JP2002138908A - Cylinder injection spark ignition type internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cylinder injection spark ignition type internal combustion engine capable of restraining deterioration of combustion due to the vaporization characteristic of injected fuel. SOLUTION: This cylinder injection spark ignition type engine 11 for igniting and burning air-fuel mixture of fuel directly injected into a combustion chamber 18 and air is provided with an EGR mechanism 31 and a temperature control mechanism 34. The EGR mechanism 31 is provided with an EGR passage 32 for connecting an exhaust passage 21 and an intake passage, and an EGR valve 33 disposed in the midway of the EGR passage 32. In the EGR mechanism 31, some of exhaust gas produced by combustion of air-fuel mixture is returned to the intake passage 19 through the EGR passage 32. The temperature control mechanism 34 controls the temperature of EGR gas flowing through the EGR passage 32 according to the cylinder temperature which is the temperature in the combustion chamber 18.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct injection spark ignition type internal combustion engine in which a mixture of fuel and air directly injected into a combustion chamber is ignited and burned by sparks. The present invention relates to a direct injection spark ignition type internal combustion engine having a mechanism for recirculating exhaust gas to an intake system through an exhaust gas recirculation passage (EGR passage).

[0002]

2. Description of the Related Art As is well known, in a direct injection spark ignition type internal combustion engine, fuel is directly injected into a combustion chamber by an injector. Then, the injected fuel is vaporized to form an air-fuel mixture, and the air-fuel mixture is ignited by an electric spark to explode and burn. In this type of internal combustion engine, the air-fuel ratio (air-fuel weight ratio) of the air-fuel mixture can be set extremely lean by stratified charge combustion, so that the fuel efficiency can be significantly improved.
Here, the term "lean" refers to a state in which the amount of fuel is smaller and the amount of air is larger than the theoretical value of the air-fuel ratio (the stoichiometric air-fuel ratio) required to completely burn the fuel.

[0003] On the other hand, in such an internal combustion engine, the combustion temperature is higher than that of a general spark ignition type internal combustion engine, and nitrogen oxides (NOx) in the exhaust gas tend to increase. Therefore,
Conventionally, this problem has been addressed by adding an exhaust gas recirculation mechanism (EGR mechanism) to the engine and recirculating exhaust gas to an intake system. As is well known, the EGR mechanism connects the exhaust passage and the intake passage by an exhaust gas recirculation passage (EGR passage), and, depending on the operating state of the internal combustion engine, an exhaust gas recirculation valve ( This is a mechanism for opening and closing the EGR valve. According to the EGR mechanism, the combustion temperature of the air-fuel mixture is reduced by the recirculated gas (EGR gas), thereby making it possible to reduce the emission amount of NOx. However, when a large amount of EGR gas is recirculated through this mechanism, for example, the EGR passage and the like may be excessively heated.
In a mode disclosed in Japanese Patent No. 87807, it has been proposed to cool the EGR gas with cooling water.

[0004]

In the direct injection spark ignition type internal combustion engine, as described above, the fuel injected into the cylinder is vaporized to form an air-fuel mixture. Explosion and combustion are performed by ignition of the air, but when the in-cylinder temperature is low, vaporization of the injected and supplied fuel is suppressed, resulting in deterioration of combustion.

On the other hand, since the EGR gas recirculated to the intake system is taken into the combustion chamber together with the intake air, the gas temperature also affects the cylinder temperature. For example, in the case of the device described in the above publication, overheating of the EGR passage and the like can be prevented by cooling the EGR gas with the cooling water, but the cooled EGR gas is introduced into the combustion chamber. This may lower the in-cylinder temperature more than necessary. For this reason, depending on the operation state of the engine, the injected fuel is not sufficiently vaporized, resulting in deterioration of fuel efficiency and exhaust emission.

The present invention has been made in view of such circumstances, and has as its object to provide a direct injection spark ignition type internal combustion engine capable of suitably suppressing deterioration of combustion due to the vaporization characteristics of injected fuel. In providing institutions.

[0007]

The means for achieving the above object and the effects thereof will be described below. In order to achieve the above object, according to the first aspect of the present invention, a mixture of fuel and air directly injected into a combustion chamber is ignited and burned by a spark, and exhaust gas discharged from the combustion chamber accompanying the combustion is emitted. In a cylinder injection spark ignition type internal combustion engine that recirculates a part of the exhaust gas to an intake system through an exhaust gas recirculation passage, a temperature for adjusting the temperature of the recirculated gas flowing through the exhaust gas recirculation passage in accordance with the in-cylinder temperature that is the temperature in the combustion chamber Adjustment means is provided.

According to the above configuration, for example, when the air-fuel ratio of the air-fuel mixture is set to a very lean side during stratified charge combustion, the combustion temperature increases and the nitrogen oxides (NOx) in the exhaust gas increase. Nitrogen oxides are reduced by exhaust gas recirculation (EGR). That is, the exhaust gas generated by the ignition is recirculated to the intake system through the exhaust gas recirculation passage, and is mixed with the intake air. Is suppressed.

Further, according to the above configuration, the temperature of the recirculation gas flowing through the exhaust gas recirculation passage can be changed by the temperature adjusting means in accordance with the in-cylinder temperature. Therefore, when the in-cylinder temperature is high and the injected fuel is vaporized satisfactorily, for example, if the reflux gas is cooled by the temperature adjusting means, the temperature of the reflux gas falls. Therefore, even when a large amount of exhaust gas is recirculated, it is possible to suppress overheating of each part of the exhaust gas recirculation mechanism and protect them from heat.

On the other hand, when the temperature in the cylinder is low and the fuel is difficult to evaporate, for example, if the cooling degree of the reflux gas by the temperature adjusting means is reduced (including the cooling stop), the temperature of the reflux gas decreases. The decrease in the in-cylinder temperature is suppressed, and the phenomenon that the fuel is more difficult to vaporize is prevented. Also, at this time, the temperature of the reflux gas rises, and the fuel is easily vaporized if the reflux gas is actively heated by the temperature control means, instead of reducing the cooling degree of the reflux gas. And mix easily with air. For this reason,
Irrespective of the condition of the engine, it is possible to suppress the deterioration of the combustion of the air-fuel mixture caused by the vaporization characteristics of the injected fuel, and it is possible to improve the fuel efficiency, exhaust emission, drivability and the like.

According to a second aspect of the present invention, in the first aspect of the invention, the temperature control means cools the recirculation gas flowing through the exhaust gas recirculation passage and operates the engine in a region where the in-cylinder temperature is low. It is assumed that the degree of cooling of the reflux gas is reduced. Here, the cooling stop is also included in reducing the cooling degree.

According to the above configuration, the recirculated gas flowing through the exhaust gas recirculation passage is basically cooled by the temperature control means. This cooling lowers the temperature of the reflux gas. However, when the in-cylinder temperature is low and the injected fuel is difficult to vaporize,
The degree of cooling is reduced. Therefore, it is possible to suppress a further decrease in the in-cylinder temperature caused by the recirculated gas, and to suppress deterioration of combustion due to deterioration of the vaporization characteristics of the injected fuel.

According to a third aspect of the present invention, in the first aspect of the present invention, the temperature adjusting means heats the recirculation gas flowing through the exhaust recirculation passage when the engine is operating in a region where the in-cylinder temperature is low. And

According to the above configuration, when the in-cylinder temperature is low and the injected fuel is not easily vaporized, the recirculated gas is heated by the temperature adjusting means when flowing through the exhaust gas recirculation passage. The reflux gas whose temperature has increased by this heating is returned to the intake system,
The temperature inside the cylinder rises. With this rise, the injected fuel is easily vaporized. Therefore, also in this case, the deterioration of the combustion due to the deterioration of the vaporization characteristics of the injected fuel can be suitably suppressed.

According to a fourth aspect of the present invention, in the third aspect of the present invention, the temperature control means further cools the recirculation gas flowing through the exhaust recirculation passage when the engine is operating in the region where the in-cylinder temperature is high. Suppose that

According to the above configuration, when the in-cylinder temperature is high, the recirculated gas is cooled by the temperature adjusting means when flowing through the exhaust gas recirculation passage. This cooling lowers the temperature of the reflux gas. Therefore, even when a large amount of exhaust gas is recirculated, overheating of each part of the exhaust gas recirculation mechanism can be suppressed. At this time, since the injected fuel is in a state of being easily vaporized, there is no fear of combustion deterioration.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment in which a direct injection spark ignition type internal combustion engine of the present invention is embodied in a multi-cylinder gasoline engine for an automobile (hereinafter simply referred to as an engine) will be described below.
This will be described with reference to FIGS.

As shown in FIG. 1, the engine 11 includes a cylinder head 12 and a cylinder block 14 having a plurality of cylinders 13 (one of which is shown in FIG. 1). A piston 15 is accommodated in each cylinder 13 so as to be able to reciprocate. Each piston 15 is connected to a crankshaft 17 via a connecting rod 16. The reciprocating motion of each piston 15 is converted into a rotary motion by a connecting rod 16 and then transmitted to a crankshaft 17.

The combustion chamber 18 is defined by the top surface of the piston 15, the inner wall surface of the cylinder 13, and the lower surface of the cylinder head 12. An intake passage 19 and an exhaust passage 21 are connected to the combustion chamber 18.
Reference numeral 21 is opened or closed by an intake valve 22 and an exhaust valve 23 supported reciprocally by the cylinder head 12.

In the intake passage 19, a throttle valve 2 is provided.
4 is rotatably supported by a shaft 24a. Axis 24
A throttle motor 26 that operates in response to a driver's depression operation of an accelerator pedal 25 is drivingly connected to a. The amount of air flowing through the intake passage 19, that is, the amount of intake air, changes according to the rotation angle (throttle opening) of the throttle valve 24.

The cylinder head 12 is provided with an injector 27 for directly injecting fuel into the combustion chamber 18.
3 is attached. The fuel injected from each injector 27 evaporates and mixes with the intake air introduced into the combustion chamber 18 through the intake passage 19 to form an air-fuel mixture. A spark plug 28 is attached to the cylinder head 12 so as to correspond to each cylinder 13. The air-fuel mixture is ignited by an electric spark of the spark plug 28, and explodes and burns. The piston 15 is reciprocated by the high-temperature and high-pressure combustion gas generated at this time, the crankshaft 17 is rotated, and the driving force of the engine 11 is obtained. In order to realize appropriate combustion, it is necessary that the injected fuel and the air are sufficiently mixed. To this end, the temperature of the combustion chamber 18 (the in-cylinder temperature) is increased to remove the injected fuel. It is important to make it easier.

In this embodiment, there are at least homogeneous combustion and stratified combustion as combustion methods of the air-fuel mixture, and these are switched according to the operating state of the engine 11. Homogeneous combustion is achieved by injecting fuel during the intake stroke (during lowering of the piston 15) when the engine 11 is under a high load, for example.
This combustion method takes a long diffusion time, promotes vaporization, uniformly mixes fuel and air to form a mixture near the stoichiometric air-fuel ratio, and then ignites. In homogeneous combustion, since ignition occurs after sufficient mixing, soot does not easily appear, and high output can be obtained because combustion proceeds smoothly.

In the stratified combustion, fuel is injected toward the top surface of the piston 15 in the latter half of the compression stroke (while the piston 15 is rising), for example, when the engine 11 is under a low load.
This is a combustion method in which the mixture is stratified and then ignited. That is, by delaying the fuel injection timing as much as possible, a layer of a rich mixture of fuel (about the stoichiometric air-fuel ratio) is formed around the ignition plug 28 before the fuel is diffused throughout the combustion chamber 18. In this method, a layer of an air-fuel mixture with a small amount of fuel is formed therearound. In the stratified combustion, when the entire air-fuel ratio in the cylinder 13 is considered, a lean state of about 30 to 50 is obtained, and the fuel efficiency is improved.

Most of the combustion gas generated in the combustion chamber 18 is discharged to the outside of the engine 11 through the exhaust passage 21 as exhaust gas. The exhaust passage 21 is provided with a catalytic converter 29 having a built-in catalyst for purifying exhaust gas flowing through the exhaust passage 21.

The engine 11 is provided with an exhaust gas recirculation mechanism (hereinafter referred to as “EGR mechanism”) 31 for recirculating a part of the exhaust gas to an intake system, for example, the intake passage 19. EG
The R mechanism 31 increases the proportion of inert gas in the air-fuel mixture to lower the maximum combustion temperature by exhaust gas mixed with the intake air due to the recirculation, and reduces nitrogen oxides (NO
x) is reduced, and is executed at least during stratified combustion in which the air-fuel ratio of the air-fuel mixture is set to the lean side. The EGR mechanism 31 includes an exhaust gas recirculation passage (hereinafter, referred to as “EGR passage”) 32 connecting the exhaust passage 21 and the intake passage 19. Here, the EGR passage 32 is connected to the exhaust passage 21 on the upstream side of the catalytic converter 29, but may be connected on the downstream side. EGR
An exhaust gas recirculation valve (hereinafter, referred to as “EGR valve”) 33 for adjusting the flow rate of the recirculated gas (hereinafter, referred to as “EGR gas”) flowing through the passage 32 is provided in the middle of the passage 32.

The EGR passage 32 is provided with a temperature adjusting mechanism 34 for adjusting the temperature of the EGR gas flowing through the EGR passage 32 according to the in-cylinder temperature. In the present embodiment, the temperature adjustment mechanism 34 includes a mechanism for cooling the EGR gas and a mechanism for heating the EGR gas.

The cooling mechanism may be of any type as long as the cooling degree can be switched in at least two stages by cooling or stopping the cooling of the EGR gas. The type which can be adjusted by is preferable. As an example, in the present embodiment, one utilizing cooling water of the engine 11 is employed. Specifically, the cooling mechanism includes a cooling water passage 38 connected to the radiator 37, and a part thereof is provided around the EGR passage 32. More specifically, a part of the EGR mechanism 31 has a double-pipe structure, and the internal space of the inner pipe is EGR.
The space between the inner tube and the outer tube forms a part of the cooling water passage 38 which forms a part of the passage 32. Cooling water passage 3
In the middle of 8, a flow control valve 39 for adjusting the flow rate of the cooling water flowing through the passage 38 is interposed.

The heating mechanism may be of any type as long as the heating degree can be switched in at least two stages by heating or stopping the heating of the EGR gas. The type which can be adjusted by is preferable. As an example, in the present embodiment, an electric (electric heat) heater 41 is employed. The electric heater 41 is heated by energization and generates a different amount of heat in accordance with the amount of energization. The electric heater 41 is arranged near, for example, around the EGR passage 32.

The engine 11 is provided with various sensors for detecting its operating state. For example, near the crankshaft 17, a crank angle sensor 42 for detecting the rotation speed (engine rotation speed) is disposed. Near the throttle valve 24, its shaft 24
A throttle sensor 43 for detecting a rotation angle (a throttle opening) of a is disposed. In the intake passage 19,
An intake pressure sensor 44 for detecting the pressure of the intake air (intake pressure) is provided on the downstream side of the throttle valve 24, and an intake temperature sensor 45 for detecting the temperature (intake temperature) in the intake passage 19 on the upstream side. Is provided. In the vicinity of the throttle valve 24, an accelerator sensor 46 for detecting an amount of depression of an accelerator pedal 25 (accelerator opening) is provided.

In order to control the injectors 27, the EGR valve 33, the flow control valve 39, the electric heater 41 and the like based on the detection values of the various sensors 42 to 46, FIG.
As shown in the figure, an electronic control unit (hereinafter referred to as “ECU”)
47 are used. The ECU 47 includes a CPU 48, a read-only memory (ROM) 49, a random access memory (RAM) 51, a backup RAM 52, an external input circuit 53, and an external output circuit 54. These circuits are connected to each other by a bus 55.

The ROM 49 stores a predetermined control program and initial data in advance. The CPU 48 has a ROM 4
Various arithmetic processes are executed according to the control program and the initial data stored in 9. The RAM 51 includes a CPU 48
Is temporarily stored. Backup RA
M52 is backed up by a battery (not shown) in order to retain various data in the RAM 51 even after power supply to the ECU 47 is stopped.

The CPU 48 inputs detection signals from the various sensors 42 to 46 via the external input circuit 53. Further, the CPU 48 calculates an engine speed, an accelerator opening, and the like based on these inputs. Further, the CPU 48
Controls the operation of each injector 27, EGR valve 33, flow control valve 39, electric heater 41, and the like based on these calculated values via an external output circuit 54, and controls fuel injection control, EGR control, EGR gas temperature control, etc. Execute

For example, the CPU 48 performs the fuel injection control based on the operating state of the engine 11, for example, the engine speed and the accelerator opening (or intake pressure).
9 to determine the basic injection amount from the map stored in advance,
This is corrected based on coefficients and correction values based on signals from various sensors, and the fuel injection amount is calculated. Then, a drive signal is output to the injector 27 via the external output circuit 54 so that the fuel thus calculated is injected.

The CPU 48 calculates a target value of the EGR opening based on the throttle opening and the engine speed as the EGR control, and controls the external output circuit 54 so that the opening of the EGR valve 33 approaches the target value. Through the EGR
The drive signal is output to the valve 33.

Next, the operation of the present embodiment configured as described above will be described. The flowchart of FIG.
A routine for controlling the temperature of the EGR gas according to the in-cylinder temperature among the processes executed by the CU 47 is shown.

According to this routine, the ECU 47 first estimates the in-cylinder temperature based on the engine operating state, and determines whether the estimated value is a value suitable from the viewpoint of the vaporization of the injected fuel. In general, the in-cylinder temperature is low when the engine load is small, and tends to increase as the load increases. Therefore, the engine load is used here as a substitute value (control parameter) for the in-cylinder temperature.

The engine load can be represented by, for example, the relationship between the engine speed and the fuel injection amount. Normally, when the engine speed is low and the fuel injection amount is small, the engine load is small, the engine speed is high,
In addition, the engine load increases as the fuel injection amount increases. For this reason, the engine load is determined based on the engine rotation speed and the fuel injection amount.

In step S101, it is determined whether or not the engine load obtained as described above belongs to the light load range. This process is performed to determine whether the in-cylinder temperature is so low that the injected fuel cannot be satisfactorily vaporized. If this condition is not met,
In step S103, it is determined whether the engine load belongs to a high load region. This process is performed in order to determine whether or not the in-cylinder temperature is sufficiently high that the injected fuel can be satisfactorily vaporized even if the temperature is somewhat lowered. Here, the light / high load region as shown in FIG. 4 refers to a region in a load region where stratified combustion is performed, and a region where the engine load is relatively small among the load regions is a light load region. A relatively large area is defined as a high load area.

In accordance with the results of the determinations in steps S101 and S103, the flow control valve 3 is referred to with reference to a predetermined map.
9 and the electric heater 41 are respectively controlled. The map used here defines the amount of electric power to the electric heater 41 in relation to the engine rotation speed and the fuel injection amount, and the map for the flow control valve 39 in the same relation to the engine rotation speed and the fuel injection amount. There are two types, one defining the opening degree, and both are stored in the ROM 49 in advance. In the former map, the electric heater 41 is energized only in a region where the engine rotation speed is low and the fuel injection amount is small, that is, only in a light load region. In addition, the amount of electricity in the light load range decreases as the engine speed decreases.
Further, the fuel injection amount is set to increase as the fuel injection amount decreases. In the latter map, the flow control valve 39 is opened only in a region where the engine rotation speed is high and the fuel injection amount is large, that is, only in a high load region. In addition, the opening degree in the high load region is set to increase as the engine rotation speed increases and the fuel injection amount increases.

If the determination condition in step S101 is satisfied, that is, if the engine load belongs to the light load range, in step S102, the flow control valve 3
9 is closed and the electric heater 41 is energized. The amount of power supply at this time is set to a value corresponding to the engine load defined by the engine speed and the fuel injection amount. In other words, the electric heater 41 is energized with an energization amount corresponding to the in-cylinder temperature. By closing the flow control valve 39, the flow of the cooling water in the cooling water passage 38 is stopped, and the degree of cooling of the EGR gas by the cooling water is reduced. On the other hand, the electric heater 41 generates heat by the energization, and the heat is transmitted to the EGR gas flowing through the EGR passage 32. This transmission heats the EGR gas and raises its temperature.

If the determination condition in step S103 is satisfied, that is, if the engine load belongs to the high load range, in step S104, the power supply to the electric heater 41 is stopped, and the flow control valve 39 is turned off. Open the valve. The opening at this time is set to a value corresponding to the engine load defined by the engine rotation speed and the fuel injection amount. In other words, the flow control valve 39 is opened at an opening corresponding to the in-cylinder temperature. The heat generation of the electric heater 41 is stopped by the stop of the power supply, and the EG generated by the electric heater 41 is stopped.
The heating effect of the R gas is eliminated. On the other hand, when the flow control valve 39 is opened, the cooling water flows in the cooling water passage 38, and the heat is transmitted to the EGR gas flowing therethrough via the EGR passage 32. This transmission cools the EGR gas and lowers its temperature.

On the other hand, if the determination condition in step S103 is not satisfied, that is, if the engine load does not belong to the light load region or the high load region, the flow control valve 39 is closed in step S105. Then, the power supply to the electric heater 41 is stopped. By closing the valve, the flow of the cooling water in the cooling water passage 38 is stopped, and E
The degree of cooling of the GR gas decreases. Further, the heat generation of the electric heater 41 is stopped by the stop of the energization, and the electric heater 4 is turned off.
1 eliminates the effect of heating the EGR gas. The temperature of the EGR gas is less affected by the cooling water and the electric heater 41.

Then, as described above, step S102,
After performing one of the processes in S104 and S105, this routine ends. According to the embodiment described above, the following effects can be obtained.

(1) As shown in FIG. 4, the EGR gas flowing through the EGR passage 32 is heated by the electric heater 41 in a light load region where the in-cylinder temperature is low and the injected fuel is difficult to vaporize. For this reason, although the vaporization of the injected fuel is originally poor in the light load region, the EG whose temperature has risen due to the above-mentioned heating is increased.
The R gas is recirculated to the intake passage 19, the temperature in the cylinder increases, and the injected fuel is easily vaporized. Therefore, EGR is always
Unlike the prior art in which the originally low in-cylinder temperature is further reduced due to the cooling of the gas, it is possible to suitably suppress the deterioration of combustion due to the poor vaporization of the injected fuel. Rather, the vaporization accompanying the rise in the cylinder temperature promotes the combustion of the air-fuel mixture, thereby improving fuel efficiency, exhaust emissions, drivability, and the like.

(2) In relation to the above (1), in the light load range of the engine 11, the amount of power to the electric heater 41 is changed according to the magnitude of the engine load. As the engine rotation speed decreases and the fuel injection amount decreases, the amount of power supply is increased to increase the degree of heating of the EGR gas. Therefore, the in-cylinder temperature can be set to a more appropriate value by heating, and the injected fuel can be easily vaporized.

(3) As shown in FIG. 4, in a high load region where the in-cylinder temperature is high, the EGR gas flowing through the EGR passage 32 is cooled by the cooling water. This cooling lowers the temperature of the EGR gas. Therefore, even when a large amount of exhaust gas is recirculated, the components of the EGR mechanism 31, for example, the EGR mechanism
It is possible to suppress overheating of the EGR pipe and the EGR valve 33 forming the passage 32 and protect them from heat. In the high load range, the injected fuel is easily vaporized because the in-cylinder temperature is sufficiently high, so that there is no fear of deterioration of combustion due to EGR gas cooling.

(4) As related to the above (3), in the high load region of the engine 11, the opening of the flow control valve 39 is changed according to the magnitude of the engine load. As the engine rotation speed increases and the fuel injection amount increases, the opening degree is increased to increase the flow rate of the cooling water flowing through the cooling water passage 38 and increase the degree of cooling of the EGR gas. Therefore, it is possible to suppress the EGR mechanism 31 from being cooled more than necessary, and to reduce the influence of the EGR gas on the in-cylinder temperature. The temperature of the EGR gas can be set to a more appropriate value with respect to the vaporization of the injected fuel and the suppression of overheating of the EGR passage and the like.

(5) Since the engine load corresponding to the in-cylinder temperature is used as a control parameter, the in-cylinder temperature can be easily estimated from the engine load without directly detecting the in-cylinder temperature. Then, based on the estimation result, the cooling of the EGR gas by the cooling water and the heating by the electric heater are appropriately performed, so that the in-cylinder temperature can be set to a more preferable value.

(6) Since the cooling water originally used in the engine is used as a refrigerant for the cooling mechanism and heat exchange is performed between the cooling water and the EGR gas, there is no need to secure a separate refrigerant. Yes.

(7) Since an electric heater is used as the heating mechanism, by heating the heater, heating can be performed efficiently in a relatively short time, and the temperature of the EGR gas can be increased.

The present invention can be embodied in another embodiment described below. In the light load region where the in-cylinder temperature is low, as a method of suppressing the in-cylinder temperature from being further lowered by the EGR gas, in the above-described embodiment, the cooling of the EGR gas is stopped and heating is performed. May be omitted. In particular,
A heating mechanism such as the electric heater 41 is omitted. Then, the flow rate control valve 39 is closed to stop the flow of the cooling water in the cooling water passage 38, or the opening degree is reduced to narrow the flow rate of the cooling water. In this case, even when the cooling water flows at the same flow rate as the high load area even in the light load area (corresponding to the conventional technology)
, The temperature of the EGR gas is less likely to decrease. Therefore, it is possible to suppress a further decrease in the in-cylinder temperature due to the EGR gas, and to suppress the deterioration of combustion due to the deterioration of the vaporization characteristics of the injected fuel.

The flow control valve 3 is used as a cooling mechanism.
Instead of 9, a valve (open / close valve) that has no opening degree adjustment function and only opens or closes the cooling water passage 38 may be used.
In this case, for example, the on-off valve may be opened in a high load region, and may be closed in other regions (including a light load region). Further, the on-off valve may be closed in a light load region, and may be opened in other regions (including a high load region). That is, the cooling with the cooling water may be prohibited in the light load region where the in-cylinder temperature is low.

In any of the above cases, in a high load region, the cooling water flows through the cooling water passage 38, and the EGR gas is cooled.
The temperature drops. In the light load region, the flow of the cooling water in the cooling water passage 38 is cut off, the cooling of the EGR gas is stopped, and the temperature decrease is suppressed. Therefore, in this case, there is no need for a map defining the opening of the flow control valve 39 in relation to the engine speed and the fuel injection amount.

Similarly, the electric heater 41 may be controlled in two modes, that is, a mode in which a predetermined amount of current is supplied and a mode in which energization is stopped, and these modes may be switched according to the engine load. In this case, a predetermined amount of current is supplied to the electric heater 41 in a light load region, and the supply of electric current is stopped in other regions (including a high load region). According to such control, in the light load region, the electric heater 41 generates heat, and the EGR gas is heated to increase the temperature. On the other hand, in the high load region, the electric heater 41 does not generate heat, and unnecessary heating of the EGR gas is not performed. Therefore, in this case, there is no need for a map defining the amount of power to the electric heater 41 in relation to the engine speed and the fuel injection amount.

In the above-described embodiment, the engine load region during stratified combustion is divided into a light load region, a high load region, and a region other than any of these regions. You may. For example, the control mode of the flow control valve 39 and the electric heater 41 may be differently divided into a light load region and a region other than the light load region.

In order to heat the EGR gas in the EGR passage 32, a heating mechanism different from the above embodiment may be adopted. FIG. 5 shows an example. This is because the exhaust passage 21
It utilizes the heat of More specifically, the temperature of the EGR gas in the EGR passage 32 and the temperature of the exhaust gas in the exhaust passage 21 are basically substantially equal. However, unburned components that are not burned in the combustion chamber 18 and mixed with the exhaust gas are exhausted by the exhaust passage 2.
There is a case where the fuel burns during the flow through the fuel cell 1 or burns when passing through the catalyst. Due to the heat resulting from the combustion, there are places in the exhaust passage 21 and the catalytic converter 29 where the temperature is higher than that of the EGR gas. Therefore, the EGR passage 32 is located upstream of the catalytic converter 29 and the exhaust passage 2
In the case of the engine 11 connected to the engine 1, a part of the EGR passage 32 (a part near the connection with the exhaust passage 21)
And the location where this temperature is high (the catalytic converter 29 in the figure)
And approach. By doing so, the electric heater 4
E without any additional heating mechanism such as 1
The GR gas can be heated.

Further, since the temperature of the exhaust passage 21 is basically higher on the upstream side, at least the portion near the connection point with the exhaust passage 21 in the EGR passage 32 is brought closer to the exhaust passage 21 on the upstream side of the same position. You may. Even in this case, the same effect as described above can be obtained. FIG. 6 shows the EGR
In the case where the passage 32 is connected to the exhaust passage 21 on the downstream side of the catalytic converter 29, an example is shown in which a part of the EGR passage 32 is brought closer to the catalytic converter 29 located upstream of the connection point.

Note that the number of heating mechanisms is not limited to one, and a plurality of heating mechanisms may be combined. For example, the electric heater 41 may be used in combination with the above-described one utilizing the heat from the exhaust passage 21.

In order to cool the EGR gas flowing through the EGR passage 32, a cooling mechanism different from the above embodiment may be employed. FIG. 7 shows an example. This utilizes the wind (running wind) 56 that flows as the vehicle travels. More specifically, a plurality of windshields 57 are arranged in the vicinity of the EGR passage 32 while being separated from each other, and each of them is rotatably supported by a shaft 57a. These windshields 57 are connected by a connecting member 58 to form a so-called parallel link. An actuator 59 such as a step motor is drivingly connected to one of the windshields 57. Further, the operation of the actuator 59 causes the predetermined windshield 57 to move the shaft 5
7a as a fulcrum, the rotation is
8 to the other draft shields 57 and all the draft shields 5
7 are simultaneously rotated to change the inclination.

When the engine load belongs to the light load region, as shown by the two-dot chain line in FIG.
The amount of the traveling wind 56 contacting the EGR passage 32 is reduced so that the EGR gas is not cooled too much. Conversely, when the vehicle belongs to the high load region, as shown by the solid line in FIG. , So that the EGR gas is efficiently cooled.

As described above, if the traveling wind generated during traveling of the automobile is used, it is not necessary to secure a new refrigerant. Further, the temperature of the EGR gas can be suitably controlled by adjusting the flow rate of the traveling wind while using a relatively small number of components and a relatively simple configuration.

The number of cooling mechanisms is not limited to one, and a plurality of cooling mechanisms may be combined. For example, one using the traveling wind 56 described above and one using the cooling water may be used in combination. -The heating mechanism and the cooling mechanism may function simultaneously, and in this case, the temperature of the EGR gas can be controlled to a more appropriate value.

In addition, technical ideas that can be grasped from the above embodiments will be described together with their effects. (1) In the direct injection spark ignition type internal combustion engine according to claim 2, the temperature adjusting means uses an engine load corresponding to the in-cylinder temperature as a control parameter, and the engine load is:
An in-cylinder injection spark ignition type internal combustion engine, wherein the degree of cooling of the recirculated gas is reduced when the engine belongs to a light load region where the in-cylinder temperature is low.

According to the above arrangement, the in-cylinder temperature can be estimated by the engine load without directly detecting the in-cylinder temperature, and the originally low in-cylinder temperature is further reduced by the cooling action of the temperature control means. Can be suppressed.

(2) In the direct injection spark ignition type internal combustion engine according to the third or fourth aspect, the temperature adjusting means uses an engine load corresponding to the in-cylinder temperature as a control parameter, and the engine load is controlled by the cylinder load. An in-cylinder injection spark ignition type internal combustion engine for heating the recirculated gas when the engine belongs to a light load region having a low internal temperature.

According to the above configuration, the cylinder temperature can be estimated by the engine load without directly detecting the cylinder temperature, the cylinder temperature is raised by the heating action of the temperature control means, and the injected fuel is vaporized. Can be easier.

(3) In the cylinder injection spark ignition type internal combustion engine according to claim 3 or 4, wherein the temperature adjusting means changes the heating degree of the recirculated gas in accordance with the cylinder temperature. Injection spark ignition type internal combustion engine.

According to the above configuration, the in-cylinder temperature can be set to a more appropriate value with respect to the vaporization of the injected fuel by changing the degree of heating of the recirculated gas. (4) The direct injection spark ignition type internal combustion engine according to claim 4, wherein the temperature adjusting means changes the degree of cooling of the recirculated gas in accordance with the cylinder temperature. organ.

According to the above configuration, by changing the degree of cooling of the recirculated gas, the temperature of the recirculated gas can be set to a more appropriate value with respect to the vaporization of the injected fuel and the suppression of overheating of the exhaust gas recirculation passage and the like. .

(5) In the direct injection spark ignition type internal combustion engine according to claim 2 or 4, the temperature control means is provided with a cooling water passage provided in the vicinity of the exhaust gas recirculation passage, and in the middle of the cooling water passage. An in-cylinder injection spark ignition type internal combustion engine, comprising: a valve provided in the engine.

According to the above configuration, heat exchange is performed between the cooling water and the recirculated gas, and the temperature of the recirculated gas having a large influence on combustion can be controlled. Further, if cooling water for cooling the engine is used, it is not necessary to secure a separate refrigerant.

(6) The in-cylinder injection spark ignition internal combustion engine according to claim 3 or 4, wherein the temperature adjusting means is provided near the exhaust gas recirculation passage and includes an electric heater which generates heat when energized. A direct injection spark ignition internal combustion engine.

According to the above configuration, the power to the electric heater can be efficiently heated in a relatively short time to increase the temperature of the recirculated gas. (7) In the direct injection spark ignition type internal combustion engine according to (2) or (4), the temperature adjusting means is a windshield supported by a shaft near the exhaust gas recirculation passage, and an actuator for changing the inclination of the windshield. And a direct injection spark ignition type internal combustion engine.

With the above configuration, if the direct injection spark ignition type internal combustion engine is mounted on an automobile, the wind (traveling wind) generated by the traveling of the automobile contacts the exhaust gas recirculation passage, and Heat exchange is performed with the reflux gas.
The flow rate of the traveling wind relating to the heat exchange is adjusted by a windshield that changes the inclination according to the operation of the actuator. In this way, the temperature of the recirculated gas can be controlled using the traveling wind.

(8) The in-cylinder injection spark ignition type internal combustion engine according to claim 3 or 4, further comprising: an exhaust passage communicating with the combustion chamber; and a catalytic converter provided in the middle of the exhaust passage. The exhaust gas recirculation passage is connected to the exhaust passage upstream of the catalytic converter, and a part of the exhaust gas recirculation passage and the catalytic converter are arranged close to each other. Injection spark ignition type internal combustion engine.

(9) The direct injection spark ignition type internal combustion engine according to claim 3 or 4, further comprising an exhaust passage connected to the combustion chamber and connected to the exhaust recirculation passage. The direct-injection spark ignition type internal combustion engine, wherein the portion is disposed in a state of being closer to a portion of the exhaust passage on the upstream side of a portion connected to the exhaust gas recirculation passage.

According to the above configurations (8) and (9), the reflux gas can be heated with a simple configuration without separately providing a heating mechanism such as an electric heater. (10) In the direct injection spark ignition type internal combustion engine according to claim 1, the temperature adjusting means is arranged near the exhaust gas recirculation passage and cools a recirculation gas flowing through the exhaust gas recirculation passage. Means for inhibiting cooling by the cooling mechanism during operation of the engine in the region where the in-cylinder temperature is low.

According to the above configuration, the lowering of the originally low cylinder temperature due to the recirculated gas can be suppressed, and the deterioration of the combustion due to the deterioration of the vaporization characteristics of the injected fuel can be suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of an embodiment of a direct injection spark ignition type internal combustion engine of the present invention.

FIG. 2 is a block diagram showing an electrical configuration of a control system of the engine.

FIG. 3 is a flowchart showing a procedure for controlling the temperature of EGR gas.

FIG. 4 is an explanatory diagram showing the concept of EGR gas temperature control.

FIG. 5 is a schematic diagram showing the configuration of another embodiment of the direct injection spark ignition type internal combustion engine of the present invention.

FIG. 6 is a schematic diagram showing the configuration of another embodiment of the direct injection spark ignition type internal combustion engine of the present invention.

FIG. 7 is a schematic diagram showing the configuration of another embodiment of the direct injection spark ignition type internal combustion engine of the present invention.

[Explanation of symbols]

11 ... engine, 18 ... combustion chamber, 19 ... intake passage, 31
... EGR mechanism, 32 ... EGR passage, 34 ... Temperature control mechanism.

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference)

Claims (4)

[Claims] An air-fuel mixture directly injected into a combustion chamber is ignited and burned by a spark, and a part of exhaust gas discharged from the combustion chamber is burned through an exhaust gas recirculation passage. A cylinder injection spark ignition type internal combustion engine, comprising: a temperature adjusting means for adjusting a temperature of a recirculation gas flowing through the exhaust gas recirculation passage in accordance with an in-cylinder temperature which is a temperature in the combustion chamber. Internal injection spark ignition type internal combustion engine. 2. The temperature control means cools the recirculation gas flowing through the exhaust gas recirculation passage and reduces the degree of cooling of the recirculation gas during operation of the engine in a region where the in-cylinder temperature is low. Item 2. An in-cylinder injection spark ignition internal combustion engine according to item 1. 3. The in-cylinder injection spark ignition type internal combustion engine according to claim 1, wherein said temperature adjusting means heats the recirculation gas flowing through said exhaust gas recirculation passage when the engine is operating in a region where said in-cylinder temperature is low. organ. 4. The in-cylinder injection spark ignition according to claim 3, wherein said temperature adjusting means further cools the recirculation gas flowing through said exhaust gas recirculation passage when the engine is operated in the high in-cylinder temperature region. Type internal combustion engine.