Automatic transmission

An automatic transmission is an automobile gearbox that can change gear ratios automatically as the vehicle moves, freeing the driver from having to shift gears manually.

Planetary GearboxPlanetary Gearbox

Direct Shift Gear BoxDirect Shift Gear Box CVTCVT

Torque ConverterPlanetary Gear SetsSet of BandsSet of Wet-Plate ClutchesHydraulic System

Gear Input Output Fixed Gear Ratio

1st 30-tooth sun 72-tooth ring Planet carrier 2.4:1

2nd

30-tooth sun Planet carrier 36-tooth ring 2.2:1

Planet carrier 72-tooth ring 36-tooth sun 0.67:1

Total 2nd 1.47:1

3rd30- and 36-tooth suns

72-tooth ring 1.0:1

OD Planet carrier 72-tooth ring 36-tooth sun 0.67:1

Reverse 36-tooth sun 72-tooth ring Planet carrier -2.0:1

BandsHydraulic Actuators

A continuously variable transmission (CVT) is a transmission which can change steplessly through an infinite number of effective gear ratios between maximum and minimum values.

Conceptualized by Leonardo da Vinci in 1490.

Toroidal CVTsToroidal CVTs Hydrostatic Hydrostatic CVTsCVTs

Pulley Based Pulley Based CVTsCVTs

Variomatic is the stepless, fully automatic transmission of the Dutch car manufacturer DAF(1958), using a drive belt and two pulleys.

Variomatic patents were transferred to a company called VDT (Van Doorne Transmissie), later taken over by Bosch.

A version with a differential was developed by Williams in the 1993 Williams FW15C CVT Formula 1 car, but it was banned.

Variomatic is commonly used in most scooters nowadays.

Nano would also be using a variomatic transmission.

Multitronic is a stepless transmission launched by Audi in 2000.

Multitronic is an advancement over Variomatic. It utilizes a chain drive and a oil cooled multi-plate clutch.

The transmission is monitored and regulated by Audi's "Dynamic Regulating Programme" (DRP), which tracks the driver's inputs, driving conditions, and engine load to compute the optimal gear ratio for fuel efficiency or maximum performance, as mandated by the user.

Multitronic also offers a number of driver-selectable fixed rations, selectable from either the gear-lever in a sequential style.

CVTs operate smoothly since there are no gear changes which cause sudden jerks.

There are 25% fewer moving parts to a CVT transmission.

They are also cheaper, but still expensive to repair.

Higher fuel consumption than the manual transmission version in city driving (ideal driving).

CVTs operate smoothly. This can give a perception of low power, because many drivers expect a jerk when they begin to move the vehicle.

Audi A4 Multitronic CVT

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