Energy Saving Analysis Using a Four-Valve Independent Metering Configuration Controlling a Hydraulic Cylinder

The field of earth moving equipment is experiencing a transformation due to the introduction of more electronic control capability and advanced control concepts. Conventional hydraulic control systems are controlled by proportional directional spool valve. The construction of the spool valve is such that a given position of the spool determines the flow in and the flow out restriction sizes. Thus, metering in and metering out are dependent or coupled. A certain restriction size on the inlet corresponds to a certain restriction size on the outlet. Therefore, we have one degree of freedom. It can provide for good motion control but it cannot achieve energy saving potential at the same time.

In this paper, the concept of ‘independent meter in / meter out’ will be emphasized. Decoupling of meter in from meter out provides for more controllability and potential for energy saving in overrunning load cases when compared with a conventional spool valve controlled hydraulic system. A four-valve configuration controlling a hydraulic cylinder will be stressed. The four-valve configuration can operate in several modes because each of the four valves is controlled separately from the others. Five of these metering modes will be pointed out.

The independent metering configuration promises more energy savings when compared to the operation of the conventional spool valve controlled systems. This paper attempts to mathematically validate this hypothesis. It will be assumed that the independent metering configuration valve assembly is operating in a Pressure Compensated Load Sense control environment which is the conventional control system on most existing earth moving equipment. It will be shown that by regulating the back pressure, which is possible when using the independent metering configuration, the system can save energy when compared to a spool-valve controlled system.