Thermo-Hydraulic Oil Loop Modeling for I.C.E. Warm-Up Investigation 2002-01-2197
Fuel consumption after a cold start remains one of the major goal of carmakers. The high friction losses due to a low oil temperature are the main sources of the consumption excess during the warm-up.
To improve the prediction of these losses, the local oil temperature in friction areas must be well represented. The local equilibrium temperature depends both on the heat flux generated by friction and on the oil flow rate. The aim of this work is to represent the thermo-hydraulic behavior of oil loops during the warm-up of a cold start.
Oil pump efficiency is evaluated considering Poiseuille and Couette flow contributions on the leaks of the pump. Computed results are validated on results gained on a test bed. The hydraulic behavior of bearings is modeled from a theoretical approach. The effects of bearing deformation are rendered by a global elasticity coefficient calibrated from results in a previous paper. Turbo compressor flow rate is expressed like bearing flow and calibrated from experimental results. Piston cooler flow rate deduced from the others terms, follow the same trend as the Hagen-Poiseuille law adapted to laminar flows in circular pipes.
A hydraulic network is build from the modeling of each component. The resolution of this network gives pressures and flow rates in each branch of the circuit. The model allows predicting oil flow rate evolution and distribution during warm-up and for a large range of running conditions (speed and load).
The computed energy balance of bearings is obtained by coupling thermal (lumped capacity model) and hydraulic models. To get good results, the crankshaft must be described by smaller lumped capacitance.
So we get a thermo-hydraulic tool to evaluate the effects for instance of the bearings clearance on oil temperature rise and friction losses during the warm-up.