When faced with new technical regulations for the LM P1 class in 2014, Audi, Toyota and Porsche opted for radically different strategies. While the conservative approach adopted by Audi paid off at the 24 Hours of Le Mans, Porsche’s strikingly innovative solution was beset with reliability problems. Toyota’s middle lane was the one that led to the World Endurance Manufacturers’ Championship title.

Fast-forward 12 months. Although the manufacturers had continued with the same technological concepts in 2015, the outcome was somewhat different – Porsche took the season by storm. Audi managed to compete in terms of performance but fell short on reliability, while Toyota had the opposite problem: a dependable car that lacked pure speed. An obsolete concept? “No,” retorted Pascal Vasselon, Technical Director of Toyota Gazoo Racing, “but times change. We had decided to use supercapacitors to store braking energy because, in our view, they were the best solution. We were proved right because, at the end of the day, we took the 2014 title. However, we knew from the outset that we’d have to switch to lithium-ion batteries as their development is progressing at a faster rate.”

Unlike road vehicles, for which storage capacity is the predominant criterion to cover the greatest possible distance, racing cars need high power density – the ability to deliver a lot of power very quickly – because energy is stored over a very short span of time, between two parts of a circuit where regulations allow the stored energy to be used.

Supercapacitors are electrochemical devices that hold one notable advantage over batteries: they release the stored energy more quickly. Unfortunately, as their industrial applications are relatively limited compared to batteries, research in this field is not moving as fast. “The hybrid culture is deeply rooted at Toyota,” Vasselon continued. “The department in charge of designing hybrid systems for production vehicles is also behind the development of the hybrid system for the endurance prototype. This means we can closely monitor progress in research and maintain strong ties with the manufacturers of all energy-related products. We have reached a point where batteries seem to be the most pertinent choice.”

While the supercapacitors are giving way to batteries, the Japanese constructor is persisting with its dual-axle braking energy recovery systems. “Although we are switching to a turbo engine, we do not feel that exhaust energy recovery is the best option,” Vasselon insisted. “Well, not for the time being at least.”

The TS050 Hybrid will be powered by a V6 turbo engine in place of the naturally aspirated V8 engine used since the early days of the project. “The naturally aspirated V8 engine served its purpose and, being reliable, it did not weigh too heavily on the development budget,” the former F1 Director at Michelin confided. “We could have gone down the V4 road, like Porsche, but we feel that the V6 offers the best compromise between reliability and performance. With the turbo, optimum output can be achieved anywhere, regardless of circumstances (altitude, temperature, and so on), whereas the naturally aspirated engine had a smaller performance window.”

While Audi have made few changes to their R18 (the flywheel technology has been axed, also in favour of Li-ion batteries) and are sticking with the same engine type, the TS050 Hybrid is radically different to its predecessor: “you have to choose the right technology at the right time,” Vasselon concluded. Will the TS050 Hybrid bring Toyota a long-coveted victory in the 24 Hours of Le Mans? We shall find out by 3pm on Sunday 19 June!

Pascal Vasselin was interviewed by Cécile Bonardel / ACO
Translation from French by David Goward