In an international racing car design competition (Formula Student Germany) a student team uses inductive sensors to monitor wheel speed, winning not only first place for engineering design, but also the top award in the category “Most innovative use of electronics”. The small sensors withstand exceptional loads and so contribute to optimum electronic reliability.
The "Formula Student" competition is intended to give budding engineers extensive practical experience in the areas of teamwork and project/cost management. Participating teams are tasked with the design and construction of a formula racing car for a fictitious market.
The team’s electronic concept includes control units for the engine and differential lock, and a multifunctional steering wheel, all of which are networked via a CAN bus system. To control the differential, monitor traction and display vehicle speed, rotational wheel speed must be detected. The team achieves this by mounting inductive sensors on a ring gear on all four wheels.
With barely 4 cm space available in the wheel carrier for integration of the sensor and its cable, sensor size is critical. In addition, when the structure of the rigid carbon fiber monocoque vibrates, every component is also subject to intense vibration. Sensors sited at its extremities can be exposed to permanent loads up to 20 G. The chosen sensors must therefore withstand extreme permanent loads, shocks and high temperature. Universal sensors, which are offered on the market specifically for racing purposes, have not worked reliably.
Inductive sensors of the type DW-AD-403-M5 are particularly suitable for such extreme conditions. These Classics family sensors (Extra Pressure range) have a stainless steel housing that ensures robustness and provides protection against corrosion. With a size of M5, they are ideal for mounting in the limited space inside the wheel. Their low weight compared with sensors used previously is another advantage.
Direct provision of digital signals avoids the processing that would be necessary with analog signals. Digital signals are evaluated in a separate data-logging module. The high speed CAN bus system makes them available to the steering wheel control electronics for conversion into speed indication and to the engine management system for traction control operation.
The sensor’s technical features, such as sensing range, temperature range and its exceptionally high maximum switching frequency, contribute significantly to the reliability of the electronic concept. Proof of this is the team's success, winning both first place for engineering design and the top award in the category: "Most innovative use of electronics".