U.S. patent application number 11/648864 was filed with the patent office on 2008-05-15 for oil supply structure for reducing friction of cam shaft.
Invention is credited to Jea Woong Yi.
Application Number | 20080110332 11/648864 |
Document ID | / |
Family ID | 39367938 |
Filed Date | 2008-05-15 |
United States Patent
Application |
20080110332 |
Kind Code |
A1 |
Yi; Jea Woong |
May 15, 2008 |
Oil supply structure for reducing friction of cam shaft
Abstract
An oil supply structure for reducing friction of a cam shaft
attached to a valve train of an automotive engine is disclosed. An
oil supply hole formed in a cam shaft is, repeatedly connected and
disconnected to a cylinder head oil supply hole during the rotation
of the cam shaft. An oil pocket is established in the form of a
concave groove in a section in the circumferential direction on an
inner circumferential surface of a cam cap assembled on the top of
the cam shaft so as to supply oil to the oil pocket only when the
cylinder head oil supply hole is connected to the cam shaft oil
supply hole. It is thus possible to supply oil to the oil pocket
through the cam shaft oil supply hole at specific points of time
and, simultaneously, to sufficiently ensure the sealing width in
other regions than the oil pocket, thus reducing oil loss and
obtaining a more efficient friction reduction.
Inventors: |
Yi; Jea Woong; (Uiwang-si,
KR) |
Correspondence
Address: |
MORGAN, LEWIS & BOCKIUS LLP (SF)
2 PALO ALTO SQUARE, 3000 El Camino Real, Suite 700
PALO ALTO
CA
94306
US
|
Family ID: |
39367938 |
Appl. No.: |
11/648864 |
Filed: |
December 29, 2006 |
Current U.S.
Class: |
92/163 |
Current CPC
Class: |
F01M 9/102 20130101 |
Class at
Publication: |
92/163 |
International
Class: |
F01M 11/02 20060101
F01M011/02 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 14, 2006 |
KR |
10-2006-0112093 |
Claims
1. An oil supply path for reducing friction of a cam shaft,
comprising: a cylinder head oil supply hole, defined inside a
cylinder head having an outlet positioned on an inner
circumferential surface of a journal part bearing-supporting the
cam shaft and an inlet is connected to an oil gallery in the
cylinder head; a cam shaft oil supply hole formed on the cam shaft
supported by the journal part of the cylinder head and penetrating
at a position to communicate with the outlet of the cylinder head
oil supply hole; and an oil pocket formed with a predetermined
length in the circumferential direction on an inner circumferential
surface, which is a friction surface with the cam shaft, of a
semicircular cam cap assembled on the cylinder head over the cam
shaft, so as to connect opening portions on one end and on the
other end of the cam shaft oil supply hole with each other, thus
supplying oil to the oil pocket from the cam shaft oil supply
hole.
2. The oil supply path for reducing friction of a cam shaft as
recited in claim 1, wherein the oil pocket is arranged to connect
the opening portion on one end of the cam shaft oil supply hole to
the opening portion on the other end of the cam shaft oil supply
hole when the opening portion on one end of the cam shaft oil
supply hole is coupled to the outlet of the cylinder head oil
supply hole.
3. The oil supply path for reducing friction of a cam shaft as
recited in claim 1 or claim 2, wherein the oil pocket is
established in the inner circumferential surface of the
semicircular cam cap from a position, which meets a hole central
extension line of the opening portion on one end of the cam shaft
oil supply hole at the point of time when the opening portion on
the other end of the cam shaft oil supply hole meets the outlet of
the cylinder head oil supply hole, to a position, which meets the
hole central extension line of the opening portion on one end of
the cam shaft oil supply hole at the point of time when the opening
portion on the other end of the cam shaft oil supply hole is
completely out of the outlet of the cylinder head oil supply
hole.
4. The oil supply path for reducing friction of a cam shaft as
recited in claim 3, wherein the oil pocket is arranged in a
specific section between a position corresponding to an angle of
about 55.degree. and a position corresponding to angle of about
85.degree. from an end point in the inner circumferential surface
of the semicircular cam cap.
5. An oil supply structure for an engine having a cam shaft carried
in a journal between a cam cap and cylinder head, the oil supply
structure comprising: a first oil supply hole defined in the
cylinder head and communicating between said journal and an oil
gallery; a second oil supply hole defined through said cam shaft
and positioned to periodically align with the first oil supply hole
upon rotation of the cam shaft, and an oil pocket formed in said
cam cap and positioned to periodically receive oil from said oil
gallery through the first and second oil supply holes upon rotation
of the cam shaft.
6. The oil supply structure of claim 5, wherein: the second oil
supply hole has a diameter and the oil pocket has a width
substantially the same as the diameter of the second oil supply
hole; and the oil pocket has a length that extends around a part of
an inner circumference of the journal in the cam cap.
7. The oil supply structure of claim 6, wherein said length of the
oil pocket is greater than said diameter of the oil pocket.
8. The oil supply structure of claim 7, wherein the oil pocket
extends for a length of about 30.degree. around an inner
circumference of the cam cap.
9. The oil supply structure of claim 8, wherein the length of the
oil pocket extends from a position about 55.degree. from an end
point of the cam cap to a position about 85.degree. from said end
point.
10. The oil supply structure of claim 6, wherein said cam shaft,
cylinder head and cam cap include plural aligned oil supply holes
and oil pockets.
11. An oil supply structure for an engine, comprising: a cylinder
head defining a first oil supply hole therein communicating with an
oil gallery; a cam shaft journal formed in the cylinder head, said
first oil supply hole communicating with said journal; a cam shaft
disposed in said journal and defining a second oil supply hole
extending therethrough in apposition disposed to periodically align
with the first oil supply hole upon rotation of the cam shaft; and
a cam cap covering the cam shaft and forming an upper journal
portion around said cam shaft, said cam cap defining an oil pocket
therein disposed to periodically communicate with the oil gallery
through said first and second oil supply holes upon rotation of the
cam shaft and second oil supply hole therein.
12. The oil supply structure of claim 11, wherein: the second oil
supply hole has a diameter and the oil pocket has a width
substantially the same as the diameter of the second oil supply
hole; and the oil pocket has a length that extends around a part of
an inner circumference of the journal in the cam cap.
13. The oil supply structure of claim 12, wherein the oil pocket
extends for a length of about 30.degree. around an inner
circumference of the cam cap.
14. The oil supply structure of claim 13, wherein the length of the
oil pocket extends from a position about 55.degree. around an inner
circumference of the cam cap from point were the cam cap meets the
cylinder head to a a position about 85.degree. from said point.
15. The oil supply structure of claim 14, wherein said cam cap
meets said cylinder head along a substantially horizontal plan that
substantially bisects the cam shaft.
16. The oil supply structure of claim 11, wherein said cam shaft,
cylinder head and cam cap define plural sets of aligned first and
second oil supply holes and oil pockets, each said set spaced
longitudinally along the cam shaft, cylinder head and cam cap.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of Korean Patent
Application No. 10-2006-0112093, filed on Nov. 14, 2006, the entire
disclosure of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an oil supply structure for
reducing friction of a cam shaft and, more particularly, to such an
oil supply structure attached to a valve train of an internal
combustion engine.
[0004] 2. Description of Related Art
[0005] In general, the respective cylinders of an automotive engine
comprise at least two valves divided into an intake valve and an
exhaust valve. The intake valve is opened just before an intake
stroke starts to intake a mixture of air and fuel into the cylinder
and the exhaust valve is opened just before an exhaust stroke
starts to exhaust combustion gas out of the cylinder.
[0006] The valves are operated by a valve train configured to make
the intake valve and the exhaust valve open and close at accurate
points of time by a crank shaft rotated by piston movement.
[0007] The valve train may comprise a cam shaft, on which a
plurality of cams are established along with an axis, a push rod, a
rocker arm transmitting the movement of the cams or of a push rod,
a tappet (or a roller) forwarding the movement of cam lobes to the
push rod, etc., and means that control intake and exhaust air
amounts and intake and exhaust times in accordance with the region
of the engine rotational speed.
[0008] Meanwhile, in sliding portions, such as the piston sliding
up and down in the cylinder, or in rotational portions, such as the
crank shaft and the cam shaft, frictional heat is generated by
direct friction with metals and thereby the friction surface is
worn away or melted down, thus causing an engine trouble.
[0009] To prevent such engine troubles, oil is supplied to the
friction surface of metals so that solid friction generated on the
friction surface of metals is converted into a liquid friction by
an oil film, thus providing a smooth operation. Because of the
importance of lubrication in an internal combustion engine, a
variety of oil supply structures have been developed. However,
conventional oil supply structures can have some drawbacks.
[0010] First, since oil is typically introduced through a hollow
flow path in the cam shaft, the peripheral structure for supplying
oil to the hollow flow path of the cam shaft is complicated and has
limitations in terms of design due to the complicated peripheral
structure for supplying oil to the hollow flow path of the cam
shaft.
[0011] Moreover, when typical conventional structures are applied
to a small sized engine, an oil pressure reduction may occur that
deteriorates the friction reduction performance, and a hollow cam
shaft applied thereto would be a factor that increases the
manufacturing cost.
[0012] Furthermore, since the amount of oil supplied to the oil
groove in conventional structures is large and the amount of oil
exhausted to the outside through the oil groove is also large, a
large quantity of oil is consumed unnecessarily.
SUMMARY OF THE INVENTION
[0013] Embodiments of the present invention provide an oil supply
path with a solid cam shaft, an oil supply hole to be connected to
an oil supply hole of the cylinder head is established on the solid
cam shaft, an oil pocket formed in a predetermined section of the
inner circumferential surface of a cam cap assembled on the top of
the cam shaft so as to supply oil to the oil pocket at specific
points of time when the oil supply holes of the cam shaft and the
cylinder head are connected to each other during the rotation of
the cam shaft and, at the same time, to sufficiently ensure the
sealing width in other regions than the oil pocket, thus preventing
the oil loss over a necessary amount and obtaining a more efficient
effect of friction reduction.
[0014] In an exemplary embodiment of the present invention, there
is provided an oil supply path for reducing friction of a cam shaft
comprising: a cylinder head oil supply hole, established inside a
cylinder head, of which an outlet is positioned on an inner
circumferential surface of a journal part bearing-supporting the
cam shaft and an inlet is connected to an oil gallery in the
cylinder head; a cam shaft oil supply hole, formed on the cam shaft
supported by the journal part of the cylinder head, penetrated at a
position to be connected to the outlet of the cylinder head oil
supply hole; and an oil pocket, established only in a specific
section of a predetermined length in the circumferential direction
on an inner circumferential surface, which is a friction surface
with the cam shaft, of a semicircular cam cap assembled on the
cylinder head over the cam shaft, so as to connect opening portions
on one end and on the other end of the cam shaft oil supply hole
with each other, thus supplying oil to the oil pocket from the cam
shaft oil supply hole.
[0015] The oil pocket may be arranged to connect the opening
portion on one end of the cam shaft oil supply hole to the opening
portion on the other end of the cam shaft oil supply hole when the
opening portion on one end of the cam shaft oil supply hole is
coupled to the outlet of the cylinder head oil supply hole.
[0016] Moreover, the oil pocket can be established in the inner
circumferential surface of the semicircular cam cap from a
position, which meets a hole central extension line of the opening
portion on one end of the cam shaft oil supply hole at the point of
time when the opening portion on the other end of the cam shaft oil
supply hole meets the outlet of the cylinder head oil supply hole,
to a position, which meets the hole central extension line of the
opening portion on one end of the cam shaft oil supply hole at the
point of time when the opening portion on the other end of the cam
shaft oil supply hole is completely out of the outlet of the
cylinder head oil supply hole.
[0017] The oil pocket also may be arranged in a specific section
between a position corresponding to an angle of about 55.degree.
and a position corresponding to angle of about 85.degree. from an
end point in the inner circumferential surface of the semicircular
cam cap.
[0018] In a further alternative embodiment of the present
invention, an oil supply structure for an engine having a cam shaft
carried in a journal between a cam cap and cylinder head includes
first and second oil supply holes and an oil pocket. The first oil
supply hole is defined in the cylinder head and communicates
between the journal and an oil gallery. The second oil supply hole
is defined through the cam shaft and positioned to periodically
align with the first oil supply hole upon rotation of the cam
shaft. The oil pocket is formed in the cam cap and positioned to
periodically receive oil from the oil gallery through the first and
second oil supply holes upon rotation of the cam shaft. The cam
shaft, cylinder head and cam cap may include plural aligned oil
supply holes and oil pockets.
[0019] The oil pocket may have a width that is substantially the
same as the diameter of the second oil supply hole, and the oil
pocket may have a length that extends around a part of an inner
circumference of the journal in the cam cap. The length of the oil
pocket may be greater than the diameter of the oil pocket. In one
such embodiment, the oil pocket extends for a length of about
30.degree. around an inner circumference of the cam cap. In a
further embodiment, the length of the oil pocket extends from a
position about 55.degree. from an end point of the cam cap to a
position about 85.degree. from the same end point.
[0020] In yet another alternative embodiment, a cylinder head
defines a first oil supply hole therein communicating with an oil
gallery, a cam shaft journal is formed in the cylinder head with
the first oil supply hole communicating with the journal, a cam
shaft is disposed in the journal and defines a second oil supply
hole extending therethrough in a position disposed to periodically
align with the first oil supply hole upon rotation of the cam
shaft, and a cam cap covers the cam shaft and forms an upper
journal portion around the cam shaft with the cam cap defining an
oil pocket therein disposed to periodically communicate with the
oil gallery through the first and second oil supply holes upon
rotation of the cam shaft and second oil supply hole therein. The
cam shaft, cylinder head and cam cap may define plural sets of
aligned first and second oil supply holes and oil pockets, each set
spaced longitudinally along the cam shaft, cylinder head and cam
cap.
[0021] In this embodiment, the oil pocket may also have a width
substantially the same as the diameter of the second oil supply
hole, and the oil pocket may also have a length that extends around
a part of an inner circumference of the journal in the cam cap. The
oil pocket may extend for a length of about 30.degree. around an
inner circumference of the cam cap, wherein the length of the oil
pocket extends from a position about 55.degree. around an inner
circumference of the cam cap from point were the cam cap meets the
cylinder head to a position about 85.degree. from that point. The
cam cap may meet cylinder head along a substantially horizontal
plan that substantially bisects the cam shaft or along a plane at
another orientation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The above and other features of the present invention will
be described with reference to certain exemplary embodiments
thereof illustrated the attached drawings in which:
[0023] FIG. 1 is a cross-sectional view depicting an oil supply
path of a cam shaft in accordance with an embodiment of the present
invention;
[0024] FIG. 2 is a perspective view depicting an oil supply hole
penetrating through a cam shaft in an oil supply path in accordance
with an embodiment of the present invention;
[0025] FIG. 3 is a plan view depicting a cam shaft in which a
plurality of oil supply holes of FIG. 8 are established penetrated
at predetermined positions of the cam shaft;
[0026] FIG. 4 is a plan view depicting an oil pocket of a cam cap
in an oil supply path in accordance with an embodiment of the
present invention;
[0027] FIG. 5 is a cross-sectional view taken along with line `A-A`
of FIG. 4;
[0028] FIGS. 6 and 7 are diagrams depicting states where an oil
pocket is opened and closed by an oil supply hole of a cam shaft in
an oil supply structure in accordance with embodiments of the
present invention, in which FIG. 6 depicts a state where the oil
pocket starts to be opened and FIG. 7 depicts a state where the oil
pocket starts to be closed; and
[0029] FIG. 8 is a graph illustrating measurement results of crank
torques required in driving intake and exhaust cams in an example
in accordance with an embodiment of the present invention and a
conventional structure.
DETAILED DESCRIPTION OF THE INVENTION
[0030] Hereinafter, exemplary embodiments of the present invention
will now be described in detail with reference to the attached
drawings.
[0031] As depicted in FIG. 1, an oil supply path in the embodiment
of the present invention can be applied to a solid cam shaft 120
inserted into the inner circumferential surface of a journal part
111 of a cylinder head 110 and supported therein. A cam cap 114 is
assembled on the cylinder head 110 by bolts, not depicted, over the
cam shaft 120.
[0032] As an oil supply path in the cylinder head 110, through
which oil is supplied to reduce friction of the cam shaft 120, an
oil supply hole 113 is formed in the cylinder head 110. An outlet
of hole 113 is positioned on the inner circumferential surface of
the journal part 111 supporting the cam shaft 120 and an oil
gallery 112 formed in the cylinder head 110 is connected to the
opposite inlet of the oil supply hole 113 and thereby the oil
supply hole 113 has a structure in which it is connected to the oil
gallery 112 in the cylinder head 110. Moreover, an oil supply hole
121 is established penetrating through the respective portions
supported by the journal part 111 of the cylinder head 110 in the
cam shaft 120, as depicted in FIGS. 2 and 3.
[0033] Referring to FIG. 3, it can be seen that the oil supply
holes 121 are formed penetrating through four supported portions
established on the cylinder head 110. The oil supply hole 121 is
disposed to communicate with the oil supply hole 1113 of the
cylinder head 110. That is, when an opening portion on one end of
the oil supply hole 121 of the cam shaft 120 meets the outlet of
the cylinder head oil supply hole 1113 while the cam shaft 120
rotates, two oil supply holes 113 and 121 on both sides communicate
with each other, thus opening the oil supply path between the
cylinder head 110 and the cam shaft 120.
[0034] An oil pocket 115 of a predetermined length is established
in the form of a concave groove in a section in the circumferential
direction on a friction surface between the outer circumferential
surface of the cam shaft 120. The cam cap 114 assembled on the
cylinder head 110 by bolts, i.e., on the inner circumferential
surface of the cam cap 114, as depicted in FIGS. 4 and 5. The oil
pocket 115 is formed at a position communicating with the oil
supply hole 121 of the cam shaft 120 and its width corresponds to
the diameter of the oil supply hole 121 of the cam shaft 120.
[0035] For example, an oil supply hole 121 of 3 mm in diameter is
established on the cam shaft 120 and an oil pocket 115 of 3 mm in
width is arranged on the inner circumferential surface of the cam
cap 114. Here, the width direction position of the oil pocket 115
is set to meet the opening portion on one end of the cam shaft oil
supply hole 121 completely in the inner circumferential surface of
the cam cap 114 so that the whole opening portion on the end of the
cam shaft oil supply hole 121 is completely opened by the oil
pocket 115 at a specific point of time when the whole opening
portion on the end of the cam shaft oil supply hole 121 meets the
oil pocket 115 of the cam cap 114 completely to open a side of the
oil pocket 115 while the cam shaft 120 rotates.
[0036] Referring to FIG. 4, it can be seen that the oil pocket 115
is established in the middle of the inner circumferential surface
of the cam cap 114 in the width direction. Moreover, an oil pocket
115 in accordance with the present invention is established in a
section of a predetermined length on the inner circumferential
surface of the cam cap 114 in the circumferential direction.
[0037] The attached FIGS. 6 and 7 are diagrams depicting states
where an oil pocket 115 is opened and closed by an oil supply hole
121 of a cam shaft 120 in an oil supply structure in accordance
with the present invention, in which FIG. 6 depicts a state where
the oil pocket 115 starts to be opened and FIG. 7 depicts a state
where the oil pocket 115 starts to be closed. The oil pocket 115
starts to be opened when it meets the opening portion on the end of
the cam shaft oil supply hole 121 while the cam shaft 120 rotates,
whereas, the oil pocket 115 starts to be closed when the opening
portion on the end of the cam shaft oil supply hole 121 is out of
the oil pocket 115.
[0038] In a state where the oil pocket 115 is opened by the opening
portion on one end of the cam shaft oil supply hole 121, the
opening portion on the other end of the cam shaft oil supply hole
121 is connected to the outlet of the cylinder head oil supply hole
113. Accordingly, an oil supply path is formed from the oil gallery
112 of the cylinder head 110, the oil supply hole 113 of the
cylinder head 110, the oil supply hole 121 of the cam shaft 120 and
the oil pocket 115 of the cam cap 114 in turn.
[0039] While the cam shaft 120 rotates, the respective portions of
the oil supply path from the oil gallery 112 of the cylinder head
110 to the oil pocket 115 of the cam cap 114 are connected to one
another so that the oil supplied from the oil gallery 112 to the
oil pocket 115 lubricates the cam shaft 120 to reduce friction.
[0040] The number of times that the respective portions of the oil
supply path are connected to one another to supply oil, i.e., the
number of times that the oil supply path from the oil supply hole
113 of the cylinder head 110 to the oil pocket 115 of the cam cap
114, is two times during one rotation of the cam shaft 120. Here,
the opening portion on one end of the cam shaft oil supply hole 121
and the opening portion on the other end of the cam shaft oil
supply hole 121 are to open the outlet of the oil supply hoe 113
and the oil pocket 115 of the cam cap 114 in turn.
[0041] The oil supply path is thus repeatedly opened and closed
during the rotation of the cam shaft 120 and oil is supplied at the
very point of time when the oil supply path is opened. Moreover,
since oil is not supplied to the cam shaft 120 at all times, but
two times when the oil supply path is opened for one rotation of
the cam shaft 120, it is possible to reduce unnecessary oil
consumption.
[0042] In establishing the oil pocket 115 on the inner surface of
the cam cap 114, the oil pocket 115 is arranged on the inner
circumferential surface of the semicircular cam cap 114 long in the
circumferential direction as depicted in FIG. 5. However, it is
positioned only in a specific section between a position
corresponding to an angle of about 55.degree. and a position
corresponding to angle of about 85.degree. from an end point of the
cam cap 114.
[0043] Here, the position corresponding to an angle of about
55.degree. is directed to a position that meets a hole central
extension line L of the opening portion on one end of the cam shaft
oil supply hole 121 at the point of time when the opening portion
on the other end of the cam shaft oil supply hole 121 meets the
outlet of the cylinder head oil supply hole 113. The position
corresponding to an angle of about 85.degree. is directed to a
position that meets the hole central extension line L of the
opening portion on one end of the cam shaft oil supply hole 121 at
the point of time when the opening portion on the other end of the
cam shaft oil supply hole 121 is completely out of the outlet of
the cylinder head oil supply hole 113.
[0044] During the rotation of the cam shaft 120, oil is supplied
from the cylinder head 110 to the oil pocket 115 of the cam cap 114
only for a short time from the point of time when the opening
portion on one end of the cam shaft oil supply hole 121 starts to
meet the outlet of the cylinder head oil supply hole 113, that is,
from the point of time when the outlet of the cylinder head oil
supply hole 113 is opened by the opening portion on one end of the
oil supply hole 121, to the point of time when the opening portion
on one end of the cam shaft oil supply hole 121 is completely out
of the outlet of the cylinder head oil supply hole 113, that is, to
the point of time when the outlet of the cylinder head oil supply
hole 113 is completely closed.
[0045] According to embodiments of the present invention configured
as described above, the oil pocket 115 is established only in a
predetermined section of the cam cap 114 to supply oil only at
specific points of time (two times for one rotation of the cam
shaft) through the oil supply holes 121 penetrating through the cam
shaft 120 and, at the same time, to ensure the sealing width
sufficiently in other regions than the oil pocket 115, thus
preventing the oil loss over a necessary amount.
[0046] That is, it is possible to established an oil supply path,
in which a groove corresponding to the oil pocket 115 is formed
over the whole section of 360.degree. along with the
circumferential direction on the inner surface of the cam cap
surrounding the cam shaft and the inner surface of the cylinder
head journal part and the oil supply hole of the cylinder head is
connected to one side of the groove; however, in this case, a large
quantity of oil is supplied to the whole groove of 360.degree.
through the oil supply hole at all times, thus consuming a large
quantity of oil.
[0047] Accordingly, the oil pocket 115 of the present invention is
established only in a specific section so that oil is supplied only
at the very point of time when the oil supply hole 121 of the cam
shaft 120 and the oil supply hole 113 of the cylinder head 110 are
connected (opened) to each other. Accordingly, it is possible to
obtain effects of reducing friction and, at the same time,
decreasing the oil consumption remarkably, and ensure an efficient
friction reduction.
[0048] Especially, accordingly to the structure in which the groove
is formed in the whole section, the sealing width between the
friction surfaces (the width of other areas than the groove area)
is reduced and thereby the oil loss becomes larger.
[0049] Accordingly, in the structure where the width of the
cylinder head journal part 111 and that of the cam cap 114 are
small (for example, in an engine of a width of 12 mm or less), a
groove can not be applied thereto to ensure a sufficient sealing
width. However, according to the oil pocket 115 established in a
specific section of the present invention, it is possible to ensure
the sealing width sufficiently in the areas other than the oil
pocket 115, thus achieving the reduction of oil loss and the
efficient friction reduction.
[0050] The following table 1 depicts results of a friction torque
test, in which a comparative example corresponds to the structure
in which oil is supplied between the outer circumferential surface
of the cam shaft and the inner circumferential surface of the cam
cap and the cylinder head journal part according to a conventional
design and an example is directed to an embodiment of the present
invention. It can be understood from the table 1 that the friction
torque reduction more than 30% is ensured in the whole area of the
engine to which an embodiment of the present invention is
applied.
TABLE-US-00001 TABLE 1 Test Results 1000 rpm Friction 2000 rpm
Torque Reduction Rate Friction Torque Reduction Rate Examples (Nm)
(%) (Nm) (%) Conventional 1.48 0.77 Invention 1.01 32.dwnarw. 0.48
38.dwnarw.
[0051] Moreover, the attached FIG. 8 is a graph illustrating
measurement results of crank torques required in driving intake and
exhaust cams in the invention and conventional structure, through
which it can be found that the crank torques in the example of the
present invention are considerably reduced compared with the
conventional structure.
[0052] As described above, according to the oil supply path for
reducing friction of the cam shaft in accordance with the present
invention, the oil pocket is established only in a predetermined
section of the cam cap to supply oil only at specific points of
time (two times for one rotation of the cam shaft) through the oil
supply holes penetrating through the cam shaft and, at the same
time, to ensure the sealing width sufficiently in other regions
than the oil pocket, thus preventing the oil loss over a necessary
amount and obtaining a more efficient effect of friction
reduction.
[0053] Moreover, since the solid cam shaft is applied to the
present invention, it is possible to solve various problems caused
when applying the hollow cam shaft, such as the complication of the
structure, limitations in design, increase in manufacturing cost,
etc.
[0054] As above, exemplary embodiments of the present invention
have been described and illustrated, however, the present invention
is not limited thereto, rather, it should be understood that
various modifications and variations of the present invention can
be made thereto by those skilled in the art without departing from
the spirit and the technical scope of the present invention as
defined by the appended claims.
* * * * *