TOWARD ADAPTIVE, MULTI-MODAL, HIGH-EFFICIENCY HYDRAULIC CONTROLS FOR AGRICULTURAL TRACTORS AND IMPLEMENTS

Modern agricultural operations require the use of high-power, technologically advanced offroad vehicles to maintain productivity; agricultural tractors like this rely on fluid power for actuation and propulsion due to the many advantages it can offer over other forms of power transmission. While portions of the hydraulic system have kept pace with recent advances in technology, the fundamental operating principle of the primary hydraulic circuits within an agricultural tractor, a load-sensing (LS) system, has remained unchanged. The LS system provides many benefits, as it allows a single pump to supply multiple actuators without sacrificing controllability and it consumes less power than previous architectures - a primary concern of mobile hydraulics. However, the LS system still wastes a sizable portion of its energy in the control valves. Significant research has been dedicated to improving this system but the architecture of a tractor poses unique challenges to implementing these high-efficiency solutions. Unlike vehicles such as excavators and wheel loaders which have a well-defined “fixed” hydraulic architecture, the tractor must not only power its onboard functions but also power a wide variety of external implements through its auxiliary hydraulic valves. These valves face distinct operating conditions which must be addressed with different control strategies. This work implements and tests the performance of several high-efficiency solutions on the high-pressure hydraulics of a 400 H.P. agricultural tractor under a wide range of operating conditions. Three solutions address the auxiliary valve's throttling losses but achieve this by different methods, reaching up to 16% efficiency improvement over baseline. When the tractor powers more advanced implements, however, the above solutions are ineffective. A control conflict between the tractor and implement can cause hydraulic efficiency to drop as low as 25% which significantly increases required engine power. Several solutions are tested to remedy this by incorporating new electrohydraulic controls and communication, or by adapting older state-of-the-art technology. The best of these solutions raises efficiency to 39% in one case, resulting in an average savings of 23.65% (normalized) hydraulic power and up to 2.5 L/hr reduction in fuel consumption. The final contribution of this work is creating an autonomous, adaptive pump control scheme to solve the control conflict with implements that are not suitable for other solutions either due to lack of equipment of incompatible communication. This solution requires no input signal from the implement, instead using only signals available on the tractor to optimize the pump delivery pressure and increase system efficiency. Experimental tests on the tractor-implement system show up to a 45.5% reduction in hydraulic power of the pump, corresponding to an increase of the overall system energy efficiency of 26.2%.