U.S. patent application number 14/349738 was filed with the patent office on 2014-10-16 for camshaft support structure.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. The applicant listed for this patent is Yoshinori Yanase. Invention is credited to Yoshinori Yanase.
Application Number | 20140305397 14/349738 |
Document ID | / |
Family ID | 48081474 |
Filed Date | 2014-10-16 |
United States Patent
Application |
20140305397 |
Kind Code |
A1 |
Yanase; Yoshinori |
October 16, 2014 |
CAMSHAFT SUPPORT STRUCTURE
Abstract
Support bases for supporting camshafts in a rotatable manner are
mounted on the cylinder head of an internal combustion engine. The
support bases are provided so as to be separated from each other in
the axial direction of the camshafts. Each of the support bases
comprises bearing portions which support the camshafts and a
through-hole which extends in the axial direction of the camshafts.
A rod is inserted through the through-holes, and the rod restricts
the bearing portions from being displaced from positions at which
the bearing portions are located while the internal combustion
engine is stopped and cold.
Inventors: |
Yanase; Yoshinori;
(Toyota-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Yanase; Yoshinori |
Toyota-shi |
|
JP |
|
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
Toyota-Shi, Aichi-Ken
JP
|
Family ID: |
48081474 |
Appl. No.: |
14/349738 |
Filed: |
October 11, 2011 |
PCT Filed: |
October 11, 2011 |
PCT NO: |
PCT/JP2011/073339 |
371 Date: |
April 4, 2014 |
Current U.S.
Class: |
123/193.3 |
Current CPC
Class: |
F01L 2001/0476 20130101;
F01L 1/46 20130101; F01L 2001/0537 20130101; F01L 1/053
20130101 |
Class at
Publication: |
123/193.3 |
International
Class: |
F01L 1/46 20060101
F01L001/46 |
Claims
1.-5. (canceled)
6. A camshaft support structure mounted on a cylinder head of an
internal combustion engine, the camshaft support structure
comprising support bases for supporting both an exhaust camshaft
and an intake camshaft to be freely rotational, the structure
comprising: the support bases are arranged apart from one another
in an axial direction of the exhaust camshaft and the intake
camshaft; each support base has bearing portions, which support the
exhaust camshaft and the intake camshaft, and a through hole, which
is formed closer to the exhaust camshaft than to the intake
camshaft and extends in the axial direction; and the through holes
receive a rod, which restricts the bearing portions from being
displaced from an arrangement position at which the bearing
portions are located when the internal combustion engine is stopped
and cold.
7. The camshaft support structure according to claim 6, wherein the
rod is made of material having higher rigidity than the support
bases.
8. The camshaft support structure according to claim 6, wherein
each support base includes a receiving member, which is mounted on
the cylinder head and receives the exhaust camshaft and the intake
camshaft, and cap members, which are mounted on a top surface of
the receiving member and form the bearing portions together with
the receiving member, and the through hole is formed in the
receiving member.
9. The camshaft support structure according to claim 6, wherein the
internal combustion engine includes a forced-induction device.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a national phase application of
International Application No. PCT/JP2011/073339, filed Oct. 11,
2011, the content of which is incorporated herein by reference.
FIELD OF THE DISCLOSURE
[0002] The present invention relates to a camshaft support
structure that includes support bases, which are mounted on the
cylinder head of an internal combustion engine and support
camshafts to be freely rotational.
BACKGROUND OF THE DISCLOSURE
[0003] Conventionally, this type of camshaft support structure has
been proposed in, for example, Patent Document 1. According to the
camshaft support structure disclosed in Patent Document 1, the
support bases, which support the camshafts to be freely rotational,
are provided apart from one another in the axial direction of the
camshafts.
[0004] With this structure, the weight of the internal combustion
engine is reduced as compared to a structure in which an outer
frame for connecting the support bases is provided, as in a
ladder-frame camshaft housing, by the weight corresponding to the
outer frame.
PRIOR ART DOCUMENTS
Patent Documents
[0005] Patent Document 1: Japanese Laid-Open Patent Publication No.
2010-209796
SUMMARY OF THE INVENTION
Problems that the Invention is to Solve
[0006] When an engine is operated, the temperature of the cylinder
head is increased by receiving heat of exhaust gas, causing the
cylinder head to be thermally deformed. Since the support bases are
arranged to abut against the cylinder head, the support bases are
thermally deformed by receiving heat from the cylinder head. This
deteriorates alignment of bearing portions, which are formed in the
support bases and support the camshafts. As a result, problems may
arise such as an increase in rotational sliding resistance of the
camshafts.
[0007] According to the structure disclosed in Patent Document 1,
the amount of heat that the support bases receive from the cylinder
head is reduced as compared to the structure with the ladder-frame
camshaft housing by the amount corresponding to the outer frame.
The thermal deformation amount of the support bases is thus reduced
to some extent. If, however, the invention is applied to an
internal combustion engine in which the exhaust gas temperature is
further increased such as an internal combustion engine provided
with a forced-induction device, the amount of heat that the support
bases receive from the cylinder head is further increased. In this
case, there are limitations in favorably reducing deterioration in
the alignment of the bearing portions of the support bases.
[0008] Accordingly, it is an objective of the present invention to
provide a camshaft support structure that favorably reduces
deterioration in the alignment of bearing portions of support
bases, which support camshafts, due to engine operation.
Means for Solving the Problems
[0009] Means for solving the above issues and advantages thereof
will now be discussed.
[0010] To achieve the foregoing objective and in accordance with
one aspect of the present invention, a camshaft support structure
mounted on a cylinder head of an internal combustion engine
includes support bases for supporting a camshaft to be freely
rotational. The support bases are arranged apart from one another
in an axial direction of the camshaft. Each support base has a
bearing portion, which supports the camshaft, and a through hole,
which extends in the axial direction of the camshaft. The through
holes receive a rod, which restricts the bearing portions from
being displaced from an arrangement position at which the bearing
portions are located when the internal combustion engine is stopped
and cold.
[0011] With this structure, the bearing portions of the support
bases mounted on the cylinder head of the internal combustion
engine support the camshaft to be freely rotational. Since the
support bases are arranged apart from one another in the axial
direction of the camshaft, the contact area between the support
bases and the cylinder head is reduced as compared to the structure
with an outer frame for connecting the support bases, such as a
ladder-frame camshaft housing. This reduces the amount of heat
received from the cylinder head, thus reducing thermal deformation
of the support bases caused by the received heat.
[0012] Furthermore, with this structure, since the rod is inserted
in the through holes formed in the support bases, the support bases
are restricted from being thermally deformed by the heat received
from the cylinder head.
[0013] The rod is assembled to the cylinder head together with the
support bases in a state in which the rod is inserted in the
through holes. The cylinder head is assembled to the cylinder block
with head bolts. The top surface of the cylinder head is slightly
distorted from a flat state due to the axial tightening force of
the head bolts. The rod is thus maintained in a state pressed by
the inner walls of the through holes, and secured to the support
bases.
[0014] The structure thus favorably reduces deterioration in the
alignment of the bearing portions of the support bases, which
support the camshaft, due to engine operation.
[0015] The rod is preferably made of material having higher
rigidity than the support bases. According to this embodiment,
thermal deformation of the support bases is reduced in an
appropriate manner. In a case in which the support bases are made
of aluminum alloy, for example, the rod may be made of
stainless-steel, which has higher rigidity than the aluminum
alloy.
[0016] As a specific structure of the support bases, each support
base preferably includes a receiving member, which is mounted on
the cylinder head and receives the camshaft, and a cap member,
which is mounted on a top surface of the receiving member and forms
the bearing portion together with the receiving member. In this
case, the through hole is preferably formed in the receiving
member.
[0017] In this case, the support bases preferably receive both an
exhaust camshaft and an intake camshaft, which each serve as the
camshaft, and the through holes are preferably formed closer to the
exhaust camshaft than to the intake camshaft.
[0018] In the internal combustion engine, high-temperature exhaust
gas is discharged to an exhaust passage through exhaust valves. The
thermal deformation of the cylinder head is thus greater in the
region closer to the exhaust camshaft. In this point, according to
the above embodiment, the through holes in which the rod is
inserted are formed closer to the exhaust camshaft than to the
intake camshaft. That is, the rod is arranged close to the region
of the receiving members of the support bases where the amount of
heat received from the cylinder head is great and the degree of
thermal deformation is great. The region of the support bases in
the vicinity of the exhaust camshaft where the amount of heat
received from the cylinder head is great is thus restricted from
being thermally deformed in an appropriate manner.
[0019] In the internal combustion engine provided with a
forced-induction device, since the temperature of exhaust gas is
higher than that without the forced-induction device, the thermal
deformation amount of the support bases caused by heat received
from the cylinder head is great. Furthermore, in the internal
combustion engine provided with a forced-induction device, since
the pressure in the cylinders is higher than that without the
forced-induction device, the cylinder head is significantly
deformed by fluctuation of the pressure in the cylinders of the
internal combustion engine. As a result, the deformation amount of
the support bases mounted on the cylinder head is increased. As
described above, in the internal combustion engine provided with a
forced-induction device, although with the camshaft support
structure that does not include the outer frame for the support
bases, the alignment of the bearing portions of the support bases
is likely to deteriorate due to engine operation. Applying the
present invention to such an internal combustion engine favorably
reduces deterioration in the alignment of the bearing portions of
the support bases due to engine operation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a plan view illustrating a planar structure of an
internal combustion engine according to a first embodiment of the
present invention as viewed from above an exhaust camshaft and an
intake camshaft;
[0021] FIG. 2 is a cross-sectional view taken along line A-A of
FIG. 1, illustrating a cross-sectional structure of the internal
combustion engine; and
[0022] FIG. 3 is a side view schematically illustrating a side
structure of the top surface of the cylinder head and the support
bases mounted on the top surface in the longitudinal direction of
the cylinder head.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] A camshaft support structure of a double overhead camshaft
(DOHC) inline 4-cylinder internal combustion engine according to
one embodiment of the present invention will now be described with
reference to FIGS. 1 to 3. The internal combustion engine of the
present embodiment is provided with an exhaust driven
forced-induction device.
[0024] FIG. 1 shows a planar structure of an internal combustion
engine as viewed from above an exhaust camshaft and an intake
camshaft. FIG. 2 shows a cross-sectional structure of the internal
combustion engine taken along line A-A of FIG. 1.
[0025] A cylinder head 1, which is provided with a valve mechanism
including exhaust valves and intake valves, is provided on the top
surface of a cylinder block 2 as shown in FIG. 2. The cylinder
block 2 and the cylinder head 1 are tightened with head bolts 3 in
a known manner (see FIGS. 2 and 3).
[0026] An exhaust camshaft 5 provided with exhaust cams 51 for
opening and closing the exhaust valves and an intake camshaft 6
provided with intake cams 61 for opening and closing the intake
valves are arranged on a top surface 1a of the cylinder head 1 to
be parallel to each other. More specifically, five support bases 4
for supporting the camshafts 5, 6 to be freely rotational are
mounted on the top surface 1a of the cylinder head 1. Only one of
the support bases 4 is shown in FIG. 2.
[0027] The support bases 4 are arranged apart from one another in
an axial direction L of the camshafts 5, 6 as shown in FIG. 1. More
specifically, the support bases 4 are arranged to be perpendicular
to the axial direction L of the camshafts 5, 6.
[0028] Each of the support bases 4 includes a receiving member 41
located on the top surface 1a of the cylinder head 1, and an
exhaust side cap member 42 and an intake side cap member 43, which
are located on the top surface of the receiving member 41 as shown
in FIG. 2. Semi-circular lower recesses 41b, 41c are formed on the
top surface of each receiving member 41 at positions corresponding
to the camshafts 5, 6.
[0029] A semicircular upper recess 42b is formed on the bottom
surface of each exhaust side cap member 42 at a position
corresponding to the associated lower recess 41b. Each lower recess
41b and the associated upper recess 42b form a circular bearing
portion 45b, which supports one of cam journals 5a of the exhaust
camshaft 5 (see FIG. 1).
[0030] Furthermore, a semicircular upper recess 43c is formed on
the bottom surface of each intake side cap member 43 at a position
corresponding to the associated lower recess 41c. Each lower recess
41c and the associated upper recess 43c form a circular bearing
portion 45c, which supports one of cam journals 6a of the intake
camshaft 6 (see FIG. 1).
[0031] Two bolt holes are formed in each exhaust side cap member 42
and the associated receiving member 41 in an axial direction C of
the cylinders with the exhaust camshaft 5 located in between. The
receiving member 41 and the exhaust side cap member 42 are
tightened to the cylinder head 1 with bolts 44L, 44S inserted in
the bolt holes.
[0032] Furthermore, each intake side cap member 43 and the
associated receiving member 41 are coupled to the cylinder head 1
with other bolts 44L in the same manner as each exhaust side cap
member 42 and the associated receiving member 41.
[0033] In a state in which the support bases 4 are mounted on the
cylinder head 1 with the bolts 44L, 44S, the cylinder head 1 is
assembled to the cylinder block 2 with the head bolts 3. The
cylinder head 1, the cylinder block 2, and the support bases 4 are
all made of an aluminum alloy.
[0034] In the present embodiment, a through hole 41d, which extends
in the axial direction L of the camshafts 5, 6, is formed in each
receiving member 41 as shown in FIG. 2. Each through hole 41d is
formed at a position closer to a center position Pex of the exhaust
camshaft 5 than to a middle position Pc between the center position
Pex of the exhaust camshaft 5 and a center position Pin of the
intake camshaft 6 in a direction perpendicular to the axial
direction L of the camshafts 5, 6. In other words, the through
holes 41d are formed closer to the exhaust camshaft 5 than to the
intake camshaft 6.
[0035] A rod 7 made of stainless-steel is inserted in the through
holes 41d. That is, the rod 7 is made of material having higher
rigidity than the support bases 4. In the present embodiment, the
outer diameter of the rod 7 is slightly smaller than the inner
diameter of the through holes 41d. The bolts 44S located closer to
the rod 7 than to the exhaust camshaft 5 are shorter than the other
bolts 44L so as not to interfere with the rod 7.
[0036] Operation of the present embodiment will now be
described.
[0037] The camshafts 5, 6 are supported to be freely rotational by
the bearing portions 45b, 45c of the five support bases 4 mounted
on the cylinder head 1. Since the support bases 4 are located
separate from one another in the axial direction L of the camshafts
5, 6, the contact area between the support bases 4 and the cylinder
head 1 is reduced as compared to a case in which an outer frame for
connecting the support bases is provided, as in a ladder-frame
camshaft housing. The amount of heat received from the cylinder
head 1 is thus reduced, which reduces thermal deformation of the
support bases 4 caused by receiving heat.
[0038] Since forced induction is performed by the forced-induction
device in the internal combustion engine of the present embodiment,
the temperature of exhaust gas is increased as compared to the
internal combustion engine without a forced-induction device. This
increases the thermal deformation amount of the support bases 4
caused by receiving heat from the cylinder head 1. Furthermore,
since the pressure in the cylinders is also increased as compared
to the internal combustion engine without the forced-induction
device, the cylinder head 1 is deformed significantly as the
pressure in the cylinders of the internal combustion engine
fluctuates. The deformation amount of the support bases 4 mounted
on the cylinder head 1 is consequently increased. As described
above, in the internal combustion engine provided with the
forced-induction device, the alignment of the bearing portions 45b,
45c in the support bases 4 is likely to deteriorate due to engine
operation although with the camshaft support structure of the
present embodiment that does not include the outer frame for the
support bases 4.
[0039] In this respect, since the rod 7 is inserted in the through
holes 41d formed in the support bases 4 in the present embodiment,
the support bases 4 are favorably restricted from being thermally
deformed due to heat received from the cylinder head 1.
[0040] Furthermore, in the internal combustion engine,
high-temperature exhaust gas is discharged to the exhaust passage
through the exhaust valves. Thermal deformation of the cylinder
head 1 is thus increased toward the region close to the exhaust
camshaft 5. In this respect, with the above-mentioned structure,
the through holes 41d in which the rod 7 is inserted are formed at
positions closer to the exhaust camshaft 5 than to the intake
camshaft 6. That is, the rod 7 is arranged in the vicinity of the
regions in the receiving members 41 of the support bases 4 where
the amount of heat received from the cylinder head 1 is great and
the degree of thermal deformation is great. Thermal deformation of
the receiving members 41 in the vicinity of the exhaust camshaft 5
is thus reduced in an appropriate manner.
[0041] Furthermore, the rod 7 is assembled to the cylinder head 1
together with the support bases 4 in a state in which the rod 7 is
inserted in the through holes 41d. The cylinder head 1 is further
assembled to the cylinder block 2 with the head bolts 3 in a state
in which the support bases 4 and the rod 7 are assembled to the
cylinder head 1. In this embodiment, the top surface 1a of the
cylinder head 1 is slightly distorted from a flat state due to the
axial tightening force of the head bolts 3 as shown in FIG. 3. The
rod 7 is thus maintained in a state pressed by the inner walls of
the through holes 41d, and secured to the support bases 4. For the
illustrative purposes, the distortion of the top surface 1a of the
cylinder head 1 is exaggerated and the rod 7 is omitted in FIG.
3.
[0042] The camshaft support structure of the present embodiment as
described above has the following advantages.
[0043] (1) The support bases 4 are arranged apart from one another
in the axial direction L of the camshafts 5, 6. Furthermore, the
bearing portions 45b, 45c, which support the camshafts 5, 6, and
the through holes 41d, which extend in the axial direction L of the
camshafts 5, 6, are formed in the support bases 4. The rod 7 is
inserted in the through holes 41d to restrict the bearing portions
45b, 45c from being displaced from the arrangement position at
which the bearing portions 45b, 45c are located when the internal
combustion engine is stopped and cold. With this structure, in the
support bases 4, which support the camshafts 5, 6, the alignment of
the bearing portions 45b, 45c is favorably restricted from
deteriorating due to engine operation. The state in which the
internal combustion engine is stopped and cold refers to a state in
which operation of the internal combustion engine is stopped and
the influence of heat caused by the previous engine operation can
be ignored.
[0044] (2) The rod 7 is made of material having higher rigidity
than the support bases 4. More specifically, the support bases 4
are made of an aluminum alloy, and the rod 7 is made of
stainless-steel, which has higher rigidity than the aluminum alloy.
With this configuration, thermal deformation of the support bases 4
is reduced in an appropriate manner.
[0045] (3) The through holes 41d are formed closer to the exhaust
camshaft 5 than to the intake camshaft 6. This structure
appropriately reduces thermal deformation of the receiving members
41 in the vicinity of the exhaust camshaft 5 where the amount of
heat received from the cylinder head 1 is great.
[0046] The camshaft support structure of the present invention is
not limited to the structure illustrated in the above described
embodiment, but may be modified as follows.
[0047] In the above-described embodiment, the present invention is
applied to an internal combustion engine provided with an exhaust
driven forced-induction device, that is, a turbocharger. The
present invention may, however, be applied to an internal
combustion engine provided with an engine driven forced-induction
device, or a supercharger.
[0048] In the above-described embodiment and the modified
embodiment, the present invention is applied to an internal
combustion engine provided with a forced-induction device. The
present invention, however, is not only applied to an internal
combustion engine provided with a forced-induction device, but may
be applied to an internal combustion engine without a
forced-induction device. In this case, although the amount of heat
the support bases receive from the cylinder head is small as
compared to that received by the engine provided with the
forced-induction device, the alignment of the bearing portions of
the support bases is favorably restricted from deteriorating due to
engine operation in the same manner as the above-described
embodiment.
[0049] As in the above-described embodiment, it is preferable that
the through holes 41d be formed closer to the exhaust camshaft 5
than to the intake camshaft 6 to prevent thermal deformation of the
receiving members 41 in the vicinity of the exhaust camshaft 5
where the amount of heat received from the cylinder head 1 is
great. The present invention, however, is not limited to this, but
through holes may be formed at, for example, the middle position Pc
between the exhaust camshaft 5 and the intake camshaft 6. In this
case also, thermal deformation of the receiving members is
restricted to some extent.
[0050] In the above-described embodiment, one through hole 41d is
formed in each of the support bases 4. Instead, two or more through
holes may be formed in each of the support bases 4, and two or more
rods may be provided corresponding to the number of the through
holes. This further reduces thermal deformation of the support
bases.
[0051] The rod 7 made of stainless-steel is illustrated in the
above-described embodiment, but the rod may be made of any material
that has higher rigidity than the support bases.
DESCRIPTION OF THE REFERENCE NUMERALS
[0052] 1 . . . cylinder head, 1a . . . top surface, 2 . . .
cylinder block, 3 . . . head bolt, 4 . . . support base, 41 . . .
receiving member, 41a . . . abutment surface, 41b, 41c . . . lower
recesses, 41d . . . through hole, 42 . . . exhaust side cap member,
42b . . . upper recess, 43 . . . intake side cap member, 43c . . .
lower recess, 44 . . . bolt, 45b, 45c . . . bearing portions, 5 . .
. exhaust camshaft, 5a . . . cam journal, 51 . . . exhaust cam, 6 .
. . intake camshaft, 6a . . . cam journal, 61 . . . intake cam, 7 .
. . rod.
* * * * *