Internal-combustion engines – Valve – Valve seat relation
Reexamination Certificate
2000-06-23
2001-06-05
McMahon, Marguerite (Department: 3747)
Internal-combustion engines
Valve
Valve seat relation
Reexamination Certificate
active
06240891
ABSTRACT:
The present invention relates to a cylinder head and particularly to a valve seat ring in the mouth of the inlet duct to a combustion chamber of the engine.
BACKGROUND TO THE INVENTION, AND STATE OF THE ART
For combustion engines to be allowed to be sold they have to fulfil legal requirements regarding exhaust emissions. Meeting those requirements involves increasingly precise control of the engine's combustion. An important factor which affects the combustion process and hence the formation of harmful emissions and the efficiency of combustion is the air movement which occurs in the combustion chamber when the fuel is sprayed in and the combustion commences. This air movement is crucially affected by the movement imparted to the inlet air entering the cylinder as a result of the configuration of the inlet duct/ducts.
In diesel engines with double inlet valves and with relatively long inlet ducts of the type referred to in SE A 9203900-7 the movement imparted to the inlet air is at a relatively small angle relative to the piston plane and is at the same time substantially tangential relative to an imaginary circle which is smaller than and concentric with the cylinder. The ducts consequently impart to the inlet air a certain rotation which can be measured by means of laboratory facilities and be used for testing duct configurations with optimum characteristics for a chosen compromise.
The configuration of such ducts of the so-called tangential type and, more particularly, their mouth leading into the combustion chamber has been found to be of great significance for achieving the desired rotation of the inlet air. A problem which arises in the casting of large series of cylinder heads is maintaining sufficiently close tolerances on the position of the ducts. A risk which arises is that subsequent milling for the incorporation of a valve seat ring may not result in the latter being totally concentric with the duct. Irregularities affecting, inter alia, the shape of edges extending into the duct may therefore occur, with consequent adverse effects on the movement of inlet air into the cylinder, and may hence cause total disruption of the desired monitoring and control of the combustion process.
European patent specification EP-A-275841 shows a valve seat in an intake duct of an internal combustion engine. A milled recess in the inlet duct houses the valve seat equipped with bilateral chamfer. The purpose is to make the machining process for obtaining a valve seat in an inlet duct less expensive.
Swedish patent specification SE A 7501689-9 refers to the configuration of the mouth of an inlet duct leading into the combustion chamber in a diesel engine without stating how the movement of the inlet air is thereby affected. The inlet duct therein referred to is of the so-called spiral type which imparts to the inlet air a pronounced spiral-like movement which has at the same time a relatively powerful vertical component. This type of inlet air movement results in combustion which is relatively unfavourable from the emission point of view and is usually avoided in modern diesel engines.
OBJECT AND SUMMARY OF THE INVENTION
The object of the present invention is to provide in a diesel engine a configuration of the mouth of a so-called tangential inlet duct leading into the combustion chamber such that the tolerance requirements for the geometrical position in the cylinder head of the duct and/or of the valve seat ring can be maintained at a level which facilitates easy and efficient manufacture of the cylinder head. The present invention achieves this by providing a valve seat ring in a recess milled into the mouth of the inlet duct, wherein the valve seat ring has an arcuate shape extending convexly into the mouth of the duct along the height of the ring, the recess has an abutment shoulder facing out of the mouth of the duct and the valve seat ring abuts the shoulder surface of the recess, and where they abut, the valve seat ring having a greater diameter than the intersection between the shoulder surface and the mouth of the duct where the recess is milled, which ensures that sharp edges due to the valve seat ring do not protrude into the inlet duct and that the latter's configuration facilitates advantageous control of the flow of inlet air into the cylinder.
In one embodiment of the invention the valve seat ring has an arcuate configuration which extends up to the shoulder surface adjacent to the inlet duct and has at least in its upper portion a radius equal to between 10 and 50% of the height of the valve seat ring. This makes it possible for the inlet air leaving the inlet duct not to be subject to substantial flow modifying disturbances even if there is a certain lack of concentricity at the connection between the inlet duct and the valve seat ring. The result is satisfactory maintaining of the directional flow imparted to the air by the tangential inlet duct even during the entry of the air into the cylinder, with consequently good conditions for serially produced engines to maintain an inlet air flow into the combustion chamber which provides the desired characteristics from the emission and fuel consumption points of view.
In a further embodiment of the invention the connection of the inlet duct to said shoulder surface is via a substantially sharp edge. This means that the direction of flow of the inlet air can be controlled for as long as possible before it enters the cylinder, thereby further enhancing the possibility of achieving a desired inlet air flow in the combustion chamber.
REFERENCES:
patent: 4011852 (1977-03-01), Rasch
patent: 5860401 (1999-01-01), Adachi et al.
patent: 0275841 (1988-07-01), None
patent: 0723074 (1996-07-01), None
patent: 2557637 (1985-07-01), None
McMahon Marguerite
Ostrolenk Faber Gerb & Soffen, LLP
Scania CV Aktiebolag (publ)
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