| 摘要 |
PROBLEM TO BE SOLVED: To make the clogging of the vent hole of a waterproof case to be detected in an early stage. SOLUTION: When the vent hole of a waterproof case gets clogged, the internal pressure of the case changes in accordance with the variation in temperature, and the differential pressure between the internal pressure P2 of the case and the atmospheric pressure becomes larger. Therefore, the pressure P1 in a suction pipe detected by means of a manifold pressure sensor is read as the atmospheric pressure and, at the same time, the internal pressure P2 of the case is detected by means of an atmospheric pressure sensor installed in the case (steps 201 and 202). Then whether or not the differential pressure between the atmospheric pressure PI and the internal pressure P2 of the case is smaller than a criterion K is discriminated (step 203) and, when the differential pressure is smaller than the criterion K, it is discriminated that the vent hole of the case is not clogged (step 204). When the differential pressure is larger than the criterion K, it is discriminated that the vent hole gets clogged and a warning lamp is turned on (steps 205 and 206).
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