Automatic Transmission / Gearbox

How a Torque converter works.

The torque converter is a type of fluid coupling that is used to transfer rotating power from the engine to the automatic transmission. The torque converter takes the place of a mechanical clutch in a vehicle with an automatic transmission.

The key characteristic of a torque converter is its ability to multiply torque when there is a substantial difference between input and output rotational speed, thus providing the equivalent of a reduction gear. Some of these devices are also equipped with a temporary locking mechanism which rigidly binds the engine to the transmission when their speeds are nearly equal, to avoid slippage and a resulting loss of efficiency.

Torque converter with lock up clutch

Torque Converter Oil Flow

In vehicles, the torque converter is a type of fluid coupling used to transmit power from the engine to the automatic gearbox. It takes the place of a clutch in a manual transmission set-up.

The torque converter has the ability to multiply torque when there is a substantial difference between input and output speed, thus providing the equivalent of a reduction gear.

Some torque converters are fitted with a "lock-up" which will lock the input to the output when the rotational speeds are almost identical.

Torque Converter

Torque Converter Oil Flow 2

In vehicles, the torque converter is a type of fluid coupling used to transmit power from the engine to the automatic gearbox. It takes the place of a clutch in a manual transmission set-up.

The torque converter has the ability to multiply torque when there is a substantial difference between input and output speed, thus providing the equivalent of a reduction gear.

Some torque converters are fitted with a "lock-up" which will lock the input to the output when the rotational speeds are almost identical.

Basic Epicyclics

An epicylic gear is a planetary gear arrangement consisting of one or more planet gears, meshed and rotating round a central sun gear. The planet gears are also meshed and rotate within an internal ring gear (Anulus). The planet gears are fixed to a planet carrier designed to rotate on the same centre as the sun gear. This arrangement has a number of modes of operation depending on which members are locked. Epicyclic gears can be based on spur gears, helical gears, or bevel gears.

Epicyclic / Planetary gear set

Planetary gears - Principle of Operation

A planetary gear train consists of 3 units:

The Sun Gear

The sun gear has external gear teeth that are permanently meshed with the planet gears.

The Planet pinions and carrier

An number of small gears (planet pinions) are mounted on axis pins, which are part of, amd equi-spaced around the carrier. The gears have external teeth and are permanently meshed with both the sun and the annulus.

The Annulus

The annulus is a ring gear, having internal teeth permanently meshed with the planet gears.

Compound planetary gears involve one or more of the following three types of structures: meshed-planet (there are at least two more planets in mesh with each other in each planet train), stepped-planet (there exists a shaft connection between two planets in each planet train), and multi-stage structures (the system contains two or more planet sets).

Compared to simple planetary gears, compound planetary gears have the advantages of larger reduction ratio, higher torque-to-weight ratio, and more flexible configurations.