EP0080175A1

EP0080175A1 - Overhead camshaft engine valve train with rotary tappet between rocker and cam

Info

Publication number: EP0080175A1
Application number: EP82110673A
Authority: EP
Inventors: Yoshimasa Hayashi
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1981-11-24
Filing date: 1982-11-18
Publication date: 1983-06-01
Also published as: JPS5891313A; JPS6059407B2

Abstract

A valve train of an overhead camshaft engine is provided with a rotary tappet (30, 30') which is interposed between a rocker arm (26) and a cam (32) and adapted to be rotatable in response to the rotation of the cam (32) while transferring motion from the cam (32) to the rocker arm (26).

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to valve trains of overhead camshaft engines and of the kind wherein a rocker is incorporated to transfer motion from a cam to a valve stem, and more particularly to the improvement in such valve trains for reducing the frictional sound and friction loss arising from the contact between the rocker and the cam.

2. Description of the Prior Art

Such valve trains as described above are known as a rocker-arm type and a swing-arm type. Figs. 1 and 2 show a prior art rocker-arm type valve train which comprises a cam 10 rotatable together with an overhead camshaft 12, a poppet valve 14 having a valve stem 14a, and a rocker arm 16 rotatable on a rocker shaft 18. The rocker arm 16 has at an end 16a thereof a cam follower 20 having a part-cylindrical cam contacting surface 20a and at the opposite end 16b thereof a valve clearance adjuster 22 positioned to contact the end of the valve stem 14a for adjusting the clearance in the valve train. The cam follower 20 is so made as to have a good resistance to wear and brazed or otherwise secured to the rocker arm 16.
The prior art valve train structured as above is encountered by a drawback in that a relatively large frictional sound and friction loss arise from the contact between the rocker arm 16 and the cam 10 since the cam contacting surface 20a and the cam surface 10a have to slide relative to each other under the bias of a valve spring 24. The large friction loss not only by itself deteriorates the operation of the valve train and therefore the performance of the engine on which the valve train is mounted but also accelerates the wear of the cam 10 and the cam follower 20 to further deteriorate the same.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a valve train which comprises a valve stem, a valve operating cam, a rocker arm operatively engaged with the valve stem and the cam for transferring motion from the cam to the valve stem and having at a part where it is operatively engaged with the cam a hole, a rotary tappet rotatable about an axis thereof in the hole and axially supported on the rocker arm, the tappet having a cam contacting surface domed to follow the cam surface of the cam, and the cam surface being
constructed and arranged to be brought into contact with the tappet at a point thereon offset from the axis of the tappet.
The above structure enables the valve train to be free from the drawbacks noted above.
It is accordingly an object of the present invention to provide a valve train of an overhead camshaft engine which is quiet in operation and efficient in power transmission.
It is another object of the present invention to provide a valve train of the above described character which can substantially eliminated the frictional sound arising from the contact between a rocker and a valve operating cam.
It is a further object of the present invention to provide a valve train of the above described character which can considerably reduce the friction loss arising from the contact between the rocker and the cam.
It is a further object of the present invention to provide a valve train of the above described character which is particularly suited for adoption to an overhead camshaft engine of the kind wherein a rocker arm is incorporated.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the valve train according to the present invention will become more clearly appreciated from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate like or corresponding parts throughout the several views thereof and wherein:

Fig. 1 is a sectional view of a prior art valve train of an overhead camshaft engine;
Fig. 2 is a sectional view taken along the line II-II of Fig. 1;
Fig. 3 is a sectional view of a valve train according to an embodiment of the present invention;
Fig. 4 is a sectional view taken along the line IV-IV of Fig. 3;
Fig. 5 is a perspective view of a rotary tappet incorporated in the valve train of Fig. 3; and
Fig. 6 is a fragmentary sectional view of a valve train according to a modified embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to Figs. 3 through 5, inclusive, a valve train according to an embodiment of the present invention is of a rocker-arm type for use in an overhead camshaft engine and comprises a rocker arm 26 rotatable on a rocker shaft 28 and having at an end 26a thereof a rotary cam follower or tappet 30 cooperating with a cam 32 rotatable together with a camshaft 34 and at the opposite end 26b thereof a valve clearance adjuster 22. The tappet 30 is formed from concentric or coaxial disk and stem portions 36 and 38 and rotatably mounted at the stem portion 38 in a hole 40 provided to the end 26a of the rocker arm 26. The disk portion 36 is located at the outer end of the stem portion 38 and has a bottom 36a whose outer surface is domed to follow the cam surface 32a and a top 36b formed with an annular projection 36c contacting the rocker arm 26 at a wall portion 26c thereof around the hole 40. The mating surfaces of the rocker arm wall portion 26c and the annular projection 36c of the tappet disk portion 36 are finished smooth and furthermore adapted to be sufficiently lubricated as will be described hereinafter.
The cam surface 32a is slanted (by an angle ranging from about 1 to 5° or so) with respect to the axis of the camshaft 34 so that the cam 32 is brought into contact with the tappet 30 at a point thereon offset from the axis of the tappet 30. That is, while the outer surface of the domed bottom 36a constitutes part of a sphere whose center coincides with the axis of the tappet 30, the point of contact between the tappet 30 and the cam 32 does not coincides with the axis of the tappet 30 and spaced away from same in the axial direction of the camshaft 34. In the meantime, the axes of the camshaft 32 and the rocker shaft 28 are arranged substantially parallel to each other, and the rocker arm 26 rocks along a plane traversing the axes of the camshaft 32 and the rocker shaft 28, as is conventional.
The rocker shaft 28 is formed with an oil passage 28a in communication with a source of oil under pressure such as an engine oil pump. The rocker arm 26 is also formed with an oil passage 26d providing communication between the oil passage 28a and the hole 40 to supply lubrication oil to the mating surfaces of the rocker arm wall portion 26c and the annular projection 36c of the tappet disk portion 36. The rocker arm 26 is further formed with an oil passage 26e in the form of an extension of the oil passage 26d, which passage 26e opens adjacent the top 36b of the tappet disk portion 36 to lubricate the cam surface 32a and the bottom 36a of the tappet disk portion 36 as well as to further provide the mating surfaces in question with lubrication oil.
In operation, when the lobe of the cam 32 is in engagement with the tappet 30, the rotation of the cam 32 causes the tappet 30 to move upwardly or downwardly together with the rocker arm end 26a and at the same time causes the tappet 30 to rotate about the axis thereof. That is, differing from the prior art valve train, the tappet 30 is successively brought into contact at different portions thereof with the cam 32 in response to the rotation of the cam 32. The valve train is thus adapted to effect a rolling contact between the tappet 30 and the cam 32, considerably reducing the frictional sound and friction loss arising from the contact between the tappet 30 and the cam 32. Further, the mating surfaces of the rocker arm wall portion 26c and the annular projection 36c of the tappet disk portion 36 are finished smooth and sufficiently lubricated, making it possible to effectively prevent the frictional sound and friction loss arising from the contact between the tappet 30 and the rocker arm 26.
In the foregoing, as indicated by the phantom line of Fig. 4, the base circle of the cam 32 may have a cylindrical cam surface to produce substantially the same effect as one having an entirely slanted cam surface as having described above.
Fig. 6 shows a modification of this invention wherein a steel ball 42 is utilized to further reduce the friction between the tappet 30' and the rocker arm 26. The steel ball 42 is inserted into the hole 40 to interpose between the closed end of the hole 40 and the inner end of the tappet stem portion 38' so that a small gap is formed between the tappet disk portion 36' and the rocker arm 26. That is, the tappet 30' is given a flat top 36'b and adapted not to contact at the top 36'b with the rocker arm 26 but to rotate on the steel ball 42. This structure makes it possible to further effectively prevent the frictional sound and friction loss arising from the contact between the tappet 30 and the rocker arm 26.
Obviously, many variations and modifications of the present invention are possible in light of the above teachings. For example, while the invention is described and shown as an application to rocker arm-type, it may be similarly applied to a swing-arm type valve train of an overhead camshaft engine. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise as specifically described.

Claims

1. A valve train of an overhead camshaft engine comprising:

a valve stem (14a);

a valve operating cam (32);

a rocker arm (26) operatively engaged with said valve stem (14a) and said cam (32) for transferring motion from the cam (32) to the valve stem (14a) and having at a part (26a) where it is operatively engaged with said cam (32) a hole (40);

a rotary tappet (30,30') rotatable about an axis thereof in said hole (40) and axially supported on said rocker arm (26), said tappet (30,30') having a cam contacting surface (36a) domed to follow the cam surface (32a) of said cam (32); and

said cam surface (32a) being constructed and arranged to be brought into contact with said tappet (30,30') at a point thereon offset from the axis of said tappet (30).

2. A valve train of an overhead camshaft engine as set forth in claim 1, wherein said cam (32) is rotatable together with a camshaft (34) and wherein said cam surface (32a) is slanted with respect to the axis of said camshaft (34).

3. A valve train of an overhead camshaft engine as set forth in claim 2, wherein said tappet (30,30') consists of concentric disk and stem portions (36,38;36',38') and rotatably mounted at said stem portion (38;38') in said hole (40).

4. A valve train of an overhead camshaft engine as set forth in claim 3, wherein said disk portion (36) is located at the outer end of said stem portion (38) and has a bottom (36a) whose outer surface constitutes said domed cam contacting surface and a top (36b) formed with an annular projection (36c) contacting said rocker arm (26) at a wall portion (26c) thereof around said hole (40).

5. A valve train of an overhead camshaft engine as set forth in claim 3, further comprising a steel ball (42) inserted into said hole (40) to interpose between the closed end of said hole (40) and the inner end of said tappet stem portion (38'), and wherein said disk portion (36') is located at the outer end of said stem portion (38') and has a bottom (36'a) whose outer surface constitutes said domed cam contacting surface and a flat top (36'b) which is kept out of contact from said rocker arm (26).

6. A valve train of an overhead camshaft engine as set forth in claim 4, wherein said rocker arm (26) is rotatable on a rocker shaft (28), and wherein said rocker shaft (28) is formed with an oil passage (28a) in communication with a source of oil under pressure and said rocker arm (26) is also formed with an oil passage (26d) providing communication between said rocker shaft oil passage (28a) and said hole (40) to mainly lubricate the mating surfaces of said rocker arm wall portion (26c) and said annular projection (36c) of said tappet disk portion (36).

7. A valve train of an overhead camshaft engine as set forth in claim 6, wherein said rocker arm (26) is further formed with an oil passage (26e) in the form of an extension of said first mentioned rocker arm oil passage (26d), which oil passage extension (26e) opens adjacent the top (36b) of said tappet disk portion (36) to lubricate said cam surface (32a) and said bottom (36a) of said tappet disk portion (36) as well as to further provide said mating surfaces with lubrication oil.

8. A valve train of an overhead camshaft engine as set forth in claim 4, wherein said rocker arm (26) is rotatable on a rocker shaft (28), and wherein said rocker shaft (28) is formed with an oil passage (28a) in communication with a source of oil under pressure and said rocker arm (26) is also formed with an oil passage (26d) providing communication between said rocker shaft oil passage (28a) and said hole (40) to mainly lubricate said steel ball (42).

9. A valve train of an overhead camshaft engine as set forth in claim 8, wherein said rocker arm (26) is further formed with an oil passage (26e) in the form of an extension of said first mentioned rocker arm oil passage (26d), which oil passage extension (26e) opens adjacent the top (36'b) of said tappet disk portion (36') to lubricate said cam surface (32a) and said bottom (36a) of said tappet disk portion (36).