U.S. patent application number 13/076566 was filed with the patent office on 2012-03-29 for valve lifter for internal combustion engine.
This patent application is currently assigned to HITACHI AUTOMOTIVE SYSTEMS, LTD.. Invention is credited to Noriomi Hosaka, Tomoya TANAKA, Seiji Tsuruta.
Application Number | 20120073534 13/076566 |
Document ID | / |
Family ID | 45814956 |
Filed Date | 2012-03-29 |
United States Patent
Application |
20120073534 |
Kind Code |
A1 |
TANAKA; Tomoya ; et
al. |
March 29, 2012 |
VALVE LIFTER FOR INTERNAL COMBUSTION ENGINE
Abstract
A valve lifter for an internal combustion engine includes 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 includes a crown surface configured to slide in
contact with an outer circumferential surface of a cam. An axis of
the crown portion is eccentric from a center of the cam in a width
direction of the cam. The crown surface is formed in a spherical
protruding shape to have its uppermost portion at a center of the
crown surface. A protruding amount of the spherical protruding
shape is set to range from 11 .mu.m to 50 .mu.m.
Inventors: |
TANAKA; Tomoya; (Atsugi-shi,
JP) ; Hosaka; Noriomi; (Hiratsuka-shi, JP) ;
Tsuruta; Seiji; (Atsugi-shi, JP) |
Assignee: |
HITACHI AUTOMOTIVE SYSTEMS,
LTD.
|
Family ID: |
45814956 |
Appl. No.: |
13/076566 |
Filed: |
March 31, 2011 |
Current U.S.
Class: |
123/90.48 |
Current CPC
Class: |
F01L 3/085 20130101;
F01L 1/143 20130101; F01L 2820/045 20130101 |
Class at
Publication: |
123/90.48 |
International
Class: |
F01L 1/14 20060101
F01L001/14 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 28, 2010 |
JP |
2010-216304 |
Claims
1. 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 .mu.m to 50
.mu.m.
2. The valve lifter as claimed in claim 1, wherein a diamond-like
carbon treatment is applied to at least the crown surface.
3. The valve lifter as claimed in claim 1, wherein the crown
portion is formed with at least one oil hole passing through the
crown portion, and the at least one oil hole is formed at a
location other than a region at which the crown surface of the
crown portion slides in contact with the cam.
4. The valve lifter as claimed in claim 1, wherein an eccentricity
amount of the axis of the crown portion relative to the center of
the cam in the width direction of the cam is set to range from 0.9
mm to 1.1 mm.
5. The valve lifter as claimed in claim 1, wherein a width of the
cam is set to range from 6 mm to 12 mm.
6. The valve lifter as claimed in claim 1, wherein whole of the
valve lifter is formed of an iron-based metal.
7. 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 .mu.m
and smaller than a boundary value below which the valve lifter
rotates by a rotational force of the cam.
8. The valve lifter as claimed in claim 7, wherein a diamond-like
carbon treatment is applied to at least the crown surface.
9. The valve lifter as claimed in claim 7, wherein the crown
portion is formed with at least one oil hole passing through the
crown portion, and the at least one oil hole is formed at a
location other than a region at which the crown surface of the
crown portion slides in contact with the cam.
10. The valve lifter as claimed in claim 7, wherein an offset
amount of the axis of the crown portion relative to the center of
the cam in the width direction of the cam falls within a range from
0.9 mm to 1.1 mm.
11. The valve lifter as claimed in claim 7, wherein a width of the
cam falls within a range from 6 mm to 12 mm.
12. The valve lifter as claimed in claim 7, wherein whole of the
valve lifter is formed of an iron-based metal.
13. 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 .mu.m, 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.
14. The valve lifter as claimed in claim 13, wherein a diamond-like
carbon treatment is applied to at least the crown surface.
15. The valve lifter as claimed in claim 13, wherein the crown
portion is formed with at least one oil hole passing through the
crown portion, and the at least one oil hole is formed at a
location other than a region at which the crown surface of the
crown portion slides in contact with the cam.
16. The valve lifter as claimed in claim 13, wherein an offset
amount of the center of the crown portion relative to the center of
the cam in the width direction of the cam falls within a range from
0.9 mm to 1.1 mm.
17. The valve lifter as claimed in claim 13, wherein a width of the
cam falls within a range from 6 mm to 12 mm.
18. The valve lifter as claimed in claim 13, wherein whole of the
valve lifter is formed of an iron-based metal.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an improvement of a valve
lifter for an internal combustion engine.
[0002] 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.
[0003] 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.
[0004] 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
[0005] 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).
[0006] 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.
[0007] 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
.mu.m to 50 .mu.m.
[0008] 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 .mu.m and smaller than a boundary value below which the valve
lifter rotates by a rotational force of the cam.
[0009] 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 .mu.m, 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.
[0010] 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
[0011] FIG. 1 is a longitudinal sectional view of a valve lifter
for an internal combustion engine in an embodiment according to the
present invention.
[0012] 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.
[0013] FIG. 3 is a longitudinal sectional view of a friction
measurement machine for measuring a friction between the valve
lifter and a cam.
[0014] FIG. 4 is a characteristic view showing a relative relation
between a crowning amount and the friction.
[0015] 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.
[0016] 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.
[0017] 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.
[0018] 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
[0019] Hereinafter, embodiments of valve lifter for an internal
combustion engine according to the present invention will be
explained in detail referring to the drawings.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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.
[0025] 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.
[0026] 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.
[0027] 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.
[0028] 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
.mu.m.
[0029] 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.
[0030] 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.
[0031] 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 .alpha.) 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) .alpha. 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.
[0032] The significance of setting the crowning amount H of the
crown surface 20 within the range from 11 .mu.m to 50 .mu.m, i.e.,
a necessity of setting the criticality for the crowning amount H
will now be explained.
[0033] 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.
[0034] 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.
[0035] 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.
[0036] 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 .mu.m to
44 .mu.m 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.
[0037] 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.
[0038] 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.degree. C. and a rotational speed of the cam shaft 32 is equal
to 300 rpm.
[0039] 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.
[0040] 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.
[0041] A reference sign 42 of FIG. 3 represents a valve lift sensor
provided in a lower portion of the cylinder base body 31.
[0042] FIG. 4 is a characteristic view showing a result of these
experiments. A horizontal axis of this graph represents the
crowning amount H (.mu.m) of the crown surface 39a, and a vertical
axis of this graph represents the friction (Nm) of the valve lifter
39 (the friction of the crown surface 39a).
[0043] In a case that the crowning amount H is approximately equal
to 5 .mu.m, the crown surface 39a is close to a flat shape.
Therefore, the friction values of the crown surface 39a range from
0.3 Nm to 0.4 Nm which are relatively large, as shown by four black
squares of FIG. 4.
[0044] Contrary to this, in a case that the crowning amount H
ranges from 11 .mu.m to 44 .mu.m, 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 .mu.m. When the
crowning amount H is approximately equal to 11 .mu.m, the friction
value of the crown surface 39a approximately ranges from 0.29 Nm to
0.3 Nm. In a range between 11 .mu.m and 44 .mu.m, the friction
value of the crown surface 39a is gradually lowered.
[0045] 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 .mu.m. Then, the
friction of the crown surface 39a is gradually reduced from a point
where the crowning amount H is equal to 11 .mu.m to a point where
the crowning amount H is equal to 44 .mu.m, when regarding the
value of 11 .mu.m as a boundary of characteristic change. That is,
from the average line of the friction values, the value of 11 .mu.m
in the crowning amount H can be recognized as the boundary of
characteristic change.
[0046] 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.
[0047] From the above experimental results, the crowning amount H
of the crown surface 39a needs the level of 11 .mu.m 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 .mu.m.
[0048] 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.
[0049] 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 .alpha. 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 .alpha. 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 .alpha. is not changed.
[0050] 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.
[0051] 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.
[0052] 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.
[0053] 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.
[0054] 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 .alpha. of the valve
lifter 11 and an input load of the drive cam 9 to the valve lifter
11.
[0055] In an experimental example shown in FIG. 7; the cam width W
is set at 10 mm, the offset amount .alpha. 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
.mu.m to 100 .mu.m, 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 .mu.m to 40 .mu.m. When the setting of the
crowning amount H varies from approximately 40 .mu.m to 100 .mu.m,
the contact-surface width a is gradually reduced from approximately
3.8 mm to 2.9 mm.
[0056] 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 .mu.m. That is, if the crowning amount H is
smaller than or equal to 50 .mu.m, 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 .mu.m, the valve lifter 11
does not rotate, as shown in FIG. 7.
[0057] 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 .mu.m, 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 .mu.m.
[0058] In an experimental example shown in FIG. 8; the cam width W
is set at 7 mm, the offset amount .alpha. 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 .mu.m
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 .mu.m to 100 .mu.m, 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.
[0059] On the other hand, since the cam width W and the offset
amount .alpha. 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 .alpha. 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 .mu.m
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 .alpha.).
[0060] That is, in this case of FIG. 8, when the crowning amount H
is gradually increased from approximately 17 .mu.m to 100 .mu.m,
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 .mu.m. 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 .mu..mu.m, and that the valve lifter
11 does not rotate if the crowning amount H is larger than 50
.mu.m.
[0061] Therefore, from the above respective experimental results,
it was found that the crowning amount H needs to be smaller than or
equal to 50 .mu.m in order to obtain the rotation of the valve
lifter 11, irrespective of the engine displacement.
[0062] 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 .mu.m to 50 .mu.m.
More preferably, the crowning amount H is set within a range from
11 .mu.m to 32 .mu.m.
[0063] 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.
[0064] 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.
[0065] 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.
[0066] 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.
[0067] 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.
[0068] 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.
[0069] Some technical structures obtainable from the above
embodiments according to the present invention will now be listed
as follows.
[0070] [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 .mu.m to 50
.mu.m.
[0071] [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 .mu.m 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).
[0072] [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 .mu.m,
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).
[0073] Accordingly, as an advantageous effect, for example, both of
the abrasion and the friction of the crown surface can be
reduced.
[0074] [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).
[0075] 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).
[0076] [e] The valve lifter as described in one of the items [a] to
[c], wherein an eccentricity amount (e.g., .alpha. 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.
[0077] According to this structure, the rotation of the valve
lifter can be secured by the rotational force of the cam.
[0078] [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.
[0079] 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.
[0080] 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.
[0081] The scope of the invention is defined with reference to the
following claims.
* * * * *