PURPOSE: To prevent the burn and abrupt deterioration of a heating element by setting a reference value for discriminating the absolute pressure in an intake pipe of an engine according to the magnitude of the atm. pressure and stopping the supply of electric current to the heating element when the absolute value in the intake pipe is above the reference value.
CONSTITUTION: An atm. pressure sensor 33 is provided to an air-fuel ratio control circuit 32 and the reference value for discriminating the absolute value in an intake manifold 23 according to the atm. pressure is set. On the other hand, an absolute pressure sensor 27 is provided to the manifold 23 and the level output corresponding to the intake absolute pressure in the manifold 23 is generated. The high load is discriminated and the supply of the current to the heating element is stopped when the intake absolute pressure above the reference value is detected by the circuit 32. The atm. pressure decreases in a high place as compared to a low place but the reference value decreases accordingly and therefore the high load condition of the engine is exactly discriminated even in the high place. The abrupt overheating of the heating element is averted by stopping the current supply to the heating element even if the exhaust gas concn. rises higher than the temp. obtd. by the heating element under the high load. The burn and abrupt deterioration of the heating element are thus prevented.
ASAKURA MASAHIKO
UEDA YASUHIRO
SEKI YASUNARI
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