U.S. patent number RE43,034 [Application Number 12/951,545] was granted by the patent office on 2011-12-20 for intake control apparatus for an engine and method.
This patent grant is currently assigned to Nissan Motor Co., Ltd.. Invention is credited to Shunichi Aoyama, Ryosuke Hiyoshi, Shinichi Takemura.
United States Patent |
RE43,034 |
Aoyama , et al. |
December 20, 2011 |
Intake control apparatus for an engine and method
Abstract
An engine intake control apparatus for an engine that comprises
at least one combustion chamber operatively connected to an intake
port and an intake valve associated with each intake port, wherein
the intake valve is adapted to open and close the intake port is
disclosed herein. The intake control apparatus comprises a variable
valve operating mechanism and a controller. The variable valve
operating mechanism is configured and arranged to selectively
change a valve closing timing and a valve lift amount of the intake
valve. The controller is configured and arranged to control the
variable valve operating mechanism when the engine is in a low load
condition. The valve closing timing is determined such that an
actual compression ratio of the engine is reduced relative to the
actual compression ratio when the engine is operating in a high
load condition. The valve lift amount is smaller when the engine is
in the low load condition relative to the valve lift amount when
the engine is in the high load condition. A method for controller
an engine is also disclosed.
Inventors: |
Aoyama; Shunichi (Yokosuka,
JP), Takemura; Shinichi (Yokosuka, JP),
Hiyoshi; Ryosuke (Yokosuka, JP) |
Assignee: |
Nissan Motor Co., Ltd.
(Yokohama, JP)
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Family
ID: |
38255004 |
Appl.
No.: |
12/951,545 |
Filed: |
November 22, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
11712322 |
Feb 28, 2007 |
7640901 |
Jan 5, 2010 |
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Foreign Application Priority Data
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Mar 1, 2006 [JP] |
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2006-054605 |
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Current U.S.
Class: |
123/90.16;
123/90.15; 123/348 |
Current CPC
Class: |
F02F
3/14 (20130101); F02D 13/0226 (20130101); F01L
1/344 (20130101); F01L 13/0021 (20130101); F02F
1/18 (20130101); F01L 13/0026 (20130101); F02B
2031/006 (20130101); Y02T 10/12 (20130101); F01L
2013/0073 (20130101); Y02T 10/18 (20130101); F01L
2820/00 (20130101); F05C 2203/08 (20130101) |
Current International
Class: |
F01L
1/34 (20060101) |
Field of
Search: |
;123/90.15,90.16,90.17,90.18,345,346,347,348,406.23,406.35 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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39 26 796 |
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Feb 1991 |
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DE |
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0 764 770 |
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Mar 1997 |
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EP |
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0 945 606 |
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Sep 1999 |
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EP |
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1 223 319 |
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Jul 2002 |
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EP |
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1 363 002 |
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Nov 2003 |
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EP |
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55-087835 |
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Jul 1980 |
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JP |
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S55-087835 |
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Jul 1980 |
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JP |
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Other References
Isuzu Ceramics Research Institute Co, Ltd., Combustion and
Combustion Chamber for Heat Insulating Engines, Japanese Society of
Mechanical Engineering Lecture Articles, No. 961-1m 1996. cited by
other .
Article entitled "Combustion and Combustion Chamber for Heat
Insulating Engines" published in Japanese Society of Mechanical
Engineers Lecture Articles, No. 96-1, 1996. cited by other.
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Primary Examiner: Chang; Ching
Attorney, Agent or Firm: Global IP Counselors, LLP
Claims
What is claimed is:
1. An engine intake control apparatus for an engine that comprises
at least one combustion chamber operatively connected to an intake
port and an intake valve associated with each intake port, wherein
the intake valve is adapted to open and close the intake port, the
intake control apparatus comprising: .Iadd.a .Iaddend.variable
valve operating mechanism configured and arranged to selectively
change a valve closing timing and a valve lift amount of the intake
valve; and .Iadd.a .Iaddend.controller configured and arranged to
control the variable valve operating mechanism .[.when the engine
is in a low load condition, wherein.]..Iadd., the controller using
the variable valve operating mechanism to set .Iaddend.the valve
closing timing .[.is determined.]. .Iadd.of the intake valve
.Iaddend.such that an actual compression ratio of the engine is
reduced relative to the actual compression ratio when the engine is
operating in a high load condition .Iadd.upon detecting that the
engine is in a low load condition and that a temperature of a
combustion chamber wall is less than or equal to a predetermined
value.Iaddend., and .[.wherein.]. .Iadd.the controller using the
variable valve operating mechanism to set .Iaddend.the valve lift
amount .[.is.]. .Iadd.of the intake valve to be .Iaddend.smaller
.[.when the engine is in the low load condition.]. relative to the
valve lift amount .Iadd.of the intake valve set by the controller
.Iaddend.when the engine is in the high load condition .Iadd.upon
detecting that the engine is in the low load condition and that the
temperature of the combustion chamber wall is less than or equal to
the predetermined value.Iaddend..
2. The intake control apparatus as described in claim 1, wherein at
least a portion of .[.the.]. wall surfaces of the combustion
chamber .Iadd.wall .Iaddend.is made of a heat insulating
material.
3. The engine intake control apparatus as described in claim 2,
wherein the heat insulating material is a ceramic material.
4. The engine intake control apparatus as described in claim 2,
wherein the heat insulating material is coated on a cylinder liner
of the engine.
5. The engine intake control apparatus as described in claim 1,
wherein .[.a cylinder wall that forms part of.]. the combustion
chamber .Iadd.wall .Iaddend.has .Iadd.a first liner part positioned
next to a piston at a top dead center side with the first liner
part having .Iaddend.a lower thermal conductivity than a .[.portion
of the cylinder wall.]. .Iadd.second liner part positioned next to
the piston .Iaddend.at a bottom dead center side.
6. The engine intake control apparatus as described in claim 5,
wherein .[.a top dead center side of the cylinder wall.]. .Iadd.the
first liner part .Iaddend.is constructed of a first material, and
the .[.bottom dead center side of the cylinder wall.]. .Iadd.second
liner part .Iaddend.is constructed of a second material, and
.[.wherein.]. the first material is a heat insulating material and
the second material is a conductive material.
7. The engine intake control apparatus as described in claim 5,
wherein .[.a.]. .Iadd.the .Iaddend.first .[.cylinder.]. liner
.[.forms the top dead center side of the cylinder wall and.].
.Iadd.part .Iaddend.is constructed of .[.the.]. .Iadd.a
.Iaddend.first material and .[.a.]. .Iadd.the .Iaddend.second
.[.cylinder.]. liner .[.forms the bottom dead center side of the
cylinder wall and.]. .Iadd.part .Iaddend.is constructed of
.[.the.]. .Iadd.a .Iaddend.second material .Iadd.that is different
from the first material.Iaddend..
8. The engine intake control apparatus as described in claim 1,
wherein .Iadd.the controller reduces .Iaddend.the valve lift amount
of the intake valves .[.is reduced sufficiently to let.].
.Iadd.thereby letting .Iaddend.an intake air flow .[.into the
combustion chamber.]. along .[.the.]. wall surfaces of the
combustion chamber .Iadd.wall .Iaddend.when the engine is in the
low load condition.
9. The engine intake control apparatus as described in claim 1,
wherein .Iadd.the controller sets .Iaddend.the valve closing of the
intake valves .[.is set.]. to occur prior to the bottom dead center
of an intake stroke when the engine is operating in the low load
condition, thereby reducing the actual compression ratio.
10. The engine intake control apparatus as described in claim 1,
wherein the variable valve operating mechanism comprises a variable
lift mechanism that selectively varies the valve lift amount of the
intake valves, and a variable valve closing timing mechanism that
selectively varies the valve closing timing of the intake
valves.
11. The engine intake control apparatus as described in claim 1,
wherein when the engine is in .[.a.]. .Iadd.the .Iaddend.low load
condition, the valve lift amount of the intake valve is increased
.Iadd.by the controller .Iaddend.when .[.a.]. .Iadd.the
.Iaddend.temperature of .[.a.]. .Iadd.the .Iaddend.combustion
chamber wall exceeds .[.a.]. .Iadd.the .Iaddend.predetermined
temperature as compared to when the temperature of the combustion
chamber wall is lower than the predetermined temperature.
12. The engine intake control apparatus as described in claim 1,
wherein when the engine is in the high load condition, the
controller actuates the variable valve operating mechanism to
increase the valve lift amount of the intake valves so as to
alleviate intake air flow from flowing along .[.the.]. wall
surfaces of the combustion chamber .Iadd.wall.Iaddend..
13. A method for controlling an engine that comprises at least one
combustion chamber that is operatively connected to an intake port
through an intake valve that selectively and variably opens and
closes the intake port, the method comprising: detecting an engine
operational condition to determine whether the engine is in a low
load condition; .[.and.]. actuating an intake valve with a valve
closing timing and a valve lift amount when the engine is in the
low load condition; .[.wherein.]. .Iadd.setting .Iaddend.the valve
closing timing .[.is determined such that.]. .Iadd.of the intake
valve to reduce .Iaddend.an actual compression ratio of the engine
.[.is reduced.]. relative to the actual compression ratio of the
engine .[.with.]. .Iadd.when .Iaddend.the engine is in a high load
condition .Iadd.upon detecting that the engine is in the low load
condition and that a temperature of a combustion chamber wall is
less than or equal to a predetermined temperature.Iaddend.; and
.[.wherein.]. .Iadd.setting .Iaddend.the valve lift amount .[.is.].
.Iadd.of the intake valve to be .Iaddend.smaller .[.when the engine
is in a low load condition.]. relative to the valve lift amount
.Iadd.of the intake valve .Iaddend.when the engine is in the high
load condition .Iadd.upon detecting that the engine is in the low
load condition and that the temperature of the combustion chamber
wall is less than or equal to the predetermined
temperature.Iaddend..
14. The method for controlling the engine as described in claim 13,
wherein when .[.a.]. .Iadd.the .Iaddend.temperature of .[.a.].
.Iadd.the .Iaddend.combustion chamber wall exceeds .[.a.].
.Iadd.the .Iaddend.predetermined temperature, the valve lift amount
is increased relative to the valve lift amount when the temperature
of the combustion chamber wall is lower than the predetermined
temperature.
15. An intake control apparatus for an engine that comprises at
least one combustion chamber operatively connected to an intake
port and an intake valve associated with each intake port, wherein
the intake valve is adapted to open and close the intake port, the
intake control apparatus comprising: variable valve operating means
for selectively changing a valve closing timing and a valve lift
amount of the intake valve; and control means for controlling the
variable valve operating means .[.when the engine is in a low load
condition, wherein.]. .Iadd.to set .Iaddend.the valve closing
timing .[.is determined.]. .Iadd.of the intake valve .Iaddend.such
that an actual compression ratio of the engine is reduced relative
to the actual compression ratio when the engine is operating in a
high load condition .Iadd.upon detecting that the engine is in a
low load condition and that a temperature of a combustion chamber
wall is less than or equal to a predetermined value.Iaddend., and
.[.wherein.]. .Iadd.to set .Iaddend.the valve lift amount .[.is.].
.Iadd.of the intake valve to be .Iaddend.smaller .[.when the engine
is in a low load condition.]. relative to the valve lift amount
.Iadd.of the intake valve set by the control means .Iaddend.when
the engine is in the high load condition .Iadd.upon detecting that
the engine is in the low load condition and that the temperature of
the combustion chamber wall is less than or equal to the
predetermined value.Iaddend..
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority from Japanese Patent Application
Ser. No. 2006-054605 filed Mar. 1, 2006, the disclosure of which,
including its specification, drawings and claims, are incorporated
herein by reference in its entirety.
TECHNICAL FIELD
The present disclosure pertains to an intake control apparatus for
an engine equipped with variable valve devices. More specifically,
the present disclosure relates to a cooling loss reduction
technology for an engine.
BACKGROUND
An intake controller is known in which timing for opening intake
valves is substantially fixed, and the effective intake stroke is
variably regulated by altering the timing for closing the intake
valves based on an engine load in an attempt to reduce the pumping
loss. Such an intake controller is disclosed in published Japanese
Patent Application No. 55-87835.
However, in the intake controller disclosed published Japanese
Patent Application No. 55-87835, because the timing for closing the
intake valves comes significantly ahead of bottom dead center BDC
in the intake stroke, the intake air in the cylinders expands
adiabatically to bottom dead center BDC despite the suction stroke,
so that the temperature inside the cylinders also drops as the
pressure inside the cylinders drops. Although the compression
stroke begins once bottom dead center BDC is passed, because almost
nothing but adiabatic expansion and compression are present until
the in-cylinder pressure at which the adiabatic expansion began is
reached, that is, the in-cylinder pressure has merely been
restored; the actual compression begins from the point at which the
in-cylinder pressure is restored. Thus, the actual compression
ratio drops significantly as the timing for closing the intake
valves comes further ahead of bottom dead center BDC. Because this
drop in the actual compression ratio results in a significant drop
in the temperature of the air-fuel mixture inside the cylinders at
compression top dead center TDC, the combustion rate drops due to
the deteriorated combustion state. According, fuel economy is
adversely impacted.
Also, when the timing for closing the intake valves is advanced in
an engine equipped with a variable valve operating mechanism, it is
feasible to improve the thermal efficiency of the engine by
adhering a heat insulating material on the wall surfaces of the
combustion chambers, partially or entirely, to prevent the pumping
loss reduction effect from being lost. However, because the heat
transfer rate increases when heat insulating materials, such as
ceramic material, are used, at a high temperature generated at high
engine load, the temperature of the intake air inside the
combustion chambers increases so that undesirable knocking occurs.
In addition, intake air filling efficiency at high load is also
essential in that the volume of air is decreased to the extent that
the temperature of the intake air increases, and a tradeoff occurs,
resulting in a drop in torque
SUMMARY
An engine intake control apparatus for an engine that comprises at
least one combustion chamber operatively connected to an intake
port and an intake valve associated with each intake port, wherein
the intake valve is adapted to open and close the intake port is
disclosed herein. The intake control apparatus comprises a variable
valve operating mechanism and a controller. The variable valve
operating mechanism is configured and arranged to selectively
change a valve closing timing and a valve lift amount of the intake
valve. The controller is configured and arranged to control the
variable valve operating mechanism when the engine is in a low load
condition. The valve closing timing is determined such that an
actual compression ratio of the engine is reduced relative to the
actual compression ratio when the engine is operating in a high
load condition. The valve lift amount is smaller when the engine is
in the low load condition relative to the valve lift amount when
the engine is in the high load condition. A method for controller
an engine is also disclosed.
BRIEF DESCRIPTION OF DRAWINGS
Other features and advantages of the present disclosure will be
apparent from the ensuing description, taken in conjunction with
the accompanying drawings, in which:
FIG. 1 is a schematic perspective view of a variable valve
operating mechanism.
FIGS. 2A-2B are schematic cross-sectional views illustrating the
operation of the variable valve operating mechanism of FIG. 1.
FIG. 3 is a chart illustrating the valve lifting characteristics of
intake valves.
FIGS. 4A is a PV (in-cylinder gas pressure/cylinder volume) diagram
illustrating the drop in the actual compression ratio associated
with the reduction of pumping loss by regulating valve closing
timing, and its effects.
FIGS. 4B and 4C illustrate different valve closing times.
FIG. 5A is a partial cross section view of a prior art piston.
FIG. 5B is a partial cross section view of an adiathermic
piston.
FIGS. 6A-6B are schematic perspective views of an engine
illustrating cooling loss recovery through intake control using a
variable valve operating mechanism.
FIG. 7A-7C are schematic cross sectional views of an engine
illustrating cooling loss recovery through intake control using a
variable valve operating mechanism.
FIG. 8 is a flow chart explaining opening/closing control of intake
valves using a variable valve operating mechanism.
FIG. 9A is a schematic perspective view of a prior art piston.
FIG. 9B is a schematic perspective view of a piston according to a
second embodiment wherein a portion of a cylinder liner in a second
embodiment is cut away.
DETAILED DESCRIPTION
While the claims are not limited to the illustrated embodiments, an
appreciation of various aspects of the apparatus is best gained
through a discussion of various examples thereof. Referring now to
the drawings, illustrative embodiments are shown in detail.
Although the drawings represent the embodiments, the drawings are
not necessarily to scale and certain features may be exaggerated to
better illustrate and explain an innovative aspect of an
embodiment. Further, the embodiments described herein are not
intended to be exhaustive or otherwise limiting or restricting to
the precise form and configuration shown in the drawings and
disclosed in the following detailed description. Exemplary
embodiments of the present invention are described in detail by
referring to the drawings as follows.
FIG. 1 is a perspective view of a configuration of a variable valve
operating mechanism that serves as an engine intake control device
according to a first embodiment. More specifically, FIG. 3 is a
perspective schematic view of the variable valve operating
mechanism that includes a variable lift mechanism 21 and a variable
phase mechanism 41. The variable lift mechanism 21 can selectively
lift intake valves with the variable phase mechanism 41 (variable
timing mechanism for intake valve closing) that may change the
phase (phase with respect to the crankshaft) of a crank angular
position at which maximum lift of the intake valves is attained to
either an advancing side or delaying side. (This crank angular
position of the intake valves will hereafter be referred to as the
"intake valve lift center angle.")
FIGS. 2A and 2B are schematic cross sectional views of variable
lift mechanism 21. FIG. 2A shows a maximum and minimum rocking
position of a rocking cam 29, to be described later, at a zero lift
position of an intake valve 31. FIG. 2B shows the maximum rocking
and minimum rocking position of rocking cam 29, to be described
later, at a full lift position of the intake valve. As used herein,
zero lift of the intake valve means that intake valve 31 is not
lifted at all (that is, the lift of the intake valve is zero), and
full lift of the intake valve means that intake valve 31 is fully
lifted.
The variable valve operating mechanism 21 similar to that
illustrated in FIGS. 2A and 2B was previously proposed in published
Japanese Patent Application Nos. 2001-051422 and 11-107725, both of
which are commonly owned by Nissan Motor Ltd, the owner of the
present application and the details of which are incorporated
herein by reference in their entireties. A brief overview of the
variable valve operating mechanism 21 will now be described.
First, variable lift mechanism 21 will be explained. Variable lift
mechanism 21 is equipped with intake valves 31, a driving shaft 22,
a first eccentric cam 23, a control shaft 32, a rocker arm 26 and
rocking cams 29. The intake valves 31 connect to a cylinder head
(not shown) in a freely slidable fashion. The driving shaft 22 is
supported in a freely rotatable fashion on cam brackets (not shown)
provided at a top of the cylinder head. The eccentric cam 23 is
fixed to the driving shaft 22 by press fitting. The control shaft
32 is provided parallel to the driving shaft 22 while supported in
a freely rotatable fashion above said driving shaft 22 using the
same cam brackets that support the driving shaft 22. The rocker arm
26 is supported in a freely rockable fashion by a second eccentric
cam 38 that is connected to the control shaft 32. The rocking cams
29 make contact with valve lifters 30 provided on a top of the
intake valves 31. The eccentric cam 23 and rocker arm 26 are linked
together by a linking arm 24. The rocker arm 26 and rocking cams 29
are linked together by linking member 28.
In FIG. 1, only one cylinder portion of a multi-cylinder internal
combustion engine that is equipped with two (2) intake valves per
cylinder is represented. Therefore, two (2) intake valves 31, valve
lifters 30, and rocking cams 29 are illustrated.
As will be described in greater detail below, the driving shaft 22
is driven via a timing chain or a timing belt by a crankshaft of
the engine, as is conventional in the art.
The first eccentric cam 23 has a generally cylindrical outer
peripheral surface and defines and axis extending therethrough. The
axis of the first eccentric cam 23 is offset from an axial center
of the driving shaft 22 by a predetermined amount. A substantially
annular portion of the linking arm 24 is rotatably fitted onto the
cylindrical outer surface of the first eccentric cam 23.
The rocker arm 26 is slidably supported generally at its center by
the second eccentric cam 38. The arm portion of the linking arm 24
is linked at a first end of the rocker arm 26 (the right end in the
diagram on the left side of FIG. 2A) using a linking pin 25. A top
part of the linking member 28 is linked to a second end of the
rocker arm 26 (the left end in the figure on the left side of FIG.
2A) using a linking pin 27. The second eccentric cam part 38
defines an axis extending therethrough. The axis of the second
eccentric cam part 38 is offset from an axial center of control
shaft 32. Thus, the rocking center of the rocker arm 26 may be
changed by varying the angular position of the control shaft
32.
Rocking cams 29 are fitted and supported around the circumference
of driving shaft 22 such that rocking cams 29 are free to rotate. A
bottom portion of the linking member 28 is mechanically linked to a
portion of a rocking cam 29 using a linking pin 37. The rocking
cams 29 include an arc-shaped base surface, which forms an arc that
is concentric to driving shaft 22, and a cam surface, which extends
from said arc-shaped base surface such that it forms a
predetermined shaped curve. The base surface and cam surface of the
rocking cams 29 are formed continuously on the bottom surface of
the rocking cams 29. The arc-shaped base surfaces and the cam
surfaces are designed to be brought into abutting contact with a
designated position of the top surfaces of the valve lifters 30,
depending on the angular position of the rocking cams 29. That is,
the arc-shaped base surfaces comprise base circle zones where the
amount of lift of the intake valves 31 (and the operating angle of
the intake valves) becomes zero and the intake valves 31 are moved
downward when the cam surfaces make contact with the valve lifters
30 as the rocking cams 29 rock. Furthermore, small ramp zones are
formed between the base circle zones and the lift zones.
As shown in the embodiment depicted in FIG. 1, the control shaft 32
is configured such that it is rotated within a predetermined
angular range by a lift controlling actuator 33 that is provided at
one end of the control shaft 32. The lift controlling actuator 33
comprises pin 34a, a hydraulic actuator 35, and a first hydraulic
device 36. The pin 34a is formed as a part of a member 34 that is
provided at a rear end of the control shaft 32. The pin 34a
protrudes from a position that is offset from the axial center of
the control shaft 32 by a predetermined amount.
The hydraulic actuator 35 rotates the control shaft 32 as it
engages the pin 34a with a beak-shaped claw 35a provided at the
front end of a plunger 35b. The first hydraulic device (for
example, a hydraulic control valve) 36 regulates the hydraulic
pressure to be applied to the hydraulic actuator 35. The first
hydraulic device 36 is controlled by control signals from an engine
control unit 39. The angle of the control shaft 32 rotation is
detected by control shaft sensors, not shown.
The operation of the variable lift mechanism 21 will now be
described. When the driving shaft 22 is rotated by the crankshaft,
the linking arm 24 moves in the vertical direction due to the cam
function of first eccentric cam 23. This action causes the rocker
arm 26 to rock accordingly. The rocking of the rocker arm 26 is
transmitted to the rocking cams 29 via the linking member 28 so as
to rock the rocking cams 29. The valve lifters 30 are thereby
depressed due to the cam function of the rocking cams 29, such that
the intake valves 31 are moved downward.
When the angle of rotation of the control shaft 32 is changed via
the lift controlling actuator 33, the initial position of the
rocker arm 26 changes. Accordingly, the initial rocking position of
the rocking cams 29 is also changed.
For example, as is also shown in FIG. 2A, when second eccentric cam
38 is positioned at a top position in the figure, the rocker arm 26
as a whole is positioned at a top position, and the end part on the
linking pin 37 side of the rocking cam 29 is pulled relatively
upward. That is, the initial position of the rocking cams 29 is
tilted in the direction to move the cam surfaces away from the
valve lifters 30, as shown in the left side of FIG. 2A. Therefore,
when the rocking cams 29 rock in conjunction with the rotation of
the driving shaft 22, the arc-shaped base surfaces of the rocking
cams 29 remain in contact with the valve lifters 30 for a
relatively long time, while the time period during which the cam
surfaces remain in contact with valve lifters 30 is relatively
brief. The overall amount that the intake valves 31 are moved is
therefore reduced, as may be seen, for example, in the right side
of FIG. 2B. The crank angular zones of the intake valves 31 (i.e.,
the operating angle of the intake valves), that is, from when the
intake valves open until they close, are also reduced.
Conversely, as is also shown in FIG. 2B, when the second eccentric
cam 38 is positioned at a bottom position, the rocker arm 26 as a
whole is positioned at a bottom position, and the end part of the
rocking cam 29 on the linking pin 37 side is pressed relatively
downward. That is, the initial position of the rocking cams 29 is
tilted in a direction to move the cam surfaces closer to the valve
lifters 30, as may be seen in the left side of FIG. 2B. Therefore,
when the rocking cams 29 rock in conjunction with the rotation of
the driving shaft 22, the position where the rocking cams 29 make
contact with the valve lifters 30 moves immediately from the
arc-shaped base surfaces to the cam surfaces. The overall amount
the intake valves 31 are lifted is therefore increased, as may be
seen in viewing the right side of FIG. 2B. The operating angle of
the intake valves 31 is also effectively increased.
Because the initial position of the second eccentric cam 38 may be
changed continuously, the valve lifting characteristics of the
intake valves 31 accordingly change continuously. That is, as shown
in FIG. 3, the lifting of both intake valves 31 (the amount of lift
for intake valves 31 and the operating angle of intake valves 31)
can be increased or decreased simultaneously. Although the
configuration of each part, for example, determines how much the
lift of the intake valves 31 and the operating angle of the intake
valves 31 are increased or decreased, the timings for opening and
closing the intake valves 31 change almost symmetrically.
Next, as also shown in FIG. 1, the variable phase mechanism 41 will
now be described. The variable phase mechanism 41 comprises a
sprocket 42 and a phase regulating actuator 43. The sprocket 42 is
provided at a front end of the driving shaft 22. The phase
regulating actuator 43 rotates the sprocket 42 and the driving
shaft 22 relative to each other within a predetermined angular
range. The sprocket 42 is mechanically linked to the crankshaft via
a timing chain or a timing belt, not shown.
In the embodiment shown, the phase regulating actuator 43 comprises
a hydraulic rotary actuator 44 and a second hydraulic device (for
example, a hydraulic control valve) 45 that is used for controlling
the hydraulic supply pressure to the hydraulic actuator 44. The
second hydraulic device 45 is controlled by control signals
received from an engine control unit 39. The phase regulating
actuator 43 functions to rotate the sprocket 42 and the driving
shaft 22 relative to each other so as to advance or delay the lift
center angle of the intake valves 31 relative to the crank angle.
That is, the overall angle is advanced or delayed without changing
the lifting characteristics of the intake valves 31 (i.e., no
valve-lift change and no working-angle change). In addition, the
changes toward the advancing or delaying side of the lift center
angle can be realized continuously. The control state of the
variable phase mechanism 41 is detected by driving shaft sensors,
not shown, and corresponds to a given rotational position of the
driving shaft 22.
In the embodiment shown, the control of variable lift mechanism 21
and variable phase mechanism 41 are not limited to a closed loop
control based on the values detected by the respective driving
shaft sensors. It is understood that a simple open loop control can
be affected according to a given driving condition.
In the embodiment shown, it is desirably that the valve lifters 30
have a known hydraulic valve clearance regulating mechanism. Such a
mechanism assists in maintaining the valve clearance substantially
at zero at all times.
In an engine equipped with the above-described variable valve
operating mechanisms (i.e., each comprising a variable lift
mechanism 21 and a variable phase mechanism 41), the amount of
intake air is regulated by regulating the opening and closing of
the intake valves 31 without dependence on a throttle valve. In the
present embodiment, it is desirable that a slight vacuum exists in
the intake system to re-circulate blow-by gas. Thus, although it is
not shown, it is also desirable to provide an appropriate throttle
mechanism or a flow-constricting mechanism in place of a throttle
valve at an upstream side of an intake path to create the
vacuum.
A characteristic of the above-described variable lift mechanism 21
is that as the timing for closing the intake valves 31 changes, the
timing for opening the intake valves 31 also changes, as
illustrated in FIG. 3. (The timing for opening the intake valves 31
is delayed as the timing for closing the intake valves 31 is
advanced.) Thus, the variable lift mechanism 21 is used in
combination with the variable phase mechanism 41 to enable opening
and closing control of the intake valves 31 at an arbitrary crank
angular position.
Accordingly, the timing for closing the intake valves 31 while the
engine load is low (i.e., during an idle condition) is controlled
using the variable valve operating mechanism comprising the
variable lift mechanism 21 and the variable phase mechanism 41 to
reduce the operating angle of the intake valves 31 more
significantly than in an engine for which the timing for closing
the intake valves 31 is fixed (see, for example, FIG. 4(C)). The
timing for closing the intake valves 31 is advanced as shown in
FIG. 4(B), and suction is stopped during the suction stroke so as
to expand or compress the intake air before and after the piston
reached bottom dead center BDC. This is done to change the actual
effective suction stroke so as to bring the pressure of the intake
air at the time of suction closer to atmospheric pressure, in
almost inverse proportion to the effective stroke, to effectively
reduce a pumping loss. This phenomenon is well known as a Miller
cycle.
Because the timing for closing intake valves 31 comes well ahead of
bottom dead center BDC, the intake air inside the cylinders expands
adiabatically to bottom dead center BDC despite the suction stroke,
and the temperature inside the cylinders also drops as the
in-cylinder pressure drops. Although the compression stroke begins
once bottom dead center BDC is passed, almost nothing but adiabatic
expansion and compression are present until the in-cylinder
pressure at which the adiabatic expansion began is reached, that
is, the in-cylinder pressure is merely restored. The actual
compression therefore begins from the point at which the
in-cylinder pressure is restored. Thus, the actual compression
ratio drops significantly as the timing for closing the intake
valves is further advanced. Because the drop in the actual
compression ratio results in a significant drop in the temperature
of the air-fuel mixture inside the cylinders at compression top
dead center TDC, the combustion rate drops due to a deteriorated
combustion state. The fuel economy therefore cannot be improved to
the extent that pumping loss is reduced, as is illustrated in FIG.
4A.
Furthermore, in FIG. 4A, the timing for closing the intake valves
31 is shown by overlaying a PV curve for an engine in which it is
fixed at a point delayed from bottom dead center BDC, as shown in
FIG. 4C, with the PV curve for an engine in which the timing for
closing the intake valves 31 is set ahead of bottom dead center BDC
using the variable valve operating mechanism 21, as shown in FIG.
4B. Here, while the pumping loss is reduced when the timing for
closing the intake valves 31 is advanced using the variable valve
operating mechanism 21, the compression temperature drops, and the
combustion state deteriorates. That is, there is a tradeoff between
reduction of the pumping loss and deterioration of the combustion
state due to a drop in compression temperature.
Thus, to keep the pumping loss reduction effect when the timing for
closing intake valves 31 is advanced using the variable valve
operating mechanism 21, a coating layer 55 made of a heat
insulating (nonmetallic) material such as a ceramic material is
formed in a layer having a predetermined thickness on the crown
surface of a piston 9. The coating layer 55 may be applied by
thermal spraying, as shown in FIG. 5B. Other suitable methods of
applying coating layer 55 may also be employed. A cylinder liner 56
may also be provided. The cylinder liner 56 may also be made of the
same heat insulating material (nonmetallic material) as used to
form the coating layer 55, such as a ceramic material. The fact
that the thermal efficiency of an engine can be improved by
reducing cooling losses using a configuration comprising said heat
insulating piston and the heat insulating material liner is well
known.
A prior art piston is shown in FIG. 5A. As is illustrated, the heat
generated by combustion escapes from the piston 9 to the cylinder
10 through piston rings 51 and 52. In contrast, in the case where
the piston and liner are constructed of an insulating material,
such as a ceramic material, transmission of heat generated by
combustion is prevented by the coating layer 55.
However, as described in an article entitled "Combustion and
Combustion Chambers of Heat insulating Engines" published in the
Japanese Society of Mechanical Engineers Lecture Articles, No.
96-1, 1996, the contents of which are incorporated herein by
reference in its entirety, because, for example, the heat transfer
rate of ceramic material increases at high temperatures, such as
those that are present at high engine loads, the in-cylinder
temperature increases, and knocking becomes inevitable. In
addition, while intake air filling efficiency at high engine loads
is essential, because the intake air temperature increases when
heat insulating pistons 9 and heat insulating liners 10 are
adopted, the volume of the air decreases to this extent, and a
tradeoff, that is, a drop in torque, occurs.
In an embodiment of the present disclosure, as shown in FIGS. 9A
and 9B, the following heat exchange control is affected to
effectively eliminate the tradeoff between a drop in torque and an
increase temperature. Basically, a ceramic (heat insulating)
material is formed as a layer (see FIG. 6A, 7A) on the wall
surfaces of a combustion chamber 61 (at least portions of piston 9,
cylinder 10, cylinder head 62 (see FIG. 7A), intake valves 31, and
exhaust valves 63) to reduce the cooling losses while at a low
engine load, while at the same time storing part of the combustion
heat in the ceramic material layer. The control is then effected
using the variable valve operating mechanism comprising the
variable lift mechanism 21 and the variable phase mechanism 41,
such that the timing for closing intake valves 31 is set ahead of
bottom dead center BDC of the intake stroke so as to reduce the
actual compression ratio while at a low engine load (when a partial
load is present) while minimizing the lift of the intake valves 31,
and the intake air is turned into a high-speed wall flow 65 (that
is, a swirl) along the wall surface of the cylinder 10 to retrieve
heat from the wall surface of cylinder 10 (cylinder liner 56--the
cylinder liner 56 may be seen in FIG. 5B, but has been eliminated
in FIGS. 6A and 6B for clarity), as shown in FIG. 6A. An increase
in the intake air temperature due to the heat retrieval from the
wall surface of the high-temperature cylinder 10 becomes highly
effective for offsetting the problematic drop in the actual
compression ratio (when the pumping loss is reduced) as a result of
the control that sets the timing for closing the intake valves 31
ahead of bottom dead center BDC of the intake stroke.
Conversely, when a high engine load is present, control is affected
to increase the lift of the intake valves 31 to lessen the wall
flow along the wall surface of cylinder 10 (cylinder liner 56). In
other words, the control operates to form a wall flow 66 which does
not pass along the wall surface of cylinder 10, as is shown in FIG.
6B. In the manner demonstrated in FIG. 6B, heat retrieval from the
wall surface of cylinder 10 is avoided to limit the drop in filling
efficiency and the occurrence of knocking which would be caused by
temperature increase in the intake air at high engine load.
As described above, in the present embodiment, the lift of the
intake valves 31 is minimized at low engine loads to facilitate the
reduction of pumping loss by reducing the effective stroke. At a
high engine loads the present embodiment takes advantage of the
characteristic that increasing the lift of intake valves 31 gives a
flow characteristic to the intake air that limits the exchange of
heat with cylinder 10 to attempt to have the occurrence of knocking
reduced and preventing a reduction of the filling efficiency at
high engine load. That is, the system is configured so as to
regulate the lift of the intake valves 31 in conjunction with the
concept of reducing pumping loss.
FIG. 7A is a schematic cross-sectional view of the entire system
that includes not only the vicinity of combustion chamber 61, but
also the variable valve operating mechanism when both the intake
valve 31 and the exhaust valve 63 are closed. FIG. 7B illustrates
the condition when the intake valve 31 is open at low engine load
as opposed to FIG. 7C, which is a partial cross-sectional view of
only the vicinity of combustion chamber 61 when the intake valve 31
is open at high engine load. In the case of the variable valve
operating mechanism shown in FIG. 7A, however, it is important to
note that the front and back views are reversed as compared to
FIGS. 2A-2B. Also, the coating layer 55 and the cylinder liner 56
shown in FIG. 5B are not shown in FIGS. 7A-7B for the sake of
clarity.
As shown in FIG. 7A, streams 67 and 68 of intake air are created
along the wall surface of the cylinder 10 when the intake valve 31
is opened very little at low engine loads. The orientation of the
streams 67 and 68 can be intensified by forming a wall portion at
part of the intake valve seat circumference (not shown). An example
of structure for such an arrangement may be found in U.S. Pat. No.
5,797,368, the contents of which is incorporated by reference in
its entirety. Strong streams of air 67 and 68 close to the speed of
sound are merged to form the high-speed wall flow 65 shown in FIG.
6A, and the flow 65 flows (becomes more likely to flow) along the
ceramic-coated wall surface of cylinder 10, that is, along cylinder
liner 56, so that the heat transfer rate between the intake air and
the wall surface of the cylinder 10 becomes extremely high, and the
intake air receives enough heat for sufficient temperature increase
from heat exchange with the wall surface of the cylinder 10.
Because the control is also affected to set the timing for closing
the intake valve 31 ahead of the bottom dead center BDC of the
intake stroke in the low engine load condition, the actual
compression ratio is reduced as was described with reference to
FIG. 4, so that effective combustion may be obtained without
knocking. In addition, because of the heat insulating effect of the
ceramic is also added during combustion, significant improvement of
fuel consumption may also be realized.
Furthermore, due to the early disappearance of a quench layer
during the engine warm-up due to the control of heat exchange
between the intake air and the wall surface of cylinder 10, an HC
reduction effect may also be expected.
However, as shown in FIG. 7C, the lift of the intake valve 31 is
increased at high engine load to reduce the wall flows along the
wall surface of cylinder 10, and the reduced streams 69 and 70 are
merged to form the wall flow 66 that does not flow along the wall
surface of cylinder 10 shown in FIG. 6B, thus preventing a drop in
the filling efficiency and preventing the occurrence of knocking
that would be caused by an increased temperature of the intake air
at high engine load conditions.
The control affected by engine control unit 39 will now be
explained with reference to the flow chart in FIG. 8. FIG. 8
illustrates the opening and closing control of the intake valves
31, and the control is executed at predetermined fixed time
intervals (for example, in one embodiment, every 10 ms).
The process begin at Step I SI, where engine rotational speed Ne
detected by a crank sensor (not shown), the engine load, the
cooling water temperature Tw detected by a water temperature sensor
(not shown), and the cylinder wall temperature Twall detected by a
wall temperature sensor 74 (best seen in FIG. 7A) are read.
As shown in FIG. 7A, the wall temperature sensor 74 is attached to
the wall surface of the cylinder 10 at a position near the cylinder
head 62. With respect to the engine load, because a basic fuel
injection pulse width Tp is computed based on the volume of intake
air detected by an air flowmeter, not shown, and the engine
rotational speed Ne for the flow (not shown in the figure) for
executing fuel injection control, for example, the basic injection
pulse width Tp should be used as the engine load. In one
embodiment, oil temperature may be used in place of the cooling
water temperature Tw detected by water temperature sensor 73.
Once the engine rotational speed Ne, the engine load, the cooling
water temperature Tw, and the cylinder wall temperature Twall are
read by the engine control unit 39, the process proceeds to Step 2
S2.
In Step 2 S2, the cooling water temperature Tw detected by the
water temperature sensor 73 is compared to a predetermined value in
order to determine whether warm-up of the engine has been
completed. If cooling water temperature Tw exceeds the
predetermined value, a decision is made that warm-up of the engine
is complete, and the process flow advances to Step 3 S3. If the
cooling water temperature Tw is less than the predetermined value,
a decision is made that warm-up of the engine is not complete, and
the process flow ends.
In Step 3 S3, a determination is made as to the driving condition
based on the detected engine rotational speed Ne and basic fuel
injection pulse width Tp. In other words, it is determined whether
the engine is within a low load region. To this end, a region to be
used as the low load region should be predetermined in advance
within a driving region which involves engine rotational speed Ne
and basic fuel injection pulse width Tp as parameters. Here,
because the temperature inside the combustion chamber 61 varies
depending on the engine specifications, the material used for the
coating layer 55 and the cylinder liner 56, and their thickness,
the boundary between the low load region and the high load region
needs to be established appropriately.
When the driving condition is within the predetermined low load
region, the process flow advances to Step 4 S4. If the driving
condition is not within the low load region, the process flow
advances to Step 7 S7.
In Step 4 S4, the cylinder wall temperature Twall detected by the
wall temperature sensor 74 is compared with a predetermined value.
Here, the predetermined value is the minimum cylinder temperature
value at which combustion does not deteriorate without heat
recovery, and it is set appropriately in advance. When the cylinder
wall temperature Twall is less than or equal to the predetermined
value, a decision is made that heat needs to be recovered from the
wall surface of cylinder 10. Accordingly, the process flow advances
to Step 5 S5. If the cylinder wall temperature Twall is greater
than the predetermined value, the process flow advances to Step
7.
In Step 5 S5, an instruction to minimize the lift of the intake
valves 31 is given to the first hydraulic device 36. The process
then proceeds to Step 6 S6. In Step 6 S6 an instruction to delay
the phase of the lift center angle of the intake valves 31 (that
is, the timing for closing the intake valves) is given to the
second hydraulic device 45 to open the intake valves 31
approximately at top dead center TDC and close them at a crank
angular position ahead of bottom dead center BDC, as shown in FIG.
4B. As a result, the intake air is turned into the high-speed wall
flow 65 along the wall surface of the cylinder 10 to recover heat
from the wall surface of the cylinder 10, as shown in FIG. 6A.
Conversely, when the driving condition is not within the low load
region, that is, when the driving condition is within the high load
region, a decision is made that there is no need to recover heat
from the wall surface of cylinder 10. Thus, the process flow
proceeds to Step 7 S7. At Step 7 S7, an instruction to increase the
lift of the intake valves 31 is given to the first hydraulic device
36 by the engine control unit 39. The process flow the proceeds to
Step 8 S8. At Step 8 S8, an instruction to delay the phase of the
lift center angle (that is, the timing for closing the intake
valves) is given to the second hydraulic device 45 to reduce the
wall flow along the wall surface of cylinder 10 and turn it into
wall flow 66 that does not flow along the wall surface of cylinder
10, as shown in FIG. 6B, to avoid heat recovery from the wall
surface of the cylinder 10. In this manner, a reduction of filling
efficiency may be avoided, as well as knocking due to an intake air
temperature increase at high load.
However, when the driving condition is within the low load region
but the cylinder wall temperature Twall exceeds the predetermined
value, a decision is also made that there is no need to recover
heat from the wall surface of cylinder 10. In this case, the
process flow also advances from Step 4 S4 to Steps 7 S7 and 8 S8.
That is, an instruction to increase the lift of the intake valves
31 is given to the first hydraulic device 36, and an instruction to
delay the phase of the lift center angle of the intake valves 31 is
given to the second hydraulic device 45 to lessen the wall flow
along the wall surface of the cylinder 10 and turn it into the wall
flow 66 that does not flow along the wall surface of cylinder 10,
as shown in FIG. 6B. This prevents heat recovery from the wall
surface of cylinder 10 to prevent filling efficiency reduction and
knocking due to an intake air temperature increase under a
condition in which the cylinder wall temperature exceeds the
predetermined value, even in the low load region.
Although it is stated above that the lift of the intake valves 31
is minimized in Step 5 S5, or the lift of the intake valves 31 is
increased in Step 7 S7, the actual extent needs to be determined
appropriately depending on the engine specifications. In such
cases, because the intensity and orientation of the flow along the
cylinder wall are affected by the timing of closing the intake
valves, the extent of the lift center angle phase advancement for
the intake valves 31 in Step 6 S6 and the extent of the lift center
angle phase delay for the intake valves 31 in Step 8 S8 also need
to be optimally determined.
As described above, according to the present embodiment, in an
engine having the intake valves 31 for opening and closing the
intake ports which open into combustion chamber 61, the variable
valve operating mechanisms 21 and 41 for variably controlling the
lift of the intake valves 31 are provided, and the lifting of
intake valves 31 is minimized at a low load condition using the
variable valve operating mechanism so as to set the timing for
closing intake valves 31 ahead of bottom dead center BDC of the
intake stroke (see Steps 3, 5, and 6 in FIG. 8). The lifting of the
intake valves 31 is increased relatively while at a high load
condition so as to bring the timing for closing the intake valves
31 close to bottom dead center BDC of the intake stroke (see Steps
3, 7, and 8 in FIG. 8). In this way, even when there is the risk of
combustion deterioration due to a drop in the compression
temperature that occurs when the actual compression ratio is
reduced to reduce the pumping loss at low engine load, the
combustion is improved through active heat exchange with the
cylinder liner 56 (cylinder 10) and by creating an intake air flow
characteristic that limits heat exchange with cylinder liner 56
(cylinder 10) at high engine load, so that knocking and reduction
of the filling efficiency at high engine load may be prevented.
According to the present embodiment, because the intake air is
introduced into combustion chamber 61 along the wall surface of
cylinder 10 (the wall surface of combustion chamber 61) when the
lifting of intake valves 31 is reduced (see FIG. 6A), the heat can
be efficiently recovered from the high-temperature cylinder 10.
According to the present embodiment, because the crown surface of
the piston 9 (coating layer 55) and the cylinder liner 56 (part of
the wall surface of combustion chamber 61) are made of a ceramic
material with effective heat insulating and heat retaining
properties, cooling losses can be reduced to improve the thermal
efficiency of the engine at a low load condition.
According to the present embodiment, because the wall temperature
sensor 74 for detecting the wall temperature of the wall surface of
the cylinder 10 (wall surface of the combustion chamber) is
provided and because lifting of the intake valves 31 is increased
when the wall temperature Twall of cylinder 10 detected by the wall
temperature sensor 74 at a low load condition is higher than a
predetermined value (see Steps 3, 4, and 7 in FIG. 8), filling
efficiency reduction and knocking that are due to an increased
intake air temperature under a condition in which cylinder wall
temperature Twall exceeds the predetermined value can be prevented
even in the low load region.
FIG. 9B is a perspective partial cutaway view showing schematically
a piston 9 in a second embodiment, wherein the structures of piston
9 and a cylinder liner 71 are shown. Conventional structures of the
piston 9 and the cylinder liner 10 are shown in FIG. 9A, for the
purpose of comparison.
Referring specifically to FIG. 9B, the cylinder liner 71 is formed
with a gradient using a composite material. In other words, the
cylinder liner 71 is divided roughly in half to form an upper liner
part 71a and a lower liner part 71b. The upper liner part 71a is
positioned next to the piston 9 at top dead center as is heat
insulating. The lower liner part 71b is positioned next to the
piston at bottom dead center and is a high heat conduction/heat
transfer area. That is, the upper liner part 71a has a heat
insulating structure which may be made primarily of a ceramic
material. The lower liner part 71b has a heat conduction structure
which may be made of a carbon nano-tube material. The lower line
part 71b has the heat conduction structure coated partially on or
blended with the inner circumferential surface of lower liner part
71b and the piston slides against this material to increase the
heat conduction/heat transfer rate near bottom dead center. In this
case, because placement of the boundary between the upper liner
part 71a and the lower liner part 71b varies depending on
individual engine specifications, it is determined accordingly.
In this second embodiment, the characteristic that the coating
layer 55 is formed to a prescribed thickness on the crown surface
of piston 9 using a heat insulating (nonmetallic) material such as
a ceramic material is identical to that which was described above
in the first embodiment.
When cylinder liner 71 is formed with a gradient using a composite
material in this way, the piston rings of piston 9 can be cooled at
the bottom dead center end, so that lubrication problems can be
prevented; in other words, sticking (adhesion) of piston 9 to the
wall surface of the cylinder (cylinder liner 71) due to the coking
that occurs when the piston rings reach a high temperature can be
prevented even when the surface temperature of upper liner part 71a
has increased.
As described above, according to the second embodiment, the wall
surface of the combustion chamber 61 (the wall surface of cylinder
10) is cylinder liner 71. The upper liner part 71a of the cylinder
liner 71 next to the piston 9 at the top dead center end is made of
a highly heat insulating material. The lower liner part 71b next to
piston 9 at the bottom dead center end is made of a highly heat
conductive material. In this way, the piston rings of piston 9 can
be cooled at the bottom dead center end, so that a lubrication
problem, that is, sticking (adhesion) of piston 9 to the wall
surface of cylinder liner 71 due to the coking that occurs when the
piston rings reach a high temperature, can be prevented even when
the liner surface temperature next to piston 9 at top dead center
has increased.
Although an example has been explained in the above embodiments in
which the wall surfaces (piston 8, cylinder 10, cylinder head 62
(see FIG. 7A), intake valves 31, and exhaust valves 63) of the
combustion chamber 61 were partially made of a material with
effective heat insulating and heat retaining properties, the entire
wall surface of combustion chamber 61 may also be made of a
material with effective heat insulating and heat retaining
properties.
In addition, although the timing for closing intake valves 31 is
set prior to bottom dead center BDC while at a low load condition
in the embodiments, it goes without saying that the present
invention may also be applied to a case in which it is set later
than bottom dead center BDC, also.
The preceding description has been presented only to illustrate and
describe exemplary embodiments of the exhaust system according to
the claimed invention. It is not intended to be exhaustive or to
limit the invention to any precise form disclosed. It will be
understood by those skilled in the art that various changes may be
made and equivalents may be substituted for elements thereof
without departing from the scope of the invention. In addition,
many modifications may be made to adapt a particular situation or
material to the teachings of the invention without departing from
the essential scope. Therefore, it is intended that the invention
not be limited to the particular embodiment disclosed as the best
mode contemplated for carrying out this invention, but that the
invention will include all embodiments falling within the scope of
the claims. The invention may be practiced otherwise than is
specifically explained and illustrated without departing from its
spirit or scope. The scope of the invention is limited solely by
the following claims.
* * * * *