Power plants – Fluid motor means driven by waste heat or by exhaust energy...
Reexamination Certificate
1999-12-28
2001-07-10
Koczo, Michael (Department: 3746)
Power plants
Fluid motor means driven by waste heat or by exhaust energy...
C060S323000
Reexamination Certificate
active
06256990
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an exhaust manifold integrally cast with a turbine housing for turbocharger.
DESCRIPTION OF PRIOR ART
Automobile engines are recently equipped with turbochargers to increase their power. The turbochargers make larger engines unnecessary, resulting in reduction in the automobiles size and the amount of an exhaust gas per unit work done. Because the turbochargers provide engines with high air/fuel ratios, it is highly expected to reduce air-polluting materials such as NOx and particulate matters in the exhaust gas.
For the purpose of preventing global warming and reducing the consumption of fossil fuel, demand is increasingly mounting to improve the fuel efficiency of automobiles. Because turbochargers serve to generate large horsepower with small fuel consumption, wasteful energy for overcoming friction pressure that increases as the displacement of engines increases can be reduced, thereby contributing to improvement in fuel efficiency.
In general, a turbocharger mounted to automobiles, etc. has a structure utilizing energy of a high-temperature, high-pressure exhaust gas guided through a manifold connected to outlets of an engine to rotate a rotor at a high speed, thereby rotating a compressor concentric with the rotor to increase the pressure of intake gas to the engine. The rotor is rotatably disposed in a turbine chamber of the turbine housing, which comprises an exhaust gas flow path for introducing the exhaust gas into a rotor chamber.
However, to mount both an exhaust manifold and a turbocharger in a limited space of an engine room in an automobile, it is important to determine the optimum shapes and sizes of these parts. Particularly when a turbine housing-integrated exhaust manifold is disposed in an automobile having the existing structure, a turbine housing cannot be mounted to the existing exhaust manifold without modifications of design. Accordingly, the exhaust manifold should be optimized in shape and size, so that it matches the turbine housing that is to be connected to the exhaust manifold.
Promising means for coping with this problem are exhaust parts obtained by integrally casting an exhaust manifold and a turbine housing, and their development has been carried out rapidly. Casting turbine housings integrally with exhaust manifolds provides exhaust parts without connections, thereby reducing the number of parts, and thus reducing assembling cost and making exhaust manifolds compact. Because there is no need for space for assembling these parts, the manifolds have high freedom of design, making it possible to provide the exhaust manifolds with the most ideal design. For instance, with respect to heat-resistant turbine housing-integrated exhaust manifolds, “Sokeizai,” published by the Sokeizai Center Foundation on Jan. 20, 1998, page 2 describes that 10 parts can be eliminated, that connections at 4 points are made unnecessary, and that the integration of parts makes it possible to reduce the size of products.
When an exhaust manifold exposed to a high-temperature exhaust gas is integrated with a turbine housing subjected to large vibration, the resultant turbine housing-integrated exhaust manifold is subjected to both stress such as thermal stress and vibration and thus likely to be deformed and cracked when designed in the conventional way. Accordingly, it is difficult to design an exhaust manifold integral with a turbine housing for a turbocharger, which can be used without causing any problems for practical applications. The above thesis concerning the heat-resistant turbine housing-integrated exhaust manifolds in “Sokeizai” neither describes nor suggests the prevention of deformation and cracking when stress such as thermal stress and vibration is applied.
OBJECT AND SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a small, long-life exhaust manifold integrally cast with a turbine housing for a turbocharger, which has a shape showing excellent strength to stress due to thermal stress by an exhaust gas and the vibration of a turbine housing.
As a result of research in view of the above object, the inventor has found that by optimizing the shape of a turbine housing-integrated exhaust manifold in a converged portion, particularly by optimizing a ratio of a radius of curvature in a neck portion via which the converged portion is connected to the turbine housing to a distance in a tangent direction from the center of the turbine housing to the exhaust gas flow path in the converged portion, the turbine housing-integrated exhaust manifold has excellent strength to mechanical stress due to the vibration of the turbine housing, thereby preventing the generation of cracks in and near the neck portion. The present invention has been completed based on this finding.
Thus, an exhaust manifold integrally cast with a turbine housing for a turbocharger according to the present invention comprises pipe portions having exhaust gas flow paths and a plurality of ports adapted to receive an exhaust gas; flanges respectively extending from the ports; a converged portion connected to the pipe portions and adapted to converge the exhaust gas flow paths in the pipe portions; and a turbine housing integrally connected to the converged portion and having a circular exhaust gas flow path therein, wherein the exhaust gas flow path in the converged portion is in a tangent direction relative to the circular exhaust gas flow path in the turbine housing, and wherein a neck portion that connects an outer surface of the turbine housing to an outer surface of the converged portion at a particular angle has a radius of curvature that is relative to the distance in a tangent direction of the exhaust gas flow path from the center of the turbine housing to the converged portion. Namely, the ratio of the radius of curvature to the distance in the tangent direction of the exhaust gas flow path from the center of the turbine housing to the converged portion is 0.13 or more.
Preferably, the ratio of the radius of curvature in the neck portion to the distance in a tangent direction of the exhaust gas flow path from the center of the turbine housing to the converged portion is 0.23 or more.
In a preferred embodiment of the present invention, ribs are formed on outer surfaces of pipe portions and converged portion. The ribs increase the mechanical strength of the pipe portions and the converged portion, thereby preventing them from being cracked by thermal stress and vibration.
In another preferred embodiment of the present invention, the turbine housing is disposed at a position deviated from a centerline connecting centers of the ports. The pipe portions are integrally connected to each other to form a V-shaped portion on a centerline side of the converged portion, and the V-shaped portion has a wall portion that is thicker than other wall portions of the exhaust manifold. With this structure, the exhaust manifold is free from cracking in its converged portion, even though the converged portion is subjected to stress by thermal expansion and shrinkage of the exhaust manifold in a tangent direction.
In a further preferred embodiment of the present invention, the converged portion is provided on one side of the ports and the pipe portions are provided on an opposing side of the ports. With this structure, the lower surface of the converged portion is not in contact with or close to an engine case, whereby the temperature of the converged portion is not extremely lower in its lower portion than in its upper portion. Thus, it is not likely that thermal stress is generated in the converged portion.
In a still further preferred embodiment of the present invention, a pair of the ports located adjacent to the converged portion are surrounded by flanges having a bridge portion extending therebetween, and the bridge portion has a slit of 3 mm or less in width extending substantially perpendicular to a centerline of the pipe portions. This slit serves to absorb thermal shrinkage in a tangent direction of the pipe
Hitachi Metals Ltd.
Koczo Michael
Sughrue Mion Zinn Macpeak & Seas, PLLC
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