JP2003074395A - Compression self-ignition type internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform a compression self-igniting combustion in an wide operation range. SOLUTION: A subsidiary chamber 10 communicated with a combustion chamber 1 through an open/close valve 11 and a subsidiary chamber fuel injection valve 12 injecting fuel to the subsidiary chamber are arranged. The open/ close valve 11 is opened and closed in a final stage of an expansion stroke before an exhaust valve 9 opens, and the burnt gas is filled up with in the subsidiary chamber 10. Fuel is reformed in the subsidiary chamber 10 by injecting the fuel from the subsidiary chamber fuel injection valve 12 during gas exchange in the combustion chamber 1 in the exhaust and the intake strokes afterward. The open/close valve 11 is opened and closed in a starting stage of a compression stroke after an intake valve 3 is closed, and the burnt gas and the reformed fuel are supplied to the combustion chamber 1. At this time, the smaller the engine load is the more the supply period of the burnt gas and the reformed fuel to the combustion chamber 1 is delayed by controlling the opening period of the valve 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compression self-ignition internal combustion engine in which fuel in a combustion chamber is made to burn by compression self-ignition.

[0002]

2. Description of the Related Art In an internal combustion engine that uses gasoline having a low ignitability as a fuel, it has been proposed to perform ignition combustion by compression self-ignition without ignition from the viewpoint of high efficiency and low emission. As such a compression self-ignition type internal combustion engine, for example, Japanese Patent Laid-Open No. 11-3438.
There is one disclosed in Japanese Patent Publication No. 74.

In this fuel cell, an auxiliary chamber communicating with the combustion chamber through an on-off valve is provided, and burned gas having a temperature higher than that of the auxiliary chamber is supplied to the combustion chamber in a stratified state, so that a gasoline mixture with poor ignitability is obtained. Is self-ignited by compression. In particular,
At the end of the expansion stroke, the open / close valve is opened to fill burned gas into the sub-chamber, and the open / close valve is opened again when the pressure in the combustion chamber during the intake stroke or compression stroke is lower than that in the sub-chamber. The fuel gas is stratified and supplied to the combustion chamber.

[0004]

However, the above-mentioned prior art does not clearly define the timing of introducing burnt gas into the combustion chamber, and the intake valve is opened during the intake stroke. Since the on-off valve is opened and burnt gas is introduced from the sub-chamber, it is possible to secure an increase in the in-cylinder average temperature required to ignite the air-fuel mixture in the compressed self-ignition fuel by filling burnt gas. However, the total amount of gas (the number of moles) in the cylinder necessary to improve the average effective pressure cannot be increased. Also, from the viewpoint of performing stable operation in the low load region, increasing the average temperature in the cylinder alone is not sufficient to maintain sufficient ignitability.

For this reason, the operating range in which the compression self-ignition combustion is performed is limited. The present invention has been made in view of such a problem, and an object thereof is to provide a compression self-ignition internal combustion engine capable of performing compression self-ignition combustion in a wide operating range.

[0006]

Therefore, the invention according to claim 1 is a compression self-ignition type internal combustion engine in which a reformed fuel is supplied into the combustion chamber and is combusted by compression self-ignition. It is characterized in that the supply timing to the engine is delayed as the load on the engine decreases.

The invention according to claim 2 is provided with a sub-chamber communicating with the combustion chamber via an on-off valve, and a sub-chamber fuel injection valve for injecting fuel into the sub-chamber. The fuel is reformed by injecting the fuel into the burned gas filled in the sub chamber by the sub chamber fuel injection valve, and the reformed fuel is supplied into the combustion chamber.

The invention according to claim 3 is characterized in that the supply timing of the reformed fuel to the combustion chamber is controlled by the opening / closing timing of the opening / closing valve. The invention according to claim 4 is characterized in that the on-off valve is opened at the beginning of the compression stroke after the intake valve of the engine is closed and at the end of the expansion stroke before the exhaust valve is opened. .

The invention according to claim 5 is characterized in that the opening timing of the opening / closing valve after closing the intake valve is delayed as the load of the engine is reduced. The invention according to claim 6 is characterized in that the opening timing of the on-off valve before the exhaust valve is opened is advanced as the load of the engine is smaller.

The invention according to claim 7 is characterized in that the opening timing of the opening / closing valve after closing the intake valve and opening timing before opening of the exhaust valve are advanced as the rotational speed of the engine is high. The invention according to claim 8 is characterized in that the opening degree of the opening / closing valve is increased as the rotational speed of the engine is increased.

The invention according to claim 9 is characterized in that the amount of fuel injected into the sub chamber is increased as the load of the engine is reduced. The invention according to claim 10 is characterized in that the sub chamber is provided on the exhaust port side of the engine.

The invention according to claim 11 is characterized in that the on-off valve is an electromagnetic valve.

[0013]

According to the first aspect of the present invention, the reformed fuel, which is easily ignited, is supplied to the combustion chamber, and the timing of supplying the reformed fuel is delayed as the load on the engine is reduced. The fuel can be locally distributed to increase the stratification degree of the fuel mixture in the cylinder.

As a result, ignitability can be improved, and good compression self-ignition performance can be secured even in the low load region. On the contrary, as the load of the engine increases, the total amount of gas in the combustion chamber also increases, and the temperature and pressure rise relatively quickly. Therefore, the supply timing of the reformed fuel is advanced accordingly. As a result, the reformed fuel can be supplied at an appropriate time according to the operating state, and the ignitability can be effectively improved.

According to the second aspect of the present invention, the sub-chamber is filled with burned gas by the opening / closing operation of the shut-off valve, and the sub-chamber fuel injection valve injects fuel into the filled high-temperature, high-pressure burned gas. By doing so, fuel with poor ignitability such as gasoline can be reformed into fuel that is easily ignited. Then, the reformed fuel (reformed fuel) can be supplied into the combustion chamber by opening the on-off valve.

According to the third aspect of the present invention, by controlling the opening / closing timing of the on-off valve, the reformed fuel can be supplied into the combustion chamber while optimally controlling the stratification degree of the fuel mixture in the cylinder. According to the invention of claim 4, the open / close valve is opened at the end of the expansion stroke before the exhaust valve of the engine is opened, so that the burned gas from the high pressure combustion chamber enters the sub chamber. Is filled. After that, the high temperature filled in the sub chamber,
By injecting fuel into the high-pressure burnt gas, the fuel with poor ignitability is used as the reformed fuel that is easily ignited. Then, by opening the on-off valve at the beginning of the compression stroke after the intake valve of the next stroke is closed, the burnt gas containing the reformed fuel is supplied from the auxiliary chamber to the combustion chamber.

The air-fuel mixture in the combustion chamber is heated by the burned gas thus supercharged, and is adiabatically compressed by the piston to reach a high temperature, and self-ignites near the compression top dead center. By repeating such a phenomenon, the supercharging pressure is increased, and good compression self-ignition performance can be secured. According to the invention of claim 5, the opening timing of the opening / closing valve after closing the intake valve is delayed as the load of the engine is smaller, so that the timing of supplying the burnt gas containing the reformed fuel to the combustion chamber is improved. By delaying, the stratification degree of the fuel mixture in the cylinder is increased. As a result, it is possible to improve the ignitability and ensure good compression self-ignition performance even in a low load region where compression self-ignition is relatively unlikely to occur.

According to the invention of claim 6, the open timing of the on-off valve before the exhaust valve is opened is set earlier as the load of the engine is smaller, so that the burned gas having high energy is filled in the sub-chamber. You can As a result, the fuel reforming effect of the fuel injected into the sub chamber can be enhanced, and good compression self-ignition performance can be secured.

According to the invention of claim 7, the opening timing of the on-off valve after the intake valve is closed and the opening timing before the exhaust valve is opened are
By increasing the rotation speed of the engine as it becomes faster, it is possible to secure the time required until ignition and to secure good compression self-ignition performance. According to the invention of claim 8, the opening degree of the on-off valve is increased as the rotation speed of the engine is higher, so that the higher the rotation speed of the engine is, the more the energy of burned gas is used in a shorter time. The salary effect can be increased. As a result, good compression self-ignition performance can be secured even in a high rotation region where it is difficult to secure the time until ignition.

According to the invention of claim 9, the amount of fuel injected into the sub-chamber is increased as the load of the engine is reduced, so that the reformed fuel amount is increased in the low load region where the ignitability deteriorates. Secure good compression self-ignition performance. According to the invention of claim 10, since the sub chamber is provided on the exhaust port side of the engine, the energy loss of the burnt gas filled in the sub chamber can be minimized.

According to the eleventh aspect of the invention, the opening / closing timing and the valve lift amount can be arbitrarily controlled by using the opening / closing valve as an electromagnetic valve.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention 4
It is a system diagram of a cycle type gasoline engine. In FIG. 1, an engine capable of switching between compression self-ignition combustion and normal spark ignition combustion in accordance with operating conditions is a combustion chamber 1, at least one intake port 2, and combustion at a downstream side of the intake port 2. An intake valve 3 arranged at the inlet of the chamber 1 and a piston 4
A fuel injection valve 5 provided in the intake port 2 for injecting fuel toward the intake valve 3, a spark plug 6 for performing spark ignition when performing spark ignition combustion, and an electronic control unit (ECU) for performing combustion control. 7 and at least one exhaust port 8
An exhaust valve 9 arranged at the outlet of the combustion chamber 1 on the upstream side of the exhaust port 8;
A sub-chamber 10 communicating with the sub-chamber 10 via an on-off valve 11;
And a sub-chamber fuel injection valve 12 for injecting fuel into the inside.

Although the fuel injection valve 5 is arranged so as to inject fuel into the intake port 2, it may be one which injects fuel directly into the combustion chamber 1. The ECU 7
Based on the engine rotation signal detected by the crank angle sensor (not shown) and the accelerator opening signal (load) detected by the accelerator opening sensor (not shown), either compression self-ignition combustion or spark ignition combustion is used. A combustion mode determination unit 13 that determines whether to perform operation, a spark ignition combustion control unit 14 that performs combustion control when performing spark ignition combustion, and a compression self-ignition combustion control that performs combustion control when performing compression self-ignition combustion. And a section 15.

The intake valve 3 and the exhaust valve 9 are variably controlled in opening / closing timing (valve timing) by an intake side cam shaft (not shown) and an exhaust side cam shaft (not shown).
In particular, there is provided a variable valve operating device capable of switching between valve timing control when performing spark ignition combustion and valve timing when performing compression self-ignition combustion. In addition,
As such a variable valve operating device, for example, Japanese Patent Application Laid-Open No. 9-
There is one disclosed in Japanese Patent No. 203307.

Then, the compression self-ignition combustion is performed in the engine rotation speed and load region as shown in FIG. 2, and the spark ignition combustion is performed in the other regions. Note that FIG.
Shows the valve timing control during compression self-ignition combustion (including valve timing control of the on-off valve 11), and FIG. 4 shows the valve timing control during spark ignition combustion.

As the opening / closing valve 11, an electromagnetically driven valve is used so that the opening / closing timing and the valve lift amount can be arbitrarily controlled. Here, various conditions for performing the compression self-ignition combustion will be described. In the compression self-ignition combustion, it is necessary to raise the temperature of the air-fuel mixture by the compression of the piston 4 and perform spontaneous ignition without performing spark ignition. When gasoline is used as the fuel, a compression ratio (for example, 12 or less) that does not impair the full load performance of spark ignition combustion cannot obtain the temperature at which spontaneous ignition occurs only by compression of the piston 4.

Therefore, it is necessary to heat the air-fuel mixture by some means before the start of compression, or to lower the temperature at which the fuel ignites. In the above conventional technique, in order to assist the compression self-ignition, the amount of burnt gas in the combustion chamber is increased to raise the temperature of the air-fuel mixture. In this case, since the temperature of the air-fuel mixture rises, the total number of moles of the fresh air and the residual burned gas is reduced.

Next, the load range of the compression self-ignition combustion will be described. Since compression self-ignition combustion occurs at multiple points in the combustion chamber space at the same time, if the local heat generation rate is high, the heat generation as a whole will be abrupt, causing a sudden pressure rise and producing a tapping sound. To do. To avoid this phenomenon,
It is necessary to increase the ratio of gas to fuel weight (hereinafter referred to as G / F) to slow the local heat generation rate. From experience, the limit G / F at which this tapping sound does not occur is about 30, and thus the amount of fuel that can be injected into the combustion chamber is limited according to the amount of gas in the combustion chamber. This means that the maximum load of compression auto-ignition combustion is limited.

In the above-mentioned conventional technique, in order to assist the compression self-ignition, the amount of burnt gas in the combustion chamber is increased to raise the temperature of the air-fuel mixture, so that the total number of moles of gas in the combustion chamber decreases. The maximum load of compression self-ignition combustion stays at a small value. Further, in the low load region, the air-fuel mixture is further diluted and burned, so that the deterioration of ignitability becomes noticeable, the combustion stability decreases, the amount of unburned fuel increases, and the exhaust performance and fuel consumption deteriorate. Invite. Further, even if the engine speed increases, the deterioration of ignitability becomes a problem.

In order to solve this problem, it is necessary to prevent the amount of fresh air from decreasing even if the amount of burnt gas in the combustion chamber is increased. That is, the burned gas may be supercharged. Further, in order to simultaneously achieve the improvement of the ignitability in the low load region and the high rotation region and expand the operating load range by the compression self-ignition combustion, it is only necessary to provide a means for reforming the fuel into a fuel that is easy to ignite. .

In the present invention, a high supercharging pressure can be generated irrespective of the conventional supercharging method such as a turbocharger or a supercharger. Furthermore, by utilizing this supercharging pressure and the high temperature of burnt gas. By reforming the fuel into a fuel that is easy to ignite, compression self-ignition combustion is possible in a wide range of operating load regions. Hereinafter, the compression self-ignition combustion according to the present embodiment will be described in detail.

First, the operation of the engine under partial load will be described step by step with reference to FIG. In the expansion stroke, the open / close valve 11 is opened before the exhaust valve 9 is opened, and then the open / close valve 11 is closed before the exhaust valve 9 is opened to fill the sub-chamber 10 with burned gas (FIG. 5 (D)). Then, as in a normal engine, gas is exchanged in the combustion chamber 1 by performing exhaust in the exhaust stroke and intake in the intake stroke (FIG. 5 (E),
(A)). During this gas exchange period, fuel is injected by the sub-chamber fuel injection valve 12 in the burned gas filled in the sub-chamber 10, and the fuel is easily ignited in the high-temperature and high-pressure space of the burned gas. It can be a reformed fuel.

Further, after closing the intake valve 3, the on-off valve 11
By opening, the burnt gas (including reformed fuel) in the sub chamber 10 is ejected and introduced into the combustion chamber 1 (FIG. 5).
(B)). As a result, the air-fuel mixture in the combustion chamber 1 is heated, and the heated air-fuel mixture is adiabatically compressed by the piston 4 to a high temperature and self-ignites near the compression top dead center (Fig. 5).
(C)), reaching the expansion stroke.

Before the exhaust valve 9 opens, the on-off valve 1 is opened again.
By opening and closing 1, the burnt gas is filled in the sub chamber 10 again. When the burned gas is introduced into the combustion chamber 1 from the sub chamber 10 at the beginning of the compression stroke, the pressure in the fuel chamber 1 increases to the same level as the pressure in the sub chamber 10. After that, when the on-off valve 11 is opened again at the end of the expansion stroke, the pressure in the combustion chamber 1 is higher due to combustion than when the on-off valve 11 is opened at the beginning of the compression stroke. For this reason, the pressure with which the burnt gas is filled in the sub-chamber 10 is increased by the on-off valve 11 at the beginning of the compression stroke.
It will be higher than when it was opened.

Therefore, at the beginning of the compression stroke of the next cycle, the burned gas is filled in the combustion chamber 1 at a higher pressure than in the previous cycle. By repeating this phenomenon, the supercharging pressure due to the burnt gas gradually increases, the pressure in the sub chamber 10 reaches about 2 bar, and the temperature reaches about 950K. The above temporal changes are shown in FIGS. Here, the opening / closing operation of the opening / closing valve 11 will be described.

As shown in FIG. 3, the on-off valve 11 is opened and closed twice after the intake valve 3 is closed and before the exhaust valve 9 is opened. By delaying the opening timing of the on-off valve 11 after closing the intake valve 3 as the load of the engine is smaller, the supply timing of the reformed fuel to the combustion chamber 1 is delayed to improve the stratification degree of the reformed fuel. It is possible to improve the ignitability of compression self-ignition combustion.

At the same time, the opening / closing valve 1 before opening the exhaust valve 9
By advancing the opening timing of No. 1, the sub-chamber 10 and the combustion chamber 1 can be communicated with each other at a time when the pressure in the combustion chamber 1 during the expansion stroke is high. As a result, the amount of burnt gas that is charged increases and the amount of burnt gas in the next cycle increases. Also, as the engine speed increases, the compression time until ignition is shortened, whereas the time required for self-ignition combustion is controlled by the chemical reaction speed, so the high speed side The ignitability deteriorates toward the head. Therefore, the opening timing of the opening / closing valve 11 after the intake valve 3 is closed and before the exhaust valve 9 is opened is advanced as the engine speed increases. As a result, the burned gas can be supplied into the combustion chamber 1 when the pressure in the combustion chamber 1 is low and the pressure in the sub-chamber 10 is high, that is, when the differential pressure is large, so that the supercharging effect by the burned gas is increased. It can be increased, and the ignitability at high rotation can be improved. The opening timing of the on-off valve 11 is shown in FIG.

As described above, stable and clean operation by compression self-ignition combustion can be performed even in the low load operation region and the high rotation region where the ignitability deteriorates. FIG. 9 shows the valve lift amount of the on-off valve 11 with respect to the engine rotation speed. As shown in the figure, in the high rotation region where the compression time becomes short, the lift amount is increased to increase the passage area of the burnt gas supplied into the combustion chamber 1 and enhance the supercharging effect. be able to. This makes it possible to further improve the ignitability in a high rotation region where the ignitability deteriorates and to perform stable and clean compression self-ignition combustion operation.

FIG. 10 shows the relationship between the engine load and the amount of fuel injected into the sub chamber 10. The total fuel injection amount is determined by the ECU 7 in response to the load demand, and at the same time, the fuel amount injected from the fuel injection valve 5 provided in the intake port 2 and the sub chamber fuel injection valve 12 injecting fuel into the sub chamber 10 The injection ratio with the amount of fuel injected from is determined. As shown in FIG. 10, the amount of fuel injected into the sub chamber 10 is increased as the load of the engine is reduced. As a result, the ratio of the reformed fuel supplied into the combustion chamber 1 increases, and the ignitability in the low load region can be improved.

FIG. 11 is a system diagram of the second embodiment of the present invention. Only the configuration of the sub chamber 10 is the first shown in FIG.
Different from the embodiment. That is, in the present embodiment, in the multi-cylinder engine, one of the exhaust ports 8'of each cylinder communicates with the combustion chamber 1'via the on-off valve 11 ', and the shutoff valve is provided downstream of the exhaust port 8'. 16 are provided. Then, by closing the shutoff valve 16, the on-off valve 11 ′ and the shutoff valve 16
And a sub-chamber 10 'is formed therebetween.

In this embodiment, when performing compression self-ignition combustion, the shut-off valve 16 is closed to operate, and the same effect as that of the above-described first embodiment can be obtained. Further, when performing spark ignition combustion, the shut-off valve 16 is opened to operate, so that it can be used as a normal exhaust port and can be operated without impairing exhaust efficiency.

[Brief description of drawings]

FIG. 1 is a diagram showing a system configuration of an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between an operating state of the engine and a combustion mode.

FIG. 3 is a diagram similarly showing a valve timing characteristic at the time of compression self-ignition combustion.

FIG. 4 is a diagram showing a valve timing characteristic during spark ignition combustion.

FIG. 5 is a diagram showing an operation for each stroke of the engine at the time of partial load.

FIG. 6 is a diagram showing an increase change in the pressure in the sub chamber due to repeated cycles.

FIG. 7 is a diagram showing an increase change in cylinder pressure due to repeated cycles.

FIG. 8 is a diagram showing the opening timing of the on-off valve during compression self-ignition combustion.

FIG. 9 is a diagram showing the lift characteristics of the on-off valve with respect to the engine rotation speed.

FIG. 10 is a diagram showing the relationship between the engine load and the amount of fuel injected into the sub chamber in the same manner.

FIG. 11 is a diagram showing a system configuration of a second embodiment of the present invention.

[Explanation of symbols]

1, 1'combustion chamber 2 intake ports 3 intake valve 4 pistons 5 Fuel injection valve 6 spark plugs 7 ECU 8, 8'exhaust port 9 Exhaust valve 10, 10 'Sub chamber 11, 11 'on-off valve 12 Sub-chamber fuel injection valve 16 shut-off valve

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F02D 13/02 F02D 13/02 H K 21/08 311 21/08 311Z 41/02 351 41/02 351 F02M 27/02 F02M 27/02 H (72) Inventor Koji Hiratani 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd. F-term (reference) 3G023 AA01 AA18 AB06 AC00 AC02 AC09 AD00 AF00 3G092 AA00 AA01 AA05 AA07 AA08 AA11 AA13 AB02 AB20 BA10 BB01 BB06 DA07 DA13 DG09 EA02 EA03 EA04 EC02 FA00 GA00 HA11Z HA13X HB01X HB02X HE01Z 3G301 HA00 HA01 HA19 HA21 KA06 LC01 MA11 MA18 NE06 NE12 PA17Z PE01Z PE03Z

Claims (11)

[Claims] 1. A compression self-ignition internal combustion engine that supplies reformed fuel into a combustion chamber and burns it by compression self-ignition, wherein the timing of supplying the reformed fuel to the combustion chamber is delayed as the load on the engine decreases. A compression self-ignition internal combustion engine characterized by the following. 2. A sub-chamber communicating with the combustion chamber via an opening / closing valve, and a sub-chamber fuel injection valve for injecting fuel into the sub-chamber, the sub-chamber being filled by the opening / closing operation of the opening / closing valve. 2. The compression self-ignition internal combustion engine according to claim 1, wherein the fuel is reformed by injecting the fuel into the burnt gas by the sub-chamber fuel injection valve, and the reformed fuel is supplied into the combustion chamber. organ. 3. The compression self-ignition internal combustion engine according to claim 2, wherein the supply timing of the reformed fuel to the combustion chamber is controlled by the opening / closing timing of the opening / closing valve. 4. The on-off valve is opened at the beginning of the compression stroke after the intake valve of the engine is closed and at the end of the expansion stroke before the exhaust valve is opened. Or claim 3
A compression self-ignition internal combustion engine as described. 5. The compression self-ignition internal combustion engine according to claim 4, wherein the opening timing of the opening / closing valve after the intake valve is closed is delayed as the load of the engine is reduced. 6. The compression self-ignition internal combustion engine according to claim 4, wherein the opening timing of the opening / closing valve before opening the exhaust valve is set earlier as the load of the engine is smaller. 7. The opening timing of the opening / closing valve after closing the intake valve and the opening timing before opening of the exhaust valve are set to be faster as the rotational speed of the engine is higher. The compression self-ignition type internal combustion engine according to any one of claims. 8. The compression self-ignition internal combustion engine according to claim 2, wherein the opening degree of the on-off valve is increased as the rotational speed of the engine is increased. 9. The compression self-ignition internal combustion engine according to claim 2, wherein the amount of fuel injected into the sub chamber increases as the load of the engine decreases. 10. The compression self-ignition internal combustion engine according to claim 2, wherein the sub chamber is provided on the exhaust port side of the engine. 11. The compression self-ignition type internal combustion engine according to claim 2, wherein the on-off valve is an electromagnetic valve.