U.S. patent application number 10/488267 was filed with the patent office on 2004-10-07 for method of controlling internal combustion engine.
This patent application is currently assigned to Yanmar Co., Ltd.. Invention is credited to Asai, Gou, Imamori, Toshikazu, Masuda, Hiroshi.
Application Number | 20040194748 10/488267 |
Document ID | / |
Family ID | 19095918 |
Filed Date | 2004-10-07 |
United States Patent
Application |
20040194748 |
Kind Code |
A1 |
Asai, Gou ; et al. |
October 7, 2004 |
Method of controlling internal combustion engine
Abstract
The invention provides a control method of intending to improve
a heat efficiency by an Atkinson cycle, improve a charging
efficiency, improve an efficiency of a supercharger and increase a
freedom of cam design. In particular, the invention relates to a
control method of opening and closing a valve in an internal
combustion engine with supercharger. An effective compression ratio
is decreased by temporarily re-opening an exhaust valve in a
compression stroke first stage, whereby a heat efficiency is
improved without excessively increasing a cylinder internal
pressure. Preferably, an exhaust valve re-opening time is set such
that the effective compression ratio/expansion ratio is within a
range from 0.5 to 0.9. Further, an exhaust valve is not temporarily
opened in a compression stroke first stage, at a time of starting
or driving under a low load, and the Atkinson cycle in accordance
with the re-opening of the exhaust valve is achieved at a time of
driving under a high load.
Inventors: |
Asai, Gou; (Osaka, JP)
; Imamori, Toshikazu; (Osaka, JP) ; Masuda,
Hiroshi; (Osaka, JP) |
Correspondence
Address: |
CROWELL & MORING LLP
INTELLECTUAL PROPERTY GROUP
P.O. BOX 14300
WASHINGTON
DC
20044-4300
US
|
Assignee: |
Yanmar Co., Ltd.
1-32, Chaya-machi, Kita-ku
Osaka
JP
530-0013
|
Family ID: |
19095918 |
Appl. No.: |
10/488267 |
Filed: |
March 2, 2004 |
PCT Filed: |
September 4, 2002 |
PCT NO: |
PCT/JP02/08963 |
Current U.S.
Class: |
123/90.17 ;
123/90.6 |
Current CPC
Class: |
Y02T 10/12 20130101;
F02D 2700/035 20130101; F01L 1/08 20130101; F01L 2800/00 20130101;
F02D 2041/001 20130101; F01L 13/0015 20130101; F02D 15/00 20130101;
F02D 13/0269 20130101 |
Class at
Publication: |
123/090.17 ;
123/090.6 |
International
Class: |
F01L 001/34 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 6, 2001 |
JP |
2001-270241 |
Claims
1. A method of controlling an internal combustion engine, wherein
an effective compression ratio is decreased by temporarily opening
an exhaust valve in a compression stroke first stage while driving
which is not while starting or driving under a low load.
2. A method of controlling an internal combustion engine as claimed
in claim 1, wherein an effective compression ratio is changed by a
range from 0.5 to 0.9 times of the expansion ratio.
3 (Cancelled)
4. A method of controlling an internal combustion engine as claimed
in any one of claims 1 or 2, wherein the internal combustion engine
is provided with a first exhaust cam having only a cam crest for an
exhaust stroke, and a second exhaust cam having a cam crest for the
exhaust stroke and a cam crest for again opening the exhaust valve
in the compression stroke first stage, and both the exhaust cams
are arranged so as to be freely switched.
5. A method of controlling an internal combustion engine as claimed
in any one of claims 1 or 2, wherein the internal combustion engine
is provided with a first exhaust cam having only a cam crest for an
exhaust stroke, and an auxiliary exhaust cam having only a cam
crest for again opening the exhaust valve in the compression stroke
first stage, and the method freely switches a single drive by means
of the first exhaust cam, and a parallel drive by means of the
first exhaust cam and the auxiliary exhaust cam.
6. A method of controlling an internal combustion engine as claimed
in claim 4, wherein the internal combustion engine is provided with
a first exhaust cam having only a cam crest for an exhaust stroke,
and an auxiliary exhaust cam having only a cam crest for again
opening the exhaust valve in the compression stroke first stage,
and the method freely switches a single drive by means of the first
exhaust cam, and a parallel drive by means of the first exhaust cam
and the auxiliary exhaust cam.
Description
TECHNICAL FIELD
[0001] The present invention relates to a control method of an
internal combustion engine, and more particularly to a control of
opening and closing a valve in an internal combustion engine
provided with a supercharger.
BACKGROUND ART
[0002] As a method of improving a heat efficiency of an internal
combustion engine, the following methods have been conventionally
employed.
[0003] [Conventional Method 1] method of increasing maximum
cylinder internal pressure
[0004] This method corresponds to a method of increasing a maximum
cylinder internal pressure so as to improve a heat efficiency, by
making a compression ratio high and making a supercharging
high.
[0005] [Conventional Method 2] method of increasing expansion ratio
of engine
[0006] It is possible to improve a heat efficiency by increasing an
expansion ratio of an engine.
[0007] [Conventional Method 3] method of achieving Atkinson cycle
by delayed closing of air supply valve or inlet valve
[0008] FIG. 23A shows an air supply stroke, FIG. 23B shows a first
stage of a compression stroke, and FIG. 23C shows a later stage of
the compression stroke. A compression start time can be delayed by
setting an air supply valve 1 in an open state until the
compression stroke first stage in which a piston 8 is ascended, and
closing the air supply valve 1 at a later time than a normal time,
as shown in FIG. 23B, at the same time of increasing the
compression ratio of the engine, whereby it is possible to reduce
an effective compression ratio and it is possible to obtain a large
expansion ratio while restricting an excessive increase of the
cylinder internal pressure. In this case, in FIGS. 23A, 23B and
23C, reference numeral 2 denotes an air supply port, reference
numeral 3 denotes a combustion chamber, reference numeral 5 denotes
an exhaust valve, and reference numeral 6 denotes an exhaust port.
FIG. 24 shows a change of an air supply valve lift in this method.
The air supply valve lift shown by a solid line corresponds to a
case of the normal cycle, and an air supply discharging period is
secured till closely a middle of the compression stroke, by
changing the air supply valve lift in the normal cycle to an air
supply valve lift shape of the delayed closing as shown by a broken
line.
[0009] FIG. 25 shows an exhaust valve opening period and an air
supply valve opening period of the internal combustion engine
formed as the Atkinson cycle as shown in FIGS. 23A, 23B, 23C and
24, a range (a crank angle) denoted by reference symbol OL is an
overlap period between the exhaust valve opening period and the air
supply valve opening period, and a crank angle range .theta.2 is an
air supply discharging period secured by the air supply valve
delayed closing.
[0010] FIG. 26 is an Atkinson cycle indicator diagram in the
internal combustion engine in FIGS. 23A to 25, a compression work
load corresponding to a hatched area is reduced in comparison with
the normal compression stroke shown by a broken line, by setting
the air supply vale closing time SC later than the normal one in
the compression stroke first stage. In this case, reference symbol
EO denotes an exhaust valve opening time, reference symbol SO
denotes an air supply valve opening time, and reference symbol EC
denotes an exhaust vale closing time. In accordance with the
Atkinson cycle of this structure, it is possible to enlarge the
expansion ratio while maintaining the maximum cylinder internal
pressure, it is possible to increase the expansion ratio without
increasing the cylinder internal pressure, and it is possible to
improve the heat efficiency.
[0011] [Conventional Method 4] method of achieving Atkinson cycle
on the basis of early dosing of air supply valve
[0012] FIG. 27A shows an air supply stroke, FIG. 27B shows an air
supply stroke later stage, and FIG. 27C shows a compression stroke.
This method is a method of achieving the Atkinson cycle by reducing
an air supply amount supplied within the combustion chamber 3 by
closing the air supply valve 1, and making the effective
compression ratio small by reducing the compression stroke, in the
air supply stroke later stage in which the piston 8 descends as
shown in FIG. 27B.
[0013] FIG. 28 shows an exhaust valve opening period and an air
supply valve opening period in the internal combustion engine shown
in FIGS. 27A, 27B and 27C. Reference symbol OL denotes an overlap
period between the exhaust valve opening period and the air supply
valve opening period, and a crank angle .theta.3 is a crank angle
(an angle of lead) between an air supply valve closing period and
an air supply bottom dead center BDC. In other words, the air
supply valve 1 is early closed the crank angle .theta.3 before the
air supply bottom dead center BDC.
[0014] FIG. 29 is an Atkinson cycle indicator diagram in the
internal combustion engine shown in FIGS. 27A, 27B, 27C and 28, a
compression work load corresponding to a hatched area is reduced in
comparison with the normal compression stroke shown by a broken
line, by quickening the air supply vale closing time SC to the air
supply stroke later stage, whereby a gas exchange work load is
reduced.
DISCLOSURE OF THE INVENTION
[0015] (Technical Problem to be Solved by the Invention)
[0016] In the method of increasing the maximum cylinder internal
pressure in accordance with the conventional method 1, when the
maximum cylinder internal pressure becomes too large, heat loss and
a friction loss are increased, and a lack of strength is generated
in each of the portions, whereby an engine reliability is lowered.
Accordingly, an improvement factor of the heat efficiency has a
limit.
[0017] In the method of increasing the expansion ratio in
accordance with the conventional method 2, since the compression
ratio is simultaneously increased in general, an increase of the
maximum cylinder internal pressure can not be avoided.
[0018] In the Atkinson cycle made by the delayed closing of the air
supply valve in accordance with the conventional method 3, the
following problems are generated.
[0019] (a) Increase of Air Supply Temperature and Decrease of
Charging Efficiency
[0020] Since a part of the supply air which is once heated in the
combustion chamber is pushed back to the air supply port on the
basis of the delayed closing effect of the air supply valve, the
temperature of the supply air which is supplied in the next air
supply stroke is increased, and the charging efficiency is
lowered.
[0021] (b) Decrease of Supercharger Efficiency at High
Supercharging Time
[0022] Since the air supply valve is opened in the compression
stroke first stage, a heated air pushed back to the air supply port
from the combustion chamber forms a resistance against the supply
air from the supercharger even when the supercharged pressure is
increased by improving a performance of the supercharger, whereby
the load of the supercharger becomes heavy. Accordingly, an air
supply flow rate is limited and the efficiency of the supercharger
is lowered. In the case that the supply air pressure ratio is
increased by increasing the supercharged pressure in a state in
which the supply air amount is limited, an engine position is
changed from a current position B1 to a position B2 as shown in
FIG. 18, and the engine comes close to a surging line B4 of the
supercharger, so that there is a risk that a surging is
generated.
[0023] (c) Wasteful Outflow of Supply Air
[0024] The closing time of the air supply valve is delayed for the
purpose of delaying the compression starting time, however, a shape
of an air supply cam is limited to a valve lift shape as shown by a
broken line in FIG. 24 in view of a design of the air supply cam
shape, the air supply valve is in a state of being largely open
near the compression bottom dead center BDC, and a large amount of
air is flown out. The waster outflow of the supply air causes a
reduction of output.
[0025] (d) Increase of Piston Loss
[0026] In the case of the internal combustion engine provided with
the supercharger, an air supply manifold pressure is higher than an
exhaust manifold pressure except the period exposed to the
influence of the exhaust gas in the other cylinders. However, since
the supply air is pushed back to the air supply port from the
combustion chamber against the air supply manifold pressure, an
ascending work load of the piston becomes high, the piston is hard
to ascend, and the loss work is increased.
[0027] In the method of early closing the air supply valve in
accordance with the conventional method 4, the following problems
exist.
[0028] (a) Decrease of Lift Amount of Air Supply Valve
[0029] Since the lift period of the air supply valve is shortened,
the lift amount of the air supply valve is limited geometrically at
a time of designing the cam, so that the flow of the supply air
from the air supply port to the combustion chamber is limited, and
it is hard to secure a sufficient air supply amount, thereby
causing a reduction of output.
[0030] (b) Decrease of Supercharger Efficiency
[0031] Since the air supply lift amount is limited in view of the
cam design, in accordance with the shortened air supply period, the
air supply amount is widely reduced, so that it is unavoidable to
use a strong supercharger in order to secure the same air supply
amount as the normal one. However, since the air supply lift amount
is small even by increasing the supercharged pressure, the air
supply amount is not increased so much, so that the supercharger
efficiency is lowered in the same manner as that of the air supply
valve delayed closing method, and comes close to the surging line
B4 of the supercharger as shown by the position B2 in FIG. 12.
Accordingly, there is a risk that the surging is generated.
[0032] (c) Increase of Gas Temperature Within Cylinder
[0033] Since the air supply valve is closed in the air supply
stroke later stage, the increase of the gas temperature within the
cylinder is large, whereby the charging efficiency is lowered, and
the compression end temperature is also increased.
[0034] (Solving Method)
[0035] In order to solve the problems mentioned above, the present
invention provides a method of controlling an internal combustion
engine for intending an Atkinson cycle of a combustion cycle by
delaying a compression starting time with utilizing an exhaust
valve, in place of contriving a closing time of the air supply
valve, and in accordance with the invention on the basis of a first
aspect, there is provided a method of controlling an internal
combustion engine, wherein an effective compression ratio is
decreased by temporarily opening an exhaust valve in a compression
stroke first stage at a time of driving which it is neither at a
time of starting nor at a time of driving under a low load.
[0036] In accordance with the invention on the basis of a second
aspect, there is provided a method of controlling an internal
combustion engine as recited in the first aspect, wherein an
expansion ratio is set higher (in a range from 15 to 20) than a
conventional engine, and an effective compression ratio is
optionally changed within a range from 0.5 to 0.9 times of the
expansion ratio.
[0037] In accordance with the invention on the basis of a fourth
aspect, there is provided a method of controlling an internal
combustion engine as recited in the first or second aspect, wherein
the internal combustion engine is provided with a first exhaust cam
having only a cam crest for an exhaust stroke, and a second exhaust
cam having the cam crest for the exhaust stroke and a cam crest for
again opening the exhaust valve in the compression stroke first
stage, and both the exhaust cams are used so as to be freely
switched.
[0038] In accordance with the invention on the basis of a fifth
aspect, there is provided a method of controlling an internal
combustion engine as recited in the first, second or fourth aspect,
wherein the internal combustion engine is provided with a first
exhaust cam having only a cam crest for an exhaust stroke, and an
auxiliary exhaust cam having only a cam crest for again opening the
exhaust valve in the compression stroke first stage, and the method
freely switches a single drive by means of the first exhaust cam,
and a parallel drive by means of the first exhaust cam and the
auxiliary exhaust cam.
[0039] (Operative Effect in Comparison with Conventional Art)
[0040] In accordance with the present invention, since the Atkinson
cycle is achieved by temporarily opening again the exhaust valve in
the compression stroke first stage so as to delay the compression
starting time and make the effective compression ratio small,
without delaying and quickening the closing time of the air supply
valve, as is different from the conventional Atkinson cycle, it is
possible to achieve a high expansion ratio while restricting the
increase of the maximum cylinder internal pressure, and achieve an
improvement of the heat efficiency, and the following effect can be
obtained.
[0041] (1) Since the exhaust valve is re-opened in the compression
stroke first stage, the freedom of designing the cam can be
maintained, and it is possible to design such as to accurately
relieve a necessary air amount to the exhaust port at a necessary
time, in comparison with the Atkinson cycle ratio in accordance
with the conventional air supply valve delayed closing or early
closing. In other words, in comparison with the air supply valve
delayed closing method, it is possible to easily design such as to
prevent a large amount of supply air from being relieved at the
compression bottom dead point, and in comparison with the air
supply valve early closing method, it is possible to design such as
to sufficiently secure the air supply lift amount.
[0042] (2) Since a part of the supply air supplied to the
combustion chamber is discharged to the exhaust port, the supply
air discharged in the manner mentioned above does not generate any
resistance against the pressure supply air entering into the
combustion chamber from the air supply port even in the case that
the performance of the supercharger is improved and the
supercharged pressure is increased. Accordingly, it is possible to
sufficiently secure the supply air flow rate, the load of the
supercharger is lightened, and the efficiency of the supercharger
is improved. In other words, since it is possible to increase the
air supply flow rate even in the case that the supercharged
pressure is increased, the position gets away from the surging line
B4 of the supercharger as shown by the position B3 in FIG. 18,
there is no fear that the surging is generated, and it is possible
to efficiently utilize the supercharger.
[0043] (3) Since a part of the supply air supplied to the
combustion chamber is discharged to the exhaust port, it is
possible to prevent the supply air temperature in the air supply
port from being increased, in comparison with the delayed dosing
method of the air supply valve, whereby it is possible to prevent
the charging efficiency from being lowered.
[0044] (4) Since a part of the supply air is relieved to the
exhaust port so as to cool the exhaust system by re-opening the
exhaust valve in the compression stroke first stage, it is possible
to shorten the overlap period between the air supply valve opening
period and the exhaust valve opening period while fixing the heat
load of the exhaust system. Since it is possible to shorten the
overlap period while fixing the heat load of the exhaust system as
mentioned above, it is possible to increase the gas work exchange
amount as shown in FIG. 21, and it is possible to increase the
cylinder residual gas as shown in FIG. 22 so as to intend to reduce
NOx on the basis of an internal EGR effect.
[0045] (5) In a multiple cylinder internal combustion engine with
supercharger, an exhaust manifold pressure is lower than an air
supply manifold pressure except a time affected by the exhaust gas
in the other cylinders. Since a part of the supply air is
discharged to the exhaust manifold, it is possible to restrict an
ascending work amount of the piston to a low level in comparison
with the air supply valve delayed closing method, so that it is
possible to make the piston loss small.
[0046] (6) It is possible to introduce an exhaust pulse from the
other cylinders in the case of well aligning the timing and the
piping, by temporarily opening the exhaust valve in the compression
stroke first stage. Accordingly, it is possible to obtain the
internal EGR effect so as to intend to prevent the NOx from being
reduced or increased.
[0047] (7) It is possible to increase the heat efficiency while
maintaining the cylinder internal pressure by making the expansion
ratio high and setting the effective compression ratio within a
range from 0.5 to 0.9 times of the expansion ratio. Further, it is
possible to inhibit a smoke from being generated, by restricting
the reduction of an excess air factor and making a combustion
injection pressure high.
[0048] (8) If the exhaust valve is set such as not to be opened in
the compression stroke first stage, at the starting time or the low
load operating time, it is possible to sufficiently secure an
evaporation of the fuel, and it is possible to maintain a starting
performance and a low load operating performance. On the other
hand, at the high load time, it is possible to achieve an
improvement of the heat efficiency by re-opening the exhaust valve
in the exhaust stroke first stage and making the Atkinson
cycle.
[0049] (9) In the case that the internal combustion engine is
provided with the first exhaust cam having only the cam crest for
the exhaust stroke, and the second exhaust cam having the cam crest
for the exhaust stroke and the cam crest for re-opening the exhaust
valve in the compression stroke first stage, and both the exhaust
cams are used so as to be freely switched, it is possible to easily
switch between the normal combustion cycle and the Atkinson cycle,
in the starting time or the low load operating time, and the high
load operating time.
[0050] (10) In the case that the internal combustion engine is
provided with the first exhaust cam having only the cam crest for
the exhaust stroke, and the auxiliary exhaust cam having only the
cam crest for re-opening the exhaust valve in the compression
stroke first stage, and the method freely switches the single drive
by means of the first exhaust cam, and the parallel drive by means
of the first exhaust cam and the auxiliary exhaust cam, it is
possible to easily switch between the normal combustion cycle and
the Atkinson cycle, in the starting time or the low load operating
time, and the high load operating time.
BRIEF DESCRIPTION OF THE DRAWINGS
[0051] FIG. 1A is a cross sectional schematic view of a cylinder
showing an air supply stroke of a control method in accordance with
the present invention;
[0052] FIG. 1B is a cross sectional schematic view of the cylinder
showing a compression stroke first stage of the control method in
accordance with the present invention;
[0053] FIG. 1C is a cross sectional schematic view of the cylinder
showing a compression stroke later stage of the control method in
accordance with the present invention;
[0054] FIG. 2 is a view showing an exhaust valve lift and an air
supply valve lift in accordance with the present invention;
[0055] FIG. 3 is a view showing an air supply valve opening period,
an exhaust valve opening period and an exhaust valve re-opening
period in accordance with the present invention;
[0056] FIG. 4 is a graph showing a relation among an exhaust valve
lift, an exhaust manifold pressure, an air supply manifold pressure
and a cylinder internal pressure at an exhaust valve re-opening
time in accordance with the present invention;
[0057] FIG. 5 is a perspective view of an exhaust cam for carrying
out the present invention;
[0058] FIG. 6 is a cross sectional view in a cross section
perpendicular to an axis of the exhaust cam in FIG. 5, in which
both the exhaust cams are described in parallel;
[0059] FIG. 7 is a perspective view of another exhaust cam for
carrying out the present invention;
[0060] FIG. 8 is a cross sectional view in a cross section
perpendicular to an axis of the exhaust cam in FIG. 7, in which
both the exhaust cams are described in parallel;
[0061] FIG. 9 is a perspective view of the other exhaust cam for
carrying out the present invention;
[0062] FIG. 10 is a cross sectional view in a cross section
perpendicular to an axis of each of the exhaust cams in FIG. 9, in
which both the exhaust cams are described in parallel;
[0063] FIG. 11 is a standard indicator diagram of an Atkinson
cycle;
[0064] FIG. 12 is an indicator diagram of an Atkinson cycle in
accordance with the present invention;
[0065] FIG. 13 is a view showing a relation between compression
ratio/expansion ratio and an excess air factor;
[0066] FIG. 14 is a view showing a relation between a fuel
injection pressure and a smoke;
[0067] FIG. 15 is a view showing a relation between a specific fuel
consumption and a maximum cylinder internal pressure;
[0068] FIG. 16 is a view showing a relation between the specific
fuel consumption and an NOx concentration;
[0069] FIG. 17 is a view showing a relation between a smoke index
and the NOx concentration;
[0070] FIG. 18 is a view showing a relation between a supply air
flow rate and a supply air pressure ratio;
[0071] FIG. 19 is a view showing a relation between an overlap
period and a fresh air blow-by rate;
[0072] FIG. 20 is an index diagram of a combustion cycle in the
case that an overlap period between the exhaust valve opening
period and the air supply valve opening period is long;
[0073] FIG. 21 is an index diagram of a combustion cycle in the
case that the overlap period between the exhaust valve opening
period and the air supply valve opening period is short;
[0074] FIG. 22 is a view showing a relation between the overlap
period and a cylinder residual gas rate;
[0075] FIG. 23A is a cross sectional schematic view of a cylinder
showing an air supply stroke of an Atkinson cycle in accordance
with a conventional air supply valve delayed closing;
[0076] FIG. 23B is a cross sectional schematic view of the cylinder
showing a compression stroke first stage of the Atkinson cycle in
accordance with the conventional air supply valve delayed
closing;
[0077] FIG. 23C is a cross sectional schematic view of the cylinder
showing a compression stroke later stage of the Atkinson cycle in
accordance with the conventional air supply valve delayed
closing;
[0078] FIG. 24 is a view showing an air supply valve lift
corresponding to FIGS. 23A, 23B and 23C;
[0079] FIG. 25 is a view showing an air supply valve opening period
and an exhaust valve opening period corresponding to FIGS. 23A, 23B
and 23C;
[0080] FIG. 26 is an index diagram of the Atkinson cycle
corresponding to FIGS. 23A, 23B and 23C;
[0081] FIG. 27A is a cross sectional schematic view of a cylinder
showing an air supply stroke of an Atkinson cycle in accordance
with a conventional air supply valve early closing;
[0082] FIG. 27B is a cross sectional schematic view of the cylinder
showing an air supply stroke later stage of the Atkinson cycle in
accordance with the conventional air supply valve early
closing;
[0083] FIG. 27C is a cross sectional schematic view of the cylinder
showing a compression stroke of the Atkinson cycle in accordance
with the conventional air supply valve early closing;
[0084] FIG. 28 is a view showing an air supply valve opening period
and an exhaust valve opening period corresponding to FIGS. 27A, 27B
and 27C; and
[0085] FIG. 29 is an index diagram of the Atkinson cycle
corresponding to FIGS. 27A, 27B and 27C.
BEST MODE FOR CARRYING OUT THE INVENTION
[0086] FIGS. 1A to 1C show a stroke change within a cylinder in the
case that the present invention is applied to a direct injection
type multiple cylinder diesel engine with supercharger. In an air
supply stroke shown in FIG. 1A, since an air supply valve 1 is
open, a supply air pressurized by the supercharger is supplied from
an air supply port 2 into a combustion chamber 3. In a compression
stroke first stage of a piston ascending process shown in FIG. 1B,
the air supply valve 1 is closed and an exhaust valve 5 is
temporarily re-opened, thereby evacuating a compressed pressure
within the combustion chamber 3 from an exhaust port 6. Further, in
a compression stroke later stage shown in FIG. 1C, the exhaust
valve 5 for re-opening mentioned above is closed, and the supply
air is substantially compressed. In other words, a compression
start time is delayed by temporarily re-opening the exhaust valve 5
in the compression stroke first stage, thereby lowering an
effective compression ratio and preventing a maximum cylinder
internal pressure from being excessively increased.
[0087] FIG. 2 shows an exhaust valve lift at a time of re-opening
the exhaust valve in FIG. 1B together with an air supply valve
lift. A shape of the air supply valve lift is the same as the
normal air supply valve lift which is neither the delayed closing
nor the early closing, and is in a slightly open state at a
compression bottom dead center BDC.
[0088] The exhaust valve at the re-opening time is structured such
as to start lifting (opening) little by little from the compression
bottom dead center BDC, start closing little by little after
maintaining a fixed amount open state for a fixed period, and close
in the middle of the compression stroke. This exhaust valve
re-opening period corresponds to a supply air discharging period
for discharging the supply air to the exhaust side.
[0089] FIG. 3 shows a relation among the exhaust valve opening
period, the air supply valve opening period and the exhaust valve
re-opening period. The exhaust valve opening period is from a later
stage of an explosion stroke to an early stage of the air supply
stroke via the exhaust stroke, the air supply valve opening period
is from a final stage of the exhaust stroke to an early stage of
the compression stroke via the air supply stroke, and an overlap
period OL between the air supply valve opening period and the
exhaust valve opening period exists in the vicinity of an exhaust
gas top dead center (a supply air top dead center) TDC. The exhaust
valve re-opening period (the supply air discharging period) is from
the air supply bottom dead center BDC to about a middle of the
compression stroke, as described in FIG. 2.
[0090] FIG. 4 shows a relation among the exhaust valve lift, an
exhaust manifold pressure, an air supply manifold pressure and a
cylinder internal pressure at an exhaust valve re-opening time.
When the exhaust gas of the other cylinders has an: influence, the
exhaust manifold pressure is temporarily higher than the air supply
manifold pressure, however, the air supply manifold pressure
pressurized by the supercharger is basically higher than the
exhaust manifold pressure, and in the embodiment, the re-opening
period (the supply air discharging period) of the exhaust valve is
positioned within the period in which the air supply manifold
pressure is higher than the exhaust manifold pressure.
[0091] A piston ascending work such as a case of a supply air
delayed closing type Atkinson cycle is reduced by temporarily
re-opening the exhaust valve so as to discharge a part of the
supply air to the exhaust port, in a period in which the exhaust
manifold pressure is lower than the air supply manifold pressure,
in the compression stroke first stage, as mentioned above.
[0092] FIG. 11 is an indicator diagram showing a summary of a
well-known theoretical Atkinson cycle (output cycle). A description
will be briefly given of a concept of the-Atkinson cycle by
utilizing FIG. 11. Reference symbol V denotes a total volume,
reference symbol V1 denotes a volume of an adiabatic compression
starting time A1, reference symbol V2 denotes a volume of an
adiabatic compression finishing time A2, reference symbol V4
denotes a volume of an adiabatic expansion starting time A4,
reference symbol V6 denotes a volume of an adiabatic expansion
finishing time (an exhaust valve opening time) A5, reference symbol
Qv denotes a heating amount of an isovolumetric heating period
(A2.fwdarw.A3), reference symbol Qp denotes a heating amount of an
isobaric(or isotacitc) heating period (A3.fwdarw.A4), reference
symbol Q1v denotes a heat dissipation amount of an isovolumetric
heat dissipating period (A5.fwdarw.A6), and reference symbol Q1p
denotes a heat dissipation amount of an isobaric heat dissipating
period (A6.fwdarw.A1).
[0093] Formulas of amount of heat in the respective periods
mentioned above are as follows.
[0094] Adiabatic compression period (A1.fwdarw.A2)
P1V1.sup..kappa.=P2V2.sup..kappa.
[0095] Isovolumetric heating period (A2.fwdarw.A3)
Qv=Cv.multidot.V2.multidot.(Pmax-P2)/R
[0096] Isobaric heating period (A3.fwdarw.A4)
Qp=Cp.multidot.Pmax.multidot.(V4-V2)/R
[0097] Adiabatic expansion period (A4.fwdarw.A5)
Pmax.multidot.V4.sup..kappa.=P5V6.sup..kappa.
[0098] Isovolumetric heat dissipating period (A5.fwdarw.A6)
Q1v=Cv.multidot.V6-(P5-P1)
[0099] Isobaric heat dissipating period (A6.fwdarw.A1)
Q1p=Cp.multidot.P1.multidot.(V6-V1)
[0100] In the above formulas, reference symbol .kappa. is a
politropic exponent, reference symbol R is a gas constant,
reference symbol Cv is an isovolumic specific heat, and reference
symbol Cp is an isopiestic specific heat.
[0101] In the Atkinson cycle, a theoretic heat efficiency .eta.th
is expressed by the following formula.
.eta.th=1-(Q1v+Q1p)/(Qv+Qp) (1)
[0102] The theoretical heat efficiency .eta.th is expressed by the
formula (2) by introducing the relations of the amount of heat and
the like and the following relations to the formula (1) of the heat
efficiency.
[0103] Engine apparent compression ratio .epsilon.=V/V2
[0104] Effective compression ratio .epsilon.'=V1/V2
[0105] EO volume ratio .nu.=V1/V6
[0106] Expansion ratio .beta.=V6/V2
[0107] Effective compression ratio/expansion ratio .phi.=V1/V6
[0108] Explosion degree .rho.=Pmax/P2
[0109] Cut.off ratio .sigma.V4/V2
.eta.th=1-{1/(.nu..phi..epsilon.).kappa.)}.times.[.nu..epsilon.{.rho.(.sig-
ma..phi.).kappa.-1+.kappa.(1-.phi.)}/{.rho.-1+.kappa..rho.(.sigma.-1)}]
(2)
[0110] The present invention set preferably such that in the
formula (2), the respective ratios are within the following ranges:
EO volume ratio .nu. is 0.8 to 0.95, effective compression
ratio/expansion ratio .phi. is 0.5 to 0.9, and apparent compression
ratio .epsilon. is 15 to 20.
[0111] [Structure of Exhaust Cam]
[0112] FIGS. 5 and 6 show an example of an exhaust cam structure
for re-opening the exhaust valve in the compression stroke first
stage. In this example, a cam crest 12 for an exhaust stroke and a
cam crest 13 for re-opening are formed in the same exhaust cam
11.
[0113] FIGS. 7 and 8 show another example of the exhaust cam
structure for carrying out the exhaust valve re-opening. This
example is provided with a first exhaust cam 21 having only the cam
crest 12 for the exhaust stroke, and a second cam 22 having the cam
crest 12 for the exhaust stroke and the cam crest 13 for
re-opening, and both the exhaust cams 21 and 22 are used so as to
be freely switched. For example, at the starting time or the low
load operation time, in order to sufficiently secure the
evaporation of the fuel and improve a heat efficiency (a maximum
cylinder internal pressure), it is preferable to set the
compression ratio high, so that the first exhaust cam 21 is
utilized. On the other hand, at the high load time, the exhaust
valve is re-opened in the compression stroke first stage by
utilizing the second exhaust cam 22, thereby making the Atkinson
cycle.
[0114] FIGS. 9 and 10 show the other example of the exhaust cam
structure. This example is provided with the first exhaust cam 21
having only the cam crest 12 for the exhaust stroke, and an
auxiliary exhaust cam 23 having only the cam crest 13 for
re-opening, and the cams are used by switching between a
simultaneous and parallel use of both the exhaust cams 21 and 23,
and an independent use of the first exhaust cam 21. For example, at
the starting time or the low load operation time, in order to
sufficiently secure the evaporation of the fuel, it is preferable
to set the compression ratio high, so that only the first exhaust
cam 21 is independently used. On the other hand, at the high load
time, the first exhaust cam 21 and the auxiliary exhaust cam 23 are
used simultaneously and in parallel, and the exhaust valve is
re-opened in the compression stroke first-stage, thereby making the
Atkinson cycle.
[0115] (Effect)
[0116] FIG. 12 is an indicator diagram of the combustion cycle in
the case of increasing the engine compression ratio, that is, the
expansion ratio, and temporarily re-opening the exhaust valve in
the compression stroke first stage. Reference symbol EO corresponds
to an exhaust valve opening time, reference symbol SO corresponds
to an air supply valve opening time, reference symbol EC
corresponds to an exhaust valve closing time, and reference symbol
SC corresponds to an air supply valve closing time, which are shown
by a black circle. Further, reference symbol REO corresponds to a
start time of an exhaust valve re-opening, and reference symbol REC
corresponds to a closing time (finishing time) of an exhaust valve
re-opening, which are shown by a white circle. By delaying the
compression start time to the time of REC in accordance with the
re-opening (REO.fwdarw.REC) of the exhaust valve, the compression
stroke corresponding to a hatched area is reduced in comparison
with the comparison stroke of the normal cycle shown by a broken
line, whereby the effective compression ratio is lowered. In
accordance with the Atkinson cycle mentioned above, it is possible
to enlarge the expansion ratio in a state in which the maximum
cylinder internal pressure is maintained approximately in the same
manner as the normal case, and the heat cycle efficiency is
improved.
[0117] By aligning the timing of the exhaust re-opening, it is
possible to introduce the exhaust pulse from the other cylinders
into the cylinder, whereby it is possible to achieve an internal
EGR effect and it is possible to intend to reduce NOx.
[0118] By re-opening the exhaust valve in the compression stroke,
it is possible to cool the exhaust valve or the like in accordance
with a blow by of the supply air, whereby it is possible to shorten
the overlap period between the exhaust valve opening period and the
air supply valve opening period while keeping the heat load of the
exhaust system constant, a gas exchange work load is improved, it
is possible to achieve a high heat efficiency, the internal EGR gas
amount is increased, and it is possible to achieve a low NOx.
[0119] FIG. 13 is a graph showing a relation between the effective
compression ratio/expansion ratio and an excess air factor. In the
case of the normal cycle to which the Atkinson cycle is not
introduced, the effective compression ratio/expansion ratio is
approximately 1. On the contrary, the heat efficiency is improved
by making the effective compression ratio/expansion ratio .phi.
small to a level within a range from 0.5 to 0.9 on the basis of the
exhaust valve re-opening. However, since the excess air factor is
lowered in accordance with a degree that the effective compression
ratio/expansion ratio is smaller than 1, the smoke is easily
generated. In order to cope with this matter, the combustion
injection pressure is made higher than the normal one, whereby the
smoke is prevented from being generated. In other words, since the
combustion injection pressure and the smoke amount are in an
inversely proportional relation as shown in FIG. 14, it is possible
to achieve an improvement of the heat efficiency and a reduction of
the smoke amount, by increasing the injection pressure while
lowering the effective compression ratio/expansion ratio .phi. to
the range from 0.5 to 0.9 as mentioned above.
[0120] FIG. 15 shows a relation between a specific fuel consumption
and a maximum cylinder internal pressure. A black circle position
{circle over (1)} corresponds to the case of the normal cycle to
which the Atkinson cycle is not introduced, a black triangle
position {circle over (5)} corresponds to a state in which the OL
period is shortened and the supply air pressure is increased at the
same time when the Atkinson cycle is introduced in accordance with
the present invention. In the position {circle over (5)}, it is
possible to widely lower the specific fuel consumption in
comparison with the position {circle over (1)}, and it is possible
to restrict the increase of the maximum cylinder internal pressure
to an allowable level in a point of a strength or the like.
[0121] A white square position {circle over (2)} and a white
triangular position {circle over (3)} correspond to a conventional
approach for improving the heat efficiency. The position runs from
the position {circle over (1)} to the position {circle over (2)}
along an arrow G1 by increasing the compression ratio and
shortening the OL period, and further runs to the position {circle
over (3)} along an arrow G3 by increasing the supply air pressure.
In the position {circle over (2)}, the maximum cylinder internal
pressure is increased to an allowable level in a point of the
strength or the like, however, the specific fuel consumption is
hardly lowered. In the position {circle over (3)}, the specific
fuel consumption is widely lowered, however, the maximum cylinder
internal pressure is excessively increased to a level in which a
lack of strength is generated.
[0122] A black square position {circle over (4)} corresponds to a
state in which the Atkinson cycle is introduced from the position
{circle over (1)} in accordance with the present invention and the
OL period is shortened. The cylinder internal pressure is lowered
to the same level as that of the normal cycle in the position
{circle over (1)}, in comparison with the position {circle over
(2)} in the conventional example, as shown by an arrow G2, and the
specific fuel consumption is lowered in comparison with the
position {circle over (2)}.
[0123] The position runs to the position {circle over (5)} by
making the supercharged pressure higher from the state in the
position {circle over (4)} mentioned above, however, the specific
fuel consumption is widely lowered as shown by an arrow G5, and the
increase of the cylinder internal pressure can be restricted to the
increase about the position {circle over (2)} mentioned above.
[0124] In this case, the position also runs to the position {circle
over (5)} as shown by an arrow G4, by introducing the Atkinson
cycle in accordance with the present invention from the position
{circle over (3)}.
[0125] FIG. 16 is a graph showing a relation between the specific
fuel consumption and the NOx. A black circle position {circle over
(1)} corresponds to the case of the normal cycle which does not
employ the Atkinson cycle, a black square position {circle over
(2)} corresponds to the case to which the Atkinson cycle is
introduced in accordance with the present invention without
changing the supercharged pressure from the position {circle over
(1)} mentioned above. In the position {circle over (2)}, the NOx is
reduced, however, the specific fuel consumption is a little
increased. In accordance with an increase of the supply air
pressure, it is possible to widely reduce the specific fuel
consumption while restricting the NOx to the same level as that of
the position {circle over (1)}, as shown by a black triangle
position {circle over (3)}.
[0126] FIG. 17 is a graph showing a relation between a smoke index
and the NOx. Positions {circle over (1)}, {circle over (2)} and
{circle over (3)} have the corresponding conditions to those in
FIG. 16. The position {circle over (2)} corresponds to the case to
which the Atkinson cycle is introduced without changing the
supercharged pressure from the position {circle over (1)}
corresponding to the normal cycle. In this position, the NOx is
reduced, however, the smoke is increased. On the contrary, it is
possible to restrict the NOx and the smoke to the same level as
those of the actual position {circle over (1)} as in the position
{circle over (3)}, by increasing the supply air pressure.
[0127] FIG. 18 is an index of a working state of a supercharger
compressor. FIG. 18 is a graph showing a supply air pressure ratio
by a vertical axis and a compressor efficiency and a surging line
with respect to a supply air flow rate by a horizontal axis. In
this drawing, reference symbol B1 shows a case of the normal cycle
to which the Atkinson cycle is not introduced, reference symbol B2
shows a case that the Atkinson cycle is formed by the air supply
valve delayed closing or the air supply valve early closing,
reference symbol B3 shows a case that the Atkinson cycle is formed
by the re-opening of the exhaust valve in accordance with the
present invention, and reference symbol B4 shows a surging line of
the supercharger.
[0128] In FIG. 18, in the Atkinson cycle formed by the air supply
valve early closing or the air supply valve delayed closing, since
the supply air is returned from the air supply valve to the air
supply port even in the case that the supply air pressure ratio is
increased by increasing the supercharged pressure, only the
supercharged pressure is increased and the supply air flow rate is
not increased as shown by the point B2, and the point comes close
to the surging line B4 of the supercharger, so that it is
impossible to efficiently utilize the supercharger.
[0129] On the other hand, in the case of the Atkinson cycle formed
by the re-opening of the exhaust valve in accordance with the
present invention, since the supply air is discharged to the
exhaust port along the flow of the supply air, the supply air flow
rate is increased together with the supply air pressure ratio by
increasing the supercharged pressure. Accordingly, the point does
not come close to the surging line B4 as is different from the
point B3, and it is possible to efficiently utilize the
supercharger.
[0130] FIG. 19 is a graph showing a relation between the overlap
period (the period OL in FIG. 3) between the exhaust valve opening
period and the air supply valve opening period, and a fresh air
blow by rate. A mass-produced cam in a graph D1 corresponds to a
case of the normal cycle which is not formed as the Atkinson cycle,
and a fresh air blow by rate in this case is set to 1.
[0131] In the case that the overlap period OL is long, an atrophied
state is formed from an air supply valve opening period SO to an
exhaust valve closing period EC as shown in FIG. 20, a hatched area
becomes small, and a loss of heat efficiency is generated. On the
other hand, in the case that the overlap period OL is simply
shortened, it is possible to secure a rising edge L from the air
supply valve opening period SO to the exhaust valve closing period
EC as shown in FIG. 21, whereby it is possible to secure the
hatched area large, and the heat efficiency is improved, however,
the fresh air blow by rate is widely reduced as shown by a graph D2
in FIG. 19, and the exhaust gas temperature becomes too high.
[0132] On the contrary, in the case that the overlap period OL is
shortened as shown by a graph D3, and the re-opening period (a
range of a crank angle .theta.1 in FIG. 3) in the compression
stroke first stage of the exhaust valve is executed by 60 degree in
accordance with the present invention, it is possible to obtain the
fresh air blow by rate in the same manner as that of the
conventional mass-produced cam D1 as shown in FIG. 19, as well as
it is possible to obtain the improvement of the heat efficiency as
described in FIG. 21, so that it is possible to prevent the exhaust
gas temperature from being increased, and it is possible to
maintain the exhaust gas load constant.
[0133] In the case that the overlap period OL is shortened as shown
by a graph D4, and the re-opening period (a range of .theta.1 in
FIG. 3) in the compression stroke first stage of the exhaust valve
is increased to 90 degree, it is possible to obtain the improvement
of the heat efficiency as described in FIG. 21, however, there is a
tendency that the fresh air blow by amount is increased too much in
the exhaust valve re-opening period.
[0134] Accordingly, in preferable, it is possible to achieve the
improvement of the heat efficiency, prevention of the exhaust gas
temperature from being increased and prevention of the fresh air
blow by from being too much, by setting the exhaust valve
re-opening period .theta.1 in FIG. 3 to about 30 to 60 degree, as
well as shortening the overlap period OL.
[0135] FIG. 22 shows a relation between a cylinder residual gas
rate and the overlap period OL. When the overlap period OL is
shortened, the cylinder residual gas rate is increased, whereby it
is possible to achieve the internal EGR effect and it is possible
to intend to reduce the NOx.
[0136] (Industrial Applicability)
[0137] The present invention can be also utilized in gas and
gasoline direct injection type internal combustion engines.
* * * * *