Abstract
The load sensing (LS) hydraulic architecture is the predominant architecture for mobile fluid power systems in agricultural tractor applications. LS systems provide good flow control to multiple actuators supplied by a single pump, minimize load disturbances, and provide higher efficiencies when compared to many other multi-actuator control structures. However, current implementations often do not take advantage of modern advancements in electro-hydraulic (EH) controls. A significant portion of available hydraulic power is used to maintain a constant pressure drop across the control valves. This article details experimental implementation and testing of a control strategy known as hybrid variable margin (HVM) on the pre-compensated LS system of a large row-crop tractor. HVM consists of an electronically controlled variable-displacement pump replacing the traditional pressure and flow compensated pump as well as introducing an electronic proportional pressure-reducing valve (ep-PRV) in the pilot line of the local pressure compensator (LPC). This gives the flexibility to control the pressure differential across the main control valve spool as well as varying the pump margin to suit the operating conditions. Experimental tests with one hydraulic function show an increase in hydraulic efficiency of 5.6% and a 6.2% reduction in the fuel consumption of the hydraulic system when operating in non-boundary conditions. Tests with two hydraulic functions show a hydraulic efficiency gain of 4.5% with a 12.2% decrease in fuel consumption by the hydraulic system.
