Automatic Transmission Types

The overwhelming majority of automatic transmissions used at present are hydromechanical.

Besides, continuously variable transmissions (CVT), belt, chain or toroidal friction machines and automated shift manual transmissions are used by a few companies (Ford, Nissan, Audi, Honda, Daimler-Chrysler) in some models, but the lack of obvious advantages keeps them from wide distribution.

Our specialists consider these AT types advantages insufficient for the Russian automotive market.

Traditional AT consists of following consequently arranged power circuit components : torque converter and mechanical planetary gear set (PGS) – pict.1.

Historically AT appeared in 30's – 40's of the previous century as a set of torque converter and two-step PGS. In these transmissions the main role in torque ratio change was assigned to torque converter with power range up to 6. But operating conditions main losses (up to 40%) were the reason of its low energy characteristics. That is why in the middle of 50's the torque converter construction development was aimed at its energy characteristics improvements and resulted in torque ratio reduction to 2.5 and the increase in planetary gear set steps up to 3.

This AT conquered the US market and kept it for more than 30 years up to middle of 80's and its very properties ( poor performance and high fuel consumption) are associated with automatic transmissions at all.

The appearance of Japanese AT was caused by increased export of Japanese automobiles in the USA in 70's and that the construction is absolutely the same with the American one. Although those were Japanese manufacturers who in the middle of 80's pushed the world on the further AT development aimed at the economy increase.

Thus this development ended in: regular increase in planetary gear set steps up to 4 (with the last one - overdrive) and torque converter blocking at partial power in OD.

At these conditions the planetary gear set efficiency is not lower than that of the mechanical transmission. Besides, fuel consumption on a highway at the speed of 90-120 km per hour is also the same.

For this reason at the beginning of 90's hydromechanical transmission was spread in Europe, where the economy is always a dominating factor. Although at other conditions, in particular during city driving, it reveals all the drawbacks of 3-speed AT.

That was the time for the European manufacturers to make a contribution to AT development. It was favoured by the fact that AT of Mercedes-Benz and ZF (BMW, Audi) had 4 gears, but without overdrive gear, because the Europeans created their AT especially for powerful high-class sedan cars to ensure high dynamic characteristics.

The addition of the “economical” overdrive gear lead to the creation of 5-speed AT, which now is associated with both dynamical and economical high-class car.

The economy increase was also supported by one more European innovation - torque converter blocking at all speeds, except the first speed, that made differences in energy characteristics minimal.

After that AT is no more reproached with poor dynamical and economical characteristics . Already following Europe 5-speed ATs appeared in USA and Japan, and are used in expensive middle- and high-class cars.

The customers' interest for the considerable improvement of dynamic performance and economy caused further development resulting in 6-speed ATs made by Mercedes and BMW (Land Rover – pict.3). The speeds quantity increasing became a kind of competition for German manufacturers.

Thus in spring 2004 BMW produced 7-speed mechatronic transmission without torque converter for V10 engine.

But this high-level competition didn't affect the AT supply on the small- and middle-class economy car market, where moderate-priced 4-speed AT are widely spread.

M echanically predetermined drawbacks of 4-speed AT – insufficient dynamics and economy – in 80's made manufacturers look for the alternative such as continuously variable transmission with 6 fixed gears in manual mode, or mechanical transmission shaft with direct shifting and 6 speeds (e.g. direct shift gearbox – DSG – by Volkswagen).

Gear quantity control increase in traditional foreign 4-speed AT leads to constructive complication and price rising .

Planetary and multyflow gears synthesis theory , created in 60's in Russia, was the base for the unique military transport transmissions. It had being developed during previous decade and together with all listed foreign AT generations design analysis, allowed Russian specialists to find optimal design for 6-12-speed AT.

This historical reference let us formulate the main requirements of competitive AT for Russian automobiles.

To ensure the competitive advantages of Russian AT for period of 5-10 years, we are planning to produce and to offer to our clients the following AT:

• With 6-8 speeds - to ensure high performance.
• With high efficiency - to ensure economy.
• With minimum assemblies and details - to ensure reliability of operation and low price.

AT of that type had been designed in the Bauman Moscow State Technical University.