Patent Application
20120255508
The present invention relates to a valve lifter of an internal combustion engine and a method of fabricating the valve lifter.
Japanese Patent Application Unexamined Publication No. 2006-144100 discloses a valve lifter of an internal combustion engine. The valve lifter is disposed between a stem end of an intake valve and a rotating cam provided on a cam shaft. The valve lifter includes a cylindrical portion slidable on an inner peripheral surface of a lifter bore of a cylinder head, and a crown portion that is integrally formed with an upper end portion of the cylindrical portion and has a crown surface on which the rotating cam rolls. The crown surface on which high pressure is exerted is formed with a hard carbon film such as a so-called diamond-like carbon (DLC) film in order to reduce friction and wear which are caused on the crown surface.
Such a valve lifter is subjected to formation of the hard carbon film on the crown surface by a given method. Subsequently, a whole outer peripheral surface of the cylindrical portion and the crown portion is subjected to finish polishing with a grind stone or the like, so that a dimensional accuracy of an outer diameter of the valve lifter can be enhanced.
However, in the valve lifter of the conventional art, when the hard carbon film is formed on the crown surface, the hard carbon film extends beyond an outer peripheral edge of the crown surface along an axial direction of the cylindrical portion, that is, wraps around the outer peripheral edge of the crown surface to reach the outer peripheral surface of the crown portion, i.e., an upper edge of the outer peripheral surface of the cylindrical portion, and then adheres and solidifies thereon.
The hard carbon film has a hardness higher than the grind stone used for finish-polishing. Therefore, when the outer peripheral surface of the crown portion is polished with the grind stone, the grind stone is worn at a polishing part thereof so that life of the grind stone will be reduced. Further, there will occur such a technological problem that the grind stone is clogged with a powder of the polished hard carbon film, thereby causing polishing deficiency.
The present invention was made in consideration of the above-described problems in the technology of the conventional art. An object of the present invention is to provide a valve lifter capable of suppressing reduction of life of the grind stone and occurrence of clogging of the grind stone, and a method of fabricating the valve lifter.
According to the present invention, in a case where an outer peripheral surface of a valve lifter having a hard carbon film on a crown surface thereof is subjected to polishing, it is possible to suppress reduction of life of the grind stone and occurrence of clogging of the grind stone.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.
In a first aspect of the present invention, there is provided a valve lifter of an internal combustion engine, including:
In a second aspect of the present invention, there is provided the valve lifter according to the first aspect, wherein the taper angle of the chamfered portion is set to not less than 1°.
In a third aspect of the present invention, there is provided the valve lifter according to the first aspect, wherein the chamfered portion has a maximum depth on a side of the crown surface which extends outwardly in a radial direction of the crown surface, the maximum depth being set to not more than 0.5 mm.
In a fourth aspect of the present invention, there is provided the valve lifter according to the first aspect, wherein the hard carbon film has a thickness of 0.5 μm to 3.0 μm.
In a fifth aspect of the present invention, there is provided the valve lifter according to the first aspect, wherein the hard carbon film is a diamond-like carbon coating film.
In a sixth aspect of the present invention, there is provided a valve lifter of an internal combustion engine, including:
In a seventh aspect of the present invention, there is provided the valve lifter according to the sixth aspect, wherein a whole area of the outer peripheral surface of the hard carbon film covering the chamfered portion is non-polished.
In an eighth aspect of the present invention, there is provided the valve lifter according to the seventh aspect, wherein the chamfered portion has a taper angle with respect to the outer peripheral surface of the cylindrical portion on which the hard carbon film is not formed, the taper angle being set to not more than 26.5°.
In a ninth aspect of the present invention, there is provided the valve lifter according to the eighth aspect, wherein the chamfered portion has a length extending toward a side of the cylindrical portion in the axial direction of the cylindrical portion, the length being set to not less than 1 mm.
In a tenth aspect of the present invention, there is provided the valve lifter according to the ninth aspect, wherein the chamfered portion has a maximum depth on a side of the crown surface which extends outwardly in a radial direction of the crown surface, the maximum depth being set to not more than 0.5 mm.
In an eleventh aspect of the present invention, there is provided the valve lifter according to the seventh aspect, wherein the hard carbon film has a thickness of 0.5 μm to 3.0 μm.
In a twelfth aspect of the present invention, there is provided the valve lifter according to the seventh aspect, wherein the hard carbon film is a diamond-like carbon coating film.
In a thirteenth aspect of the present invention, there is provided a method of fabricating a valve lifter of an internal combustion engine, the valve lifter including a cylindrical portion slidably moveable in a bore formed in the internal combustion engine, and a crown portion formed on one axial end portion of the cylindrical portion and integrally formed therewith, the crown portion having a crown surface that is contacted with a cam of the internal combustion engine, the method including the steps of:
In a fourteenth aspect of the present invention, there is provided the method of fabricating a valve lifter according to the thirteenth aspect, wherein the step of polishing the outer peripheral surface of the cylindrical portion is conducted with a grind stone.
In a fifteenth aspect of the present invention, there is provided the method of fabricating a valve lifter according to the fourteenth aspect, wherein the grind stone is held in non-contact with at least an outer peripheral surface of the hard carbon film covering the chamfered portion during the step of polishing the outer peripheral surface of the cylindrical portion.
In a sixteenth aspect of the present invention, there is provided the method of fabricating a valve lifter according to the fifteenth aspect, wherein the grind stone is held in non-contact with the hard carbon film during the step of polishing the outer peripheral surface of the cylindrical portion.
An embodiment of a valve lifter of an internal combustion engine and a method of fabricating the valve lifter, according to the present invention, will be described in detail hereinafter by referring to the accompanying drawings. In the embodiment, the slide member is used as a valve lifter in an internal combustion engine, which has a slide surface slidable relative to a cam so as to open and close an engine valve of the internal combustion engine. For ease of understanding, various directional terms, directional terms such as “upper”, “lower”, “upward”, “downward”, etc. are used in the following description, but merely denote directions as viewed in the drawings.
Referring to
In
Intake valve 4 has head 4a on a lower end portion of a valve stem thereof. Head 4a is seated onto and unseated from annular valve seat 2a formed on the open end of intake port 2. Spring retainer 13a is fixed to upper stem end portion 4b of intake valve 4. Valve spring 14 is installed between spring retainer 13a and a bottom surface of support hole 1a formed in an upper end portion of cylinder head 1. Intake valve 4 is biased in a closing direction thereof by a biasing force of valve spring 14. Exhaust valve 5 has head 5a on a lower end portion of a valve stem thereof. Head 5a is seated onto and unseated from annular valve seat 3a formed on the open end of exhaust port 3. Spring retainer 13b is fixed to upper stem end portion 5b of exhaust valve 5. Valve spring 15 is installed between spring retainer 13b and a bottom surface of support hole 1b formed in the upper end portion of cylinder head 1. Exhaust valve 5 is biased in a closing direction thereof by a biasing force of valve spring 15.
As shown in
Valve lifter 11 is disposed between intake valve 4 and drive cam 9. Valve lifter 12 is disposed between exhaust valve 5 and drive cam 10.
Each of valve lifters 11, 12 is a direct acting valve lifter, and formed into an integral body made of carbon steel as iron-based metal. As shown in
Thus, valve lifter 11 on the intake side and valve lifter 12 on the exhaust side have same construction. Therefore, for the sake of convenience, only valve lifter 11 on the intake side according to the embodiment of the present invention will be explained in detail hereinafter.
Crown portion 18 of valve lifter 11 has a generally disk shape and a relatively large wall thickness. Crown portion 18 has circular crown surface 20 on an upper end thereof with which outer peripheral surface 9a of drive cam 9 is slidably contacted via hard carbon film 22 (see
As shown in
Chamfered portion 21 has a predetermined size, i.e., taper angle θ, length L and depth Z as shown in
As shown in
Film thickness W of DLC coating film 22 is set within a range of from 0.5 μm to 3.0 μm. In this embodiment, the film thickness W is set to about 1.0 μm.
A method of fabricating valve lifter 11 according to this embodiment will be explained hereinafter. In a first step, a substrate of valve lifter 11 which is made of carbon steel is formed into an integral body by forging. The substrate includes skirt portion 17, disk-shaped crown portion 18 and boss portion 19 which are integrally formed.
Next, in a second step, chamfered portion 21 having an annular shape and the above-specified predetermined size (i.e., length L, taper angle θ and depth Z as shown in
Subsequently, in a third step, DLC coating film 22 is formed on crown surface 20 and chamfered portion 21 by a suitable surface treatment, for instance, arc ion plating.
Specifically, as shown in
For the above reason, in order to suppress deposition of carbon particles 22a onto outer peripheral surface 17a of skirt portion 17, the surface treatment is carried out by a masking jig (not shown) that is made of a suitable material such as rubber and configured to cover the whole outer peripheral surface of the substrate of valve lifter 11 except for crown surface 20, i.e., outer peripheral surface 17a of skirt portion 17 and an outer peripheral surface of crown portion 18. However, in order to enhance productivity, the masking jig is held in place with a fine clearance between outer peripheral surface 17a of skirt portion 17 and the outer peripheral surface of crown portion 18. As a result, as shown in
Subsequent to the third step, in a fourth step, as shown in
Since only a slight amount of carbon particles are deposited on chamfered portion 21, it is difficult to measure a thickness of peripheral portion 22b of DLC coating film 22. In addition, in such a case, an error in measurement of the thickness of peripheral portion 22b tends to occur. Therefore, in
As seen from
Generally, in the conventional valve lifter having a chamfered portion on an upper end portion thereof, an axial distance on the chamfered portion from the crown surface is within a range of from about 0.3 mm to about 0.5 mm. In
In order to thus reduce by half the thickness of peripheral portion 22b of DLC coating film 22 on chamfered portion 21 of crown portion 18, it is desired to set the length L of chamfered portion 21 to not less than 1 mm. In this embodiment, the length L of chamfered portion 21 is set to about 1 mm.
Further, it is possible to suppress deposition of carbon particles onto the outer peripheral surface of crown portion 18 by increasing the depth Z and the length L of chamfered portion 21. However, in a case where chamfered portion 21 is excessively expanded by increasing these parameters, reduction of a diameter of crown surface 20 or increase in outer diameter of skirt portion 17 will be caused to thereby adversely influence function of valve lifter 11.
In view of the above problems, in this embodiment, the depth Z and the length L of chamfered portion 21 are not changed, but the taper angle θ of chamfered portion 21 is set to 26.5°. As a result, taper angle θ of chamfered portion 21 is an acute angle with respect to outer peripheral surface 17a of skirt portion 17.
Specifically, as shown in
Accordingly, it is necessary to set a minimum taper angle θ of chamfered portion 21 to an angle with which an inherent friction reducing function of chamfered portion 21 can be attained. If the minimum taper angle θ is not smaller than a maximum inclination angle θ1 of valve lifter 11 with which valve lifter 11 can be slidably moved within guide bore 16a in an inclined state, chamfered portion 21 can attain the friction reducing function.
The maximum inclination angle θ1 of valve lifter 11 is determined on the basis of minimum value of inner diameter D of guide bore 16a, maximum value of clearance ΔD between the inner peripheral surface of guide bore 16a and the outer peripheral surface of valve lifter 11, and minimum value of axial length L1 of valve lifter 11 except for chamfered portion 21.
The maximum inclination angle θ1 of valve lifter 11 is calculated by the following expressions based on the relationship between inclination angle θ1 of valve lifter 11 within guide bore 16a and chamfered portion 21 of valve lifter 11 as shown in
α=tan−1(d/L1)
β=sin−1(D/X)=sin−1D/√(L12+d2)
θ1=β−α
In the above expressions, d denotes outer diameter of valve lifter 11 which is obtained by subtracting the clearance ΔD from the inner diameter D of guide bore 16a. For instance, under a condition that the inner diameter D of guide bore 16a is 20.0 mm at minimum, the axial length L1 of valve lifter 11 except for chamfered portion 21 is 10 mm at minimum, and the clearance ΔD is 0.1 mm at maximum, the maximum inclination angle θ1 of valve lifter 11 as calculated is smaller than 0.58°. Therefore, in this case, the minimum taper angle θ of chamfered portion 21 can be set to not smaller than 1° to thereby attain the friction reducing function of chamfered portion 21.
From the above viewpoint, in order to reduce by half the thickness of peripheral portion 22b of DLC coating film 22 without adverse influence on the function of valve lifter 11, it is desired to set the taper angle θ of chamfered portion 21 within a range of from 1° to 26.5°.
Further, in order to fulfill the above conditions, in this embodiment, the taper angle θ of chamfered portion 21 is set to 26.5°, and the length L of chamfered portion 21 is set to 1 mm. As a result, the depth Z extending between the outer peripheral edge of crown surface 20 and the plane P containing an extension line that extends from outer peripheral surface 17a of skirt portion 17 in the axial direction of skirt portion 17 becomes 0.5 mm.
Accordingly, in the fourth step as shown in
As a result, occurrence of partial wear of the grind stone can be suppressed to thereby increase life of the grind stone. Furthermore, it is possible to effectively avoid occurrence of clogging of the grind stone which is caused by powder of the hard carbon film polished, and therefore, suppress occurrence of a polishing defect.
The present invention is not limited to the above embodiment, and can also be applied to valve lifter 12 on the exhaust side.
Further, any other material except for DLC as an amorphous carbon material can be used for hard carbon film 22.
In addition, the valve lifter of the present invention can be applied to any other type of internal combustion engine which is different in piston displacement from that of the above embodiment.
This application is based on a prior Japanese Patent Application No. 2011-85956 filed on Apr. 8, 2011, the entire contents of which is hereby incorporated by reference.
Although the invention has been described above by reference to a certain embodiment of the invention, the invention is not limited to the embodiment described above. Modifications and variations of the embodiment described above will occur to those skilled in the art in light of the above teachings. The scope of the invention is defined with reference to the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-085956 | Apr 2011 | JP | national |
