Patent ID: 7487647

Claim:
Method for controlling air-conditioning systems having an expansion valve which is positioned between an external heat exchanger on the high pressure side and an internal heat exchanger on the low pressure side having a valve housing, in which an entry pressure is present in a feed opening on the high-pressure side and an exit pressure is present in a discharge opening on the low-pressure side, having a valve-closure member, which is moved in the opening direction out of a valve seat of a passage opening, which is arranged between the feed opening and the discharge opening, to allow the refrigerant to flow through and having an opening or closing movement of the valve-closure member over a range which is at least partially to be regulated is controlled as a function of the level of a pressure difference between the entry pressure of the feed opening and the exit pressure of the discharge opening, wherein said method comprises the steps of: determining a coefficient of performance for the range to be regulated for the opening and closing movement of the valve-closure member, which is defined by the ratio between the refrigerant capacity of the internal heat exchanger and a working power of the compressor, determining the optimum of the coefficients of performance in the supercritical range and the sub-critical range by the maximum refrigeration capacity for the lowest possible working power of the compressor, and deriving from the optimum of the coefficients of performance the opening characteristic curve of the valve-closure member, which is determined based on the respective pressure difference between the high and low pressure side, on the temperature upstream of the valve-closure member and on the mass flow.