VALVE LIFTER FOR INTERNAL COMBUSTION ENGINE

BACKGROUND OF THE INVENTION

The present invention relates to an improvement of a valve lifter for an internal combustion engine.

U.S. Patent Application Publication No. 2001/0047782 corresponding to Japanese Patent Application Publication No. 2001-342810 (hereinafter referred to as, patent document 1) discloses a previously-proposed valve lifter for transmitting a rotation of cam shaft to intake and exhaust valves in a four-cycle internal combustion engine. In this technique, the valve lifter is formed approximately in a covered-tube shape, and includes a tubular skirt portion and a crown portion formed integrally with an upper end portion of the skirt portion. A drive cam of the cam shaft rotates and slides in contact with a flat crown surface of the crown portion. Thereby, a rotational motion of the cam is converted to a reciprocating motion so that a rotational force of the cam is transmitted to the intake valve and the exhaust valve.

However, since the crown surface is formed in the flat shape in the above previously-proposed valve lifter, there is a technical problem that a sliding friction of the drive cam is large.

Therefore, Japanese Patent Application Publication No. 2004-225610 (hereinafter referred to as, patent document 2) discloses another previously-proposed valve lifter. In this technique, the crown surface is formed in a spherically-protruding shape in order to reduce the sliding friction of the cam.

SUMMARY OF THE INVENTION

However, in the technique disclosed by the patent document 2, if a protruding amount (crowning amount) of the crown surface is excessively large, there is a risk that a free rotation of the valve lifter during operation is lost and a surface pressure in a sliding portion of the drive cam becomes high to cause a local abrasion (wear-out).

It is therefore an object of the present invention to provide a valve lifter devised to reduce both of the friction of the crown surface and the abrasion.

According to one aspect of the present invention, there is provided a valve lifter for an internal combustion engine, comprising: a skirt portion formed in a tubular shape; and a crown portion formed integrally with an axially one end side of the skirt portion, the crown portion including a crown surface configured to slide in contact with an outer circumferential surface of a cam, wherein an axis of the crown portion is eccentric from a center of the cam in a width direction of the cam, wherein the crown surface is formed in a spherical protruding shape to have its uppermost portion at a center of the crown surface, wherein a protruding amount of the spherical protruding shape is set to range from 11 μm to 50 μm.

According to another aspect of the present invention, there is provided a valve lifter for an internal combustion engine, comprising: a skirt portion formed in a tubular shape; and a crown portion formed integrally with an axially one end side of the skirt portion, the crown portion including a crown surface configured to slide in contact with an outer circumferential surface of a cam, wherein an axis of the crown portion is located to be offset from a center of the cam in a width direction of the cam, wherein the crown surface is formed in a spherical protruding shape to have its uppermost portion at a center of the crown surface, wherein a protruding amount of the spherical protruding shape is larger than 11 μm and smaller than a boundary value below which the valve lifter rotates by a rotational force of the cam.

According to still another aspect of the present invention, there is provided a valve lifter for an internal combustion engine, comprising: a skirt portion formed in a tubular shape; and a crown portion formed integrally with an axially one end side of the skirt portion, the crown portion including a crown surface configured to slide in contact with an outer circumferential surface of a cam, wherein a center of the crown portion is located to be offset from a center of the cam in a width direction of the cam, wherein the crown surface is formed in a spherical protruding shape to have its uppermost portion at a center of the crown surface, wherein a protruding amount of the spherical protruding shape is set to be larger than 11 μm, wherein the protruding amount of the spherical protruding shape is set to be smaller than a boundary value below which a contact portion between the outer circumferential surface of the cam and the crown surface forms an asymmetrical shape with respect to a center line of the crown surface perpendicular to the width direction of the cam.

The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a valve lifter for an internal combustion engine in an embodiment according to the present invention.

FIG. 2 is a sectional view showing a main part of the internal combustion engine to which the valve lifter in the embodiment has been applied.

FIG. 3 is a longitudinal sectional view of a friction measurement machine for measuring a friction between the valve lifter and a cam.

FIG. 4 is a characteristic view showing a relative relation between a crowning amount and the friction.

FIG. 5A is a sectional view showing a contact state between a crown surface of the valve lifter and the cam. FIG. 5B is a sectional view showing an offset amount of the valve lifter relative to the cam.

FIGS. 6A to 6C are schematic views each showing a contact-surface width between the crown surface of the valve lifter and an outer circumferential surface of the cam.

FIG. 7 is a characteristic view showing a rotational region of the valve lifter and a nonrotational region of the valve lifter, on the basis of a relation between the contact-surface width and the crowning amount of the crown surface.

FIG. 8 is a characteristic view showing the rotational region of the valve lifter and the nonrotational region of the valve lifter, on the basis of a relation between the contact-surface width and the crowning amount of the crown surface.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of valve lifter for an internal combustion engine according to the present invention will be explained in detail referring to the drawings.

FIG. 2 is a view showing a main part of the internal combustion engine to which a valve lifter according to the present invention is applied. In FIG. 2, as one example, the valve lifter according to the present invention is applied to intake and exhaust sides of a four-cycle gasoline engine having four cylinders.

This internal combustion engine includes two intake valves 4 and two exhaust valves 5 per one cylinder. Each of the two intake valves 4 is an engine valve functioning to open and close an intake port 2 formed inside a cylinder head 1. On the other hand, each of the two exhaust valves 5 is an engine valve functioning to open and close an exhaust port 3 formed inside the cylinder head 1. Each intake valve 4 is disposed slidably through a valve guide 6a, and each exhaust valve 5 is disposed slidably through a valve guide 6b. Moreover, an intake-side cam shaft 7 is supported through a cam-shaft bearing by an upper end portion of the cylinder head 1. In the same manner, an exhaust-side cam shaft 8 is supported through a cam-shaft bearing by the upper end portion of the cylinder head 1. On an outer circumferential surface of the intake-side cam shaft 7, a drive cam 9 for opening the intake valve 4 is provided integrally with the intake-side cam shaft 7. In the same manner, on an outer circumferential surface of the exhaust-side cam shaft 8, a drive cam 10 for opening the exhaust valve 5 is provided integrally with the exhaust-side cam shaft 8.

The intake valve 4 includes an umbrella portion 4a at a lower end side of a valve stem of the intake valve 4, and similarly, the exhaust valve 5 includes an umbrella portion 5a at a lower end side of a valve stem of the exhaust valve 5. The umbrella portion 4a is seated on and moved away from an annular valve seat 2a, and similarly, the umbrella portion 5a is seated on and moved away from an annular valve seat 3a. The valve seat 2a is provided at an opening end of the intake port 2, and similarly, the valve seat 3a is provided at an opening end of the exhaust port 3. A spring retainer 13a is fixed to a stem end 4b of the valve stem which is located in an upper end portion of the intake valve 4, and similarly, a spring retainer 13b is fixed to a stem end 5b of the valve stem which is located in an upper end portion of the exhaust valve 5. A valve spring 14 is provided resiliently between the spring retainer 13a and a bottom surface of a supporting hole 1a formed in the upper end portion of the cylinder head 1, and similarly, a valve spring 15 is provided resiliently between the spring retainer 13b and a bottom surface of a supporting hole 1b formed in the upper end portion of the cylinder head 1. The intake valve 4 is biased or urged in its closing direction by a biasing force of the valve spring 14, and similarly, the exhaust valve 5 is biased or urged in its closing direction by a biasing force of the valve spring 15.

As shown in FIGS. 2 and 5, each of the drive cams 9 and 10 has a general structure. When viewed in a lateral direction (axial direction) of each cam 9, 10, each cam 9, 10 is formed in an egg shape or oval shape as shown in FIG. 5A. Each cam 9, 10 has a predetermined cam width W, as viewed in a direction perpendicular to the lateral direction, as shown in FIG. 5B.

Moreover, a valve lifter 11 is interposed between the intake valve 4 and the drive cam 9, and similarly, a valve lifter 12 is interposed between the exhaust valve 5 and the drive cam 10. Each of these valve lifters 11 and 12 is of direct-acting type, and is integrally formed of a carbon steel which is an iron-based metal. The valve lifter 11 provided for the intake side has the same structure as that of the valve lifter 12 provided for the exhaust side. Hence, hereinafter, detail explanations will be given only about the intake-side valve lifter 11 for the purpose of simplification of the disclosure.

That is, as shown in FIGS. 1 and 2, the valve lifter 11 mainly includes a skirt portion 17, a crown portion 18 and a circular boss portion 19. The skirt portion 17 is formed in a circular tube shape, and is retained slidably in upward and downward directions (i.e., in an axial direction of the intake valve 4) in a guide hole 16. This guide hole 16 is formed in the upper end portion of the cylinder head 1. The crown portion 18 is formed integrally with an upper end portion of the skirt portion 17 which is an axially one end portion of the skirt portion 17. The boss portion 19 is formed integrally with the crown portion 18 substantially at a center portion of a lower surface of the crown portion 18. The stem end 4b is in contact with the boss portion 19.

The skirt portion 17 is formed in a thin-walled circular-tube shape. An outer circumferential surface 17a of the skirt portion 17 slides in contact with an inner circumferential surface of the guide hole 16 with a predetermined friction.

The crown portion 18 is formed in a relatively thick-walled shape. The crown portion 18 includes a crown surface 20 as an upper surface of the crown portion 18, and includes an oil hole 21 passing through the crown portion 18 in the axial direction of intake valve 4. The crown surface 20 is formed in a spherical convex shape, i.e., in a spherically protruding shape. An outer circumferential surface 9a of the drive cam 9 slides in contact with the crown surface 20. The oil hole 21 is formed in a region except a contact-sliding portion between the crown surface 20 and the outer circumferential surface 9a of the drive cam 9, and functions to guide lubricating oil to an inside of the valve lifter 11.

Whole of the crown surface 20 is formed in a convex spherical-surface shape having a predetermined radius. Thereby, a center Y of the crown surface 20 which lies on an axis of the valve lifter 11 (=axis of the crown portion 18) is a highest (uppermost) point of the crown surface 20. An outer circumferential edge 20a of the crown surface 20 is a lowest (lowermost) point of the crown surface 20 (when regarding the axial direction of the intake valve 4 as up-down direction). A protruding amount (crowning amount) H given between the outer circumferential edge 20a and a top 20b located at the center Y is set within a range from 11 m to 50 μm.

This range of the crowning amount H is set according to a magnitude of friction of the valve lifter 11 and according to a presence/absence of rotation of the valve lifter 11 in the guide hole 16. A significance of this criticality, i.e., a significance of specifying the range of the crowning amount H is based on experimental results obtained by inventors of the present application, and will be explained later in concrete terms.

Moreover, a so-called diamond-like carbon (DLC) treatment which is a generally-known surface treatment technique is applied to the entire crown surface 20. Thereby, a surface treatment layer is formed which has a high hardness and a low frictional resistance.

As shown in FIG. 5B, the center Y of the crown surface 20 is eccentric (offset) from a center X of the drive cam 9 (i.e., a center of the cam width W) in the width direction of the drive cam 9, by an amount (offset amount α) ranging from 0.9 mm to 1.1 mm to the left side of FIG. 5B. This range is set for ensuring that the valve lifter 11 itself is rotated by a friction generated between the outer circumferential surface 9a and the crown surface 20 with the rotation of the drive cam 9. That is, if the offset amount (eccentricity amount) α of the crown surface 20 falls within the above-mentioned range (0.9 mm to 1.1 mm), the rotation of the valve lifter 11 can be secured by a rotational force of the drive cam 9.

The significance of setting the crowning amount H of the crown surface 20 within the range from 11 μm to 50 μm, i.e., a necessity of setting the criticality for the crowning amount H will now be explained.

At first, in order to finally calculate the friction between the crown surface 20 and the drive cam 9, a cam torque T of the cam shaft 7 and a friction between the outer circumferential surface 17a of the skirt portion 17 of the valve lifter 11 and the inner circumferential surface of the guide hole 16 are detected in advance by using a measurement machine 30 (test device) for experimental use as shown in FIG. 3.

The experimental measurement machine 30 is constructed so as to imitate a part of the internal combustion engine. A brief explanation about the structure of this measurement machine 30 will be given as follows. As shown in FIG. 3, front and rear two bearings 33 and 33 are provided on a cylinder base body 31 which is formed in a substantially circular-tube shape and which corresponds to the cylinder head of the internal combustion engine. A single cam shaft 32 which corresponds to the cam shaft 7 is rotatably supported by the front and rear two bearings 33 and 33. A single drive cam 32a is provided integrally with the cam shaft 32 at a location between both the bearings 33 and 33. A drive pulley 34 for driving a rotation of the cam shaft 32 by a drive mechanism (not shown) is provided at one end portion of the cam shaft 32.

A bearing 35 formed substantially in a circular-tube shape is provided inside an upper end portion of the cylinder base body 31. A single engine valve 36 which corresponds to the intake valve 4 or the exhaust valve 5 is retained through a valve retainer 37 in the bearing 35 to be able to slide in the upward and downward directions. Moreover, the engine valve 36 is biased or urged in its closing direction by a valve spring 38. A valve lifter 39 is interposed between a stem end 36a of the engine valve 36 and the drive cam 32a.

The bearing 35 includes a small-diameter sleeve in an inner circumference thereof. The valve lifter 39 is retained by a small-diameter sleeve 35a of the bearing 35 to be able to slide in contact with the small-diameter sleeve 35a. An entire crown surface 39a of the valve lifter 39 is formed in a spherical convex shape (protruding spherical-surface shape). For the experiments using the experimental measurement machine 30, various valve lifters 39 were prepared that include one having its crown surface 39a formed by a small curvature radius and another having its crown surface 39a formed by a large curvature radius (at which the crown surface 39a is close to a flat shape). That is, multiple valve lifters 39 whose crowning amounts H can approximately cover a range from 5 μm to 44 μm were prepared. The valve lifter 39 which should be set in the experimental measurement machine 30 was selected from and changed to the prepared multiple valve lifters 39 for the experiments.

Moreover, a friction sensor 40 for measuring a lateral-surface friction between the small-diameter sleeve 35a and an outer circumferential surface of a skirt portion of the valve lifter 39 was provided on an upper end portion of the bearing 35. Also, on the upper end portion of the bearing 35, a cam torque sensor 41 for measuring a cam torque of the cam shaft 32 was provided.

These measurements were performed by the friction sensor 40 and the cam torque sensor 41, after a lapping was conducted for two hours under a condition that an oil-temperature is equal to 80° C. and a rotational speed of the cam shaft 32 is equal to 300 rpm.

That is, when the drive pulley 34 is driven and rotated, the drive cam 32a rotates through the cam shaft 32. Thereby, the drive cam 32a slides in contact with the crown surface 39a of the valve lifter 39, and thereby, the valve lifter 39 slides in contact with an inner surface of the small-diameter sleeve 35a in the upward and downward directions. Thus, a rotational motion is converted into a reciprocating motion by the valve lifter 39. By receiving this reciprocating motion, the engine valve 36 slides in contact with an inner surface of the valve retainer 37 in the upward and downward directions with the biasing force of the valve spring 38, so that the engine valve 36 carries out the opening/closing actuation.

In these experiments, as mentioned above, friction values of crown surfaces 39a each of which is accompanied with the rotation of the drive cam 32a were calculated based on the respective detection values of the lateral-surface friction sensor 40 and the cam torque sensor 41, by selecting the valve lifters 39 having values of crowning amount H different from one another. In detail, a numeric value of lateral-surface friction detected by the lateral-surface friction sensor 40 was converted into a numeric value of lateral-surface friction torque. Then, the numeric value of lateral-surface friction torque was subtracted from a (total) torque numeric value detected by the cam torque sensor 41. Then, a value obtained by this subtraction was regarded as each friction value of the crown surface 39a.

A reference sign 42 of FIG. 3 represents a valve lift sensor provided in a lower portion of the cylinder base body 31.

FIG. 4 is a characteristic view showing a result of these experiments. A horizontal axis of this graph represents the crowning amount H (μm) of the crown surface 39a, and a vertical axis of this graph represents the friction (N·m) of the valve lifter 39 (the friction of the crown surface 39a).

In a case that the crowning amount H is approximately equal to 5 μm, the crown surface 39a is close to a flat shape. Therefore, the friction values of the crown surface 39a range from 0.3 N·m to 0.4 N·m which are relatively large, as shown by four black squares of FIG. 4.

Contrary to this, in a case that the crowning amount H ranges from 11 μm to 44 μm, the friction of the crown surface 39a is gradually lowered, as shown by black triangles of FIG. 4. In particular, the friction of the crown surface 39a is rapidly decreased in a range smaller than or equal to 11 μm. When the crowning amount H is approximately equal to 11 μm, the friction value of the crown surface 39a approximately ranges from 0.29 N·m to 0.3 N·m. In a range between 11 μm and 44 μm, the friction value of the crown surface 39a is gradually lowered.

A sequential line of FIG. 4 is an average line of the friction values of the crown surface 39a with reference to the crowning amount H. As is clear from this sequential average line; the friction of the crown surface 39a is large in the case that the crowning amount H is smaller than or equal to 11 μm. Then, the friction of the crown surface 39a is gradually reduced from a point where the crowning amount H is equal to 11 μm to a point where the crowning amount H is equal to 44 μm, when regarding the value of 11 μm as a boundary of characteristic change. That is, from the average line of the friction values, the value of 11 μm in the crowning amount H can be recognized as the boundary of characteristic change.

In FIG. 4, the crown surfaces 39a of the valve lifters 39 having approximately same level in the crowning amount H as each other take the friction values slightly different from each other. This is attributed to an operational dispersion (minor variations) of the experimental measurement machine 30 and the like.

From the above experimental results, the crowning amount H of the crown surface 39a needs the level of 11 μm at the minimum for the purpose of reducing the friction of the crown surface 39a. It is more preferable that the crowning amount H of the crown surface 39a is set at a level larger than 11 μm.

Next, the present/absence of the rotation of the valve lifter 11 in the guide hole 16 which is caused with the rotation of the drive cam 9 will now be explained on the basis of experimental results in which a contact width (contact-surface width) between the crown surface 20 and the outer circumferential surface 9a of the drive cam 9 was changed.

FIG. 5A schematically shows a relation between the drive cam 9 and the valve lifter 11. FIG. 5B schematically shows the cam width W and the offset amount α of the valve lifter 11 relative to the drive cam 9. Each of FIGS. 6A to 6C shows the contact-surface width a between the outer circumferential surface 9a of the drive cam 9 and the crown surface 20 of the valve lifter 11. That is, as shown in FIG. 5B, a shaft center of the valve lifter 11, i.e., the center Y of the crown surface 20 is arranged to be offset (deviated) by the amount α from the center X of the cam width W of the drive cam 9. Accordingly, basically, the valve lifter 11 rotates by receiving a friction caused by the rotation of the drive cam 9. As shown in FIGS. 6A to 6C, a magnitude of the contact-surface width a is changed according to the crowning amount H of the crown surface 20 even if the setting of the offset amount α is not changed.

Specifically, in the case that the crowning amount H is small, i.e., in the case that the crown surface 20 is close to a flat shape (even surface); the contact-surface width a is large as shown by reference sign a1 in FIG. 6A. In this case, the rotational force by the friction of the drive cam 9 is applied to the valve lifter 11 so that the valve lifter 11 is rotated. In this case, the contact surface between the crown surface 20 and the outer circumferential surface 9a of the drive cam 9 forms an asymmetrical shape with respect to the center line Y of the crown surface 20 perpendicular to the width direction of the drive cam 9, as shown in FIG. 6A.

In a case that the crowning amount H is somewhat large (fairly large), the contact-surface width a is somewhat small (fairly small) as shown by reference sign a2 of FIG. 6B. However, also in this case, the rotational force by the friction of the drive cam 9 is applied to the valve lifter 11 so that the valve lifter 11 is rotated.

On the other hand, in a case that the crowning amount H is excessively large, the contact-surface width a becomes small as shown by reference sign a3 of FIG. 6C. In this case, the rotational force by the friction of the drive cam 9 is not (sufficiently) applied to the valve lifter 11 so that the valve lifter 11 is not rotated. In this case, the contact surface between the crown surface 20 and the outer circumferential surface 9a of the drive cam 9 forms a symmetrical shape with respect to the center line Y of the crown surface 20, as shown in FIG. 6C.

In sum, the presence or absence of the rotation of the valve lifter 11 inside the guide hole 16 greatly depends on the crowning amount H of the crown surface 20. In other words, it is determined whether the valve lifter 11 rotates or does not rotate inside the guide hole 16, by the crowning amount H of the crown surface 20.

FIGS. 7 and 8 show experimental results of an investigation on presence or absence of the rotation of valve lifter 11. FIGS. 7 and 8 show relations between the crowning amount H of the crown surface 20 and the contact-surface width a, by changing the cam width W of the drive cam 9, the offset amount α of the valve lifter 11 and an input load of the drive cam 9 to the valve lifter 11.

In an experimental example shown in FIG. 7; the cam width W is set at 10 mm, the offset amount α is set at 1 mm, and the input load is set at a relatively high value. That is, this experimental example of FIG. 7 corresponds to the case of an engine having a large displacement (volume), i.e., FIG. 7 shows a case that the valve lifter 11 and the drive cam 9 are applied to a large-displacement engine. In this case of FIG. 7, as (the setting of) the crowning amount H becomes larger from approximately 20 μm to 100 μm, the contact-surface width a becomes smaller. Particularly, the contact-surface width a decreases rapidly from 7.0 mm to approximately 3.7 mm when the crowning amount H varies from approximately 20 μm to 40 μm. When the setting of the crowning amount H varies from approximately 40 μm to 100 μm, the contact-surface width a is gradually reduced from approximately 3.8 mm to 2.9 mm.

In this case, it was found that the valve lifter 11 becomes unable to rotate when the contact-surface width a becomes smaller than approximately 3.5 mm, and that the valve lifter 11 rotates when the contact-surface width a is larger than or equal to approximately 3.5 mm. This boundary point of approximately 3.5 mm in the contact-surface width a is realized when the crowning amount H is equal to 50 μm. That is, if the crowning amount H is smaller than or equal to 50 μm, the valve lifter 11 rotates by an influence of the contact-surface width a. On the other hand, if the crowning amount H is larger than 50 μm, the valve lifter 11 does not rotate, as shown in FIG. 7.

In particular, the diamond-like carbon (DLC) given to whole of the crown surface 20 causes the frictional resistance of the crown surface 20 to be small. Hence, the force for rotating the valve lifter 11 itself by the rotation of the drive cam 9 has been reduced. Therefore, the crowning amount H is set to fall within a range smaller than or equal to 50 μm, which corresponds to a range larger than or equal to 3.5 mm in the contact-surface width a. It is more preferable that the crowning amount H is set to fall within a range smaller than or equal to 32 μm.

In an experimental example shown in FIG. 8; the cam width W is set at 7 mm, the offset amount α is set at 0.5 mm, and the input load is set at a relatively low value. That is, this experimental example of FIG. 8 corresponds to the case of an engine having a small displacement (volume), i.e., FIG. 8 shows a case that the valve lifter 11 and the drive cam 9 are applied to a small-displacement engine. Since the input load is low in this case of FIG. 8, a force for pressing the drive cam 9 to the crown surface 20 is low. Hence, the contact-surface width a is small as compared with the case of FIG. 7. In the case of FIG. 8, when the setting of the crowning amount H varies from approximately 18 μm to 50 m, the contact-surface width a is rapidly reduced from approximately 7.0 mm to approximately 2.5 mm. When the setting of the crowning amount H varies from 50 μm to 100 μm, the contact-surface width a is gradually reduced from approximately 2.5 mm to 2.2 mm. A characteristic line of FIG. 8 has a tendency to be lower than a characteristic line of FIG. 7.

On the other hand, since the cam width W and the offset amount α are small, the minimum permissible value (the boundary point) of the contact-surface width a below which the valve lifter 11 is not rotated is smaller than the case of FIG. 7. In the case that the cam width W is equal to 7 mm and that the offset amount α is equal to 0.5 mm as this experimental example of FIG. 8, the minimum permissible value of the contact-surface width a is equal to 2.5 mm. At this time, the crowning amount H of the crown surface 20 is equal to 50 μm which is little different from that of the case of FIG. 7. That is, a range of the crowning amount H of the crown surface 20 which can rotate the valve lifter 11 is not influenced by a difference of the displacement of internal combustion engine (i.e., a difference in the input load, the cam width W and the offset amount α).

That is, in this case of FIG. 8, when the crowning amount H is gradually increased from approximately 17 μm to 100 μm, the contact-surface width a is reduced with this gradual increase of the crowning amount H. In this case, it was found that the valve lifter 11 becomes unable to rotate when the contact-surface width a becomes smaller than approximately 2.5 mm, and that the valve lifter 11 rotates when the contact-surface width a is larger than or equal to approximately 2.5 mm. This boundary point of approximately 2.5 mm in the contact-surface width a is realized when the crowning amount H is equal to 50 μm. That is, it was found that the valve lifter 11 rotates by the influence of (by the relation with) the contact-surface width a if the crowning amount H is smaller than or equal to 50 μμm, and that the valve lifter 11 does not rotate if the crowning amount H is larger than 50 μm.

Therefore, from the above respective experimental results, it was found that the crowning amount H needs to be smaller than or equal to 50 μm in order to obtain the rotation of the valve lifter 11, irrespective of the engine displacement.

Therefore, in this embodiment according to the present invention, the crowning amount H of the crown surface 20 of the valve lifter 11 is set within a range from 11 μm to 50 μm. More preferably, the crowning amount H is set within a range from 11 μm to 32 μm.

By virtue of this setting, the friction between the crown surface 20 and the outer circumferential surface 9a of the drive cam 9 can be sufficiently reduced while ensuring a free rotation of the valve lifter 11. Thereby, an abrasion of the crown surface 20 can be sufficiently suppressed.

Moreover, in this embodiment, since the valve lifter 11 is formed of carbon steel as mentioned above, the abrasion at the contact-sliding portion of the crown surface 20 with the drive cam 9 can be further inhibited from occurring.

Moreover, in this embodiment, the oil hole 21 of the crown portion 18 is formed in a region which does not overlap with the contact-sliding portion between the crown surface 20 and the drive cam 9, as mentioned above. Accordingly, lubricating oil can be aggressively supplied to a spot between the boss portion 19 of the crown portion 18 and the stem end 4b of the intake valve 4, and also, abrasion and peel-off (or detachment) of a hole edge of the oil hole 21 and the like can be inhibited from occurring by the sliding motion of the drive cam 9.

Although the invention has been described above with reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art in light of the above teachings.

For example, the present invention is applicable also to internal combustion engines each having a displacement specification other than the large and small displacements mentioned in the above experimental examples.

Although the intake-side valve lifter 11 has been explained in the above embodiments, a crowning amount of crown surface of the exhaust-side valve lifter 12 is also set in the same manner as the intake-side valve lifter 11.

Some technical structures obtainable from the above embodiments according to the present invention will now be listed as follows.

[a] A valve lifter for an internal combustion engine, comprising: a skirt portion (e.g., 17 in the drawings) formed in a tubular shape; and a crown portion (e.g., 18 in the drawings) formed integrally with an axially one end side of the skirt portion (e.g., 17 in the drawings), the crown portion (e.g., 18 in the drawings) including a crown surface (e.g., 20 in the drawings) configured to slide in contact with an outer circumferential surface (e.g., 9a in the drawings) of a cam (e.g., 9 in the drawings), wherein an axis of the crown portion (e.g., 18 in the drawings) is eccentric from a center of the cam (e.g., 9 in the drawings) in a width direction of the cam (e.g., 9 in the drawings), wherein the crown surface (e.g., 20 in the drawings) is formed in a spherical protruding shape to have its uppermost portion at a center of the crown surface (e.g., 20 in the drawings), wherein a protruding amount (e.g., H in the drawings) of the spherical protruding shape is set to range from 11 μm to 50 μm.

[b] A valve lifter for an internal combustion engine, comprising: a skirt portion (e.g., 17 in the drawings) formed in a tubular shape; and a crown portion (e.g., 18 in the drawings) formed integrally with an axially one end side of the skirt portion (e.g., 17 in the drawings), the crown portion (e.g., 18 in the drawings) including a crown surface (e.g., 20 in the drawings) configured to slide in contact with an outer circumferential surface (e.g., 9a in the drawings) of a cam (e.g., 9 in the drawings), wherein an axis of the crown portion (e.g., 18 in the drawings) is located to be offset from a center of the cam (e.g., 9 in the drawings) in a width direction of the cam (e.g., 9 in the drawings), wherein the crown surface (e.g., 20 in the drawings) is formed in a spherical protruding shape to have its uppermost portion at a center of the crown surface (e.g., 20 in the drawings), wherein a protruding amount (e.g., H in the drawings) of the spherical protruding shape is larger than 11 μm and smaller than a boundary value below which the valve lifter rotates (i.e. a boundary value at which the valve lifter starts to rotate) by a rotational force of the cam (e.g., 9 in the drawings).

[c] A valve lifter for an internal combustion engine, comprising: a skirt portion (e.g., 17 in the drawings) formed in a tubular shape; and a crown portion (e.g., 18 in the drawings) formed integrally with an axially one end side of the skirt portion (e.g., 17 in the drawings), the crown portion (e.g., 18 in the drawings) including a crown surface (e.g., 20 in the drawings) configured to slide in contact with an outer circumferential surface (e.g., 9a in the drawings) of a cam (e.g., 9 in the drawings), wherein a center of the crown portion (e.g., 18 in the drawings) is located to be offset from a center of the cam (e.g., 9 in the drawings) in a width direction of the cam (e.g., 9 in the drawings), wherein the crown surface (e.g., 20 in the drawings) is formed in a spherical protruding shape to have its uppermost portion at a center of the crown surface (e.g., 20 in the drawings), wherein a protruding amount (e.g., H in the drawings) of the spherical protruding shape is set to be larger than 11 μm, wherein the protruding amount (e.g., H in the drawings) of the spherical protruding shape is set to be smaller than a boundary value below which a contact portion between the outer circumferential surface (e.g., 9a in the drawings) of the cam (e.g., 9 in the drawings) and the crown surface (e.g., 20 in the drawings) forms an asymmetrical shape (i.e., a boundary value at which the contact portion starts to form an asymmetrical shape) with respect to a center line of the crown surface (e.g., 20 in the drawings) perpendicular to the width direction of the cam (e.g., 9 in the drawings).

Accordingly, as an advantageous effect, for example, both of the abrasion and the friction of the crown surface can be reduced.

[d] The valve lifter as described in one of the items [a] to [c], wherein the crown portion (e.g., 18 in the drawings) is formed with at least one oil hole (e.g., 21 in the drawings) passing through the crown portion (e.g., 18 in the drawings), and the at least one oil hole (e.g., 21 in the drawings) is formed at a location other than a region at which the crown surface (e.g., 20 in the drawings) of the crown portion (e.g., 18 in the drawings) slides in contact with the cam (e.g., 9 in the drawings).

According to this structure, since the oil hole (e.g., 21 in the drawings) is formed at a location other than the region within which the cam (e.g., 9 in the drawings) slides in contact with the crown surface (e.g., 20 in the drawings), lubricating oil can be aggressively supplied to a spot between the engine valve and a lower-surface side portion of the crown portion. Moreover, the abrasion and peel-off of hole edge of the oil hole (e.g., 21 in the drawings) and the like can be inhibited from occurring by the contact-sliding motion of the cam (e.g., 9 in the drawings).

[e] The valve lifter as described in one of the items [a] to [c], wherein an eccentricity amount (e.g., α in the drawings) of the center or axis of the crown portion (e.g., 18 in the drawings) relative to the center of the cam (e.g., 9 in the drawings) in the width direction of the cam (e.g., 9 in the drawings) is set to range from 0.9 mm to 1.1 mm.

According to this structure, the rotation of the valve lifter can be secured by the rotational force of the cam.

[f] The valve lifter as described in one of the items [a] to [c], wherein whole of the valve lifter is formed of an iron-based metal.

According to this structure, the occurrence of the abrasion (wear-out) can be further suppressed in the sliding portion of the valve lifter with which the cam slides in contact. It is more preferable that the valve lifter is formed of carbon steel.

This application is based on prior Japanese Patent Application No. 2010-216304 filed on Sep. 28, 2010. The entire contents of this Japanese Patent Application are hereby incorporated by reference.

The scope of the invention is defined with reference to the following claims.

VALVE LIFTER FOR INTERNAL COMBUSTION ENGINE

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