U.S. patent application number 14/640840 was filed with the patent office on 2015-09-10 for metal gasket.
This patent application is currently assigned to Nippon Leakless Industry Co., Ltd.. The applicant listed for this patent is Nippon Leakless Industry Co., Ltd.. Invention is credited to Shinichi Hirayama, Koichi Nakajima, Masashi Suzuki, Osamu Tosa.
Application Number | 20150252887 14/640840 |
Document ID | / |
Family ID | 53938811 |
Filed Date | 2015-09-10 |
United States Patent
Application |
20150252887 |
Kind Code |
A1 |
Tosa; Osamu ; et
al. |
September 10, 2015 |
METAL GASKET
Abstract
There is provided a metal gasket that is less susceptible to
lift and thrust phenomenon of housings and can effectively function
as a sealing at a blowhole. The metal gasket includes an embossment
portion provided with a pair of outer inclined portions and a pair
of inner inclined portions. The metal gasket and satisfies the
following relationships: Mh2/Mh1=1.10-1.81, W3>W1, and W3>W2,
where Mh1 and Mh2 are vertical lengths, and W1, W2 and W3 are
horizontal lengths. When the gasket is sandwiched in between two
housings, tip ends abut on the housing to form two seal lines, and
root ends, and another tip end abut on the housing H2 to form three
seal lines.
Inventors: |
Tosa; Osamu; (Saitama,
JP) ; Hirayama; Shinichi; (Saitama, JP) ;
Nakajima; Koichi; (Saitama, JP) ; Suzuki;
Masashi; (Saitama, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nippon Leakless Industry Co., Ltd. |
Tokyo |
|
JP |
|
|
Assignee: |
Nippon Leakless Industry Co.,
Ltd.
Tokyo
JP
|
Family ID: |
53938811 |
Appl. No.: |
14/640840 |
Filed: |
March 6, 2015 |
Current U.S.
Class: |
277/639 |
Current CPC
Class: |
F16J 15/0818 20130101;
F16H 57/029 20130101; F16J 15/0887 20130101 |
International
Class: |
F16H 57/029 20060101
F16H057/029; F16J 15/08 20060101 F16J015/08 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 7, 2014 |
JP |
2014-045469 |
Claims
1. A metal gasket comprising a frame shaped base extending
horizontally and an embossment portion extending along the base and
sandwiched in between two housings, wherein the embossment portion
includes a pair of outer inclined portions connecting to the base
and projecting respectively toward one of the housings, and a pair
of inner inclined portions connecting to tip ends of the respective
outer inclined portions, projecting respectively toward the other
of the housings and connecting to each other at their tip ends, the
following relationships are satisfied: Mh2/Mh1=1.10-1.81, W3>W1,
and W3>W2, where, in a cross-section perpendicular to the
extending direction of the embossment portion, P1 and P2 are
respective intersections between a horizontal line of a front side
of the base facing the one housing and inclined lines of front
sides of the outer inclined portions; P3 and P4 are respective
intersections between the inclined lines of the front side of the
outer inclined portions and inclined lines of front sides of the
inner inclined portions; P5 is an intersection between the inclined
lines of the front sides of the inner inclined portions; Mh1 is a
vertical length from P1 to P3; Mh2 is a vertical length from P3 to
P5; W1 is a horizontal length from P1 to P5; W2 is a horizontal
length from P2 to P5; and W3 is a horizontal length from P3 to P4,
and wherein when the metal gasket is sandwiched in between the
housings, the tip ends of the outer inclined portions abut on the
one of the housings to form two seal lines, and root ends of the
outer inclined portions and the tip end of the inner inclined
portions abut on the other of the housing to form three seal
lines.
2. The metal gasket according to claim 1, wherein the base is
formed with a bolt hole through which a bolt is inserted to fasten
the housings, and the embossment portion includes a winding
embossment portion in which the pair of the inner inclined portions
terminate adjacent to the bolt hole and the pair of the outer
inclined portions extend with the bolt hole being therebetween.
Description
TECHNICAL FIELD
[0001] The present invention relates to a metal gasket mounted
between two housings accommodating a transmission or the like to
prevent oil leakage. In particular, the present invention relates
to a technology that ensures an effective sealing function of the
metal gasket for a long time even under an occurrence of a lift-up
phenomenon where a gap between the two housings becomes larger or a
thrust phenomenon where housings move along the joint surfaces, or
even if a blowhole exists on the joint surfaces.
BACKGROUND ART
[0002] A first housing accommodating a transmission combined with
an internal combustion engine or the like, and a lid-shaped second
housing are assembled together by bolts with a metal gasket being
interposed therebetween. By tightening the bolts that fastening the
two housings, embossments provided on the metal gasket are
compressed and elastically deformed. Thus, the embossments generate
restoration forces which form seal lines on the joint surfaces of
the housings to prevent oil leakage or the like therefrom. Such
metal gasket provided with embossments is known from, for example,
openly published Japanese Patent Application Publication No.
2011-047508, openly published Japanese Utility Model Application
Publication No. H2-021370, and openly published Japanese Patent
Application No. H11-230355.
[0003] The embossment of a metal gasket described in openly
published Japanese Patent Application Publication No. 2011-047508
has an initial shape that a flat portion with a large width
projects in the cross section as shown in FIG. 5 of the
publication. Prior to a state where the metal gasket is placed
between the two housings H1, H2 and the bolts are tightened, a
center portion of an embossment 100 abuts the housing H1, and root
ends of the embossment 100 abut the lower housing H2, as shown in
FIG. 11A of the present application. When the bolts are tightened,
the embossment 100 is compressed as shown in FIG. 11B, and the
compression causes a concave depression of the embossment 100 to
form two seal lines 101, 102 with respect to the housing H1, and
three seal lines 103, 104 and 105 with respect to the housing
H2.
[0004] The embossment of the metal gasket described in openly
published Japanese Utility Model Application Publication No.
H2-021370 has an initial shape that is triangular with a sharpened
top as shown in FIG. 3 in the publication. Prior to a state where
the metal gasket is placed between the two housings H1, H2 and the
bolts are tighten, a top portion of an embossment 200 is reversely
deformed to have an M-shape as shown in FIG. 12A of the present
application. As a result, two upper end portions abut the housing
H1, and two lower ends abut the housing H2. The deformed top
portion is suspended in the air. When the bolts are tightened, two
seal lines 201,202 are formed with respect to the housing H1, and
the deformed top portion is pressed against the housing H2 to form
three seal lines 203, 204 and 205, as shown in FIG. 12B.
[0005] The embossment of the metal gasket described in openly
published Japanese Patent Application No. H11-230355 has an initial
shape that a central portion and two side portions project in
opposite directions as shown in FIG. 2 in the publication. When the
metal gasket is placed between the two housings H1, H2 and the
bolts are tightened, two seal lines 301, 302 are formed with
respect to the housing H1, and a seal line 303 is formed with
respect to the housing H2 as shown in FIG. 13 of the present
application. It is noted that, for the convenience of explanation,
FIG. 13 is drawn by flipping FIG. 2 of the publication upside
down.
[0006] When the temperature changes associated with repeated
operations and non-operations of an internal combustion engine or a
gear engagement due to a shift of the transmission occurs,
phenomena such as a lift-up HL which spreads the gap between the
two housings H1 and H2 in the vertical direction, and a small
thrust HS in the horizontal direction are observed in the housings
H1, H2 as shown in FIG. 14. If such phenomena remain for a long
time, the embossments lose their resilience to reduce the surface
pressure of the seal lines and thus the sealing function against
oil or the like is deteriorated. In particular, the embossments
described in openly published Japanese Patent Application
Publication No. 2011-047508 and openly published Japanese Utility
Model Application Publication No. H2-021370 have a structure that
increase the number of contact points against the housings by
tightening the bolts to cause the deformation from the original
cross-sectional shape. Once the lift-up or thrust phenomenon
occurs, the number of contact points decreases to impair the
sealing function.
[0007] In a case where a metal gasket is used for a transmission,
the oil pressure in the transmission is relatively low. Thus,
instead of using a stainless steel material which has higher
resilience and is used for sealing high-pressure combustion gas, it
is preferable to use a steel material which has lower resilience
but is less expensive. However, when the steel material is used,
because of its lower resilience, it is concerned that the sealing
function is reduced significantly by the lift-up phenomenon. For
this reason, the metal gasket made of a steel material and
employing the technique described in openly published Japanese
Patent Application Publication No. 2011-047508 and openly published
Japanese Utility Model Application Publication No. H2-021370 is
assumed to be readily affected by the lift-up and thrust
phenomenon. In order to suppress the influence of the thrust
phenomenon, it is important to place the embossments stably on the
housings H1, H2. To this end, it is important to increase the
surface pressure of the seal lines. However, it is difficult to
increase the surface pressure of all seal lines in the case where
the steel material is used, so that it has been demanded to ensure
a sufficient stability of the placed embossments against the thrust
phenomenon.
[0008] In addition, when the housings H1, H2 are made by
die-casting, blowholes C1, C2 may be formed at any size at any
position on the joint surfaces of the housings H1, H2 as shown in
FIGS. 15A and 15B. The term "blowhole" as used herein refers to a
fine recessed portion remaining on the joint surfaces of the
housings after being produced by die-casting. When the blow holes
C1, C2 are present in the vicinity of the seal lines, gaps may be
formed between the blowholes C1, C2 and the seal lines. In
addition, the surface pressure is reduced due to blowholes C1, C2
even if no gap is formed. Therefore, there is a risk that oil may
flow over the seal lines. For this reason, the embossments
described in openly published Japanese Patent Application
Publication No. 2011-047508 and openly published Japanese Utility
Model Application Publication No. H2-021370 have more contact
points with respect to the housings as discussed above to reduce
the influence of the blowholes C1, C2. However, the number of
contact points may be reduced by the lift-up and thrust phenomena,
so that it is still possible that oil or the like may leak.
Moreover, the embossment described in openly published Japanese
Patent Application No. H11-23035 has fewer contact points and thus
higher surface pressure of seal lines than the embossments
described in openly published Japanese Patent Application
Publication No. 2011-047508 and openly published Japanese Utility
Model Application Publication No. H2-021370, so that it is assumed
that the number of contact points is maintained even if the lift-up
and thrust phenomena occur. However, since the initial number of
contact points is small, the influence of the blowholes C1, C2 is
inevitable.
[0009] It is common that the bolts for fastening the housings H1,
H2 are inserted into bolt holes formed on the metal gasket. In
openly published Japanese Patent Application Publication No.
2011-047508, the bolt holes are provided on the outside of the
embossment to prioritize the position of the embossment. In this
case, however, the peripheral size of the metal gasket becomes
larger, and the sizes of the housings H1, H2 also increase. For
this reason, although the bolt holes are preferably provided at the
widthwise central portion of the metal gasket as shown in FIG. 16A,
oil may penetrate into gaps G1, G2 and G3 between seal lines due to
the decrease of the surface pressure on the seal lines caused by
the lift-up and thrust phenomena, or the blowholes C1, C2, flow
into the bolt hole 4 through the gaps G1 to G3, and eventually flow
away through a bolt through hole of the housing H1.
SUMMARY
[0010] The present invention aims to solve such conventional
problems and to provide a metal gasket which is less susceptible to
the lift-up and the thrust phenomena and can effectively exert
sealing function against the blowholes on the joint surfaces of
housings. In addition, the present invention aims to provide a
metal gasket in which the seal function of the peripheral bolt
holes does not impair even if the bolt holes are provided at the
central portion of the metal gasket.
[0011] The present invention provides a metal gasket comprising a
frame shaped base extending horizontally and an embossment portion
extending along the base and sandwiched in between two housings,
wherein the embossment portion includes a pair of outer inclined
portions connecting to the base and projecting respectively toward
one of the housings, and a pair of inner inclined portions
connecting to tip ends of the respective outer inclined portions,
projecting respectively toward the other of the housings and
connecting to each other at their tip ends, the following
relationships are satisfied:
Mh2/Mh1=1.10-1.81, W3>W1, and W3>W2,
where, in a cross-section perpendicular to the extending direction
of the embossment portion, P1 and P2 are respective intersections
between a horizontal line of a front side of the base facing the
one housing and inclined lines of front sides of the outer inclined
portions; P3 and P4 are respective intersections between the
inclined lines of the front side of the outer inclined portions and
inclined lines of front sides of the inner inclined portions; P5 is
an intersection between the inclined lines of the front sides of
the inner inclined portions; Mh1 is a vertical length from P1 to
P3; Mh2 is a vertical length from P3 to P5; W1 is a horizontal
length from P1 to P5; W2 is a horizontal length from P2 to P5; and
W3 is a horizontal length from P3 to P4, and wherein when the metal
gasket is sandwiched in between the housings, the tip ends of the
outer inclined portions abut on the one of the housings to form two
seal lines, and root ends of the outer inclined portions and the
tip end of the inner inclined portions abut on the other of the
housings to form three seal lines.
[0012] The base is preferably formed with a bolt hole through which
a bolt is inserted to fasten the housings, and the embossment
portion includes a winding embossment portion in which the pair of
the inner inclined portions terminate adjacent to the bolt hole and
the pair of the outer inclined portions extend with the bolt hole
being therebetween.
[0013] The metal gasket according to the present invention has the
embossment portion placed on the base extending horizontally, and
the embossment portion is composed of a pair of outer inclined
portions projecting respectively toward one of the housings, and a
pair of inner inclined portions projecting respectively toward the
other of the housings and connecting to each other at their tip
ends. The metal gasket also satisfies the following
relationships:
Mh2/Mh1=1.10-1.81, W3>W1, and W3>W2,
where Mh1 is a vertical length from P1 to P3; Mh2 is a vertical
length from P3 to P5; W1 is a horizontal length from P1 to P5; W2
is a horizontal length from P2 to P5; and W3 is a horizontal length
from P3 to P4. This allows the tip ends of the inner projections to
be located below the base in the initial cross-sectional shape of
the embossment portion, which ensures a good sealing function even
under the lifting or thrust phenomenon. In addition, the embossment
portions form multiple seal lines with respect to each of the
housings. That is, two seal lines are formed on the one of the
housings, and three seal lines are formed on the other of the
housings. As a result, the sealing function can be effectively
exhibited even if the blowhole is present on the joint surface.
[0014] When the base is formed with a bolt hole, the embossment
portion may include a winding embossment portion in which the pair
of the inner inclined portions terminate adjacent to the bolt hole
and the pair of the outer inclined portions extend with the bolt
hole being therebetween. As a result, a malfunction such as a
leakage of oil or the like through the bolt hole can be prevented.
In addition, the winding embossment portion allows the bolt hole to
be placed in the central portion of the base so that the external
diameter of the metal gasket can be reduced.
BRIEF DESCRIPTION OF DRAWINGS
[0015] FIG. 1 is a plan view illustrating an embodiment of a metal
gasket according to the present invention.
[0016] FIG. 2 is a cross-sectional view illustrating a state where
the metal gasket shown in FIG. 1 is placed between two
housings.
[0017] FIG. 3 is a cross-sectional view of the metal gasket shown
in FIG. 1 taken along the line X1-X1.
[0018] FIG. 4 is a cross-sectional view illustrating a state where
bolts of the housings have been tightened from the state as shown
in FIG. 2 to hold the metal gasket between the housings.
[0019] FIG. 5 is a partial enlarged view of a peripheral portion of
the bolt hole shown in FIG. 1.
[0020] FIG. 6A is a cross-sectional view taken along the line Y1-Y1
of FIG. 5.
[0021] FIG. 6B is a cross-sectional view taken along the line Y2-Y2
of FIG. 5.
[0022] FIG. 6C is a cross-sectional view taken along the line X2-X2
of FIG. 5.
[0023] FIG. 7A to 7L illustrate color changes of pressure-sensitive
papers after seal line surface pressure tests are performed with
respect to the base.
[0024] FIGS. 8A and 8B illustrate color changes of
pressure-sensitive papers after seal line surface pressure tests
are performed with respect to the peripheral portion of the bolt
hole shown in FIG. 5
[0025] FIGS. 9A and 9B illustrate color changes of
pressure-sensitive papers after seal line surface pressure tests
are performed with respect to the peripheral portion of the bolt
hole shown in FIG. 16.
[0026] FIG. 10 illustrates measurement results of stress relaxation
rate.
[0027] FIGS. 11A and 11B show a conventional metal gasket where
FIG. 11A illustrates a state where the conventional metal gasket is
placed between two housings, and FIG. 11B illustrates a state where
the conventional metal gasket is sandwiched between two
housings.
[0028] FIGS. 12A and 12B show another conventional metal gasket,
where FIG. 12A illustrates the conventional metal gasket being
placed between two housings, and FIG. 12B illustrates the
conventional metal gasket being sandwiched between two
housings.
[0029] FIG. 13 illustrates yet another conventional metal gasket
being sandwiched between two housings.
[0030] FIG. 14 is a plan view of a conventional metal gasket for
illustrating the lift-up and thrust phenomena of housings.
[0031] FIG. 15A is a cross-sectional view illustrating blowholes
formed on the joint surfaces of the housings.
[0032] FIG. 15B is a plan view illustrating the blowholes formed on
the joint surfaces of the housings.
[0033] FIG. 16A is a plan view illustrating a state where oil flows
into the bolt hole.
[0034] FIG. 16B is a cross-section view illustrating the state
where oil flows into the bolt hole.
DESCRIPTION OF EMBODIMENTS
[0035] Embodiments of the present invention are described in detail
below with reference to the drawings.
[0036] The metal gasket 1 shown in FIG. 1 is formed with a gasket
substrate having an embossment portion formed by a press molding,
and the gasket substrate is made of a thin metal plate (e.g. a
stainless or steel material) coated with a sealing material such as
rubber or the like on the surface. As shown in FIG. 2, the metal
gasket is placed, for example, between two housings H1, H2
accommodating a transmission or the like, and used under a state
where the metal gasket is sandwiched between the two housings H1,
H2 fastened to each other by bolts or the like. The provision of
the sealing material can prevent a metal-to-metal contact between
the metal gasket and the housings, as well as it can provide a
micro-sealing function that absorbs any small irregularities on the
joint surface of the housing which have been formed when the joint
surfaces is subjected to a milling process. It is noted that FIG. 2
illustrates a state prior to the metal gasket being sandwiched
between the housing H1, H2 (being fastened by bolts).
[0037] The metal gasket 1 includes a frame shaped base 2 extending
horizontally, and an embossment portion 3 extending along the base
2 on the widthwise inner side thereof. The base 2 of this
embodiment has a general D-shape in the plan view, but the shape
and size may be variously altered depending on the transmission and
the housings H1, H2. The width of the base 2 of this embodiment
remains the same over the entire circumference except for the
later-described enlarged diameter portion. The width may also be
variously altered depending on the housings or the like.
[0038] As shown in FIG. 3, the cross-section (referred to below
simply as the "cross-section") of the embossment portion 3
perpendicular to the extending direction along the base 2 has
generally an "M" shape similar to the shape formed by reversely
folding the tip end of a mountain. This is discussed further in
detail with reference to FIGS. 2 and 3. The embossment portion 3
includes a pair of outer inclined portions 3a, 3b connecting to the
base 2 and projecting respectively toward one of the housings H1,
and a pair of inner inclined portions 3e, 3f connecting to tip ends
3c, 3d of the respective outer inclined portions 3a, 3b projecting
respectively toward the other of the housings H2 and connecting to
each other at their tip ends 3g. In FIG. 3, the reference signs 3h,
3i represent the root ends of the respective outer inclined
portions 3a, 3b. Further, the tip ends 3c, 3d, 3g and the root ends
3h, 3i are the portions which abut the housings H1, H2 to form seal
lines with respect to the housings H1, H2 when the metal gasket 1
is sandwiched by the housings H1, H2. (hereinafter, the same
reference signs 3c-3i are assigned to the seal line formed by the
tip ends 3c, 3d, 3g and the root ends 3h, 3i).
[0039] The embossment portions 3 are further discussed below.
Assuming a side of the metal gasket 1 facing toward the housing H1
is a front side, the following relationships are satisfied in the
cross-section as shown in FIG. 3:
Mh2/Mh1=1.10-1.81, W3>W1, and W3>W2,
where P1 and P2 are respective intersections between a horizontal
line L1 of the front side of the base 2 and inclined lines L2, L3
of front sides of the outer inclined portions 3a, 3b; P3 and P4 are
respective intersections between the inclined lines L2, L3 of the
front side of the outer inclined portions 3a, 3b and inclined lines
L4, L5 of front sides of the inner inclined portions 3e, 3f; P5 is
an intersection between the inclined lines L4, L5 of the front
sides of the inner inclined portions 3e, 3f; Mh1 is a vertical
length from P1 to P3; Mh2 is a vertical length from P3 to P5; W1 is
a horizontal length from P1 to P5; W2 is a horizontal length from
P2 to P5; and W3 is a horizontal length from P3 to P4. That is, the
embossment portion 3 projects toward the front side beyond the base
portion 2 at the tip ends 3c, 3d, and toward the back side beyond
the base portion 2 at the tip end 3g. In addition, the distance
between tip ends 3c and 3g (opposite from 3g) is larger than the
distance between the tip end 3g and the root end 3h, and the
distance between tip end 3g and the root end 3i.
[0040] The embossment portion 3 having such shape and dimensional
relationships can form two seal lines 3c, 3d on the joint surface
of the housing H1 and three seal lines 3g, 3h, and 3i on the joint
surface of the housing H2 when sandwiched between the housings H1,
H2 as shown in FIG. 4. That is, the metal gasket 1 forms a
plurality of seal lines with respect to one housing, and, in
particular, three seal lines with respect to the housing H2, which
allows the metal gasket 1 to be less susceptible to blowholes.
Since the shapes of the metal gasket 1 before and after being
sandwiched between the housings H1, H2 do not differ significantly
(i.e., tip ends 3c, 3d, 3g and root ends 3h, 3i for forming seal
lines project initially), the number of contact points does not
change even if the lift-up phenomenon occurs, and thus the sealing
function can be maintained effectively. In addition, the tip end 3g
projects from the base 2 to enhance the surface pressure of the
seal lines, so that the placement of the embossment portion 3 can
be stabilized. The embossment portion 3 has a shape widthwise
symmetric with the tip end 3g as being its center and a width W3
between the tip ends 3c, 3d facing the tip end 3g is large, so that
the placement of the embossment portion 3 can be more
stabilized.
[0041] As shown in FIG. 3, the tip ends 3c, 3d, 3g of this
embodiment form an R-shaped cross-section. This shape enlarges the
widths of the seal lines when the metal gasket is sandwiched
between the housings H1, H2, and can reduce the influence of the
blowholes further.
[0042] As shown in FIG. 1, the base 2 is provided with bolt holes 4
(a total of eight bolt holes in this embodiment) through which
bolts are inserted to fasten the housings H1, H2 together. The bolt
holes 4 are provided at the widthwise center of the base 2. An
expanded diameter portion 2a is provided on the base 2 to surround
the bolt holes 4.
[0043] The embossment portion 3 on the expanded diameter portion 2a
is described in detail below with reference to FIGS. 3, 5 and 6A to
6C. In FIG. 5, the reference signs D1 and D2 indicate lines having
sizes larger than predetermined seizes with respect to the
hole-diameters of the bolt holes 4. In this embodiment, the
reference sign D1 represents a line located outside of the
hole-diameter of the bolt holes 4 by 7 mm, and the reference sign
D2 represents a line located outside of the hole-diameter of the
bolt holes 4 by 1.5 mm.
[0044] As shown in FIG. 5, the seal lines 3c, 3d, 3g, 3h, and 3i
extend linearly in the area outside of the line D1. The seal line
3c is divided into two seal lines 3c and 3c1 beyond the line D1
while forming a flat portion widthwise inwardly as shown in FIG. 6.
Similarly, the seal line 3d is divided into two seal lines 3d and
3d1 while forming a flat portion widthwise inwardly. The seal lines
3h, 3i extend along the outer edge of the expanded diameter portion
2a with the bolt hole 4 in being situated therebetween. That is,
the outer side portion of the expanded diameter portion 2a in the
radial direction spreads from the line D1 radially outwardly so as
to surround the bolt holes 4 and has the largest spread width at
the position passing through the center of the bolt holes 4.
Subsequently, the outer side portion is shaped so as to converge
toward the line D1 on the opposite side.
[0045] The vertical length Mh2 of the seal line 3g has a length at
outside of the line D1 as shown in FIG. 3, and, after passing the
line D1, it gradually reduces the length as shown in FIG. 6A to
eventually disappear at inside of the line D2 as shown in FIG. 6B.
The seal lines 3c1, 3d1 divided from the seal lines 3c, 3d,
respectively, approach to each other after passing the line D1, and
merge together at the line D2 as shown in FIG. 5. That is, a gap G1
formed above the seal line 3g shown in FIGS. 3 and 6A gradually
decreases after passing the line D1, and completely disappears at
the line D2.
[0046] In this way, the embossment portion 3 extends at the
expanded diameter portion 2a so as not to pass through but to
detour the bolt hole 4 (hereinafter, the embossment portion at the
expanded diameter portion 2a is referred to as "the winding
embossment portion 3j"). Thus, even if oil or the like enters the
gap G1, G2 or G3 between the seal lines, it can be prevented from
entering into the bolt hole, as shown in FIG. 16B. In addition, the
inner cross-section of the line D2 at the winding embossment
portions 3j has a shape similar to a half embossment with a single
slope structure as shown in FIGS. 6B-6C. That is, the winding
embossment portion has a cross-sectional shape that can be
compressed easier than the M-shape that the rest of the embossment
portion 3 has, so that, when it is tightened with a bolt, the
embossments can be completely compressed at immediately below the
bolt. Therefore, it is possible to more reliably prevent the
outflow of oil from the bolt holes 4.
Examples
[0047] Inventors of the present invention have paid attention to
the prior art of a metal gasket 300 as shown in FIG. 13 in order to
verify the performance of the metal gasket configured as described
above. In other words, in order to increase the surface pressure of
the seal line at the tip end 3g, it is necessary to make the value
of Mh2 larger than the value of Mh1 (i.e., to set the value of
Mh2/Mh1 to 1 or more). However, when the value of Mh2/Mh1 is
excessively large, there will be only a total of three seal lines
formed as is the case with the metal gasket 300. In this
connection, the inventors assumed that there might be a
particularly preferred range for the relationship of Mh2/Mh1, and
experimentally made various metal gaskets with Mh1 being fixed to
0.21 mm, and Mh2 divided into 12 levels within a range of 0.13
mm-0.43 mm. All of the metal gaskets thus made were made of steel
material, and satisfy the relationships of W3>W1 and W3>W2.
The tip ends 3c, 3d, and 3g had an R-shape (radius r=2.5 mm), and
the rubber used as seal material had a thickness of 24 .mu.m and a
hardness of Hs70.
[0048] The performances of the metal gasket were examined by an oil
pressure seal test and a seal line surface pressure test. The oil
pressure seal test was carried out for the metal gasket as shown in
FIGS. 1 and 3. In the test, the base 2 extending lineally and
located between two expanded diameter portions 2a was clamped by
housing jigs, pressurized oil was allowed to flow into the gap
among the housing jigs, and whether the oil leaked over the metal
gasket was verified. The housing jigs were so fabricated that a
blowhole presumably occurs, and thus were provided with recessed
portions (herein, having a diameter of 2 mm) at positions
immediately above each of the tip ends 3c, 3d and 3g and
immediately below each of the root ends 3h, 3i when the metal
gasket was clamped. In addition, the gap between the recessed
portions corresponding to the tip ends 3c, 3d was 3 mm.
[0049] As shown in FIG. 4, the seal line surface pressure test was
carried out in such a manner that the pressure sensitive papers
were placed between the upper housing and the metal gasket as well
as between the lower housing and the metal gasket, and the color
changes of the pressure sensitive papers after the metal gasket was
clamped were used for evaluations. A pressure measurement film (for
low pressure usage) available from Fuji Film Co., Ltd. was used as
the pressure sensitive paper. In FIGS. 7A-7L, the colored (black)
portions indicate portions where the color of the pressure
sensitive paper had been changed. In addition, FIGS. 7A to 7F show
the color changes of the pressure sensitive paper placed between
the upper housing and the metal gasket, and FIGS. 7G to 7L show the
color changes of the pressure sensitive paper placed between the
lower housing and the metal gasket. Further, the results of
Comparative Example 1 are shown in FIGS. 7A and 7G, the results of
Comparative Example 2 are shown in FIGS. 7B and 7H, the results of
Comparative Example 4 are shown in FIGS. 7C and 7I, the results of
Example 1 are shown in FIGS. 7D and 7J, the results of Example 6
are shown in FIGS. 7E and 7K, and the results of Comparative
Example 5 are shown in FIGS. 7F and 7L. The corresponding
relationships between the color changes of the pressure sensitive
paper and the tip ends 3c, 3d, and 3g and root ends 3h, 3i are
represented in FIGS. 7D and 7J. The color changes of the
pressure-sensitive paper for Comparative Example 3, Examples 2 to
5, and Comparative Example 6 are omitted. The distribution of the
colored portions in Comparative Example 3 is denser than that in
Comparative Example 2, but is less dense than that in Comparative
Example 4. The distribution of the colored portions in Examples 2-5
is denser than that in Comparative Example 1, but less dense than
that in Comparative Example 6, and the density increases from
Examples 2 to 5 in this order. In addition, likewise in Comparative
Example 5, it is observed that Comparative Example 6 has a line
which is white out in the widthwise central portion of the seal
line 3g.
[0050] The results of the two tests and the specs of the metal
gasket used are shown in Table 1.
TABLE-US-00001 TABLE 1 Mh2 Mh2/ Oil Pressure Seal Line Surface
Shape (mm) Mh1 Seal Test Pressure Test Comparative FIG. 11 0.13
0.57 NG NG FIGS. 7A, 7G Example 1 Comparative FIG. 12 0.15 0.71 NG
NG FIGS. 7B, 7H Example 2 Comparative FIG. 3 0.17 0.81 NG NG --
Example 3 Comparative FIG. 3 0.2 0.95 Good NG FIGS. 7C, 7I Example
4 Example 1 FIG. 3 0.23 1.10 Good Good FIGS. 7D, 7J Example 2 FIG.
3 0.26 1.23 Good Good -- Example 3 FIG. 3 0.3 1.43 Good Good --
Example 4 FIG. 3 0.32 1.52 Good Good -- Example 5 FIG. 3 0.35 1.67
Good Good -- Example 6 FIG. 3 0.38 1.81 Good Good FIGS. 7E, 7K
Comparative FIG. 3 0.41 1.95 Good NG FIGS. 7F, 7L Example 5
Comparative FIG. 3 0.43 2.04 Good NG -- Example 6 Oil pressure
test: Good = No leakage of oil was observed NG = Leakage of oil was
observed Seal line surface pressure test: Good = surface pressure
of the seal line was sufficient NG = surface pressure of the seal
line was insufficient
[0051] During the oil pressure seal test, the oil leaked over the
metal gasket in Comparative Examples 1 to 3. In addition, during
the seal line surface pressure test the colored portions of the
seal lines (seal line 105 in FIG. 11B, seal line 205 in FIG. 12B)
located in the lower center were sparse in Comparative Example 1
and Comparative Example 2 as shown in FIGS. 7G and 7H, which
indicates that the surface pressure of the seal line was
insufficient. The colored portions of the seal lines 3c, 3d in
Comparative Example 5 and Comparative Example 6 were sparse as
shown in FIG. 7F, and there was a line which was white out at the
widthwise central portion of the seal line 3g as shown in FIG. 7L.
That is, it was observed that the surface pressure on the seal
lines 3c, 3d, and 3g were insufficient. On the other hand, the
results of Examples 1 to 6 were good. That is, when the embossment
portions having the shape shown in FIG. 2 satisfied the
relationships of Mh2/Mh1=1.10-1.81, W3>W1, and W3>W2, it was
confirmed that the leakage of oil could be prevented as well as the
surface pressure of the seal lines could be secured. Even if the
blowholes were located immediately above or immediately below the
seal lines, as long as they had the diameter of 2 mm or less, it
was observed that the oil leakage could be prevented. Also, even if
the blowholes had the diameter of 3 mm, as long as they were
located between two seal lines, it was observed that the oil
leakage could be prevented.
[0052] The expanded diameter portion provided with a bolt hole was
evaluated with the above-mentioned seal line surface pressure test.
FIGS. 8A-8B show the results of the tests performed for the
expanded diameter portions according to the present invention
illustrated in FIG. 1, FIG. 5, and FIG. 6. FIG. 8A illustrates the
result obtained between the upper housing and the metal gasket, and
FIG. 8B illustrates the result obtained between the lower housing
and the metal gasket. FIGS. 9A and 9B show the result of the test
performed for the expanded diameter portion in which the seal line
3g was connected to the bolt hole 4 (see FIG. 16). Furthermore,
FIG. 9A illustrates the result obtained between the upper housing
and the metal gasket, and FIG. 9B illustrates the result obtained
between the lower housing and the metal gasket.
[0053] In FIGS. 9A and 9B, the white line passes over the colored
portion surrounding the bolt hole 4. That is, the metal gasket 1 in
which the seal line 3g is connected to the bolt hole 4 has an area
where the surface pressure of the seal line is insufficient around
the bolt hole as shown in FIG. 16A, so that, when oil enters the
gaps G1 to G3 as shown in FIG. 16B, the oil may flow into the bolt
hole 4. In contrast, the entire periphery area of the bolt hole 4
is surrounded by the colored portions in FIGS. 8A and 8B. That is,
since the periphery area of the bolt hole 4 is clamped by the
housings with a sufficient surface pressure in the metal gasket
shown in FIG. 5, even if the oil penetrates into the gaps G1 to G3,
the oil leakage from the bolt hole 4 can be prevented.
[0054] Moreover, if the sealing material applied on the surface of
the metal gasket 1 has too small thickness, it cannot sufficiently
exhibit the sealing property; if the sealing material has too large
thickness, a torque down which reduces the bolt axial force may
easily occur due to temperature changes and the plastic deformation
of the sealing material associated with the repetition of the
operation and non-operation of the internal combustion engine.
Therefore, in order to evaluate the influences of the film
thickness of the rubber used as the sealing material, an oil
pressure seal test and a measurement of stress relaxation rate were
carried out.
[0055] For the oil pressure seal test, metal gaskets with film
thicknesses of the rubber of 16 .mu.m, 24 .mu.m, 35 .mu.m, 47
.mu.m, and 57 .mu.m were prepared. The metal gaskets were clamped
by the above-mentioned housing jigs and pressurize oil was
supplied. The oil leakage was verified with respect to each metal
gasket. The hardness of rubber of all of the metal gaskets was
Hs70. The shape of the metal gasket was, among Comparative Examples
1-4 and Examples 1-8, similar to that of Comparative Example 4 of
which the surface pressure of the seal line was determined as
insufficient although the oil leakage was not observed. As a
result, although an oil leakage was observed in the metal gasket
with the rubber having a film thickness of 16 no oil leakage was
observed in the metal gaskets with the rubber having a film
thickness of 24 .mu.m or more. Therefore, it is found that the film
thickness of the rubber not less than 24 .mu.m provides a
sufficient sealing property.
[0056] For the measurement of the stress relaxation rate, test
specimens were prepared by cutting metal gaskets with film
thicknesses of the rubber of 16 .mu.m, 24 .mu.m, 35 .mu.m, 47
.mu.m, and 57 .mu.m into predetermined sizes. the test specimens
were placed between two pieces of plates, and the plates were
fastened by bolts to clamp the test specimens with predetermined
bolt axial force. After the test specimens were left at
predetermined temperature for a predetermined time, the reduction
of the bolt axial force was evaluated. Specifically, a strain gauge
had been attached to the bolt, and, for each of the test specimens,
an elongation (elongation before heating) S1 of the bolt while
being clamped with predetermined bolt axial force and a restoration
length (restoration after heating and cooling) S2 obtained when the
bolt was loosened after the heat treatment and cooling. A stress
relaxation rate (%) for each of the test specimens was calculated
by the formula: stress relaxation rate (%)=(S1-S2)/S1*100. The
results are shown in FIG. 10. FIG. 10 shows that no significant
change was observed in cases of the film thicknesses of rubber of
16 .mu.m to 47 .mu.m, significant changes of the stress relaxation
rate (great reductions of the bolt axial force) were observed in
cases of the film thickness of rubber of 47 .mu.m to 57 .mu.m.
Accordingly, in order to maintain the sealing property for a long
period of time while absorbing the temperature change, it was found
that the film thickness of rubber is preferably 47 .mu.m or
less.
[0057] That is, from the results of the oil pressure seal test and
the measurement of stress relaxation rate, it was found that the
film thickness of rubber is preferably in the range of 24 .mu.m to
47 .mu.m to maintain a sufficient sealing performance for a long
period of time.
[0058] In accordance with the present invention, it is possible to
provide a metal gasket which can be less susceptible to the lift
and thrust phenomena, and is capable of effectively exhibiting
sealing function against blowholes on the joint surfaces of
housings. Moreover, it is possible to provide a metal gasket in
which the sealing function is not impaired even if the bolt holes
are provided at the central portion of the metal gasket.
* * * * *