Gearing up for the future
Making hybrids and electric vehicles go further requires more efficient transmissions as well as better batteries
- Published in Features.
Gaining traction: Integration will accelerate electrification
With the exception of carbon dioxide, few topics polarise opinion quite as much as electrification. The two are directly related of course but, although the targets for CO2 reduction are well understood, the technologies used to get there are not so clearly defined.
Better combustion engines and transmissions are certainly the best way to start, and great progress is being made here. But what comes next is proving rather more difficult to predict.
In the 1990s, hydrogen fuel cells were going to be the magic bullet solution to the tailpipe emissions problem but cost and durability issues were not overcome, and we’re still waiting.
Then it was battery-electric vehicles. Although the first generation of lithium-ion-powered EVs such as the Nissan Leaf and Renault Fluence have now reached the market, the rate of improvement in battery performance has not been as rapid as first predicted and costs are still high.
And although electric motors are highly efficient, this does not remain so over the entire operating map. Almost all EVs rely on a fixed reduction gear, because this is simple and low cost, but more complex transmissions would improve overall efficiency. There’s a lot of room for further development, and in the future there will still be a need for more speeds.
“A few years ago the hypothesis was that e-mobility would wipe out conventional powertrains and in future we’d only see EVs with batteries and final drives,” said Rolf Najork, Schaeffler’s vice-president of R&D for transmissions systems. “I think we’ll have to wave goodbye to this thesis. Transmission people don’t have to fear e-mobility.”
It starts with the batteries. Energy density of even the most advanced lithium-ion technology is extremely low compared to fossil fuels. Even if chemistries improve enough to deliver 250Wh/kg, this compares extremely unfavourably to gasoline’s 12,000Wh/kg.
To put that in context, 20 litres of liquid hydrocarbons can power a typical vehicle for 400km; the equivalent lithium-ion battery would only take you 50km – not very competitive. Experimental lithium-air battery chemistries could double that range but these are lab technologies only and are many years away. “The combustion engine will stay with us for several decades but there will be hybridisation – EVs require a quantum leap in battery technology,” said Najork.
The improvements in cell chemistries and battery management systems needed to get there could take decades and will cost the industry billions to get into series production. So there’s a good business case for developing more advanced transmissions for next-generation hybrids and EVs which can increase vehicles’ range, packaging or cost.
Taking a C-segment vehicle as the baseline for simulations, Schaeffler has been looking at what improvements could be achieved with more complex electric drives. Going from a first-generation power-split hybrid with a simple planetary gearset, the firm added a second gearset and associated brake, clutch and actuation system. Keeping driving performance at the same level, this vehicle was run through the test cycle. The results of the simulation were pretty encouraging.
