A gasket is described configured to be mounted on a valve of an internal combustion engine, having a central axis and comprising: an annular elastically deformable sealing element, having a radially internal surface having a first portion, adapted to cooperate with contact with a stem of the valve, and a second portion, configured to cooperate with contact with a guide element in a sliding manner of the aforementioned stem; and an annular support member, arranged coaxially on at least part of the sealing element so that the latter is pressed radially between the support member and the valve; the second portion has a circumferential surface section and a plurality of discrete bumps, projecting cantilevered from the circumferential surface section so as to cooperate with contact in use with the guide element, angularly spaced from each other around the axis and forming a discontinuous undulation of the radially internal surface.

A gasket is described configured to be mounted on a valve of an internal combustion engine, having a central axis and comprising: an annular elastically deformable sealing element, having a radially internal surface having a first portion, adapted to cooperate with contact with a stem of the valve, and a second portion, configured to cooperate with contact with a guide element in a sliding manner of the aforementioned stem; and an annular support member, arranged coaxially on at least part of the sealing element so that the latter is pressed radially between the support member and the valve; the second portion has a circumferential surface section and a plurality of discrete bumps, projecting cantilevered from the circumferential surface section so as to cooperate with contact in use with the guide element, angularly spaced from each other around the axis and forming a discontinuous undulation of the radially internal surface.

The present invention provides a hollow engine valve achieving high durability while suppressing an increase in manufacturing cost, and a manufacturing method therefor. A manufacturing method for a hollow engine valve comprises: a step of forming, by forging, a solid round bar as a material of a valve main body into a valve main body intermediate member provided with a semifinished product valve head portion corresponding to a valve head portion and a solid stem portion corresponding to a valve stem portion; a step of performing cutting process with respect to the valve main body intermediate member across the solid stem portion and the semifinished product valve head portion for forming a semifinished product hollow hole with a bottom corresponding to a hollow hole, thereby forming the valve main body intermediate member into a valve main body semifinished product provided with the semifinished product valve head portion and a semifinished product valve stem portion; and a step of performing necking process with respect to the valve main body semifinished product for squeezing the semifinished product valve stem portion step by step, thereby reducing the diameter of the semifinished product valve stem portion and increasing the length of the stem of the semifinished product valve stem portion, to form the valve main body semifinished product into the valve main body.

The present invention provides a hollow engine valve achieving high durability while suppressing an increase in manufacturing cost, and a manufacturing method therefor. A manufacturing method for a hollow engine valve comprises: a step of forming, by forging, a solid round bar as a material of a valve main body into a valve main body intermediate member provided with a semifinished product valve head portion corresponding to a valve head portion and a solid stem portion corresponding to a valve stem portion; a step of performing cutting process with respect to the valve main body intermediate member across the solid stem portion and the semifinished product valve head portion for forming a semifinished product hollow hole with a bottom corresponding to a hollow hole, thereby forming the valve main body intermediate member into a valve main body semifinished product provided with the semifinished product valve head portion and a semifinished product valve stem portion; and a step of performing necking process with respect to the valve main body semifinished product for squeezing the semifinished product valve stem portion step by step, thereby reducing the diameter of the semifinished product valve stem portion and increasing the length of the stem of the semifinished product valve stem portion, to form the valve main body semifinished product into the valve main body.

An engine valve includes a stem, a head comprising an outer lip surface, a seating surface extending from the outer lip surface toward the stem, and a combustion surface extending from the outer lip surface on the opposite side of the head as compared to the seating surface. The combustion surface includes a first convex arcuate surface spaced away from the outer lip surface, at least partially forming a raised ring, and a first concave arcuate surface spaced away from the outer lip surface, at least partially forming a dimple.

An engine valve includes a stem, a head comprising an outer lip surface, a seating surface extending from the outer lip surface toward the stem, and a combustion surface extending from the outer lip surface on the opposite side of the head as compared to the seating surface. The combustion surface includes a first convex arcuate surface spaced away from the outer lip surface, at least partially forming a raised ring, and a first concave arcuate surface spaced away from the outer lip surface, at least partially forming a dimple.

Generally, a rotatable valve assembly operative in an internal combustion engine is provided. The rotatable valve assembly may comprise a valve body rotatably supported in the cylinder head. The valve body may have various shapes which may allow to maximize an effective working area of a combustion chamber head and at the same time to decrease an overall space occupied by a cylinder head of the engine. The rotatable valve assembly may directly utilize an engine's camshaft rotational motion to drive the rotational motion of the valve body, thereby eliminating a need in dedicated mechanisms that convert the camshafts rotational motion into linear translational motion typically utilized in current cylinder heads. Finally, rotational motion of the valve body may reduce a time required to reach a maximal effective working area for air-fuel mixture supply and/or gas exhaust and/or may provide a smoother and quitter engine operation.

An exhaust valve assembly for a two-stroke internal combustion engine has a valve actuator, and a two-part valve having a primary and secondary valves defining first and second decompression passages respectively. The primary valve is operatively connected to the valve actuator. The primary valve is in first, second and third primary valve positions when the valve actuator is in first, second and third actuator positions respectively. The secondary valve is in a first secondary valve position when the valve actuator is in the first or the second actuator position and in a second secondary valve position when the valve actuator is in the third actuator position. The first and second valve decompression passages fluidly communicate with each other when the valve actuator is in the second actuator position, and are fluidly separate from each other when the valve actuator is the first or the third actuator position.

An exhaust valve assembly for a two-stroke internal combustion engine has a valve actuator, and a two-part valve having a primary and secondary valves defining first and second decompression passages respectively. The primary valve is operatively connected to the valve actuator. The primary valve is in first, second and third primary valve positions when the valve actuator is in first, second and third actuator positions respectively. The secondary valve is in a first secondary valve position when the valve actuator is in the first or the second actuator position and in a second secondary valve position when the valve actuator is in the third actuator position. The first and second valve decompression passages fluidly communicate with each other when the valve actuator is in the second actuator position, and are fluidly separate from each other when the valve actuator is the first or the third actuator position.

An engine valve and a method of producing the engine valve are provided. The engine valve includes a shaft part and an umbrella part formed at one end of the shaft part. The engine valve opens and closes an intake port or an exhaust port of a combustion chamber of an internal combustion engine. Further, at least a portion of the engine valve that extends from the umbrella part to a position on the shaft part in a longitudinal direction thereof includes a valve body made of steel or nickel alloy, and a core member made of copper or copper alloy and provided inside the valve body.