A counterweight forms a crankshaft of an engine, and includes: an arm connecting a crank journal and crank pin of the crankshaft; a neck extending from a first connection face of the arm in a direction opposite to the crank pin; and a substantially fan-shaped weight continuous with a portion of the neck opposite to the crank journal. The weight has left and right shoulders continuous with the neck, and each of the shoulders is tilted to be away from the neck at an angle with respect to a horizontal line orthogonal to a crankshaft center when viewed along the crankshaft center, the angle being 15 or more and 22.5 or less.

An internal combustion engine including at least two cylinders with parallel longitudinal axes, each cylinder including an opening and a piston capable of moving in translation inside the cylinder, the respective openings of the cylinders facing each other, the pistons being in kinematic relation with a connecting rod-crank mechanism including: a spacer connecting the pistons, suitable for maintaining a fixed spacing between the pistons, the pistons being respectively attached to the arms of the spacer, a crankshaft rotating about an axis, arranged between the openings of the cylinders and between the longitudinal axes of the cylinders, the crankshaft comprising a crank pin, a rocker rotating about the crank pin, at least one connecting rod including a first so-called bottom end, rigidly attached to the spacer and a second so-called head end, rigidly attached to one of the ends of the rocker.

A camshaft assembly includes a base shaft, an axially movable structure having a barrel cam and a plurality of lobe packs, and an actuator. The barrel cam defines a single control groove having an enlarged region and a converged region. The actuator includes an actuator body with first and second pins. Each of the first and second pins moves relative to the actuator body between a retracted position and an extended position. The axially movable structure may move from a first position to a second position when the second pin rides along at least a portion of a second side of the enlarged region and then enters the converged region. The axially movable structure may also move from a second position to a first position when the first pin rides along at least a portion of a first side of the enlarged region before entering the converged region.

An internal combustion engine includes a crankshaft including an outer crankshaft gear and an in-line balance shaft system coupled to the crankshaft. The in-line balance shaft system is configured to balance reciprocating inertial forces of the internal combustion engine, the in-line balance shaft system is configured to provide concurrent and counter-rotating balance forces. The in-line balance shaft system includes a planetary gear set coupled to the crankshaft. The planetary gear set is coupled to the outer crankshaft gear such rotation of the crankshaft drives the planetary gear set. The planetary gear set includes an input gear and an output gear. The input gear is coupled to the crankshaft such that rotation of the crankshaft causes rotation of the input gear.

An engine includes: a cylinder head that forms an intake port connected to a combustion chamber; a throttle body that is joined to the intake port and adjusts a degree of an opening of an intake passage by rotating a throttle vale around a rotation axis of a valve shaft, the throttle vale being fixed to the valve shaft; and a case that stores a drive member and supports a drive motor, the drive member being fixed to the valve shaft, the drive motor generating a drive force that is transmitted to the drive member. The case overlaps with the intake port as seen in a side view. Accordingly, in the engine, it is possible to reduce the volume of the intake passage between the throttle valve and the combustion chamber.

Intake ports include a second port configured such that a flow rate of flowing gas is adjusted via a swirl control valve. When a surge tank is viewed in a cylinder axis direction, first and second branched passages are connected with a space being interposed therebetween in a cylinder array direction, and are connected to the surge tank on extension lines, each of which extends from an upstream end portion of an independent passage connected to the second port to an opposite side of each cylinder.

An internal combustion engine includes one or more unopposed cylinder units where each cylinder unit drives the crankshaft via a yoke assembly rather than a conventional connecting rod. The yoke assembly is formed by a connecting rod assembly that can have an upper portion having a connecting member connected to the piston, and a lower portion. The connecting rod assembly moves exclusively along the bore axis of the cylinder, with no side to side motion. The connecting rod assembly also defines a transverse slot in the yoke portion in which a connecting rod bearing housing reciprocates with motion of a connecting rod journal on the crankshaft within the transverse slot. Since the motion of the connecting rod is linear, and the connecting rod bearing housing moves circularly, there are no secondary forces resulting in an inline engine using the unopposed cylinder unit configuration.

An internal combustion engine includes a reduction gear including: at one end thereof, a small-diameter gear in mesh with a one-way clutch gear; and at an opposite end thereof, a large-diameter gear in mesh with a drive gear of a starter motor. The starter motor has a driveshaft disposed below a rotation axis of the reduction gear and within a width of the large-diameter gear as viewed in an axial direction. Accordingly, in the internal combustion engine, it is possible to efficiently dispose components in a reentrant space formed between a crankcase and a cylinder block.

A cylinder unit includes a piston disposed in the cylinder bore that is connected to a piston connecting frame member. The piston connecting frame member replaces a conventional connecting rod, and reciprocates exclusively along the bore axis. A crank connecting member has a linear rail at its top that is captured in a transverse gap along the bottom of the piston connecting frame member, and converts the circular movement of a crank throw to linear motion of the piston connecting frame member.

To provide an internal combustion engine that can be manufactured at low cost and be downsized by simplifying its lubrication system in the crankcase. An engine 9 includes: a crankcase; a cylinder equipped with a cylinder bore; a crankshaft; a balancer mechanism for reducing vibration of the engine by power transmitted from the crankshaft; a breather chamber provided on a top surface of the crankcase and disposed behind the cylinder; and a lubrication system for supplying lubricating oil to the crankshaft and the balancer mechanism. The balancer mechanism includes a first balancer disposed at a position farther from the cylinder bore than an idler gear. The lubrication system includes a balancer lubricating-oil passage branching off from a main gallery and reaching the first balancer across the breather chamber in a plan view.