Automatic Transmissions

Did you know that the original version of the modern type of automatic transmission is nearly 100 years old? This is true, however it took about 20 years to reach the automobile!

The first automatic transmission that we would recognise today was developed in the early 1920s by Alfred Horner Munro, a Canadian engineer, who developed his to use compressed air to act as the driver of the mechanism. Compressed air quickly loses its pressure so the transmission couldn’t deal with most applications and apparently never saw a commercial use despite several patents being purchased in Canada and other countries.

However there was a form of automatic transmission developed in the very early days of the automobile – using flyweights that helped change the gear based on the engine speed. It had two speeds with the higher gear being used when the engine speed was increased. Manufacturers were constantly researching ways to improve the operation of their vehicles and so “semi-automatic” gearboxes were appearing where the driver had less to do when changing gears.

It was the early 1930s that the first automatic transmission using hydraulic fluid was developed. There is a contradiction in the history books over who actually invented it. Some say that ZF in Germany (founded by Count Zeppelin) developed them after the First World War and others suggest that a couple of Brazilian engineers figured it out and sold their work to General Motors. Certainly GM had an early version of their “Hydramatic” in use during the Second War fitted to heavy military vehicles.

GM with their Oldsmobile and Cadillac brands were the first to sell consumer cars with a hydraulic automatic gearbox – an evolution of the pre-war Hydramatic system. This gearbox soon spread through the US General Motors brands and even into the future AMC brands of Nash, Hudson and Kaiser. In Europe, Bentley and Rolls Royce adopted it too. That probably prompted Mercedes-Benz to develop their own design.

The next stage in the automatic gearbox life was the introduction of the torque converter which smoothed out the gear changes. Again, the US was at the forefront with Buick delivering their “Dynaflow” gearbox in the late 1940s followed by Packard and Chevrolet.

Interestingly, Chrysler were the last to market with their Powerflite and Torqueflite boxes, despite being at the forefront of research into fluid couplings in the 1930s. They appeared to have concentrated on one form of transmitting rotating power rather than considering the torque converter. However, they possibly have had the gearbox that has lasted the longest in the market!

All these gearboxes only had 2 or 3 gear ratios for forward movement and over the decades the designs have grown ever bigger with now 8 or 9 forward motion gear ratios fitted. Combined with ever more complex software systems in engine management systems, the current automatic gearboxes can be very smooth and are connected to the other systems for suspension and traction control to help with the one issue I dislike about the boxes:

I have always felt that cars at a mid-range price can be quite dangerous using an automatic gearbox when the car is pushed hard. Many times I have had a car change down on the exit of a corner which unbalances the vehicle just as the power is being delivered and I wonder if this is a factor in younger drivers crashing a car in wet or slippery conditions and sliding off into the nearest solid object like a tree.

As an example, the last few cars I have had with a semi automatic gearbox have been quite bad at changing gears too early when in full auto mode. So much so that in commuting traffic, the car can change gear once or twice a minute as the speed changes and so I typically have to leave it in manual mode to control the smoothness of the drive.

I’m not a fan of the fully automatic gearbox, I still like to control the vehicle I drive, however I do respect that this type of gearbox is very suited to many conditions that drivers are in.