Internal-combustion engines – Poppet valve operating mechanism – Tappet
Utility Patent
1993-09-03
2001-01-02
Lo, Weilun (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
Tappet
C123S090600, C123S090330, C123S188900, C074S569000
Utility Patent
active
06167856
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to internal combustion engines and, more particularly to, a low friction valve train for an internal combustion engine.
2. Description of the Related Art
It is known to construct valve trains for opening and closing valves in engines such as internal combustion engines. Such a valve train may be a direct acting hydraulic bucket tappet valve train for an overhead cam type internal combustion engine. Generally, the valve train includes a tappet which contacts a cam on a cam shaft which is used to translate rotational motion of the cam shaft into axial motion of the valve. The valve is closed by a valve spring which biases the valve in a closed position.
The valve train includes a hydraulic lash adjuster which compensates for a change in valve length due to thermal expansion caused by temperature changes as well as valve seat wear. This type of valve train is a high pressure system which, through hydraulic pressure generated by the lubrication system, keeps the valve lifter in proper contact with the cam to perform the valve opening/closing function. The constant hydraulic pressure continuously applied to the valve to maintain proper contact with the cam, in addition to the forces induced by the cam, results in increased friction losses and significant wear to the components of the valve train.
However, the hydraulic pressure is expected to provide hydrodynamic film lubrication between a journal of the cam and bearing surfaces of the cam shaft, and the tappet surface and the cam surfaces. Because of the high unit loads, the valve train operates in a predominantly boundary-to-mixed lubrication regime of a Stribeck diagram, particularly in the 750-2000 engine speed range. This speed range represents more than 80% of the driving cycle for passenger vehicle operation. Because the operation is in the predominantly boundary-to-mixed lubrication regime, the contacting components are subject to significant wear, as much as 30 to 150 microns on the cam during the life of the engine.
Additionally, engine speed is limited by the incidence of “valve toss” which is due to the reciprocating mass of the valve train. Reducing the valve train mass decreases the forces due to inertia and, as a result, permits higher engine operating speeds which, in turn, result in greater engine output. Further, reducing the friction between the moving components significantly reduces the wear and eliminates the need for a heavy, complex and expensive hydraulic system and enables the engine to operate at normal hydraulic pressures without the friction losses and corresponding wear encountered in standard hydraulic systems. The reduction in friction, in turn, results in fuel economy improvement and the reduction in wear improves component durability and, as a consequence, engine life. Thus, there is a need in the art to reduce the mass of the valve train and friction between moving components of the valve train. There is also a need in the art to use relatively low cost and easily formed components of the valve train.
SUMMARY OF THE INVENTION
Accordingly, the present invention is a unique lightweight and low friction valve train for an engine such as an internal combustion engine. In general, the valve train includes a cam shaft having at least one cam, the outer surfaces thereof treated such that the treated surface has an open porosity. A solid film lubricant is impregnated on the treated surfaces. The valve train further includes a lightweight tappet having a peripheral surface treated such that the treated surface has an open porosity. The treated surface is impregnated with a solid film lubricant. The tappet includes an insert which contacts the cam. The insert of the tappet includes a wear resistant contact surface. In addition, a valve guide may have an inner surface treated to create an open porosity and impregnated with a solid film lubricant to reduce the friction at the valve/valve guide interface. The solid film lubricant has an affinity for oil and promotes rapid formation of a stable oil film to reduce friction between the components.
Additionally, the present invention is a low friction cam shaft for actuating at least one valve of an internal combustion engine. The cam shaft includes a shaft member extending longitudinally and at least one cam secured to the shaft member. The cam is made of a plurality of density metal materials and has an outer surface impregnated with a solid film lubricant that has an affinity for oil and promotes rapid formation of a stable oil film to reduce friction therebetween.
One advantage of the present invention is that a low friction valve train is provided for an internal combustion engine Another advantage of the present invention is that a solid film lubricant is applied to the contacting surfaces of the valve train, thereby reducing contact pressures which correspondingly reduces friction and wear. Yet another advantage of the present invention is that the valve train incorporates a solid film lubricant to avoid the frictional losses occurring as a result of hydraulic loading of the tappet against the cam. A further advantage of the present invention is that the solid film lubricant applied to components of the valve train results in the frictional losses and corresponding wear being significantly reduced, thereby obviating the need for a heavy, complex and expensive hydraulic system. A still further advantage of the present invention is that a lightweight and low friction cam shaft is provided by using dual/multiple density powder metal lobes interspersed with a solid film lubricant and attached to a hollow shaft. Yet a further advantage of the present invention is that the composite powder metal cam shaft is easily formed, result ng in a relatively low cost. Additionally, such a low friction valve train will reduce or eliminate wear during oil starved conditions such as cold start and, thus, increase component life and engine life significantly.
Other objects, features and advantages of the present invention will be readily appreciated as the same becomes better understood after reading the following description in conjunction with the accompanying drawings.
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Cikanek Harry Arthur
German Daniel Joseph
Kabat Daniel Michael
Rao Vemulapalli Durga N.
Ford Global Technologies Inc.
Lo Weilun
May, Esq. Roger L.
Melotik, Esq. Lorraine S.
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