| 摘要 |
PROBLEM TO BE SOLVED: To suppress power consumption of a heater to thaw frozen urea water by sensing accurately the frozen condition of urea water. SOLUTION: The exhaust emission control device of an engine 14 has a catalyst 18 installed in an exhaust passage 12 to reduce nitrogen oxide in the exhaust gas, a tank 16 to store urea water, a urea water feeding means 22 to feed the urea water from the tank 16 into the exhaust passage 12 located upstream of the catalyst 18, and a level sensor 30 installed inside the tank 16 for sensing the surface level of the urea water by sensing the change in the electrostatic capacitance between a pair of electrodes 30b while the urea water existing between the electrodes 30b is used as dielectric substance, wherein the arrangement further includes the heater 32 to heat the urea water in the tank 16, a frozen condition sensing means to sense the frozen condition of the urea water on the basis of the output value when a voltage is impressed on the pair of electrodes 30b of the level sensor 30, and a heater control means to control the current fed to the heater 32 in accordance with the frozen condition of the urea water sensed by the frozen condition sensing means. COPYRIGHT: (C)2010,JPO&INPIT
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