Note: Descriptions are shown in the official language in which they were submitted.
CA 02676569 2009-08-26
OIL STRAINER STRUCTURE OF ENGINE AND
OIL RETURN STRUCTURE OF ENGINE
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention generally relates to an oil strainer structure of an
engine,
which includes an oil strainer for filtering oil in an oil pan, the oil
strainer being
arranged between a balancer housing and the oil pan of the engine and
supported by the
balancer housing.
Also, the present invention generally relates to an oil return structure of an
engine, which includes an oil return member for returning oil separated from
blowby
gas to an oil pan, the oil return member being arranged between a balancer
housing and
the oil pan of the engine.
DESCRIPTION OF THE RELATED ART
Japanese Patent Application Laid-open No. 2001-74105 discloses an oil
strainer structure of an engine in which a balancer housing is supported on a
lower
surface of a lower block which holds a crankshaft of the engine between itself
and the
cylinder block; and an oil strainer for filtering oil that is suctioned from
the oil pan into
the oil pump is integrally housed in the lower surface of a lower housing part
of the
balancer housing.
Because blowby gas leaked out of a combustion chamber into a crankcase
contains oil, it is necessary to separate the oil from the blowby gas in a gas-
liquid
separating chamber formed in a cylinder head, return the blowby gas to an
intake
system, and return the oil to the oil pan.
In addressing this problem, Japanese Patent Application Laid-open No.
2003-201815 discloses an oil return structure of an engine in which a balancer
housing
is supported on a lower surface of a lower block joined to a lower end of a
cylinder
block, and an oil return passage is formed inside the cylinder block, the
lower block and
the balancer housing so as to return the oil from the gas-liquid separating
chamber
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formed in the cylinder head to the oil pan.
However, in the oil strainer structure disclosed in Japanese Patent
Application
Laid-open No. 2001-74105, the oil strainer is integrally housed in the lower
housing
part of the balancer housing; and thus, the position of the oil strainer is
limited to a
space between the two balancer shafts, which causes the problems in that it is
difficult
to arrange the oil suction hole at an appropriate position, and it is
difficult to secure a
sufficient area of a strainer element of the oil strainer and a sufficient
cross-sectional
area of oil flow.
When the oil strainer and the oil return passage are integrally formed with
the
balancer housing, a significant limitation is imposed on flexibility in
positioning of the
oil suction hole of the oil strainer and positioning of the oil outlet hole of
the oil return
passage. Then, it is conceivable to provide the oil strainer and the oil
return member (a
member where an oil return passage is formed) separately from the balancer
housing.
In this case, however, the number of components increases in both the oil
strainer and
the oil return member. Thus, it is desired to minimize the increase in the
number of
components.
Also, when waves are formed on the liquid surface of the oil in the oil pan
due
to acceleration, deceleration or turn of the vehicle, air is mixed in the oil
suctioned
through the oil strainer, leading to a possibility that the oil pump does not
normally
operates. Thus, in the conventional structural arrangements, a baffle plate is
provided
inside the oil pan to suppress the formation of waves on the liquid surface of
the oil, but
this increases the number of components. Thus, it is desired to suppress the
wave
formation on the liquid surface of the oil without providing a dedicated
baffle plate.
Further, in the oil return structure disclosed in Japanese Patent Application
Laid-open No. 2003-201815, the oil outlet hole of the oil return passage
directly opens
in the lower surface of the balancer housing, and is located so as to be
adjacent to the oil
suction hole of the oil strainer formed integrally with the balancer housing.
Therefore,
a negative pressure is generated by suction of the oil pump in the vicinity of
the oil
suction hole of the oil strainer, and the negative pressure affects the oil
outlet hole of the
oil return passage, which may adversely affect the separation of the oil from
the blowby
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gas in the gas-liquid separating chamber.
In order to eliminate this drawback, it is desirable that the oil outlet hole
of the
oil return passage is positioned away from the oil suction hole of the oil
strainer, but it is
difficult to freely select the position of the oil outlet hole because the oil
outlet hole
opens directly in the lower surface of the balancer housing.
SUMMARY OF THE INVENTION
The present invention has been made under the above-described circumstances,
and a first object of the invention is to enable a high-performance oil
strainer to be
arranged in a narrow space between a balancer housing and an oil pan.
A second object of the invention is to minimize the number of components of
the oil strainer and an oil return member, both of which are provided under
the balancer
housing.
A third object of the invention is to cause the oil strainer provided under
the
balancer housing to function as a baffle plate.
A fourth object of the invention is to enhance the degree of flexible
arrangement of an oil return member for returning oil separated from blowby
gas to a
space between the balancer housing and the oil pan.
In order to achieve the first object, according to a first feature of the
present
invention, there is provided an oil strainer structure of an engine, which
includes an oil
strainer for filtering oil in an oil pan, the oil strainer being arranged
between a balancer
housing and the oil pan of the engine and supported by the balancer housing,
the oil
strainer including: a lower member which is a die-molded article having an oil
suction
hole opening in the oil stored in the oil pan; an upper member which is a die-
molded
article having an oil discharge hole leading to the oil pump; and a strainer
element, the
lower member and the upper member being joined to each other with an outer
peripheral portion of the strainer element held between joint surfaces of the
upper and
lower members.
With this structural arrangement, the oil strainer is formed by joining
together
the die-molded lower member having the oil suction hole opening in the oil
stored in the
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oil pan and the die-molded upper member having the oil discharge hole leading
to the
oil pump. When the two members are joined together, the outer peripheral
portion of
the strainer element is held between the joint surfaces of the two members.
The oil
strainer is supported by the balancer housing. Thus, it is possible to form
the oil
strainer into a flat shape so as to be compactly arranged in a narrow space
between the
lower surface of the balancer housing and the bottom surface of the oil pan,
and to also
maximize an area of the strainer element to prevent clogging. Further, the
lower
member and the upper member, which are die-molded articles, are highly
flexible in
their shapes, whereby the oil suction hole and the oil discharge hole can be
arranged in
the most suitable positions, and the cross-sectional area of oil flow can be
sufficiently
secured.
According to a second feature of the present invention, in addition to the
first
feature, the oil strainer has a cross-sectional area decreasing from the oil
suction hole to
the oil discharge hole.
With this structural arrangement, the cross-sectional area of the oil strainer
decreases from the oil suction hole to the oil discharge hole. Accordingly,
the flow
rate of the oil suctioned from the oil pan that flows through the oil strainer
can be
gradually increased, thereby minimizing resistance generated by the suction of
oil into
the oil pump.
In order to achieve the second object, according to a third feature of the
present
invention, there is provided an oil strainer structure of an engine,
comprising: an oil
strainer for filtering oil in an oil pan, the oil strainer including two
members joined to
each other and being supported on a lower surface of a balancer housing of the
engine,
wherein an oil return member for returning oil separated from blowby gas is
formed by
two members joined to each other, and wherein one of the two members forming
the oil
return member is commonly used as one of the two members forming the oil
strainer.
With this structural arrangement, one of the two members joined together to
form the oil strainer for filtering the oil in the oil pan is also used as one
of the two
members joined together to form the oil return member for returning the oil
separated
from the blowby gas to the oil pan. Therefore, the number of members is
reduced to 3
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instead of 4 in the case where no member is shared by the oil strainer and the
oil return
member, thereby reducing the number of components of the oil strainer and the
oil
return member as well as the cost.
According to a fourth feature of the present invention, in addition to the
third
feature, the commonly used member is a lower member; and the lower member and
a
first upper member that is joined to the balancer housing constitute the oil
strainer, and
the lower member and a second upper member that is joined to the balancer
housing
constitute the oil return member.
With this structural arrangement, the first upper member and the second upper
member, which are joined to the balancer housing, are separate members.
Therefore,
the first and second upper members become high-precision parts to facilitate
their being
joined together, thereby suppressing leakage of the oil through the joint
portion.
In order to achieve the third object, according to a fifth feature of the
present
invention, there is provided an oil strainer structure of an engine, having:
an oil strainer
for filtering oil in an oil pan, the oil strainer being supported on a lower
surface of a
balancer housing of the engine, wherein the oil strainer is supported so as to
bridge
between opposite ends of the balancer housing.
With this structural arrangement, the oil strainer for filtering the oil in
the oil
pan is supported on the lower surface of the balancer housing so that the oil
strainer
bridges between the opposite ends of the balancer housing. Therefore, the oil
strainer
can prevent the liquid surface of the oil stored in the oil pan from moving
with
acceleration, deceleration or turn of the vehicle, that is, the oil strainer
can function as a
baffle plate. Thus, it is possible to eliminate or downsize the conventional
baffle plate,
thereby contributing to reduction in the number of components and the cost.
According to a sixth feature of the present invention, in addition to the
fifth
feature, the structure further comprises a rib which is projectingly provided
on an upper
or lower surface of the oil strainer.
With this structure, the rib is projectingly provided on the upper or lower
surface of the oil strainer. Therefore, the rib can enhance the rigidity of
the oil strainer,
and further enhance the function of the baffle plate excreted by the oil
strainer.
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According to a seventh feature of the present invention, in addition to the
fifth
or sixth feature, the structure further comprises an oil return member for
returning oil
separated from blowby gas to the oil pan, the oil return member being
integrally formed
at a joint portion where an end of the oil strainer is joined to the balancer
housing.
With this structural arrangement, the oil return member is formed integrally
at
the joint portion where the end of the oil strainer is joined to the balancer
housing.
Therefore, it is possible to reduce the number of components as compared with
the case
where the oil return member and the balancer housing are separately provided.
In order to achieve the fourth object, according to an eighth feature of the
present invention, there is provided an oil return structure of an engine,
having: an oil
return member for returning oil separated from blowby gas to an oil pan, the
oil return
member being arranged between a balancer housing and the oil pan of the
engine, the
oil return member including: an upper member which is a die-molded article
having an
oil inlet hole leading to an oil return passage in the balancer housing; and a
lower
member which is a die-molded article having an oil outlet hole opening in the
oil in the
oil pan, the upper and lower members being joined to each other.
With this structural arrangement, the oil return member is formed by joining
together the upper member having the oil inlet hole leading to the oil return
passage of
the balancer housing and the lower member having the oil outlet hole opening
in the oil
in the oil pan. Therefore, it is possible to enhance the flexibility in
determining the
position of the oil outlet hole. Accordingly, the oil outlet hole can be
arranged in a
position where the oil outlet hole is less susceptible to the influence of the
negative
pressure generated by suction of the oil at the inlet hole of the oil strainer
arranged
inside the oil pan, thereby reliably performing gas-liquid separation between
the blowby
gas and the oil. Further, the lower member and the upper member, which are
die-molded articles, are highly flexible in their shapes, whereby the oil
outlet hole can
be reliably arranged below the liquid surface of the of oil in the oil pan to
prevent the
pressure fluctuation in the crankcase from affecting the gas-liquid
separation.
The above and other objects, features and advantages of the invention will
become apparent from preferred embodiments taken in conjunction with the
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accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figs. 1 to 9 show a first embodiment of the invention, wherein
Fig. 1 is a front view of an engine;
Fig. 2 is a cross-sectional view taken along line 2-2 of Fig. 1;
Fig. 3 is a view in direction of arrow 3-3 of Fig. 2;
Fig. 4 is a view in direction of arrow 4-4 of Fig. 2;
Fig. 5 is a cross-sectional view taken along line 5-5 of Fig. 3;
Fig. 6 is a cross-section taken along line 6-6 of Fig. 3;
Fig. 7 is an exploded perspective view of an oil strainer viewed from
obliquely
below;
Fig. 8 is an exploded perspective view of the oil strainer viewed from
obliquely
above; and
Fig. 9 is a perspective view of a balancer device equipped with the oil
strainer.
Fig. 10 is a view corresponding to Fig. 8 according to a second embodiment of
the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A first embodiment of the present invention will be described with reference
to
Figs. 1 to 9.
Figs. 1 and 2 show the following structural arrangement. A lower block 12 is
fixed to a lower surface of a cylinder block l l of a diesel engine E of an
automobile.
An oil pan 13 is fixed to the lower surface of the lower block 12. Provided on
a lower
surface of the lower block 12 is a balancer device 14 which reduces secondary
vibration
of the engine E, and which is housed in the oil pan 13. A crankshaft 15 is
rotatably
supported between the cylinder block 11 and the lower block 12. A drive
sprocket 16
is provided at an end of the crankshaft 15. A driven sprocket 17 is provided
at an end
of a drive balancer-shaft 29 of the balancer device 14. An endless chain 18 is
wound
around the drive and driven sprockets 16 and 17.
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Figs. 3 to 6 show the following structural arrangement. The balancer device
14 has a balancer housing 19 including an upper housing part 20 and a lower
housing
part 21. The upper and lower housing parts 20 and 21 are joined together by a
plurality of bolts 22. A right-side housing part 23 is joined to the balancer
housing 19
on an end face on the right side of the vehicle. A left-side housing part 25
is joined to
the balancer housing 19 on an end face on the left side of the vehicle. The
balancer
housing 19 is fixed to the lower surface of the lower block 12 with two bolts
27 and 27
penetrating the upper and lower housing parts 20 and 21, and with another two
bolts 28
and 28 penetrating the right-side housing part 23.
The balancer housing 19 supports the drive balancer-shaft 29 and a driven
balancer-shaft 30 which are parallel to each other. Provided on the drive
balancer-shaft 29 are the driven sprocket 17, a drive gear 31, a first
balancer-weight 32
and a second balancer-weight 33, sequentially from one end to the other end of
the drive
balancer-shaft 29. Provided on the driven balancer-shaft 30 are a driven gear
34, a first
balancer-weight 35 and a second balancer-weight 36, sequentially from one end
to the
other end of the driven balancer-shaft 30. The endless chain 18 is wound
around the
drive sprocket 16 provided on the crankshaft 15 and the driven sprocket 17
provided on
the drive balancer-shaft 29. The drive gear 31 provided on the drive balancer-
shaft 29
meshes with the driven gear 34 provided on the driven balancer-shaft 30.
Accordingly, when the engine E operates, the rotation of the crankshaft 15 is
transmitted to the drive balancer-shaft 29 via the drive sprocket 16, the
endless chain 18
and the driven sprocket 17; and the rotation of the drive balancer-shaft 29 is
transmitted
to the driven balancer-shaft 30 via the drive gear 31 and the driven gear 34.
In this
structural arrangement, the number of teeth of the drive sprocket 16 on the
crankshaft
15 is set at twice the number of the teeth of the driven sprocket 17 on the
drive
balancer-shaft 29, while the drive and driven gears 31 and 34 have the same
number of
teeth. Consequently, the drive and driven balancer-shafts 29 and 30 rotate in
directions
opposite to each other, at the same rotational speed that is twice the
rotational speed of
the crankshaft 15, so that the first and second balancer weights 32, 33: 35,
36 provided
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on the drive balancer-shaft 29 and the driven balancer-shaft 30 reduce the
secondary
vibration in the engine E.
Fig. 6 clearly shows the following structure. An oil pump 37, which is a
trochoidal pump, has a circular-shaped pump chamber 23a which opens in the
joint
surface of the right-side housing part 23 with respect to the upper and the
lower housing
parts 20 and 21. An outer rotor 38 and an inner rotor 39 are housed inside the
pump
chamber 23a such that they mesh with each other. A suction port 40 facing the
pump
chamber 23a communicates with a suction passage 41 which opens in the lower
surface
of the lower housing part 21. A discharge port 42 facing the pump chamber 23a
communicates with a discharge passage 43 (see Fig. 3), which opens in the
upper
surface of the right-side housing part 23; that is, in the joint surface
between the
right-side housing part 23; and the lower block 12.
Next, an oil strainer 51 for filtering the oil suctioned from the oil pan 13
into
the oil pump 37 will be described with reference to Figs. 4 to 9.
Figs. 7 and 8 show the following structure. The oil strainer 51 is constituted
by total four members: a lower member 52, a first upper member 53 and a second
upper
member 54, all of which are injection-molded from a synthetic resin into a
die; and a
strainer element 55 made of a synthetic resin mesh.
The lower member 52 includes: a main-body portion 52a, a support-arm
portion 52b, an oil-return-passage formed portion 52c and an oil-discharge-
pipe portion
52d. The main-body portion 52a has a shallow container shape with an open
upper
surface and curved into a comma shape. The support-arm portion 52b has a plate
shape extending obliquely upward from a part of the outer periphery of the
main-body
portion 52a. The oil-return-passage formed portion 52c has a linear shape
connecting
to an upper end of the support-arm portion 52b. The oil-discharge-pipe portion
52d
has a pipe shape extending downward from an end of the oil-return-passage
formed
portion 52c. A rectangular-shaped oil suction hole 52f opens in the main-body
portion
52a on one end side (wider side). A gutter-shaped groove 52g is formed in an
upper
surface of the oil-return-passage formed portion 52c, and communicates with
the
oil-discharge-pipe portion 52d. An oil outlet hole 52e opens at a bottom end
of the
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oil-discharge-pipe portion 52d, and is located below the liquid surface of the
oil stored
in the oil pan 13. Therefore, the pressure fluctuation in the crankcase does
not affect
the intake system via the oil-return passage 581eading to the cylinder head.
The first upper member 53 has substantially the same shape as that of the
main-body portion 52a of the lower member 52, and is formed into a shallow
container
shape with an open lower surface. An oil discharge hole 53a is formed in the
first
upper member 53 on the other end side (narrower side) so as to penetrate
upward the
first upper member 53.
The second upper member 54 has substantially the same shape as that of the
oil-return-passage formed portion 52c of the lower member 52. A gutter-shaped
groove 54a is formed in the lower surface of the second upper member 54 so as
to face
the gutter-shaped groove 52g of the oil-return-passage formed portion 52c. An
oil
inlet hole 54b is formed in the second upper member 54 at an end on a side
opposite to
the oil-discharge-pipe portion 52d. Mounting bosses 54c and 54d each having a
bolt-hole are projectingly formed on opposite sides of the oil inlet hole 54b.
The lower surfaces of the first and second upper members 53 and 54 are
respectively joined by fusing to the upper surfaces of the main-body portion
52a and the
oil-return-passage formed portion 52c. In this process, the outer peripheral
portion of
the strainer element 55 is held and fixed between the lower surface of the
first upper
member 53 and the upper surface of the main-body portion 52a of the lower
member 52.
As a result, a dirty chamber 56 is defined between the strainer element 55 and
the
main-body portion 52a of the lower member 52, and a clean chamber 57 is
defined
between the strainer element 55 and the first upper member 53. The oil return
passage
58 is formed between the groove 52g in the oil-return-passage formed portion
52c of the
lower member 52 and the groove 54a of the second upper member 54. The opposite
ends of the oil return passage 58 communicate with the oil inlet hole 54b and
the
oil-discharge-pipe portion 52d.
The oil strainer 51 comprises the lower member 52, the first upper member 53
and the second upper member 54, all of which are synthetic resin die-molded
articles,
and thus has a high flexibility in designing the shape. Accordingly, the
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high-performance oil strainer 51 can be arranged in the narrow space between
the
balancer housing 19 and the oil pan 13. More particularly, in the oil suction
route to
the oil pump 37, the oil suction hole 52f and the oil discharge hole 53a can
be arranged
in the most suitable positions, and the cross-sectional area of oil flow can
be sufficiently
secured. Also, in the oil returning route for returning the oil separated from
the
blowby gas, the oil outlet hole 52e can be arranged in a position sufficiently
away from
the oil suction hole 52f, and can be kept below the liquid surface of the oil.
As clearly shown in Fig. 4, the oil strainer 51 structured as described above
is
fastened to the lower housing part 21 of the balancer housing 19 with three
bolts 59
penetrating from below the bolt-holes of the three mounting bosses 53b, 53c
and 53d of
the first upper member 53, and is fastened to the upper housing part 20 of the
balancer
housing 19 with two bolts 60 and 60 penetrating from above the bolt-holes of
the two
mounting bosses 54c and 54d of the second upper member 54. In this structural
arrangement, the two mounting bosses 54c and 54d of the second upper member 54
are
fixed to the end portion of the upper housing part 20 on the drive balancer-
shaft 29 side;
the mounting bosses 53b and 53c of the first upper member 53 are fixed to the
lower
housing part 21 on the driven balancer-shaft 30 side; and the remaining
mounting boss
53d of the first upper member 53 is fixed to the lower housing part 21 between
the drive
balancer-shaft 29 and the driven balancer-shaft 30. Consequently, the oil
strainer 51 is
supported at a position so as to cover the lower surface of the lower housing
part 21.
In the above-described mounted state, the oil discharge hole 53a of the first
upper member 53 communicates, through the suction passage 41 opening in the
lower
surface of the lower housing part 21, with the suction port 40 of the oil pump
37 (see
Fig. 6). Also, the oil inlet hole 54b of the second upper member 54
communicates,
through an oil return passage 20a opening in the lower surface of the upper
housing part
20, with the oil return passage 23b which opens in the joint surface of the
right-side
housing part 23 with respect to the lower block 12 (see Fig. 9). The oil
return passage
23b of the right-side housing part 23 communicates, through another oil return
passage
(not illustrated) penetrating the lower block 12 and the cylinder block 11,
with a
labyrinth-type gas-liquid separating chamber (not illustrated) formed in the
cylinder
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head.
Next, the operation of the first embodiment of the present invention will be
described.
When the engine E operates, the rotation of the crankshaft 15 is transmitted
to
the drive balancer-shaft 29 via the endless chain 18, and the rotation of the
drive
balancer-shaft 29 is transmitted to the driven balancer-shaft 30 via the drive
and driven
gears 31 and 34. Thus, the oil pump 37 connected to the driven balancer-shaft
30
starts to operate.
As a result, the oil stored in the oil pan 13 is suctioned into the oil
strainer 51
through the oil suction hole 52f formed in the lower member 52 of the oil
strainer 51;
passes from the dirty chamber 56 through the strainer element 55 while being
filtered
thereby; passes from the clean chamber 57 through the oil discharge hole 53a
of the first
upper member 53; and further passes through the suction passage 41 of the
lower
housing part 21 of the balancer housing 19 (see Figs. 3 and 6) and the suction
port 40 of
the right-side housing part 23, and is suctioned into the oil pump 37.
The oil discharged to the discharge port 42 of the oil pump 37 is supplied
from
the discharge passage 43 of the right-side housing part 23 (see Fig. 3) to the
lower block
12, and then branches therefrom into plural routes and used to lubricate a
journal
portion of the crankshaft 15 and a valve operating mechanism.
The main-body portion 52a of the lower member 52 and the second upper
member 54 dividing the interior of the oil strainer 51 into the dirty chamber
56 and the
clean chamber 57, has a vertically flat shape, and the outer peripheral
portion of the
strainer element 55 having a large area is held between the lower member 52
and the
second upper member 54. Therefore, it is possible to minimize the increase in
the flow
resistance of the oil, and to prevent the clogging of the strainer element 55.
As clearly shown in Figs. 7 and 8, the oil strainer 51 is made thinner on the
oil
suction hole 52f side and thicker on the oil discharge hole 53a side in order
to avoid any
interference with the bottom surface of the oil pan 13. However, the oil
strainer 51 is
made wider on the oil suction hole 52f side and narrower on the oil discharge
hole 53a
side, thereby preventing the sudden change in the cross-sectional area of oil
flow to
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minimize the increase in the flow resistance of the oil. Particularly because
the
cross-sectional area of the passage of the oil strainer 51 gradually decreases
from the oil
suction hole 52f side to the oil discharge hole 53a side, the flow rate of the
oil flowing
from the oil suction hole 52f to the oil discharge hole 53a slowly increases,
thereby
reducing the flow resistance against the oil flowing into the oil pump 37.
The blowby gas that leaks out of the combustion chamber of the engine E is
supplied to the cylinder head while containing the oil; and is subjected to
the gas-liquid
separation in the gas-liquid separating chamber provided in the cylinder head
to separate
therefrom the oil. Consequently, the gas is returned to the intake system and
the oil is
returned to the oil pan 13. The oil separated from the blowby gas flows down
through
an oil return passage (not shown) formed in the cylinder block 11 and the
lower block
12; passes through the oil return passage 23b (see Figs. 3 and 9) in the right-
side
housing part 23 of the balancer housing 19 joined to the lower block 12 and
through the
oil return passage 20a (see Figs. 3 and 9) in the upper housing part 20; and
flows into
the oil inlet hole 54b of the second upper member 54 of the oil strainer 51
(see Figs.8
and 9).
The oil that flows flowed into the oil inlet hole 54b of the second upper
member 54, passes through the oil return passage 58 formed between the
oil-return-passage formed portion 52c of the lower member 52and the second
upper
member 54, further through the oil-discharge-pipe portion 52b of the lower
member 52,
and returns to the undersurface of the oil stored in the oil pan 13 through
the oil outlet
hole 52e located below the liquid surface of the oil in the oil pan 13.
As described above, the oil return passage 58 and the oil-discharge-pipe
portion
52d for returning the oil separated from the blowby gas to the oil pan 13, are
formed
integrally with the oil strainer 51. Consequently, the number of components
and the
number of assembling steps are reduced as compared with the case where the oil
return
passage 58 and the oil-discharge-pipe section 52d are formed separately from
the oil
strainer 5 1.
As described above, the lower member 52 forming a part of the oil strainer 51
for filtering the oil in the oil pan 13 is also used for forming a part of the
oil return
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member for returning the oil separated from the blowby gas to the oil pan 13.
Consequently, the number of members is reduced to 3, instead of 4, in the case
where no
member is commonly used, thereby reducing the number of components of the oil
strainer 51 and the oil return member to reduce the cost.
In addition, because the first and second upper members 53 and 54 which are
joined to the balancer housing 19 are separate members, they can be high-
precision
parts, thereby facilitating joining them to the balancer housing 19 to
suppress the
leakage of oil out of the joint portion. Assuming that the first and second
upper
members 53 and 54 are integrated into a single member, the single member
becomes
large in dimensions, and also the oil discharge hole 53a and the oil inlet
hole 54b are
required to be formed in the single member which requires a severe dimensional
accuracy in aligning the oil discharge hole 53a and the oil inlet hole 54b
respectively
with the suction passage 41 and the oil return passage 20a of the balancer
housing 19.
Therefore, this structural arrangement results in an increased processing
cost.
Depending on the positional relationship between the oil suction hole 52f and
the oil outlet hole 52e in the oil strainer 51, the negative pressure
generated by suction
of the oil pump 37 and acting on the oil suction hole 52f may affect the oil
outlet hole
52e, leading to a possibility that the negative pressure adversely affects the
separation of
the oil from the blowby gas in the gas-liquid separation chamber leading to
the oil outlet
hole 52e. However, according to the present embodiment, the positional
relationship
between the oil suction hole 52f and the oil outlet hole 52e can be flexibly
established
by using the oil return passage 58 formed between the oil-return-passage
formed portion
52c of the lower member 52 and the second upper member 54 so as to avoid the
influence of the negative pressure generated by suction of the oil pump 37.
Further, the oil-discharge-pipe portion 52d is formed in the lower member 52
so as to project downward, and the oil outlet hole 52e opens at the bottom end
of the
oil-discharge-pipe portion 52d. Consequently, the pressure fluctuation in the
crankcase
is prevented from adversely affecting the gas-liquid separation.
Furthermore, the oil strainer 51 is supported so as to provide a bridge
between
the opposite end of the balancer housing 19, and partitions the space between
the lower
14
CA 02676569 2009-08-26
surface of the balancer housing 19 and the bottom surface of the oil pan 13.
Consequently, the oil strainer 51 functions as a baffle plate for suppressing
the
fluctuation of the liquid surface of the oil due to acceleration, deceleration
or turn of the
vehicle, thereby reliably preventing cavitation in the oil pump 37 due to air
mixed into
the oil. Therefore, it is possible to eliminate the need to provide a
dedicated baffle
plate, and downsize the conventional baffle plate, thereby reducing the number
of
components and the cost. Particularly because the support-arm portion 52b
connecting
together the main-body portion 52a and the oil-return-passage formed portion
52c of the
lower member 52 is formed into a plate shape, the support-arm portion 52b can
effectively suppress the movement of the oil to enhance the function of the
oil strainer
as a baffle plate.
Next, a second embodiment of the present invention will be described with
reference to Fig. 10.
In the second embodiment, a rib 53e is integrally formed on an upper surface
of
a first upper member 53 of an oil strainer 51 so as to project upward toward a
lower
surface of a lower housing part 21 of a balancer housing 19. The direction in
which
the rib 53e extends is substantially orthogonal to the direction in which a
support-arm
portion 52b of a lower member 52 extends.
Because the rib 53e is integrally formed on the first upper member 53 as
described above, it is possible to enhance rigidity of the oil strainer 51,
and also
effectively suppress formation of waves on the liquid surface of the oil by
causing the
rib 53e to function as a baffle plate. Particularly because the rib 53b
extends in the
direction orthogonal to the direction in which the support-arm portion 52b
extends, it is
possible to suppress the waves regardless of the direction in which the oil
moves.
The embodiments of the present invention have been described above, but
various changes in design may be made without departing from the subject
matter of the
present invention.
For example, in the embodiments, the oil return passage 58 and the
oil-discharge-pipe portion 52d for returning the oil separated from the blowby
gas to the
oil pan 13 are formed integrally with the oil strainer 51, but they may be
formed
CA 02676569 2009-08-26
separately from the oil strainer 51.
Also, in the above embodiments, the lower member 52, the first upper member
53 and the second upper member 54 are die-molded synthetic resin articles, but
they can
be die-molded metal articles (pressed products or die-cast products) or any
other articles
made not by die-molding.
16
