Abstract

The design of a hydraulic pump or motor with a variable displacement could be much simpler if a rotating valve plate could be used to vary the displacement. An essential aspect of the rotating valve plate is however that the passage of the cylinder ports from one kidney to the other often occurs while the pistons are moving. Experiments have revealed that this leads to high pressure spikes and cavitation. Because of this it is an unwritten rule that in hydraulic pumps and motors the passage of the so-called valving lands has to take place in the top and bottom dead centres.

Against this rule there is a new hydraulic transformer developed (the Innas Hydraulic Transformer or IHT) in which the rotating valve plate is introduced again. In stead of varying the displacement the position of the valve plate now defines the pressure ratio between the load and the supply port. As will be shown this has a crucial effect on the valving land phenomena. In stead of increasing pressure pulsation’s and cavitation the rotating valve plate can now help to reduce these effects.

Keywords: hydraulic transformer, valve plate, pressure pulsations, cavitation