Experimental investigation on the torque loss of an automobile air conditioning system

An automobile air conditioner (A/C) compressor is usually driven by an engine crankshaft, and thus the A/C system may be considered a device that consumes torque from the engine. In order not to degrade the engine performance, therefore, the torque demand by the A/C system should be predicted and compensated accurately. In the present study, the steady-state A/C compressor torque loss is investigated experimentally. The A/C system is instrumented to measure temperatures of the A/C refrigerant while the vehicle is being driven at several cruise speeds with different outside air temperatures and engine speeds (RPM). Other required data are collected from the sensors that are already implemented to the vehicle. A computer program is written to analyse the data thermodynamically, and thus the compressor torque values are obtained at various vehicle-operating conditions. Finally, the experimental result in the present study is compared with the torque loss map provided by Powertrain Control Module (PCM). The map is re-calibrated based on the present experimental results. In addition, the A/C system performance at different operating conditions is evaluated by examining the isentropic efficiency of the compressor and the coefficient of performance (COP) of the A/C system.