Cylinder head gasket with areas of relatively high rigidity

A cylinder head gasket is disposed between a cylinder head and a cylinder block having different coefficients of thermal expansion. The cylinder head gasket has a bore grommet including a cylinder block side portion which is enlarged in a direction away from the cylinder bore hole on an exhaust side and on an end opposite to a chain or gear casing end.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a cylinder head gasket for an internal 
combustion engine disposed between a cylinder head and a cylinder block, 
each having different coefficients of thermal expansion from each other. 
2. Description of Related Art 
Japanese Utility Model Publication No. HEI 2-69174 discloses a cylinder 
head gasket disposed between a cylinder head and a cylinder block. In this 
cylinder head gasket, a surface of a head bolt hole and opposing surfaces 
of a portion of the gasket surrounding the head bolt hole are covered with 
a thin metal plate. The metal plate is extended to a bore grommet to be 
formed integrally with the bore grommet. Therefore, the metal plate 
actually enlarges upper and lower portions (ears) of the bore grommet up 
to the head bolt hole positions, so that the cylinder head gasket is 
locally strengthened by the enlarged ears of the bore grommet. 
However, if the above-described conventional cylinder head gasket is used 
as a gasket disposed between a cylinder head and a cylinder block having a 
smaller coefficient of thermal expansion than the cylinder head (for 
example, an aluminum alloy cylinder head and a cast iron cylinder block), 
then a problem may arise. During operation of the internal combustion 
engine, the cylinder block facing ear of the grommet will expand by the 
same amount as the cylinder block restricted by the cylinder block. 
However, the cylinder head facing ear of the grommet will expand by the 
same amount as the cylinder head restricted by the cylinder head, causing 
an expansion difference between the cylinder block facing ear and the 
cylinder head facing ear of the grommet. As a result, a shear deformation 
is generated between opposite surfaces of the cylinder head gasket, 
accompanied by excessively large strains generated in a core plate of the 
cylinder head gasket and graphite plate laminated layers provided on 
opposite sides of the core plate. In an extreme case, this is accompanied 
by cracking at roots of erected portions formed by punching in the core 
plate, destruction of the graphite plate laminated layers, and leakage of 
gas and water. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a cylinder head gasket 
which has improved strength and which will not be destroyed, even if the 
cylinder head gasket is used between a cylinder head and a cylinder block 
having different coefficients of thermal expansion, respectively. 
To achieve the above object, a cylinder head gasket in accordance with the 
present invention has increased rigidity on an exhaust side and/or a side 
opposite to a chain or gear casing side of the cylinder head gasket. This 
is accompanied by enlarging only a cylinder block facing portion (ear) of 
a bore grommet of the cylinder head gasket in a direction away from a 
cylinder bore hole of the cylinder head gasket.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
First, general structures of a cylinder head gasket in accordance with one 
embodiment of the present invention will be explained with reference to 
FIGS. 1 and 3. 
The cylinder head gasket 10 is disposed between a cylinder block 12 (see 
FIG. 3) and a cylinder head 14 (see FIG. 3) of an internal combustion 
engine (not seen here). The cylinder block 12 has, for example, a smaller 
coefficient of thermal expansion than the cylinder head 14. More 
particularly, the cylinder block 12 may be made from cast iron and the 
cylinder head 14 may be made from an aluminum alloy. The cylinder head 14 
is fastened to the cylinder block 12 by a plurality of head bolts, so that 
the cylinder head gasket 10 is squeezed between the cylinder block 12 and 
the cylinder head 14 (see, for example, FIG. 3). 
The cylinder head gasket 10 includes at least one (in most cases, a 
plurality of) cylinder bore hole 16. Hereinafter, a case where a plurality 
of cylinder bore holes 16 are formed in the gasket 10 will be explained. 
The cylinder head gasket 10 includes a chain or gear casing end (a driving 
element end) 24 at one end of a row of the plurality of cylinder bore 
holes 16, where a chain or gear passing hole 18 is formed in the cylinder 
head gasket 10. The cylinder head gasket 10 includes an exhaust side 20 on 
one side of the row of cylinder bore holes 16, in a direction 
perpendicular to the direction of the row of cylinder bore holes 16, and 
an intake side 22 on the other side of the row of cylinder bore holes 16, 
in the direction perpendicular to the row of cylinder bore holes 16. 
In the internal combustion engine, air is suctioned from the intake side, 
and a mixture of fuel and the air is burned in a combustion chamber formed 
in the cylinder bore. High temperature exhaust gas is exhausted through 
the exhaust side. Therefore, in the cylinder block 12 and the cylinder 
head 14, a temperature on the exhaust side is generally higher than that 
on the intake side. 
Engine cooling water enters a water jacket formed in the cylinder block 12 
from the chain or gear casing side (which corresponds to a front side of 
the cylinder block 12), then flows from the front side of the cylinder 
block 12 to a rear side of the cylinder head 14, and from the rear side of 
the cylinder head 14 to the front side of the cylinder head 14. Therefore, 
the temperature of the cylinder head 14 is generally higher than that of 
the cylinder block 12. 
In the cylinder head gasket 10, a plurality of head bolt holes 28 for 
receiving a respective cylinder head bolt, a plurality of water holes 30 
for letting engine cooling water pass therethrough, at least one oil hole 
32 for letting lubricant oil pass therethrough, and at least one oil 
return hole 34 for letting return oil pass therethrough are formed. 
As illustrated in FIGS. 1 and 3, the cylinder head gasket 10 includes a 
steel core plate 36, graphite plate laminated layers 38 provided on 
opposite sides of the core plate 36 in a thickness direction of the core 
plate 36, a bore grommet 40, and a wire ring 42 disposed within the bore 
grommet 40. The core plate 36 is made from steel (for example, selected 
from the group composed of Japanese Industrial standard, SECC, SCP, and 
SVS) and has a coefficient of thermal expansion substantially equal to a 
coefficient of thermal expansion of cast iron. Each graphite plate of the 
laminated layers 38 is made of material including graphite as a main 
component thereof. The bore grommet 40 is made from metal, more 
particularly, stainless steel. The wire ring 42 is made from iron or low 
alloy steel. As shown in FIG. 5, the cylinder head gasket 10 further 
includes an eyelet 44 provided around the head bolt hole 28. The eyelet 44 
includes a portion 44a extending axially along an inside surface of the 
head bolt hole 28 and portions 44b extending along opposite surfaces of 
the gasket at opposite ends of the portion 44a. It is not necessary to 
provide eyelets for the oil hole 32 or the oil return hole 34. 
Structures and operation thereof unique to the present invention will now 
be explained. 
As illustrated in FIGS. 1 and 2, the exhaust side 20 of the cylinder head 
gasket 10 is selectively made more rigid than the intake side 22 of the 
cylinder head gasket 10 by enlarging the bore grommet 40 in a direction 
away from the cylinder bore hole 16, mainly toward the exhaust side. 
Hatched portion 40A in FIG. 2 shows the enlarged portion of the grommet. 
An intake side portion 40A' of the hatched portion 40A is not necessarily 
provided. 
Further, as illustrated in FIGS. 1 and 2, the rear end (an end 26 opposite 
to the chain or gear casing side 24) of the cylinder head gasket 10 is 
selectively made more rigid than the chain or gear casing end 24 of the 
cylinder head gasket 10 by enlarging the bore grommet 40 in a direction 
away from the cylinder bore hole 16, mainly toward the rear end of the 
cylinder head gasket 10. Hatched portion 40A corresponds to the enlarged 
portion of the grommet. 
As illustrated in FIG. 3, the enlarged portion 40A of the bore grommet 40 
for increasing rigidity is formed in a cylinder block facing surface of 
the cylinder head gasket 10, i.e., a surface contacting the cylinder block 
12. More particularly, the bore grommet 40 has opposite portions or ears 
40a and 40b (one 40a extending along an upper surface of the cylinder 
block 12 and the other 40b extending along a lower surface of the cylinder 
head 14). The above-mentioned higher rigidity is formed in the bore 
grommet 40 by enlarging the only cylinder block facing portion, i.e., ear 
40a, in a direction away from the cylinder bore hole 16. The enlarged 
portion 40A is made of stainless steel. The cylinder head facing portion, 
i.e., ear 40b, is not enlarged. 
A greater thermal expansion difference between the cylinder block 12 and 
the cylinder head 14 arises more on the exhaust side than on the intake 
side of the engine. Because the cylinder block 12 and the cylinder head 14 
are most strongly fixed to each other at the chain or gear casing, a 
relative expansion difference between the cylinder block 12 and the 
cylinder head 14 is small on the chain or gear casing end 24. Therefore, 
the thermal expansion difference is more likely to cause the cylinder 
block 12 and cylinder head 14 to move relative to each other at end 26 
opposite to the chain or gear casing end 24. As a result, a great shear 
force is likely to act on the exhaust side 20 and the end 26 opposite to 
the chain or gear casing of the cylinder head gasket 10. However, because 
exhaust side 20 and end 26 of the cylinder head gasket 10 are selectively 
made more rigid and strong, according to the present invention, by 
enlarging the cylinder block facing portion 40a of the bore grommet 40, 
the cylinder head gasket 10, including the core plate 36 and the graphite 
plate laminated layers 38, is protected from destruction. 
In this instance, since the core plate 36 is made from steel, an amount of 
thermal expansion of the core plate 36 is substantially equal to that of 
the cylinder block 12, which is made from cast iron. Although the enlarged 
portion 40A of the bore grommet 40 is made from stainless steel, the 
thermal expansion of enlarged portion 40A is restricted by the cylinder 
block 12, so that the amount of the thermal expansion of the enlarged 
portion 40A is substantially equal to that of the cylinder block 12. 
Although the aluminum alloy cylinder head 14 thermally expands more than 
the core plate 36, the cylinder head 14 causes slippage at a contact 
surface with the graphite plate laminated layer 38. As a result, thermal 
stresses are dissipated in the core plate 36, so that cracking in the core 
plate 36 is prevented. Further, because the thermal expansion of the 
enlarged portion 40A of the bore grommet 40 is restricted to about the 
same amount as the cylinder block 12, a large shear force does not act on 
the portion of the graphite plate laminated layer 38 disposed between the 
enlarged portion 40A of the bore grommet 40 and the core plate 36, so that 
the layer 38 will not be destroyed. 
As illustrated in FIG. 3, the core plate 36 has a plurality of erected 
portions (nails) 36a, each protruding in a thickness direction of the core 
plate 36. The erected portions 36a generally protrude alternately in 
opposite directions, as seen in this cross-sectional view. The erected 
portion 36a can be formed by the punching a plate and erecting the punched 
tag. Since the erected portion 36a engage the graphite plate laminated 
layers 38, the core plate 36 and the graphite plate laminated layers 38 
move integrally with each other when they thermally expand. 
However, as illustrated in FIG. 4, formation of the erected portions 36a is 
omitted in the vicinity of the water holes 30 on the portions of the 
cylinder head gasket 10 having a higher rigidity, (i.e., on the end 26 
opposite to the chain or gear casing side and on the exhaust side 20). 
Hatched portion 46 in FIG. 4 shows where formation of the erected portions 
is omitted. 
When a crack starts in the core plate 36, it starts at a hole which is 
formed when forming the erected portion. However, because formation of 
such a hole is omitted at a portion where a significant shear force is 
expected to act, cracking is effectively prevented, even if a great shear 
force acts on the core plate 36. 
As illustrated in FIG. 3, a heat resistant lubricant coating layer 52 is 
formed on a cylinder head facing surface of the cylinder head gasket, more 
particularly, on a cylinder head facing surface of the graphite plate 
laminated layer 38 of the cylinder head gasket 10. The lubricant material 
is, for example, a synthetic resin having a low coefficient of friction 
(for example, silicone resin), graphite, or carbon. A thickness of the 
coating layer is in the range of about 20 to 30 microns. 
Due to the lubricant coating layer 52, when a difference in thermal 
expansion arises between the cylinder head gasket 10 and the lower surface 
of the cylinder head 14, the cylinder head gasket 10 and the cylinder head 
14 can slip relative to each other. As a result, a shear force does not 
act on the cylinder head gasket 10, and destruction of the cylinder head 
gasket 10 is prevented. 
As illustrated in FIG. 5, the cylinder block facing portion (ear) 40a of 
the bore grommet 40 has a cylinder bore surrounding portion 40ac, the 
enlarged portion 40A, and a bolt hole surrounding portion 40ab which is 
covered with the portion 44b of the eyelet 44. The cylinder block facing 
portion 40a of the bore grommet 40 has a first step portion 48 between the 
cylinder bore surrounding portion 40ac and the enlarged portion 40A and a 
second step portion 50 between the enlarged portion 40A and the bolt hole 
surrounding portion 40ab before the cylinder head gasket 10 is squeezed 
between the cylinder head 14 and the cylinder block 12 so that the 
enlarged portion 40A recedes from an extension of the cylinder bore 
surrounding portion 40ac and the bolt hole surrounding portion 40ab 
recedes from an extension of the enlarged portion 40A. Those steps 48 and 
50 have a height of about 50 microns. 
Since the head bolts fasten cylinder head 14 to the cylinder block 12, the 
cylinder head gasket 10 receives a greatest compressive force in the 
vicinity of a bolt hole 28. Since a gasket surface pressure decreases 
gradually in a direction away from the bolt hole 28, the surface pressure 
at the bore grommet 40 is relatively not large. With the enlarged portion 
40A of the bore grommet 40, since it is made from metal, it cannot easily 
follow the upper surface of the cylinder block 12 with a uniform pressure. 
Further, if the portion 44b of the eyelet 44 rides on the enlarged portion 
40A of the bore grommet, a gap will be caused between the enlarged portion 
40A of the bore grommet and the upper surface of the cylinder block 12 to 
cause a gas and water leakage. However, in the present invention, since 
those step portions 48 and 50 are provided in the cylinder head gasket 10, 
the gasket surface pressure when the gasket is squeezed is optimized, 
whereby the seal characteristic is improved and gaps do not occur in the 
vicinity of the eyelet 44. 
Preferably, as illustrated in FIG. 6, a contour of a cross section of the 
wire ring 42 disposed within the bore grommet 40 has a shape having 
straight sides, for example, a shape defined by parallel straight sides 
and semicircles connecting the straight sides. For reference, FIG. 7 shows 
a cross section of the conventional gasket wherein the bore grommet 102 
does not have an enlarged portion and the cross section of the wire ring 
100 is circular. 
In the case where the cross section of the wire ring is circular as shown 
in FIG. 7, an area of the contact surface between the bore grommet 102 and 
the wire ring 100 is very small. As a result, as illustrated in FIG. 7, 
surface pressures between the bore grommet and the cylinder block and 
between the bore grommet and the cylinder head concentrate at the contact 
point therebetween. Therefore, when the wire ring 100 causes a permanent 
deformation during use, the surface pressure will greatly decrease, 
degrading the seal characteristic. In contrast, in the present invention, 
since the wire ring 42 contacts the bore grommet 40 at flat portions as 
shown in FIG. 6, the surface pressure is distributed over the flat 
portion, so that the wire ring 42 is unlikely to cause a permanent 
deformation and a good seal characteristic can be maintained for a long 
time period. 
According to the present invention, the following advantages are obtained: 
First, since the exhaust side 20 of the cylinder head gasket is selectively 
made more rigid than the intake side 22, destruction of the cylinder head 
gasket 10 can be effectively prevented. 
Second, since the end 26 opposite to the chain or gear casing end 24 of the 
cylinder head gasket 10 is selectively made more rigid than the chain or 
gear casing end 24, destruction of the cylinder head gasket 10 can be 
effectively prevented. 
Third, in a case where the higher rigidity is embodied in the cylinder 
block side surface of the cylinder head gasket 10, an amount of thermal 
expansion of the cylinder block facing surface is restricted to be 
substantially the same as that of the cylinder block 12, so that 
excessively large thermal stresses will not be caused in the core plate 
36, which has a coefficient of thermal expansion substantially equal to 
that of the cylinder block 12. As a result, destruction of the core plate 
36 is effectively prevented. 
Fourth, in a case where the higher rigidity is embodied in the bore grommet 
40 by enlarging the cylinder block facing portion 40a of the bore grommet 
40, the graphite plate laminated layer 38 between the core plate 36 and 
the cylinder block side portion 40a of the bore grommet 40 is protected 
from destruction. 
Fifth, in a case where step portions 48 and 50 are provided in the cylinder 
block facing portion 40a of the bore grommet 40, the gasket surface 
pressure becomes substantially uniform and the seal characteristic is 
improved. 
Sixth, in a case where erected portions 36a are formed in the core plate 
36, the core plate 36 and the graphite plate laminated layer 38 are made 
effectively integral with each other in movement. Since the core plate 38 
and the expanded portion 40A of the grommet 40 thermally expand by about 
the same amount, no great relative thermal expansion difference will be 
generated between the graphite plate laminated layer 38 and the expanded 
portion 40A of the grommet 40 so that destruction of the cylinder head 
gasket 10 is effectively prevented. 
Seventh, in a case where formation of the erected portion 36a is omitted in 
the vicinity of the water holes 30 on the exhaust side and the end 
opposite to the chain or gear casing side, cracking in the core plate 36 
is effectively prevented. 
Eighth, in a case where a lubricant coating layer 52 is formed on the 
cylinder head facing surface of the cylinder head gasket 10, the cylinder 
head 14 and the cylinder head gasket 10 can slip relative to each other 
when any thermal expansion difference occurs between the cylinder head 14 
and the cylinder head gasket 10, so that destruction of the cylinder head 
gasket 10 is effectively prevented. 
Ninth, in a case where the wire ring 42 has a cross section having straight 
sides at which the wire ring 42 contacts the bore grommet 40, surface 
pressure concentration and local permanent deformation of the wire ring 42 
are prevented, so that a good seal characteristic can be obtained for a 
long period of time. 
Although only one embodiment of the present invention has been described in 
detail above, it will be appreciated by those skilled in the art that 
various modifications and alterations can be made to the particular 
embodiments shown without materially departing from the novel teachings 
and advantages of the present invention. Accordingly, it is to be 
understood that all such modifications and alterations are included within 
the spirit and scope of the present invention as defined by the following 
claims.