JP2000274277A - Controller for spark ignition type direct-injection engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep an NOx catalyst within an active temperature range in a large number of driving areas to reduce emission. SOLUTION: In this controller for a spark ignition type direct-injection engine, an NOx catalyst for reducing NOx in exhaust gas in a lean area, wherein an excess air ratio λ is larger than 1, is disposed in an exhaust passage of an engine, a low load and low engine speed area is a lean stratified combustion area, and a middle/high engine speed area is a uniform combustion area of an air-fuel ratio of 15 or less. The exhaust passage between the engine and the NOx catalyst has a heat-insulating arrangement and/or a heat-insulating structure. The excess air ratio λ in the stratified combustion area is set to 1.3 or higher, while a fuel injection ode in a partial load area of the middle/high engine speed area is set to an intake divided injection mode, wherein fuel is dividedly injected from an early stage to a middle stage in an intake stroke.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control system for a spark-ignition direct-injection engine, and more particularly, to a spark-ignition direct-injection engine in which lean burn is performed by stratified combustion in a low-load and low-speed region. It relates to a control device.

[0002]

2. Description of the Related Art Under predetermined conditions such as low load and low speed,
There has been proposed a spark ignition type direct injection engine that performs so-called lean combustion in which fuel is burned at an air-fuel ratio larger than the stoichiometric air-fuel ratio. In such a spark ignition type direct injection engine, when the air-fuel ratio is in a so-called lean state where the air-fuel ratio is larger than the stoichiometric air-fuel ratio, NOx in the exhaust gas is adsorbed and exhausted in order to reduce nitrogen oxides (NOx) generated during lean combustion. There is an exhaust pipe provided with a NOx catalyst for reducing adsorbed NOx when the air-fuel ratio is in a so-called rich state in which the air-fuel ratio is equal to or lower than the stoichiometric air-fuel ratio while reducing the NOx inside. This NOx catalyst adsorbs NOx in the lean state, and performs the same function as the three-way catalyst in the rich state.

[0003]

However, the NOx catalyst as described above has a narrow effective temperature range, and therefore, when the engine is not sufficiently heated immediately after the cold start of the engine, or when the engine is idling and the load is low. For example, when the exhaust gas temperature is low due to lean combustion performed at times, the temperature does not reach this temperature range, and there is a problem that the emission deteriorates. In addition, since the exhaust gas temperature becomes high even in a relatively frequently used operation region such as during high-speed steady running, there is a problem that the NOx catalyst becomes hot and cannot function effectively.

The present invention has been made in view of the above problems, and provides a spark ignition type direct injection engine capable of maintaining a NOx catalyst within an active temperature range in many operating regions to reduce emissions. The purpose is to do.

[0005]

In order to achieve the above object, the present invention provides a NOx catalyst for reducing NOx in exhaust gas in a lean region where an excess air ratio λ is larger than 1 in an exhaust passage of an engine. A control apparatus for a spark-ignition direct-injection engine in which a low-load / low-speed region is a lean stratified combustion region and a middle / high-speed region is a uniform combustion region having an air-fuel ratio of 15 or less. The exhaust passages between them have an adiabatic arrangement and / or an adiabatic structure, the λ of the stratified combustion region is 1.3 or more, and the fuel injection form of the partial load region in the middle and high speed regions is changed from the previous period of the intake stroke. Intake split injection is performed in which fuel is split and injected over the middle period. As a preferable split fuel injection mode, for example, the crank angle of the intake stroke is 30 degrees and 80 degrees.
Near each degree, there are two split injections that inject fuel.

[0006] According to such a configuration, since the exhaust path to the NOx catalyst is a heat insulating arrangement and / or a heat insulating structure, the amount of heat radiation in this exhaust path is reduced. Therefore, immediately after the cold start of the engine, the temperature of the NOx catalyst quickly rises to the activation temperature, and the stratified combustion region in which the exhaust gas temperature is relatively low and λ is 1.3 or more (in particular, the idle region or the idle region) Even in the vicinity (low rotation / low load region), the temperature of the exhaust gas flowing into the NOx catalyst is hardly reduced, and the temperature of the NOx catalyst falls within a temperature range in which NOx purification (including NOx adsorption) is efficiently performed. Will be maintained.

[0007] Further, in the engine middle / high speed region, the combustion is a uniform combustion region having an air-fuel ratio of 15 or less. When the engine is in the partial load region, the fuel injection mode is divided and started from the first half to the middle of the intake stroke. The intake split injection is used. Specifically, for example, the fuel is injected into the fuel injection device in two stages, an early injection and a late injection, from the first half to the middle of the intake stroke. In this case, the early-injected fuel is thereafter diffused uniformly with the increase in the volume of the combustion chamber due to the downward movement of the piston until the late-stage injection is started. Also, the remaining fuel injected late is diffused into the increased combustion chamber and becomes uniform. As a result, a uniform air-fuel mixture is generated in the combustion chamber, and the combustion speed is increased in the combustion stroke after the compression stroke, so that the combustion efficiency is increased and the exhaust gas temperature is decreased.

Further, since the injection timing of each of the split injections is set earlier than the central timing of the intake stroke, the early injection is performed when the descending speed of the piston is high and the accompanying intake flow velocity is high. As a result, both early and late injections are performed in the first half of the intake stroke. As a result, the late injected fuel adheres to the cylinder wall near the bottom dead center of the piston (end of the intake stroke), thereby hindering fuel equalization. And the time until the ignition, that is, the time until the fuel is vaporized and atomized, can be secured long. By these or synergistic actions, the vaporization and atomization of fuel in the combustion chamber can be greatly promoted and the uniformity can be greatly increased, and the combustion efficiency of the engine can be further increased and the exhaust gas temperature can be further reduced. .

Therefore, the fuel is split and injected in the intake air.
In the partial load region of the uniform combustion with the air-fuel ratio of 15 or less, the exhaust gas temperature is lowered by such intake split injection. As a result, overheating of the NOx catalyst due to high-temperature exhaust gas in the middle / high rotation / partial load region caused by the heat insulating arrangement or the heat insulating structure of the exhaust passage is suppressed. In the partial load region, the temperature of the NOx catalyst can be maintained within a temperature range in which NOx purification (including NOx adsorption) is efficiently performed in the lean region. Therefore, NOx
The catalyst can be maintained at a high NOx purification rate over a wide operating range, and emission is improved.

In a preferred form of the invention, the thermal insulation arrangement comprises:
An exhaust port opening of the engine and an exhaust passage connected to the exhaust port opening are disposed on the vehicle rear side of the engine body, and the NOx catalyst is disposed on the vehicle rear side of the engine body. According to such a configuration,
At least a part of the exhaust path (exhaust pipe) to the NOx catalyst is arranged in a space behind the engine where the influence of the traveling wind is small, and the exhaust path to the NOx catalyst is shortened. Since the amount of heat radiation in the exhaust path from the engine to the NOx catalyst is reduced as compared with the configuration extending from
The amount of heat radiation from the exhaust pipe located between the x catalysts is reduced. As a result, immediately after the cold start, the temperature of the NOx catalyst quickly rises to the activation temperature.

In a preferred embodiment of the invention, the engine is mounted such that the cylinder rows are arranged in the axle direction, and an exhaust port opening is formed in the engine side wall on the vehicle rear side among a pair of engine side walls extending in the cylinder row direction. Are located. According to such a configuration, a so-called horizontal engine is
Since the traveling wind hitting the exhaust pipe from the engine to the NOx catalyst is blocked, the temperature of the exhaust gas entering the NOx catalyst is unlikely to decrease at this exhaust pipe portion. In a preferred form of the invention,
The heat insulating structure is a heat insulating structure in which a double exhaust pipe having a heat insulating space is disposed in an exhaust passage from the engine to the NOx catalyst. According to such a configuration, the NOx
In the exhaust path to the catalyst, the dual exhaust pipe makes it difficult for the exhaust gas temperature to decrease.

In a preferred embodiment of the present invention, a uniform combustion region having an air-fuel ratio of 15 or less is provided adjacent to the stratified combustion region,
The fuel injection mode in the uniform combustion region is defined as split intake injection. According to such a configuration, adjacent to the stratified combustion region in the lean state, it is not a uniform combustion region with an intermediate air-fuel ratio (16 to 19) in which the amount of NOx emission from the engine is large and the exhaust gas temperature is relatively high. Therefore, there is a uniform combustion region by the split intake injection with an air-fuel ratio of 15 or less. Therefore, in the region adjacent to the lean stratified combustion region, an increase in NOx emission can be suppressed, an increase in exhaust gas temperature can be suppressed, and overheating of the NOx catalyst can be suppressed in a wide operating range.

In a preferred embodiment of the present invention, exhaust gas recirculation (EGR) is performed in a region where split intake injection is performed. According to such a configuration, the combustion stability is enhanced by the intake split injection, so that the recirculation amount of the exhaust gas can be significantly increased. As a result, during combustion,
A large amount of inert gas (recirculated exhaust gas) that does not contribute to combustion is present in the cylinder, and the large amount of inert gas deprives heat generated during combustion, and thus the exhaust gas generated by combustion. Temperature greatly decreases. As described above, according to the above-described configuration, a large amount of EGR is made possible by the split injection of fuel, and as a result, the exhaust gas temperature is suppressed to a lower level, so that the NOx catalyst is not overheated and the NOx generation is suppressed. The fuel consumption can be improved by further reducing the amount and further reducing the pumping loss of the engine.

In a preferred embodiment of the present invention, the fuel injection mode in the low-load side region in the middle / high rotation range is configured to be the intake split injection. According to such a configuration,
In a low-load region in a high rotation region, the intake split injection suppresses a rise in the temperature of the exhaust gas. As a result, medium-, high-speed, and low-load-side regions where the frequency of use is high and the exhaust gas temperature is relatively high, specifically, high-speed constant-speed traveling (highway traveling in the high-speed stage of the transmission) At times,
Overheating of the NOx catalyst is suppressed.

In a preferred embodiment of the present invention, the upper limit value N3 of the engine speed in the region where the split intake injection is performed is in the range of 2/4 to 3/4 of the rated engine speed, and In the engine rotation range from the upper limit N2 to the N3, the low load region including the load / load line indicating the driving load when the vehicle travels on a substantially flat road at a constant speed in a high gear position, and is substantially high except for the full load. In the load range up to the load region, the fuel injection mode is the intake split injection, the excess air ratio λ is approximately 1, and the EGR ratio in the low load region near the load / load line is 10% or more. It is configured.

In this specification, the EGR rate is defined as {(CO2 concentration in intake air)-(CO2 concentration in air)} /
｛(CO2 concentration in exhaust gas)-(CO2 concentration in intake air)｝
Which means EGR amount (recirculated exhaust gas amount) / new air amount. Therefore, the EGR rate 100
Percent means that fresh air and exhaust gas are the same amount, and 10% means that the EGR amount is one of the fresh air amount.
Means 0%. According to such a configuration, split injection is performed in the engine operation region where the operation frequency is high and the temperature of the catalyst is likely to be high (the engine operation region in which the vehicle runs at a high speed at a constant speed in a high gear stage). EGR is possible. Then, due to the synergistic effect of the intake split injection and the high ratio of EGR, the exhaust gas temperature decreases (the increase in the exhaust gas temperature is suppressed), and the NOx catalyst can be maintained in a temperature range in which the NOx purification rate is high. Further, the upper limit value N3 of the engine speed in the region where the intake split injection is performed is set to 2/4 to 3/4 of the rated engine speed.
, The degree of freedom in setting the injection interval of the split injection is increased.

According to a preferred embodiment of the present invention, in the region on the higher load side than the stratified combustion region, the fuel injection mode is set at the engine speed N1 or higher which is lower than the upper limit N2 of the engine speed in the stratified combustion region. Is the intake split injection, and at an engine speed less than the N1, the fuel injection mode is configured to be the intake batch injection in which the fuel is injected collectively during the intake stroke. This intake batch injection is not necessarily
It does not have to be performed during the first half and the middle of the intake stroke. According to such a configuration, when the high-temperature intake air is charged, the temperature of the air-fuel mixture rises and knocking is likely to occur. Even in the case of rapid acceleration, in the high-load region on the lower rotation side than N1 where the vehicle jumps in such an operating state, since the intake batch injection is performed, the fuel is intensively injected into the cylinders. , Knocking is suppressed. In a preferred embodiment of the present invention, in the uniform combustion region, exhaust gas recirculation (EGR) is performed in a region adjacent to the stratified combustion region, and an EGR rate at the time of the intake split injection of N1 or more is less than the N1 during the batch injection of intake. Is set to be larger than the EGR rate. According to such a configuration, in a region where the exhaust gas temperature rises due to an increase in the engine rotational speed and the engine rotational speed is higher than N1, the EGR rate is set to be higher than that in the simultaneous intake injection since the intake split injection is performed. As a result, the exhaust gas temperature is reduced, and the temperature rise of the NOx catalyst is suppressed.

According to a preferred embodiment of the present invention, when the temperature of the NOx catalyst is high, the fuel is divided and injected in the intake stroke when the engine speed is lower than N1. When the NOx catalyst temperature is high, such as in a high-speed or high-load vehicle running state, or in a vehicle running state decelerated from high-speed driving, when the vehicle stops without intake air cooling due to running wind or when the vehicle accelerates rapidly from a very low speed Knocking is less likely to occur. Therefore, according to such a configuration, when the temperature of the NOx catalyst is high,
Even in the lower rotation speed region than N1, the fuel is divided and injected in the intake stroke to lower the exhaust gas temperature. Along with this, it is possible to increase the EGR rate and further reduce the exhaust gas temperature.

According to a preferred embodiment of the present invention, in the stratified charge combustion region, the temperature of the NOx catalyst is set to a predetermined temperature at which the NOx reduction rate in the lean region of the NOx catalyst starts to decrease or a high temperature state near the predetermined temperature. When it reaches, the fuel is divided and injected in the intake stroke, and uniform combustion with an air-fuel ratio of 15 or less for performing exhaust gas recirculation (EGR) is performed. According to such a configuration, when the temperature state of the NOx catalyst becomes high, even in the stratified combustion state of λ1.3 or more, the air-fuel ratio of 15 or less for performing the intake split injection and the exhaust gas recirculation (EGR) is uniform. Since combustion is performed, exhaust gas purification is performed by the three-way function of the NOx catalyst, and a decrease in NOx adsorption of the NOx catalyst in a lean region (a region where λ is greater than 1) due to a high temperature is compensated for. That is, the temperature range in which the three-way function of the NOx catalyst is high corresponds to the NOx in the lean region of the NOx catalyst.
x Adsorption function is wider than high temperature range (wider to high temperature side)
When the temperature state of the NOx catalyst becomes high, NOx
The catalyst performs a three-way function, and the N
It is possible to prevent an increase in NOx emission due to low Ox adsorption function.

According to a preferred embodiment of the present invention, an air-fuel ratio of 1
When a transition is made from a uniform combustion region of 5 or less to a preset stratified combustion region of λ of 1.3 or more, uniform combustion with an air-fuel ratio of 15 or less in which the intake split injection is performed and exhaust gas recirculation (EGR) is performed. Is configured to do so. According to such a configuration, when the temperature state of the NOx catalyst is high, even if the transition is made from the uniform combustion region to the stratified combustion region of λ1.3 or more, the split intake air injection and the exhaust gas recirculation ( Since the air-fuel ratio is equal to or less than 15 for performing EGR), exhaust gas purification is performed by the three-way function of the NOx catalyst, and NOx can be reduced. Specifically, NOx is reduced together with CO and HC. Further, since a large amount of EGR is made possible by the split intake injection, the pumping loss of the engine can be reduced while reducing NOx, and even though the air-fuel ratio is changed to 15 or less, deterioration of fuel efficiency can be reduced, and NOx can be reduced. It is possible to achieve both reduction and fuel economy. According to a preferred embodiment of the present invention, the region where uniform combustion with an air-fuel ratio of 15 or less is performed when the NOx catalyst is at or near the predetermined temperature is a high-speed side region of the stratified combustion region. It is configured. According to such a configuration, when the NOx reduction rate is deteriorated due to overheating of the NOx catalyst, the high-speed side region (relative region of the lean region) in the stratified combustion region in which the NOx emission from the engine is relatively large. (Where the NOx emission from the engine is relatively large) is the uniform combustion at an air-fuel ratio of 15 or less where the intake air splitting and the EGR are performed. By function, N in this area
Ox can be reduced. Further, the deterioration of fuel efficiency due to the change to the uniform combustion is suppressed by the high ratio of EGR due to the intake air split. In this way, both reduction of NOx and suppression of deterioration of fuel efficiency are achieved.

According to a preferred embodiment of the present invention, when the NOx catalyst is at or near the predetermined temperature, in the low rotation speed side region of the stratified combustion region where λ is 1.3 or more,
Batch injection of fuel during intake stroke and exhaust gas recirculation (EGR)
Is performed to perform uniform combustion at an air-fuel ratio of 15 or less. According to such a configuration, even in the low rotation speed region in the stratified combustion region, it is possible to achieve both the purification of exhaust gas by the three-way function of the NOx catalyst and the suppression of fuel consumption. According to a preferred embodiment of the present invention, at the time of acceleration, when the engine operating state determined by the load and the number of revolutions of the engine is in the high rotation side region of the stratified combustion region,
It is configured to perform uniform combustion with an air-fuel ratio of 15 or less for performing intake split injection and exhaust gas recirculation (EGR). According to such a configuration, at the time of acceleration in which NOx emission from the engine is relatively large, the three-way function of the NOx catalyst causes N
Acceleration is ensured while Ox is sufficiently reduced. According to a preferred embodiment of the present invention, the air-fuel ratio of 1 by the intake split injection performed in the high rotation speed region of the stratified combustion region is set.
The EGR rate in uniform combustion of 5 or less is configured to be 30% or more. According to such a configuration, by dividing and injecting the fuel in the intake stroke,
Since a high rate of EGR is possible, this high rate of EGR
, The temperature of the NOx catalyst is reduced to N
Ox can be reduced to a temperature range that can be efficiently purified.

According to a preferred embodiment of the present invention, when the engine is cold, uniform combustion with an air-fuel ratio of 15 or less is performed even at the time of the low load and low rotation, and a three-way catalyst is arranged upstream of the NOx catalyst. Configuration. According to such a configuration, when the engine is cold, uniform combustion with an air-fuel ratio of 15 or less is performed even at a low load and a low rotation, so that the exhaust gas temperature increases and the temperature of the catalyst quickly rises. Further, since the three-way catalyst is arranged on the upstream side of the NOx catalyst, the temperature of the three-way catalyst tends to increase. In a preferred embodiment of the present invention, when the temperature state of the three-way catalyst is a high temperature state regardless of the operation state, uniform combustion with an air-fuel ratio of 15 or less for performing intake split injection and exhaust gas recirculation (EGR) is performed. ing. According to such a configuration, the three-way catalyst hardly reaches the heat-resistant temperature limit, so that the three-way catalyst can be arranged closer to the engine. For this reason, the temperature of the three-way catalyst is rapidly raised at the time of cooling, and the emission during cold is improved. In a preferred embodiment of the present invention, exhaust gas recirculation (EGR) is performed in both the uniform combustion region where fuel is dividedly injected and the stratified combustion region. According to such a configuration, reduction of NOx emission from the engine and improvement of fuel efficiency can be achieved in a wide operating range.

In order to achieve the above object, another invention of the present application discloses a fuel cell system in which a NOx catalyst for reducing NOx in exhaust gas in a lean region where an excess air ratio λ is greater than 1 is provided in an exhaust passage separated from an exhaust manifold. In a control device for a direct-injection spark-ignition engine, wherein a low-load / low-speed region is a lean stratified combustion region, and a middle / high-speed region is a uniform combustion region having an air-fuel ratio of 15 or less, the engine comprises a cylinder An exhaust port opening is provided on an engine side wall on the vehicle front side of a pair of engine side walls extending in the direction of the cylinder line, and an exhaust pipe connected to the exhaust manifold is provided. The NOx catalyst extends to the vehicle rear side of the engine through the lower portion of the engine, and the NOx catalyst is disposed in a portion of the exhaust pipe downstream of the engine below the engine. An exhaust pipe located between the manifold and the lower portion of the engine and located upstream of the NOx catalyst is a double exhaust pipe having an adiabatic space, and has a λ of 1.3 or more in the stratified combustion region, The fuel injection mode of the partial load region in the middle and high rotation regions is divided into intake injections in which the injection is started from the first half to the middle period of the intake stroke, and the air-fuel ratio is adjacent to the stratified combustion region.
The following uniform combustion region is provided, and the fuel injection mode in the uniform combustion region is the intake split injection.

According to such a configuration, the heat release from the exhaust gas is suppressed by the double exhaust pipe, and the temperature of the catalyst is quickly raised immediately after the engine is started, when the vehicle is stopped or when the vehicle is running at a constant speed. . Further, even in a stratified combustion region where the exhaust gas temperature is relatively low and λ is 1.3 or more, the temperature of the exhaust gas flowing into the NOx catalyst becomes lower than that of the NOx catalyst.
x purification (including NOx adsorption) is maintained within a temperature range in which the purification is efficiently performed. Further, in the engine middle / high rotation region, the air-fuel ratio is a uniform combustion region of 15 or less,
When the fuel injection mode is in the partial load region, the fuel injection mode is the intake split injection in which the injection is started from the first half to the middle period of the intake stroke. The gas temperature drops,
In the middle / high rotation / partial load range, the temperature of the NOx catalyst can be maintained within a temperature range in which NOx purification (including NOx adsorption) is efficiently performed in the lean range. For this reason, the NOx catalyst can be maintained at a high NOx purification rate in a wide operating range, and emission is improved.

According to a preferred embodiment of the present invention, when the engine is cold, the air-fuel ratio is 15 even at the low load and low speed.
The following homogeneous combustion is adopted, and a three-way catalyst is arranged upstream of the NOx catalyst. According to such a configuration, the three-way catalyst is disposed on the front side of the engine and is cooled by the traveling wind, so that overheating is suppressed and the direct flow to the exhaust manifold is suppressed. The temperature can be quickly increased immediately after the cold start, and the cold emission can be improved. According to a preferred embodiment of the present invention, regardless of the operation state, when the temperature state of the three-way catalyst is a high temperature state, the air-fuel ratio is 15 or less at which fuel is divided and injected during the intake stroke and exhaust gas recirculation (EGR) is performed. Is configured to perform uniform combustion.
According to such a configuration, the temperature of the exhaust gas downstream of the three-way catalyst tends to increase and the temperature of the NOx catalyst also tends to increase due to the reaction of the three-way catalyst due to uniform combustion at an air-fuel ratio of 15 or less. By the split injection and the EGR, the temperature of the NOx catalyst is prevented from becoming higher than the temperature range in which the NOx purification rate in the lean region is high, and the operation mode can be promptly shifted to the lean burn operation mode. According to a preferred embodiment of the present invention, the upper limit value N3 of the engine speed in the region where the intake split injection is performed is set to a range of 2/4 to 3/4 of the rated engine speed, and the engine speed in the stratified combustion region is reduced. In the engine rotation range from the upper limit N2 to the N3, the low load region including the load / load line indicating the driving load when the vehicle travels on a substantially flat road at a constant speed in a high gear position, and is substantially high except for the full load. In the load range up to the load range, the fuel injection mode is the intake split injection, the excess air ratio λ is approximately 1, and the EGR in the low load range near the load / load line.
The rate is set to 10% or more.

According to such a configuration, the engine operating region where the operating frequency is high and the temperature of the catalyst is likely to be high (the engine operating region where the vehicle travels at a high speed at a constant speed in a high gear stage).
Therefore, since the intake is divided into injections, a high ratio of EGR of 10% or more can be achieved. Then, due to the synergistic effect of the intake split injection and the high ratio of EGR, the exhaust gas temperature decreases (the increase in the exhaust gas temperature is suppressed), and the NOx catalyst can be maintained in a temperature range in which the NOx purification rate is high. Further, the upper limit value N3 of the engine speed in the region where the intake split injection is performed is set to 2/4 to 3/3 of the rated engine speed.
Since the range is set to 4, the degree of freedom in setting the injection interval of the split injection is increased.

[0027]

Next, preferred embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram showing an overall configuration of a control device A for a direct injection engine according to a first embodiment of the present invention. The engine 1 controlled by the control device A is, for example, an in-line four-cylinder engine mounted on a vehicle. The engine 1 has four first to fourth cylinders 2, 2,... (Only one is shown), and a piston 3 is inserted into each cylinder 2 so as to be able to reciprocate.
A combustion chamber 4 is defined in the cylinder 2 by the piston 3. An ignition plug 6 connected to an ignition circuit 5 is attached to a position on the cylinder axis on the upper wall of the combustion chamber 4 so as to face the combustion chamber 4. In addition, the side wall of the combustion chamber 4 is located at a position that does not interfere with the moving piston 3.
An injector (fuel injection valve) 7 is attached to inject fuel directly into the combustion chamber 4.

Although described in detail later, the injector 7 includes a high-pressure fuel pump 71 and a pressure regulator 7.
The fuel supply circuit 70 is connected to the injector 7 while adjusting the fuel from the fuel tank 74 to an appropriate pressure.
It is configured to supply to. Further, a fuel pressure sensor 8 for detecting the fuel pressure is provided. When fuel is injected by the injector 7 in the latter half of the compression stroke of the cylinder 2, the fuel spray is trapped in a cavity (not shown) formed in the top surface of the piston 3, and near the ignition plug 6. A relatively dense mixture is formed. On the other hand, when the fuel is injected by the injector 7 in the intake stroke of the cylinder 2, the fuel spray diffuses into the combustion chamber 4 and mixes with the intake air (air) to form a uniform mixture in the combustion chamber 4.

The combustion chamber 4 is connected to an intake passage 10 via an intake valve 9 by an intake port (not shown).
The intake passage 10 supplies the intake air filtered by the air cleaner 11 to the combustion chamber 4, and detects a quantity of intake air taken into the engine 1 in order from an upstream side to a downstream side. A sensor 12, an electric throttle valve 1 for restricting the intake passage 10, and a surge tank 1
4 are provided. The electric throttle valve 13
Is not mechanically connected to an accelerator pedal (not shown), and is driven by a motor 15 to open and close. Further, a throttle opening sensor 16 for detecting the opening of the throttle valve 13 and an intake negative pressure sensor 17 for detecting an intake negative pressure in the surge tank 14 are provided. The intake passage 10 downstream of the surge tank 14 is an independent passage 10a branched for each cylinder 2, and the downstream end of each independent passage 10a is further branched into two and communicates with the intake port. The swirl control valve 18 is provided on one of the branches. The swirl control valve 18 is driven by an actuator 19 to open and close.
Is opened, the intake air is supplied to the combustion chamber 4 only from the other branch passage to generate a strong intake swirl, while the intake swirl is weakened as the swirl control valve 18 opens. In addition, a swirl control valve opening sensor 20 for detecting the opening of the swirl control valve 18 is provided.

An exhaust passage 22 for discharging combustion gas from the combustion chamber 4 is provided. An upstream end of the exhaust passage 22 is branched for each cylinder 2 to form an exhaust manifold 22a, and these exhaust manifolds 22a are connected to an exhaust port (not shown). Is connected to each combustion chamber 4 via an exhaust valve 23. In the exhaust passage 22, an O ₂ sensor 24 for detecting the oxygen concentration in the exhaust gas and a catalyst 25 for purifying the exhaust gas are arranged in order from the upstream side to the downstream side. The O ₂ sensor 24
Is used to detect the air-fuel ratio based on the oxygen concentration in the exhaust gas, and has a characteristic that the output changes suddenly when the air-fuel ratio is at the stoichiometric air-fuel ratio.

The catalyst 25 has a cordierite carrier (not shown) having a honeycomb structure in which a large number of through holes extending parallel to each other along an axial direction (flow direction of exhaust gas) are opened. The catalyst layer is formed on the wall surface of the through hole. While the catalyst 25 adsorbs NOx in a lean state where the air-fuel ratio is higher than the stoichiometric air-fuel ratio, when the air-fuel ratio becomes rich near or below the stoichiometric air-fuel ratio, the adsorbed NOx is released and reduced and purified. A lean NOx catalyst of the NOx adsorption reduction type is used. A catalyst having such NOx adsorption / reduction performance is characterized by its NO.
It is known that the x-purification performance has a characteristic that strongly depends on the temperature state, and the NOx purification rate of the catalyst becomes extremely high in a predetermined temperature range (for example, 250 to 400 ° C.), while in a high temperature state higher than that. Decreases rapidly with increasing temperature.

Further, an upstream end of an EGR passage 26 is branched and connected to the exhaust passage 20 upstream of the O ₂ sensor 24, and a downstream end of the EGR passage 26 is provided between the throttle valve 13 and the surge tank 14. And a part of the exhaust gas is recirculated to the intake system. Near the downstream end of the EGR passage 26, an electric EGR valve 27 whose opening can be adjusted is disposed.
The amount of exhaust gas recirculated through the passage 26 (hereinafter, referred to as an EGR amount) is adjusted. Further, a lift sensor 28 for detecting a lift amount of the EGR valve 27 is provided.

The fuel supply circuit 70 includes an injector 7
A fuel passage 75 connects the fuel tank 74 to the fuel tank 74. The fuel is pumped up by a low-pressure fuel pump 76 disposed in the fuel tank 74 and supplied to the injector 7. A low-pressure pressure regulator 72, a fuel filter 77, and a high-pressure supply pump 71 are disposed in the middle of the fuel passage 75 in order from the upstream side. The fuel discharged from the low-pressure fuel pump 76 is regulated by the low-pressure pressure regulator 72. After being pressurized, the pressure is further increased by the high-pressure fuel pump 71, and the high-pressure fuel is supplied to the injector 7.

The excess fuel supplied to the injector 7 is supplied to the fuel passage 7 between the low-pressure pressure regulator 72 and the fuel filter 77 through the return passage 78.
Returned to 5. A high-pressure pressure regulator 73 is provided in the middle of the return passage 78, and surplus fuel is returned to the upstream side of the high-pressure fuel pump 71 while the flow rate is adjusted by the high-pressure pressure regulator 73, and supplied to the injector 7. The pressure of the supplied fuel is adjusted appropriately.

Further, there is provided a linear purge device (evaporated fuel supply means) 80 for recovering the evaporated fuel in the fuel tank 74 and supplying it to the intake system of the engine 1. The linear purge device 80 includes a canister 81 that adsorbs evaporated fuel, an introduction passage 82 that guides the evaporated fuel from the fuel tank 74 to the canister 81, and a purge passage 83 that communicates the canister 81 and the intake passage 10. I have.

The purge passage 83 communicates with the canister 8.
The fuel vapor adsorbed by the suction valve 1 is sucked out by the intake negative pressure and supplied to the intake passage 10 between the throttle valve 13 and the surge tank 14, and a purge valve 84 composed of a duty solenoid valve is provided on the way. Is provided. The supply amount (purge amount) of the evaporated fuel amount to the intake passage 10 is continuously adjusted by the duty control of the opening degree of the purge valve 84.

The ignition circuit 5 of the ignition plug 6, the injector 7, the drive motor 15 of the electric throttle valve 13, the actuator 19 of the swirl control valve 18, the electric EGR
The valve 27, the purge valve 84, etc.
(Hereinafter referred to as ECU). On the other hand, this ECU 40, the air flow sensor 12, a throttle opening sensor 16, the output signals such as the intake negative pressure sensor 17, the swirl control valve opening sensor 20, O ₂ lift sensor 28 of the sensor 24, EGR valve 27 is In addition, a water temperature sensor (temperature state detecting means) 30 for detecting a cooling water temperature (engine water temperature) of the engine 1, an intake air temperature sensor 31 for detecting an intake air temperature, an atmospheric pressure sensor 32 for detecting an atmospheric pressure The output signals of a rotation speed sensor 33 for detecting the engine speed and an accelerator opening sensor 34 for detecting the opening (depression amount) of an accelerator pedal are input.

Next, the positional relationship between the engine 1 and the like and the vehicle will be described with reference to FIGS. FIG. 2 is a schematic view of the front portion of the vehicle equipped with the engine 1 as viewed from the vehicle width direction, and FIG. 3 is a schematic diagram of the engine 1 mounted on the vehicle viewed from the rear, ie, from the driver's seat direction. is there. As shown in FIGS. 2 and 3, the engine 1 is positioned adjacent to the transmission M and behind the radiator 89 so that the cylinder rows are arranged in the axle (vehicle width) direction.
It is arranged in an engine room R formed under the hood B of the vehicle. The exhaust port opening 90 formed in the side wall of the engine 1 is located on the vehicle rear side. The exhaust manifold 22a connected to the exhaust port opening 90 is
The rear side of the engine 1 extends downward and is connected to each other to form an exhaust pipe 22. The exhaust pipe 22 extends downward on the rear side of the engine 1 substantially in parallel with the rear wall of the engine 1, bends toward the vehicle rear side at substantially the same height as the lower end of the engine 1, and faces toward the vehicle rear side. Extending. The downstream end of the exhaust pipe 22 is connected via a flexible joint 92 to a catalyst (NOx catalyst) 25 disposed below the floor panel P. That is, in this embodiment, the exhaust port 90 is connected to the exhaust manifold 22.
a through the exhaust pipe 22 and the catalyst (NO
The x-catalysts) 25 are arranged on the rear side of the main body of the engine 1 on the vehicle, and these are arranged in an adiabatic manner where heat is not easily taken away by the traveling wind.

Engine control device A according to this embodiment
Switches the mode of fuel injection by the injector 7 (fuel injection timing, air-fuel ratio, etc.) to operate the engine 1 in a different combustion state, that is, combustion mode control means for switching the combustion mode (operation mode) of the engine 1 To E
The CU 40 is provided.

The combustion mode control means includes the engine 1
Operating in a lean state where the air-fuel ratio is greater than or equal to the stoichiometric air-fuel ratio, or in a rich state where the air-fuel ratio is equal to or less than the stoichiometric air-fuel ratio, at what point in the stroke of the fuel injection, and whether the fuel injection is batch or split The engine control data such as whether or not to perform exhaust gas recirculation is preset as a plurality of control maps according to the engine speed and the engine load,
The engine control device is configured to switch the operating state of the engine based on the control map.

More specifically, when the engine 1 is in the basic control mode after warm-up, as shown in FIG. 4A, the operating region on the low load / low rotation side has an excess air ratio λ of 1. Three or more stratified lean burn regions I (including I ') are set, and the fuel is injected at a time during the compression stroke to set the injection mode. Further, in the operating regions II, III and IV adjacent to the stratified lean burn region I (I ′) on the side of high load or high rotation, λ is 1
That is, a uniform combustion region having an air-fuel ratio of 15 or less is defined as an enrichment region V, and a region on the high-load / high-rotation side of the uniform combustion region is defined as an enrichment region V. Of this uniform combustion area,
A low rotation region II in which the engine speed is less than N1 (for example, 1200 rpm) and N3 (for example, 3) in which the engine speed is a value in the range of 2/4 to 3/4 of the rated speed of the engine 1.
500 rpm) or higher and the upper limit engine speed N2 (for example, 2250 rpm) in the stratified lean burn region I.
In a region IV consisting of a low-load region of the operation region from m) to N3, the collective intake injection for performing the collective injection of the fuel in the intake stroke is performed. Further, a region III of the uniform combustion region other than II and IV, that is, a region excluding a full load region and a region where the load is extremely low when the engine speed is in the range of N1 to N2.
In III, split intake injection is performed in which fuel is injected in two splits from the first half to the middle of the intake stroke. As the intake split injection, for example, an injection mode in which fuel is split into two and injected when the crank angle of the intake stroke is around 30 degrees and 80 degrees is preferable.

As is clear from FIG. 4A, the region I
(Including I ′) and the regions II ′ and III ′ adjacent to the region I of the regions II and III, that is, the regions other than the high-load region of the regions II and III, the EGR is performed. It is configured as follows. A load / load line at a high speed stage of the transmission indicated by a chain line in FIG. 4A (a line indicating a driving load when a vehicle travels on a substantially flat road surface at a high speed gear stage at a constant speed of, for example, about 100 km / h). ) Indicates that the engine speed is from N2 to N
In the range between 3, the region III 'is entered. Therefore, in this embodiment, when the vehicle travels at a constant speed at a high speed on a substantially flat road surface in the range of the engine speeds N2 and N3, the engine 1 performs the fuel split injection and the EGR.
Will be operated with uniform combustion. In addition, the EGR in the area near the road / load line in the area III '
The rate is set to 10% or more, and the synergistic effect of the intake split injection and the high rate of EGR suppresses an increase in the exhaust gas temperature in this vicinity. In addition, region III '
Is controlled to be higher than the EGR rate in the region II ′. In addition, when the engine is cold, as shown in FIG. 4B, a uniform combustion region where λ is 1 (or approximately 1) is set except for an enrichment region in a high rotation or high load region.

Further, even after the warm-up, the injection mode shown in FIG. 4C is set at the time of acceleration or during a transition period when the temperature of the catalyst is high. This injection mode is basically the same as the injection mode of FIG. 4A. However, in the high load / high rotation side region of the stratified lean combustion region of the basic injection mode, the fuel is divided into two in the intake stroke. In the other stratified lean burn region in the basic injection mode, the fuel is injected in a lump during the intake stroke to be in the injection mode, which is different from the basic mode in that there is no stratified lean burn region. That is, stratified lean combustion is stopped in order to suppress an increase in NOx emission from the engine during acceleration, and stratified lean combustion is performed even in a high temperature state in which the NOx reduction rate in the lean region is reduced due to overheating of the catalyst. And stop each, NO
The x-catalyst performs uniform combustion with an air-fuel ratio of 15 or less that can perform a three-way function. Specifically, as shown in FIG. 4C,
The portion on the high rotation side of the stratified combustion region in the basic mode (FIG. 4A) is a part of the uniform combustion region VI of the split intake injection. Then, the EGR rate in the high load / high rotation side portion of the stratified combustion region is controlled to be 30% or more. Thus, when the engine speed changes from N1 to N3
Area except for the full load area and the area with extremely low load
VII is basically a uniform combustion region by intake split injection in which fuel is injected in two splits from the first half to the middle of the intake stroke. However, in the region of the rotational speed N1 orange, the fuel injection timing is not limited to the first half to the middle period during the intake stroke, and is configured to be divided and injected at any time during the intake stroke. preferable. A region other than the enrichment region is defined as a uniform combustion region VIII by the batch injection.

Next, the specific control of the fuel injection performed by the ECU 40 will be described with reference to the flowchart of FIG. FIG.
As shown in the figure, in step S1 after the start, the accelerator opening, the engine speed, the atmospheric pressure, the O2 concentration in the exhaust, the intake air amount, the water temperature, the intake air temperature, the throttle opening, the EGR valve opening, etc. Read. Next, step S
In 2, the target engine load is calculated. That is,
The indicated average effective pressure (Pi), which is the target load in the stratified combustion region, is obtained from the accelerator opening and the engine speed, and the target engine load in the uniform combustion region is obtained from the engine speed, intake air temperature, and atmospheric pressure (ie, intake air amount). The intake charging efficiency (ce) is calculated. Next, at step S3, the water temperature is reduced to a predetermined temperature W to determine whether the engine is in a cold state.
It is determined whether it is T1 or more. As WT1,
For example, a temperature between 45 and 60 degrees Celsius is selected.
When NO is determined in S3, that is, when it is determined that the water temperature is lower than WT1, the engine is cold, so that the process proceeds to step S4, and the uniform combustion mode of the intake batch injection without EGR is selected.

If YES in step S3, that is, if it is determined that the water temperature is equal to or higher than WT1, the process proceeds to step S5 to determine whether or not the engine is in a region where stratified combustion is performed, that is, whether or not the engine speed is in a low load region less than N2. Is determined. Step S
If NO in step 5, that is, if it is determined to be in the region where uniform combustion is performed, the process proceeds to step S6, and whether or not the region is where fuel injection is performed by split intake air, that is, if the engine speed is N1
It is determined whether or not the load is in the partial load region excluding the full load region and the region with extremely low load. If NO in step S6, that is, if it is determined that the region is not the region in which the intake split injection is performed, the process proceeds to step S7,
It is determined whether the engine speed is equal to or lower than a predetermined speed N1. NO in step S7, that is, when the engine speed is N
When it is determined that the value is higher than 1, the process proceeds to step S8, and the uniform combustion mode based on the collective intake injection is selected.

If YES in step S7, that is, if it is determined that the engine speed is not more than N1, step S9
Then, it is determined whether the temperature of the NOx catalyst 25 is equal to or lower than the predetermined temperature CT2. Here, as the predetermined temperature CT2, for example, a temperature of 450 to 500 degrees Celsius near the upper limit of the activation temperature range of the NOx catalyst 25 is selected. If YES in step S9, that is, if the temperature of the NOx catalyst 25 is CT2
When it is determined that the following conditions are satisfied, the process proceeds to step S8, and the uniform combustion mode based on the batch intake air injection is selected.
On the other hand, if NO in step S9, that is, if it is determined that the temperature of the NOx catalyst 25 is higher than CT2, step S1 is performed to reduce the temperature of the exhaust gas and suppress overheating of the catalyst 25.
The process proceeds to 0, and the uniform combustion mode based on the split intake injection is selected. Also, if YES in step S6, that is, if it is determined that the region is where the intake split injection is performed, step S10 is also performed.
To select the uniform combustion mode based on the intake split injection.

If YES in step S5, that is, if it is determined that the stratified charge combustion is to be performed, the process proceeds to step S11 to determine whether or not the vehicle is in an acceleration state. Step S1
If YES in step 1, that is, if it is determined that the vehicle is accelerating in the region where stratified combustion is performed, the process proceeds to step S12, and it is determined whether the engine speed is equal to or higher than the predetermined speed N1. In step S12, NO, that is, when the engine speed is N1
If it is determined that the value is less than the predetermined value, the process proceeds to step S8, and the uniform combustion mode based on the collective intake injection is selected.
On the other hand, if YES in step S12, that is, if it is determined that the engine speed is equal to or higher than N1, step S10
To select the uniform combustion mode based on the intake split injection.

If NO in step S11, that is, if it is determined that the vehicle is not in the accelerated state, the process proceeds to step S13, where it is determined whether the temperature of the NOx catalyst 25 is equal to or lower than a predetermined temperature CT1. Here, as the predetermined temperature CT1, for example, a temperature of 400 to 450 degrees Celsius near the upper limit of the activation temperature range of the NOx catalyst 25 is selected. If NO in step S13, that is, if it is determined that the temperature of the NOx catalyst 25 is higher than CT1, the process proceeds to step S12,
Step S8 or step S, depending on the engine speed
Proceed to any of 10. YES in step S13, that is, NO
When it is determined that the temperature of the x catalyst 25 is equal to or lower than CT1, the process proceeds to step S14, where it is determined whether or not the region is where fuel is divided and injected in the compression stroke. If it is determined, the process proceeds to step S15, where the stratified combustion mode by split injection in the compression stroke is selected. If NO, that is, if it is not the region to be subjected to compression split, the process proceeds to step S16, where stratification by batch injection in the compression stroke is performed. The combustion mode is selected.

When each combustion mode is selected in steps S4, S8, S10, S15 and S16, step S1 is performed.
The program proceeds to 7, and the fuel injection amount, injection timing, ignition timing, throttle opening, and EGR valve opening are calculated from each control map for each injection mode. Specifically, the ECU 40 has an engine control map as shown in FIG. First, a throttle opening and a fuel injection amount are calculated from a target air-fuel ratio map set corresponding to a target engine load and an engine speed. Here, if an air-fuel ratio map is provided for each throttle opening and each fuel injection amount, the accuracy is further improved. Further, based on the EGR map, the injection timing map, and the ignition timing map set corresponding to the target load and the engine speed (however, in the uniform combustion region, the actual load and the engine speed), the EGR rate, the injection timing, The ignition timing is calculated respectively. further,
From the EGR rate, the EGR valve opening in the operating state is calculated. As a result, an injection state corresponding to the injection mode shown in FIGS. 4A, 4B, and 4C is determined.

Next, at step S18, the throttle valve is set, at step S19 the injection valve is set, and further at step S20.
Respectively, the fuel injection valves are driven, and ignition is executed in step S21. Further, in step S22, the temperature of the catalyst 25 is estimated from operating states such as the engine speed, the intake air temperature, and the fuel injection amount, and the process returns. This estimated catalyst temperature is used in the next step S9 and step S1.
Used in 3. Preferably, the catalyst temperature immediately after the start of the engine is estimated from the elapsed time since the engine was stopped, the water temperature, and the like.

FIGS. 7 and 8 are diagrams showing the characteristics of the engine 1. FIG. 7 shows the engine characteristics during high-speed running.
FIG. 8 shows engine characteristics near the maximum EGR rate. As is clear from these figures, the split injection (split intake injection) has a higher E ratio than the batch injection.
GR becomes possible, and when compared at the same rate of EGR, both the fuel efficiency and the exhaust gas temperature have lower values for the split injection. Therefore, the intake split injection has a high rate of E
Exhaust passage that enables GR and reduces exhaust gas temperature by the amount indicated by the arrow in the figure by a synergistic effect with the effect of reducing the exhaust gas temperature of the split injection itself, and is effective immediately after starting the engine at cold or stratified lean combustion, etc. It can be understood that the configuration or arrangement of the above is possible. Here, the point at which the fluctuation rate of the indicated average effective pressure (Pi), that is, (Pi fluctuation width / Pi average value) of the same cylinder (own cylinder) is 5% is defined as the combustion stability limit.
In addition, the set point is a point that takes a margin from the combustion stability limit in consideration of the external environment of the engine and individual differences,
The point where the Pi variation is between 3 and 3.5%. FIG.
Is a drawing similar to FIG. 2 showing a modification of the first embodiment. This modification has the same basic configuration as that of the first embodiment.
The second embodiment differs from the first embodiment in that the exhaust pipe connecting the a and the flexible joint 92 is a double-structured exhaust pipe 122 having a heat insulating space.

FIGS. 10 and 11 show the exhaust pipe 122 of FIG.
It is sectional drawing which shows the upstream end connected to the exhaust manifold 22a, and the downstream end connected to the flexible joint 92, respectively. As is clear from FIG. 10, the exhaust pipe 122 is arranged such that an outer pipe 123 as a large-diameter pipe and an inner pipe 124 as a small-diameter pipe are overlapped so as to form an annular heat insulating space 125 therebetween. I have. FIG.
As shown in the figure, at the upstream end of the exhaust pipe 122, the outer pipe 123 is reduced in diameter so that its inner diameter is substantially equal to the outer diameter of the inner pipe 124, and directly overlaps the inner pipe 124. ing. Further, the ends of both tubes 123 and 124 are aligned and inserted into the connection flange 126, and the upstream end portions of the outer tube 123 and the inner tube 124 are welded in the vicinity of the funnel 126. As shown in FIG. 11, on the downstream end side of the exhaust pipe 122, only the outer pipe 123 is connected to the connection flange 127, and the downstream end of the inner pipe 124 is connected to the outer pipe 12
3 is located upstream of the downstream end. The downstream end portion of the inner tube 124 is positioned with respect to the outer tube 123 via an annular heat-resistant mat 128 having substantially the same thickness as the heat insulating space 124 so as to allow the inner tube 124 to expand and contract in the axial direction due to heat. ing. In the modified example configured as described above, the same control as in the first embodiment is performed, but the exhaust pipe 122
Is a heat-insulating zone structure having a double structure, so that the exhaust gas passing therethrough is less likely to lose heat in this portion. Therefore,
It becomes easy to quickly raise the temperature of the catalyst 25 after the cold start, and to maintain the temperature of the catalyst 25 at a predetermined temperature or more during stratified lean combustion.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 12 is a drawing similar to FIG. 2 showing the second embodiment. As is clear from FIG.
The second embodiment has the same basic configuration as the first embodiment, but the second embodiment has an exhaust manifold 2.
The third embodiment differs from the first embodiment in that a three-way catalyst 200 is arranged between the exhaust pipe 22 and the exhaust pipe 22. Therefore, FIG.
Then, the same components as those in the first embodiment are denoted by the same reference numerals as in FIG. Further, a third embodiment of the present invention will be described with reference to FIGS. FIG. 13 is a drawing similar to FIG. 2 showing the third embodiment, and FIG.
3 is a schematic drawing of the engine No. 3 as viewed from the front side of the vehicle. As is clear from FIGS. 13 and 14, the third embodiment has the same basic configuration as the second embodiment, but the third embodiment has an exhaust port located on the front side of the vehicle. The second embodiment differs from the second embodiment only in that the engine is mounted on the vehicle so that the exhaust pipe on the downstream side of the three-way catalyst has the same double structure as the modification of the first embodiment. different. Therefore, in FIG. 13, the same components as those of the other embodiments are denoted by the same reference numerals as in FIG.

As shown in FIGS. 13 and 14, the engine 300 is adjacent to the transmission M and the radiator 89 such that the cylinder rows are arranged in the axle (vehicle width) direction.
And in the engine room R formed below the hood B of the vehicle. Exhaust port opening 390 formed in the side wall of engine 300
Is located on the rear side of the vehicle. Exhaust port opening 390
The exhaust manifold 322a connected to the
Of the three-way catalyst 200 are connected to each other at a portion of the three-way catalyst 200 to form an exhaust pipe 322 having a double structure. The exhaust pipe 322 extends downward on the front side of the engine 300 substantially parallel to the front wall of the engine 300, bends toward the vehicle rear side at a height lower than the lower end of the engine 300, and bends below the engine 300. And extends toward the rear of the vehicle. The downstream end of the exhaust pipe 322 is connected via a flexible joint 92 to a catalyst (NOx catalyst) 25 disposed below the floor panel P. Therefore, in this embodiment, the NOx catalyst is arranged on the downstream side of the exhaust pipe 322 from below the engine 300.

Next, fuel injection control performed by the ECUs of the second and third embodiments will be described with reference to FIG. FIG. 15 is a flowchart showing the fuel injection control performed in the second and third embodiments, similarly to FIG. 5.

The flowchart of FIG. 15 is substantially the same as the flowchart of FIG. 5, except that the second and third embodiments have the three-way catalyst 200 on the upstream side of the NOx catalyst. And step S5, the temperature of the three-way catalyst 200 is raised to the predetermined temperature CT3 (for example, 80 degrees Celsius).
0)), and if YES in step S30, that is, if it is determined that the temperature of the three-way catalyst 200 is higher than CT3, the process proceeds to step S8 to reduce the temperature of the exhaust gas. NO, that is, when it is determined that the temperature of the three-way catalyst 200 is equal to or lower than CT3,
The point is to proceed to step S5.

The present invention is not limited to the embodiments described above, and various changes and modifications can be made within the scope of the matters described in the claims.

[0058]

According to the present invention having such a configuration, the spark ignition can reduce the emission by maintaining the NOx catalyst within a temperature range in which the NOx catalyst can function effectively in many operating regions. A direct injection engine is provided.

[Brief description of the drawings]

FIG. 1 is a drawing showing a schematic configuration of a control device A for a direct injection engine according to a first embodiment of the present invention.

FIG. 2 is an engine 1 according to the first embodiment of the present invention.
1 is a schematic drawing of a front portion of a vehicle equipped with a vehicle viewed from a vehicle width direction.

FIG. 3 is a schematic drawing of the engine 1 of FIG. 2 as viewed from the rear, that is, from the driver's seat direction.

FIG. 4A is a view showing a fuel injection mode after the engine is warmed up.

FIG. 4B is a view showing a fuel injection mode when the engine is cold.

FIG. 4C is a view showing a fuel injection mode in a transition period after the engine is warmed up.

FIG. 5 is a flowchart showing specific control of fuel injection performed in the first embodiment.

FIG. 6 is a drawing showing an engine control map used in the first embodiment.

FIG. 7 is a drawing showing engine characteristics during high-speed running.

FIG. 8 is a drawing showing engine characteristics near the maximum EGR rate.

FIG. 9 is a drawing similar to FIG. 2 showing the first embodiment.

FIG. 10 is a cross-sectional view showing an upstream end of the exhaust pipe 122 connected to the exhaust manifold 22a.

11 is a cross-sectional view showing a downstream end connected to a flexible joint 92. FIG.

FIG. 12 is a view similar to FIG. 2, showing a second embodiment.

FIG. 13 is a view similar to FIG. 2, showing a third embodiment.

FIG. 14 is a schematic drawing of the engine of FIG. 13 as viewed from the front side of the vehicle.

FIG. 15 is a flowchart showing specific control of fuel injection performed in the second and third embodiments.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine 4 Combustion chamber 7 Injector (fuel injection valve) 22 Exhaust passage 22a Exhaust manifold 25 Catalyst (NOx) 40 ECU

Continued on the front page F term (reference) 3G062 AA07 BA02 BA05 CA00 CA02 CA04 CA07 CA08 DA01 FA05 FA13 FA17 GA00 GA01 GA02 GA04 GA06 GA08 GA09 GA12 GA13 GA15 GA17 GA21 GA30 3G301 HA01 HA13 HA14 HA16 HA17 JA21 KA05 KA08 KA09 KA13 KA24 KA04 KA04 LC03 MA01 MA11 MA19 MA26 NA08 NB11 ND01 NE17 NE23 PA04Z PA07Z PA09Z PA10Z PA11Z PA17Z PB03Z PC02Z PD02A PD02Z PD12Z PD15Z PE01Z PE08Z PF03Z PF07Z

Claims (24)

[Claims] 1. A NOx catalyst for reducing NOx in exhaust gas in a lean region where an excess air ratio λ is larger than 1 is disposed in an exhaust passage of an engine, and a low load / low speed region is a stratified combustion region in a lean state. In a control apparatus for a spark ignition type direct injection engine in which a middle / high rotation region is a uniform combustion region having an air-fuel ratio of 15 or less, an exhaust passage between the engine and the NOx catalyst is provided with an adiabatic arrangement and / or an adiabatic structure. Λ of the combustion region is set to 1.3 or more, and the fuel injection mode of the partial load region in the middle / high rotation region is an intake split injection in which fuel is split and injected from the first half to the middle of the intake stroke. A control device for a spark ignition type direct injection engine. 2. The heat-insulating arrangement further comprises: disposing an exhaust port opening of an engine and an exhaust passage connected to the exhaust port opening on a vehicle rear side of the engine body.
The control device for a spark ignition type direct injection engine according to claim 1, wherein a catalyst is arranged on a rear side of a vehicle of the engine body. 3. The engine is mounted such that a cylinder row is arranged in the axle direction, and an exhaust port opening is disposed on an engine side wall on a vehicle rear side among a pair of engine side walls extending in the cylinder row direction. The control device for a spark ignition type direct injection engine according to claim 2. 4. The heat-insulating structure is configured to generate NO from the engine.
The control device for a spark ignition direct injection engine according to any one of claims 1 to 3, wherein the control device has a heat insulating structure in which a double exhaust pipe having a heat insulating space is disposed in an exhaust passage leading to the x catalyst. 5. An air-fuel ratio of 15 adjacent to the stratified combustion region.
The control device for a spark ignition type direct injection engine according to claim 1, wherein the following uniform combustion region is provided, and a fuel injection mode in the uniform combustion region is the intake split injection. 6. The control device for a spark ignition type direct injection engine according to claim 1, wherein exhaust gas recirculation (EGR) is performed in a region in which the intake split injection is performed. 7. The control device for a spark ignition type direct injection engine according to claim 1, wherein the fuel injection mode in the low load side region in the middle / high rotation region is the intake split injection. 8. An upper limit value N3 of an engine speed in a region where the intake split injection is performed is set to a value equal to or less than 2/4 of a rated engine speed.
In the engine rotation range from the upper limit value N2 of the engine rotation speed in the stratified combustion region to the above N3 in the range of 3/4, the road load indicating the driving load when the vehicle travels at a constant speed on a substantially flat road at a high gear stage. From low load area including load line,
In the load range up to the substantially high load region excluding the full load, the fuel injection mode is the intake split injection, the excess air ratio λ is approximately 1, and the EGR ratio in the low load region near the load / load line is 10%. The control device for a spark ignition type direct injection engine according to claim 5 or 7, wherein the control value is not less than a percentage. 9. In a region on a higher load side than the stratified combustion region, a fuel injection mode is the intake split injection at an engine speed N1 or more that is lower than an upper limit N2 of the engine speed in the stratified combustion region, 6. The control device for a spark ignition type direct injection engine according to claim 1, wherein the fuel injection mode is a collective intake injection in which fuel is collectively injected in an intake stroke at an engine speed less than N1. 10. In the uniform combustion region, exhaust gas recirculation (EGR) is performed in a region adjacent to the stratified combustion region, and an EGR rate at the time of the N1 or more intake partial injection is less than the N1 intake batch injection. The control device for a spark ignition type direct injection engine according to claim 9, wherein the control device is set to be larger than the EGR rate. 11. The control of the spark ignition type direct injection engine according to claim 9, wherein when the temperature of the NOx catalyst is high, fuel is dividedly injected during an intake stroke at an engine speed lower than N1. apparatus. 12. In the stratified combustion region, when the temperature of the NOx catalyst reaches a predetermined temperature at which the NOx reduction rate of the NOx catalyst starts to decrease or a high temperature state near the predetermined temperature, the fuel is divided into intake strokes. And recirculation (E
2. A uniform combustion with an air-fuel ratio of 15 or less for performing GR).
3. The control device for a spark ignition type direct injection engine according to 1.). 13. A uniform combustion region having an air-fuel ratio of 15 or less,
When λ shifts to a preset stratified charge combustion region of 1.3 or more, the intake split injection is performed and the exhaust gas recirculation (EG
The control device for a spark-ignition direct injection engine according to claim 1, wherein uniform combustion with an air-fuel ratio of 15 or less in which R) is performed is performed. 14. The region in which uniform combustion with an air-fuel ratio of 15 or less is performed when the NOx catalyst is at or near the predetermined temperature is a high rotation side region of the stratified combustion region. Control device for spark-ignition direct injection engine. 15. When the NOx catalyst is at or near the predetermined temperature, in the low-speed side region of the stratified combustion region having λ of 1.3 or more, fuel is injected at a time during the intake stroke and exhaust gas recirculation ( The control device for a spark ignition type direct injection engine according to claim 1, wherein uniform combustion with an air-fuel ratio of 15 or less in which EGR is performed is performed. 16. An acceleration split injection and an exhaust gas recirculation (EGR) are performed when an engine operating state determined by an engine load and a rotation speed is in a high rotation side region of the stratified combustion region during acceleration. Air-fuel ratio 15
The control device for a spark ignition type direct injection engine according to claim 1, wherein the following uniform combustion is performed. 17. The spark according to claim 14, wherein an EGR rate in uniform combustion with an air-fuel ratio of 15 or less by the intake split injection performed in a high rotation speed region of the stratified combustion region is 30% or more. Control device for ignition type direct injection engine. 18. The engine according to claim 1, wherein, when the engine is cold, uniform combustion with an air-fuel ratio of 15 or less is performed even at the time of the low load and low rotation, and a three-way catalyst is arranged upstream of the NOx catalyst. Control device for spark-ignition direct injection engine. 19. The method according to claim 1, wherein when the temperature of the three-way catalyst is high regardless of the operating condition, uniform combustion with an air-fuel ratio of 15 or less for performing the intake split injection and the exhaust gas recirculation (EGR) is performed. Control device for spark-ignition direct injection engine. 20. Exhaust gas recirculation (EG) in both the uniform combustion region by the intake split injection and the stratified combustion region.
The control device for a spark ignition type direct injection engine according to claim 1, wherein R) is performed. 21. A NOx catalyst for reducing NOx in exhaust gas in a lean region where an excess air ratio λ is greater than 1 is disposed in an exhaust passage separated from an exhaust manifold, and stratified combustion in a low load / low rotation region in a lean state. In a control apparatus for a spark ignition type direct injection engine, wherein the engine is a region, and the middle / high rotation region is a uniform combustion region having an air-fuel ratio of 15 or less, the engine is mounted such that the cylinder rows are arranged in the axle direction. An exhaust port opening is provided in the engine side wall on the vehicle front side of the pair of engine side walls extending in the direction, and an exhaust pipe connected to the exhaust manifold extends to the vehicle rear side of the engine through a lower portion of the engine, and the NOx catalyst Is disposed at a portion downstream of the engine below the exhaust pipe, and extends between the exhaust manifold and the engine below. And the NO
The exhaust pipe located on the upstream side of the x-catalyst is a double exhaust pipe provided with an adiabatic space, wherein λ of the stratified combustion region is set to 1.3 or more, The fuel injection mode is an intake split injection in which injection is started from the first half to the middle of the intake stroke, and a uniform combustion region having an air-fuel ratio of 15 or less is provided adjacent to the stratified combustion region, and fuel injection in the uniform combustion region is performed. A control device for a spark ignition type direct injection engine, wherein the form is the intake split injection. 22. The engine according to claim 21, wherein when the engine is cold, uniform combustion with an air-fuel ratio of 15 or less is performed even at the time of low load and low rotation, and a three-way catalyst is disposed upstream of the NOx catalyst. Control device for spark-ignition direct injection engine. 23. Regardless of the operating state, when the temperature state of the three-way catalyst is high, an air-fuel ratio of 15 for dividing and injecting fuel during an intake stroke and performing exhaust gas recirculation (EGR) is provided.
The control device for a spark ignition type direct injection engine according to claim 22, which performs the following uniform combustion. 24. The upper limit N3 of the engine speed in the region where the split intake injection is performed is set to 2/4 of the rated engine speed.
In the engine rotation region from the upper limit value N2 of the engine rotation speed in the stratified combustion region to the aforementioned N3,
In a load range from a low load region including a load / load line indicating a driving load when a vehicle travels on a substantially flat road at a constant speed at a high gear position, to a substantially high load region excluding a full load, the fuel injection mode is set as described above. Intake split injection and excess air ratio λ is approximately 1
22. The control device for a spark ignition direct injection engine according to claim 21, wherein an EGR rate in a low load region near the load / load line is 10% or more.