Hollow valve for internal combustion engine, and internal combustion engine having the hollow valve

Abstract

In a hollow valve for an internal combustion engine, including a stem portion, an umbrella portion provided at one end of the stem portion, a gastight cavity that communicates the interior of the stem portion with that of the umbrella portion, and a coolant contained in the cavity, the umbrella portion has a wall portion (a lower cap) having a combustion-chamber-side wall that forms a part of a wall of a combustion chamber of the engine, and a cavity-side wall that forms a part of a wall of the cavity, and at least one high-thermal-conductivity member is provided on the cavity-side wall, for conduction of heat between the wall portion and one of at least the coolant and the stem portion as a heat-conduction medium.

1 . A hollow valve for an internal combustion engine, comprising:
 a stem portion;   an umbrella portion provided at one end of the stem portion, said stem portion and said umbrella portion cooperating with each other to form a gastight cavity that communicates an interior of the stem portion with an interior of the umbrella portion; and   a coolant contained in the cavity, wherein:   the umbrella portion has a wall portion having a combustion-chamber-side wall that forms a part of a wall of a combustion chamber of the internal combustion engine, and a cavity-side wall that forms a part of a wall of the cavity; and   at least one high-thermal-conductivity member is provided on the cavity-side wall, for conduction of heat between the wall portion of the umbrella portion and at least one of the coolant and the stem portion as a heat-conduction medium.   
   
   
       2 . The hollow valve according to  claim 1 , wherein said at least one high-thermal-conductivity member has a directional characteristic in heat conduction between one end thereof that is in contact with the cavity-side wall and the other end that is in contact with the heat-conduction medium. 
   
   
       3 . The hollow valve according to  claim 1 , wherein said at least one high-thermal-conductivity member comprises a carbon-fiber reinforced metal. 
   
   
       4 . The hollow valve according to  claim 3 , wherein:
 the carbon-fiber reinforced metal includes a metal, and carbon fibers; and   the metal is exposed at the opposite ends of the carbon-fiber reinforced metal.   
   
   
       5 . The hollow valve according to  claim 1 , wherein said at least one high-thermal-conductivity member comprises a plurality of high-thermal-conductivity members that form a convex portion that protrudes in substantially the same direction as an axial direction of the stem portion, so as to transfer heat of the wall portion to the coolant. 
   
   
       6 . The hollow valve according to  claim 5 , wherein said plurality of high-thermal-conductivity members that form the convex portion are formed such that the length of the high-thermal-conductivity members increases toward a central portion of the cavity-side wall. 
   
   
       7 . The hollow valve according to  claim 1 , wherein said at least one high-thermal-conductivity member is placed in position so as to transfer heat between the cavity-side wall and a wall close to one end of the stem portion remote from the umbrella portion. 
   
   
       8 . The hollow valve according to  claim 1 , wherein said at least one high-thermal-conductivity member comprises a first high-thermal-conductivity member placed in position so as to transfer heat between a central portion of the cavity-side wall and the heat-conduction medium, and a second high-thermal-conductivity member placed in position so as to transfer heat between a peripheral portion of the cavity-side wall and a wall of the cavity which is close to a valve seat of the umbrella portion. 
   
   
       9 . The hollow valve according to  claim 1 , wherein said at least one high-thermal-conductivity member comprises a plurality of high-thermal-conductivity members each connecting a peripheral portion of the cavity-side wall with a wall of the cavity which is close to a valve stem guide that surrounds a part of the stem portion, at the opposite ends thereof, said plurality of high-thermal-conductivity members being arranged in radial directions to radiate from a center axis of the hollow valve. 
   
   
       10 . An internal combustion engine, comprising:
 an intake valve having a structure of the hollow valve for the internal combustion engine as defined in  claim 1 ; and   an exhaust valve having a structure of the hollow valve for the internal combustion engine as defined in  claim 1 .   
   
   
       11 . The internal combustion engine according to  claim 10 , wherein the number of the high-thermal-conductivity members provided in the exhaust valve is larger than the number of the high-thermal-conductivity members provided in the intake valve.