A moment-cancelling, four-stroke engine is disclosed. The engine includes a first cylinder having a first piston and a second cylinder having a second piston, a first crankshaft operably connected to the first piston and a second crankshaft operably connected to the second piston. The first crankshaft rotates in a first direction and the second crankshaft rotates in a second direction that is opposite the first direction to cancel the moments applied to the engine and reduce engine vibration.

A moment-cancelling, four-stroke engine is disclosed. The engine includes a first cylinder having a first piston and a second cylinder having a second piston, a first crankshaft operably connected to the first piston and a second crankshaft operably connected to the second piston. The first crankshaft rotates in a first direction and the second crankshaft rotates in a second direction that is opposite the first direction to cancel the moments applied to the engine and reduce engine vibration.

A poppet valve has an elongated stem that is configured to extend along a longitudinal axis. The poppet valve further includes a valve body that is disposed laterally with respect to the longitudinal axis and located in a spaced apart relation with an end of the elongated stem. The valve body has a pair of opposing faces disposed co-axial with the longitudinal axis of the elongated stem. The poppet valve also includes at least two arcuately shaped appendages depending downwardly from the end of the elongated stem and extending away from the longitudinal axis of the elongated stem. An end of each appendage is disposed in abutment with an annular region defined on one of the opposing faces of the valve body, a perimeter of the annular region being larger than a perimeter of the elongated stem measured about the longitudinal axis.

Provided is an internal combustion engine including a sparkplug disposed in the vicinity of the center portion of an upper wall surface of a combustion chamber. Tumble flow generated during lean burn operation is controlled such that the tumble flow shape changes according to the engine rotation speed between a first tumble shape (usual tumble shape) in which the flow direction of a gas around the sparkplug at the time of ignition is direction from an intake valve side toward an exhaust valve side in a latter half of a compression stroke, and a second tumble shape ( tumble shape) in which the flow direction of the gas is reversed in the latter half of the compression stroke from the direction from the intake valve side toward the exhaust valve side to the direction from the exhaust valve side toward the intake valve side.

Provided is an internal combustion engine including a sparkplug disposed in the vicinity of the center portion of an upper wall surface of a combustion chamber. Tumble flow generated during lean burn operation is controlled such that the tumble flow shape changes according to the engine rotation speed between a first tumble shape (usual tumble shape) in which the flow direction of a gas around the sparkplug at the time of ignition is direction from an intake valve side toward an exhaust valve side in a latter half of a compression stroke, and a second tumble shape ( tumble shape) in which the flow direction of the gas is reversed in the latter half of the compression stroke from the direction from the intake valve side toward the exhaust valve side to the direction from the exhaust valve side toward the intake valve side.

An intake valve for an internal combustion engine is provided. The intake valve includes a valve stem with a hole in the valve stem forming an air channel there through that allows intake air to flow from an intake passage, through the air channel, into a cylinder of the internal combustion engine.

Methods and systems are provided for generating tumble in intake air by creating an asymmetrical annulus opening for flowing intake air into a combustion chamber of an engine cylinder. The asymmetrical annulus opening may be created by changing an angle of an intake valve disc of an intake valve. The angle of the intake valve disc may be varied based on engine operating parameters by extending or retracting one or more connect rods coupled to an annulus tumble guide movably housed inside an annulus channel.

A metallic hollow valve for an internal combustion engine of a utility vehicle may include a tubular valve stem and a valve head merging into the valve stem. The valve head may have an outer diameter that is enlarged compared to the valve stem. The valve stem and the valve head may together delimit a hollow space. The valve stem may have an outer diameter of more than 7 mm, for example between 8 mm and 11 mm. The valve stem may have an inner diameter of at least 4.5 mm, for example between 5 mm and 7 mm.

A metallic hollow valve for an internal combustion engine of a utility vehicle may include a tubular valve stem and a valve head merging into the valve stem. The valve head may have an outer diameter that is enlarged compared to the valve stem. The valve stem and the valve head may together delimit a hollow space. The valve stem may have an outer diameter of more than 7 mm, for example between 8 mm and 11 mm. The valve stem may have an inner diameter of at least 4.5 mm, for example between 5 mm and 7 mm.

In an internal combustion engine, an angle defined by an axis of a boundary of an intake port adjoining a valve seat and a cylinder axis is greater than an angle defined by the axis of the valve seat and the cylinder axis. A step between a first inner wall and a second inner wall, the first inner wall being a portion of an inner wall of the valve seat that is closest to the cylinder axis and the second inner wall being a portion of an inner wall of the boundary of the intake port that is closest to the cylinder axis. The first inner wall is located on the outer side in the radial direction of the intake port than the second inner wall.