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CVT Evolution Part 2: Transmission “Rivals” Learning From Each Other

Transmission is evolving
different engines have revolution zones where it can run with good fuel efficiency, and transmission targets this ideal zone and thus mileage improves.

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2013/05/27

Transmission helps improve fuel efficiency
In the previous article in this series we looked at the three types of automatic transmission systems and how among them, CVT is unique. Let’s quickly review: The three main types of automatic transmission are conventional automatic transmission (AT), dual clutch transmission (DCT), and continuously variable transmission (CVT).

CVT and DCT appeared after regular AT and are now included in the features of many automobiles, each working towards improving daily fuel efficiency. Here it’s important that we learn about the relationship between car gasoline mileage and transmission.

Transmission can improve car fuel efficiency in two ways. One way is by raising the efficiency of transmission itself. As transmission efficiency increases, it is possible to transfer it to the tires without loss of engine power.

Another way is how transmission allows us to use the areas of the engine that have good efficiency. What does this mean? Well, different engines have revolution zones where it can run with good fuel efficiency, and transmission targets this ideal zone and thus mileage improves.

The results on the powertrain due to improved transfer efficiency and engine efficiency greatly affect vehicle mileage, and thus any transmission works to improve efficiency. However, their main approaches are different. In particular, let’s look at how DCT and CVT contrast.
Comparison of Engine Efficiency for CVT and DCT during Acceleration
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The diagram above compares CVT and DCT for starting off, acceleration and cruising. The best fuel efficiency can be realized by continuously using the area where efficiency is good for the engine (the green area) from an early stage.
Dual clutch transmission, as the name suggests, has two clutches, one for the odd-numbered gears (first, third, fifth) and one for the even-numbered gears (second, fourth, sixth). When you shift gears, the alternate gear is already selected, and gear changing becomes faster. DCT’s approach is to raise transmission transfer efficiency in order to improve fuel efficiency. It has the same kind of mechanisms as manual transmission and, with its high transmission efficiency, in particular it can extend mileage when cruising at high speeds.
CVT skillfully uses the engine’s “best” parts
On the other hand, CVT raises fuel efficiency by using the most efficient parts of the engine. As we saw before, CVT can set the transmission gear ratio freely, and is characterized by gear changing and driving that is seamless. This transmission gear ratio can set the range of the ratio widely and whether at low speed or high speed, it is able to continue using the area that is best for mileage.

In other words, CVT tries to improve fuel efficiency by maximizing the engine’s potential. Compared to DCT, CVT is able to use the efficient parts of the engine as soon as it starts up.

CVT has also been evolving from year to year. The challenge of upgrading transfer efficiency has now been achieved, along with expanding the transfer gear ratio. It has become possible to run on the engine’s optimum rpm, with a much wider range of speed than previously.

And not only the mechanics, the software that controls CVT has also been evolving. Now it can interpret the driver’s commands through the operation of the accelerator and steering for optimal shift control. On top of improving the fuel efficiency, CVT’s capabilities are advancing to allow you to drive just as you want.

As we have seen, upgrading the performance of the transmission is indispensable for improving car fuel efficiency. And these three representative types of transmission are set to keep on evolving even more in the future.



Read the first article in this series,
CVT Evolution Part 1: Seamless Driving and Improved Fuel Efficiency!