It relates m particular, but not necessarily exclusively, to a method of and apparatus for measuring mass load of a component of a vehicle. It also relates to a vehicle including the apparatus.

In order to reduce damage caused to road surfaces by road vehicles, especially heavily laden trucks, authorities m various countries throughout the world pass laws restricting the maximum permissable axle mass load of a vehicle. Generally, m order to ascertain whether or not an axle mass load is within the permissable legal limit, it is necessary to measure the axle load of the vehicle on a conventional weighbridge. It is an object of this invention, inter alia, to offer a solution to this problem.

In accordance with the invention, there is provided a method of measuring mass load of at least a vehicle component, the method including sensing a pressure exerted on a fluid m a fluid chamber by the vehicle component; at least damping any surges m pressure derived from the fluid chamber; and measuring the pressure by pressure measuring means .

The method may include isolating any surges m pressure from the pressure measuring means by protection means.

The method may include selectively activating isolation means when surges m pressure are expected to occur. For example, the isolation means may be activated prior to driving the vehicle.

The sensing means may be positioned proximate a vehicle component m the form of an axle of the vehicle thereby to measure axle mass load of the vehicle on a support surface. In other embodiments, the sensing means may be positioned between a vehicle component in the form of a load support and a chassis of the vehicle thereby to measure mass load of the load ^'support of the vehicle. For example, the load support may be a load bed of the vehicle.

The method may include monitoring at least an ambient temperature of the pressure sensing means; and compensating for changes in pressure due to a variation in the ambient temperature.

Typically, a substantially identical fluid is used in the pressure reference means so that the physical properties, and thus the temperature dependent characteristics of the two fluids are substantially identical.

The method typically includes monitoring a temperature of the fluid in the pressure sensing means.

The method may include measuring the mass load at two different inclinations of the vehicle and calculating from the pressure exerted on the fluid a force representative of a resultant mass load which is equivalent to a weight of the vehicle on a level road surface.

Further in accordance with the invention, there is provided measuring apparatus for measuring mass load of at least a component of a vehicle, the apparatus including sensing means positionable in use to sense the mass load of the component and operable to provide a pressurised fluid output dependent upon the mass load; and pressure measuring means operatively connected in flow communication with the sensing means and operable to provide an output reading which is dependent upon the mass load.

The sensing means may include a plurality of sensors, each sensor being positioned in use to sense axle mass load proximate a wheel of the vehicle with which the sensor is operatively associated.

The sensing means may include a fluid chamber positioned proximate an axle of the vehicle in use, the fluid chamber operatively including a fluid which is subject to a change in pressure upon a change in axle mass load.

The sensing means is typically shaped and dimensioned to fit between an axle and a body of the vehicle in such a fashion so as to sense the axle mass load proximate a wheel of the vehicle. The fluid chamber may be generally circular in outline and may include a central passage through which a mounting component of the vehicle extends in use.

Preferably, the fluid chamber includes a radial passage which leads into the central passage so that the mounting component is transversely displaceable into the central passage.

The sensing means may include a plurality of sensors, each sensor being positioned in use between a vehicle component in the form of a load support, and a chassis of the vehicle thereby to sense the mass load exerted by the load support .

The sensors are typically placed at spaced apart locations below the load support thereby to sense the mass load of the load support at the spaced apart locations.

The measuring apparatus may include at least damping means operatively connected between the sensing means and the pressure measuring means, the damping means being operable at least to damp any pressure surges present in the pressurised fluid output of the pressure sensing means .

The measuring apparatus may include isolating means operable to isolate any pressure surges present in the pressurised fluid output of the pressure sensing means.

The measuring apparatus preferably includes pressure reference means for providing a reference pressure to compensate for the effect of temperature changes in pressure of the pressurised fluid.

The pressure measuring means is typically a differential pressure measuring device which has its one inlet port connected to the pressure sensing means and its other inlet port connected to the pressure reference means in use.

The pressure reference means may be substantially similar to the pressure sensing means and is arranged so that, in use, pressure exerted on the pressure reference means is independent of the mass load of the component of the vehicle.

The invention extends to a vehicle which includes measuring apparatus as hereinbefore described.

The invention is now described, by way of example, with reference to the accompanying diagrammatic drawings.

In the drawings,

Figure 1 shows a schematic diagram of measuring apparatus, in accordance with the invention, for measuring axle mass load of a vehicle;

Figure 2 shows a side view of a pressure sensor, of the measuring apparatus of Figure 1, mounted to a suspension system of the vehicle;

Figure 3 shows a schematic diagram of a further embodiment of measuring apparatus, also in accordance with the invention, which includes a pulse damping device; Figure 4 shows a schematic side elevation of the vehicle supported at a first inclination and exerting a first force on the pressure sensors;

Figure 5 shows a schematic side elevation of the vehicle supported at a second inclination and exerting a second force on the pressure sensors;

Figure 6 shows a schematic side elevation of the vehicle of Figures 4 and 5 exerting a force on a horizontal or level road surface ;

Figure 7 shows an embodiment of a pressure sensor, also in accordance with the invention, included in the measuring apparatus of Figures 1 and 3 ;

Figure 8 shows a top plan view of a further embodiment of a pressure sensor; Figure 9 shows a cross-section of the pressure sensor taken at IX - IX in Figure 8 ; and

Figure 10 shows a schematic representation of a further embodiment of measuring apparatus, in accordance with the invention, for measuring the mass load of a load support.

Referring to the drawings, reference numeral 10 generally indicates measuring apparatus, in accordance with the invention, for measuring axle mass load of a vehicle 12 (see Figures 4 to 6) . The measuring apparatus 10 includes a plurality of pressure sensors 14 connected via primary fluid conduits 16 to a first inlet port of a differential pressure measuring device 18. A second inlet port of the measuring device 18 is connected via a secondary fluid conduit 20 to a reference pressure sensor 22 which is substantially similar to the arrangement of pressure sensors 14 insofar as volume of fluid is concerned. In use, as will be described in more detail below, pressure sensed on a fluid 24 (see Figures 1 to 3) , which is exerted by various axles in an axle group of the vehicle 12 on the pressure sensor 14, as a result of the mass of the vehicle 12, is fed to the measuring device 18 which provides an indication of the cumulative mass load of the vehicle 12.

Although the measuring apparatus 10 shown in Figure 1 includes a plurality of pressure sensors 14 which are connected to a single differential pressure measuring device 18, in other embodiments of the invention each pressure sensor 14 is connected via its associated primary fluid conduit 16 and via protection means in the form of a damping device 26 to a dedicated conventional pressure measuring device 28 (see Figure 2) . In other embodiments of the invention, the damping device 26 is a device which is selectively operable to isolate the pressure measuring device 18 from the pressure sensors 14. In a yet further embodiment, the device is operable to delay or retard transmission of pressure spikes to the pressure measuring device 18, e.g. by way of a restriction orifice.

Each pressure sensor 14 is defined by a fluid chamber (see Figure 7) which is typically made of a plastics material and defines a void 30 in which the fluid 24 is located. The pressure sensor 14 includes a central passage 32 and a transverse passage 34 to enable a component 36, typically a bolt, a shock absorber or the like, to be inserted through the transverse passage 34 into the central passage 32. Accordingly, the pressure sensor 14 may surround the component 36.

The pressure sensor 14, in certain embodiments of the invention as shown in Figure 2, is positioned and mounted in operative communication with a suspension arrangement 38 (see Figure 2) of the vehicle 12. In particular, the pressure sensor 14 is clamped between attachment means 40 for attaching an axle (not shown) of the vehicle 12 to leaf springs 42 of the vehicle 12. Typically, spaced U-bolts 44 are then tensioned resulting in an initial pressure (Pi) being exerted on the fluid 24 which is fed via a primary fluid conduit 16 to the measuring device 28. The effect of the initial pressure (Pi) on the total axle mass load of the vehicle 12 is eliminated by zeroing the conventional pressure measuring device 28 in use. It is to be appreciated, however, that the pressure sensor 14 may be of any other shape or form and mounted in any position relative to the axle of the vehicle 12 so that an increase in the mass of the vehicle 12 results in an increase in the pressure exerted on the fluid 24.

In order to compensate for variations in pressure due to temperature (Pt) , in certain embodiments of the invention the reference pressure sensor 22, which is substantially similar to the pressure sensor 14, is connected via the secondary fluid conduit 20 to the differential pressure measuring device 18 (see Figure 3) . Typically the measuring apparatus 10.1 shown in Figure 3 is mounted proximate each wheel 56 (see Figures 4 to 6) of the vehicle 12 so that an independent measurement of the pressure exerted at the associated wheel 56 may be measured. The damping device 26 is connected via a tertiary fluid conduit 46 to the first inlet port of the measuring device 18. The measuring apparatus 10.1 is arranged so that the volume of fluid in the pressure sensor 14, the primary fluid conduit 16, the damping device 26, and the tertiary fluid conduit 46 is equal to the volume of fluid in the reference pressure sensor 22 and the secondary fluid conduit 20. Accordingly, an increase in temperature will increase the volume of fluid in each fluid circuit equally. As the device 18 is a differential pressure measuring device, an increase or decrease in pressure due to temperature variation in the fluid in the primary sensor 14, the primary fluid conduit 16, the damping device 26, and the tertiary fluid conduit 46 may be compensated for by the reference pressure sensor 22 and the secondary fluid conduit 20. Preferably, the physical properties of the fluids in the pressure sensor 14 and the reference pressure sensor 20 are identical. However, if the physical properties of the fluids in the two circuits are not identical, a scaling coefficient may be used accurately to compensate for the effect of temperature variations on the measuring apparatus 10, 10.1.

When the vehicle 12 is in transit, dynamic forces exerted on the pressure sensor 14 typically result in pressure surges or spikes which are fed towards the pressure sensor 18 via the primary fluid conduit 16. These surges or spikes may be of considerable magnitude and, if fed directly to the measuring device 18, they may damage the device 18. Accordingly, the damping device 26 and, in other embodiments, an isolating device is included to damp or isolate any pressure surges or spikes thereby to protect the measuring device 18.

Referring in particular to Figures 4 to 6 of the drawings, the apparatus 10 further includes an inclinometer 48 for measuring the inclination of the vehicle 12 at a first inclination 50 and at a second inclination 52 relative to a hypothetically level road 54 (see Figure 6) . When carrying out the method, the vehicle 12 is positioned at the first inclination 50 and, by means of the measuring arrangement shown in Figure 3, the force exerted by the vehicle proximate each wheel 56 is measured by the measuring apparatus 10.1, which has its differential pressure measuring device 18 calibrated to indicate force exerted on the pressure sensor 14. For example, in order to calculate the force F_H from forces F_j and F₂ measured by the measuring apparatus 10.1 at the first and second inclinations 50, 52 respectively, the following formula may be used

tan β

F₂ - F, tan

H =

1 - tan β tan a

where

F_H = force exerted on the hypothetically level road 54;

F, = measured first force at the first inclination 50;

F₂ = measured second force at the second inclination 52; a = first inclination 50 measured by the inclinometer 48; and β = second inclination 52 measured by the inclinometer 48.

Instead of measuring the second force F₂ and the second inclination 52 as absolute values, deviations in force and inclination relative to the first force F, and the first inclination 50 may be measured by means of the following formula

F, sin β cos β - F₂ sin a cos a

FH cos a cos β sin (β-α)

The measuring apparatus 10, 10.1 defines "on-board" apparatus for determining the equivalent axle mass load that the vehicle 12 would exert on the hypothetically level road 54 by monitoring pressure exerted on the pressure sensors 14. The pressure sensed is transmitted via the fluid 24 to the differential pressure measuring device 18 which is calibrated to provide a reading of the force exerted on the pressure sensor 14. The equivalent axle mass load is then determined from the formula set out above_and, in this regard, the Inventor believes that the invention of RSA Patent No. 96/5052 may be used in combination with the measuring apparatus 10, 10.1

It is to be appreciated that the pressure sensor 14 may, in certain embodiments of the invention, be defined by a conventional hydraulic shock-absorber or the like and the pressure within the shock absorber may then be sensed and fed via a fluid conduit, corresponding to the primary fluid conduit 16, to a pressure measuring device. In other embodiments of the invention, the pressure sensor 14 may be a piston and cylinder arrangement .

Referring to Figures 8 and 9 of the drawings, reference numeral 70 generally indicates a further embodiment of a pressure sensor in accordance with the invention. The pressure sensor 70 includes a composite circular body 72 which defines a void 30 in which a fluid is received in use.

The body 72 includes a base ring 74 (see Figure 9) and an upper ring 76. The base ring 74 and the upper ring 76 have similar inner and outer diameters and define a central portion in which a hollow tightening pin 78 is receivable. The tightening pin 78 has a collar 80 which abuts a recess in the base ring 74, and a screw-threaded upper portion 82 which receives a nut 84 (see Figures 8 and 9) . Twelve circumferentially equally spaced bolts 86.1 to 86.12, with corresponding nuts, hold a circular diaphragm 88 snugly and sealingly captive between the base ring 74 and the upper ring 76 (see Figure 9J . The base ring 74 includes a circular recess 90 which defines the void 30 and which includes a circular spacer ring insert 92. Further, the pressure sensor 70 includes a circular plunger 94 on which a force is exerted by a body component of the vehicle as shown by arrow 96 in Figure 9.

In use, the pressure sensor 70 is mounted either under the load support 62 of the vehicle or proximate leaf springs 42 of the vehicle so that pressure is exerted on the circular plunger 94 which is dependent on the mass load of the vehicle 12. As the mass load of the vehicle 12 varies, the plunger 94 exerts a greater or lesser force on the fluid in the void 30 by displacement of the diaphragm 88. The void 30 is connected via a flow passage 98 (see Figure 8) to an hydraulic fitting which is connected to the primary fluid conduits 16. Thus, in use, depending upon the force exerted by the plunger 94, the pressure of the fluid may vary as hereinbefore described. As a safety precaution, in the event of the diaphragm 88 shearing due to an excessively high force, travel of the plunger 94 is restricted by the spacer insert 92 so that displacement of the vehicle component is not substantially affected.

The measuring apparatus 10, 10.1 may be arranged in a variety of different configurations dependent upon whether the axle mass load of a single axle or that of a multi-axle system is to be measured. In certain embodiments, the measuring apparatus 10, 10.1 is arranged to measure axle mass load of each axle separately as shown in Figures 2 and 3. Alternatively or in addition, the total mass of the vehicle 12 may be measured with the arrangement shown in Figure 1, using only one pressure measuring device 18.

Further, the measuring devices 18, 28 may provide electronic output signals which may be fed into a processor to execute mathematical functions and provide a variety of readings on the mass load of each axle, the total mass load of the vehicle, or the like.

Referring in particular to Figure 10 of the drawings, reference numeral 60 generally indicates a further embodiment of measuring apparatus in accordance with the invention which is arranged and positioned to measure the mass load exerted by a component of the vehicle in the form of a load support 62 on a chassis 64 of a vehicle 12. The measuring apparatus 60 resembles the measuring apparatus 10, 10.1 and, accordingly, like reference numerals have been used to indicate the same or similar features unless otherwise indicated.

The measuring apparatus 60 includes four pressure sensors 14.1 to 14.4 which are connected to a weight indicator 66 via primary fluid conduits 16. The weight indicator 66 includes protection means in the form of a damping device (not shown) to damp spikes which may be induced in the pressure sensors 14.1 to 14.4 via the load support 62 whilst the vehicle 12 is in motion. As shown in Figure 10, the pressure sensors 14.1 and 14.2 are located between the load support 62 and the chassis 64 towards a front of the vehicle 12 and the pressure sensors 14.3 and 14.4 are located between the load support 62 and chassis 64 towards a tail end of the vehicle 12. Depending upon the load carried by the load support 62, and in a similar fashion as described above, the measuring apparatus 60 is operable to measure the distribution and magnitude of the load supported by the load support 62.

The Inventor believes that the invention, as illustrated, provides a relatively simple method and apparatus 10, 10.1, 60 for measuring mass load of a component of the vehicle 12, e.g. axle mass load or load support mass load. As the apparatus 10, 10.1, 60 includes the damping device 26, damage to the measuring devices 18, 28, 66 by pressure surges sensed by the sensors 14 when the vehicle 12 is, for example, in motion may be reduced. The Inventor also believes that, by means of the measuring apparatus 10, 10.1, the axle mass load of the vehicle 10 may be determined "on-board" without taking the vehicle 12 to a conventional weigh bridge.

The Inventor further believes that, as displacements in compression of suspension systems, or the like which could result in hysteresis errors are not monitored but rather a pressure exerted on the fluid 24, enhanced accuracy may be obtained by means of the measuring apparatus 10, 10.1.

Claims

CLAIMS :

1. A method of measuring mass load of at least a vehicle component, the method including sensing a pressure exerted on a fluid in a fluid chamber by the vehicle component; at least damping any surges in pressure derived from the fluid chamber; and measuring the pressure by pressure measuring means .

2. A method as claimed in Claim 1, which includes isolating any surges in pressure from the pressure measuring means by protection means.

3. A method as claimed in Claim 2, which includes selectively activating isolation means when surges in pressure are expected to occur.

4. A method as claimed in any one of the preceding claims, in which the sensing means is positioned proximate a vehicle component in the form of an axle of the vehicle thereby to measure axle mass load of the vehicle on a support surface.

5. A method as claimed in any one of the preceding claims 1 to 3 inclusive, in which the sensing means is positioned between a vehicle component in the form of a load support and a chassis of the vehicle thereby to measure mass load of the load support of the vehicle.

6. A method as claimed in any one of the preceding claims, which includes monitoring at least an ambient temperature of the pressure sensing means; and compensating for changes in pressure due to a variation in the ambient temperature .

7. A method as claimed in Claim 6, which includes monitoring a temperature of the fluid in the pressure sensing means .

8. A method as claimed in any one of the preceding claims, which includes measuring the mass load at two different inclinations of the vehicle and calculating from the pressure exerted on the fluid a force representative of a resultant mass load which is equivalent to a weight of the vehicle on a level road surface.

9. Measuring apparatus for measuring mass load of at least a component of a vehicle, the apparatus including sensing means positionable in use to sense the mass load of the component and operable to provide a pressurised fluid output dependent upon the mass load; and pressure measuring means operatively connected in fluid communication with the sensing means and operable to provide an output reading which is dependent upon the mass load.

10. Measuring apparatus as claimed in Claim 9, in which the sensing means include a plurality of sensors, each sensor being positioned in use to sense axle mass load proximate a wheel of the vehicle with which the sensor is operatively associated.

11. Measuring apparatus as claimed in Claim 9 or Claim 10, in which the sensing means includes a fluid chamber positioned proximate to an axle of the vehicle in use, the fluid chamber operatively including a fluid which is subject to a change in pressure upon a change in axle mass load.

12. Measuring apparatus as claimed in Claim 11, in which the sensing means is shaped and dimensioned to fit between an axle and a body of the vehicle in such a fashion so as to sense the axle mass load proximate a wheel of the vehicle.

13. Measuring apparatus as claimed in Claim 11 or Claim 12, in which the fluid chamber includes a central passage through which a mounting component of the vehicle extends in use.

14. Measuring apparatus as claimed in Claim 13, in which the fluid chamber includes a radial passage which leads into the central passage so that the mounting component is transversely displaceable into the central passage.

15. Measuring apparatus as claimed in Claim 9, in which the sensing means include a plurality of sensors, each sensor being positioned in use between a vehicle component in the form of a load support, and a chassis of the vehicle thereby to sense the mass load exerted by the load support .

16. Measuring apparatus as claimed in Claim 15, in which the sensors are placed at spaced apart locations below the load support thereby to sense the mass load of the load support at the spaced apart locations.

17. Measuring apparatus as claimed in any one of the preceding claims 9 to 16 inclusive, which includes at least damping means operatively connected between the sensing means and the pressure measuring means, the damping means being operable at least to damp any pressure surges present in the pressurised fluid output of the pressure sensing means.

18. Measuring means as claimed in any one of the preceding claims 9 to 17 inclusive, which includes isolating means operable to isolate any pressure surges present in the pressurised fluid output of the pressure sensing means .

19. Measuring apparatus as claimed in any one of the preceding claims 9 to 18 inclusive, which includes pressure reference means for providing a reference pressure to compensate for the effect of temperature changes in pressure of the pressurised fluid.

20. Measuring apparatus as claimed in Claim 19, in which the pressure measuring means is a differential pressure measuring device which has its one inlet port connected to the pressure sensing means and its other inlet port connected to the pressure reference means in use.

21. Measuring apparatus as claimed in Claim 19 or Claim 20, in which the pressure reference means is substantially similar to the pressure sensing means and is arranged so that, in use, pressure exerted on the pressure reference means is independent of the mass load of the component of the vehicle.

22. A vehicle which includes measuring apparatus as claimed in any one of the preceding claims .

23. A method of measuring mass load of at least a vehicle component, substantially as described and illustrated herein.

24. Measuring apparatus, substantially as described and illustrated herein.

25. A vehicle including measuring apparatus for measuring mass load of a vehicle component substantially as described and illustrated herein.