Automatic Transmission History

Today’s automatic transmission can follow back to the early horseless carriage gearbox. It was developed in 1904 by the Sturtevant brothers in Boston. In the automatic transmission’s earliest form it had only two forward speeds. The shift between gears was controlled by flyweights that were driven by the engine. When the vehicle went into higher engine speeds the flyweights would pull out and push the vehicle into the higher gear. As the vehicle and engine speed would slow the weights would contract and allow the vehicle to shift back into the low gear. During this time metal science had not come as far and the strength was not durable. This means that many of these transmissions would fail with little to no warning.

Addition Of Reverse & User Control

Ford’s Model T was the next big phase of development of what we now use in our vehicles. The development of a reverse gear plus the user actuated transmission were big advancements in transmission technology. The pedals in the vehicle controlled the transmissions’ friction elements. In this case these were clutches and bands. This type of transmission required user skill to make a smooth start and know when to shift, but in some respects was easier to use than today’s unsynchronized manual transmission.

General Motors and REO developed semi-automatic transmissions in 1934. These were considerably easier to operate than the fully manual transmissions. These vehicles did feature a clutch that the user had to use to engage the motor with the transmission. The General Motors transmission at this time used a power shifting planetary gearbox. This unit was sensitive to road speed, and hydraulically controlled.

Introduction Of Fluid Couplings

During the 1930’s the automotive world also started to try to solve the problem of how to prevent the motor from stalling at a stop while the transmission was in gear. The answer was the fluid coupling. The first mass produced automatic transmission was the Hyrda-Matic transmission that was released by General Motors.

The Hydra-Matic was an available option for purchase on Oldsmobiles and later GM’s Cadillacs. These transmissions had the fluid coupling and hydraulically controlled planetary gearsets. This made it possible to have 4 forward speeds and included a reverse gear. The transmission was sensitive to road speed and throttle position. This meant the vehicle would automatically up and down shift to adjust for operating conditions.

GM started featuring the Hydra-Matic in both the Pontiac and Cadillac lines and started selling the transmission to other auto makers. Some of the biggest names in automotive manufactures began buying and installing these transmission in their vehicle lines. This included Rolls-Royce, Bentley, Hudson, Nash, and Kaiser.

The original Hydra-Matic possessed two of the most sought after features that are incorporated in today’s transmissions. These are the good ratio spread and overdrive. With well designed ratios there was good acceleration and excellent “step-off”. In the higher gears the fluid coupling only handled some of the engine’s torque. This translated to a good degree of efficiency. This made the early version of the automatic transmission similar to today’s lock-up torque converter.