SAW Case Studies

McLaren Applied IndyCar engine torque sensors

IndyCar starts torquing with a British accent

Fans of American IndyCar racing are always assured of hyper exciting racing, thanks to a regulation that allows engine and gearbox designs to be upgraded twice a season so that all cars remain competitive throughout the year. This innovative rule is only possible thanks to very special torque sensor developed by Transense Technologies and fitted to every car.

Each season a new car is developed by the race team, utilising a design that meets criteria, created by the sport’s organising body, IndyCar LLC. As part of these guidelines, they must incorporate approved engines built by either Chevrolet or Honda and an electronically-assisted six-speed semi-automatic sequential gearbox supplied by a British company. Similar requirements apply to the steering, chassis, cockpit and other parts of the car, so that all the cars are sufficiently similar to be competitive with one another. However, the constructors work hard to optimise their designs for maximum performance, either over the whole series or just for the premier event of the year, the Indianapolis 500.

In earlier years, the eventual series winner would become apparent mid-season by consistently outperforming other teams. This is a common issue in many motor sport series, but rather than accept a predictable outcome IndyCar set out to find a way to keep the competition razor sharp right to the end.

After a long and comprehensive analysis, comparing the performance data of all the cars in each series, it was identified that in reality some cars show some power advantages over others. Furthermore, some of the cars saw their power drop slightly over the course of several races. The difference between the cars was only two or three percent at most, but enough to make a tangible difference.

Recognising that no matter how detailed the constructors’ design criteria this difference between cars could never be engineered out, IndyCar agreed on an alternative practical solution. It would monitor the cars’ performance and twice a year allow teams whose car had lost power to re-engineer them. For this to be effective it was necessary to measure the cars’ torque output in live race conditions, rather than rely on static tests carried out in a workshop.

Measuring the torque of an IndyCar’s drive shaft was never going to be an easy ask, as any viable solution had to be robust enough survive the extreme conditions of a long race and sensitive enough to capture data from a drive train working at the limits of its technical capacity in an environment that is extremely hot and vibrating outrageously. Several possible approaches were considered by the main supplier who quickly realised that the answer lay with Surface Acoustic Wave (SAW) technology as the most advantageous. Fortunately, the leading proponents of this is the British company, Transense Technology PLC who had also developed a successful sensor for the F1 KERS (Kinetic Energy Recovery) system, would support IndyCar’s solution.

Transense Technologies is built on its ability to measure rotary torque in demanding and hostile environments. SAWs are actually sound waves generated by a body in motion, their frequency and amplitude being proportional to speed and power. A Transense sensor mounted close to a rotating driveshaft will pick up and measure in real time these using RF (radio frequency) resonance across a quartz substrate.

Being quartz based, the sensors are tiny, light and ultra-reliable. Importantly they operate wirelessly and without the need for a battery or indeed being affected by magnetic fields which is a common factor in rotating components. As well as being able to measure torque they can be used in other applications to measure strain, temperature, pressure and thrust. As such they can also be used in robotic, aeronautics, precision control and industrial machinery. They are equally suitable for condition monitoring and predictive maintenance applications where cost reduction, improved reliability and uptime through efficiency are significant drivers.

For IndyCar, Transense assembled a SAW sensor fixed to the driveshaft with a transceiver antenna (coupler) that wraps around the shaft. The transceiver static antenna (coupler) is a few millimetres away, so that the wireless communication is ensured as 100% reliable.

Transense patented SAW sensor technology has helped IndyCar bring extra challenge and excitement to its class of motor sport, a result that keeps the fans attending race days and helps drive up car performance a little each year. Other classes of motor racing such as Formula 1, 2 and Nascar are also looking on with a view to adopting similar rules and technology. Transense SAW sensors will soon become motorsports industry standard technology for the measurement of torque.

More information about McLaren Applied's activities with Transense SAW torque sensing technology here.