Hydraulic Flow Ripple Cancellation Using the Primary Flow Source

Flow ripple is generally considered to be a negative attribute of positive displacement units as the resulting pressure ripple can cause unsteady behavior in the overall system as well as generate significant audible noise that can spread throughout the entire hydraulic system. Passive methods of attenuating pressure ripple have included both pump design and adding compliant elements such as pulsation dampers and Helmholtz-style resonators that are often limited in their effectiveness and introduce compromises with regards to system size and response time. Active techniques have also been investigated and typically seek to employ a secondary flow source to actively cancel the flow pulsations, often with the use of feedback sensors such as pressure transducers. Some techniques using speed variation of the pump have been investigated theoretically and pointed to the limitations of the technique when applied to piston pumps of a certain size. This paper will discuss the theory and implementation of a feed-forward motor torque control algorithm to reduce flow ripple and therefore pressure ripple by influencing the speed of a relatively-high volumetric displacement low-inertia pump through open loop control of the driving motor torque. The application under consideration is that of a gerotor pump/motor in lockstep fluid communication with a compact hydraulic actuator. The commercial application for the compact hydraulic actuators used in this study is for use as localized force sources in a fully active suspension system of sedan-sized automobiles.