No abstract

A lv Port opening area of the orifice of the unloading DC valve (m 2) A port Port opening area of the port of the soft switch (m 2) A P_x Port opening area of the DCV (m 2) A ss Area of the piston of the soft switch (m 2) A v Valve orifice area (m 2) C Single port energy storage capacitor element in bond graph model C d Coefficient of discharge C D Coefficient of flow through check valve C ss Radial clearance of the piston of the soft switch (µm) De Effort dictator element in bond graph model Df Flow dictator element in bond graph model D m Volume displacement rate of the hydro-motor (m 3 rad −1) D p Volume displacement rate of the radial piston pump (m 3 rad −1) e Effort in bond graph model E throtloss Throttling energy loss (J) f Flow in bond graph model F preload Preload of the spring of the soft switch (N) I Single port energy storage inertial element in bond graph model J Load inertia of the rotating shaft of the hydro-motor (kg m 2) K Bulk modulus of air free flowing fluid (N m −2

Throttling and fluid compressibility losses are the major losses which occur during the valve transition in a switched mode hydraulic circuit. To minimize the throttling energy loss, a soft switch concept with lock and release mechanism was introduced by different researchers. In the literature, two different kinds of soft switches, one locking and another passive, were introduced in a hydraulic circuit. Thereafter, experimental validation was reported considering only a locking-type soft switch. But the influence of the passive soft switch on the performance of the hydraulic system was not reported. In this article, how the passive soft switch would affect the system efficiency has been investigated through bond graph model simulation. It has been shown both numerically and experimentally by other researchers that the use of a passive soft switch and a locking mechanism, depending upon configuration, can lead to more than 66.1% reduction in throttling energy loss. In this article, it has been further shown that an additional 3.25% throttling energy is saved when the passive soft switch is discarded from the system and only the locking mechanism is retained. The critical parameters of the locking soft switch have been optimized through multi-run simulation and, thereafter, a relationship between the critical parameters of the locking soft switch and the throttling energy loss of the valve has been obtained by using multiple regression analysis. Also, the variations of energy losses with respect to different valve orifice areas, duty cycles, and pulse width modulation frequencies are investigated through simulation.

Different strategies for improving the energy efficiency of a power hydraulic system have been reviewed in this article. The energy-saving scheme is classified into three categories: S ystem design, Improving components or product functions and Loss reduction. The sub-categories of energy-saving strategies are discussed briefly. Also, different energy-saving potentials of power hydraulic system are presented in tabular form for clear understanding on the chronological development toward energy-efficient fluid power system.