Turbocharger and fan drive from Holset
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• A turbocharger designed for powers of 200 bhp to 350 bhp, known as the type 34, will be exhibited at Earls Court by Holset Engineering Co Ltd, Turbridge, Huddersfield, together with a fan-drive-control unit that is available in torque-limiting and air-temperature-sensitive versions. Holset fan drives have been employed on passenger cars for some time.
Design features of the type 34 turbocharger include a compressor-flow range of 200/700 cu ft /min at a pressure ratio of 2.1 to 1 and a single fully floating bearing that provides for rotor speeds in excess of 100,000 rpm and for operation up to a pressure ratio of 3 to 1. Holset says that the company's turbochargers have a life between overhauls of 150,000 miles. Both types of fan drive incorporate a shear-type fluid coupling, the drive being transmitted from the disc drive or driving member to the housing or driven member through a film of silicone fluid. The torque capacity of the torque-limiting drive is determined by the physical properties and viscosity of the fluid film. In practice, the torque limit of the coupling is the torque required to drive the fan at the required maximum speed. It is applicable to fans up to 610mm diameter.
A hi-metallic sensing element is a feature of the air-temperature sensing fan drive that varies the area of the fluid film and therefore the fan speed in accordance with changes in temperature of the air stream.