Cylinder for multi-cylinder type engine

Each of a plurality of cylinder liners has a cooling liquid groove at its outer circumferential surface and has a flat surface over an entire axial length at a part of the outer circumferential surface. The cylinder liners are inserted in bores of a cylinder block with flat surfaces of adjacent liners abutting each other and the grooves at the flat surfaces being coincident with each other.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a cylinder for a multi-cylinder type engine, and 
more particularly a cylinder of which cooling is carried out by flowing 
cooling liquid in grooves formed at the outer circumferential surfaces of 
cylinder liners inserted into a cylinder block. 
2. Description of the Related Art 
It is known in the prior art to provide a cylinder for a multi-cylinder 
type engine in which an outer circumferential surface of each of the 
cylinder liners is formed with a cooling liquid groove, the cylinder liner 
is fitted into a bore part of a cylinder block, a space defined between an 
inner circumferential surface of the bore part in the cylinder block and 
the cooling liquid groove forms a cooling liquid flow passage, cooling 
liquid is flowed at a high speed in the cooling liquid flow passage so as 
to cool the cylinder liner. 
With the foregoing arrangement, the cylinder block is provided with a 
plurality of spaced-apart bores through which the cylinder liners are 
inserted, and an inter-bore pitch is larger than an outer diameter of each 
of the cylinder liners. 
SUMMARY OF THE INVENTION 
In recent years, an engine has been required to have a smallsized and light 
weight unit. The present invention may respond to this requirement. That 
is, it is an object of the present invention to provide a cylinder for a 
multi-cylinder type engine in which an inter-bore pitch (a pitch between 
the cylinder liners) can be made smaller than an outer diameter of the 
cylinder liner and the cylinder block can be made smaller in size and 
lighter in weight. 
The cylinder for a multi-cylinder type engine of the present invention is 
comprised of a plurality of cylinder liners, each having a cooling liquid 
groove at an outer circumferential surface and having a flat surface at a 
part of the outer circumferential surface and a cylinder block having 
bores into which said plurality of cylinder liners are inserted, wherein 
said plurality of cylinder liners are arranged with said flat surfaces 
abutted to each other, arranged such that the cooling liquid grooves at 
said flat surfaces are coincided to each other and then the cylinder 
liners are inserted into the bores of the cylinder block. 
As the cooling liquid groove, the groove comprising a plurality of annular 
grooves and axial grooves to cause said annular grooves to be communicated 
or helical groove or the like is applied. 
Since a part of the outer circumferential surface of the cylinder liner 
forms a flat surface and the adjoining cylinder liners are arranged with 
their flat surfaces abutted to each other, a pitch between the cylinder 
liners can be made smaller than an outer diameter of the cylinder liner. 
Due to this fact, the cylinder block can be made smaller in size and 
lighter in weight, resulting in that the engine can be made smaller in 
size and lighter in weight. 
In addition, the cooling liquid flowing in the cooling liquid groove formed 
in a circumferential direction shows a fast flow speed at the portion of 
the flat surface due to the fact that a sectional area of the groove at 
the flat surface is reduced. Accordingly, since a coefficient of 
heat-transfer of the cooling liquid at that location is increased, the 
adjoining locations of the cylinder liners are cooled more than that of 
other circumferential locations. Due to this fact, the circumferential 
location in the cylinder liner where an efficiency of thermal dispersion 
of the cylinder block is poor is cooled more, resulting in that it may 
contribute to a uniform formation of the temperature in the 
circumferential directions of the cylinder liner.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The above and other objects and features of the present invention will be 
made more apparent in view of the detailed description and the 
accompanying drawings. 
Referring now to the drawings, the cases in which the present invention is 
applied to a series-connected four-cylinder type engine will be described. 
In FIGS. 1 to 4, each of the cylinder liners 1 is formed with cooling oil 
grooves at its outer circumferential surface. The cooling oil grooves are 
comprised of a plurality of annular grooves 2 formed in equal-spaced apart 
relation in an axial direction of the cylinder liner, a plurality of axial 
grooves 3 for communicating the adjoining annular grooves 2 to each other 
and an axial discharging groove 4 communicating with the lowermost annular 
groove 2. Said axial grooves are arranged as one in a circumferential 
direction and are alternately arranged along an axial direction at 
locations spaced apart by 180.degree. in a circumferential direction. The 
aforesaid axial discharging groove 4 is arranged at position spaced apart 
by 180.degree. in a circumferential direction with the axial groove 3 just 
above the axial discharging groove 4. A part of the outer circumferential 
surface of each of the cylinder liners 1 forms a flat surface 5 over an 
entire axial length of it, the adjoining cylinder liners 1 are arranged 
with the flat surfaces 5 abutted to each other and at the same time they 
are arranged with the annular grooves 2 at the flat surfaces 5 coincided 
to each other. That is, each of the cylinder liners 1 at both ends has one 
flat surface 5 at the circumferential position spaced apart from the axial 
grooves 3 and 4 as viewed in FIG. 1. Each of the cylinder liners 1 at 
intermediate positions has two flat surfaces 5 at the circumferential 
positions spaced apart from the axial grooves 3 and 4, and the two flat 
surfaces 5 are arranged at positions spaced apart by 180.degree. in the 
circumferential direction. Then, the cylinder block 6 is provided with 
bores 7 to which four cylinder liners 1 abutted to each other are fitted. 
The four cylinder liners 1 abutted to each other are fitted into the bores 
7, and the stepped parts 9 arranged at the circumferences of the lower 
ends of the cylinder liners 1 are mounted on the liner receiving portions 
8 arranged to be projected at the inner circumferential sides at the lower 
ends of the bores 7. The aforesaid liner receiving portion 8 and the 
stepped part 9 are arranged at portions except the axial discharging 
groove 4. Accordingly, since a pitch between the cylinder liners 1 is 
smaller than an outer diameter of each of the cylinder liners 1, a size of 
the cylinder block 6 can be decreased and the engine can be made smaller 
in size and lighter in weight. 
Then, the engine lubricant as cooling oil is flowed at a fast speed from an 
upper part toward a lower part in the cooling oil groove in the cylinder 
liner 1 so as to cool the cylinder liner and then the cooling oil is 
discharged from the axial discharging groove 4 into an oil pan not shown. 
In this case, although the cooling oil flows in sequence in the annular 
grooves 2 from an upper part to the lower part through the axial grooves 
3, the cooling oil flowing in the annular grooves 2 shows a fast flow 
speed at the portion of the flat surface 5 due to a reduced sectional area 
of the groove at the flat surface 5 (refer to FIGS. 3 and 4). Accordingly, 
since a coefficient of heat-transfer of the cooling oil at that location 
is increased, the adjoining portions of the cylinder liners 1 are cooled 
more as compared with that of other circumferential locations. Due to this 
fact, the circumferential location in the cylinder liner where an 
efficiency of thermal dispersion of the cylinder block is poor is cooled 
more, with the result that the temperature in the circumferential 
direction in the cylinder liners 1 can be made uniform. 
In addition, the cooling liquid groove which can be applied to the present 
invention is not limited to the foregoing grooves, but other grooves can 
be applied. For example, there is a helical groove or one disclosed in 
Japanese Utility Model Application No. 62-60967 previously filed by the 
present applicant, i.e. the cooling liquid groove has a plurality of 
annular grooves, these plurality of annular grooves are divided into a 
plurality of groups of annular grooves, each of said groups of annular 
grooves has two axial grooves to cause said annular grooves to be 
communicated to each other and forming an outlet and an inlet for the 
cooling liquid, and said adjoining groups of annular grooves are 
communicated in series to each other by an outlet and an inlet for the 
cooling liquid. 
An example of the cooling liquid groove will be described in reference to 
FIG. 5. An outer circumferential surface of the cylinder liner 10 is 
formed with eighteen annular grooves 14 spaced apart in an axial 
direction. These annular grooves 14 can be divided into three groups of 
annular grooves. 
The three groups of annular grooves are the first group 14A of annular 
grooves ranging from the first annular groove 14 at the upper end of the 
cylinder liner to the fourth annular groove 14, the second group 14B of 
annular grooves ranging from the fifth annular groove 14 to the tenth 
annular groove 14 and the third group 14C of annular grooves ranging from 
the eleventh annular groove 14 to the last eighteenth annular groove 14. 
In the first group 14A of annular grooves, two axial grooves 15 and 16 to 
cause the annular grooves 14 to be communicated to each other are provided 
at two positions spaced apart by 180.degree. in a circumferential 
direction of the cylinder liner 10, in which one axial groove 15 forms a 
cooling liquid inlet and the other axial groove 16 forms a cooling liquid 
outlet. Similarly, in the second group 14B of annular groove, two axial 
grooves 17 and 18 to cause the annular grooves 14 to be communicated to 
each other are provided at the same two positions in the circumferential 
direction as the axial grooves 15 and 16 of the first group 14A of annular 
grooves, in which the axial groove 17 located at the cooling liquid outlet 
side of the first group 14A of annular grooves forms a cooling liquid 
inlet and the other axial groove 18 forms a cooling liquid outlet. Also in 
the third group 14C of annular grooves, two axial grooves 19 and 20 to 
cause the annular grooves 14 to be communicated to each other are provided 
at the same two positions in the circumferential direction as the axial 
grooves 17 and 18 of the second group 14B of annular grooves in their 
circumferential directions, in which the axial groove 19 located at the 
cooling liquid outlet side of the second group 14B of annular grooves 
forms a cooling liquid inlet and the other axial groove 20 forms a cooling 
liquid outlet. 
The axial groove 16 forming the cooling liquid outlet of the first group 
14A of annular grooves and the axial groove 17 forming the cooling liquid 
inlet of the second group 14B of annular grooves are communicated in 
series by the axial groove 21 which is located at the same circumferential 
location as those of said axial grooves 16 and 17 and is formed at the 
outer circumferential surface of the cylinder liner 10 between the fourth 
annular groove 14 and the fifth annular groove 14. In addition, similarly, 
the axial groove 18 forming the cooling liquid outlet of the second group 
14B of annular grooves and the axial groove 19 forming the cooling liquid 
inlet of the third group 14C of annular grooves are communicated in series 
by the axial groove 22 which is located at the same circumferential 
location as those of said axial grooves 18 and 19 and is formed at the 
outer circumferential surface of the cylinder liner 10 between the tenth 
annular groove 14 and the eleventh annular groove 14. 
Then, the aforesaid annular grooves 14 have a rectangular shape in section 
and all the sectional areas are the same to each other. 
Flow of the cooling liquid will be described as follows. The cooling liquid 
flowed into the axial groove 15 forming the inlet of the first group 14A 
of annular grooves of the cylinder liner 10 flows to an opposite side in 
180.degree. in the annular grooves 14 of the first group 14A of annular 
grooves and then the cooling liquid flows from the axial groove 16 forming 
the outlet of the first group 14A of annular grooves into the axial groove 
17 forming the inlet of the second group 14B of annular grooves. Then, the 
cooling liquid flows to an opposite side in 180.degree. in the annular 
grooves 14 of the second group 14B of annular grooves and flows from the 
axial groove 18 forming the outlet of the second group 14B of annular 
grooves into the axial groove 19 forming the inlet of the third group 14C 
of annular grooves. The cooling liquid then flows to an opposite side in 
180.degree. in the annular grooves 14 of the third group 14C of annular 
grooves and further flows out of the axial groove 20 forming the outlet of 
the third group 14C of annular grooves into the passage arranged in the 
cylinder block. It is of course apparent that the discharging of the 
cooling liquid may be carried out by forming the discharging grooves in 
the cylinder liner in the same manner as that of the aforesaid preferred 
embodiment and discharging it into an oil pan. 
In this case, the three groups 14A, 14B and 14C of annular grooves has a 
ratio of 2 : 3 : 4 in a total sectional areas of the annular grooves for 
the cooling liquid. A flow speed of the cooling liquid flowing in each of 
the groups 14A, 14B and 14C of annular grooves is as follows. A flow speed 
of the cooling liquid at the second group 14B of annular grooves is faster 
than that of the cooling liquid at the third group 14C of annular grooves, 
and a flow speed of the cooling liquid at the first group 14A of annular 
grooves is faster than that of the cooling liquid at the second group 14B 
of annular grooves. 
Accordingly, the coefficient of heat-transfer of the cooling liquid is 
increased as it goes up to the upper part of the cylinder liner 10, 
resulting in that a cooling capability is increased from a lower part 
toward an upper part and an appropriate cooling corresponding to the 
temperature gradient in an axial direction of the cylinder liner is 
carried out. Also in the case of this cooling liquid groove, it is 
preferable that the flat surface to be formed at a partial circumferential 
outer surface of the cylinder liner is arranged at the circumferential 
position spaced apart from the axial groove in the same manner as that of 
the aforesaid preferred embodiment due to the fact that a uniform 
temperature can be attained in the circumferential direction. 
Although in the aforesaid preferred embodiment, the sectional shape of the 
annular groove is a rectangular one, this is not limited to the 
rectangular one but it may be a V-shape, a semi-circular one and there is 
no specific limitation. However, in order to increase a thermal transfer 
area, a rectangular shape in the present preferred embodiment or a square 
shape is preferable. 
In the aforesaid preferred embodiment, a plurality of annular grooves 
spaced-apart in an axial direction of the cylinder liner are divided into 
the three groups of annular grooves and a total sectional areas of the 
annular grooves for the cooling liquid in each of the groups of annular 
grooves is decreased from a lower part toward an upper part. However, it 
is also preferable that the annular grooves may be divided into two groups 
of annular grooves or more than three groups of annular grooves and then a 
total sectional areas of the annular grooves for the cooling liquid in 
each of the groups of annular grooves may be decreased from a lower part 
toward an upper part. 
Although in the aforesaid preferred embodiment, a plurality of annular 
grooves are divided into a plurality of groups of annular grooves, it is 
also preferable that a plurality of annular grooves may be divided into 
one annular groove and a plurality of groups of annular grooves, said one 
annular groove is the first annular groove as counted from an upper end of 
the cylinder liner, each of said groups of annular grooves has two axial 
grooves to cause said annular grooves to be communicated to each other and 
forming an outlet and an inlet for the cooling liquid, said adjoining 
groups of annular grooves are communicated in series to each other by an 
outlet and an inlet for the cooling liquid, a total sectional areas of the 
annular grooves for the cooling liquid in each of said groups of annular 
grooves is decreased from a lower part toward an upper part in an axial 
direction of the cylinder liner, and said one annular groove is 
communicated with the inlet for the cooling liquid in said adjoining group 
of annular grooves. 
It is of course that the cooling liquid is not limited to the cooling oil, 
but other cooling water or the like can be used. 
Although the present invention invented by the present inventor has been 
described practically in reference to the preferred embodiments, it is 
apparent that the present invention is not limited to the aforesaid 
preferred embodiments, but various modifications can be attained without 
departing from its spirit and scope.