When visiting the IAA transportation auto show in Hanover, Germany, I saw an old friend. On the stand of Bosch, there was this tiny part with an opened interior — the way they sometimes show the inner workings of machinery. Doubting my eye, I lowered my head to look closer, and behind me someone said: “Yes, it is what you think it is.” It was said in Dutch, too.
What I was looking at was a Dutch development of the continuous variable transmission, or CVT.
A Dutch carmaker (DAF) put it in a small car, called the “Dafodil,” and sold many of those easy-to-drive vehicles to mainly older people. That was a shame, because besides being perfect for older people, it was also great for rally driving. It was in a separate class, because it was unfair for non-CVT cars to compete against it.
The problem for wider acceptance of the technology was the elastic rubber pull belt. It snapped sometimes and could not handle the forces bigger cars would use. When it did break, you had to wait for route assist services to come to your rescue and replace the belt.
The technical solution was a steel pushbelt. It was easy on paper. Only, the machinery to produce the belts at volume did not exist. A pushbelt is made of many thin, high-precision manufactured, hardened steel plates. It took many years more than expected to produce the belts. In the meantime, the car company got sold and the belt factory went broke. The belt factory that got the production working was bought by Bosch.
Now the limit for application of the CVT is no longer only for small, light cars. It is good for medium trucks up to 7.5 tons. That is why it was prominently present at IAA. It can deliver the same performance with a smaller battery and a lighter electric motor. Saving 10% on the 50kWh battery of a small private car is a lot less than saving 10% on the 150kWh battery of a medium truck.
The business case as presented by Bosch for trucks is saving on battery, motor, and weight. At the same time, the OEM can save on development and production by using one powertrain for a wide variety of different trucks and use cases.
For private cars with smaller batteries, these savings will often just cover the costs of the CVT. That is a less interesting proposition for carmakers. We know from Porsche’s use of a transmission in the Taycan that shifting gears can improve performance and efficiency. Porsche uses only two gears. A CVT can provide a thousand different gears or more. It can optimize the reduction between motor and wheels for sporty driving or for towing. It can do it for mountains, highway, city, or eco driving. It can do this automatically, or it can enhance the effectiveness of the different driving modes a driver can select.
For private cars, the economies of scale are less of an argument. Trucks are made in many different smaller series compared to private cars. The increases in performance and range are the convincing arguments for carmakers.
Bosch claims a 13% faster acceleration (80–120 km/h), a 4% efficiency gain, and a 11% higher top speed, offering improved performance with lower energy consumption without the discomfort of changing gears. It is logical for the fine tuning of next-generation electric powertrains.
Currently, most OEMs are focused on getting working models to market for a competitive price. They are finding this harder than anticipated. The Zoe, the LEAF, the e-tron, and the Bolt were one-of-a-kind designs. We have seen an interim generation with converted and multiple powertrain platforms. With the introduction of the MEB toolkit from Volkswagen Group, we entered the area of dedicated architectures.
Now we will see the optimizations. Besides megacasts, structural batteries, LFP batteries, and heat pumps, CVTs can be one of those next-generation technologies.
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Source: Clean Technica