What's the difference between CVT, DSG, and normal automatic transmissions?

A conventional automatic transmission is the one that we have been used to in cars dating back to the 1940s.

Holden introduced its first automatic in 1961 with the EK model. A conventional transmission is one with a torque convertor between the engine and transmission so provide smooth easy drivaways. It basically disconnects just above idle speed so the engine can idle, but engages again when you accelerate away.

The transmission uses fluid to operate the various clutches inside the transmission for smooth shifting. The conventional transmission has proven to be very reliable over the years, but it isn’t the most efficient in terms of fuel consumption, particularly when compared to a manual gearbox. Engineers have been trying for years to make a more efficient transmission that has the smoothness of operation and the efficiency of a manual gearbox.

The two most successful have been the CVT “Continuously Variable Transmission) and the dual-clutch transmission, such as VW’s DSG and Ford’s Powershift. The CVT is designed to keep the engine revving at its most fuel-efficient speed by continuously varying the gearing.

To do that it uses a system of pulleys and a belt. It seems odd when driving it because the engine sounds like it’s revving its head off at a constant speed instead of climbing and dropping as it would normally do. The CVT was first used on a small DAF car in the 1970s, and picked up by Volvo when it took over DAF. It took a long time to develop the transmission, particularly the drive belt, to be used on anything other than a very small engine. Those problems have largely been fixed, but you’re correct that Nissan, and also Honda, had troubles when they first used the CVT.

The dual-clutch transmission is really a manual gearbox with two clutches that operate in synch with each other, one releasing one gear while the other engaging another gear. VW, Ford and Holden have had a lot of trouble with it, mostly related to the clutch packs, and the electronics.

It should be noted that both the CVT and the dual-clutch auto are more fuel-efficient that the conventional automatic, and both now seem to be largely trouble free.