<P> A slightly different approach to CVT is the concept of toroidal CVT or infinitely variable transmission (IVT). These concepts provide zero and reverse gear ratios . </P> <P> Some hybrid vehicles, notably those of Toyota, Lexus and Ford Motor Company, have an electronically controlled CVT (E-CVT). In this system, the transmission has fixed gears, but the ratio of wheel - speed to engine - speed can be continuously varied by controlling the speed of the third input to a differential using motor - generators . </P> <P> A dual - clutch transmission, or DCT (sometimes referred to as a twin - clutch transmission or double - clutch transmission), is a modern type of semi-automatic transmission and electrohydraulic manual transmission . It uses two separate clutches for odd and even gear sets . It can fundamentally be described as two separate manual transmissions (with their respective clutches) contained within one housing, and working as one unit . They are usually operated in a fully automatic mode, and many also have the ability to allow the driver to manually shift gears in semi-automatic mode, albeit still using the transmission's electro - hydraulics . </P> <P> Also known as semi-automatic transmission (SAT) and several other names, this automatic transmission type utilizes a regular clutch and gear setup but automates the action by the use of sensors, actuators, processors, and pneumatics . The AMTs were born out of the need to make automatic cars affordable and fuel efficient . These are very simple and affordable . They're also not very expensive to repair . Fuel efficiency is their top priority and it rivals that of manual transmissions . AMT is based on an electronic control unit and a hydraulic system that supervise the use of the clutch and the gear shifting, allowing the driver to change gear without using the clutch, either sequentially or fully automatically . </P>

What is shifting gears in an automatic car