Application Note

Refuelling Level Sensors for Le Mans Michelin Green X Challenge

Pit-lane refuelling tank level sensors for Le Mans Michelin Green X Challenge provide real-time results

Since its inception in 1923, the Le Mans 24 Hours has provided car and component manufacturers with a unique testing ground for their equipment, with much of the new technology and techniques making their way into mainstream automotive applications.

Automotive braking systems, lighting, suspension and tyres have all benefited from development within Le Mans racing and more recently focus has shifted towards performance, fuel efficiency and safety.

Since 2007, in association with the Automobile Club de l’Ouest (ACO), Michelin has recognised those teams who succeeded in combining performance with energy efficiency. In 2009, the Michelin® Green X® Challenge was introduced to the Le Mans 24 Hours, Le Mans Series and American Le Mans Series. Competitors who succeeded in consuming the least fuel while optimising performance were rewarded, with the team coming out on top after five rounds of the Le Mans Series automatically entered into the following year’s Le Mans 24 Hours.

The Michelin® Green X® Challenge result relies on accurately monitoring each team’s fuel usage for the duration of an event. Any inaccuracy or unreliability could lead to an unfair outcome. It was therefore imperative for the ACO to choose a device that could offer a high level of accuracy whilst remaining reliable and repeatable across the pit-lane.

Monitoring fuel consumption

In 2010, the ACO approached Gill Sensors with a view to providing an accurate, reliable level sensor capable of being used in each of the regulation fuels. With a reliable history supplying refuelling rig level sensors to teams in the IRL series (and former Champ Car series), as well as the supply of on-car fuel and oil level sensors to teams in both the European and American Le Mans Series, we were confident that we would be able to help.

Managing different fuel types

Capacitive level sensors monitor the dielectric constant of the liquid, so in order to achieve a highly accurate output it is essential for the sensor to be calibrated in the appropriate liquid. With multiple fuels used in Le Mans Racing, the use of a generic capacitive level sensor across the entire pit lane has typically not been possible, as the sensor would have had to be re-calibrated in each team’s fuel. With around 50 teams competing in some events, this was clearly not an option.

An advantage of Gill liquid level sensors is their ability to store up to twelve different calibration files within the sensor on-board memory, so calibrating in multiple fuel types at the factory is not a problem.

The sensors were therefore calibrated in both diesel and petroleum as specified by the ACO, with the relevant calibration file easily accessible via a simple software interface.

Sensor design & installation kit

The dimensions of each team’s refuelling rig are stipulated by the FIA and enforced within the ACO regulations, so it was possible to produce all sensors to a common design, which allowed for the agreed tolerances of the tank.

Gill designed a mounting boss kit to allow installation of both the sensor and a seal plate, for use when the sensor was not required (during testing etc).

As with all Gill pit-lane refuelling rig level sensors, independent isolation of the sensor was required to avoid potential electrical ground loop interference. To achieve this, custom inserts were designed into the mounting flange to avoid the sensor contacting the fuel tank, ensuring a repeatable, reliable continuous signal could be maintained at all times.

An integrated Deutsch ASL 5-pin connector was also used to simplify the installation and connection.

Processing and using the output signal

Each sensor was calibrated to provide a linear 0.25V to 4.75V analogue output over the full depth of the tank. When connected to the sensor, an external control box (manufactured by a third-party) received the analogue signal and transmitted the data wirelessly to race control, where the information was used to determine fuel efficiency.

As mentioned earlier, the Michelin® Green X® Challenge rewards those teams who combine the highest performance with the best fuel economy. Each competitor is awarded an ‘Energy Efficiency Index’, which is calculated by dividing their average speed (V), excluding pit stops, by their average fuel consumption (C) over the course of the race (where ‘C’ is calculated directly from the liquid level sensor output).

Formula: EEI = V / C

The competitor with the highest overall EEI result over the Le Mans season or 24 Hour race is crowned the winner of the Michelin Green X Challenge for that particular event.

Real-time results

Results provided by the sensors were transmitted, processed and displayed in real-time. This allowed spectators and race fans to see the provisional standings of the Michelin® Green X® Challenge both via the internet and on track-side monitors during a race in real-time – a first at Le Mans.