The next big things: the Lexus multi-stage hybrid

Published: 08 August 2016

► Chief engineer Koji Sato on the tech in the LC coupe
► The rundown on Lexus’s performance hybrid system

► How it emulates a ten-speed transmission

> For me it began with the LF-LC concept. The moment I saw it I knew we had to build it. Many other people said the same: Lexus, please build this car. But it was easier said than done. To create a car that stirs the soul and captures the heart we have to challenge ourselves. For me, LC means Lexus Challenge.

> The challenge was to incorporate production considerations and constraints into a design study. So we created a cross team with designers, r&d and production engineers. We had one common objective: to achieve the best design and the best dynamics.

> We wanted to launch a hybrid version of LC. But how to combine our new requirements for superior driving feel with a hybrid powertrain? We clearly felt the need to achieve a breakthrough. So we started brainstorming on how to improve both the driving performance and the system’s efficiency.

> The starting point was the instant torque feeling you get with an electrical motor, because it can respond more quickly than a conventional engine. [But our traditional hybrid’s] benefit fades under heavy acceleration, as engine speed rises and then stays flat, even while acceleration builds. This creates a feeling of ‘disconnect’ between higher engine noise and actual vehicle acceleration.

> Our solution was to add a four-speed automatic transmission to the hybrid powertrain. This is what we call the Lexus multi-stage hybrid system in the LC500h. By adding physical gears we are able to keep the engine speed, the rpm, much more aligned with the driver’s input. It allows us to make the best use of the electric motor and to have more direct acceleration feel – helping create a new taste for the driving hybrid. Hybrid is not just an eco device anymore.

> Still we have the CVT system in the front. And then right after the CVT and motor generator one and two, we have the shifting control mechanism, setting a more appropriate level for low- and high-speed driving. The efficiency is going up and at the same time we can create more power.

> We have created a brand new manual mode for an even more engaging driving experience, combining the CVT and the automatic to emulate a 10-speed gearbox that shifts faster than a dual-clutch alternative. Moreover, thanks to the use of a lightweight electrical motor and a brand new lithium-ion battery pack, we are able to completely offset the weight of the additional transmission. The result is simple – a great driving experience from a hybrid powertrain.

> With a 3.5-litre petrol V6, the LC500h powertrain delivers 359 horsepower, and it will accelerate 0-100km/h [62mph] in less than five seconds. Of course, these are only facts and figures – more important is the excitement of the driver when he gets behind the wheel. Really, we can’t wait to let you drive this car. Our feeling is that you won’t be disappointed.

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By CJ Hubbard

Former CAR magazine associate editor, road tester, organiser, extremely variable average wheel count

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