-2-
FIELD OF INVENTION
This invention relates to a cooling structure for cylinder block of engine
to improve engine knock mitigation characteristics. The invention is
particularly employed to improve cooling of inter bore region in the
cylinder block.
BACKGROUND/PRIOR ART OF THE INVENTION
A cooling structure is known to have been provided for cooling cylinder
block of engine. The cylinder block comprises a cylinder liner assembly
and a coolant jacket surrounding the liner assembly. The cylinder liner
assembly includes a plurality of bore regions with liner along the
circumferential direction of the bores, which are surrounded by the
coolant jacket in which cooling medium flows. Some provisions are
currently available for cooling region around the bore(s) of cylinder block,
which are discussed herein below:
Now reference may be made to fig. 1, in which a cylinder block (1) is
mounted with cylinder head (2) on its top with a gasket (3) therebetween.
Said gasket is having a plurality of holes, through which cooling medium
flows so as to cool the area around the bore regions of the cylinder block.
The coolant passage holes are indicated by the reference numeral (4) in
figure 1.
However, the disadvantage with the above design is that, inter bore
region can't be cooled. This is because using gasket holes to direct water
flow towards inter bore locations is limited in terms of proximity to
narrowest region where the heat flux is maximum. Additionally with
plurality of holes in the gasket to guide water into various location in the
cylinder head, only limited mass flow rate can be achieved for a
particular gasket hole, which limits the amount of heat to be dissipated
from inter bore region. Also by way of conventional water flow due to
-3-
layout of water jacket, it difficult to direct water flow towards this region
(as indicated in fig.2), which requires change in momentum of fluid.
In order to address the aforesaid issue another cooling structure has
been suggested in the art, for which reference may be made to fig. 3. In
this, together with the flow of coolant around the bore regions as
discussed in the first prior art, atleast two drill holes (1) intercepting
water jacket (2) are drilled in the inter bore region of the cylinder block
(3) so as to direct the coolant to the inter bore region for cooling the
entire circumferential area of the bore.
However, for forced flow of coolant using drilled holes in inter bore region
there is a limitation for use of this technique in engines where gap
between two bores is small, since the gap is too small to accommodate
drilled passage with adequate wall thickness. Therefore this approach in
cooling this region is limited in application only to engines with higher
gap between bores which is counterproductive to objectives of fuel
efficient engine design i.e. higher engine weight, higher loss to coolant
leading to lower brake thermal efficiency.
Another disadvantage common to both prior arts is use of water and
glycol based coolant medium which even with pressurized circuit have
boiling point of around 110-120 degree Celsius which when employed in
cooling high heat flux locations could lead to localized boiling phenomena
which can lead to lower heat transfer than desired at this critical
location.
Thus, cooling inter bore region in cylinder block presents new challenges
with increasing compression ratios increasingly being employed in
gasoline engines for improving fuel efficiency. This has become more
critical since this area is very difficult to cool using coolant flow because
attaining
-4-
coolant flow in this region is very difficult due to layout of water jacket.
This region is now increasingly becoming bottle neck for increasing
compression ratio. Because of high temperature in this region there is an
increased tendency of end charge to auto detonate leading to engine
knock which severely affects low end torque output from gasoline engine.
This necessitates use of lower compression ratio due to poor vehicle
drivability as a result of knocking due to high end charge temperatures.
More over sustained high temperatures in this region due to high heat
flux and inadequate cooling results in part durability related issues as
well.
Further, reference may be made to the following technologies relating to
cooling structure of cylinder block of engine.
US20050217615; A cooling structure for uniformly cooling a bore wall of
a cylinder block using a cooling medium, the bore wall surrounding
plural bore regions, includes a water jacket portion which is provided so
as to surround an entire outer periphery of the bore wall, and which is
supplied with the cooling medium. A water jacket spacer which is
inserted in the water jacket portion with a passage through which the
cooling medium in a portion of an inter-bore region is transferred to
another portion of the inter-bore region and a flow promotion device
which increases a flow rate of the cooling medium flowing in the passage.
Another prior art discloses a cylinder block that includes a coolant
passage that guides coolant inside of a water jacket, inside of an interbore
partition wall. The coolant passage is formed by a head-side drill
hole that opens at a position away from a center portion of a top surface
of the inter-bore partition wall and is formed inclined with respect to an
extending direction of an axis of a cylinder bore so as to come closer to
the center portion of the inter-bore partition wall farther away from the
top surface, and a jacket-side drill hole that is communicated with a tip
-5-
end portion of the head-side drill hole and opens into the water jacket
and is formed inclined with respect to the extending direction of the axis
toward the opening so as to gradually come closer to the top surface.
Another known art is directed to a cylinder block of an internal
combustion engine is provided with a plate-shaped reinforcing part
connecting adjacent cylinder bore walls. A space surrounded by the
reinforcing part and the adjacent cylinder bore walls is used as a cooling
hole and cooling water is supplied to the cooling hole. The cooling hole
and a water jacket are communicated by an inter cylinder bore cooling
passage.
Another provision includes water jackets between bores and cooling
holes (drilled holes) between bores connected with the water jackets and
opening to an upper surface of a cylinder block formed on the partition
wall between the cylinder bores of the cylinder block. An upper water
jacket and a lower water jacket are provided on a cylinder head and one
which has lower pressure out of the upper water jacket and the lower
water jacket is connected with the cooling holes between bores.
In all of the above designs, a plurality of holes are required to be provided
additionally specifically for the purpose of cooling. The cooling medium is
primarily water based coolant.
Most of the above cooling structures are used for cooling of cylinder
block.
Therefore, the invention has been proposed to cool specific regions of the
cylinder block structure, which are difficult to cool using conventional
cooling structure mentioned hereinabove.
-6-
OBJECTS OF THE INVENTION
A primary object of the present invention is to propose a cooling
structure for cylinder block of engine to improve engine knock mitigation
characteristics.
Another object of the present invention is to propose a cooling structure
for cylinder block of engine to improve engine knock mitigation
characteristics which overcomes disadvantages associated with the
known art(s).
Further object of the present invention is to propose a cooling structure
for cylinder block of engine to improve engine knock mitigation
characteristics, which is used to improve cooling of inter bore region in
the cylinder block of engine.
Yet another object of the present invention is to propose a cooling
structure for cylinder block of engine to improve engine knock mitigation
characteristics which causes efficient cooling of entire region around the
bore of cylinder block.
Still another object of the present invention is to propose a cooling
structure for cylinder block of engine to improve engine knock mitigation
characteristics which is reliable.
SUMMERY OF THE INVENTION
According to this invention, there is provided a cooling structure for a
cylinder block of engine to improve engine knock mitigation
characteristics comprising a drill hole in a critical inter bore region of the
cylinder block to improve cooling thereof.
-7-
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Further objects and advantages of this invention will be more apparent
from the ensuing description when read in conjunction with the
accompanying drawings and wherein:
Fig. 1 and 2
shows: conventional arrangement for cooling of surrounding
area around bore regions of cylinder block of engine.
Fig. 3 shows: A cooling structure for cooling of inter bore region of
cylinder block according to the prior art.
Fig. 4 shows: An exemplary embodiment of cooling structure for
improvement in cooling of particularly inter bore
region in accordance with the present invention.
DETAIL DESCRIPTION OF THE PRESENT INVENTION WITH
REFERENCE TO THE ACCOMPANYING DRAWINGS:
The instant invention is directed to a cooling structure for cylinder block
of engine to improve engine knock mitigation characteristics. The
improvement in cooling of inter bore region in the cylinder block is
achieved by making use of existing lubrication circuit, which is subjected
to change by shifting a drill hole positioned in the vicinity of a bore
located towards end of the cylinder block.
Now referring to fig. 4, the drill hole (A) of the lubrication circuit is
disposed in the critical inter bore region of the highest temperature.
There is decrease in temperature of subsequent inter bore regions.
Therefore, such hole (A) can be optionally provided in the subsequent
inter bore region (s) according to the requirement.
-8-
The oil hole (drill hole) is a continuous hole penetrated throughout the
cylinder block from the base of cylinder block upto its top surface. Thus
inlet of the hole is at the base and outlet is on the top surface. The oil
flow takes place from any of the oil galleries from the interception point
upto top surface of the block.
The oil hole is disposed vertically. Alternately, it is angular. The outlet is
located at any point of the inter bore region preferably at the centre point
for uniform cooling in case adequate wall thickness is available.
The hole constitutes a passage for oil for lubrication as well as for cooling
of inter bore region. Thus, the invention serves dual purpose of
lubrication and cooling by means of only lubrication circuit. This is
because for improving the heat transfer in the concentrated area engine
oil is used as a cooling medium,which has much higher boiling point as
compared to water based coolant thus making it more suitable to cool
locations where temperature can be of the order of 300 degree Celsius or
more. Additionally use of small diameter cylinder (drilled gallery) can
increase the velocity of cooling medium significantly which greatly
enhances the heat transfer coefficient in part compensating for the lower
temperature differential for heat transfer between the metal and oil as
compared to use of water based coolant. Also the specific heat for oil is
almost half of water based coolant but the close proximity of oil flow
through a drilled passage to high temperature inter bore location leads to
better cooling of the same.
The cooling of inter bore region due to provision of oil hole in conjunction
with cooling due to layout of water jacket with gasket hole leads to
efficient cooling of entire area around the bore hole (s).
-9-
The invention is specifically applicable to engines with small inter bore
region with closed block deck structure where heat flux in inter bore
region is higher than conventional I.C engines due to low wall thickness
between bores, typically of the order of 6-8 mm. Specifically applicable to
new generation of heavily downsized gasoline engine where inter bore
region is kept smaller for attaining lower engine weight along with higher
structural rigidity to cope with increased peak firing pressures and also
to improve NVH refinement. Another benefit of lower bore pitch is lower
heat loss to engine cooling system which translates to better thermal
efficiency of I.C engines for a given compression ratio.
Advantageous Features
- More proximity to high heat flux area leads to better cooling as
compared to prior art.
- Improvement in cooling high temperature locations like inter bore
region due to use of oil as cooling medium whose boiling point is
much higher than conventional water based coolant.
- Forced flow of oil due to machined oil gallery leads to better mass
flow rate than water since due to layout of water jacket with gasket
hole based cooling there is a sudden change in direction of coolant
which is difficult to achieve since fluid takes path of least flow
resistance.
- Attaining high flow rate than water based gasket hole since water
pump flow is divided over multitude of holes to cool the cylinder
head structure evenly.
-10-
- Lower temperatures at inter bore region comparatively resulting in
better durability of cylinder block structure.
- Using oil specifically as coolant in high heat flux location leads to
faster rate of oil warming which translates into lower viscosity of oil
sooner after cold vehicle starts leading to improved fuel efficiency.
- Achievement of lower temperatures which directly leads to spark
advance at high load low RPM zones, thereby enabling use of
higher compression ratios leading to reduction in fuel
consumption or improved fuel efficiency.
It is to be noted that the present invention is susceptible to
modifications, adaptations and changes by those skilled in the art. Such
variant embodiments employing the concepts and features of this
invention are intended to be within the scope of the present invention,
which is further set forth under the following claims:-

WE CLAIM:
1. A cooling structure for a cylinder block of engine to improve
engine knock mitigation characteristics comprising a drill hole
in a critical inter bore region of the cylinder block to improve
cooling thereof.
2. A cooling structure for cylinder block of engine as claimed in
claim 1, wherein the drill hole constitutes a passage for flow of
coolant medium therethrough.
3. A cooling structure for cylinder block of engine as claimed in
claim 1 or 2, wherein the coolant medium comprises engine oil,
which is used for lubrication as well as for cooling of inter bore
region.
4. A cooling structure for cylinder block of engine as claimed in
any of the preceding claims, wherein the drill hole is preferably
disposed in the critical inter bore region of the highest
temperature.
5. A cooling structure for cylinder block of engine as claimed in
any of the preceding claims, wherein the drilled hole may be
provided in other inter bore regions according to the
requirement.
6. A cooling structure for cylinder block of engine as claimed in
any of the preceding claims, wherein the drilled hole is a
continuous hole penetrated from base of cylinder block upto its
top surface (inter bore region) with inlet at the base and outlet
at the inter bore region.

7. A cooling structure for cylinder block of engine as claimed in
any of the preceding claims, wherein the drilled oil hole is
disposed vertically.
8. A cooling structure for cylinder block of engine as claimed in
any of the preceding claims, wherein the drilled oil hole follows
an angular path by being inclined.
9. A cooling structure for cylinder block of engine as claimed in
any of the preceding claims, wherein the drilled oil hole is a part
of a lubrication circuit, for provision of which the circuit is
subjected to change such as herein described.
10. A cooling structure for cylinder block of engine as claimed in
any of the preceding claims, is associated with the
advantageous features such as herein described.