A crankshaft in which vibrations can be damped effectively without changing a design of a crankcase. The crankshaft comprises a first crank section located at one end of the crankshaft, and a second crank section located at the other end of the crankshaft. In the first crank section, a mass of a first inner balance weight is greater than a mass of a first outer balance weight. In the second crank section, a mass of a second inner balance weight is greater than a mass of a second outer balance weight.

A crankshaft in which vibrations can be damped effectively without changing a design of a crankcase. The crankshaft comprises a first crank section located at one end of the crankshaft, and a second crank section located at the other end of the crankshaft. In the first crank section, a mass of a first inner balance weight is greater than a mass of a first outer balance weight. In the second crank section, a mass of a second inner balance weight is greater than a mass of a second outer balance weight.

Embodiments are directed toward an engine. In some embodiments, the engine includes a water pump and a balancer shaft. In some embodiments, the water pump has a plain bearing. In some embodiments, plain bearing is supplied with pressurized oil. In some embodiments, the balancer shaft drives the water pump as well as cam shafts.

Lubricating oil has a kinematic viscosity in a range of 1 mm.sup.2/S to 7 mm.sup.2/S at 40° C., has a mass average molecular weight in a range of 150 to 400, and contains 0.5% by mass or more of a high molecular weight component. The high molecular weight component has a mass molecular weight of greater than or equal to 500. A crankshaft serving as a shaft part of a compression element includes a main shaft that includes a sliding surface. In a case where the sliding surface is a single sliding surface, a length of the single sliding surface in an axial direction is a single sliding length L, whereas in a case where the sliding surface is divided into a plurality of sliding surfaces, a length of one of the sliding surfaces in the axial direction, the one sliding surface having a least length in the axial direction among the plurality of sliding surfaces, is the single sliding length L, and a ratio L/D of the single sliding length L to an external diameter D of the main shaft is less than or equal to 2.0.

Systems and methods are described for a reciprocating mechanism. The system includes at least one axially translating y-axis component configured to reciprocate substantially along a y-axis with a reciprocating motion of a piston assembly relative to a base. The system also includes at least one x-axis component slidingly coupled via at least one bearing assembly to and translating with the at least one y-axis component along the y-axis. The at least one x-axis component is configured to reciprocate substantially perpendicularly to the y-axis relative to the at least one y-axis component, and includes an orbital output component and an orbital linking component disposed substantially concentric with the orbital output component. The system also includes a stationary output component rotatably attached to the base in a direction that is substantially perpendicular to both the x-axis and y-axis, and a stationary linking component rotatably attached to the base in a direction that is substantially concentric with the stationary output component.

An internal combustion engine, including a pair of opposed pistons, a pair of opposed cylinders, and an output shaft, wherein each of the pistons is arranged for reciprocating motion within a respective one of the cylinders, driven by combustion, and the pistons are coupled to the output shaft by a coupling such that said reciprocating motion of the pistons drives rotation of the output shaft, wherein the coupling includes a connecting rod coupled to the opposed pistons, and the coupling further includes a crankshaft rotatably mounted within a slider bearing, the slider bearing being formed of separable parts and having unitary sides for sliding contact within the connecting rod.

Presented are crankshaft assemblies with internal stiffening structures, methods for making/using such crankshaft assemblies, and internal combustion engines equipped with such crankshaft assemblies. A crankshaft body, which is formed with a first material, includes multiple bearing journals that are mutually coaxial to rotate on a crankshaft axis and spaced from each other along the length of the crankshaft. Each bearing journal has an internal journal cavity. Multiple crankpins are longitudinally spaced from each and axially offset from the crankshaft's rotational axis. Each crankpin has an internal crankpin cavity. Multiple crank webs project radially from the crankshaft axis and interconnect the bearing journals with the crankpins. Each crank web has an internal web cavity. Disposed within the journal cavities, crankpin cavities, and/or web cavities is a stiffening bar formed with a second material having a modulus of elasticity that is greater than the modulus of elasticity of the first material.

Presented are crankshaft assemblies with internal stiffening structures, methods for making/using such crankshaft assemblies, and internal combustion engines equipped with such crankshaft assemblies. A crankshaft body, which is formed with a first material, includes multiple bearing journals that are mutually coaxial to rotate on a crankshaft axis and spaced from each other along the length of the crankshaft. Each bearing journal has an internal journal cavity. Multiple crankpins are longitudinally spaced from each and axially offset from the crankshaft's rotational axis. Each crankpin has an internal crankpin cavity. Multiple crank webs project radially from the crankshaft axis and interconnect the bearing journals with the crankpins. Each crank web has an internal web cavity. Disposed within the journal cavities, crankpin cavities, and/or web cavities is a stiffening bar formed with a second material having a modulus of elasticity that is greater than the modulus of elasticity of the first material.

An internal combustion engine is provided, which includes an engine body provided with a cylinder and a piston reciprocatably accommodated in the cylinder, a crankshaft that converts reciprocating movement of the piston into rotational movement, and a bearing member pivotally supporting the crankshaft via lubricating oil. The crankshaft includes a crank journal pivotally supported by the bearing member, and a counterweight extending radially outward from an axial end part of the crank journal. The crank journal has a recess formed in a part thereof corresponding to the extended position of the counterweight, the recess being depressed radially inwardly. The recess is deeper at the axial end part of the crank journal than an axial center part.

An engine device having a flywheel housing in which a flywheel that is rotated integrally with a crankshaft is accommodated on one side portion of a cylinder block, in which the cylinder block is integrally formed with housing bracket portions each protruding in a direction away from the crankshaft from each of opposite side portions of the cylinder block extending along a crankshaft axial direction, the housing bracket portions protruding from end portions of the opposite side portions close to the one side portion, and a space surrounded by the one side portion, the housing bracket portions, and the flywheel housing constitutes a gear case for accommodating therein a gear train.