Patent ID: 8905321

Claim:
A crane having a drive engine, a pump driven by the drive engine, and a hydraulic system for powering main crane functions, and wherein: a) the drive engine is cooled by an engine coolant loop that also directs the coolant to a heat exchanger that thereby provides heat to the operator cab, and b) the hydraulic system includes an auxiliary hydraulic sub-system imposing a horsepower load to the drive engine, the auxiliary hydraulic sub-system comprising: i) at least one pressure reducing relieving valve that limits inlet pressure to the auxiliary hydraulic sub-system in order to protect the sub-system from over pressurization, the inlet pressure being the set point of the pressure reducing relieving valve, which is less than the peak pressure produced by the pump; ii) a coolant temperature detection switch detecting temperature of engine coolant circulated in the engine coolant loop; iii) a solenoid-operated control valve that turns the auxiliary hydraulic sub-system on and off; iv) a pilot operated relief valve that generates and maintains a pressure needed for a desired horsepower load on the drive engine; and v) a controller that responds to a signal from the coolant temperature detection switch indicating that the temperature of the engine coolant is below a predetermined operating temperature causing the solenoid-operated control valve to open and the pump to deliver hydraulic fluid flow to the pilot operated relief valve via the solenoid-operated control valve; vi) the pilot operated relief valve opening upon reaching a set pressure such that the pressure reducing relieving valve, solenoid-operated control valve and the pilot operated relief valve provide a flow rate and pressure to impose a horsepower load on the engine that brings the engine coolant temperature to the predetermined operating temperature.