| 摘要 |
<p>A decision unit carries out several operations. It sends a closing signal for the shutter if the first difference exceeds the first step level or if the second difference exceeds the second step level. The unit sends an opening signal to the shutter if the first and second differences do not exceed the first and second step levels and if then the second difference exceeds the third step value. It sends a maintaining signal to the shutter if the first and second differences do not exceed their step levels and if then the second does not exceed the third step level. The ventilation control system includes at least a gas sensor (10, 12) which delivers a signal representing a ambient air pollution level. An electronic circuit (14,16) responds to the signal by acting on a shutter control unit which admits air into the vehicle (26), so as to avoid air input whose pollution level exceeds a given level. The circuit includes: (a) means to provide, at regular intervals, measurements of the signal amplitude delivered by the sensor; means to calculate a first reference value by the average (short average), of the measurements in a first time interval and a second average reference value (long average) of the measurements in a second time interval greater than the first; means to calculate a first difference between each measure of the short average and a second difference between each measure of the long average, and; a decision unit which compares the first and second differences with set levels and depending upon the result, sends to the control unit an opening or closing signal to the air admission shutter.</p> |
