Intake engine valves

Abstract

An intake engine valve may have a tapered portion positioned between a valve head and a valve stem tapering from a larger size to a smaller size in the direction of the valve stem. The valve stem may include a small diameter portion positioned between a guide stem portion And a stem end portion on the side of the tapered portion and having a diameter smaller than a diameter or diameters of the guide stem portion and the stem end portion. The guide stem portion may be guided by a valve guide of the engine.

What is claimed is: 
     
         1 . A forged intake engine valve used for opening and closing an intake port of an engine, comprising:
 a valve head;   a valve stem; and   a tapered portion positioned between the valve head and the valve stem and having a tapered surface tapering from the valve head towards the valve stem, the tapered surface extending along a straight line as viewed in its cross-section and having a taper angle; and   wherein the valve stem includes a small diameter portion positioned between a guide stem portion and a stem end portion on a side of the tapered portion and having a diameter smaller than both a diameter of the guide stem portion and a diameter of the stem end portion, the guide stem portion being configured to be guided by a valve guide of the engine.   
     
     
         2 . The forged intake engine valve according to  claim 1 , wherein the tapered surface and a backside surface of the valve head are left as forged surfaces without being machined. 
     
     
         3 . The forged intake engine valve according to  claim 1 , wherein the small diameter portion is formed such that a terminal end of the small diameter portion on the side of the stem guide portion is positioned proximal to an axial end of the valve guide on the side of the intake port when the engine valve is in an opened position. 
     
     
         4 . The forged intake engine valve according to  claim 2 , wherein the small diameter portion is formed such that a terminal end of the small diameter portion on the side of the stem guide portion is positioned proximal to an axial end of the valve guide on the side of the intake port when the engine valve is in an opened position. 
     
     
         5 . The forged intake engine valve according to  claim 1 , wherein the taper angle of the tapered portion is about 20°. 
     
     
         6 . The forged intake engine valve according to  claim 1 , wherein the small diameter portion includes opposite end portions with curved outer surfaces respectively smoothly connected to outer surfaces of the guide stem portion and the stem end portion. 
     
     
         7 . The forged intake engine valve according to  claim 2 , wherein:
 the backside surface of the valve head has a concave surface positioned on the side of the small diameter portion and an inclined surface positioned on the side opposite the small diameter portion;   the concave surface has a radius; and   the inclined surface is configured as a tapered surface extending along a straight line and tapering toward the concave surface.   
     
     
         8 . An intake engine valve need for opening and closing an intake port of an engine, comprising:
 a valve head;   a valve stem; and   a tapered portion positioned between the valve head and the valve stem and tapering towards the valve stem, an outer circumferential surface of the tapered portion being formed as a tapered surface extending along a straight line in a cross-sectional view and also having a taper angle; and   wherein the valve stem includes a small diameter portion positioned between a guide stem portion and a stem end portion on the side of the tapered portion and having a diameter smaller than both a diameter of the guide stem portion and a diameter of the stem end portion, the guide stem portion being configured to be guided by a valve guide of the engine.