E-Mobility Engineering 016 l Aurora Powertrains eSled dossier l In Conversation: Thomas de Lange l Automated manufacturing focus l Torque sensing insight l Battery Show Europe 2022 report l Sodium batteries insight l User interfaces focus

measuring the current, which can lead to inaccuracies in the calculated torque, negatively impacting the dynamic performance of the machine. Why is accurate torque measurement needed? Despite the present state of the art being to use advanced torque estimation techniques, there are many reasons why it is desirable for accurate torque measurement of a rotating load driven from an e-machine. By measuring rather than estimating the motor torque, it’s possible to calculate load power and thus efficiency independently, where the power of the machine is equal to the measured torque multiplied by the rotational shaft speed. A good example of that is a motor test dynamometer, where torque accuracy is paramount when characterising the desired load, which could be another e-machine or any rotating load such as a pump or fan. In order to differentiate the characteristics of the load, they need to be decoupled from the inaccuracies of the estimated torque measurement of the e-machine. To do that, a rotary torque transducer is typically used, the most common of which is an inline rotary torque transducer located between the e-machine and the load via flexible shaft couplings, which are needed to adequately mount the transducer and prevent it from being subject to off-axis bending loads. There are however several disadvantages with this type of rotary torque transducer, such as cost, shaft alignment, additional mechanical shaft harmonics and balancing constraints, as well as their susceptibility to background electromagnetic noise. The cost of these types of transducer can vary considerably depending on the specific application. For example, a typical 500 Nm transducer rated for 10,000 rpm is several thousand pounds. There are additional costs associated with this type of configuration, such as those associated with the flexible shaft couplings. Different types of sensor technology are used in these torque transducers. One type are strain gauges with short- range telemetry and inductive power transfer, which use low-cost gauges bonded onto the shaft inside the torque transducer. The gauges are measured by electronics on the rotating shaft, which transmits the measured signals via the telemetry. In the past, slip rings and brushes were used to get power and signals on and off the shaft, but that has largely been superseded by the use of telemetry and inductive power transfer. Another type are displacement sensors that use optical or inductive sensing elements to measure the relative position of two rotating discs attached to the shaft inside the transducer. By accurately measuring the position of the two discs, the twist angle of the shaft can be calculated, which can then be used to calculate the torque being imposed onto the shaft. Both approaches require that an element of twist or flex be built into the transducer shaft to create either a shaft strain of a magnitude that can be measured or an amount of angular twist in the shaft that can be measured by the displacement sensors. In both cases, the shaft torsion can lead to system dynamic stability issues during more demanding test cycles. Displacement sensors have found applications in production torque sensing systems, for example in automotive electric power-assisted steering (EPAS). A small amount of twist in the steering system shaft is required to generate a measurable displacement by the displacement torque sensor, but that leads to a reduction in steering feel or vagueness, which is often a common criticism of vehicles fitted with EPAS. This has meant that for traction motor applications, torque sensing is limited to a laboratory or test track environment. Integrating a high-speed dynamic torque sensor into the electric motor is desirable but has not been possible owing to the inherent limitations of the torque sensing technology on the market at the moment. So, workaround methods have been developed. A potential new solution Surface Acoustic Wave (SAW) sensor technology provides a wireless, passive, non-contact sensing system consisting of two main components. The first are SAW sensing elements connected to a close-coupled antenna (also called an RF coupler) mounted on the machine shaft. The second is an electronic interrogation unit called a reader, which is connected to a stationary antenna or RF coupler mounted off the shaft in fairly close proximity to the rotating part. The reader sends an ultra-low power RF interrogation signal that is transmitted to the SAW element through the antenna or RF coupler. The sensing element does not require any other power source or electronics on the shaft; it works as a passive back- scatterer that reflects the interrogation signal back to the reader. The back-scattered signal is affected by strain and temperature by a known amount. The reader analyses SAW devices are manufactured by creating the SAW pattern on a quartz wafer, which is then diced into chiplets 46 Winter 2022 | E-Mobility Engineering