High-precision torque measurement technology for e-mobility testing

MANNER: Advancements in e-mobility demand new test stand concepts. With e-motors operating at much higher speeds than combustion engines, test stand concepts for next-generation electric mobility need to be redesigned and adapted to meet these requirements. MANNER draws on years of experience in the turbine industry to offer torque sensor designs that fit these needs.

Typical applications

Developments in e-mobility technology aim to significantly reduce the weight of the engine while maintaining the performance level, which reduces both cost and footprint.  Even today, speed demands in the e-mobility industry of up to 22,000 rpm far exceed the speeds of combustion engines and are more in line with Formula 1 standards.
While these levels are extremely high already, more savings can be achieved through even higher speeds. Initial design concepts for speeds of up to 35,000 rpm have already been developed.

The automotive industry has not yet had to deal with speeds of that level – we have entered new technological territory. Aviation turbine manufacturers, on the other hand, are well accustomed to and have extensively researched such speeds.  Conventional automotive test stand concepts based on modular, component-centric designs are no longer adequate.  Solutions that address next-generation electric mobility requirements necessitate a new and innovative approach.

Challenges

To accommodate speeds of that level, the drive train needs to be considered from a vibration point of view. The resonant frequencies of the individual components are crucial to the overall stability of the shaft. At these high speeds, torsional ‘soft elements’, such as couplings that compensate for parasitic forces like bending moments, lateral and axial forces, are critical.
Parasitic forces not only affect drive technology, but also the underlying measurement technology. Again, high-precision torque measurements to determine efficiency are of central importance. But conventional torque-sensing concepts no longer suffice. The relevant high resonances, low crosstalk between parasitic loads and torque measurements, and high radial forces require novel torque sensor designs. The same design criteria apply here as with turbo machines and turbine test stands.

Sensors of this kind will also need to be integrated into test stand gearboxes. Where the additional lubrication of slide bearings is required, hollow shaft versions are often used to facilitate the flow of the lubricant. The required temperature resistance significantly exceeds the standard 85 °C. For climatic test systems, the temperature range is -40 °C to 150 °C, and the integrated approach often necessitates a customized design. Particular emphasis has been placed on the robustness of the measuring equipment.

Solution

Long-standing partnerships in the aviation industry, in particular the turbine sector, have provided MANNER Sensortelemetrie with extensive experience in the manufacture of suitable sensors.

By continuously advancing the design and implementation of sensors for turbines and turbocharger test stands, MANNER has acquired highly specialized expertise over the last 15 years, ranging from mechanical design to high-precision torque measurements at high ambient temperatures of up to 160° C and, of course, its contact-free transmission technology – sensor telemetry.

Test stand operations for electric motors require high-precision measuring equipment. Today's standard accuracy class is 0.05, and this level of accuracy should extend beyond static calibration testing at a standard temperature of 22 °C and apply across the entire operating temperature range. A particular challenge with test stands for electric motors is the increased and continuously changing ambient temperature. We know that with a rise in temperature the modulus of elasticity changes by approximately 2.5%. That is quite significant. Another point worth noting is the speed-dependent zero point error.

To overcome these challenges, MANNER has developed temperature- and speed-compensating torque sensors that ensure consistent, high accuracy for the entire operating range. The acquired torque values are digitised within the rotor to allow contactless digital transmissions to a signal pick-up device. An integrated signal processor in the processing unit converts, in real-time, the raw data for the measured profile into compensated values. This process is based on the parallel-acquired temperature and speed. In modern test stands, the acquired data are typically transmitted digitally via EtherCAT, CAN or Ethernet to the test stand data collection system.

The sensor quality is monitored through an air-conditioned calibration rig with ambient temperatures from -40 to 160 °C. Rotational speed testing ensures that the sensor is controlled independently from rotational speed.

For standard applications we recommend the HS-Torque range. The high nominal speeds of up to 35000 min-1 are no challenge for the HS-Torque design. HS-Torque sensors have been used in turbine testing successfully for over 15 years.

The range includes 200 Nm, 500 Nm, 1 kNm, and 2 kNm sensors.

The optional hollow shaft supports complex test stand set-ups. Oil supply at the centre or actuator systems is not a problem.