Internal-combustion engines – Starting device – Compression relieving type
Reexamination Certificate
1999-07-21
2001-08-07
Dolinar, Andrew M. (Department: 3747)
Internal-combustion engines
Starting device
Compression relieving type
Reexamination Certificate
active
06269786
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to compression release mechanisms for internal combustion engines.
It is often desirable to relieve the pressure in an engine combustion chamber during starting so that it is easier for the piston to reciprocate in the engine and thus easier for the operator to manually pull the starter rope. Known compression release mechanisms lessen the pull force required to start the engine, and minimize operator fatigue during starting.
One typical compression release mechanism is disclosed in U.S. Pat. No. 3,381,676 issued May 7, 1968 to Campen. The Campen compression release mechanism includes a centrifugally-responsive flyweight, a torsional spring attached to the flyweight, and a central pin which engages a valve tappet at engine starting speeds. At higher engine speeds, the flyweight moves radially outwardly so that the pin disengages the valve tappet when the engine is running.
It is known to use a compression release mechanism for multi-cylinder engines. For example, U.S. Pat. No. 5,809,958 issued Sep. 22, 1998 to Gracyalny discloses a centrifugally-responsive flyweight to which is connected a compression release shaft disposed externally of the camshaft. The compression release shaft is connected at one end to the flyweight and extends through respective bores in two cams lobes. The release shaft includes two D-shaped cross-sectional portions which engage two respective lift members. One disadvantage of such an arrangement is that the bores for the release shaft must be drilled subsequently to heat treating the cams. Consequently, the drilling operation is more difficult, time consuming and expensive because the heat treated cams are much harder. Another disadvantage of such an arrangement is that the drilling operation is more difficult in that two separate bores must be drilled. This introduces the possibility of mislocating the bores with respect to one another. Another disadvantage of such an arrangement is that the release shaft is supported by a minimum bearing surface, viz., the two bores in the cams. Consequently, the material from which the release shaft is made must be sufficiently strong.
Japanese No. 2-67409(A) to Yoshiharu Isaka also discloses a compression release mechanism for use with multiple cylinders. A flyweight is disposed on the internal side of the cam gear and has a compression release shaft connected thereto. The compression release shaft is disposed internally of the camshaft and includes two D-shaped cross sectional portions therealong, each of which engages a separate lift member, which in turn engage separate valve tappets.
It is desirable to further reduce the cost and at the same time, simplify the assembly of a compression release mechanism.
SUMMARY OF THE INVENTION
The present invention provides a low cost, easy to assembly mechanical compression release for a single or multi-cylinder engine. Specifically, the compression release assembly of the present invention comprises a compression release shaft having at least two segments disposed substantially within a bore in the camshaft. Such an arrangement is easier to assemble and allows production from lower cost parts.
In one form thereof, the present invention provides a compression release mechanism for relieving compression during engine starting in an internal combustion engine having a camshaft rotatably disposed within a housing. The mechanism comprises a compression release shaft disposed substantially within the camshaft and comprising first and second compression release shaft segments. A flyweight member is connected to the compression release shaft. A lift member is reciprocably disposed in the camshaft. The lift member engages the compression release shaft so that the lift member extends outwardly from the camshaft and is adapted to engage a valve actuation device.
In a preferred form, the inventive compression release mechanism includes the first and second compression release shaft segments being axially non-interlocking and rotationally interlocking. In other words, rotation of one of the segments necessarily produces rotation of the other segment therewith. However, the connection between the two separate segments are not held together axially where they interface within the bore in the camshaft. Instead, one end of the release shaft is engaged by a side surface of a cam whereas the housing engages the flyweight member which is connected to the other shaft segment. It is thus the bearing surfaces of the housing and the cam that hold the two segments together within the bore.
In another preferred embodiment, the first compression release shaft segment is integrally formed with the flyweight member, both of which are manufactured using powder metal technology.
One advantage of the present invention is that the bore in the camshaft which contains the compression release shaft can be drilled in a simple one step drilling operation without interruption. By contrast, certain prior art devices require drilling through a first cam lobe and then a second cam lobe. This multiple step prior art drilling operation results in burrs on the outside of the cam surface that have to be smoothed and also introduces the possibility that the drill point becomes mislocated after it exits the first cam lobe and enters the second cam lobe.
Another advantage of the present invention is that the bore for the compression release shaft is disposed sufficiently within the surface of the camshaft so that the cams can be heat treated after drilling the compression release shaft bore in the camshaft. Advantageously, the camshaft metal is softer and therefore easier to drill prior to the heat treating.
Another advantage of the present invention is that the compression release shaft and/or the flyweight member can be formed using powder metal technology. By making the flyweight member from a metal powder, its weight can be adjusted by infiltrating copper or other dense metal into the pressed powder, which in turn allows the speed at which the compression release mechanism disengages to be finely tuned. Furthermore, expensive stamping and machining is avoided. Further still, the process of forming the parts from powder metal is reliable and consistently repeatable.
Still another advantage of the present invention is that no fasteners are needed to hold the two segments of the compression release shaft together. Yet, because the compression release shaft is disposed within the camshaft, a large bearing surface is provided therefor so that the two segments rotationally interlock one another without being fastened together. Such an arrangement would not be possible with the compression release shaft disposed externally of the camshaft as in prior art configurations.
Yet another advantage of the present invention is that the compression release shaft formed of separate segments is easier to install as part of the engine assembly process.
Yet another advantage of the present invention is that a two-piece compression release shaft can be made more cost effectively. Further advantageously, one of the compression release shaft segments can be formed integral with the flyweight member using powder metal technology.
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Koehler Scot A.
Miller William M.
Snyder Dale D.
Sterr Randall E.
Baker & Daniels
Dolinar Andrew M.
Tecumseh Products Company
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