GB1603698A

GB1603698A - Device for the measurement of torques

Info

Publication number: GB1603698A
Application number: GB1546078A
Authority: GB
Original assignee: Carl Schenck AG
Current assignee: Carl Schenck AG
Priority date: 1977-05-28
Filing date: 1978-04-19
Publication date: 1981-11-25
Also published as: FR2392374B1; FR2392374A1; DE2724344C3; DE2724344A1; DK402677A; IT1088793B; JPS542172A; DE2724344B2

Description

(54) A DEVICE FOR THE MEASUREMENT OF TORQUES (71) We, CARL SCHENCK AG of Landwehrstrasse 55, Darmstadt 61, Federal Republic of Germany, a German body corporate, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to a device for the measurement of torques which device has a lever mounted on one side, said lever being engaged by a force-measuring device and a pneumatic cylinder.

This type of device is known from German Offenlegungsschrift No. 2446 047 for the purpose of amplifying the small pressure corresponding to the measured force without requiring an expensive pneumatic measurement amplifier. With this device which is built for small forces, two nozzle baffle plate systems engage the lever arm, one of these systems acting as a controlled nozzle, therefore as a sensor which, ideally, does not exercise any reaction effects on the lever. A second such system is acted upon by the amplified pressure of the controlled nozzle and acts as a compensating nozzle which keeps a balance in the force acting on the lever. As a result of the dimensioning selected, the pressure of the compensating nozzle is greater than the pressure of the control nozzle, this pressure is proportional to the force and may be further processed as desired. This device only serves to measure small forces in a single measurement range, the nozzle-baffle plate system is in fact favourable in terms of cost but the measurement values are dependent on displacement. Furthermore, the device operates inaccurately as a result of the unavoidable play at the beginning of the measurement region. Furthermore, from Transactions of the A.S.M.E., May 1948, pages 271 to 278, a compressed air driven force-measuring device is known for the purpose of measuring forces or torques. In this device, compressed air is fed into a chamber closed by a diaphragm as long as the force to be measured is equal to the force exercised on the diaphragm, i.e. nulldeflection position. When the force changes, compressed air is admitted or exhausted from the chamber until the diaphragm is in its null-deflection position.

In equilibrium, the pressure in the measuring device is proportional to the force to be measured.

The invention therefore seeks to create a device for measuring torques having force measuring devices with switchable measurement ranges, which devices operate with a high degree of accuracy even at the beginning of the measurement ranges.

According to the invention there is provided a device for torque measurement comprising a pivoted lever to which the torque is applied, a force-measuring device using a null-deflection diaphragm operated by compressed air and engaging the lever for actuation thereby, a pneumatic cylinder acting on the lever and valve means for selectively connecting the pneumatic cylinder to air at a predetermined pressure or to the force-measuring device, the forcemeasuring device and the pneumatic cylinder being adapted to act in a direction to balance the applied torque.

This device is worth its price in manufacture and in operation and operates free-from wear despite the torques arising of up to 3000Nm. With a preferred embodiment, pressure is present in the diaphragm force measuring device when no torque is applied to the lever and the preselectable pressure of the cylinder may be equal to this initial pressure of the forcemeasuring device.

This embodiment has the substantial advantage that in each measurement range, the same pressures correspond to the end points on the scale and that the torque of the device, pre-determined in terms of design, which is given even at an applied torque of zero, is compensated in all of the measurement ranges without any additional forces.

With another embodiment, the preselectable pressure of the cylinder may be the ambient pressure. Thus it is advantageous if, at the same time as connecting the cylinder to the diaphragm measuring device, an additional force may be applied to the lever, said force being applied in an advantageous manner by a spring. As a result, the same pressures are assigned in each measurement range to the end points on the scale.

When using the device in accordance with the invention for the measurement of braking torque of powered vehicle brakes, two measurement ranges are normally provided one for torque measurement up to approximately 600 Nm, corresponding to the braking torque of a passenger vehicle the other measurement range extending to 3,000 Nm, the braking torque range of a lorry. However more than two measurement ranges are desirable and this may be achieved by further pneumatic cylinders being capable of pneumatic connection selectively to predetermined pressures or to the force measuring device and the pneumatic cylinder. Since the dimensions of the components of the device do not correspond to the theoretical values calculated, it is advisable if the distances of the force measuring device and the pneumatic cylinder from the lever pivot are adjustable parallel to the lever.

Fundamentally, the pneumatic cylinder may be a commercially available device comprising a piston and cylinder. These machines are relatively expensive however, the furthermore involve hysteresis. If the pneumatic cylinder is a metal bellows closed at the base surface, its interior being filled substantially by a closed body, then a hysteresis and wear-free component is created which is more reasonably priced, moreover, than the commercially available pneumatic cylinders, The invention will now be described in greater detail, by way of example, with reference to the drawings, in which: Flg. I shows a device in which the preselectable pressure of a cylinder is equal to the initial pressure of a force measuring device; Fig. 2 shows a device in which the preselectable pressure of the cylinder is the external pressure; Fig. 3 shows a fundamentally similar device to that of- Figure 1 but a further pneumatic cylinder engages the lever for a third measurement range; and Fig. 4 shows a preferred embodiment of the pneumatic cylinder.

In Figure 1 an air operated force measuring device 2 and a pneumatic cylinder 3 engage a lever 1 at different distances along the lever to which the torque to be measured is applied. In order that the device should not be unstable, a damper 4 is arranged on the other side of the lever, but this may also be applied at another point of the lever without changing the operability. A compressed air line 5 with compressed air, at for example, 4.5 bar or greater is connected to the force measuring device 2 by means of the line 6.

Furthermore, the compressed air line 5 supplies a pneumatic controller 7 the output pressure of which may be adjusted to a predetermined value independently of the input pressure. The torque to be measured may be applied at any suitable point, in particular at the lever pivot.

Should a torque be measured in the small measurement range then the cylinder 3 is connected to the output of the pneumatic controller 7 via the valve 8, said controller 7 being set to a predetermined pressure. As a result of the construction of the lever, the lever itself provides a torque (e.g. as a result of its weight) even without a torque to be measured being present.If the arrangement is used for the measurement of the braking torque of powered vehicle brakes, then the quite substantial mass of the drive motor and possibly of the gearing is added to the mass of the lever. In order to balance out this "internal" or initial torque and at the same time in order to bring about freedom from play of the measurement device, the force-measuring device is acted upon by an initial pressure of, for example, 0.4 bar which maintains balance for a part of an initial torque. The remainder of the initial torque is compensated for by the cylinder 3 and, in fact, this is achieved by changing the starting pressure of the controller by such a pressure that the predetermined initial pressure in the force-measuring device 2, for example 0.4 bar, prevails and therefore the value zero in indicated on an indicating device 11. If a calibration torque is present and the pressure relationships thereto are established, then, because of the linear nature of the force-measuring device 2, the scale of the small measurement range is fundamentally laid down. If the valve 8 is moved into the position A then the forcemeasuring device 2 and the cylinder 3 are connected together pneumatically.

Depending on the effective lever lengths at which the device 2 and the cylinder 3 engage, as well as depending on the pressure areas of the force-measuring device in the 2 and the pressure areas in the cylinder 3 then, at the same pressure, a larger force is applied to the lever 1 than in the small measurement range, in other words a higher torque is indicated by the same pressure. Basically, calibration of the measurement range may also be achieved by determining the zero point of a calibration moment. The described device is operable but difficult to operate since, in each measurement range the zero torque of the maximum torque corresponds to different pairs of pressures.

In practice, the procedure is such that initially the pressure areas of the diaphragm of the device 2 and the pressure areas of the cylinder 3 are determined theoretically, for example the surface of the cylinder of the device 2 is in a ratio of 4 to 1 with the same effective lever arm if a measurement range of 5 to 1 is desired. If the cylinder 3 and device 2 engage different lengths of lever from the fulcrum the ratio of the measurement range. The device 2 is fed observations, in practice, the ratio of the pressure areas of the device 2 and the cylinder 3 as well as the theoretical lever arm lengths are predetermined. Moreover the weight of the lever 1 is known and may be brought to the theoretical value using compensating weights.

Adjustment of the device takes place in the following manner: The measuring device 2 and the cylinder 3 are fixed to the lever at the theoretically provided lever arm lengths for the first measurement range. The device 2 is fed with compressed air and carries the lever 1 on its own. The indicating device 11 will show a value which is greater than zero.

However the null deflection position of the diaphragm of the device 2 and thus the position of equilibrium of the lever 1 is given thereby. The cylinder 3 is now adjusted in height so that it just touches the lever in this position of equilibrium of the lever 1 without exerting a force on the lever I in a vertical direction. By actuating the pneumatic controller 7 the cylinder 3 is then fed with compressed air until the indicating device 11 shows the value zero, i.e. the device 2 has a pressure of 0.4 bar for example. A calibration moment is now applied to the lever 1, this moment corresponding to full deflection, for example 600 Nm. Because of the tolerances due to manufacturing, the actual pressure areas of the device 2 and the cylinder 3 do not correspond to the theoretical values so that with the calibration moment, the indicating device 11 will show a value only in the region of full deflection. To adjust this, for example if full deflection is exceeded, the device cell 2 is moved away from the fulcrum 9 of the lever 1 and parallel to the lever arm until full deflection is indicated. Thereafter the lever 1 is relieved of the calibration moment and in the manner described, by actuating the pneumatic controller 7 the initial pressure of the cell is set in the case of equilibrium to a value (for example) of 0.4 bar. By applying the calibration moment to the lever 1, the setting may be checked and if necessary repeatedly adjusted. The small measurement range of the system is then correctly aligned if the indicating device 11 shows full deflection with the calibration moment and the value zero without a moment. The position of the measuring device 2 is finally fixed.

In order to calibrate the device for the second measurement range, which may extend for example up to 3,000 Nm, the process is as follows: The valve 8 is brought into the position A whereby the dynamometrical cell 2 and the cylinder 3 are connected together pneumatically. Then the torque of the lever 1 is measured without a calibration moment. If, for example, the indicating device 11 shows a value which is smaller than zero, then the cylinder 3 is too far away from the fulcrum 9 of the lever 1. The cylinder 3 is now displaced towards the fulcrum 9 parallel to the lever 1 until the indicator device 11 shows the value zero.

Thus the device is adjusted for the second measurement range, adjustment may be checked by applying a further calibration moment. It may be ensured by this type of adjustment that the preset pressure of the cylinder 3 is equal to the predetermined initial pressure of the measuring device 2.

Figure 3 shows a basically similar device to that of Figure 1 which has however a third measurement range, for which reason a third pneumatic cylinder 12 engages the lever 1. Adjustment of the device in accordance with Figure 3 takes place in the first measurement range as described above, whereby the cylinder 3 and the cylinder 12 are simultaneously connected to the output of the controller 7 and the valve 13 is open.

The second measurement range is set by bringing the valve 8 into the position A whereby cylinder 3 and measuring device 2 are connected together pneumatically.

When the valve 13 is open, a pressure is built up in the third cylinder 12 by actuating the pneumatic controller 7 to the point where the lever 1 is again in equilibrium. A calibration weight corresponding, for example, to full deflection of the second measurement range is caused to act on the lever 1 and the cylinder 3 is adjusted in the described manner parallel to the lever 1 until the indicating device 11 shows full deflection in the second measurement range. In order to adjust for the third measurement range. In order to adjust for the third measurement range, the valve 13 is brought into the position B so that the device 2, cylinder 3 and third cylinder 12 are connected together pneumatically. Without a calibration moment, the third cylinder 12 is adjusted parallel to the lever 1 until the indicating device 11 shows the value zero.

Thus the third measurement range is set and, by applying a further calibration moment, adjustment may be checked. Of course the invention is not limited to the three measurement ranges, further pneumatic cylinders may be provided in the same manner and the device may be adiusted accordinglv.

Figure 2 shows a different embodiment of the invention in which the preselectable pressure of the cylinder 3 is the ambient pressure. As a result the pneumatic controller 7 may be dispensed with but a force must be applied additionally to the lever 1 by a spring or a weight and moreover a connection device is required for this. The device shown corresponds substantially to that shown in Figure 1, the same parts are indicated by the same reference symbols.

The measuring device 2, the cylinder 3 and the damper 4 engage the lever 1.

Adjustment of the first measurement range takes place in the following manner: the valve 8 connects the cylinder 3 to the ambient air. Compressed air is applied to the compressed air line 5 which is connected, in the one hand, to the device 2 and, on the other hand, to the cylinder 21 via the valve 20 which is open. The piston 23 of the cylinder 21 is pressed upwards thereby, whereby a spring 22 is raised from the lever 1. By displacing the device 2 parallel to the lever until the indicator device shows the value zero, the first measurement range of the device is set. A check is possible by applying a calibration moment. In order to adjust the second measurement range, the valve 8 is brought into the position A whereby the measurement device 2 and the cylinder 3 are connected together pneumatically. At the same time the valve 20 connects the cylinder 21 to the ambient air, and the spring 22 comes into engagement with the lever 1. The spring 22 is so dimensioned that the spring force balances the force which is exercised by the cylinder 3 during the initial pressure, which corresponds to the indication zero on the indicator device 11.

The adjustment for the tolerances of the cylinder 3 which are determined by manufacture and of the adjustment necessary to the spring 22 take place so that, without any externally applied moment, the spring force is varied by displacing the deflection point 24 perpendicularly to the lever 1 until the indicator device 11 shows the value zero. Then a calibration moment corresponding, for example, to full deflection of the second measurement range is applied to the lever 1. If the indicator device 11 now shows a value which is, for example, smaller than full deflection, then the cylinder 3 is displaced parallel to the lever 1 in the direction of the fulcrum 9. After removing the calibration moment in the manner described the deflection point 24 of the spring must by adjusted until the indicator device 11 shows the value zero. The exact adjustment of the zero value or full deflection takes place repeatedly. Instead of the spring 22, a weight may be applied to the lever 1 as an additional force. A weight has the advantage in relation to the spring that the force is not dependent on temperature. Of course even in the device according to Figure 2, several measurement ranges may be achieved by means of further pneumatic cylinders and corresponding springs.

Instead of applying the required additional force in the second measurement range, the lever I may be relieved in the first measurement range for example by means of a spring whereby care must be taken that the entire mass of the lever is sufficiently large that in the second measurement range, with the required initial pressure, the measuring device 2 and cylinder 3 balances the lever without further additional forces.

Figure 4 shows the preferred embodiment of the pneumatic cylinder 3. A metal bellows 40 is soldered or adhered to one base surface having a flange 41, said flange may be fixed to the lever 1 by means of a bolt 42. The other base surface of the metal bellows 40 is soldered or adhered to the flange 43 containing the compressed air line 44. The flange 43 is screwed to the base frame 45 of the device. In itself, the cylinder is operable in the form described but the large volume of the cylinder causes a considerable threshold time. Therefore the volume is reduced by a body 46 which does not transmit air, which may be an aluminium cylinder fixed to the flange 41.

WHAT WE CLAIM IS: 1. A device for torque measurement comprising a pivoted lever to which the torque is applied, a force-measuring device using a null deflection disphragm operated by compressed air and engaging the lever for actuation thereby, a pneumatic cylinder acting on the lever and valve means for selectively connecting the pneumatic cylinder to air at a predetermined pressure or to the force-measuring device, the forcemeasuring device and the pneumatic cylinder being adapted to act in a direction to balance the applied torque.

2. A device according to Claim 1, wherein a predetermined initial pressure is present on the force-measuring device when no torque is applied to the lever and the predetermined pressure of the cylinder is

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. a calibration moment, the third cylinder 12 is adjusted parallel to the lever 1 until the indicating device 11 shows the value zero. Thus the third measurement range is set and, by applying a further calibration moment, adjustment may be checked. Of course the invention is not limited to the three measurement ranges, further pneumatic cylinders may be provided in the same manner and the device may be adiusted accordinglv. Figure 2 shows a different embodiment of the invention in which the preselectable pressure of the cylinder 3 is the ambient pressure. As a result the pneumatic controller 7 may be dispensed with but a force must be applied additionally to the lever 1 by a spring or a weight and moreover a connection device is required for this. The device shown corresponds substantially to that shown in Figure 1, the same parts are indicated by the same reference symbols. The measuring device 2, the cylinder 3 and the damper 4 engage the lever 1. Adjustment of the first measurement range takes place in the following manner: the valve 8 connects the cylinder 3 to the ambient air. Compressed air is applied to the compressed air line 5 which is connected, in the one hand, to the device 2 and, on the other hand, to the cylinder 21 via the valve 20 which is open. The piston 23 of the cylinder 21 is pressed upwards thereby, whereby a spring 22 is raised from the lever 1. By displacing the device 2 parallel to the lever until the indicator device shows the value zero, the first measurement range of the device is set. A check is possible by applying a calibration moment. In order to adjust the second measurement range, the valve 8 is brought into the position A whereby the measurement device 2 and the cylinder 3 are connected together pneumatically. At the same time the valve 20 connects the cylinder 21 to the ambient air, and the spring 22 comes into engagement with the lever 1. The spring 22 is so dimensioned that the spring force balances the force which is exercised by the cylinder 3 during the initial pressure, which corresponds to the indication zero on the indicator device 11. The adjustment for the tolerances of the cylinder 3 which are determined by manufacture and of the adjustment necessary to the spring 22 take place so that, without any externally applied moment, the spring force is varied by displacing the deflection point 24 perpendicularly to the lever 1 until the indicator device 11 shows the value zero. Then a calibration moment corresponding, for example, to full deflection of the second measurement range is applied to the lever 1. If the indicator device 11 now shows a value which is, for example, smaller than full deflection, then the cylinder 3 is displaced parallel to the lever 1 in the direction of the fulcrum 9. After removing the calibration moment in the manner described the deflection point 24 of the spring must by adjusted until the indicator device 11 shows the value zero. The exact adjustment of the zero value or full deflection takes place repeatedly. Instead of the spring 22, a weight may be applied to the lever 1 as an additional force. A weight has the advantage in relation to the spring that the force is not dependent on temperature. Of course even in the device according to Figure 2, several measurement ranges may be achieved by means of further pneumatic cylinders and corresponding springs. Instead of applying the required additional force in the second measurement range, the lever I may be relieved in the first measurement range for example by means of a spring whereby care must be taken that the entire mass of the lever is sufficiently large that in the second measurement range, with the required initial pressure, the measuring device 2 and cylinder 3 balances the lever without further additional forces. Figure 4 shows the preferred embodiment of the pneumatic cylinder 3. A metal bellows 40 is soldered or adhered to one base surface having a flange 41, said flange may be fixed to the lever 1 by means of a bolt 42. The other base surface of the metal bellows 40 is soldered or adhered to the flange 43 containing the compressed air line 44. The flange 43 is screwed to the base frame 45 of the device. In itself, the cylinder is operable in the form described but the large volume of the cylinder causes a considerable threshold time. Therefore the volume is reduced by a body 46 which does not transmit air, which may be an aluminium cylinder fixed to the flange 41. WHAT WE CLAIM IS:

1. A device for torque measurement comprising a pivoted lever to which the torque is applied, a force-measuring device using a null deflection disphragm operated by compressed air and engaging the lever for actuation thereby, a pneumatic cylinder acting on the lever and valve means for selectively connecting the pneumatic cylinder to air at a predetermined pressure or to the force-measuring device, the forcemeasuring device and the pneumatic cylinder being adapted to act in a direction to balance the applied torque.

equal to this initial pressure of the diaphragm measuring device.

3. A device according to Claim 1, wherein the predetermined pressure of the cylinder is the ambient pressure.

4. A device according to Claim 3, wherein means are provided for applying an additional force to the lever to the forcemeasuring device.

5. A device according to Claim 4, wherein the means for applying additional force comprise a spring.

6. A device according to any of the preceding Claims, wherein one or more further pneumatic cylinders engage the lever, these further cylinders being capable of pneumatic connection selectively to predetermined pressures or to the forcemeasuring device and the pneumatic cylinder. ~~~~~~~~~~~~~~~~~~~

7. A device according to any one of the preceding Claims, wherein the distances of the force-measuring device and the pneumatic cylinder(s) from the lever pivot are adjustable parallel to the lever.

8. A device according to any one of the preceding Claims wherein that the or each pneumatic cylinder is a metal bellows closed at the base surfaces, its interior being filled substantially by a closed body.

9. A device for torque measurement substantially as described herein with reference to the drawings.