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.

Description

INCORPORATION BY REFERENCE[0001]The disclosure of Japanese Patent Application No. 2007-178867 filed on Jul. 6, 2007, including the specification, drawings and abstract, is incorporated herein by reference in its entirety.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]This invention relates to a hollow valve for an internal combustion engine for use in an intake / exhaust valve actuating mechanism of the internal combustion engine, and also relates to an internal combustion engine in which the hollow valve or valves is / are mounted.[0004]2. Description of the Related Art[0005]In an intake / exhaust valve actuating mechanism of an internal combustion engine, a valve is provided for permitting or interrupting communication between an intake port and the combustion chamber or between an exhaust port and the combustion chamber. Generally, the valve is roughly divided into an umbrella portion and a stem portion, and the stem portion is adapted to reciprocate in its axial direc...

AI Technical Summary

Benefits of technology

[0013]In the hollow valve for the internal combustion engine according to the first aspect of the invention, heat of the wall portion is taken or absorbed by the high-thermal-conductivity member(s), so that the wall portion is cooled. The heat taken by the high-thermal-conductivity member(s) is transferred to a heat-conduction medium, such as a coolant, and is finally transferred from the heat-conduction medium to a cylinder head. Thus, the hollow engine valve permits highly efficient cooling of the umbrella portion that is most likely to be heated to a high temperature.

[0017]With the above arrangement, the coolant the level of which is raised by the convex portion under the reciprocating motion of the valve reaches the upper side of the stem portion, so that the heat which the coolant takes from the high-thermal-conductivity members is transferred to the upper side of the stem portion. Thus, the hollow engine valve provides a high cooling effect, in particular, a high effect of cooling the umbrella portion.

[0021]With the above arrangement, the heat of the wall portion is transferred to a portion of the umbrella portion that is close to the valve seat, as well as the heat-conduction medium (the coolant or stem portion). Accordingly, when it is not desired to raise the temperature of the stem portion, which would result in an increase in the temperature of intake air, the high-thermal-conductivity member are placed in position so that a relatively large amount of heat is dissipated to the portion close to the valve seat, thereby to suppress or prevent a temperature rise of the intake air.

[0022]In the hollow valve for the internal combustion engine according to the invention, the high-thermal-conductivity members have a high capability of dissipating heat, and heat is transferred from the high-thermal-conductivity members to the heat-conduction medium, so that the umbrella portion, in particular, can be favorably cooled.

[0024]In the internal combustion engine according to the second aspect of the invention, the umbrella portions of the intake valve and exhaust valve are cooled with improved efficiency, so that the engine is less likely to suffer from knocking. Owing to the effect of suppressing or preventing knocking, the ignition timing can be advanced as needed, thus assuring improved output performance of the engine.

[0026]In the above case, the larger number of high-thermal-conductivity members are provided in the exhaust valve on the exhaust side where the valve is more likely to be exposed to hot gas, than that provided in the intake valve on the air intake or induction side, thus assuring a sufficient cooling effect. Since the intake / exhaust valves used in the engine according to the second aspect of the invention can change the degree of cooling simply by adjusting the number of the high-thermal-conductivity members provided in the valve, all of the components can be shared between the exhaust valve and the intake valve, and the internal combustion engine can be manufactured at reduced cost.

Problems solved by technology

Therefore, the heat transfer medium (coolant) does not necessarily contact uniformly with the respective walls of the umbrella portion and stem portion in the cavity, and the umbrella portion and the stem portion may not be cooled uniformly.

Namely, in the hollow engine valve of the related art, even if heat is transferred to the heat transfer medium in a certain portion of the umbrella portion in the cavity, so that the heat can be dissipated to an object, such as a stem portion, to which heat is to be transferred, the heat transfer medium may not be able to contact a wall of the cavity in another portion of the umbrella portion, and thus cannot take heat from this portion.

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