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Cooler from Plessey

12th November 1976
Page 36
Page 36, 12th November 1976 — Cooler from Plessey
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PLE_SSEY HYDRAULICS of Swindon, Wilts, has announced a temperature-controlled hydraulic drive system for vehicle engine cooling fans.

Drive for the fan comes from a gear-type hydraulic motor supplied with pressurised oil, piped from an engine-mounted gear pump.

The oil supply to the fan motor is regulated by a temperature. controlled by-pass switching valve which controls the fan's speed according to engine temperature, and trims it to a predetermined maximum speed independent of engine revs.

Plessey claims that there are several advantages to this system, including a considerable reduction in power to drive the fan when cold, less noise and greater design freedom for locating the vehicles radiator due to the flexibility of the drive system.

In use, the fan idles when cold but starts up and increases in speed with a hot engine until the trim speed is reached.

This trim speed is factory adjustable.

A wax filled element is inserted in the vehicles cooling system and this provides the engine temperature signal. This element controls the flow area of the motor by-pass valve so that the valve is fully open when the engine is cold.

As the engine becomes hot, the temperature signal fully closes the valve which makes the fan motor operate in a direct hydrostatic mode such that the fan speed is a function of engine speed up to the trim point.

Each change of fan speed with temperature is gradual to prevent sudden noise level changes.

The transmission of the system is formed from high pressure gear pumps and motors which are suitable for fans up to I I kw. (15 bhp).

Both pumps and motors have displacements of up to 20cc (1.2 c in) Plessey believes that the fan drive system will be particularly suitable for heavy commercials where it may even provide an extra power source to drive auxiliary vehicle functions.

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