| 摘要 |
PROBLEM TO BE SOLVED: To enable accurate metering of a mixture by installing oxygen sensors before starting catalysts that are provided in a prescribed arrangement in each of distribution pipes of an exhaust system and installing an additional oxygen sensor after the starting catalyst of at least one distribution pipe. SOLUTION: In a six-cylinder engine 10, in which each of exhaust passageways of three cylinders is connected to exhaust distribution pipes 12, 14, advance catalysts, i.e., starting catalysts VK1, VK2, are provided in a prescribed arrangement in each of the distribution pipes 12, 14. A main catalyst HK is provided in a prescribed arrangement at a location downstream from the advance catalysts VK1, VK2 in a main pipe 20 that connects the distribution pipes 12, 14. An oxygen sensor is installed in each of the distribution pipes 12, 14 before the advance catalysts VK1, VK2. To determine aging action of these oxygen sensors 26, 28, jump type oxygen sensors 30, 24 are located at a downstream side of the advance catalyst VK1 and at a downstream side of the main catalyst HK, respectively. In addition, a temperature sensor 32 is provided in a place downstream from the advance catalyst VK2.
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