Control Design of a Hydraulic Cooling Fan Drive for Off-Road Vehicle Diesel Engine With a Power Split Hydraulic Transmission

The engine cooling fan drive is crucial for an engine as it ensures safe and efficient engine operation. In heavy-duty mobile machine, the engine cooling fan consumes a considerable amount of engine power. To meet high cooling demand a hydraulic fan drive is usually employed. A simple and cost-effective way is to use two fixed displacement hydrostatic units and a pressure relief valve where it has severe valve throttling losses. A more efficient way is to use a variable displacement pump to drive a fixed displacement motor. It eliminates valve throttling however the drive efficiency is still relatively low due to variable pump displacement control. Therefore, an engine cooling fan drive system with a power split hydraulic transmission was proposed in the previous study. The hydraulic transmission is a compact unit with both pumping and motoring functions. The fan speed is controlled by adjusting the transmission outlet pressure. Although previous results showed the system has relatively higher drive efficiency than conventional hydraulic fan drive at different fan speeds, the control design, and system dynamic performance have not yet been studied. Therefore, in this article, the control design of the cooling fan drive system with power split hydraulic transmission is studied. A feedforward controller based on transmission characteristics is designed to achieve better system performance. A hydraulic fan drive test bench is developed to evaluate system control design. The system dynamic performance with feedforward and feedback controls are compared through both simulation and experimental studies.