Torque Converters are a way to transfer power from an internal combustion engine to the driving wheels without using a mechanical clutch. Many automatic transmissions use them and most are fluid couplings. To confuse the topic further, vehicles have used fluid couplings to connect an engine to a transmission before the torque converter was invented!
Fluid couplings as their name suggests use hydraulic fluid to enable power to be transmitted between the source and the output device and you may need a degree in science to fully understand the theory behind it. The concept for the fluid coupling has been around almost since the birth of the car and some manufacturers used them to help deliver power in cars and trucks in the 1920s and 30s. They are simply a shell housing containing two turbines that move the fluid. Incidentally, one of the pioneers in this field was Alf Lysholm, a Swedish engineer who also pioneered superchargers using the same ideas.
The Torque Converter (and name) was developed by a Romanian engineer, George Constantinescu whilst living in the UK. His earlier claim to fame was developing the gearing that allowed a machine gun to fire through a spinning propeller on early aircraft. During the 1920s, Constantinescu wanted to build a cheap car for the worker that was easier to use than others on the market which were sold to wealthier people. It was to have a very high mileage and be very efficient. Clearly others in Europe were having the same ideas at the same time aka the Volkswagen!
Constantinescu wanted to develop an automatic clutch that fully replaced the manual clutch/gearbox of the time and used a fluid coupling as the base of the system. The core concept was to smooth out the power delivery from the engine and deliver it to the driving wheels. The key advantage over a normal fluid coupling is that the Torque Converter can increase the power under certain conditions. It seems that the original design was a forerunner of today’s Continuously Variable Transmissions (CVT), however the idea was merged with the classic gearbox to give the ancestor of today’s automatics.
What Constantinescu did was to add a “stator” to the fluid coupling in between the two turbines – one connected to the engine and one to the load (driving wheels). This changed the flow of the fluid (oil) from one turbine to another. The stator is now fitted to a clutch that prevents the driving and driven shafts from being connected when the driven shaft is rotating faster than the driving shaft, thus preventing a failure. This idea came from the evolution of the bicycle – as did many early automotive engineers!
By 1923, he had a prototype car completing tests and being shown at exhibitions and this caught the eye of General Motors who bought an option to licence the Torque Converter for their own vehicles. Unfortunately they eventually declined to exercise the option and with the tax man after him, Constantinescu sold off the patents with the cars and worked his magic on railway systems instead.
The Torque Converter though, took on a life of its own with GM brands like Buick and Chevrolet using the concept in their cars from the late 1940s. Buick had redeveloped their designs from heavy war machinery, shrinking the components down to suit the road cars. This lead to other GM brands and their competitors to bring out their own versions under great names like Dynaflow, Turboglide and UltraMatic.
Today, Torque Converters are manufactured by the big gearbox suppliers like Allison and BorgWarner in the US, Valeo and ZF in Europe and even several Japanese manufacturers. Most automatic gearboxes in cars now have a Torque Converter as standard and they are also used in very heavy machinery for their efficiency in power delivery.