Complexed cylinder block

A composite cylinder block, comprising a main block body made of a metal material and an outer member made of a synthetic resin material and heat-welded to the main block body by heating of the main block body,

• wherein the main block body comprises:
• a lower deck plate-shaped along a plane orthogonal to a cylinder axis direction, a lower surface of the lower deck including a heated surface to which heat is applied during heat welding;
• a base part provided on an upper surface of the lower deck;
• a plurality of cylinder walls standing upward from a top surface of the base part while being surrounded by the outer member surrounding to define a water jacket between the cylinder walls and the outer member, the cylinder walls defining therein cylinder bores with lower ends of the cylinder bores being open at the lower surface of the lower deck;
• and
• a main bearing part protruding downward from the lower surface of the lower deck,
• wherein the main block body has a flat main-block-side mating surface defined by the top surface of the base part around the cylinder walls,
• wherein the outer member has a flat outer-member-side mating surface,
• wherein a welding rib is provided on the outer-member-side mating surface in the form of a bead extending continuously over an entire circumference around the plurality of cylinder walls so that the outer-member-side mating surface and the main-block-side mating surface are welded to each other with melting of the welding rib, and
• wherein the entire welded surfaces of the main block body and the outer member are in one plane orthogonal to the cylinder axis direction.