Optimal design of the cross-angle for pulsation reduction in variable displacement pumps

The cross-angle, illustrated in this paper, is a fixed displacement angle around the axis perpendicular to the normal trunnion axis. With the cross-angle, the traditional piston dead centres will change as the normal displacement angle is varied. The result is a behaviour similar to that of the revolving valve plate technique, but without any movable parts. When using the cross-angle in a constant pressure system with a variable pump, the desired dead centre for optimal pre-compression coincides with the obtained dead centre for a wide range of displacement angles. This implies that when the cross-angle is used, the flow ripple becomes less sensitive to changes in displacement angles. The cross-angle does not serve as an alternative to the different design features developed, but rather as a complement for preserved effective flow ripple reduction over a wide range of displacement angles. In this study, non-gradient optimisation techniques, such as genetic algorithms and the Complex method, are used together with extensive simulation models in order to find the optimal cross-angle for a variable displacement pump. Furthermore, with the help of optimisation, the trade-offs between attributes such as low flow ripple peak-to-peak value, avoidance of large cylinder pressure-peaks and cavitation have been studied. Thereby, increased insight is gained into what possibilities the cross-angle offers regarding to reduction of pump ripple for a variable displacement pump.