Fluid coupling

A fluid coupling or hydraulic coupling is a hydrodynamic device used to transmit rotating mechanical power. It has been used in automobile transmissions as an alternative to a mechanical clutch. It also has widespread application in marine and industrial machine drives, where variable speed operation and controlled start-up without shock loading of the power transmission system is essential.

The fluid coupling originates from the work of Dr. Hermann Föttinger, who was the chief designer at the AG Vulcan Works in Stettin. His patents from 1905 covered both fluid couplings and torque converters.

Dr Bauer of the Vulcan-Werke collaborated with English engineer Harold Sinclair of Hydraulic Coupling Patents Limited to adapt the Föttinger coupling to vehicle transmission in an attempt to mitigate the lurching Sinclair had experienced while riding on London buses during the 1920s Following Sinclair's discussions with the London General Omnibus Company begun in October 1926 and trials on an Associated Daimler bus chassis Percy Martin of Daimler decided to apply the principle to the Daimler group's private cars.

During 1930 The Daimler Company of Coventry, England began to introduce a transmission system using a fluid coupling and Wilson self-changing gearbox for buses and their flagship cars. By 1933 the system was used in all new Daimler Lanchester and BSA vehicles produced by the group from heavy commercial vehicles to small cars. It was soon extended to Daimler's military vehicles. These couplings are described as constructed under Vulcan-Sinclair and Daimler patents.

In 1939 General Motors Corporation introduced Hydramatic drive, the first fully automatic automotive transmission system installed in a mass-produced automobile. The Hydramatic employed a fluid coupling.

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