METHOD FOR ADJUSTING A PIEZOELECTRIC TORQUE SENSOR

Abstract

The invention relates to a method for adjusting a piezoelectric torque sensor of a measuring apparatus, which can be part of a test bench, for determining a torque applied to a test piece due to a force flux, wherein the measuring apparatus comprises a piezoelectric torque sensor and a second torque sensor based on a different measuring principle which is designed to continuously detect static torques, wherein the measuring apparatus is configured such that both torque sensors measure torques in the force flux, whereby a target measurement signal of the piezoelectric torque sensor is determined on the basis of a torque measurement by the second torque sensor, and whereby the detected measurement signal of the piezoelectric torque sensor is adjusted and output on the basis of the determined target measurement signal.

Claims

1. A method for adjusting a piezoelectric torque sensor of a measuring apparatus, which is preferably part of a test bench, for determining a torque applied to a test piece due to a force flux, wherein the measuring apparatus comprises a piezoelectric torque sensor and a second torque sensor based on a different measuring principle which is designed to continuously detect static torques, wherein the measuring apparatus is configured such that both torque sensors measure torques in the force flux, whereby a target measurement signal of the piezoelectric torque sensor is determined on the basis of a torque measurement by the second torque sensor, and whereby the detected measurement signal of the piezoelectric torque sensor is adjusted and output on the basis of the determined target measurement signal.

2. The method according to claim 1, wherein the target measurement signal of the piezoelectric torque sensor is determined in a quasi-stationary frequency range of an oscillation frequency of the torque on the measuring apparatus, particularly in a frequency range below 50 Hz, preferably between approximately 5 Hz and approximately 50 Hz.

3. The method according to claim 1, wherein the target measurement signal of the piezoelectric torque sensor is determined in a frequency range of torque oscillation frequency in which no natural oscillation or respectively resonance modes occur in a test environment, in particular on the test bench, preferably at a torque oscillation frequency of less than approximately 20 Hz, preferably less than approximately 10 Hz.

4. The method according to claim 2, wherein the adjustment is made during test piece operation, wherein torque in the desired frequency range is isolated by means of a frequency filter, in particular using a Fourier analysis.

5. The method according to claim 1, wherein the target measurement signal of the piezoelectric torque sensor is further determined on the basis of a speed measurement in relation to the test piece.

6. The method according to claim 1, wherein the target measurement signal of the piezoelectric torque sensor is determined using the following equation:
M.sub.Piezo_cal=M.sub.W−(J.sub.W+J.sub.UUT){dot over (ω)}.sub.W−M.sub.R wherein M.sub.Piezo_cal is the target measurement signal, M.sub.W is the torque measured by the second torque sensor on a shaft or shaft assembly which is connected to the test piece in rotating fixed manner or is a component of the test piece, J.sub.W is a moment of inertia of a shaft or a shaft assembly which is connected to the test piece in rotating fixed manner or is a component of the test piece, J.sub.UUT is the test piece moment of inertia, {dot over (ω)}.sub.W is a time derivative of a measured speed of a shaft or shaft assembly which is connected to the test piece in rotating fixed manner or is a component of the test piece, M.sub.R is a frictional torque caused in particular by a bearing and/or gear mechanism.

7. The method according to claim 6, wherein the shaft assembly comprises a gear mechanism and wherein the second torque sensor is arranged in a second section rotating at a lower speed relative to the gear mechanism and the piezoelectric torque sensor is arranged in a first section rotating at a higher speed relative to the gear mechanism.

8. The method according to claim 1, wherein the piezoelectric torque sensor measures a reactive torque at least at one support point of the test piece in order to determine a torque applied to the test piece.

9. A computer program containing instructions which, when executed by a computer, prompts it to execute the steps of a method according to claim 1.

10. A computer-readable medium on which a computer program according to claim 9 is stored.

11. A test bench for machines, preferably electric machines, for measuring dynamic torques, wherein the test bench comprises: a piezoelectric torque sensor; an adjustment means (12) configured to adjust the piezoelectric torque sensor (3); and a second torque sensor based on a different measuring principle which is designed so as to continuously detect a static component of the torque, whereby both torque sensors are configured and arranged on the test bench so as to measure torques in a force flux on the test bench.

12. The test bench according to claim 11, wherein the piezoelectric torque sensor is designed and arranged so as to be able to measure a force in the force flux between a test piece and a supporting apparatus for supporting the test piece.

13. The test bench according to claim 11 having a load apparatus, in particular a dynamometer or a brake, for applying a load to a test piece.

14. The test bench according to claim 13 having a gear mechanism, in particular a booster gear, which is arranged in the force flux between the load apparatus and the test piece, wherein the piezoelectric torque sensor is arranged so as to detect the torques on a first side of the force flux relative to the gear mechanism on which the test piece can be arranged, and the second torque sensor is arranged so as to detect the torques on a second side of the force flux relative to the gear mechanism on which the load apparatus is arranged.

15. The test bench according to claim 11, wherein the measuring principle of the second torque sensor is based on strain gauges and the second torque sensor is preferably a measuring flange.

16. The test bench for measuring dynamic torques according to claim 11, wherein the test bench is configured to realize a method according to claim 1.

Description

[0044] Further features and advantages derive from the following description of the exemplary embodiments referencing the figures. Shown therein at least partly schematically:

[0045] FIG. 1 an exemplary embodiment of a test bench having a piezoelectric torque sensor and a second torque sensor;

[0046] FIG. 2 a block diagram of a method for adjusting a piezoelectric torque; and

[0047] FIG. 3 an exemplary embodiment of a control process for adjusting a measurement signal of a piezoelectric torque sensor.

[0048] FIG. 1 shows an exemplary embodiment of a test bench 1 for testing machines.

[0049] The invention is explained in the following based on a test bench 1 for testing an electric machine 5. It is however obvious to the person skilled in the art that the exemplary embodiments as described are also applicable to other types of machines, particularly electromechanical energy converters or chemical-mechanical energy converters.

[0050] The test bench 1 preferably has a dynamometer 7 with which a load able to act upon the electric machine to be tested can be provided, in particular a driving torque or a braking torque.

[0051] The depicted test bench 1 preferably serves in testing electric machines which in regular operation operate at comparatively high speeds of more than 10,000 rpm, preferentially more than 35,000 rpm, and most preferentially more than 100,000 rpm. These are for example the electric drives of compressors such as turbochargers, for example, or electric drive motors for electric vehicles. A dynamometer 7 cannot provide or respectively accommodate such high speeds. Therefore, the test bench 1 preferably comprises a gear mechanism 8, in particular a so-called booster gear, which converts a rotational speed on the shaft sections 10b, 10c connecting the dynamometer 7 to the booster gear 8 in rotating fixed manner to a higher speed. This higher converted speed is transmitted to the electric machine 5 to be tested via the shaft section 10a connecting the booster gear 8 and the electric machine 5 to be tested in rotating fixed manner. Conversely, a rotational speed provided by the electric machine 5 to be tested via the booster gear 8 is converted into a speed and torque range within which the dynamometer 7 can be operated.

[0052] The gear mechanism 8 forms a shaft assembly together with various shafts or sections of a shaft 10a, 10b, 10c. Depending on which components are to be tested, a test piece is composed of the electric machine 5 alone or the electric machine 5 and at least part of the shaft assembly.

[0053] As FIG. 1 depicts, the dynamometer 7, the booster gear 8 and the electric machine 5 to be tested are mounted on the same base 11. The electric machine 5 to be tested is thereby supported against the base 11 by a supporting apparatus 6. The supporting apparatus 6 thereby provides those reactive forces for the electric machine 5 to be tested for supporting a force flux and a power flux between the electric machine 5 to be tested and the dynamometer 7.

[0054] Preferably, the supporting apparatus 6 is thereby designed, as shown in FIG. 1, such that the electric machine 5 to be tested is mounted on that side, in particular the front side, at which a shaft of the electric machine 5 is arranged or at which the shaft section 10a can be coupled to the shaft of the electric machine respectively. As shown in FIG. 1, this arrangement offers the advantage of the torque sensor 3 being able to be arranged between the supporting apparatus 6 and the electric machine to be tested 5 such that a large portion of the torque acting on the electric machine to be tested 5 is applied to the piezoelectric torque sensor 3. In particular, this arrangement enables minimizing or even eliminating a force shunt not running through the piezoelectric torque sensor 3. Preferably, with this type of bearing, the electric machine to be tested 5 has a passage for the shaft of the electric machine 5 to be tested or, respectively, the shaft or shaft section 10a through the piezoelectric torque sensor 3 and the supporting apparatus 6 as well as the piezoelectric torque sensor 3 and the supporting apparatus 6. This passage is preferably designed as a hole.

[0055] However, the electric machine 5 to be tested can also be mounted in a different way, for example on that side facing the base 11 or that side facing away from the base in a type of suspended support, or even on the other lateral sides of the electric machine 5 to be tested. Details on the supporting of the electric machine 5 to be tested as shown in FIG. 1 and further mounting options as well as on the determination of the reactive forces by means of the piezoelectric torque sensor 3 can be learned from the introductory part of document WO 2019/144172 A1.

[0056] The test bench arrangement of the test bench 1 is divided into two sides I, II by the booster gear 8. On a first side I, on which the electric machine 5 to be tested is arranged, the shaft assembly rotates at a higher speed, whereby a lower torque is applied to the shaft assembly. This section of the shaft assembly is thus also referred to as the first section I of the shaft assembly in the present description.

[0057] On the other output side of the booster gear 8, designated as second side II, shaft sections 10b, 10c rotate at lower speed and higher applied torque. Typically, the gear ratio of the booster gear 8 is approximately 3:1 to 10:1. This section of the shaft assembly is thus also referred to as the second section II of the shaft assembly in the present description.

[0058] The shaft assembly or respectively powertrain, which preferably consists of the electric motor 5, the shaft sections 10a, 10b, 10c, the booster gear 8 and the dynamometer 7, constitutes an oscillatory system. Depending on the design of the test bench 1 and the electric machine 5 to be tested, oscillation resonance or eigenmodes are typically greater than 50 Hz.

[0059] In order to determine the torque acting on the electric machine to be tested due to a force flux from or to the dynamometer 7, the test bench 1 comprises piezoelectric torque sensor 3. This torque sensor 3 preferably does not thereby directly determine the torque applied to the electric machine 5 to be tested via shaft section 10a but rather indirectly the reactive torque with which the electric machine 5 to be tested is supported on the supporting apparatus 6. Furthermore, the test bench 1 comprises a second torque sensor 4 which is not based on the piezoelectric measuring principle but rather uses another measuring principle to measure the torque. Preferably, so-called strain gauges as are generally known from the prior art are used here. Preferably, the second torque sensor 4 is designed as a measuring flange which measures the torque between the two shaft sections 10b and 10c.

[0060] The arrangement of the two torque sensors shown in FIG. 1 is particularly advantageous for the adjustment of the piezoelectric torque sensor 3 since more modest oscillations generally occur in the second section II of the shaft assembly which rotates at a lower speed and measurement by way of the second torque sensor 4 using strain gauges is consequently precise. Strain gauge-based sensors are namely only suitable for dynamic measurements to a limited extent.

[0061] In contrast, the piezoelectric torque sensor 3 is arranged in the first section I of the shaft assembly, directly on the electric machine 5 to be tested on which the applied torque is also to be determined. Due to the direct arrangement of the piezoelectric torque sensor on the test piece, a highly accurate measurement of the applied torque can be achieved.

[0062] A speed sensor 9 able to determine rpm is arranged to determine the rotational speed of the shaft assembly, particularly in the area of the second section of the shaft assembly II. In FIG. 1, the speed sensor 9 determines the speed of the dynamometer 7 shaft and thus the speed of shaft sections 10b and 10c. A rotational speed in the first section I of the shaft assembly can therefore also be inferred from the selected gear ratio of the booster gear 8.

[0063] Based on the torque M.sub.W measured by the second torque sensor 4 and the speed ω.sub.W measured by speed sensor 9, a target measurement signal M.sub.Piezo_cal can be calculated subject to the frictional torque M.sub.R, induced in particular by a bearing and/or booster gear 8, the moment of inertia J.sub.W of the shaft assembly and the moment of inertia J.sub.UUT of the electric machine 5 to be tested. This will be explained in greater detail below in relation to the inventive method 100 for adjusting a piezoelectric torque sensor.

[0064] At the same time, the piezoelectric torque sensor 3 can measure an actual measurement signal M.sub.Piezo of the torque applied to the piezoelectric torque sensor 3.

[0065] In order to calibrate the actual measurement signal of the piezoelectric torque sensor 3, the test bench 1 preferably further comprises adjustment means 12. This is preferably part of a data processing system of the test bench 1, but can also be part of an external data processing system. After the actual torque signal M.sub.Piezo has been calibrated, the piezoelectric torque sensor 3 can be adjusted by means of the adjustment means 12. Preferably, a model stored in the adjustment means 12 is thereby used for the calibration/adjustment. This model will also be explained in greater detail below in relation to method 100.

[0066] FIG. 2 shows a block diagram of an exemplary embodiment of a method 100 for adjusting a piezoelectric torque sensor of a measuring apparatus 2. Preferably, such a measuring apparatus 2 is part of a test bench 1 as described above in relation to FIG. 1.

[0067] The adjusting of the piezoelectric torque sensor 3 occurs while the test bench is in operation. To that end, the electric machine 5 to be tested applies a torque to the dynamometer 7 via the shaft assembly or, vice versa, a torque is applied from the dynamometer 7 to the electric machine 5 to be tested.

[0068] Preferably, the test bench 1 is operated at comparatively low shaft assembly speeds during adjustment, wherein the speed in the second section II of the shaft assembly is preferably less than 50 rpm. Depending on the design of the test bench 1 and test piece, low torque oscillation frequencies of less than approximately 10 Hz, preferably less than approximately 5 Hz, even more preferentially less than approximately 1 Hz, are to be expected at rotational speeds in this range of magnitude.

[0069] These frequency ranges of oscillation frequencies are selected such that there is spacing from the resonant frequencies or eigenmodes of the total system consisting of test bench 1 and test piece. The resonant frequencies or eigenmodes are generally around 50 Hz.

[0070] Further preferably, these frequency ranges of oscillation frequencies suited to adjustment are isolated by means of a frequency filter, in particular using a Fourier analysis. In this case, the rotational speed during test bench operation is not significant to the adjustment.

[0071] During operation, the piezoelectric torque sensor 3 measures a torque applied to the electric machine 5 to be tested; 101a. As already explained with reference to FIG. 1, the reactive forces via which the electric machine 5 to be tested is supported on the supporting apparatus 6 are thereby preferably detected by the piezoelectric torque sensor 3. In contrast, the second torque sensor 4 detects a torque in the shaft assembly and thus at a relatively further distance from the electric machine 5 to be tested 5; 101b. In the case of a test bench 1 or test piece comprising a gear mechanism 8, as shown in FIG. 1, the second torque sensor 4 is preferably arranged in that region II of the shaft assembly with the lower prevailing rotational speed.

[0072] A target measurement signal M.sub.Piezo_cal is calculated on the basis of the torque measurements M.sub.w by the second torque sensor 4 and the speed measurement ω.sub.W by speed sensor 9; 102. Preferably, the target measurement signal is thereby determined on the basis of the following equation:

M.sub.Piezo_cal=M.sub.W−(J.sub.W+J.sub.UUT){dot over (ω)}.sub.W−M.sub.R

[0073] In principle, however, only the torque M.sub.W measured by means of the second torque sensor 3, potentially allowing for frictional torque M.sub.R, can be used as an approximation in determining the target measurement signal M.sub.Piezo_cal.

[0074] The detected measurement signal M.sub.Piezo is corrected on the basis of the determined target measurement signal M.sub.Piezo_cal, 103. Further preferably, the corrected measurement signal is output; 104.

[0075] The correction of the measurement signal M.sub.Piezo detected by the piezoelectric torque sensor 3 is preferably made on the measurement signal/target measurement signal in a control process.

[0076] An exemplary embodiment of such a control process is depicted in FIG. 3.

[0077] Preferably, the measurement signal M.sub.Piezo is corrected by being compared to the target measurement signal M.sub.Piezo_cal The correction values determined in this way, which are preferably determined at comparatively low torque oscillation frequencies, are applicable to the entire range of measurement, in particular also to higher torque oscillation frequencies.

[0078] In one preferential embodiment, a model can further be generated, by means of which the target measurement signal M.sub.Piezo_cal can be determined as a function of the torque oscillation frequency based on the measurements of the second torque sensor 4.

[0079] Substantially, the control process shown in FIG. 3 represents the equation given above for calculating the target measurement signal M.sub.Piezo_cal.

[0080] The rotational speed of the shaft ω.sub.W is derived over time and multiplied by the sum of the moments of inertia of the shaft assembly and the electric machine 5 to be tested. The frictional torque M.sub.R, which is in particular a function of the speed n and a gear ratio T, and the previously calculated product are subtracted from the torque M.sub.w measured via the second torque sensor 4. The calculated signal is subjected to a low-pass filter LP, which yields the target measurement signal M.sub.Piezo_cal This target measurement signal M.sub.Piezo_cal is subtracted from a measurement signal M.sub.Piezo corrected on the basis of an old adjustment and likewise having been run through a low-pass filter LP. Preferably, the indicated low-pass filters LP thereby have the same characteristics, particularly the same dynamics, limit frequencies, orders and types. Providing the low-pass filter enables isolating those oscillation frequencies which are suited to adjusting the measurement signal of the piezoelectric torque sensor.

[0081] The difference is fed to an integrator 1/s. When the calculated acceleration of the shaft's rotation is less than limit value Limit, a previous adjustment is replaced by a new value of S in an integrator 1 and used to correct the measurement signal M.sub.Piezo measured by the piezoelectric torque sensor 3.

[0082] Allowing for a limit value Limit for the acceleration of the rotation ensures that there is only an adjustment change up to a certain oscillation frequency.

[0083] The exemplary embodiments described above are only examples which are in no way intended to limit the scope of protection, application and configuration. Rather, the foregoing description is to provide the person skilled in the art with a guideline for implementing at least one exemplary embodiment, whereby various modifications can be made, particularly as regards the function and arrangement of the described components, without departing from the scope of protection resulting from the claims of its and equivalent combinations of features. In particular, individual exemplary embodiments may be combined with one another.

LIST OF REFERENCE NUMERALS

[0084] 1 test bench [0085] 2 measuring apparatus [0086] 3 piezoelectric torque sensor [0087] 4 second torque sensor [0088] 5 electric machine [0089] 6 supporting apparatus [0090] 7 dynamometer [0091] 8 gear mechanism [0092] 9 speed sensor [0093] 10a, 10b, 10c shaft [0094] 11 base [0095] 12 adjustment means