WO2004027366A1

WO2004027366A1 - Device for measuring the amplitude of a force produced on an axis and a vehicle provided with said device

Info

Publication number: WO2004027366A1
Application number: PCT/CH2002/000523
Authority: WO
Inventors: Alain Schorderet
Original assignee: Ecole Polytechnique Federale De Lausanne (Epfl)
Priority date: 2002-09-20
Filing date: 2002-09-20
Publication date: 2004-04-01
Also published as: AU2002328238A1

Abstract

The inventive device for measuring forces, in particular radial forces produced on an axis or another piece, for example on the axis of the rear wheel of a motorcycle. Said device comprises a measuring sleeve (1) arranged around an axis (3) in such a way that a force to be measured is produced thereon by means of said sleeve. Said device also comprises a strain gauge (40) which makes it possible to determine the deformation amplitude of the part of the measuring sleeve in order to deduct the amplitude of the produced force. The invention can be used for measuring the tensile stress of a motorcycle chain.

Description

Device for measuring the amplitude of a force applied to a part, and vehicle fitted with this device

The present invention relates to a device making it possible to measure the amplitude and / or the direction of a force applied to a part, in particular to a cylindrical part, for example an axis. In particular, the present invention relates to a device making it possible to measure the amplitude and / or the direction of a force applied radially on an axis.

In the automobile and motorcycling sector in particular, it is often useful to be able to measure, while driving, the forces, that is to say the forces and the torques, applied at different points of a moving vehicle. For example, during motorcycling competition tests, a precise knowledge of the torque supplied by the engine and the forces passing through the tires makes it possible to optimize the engine settings and the choice of tires. Out of competition, force or torque measurement sensors can be used to control various vehicle accessories, for example an anti-lock brake system, the suspension, a gearbox, etc.

Different solutions have been proposed in the prior art or have been imagined in the context of the development of this invention in order to measure these efforts.

The vertical force applied to a tire can for example be measured using pressure sensors installed in the tires of the vehicle. These sensors are inexpensive, but require a radio interface to transmit the measurement results from the rotating tire. In addition, the measurement is highly dependent on the temperature of the tire.

It has also been imagined to place a load cell on each bearing of the wheels of a motorcycle. By a balance of forces, the forces applied to each tire can be calculated. This solution allows take a measurement near the point of application of the force; the connection is also simple since the measurement system is located on the bearings which are not rotating. However, the volume available in the bearings is limited and the cost of miniature load cells prohibitive.

Rim deformation can be measured by placing strain sticks directly on the rim sticks. However, this solution requires a thorough knowledge of the behavior of the rim under load. In addition, a wireless link is also necessary to transmit the measurement result from the sensors located on a rotating part.

The forces in the shock absorber tubes can be measured by load cells. In order to deduce therefrom the forces applied to the tires, the dynamics of the suspended part of the vehicle must however be known, which is not always the case. Furthermore, the installation of sensors in the shock absorbers poses reliability problems.

The force applied to the shock absorbers and therefore to the wheel can be calculated by measuring the deflection position of the shock absorbers. This solution however requires precise knowledge of the dynamic behavior of the shock absorber, which is not always the case.

None of the above solutions can directly measure the torque supplied by the engine. In the case of motorcycles, this torque can be measured by placing the rear wheel on measuring rollers. This laboratory solution is not suitable for measuring the torque in situ when driving or on a circuit.

An object of the present invention is therefore to propose a simple, light and economical device which makes it possible to measure the torque supplied by the engine to the transmission wheels of a vehicle, in particular of a motorcycle, when driving. According to the invention, this object was firstly achieved by very precisely determining the nature of the forces and torques applied to the driving wheel of a vehicle. In the case of a motorcycle, the situation is illustrated with the aid of Figures 1 and 2 which are part of the invention. The motorbike wheel illustrated comprises a rim 80 fitted with a tire 81 and rotated about a fixed axis 3. The axle is fixed by a nut 90 to a swinging arm 9. A toothed crown 71 is screwed by means nuts (6 in this example) on a crown carrier 7 (visible in Figure 2) and driving the rim in rotation. The crown is driven by the chain 72 or by a belt.

According to the invention, a sleeve 1 whose role will be explained below is mounted around the axis 3. Bearings or bearings 5 are hooped or glued on the sleeve 5 so as to allow the rotation of the crown holder 7 relative to axis 3.

The traction force Fc exerted by the chain is transmitted via the crown 71 to the crown holder 7, generating a torque Mr = Fc X Rc where Rc is equal to the diameter of the crown. To fix the ideas, the tensile force Fa can be, depending on the motorcycle, between 10O00 and 15O00 N. The applied torque causes the rim 80 to rotate and the motorcycle to move. If the sum of the forces is equal to zero, the reaction force Fa exerted by the bearings 5 on the axis 3 of the wheel is of equal amplitude and in the opposite direction to the force Fc.

The force Fc exerted by the chain, and therefore the torque Mr, can thus be determined by measuring the radial force exerted on the axis 3 by the bearings 5.

Another object of the present invention is therefore to propose a device making it possible to measure the forces, in particular the radial forces, exerted on the axis 3.

According to the invention, this object is achieved by means of a device comprising a measuring socket arranged so that the force to be measured is applied to a workpiece via the measuring sleeve. The device comprises a measuring element making it possible to determine the amplitude of the deformation of a portion of the measuring sleeve in order to deduce therefrom the amplitude of the force applied.

This solution has the advantage of allowing a measurement very close to the point of application of the forces on the axis, without disturbing the measurement or the operation of the device being measured, and without increasing the mass driven in rotation.

This solution also has the advantage of allowing measurement on a fixed element, that is to say the axle, avoiding the difficulty of transmitting information from measurement sensors mounted on moving parts.

It has moreover been found that the same device, or a suitable device, can also be used to measure the amplitude and / or the direction of forces or moments exerted on the axis, or on any massive part or hollow, in a radial or even non-radial direction. Furthermore, the use of the imagined device is not limited to the measurement of forces or torques exerted on the axle of a vehicle, but can also be used for example to measure the force exerted by a tool on the spindle or spindle of a machine tool.

In a preferred variant of the invention, the measuring device of the invention comprises several measuring portions deformed by the force or the torque to be measured, several measuring elements making it possible to measure the deformations undergone by the different measuring portions in order to d '' deduce both the amplitude and the direction of the force exerted.

In order to reduce the mass of the device, the socket used preferably includes hollow cavities which also make it possible to place the measurement element or elements therein. However, care should be taken to limit the diameter and the total size of the device. The invention will be better understood on reading the description illustrated by the appended figures which show:

Figure 1 already commented on a motorcycle rear wheel equipped with the device of the invention.

FIG. 2 already commented on a diagram representing the forces applied to a wheel axle equipped with the device of the invention.

Figure 3 a longitudinal section of a motorcycle axle portion provided with the device of the invention.

Figure 4 a top view in section of the measuring device of the invention.

Figure 5 an electrical block diagram of the complete measurement system.

Although the example described relates more precisely to the case of the measurement of the radial force exerted by the bearings on the axle of the rear wheel of a motorcycle, those skilled in the art will understand that the invention can also be applied to axles or other axles of other vehicles, including for example bicycles, scooters, automobiles, trucks, trains, etc., or to the measurement of forces and torques, in particular of radial forces, exerted on the machine tool spindles.

Figure 3 illustrates a longitudinal section of an axle portion (axle) of a motorcycle rear wheel equipped with the device of the invention. The axis 3 is fixed by means of a nut 90 to an oscillating arm 9. A mounting sleeve 30 is mounted, for example hooped or driven by a mechanical stop, on the axis 3. This mounting sleeve 30 makes it possible to mounting other measuring devices on the axle 3, for example to measure the bending of this axle; it also makes it possible to adjust the internal diameter of the measuring sleeve 1 to the external diameter, not always known with precision, of the axis 3. In a variant, the mounting socket 30 could be eliminated or integrated into the measuring socket 1.

The measuring sleeve of the invention is illustrated with the number 1. It comprises an internal ring (or rim) 10 hooped or glued, on the mounting sleeve 30 and an external ring or rim 11. The two rings 10, 11 are connected by spokes 12, 13 described below.

A bearing or bearing 5, for example a ball, roller or needle bearing, is hooped or glued to the external face of the external ring 11; a bearing surface 14 on the ring 11 makes it possible to control the longitudinal position of the bearing 5 along the axis. A crown carrier 7 mounted around the bearing 5 can thus pivot with reduced friction around the axis 3. The toothed crown 71 is fixed to the crown carrier 7 by means of bolts 73. The crown 71 is rotated by the traction exerted by the chain 72 (not shown in this figure). The forces are transmitted to the crown carrier 7 via the bolts 73. The rotation of the crown carrier is transmitted via studs 70 to the rim 80 (shown in FIG. 1) of the wheel.

In order to adapt to commercially available crowns and rims, preferably use six bolts 73 to fix the crown 71 and five studs 70 to fix the rim 80. The angular distance between the five studs and the six through holes of the bolts in the crown holder 7 is therefore irregular, causing a different “rigidity” between the different pairs of studs 70 and bolts 73. The forces transmitted by the crown are therefore not distributed homogeneously in the crown holder 7 and therefore in the bearings 5, which could distort the measurement. Calculations have shown that an angular difference of 4 ° between the initial stud and the initial bolt is optimal for homogenizing the forces present in the drive studs 70 and reducing the hysteresis. In a variant, it is also possible to use the same number of bolts and studs, for example five bolts 73 and five studs 70. The measuring socket 1 is shown in FIG. 4. In this example, it has three first spokes, or beams, 12 and three second spokes, or webs, 13. The inner ring 10 and the outer ring 11 are relatively thick and not very deformable. . The rigidity of the inner ring 10 is further reinforced by the axis 3 of conventional steel and the adapter sleeve 30 with which it is directly in contact. In the same way, the rigidity of the outer ring is reinforced by that of the bearings 5 made of conventional steel or even by lateral flanges.

On the other hand, the application of a radial force on the external face of the ring 11 causes a deformation of the first and second rays. The first spokes 12 are relatively massive and their width is equal to that of the sleeve; they therefore deform little, essentially in traction-compression and in bending. On the other hand, the second spokes 13 are substantially thinner in order to amplify their deformation; in addition, their width is much less than that of the bush 1. The application of a radial force on the bush 1 causes a deformation in buckling and in bending, of much greater amplitude, of these second spokes 13.

The second spokes 13 consist of an almost radial portion 130 and a curved, non-radial measurement portion 131. The measurement portion 131 is thinner than the radial portion 130, so that under the effect of a radial external force the radial portion 130 moves practically without deformation while the amplitude of the deformation of the measurement portion 131 is maximum. This characteristic increases the sensitivity of the measurement.

In a preferred embodiment, the deformation of the measurement portions is measured using strain gauges 40 (strain gauges) directly bonded to the external face of the measurement portion of at least one second radius 13. The portion curved 131 of the second spokes 13 is therefore, in this example, closer to the inner ring 10 than to the outer ring 11 of the measuring socket. However, it would be possible to reverse this arrangement and paste the constraint on the internal face of the curved spokes 13. It is also possible to place a measurement element on each side of at least one spoke 13, or to place several strain gauges per spoke 13 in order to have several measurement points per Ray.

In the example illustrated, the first three radii 12 are regularly spaced 120 ° apart. The three second spokes 13 are also regularly spaced 120 ° apart; however, the curvature of one of the spokes is reversed compared to that of the other two. This characteristic makes it possible to bring the radial portion 130 of two second spokes 13 closer to the same first radius 12. In order to increase the amplitude of the deformations on at least two second closely spaced spokes 13, the sleeve 1 will be oriented so that the base of these closely spaced radii is opposite the point of application of the applied force, when this point is known. In the case of a motorcycle rear wheel, for example, the sleeve 1 will be placed so that the two closely spaced spokes 13 (at the top in FIG. 4) are oriented towards the rear of the motorcycle. However, this orientation can be modified in order to favor certain measurement characteristics.

Those skilled in the art will understand that other arrangements are possible, and that the invention is not limited to measuring sockets comprising three first radii and three second radii; the number of each type of department can be changed independently. In particular, it is possible to use only two symmetrical second spokes 13, or even a single second spoke 13, while retaining three first spokes 12. The arrangement illustrated however has the advantage of being symmetrical and of obtaining a light yet rigid measuring sleeve.

It is possible to place a measurement element 40, for example a strain gauge, on each measurement portion 131. In an economical version, a single strain gauge is used in order to determine only the amplitude of the force applied. In a preferred version of the invention, two strain gauges will be used on the two spokes 13, the base of which is brought together to provide two measurement values to determine both the amplitude and the direction of the applied force. Three strain gauges make it possible to increase the sensitivity by determining the amplitude and / or the direction of the force using two equations involving for example two displacement differences measured by two gauges.

Preferably, strain gauges 40 will be used, each making it possible to measure the deformations in two orthogonal directions. The first measurement direction is used to measure the deformation of the measurement portion 131 under the effect of the external force. The second measurement direction is used only to detect elongations caused by possible thermal expansion. The strain gauge 40 will therefore be placed so that the application of the force to be measured causes only minimal deformation of the measurement portion 131 in the second measurement direction.

In the preferred example described, the measuring socket 1 is disposed inside the bearings 5. The measuring socket 1 is thus secured to the fixed axis 3. This solution has the advantage of allowing a connection between the transducers on the measuring socket 1 and the associated electronic system by means of simple wires. It is however also possible to place the measuring sleeve 1 outside the bearings 5, that is to say in the case of a motorcycle between the bearings 5 and the crown carrier 7. In this case, the forces transmitted by the crown carrier 7 are transmitted to the axis 3 via the measuring sleeve 1 then the bearings 5. This variant is in particular suitable for systems in which the central axis is rotating while the outer ring of bearings 5 is fixed. However, it can also be used in motorcycles or other fixed axis systems, for example when one wishes to avoid increasing the diameter of the bearings. In this case, a wireless link, for example a radio or capacitive link, may be adopted.

In a variant not illustrated of the invention, the tensile force of the chain transmitted by the measuring sleeve 1 is not applied to the axis 3, but directly to the swing arm 9 of the motorcycle by one of the side faces of the measuring socket 1. In this variant, a clearance can be provided between the measuring socket 1 and the axis 3 of the wheel. One of the lateral faces of the measuring socket 1 is then in abutment with the oscillating arm to transmit the tensile force to it. In this variant, as in the illustrated variants, the application of this force however causes a deformation of the radii of the measuring sleeve which can be measured to determine in the same way the amplitude and the direction of the transmitted forces.

The measuring socket 1 is preferably made of a material that is more easily deformable than conventional steel, for example Maraging steel, the Young's coefficient of which is 1.1 times lower than that of conventional steel. It can be manufactured by first turning the large diameters of the inner and outer ring. The cavities between the spokes are then milled. We can then drill any holes and threads, as well as holes for the passage of EDM wires. The second fine spokes 13 are then machined by electroerosion before carrying out the finishing operations, in particular turning operations.

This construction makes it possible to obtain, in the case of a measuring socket used for a rear axle of a motorcycle, a relatively small size, for example less than 65mm, and a reduced weight. The weight and rigidity in normal, transverse and torsional mode are however sufficient to avoid any risk of resonance if the frequency of the vibrations is close to the natural frequency of the part. Simulations have shown that the proposed construction makes it possible to obtain natural frequencies greater than 1000 Hz in all the modes.

Figure 5 schematically illustrates the electrical circuit used in the context of the invention. In this example, the circuit comprises two gauges 40 described above and connected by electrical wires 41 to amplifiers 42. The amplifiers 42 can for example be mounted on the swinging arm of the motorcycle or even, if the space available is sufficient, directly in the bush 1 inside the axle. The signals amplified and possibly filtered by the amplifiers 42 are transmitted to a microcontroller 43 which converts them into digital values and performs temperature corrections on the basis of the indications provided by the strain gauges according to the second direction of measurement. In a variant, the temperature corrections are carried out directly by the amplifiers 42, which makes it possible to simplify the programming of the microcontroller and to reduce the number of cables required between the amplifiers and the microcontroller. The microcontroller then determines, using preprogrammed algorithms or preset conversion tables, the value of the radial force applied to the socket 1 from the indications of the strain gauges 40.

It is also possible to program the microcontroller 43 so that it directly determines from the indications of the strain gauges 40 the value of the tensile force Fa applied by the chain, or even the value of the torque Mr applied by the crown to the rim. Those skilled in the art will also understand that the microcontroller can also be programmed to determine other non-radial forces or even torques applied to the sleeve 1. In this case, more optimal arrangements of radii and / or strain gauges could however be adopted.

The parameters used by the algorithms or the conversion table to determine the forces applied to the measuring socket 1 from the values provided by the strain gauges 40 can be determined during a calibration operation of the motorcycle or of the model motorcycle, vehicle or vehicle model respectively. The torque Mr corresponding to each pair of values provided by two gauges 40 can for example be determined by placing the motorcycle on torque measuring rollers or on an independent static or dynamic calibration bench.

The system of the invention further comprises an input-output module 44 preferably comprising a display to indicate the value of the force or torque measured and of the data input means, for example a keyboard or buttons, for manipulating the display and the measurement system. An interface with external devices, for example a serial interface of RS232 type or a radio interface, can be provided for transmitting the measured values, or even a history of values stored in memory, to an external device, for example a computer. It is also possible to dispense with the display module 44 and transmit the measurement results in real time to a remote device.

Claims

claims

1. Device making it possible to measure the amplitude of a force applied to a part (3), characterized by a measuring sleeve (1) transmitting said force to said part,, at least one measuring portion (131) of said sleeve being deformed by said force, the device comprising a measuring element (4) making it possible to determine the amplitude of the deformation of the measuring portion (131) in order to deduce therefrom the amplitude of said force.

2. Device according to claim 1, intended to measure the amplitude of a force applied to an axis (3) passing through the center of said socket.

3. Device according to one of claims 1 or 2, said measuring socket (1) comprising a plurality of measuring portions (131) deformed by said force and a plurality of measuring elements (40) for determining the amplitude of the deformations of said measuring portions, said measuring portions (131) being arranged so that the amplitude and the direction of said force can be determined from signals from said measuring elements (40).

4. Device according to one of claims 1 to 3, said measuring sleeve (1) comprising an inner ring (10) and an outer ring

(11) connected by spokes (12, 13) deformed in buckling, in tension-compression and / or in bending by the application of said force, the one or more measuring elements (40) making it possible to measure the deformation of at least one of said spokes (13).

5. Device according to claim 4, said spokes comprising several first spokes (12) deformed essentially in tension-compression and / or in bending and several second spokes (13) deformed essentially in buckling and / or in bending, the said element or elements measurement (40) for measuring the deformation of said second rays.

6. Device according to claim 5, said second spokes (13) comprising an approximately radial portion (130) and a curved and non-radial measurement portion (131), the one or more measurement elements (40) making it possible to measure the deformation of said measuring portions (131).

7. Device according to one of claims 5 or 6, the width and / or the thickness of said second rays (13) being less than the width respectively the thickness of said first rays (12).

8. Device according to one of claims 5 to 7, comprising three first spokes (12) regularly distributed over the circumference of said measuring socket (1) and three second spokes (13) regularly distributed over the circumference of said measuring socket (1), the curvature of one of said second spokes (13) being reversed with respect to the curvature of the other two second spokes (13).

9. Device according to one of claims 1 to 8, wherein said measuring elements (40) are strain gauges.

10. Device according to claim 9, comprising at least one amplifier (42) for amplifying the signals of said strain gauges (40).

11. Device according to one of claims 1 to 10, the angular position of said measuring socket (1) being linked to that of said part (3).

12. Device according to one of claims 1 to 11, comprising a bearing or bearing (5) on the outer periphery of said measurement socket (1), said force being applied to said part (3) via said bearing or bearing.

13. Device according to claim 12, comprising a crown carrier (7) on the outer periphery of said bearing or bearing (5), said crown holder being provided with fixing means (70) making it possible to fix a rim (80) therefor for a vehicle, said part being an axis of said rim (3) fixed when said rim (70) is in rotation.

14. Device according to claim 12, comprising a crown carrier (7) on the internal periphery of said bearing or bearing (5), said crown carrier being provided with fixing means (70) making it possible to fix a rim (80) ) for a vehicle, said part being a fixed axis (3) when said rim (70) is in rotation.

15. Device according to one of claims 13 or 14, said crown holder being provided with fixing means (70) for fixing a rim (80) of a motorcycle.

16. Device according to claim 13, intended to equip a vehicle towing wheel.

17. Automobile equipped with a device according to one of claims 1 to 14.

18. Tool-holder spindle for a machine tool equipped with a device according to one of claims 1 to 12.