BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The invention relates to the cooling of a piston in an internal combustion engine,
and more particularly, the cooling of a piston in which a cooling channel is formed.
2. Description of Related Art
[0002] The piston of an internal combustion engine is fitted with an annular piston ring
having a cut (an abutment). The piston ring may have two end faces opposite each other
via an abutment and provided with elastic resin pieces respectively (e.g., see Japanese
Patent Application Publication No.
2010-031789 (
JP-A-2010-031789)).
[0003] Generally, some of the heat generated during combustion of fuel in the combustion
chamber of a cylinder is transferred to the piston ring via the piston. Thus, if the
amount of the heat generated in the combustion chamber increases, the amount of thermal
expansion of the piston ring also increases. As a result, the width of the abutment
(a gap); decreases, and the amount of compression loss and the amount of blow-by gas
are reduced.
[0004] However, if the amount of the heat generated in the combustion chamber increases
further, the amount of thermal expansion of the piston ring further increases. Therefore,
the opposite end faces of the abutment may bump against each other. If the opposite
end faces of the abutment bump against each other, the stress applied to the piston
ring may increase and thereby cause the contact load between the piston ring and a
cylinder bore wall surface to increase. These problems are remarkable when it comes
to the piston ring closest to the combustion chamber (a top ring).
[0005] One possible approach to mitigate this problem is to widen the gap of the abutment.
However, if the amount of the heat generated in the combustion chamber or when the
temperature of the piston is low, the amount of compression loss and the amount of
blow-by gas may increase due to the increased width of the abutment gap. Document
JP2009-287486 provides a cooling system for a piston with a top ring groove and a cooling channel
located adjacent to the top ring groove.
SUMMARY OF THE INVENTION
[0006] The invention reduces the variation width of a temperature of the top ring in a system
for cooling the piston of an internal combustion engine.
[0007] The inventor has found out that the temperature of the top ring can be adjusted with
the aid of a cooling channel provided in a piston. That is, as a result of strenuous
experiments and verifications, the inventor has found out that the variation width
of the temperature of a piston ring during the operation of the internal combustion
engine is reduced by arranging the cooling channel adjacent to a top ring groove of
the piston in which the top ring is fitted and adjusting the amount of oil supplied
to the cooling channel in accordance with the amount of heat generated in a combustion
chamber.
[0008] Thus, according to one aspect of the invention, a cooling system for a piston of
an internal combustion engine is equipped with a piston that includes a top ring groove
provided in an outer peripheral face of the piston and fitted with a top ring and
a cooling channel designed as an oil passage provided in the piston and located adjacent
to the top ring groove, an oil supply portion that supplies oil to the cooling channel,
and a control portion that sets an amount of oil supplied from the oil supply portion
to the cooling channel larger when an amount of heat generated in a combustion chamber
is large than when the amount of heat generated in the combustion chamber is small.
[0009] The heat generated in the combustion chamber is transferred to a top face of the
piston. The heat transferred to the top face of the piston is transferred in the piston
mainly from the top face of the piston toward the top ring groove, and is discharged
from the top ring groove to a cylinder bore wall surface via the top ring.
[0010] When the amount of the heat generated in the combustion chamber is large, the ratio
of the amount of the heat transferred from the top ring to the cylinder bore wall
surface to the amount of the heat transferred from the piston to the top ring is small.
Thus, when the amount of the heat generated in the combustion chamber is large, the
amount of rise in the temperature of the top ring is large.
[0011] In contrast, when the amount of the heat generated in the combustion chamber is small,
the ratio of the amount of the heat transferred from the top ring to the cylinder
bore wall surface to the amount of the heat transferred from the piston to the top
ring is large. Thus, when the amount of the heat generated in the combustion chamber
is small, the amount of rise in the temperature of the top ring is small.
[0012] As described hitherto, the temperature of the top ring greatly changes in accordance
with the amount of the heat generated in the combustion chamber. When the temperature
of the top ring greatly changes, the size of the abutment gap also greatly changes
correspondingly. Thus, in the case where the top ring is formed such that the abutment
gap assumes a suitable size when the temperature of the top ring is low, opposed end
faces of the abutment bump against each other when the temperature of the top ring
becomes high. In contrast, when the top ring is formed such that the abutment gap
assumes a suitable size when the temperature of the top ring is high, the abutment
gap becomes excessively wide when the temperature of the top ring becomes low.
[0013] In contrast, in the case where the cooling channel is arranged adjacent to the top
ring groove, especially in the case where the cooling channel is arranged on a transfer
path from the top face of the piston to the top ring groove, the heat transferred
from the top face of the piston to the top ring groove is absorbed by the oil in the
cooling channel.
[0014] Accordingly, in the case where the amount of the oil flowing through the cooling
channel is made large when the amount of the heat generated in the combustion chamber
is large, the amount of that heat traveling from the top face of the piston toward
the top ring groove which is absorbed by the oil in the cooling channel becomes large.
Thus, the amount of the heat transferred from the top face of the piston to the top
ring groove can be prevented from becoming excessively large. As a result, the temperature
of the top ring can be prevented from becoming excessively high when the amount of
the heat generated in the combustion chamber is large.
[0015] However, when the amount of the oil flowing through the cooling channel is made small
when the amount of the heat generated in the combustion chamber is small, the amount
of that heat traveling from the top face of the piston toward the top ring groove
which is absorbed by the oil in the cooling channel becomes small. Thus, the amount
of the heat transferred from the top face of the piston to the top ring groove can
be prevented from becoming excessively small. As a result, the temperature of the
top ring can be prevented from becoming excessively low when the amount of the heat
generated in the combustion chamber is small.
[0016] It should be noted that most of the heat transferred from the combustion chamber
to the piston may be discharged to the cylinder bore wall surface when the amount
of the heat generated in the combustion chamber is extremely small (e.g., when the
internal combustion engine is operated at low load and low rotational speed). In such
a case, the temperatures of the piston and the top ring may fall after temporarily
rising.
[0017] In this view, the control portion according to the aspect of the invention may set
the amount of the oil supplied from the oil supply portion to the cooling channel
to zero (stop the oil supply portion) when the amount of the heat generated in the
combustion chamber is equal to or smaller than a predetermined lower limit. "The lower
limit" mentioned herein is a value at which the temperature of the top ring is considered
to become lower than a presupposed temperature range (a temperature range where the
abutment gap of the top ring assumes a supposed size), and is determined in advance
through an adaptation processing with the aid of an experiment or the like.
[0018] When the oil supply portion is stopped, the amount of the heat discharged from the
piston to oil is substantially zero. Further, when the oil supply portion is stopped,
the interior of the cooling channel is filled with air. The air in the cooling channel
functions as a heat insulation layer for reducing or shutting off the heat transferred
from the top face of the piston to the top ring groove. Thus, the amount of the heat
discharged from the piston to the cylinder bore wall surface decreases.
[0019] As described hitherto, when the amount of the heat discharged from the piston to
oil and the amount of the heat discharged from the piston to the cylinder bore wall
surface are reduced, the temperature of the piston (particularly a region around the
top ring groove) is restrained from falling. When the temperature of the region around
the top ring is restrained from falling, the temperature of the top ring is also restrained
from falling correspondingly.
[0020] As described above, when the amount of the heat supplied from the oil supply portion
to the cooling channel is adjusted, the temperature of the top ring is held equal
to a substantially constant temperature (hereinafter referred to as "a suitable temperature").
As a result, during the operation of the internal combustion engine, the size of the
abutment gap can be held substantially constant.
[0021] When the size of the abutment gap of the top ring is held substantially constant
during the operation of the internal combustion engine, the top ring can be designed
such that the abutment gap assumes a desired size at the aforementioned suitable temperature.
As a result, the amount of compression loss and the amount of blow-by gas can also
be minimized regardless of the amount of the heat generated in the combustion chamber.
[0022] It should be noted herein that the amount of the heat generated in the combustion
chamber is correlated with the amount of fuel injection. Thus, the control portion
may adjust the amount of the oil supplied from the oil supply portion to the cooling
channel using the amount of fuel injection as a parameter. Further, since the amount
of fuel injection is determined using an engine load and an engine speed as parameters,
the control portion may adjust the amount of the oil supplied from the oil supply
portion to the cooling channel using the engine speed and the engine load as parameters.
[0023] In the meantime, the pressure in a space surrounded by the top ring, the piston,
and the cylinder bore (hereinafter referred to as "a first space") changes substantially
in synchronization with changes in the pressure in the combustion chamber. In contrast,
the pressure in a space surrounded by the top ring, the second ring, the piston, and
the cylinder bore (hereinafter referred to as "a second space") changes with a delay
from changes in the pressure in the combustion chamber. The time lag in this case
increases as the flow rate of the blow-by gas flowing from the abutment gap of the
top ring into the second space decreases. That is, the aforementioned time lag increases
as the abutment gap of the top ring decreases.
[0024] Accordingly, when the abutment gap of the top ring is made as narrow as possible,
the aforementioned time lag becomes long. Thus, the pressure in the second space may
become higher than the pressure in the first space. In such a case, since the top
ring floats up in the top ring groove, the sealability of the top ring may also deteriorate.
[0025] It should be noted that the phenomenon in which the pressure in the second space
becomes higher than the pressure in the first space is likely to be caused when the
amount of the heat generated in the combustion chamber is large. This is considered
to result from the fact that the outer diameter of a second land of the piston (a
region between the top ring groove and the second ring groove) increases to reduce
the volume of the second space when the amount of the heat generated in the combustion
chamber is large.
[0026] Thus, the cooling channel according to the aspect of the invention may be so formed
as to be located adjacent to the second land as well as the top ring groove. According
to this construction, when the amount of the heat generated in the combustion chamber
is large, the heat of the second land is absorbed by the oil in the cooling channel.
As a result, the temperature of the second land is restrained from rising.
[0027] When the temperature of the second land is restrained from rising, the outer diameter
of the second land is restrained from increasing (the second land is restrained from
thermally expanding). As a result, the decrease in the volume of the second space
is alleviated. When the decrease in the volume of the second space is alleviated,
the phenomenon in which the pressure in the second space becomes higher than the pressure
in the first space is unlikely to be caused.
[0028] Further, the control portion according to the aspect of the invention may control
the oil supply portion such that the amount of the oil supplied from the oil supply
portion to the cooling channel becomes larger when the internal combustion engine
is being warmed up than when the internal combustion engine has been warmed up, for
an equivalent engine load and an equivalent engine speed.
[0029] The temperature difference between the piston and the cylinder bore is large when
the internal combustion engine is being warmed up. This is because the piston is directly
warmed by the heat generated in the combustion chamber but the cylinder bore is indirectly
warmed receiving the heat discharged from the piston. Furthermore, since the cylinder
bore is larger in thermal capacity than the piston, the speed of rise in the temperature
of the cylinder bore is lower than the speed of rise in the temperature of the piston.
[0030] When the temperature difference between the piston and the cylinder bore is large,
the piston is expanded (the outer diameter of the piston is increased) whereas the
cylinder bore is hardly expanded (the inner diameter of the cylinder bore is hardly
increased). Thus, the clearance between the piston and the cylinder bore and the clearance
between the piston ring and the cylinder bore are small. As a result, the piston,
the piston ring, the cylinder bore, and the like may be abraded, and the degree of
friction therebetween may be increased.
[0031] In this view, in the case where the amount of the oil supplied from the oil supply
portion to the cooling channel is made larger when the internal combustion engine
is being warmed up than when the internal combustion engine has been warmed up, the
thermal expansion of the piston is alleviated. As a result, the aforementioned problem
can be prevented from being caused.
[0032] Further, the control portion according to the aspect of the invention may continue
to operate the oil supply portion when the temperature of coolant for the internal
combustion engine is equal to or higher than a predetermined upper-limit coolant temperature
or when the temperature of oil (the oil temperature) is equal to or higher than a
predetermined upper-limit oil temperature. In other words, the oil supply portion
may be prohibited from stopping when the coolant temperature is equal to or higher
than the upper-limit coolant temperature or when the oil temperature is equal to or
higher than the upper-limit oil temperature. "The upper-limit coolant temperature"
mentioned herein and "the upper-limit oil temperature" mentioned herein are obtained
by subtracting a predetermined margin from a temperature at which the internal combustion
engine is considered to be overheated and a temperature at which an oil film is considered
to be broken respectively. When the oil supply portion is thus controlled, the internal
combustion engine can be prevented from being overheated, and the oil film can be
prevented from being broken.
[0033] According to the above aspect of the invention, in the system for cooling the piston
of the internal combustion engine, the variation width of the temperature of the top
ring can be reduced. Thus, the abutment gap of the top ring can be held equal to a
preferable clearance, and the amount of compression loss and the amount of blow-by
gas can be made as small as possible.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] Features, advantages, and technical and industrial significance of exemplary embodiments
of the invention will be described below with reference to the accompanying drawings,
in which like numerals denote like elements, and wherein:
FIG 1 shows the overall structure of a cooling system for a piston according to the
first embodiment of the invention;
FIG 2 is a cross-sectional view of the piston according to the first embodiment of
the invention;
FIG. 3 shows the correlation between a temperature difference ΔT, an engine load Q,
and an engine speed Ne;
FIG. 4 is a view schematically showing a map prescribing a relationship among the
amount of oil injection, the engine load Q, and the engine speed Ne in the first embodiment
of the invention;
FIG 5 is a schematic view of the heat transfer path in the piston;
FIG. 6 is a cross-sectional view of a piston according to the second embodiment of
the invention;
FIG. 7 is an enlarged view of the gap between the piston and a cylinder bore wall
surface;
FIG. 8 shows changes in the pressure Pv1 in a first space and changes in the pressure
Pv2 in a second space;
FIG. 9 is a schematic view of a phenomenon in which a top ring floats up;
FIG. 10 is a schematic view of a map prescribing a relationship among the amount of
oil injection, the engine load Q, and the engine speed Ne in the third embodiment
of the invention;
FIG. 11 is shows the changes in a coolant temperature over time;
FIG 12 is a schematic view of a map prescribing a relationship among the amount of
oil injection, the engine load Q, and the engine speed Ne in when an internal combustion
engine is steadily operated while being warmed up;
FIG 13 is a schematic view of a map prescribing a relationship among the amount of
oil injection, the engine load Q, and the engine speed Ne when the internal combustion
engine is operated under intermediate load and at intermediate rotational speed while
being warmed up;
FIG 14 is a schematic view of a map prescribing a relationship among the amount of
oil injection, the engine load Q, and the engine speed Ne when the internal combustion
engine is operated under high load and at high rotational speed while being warmed
up;
FIG 15 is a schematic view of a map prescribing a relationship among the amount of
oil injection, the engine load Q, and the engine speed Ne when the coolant temperature
is lower than that in the example shown in FIG. 12;
FIG 16 is a schematic view of a map prescribing a relationship among the amount of
oil injection, the engine load Q, and the engine speed Ne when the coolant temperature
is lower than that in the example shown in FIG. 13; and
FIG. 17 is a schematic view of a map prescribing a relationship among the amount of
oil injection, the engine load Q, and the engine speed Ne when the coolant temperature
is lower than that in the example shown in FIG. 14.
DETAILED DESCRIPTION OF EMBODIMENTS
[0035] Example embodiments of the invention will be described below with reference to the
drawings. The dimensions, materials, shapes, relative arrangement and the like of
components described in the example embodiments of the invention are not intended
to limit the technical scope of the invention thereto unless otherwise specified.
[0036] The first embodiment of the invention will be described on the basis of FIGS. 1 to
5. FIG. 1 shows the overall structure of an internal combustion engine to which the
invention is applied. FIG. 2 is a cross-sectional view of a piston according to the
first embodiment of the invention.
[0037] An internal combustion engine 1 may be a compression-ignition internal combustion
engine (a diesel engine) having a plurality of cylinders 2. It should be noted that
only one of the plurality of the cylinders 2 is shown in FIG. 1. A piston 3 is slidably
fitted in each cylinder 2 of the internal combustion engine I so that the piston may
reciprocate in the axial direction of the cylinder. The piston 3 is coupled to a crankshaft
(not shown) via a connecting rod 4.
[0038] A generally cylindrical combustion chamber 30 is formed in the top face of the piston
3. In addition, three annular grooves 31, 32, and 33 are formed in an outer peripheral
face of the piston 3. The annular groove 31 is located closest to a top dead center
(at the highest position in FIG. 2), and is fitted with a top ring 5 (the annular
groove 31 will be referred to hereinafter as the "top ring groove 31"). The annular
groove 32 is located directly below the top ring groove 31 and it fitted with a second
ring 6 (the annular groove 32 will be referred to hereinafter as the "second ring
groove 32"). The annular groove 33 is located closest to a bottom dead center (at
the lowest position in FIG. 2), and is fitted with an oil ring 7 (hereinafter, the
annular groove 33 will be referred to as the "oil ring groove 33"). It should be noted
that the top ring 5, the second ring 6, and the oil ring 7 are annular members equipped
with abutments.
[0039] The top ring groove 31 is formed in the outer peripheral face of an abrasion-resistant
loop 300 that is cast in the piston 3. The abrasion-resistant loop 300 is an annular
member formed of a material harder and more resistant to abrasion than the piston
3 (e.g., a Ni-Cr-Cu cast iron material).
[0040] A hollow abrasion-resistant loop 310 is cast in an inside of the abrasion-resistant
loop 300. The hollow abrasion-resistant loop 310 is an annular member that is U-shaped
in cross-section and has an opening portion on an outer periphery side thereof. The
outer periphery side of the hollow abrasion-resistant loop 310 abuts on an inner peripheral
face of the abrasion-resistant loop 300. That is, the opening portion of the hollow
abrasion-resistant loop 310, which is U-shaped in cross-section, is closed up by the
inner peripheral face of the abrasion-resistant loop 300. An annular space 34 surrounded
by the hollow abrasion-resistant loop 310 and the abrasion-resistant loop 300 functions
as a passage for oil supplied from a later-described oil jet 8 (the space 34 will
be referred to hereinafter as "a cooling channel 34").
[0041] Communication passages 35 and 36 through which an opening portion formed through
a bottom face of the piston 3 communicates with the cooling channel 34 are formed
through the piston 3. The communication passage 35 as one of the communication passages
35 and 36 functions as a passage through which the oil injected from the oil jet 8
is introduced into the cooling channel 34 (the communication passage 35 will be referred
to hereinafter as "an introduction passage 35"). The communication passage 36 as the
other of the communication passages 35 and 36 functions as a discharge passage from
which the oil flowing out from the cooling channel 34 is discharged (the communication
passage 36 will be referred to hereinafter as "a discharge passage 36").
[0042] The internal combustion engine 1 is equipped with the oil jet 8, which injects oil
from a bottom dead center side to a top dead center side in the cylinder 2. It should
be noted that the oil jet 8 is so arranged as to be located below the piston 3 when
the piston 3 is located at the bottom dead center. Furthermore, the oil jet 8 is arranged
and formed such that the oil injected from the oil jet 8 is oriented toward the introduction
passage 35.
[0043] The oil jet 8 communicates with an oil pan 10 via a supply passage 9. The supply
passage 9 is provided at a midway position thereof with an oil pump 11 that sucks
up the oil in the oil pan 10. A flow rate adjusting valve 12 is arranged in the supply
passage 9 between the oil jet 8 and the oil pump 11. The flow rate adjusting valve
12 is a valve that adjusts the amount of the oil flowing in the supply passage 9.
The amount of the oil injected from the oil jet 8 (the amount of oil injection) is
increased or reduced through the adjustment of the flow rate of the oil in the supply
passage 9 by the flow rate adjusting valve 12. It should be noted that the oil jet
8 functions as the oil supply portion of the invention.
[0044] It should be noted that an electrically operated valve mechanism whose ratio between
an open-valve time and a closed-valve time is subjected to duty control or an electrically
operated valve mechanism whose opening degree can be changed continuously or stepwise
can be employed as the flow rate adjusting valve 12. Further, the flow rate adjusting
valve 12 may be a valve mechanism including a check valve that opens when the pressure
of oil is equal to or higher than a certain value and a pressure adjusting valve that
adjusts the pressure of the oil in the supply passage 9.
[0045] The supply passage 9 is provided with a return passage 13 that bypasses the oil pump
11. This return passage 13 is a passage for returning a surplus amount of oil from
that region of the supply passage 9 which is located downstream of the oil pump 11
to that region of the supply passage 9 which is located upstream of the oil pump 11.
A one-way valve (a check valve) 14 that allows only the flow of oil from that region
of the supply passage 9 which is located downstream of the oil pump 11 toward that
region of the supply passage 9 which is located upstream of the oil pump 11 is arranged
in the return passage 13.
[0046] The internal combustion engine 1 thus constructed is accompanied by an ECU 15. The
ECU 15 is an electronic control unit equipped with a CPU, a ROM, a RAM, a backup RAM,
and the like. Output signals of various sensors such as a coolant temperature sensor
16, a crank position sensor 18, an accelerator position sensor 19, an oil temperature
sensor 20, and the like are input to the ECU 15.
[0047] The coolant temperature sensor 16 is a sensor that outputs an electric signal correlated
with a temperature of the coolant circulating through the internal combustion engine
1. The crank position sensor 18 is a sensor that outputs an electric signal correlated
with a rotational position of a crankshaft. The accelerator position sensor 19 is
a sensor that outputs an electric signal correlated with a depression amount of an
accelerator pedal (an engine load). The oil temperature sensor 20 is a sensor that
outputs an electric signal correlated with a temperature of the oil circulating through
the internal combustion engine 1 (an oil temperature).
[0048] On the basis of the output signals of the aforementioned various sensors, the ECU
15 performs the control of the amount of the oil supplied from the oil jet 8 to the
cooling channel 34 (which will be referred to hereinafter as "oil jet control) as
well as known types of control such as fuel injection control and the like. A method
of performing oil jet control will be described hereinafter. It should be noted that
the control portion according to the invention is realized through the performance
of oil jet control by the ECU 15.
[0049] Oil jet control according to this embodiment of the invention is designed to adjust
the amount of oil injection from the oil jet 8 such that the temperature of the top
ring 5 becomes substantially constant. That is, oil jet control according to this
embodiment of the invention is designed to adjust the amount of oil injection from
the oil jet 8 such that the abutment gap of the top ring 5 becomes substantially constant.
[0050] The temperature of the top ring 5 changes in accordance with the amount of the heat
generated in the combustion chamber 30. For example, when the amount of the heat generated
in the combustion chamber 30 is large, the amount of the rise in the temperature of
the piston 3 is large. Therefore, the amount of the rise in the temperature of the
top ring 5 is also large correspondingly.
[0051] When the temperature of the top ring 5 becomes high, the top ring 5 thermally expands
to narrow the abutment gap. When the temperature of the top ring 5 further rises,
opposed end faces of the abutment gap bump against each other to generate a force
acting to increase the outer diameter of the top ring 5.
[0052] In this case, when the temperature of an inner wall surface of the cylinder 2 (a
cylinder bore wall surface) is high, the aforementioned force is counterbalanced due
to an increase in the inner diameter of the cylinder 2. However, when the temperature
of the cylinder bore wall surface is lower than the temperature of the piston 3 and
the difference between the temperatures is large, the top ring 5 and the cylinder
2 are tightened. Thus, the stress applied to the top ring 5 may become excessively
large, or the contact load between the top ring 5 and the cylinder bore wall surface
may become excessively large.
[0053] Thus, the size of the abutment gap needs to be determined such that the opposed end
faces of the abutment do not press each other when the temperature of the top ring
5 is high and the temperature of the cylinder bore wall surface is low. However, in
the case where the size of the abutment gap is determined according to this method,
when the temperature of the top ring 5 is low, the abutment gap may become excessively
wide to cause a compression loss or an increase in the amount of blow-by gas.
[0054] Thus, in the oil jet control according to this embodiment of the invention, the ECU
15 so adjusts the amount of oil injection as to suppress the rise in the temperature
of the top ring 5 when the amount of the heat generated in the combustion chamber
30 is large (when the difference in temperature between the piston 3 and the cylinder
bore wall surface is large) and suppress the fall in the temperature of the top ring
5 or promote the rise in the temperature of the top ring 5 when the amount of the
heat generated in the combustion chamber 30 is small (when the difference in temperature
between the piston 3 and the cylinder bore wall surface is small).
[0055] The amount of the heat generated in the combustion chamber 30 changes in accordance
with the amount of the fuel burned in the combustion chamber 30, namely, the amount
of fuel injection. In principle, the amount of fuel injection is determined using
a load Q of the internal combustion engine 1 (an engine load) and a rotational speed
Ne of the internal combustion engine 1 (an engine speed) as parameters. Thus, in this
embodiment of the invention, an example in which the amount of oil injection is adjusted
using the engine load Q and the engine speed Ne as parameters will be described.
[0056] FIG. 3 is a view showing a relationship among a temperature difference ΔT, the engine
load Q, and the engine speed Ne. "The temperature difference ΔT" mentioned herein
is a difference between the temperature of the piston 3 (preferably the temperature
of the top ring groove 31) and the temperature of the cylinder bore wall surface.
[0057] In FIG. 3, when the engine load Q and the engine speed Ne are low, the amount of
the heat generated in the combustion chamber 30 is smaller than when the engine load
Q and the engine speed Ne are high. Thus, the temperature difference ΔT is small,
and the abutment gap of the top ring 5 is wide.
[0058] In contrast, if the engine load Q and the engine speed Ne are both high, the amount
of the heat generated in the combustion chamber 30 is larger than when the engine
load Q and the engine speed Ne are low. Thus, the temperature difference ΔT is large,
and the abutment gap of the top ring 5 is narrow.
[0059] In this view, the ECU 15 controls the flow rate adjusting valve 12 such that the
amount of oil injection from the oil jet 8 becomes larger when the amount of the heat
generated in the combustion chamber 30 is large than when the amount of the heat generated
in the combustion chamber 30 is small. In other words, the ECU 15 controls the flow
rate adjusting valve 12 such that the amount of oil injection from the oil jet 8 becomes
larger when the temperature difference ΔT is large than when the temperature difference
ΔT is small.
[0060] More specifically, the ECU 15 may control the flow rate adjusting valve 12 according
to a map shown in FIG. 4. The map shown in FIG. 4 is a map determining a relationship
among the engine load Q, the engine speed Ne, and the amount of oil injection.
[0061] In FIG. 4, when the engine load Q and the engine speed Ne are high (a region A in
FIG. 4), the amount of oil injection is set to a maxim amount. When the engine load
Q and the engine speed Ne are low (a region C in FIG. 4), the amount of oil injection
is set equal to zero (the oil jet 8 is stopped). However, oil may be injected for
the purpose of lubricating a space between the piston 3 and the cylinder bore wall
surface or lubricating a space between the piston 3 and the connecting rod 4. Further,
when the engine load Q and the engine speed Ne are in a region between the region
A and the region C (a region B in FIG. 4), the amount of oil injection is made smaller
than the aforementioned maximum amount. It should be noted that the region C in FIG.
4 is a region where the amount of the heat generated in the combustion chamber 30
is equal to or smaller than a lower limit. "The lower limit" mentioned herein is a
value at which the temperature of the top ring 5 may be lower than a later-described
suitable temperature.
[0062] It should be noted herein that part of the heat generated in the combustion chamber
30 is transferred from the top face of the piston 3 toward the top ring groove 31
and discharged from the top ring groove 31 to the cylinder bore wall surface. More
specifically, as shown in FIG 5, the heat transferred from inside the combustion chamber
30 to the piston 3 is mainly transferred from an upper edge portion 30a of the combustion
chamber 30 in the piston 3 toward the top ring groove 31 (the abrasion-resistant loop
300) (see an arrow in FIG. 5). In this view, when the cooling channel 34 is arranged
inside the top ring groove 31, this cooling channel 34 is located on a path of the
heat. In other words, it is preferable that the cooling channel 34 be arranged on
the path of the aforementioned heat.
[0063] Thus, in the case where the amount of oil injection is set to the maximum amount
when the engine load Q and the engine speed Ne are high, most of the heat traveling
from the upper edge portion 30a toward the top ring groove 31 is absorbed by the oil
in the cooling channel 34. As a result, the temperatures of the piston 3 and the top
ring groove 31 are restrained from rising, and the temperature of the top ring 5 is
also restrained from rising correspondingly.
[0064] In the case where the temperature of the top ring 5 is restrained from rising when
the engine load Q and the engine speed Ne are high, the opposed end faces of the abutment
of the top ring 5 can be prevented from bumping against each other. Therefore, the
contact load between the top ring 5 and the cylinder bore wall surface can be prevented
from becoming excessively large.
[0065] However, if the amount of oil injection is set to zero when the engine load Q and
the engine speed Ne are low, the interior of the cooling channel 34 is filled with
air. The air in the cooling channel 34 functions as a heat insulating layer that shuts
off the heat traveling from the upper edge portion 30a toward the top ring groove
31. Thus, the amount of the heat discharged from the piston 3 to the cylinder bore
wall surface decreases. As a result, the temperatures of the piston 3 and the top
ring groove 31 are restrained from falling, and the temperature of the top ring 5
is also restrained from falling correspondingly.
[0066] In the case where the temperature of the top ring 5 is restrained from falling when
the engine load Q and the engine speed Ne are low, the abutment gap of the top ring
5 can be prevented from becoming excessively wide. Thus, an increase in the amount
of compression loss and an increase in the amount of blow-by gas can be voided. Further,
when the temperature of the top ring groove 31 is restrained from falling, the temperature
of the atmosphere in a gap (a crevice) between a top land of the piston 3 and the
cylinder bore wall surface is held high. When the temperature of the atmosphere in
the crevice is high, the temperature of the gas flowing through the abutment gap of
the top ring 5 is also higher than when the temperature of the atmosphere in the crevice
is low. As a result, the mass of the gas flowing through the abutment gap of the top
ring 5 further decreases.
[0067] In the case where the amount of oil injection is made smaller than the maximum amount
when the engine load Q and the engine speed Ne are in an intermediate load/intermediate
rotational speed range, the amount of the heat absorbed by oil from the piston 3 is
prevented from becoming much larger than the amount of the heat traveling from the
upper edge portion 30a toward the top ring groove 31. As a result, the piston 3 and
the top ring groove 31 are restrained from being overcooled, and the top ring 5 is
also restrained from being overcooled. It should be noted that the amount of oil injection
in the aforementioned region B of FIG. 4 may be a fixed amount, but may also be an
amount that is changed in accordance with the engine load Q and the engine speed Ne.
The amount of oil injection in this case may be made larger when the engine load Q
is high than when the engine load Q is low, and may be made larger when the engine
speed Ne is high than when the engine speed Ne is low. Further, the amount of oil
injection is increased as an amount of fuel injection increases.
[0068] The temperature of the top ring 5 can be held substantially constant (at the suitable
temperature) regardless of the operation state of the internal combustion engine 1,
through the performance of oil jet control by the ECU 15 as described above. "The
suitable temperature" mentioned herein is a temperature at which the abutment gap
is the narrowest within such a range that the opposed end faces of the abutment of
the top ring 5 do not bump against each other. It should be noted that the top ring
5 is designed such that the abutment gap has a desired size at the aforementioned
suitable temperature.
[0069] In consequence, the cooling system for the piston according to this embodiment of
the invention makes it possible to prevent the abutment gap of the top ring 5 from
becoming excessively narrow to cause the opposed end faces of the abutment to bump
against each other when the amount of the heat generated in the combustion chamber
30 is large, and to prevent the abutment gap of the top ring 5 from becoming excessively
wide to cause an increase in the amount of compression loss or an increase in the
amount of blow-by gas when the amount of the heat generated in the combustion chamber
30 is small.
[0070] It should be noted that although the example in which the oil jet 8 is stopped when
the engine load Q and the engine speed Ne are low has been described in this embodiment
of the invention, the oil jet 8 may be prohibited from being stopped when an output
signal of the coolant temperature sensor 16 (a coolant temperature) indicates a temperature
equal to or higher than an upper-limit coolant temperature or when an output signal
of the oil temperature sensor 20 (an oil temperature) indicates a temperature equal
to or higher than an upper-limit oil temperature. "The upper-limit coolant temperature"
mentioned herein and "the upper-limit oil temperature" mentioned herein are obtained
by subtracting a predetermined margin from a temperature at which the internal combustion
engine may be overheated or a temperature at which an oil film may be broken respectively.
When the oil jet 8 is thus prohibited from being stopped, the internal combustion
engine 1 can be prevented from being overheated, and the oil film can be prevented
from being broken.
[0071] Next, the second embodiment of the invention will be described on the basis of FIGS.
6 to 9. Only the structural details of the second embodiment that differ from those
of the first embodiment of the invention will be described below.
[0072] The difference between the first embodiment of the invention and the second embodiment
of the invention lies in the structure of the cooling channel. In the first embodiment
of the invention, the cooling channel is arranged to cool the top ring groove in a
concentrated manner. However, in the second embodiment, the cooling channel is arranged
to cool a second land 37 as well as the top ring groove.
[0073] FIG. 6 is a cross-sectional view of the piston 3 according to the second embodiment
of the invention. In FIG 6, components identical to those of the first embodiment
(see FIG. 2) are denoted by the same reference symbols. The abrasion-resistant loop
300 according to this embodiment extends further in the axial direction of the cylinder
than that of the first embodiment. More specifically, the abrasion-resistant loop
300 has a width ranging from the top land of the piston 3 to a third land thereof.
[0074] A second ring groove 32, as well as the top ring groove 31, is formed in the abrasion-resistant
loop 300. Accordingly, the abrasion-resistant loop 300 located between the top ring
groove 31 and the second ring groove 32 serves also as the second land 37.
[0075] The hollow abrasion-resistant loop 310, which is substantially equal in width to
the abrasion-resistant loop 300 of the piston 3, is cast in the inside of the abrasion-resistant
loop 300. The hollow abrasion-resistant loop 310 is an annular member with a U-shaped
cross-section as in the first embodiment of the invention. The opening portion of
the hollow abrasion-resistant loop 310 is closed up by the inner peripheral face of
the abrasion-resistant loop 300. The annular space 34 surrounded by the hollow abrasion-resistant
loop 310 and the abrasion-resistant loop 300 functions as a cooling channel.
[0076] In the case where the same oil jet control as in the first embodiment of the invention
is performed for the piston 3 thus constructed, when the amount of the heat generated
in the combustion chamber 30 is large (when the engine load Q and the engine speed
Ne are high), the temperature of the top ring 5 is restrained from rising, and the
temperature of the second land 37 is also restrained from rising.
[0077] It should be noted herein that FIG 7 is an enlarged view of a gap between the piston
3 and a cylinder bore wall surface. In FIG. 7, V1 denotes a space (a first space)
surrounded by the top ring 5, the piston 3 (the top land), and the cylinder bore wall
surface. In FIG 7, V2 denotes a space (a second space) surrounded by the top ring
5, the piston 3 (the second land 37), the second ring 6, and the cylinder bore wall
surface.
[0078] As shown in FIG. 8, a pressure Pv1 in the first space V1 changes substantially in
synchronization with the pressure in the combustion chamber 30 (see a solid line in
FIG. 8). In contrast, a pressure Pv2 in the second space V2 changes with a delay from
the pressure in the combustion chamber 30 (see the single-dash chain line in FIG.
8). The time lag in this case increases as the abutment gap of the top ring 5 decreases.
Thus, as described in the first embodiment of the invention, when the abutment gap
of the top ring 5 is made as narrow as possible, there may be a period in which the
pressure Pv2 in the second space V2 is higher than the pressure Pv1 in the first space
V1 (see a hatched region in FIG. 8).
[0079] Especially when the engine load Q and the engine speed Ne are high, in other words,
when the difference in temperature between the second land 37 and the cylinder bore
wall surface is large, the volume of the second space V2 is reduced, so that the pressure
Pv2 in the second space V2 is likely to become higher than the pressure Pv1 in the
first space V1.
[0080] When the pressure Pv2 in the second space V2 becomes higher than the pressure Pv1
in the first space V1, a phenomenon in which the top ring 5 floats up to the top dead
center side in the direction of the axis of the cylinder in the top ring groove 31
occurs as shown in FIG 9. When the top ring 5 thus floats up, blow-by gas may leak
from the gap between the top ring 5 and the top ring groove 31.
[0081] In contrast, in the case where the temperature of the second land 37 is restrained
from rising when the engine load Q and the engine speed Ne are high, the outer diameter
of the second land 37 is restrained from increasing, or the outer diameter of the
second land 37 is reduced. In this case, the volume of the second space V2 is restrained
from decreasing, or the volume of the second space V2 is increased. As a result, the
pressure Pv2 in the second space V2 is unlikely to rise.
[0082] Further, when the temperature of the second land 37 is restrained from rising, the
volume of the gas present in the second space V2 is also restrained from increasing.
As a result, the pressure Pv2 in the second space V2 is more unlikely to rise. Furthermore,
the second ring groove 32 and the second ring 6 are cooled in no small measure by
the oil in the cooling channel 34. Therefore, the abutment gap of the second ring
6 increases. When the abutment gap of the second ring 6 increases, the gas in the
second space V2 is discharged from the abutment gap. As a result, the pressure Pv2
in the second space V2 can be more reliably prevented from becoming higher than the
pressure Pv1 in the first space V1.
[0083] According to the embodiment of the invention described above, the pressure Pv2 in
the second space V2 is prevented from becoming higher than the pressure Pv1 in the
first space V1. Therefore, in addition to an effect equivalent to that of the first
embodiment of the invention, the phenomenon in which the top ring 5 floats up can
also be suppressed. As a result, the amount of blow-by gas can be restrained from
increasing due to a deterioration in the sealability of the top ring 5.
[0084] Next, the third embodiment of the invention will be described on the basis of FIG.
10. In this case, the constructional details different from those of the first embodiment
of the invention will be described, and the constructional details identical to those
of the first embodiment of the invention will not be described.
[0085] The difference between the first embodiment of the invention and this embodiment
of the invention consists in that the method of performing oil jet control is changed
depending on whether the internal combustion engine 1 is being warmed up or has been
warmed up. The piston 3 is smaller in thermal capacity than the cylinder block. Furthermore,
while the cylinder bore wall surface indirectly receives the heat of the combustion
chamber 30 via the piston 3 and a piston ring, the piston 3 directly receives the
heat of the combustion chamber 30. Thus, the temperature difference ΔT between the
piston 3 and the cylinder bore wall surface is likely to be larger when the internal
combustion engine 1 is being warmed up than when the internal combustion engine 1
has been warmed up.
[0086] When the temperature difference ΔT between the piston 3 and the cylinder bore wall
surface becomes large, the difference between the amount of the increase in the outer
diameter of the top ring 5 and the amount of the increase in the inner diameter of
the cylinder 2 increases. As a result, the stress applied to the top ring 5 may become
excessively large, or the contact load between the top ring 5 and the cylinder bore
wall surface may become excessively large.
[0087] The ECU 15 control the oil jet 8 so that the oil injection amount as the internal
combustion engine 1 is being warmed up is greater than that when the internal combustion
engine 1 has been warmed up. FIG. 10 is a schematic view of a map shows the correlation
between the oil injection amount, the engine load Q, and the engine speed Ne. In FIG.
10, the borders between the regions A, B, and C when the internal combustion engine
1 is being warmed up are shown with solid lines. In FIG. 10, the borders between the
regions A, B, and C when the internal combustion engine 1 has been warmed up are shown
with single-dash chain lines.
[0088] As shown in FIG. 10, the respective borders shift toward a low load/speed side when
the internal combustion engine 1 is being warmed up than when the internal combustion
engine 1 has been warmed up. Therefore, the oil injection amount from the oil jet
8 is greater when the internal combustion engine 1 is being warmed up than when the
internal combustion engine 1 has been warmed up.
[0089] As a result, when the internal combustion engine 1 is being warmed up, the difference
between the amount of the increase in the outer diameter of the top ring 5 and the
amount of the increase in the inner diameter of the cylinder 2 is prevented from becoming
larger than when the internal combustion engine 1 has been warmed up. Thus, even when
the internal combustion engine 1 is being warmed up, the application of excessive
stress to the top ring 5 may be prevented, and the contact load between the top ring
5 and the cylinder bore wall surface can be prevented from becoming excessively large,
while minimizing the increases in compression loss and the amount of blow-by gas.
[0090] Next, the fourth embodiment of the invention will be described on the basis of FIGS.
11 to 17. In following description, only the structural details the fourth embodiment
that differ from those of the third embodiment of will be described.
[0091] In the third embodiment of the invention, the method of performing oil jet control
when the internal combustion engine 1 is steadily operated while being warmed up has
been described. However, in the fourth embodiment of the invention, a method of performing
oil jet control when the internal combustion engine 1 is transiently operated during
warm up will be described.
[0092] When the internal combustion engine 1 is transiently operated after cold start, there
occurs a situation in which the temperature of the cylinder bore wall surface (the
cylinder block) hardly rises although the temperature of the piston 3 rapidly rises.
In such a case, the temperature difference ΔT between the piston 3 and the cylinder
bore wall surface may become larger. When the temperature difference ΔT between the
piston 3 and the cylinder bore wall surface becomes large, the difference between
the amount of the increase in the outer diameter of the top ring 5 and the amount
of the increase in the inner diameter of the cylinder 2 increases. As a result, the
stress applied to the top ring 5 may become excessively large, or the contact load
between the top ring 5 and the cylinder bore wall surface may become excessively large.
This problem becomes more remarkable as the rate of the rise in the temperature of
the piston 3 (the speed at which the temperature rises) increases and as the temperature
of the cylinder bore wall surface falls.
[0093] Thus, in this embodiment of the invention, the method of performing oil jet control
is changed using the rate of the rise in the temperature of the piston 3 and the temperature
of the cylinder bore wall surface as parameters. For example, the ECU 15 controls
the flow rate adjusting valve 12 such that the amount of oil injection becomes larger
when the rate of the rise in the temperature of the piston 3 is high and the temperature
of the cylinder bore wall surface is low than when the rate of the rise in the temperature
of the piston 3 is low and the temperature of the cylinder bore wall surface is high.
The engine load Q and the engine speed Ne remain equivalent regardless of whether
"the rate of the rise in the temperature of the piston 3 is high and the temperature
of the cylinder bore wall surface is low" as mentioned herein or "the rate of the
rise in the temperature of the piston 3 is low and the temperature of the cylinder
bore wall surface is high" as mentioned herein.
[0094] The rate of the rise in the temperature of the piston 3 is correlated with the rate
of the rise in the coolant temperature. Thus, the amount of change in the coolant
temperature per a certain time can be used as the rate of the rise in the temperature
of the piston 3. Further, the temperature of the cylinder bore wall surface is substantially
equal to the temperature of the coolant flowing through the cylinder block. Thus,
the output signal of the coolant temperature sensor 16 (the coolant temperature) can
be used as the temperature of the cylinder bore wall surface.
[0095] FIG. 11 shows the changes in the coolant temperature over time. The two-dash chain
line X1 in FIG. 11 shows changes in the coolant temperature when the internal combustion
engine 1 is steadily operated while being warmed up. The single-dash chain line X2
in FIG. 11 indicates changes in the coolant temperature when the internal combustion
engine 1 is operated at intermediate load/speed while being warmed up. In FIG. 11,
changes in the coolant temperature when the internal combustion engine 1 is operated
at high load/speed while being warmed up are shown with a solid line X3. In addition,
thw0 shows the coolant temperature during the performance of oil jet control. In FIG.
11, ΔP1, ΔP2, and ΔP3 indicate the amounts of change in the coolant temperature (the
rates of increase in the temperature) for a predetermined time t for each of X1, X2,
and X3.
[0096] As indicated by the two-dash chain line X1 in FIG. 11, when the internal combustion
engine 1 is steadily operated while being warmed up, the ECU 15 controls the amount
of oil injection in accordance with the map shown in FIG. 12. It should be noted that
the map shown in FIG. 12 is equivalent to the map described in the third embodiment
of the invention (see FIG. 10), and that the borders A, B, and C are shifted toward
the low load/speed side relative to when the internal combustion engine 1 has been
warmed up.
[0097] Then, the rate ΔP2 of temperature increase when the internal combustion engine 1
is operated at intermediate load/speed while being warmed up is higher than the rate
ΔP1 temperature increase when the internal combustion engine 1 is idling while being
warmed up. Thus, when the internal combustion engine 1 is operated at intermediate
load/speed while being warmed up, the temperature difference ΔT between the piston
3 and the cylinder block is greater than that when the internal combustion engine
1 is idling while being warmed up.
[0098] Thus, as indicated by the single-dash chain line X2 in FIG. 11, when the internal
combustion engine 1 is operated at intermediate load/speed while being warmed up,
the ECU15 controls the amount of oil injection in accordance with the map shown in
FIG. 13. The solid lines in FIG. 13 indicate borders between the regions A, B, and
C when the internal combustion engine 1 is operated at intermediate load/speed while
being warmed up. The chain lines in FIG. 13 indicate the borders between the regions
A, B, and C when the internal combustion engine 1 is steadily operated while being
warmed up.
[0099] In FIG. 13, the borders between the regions A, B, and C when the internal combustion
engine 1 is operated at intermediate while being warmed up is shifted toward the low
load/speed side relative to the borders between the regions A, B, and C when the internal
combustion engine 1 is steadily operated while being warmed up. Thus, more oil is
injected when the internal combustion engine 1 is operated at intermediate load/ speed
during warm-up than when the internal combustion engine I is steadily operated during
warm-up.
[0100] Further, the rate ΔP3 at which temperature increases when the internal combustion
engine 1 is operated at high load/ speed during warm up is higher than the rate ΔP2
at which temperature increases when the internal combustion engine 1 is operated at
intermediate load/speed during warm up. Thus, if the internal combustion engine I
is operated at high load/speed during warm up, the temperature difference ΔT between
the piston 3 and the cylinder block is expected to become larger than when the internal
combustion engine 1 is operated at intermediate load/ speed during warm up.
[0101] Thus, as indicated by the solid line X3 in FIG. 11, when the internal combustion
engine 1 is operated at high load/speed during warm up, the ECU 15 controls the amount
of oil injected in accordance with to a map shown in FIG. 14. The solid line in FIG.
14 indicates the border between the regions A and B when the internal combustion engine
1 is operated at high load/speed during warm up. The chain line in FIG. 14 indicates
the border between the regions A and B when the internal combustion engine 1 is operated
at intermediate load/speed while being warmed up.
[0102] In FIG. 14, the border between the regions A and B when the internal combustion engine
1 is operated at high load/speed during warm up is shifted toward the low load/speed
side relative to the border between the regions A and B when the internal combustion
engine 1 is operated at intermediate load/speed while being warmed up. Furthermore,
in the map shown in FIG. 14, a region for stopping the oil jet 8 (a region corresponding
to the region C in each of FIGS. 12 and 13) is eliminated. That is, even when the
internal combustion engine 1 makes a transition from a high load/high rotational speed
operation range to a low load/low rotational speed operation range, a small amount
of oil is injected from the oil jet 8.
[0103] Thus, the amount of oil injection in the case where the internal combustion engine
1 is operated at high load/high rotational speed while being warmed up is larger than
the amount of oil injection in the case where the internal combustion engine 1 is
operated at intermediate load/intermediate rotational speed while being warmed up.
As a result, the temperature difference ΔT between the piston 3 and the cylinder bore
wall surface can be restrained from increasing.
[0104] It should be noted that the temperature difference ΔT between the piston 3 and the
cylinder bore wall surface may become larger when the coolant temperature (the temperature
of the cylinder bore wall surface) during the performance of oil jet control is lower
than the aforementioned value thw0 than when the coolant temperature is equal to thw0.
It is thus desirable that the amount of oil injection be made larger when the coolant
temperature is lower than thw0 than when the coolant temperature is equal to thw0.
[0105] For example, when the internal combustion engine 1 is steadily operated while being
warmed up, the ECU 15 controls the amount of oil injection according to a map shown
in FIG 15. It should be noted that solid lines in FIG 15 indicate the borders between
the regions A, B, and C in the case where the coolant temperature is lower than thw0
respectively, and that single-dash chain lines in FIG 15 indicate the borders between
the regions A, B, and C in the case where the coolant temperature is equal to thw0
respectively (which are equivalent to the borders between the regions A, B, and C
in FIG. 12 respectively).
[0106] In FIG 15, the borders between the regions A, B, and C in the case where the coolant
temperature is lower than thw0 shift more to the low load/low rotational speed side
than the borders between the regions A, B, and C in the case where the coolant temperature
is equal to thw0 respectively. Thus, the amount of oil injection in the case where
the internal combustion engine 1 is steadily operated while being warmed up increases
as the coolant temperature falls. As a result, even when the coolant temperature (the
temperature of the cylinder bore wall surface) becomes low, the temperature difference
ΔT between the piston 3 and the cylinder bore wall surface is restrained from increasing.
[0107] Further, when the internal combustion engine 1 is operated at intermediate load/intermediate
rotational speed while being warmed up, the ECU 15 controls the amount of oil injection
according to a map shown in FIG 16. It should be noted that a solid line in FIG. 16
indicates the border between the regions A and B in the case where the coolant temperature
is lower than thw0, and that the single-dash chain line in FIG. 16 indicate the border
between the regions A and B in the case where the coolant temperature is equal to
thw0 (which is equivalent to the border between the regions A and B in FIG 13).
[0108] In FIG. 16, the border between the regions A and B in the case where the coolant
temperature is lower than thw0 shifts more toward the low load/low rotational speed
side than the border between the regions A and B in the case where the coolant temperature
is equal to thw0. Furthermore, in the map shown in FIG. 16, a region for stopping
the oil jet 8 (a region corresponding to the region C in FIG. 13) is eliminated. Thus,
the amount of oil injection in the case where the internal combustion engine 1 is
operated at intermediate load/intermediate rotational speed while being warmed up
increases as the coolant temperature falls. As a result, even when the coolant temperature
(the temperature of the cylinder bore wall surface) becomes low, the temperature difference
ΔT between the piston 3 and the cylinder bore wall surface is restrained from increasing.
[0109] Furthermore, when the internal combustion engine 1 is operated at high load/high
rotational speed while being warmed up, the ECU 15 controls the amount of oil injection
according to a map shown in FIG 17. In the map shown in FIG 17, a region in which
a small amount of oil is injected from the oil jet 8 (a region corresponding to the
region B in FIG. 14) is eliminated. That is, the amount of oil injection is set equal
to a maximum amount in all operation ranges of the internal combustion engine 1. Thus,
even in the case where the internal combustion engine 1 is operated at high load/high
rotational speed when the internal combustion engine 1 is being warmed up and the
temperature of the cylinder bore wall surface is low, the temperature difference ΔT
between the piston 3 and the cylinder bore wall surface can be restrained from increasing.
[0110] According to the embodiment of the invention described above, even in the case where
the rate ΔP of the rise in the temperature of the piston 3 becomes high when the internal
combustion engine 1 is being warmed up, the temperature difference ΔT between the
piston 3 and the cylinder bore wall surface can be restrained from increasing. As
a result, the amount of the increase in the outer diameter of the top ring 5 can be
held small. Thus, the stress applied to the top ring 5 can be prevented from becoming
excessively large, and the contact load between the top ring 5 and the cylinder bore
wall surface can be prevented from becoming excessively large.
[0111] It should be noted that although the example in which a changeover among the maps
is made using the coolant temperature during the performance of oil jet control and
the rate ΔP of the rise in the coolant temperature as parameters has been described
in this embodiment of the invention, a function expression covering the aforementioned
relationships shown in FIGS. 12 to 17 may be used. That is, the amount of oil injection
may be determined using a function expression whose arguments are the coolant temperature,
the rate of the rise in the temperature, the engine load Q, and the engine speed Ne.
[0112] Further, in this embodiment of the invention, the example in which the rate of the
rise in the coolant temperature is used as the rate of the rise in the temperature
of the piston 3 has been described. However, some time lag may be produced until changes
in the temperature of the piston 3 are reflected by the coolant temperature.
[0113] Thus, it is also appropriate to calculate an amount of the heat transferred from
the combustion chamber 30 to the piston 3 using the amount of fuel injection as a
parameter, and make a changeover among the maps using a result of the calculation
and the temperature of the cylinder bore wall surface (the coolant temperature) as
parameters. In this case, an amount Hq of the heat transferred from the combustion
chamber 30 to the piston 3 per a certain time tinj may be calculated on the basis
of an expression shown below.
In the aforementioned expression, Hinj represents a small amount (J/g) of heat generation
of fuel, and ΣFinj represents a sum of amounts Finj of fuel injection within the certain
time tinj.
[0114] The ECU 15 may control the flow rate adjusting valve 12 such that the amount of oil
injection becomes larger when the amount Hq of the heat calculated according to the
aforementioned expression is large and the coolant temperature (the temperature of
the cylinder bore wall surface) is low than when the amount Hq of the heat is small
and the coolant temperature (the temperature of the cylinder bore wall surface) is
high.
[0115] According to this method, oil jet control can be performed in accordance with the
actual temperature of the piston 3.
[0116] It should be noted that the ECU 15 may simultaneously calculate an amount of oil
injection on the basis of the rate ΔP of the rise in the coolant temperature and calculate
an amount of oil injection on the basis of the amount Hq of the heat transferred from
the combustion chamber 30 to the piston 3, and may control the flow rate adjusting
valve 12 in accordance with the larger one of two results of the calculation. According
to this method, the temperature difference ΔT between the piston 3 and the cylinder
bore wall surface can be more reliably restrained from increasing.
[0117] Next, the fifth embodiment of the invention will be described. In this case, the
constructional details different from those of the first embodiment of the invention
will be described, and the constructional details identical to those of the first
embodiment of the invention will not be described.
[0118] In this embodiment of the invention, an example in which oil jet control is performed
when the cylinder bore wall surface is overcooled as in a case where there is a malfunction
in the cooling system of the internal combustion engine 1, especially a case where
a thermostat valve seizes in an open-valve state will be described.
[0119] In the case where the thermostat valve seizes in an open-valve state, even when the
coolant temperature is lower than a valve-opening temperature (or a valve-closing
temperature) of the thermostat valve, the coolant flows through a radiator. Thus,
the coolant temperature may further fall. When the coolant temperature thus falls,
the cylinder bore wall surface is overcooled.
[0120] In the case where the cylinder bore wall surface is overcooled, even when the amount
of the heat generated in the combustion chamber 30 is small, the temperature difference
ΔT between the piston 3 and the cylinder bore wall surface may increase. When the
temperature difference ΔT between the piston 3 and the cylinder bore wall surface
increases, the amount of increase in the outer diameter of the top ring 5 may become
excessively large with respect to the amount of increase in the inner diameter of
the cylinder 2. As a result, even when the amount of the heat generated in the combustion
chamber 30 is small, the stress applied to the top ring 5 may become excessively large,
or the contact load between the top ring 5 and the cylinder bore wall surface may
become excessively large.
[0121] In this view, during oil jet control according to this embodiment of the invention,
the ECU 15 sets the amount of oil injection to the maximum amount regardless of the
operation state (the engine load Q and the engine speed Ne) of the internal combustion
engine 1 as in the case of the aforementioned map of FIG. 17 when there is a malfunction
in the cooling system.
[0122] In this case, as a method of detecting a malfunction in the cooling system, it is
possible to use a method in which it is determined that there is a malfunction in
the cooling system when the rate of fall in the coolant temperature (the speed at
which the temperature falls) is higher than a predetermined upper-limit rate of fall
or when the amount of fall in the coolant temperature is larger than a predetermined
upper-limit amount of fall. "The upper-limit rate of fall" mentioned herein is a rate
of fall in the case where there is a malfunction in the thermostat valve in the open-valve
state or a value obtained by subtracting a predetermined margin from this rate of
fall. Further, "the upper-limit amount of fall" may be an amount of fall in temperature
in the case where the thermostat valve seizes in the open-valve state or a value obtained
by subtracting a predetermined margin from this amount of fall in temperature.
[0123] According to this embodiment of the invention, when there is a malfunction in the
cooling system, the temperature difference between the piston 3 and the cylinder bore
wall surface can be prevented from increasing. As a result, the outer diameter of
the top ring 5 is restrained from increasing. Thus, when the amount of the heat generated
in the combustion chamber 30 is small, the stress applied to the top ring 5 can be
prevented from becoming excessively large, and the contact load between the top ring
5 and the cylinder bore wall surface can be prevented from becoming excessively large.
[0124] It should be noted that at least two or all of the first to fifth embodiments of
the invention can be combined with one another. As a result, the abutment gap of the
top ring 5 can be held substantially constant in various cases, for example, a case
were the internal combustion engine 1 is being warmed up, a case where the internal
combustion engine 1 has been warmed up, a case where there is a malfunction in the
cooling system of the internal combustion engine 1, and the like.
[0125] Further, in each of the first to fifth embodiments of the invention, the cooling
channel 34 is constructed of the hollow abrasion-resistant loop. However, any construction
may be adopted as long as the cooling channel 34 is arranged adjacent to the top ring
5 (and the second land 37).