Metal working – Method of mechanical manufacture – Prime mover or fluid pump making
Reexamination Certificate
2000-01-12
2002-11-05
Cuda-Rosenbaum, I. (Department: 3729)
Metal working
Method of mechanical manufacture
Prime mover or fluid pump making
C029S447000, C029S508000
Reexamination Certificate
active
06473964
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable.
FEDERALLY SPONSORED RESEARCH
Not Applicable.
TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION
The present invention is generally directed to a method for attaching first and second members, and subsequently adjusting the shape and/or dimensions of at least one of the members. More particularly, the present invention is directed to a method of attaching one or more cam lobes and other individual camshaft elements, such as, for example, sprockets, bearing races and gears, to a camshaft tube at desired axial and angular orientations about the tube, and subsequently adjusting the shape and/or dimensions of at least one of the attached elements. In this way, the cam lobes and components may be adjusted to meet dimensional tolerances necessary for proper assembly of the camshaft into a combustion engine or other apparatus.
The method of the present invention may be utilized in applications wherein it is desirable to attach first and second members and subsequently adjust the shape and/or dimensions of at least one of the members. Examples of such applications include the fabrication of camshafts for internal combustion engines and other applications and the assembly of complex gear forms on rotatable shafts. The present method is particularly useful when applied in the fabrication of camshafts wherein cam lobes and, possibly, other camshaft elements such as sprockets, bearing races, and gears, are installed in precise locations on the outer surface of a camshaft tube. Camshafts fabricated according to the method of the invention may be used to engage push rods, lifters, impellers, rotors, gears, pulleys or other movable members.
DESCRIPTION OF THE INVENTION BACKGROUND
Camshafts for piston-driven internal combustion engines typically include several cam lobes with lobe-shaped outer surfaces that operate to move push rods, lifters, or other movable members in a precise pattern. As the camshaft rotates, the cam lobes must engage the movable members at proper positions and with proper timing. Therefore, the cam lobes must be positioned on the camshaft at precise relative axial positions and angular orientations.
A camshaft
10
of a typical construction adapted for use in an internal combustion engine is depicted in FIG.
1
. The camshaft
10
generally includes a camshaft tube
11
. Several cam lobes
12
are affixed to the outer surface of the camshaft tube
11
. Other camshaft components such as, for example, gear
16
, may be affixed to the outer surface of the camshaft tube
11
. Although generically referred to herein as a “camshaft tube”, that element, although typically hollow, need not be cylindrical and may have any overall shape and uniform or non-uniform cross-section suitable for receiving and rotating the several cam lobes and other camshaft components. Accordingly, “camshaft tube” is used herein to refer generally to the central rotating component of a camshaft to which the cam lobes are affixed and is not limited to any particular cylindrical or non-cylindrical configuration.
The lobe-shaped region of each cam lobe has a predetermined shape and is dimensioned to accurately control movement of the movable member it engages. More specifically, the profile of the cam lobe
12
, and particularly the shape and dimensions of the lobe-shaped region
13
, are such that as the camshaft tube
11
rotates, the motion of the cam lobe
12
imparts a precise rocking or reciprocating motion to the movable member it engages. In
FIG. 1
, for example, the movable members illustrated adjacent a cam lobe
12
are a lifter
14
and a push rod
15
. As the camshaft
10
rotates, the surface shape and dimensions of each cam lobe
12
, along with their various angular and axial positions along the length of the camshaft tube
11
, work in conjunction to properly move the push rods
15
of the engine in a desired pattern and timing. This synchronized motion ensures that the intake and exhaust valves of all engine cylinders operate correctly.
Camshafts combining a camshaft tube and several cam lobes traditionally were manufactured as a single component by casting or forging. This method of fabrication is time-consuming and expensive, and produces camshafts with limited dimensional accuracy. Therefore, extensive grinding and/or polishing is required to shape the individual cam lobes and other camshaft components and appropriately adjust the shape and dimensions of the surfaces of each of the components. Absent such extensive finishing work, the cam lobes would not properly engage their associated movable members. Forged or cast camshafts are necessarily composed of material of a substantially homogenous chemical composition. This is a disadvantage inasmuch as it may be desirable for the camshaft tube and the cam lobes to have substantially different physical properties so as to optimally withstand the significantly different mechanical forces experienced by the several components.
To address the deficiencies inherent in the casting and forging methods of camshaft fabrication, more recently camshafts have been fabricated by separately producing the camshaft tube and the cam lobes and then installing the cam lobes onto the outer surface of the camshaft tube at desired locations. In the case of the camshaft
10
of
FIG. 1
, for example, individual cam lobes
12
having a configuration as generally shown in
FIG. 2
may be separately fabricated and then positioned about the camshaft tube
11
. The components are assembled by disposing the camshaft tube
11
through the bore
17
in each cam lobe, and then affixing the cam lobes
12
to the outer surface of the camshaft tube
11
in desired axial positions and angular orientations. This fabrication method provides greater flexibility relative to the casting and forging methods, and the materials from which the camshaft tube, the cam lobes, and the other components installed on the camshaft are constructed may differ. For example, the cam lobes may be produced from a material particularly resistant to thermal stress and repetitive contact fatigue, while the camshaft tube may be produced from less expensive material such as a machined mild steel.
Fabricating camshafts by installing separately produced cam lobes onto a camshaft tube has the inherent disadvantage that the cam lobes and other camshaft elements must be precisely positioned when affixed. Also, the surface of each cam lobe must have the required shape and dimensions so that it is precisely oriented relative to each other cam lobe surface and relative to the camshaft tube. Accordingly, when fabricating camshafts in this manner, after the cam lobes are installed on the camshaft tube it is common to grind the surfaces of the cam lobes using one or more grinding steps so as to adjust each cam lobe profile and, possibly, adjust the relative angular orientations of the several cam lobes. In an alternate process, the internal diameter of each cam lobe is ground to adjust the tolerances that will be achieved once the cam lobes have been installed on the camshaft tube. Grinding the internal diameters or exterior surfaces of the cam lobes in a precise manner is problematic and, for example, accurately grinding cam lobes produced from powder metal material can be complex and expensive. More generally, grinding of cam lobes requires the use of expensive grinding machines, is a relatively slow process, and requires expensive grinding wheels that must be replaced often.
Accordingly, a need exists for a method of fabricating camshafts wherein cam lobes produced separately from the camshaft tube may be affixed to the exterior surface of the camshaft tube at precise axial positions and angular orientations, and then the cam lobes may be adjusted to proper shape and/or dimensions without employing a grinding operation. More generally, the inventor perceives that a need exists for a method of attaching first and second members wherein, subsequently, the shape and/or dimensions of at least one of the members may be adjusted by a technique oth
Anderson Gary L.
Kosco John C.
Cuda-Rosenbaum I.
Keystone Investment Corporation
Kirkpatrick & Lockhart LLP
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