An internal combustion engine has a multi-joint crank drive wherein the multi-joint crank driver includes a plurality of coupling members which are rotatably supported on crank pins of a crank shaft and a plurality of hinged connecting rods which are rotatably supported on crank pins of an eccentric shaft wherein each of the coupling members is pivotally connected to a piston connecting rod of a piston of the internal combustion engine and one of the articulation connecting rods. In order to enable to largely or completely compensate inertia forces, it is proposed according to the invention to equip the internal combustion engine with a single balance which serves for neutralizing second order inertia forces.

An offset in-line four cylinder engine has reduced vibration generated by a secondary inertia couple based on lateral pressures from pistons. A reference line passes through a shaft center of a crankshaft and is parallel or substantially parallel to cylinder axes of four cylinders as viewed in the axial direction of the crankshaft. As viewed in the axial direction of the crankshaft, the direction in which the reference line extends is referred to as first direction, and the direction perpendicular to the first direction is referred to as second direction. A distance between the shaft center of a first balancer shaft and the reference line as measured in the second direction is different from the distance between the shaft center of a second balancer shaft and the reference line as measured in the second direction, or a magnitude of a first unbalancing portion is different from a magnitude of the second unbalancing portion.

A balance assembly for an engine is provided. The balance assembly includes a first electric motor coupled to the engine and configured to rotate a first eccentric mass relative to the engine, the first eccentric mass being coupled to a first shaft of the first electric motor, and a second electric motor coupled to the engine and configured to rotate a second eccentric mass relative to the engine, the second eccentric mass being coupled to a second shaft of the second electric motor. The first and second electric motors are configured to rotate the first and second eccentric masses in order to balance a vibration characteristic of the engine.

A force and moment canceling reciprocating mechanism for a power-driven tool may include a transmission including an input gear assembly and an output gear assembly, coupled to a reciprocating mechanism. The input gear assembly may include a first input gear coaxially aligned with a second input gear. The output gear assembly may include a first output gear coaxially arranged with a second output gear. The reciprocating mechanism may be coupled to the output gear assembly, to convert rotational motion to linear motion, for output to an output accessory of the tool. One or both of the first and second input gears may include counterweights, or counterweight masses, and one or both of the first and second output gears may include counterweights, or counterweight masses. The counterweighting of the input and output gear assemblies may provide for the cancelation of forces and moments generated by the operation of the motor and the transmission, and the reciprocal motion of the reciprocating mechanism.

A balancer structure for an internal combustion engine and the internal combustion engine are provided. A transmission driving gear are arranged to be rotatable integrally with a crankshaft. A transmission driven gear is arranged to be rotatable integrally with a first balance shaft. The transmission driven gear meshes with the transmission driving gear. A balancer driving gear is arranged to be rotatable integrally with the first balance shaft. A balancer driven gear is arranged to be rotatable integrally with the second balance shaft. The balancer driven gear meshes with the balancer driving gear. The first balance shaft includes an output portion. The output portion outputs torque to an engine-driven accessory.

Disclosed is a balancer device for an internal combustion engine, wherein: a pump mounting fixing part to which an oil pump is fixed is formed on an end surface of a lower housing member; a gear accommodation part in which a pump driving gear and a reduction gear are accommodated is provided between the oil pump and the pump mounting fixing part; a rigidity-reinforcing part in which an oil discharge passage is defined in communication with a discharge port of the oil pump is formed on the lower housing member so as to extend in a direction of extension of first and second balancer shafts on an outer side of the lower housing member; and a portion of the pump mounting fixing part formed on the end surface of the lower housing member and the rigidity-reinforcing part are made integral with each other.

A piston internal combustion engine with generator has two cylinders and cylinder heads and pistons with connecting rods and two crankshafts which are connected by gears with a ratio of 1:−1 (with opposite direction of rotation). The first crankshaft with the gear is mounted parallel to the second crankshaft with the second gear in one engine case such, that the gears engage. The first crankshaft is coupled to the first generator rotor and the second crankshaft is coupled to the second generator rotor or the flywheel. The moment of inertia of the first crankshaft assembly with the first gear and the first generator rotor is equal to the moment of inertia of the second crankshaft assembly with the second gear and the second generator rotor or flywheel. The cylinders with the pistons and are positioned perpendicularly to the plane of symmetry between the crankshafts, with the axes of the pair of cylinders lying in a plane with the both pistons being at the top dead center simultaneously.

A gear configured to rotate as a unit with a shaft, the gear includes: a plurality of annular grooves formed on both side surfaces of the gear in a direction of a rotation axis of the shaft, at least partially overlapped when viewed from the direction of the rotation axis, and at least partially overlapped in a radial direction with respect to the rotation axis.

Disclosed is a balancer device for an internal combustion engine, wherein: a pump mounting fixing part to which an oil pump is fixed is formed on an end surface of a lower housing member; a gear accommodation part in which a pump driving gear and a reduction gear are accommodated is provided between the oil pump and the pump mounting fixing part; a rigidity-reinforcing part in which an oil discharge passage is defined in communication with a discharge port of the oil pump is formed on the lower housing member so as to extend in a direction of extension of first and second balancer shafts on an outer side of the lower housing member; and a portion of the pump mounting fixing part formed on the end surface of the lower housing member and the rigidity-reinforcing part are made integral with each other.

Balancer device has upper and lower housings 3 and 4 having therein an accommodation section 10, a pair of drive and driven side shafts 5 and 6 which are rotatably supported by four plain bearings 11 to 14 provided in the accommodation section and to which a rotation force is transmitted from a crankshaft, and arc band-shaped thrust receiving portions 32a and 33a which thrust flange portions of drive and driven gears 8 and 9 provided at the drive and driven side shafts respectively can contact from a thrust direction. First and second oil storing grooves 34 and 35, groove passages 36 and 37 and vertical groove passages 38a to 39b are formed at the thrust receiving portions on a gravity direction lower side with respect to a meshing portion of the both gears. With this configuration, it is possible to suppress occurrence of abrasion of the thrust receiving portion.