Camshaft lubrication system

Details Camshaft lubrication system Camshaft lubrication system

2001-07-31

2003-10-14

Denion, Thomas (Department: 3748)

Internal-combustion engines

Poppet valve operating mechanism

Lubrication

C123S090330, C123S090600, C123S1960CP, C184S006500, C074S567000

Reexamination Certificate

active

06631701

ABSTRACT:

BACKGROUND OF THE INVENTION
Specifically, a camshaft system for aircraft engines configured to provide a camshaft lubrication system that enhances the transfer of lubricant to camshaft surfaces even when the aircraft is operated in a manner that locates the rotation axis of the hollow camshaft from horizontal. Generally, an enhanced camshaft lubrication system for hollow camshafts rotationally journaled in a plurality of bearings.
Camshaft systems in aircraft engines are difficult to lubricate. Conventional aircraft engine technology utilizes valves that are operationally responsive to rotating cam surfaces on a camshaft rotationally journaled in a plurality of bearings. The complicated movements of the camshaft and valve systems make the journaled surfaces and the cam surfaces of the camshaft subject to wear during engine operation. Especially, contact between the cam lobe surface and the mating lifter face, tappet, rocker arm, or the like can be subject to an extremely high loading. This high load between the contact surfaces makes fluid lubrication of the sliding surfaces difficult requiring the use of high pressure additives to lubricants.
As a result, conventional aircraft camshaft lubrication technology may be insufficient to prevent frictional power loss, or prevent damage to the cam surfaces, such as pitting, spalling, scuffing, or the like, of the slidingly engaged surfaces. The subsequent failure of the camshaft systems in aircraft engines due to a lack of lubrication at critical times in the camshaft operating cycle has been documented. Firewall Forward Technologies Technical Report No. 1, Firewall Forward Technologies 5212 Cessna Drive, Loveland, Colo. 80538, hereby incorporated by reference herein.
Because there is a large commercial demand for enhanced lubrication systems to resolve the problem of insufficient lubrication of camshaft components during such critical times in the camshaft operating cycle, various types of conventional engine and camshaft lubrication systems have been developed. However, even in light of existing commercial demand and the variety of conventional lubrication technologies that have been developed over the years, significant problems remain unresolved in providing camshaft lubrication technology that provides sufficient lubrication to camshaft components during operation of aircraft engines.
As shown by U.S. Pat. No. 4,991,549, hereby incorporated by reference herein, a conventional method of lubricating camshaft surfaces may be by configuring the cylinder head of the engine to provide “wells” or catch areas in which the lubricant can collect. A significant problem with well type technology may be that the lubricant collected in the wells or catch areas is unfiltered lubricant. As such, the wells or catch areas may accumulate particulate or debris from the unfiltered lubricant. The particulate or debris may then be transferred to the cam lobe surfaces resulting in wear or damage to these surfaces. Another significant problem with well or catch area technology may be that the lubricant migrates in response to the orientation of the engine or the acceleration of the aircraft. As such, the amount of lubricant collected in a particular location may vary significantly depending on the engine orientation (pitch, roll, or yaw) or the acceleration of the aircraft. As the lubricant migrates in response to orientation of the engine or acceleration the amount of lubricant available for transfer to the cam lobes, the amount of lubricant actually transferred to the surface of the cam lobes, or the placement of the lubricant with respect to the cam lobe surface may vary during the operation of the engine. An additional problem with well or catch area technology may be that the oil collected in the wells may be hot. As lubricant circulates through an engine during operation the temperature of the lubricant rises. By the time it is collected in a well or catch area, the lubricant may be sufficiently hot that the lubrication properties of the oil are diminished. A further problem with well or catch area lubrication technology may be the lubricant may not collect or transfer properly to the cam lobe surfaces when the lubricant is cold. Because cold lubricants may exhibit high flow resistance, a cold lubricant may not collect readily into wells or catch areas. As such, there may be little lubricant or a reduced amount of lubricant for transfer to the cam lobe surfaces and little or no lubricant may actually be transferred to the cam lobe surfaces when the engine is started cold.
Similarly, as shown by U.S. Pat. Nos. 4,329,949 and 4,343,270, each hereby incorporated by reference herein, a conventional method of lubricating camshaft surfaces may be to configure the cylinder head, the cylinder head cover, or other engine component to collect excess lubricant so that it may drip onto the cam lobe surfaces. As above, the lubricant may be unfiltered and transfer particulate or other debris to the cam lobe surfaces resulting in unnecessary wear to such surfaces, the amount of lubricant available for transfer to the cam lobe surfaces or the amount actually transferred to the cam lobe surfaces may vary depending on the migration of the lubrication in response to orientation of the engine or the acceleration of the aircraft, the lubricant may have been preheated to a high temperature prior to being dripped onto the cam lobe surfaces, or the lubricant may fail to collect or drip onto the cam lobe surfaces properly when cold.
Another conventional method of lubricating camshaft surfaces may be to spray lubricant onto the camshaft surfaces as disclosed by U.S. Pat. Nos. 6,173,689; 3,628,513; 3,958,541; and 4,343,270, each hereby incorporated by reference herein. In addition to the significant problems discussed above, a further significant problem with spraying lubricant onto camshaft surfaces can be that it results in high oil consumption. As lubricant is sprayed a portion of the lubricant can remain in suspension or mist for a sufficiently long duration and in amounts that may overwhelm the lubricant separator system. The lubricant would then be driven from the engine through the crankcase breather system. Another significant problem with spraying lubricant may be low lubricant pressure or the necessity of increasing the capacity of the lubricant pump. In aircraft, size and weight restrictions may make additional or larger components impractical or impossible to incorporate. Moreover, aircraft engine design and safety specifications are regulated by the federal law which may prohibit the use of spray type technology in aircraft. For example, the usable oil tank capacity may not be less than the product of the endurance of the airplane under critical operation conditions and the maximum oil consumption of the engine under the same conditions, plus a suitable margin to ensure adequate circulation and cooling. 14 C.F.R. §23.1011(c), hereby incorporated by reference herein.
Another conventional method of lubricating camshaft surfaces may be to supply lubricant to the hollow interior of the camshaft and then subsequently deliver the lubricant to the exterior surface of the camshaft as disclosed by U.S. Pat. Nos. 5,450,665; 4,615,310; and Japanese Abstract No 5503755A, each hereby incorporated by reference herein. A significant problem with utilizing the interior of hollow camshafts to deliver lubricant to the cam lobe surfaces may be that lubricant supplied to the interior of the hollow camshaft is not uniformly distributed over the interior surface of the hollow camshaft. As disclosed by Japanese Abstract No. 5503755A, a single feed hole at the drive end of a camshaft (or a single feed hole to the camshaft interior from the drive end bearing) supplies the lubricant to the interior of the camshaft to be distributed to all the cam lobe surfaces and all the camshaft bearings. When lubricant is supplied to the interior of a hollow camshaft through a single feed hole it can take a duration of time for a layer of lubricant to form over the entire interior surface of the cams

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