Motor engine having an oxygen sensor

A motor engine having an oxygen sensor, including:

• a cylinder head, including a main body and a protruding tube protruding outwardly from the main body, the main body and the protruding tube being integrally formed of one piece, the main body including a first end portion configured to be assembled to a transmission gear assembly, a second end portion disposed opposite to the first end portion, and a combustion chamber, the second end portion configured to be assembled to a cylinder, the protruding tube having a protrusive receptacle protruding outwardly therefrom, the main body defining an axial direction passing through the first end portion and the second end portion;
• an exhaust passage, communicated with the combustion chamber and the protruding tube;
• wherein the oxygen sensor is inserted into the protrusive receptacle of the protruding tube, the oxygen sensor includes a sensing portion which is inserted into the exhaust passage;
• wherein as viewed in a lateral direction of the cylinder head, the main body has two lateral surfaces disposed on the two opposite sides along the axial direction, the main body defines two boundary lines respectively at least extending along the two lateral surfaces, the oxygen sensor and the main body are in an overlapping arrangement and the oxygen sensor does not protrude out of the two boundary lines;
• wherein the protruding tube has an exhaust opening at downstream of the exhaust the exhaust opening is configured to be connected with an exhaust tube;
• wherein the protruding tube protrudes outwardly relative to an outer surface of the cylinder head, as viewed in the axial direction the oxygen sensor is overlapped with the protruding tube and does not protrude out of the protruding tube.