Improving Winter Fuel Economy by Using Weather Information

When the air conditioning (A/C) is turned on, for a cabin climate control system in vehicles, the compressor operation starts and the intake air to the HVAC is to be cooled after the evaporator. This is not only used for cooling the air temperature but also to dehumidify the air. Therefore, even in winters, for a typical automatic climate control system, compressor will automatically operate in order to prevent window from fogging despite its effect on fuel economy. In this process, the air is first cooled to get dried and then heated at the heater core so as to provide dry and hot air to the cabin. As a previous implementation, a humidity sensor was installed on the upper top of the wind shield. Humidity sensor detects the humidity on the wind shield surface and when the probability of window fogging is low the compressor operation is disabled automatically so that we can prevent useless operations of the compressor and increase fuel economy. However, humidity sensor requires some space to be installed and the cost is relatively expensive compared with other HVAC equipped sensors. In this study, we invented a system that disables the compressor operation when the fogging probability is low without using the conventional humidity sensor. In this system, we obtain real-time weather information from out-car database with data communication module (DCM) which will be standardly equipped in upcoming Toyota vehicles. We built a control logic that judges if the probability of window fogging is high or low in the undergoing situation by using weather information. As a result of real-world driving test for two months in Aichi, Japan, the system reduced 60% of compressor operation in winters and demonstrated 1.5% improvement in fuel consumption.