Low friction cam shaft

Information

  • Patent Grant
  • 6167856
  • Patent Number
    6,167,856
  • Date Filed
    Friday, September 3, 1993
    31 years ago
  • Date Issued
    Tuesday, January 2, 2001
    23 years ago
Abstract
A low friction cam shaft for actuating at least one valve of an internal combustion engine includes a shaft member extending longitudinally, at least one cam secured to the shaft member, the cam being made of a plurality of density metal materials and having 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.
Description




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.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a partial fragmentary view of a valve train, according to the present invention, illustrated in operational relationship to an engine.





FIG. 2

is an enlarged view of a tappet assembly for the valve train of FIG.


1


.





FIG. 3

is an exploded view of a portion of the tappet assembly of FIG.


2


.





FIG. 4

is an enlarged view of the portion of the tappet assembly of

FIG. 3

as assembled.





FIG. 5

is an enlarged view of a portion of the tappet assembly in circle


5


of FIG.


4


.





FIG. 6

is an enlarged view of a cam for the valve train of FIG.


1


.





FIG. 7

is an enlarged view of a valve and valve guide for the valve train of FIG.


1


.





FIG. 8

is an enlarged view of a valve and valve seat for the valve train of FIG.


1


.





FIG. 9

is an enlarged view of a portion of the valve train of

FIG. 1

prior to break-in.





FIG. 10

is a view similar to

FIG. 9

after break-in.





FIG. 11

is a perspective view of a low friction cam shaft, according to the present invention, for the valve train of FIG.


1


.





FIG. 12

is a sectional view taken along line


12





12


of FIG.


11


.





FIG. 13

is a sectional view taken along line


13





13


of FIG.


12


.











DESCRIPTION OF THE PREFERRED EMBODIMENT(S)




Referring to the drawings and in particular

FIG. 1

thereof, a valve train


12


, accordingly to the present invention, is illustrated in operational relationship to an engine, generally indicated at


14


, such as an internal combustion engine. The engine


14


includes a cylinder or engine block


15


having at least one, preferably a plurality of hollow cylinders


16


therein. The engine


14


also includes a cylinder or engine head


18


secured to the cylinder block


15


by suitable means such as fasteners (not shown). The cylinder head


18


has an intake passageway


20


and an exhaust passageway


22


communicating with the cylinders


16


.




The valve train


12


includes at least one, preferably a plurality of valve assemblies, generally indicated at


24


for opening and closing the intake passageway


20


and exhaust passageway


22


. Preferably, separate valve assemblies


24


are used for the intake passageway


20


and the exhaust passageway


22


. The valve train


12


also includes at least one, preferably a plurality of cam shafts


26


for opening and closing the valve assemblies


24


. The cam shaft


26


includes a shaft member


27


rotatably supported within the cylinder head


18


as is known in the art. The cam shaft


26


has at least one, preferably a plurality of cams


28


which contact and move the valve assemblies


24


. The cams


28


have a base circle portion


30


and a lobe portion


32


.




Each valve assembly


24


includes a valve


34


having a head portion


35


and a stem portion


36


slidably disposed in a valve guide


37


. The valve guide


37


is disposed in an aperture


38


of the cylinder head


18


as is known in the art. The valve assembly


24


also includes a tappet assembly


39


contacting one end of the stem portion


35


of the valve


34


and engaging a cam


28


of the cam shaft


26


. The tappet assembly


39


is slidably disposed in a tappet guide aperture


40


of the cylinder head


18


as is known in the art. The valve assembly


24


further includes a valve spring


41


disposed about the stem portion


35


of the valve


34


and having one end contacting the cylinder head


18


and the outer end contacting a valve spring retainer


42


disposed about the stem portion


35


. The valve spring


41


urges the head portion of the valve


34


into engagement with a valve seat


43


to close a corresponding intake or exhaust passageway


20


,


22


. The valve seat


43


is disposed in a recess


44


of the cylinder head


18


at the end of the intake or exhaust passageway


20


,


22


adjacent the cylinder


16


.




Referring now to

FIG. 2

, a tappet assembly


39


, according to the present invention, is illustrated. The tappet assembly


39


includes a tappet body


46


which is generally cylindrical in shape and having a hollow interior


47


to receive the stem portion


35


of the valve


34


. Preferably, the tappet body


46


is made from a metal material such as a die cast strength aluminum or magnesium alloy. The outer periphery or surface of the tappet body


46


is hard anodized. The anodizing process results in a coating which is submicroscopically porous, e.g., a pore size of approximately 3-10 microns, for allowing a solid film lubricant


50


to be impregnated within the tappet body


46


prior to finish grinding. It is important that the depth of the anodized layer be adequate, approximately 30-40 microns, to support the bearing loads. Also, the anodizing process should produce a suitable anodized layer of sufficient depth and integrity that it does not crumble under fatigue loading. The solid film lubricant


50


must be impregnated to a depth of at least a few microns greater than the expected wear, e.g., if expected wear is around 30 microns then a solid film lubricant impregnation to approximately 35-40 microns is satisfactory.




The solid film lubricant


50


, as used herein, is a solid lubricant that has a coefficient of friction of 0.02-0.1 at 600° F. The solid film lubricant


50


is preferably a composite, by volume, of 40% graphite, 20% MoS


2


and the remainder a thermally stable (does not decompose up to 375° C. or 700° F.) polymer such as polyarylsulfone or a high temperature epoxy such as bisphenol A and vinyl butoryl combined with dicyandianide. The solid film lubricant


50


of the type described here promotes rapid stable oil film formation due to its affinity for conventional lubricating oils. The solid film lubricant


50


may also be a metal matrix composite having about 40% graphite and the remainder aluminum or cast iron. Such metal matrix composites may be formed by powder metallurgy or other suitable means to provide a porus material that can expose graphite for intermittent or supplementary lubrication purposes. Up to 13% of the graphite may be substituted with boron nitride. The solid lubricant may also include up to 10% copper and one of LiF, NaF, and CaF as a substitute for the MoS


2


. It should be appreciated that other compositions suitable as solid film lubricants may also be used.




As illustrated in

FIGS. 2 through 5

, the tappet assembly


39


also includes a cavity


51


at an upper end thereof. The cavity


51


is generally cylindrical in shape. The tappet assembly


39


also includes a wear resistant insert


52


having a contacting surface


54


which contacts a cam


28


or a cam shaft


26


. Preferably, the insert


52


is made of ceramic material but may also be manufactured from a high strength steel, toughened alumina or silicon nitride sintered. The insert


52


is machined to fit in the cavity


51


of the tappet body


46


. The insert


52


and cavity


51


are matched for a smooth fit. Preferably, the sides of the insert


52


and the cavity


51


include complementary inverse tapers


57


and


58


, respectively, to lock the insert


52


within the cavity


51


. The insert


52


is secured within the cavity


51


through a shrink-f it process. The shrink-fit process includes heating the tappet body


46


to a temperature approximately 100° F. higher than the engine operating temperature (approximately 310° F.), and cooling the insert


52


to a temperature below a low end ambient temperature (approximately −50° F.) after which the insert


52


is placed in the cavity


51


. When the tappet assembly


39


is brought to room temperature, the tappet body


46


shrinks around the insert


52


because of the significantly higher thermal expansion of the tappet body


46


relative to that of the insert


52


. This process insures that the insert


52


remains in compression during the entire operating range of engine temperatures. It should be appreciated that the insert


52


may also be secured to the tappet body


46


through the use of a lock ring


59


engaging corresponding annular grooves


59




a


and


59




b


formed in both the insert


52


and the tappet body


46


, respectively.




Referring to

FIG. 6

, a cam


28


of the cam shaft


26


is shown. The base circle portion


30


of the cam


28


includes an interior portion


60


made from a metal material of a soft/low carbon steel to minimize stresses occurring during rotation of the cam shaft


26


. The interior portion


60


is mechanically secured to a fluted or roughened portion


62


of the shaft


27


. The lobe portion


32


and the remaining portion of the base circle portion


30


of the cam


28


are made from a metal material such as a porous medium/high carbon Ni—Cr alloy steel. The outer periphery or surfaces of the base circle portion


30


and lobe portion


32


are hardened to a normally specified hardness level for a cam surface (usually around Rc


55


) utilizing any one of the well known processes, e.g. carbo nitrating. Generally, the porosity extends only to a depth of less than 1.0 mm. The porosity enables the outer surfaces of the cam


28


to be impregnated with the solid film lubricant


50


. The depth of the solid film lubricant


50


impregnation should be at least a few microns greater than the expected wear as previously described.




Referring to

FIG. 7

, the valve guide


37


is shown. The valve guide


37


has an inner surface


66


impregnated with the solid film lubricant


50


to reduce the friction between the stem portion


35


of the valve


34


and the valve guide


37


. Preferably, the inner surface


66


of the valve guide


37


includes a wear resistant porous layer formed by a suitable means to facilitate impregnation of the solid film lubricant


50


as previously described.




Referring to

FIG. 8

, the valve seat


43


is shown. The valve seat


43


has an outer surface


68


also impregnated with the solid film lubricant


50


to reduce the friction and corresponding wear occurring between the head portion


35


and valve seat


43


. Alternatively, the outer surface of the head portion


35


of the valve


34


may be impregnated with the solid film lubricant


50


and the head portion


35


may be hollow with a wear resistant insert at the lower end thereof. It should be appreciated that the valve seat


43


is treated to form a wear resistant porous layer as previously described.




Referring to

FIG. 9

, a portion of the solid film lubricant


50


on a corresponding valve train component such as the tappet body


46


prior to break in is illustrated. The solid film lubricant


50


is impregnated to an effective wear depth and includes a superficial layer. After engine break in, the layer of solid film lubricant


50


forms a stable low friction wear resistant film as illustrated in FIG.


10


.




In operation, the solid film lubricant


50


promotes the formation of a stable lubrication film. The stable lubrication film reduces friction occurring at higher operating speeds where hydrodynamic lubrication is predominate. Rapid formation of a lubrication film significantly reduces cam wear by reducing the friction at lower engine speeds.




Referring to

FIGS. 11 through 13

, a low friction cam shaft


70


, according to the present invention, is shown for the valve train


12


. The cam shaft


70


may be used in place of the cam shaft


26


for opening and closing the valve assemblies


24


. The cam shaft


70


includes a shaft member, generally indicated at rotatably supported within the cylinder head as is known in the art. The shaft member


72


has a shaft


74


extending longitudinally and is an extruded hollow or tubular member. The shaft member


72


also has ends


76


which are solid and have a portion


77


disposed within the ends of the shaft


74


. Preferably, the shaft member


72


has an outer periphery or surface


78


which is roughened, fluted or knurled for a function to be described.




Preferably, the shaft member


72


is made from a metal material such as a die cast strength aluminum or magnesium alloy. The outer surface


78


is hard anodized. The anodizing process results in a coating which is submicroscopically porous, e.g., a pore size of approximately 3-10 microns, for allowing the solid film lubricant


50


to be impregnated prior to finish grinding. It is important that the depth of the anodized layer be adequate, approximately 30-40 microns, to support the bearing loads. Also, the anodizing process should produce a suitable anodized layer of sufficient depth and integrity that it does not crumble under fatigue loading. The solid film lubricant


50


must be impregnated to a depth of at least a few microns greater than the expected wear, e.g., if expected wear is around 30 microns, then the solid film lubricant


50


should be impregnated to approximately 35-40 microns.




The cam shaft


70


also includes at least one, preferably a plurality of bearing members


80


disposed about the shaft member


72


at predetermined positions longitudinally therealong. The bearing members


80


may have an outer diameter greater than an outer diameter of the shaft


74


. The bearing members


80


are integral with the shaft member


72


and are formed by grinding the outer surface


78


to a predetermined dimension. The bearing members


80


may have at least one, preferably a plurality of grooves or furrows


82


extending transversely and spaced circumferentially thereabout. It should be appreciated that the bearing members


80


have the solid e film lubricant


50


embedded in the outer bearing surface thereof.




The cam shaft


70


further includes at least one, preferably a plurality of cams, generally indicated at


84


, which contact and move the valve assemblies


24


. The cams


84


are formed by powder metallurgy from, at least two, preferably a plurality of density metal powders to form a composite metal interspersed with the solid film lubricant


50


. The cams


84


have a base circle portion


86


and a lobe portion


88


. The base circle portion


86


includes an interior portion


90


made from a first density powder metal material such as a soft/low carbon steel to minimize stresses occurring during rotation of the cam shaft


70


. The interior portion


90


is mechanically secured to the outer surface


78


of the shaft member


72


, for example, by internal mechanical twist or pressurizing hydraulic fluid as is known in the art. The lobe portion


88


and the remaining portion of the base circle portion


86


are made from a second density powder metal material such as porous metallic high carbon (approx. 0.5 C) Ni—Cr alloy steel.




The outer periphery or surfaces of the base circle portion


86


and lobe portion


38


are hardened to a normally specified hardness level for a cam surface (usually around Rc


55


) utilizing any one of the well known processes, e.g. carbo nitrating. Generally, the porosity extends only to a depth of less than 1.0 mm. The porosity enables the outer surfaces of the cam


84


to be impregnated with the solid film lubricant


50


. The depth of the solid film lubricant


50


impregnation is at least a few microns greater than the expected wear as previously described. For example, in the case of the cam


84


, the expected wear is around 30 microns and therefore the impregnation of the solid film lubricant


50


is approximately 35 to 40 microns in depth. It should be appreciated that “density” refers to porousity and that the second density powder metal material is five to ten percent porous whereas the first density powder metal material is less than one percent porous.




Alternatively, the outer surfaces of the base circle portion


86


and lobe portion


88


can be made porous by the addition of an arc plasma spray coating. The coating can be any suitable hard material such as Silicon (Si) or Tungsten Carbide dispersed in Nickel (Ni) and the porousity generated by controlling particle size. The coating may be an iron base material such as FeCrNi or commercial available Triboloy (Ni


18


Cr


16


Al


4


alloy). The coating is of a sufficient thickness such as one hundred fifty (150) microns. It should be appreciated that the porous coating is impregnated with the solid film lubricant


50


. It should also be appreciated that the coating is applied by conventional arc plasma spray processes as is known in the art.




Accordingly, the solid film lubricant


50


on the valve train


10


reduces friction losses, the contact forces due to the elimination of hydraulic loading, and reduces inertia forces due to a significant reduction in the reciprocating mass. As a result, the valve train


10


permits significantly higher engine operating speeds and a reduction in friction and wear which extends corresponding engine life. Because of the significantly reduced wear, the valve train


10


does not require adjustment for life of the engine nor does it require a hydraulic lash adjustment and the attendant precision machining and hydraulic lubrication requirements. Also, the low friction cam shaft


70


provides a reduction in friction for the valve train


12


while using relatively low cost, easily formed composite powder metal cams


84


interspersed with solid film lubricant


50


.




The present invention has been described in an illustrative manner. It is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation.




Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described.



Claims
  • 1. A low friction cam shaft for actuating at least one valve of an internal combustion engine comprising:a shaft member extending longitudinally and having a first outer surface; at least one cam secured to said shaft member; and said at least one cam being made of a plurality of density metal materials, said at least one cam having a base circle portion and a lobe portion, said base circle portion having an interior portion and an outer portion, said outer portion of said base circle portion and said lobe portion being made of one of said density metal materials, said interior portion being made of another of said density metal materials, said interior portion having a porosity less than said lobe portion and said outer portion of said base circle portion, said outer portion of said base circle portion and said lobe portion having a second outer surface, said first and second outer surfaces having an open porosity and are 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.
  • 2. A low friction cam shaft as set forth in claim 1 wherein one of said density metal materials is a porous medium to high carbon Ni—Cr alloy steel, said solid film lubricant being impregnated within the open porosity.
  • 3. A low friction cam shaft as set forth in claim 2 wherein one of said density metal materials is a soft and low carbon steel.
  • 4. A low friction cam shaft as set forth in claim 1 wherein said interior portion is made of a soft and low carbon steel.
  • 5. A low friction cam shaft as set forth in claim 4 therein said lobe portion and said outer portion of said base circle portion are made of a porous medium to high carbon Ni—Cr alloy steel.
  • 6. A low friction cam shaft as set forth in claim 1 wherein said shaft member has a hollow shaft with said first outer surface that is either one of roughened and fluted and knurled.
  • 7. A low friction cam shaft as set forth in claim 6 wherein said shaft member has solid ends with a portion disposed within said shaft.
  • 8. A low friction cam shaft as set forth in claim 1 including at least one bearing member on said shaft member.
  • 9. A low friction cam shaft as set forth in claim 8 wherein said bearing member has at least one furrow extending along the longitudinal direction of said shaft member.
  • 10. A low friction cam shaft as set forth in claim 1 wherein said solid film lubricant is comprised of graphite, boron nitride, molybdenum disulfide in a high temperature polymer base.
  • 11. A low friction cam shaft for actuating at least one valve of an internal combustion engine comprising:a shaft member extending longitudinally and having ia first outer surface; at least one cam secured to said shaft member having a base circle portion and lobe portion, said base circle and lobe portions having a second outer surface, said first and second outer surfaces having an open porosity and are impregnated with a solid film lubricant comprised of graphite and at least one of molybdenum disulfide and boron nitride in either one of a high temperature polymer and epoxy base, the solid film lubricant has an affinity for oil and promotes rapid formation of a stable oil film to reduce friction therebetween.
  • 12. A low friction cam shaft as set forth in claim 11 wherein said at least one cam is made of a plurality of density powder metal materials.
  • 13. A low friction cam shaft as set forth in claim 11 wherein an interior portion of said base circle portion is formed of a soft and low carbon steel.
  • 14. A low friction cam shaft as set forth in claim 11 wherein said lobe portion and a remainder of said base circle portion are formed of a porous medium to high carbon Ni—Cr alloy steel.
  • 15. A low friction cam shaft as set forth in claim 11, including at least one bearing member on said shaft member.
  • 16. A low friction cam shaft as set forth in claim 15 wherein said at least one bearing member includes at least one furrow extending along the longitudinal direction of said shaft member.
  • 17. A low friction cam shaft for actuating at least one valve of an internal combustion engine comprising:a shaft member extending longitudinally and having a first outer surface; at least one cam secured to said shaft member having a base circle portion and lobe portion, said base circle and lobe portions having a second outer surface, wherein an interior portion of said base circle portion is a soft low carbon steel; wherein said lobe portion and a remainder of said base circle portion are formed of a porous medium to high carbon Ni-Cr alloy steel; and at least one bearing member on said shaft member having a third outer surface with at least one furrow extending along the longitudinal direction of said shaft. member; said first and second and third outer surfaces having an open porosity and are impregnated with a solid film lubricant, the solid film lubricant has an affinity for oil and promotes rapid formation of a stable oil film to reduce friction therebetween.
  • 18. A low friction cam shaft for actuating at least one valve of an internal combustion engine comprising:a shaft member extending longitudinally and having a first outer surface; at least one cam secured to said shaft member having a base circle portion and lobe portion, said base circle and lobe portions having a second outer surface, said first and second outer surfaces having an open porosity and are 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.
  • 19. A low friction cam shaft for actuating at least one valve of an internal combustion engine comprising:a shaft member extending longitudinally and having a first outer surface; at least one cam secured to said shaft member having a base circle portion and lobe portion, said base circle and lobe portions having a second outer surface, at least one bearing member on said shaft member having a third outer surface; said first and second and third outer surfaces having an open porosity and are impregnated with a solid film lubricant, the solid film lubricant has an affinity for oil and promotes rapid formation of a stable oil film to reduce friction therebetween.
CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application is a Continuation-In-Part of Ser. No. 07/975,320, filed Nov. 12, 1992, now abandoned and entitled “Low Friction Valve Train”.

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Continuation in Parts (1)
Number Date Country
Parent 07/975320 Nov 1992 US
Child 08/115974 US