JP2001336435A - Six-cycle internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a six-cycle internal combustion engine with intake and exhaust and engine control mechanisms of simple structure, thereby inhibiting the increase in costs and making the engine operate more efficiently so as to enhance fuel economy and emission control properties. SOLUTION: A six-cycle internal combustion engine performs in sequence a series of operations of an intake stroke, a first compression stroke, a first expansion stroke, a second compression stroke, a second expansion stroke, and an exhaust stroke. The engine is so constituted that it has a first combustion stage where the fuel is burned in the state of a thin layer at a lean air-fuel ratio through the intake stroke, the first compression stroke, and the first expansion stroke, and a second combustion stage where an additional fuel is injected into the gas burned in the first combustion stage, and at the same time, the additional fuel is burned through the second compression stroke and the second expansion stroke.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a six-cycle internal combustion engine suitable for use in a direct injection internal combustion engine.

[0002]

2. Description of the Related Art In recent years, there has been proposed a technique for purifying exhaust gas by making a combustion cycle unique to a 6-cycle in-cylinder injection internal combustion engine so that more complete combustion can be realized. For example, Japanese Patent Application Laid-Open No. 9-291830 discloses that the first intake stroke → compression stroke → expansion stroke → first exhaust stroke → second intake stroke → second exhaust stroke in order of six strokes in total. A direct injection six-cycle gasoline engine that completes a combustion cycle is disclosed. According to this technique, the intake stroke and the exhaust stroke are each performed twice within one combustion cycle, and the exhaust gas after combustion is completely removed from the cylinder to prepare for the next combustion. Is approaching complete combustion to improve combustion efficiency and promote exhaust gas purification.

Japanese Patent Application Laid-Open No. H11-62614 discloses that one combustion cycle is completed in a total of six strokes in the order of an intake stroke, a first compression stroke, a decompression stroke, a second compression stroke, an expansion stroke, and an exhaust stroke. A six-stroke direct injection engine is disclosed. According to this technique, the liquid fuel injected in the first compression stroke is once vaporized in the first compression stroke, so that uniform mixing with the fuel air is realized, thereby increasing the combustion efficiency and generating graphite. Can be suppressed.

Japanese Patent Application Laid-Open No. 11-62614 further discloses a pressure reduction stroke → first compression stroke → intake stroke → second stroke.
There is also disclosed a six-cycle direct injection engine that completes one combustion cycle in a total of six strokes in the order of compression stroke → expansion stroke → exhaust stroke. According to this technology, the liquid fuel injected in the decompression process is vaporized by the decompression process, so that uniform mixing of the fuel and the air is realized, thereby increasing the combustion efficiency and suppressing the generation of graphite. Become.

[0005]

However, the technology described in each of the above publications can promote the purification of exhaust gas by improving the combustion efficiency, but combustion is performed only once in six cycles. Therefore, the output is likely to be insufficient, and if the intake and exhaust are performed twice, the pumping loss will increase, causing the efficiency of the engine to deteriorate, and the exhaust gas purification will be limited.

The present invention has been made in view of the above problems, and has been made to improve the fuel efficiency and exhaust gas performance by operating an engine efficiently.
It is an object to provide a cycle internal combustion engine.

[0007]

Therefore, in the six-stroke internal combustion engine according to the present invention, the intake stroke, the first compression stroke, the first expansion stroke, the second compression stroke, the second expansion stroke,
The exhaust stroke is sequentially performed. First, as the first combustion process, the fuel is subjected to the lean stratified combustion at a lean air-fuel ratio through the intake stroke, the first compression stroke, and the first expansion stroke, and then the second combustion process is performed. The additional fuel is injected into the burned gas generated in the first combustion process, and the additional fuel is burned through the second compression stroke and the second expansion stroke.

Accordingly, the intake and exhaust strokes with pumping loss are performed once every six cycles, whereas the combustion that generates output is performed twice every six cycles. Therefore, the efficiency is higher than in four cycles. The fuel efficiency is also improved. Further, in the second combustion process, the additional fuel is injected into the high-temperature burned gas generated in the first combustion process. Therefore, the additional fuel is quickly vaporized and decomposed in a high-temperature atmosphere to be activated, and extremely easily burned. Become. For this reason, in the second combustion process, re-reaction of the unburned gas is promoted, and highly efficient combustion can be realized.
The emission of NOx and HC can be sufficiently suppressed.

Moreover, in the first combustion step, the combustion is performed at a lean air-fuel ratio, so that the pumping loss is reduced and more efficient combustion can be realized. After the first combustion step, the burned gas contains a large amount of oxygen. Since it remains, the combustion efficiency in the second combustion process can be further improved. In addition, in the first combustion process, lean stratified combustion is performed, so that more efficient combustion can be realized. After the first combustion process, unburned matter and oxygen are more likely to coexist, and the second combustion process has The combustion efficiency can be further improved.

In the six-stroke internal combustion engine according to the present invention, the intake stroke, the first compression stroke, the first expansion stroke, the second compression stroke, the second expansion stroke, and the exhaust stroke are sequentially executed. As a first combustion process, the fuel is burned through the above-described intake stroke, first compression stroke, and first expansion stroke.
As a combustion process, additional fuel is injected into the burned gas generated in the first combustion process, and the additional fuel is burned through the second compression stroke and the second expansion stroke. On this occasion,
Control is performed so that the total air-fuel ratio of the fuel burned in the first combustion process and the fuel burned in the second combustion process becomes stoichiometric.

Therefore, the intake and exhaust strokes with pumping loss are performed once every six cycles, whereas the combustion that generates output is performed twice every six cycles. Therefore, the efficiency is higher than in four cycles. The fuel efficiency is also improved. Further, in the second combustion process, the additional fuel is injected into the high-temperature burned gas generated in the first combustion process. Therefore, the additional fuel is quickly vaporized and decomposed in a high-temperature atmosphere to be activated, and extremely easily burned. Become. For this reason, in the second combustion process, re-reaction of the unburned gas is promoted, and highly efficient combustion can be realized.
The emission of NOx and HC can be sufficiently suppressed. As a result, both low fuel consumption and exhaust gas purification can be achieved at a high level.

Further, since the total air-fuel ratio of the fuel burned in the first combustion process and the fuel burned in the second combustion process is stoichiometric, the exhaust gas can be efficiently purified and the three-way catalyst and the air-fuel ratio feedback control can be performed. Easy application. In this case, an exhaust air-fuel ratio detecting means is provided, and the amount of the additional fuel injection is set so that the sum of the fuel burned in the first combustion process and the fuel burned in the second combustion process becomes stoichiometric with respect to the intake air amount. Is preferably controlled, whereby the exhaust air-fuel ratio can be feedback controlled efficiently and stoichiometrically.

In the six-stroke internal combustion engine of the present invention, the intake stroke, the first compression stroke, the first expansion stroke, and the second
The compression stroke, the second expansion stroke, and the exhaust stroke are sequentially performed. First, as the first combustion process, the intake stroke, the first compression stroke,
The fuel is burned through a first expansion stroke, and then, as a second combustion process, additional fuel is injected into the burned gas generated in the first combustion process, and the second compression stroke and the second expansion stroke are performed. Then, the additional fuel is burned. At this time, the combustion in the first combustion process is spark ignition combustion, and the combustion in the second combustion process is compression ignition combustion.

Therefore, the intake and exhaust strokes with pumping loss are performed once every six cycles, whereas the combustion that generates output is performed twice every six cycles. Therefore, the efficiency is higher than that in four cycles. The fuel efficiency is also improved. Further, in the second combustion process, the additional fuel is injected into the high-temperature burned gas generated in the first combustion process. Therefore, the additional fuel is quickly vaporized and decomposed in a high-temperature atmosphere to be activated, and extremely easily burned. Become. For this reason, in the second combustion process, re-reaction of the unburned gas is promoted, and highly efficient combustion can be realized.
The emission of NOx and HC can be sufficiently suppressed. As a result, both low fuel consumption and exhaust gas purification can be achieved at a high level.

Furthermore, since the combustion in the first combustion process is spark ignition combustion, the combustion timing in the first combustion process can be appropriately controlled, and the combustion in the second combustion process is compression ignition combustion (self ignition). Therefore, the emission levels of NOx and HC can be efficiently reduced. In this case, it is preferable to inject the additional fuel between the latter half of the first expansion stroke and the latter half of the second expansion stroke, whereby the mixture of the burned gas and the additional fuel can be made more uniform, Combustion in the second combustion process can be surely made as homogeneous charge compression ignition combustion, and NOx or H
The C emission level can be reduced more efficiently.

In the fuel injection in the first combustion step, it is preferable that the fuel be injected directly into the cylinder of the internal combustion engine in the first compression stroke. Unburned matter and oxygen are more likely to coexist in the combustion gas, and the combustion efficiency in the second combustion process can be further improved. Further, in the additional fuel injection in the second combustion process, it is preferable that fuel be directly injected into a cylinder of the internal combustion engine in the first expansion stroke, the second compression stroke, or both strokes, Thereby, the additional fuel can be efficiently burned.

When the engine is under a high load, the operation may be changed to a four-cycle operation in which combustion is performed once every four cycles. In this case, the output can be efficiently secured when the engine is under a high load. Further, in the inventions according to the first and second aspects, if the combustion in the second combustion process is spark ignition combustion, the combustion timing in the second combustion process can be appropriately controlled, and CO ₂ is diluted and NO
The emission level of x can be efficiently reduced. Furthermore, if the combustion in the first combustion process is spark ignition combustion,
Combustion timing can be appropriately controlled, and combustion can be performed more reliably.

Alternatively, if the combustion in the second combustion process is compression ignition combustion, the emission levels of NOx and HC emissions can be efficiently reduced. Also in this case, it is preferable that the combustion in the first combustion process is spark ignition combustion so that the combustion timing can be appropriately controlled and combustion is performed more reliably.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIGS. 1 to 6 show a six-cycle internal combustion engine as an embodiment of the present invention.
First, a configuration of a direct injection type 6-cycle internal combustion engine (hereinafter, also referred to as a 6-cycle engine or simply an engine) according to the present embodiment will be described.

As shown in FIG. 1, the cylinder head 2 of the engine 1 has a spark plug 4 for each cylinder 3 and a fuel injection valve 6 as a fuel injection means which opens directly into the combustion chamber 5.
The ignition plug 4 is driven by an ignition coil 4A, and the fuel injection valve 6 is driven by a driver 6A.
A piston 8 connected to a crankshaft 7 is provided in the cylinder 3, and a hemispherically concave cavity 9 is formed on a top surface of the piston 8.

The cylinder head 2 has an intake port 11 that can communicate with the combustion chamber 5 through an intake valve 10 and an exhaust port 13 that can communicate with the combustion chamber 5 through an exhaust valve 12. The intake port 11 is disposed substantially vertically above the combustion chamber 5, and cooperates with the cavity 9 on the top surface of the piston 8 to form a reverse tumble flow by intake air in the combustion chamber 5. A water temperature sensor 16 for detecting a cooling water temperature is provided on a water jacket 15 on the outer periphery of the cylinder 3, and a crank angle sensor 17 for outputting a signal at a predetermined crank angle position is provided on the crankshaft 7. Each of the camshafts 18 and 19 for driving the cylinder 12 is provided with a cylinder identification sensor (cam angle sensor) 20 for outputting a cylinder identification signal according to the position of the camshaft.

The camshafts 18, 19 and the intake valve 1
0 and an exhaust valve 12, a variable valve operating mechanism 41 is provided, which operates in a mode corresponding to a general four-cycle operation, that is, when the crankshaft 7 rotates twice, the intake valve 10 and the exhaust valve A mode in which each of the valves 12 makes one rotation,
An operation mode corresponding to the 6-cycle operation described later, that is,
When the crankshaft 7 rotates three times, the mode in which both the intake valve 10 and the exhaust valve 12 make one rotation can be selectively switched. Since various known mechanisms can be applied to the variable valve mechanism 41, the description is omitted.

The intake system includes an air cleaner 21,
Intake pipe 22, throttle body 23, surge tank 2
4, the intake manifold 25 is arranged in this order, and the intake port 11 is provided at the downstream end of the intake manifold 25. The throttle body 23 is provided with an electronically controlled throttle valve (ETV) 30 as air amount adjusting means for adjusting the amount of air flowing into the combustion chamber 5.
The opening degree control of 0 can perform not only control according to the accelerator opening degree, but also idle speed control and control for introducing a large amount of intake air during lean operation, which will be described later. Further, an air flow sensor 37 for detecting an intake air flow rate is provided immediately downstream of the air cleaner 21, a throttle position sensor 38 for detecting a throttle opening of the ETV 30 and a fully closed ETV 30 for the throttle body 23 to output an idle signal. An output idle switch 39 is provided.

The exhaust system includes an exhaust manifold 26 having an exhaust port 12 and an exhaust pipe 27 in this order from the upstream side. A three-way catalyst 29 for purifying exhaust gas is interposed in the exhaust pipe 27, and the exhaust manifold 26 is provided in the exhaust manifold 26. , O ₂ sensor 40 are provided. Although the fuel supply system is not shown, the pressure is a predetermined high pressure [several tens of atmospheres (for example, 2 to 7MPa).
a) is adjusted to the fuel injection valve 6,
High-pressure fuel is injected from the fuel injection valve 6.

Then, the spark plug 4, the fuel injection valve 6, E
In order to control the operation of each engine control element such as the TV 30, an electronic control unit (ECU) 60 having a function as control means of the internal combustion engine is provided. The ECU 60 includes an input / output device, a storage device for storing a control program, a control map, and the like, a central processing unit, a timer and a counter, and the like. The ECU 60 controls each of the above-described engine control elements based on position information and the like.

In particular, the present engine is a direct injection engine, which can perform fuel injection at an arbitrary timing, performs uniform mixing and uniform combustion by fuel injection mainly in the intake stroke, and also performs injection mainly in the compression stroke. By the fuel injection, stratified combustion can be performed using the above-mentioned reverse tumble flow. The operation mode related to the air-fuel ratio of the present engine includes a stoichiometric operation mode in which the air-fuel ratio is kept close to the stoichiometric air-fuel ratio by feedback control based on information detected by the O ₂ sensor 40, and an air-fuel ratio richer than the stoichiometric air-fuel ratio. An enrich operation mode and a lean operation mode in which the air-fuel ratio is made leaner than the stoichiometric air-fuel ratio to perform lean combustion are provided.

The above-mentioned enrichment operation mode includes
This is a general four-cycle operation in which the combustion cycle is performed by four strokes of an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke. In the case of the present engine, the compression stroke and the expansion stroke are each performed twice in one combustion cycle. Cycle operation is also possible, and the above-mentioned lean operation mode includes this six-cycle operation. This 6 cycle operation mode
Two combustion processes, a first combustion process mainly composed of stratified combustion and a second combustion process mainly composed of uniform combustion, are provided in one combustion cycle. In the stoichiometric operation mode, the low load region (target Pe) in the stoichiometric operation mode region is used.
There 6 cycles operating at less than the predetermined value Pe ₀₎ is executed, the high-load region (target Pe stoichiometric operation mode area is 4-cycle operation at a predetermined value Pe ₀ or more) is performed. In addition,
In the six-cycle stoichiometric operation mode, the total air-fuel ratio is controlled to stoichiometric.

In the ECU 60, based on a map (not shown), one of the operation modes according to the engine rotation speed (hereinafter referred to as the engine rotation speed) Ne and the target value (target Pe) of the average effective pressure Pe indicating the engine load state. When the engine speed Ne is small and the target Pe is very small, the lean operation mode (6 cycles) or the compression lean operation mode (4 cycles) is selected, and the engine speed Ne and the target Pe are changed. As the number increases, the operation mode is selected in the order of stoichiometry (6 cycles), stoichiometry (4 cycles), and enrichment (4 cycles). At this time, switching between the four cycles and the six cycles is performed using the variable valve mechanism 41.

As described above, in the case of this engine, the mode of the six-cycle operation is performed when the target Pe is a partial load except for a high load having a predetermined value Pe ₀ or more. Here, the six-cycle operation of the engine will be described. As shown in FIG.
The first compression stroke, the first expansion stroke, the second compression stroke, the second expansion stroke, and the exhaust stroke are sequentially executed, and the fuel is emptied through the intake stroke, the first compression stroke, and the first expansion stroke. A first combustion process of performing lean stratified combustion at a fuel ratio; and a second combustion process of injecting additional fuel into burned gas generated in the first combustion process to burn the additional fuel through a second compression stroke and a second expansion stroke. It has two combustion processes. Each of these steps is shown in Figure 4 (Figure 4 is a log-log graph)
As shown in the PV diagram of FIG.

As shown in FIG. 2, in the first combustion process, fuel injection can be performed at any time during the intake stroke or the first compression stroke. An example is shown in which the main fuel injection (first injection) is performed during the compression stroke. In the first combustion process, fuel injection can be performed at any time during the first expansion stroke and the second compression stroke. However, in this embodiment, additional fuel is injected during the first expansion stroke. An example is shown in which injection (second injection) is performed.

In the six-cycle stoichiometric operation mode, the ECU 60 sets the main fuel injection (first injection).
And the additional fuel injection (second injection) controls the total fuel injection amount so that the total amount of injected fuel gives stoichiometric (stoichiometric air-fuel ratio) to the amount of air taken in during the intake stroke. It is supposed to. In the present embodiment, approximately a little less than half of fuel is injected by the main fuel injection (that is, the in-cylinder equivalence ratio is set to approximately 0.5), and the remaining approximately half of the slightly more amount is injected by additional fuel injection. By injecting fuel (that is, the in-cylinder equivalent ratio is set to 1.0),
The stoichiometric operation is performed.

That is, in order to make the total air-fuel ratio (intake air amount / total amount of injected fuel) stoichiometric, the fuel injection amount is feedback-controlled based on the information detected by the O ₂ sensor 40 as in the general stoichiometric operation. It is sufficient that the total amount of the injected fuel can be set by the same feedback control as in the general stoichiometric operation. Then, the main fuel injection and the additional fuel injection may be performed by injecting half the amount of the set total amount of the injected fuel.

Further, in order to perform the stoichiometric operation in six cycles with higher accuracy, a provisional total amount of the injected fuel is set from the information of the O ₂ sensor 40 obtained before the time of the main fuel injection, and based on this, Amount (here, the sum of 1
) (A little less than / 2) (the first injection), and the final total amount of the injected fuel is set from the information of the O ₂ sensor 40 obtained immediately before the subsequent additional fuel injection, and the total amount is set. Additional fuel is injected with the amount obtained by subtracting the first injection from the amount (2
The second injection).

In the lean operation mode, the first injection amount and the second injection amount are determined according to the target Pe and the engine speed Ne so that the total amount of the injected fuel becomes lean with respect to the intake air amount. At the same time, the intake air amount is controlled by the electronic throttle. Further, in the present embodiment, as shown in FIG. 2, in the first combustion process, ignition is performed by the spark plug 4 immediately before the top dead center of the first compression stroke, and in the second combustion process, the second compression stroke is performed. Immediately before top dead center. However, in the second combustion process, if the in-cylinder temperature is sufficiently high, self-ignition occurs in the compression stroke. Therefore, if combustion can be reliably performed by compression self-ignition, ignition by the ignition plug 4 is performed as shown in FIG. Try not to do it. Whether or not compression self-ignition is possible depends on the engine speed, engine load, the ratio of the first and second fuel injection amounts, and the like. In the case of a gasoline engine, in the first combustion process, the in-cylinder temperature generally does not become so high as to cause self-ignition.

In the stoichiometric operation mode, when the load is high or in the enrichment operation mode, normal four-cycle operation is performed instead of six-cycle operation. Since the six-cycle internal combustion engine as one embodiment of the present invention is configured as described above, the target Pe is set to the predetermined value Pe _0.
At a partial load of less than, as shown in FIG. 2, six cycles of operation are performed in the order of the intake stroke, the first compression stroke, the first expansion stroke, the second compression stroke, the second expansion stroke, and the exhaust stroke.

That is, first, when the piston 8 is lowered, the intake valve 10 is opened (the exhaust valve 12 is closed, of course) to suck air (intake stroke). Next, when the piston 8 rises, both the intake valve 10 and the exhaust valve 12 are closed, and as shown in FIG. 5A, fuel is injected from the fuel injection valve 6 (main fuel injection) while the piston 8 rises. (First compression stroke). In the stoichiometric operation mode, this main fuel injection is performed so that the air-fuel ratio becomes approximately に 対 し て of the stoichiometric amount with respect to the amount of air taken in during the intake stroke so that the in-cylinder equivalent ratio becomes approximately 0.5.
Amount of fuel is injected. Further, in the case of the lean operation mode, approximately 1 / l of the fuel amount corresponding to the target lean air-fuel ratio.
Two quantities of fuel are injected.

Further, when the piston 8 reaches the vicinity of the compression top dead center, spark ignition is performed by the spark plug 4. Thus, the first combustion is performed as shown in FIG. As shown in FIG. 5C, the first combustion is performed by collecting a ignitable mixture having a high fuel concentration near the spark plug 4 while keeping the overall air-fuel ratio lean. (Stratified combustion), and the first expansion stroke is performed.

As shown in FIG. 5D, during the first expansion stroke after the first combustion (first combustion process), or during the second compression stroke (not shown), the high-temperature burned gas is discharged. When additional fuel is injected into the cylinder, the fuel, many active species (combustible components) in the burned gas, and excess oxygen coexist in a high-temperature atmosphere in the cylinder. In the subsequent second compression stroke, the high-temperature gas is compressed, so that the decomposition of the fuel is promoted at a high temperature and a high pressure, and the mixing of the air and the fuel is also promoted, as shown in FIG. Thus, if spark ignition is performed by the spark plug 4 near the top dead center of the second compression stroke, the second combustion (second combustion process) is performed extremely efficiently.

If the in-cylinder temperature is sufficiently high, FIG.
As shown in (f), the end of the compression stroke (near top dead center of the second compression stroke) without spark ignition by the spark plug 4.
The fuel in the cylinder is ignited by the temperature and pressure. In this case, if the interval from the end of the additional fuel injection to the top dead center of the second compression stroke is sufficient, the mixing of the fuel and the burned gas proceeds to form a homogeneous mixture, and the mixture in the cylinder (combustion chamber)
The multi-point self-ignition ignited at each part in the inside makes the second combustion (second combustion process) extremely efficient.

According to the six-cycle operation of the present engine performed as described above, the lean stratified spark ignition combustion (combustion in the first combustion process) by the compression stroke injection (main fuel injection) immediately after the intake stroke has a pumping loss. Small and highly efficient combustion. In the combustion in the second combustion process performed immediately after the combustion in the first combustion process, fuel is further injected into a high-temperature burned gas containing a large amount of highly active unburned matter and oxygen during the reaction, The injected fuel itself is rapidly vaporized and decomposed and activated in a high-temperature atmosphere, so that it becomes extremely easy to burn. According to this combustion (combustion in the second combustion process), HC
Since the above-mentioned unburned matter containing NOx and NOx also reacts at the same time, the operation becomes extremely efficient, and the component (emission) to be purified in the exhaust gas becomes extremely low.

When the combustion in the second combustion process is performed by spark ignition, NOx in the residual gas is changed to CO2 in the residual gas.
_{It can} be diluted by ₂ to lower NOx emission levels. On the other hand, when the combustion in the second combustion process is performed by the compression ignition, since the multi-point ignition of the premixed gas is performed as described above, the emission amounts of both NOx and HC can be extremely low. , Combustion efficiency is increased.

Further, since the exhaust gas resulting from the first combustion process and the second combustion process is discharged in the exhaust stroke after the combustion as described above, the actual emission discharged outside the engine is extremely low. become. In particular, in the six-cycle stoichiometric operation mode, the feedback control by the O ₂ sensor can be applied as described above, and the three-way catalyst 29 which generally has a high exhaust gas purification rate of about 95% can be applied. Emissions emitted from 27 are further reduced.

In addition, the intake and exhaust strokes with pumping loss are performed once in each of six cycles (six strokes), which is two thirds of that in the case of a four-stroke engine, and the combustion that generates output is two in six cycles (six strokes). Since the number of times is four times, which is three-fourths of the case of a four-cycle engine, the efficiency is higher than that of a four-cycle engine, so that good fuel economy characteristics can be obtained.

Further, it is possible to abolish the introduction of the external EGR into the intake system, and it is possible to avoid the contamination of the intake system and the accumulation of carbon in the intake system. Further, since the lean NOx catalyst can be eliminated, the cost can be reduced and the control of the engine can be simplified.
FIG. 6 is a diagram showing NOx emissions, HC emissions, and net fuel consumption rates.
The line relates to four-cycle lean stratified combustion, and the line c relates to the present six-cycle operation. 1 is for NOx emission,
2 relates to the amount of HC emissions, and 3 relates to the net fuel efficiency.
FIG. 6 shows that according to the six-cycle operation, the NOx emission, HC emission, and net fuel efficiency are improved in a wide shaft torque range (engine load range).

Incidentally, the six-cycle internal combustion engine of the present invention is not limited to the above embodiment, and can be implemented in various modifications without departing from the spirit of the present invention. For example, in the above embodiment, the injection timing of the additional fuel is performed during the first expansion stroke. However, the injection timing of the additional fuel is determined during the first compression stroke as shown in FIGS. Even if the process is performed from the stroke to the second compression stroke, it is conceivable that the additional fuel may be sufficiently activated or mixed with the air, and such a setting is also possible.

In the above-described embodiment, the main fuel injection (first injection) is made slightly less than half of the total amount (0.5 in equivalent ratio).
However, the lean stratified combustion performed in the first combustion process is difficult to burn with a large amount of inert gas if the equivalent ratio is too large, and stable ignition cannot be performed if the equivalent ratio is too small. It is desirable to set it in the range of about 0.1 to 0.5, and it can be set appropriately within such a range.

However, the ratio between the first injected fuel amount and the second injected fuel amount depends on the vibration caused by the difference between the first combustion and the second combustion and the high-temperature self-ignition of the second combustion. Affects residual gas volume and temperature to achieve. If the first injection fuel amount is made too rich, the residual gas concentration becomes excessive (corresponding to an EGR rate of 100% at an equivalent ratio of 0.5). Therefore, the first injection fuel amount may be limited from this point as well. It is necessary, and in consideration of these, it is desirable to limit the first injected fuel amount and increase the second injected fuel amount accordingly.

Also, in this embodiment, only 6
Although the cycle is applied, this takes into account that if the load is large, the intake amount becomes insufficient, and the advantage of 6 cycles cannot be obtained. For example, due to supercharging, a sufficient intake amount can be obtained even in a large load region. If it is obtained, six-cycle operation may be applied to a large load region. In this case, as shown by the chain line in FIG. 6, even when the shaft torque is large (high engine load), the net fuel efficiency is improved.

Further, a configuration in which all the six-cycle operation regions are set to the stoichiometric operation or a configuration in which only the six-cycle operation is performed (the four-cycle operation is not performed) is also conceivable.

[0050]

As described above in detail, according to the six-stroke internal combustion engine of the present invention according to the first to third aspects, the intake and exhaust strokes with pumping loss are performed once every six cycles. Since the combustion that generates output is performed twice in six cycles, the efficiency and fuel efficiency are improved as compared with four cycles, and the high temperature burned gas generated in the first combustion process is obtained in the second combustion process. Since the additional fuel is injected into the fuel, the additional fuel is rapidly vaporized and decomposed in a high-temperature atmosphere and activated, and becomes extremely easy to burn, and promotes the re-reaction of the unburned gas to achieve high-efficiency combustion. As a result, the emission of NOx and HC can be sufficiently suppressed. As a result, both low fuel consumption and exhaust gas purification can be achieved at a high level.

Further, according to the six-stroke internal combustion engine of the present invention, in the first combustion process, the lean stratified combustion is performed, so that the pumping loss is reduced and the combustion is more efficiently performed. Can be realized, and the unburned matter and oxygen can coexist more easily after the first combustion process, and the combustion efficiency in the second combustion process can be further improved.
According to the six-stroke internal combustion engine of the present invention, the total air-fuel ratio of the fuel burned in the first combustion process and the fuel burned in the second combustion process is stoichiometric, so that the exhaust gas is efficiently exhausted. Purification can be performed, and application of three-way catalyst and air-fuel ratio feedback control becomes easy.

Further, according to the six-cycle internal combustion engine of the present invention, the combustion timing in the first combustion process can be appropriately controlled, and the combustion can be reliably performed. The emission levels of NOx and HC can be reduced more efficiently.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a six-cycle internal combustion engine as one embodiment of the present invention.

FIG. 2 is a time chart showing an operation of a six-cycle internal combustion engine as one embodiment of the present invention.

FIG. 3 is a time chart showing an operation of a six-cycle internal combustion engine as one embodiment of the present invention.

FIG. 4 is a PV diagram showing an operation of the six-cycle internal combustion engine as one embodiment of the present invention.

FIG. 5 is a schematic sectional view showing the operation of a six-cycle internal combustion engine as one embodiment of the present invention in the order of (a) to (f).

FIG. 6 is a diagram showing an effect of a six-cycle internal combustion engine as one embodiment of the present invention.

FIG. 7 is a time chart showing an operation of a modified example of the six-cycle internal combustion engine as one embodiment of the present invention.

FIG. 8 is a time chart showing an operation of a modified example of the six-cycle internal combustion engine as one embodiment of the present invention.

[Explanation of symbols]

 1 6-cycle internal combustion engine (engine) 4 Spark plug 6 Fuel injection valve 41 Variable valve mechanism 60 ECU

Continuing from the front page (72) Inventor Osamu Nakayama 5-33-8 Shiba, Minato-ku, Tokyo Inside Mitsubishi Motors Corporation (72) Inventor Hiromitsu Ando 3-33-8 Shiba 5-minute, Minato-ku, Tokyo Mitsubishi Motors Corporation F term in the company (reference) 3G301 HA00 HA04 JA02 JA24 JA25 JA26 ND01 NE14 PA01Z PA11Z PC02A PC02Z PD13Z PE01Z

Claims (3)

[Claims] 1. A six-stroke internal combustion engine that sequentially executes an intake stroke, a first compression stroke, a first expansion stroke, a second compression stroke, a second expansion stroke, and an exhaust stroke. A first combustion process in which fuel is subjected to lean stratified combustion at a lean air-fuel ratio through a first expansion stroke; and additional fuel is injected into burned gas generated in the first combustion process, and the second compression stroke, A six-stroke internal combustion engine comprising a second combustion step of burning the additional fuel through a second expansion stroke. 2. A six-stroke internal combustion engine that sequentially executes an intake stroke, a first compression stroke, a first expansion stroke, a second compression stroke, a second expansion stroke, and an exhaust stroke, wherein the intake stroke, the first compression stroke, and the first compression stroke. A first combustion process in which fuel is burned through a first expansion process, additional fuel is injected into the burned gas generated in the first combustion process, and a second combustion process is performed through the second compression process and the second expansion process. A second combustion process for burning the additional fuel, wherein the total air-fuel ratio of the fuel burned in the first combustion process and the fuel burned in the second combustion process is controlled to be stoichiometric. 6-cycle internal combustion engine. 3. A six-stroke internal combustion engine that sequentially executes an intake stroke, a first compression stroke, a first expansion stroke, a second compression stroke, a second expansion stroke, and an exhaust stroke, wherein the intake stroke, the first compression stroke, and the first compression stroke. A first combustion process in which fuel is burned through a first expansion process, additional fuel is injected into the burned gas generated in the first combustion process, and a second combustion process is performed through the second compression process and the second expansion process. A second combustion process for burning the additional fuel, wherein the combustion in the first combustion process is spark ignition combustion, and the combustion in the second combustion process is compression ignition combustion. Internal combustion engine.