The development of Renault’s advanced E-TECH powertrains all began with a LEGO model. The next step was how to transform the toy prototype into a real, working engine. This was the challenge facing Ahmed Ketfi-Cherif, Renault’s Mechatronics Synthesis Architect.

Ahmed was one of the people who Nicolas Fremau, designer of the initial LEGO prototype, consulted in order to bring the E-TECH hybrid powertrain – and Renault’s wider hybrid plans – to life. He said: “Going from the LEGO adventure to reality was a massive challenge. It taught me a lot.”

Smooth operation was a priority

Ahmed, who works as a control specialist, needed to ensure that transitions between driving modes were possible with a simple ‘dog clutch’, a system normally reserved for motorsport, and that the finished product would be up to the high standard demanded by the customer.

The dog clutch system – which replaces both a sprocket and synchronising ring in a clutchless configuration – is a gearbox boasting superior efficiency due to the reduced number of components.

This particular type of ‘flat’ version works well over time and is more reliable than other types of dog clutch. However, the team needed to find a solution to make the system smoother, as the components are less likely to fit together than in alternative setups such as a ‘roof’ dog clutch.

“We’re used to using dog clutches in Formula One, for a racing engine. But it was something completely new for a ‘general public’ engine. We had to make this simple object usable by customers,” explains Ahmed Ketfi-Cherif, with a smooth and refined drive of much higher importance than winning lap times.

Cleverly adding a high-voltage starter generator

Ahmed quickly came up with the solution to ensure enhanced smoothness by adding a second electric motor, called a High-voltage Starter Generator (HSG). “Its role is to replace the synchronisers of a traditional gearbox to facilitate the clutch and therefore the gear change. By working in conjunction with the electric motor, it allows very precise regulation of the speed of rotation of the gearbox for smooth gear changes.”

From this, the original LEGO model concept was updated and tested on the road. They discovered the HSG brought other benefits with immediate torque contribution smoothing acceleration at low speeds, avoiding any break in torque delivery when changing gears.

This also meant the system could operate as a series hybrid for enhanced comfort and flexibility, without the need for an excess of stored energy or a charging socket. Ahmed said: “The possibilities for use in the range were multiplied”, with both E-TECH hybrid and E-TECH plug-in hybrid powertrains now possible.

At the end of these tests, the E-TECH development teams were reassured that what had worked in the LEGO concept and in simulation also worked “extremely well” in real life.

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