In an internal combustion engine, an oil return passage extending from a breather chamber can be formed without increasing the number of component parts and without increasing the size of the internal combustion engine. The internal combustion engine (1) comprises an engine block (30) defining a cylinder (2); a case member (19) fastened to a lower part of the engine block to define a crank chamber jointly with the engine block; a bearing member (50) fastened to the engine block in the crank chamber to rotatably support a crankshaft; a breather chamber (113) defined in the engine block; an inlet passage (112) formed in the engine block to communicate the crank chamber with the breather chamber; a connection pipe (114) communicating the breather chamber with an intake device; and an oil return passage (150) formed at least in the bearing member, and extending from a bottom part of the breather chamber to an oil return port (147) opening at an outer surface of the bearing member. The oil return port may be provided in a lower part of the bearing member.

An internal combustion engine includes a crankshaft. The crankshaft includes multiple crank journals, at least two crank pins positioned between two of the multiple crank journals that neighbor one another, and at least one pin arm. Each pin arm may be positioned between two of the crank pins neighboring one another. Arrangements may include multiple crankshaft supports and multiple thrust bearings. These elements may be distributed about the crankshaft such that two or more of the multiple crankshaft supports have at least one associated thrust bearing. Each of the crankshaft supports having the associated thrust bearing may support one of the multiple the crank journals. Each thrust bearing may be positioned between the crankshaft and the crankshaft support having the associated thrust bearing.

A sliding bearing that is disposed in a cylinder block and supports a journal portion of a crankshaft, including: a semi-annular first split bearing having a first circumferential end surface; and a semi-annular second split bearing having a second circumferential end surface. The first and second circumferential end surfaces contact each other, the first split bearing has a same outer diameter as an outer diameter of the second split bearing, the second split bearing has a thickness at a second circumferentially central position that is greater than a thickness of the first split bearing at a first circumferentially central position, the thickness of the first split bearing is decreased from the first circumferentially central position toward the first circumferential end surface, the thickness of the second split bearing is decreased from the second circumferentially central position toward the second circumferential end surface.

A cylinder block for an internal combustion engine includes a metal section and a resin section. The metal section includes: a cylinder liner; head bolt female screw portions that are screwed onto male screw portions of head bolts that fasten the cylinder block and a cylinder head; crank cap bolt female screw portions that are screwed onto male screw portions of crank cap bolts that fasten the cylinder block and crank caps and columnar portions that connect the head bolt female screw portions; and the crank cap bolt female screw portions. The cylinder liner and the columnar portions are integrated with each other.

A cylinder block has a different amount of oil supply for each journal, in which a plurality of bearing saddles are arranged at intervals and main bearings, which support main journals of a crank shaft, are respectively mounted to the plurality of bearing saddles. The bearing saddles comprise oil galleries formed in the cylinder block. Oil chambers are recessed from surfaces of the plurality of bearing saddles, to which an oil is supplied through the oil galleries, and communicate with end portions of the oil galleries to store the oil supplied from the oil galleries. The main bearings have oil holes through which the oil introduced into the oil chambers flow to the main journals. The amount of oil supplied to the main journals is determined according to an overlapped amount between the oil chambers and the oil holes.

A bearing cap (1) is attached to a bulkhead (22) of a cylinder block (21) made of a light metal through a pair of bolts (24). The bearing cap (1) has a frame (2) made of an iron-based metal and a cast light-alloy part (3). The frame (2) has a pair of pillar parts (9) through which the bolts (24) extend and a circular-arc-shaped arch section (10). At high temperatures, the span of the pair of the bolts (24) increases due to thermal expansion of the light-alloy material, and the pair of the pillar parts (9) expand. This causes the middle part of the arch section (10) to shift upward, thereby suppressing an increase in bearing clearance.

An engine bed plate includes a plurality of partition walls provided in a casing and dividing an interior of the casing to define a plurality of crank chambers. A first ventilation hole is provided in a front wall and each of the plurality of partition walls. The first ventilation hole is formed in a horizontal direction to ventilate the plurality of crank chambers.

The bearing apparatus 1 includes a crankshaft having multiple journals, main bearings supporting the crankshaft, and a bearing housing. The plurality of journals include a first journal with a lubricating oil passage and a second journal without a lubricating oil passage. The first and second journals are supported by first and second main bearings, respectively. The bearing housing is constituted by an Al-alloy upper housing and an Fe-alloy lower housing. The depth of the oil groove of the upper half bearing of the second main bearing at least in a ±45° region is equal to or smaller than a half of the depth of the oil groove of the upper half bearing of the first main bearing in the ±45° region.

A first angle portion where part of a bearing cap side wall portion is cut out and a second angle portion where part of a bearing cap bottom surface portion is cut out are formed in a region (an angle region of a bearing cap) including a part where respective extension portions of the bearing cap side wall portion and the bearing cap bottom surface portion intersect each other, and a gap is provided between the crankcase side wall portion of a journal wall and the first angle portion and between a crankcase bottom surface portion and the second angle portion.

Described is a crankcase and a method for assembling a multi-part crankcase. The method can include providing a cylinder block and a bearing tunnel upper part. The cylinder block has a plurality of threaded holes into each of which a stud screw is screwed, where the stud screws protrude from the cylinder block. The bearing tunnel upper part has a plurality of through-holes, where each of the through-holes is arranged coaxially to a corresponding stud screw. On a side facing the cylinder head, each of the through-holes has an internal thread having a first direction of rotation. A plurality of threaded sleeves, each threaded sleeve has an internal thread that has a second direction of rotation, an external thread that has a first direction of rotation, and a driver profile for inserting a screwdriver tool in a positive-locking manner, are provided.