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A new hydraulic cam follower with variable valve timing (VVT) properties is described. Experimental results show that the point of closure of the valve may be delayed as a linear function of engine speed without external control. No other parameter of the valve event is modified by the device. An obvious application is the control of intake valve timing for engines with a wide speed range, where the point of valve closure could be scheduled with engine speed in order to maximise the trapped mass, hence improving the torque curve at low and high speeds. The device is considered for application to the Ford 2.5 litre DI diesel engine, where it may be used to retard inlet valve closure from close to bottom dead centre (BDC) at cranking speed to 50-60 deg after BDC at rated speed.

A novel method for evaluating the source flow ripple and source impedance of positive displacement hydraulic pumps is described. The method is based on the measurement and frequency domain analysis of pressure standing waves in a pipe, and uses a secondary source of pressure ripple for excitation of the pump under test. The method is convenient, accurate and versatile and forms the basis of a new British Standard for measurement of a pump fluid-borne noise rating. Representative results are presented for an oil hydraulic pump and for a plunger pump for water-based fluid.