When the Z.E. on-demand hybrid rechargeable powertrain was first presented to Renault production-side managers and executives, the engineering teams were unaware that their work had scarcely begun. Very soon it was no longer about Entry and M0, but M1, the versatile and compact models like the Mégane. Thus it was on a Mégane that the calibration benchmarks were carried out for the future E-TECH powertrain. So the LocoDiscoBox had to be changed to make it compatible with this model and the services required of it. Two paths were identified for action: the addition of a second electric motor for low speeds and the addition of a fourth gear on the internal combustion engine for high speeds.
There was this problem of a flat spot between the first and second gears, at low speed, so the solution to us seemed to be the replacement of the synchronisers of a conventional gearbox with a small electric motor to facilitate clutching and smooth the acceleration with its instant torque boost. Another key point was controlling how the dog clutches work. That wasn’t easy because we had the flat dog clutches used in Formula 1, not pitch dog clutches. Flat clutches work better over time, so they’re more reliable. But the downside is they might not mesh so well. We would have to run the idea past some control specialists.
The HSG (High-voltage Starter Generator) motor we had choosen allowed the system to work as a series hybrid at low speeds for more smoothness and flexibility. It didn’t need a lot of stored power so we could reduce the battery capacity and take out the charging socket. The future E-TECH powertrain, with a rechargeable hybrid base, had just branched off into a “simple” hybrid version. Now we had a lot more potential uses in the range!
All of which was good news for Nissan, member of the Alliance with Renault, which had played a role in the development and product adaptation of this future E-TECH powertrain, in the knowledge that the latter would very likely be used in its models and markets. The Japanese were particularly concerned with driving pleasure, and while they appreciated the benefits of the second electric motor, they wanted to go a step further. This involved the addition of the fourth gear to the dog clutch gearbox to improve the feel at higher speeds.
The LocoDiscoBox transmission was based on three gears for three well-defined driving situations: city, road and motorway. By adding the HSG motor, we could improve the feel and reduce fuel consumption in the ‘city’ gear. We needed to do the same at the top end, and it occurred to us to add a fourth gear. This meant we could completely disengage the main electric engine when it wasn’t being used – typically on the motorway. That reduced drag and saved around 1 kW, or 3 to 4% of the consumption. The idea was to keep only those components necessary for traction connected to the wheel, and not use a big electric engine to do something we could do with a small motor. So the smaller HSG took the job of producing electricity for the components, instead of the big electric engine.
The last gain was made on the small gearbox turning the motors, allowing the crabots to engage when shifting gears. With flat crawlers and the single-spring assist system replacing the synchronizers, engineers were able to use small motors of less than 100 watts, as opposed to the usual double or triple. This also helped reduce the size of the transmission.
Now the architecture of the future E-TECH powertrain was clearly laid out. But there were still two component choices to be made: the electric engine and the combustion engine.
In order to allocate development and production resources across the Alliance, we have chosen to use existing Nissan components rather than buying them. This guided the choice of the main electric motor, but also and above all the combustion engine. The H4BT engine used at the start of the adventure was a little old and lacked efficiency on the fuel consumption side. We also aimed to meet the future Euro 6d-FULL emissions standards. The only candidate was the HR15Gen3 engine (an atmospheric 4-cylinder petrol engine used by Nissan in particular for the Chinese and Korean markets) whose 1.5 litre capacity exactly matched the requirements. It was compact, it offered the right performance and output, and it was the best candidate in the Alliance component bank. It was adopted in 2015.
E-TECH Powertrain Project Leader
To go further than simply complying with anti-pollution standards and have the option of adding a GPF (Gazoline Particulate Filter) on the combustion engine, it was decided in 2016 to replace the HR15 engine with another naturally aspirated four-cylinder engine from the Alliance, the HR16. This required a great deal of adaptation work (engine mapping, modification of certain parts such as the pistons, connecting rods and crankshaft on the test cars) but the results soon proved satisfactory.
The HR16 engine was a good compromise, getting the best out of the innovative dog-clutch transmission. It’s an atmospheric engine with the contribution of the electric motors compensating for the lack of a turbocharger at low speeds. Its main use is for its optimal-efficiency speed, especially when it works as the generator to recharge the battery. It also fits the bill as it optimises costs for an E-TECH powertrain that is intended for core-range, or in time even, entry-level vehicles. It’s the final piece in the puzzle, and the E-TECH powertrain that we know today came into being.
At the beginning, plenty of people told us “it’ll never work!” It was a very risky gamble for sure, especially wanting to replace the synchronised gearbox with an electric motor. But gradually the whole company ended up adopting the idea: the product and vehicle projects teams, right up to top management. Lots of staff in engineering and beyond got fired up for this project and lots of self-motivation was generated. That’s what makes a company worth its salt too. The E-TECH powertrain was a slightly crazy success that we can all be proud of.