Individual throttle-type or unequal interval combustion-type multi-cylinder engine unit

A multi-cylinder engine unit of an individual-throttle type or an unequal-interval-combustion type, comprising:

• a plurality of cylinders respectively cooperating with a plurality of pistons to define a plurality of combustion chambers;
• a plurality of individual exhaust pipes corresponding to the plurality of cylinders, and being configured to allow exhaust gases from the plurality of cylinders to respectively flow therethrough;
• an exhaust manifold, including:
• a merge portion into which the plurality of individual exhaust pipes merge, and
• a catalyst disposed downstream of the merge portion in a flow direction of the exhaust gas;
• a pre-catalyst oxygen sensor group for detecting a first percentage of oxygen in the exhaust gas, the pre-catalyst oxygen sensor group being disposed between the plurality of cylinders and the catalyst for all paths of the exhaust gases flowing into the catalyst from the plurality of cylinders;
• a post-catalyst oxygen sensor for detecting a second percentage of oxygen, the post-catalyst oxygen sensor being disposed in the exhaust manifold, and downstream of the catalyst in the flow direction of the exhaust gas;
• and
• a control device configured to
• detect a cylinder-to-cylinder imbalance in air-fuel ratio between the plurality of cylinders using a detection result obtained by the pre-catalyst oxygen sensor group, and
• detect a deterioration of the catalyst using at least a partial detection result obtained by the pre-catalyst oxygen sensor group and a detection result obtained by the post-catalyst oxygen sensor,
• without using an air-fuel ratio sensor, wherein
• the pre-catalyst oxygen sensor group includes a plurality of oxygen sensors that is equal in number to the plurality of individual exhaust pipes, each oxygen sensor detecting the first percentage of oxygen in the exhaust gas flowing in a different one of the plurality of individual exhaust pipes.