Metal working – Method of mechanical manufacture – Prime mover or fluid pump making
Reexamination Certificate
2000-12-19
2002-09-03
Denion, Thomas (Department: 3748)
Metal working
Method of mechanical manufacture
Prime mover or fluid pump making
C029S888010, C123S090600, C074S567000
Reexamination Certificate
active
06442835
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to a camshaft and more particularly to a camshaft having reduced weight and added wear resistance at a plurality of lobe areas of the camshaft.
BACKGROUND
One such component of the internal combustion engine is a camshaft, which is rotated by the driving force of the crank shaft so as to open and close the intake and exhaust valves at a specified timing. In order to open and close the intake and exhaust valves, the camshaft includes cams, each having a lobe which contacts and lifts respective rocker arms of the intake and exhaust valves during rotation of the camshaft. However, it has been found that the extensive contact between the lobes of the camshaft and respective rocker arms of the intake and exhaust valves causes lobe wear due to fatigue from high contact stresses. This problem, in turn, results in camshaft failure or inefficiencies in the performance of the engine.
A camshaft failure includes cracking of the shaft of the camshaft or any components thereof such as the cam. This usually results in a catastrophic failure of the internal combustion engine. On the other hand, inefficiencies in the performance of the engine include improper contact between the lobe of the cam and the respective rocker arms of the intake and exhaust valves resulting in the respective intake and exhaust valves from properly or fully opening. This may result in poor air-to-fuel ratios or inadequate discharging of exhaust gases, both of which result in poor fuel consumption or rough engine performance. Improper discharging of the exhaust gases also results in carbon build-up on the cylinder walls, which may also lead to poor fuel consumption and the like.
Manufacturers of internal combustion engines are continuously seeking ways to improve the efficiency and reliability of the internal combustion engine. These efficiencies are typically provided by improving the efficiency and reliability of each component of the internal combustion engine, including the camshaft. With regard to the camshaft, manufacturers have attempted to reduce the weight of the camshaft as well as use different camshaft materials in order to add torsional strength to the shaft of the camshaft. Although manufacturers have made great strides in improvements to the camshaft over the years, manufacturers have not yet provided a reduced weight camshaft with wear resistant properties at the lobe of the camshaft. This is mainly due to the manufacturing processes used by manufacturers such as, for example, green sand casting or forging, which leads to non-uniformity of material distribution (i.e., dense materials migrating toward one side of the camshaft) as well as increased camshaft weight, both resulting in a decrease in the efficiency of the internal combustion engine.
U.S. Pat. No. 5,004,370 to Swars issued on Apr. 2, 1991 discloses a hollow shaft having drive elements (e.g., cams) with axially varied properties. The drive elements are secured on the hollow shaft by expansion of the hollow shaft, and includes a separate wear layer produced by an induction-hardened process. This separate wear layer, however, is not distributed throughout the drive elements, nor is it distributed within the hollow shaft. Accordingly, the apparatus of Swars has a tendency to wear during the use of the internal combustion engine, and does not appear to adequately withstand high torsional or contract stresses.
The present invention is directed to overcoming one or more of the problems as set forth above.
DISCLOSURE OF THE INVENTION
In one aspect of the present invention a camshaft is provided. The camshaft includes a shaft made of a base material. A cam is located on the shaft. A lobe projects from the cam and is partly composed of the base material and a wear resistant material distributed on the outer surface of the lobe.
In another aspect of the present invention, the camshaft includes a shaft and a cam located on the shaft. A lobe extends from the cam and is composed of a wear resistant material which is denser than a base material used for the composition of the shaft.
In still another aspect of the present invention, the camshaft is adapted for use in an internal combustion engine. The internal combustion engine includes a cylinder block having a cylinder. A piston assembly is located within the cylinder and a crankshaft is connected to the piston assembly. A valve assembly communicates with the cylinder. A camshaft opens the valve assembly and includes a shaft. A cam, having a lobe, is located on the shaft. The lobe is composed of wear resistant material which is more dense than a material used for the camshaft.
REFERENCES:
patent: 3704746 (1972-12-01), Thompson
patent: 3747668 (1973-07-01), Schroll et al.
patent: 3929181 (1975-12-01), Beyer et al.
patent: 4549339 (1985-10-01), Lajoye
patent: 4595556 (1986-06-01), Umeha
patent: 4614225 (1986-09-01), Ernst et al.
patent: 4652724 (1987-03-01), Morita
patent: 4804033 (1989-02-01), Hepworth et al.
patent: 4905538 (1990-03-01), Watanabe
patent: 5004370 (1991-04-01), Swars
patent: 5228498 (1993-07-01), Harada et al.
patent: 5778530 (1998-07-01), Nakamura
patent: 6171713 (2001-01-01), Smith
patent: 5010417 (1993-01-01), None
Majewski Thomas
Pollard Michael J.
Caterpillar Inc.
Corrigan Jaime
Denion Thomas
Whitham, Curtis & Whitham, PLC
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