JP2000161109A - Control device for diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress smoke increase in exhaust gas by improving the burning state while complying with an increase in required output, and reduce the generation of NOx when the operating condition is shifted from a steady operating condition to an accelerated operating condition in a diesel engine where an air fuel ratio A/F of a combustion chamber is indirectly controlled by adjusting the recirculation quantity of exhaust gas. SOLUTION: When the engine is shifted from a steady operating condition to an accelerated operating condition, the recirculation quantity of exhaust gas is reduced with increase of the quantity of fuel injection, and the fuel injection by an injector is divided into two stages, that is, in an early time injection where the injection of more than one-third the total quantity of injection in one burning cycle is started at BTDC 90 deg. CA, and in a later time injection where the injection of remaining fuel is started in the neighborhood of a top dead center in compression stroke. Then, the later injection timing is advanced ahead of the fuel injection timing in the steady operating condition immediately before the operating condition is shifted to the accelerated operating condition. The early time injection can be further divided into two stages.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technical field related to a fuel injection control at the start of an acceleration operation of a so-called direct injection diesel engine in which fuel is directly injected into a combustion chamber in a cylinder.

[0002]

2. Description of the Related Art Conventionally, as a control device for a diesel engine of this type, for example, as disclosed in Japanese Patent Application Laid-Open No. H8-144867, the amount of exhaust gas recirculated to an intake system is adjusted to indirectly combust combustion. There is known an apparatus in which an air-fuel ratio (excess air rate) of a chamber is controlled. In this engine, an exhaust gas recirculation passage (hereinafter, referred to as an EGR passage) that recirculates a part of exhaust gas to an intake system of an engine, and an exhaust gas recirculation amount control valve (hereinafter, referred to as an EGR passage) that is operated by an actuator to adjust the amount of exhaust gas recirculated in the EGR passage. An EGR valve), detects the air-fuel ratio of the combustion chamber based on an output signal from an air-fuel ratio sensor provided in the exhaust passage, and controls the opening of the EGR valve according to the detection result. I have to.

[0003] That is, in the conventional example, the NOx emission concentration can be reduced as the air-fuel ratio of the combustion chamber is reduced, but on the other hand, when the air-fuel ratio is too small, the amount of smoke generated increases rapidly. In consideration of the above characteristics, the control target value of the air-fuel ratio is set to a value as small as possible (a value on the rich side) within a range in which the smoke amount does not rapidly increase, so as to reduce NOx and smoke in the exhaust gas.

[0004]

In recent years, the need for purifying the exhaust gas of automobile engines has been further strengthened from the viewpoint of environmental protection. Since it is difficult to reduce and purify, it is required to further reduce the generation of NOx itself due to combustion.

[0005] On the other hand, from the viewpoint of the improvement of the marketability, there is also a demand to increase the engine output to improve the so-called vehicle start-up.
It is necessary to simultaneously meet the conflicting demands for reduction of the temperature.

[0006] Further, in the case of a diesel engine, there is a specific problem that smoke is generated when the engine is accelerated when the vehicle starts moving. This is because, for example, when the vehicle starts, the fuel injection amount must be increased in order to respond to the driver's acceleration request despite the low engine speed range where the intake air flow is weak. It is believed that this is due to a temporary worsening of the mixed state of.

Considering the problem of smoke at the time of acceleration of the engine, when the air-fuel ratio is controlled as in the above-mentioned prior art, the exhaust gas recirculation amount is usually reduced when the vehicle starts, and the intake air Since the amount increases, it is considered that the air-fuel ratio can be maintained at the target value even when the fuel injection amount increases, thereby reducing smoke.
However, in practice, when the accelerator pedal is depressed by the driver, the fuel injection amount is immediately increased, while the intake air amount is delayed later, so that the air-fuel ratio is temporarily excessively rich. And smoke cannot be reduced sufficiently.

[0008] On the other hand, the generation of smoke can be suppressed by advancing the timing of fuel injection at the start of a vehicle or the like to promote mixing of fuel and air and sufficiently vaporize and atomize the fuel. Conceivable. However, in such a case, the so-called premixed combustion becomes extremely violent in combination with an increase in the amount of fuel, and there is a harmful effect of causing a remarkable increase in the amount of generated NOx, which is not realistic.

The present invention has been made in view of the above points, and an object of the present invention is to increase a required output to an engine by devising a fuel injection procedure during an acceleration operation of a diesel engine. While responding, the combustion state is improved to sufficiently suppress the increase in smoke in exhaust gas, and NOx
Is to reduce.

[0010]

In order to achieve the above object, according to the present invention, when the engine shifts from a steady operation state to an acceleration operation state, fuel is divided into multiple stages in a compression stroke of each cylinder. Injection (hereinafter, also referred to as multi-stage injection), and the last of the injections is terminated earlier than the fuel injection in the steady operation state.

Specifically, as shown in FIG. 1, the invention according to claim 1 includes a fuel injection valve 5 for injecting fuel into a combustion chamber 4 in a cylinder of the engine 1, and the fuel by the fuel injection valve 5 The premise is a diesel engine control device A that controls at least the injection amount. And engine 1
Determination means 35a for determining that the engine 1 has shifted to the acceleration operation state, and when the acceleration determination means means 35a determines that the engine 1 has shifted to the acceleration operation state, the fuel injection by the fuel injection valve 5 is performed by the cylinder. 30 ° before top dead center of compression
Injection timing control means 35b for executing in multiple stages including early injection performed in the compression stroke before CA (hereinafter referred to as BTDC 30 ° CA) and late injection performed in the vicinity of compression top dead center.
The early injection is performed by injecting 1/3 or more of the fuel injection amount in one combustion cycle for each cylinder, and the late injection is performed by compressing the remaining fuel with the compression just before the acceleration determination. It is assumed that the fuel is injected earlier than the fuel injection near the top dead center.

With the above configuration, when the driver of the vehicle depresses the accelerator and the engine 1 shifts from, for example, a steady operation state to an acceleration operation state, the fuel injection amount is increased according to the accelerator operation, and One-third or more of the fuel injection amount in one combustion cycle for each cylinder 2 is injected early in the compression stroke and before BTDC 30 ° CA. This early-injected fuel is sufficiently mixed with air and sufficiently vaporized and atomized by the flow of air in the cylinder, so that the fuel gradually reacts with the surrounding oxygen with the rise of the cylinder pressure due to the rise of the piston 3. Become. When the temperature of the entire combustion chamber reaches the so-called self-ignition temperature at the end of the compression stroke, the combustion chamber explosively burns. On the other hand, the remaining fuel is injected late in the vicinity of the compression top dead center, and burns rapidly after a very short ignition delay period.

[0013] In such a combustion state, first, the fuel spray which is injected early and spreads relatively large is sufficiently vaporized and atomized and mixed with air to burn well.
The air utilization rate in the combustion chamber 4 becomes extremely high. In addition, the fuel gradually reacts with the surrounding oxygen and transitions to an explosive combustion state, so that the combustion pressure and combustion temperature rise excessively sharply after the combustion chamber temperature reaches the self-ignition temperature. Not be. This can significantly reduce NOx generation.

Further, as a result of the early injection of a large amount of fuel, the injection amount of the late injection near the compression top dead center does not become excessively large even if the total fuel injection amount becomes considerably large. In addition, since the timing of the latter injection is earlier than the injection timing in the steady operation state immediately before the acceleration determination,
The fuel spray is injected into the combustion chamber whose temperature and pressure are gradually increasing due to the weak combustion of the early injected fuel, and is well mixed with the air and sufficiently vaporized and atomized, and rapidly and successfully. Burned. Thereby, even if the total amount of fuel injection is considerably large, the increase in smoke can be sufficiently suppressed.

Further, since the fuel spray injected in the latter stage is injected into the combustion chamber where combustion has already started, the combustion does not become excessively violent even if the injection timing is advanced. That is, even if the injection timing is set earlier than in the steady operation state, this does not cause a significant increase in the NOx generation amount.

Therefore, according to this configuration, when the operation state of the engine 1 shifts from the steady operation state to the acceleration operation state, even if the fuel injection amount is increased to increase the engine output, the smoke in the exhaust gas increases. Can be sufficiently suppressed, and NOx can be reduced as compared with the conventional case.

As shown in FIG. 1, the invention according to claim 2 includes a fuel injection valve 5 for injecting fuel into the in-cylinder combustion chamber 4 of the engine 1 and the fuel injection valve 5 according to an accelerator operation amount. Injection amount control means 35c for controlling fuel injection amount
An exhaust gas recirculation passage 23 for recirculating a part of the exhaust gas to the intake system 10 of the engine 1; an exhaust gas recirculation amount control valve 24 for adjusting the amount of exhaust gas recirculated in the exhaust gas recirculation passage 23; The exhaust gas recirculation control means 35d which feedback-controls the opening degree of the exhaust gas so that the recirculation state quantity relating to the recirculation state of the exhaust gas becomes a target value set in accordance with the operation state of the engine 1 is controlled by a diesel engine control device A It is a premise. The exhaust recirculation control unit 35d is provided with an acceleration determination unit 35a for determining that the engine 1 has shifted to the accelerated operation state, and determines whether the transition of the engine 1 to the accelerated operation state is determined by the acceleration determination unit 35a. The exhaust gas recirculation control valve 35 is operated to the closed side, the exhaust gas recirculation control is performed by the exhaust gas recirculation control means 35d, and the acceleration determination means 35a switches the engine 1 to the accelerated operation state. When the transition is determined, the fuel injection by the fuel injection valve 5 is terminated at the first injection ending in the compression stroke of the cylinder and the last injection ending earlier than the fuel injection near the compression top dead center immediately before the acceleration determination. The injection timing control means 35b which is executed in multiple stages including the following is provided.

With the above configuration, when the driver of the vehicle depresses the accelerator and the engine 1 shifts from, for example, a steady operation state to an acceleration operation state, the engine 1 responds to the accelerator operation in the same manner as in the first aspect. The fuel injection amount is increased, and at least one early injection including the first injection ending in the compression stroke of the cylinder and the last injection near the compression top dead center (late injection) are performed. The injection timing is performed earlier than the fuel injection in the steady operation state immediately before the acceleration determination. As a result, similarly to the first aspect of the invention, it is possible to sufficiently suppress the increase in smoke in the exhaust while increasing the engine output, and to reduce NOx.

At the same time, with the increase in the fuel injection amount, the exhaust gas recirculation amount control valve 2 is controlled by the exhaust gas recirculation control means 35d.
4 is actuated on the closing side, and the amount of fresh intake air increases due to the decrease in the amount of exhaust gas recirculation, so that the engine output can be further increased and the increase in smoke can be further suppressed.

According to the third aspect of the present invention, the first or second aspect is provided.
The injection timing control means in the invention according to any one of
When the engine is in the low-speed operation range, multi-stage fuel injection is executed. As a result, when the engine is in the low-speed operation range, the filling efficiency of the cylinder is lower than that in the medium-speed operation range, so that the smoke amount may increase especially when the engine is shifted from the low-speed operation range to the acceleration operation state. This is strong. Therefore, in such a case, it is particularly effective to reduce NOx and smoke by multi-stage fuel injection and advancement of the late injection timing.

According to a fourth aspect of the present invention, the injection timing control means in the second aspect of the present invention controls the fuel injection by the fuel injection valve to be at least / of the fuel injection amount in one combustion cycle for each cylinder. In the compression stroke before 30 ° CA before the compression top dead center.

By doing so, the early injection is performed before BTDC 30 ° CA in the compression stroke of the cylinder, so that the fuel spray can be sufficiently widened, mixed well with air and vaporized and atomized, and the air utilization rate can be improved. Can be increased. At this time, the fuel injection amount in one combustion cycle of the cylinder is 1
By injecting / 3 or more, the fuel spray can be maintained in a concentration state capable of self-ignition. Further, since the remaining fuel amount is less than 2/3 of the total injection amount, the fuel injected near the compression top dead center can be burned quickly and without burning. Therefore, the function and effect of the invention described in claim 2 can be sufficiently obtained.

According to a fifth aspect of the present invention, in the second aspect of the present invention, an intake air amount sensor for measuring an intake air amount in an intake passage of the engine is provided, and the exhaust gas recirculation control means opens the exhaust gas recirculation amount adjusting valve. The feedback control is performed so that the air-fuel ratio of the combustion chamber obtained based on the intake air amount and the fuel injection amount measured by the intake air amount sensor becomes a target value.

With this configuration, the actual air-fuel ratio of the combustion chamber can be obtained based on the intake air amount detected by the intake air amount sensor and the fuel injection amount controlled by the injection amount control means. By controlling the opening of the control valve, feedback control can be performed with high accuracy so that the air-fuel ratio of the combustion chamber becomes a target value. In other words, by performing high-precision air-fuel ratio control and fuel injection timing control together, it is possible to achieve both high-dimensional reduction of NOx in exhaust gas and suppression of smoke at the time of starting the vehicle.

According to a sixth aspect of the present invention, the exhaust gas recirculation control means according to the fifth aspect of the present invention has a target air-fuel ratio map in which a target value of an air-fuel ratio corresponding to an operating state of the engine is set, and The control means has a target fuel injection amount map in which a target value of the fuel injection amount corresponding to the operating state of the engine is set.

Thus, the control by the injection amount control means and the exhaust gas recirculation control means are both performed with high accuracy and responsiveness by reading the target value from a preset map. Therefore, by performing such high-accuracy and high-response air-fuel ratio control, reduction of NOx in exhaust gas and suppression of smoke at the time of starting of the vehicle can be achieved at a higher level.

According to a seventh aspect of the present invention, in the second aspect of the invention, there is provided a closing operation detecting means for detecting that the exhaust gas recirculation amount control valve has actually been operated to the closing side, and the injection timing control means comprises When the closing operation detecting means detects the closing operation of the exhaust gas recirculation amount control valve, multi-stage fuel injection is started.

That is, immediately after the engine shifts to the accelerating operation state, the exhaust gas recirculation amount may become excessively large due to the operation delay of the exhaust gas recirculation control valve. If it does, there is a possibility that the combustion state may worsen and smoke may increase. Therefore, in the present invention, when the actual closing operation of the exhaust gas recirculation amount control valve is detected by the closing operation detecting means, the multi-stage fuel injection and the advance of the late injection timing are started to increase the smoke increase. This can avoid the adverse effect.

According to an eighth aspect of the present invention, in the second aspect of the present invention, an intake air amount sensor for measuring an intake air amount in an intake passage of the engine is provided, and the injection timing control means is measured by the intake air amount sensor. When the air-fuel ratio of the combustion chamber obtained based on the intake air amount and the fuel injection amount becomes equal to or higher than a set value, multi-stage fuel injection is started.

With this configuration, when the engine shifts to the accelerated operation state, the actual air-fuel ratio of the combustion chamber is determined based on the intake air amount measured by the intake air amount sensor and the fuel injection amount controlled by the injection amount control means. Is required. Then, when the obtained air-fuel ratio becomes equal to or more than the set value, the multi-stage fuel injection and the advance of the late injection timing are started. That is, when the actual air-fuel ratio of the combustion chamber becomes equal to or higher than the set value during the transition to the acceleration operation state of the engine, that is, after confirming that the exhaust gas recirculation amount is not excessively large, the multi-stage injection of fuel and the latter By starting the advance of the injection, it is possible to reliably avoid the adverse effect of the increase in smoke caused by the multi-stage injection immediately after the acceleration.

According to the ninth aspect of the present invention, the seventh or eighth aspect is provided.
The injection timing control means in any one of the inventions is configured to return the timing of the last fuel injection to the fuel injection timing immediately before the acceleration determination after a predetermined period has elapsed after the engine has shifted to the acceleration operation state. . The predetermined period is a period corresponding to the initial stage of the acceleration operation of the engine, and may be set to correspond to, for example, the elapsed time after the engine is shifted to the acceleration operation state, a change in the crank angle, and the like.

Thus, when the engine shifts to the acceleration operation state, first, during the period when the air-fuel ratio is particularly rich due to the increase in the fuel injection amount and the shortage of the intake air amount, the timing of the late injection is set. By advancing, smoke can be preferentially suppressed out of NOx and smoke in the exhaust gas. On the other hand, if the air-fuel ratio of the combustion chamber thereafter changes to the lean side, the timing of the late injection can be returned to correspond to that, and both NOx and smoke can be reduced.

According to a tenth aspect of the present invention, in the second aspect of the invention, the exhaust gas recirculation passage is connected to the intake passage of the engine, and the intake recirculation passage is upstream of the connection with the exhaust gas recirculation passage. An intake throttle valve is disposed in the intake passage of the engine, and intake throttle valve control means for controlling the intake throttle valve to be in a closed state in the low-speed low-load operation region of the engine compared to other operation regions is provided. Configuration.

That is, in general, in a diesel engine, the negative pressure in the intake passage is so small that it is difficult to secure a sufficient amount of exhaust gas to be recirculated through the exhaust gas recirculation passage. Increasing the differential pressure has been performed. In such an engine, when the engine shifts to the accelerated operation state, the intake air flow resistance is increased by the intake throttle valve, so that the amount of intake air to the combustion chamber tends to be insufficient, and smoke may increase. This is particularly strong. Therefore, in the diesel engine equipped with the intake throttle valve, by performing the exhaust gas recirculation control and the multi-stage injection of the fuel at the time of transition to the acceleration operation state of the engine, it is possible to reduce NOx while suppressing smoke. It has an extremely effective action.

According to an eleventh aspect of the present invention, in any one of the first and second aspects, there is provided a common rail type fuel injection system in which a fuel injection valve is connected to a pressure accumulating chamber for storing fuel in a high pressure state higher than an injection pressure. I do. Thereby, the configuration of the fuel injection system is embodied, and the control of the fuel injection timing by the injection timing control means is realized.

According to a twelfth aspect of the present invention, the injection timing control means according to any one of the first and second aspects of the present invention, when the engine is in a steady operation state, controls the fuel injection by the fuel injection valve to the compression top dead center. It is configured to be executed collectively in the vicinity.

That is, in general, when multi-stage injection of fuel is performed, a part of the combustion power of the fuel injected early becomes so-called reverse driving force, and there is a difficulty that the fuel efficiency of the engine is slightly deteriorated. According to the present invention, when the engine is in the steady operation state, the fuel injection is collectively executed in the vicinity of the compression top dead center without performing the multi-stage injection, so that the deterioration of the fuel efficiency due to the multi-stage injection can be suppressed.

According to a thirteenth aspect of the present invention, the injection timing control means according to any one of the first and second aspects of the present invention is configured such that when the engine is in a low-speed low-load operation range in a steady operation state, the fuel injection valve is used. The fuel injection is divided into the main injection near the compression top dead center and the pilot injection immediately before the main injection. As a result, in the low-speed low-load operation region of the engine, by performing the pilot injection, the rise of the combustion pressure during the premixed combustion of the main injection can be moderately moderated, thereby reducing the engine operation noise. can do.

[0039]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) (Overall Configuration) FIG. 1 shows an overall configuration of a diesel engine control device A according to Embodiment 1 of the present invention, and 1 is, for example, a four-cylinder mounted on a vehicle equipped with a manual transmission. It is a diesel engine. This engine 1
Has four cylinders 2, 2, ... (only one is shown),
A piston 3 is inserted into each cylinder 2 so as to be able to reciprocate, and a combustion chamber 4 is defined in each cylinder 2 by the piston 3. An injector 5 is disposed at a substantially central portion of the upper surface of the combustion chamber 4 with the injection hole at the tip end facing the combustion chamber 4, and is opened and closed at a predetermined injection timing for each cylinder. The fuel is directly injected into the combustion chamber 4.

Each of the injectors 5 is connected to a common common rail (accumulator) 6 for storing high-pressure fuel.
The common rail 6 is provided with a pressure sensor 6 a for detecting an internal fuel pressure (common rail pressure), and is connected to a high-pressure supply pump 8 driven by a crankshaft 7. The high-pressure supply pump 8 operates so that the fuel pressure in the common rail 6 detected by the pressure sensor 6a is maintained at a predetermined value or more (for example, 40 MPa during idle operation and 80 MPa or more in other operation states). A crank angle sensor 9 for detecting the rotation angle is provided at one end of the crank shaft 7. The crank angle sensor 9 includes a plate to be detected (not shown) provided at an end of the crankshaft 7 and an electromagnetic pickup disposed so as to face the outer periphery thereof. A pulse signal is output in response to the passage of the projection formed over the entire outer periphery.

Reference numeral 10 denotes an intake passage for supplying intake air (air) filtered by an air cleaner (not shown) to the combustion chamber 4 of the engine 1. The downstream end of the intake passage 10 is connected to a surge tank (not shown). Each cylinder 2 is branched and connected to a combustion chamber 4 of each cylinder 2 by an intake port. Further, a supercharging pressure sensor 10a for detecting a supercharging pressure supplied to each cylinder 2 in the surge tank is provided.
In the intake passage 10, an air flow sensor (intake amount sensor) 11 for detecting an intake flow rate to be taken into the engine 1 in order from an upstream side to a downstream side, and a turbine 2 described later.
1, a blower 12 for compressing the intake air, an intercooler 13 for cooling the intake air compressed by the blower 12, and an intake throttle valve 14 for reducing the sectional area of the intake passage 10.
Are provided respectively. This intake throttle valve 14
A butterfly valve provided with a notch so that intake air can flow even in the fully closed state. The magnitude of the negative pressure acting on the diaphragm 15 is controlled by a negative pressure control electromagnetic valve 16 like the EGR valve 24 described later. By being adjusted, the opening degree of the valve is controlled.

The air flow sensor 11 is a constant temperature hot film air flow sensor capable of reliably detecting the air flow rate even if there is a variation in the flow velocity. , And hot films disposed upstream and downstream of the heater, and based on the temperature of the two hot films, the intake passage 10 is connected to the downstream side (each cylinder). 2) and a reverse flow toward the upstream side are respectively detected. Only the air flow in the forward direction can be measured based on the value measured by the air flow sensor 11, and it is possible to avoid an error due to a backflow in controlling the exhaust gas recirculation amount.

In FIG. 1, reference numeral 20 denotes an exhaust passage for discharging combustion gas from the combustion chamber 4 of each cylinder 2. The upstream end of the exhaust passage 20 is branched and the combustion port of each cylinder 2 is opened by an exhaust port (not shown). It is connected to room 4. The exhaust passage 20 includes, in order from the upstream side to the downstream side, a turbine 21 that is rotated by the exhaust flow, HC in the exhaust gas,
A catalytic converter 22 capable of purifying CO and NOx and particulates is provided.

As shown in FIG. 2, the turbocharger 25 comprising the turbine 21 and the blower 12
A plurality of flaps 21b, 21b,... Are provided so as to surround the entire circumference of the turbine 21a, and each flap 21b rotates so as to change the nozzle cross-sectional area A of the exhaust passage. VGT (Variable Geometry Turbo). In the case of this VGT, as shown in FIG. 2A, the flaps 21b, 21b,. The supercharging efficiency can be improved even in the low rotation speed range. On the other hand, as shown in FIG.
If b,... are positioned so that their tips face the center of the turbine 21 and the nozzle cross-sectional area A is increased, high supercharging efficiency can be obtained even in a high rotation range of the engine 1 having a large exhaust flow rate.

The exhaust passage 20 is located upstream of the turbine 21 and is branched and connected to an upstream end of an exhaust gas recirculation passage (hereinafter referred to as an EGR passage) 23 for recirculating a part of exhaust gas to the intake side. The downstream end of the EGR passage 23 is connected to the intake passage 10 on the downstream side of the intake throttle valve 14 with respect to the intake air. Exhaust gas recirculation amount control valve (hereinafter EG)
An EGR valve 24 recirculates a part of the exhaust gas from the exhaust passage 20 to the intake passage 10 while adjusting the flow rate.

The EGR valve 24 is, as shown in FIG.
A valve rod 24b is fixed to a diaphragm 24a that partitions the valve box, and a valve body 24c for linearly adjusting the opening degree of the EGR passage 23 and a lift sensor 26 are provided at both ends of the valve rod 24b. The valve body 24c has a spring 2
While being biased in the closing direction (downward in the figure) by 4d, a negative pressure passage 27 is connected to a negative pressure chamber (a chamber above the diaphragm 24a) of the valve box. The negative pressure passage 27 is connected to a vacuum pump (negative pressure source) 29 via a negative pressure control electromagnetic valve 28, and the electromagnetic valve 28 communicates with the negative pressure passage 27 according to a control signal from an ECU 35 described later. By shutting off, the negative pressure for driving the EGR valve in the negative pressure chamber is adjusted, whereby the opening of the EGR passage 23 is linearly adjusted by the valve body 24c.

That is, as shown in FIG. 4 (a), the negative pressure for driving the EGR valve increases (lower pressure) as the current increases, and is proportional to the negative pressure for driving the EGR valve. As shown in (5), the lift amount of the EGR valve body 24c changes. However, hysteresis is observed in the change in the lift amount of the EGR valve main body 24c.

The flap 21 of the turbocharger 25
A diaphragm 30 is attached to each of b, 21b,... similarly to the EGR valve 24, and the negative pressure acting on the diaphragm 30 is adjusted by an electromagnetic valve 31 for negative pressure control, so that the flaps 21b, 21b,. The amount of operation of ... is adjusted.

Each of the injectors 5, high-pressure supply pump 8, intake throttle valve 14, EGR valve 24, turbocharger 25
Are the control unit (Electronic Control Unit: hereinafter referred to as ECU) 3
5 to be operated by a control signal from the control unit 5. On the other hand, the ECU 35 includes an output signal from the pressure sensor 6a, an output signal from the crank angle sensor 9, an output signal from the air flow sensor 11, an output signal from the lift sensor 26 of the EGR valve 24, An output signal from an accelerator opening sensor 32 for detecting an operation amount (accelerator opening) of an accelerator pedal (not shown) by a driver of the vehicle and an output signal from a water temperature sensor for detecting a cooling water temperature of the engine 1 (not shown). At least it has been entered.

(Overall Configuration of Control System) The ECU 3
The basic processing of the engine control in FIG. 5 is schematically shown in the block diagram of FIG. 5, and the basic fuel injection amount is basically determined based on the accelerator opening and the EG
The EGR rate is adjusted by the operation of the R valve 24 to control the air-fuel ratio (recirculation amount) of each cylinder uniformly and with high accuracy. Further, control of the common rail pressure by operation of the high-pressure supply pump 8, operation control of the intake throttle valve 14, and operation control (VGT control) of the flaps 21b, 21b, ... of the turbocharger 25 are performed.

The EGR rate refers to the ratio of the recirculated exhaust gas amount (EGR amount) to the total exhaust gas amount. That is, E
GR ratio = EGR amount / total exhaust amount Here, the distribution of the exhaust gas recirculated from the EGR passage 23 to the intake passage 10 to the cylinders 2 differs, and in addition, the air intake characteristics per cylinder also vary. EG in the EGR passage 23
Even if the opening of the R valve 24 is the same, the EG in each cylinder 2
The deviation in the R ratio and the intake air amount deviation varies, and the intake air amount is small in a cylinder with a high EGR ratio and large in a cylinder with a low EGR ratio. Therefore, a target air-fuel ratio common to all the cylinders 2 is basically determined, the intake air amount is detected for each cylinder, and the exhaust gas is returned to each cylinder so as to reach the target air-fuel ratio according to the intake air amount. The flow rate is controlled. That is, E to the intake air amount of each cylinder 2
Instead of making the GR amount ratio uniform, the exhaust gas recirculation amount is controlled for each cylinder with a predetermined air-fuel ratio as a target, whereby the air-fuel ratio of each cylinder 2 is controlled uniformly and with high accuracy. be able to.

Specifically, the ECU 35 includes a two-dimensional map 36 in which the optimum value of the target torque trqsol is experimentally determined and recorded with respect to changes in the accelerator opening Acc and the engine speed Ne. The target fuel injection amount Fsol with respect to changes in the number Ne, the target torque trqsol, and the fresh air amount (this is the intake air amount and does not include fuel. The same applies hereinafter) FAir changes.
The three-dimensional map 37 as a target fuel injection amount map, which is obtained by experimentally determining and recording the optimum value of the engine, and the optimum value of the target air-fuel ratio A / Fsol with respect to changes in the engine speed Ne and the target torque trqsol. A two-dimensional map 38 as a target air-fuel ratio map, which is determined and recorded, is electronically stored in a memory.

The target air-fuel ratio A / Fsol is a control target value for determining the exhaust gas recirculation amount so as to achieve both reduction of NOx and reduction of smoke. That is, as shown in FIG. 6, as the relationship between the air-fuel ratio of the diesel engine and the NOx amount in the exhaust gas is illustrated, the NOx amount tends to increase as the air-fuel ratio increases. If it is lowered, the generation of NOx can be reduced.

However, as shown in the example of FIG. 7, according to the relationship between the air-fuel ratio of the same engine and the smoke value in the exhaust, when the air-fuel ratio becomes lower than the air-fuel ratio which has changed to the rich side, the smoke amount becomes smaller. It turns out that it increases suddenly. That is, NOx
There is a limit to increasing the amount of exhaust gas recirculation to reduce the amount. Therefore, in the control device A of this embodiment, the target air-fuel ratio A / Fsol is set to be as rich as possible before the smoke amount starts to rapidly increase in order to achieve both reduction of the NOx amount in the exhaust gas and suppression of increase in the smoke amount. It is set to the value on the side.

Fuel Injection Control Specifically, first, the target torque calculating section 41 uses the accelerator opening Acc detected by the accelerator opening sensor 32 and the engine speed Ne detected by the crank angle sensor 9 to generate the target torque. The target torque trqsol is determined with reference to the two-dimensional map 36 on the memory. This target torque trqsol
And the fresh air amount FA measured by the air flow sensor 11
Using ir and the engine speed Ne, the target injection amount calculation unit 4
In step 2, the target injection amount Fsol is determined with reference to the three-dimensional map 37 in the memory. And this target injection amount Fs
Based on ol and the common rail pressure CRP controlled as described later, the excitation time of each injector 5 is determined and controlled. Thus, by determining the target injection amount Fsol with reference to the preset map 37, the fuel injection control can be executed with high accuracy and high responsiveness. The target torque calculator 41 and the target injection amount calculator 42 correspond to the injection amount controller 35c (see FIG. 1).

Exhaust gas recirculation control On the other hand, using the target torque trqsol and the engine speed Ne obtained in the target torque calculation section 41, the target air-fuel ratio calculation section 43 refers to the two-dimensional map 38 in the memory, A target air-fuel ratio A / Fsol for achieving both NOx and smoke is determined. As described above, by determining the target air-fuel ratio A / Fsol with reference to the preset map 38, control accuracy and responsiveness are improved. The target air-fuel ratio A / Fsol and the target injection amount calculation unit 42
The target fresh air amount FAsol is calculated in the target fresh air amount calculation unit 44 using the target injection amount Fsol obtained in (1).
ol = Fsol × A / Fsol), and the new air amount control unit 45 performs the new air amount control with the target new air amount FAsol as a target. This fresh air control does not directly adjust the fresh air supply amount itself, but changes the fresh air amount by adjusting the recirculation amount of exhaust gas. That is, instead of determining the correction amount of the fresh air, the EGR is performed based on the target fresh air amount FAsol.
The operation amount EGRsol of the valve 24 is determined, and the opening of the EGR valve is controlled so as to correspond to the operation amount EGRsol. The target air-fuel ratio calculation unit 43, the target fresh air amount calculation unit 44, and the fresh air amount control unit 45 correspond to the exhaust gas recirculation control unit 35d.

Common Rail Pressure Control The ECU 35 also electronically stores a two-dimensional map 50 in which an optimum experimentally determined common rail pressure CRPsol in response to changes in the target torque trqsol and the engine speed Ne is recorded in a memory. The common rail pressure calculation unit 4 is provided using the target torque trqsol obtained by the target torque calculation unit 41 and the engine speed Ne.
In step 6, the target common rail pressure CRPsol is calculated with reference to the map 50, and the calculated common rail pressure CRPsol is used to control the common rail pressure.

In the map 50, the common rail pressure CRPsol is set so as to increase as the engine speed Ne increases and as the target torque trqsol increases. This is because the valve opening time of the injector 5 must be relatively shortened as the engine speed Ne increases, so that the injection pressure needs to be increased to secure the injection amount. On the other hand, in the low rotational speed range of the engine 1, it is preferable to inject fuel over a certain long period of time and to widely spread the fuel spray by the air flow in the cylinder. Therefore, the valve opening time of the injector 5 is lengthened. In addition, the injection pressure is reduced accordingly. Further, as for the target torque, it is necessary to increase the fuel injection amount as the load on the engine 1 increases, so the injection pressure is increased to secure the injection amount.

The intake throttle valve control ECU 35 stores in a memory a two-dimensional map 51 in which an optimum target intake throttle amount THsol determined experimentally in response to changes in the target fuel injection amount Fsol and the engine speed Ne is stored in a memory. The target injection amount Fsol and the engine speed obtained by the target injection amount calculation unit 42 are stored.
Using Ne and the target intake throttle amount calculation unit 47, the target intake throttle amount THsol is calculated with reference to the map 51,
Using this, the opening of the intake throttle valve 14 is controlled. The target injection amount calculation section 42 corresponds to the intake throttle valve control means 35e.

VGT Control Further, the ECU 35 electronically stores, in a memory, a two-dimensional map 52 recording an experimentally determined optimum target supercharging pressure Boostsol with respect to changes in the target torque trqsol and the engine speed Ne. The target supercharging pressure Boostsol is stored in the target supercharging pressure calculating unit 48 with reference to the map 52 using the target torque trqsol obtained in the target torque calculating unit 41 and the engine speed Ne. Is calculated. Using the target boost pressure Boostsol and the intake pressure Boost of the intake passage 10 downstream of the intake throttle valve 14 detected by the boost pressure sensor 10a, the boost pressure control unit 49 sets the intake pressure Boost to the target boost pressure. Supply pressure Boostsol
Flaps 21b and 21 of the turbocharger 25 such that
Calculate the opening degree VGTsol of b,.
1b, 21b,... Are controlled to have an appropriate opening degree.

(Overall Flow of Exhaust Gas Recirculation Control and Fuel Injection Amount Control) Next, the overall flow of exhaust gas recirculation and fuel injection amount control by the ECU 35 will be described with reference to FIG.
This control is executed in synchronization with the rotation of the engine 1 in accordance with a control program stored electronically on a memory.

First, as shown in steps S1 to S3 in the figure, suction is performed for each cylinder based on the intake air amount detected by the air flow sensor 11 and the crank angle (° CA) detected by the crank angle sensor 9. Air volume FAir
Is required. Further, the target fuel injection amount Fsol is obtained based on the engine speed Ne obtained by the output from the crank angle sensor 9, the accelerator opening Acc detected by the accelerator opening sensor 32, and the intake air amount FAir (step). S4 to S6).

Subsequently, a transient determination is made as to whether the engine 1 is in a steady operation state with a low load or a medium load or in an acceleration operation state based on the accelerator opening Acc, the engine speed Ne, and the like (step S1). S7) At the time of steady operation, a basic target air-fuel ratio is set, a target intake air amount is obtained based thereon, basic control of the EGR valve is performed, and this basic control is performed based on the intake air amount FAir of each cylinder. It is corrected by the EGR valve control for each (step S8
To S11). On the other hand, during acceleration operation, the target air-fuel ratio during acceleration is set, and EGR valve control and injection amount control during acceleration are performed (steps S12 to S14).

(Calculation of Intake Air Volume for Each Cylinder) The intake air flow rate detected by the air flow sensor 11 is, for example, as shown in FIG. It can be seen that the hatched portion in the drawing is the backflow of intake air, and the integrated value obtained by subtracting this backflow, that is, the amount of intake air actually drawn into each cylinder 2 slightly fluctuates. .

FIG. 10 shows a specific control procedure when calculating the intake air amount for each cylinder using the air flow sensor 11 (steps S1 to S3 in FIG. 8). That is,
First, the intake air flow rate detected by the air flow sensor 11 is integrated, and the elapsed time at that time is measured. Each time the crank angle changes by 180 ° CA, the integral value Q (180 ( = FAir) is the intake air amount Qi of the cylinder (i), and the required time (crank timer time T) is the crank interval Ti of the cylinder (i).
And Then, the average value of the obtained intake air amounts Qi of the four cylinders is obtained as a basic intake air amount Qav (step A1).
~ A7). For convenience, cylinder numbers "0, 1, 2, 3" in the order of ignition are given to each of the four cylinders.

The rate of change ΔQi = Qi / Qi−1 of the intake air amount of the cylinder (i) and the rate of change ΔTi = Ti /
Ti-1 is determined with reference to the cylinder (i-1) which is one stroke earlier than the cylinder (i) to be in the intake stroke, and subsequently, the change index ΔQti = ΔQi of the intake air amount in consideration of the intake stroke time. / ΔTi is determined (steps A8 to A10). Here, ΔTi is taken into consideration due to torque fluctuation (angular velocity fluctuation of crankshaft 7).
This process is particularly effective during idling operation with large torque fluctuations. Then, based on the change index ΔQti, an intake air amount characteristic ΔQt ′ (i) for each cylinder is obtained by the following equation (step A11).

ΔQt ′ (i) = ΔQti × r + ΔQti ′ × (1-r) where 0 <r ≦ 1 Here, ΔQti ′ is the previous value of the change index ΔQti, and the above operation is repeatedly executed. The current value and the previous value of the change index ΔQti are respectively reflected at a predetermined ratio in the intake air amount characteristic ΔQt ′ (i) of the cylinder (i), and the individual difference between the cylinders with respect to the intake air amount gradually increases. It becomes clearer.

(Transient Determination) FIG. 11 shows a specific control procedure of the transient determination (steps S4 to S7 in FIG. 8). This transient determination is an acceleration determination, and a determination based on a change in the accelerator opening and a determination based on a change in the fuel injection amount are performed. That is, when the engine 1 shifts from the steady operation state to the acceleration operation state, it is necessary to increase the intake air amount in accordance with the increase in the fuel injection amount. The recirculation amount is reduced, and is a transient determination for executing such control of the EGR valve 24. During deceleration of the vehicle, fuel injection is interrupted except for a part of the operating range (fuel cut). At that time, the opening of the EGR valve 24 is set to zero so that exhaust gas recirculation is not performed.

Specifically, first, as a determination procedure based on the change in the accelerator opening Acc, the fuel injection amount is calculated from the three-dimensional map 37 in FIG. 5 using the accelerator opening Acc, the engine speed Ne, and the intake air amount Qav. F (= target injection amount Fsol) is read, and a change amount ΔAcc = Acc−Acc ′ is obtained based on the current value Acc and the previous value Acc ′ of the accelerator opening (steps B1 to B3). On the other hand, the acceleration determination reference αcc is read from the two-dimensional map using the fuel injection amount F and the engine speed Ne (step B4).

The acceleration determination criterion αcc is used for making an acceleration determination based on the accelerator opening change amount ΔAcc. For example, the higher the engine speed Ne becomes, the larger it becomes, and it becomes difficult to determine that the vehicle is accelerating. The fuel injection amount F and the engine speed Ne are set so as to correspond to the fuel injection amount F and the engine speed Ne such that the larger the injection amount F becomes, the easier it is to determine the acceleration, and the set map is electronically stored in the memory. ing. In addition, since the exhaust gas recirculation amount is originally large during low load operation, the exhaust gas recirculation amount must be promptly reduced when the increase in the accelerator opening (increase in fuel injection amount) is large. Therefore, αcc is set so as to decrease as the fuel injection amount increases.

When the acceleration coefficient α = ΔAcc / αcc is larger than 1, it is determined that the engine 1 is in the accelerating operation state, and the target air-fuel ratio TA / F (= A / A Fs
ol), the EGR valve operation amount KTegr (=
Read EGRsol from the map (Steps B5 to B)
7). That is, the larger the change in the accelerator opening, the more quickly the exhaust gas recirculation amount needs to be reduced. Therefore, the map of the EGR valve operation amount KTegr shows that the opening degree of the EGR valve 24 increases as the acceleration coefficient α increases. The amount of operation is experimentally determined and set so that is smaller, and is electronically stored in the memory.

Subsequently, an acceleration determination based on a change in the fuel injection amount is performed. In the case of the acceleration determination based on the accelerator opening, the EGR valve operation amount is determined based on the determination, so to speak, but in the case of the acceleration determination based on the next fuel injection amount, the actual acceleration request is A check is performed based on the injection amount, and control is performed in accordance with the acceleration demand.

That is, the rate of change ΔF = F / F ′ is determined based on the current value F and the previous value F ′ of the fuel injection amount, and a two-dimensional map is obtained using the fuel injection amount F and the engine speed Ne. The acceleration criterion Fk is read (steps B8, B
9). This Fk is set in the same way as the αcc and is electronically stored in the memory. Then, the injection amount change coefficient β
When ΔF / Fk is greater than 1, it is determined that the vehicle is in the accelerated operation state, and the process proceeds to control during acceleration.
0, B11).

(Control in Steady State) The control in the steady state is shown in FIG. 12, and the target torque Ttrq is obtained from the two-dimensional map 36 in FIG. 5 using the engine speed Ne and the accelerator opening Acc.
(= Trqsol), the target air-fuel ratio TA / F (= A / Fsol) is read from the two-dimensional map 38 using the Ttrq and Ne, and the target air-fuel ratio TA / F is multiplied by the fuel injection amount F. Then, the target intake air amount TQ (= FAsol) is calculated (steps C1 to C3).

The target air-fuel ratio TA / F is set to NO as described above.
The value is set so that both the x reduction and the smoke reduction can be achieved. The value is set in the operating range of the engine 1, that is, the engine speed Ne and the engine torque Ttrq (in other words,
It is slightly different depending on the fuel injection amount F). For example, in an operation region in which sufficient supercharging is performed by the turbocharger 25, the in-cylinder compression temperature increases due to the high intake air charging efficiency, and the air flow in the combustion chamber 4 increases to increase the air-fuel ratio. The mixing state is also good, and the generation of smoke is extremely reduced. Therefore, the target air-fuel ratio can be set smaller (toward the rich side) in the high speed range (region where the supercharging pressure is high) and the low speed range of the engine 1.

Following the calculation of the target intake air amount TQ, an intake air amount deviation Qerr = TQ-Qav is obtained, and the basic EGR valve operation amount Tegr (= EGRsol) is determined in accordance with the PID control law so that the deviation Qerr becomes zero. (Steps C4 and C5).
That is, for example, a proportional control term obtained by integrating the control gain (P gain) of the proportional control operation with the deviation Qerr, and an integral control term obtained by integrating the control gain (I gain) of the integral control operation with the integrated value of the deviation Qerr. The basic EGR valve operation amount Tegr is determined by adding the differential value of the deviation Qerr to the differential control term obtained by integrating the control gain (D gain) of the differential control operation. Here, the control gain of the proportional control operation is obtained by multiplying a basic value by a gain coefficient K, and by reducing or increasing the gain coefficient K as described later,
The responsiveness and convergence of the control can be changed.

Following the determination of the basic EGR valve operation amount Tegr, the absolute value of the accelerator opening change amount ΔAcc is changed to a predetermined threshold value Tha
A condition for confirming a steady operation state that a state smaller than cc continues for a predetermined number of n cycles and fuel injection is performed is checked (step C6). Then, when the steady state of operation is confirmed, (i = 0, 1,
2, 3), the intake air amount characteristic ΔQt '(i) obtained above and EG
An EGR valve correction operation amount ΔTegr (i) for each cylinder is calculated based on the R correction gain E (i) (step C7). That is, ΔTegr (i) = ΔQt ′ (i) × E (i) + ΔTegr (i) ′ where ΔTegr (i) ′ is the previous value of the EGR valve correction operation amount of the cylinder (i). Then, in the above calculation, ΔQt ′
The value of (i) itself is emphasized, but by repeating the calculation, the EGR valve correction operation amount gradually reaches an appropriate value according to the individual difference between the cylinders.

In this way, for example, i = 0, 1,
After obtaining the EGR valve correction operation amounts of all four cylinders in the order of 2, 3 and then, when the cylinder number i = 3 (step C8), the average value ΔTegr-av of the EGR valve correction operation amounts for the four cylinders is calculated. Ask. Although this average value should originally be zero, when the calculation in step C7 is performed, the average value becomes negative or positive due to various factors, and the average value becomes negative or positive based on the basic EGR valve operation amount Tegr. The original purpose of correcting and controlling the EGR valve operation amount of the cylinder 2 is impaired.
Therefore, when the average value ΔTegr-av becomes negative, the absolute value is added to ΔTegr (i) of each of the cylinders 2, and when the average value ΔTegr-av becomes positive, the absolute value is subtracted, so that the average value ΔTegr-av becomes zero. Correct (step C9).

The ΔTegr thus obtained is
(i) is added to the basic EGR valve operation amount Tegr, and each cylinder 2
EGR valve operation amount Tegr (i) is obtained (step C10),
Proceed to step D1 in FIG.

(Control at Acceleration Determination Based on Acceleration Coefficient α)
On the other hand, when the acceleration is determined in step B6 in FIG. 11, the transient target EGR valve operation amount KTegr obtained in step B7 varies depending on the magnitude of the acceleration coefficient α and TA / F, and the acceleration coefficient α Is larger than a predetermined value, the opening of the EGR valve 24 is set to zero. That is, when the driver's request for acceleration is large, the exhaust gas is not recirculated and the intake air amount of each cylinder 2 is maximized. Therefore, the increase in the fuel injection amount is suppressed while suppressing the increase in the smoke amount. The engine output can be increased.

In this case, a control for giving a preset to the EGR valve 24 is performed so that when the engine 1 shifts from the acceleration operation state to the steady operation state again, the exhaust gas recirculation control can be promptly shifted. I do. That is, when the EGR passage 23 is closed by the EGR valve 24,
A predetermined EGR valve driving negative pressure (preset negative pressure) is applied to the negative pressure chamber so that the force of pressing the valve body 24c against the valve seat by the spring 24d becomes as small as possible, and thus the pressing force becomes zero. And the pressing force in the closing direction by the spring 24d is balanced with the negative pressure for driving the EGR valve. The preset negative pressure is, as shown in FIG. 4B, the EGR valve driving negative pressure at the time when the EGR valve 24 is controlled to close and the EGR valve lift reaches zero.

Specifically, a control flow for applying a preset negative pressure to the EGR valve 24 is as shown in FIG. That is, first, the EGR valve operation amount Tegr is
If the lift amount of the valve 24 is an operation amount that becomes zero, the value EGRVliFt of the lift sensor 26 is read (step D1,
D2). When the value EGRVliFt is larger than the value EGRV0 corresponding to the lift amount of zero, the EGR valve control is performed until the value becomes equal to the value EGRV0 (steps D3 and D3).
4) The negative pressure for driving the EGR valve is reduced until it becomes the preset negative pressure EGRV0.

On the other hand, in step D1, the EGR
If the valve operation amount Tegr is not the operation amount corresponding to the lift amount zero, the normal EGR valve control is executed without performing the procedures of steps D2 and D3 (steps D1 → D
4) Then return.

(Control at Acceleration Judgment Based on Injection Quantity Change Coefficient β) When the acceleration judgment is made in step B11 of FIG. 11, first, as shown in each step of FIG. Using the fuel injection amount F and the engine speed Ne, KTA / F is read from a three-dimensional map in which the optimum transient target air-fuel ratio KTA / F (= A / Fsol) in these changes is recorded (step G1). The transient target air-fuel ratio KTA / F is leaner than the steady-state target air-fuel ratio TA / F so that the engine output can be quickly increased while reducing the amount of exhaust gas recirculation and suppressing the generation of smoke. Is set to Although not shown, the three-dimensional map shows the change of each value such that the smaller the fuel injection amount F, the larger the injection amount change coefficient β, and the lower the engine speed Ne, the closer to the lean side. The optimum value of KTA / F with respect to is recorded experimentally and stored electronically in a memory.

Subsequently, the transient target air-fuel ratio KTA / F
A target intake air amount TQ (= FAsol) during transition is calculated based on the fuel injection amount F and the fuel injection amount F (step G2). And
Based on this TQ, the EGR valve operation amount is determined in the same manner as in the above-mentioned steady operation, and the amount of exhaust gas is rapidly reduced to increase the amount of intake air (step G below).
Steps C4 to C6 in FIG. 12 following Step 5 and steps D1 to D4 in FIG. 13).

As described above, even when the transient target air-fuel ratio KTA / F is set leaner than the steady state, when the engine 1 shifts to the acceleration operation state, the fuel is injected into the combustion chamber 4 of each cylinder 2. There is a risk that the fuel will temporarily become excessive. Therefore, in this flow, a certain restriction is provided in order to suppress an increase in the amount of fuel. That is, the limit air-fuel ratio LimitA / F is read from the map of the fuel injection amount F and the engine speed Ne (step G3). Then, a limit value FLimit of the fuel injection amount is calculated based on the obtained limit air-fuel ratio LimitA / F and the current intake air amount Q (i), and the basic injection amount F and the limit value FLim
The smallest value among it and the maximum injection amount Fmax is set as the target injection amount TF, and the process proceeds to step C4 in FIG. 12 (steps G4 and G5).

The relationship between the limit air-fuel ratio LimitA / F, the target air-fuel ratio KTA / F during transition and the target air-fuel ratio TA / F during steady state is shown in FIG.
5, the transient target air-fuel ratio KTA / F is set to be leaner than the steady-state target air-fuel ratio TA / F, and conversely, richer than the steady-state target air-fuel ratio TA / F. The limit air-fuel ratio LimitA / F is set. This limit air-fuel ratio LimitA
The limit smoke amount corresponding to / F is slightly larger than the limit smoke amount in the steady state, and is, for example, about 2 BU. In addition, the limit air-fuel ratio LimitA / F can be basically set to the lean side as the fuel injection amount increases, and to the rich side as the engine speed increases, and the fuel injection amount F and the engine speed Ne can be set. The optimum value experimentally obtained for the change of is stored electronically in the memory.
The basic injection amount F is based on the engine speed Ne and the accelerator opening.
Acc is the fuel injection amount determined by Acc and the maximum injection amount Fm
ax is the upper limit of the fuel injection amount that does not cause the destruction of the engine 1.

(Intake Throttle Valve Control) Next, the intake throttle valve control by the ECU 35 will be described in detail with reference to FIGS.
This will be described based on the flowchart shown in FIG. This control is executed in synchronization with the rotation of the engine 1 in accordance with a control program electronically stored in a memory, similarly to the exhaust gas recirculation control.

First, similarly to the exhaust gas recirculation control, the accelerator opening Acc and the engine speed Ne are detected, and the fuel injection amount F
Is read (steps H1 to H3), and it is determined whether or not the accelerator is in the returned state based on the output signal from the accelerator opening sensor 32 (step H4). That is, if the accelerator operation amount suddenly decreases by a predetermined amount or more and the accelerator opening becomes substantially zero, the process proceeds to step H5, where the value of the accelerator return determination flag Flag is set to Flag = 1, and the following step H6 Then, the counter for measuring the elapsed time from the determination of the accelerator return state is reset (Tup = 0), and thereafter, the process proceeds to step H9.

On the other hand, in step H7, in which it is determined in step H4 that the accelerator is not in the return state and NO, it is determined whether or not the value of the accelerator return determination flag Flag is 1, and if Flag = 0 is NO. Step H12 described later
On the other hand, if Flag = 1 and YES, the process proceeds to step H8 where the value of the counter is incremented (Tup
= Tup + Δt), and proceeds to step H9.

In step H9, the counter value T
It is determined whether or not up is equal to or less than a predetermined value Tup1 corresponding to a predetermined time set in advance, and the counter value Tup is set to the predetermined value Tup1.
If the determination is NO, the process proceeds to step H11. On the other hand, if the counter value Tup is equal to or less than the predetermined value Tup1 and the determination is YES, that is, from when the accelerator return state is determined until a predetermined time elapses, Proceed to step H10,
A gain correction coefficient γ1 for correcting the control gain of the EGR valve is read from the two-dimensional map.

This two-dimensional map is a map in which a relatively large value γ1 is set as the gain correction coefficient γ so that the response of the EGR valve control increases in response to the accelerator return state, and is illustrated in FIG. As described above, the optimum gain correction coefficient value γ1 corresponding to the intake throttle amount TH and the engine speed Ne.
Was experimentally determined and recorded. The value of γ1 is 0
In the range of <γ1 <1, the engine speed Ne is set to be smaller as the engine speed Ne is higher and the intake throttle amount TH is larger. The intake throttle amount TH used in this step is a value set in the previous control cycle.

On the other hand, in step H11, where it was determined that the counter value Tup was larger than the predetermined value Tup1 in step H9 and the process proceeded, the accelerator return determination flag is cleared (Flag = 0). That is, if the predetermined time has elapsed after the accelerator return state is determined, the determination in step H7 in the next control cycle is NO, and the process proceeds to step H12. In this step H12, the two-dimensional map ( The gain correction coefficient γ2 is read from another two-dimensional map similar to that shown in FIG. 17). In this other two-dimensional map, a gain correction coefficient γ2 in a normal state in which the accelerator is not returned is set, and γ2 <γ1 in all setting regions of the map.

Following steps H10, H11, H12, step H13 in the flowchart of FIG.
Then, it is determined whether or not the engine 1 is in an idling operation state. That is, if YES in the idling operation state where the accelerator is fully closed and the running speed of the vehicle is zero, the flow proceeds to step H17 described later, while if NO in the idling operation state, the flow proceeds to step H14 to search the intake throttle map. This intake throttle map is equivalent to the map 51 in FIG. 5, but in detail, as shown in FIG. 19, the optimal intake throttle amount corresponding to the fuel injection amount F and the engine speed Ne.
TH (= THsol) is a digital two-dimensional map determined and recorded experimentally.

According to this map, when the engine 1 is in the high rotation range or the high load range and the fuel injection amount F or the engine speed Ne is large, the intake throttle amount TH is set to zero, and the intake throttle valve is set. 14 is controlled to the fully open state. That is, since the differential pressure between intake and exhaust is high in the high speed region of the engine 1, the amount of exhaust gas recirculation increases, and the amount of intake air tends to be insufficient. According to the intake throttle map, the intake throttle valve 14 is controlled to a fully open state in a high rotation range or a high load range of the engine 1 due to the shortage of the intake air. The smoke is prevented from increasing.

According to the above-mentioned map, in a relatively low-load operation state excluding a high rotation range or a high load range, the intake throttle amount TH decreases as the fuel injection amount F decreases and the engine speed Ne increases. Is set to be larger as the value is lower.
That is, the lower the engine speed Ne, the lower the differential pressure between the intake and exhaust, and accordingly, the opening degree of the intake throttle valve 14 is controlled to be small, and the differential pressure between the intake and exhaust is increased to increase the exhaust pressure. To ensure a sufficient amount of reflux.

Following step H14, step H
In 15, it is determined whether or not the intake is to be reduced based on the value of the accelerator return determination flag Flag and the search result of the intake throttle map. That is, Flag = 0 or Flag
Even if = 1, if the engine 1 is in a high-load or high-speed operation state and NO to restrict the intake, the process proceeds to step H19, while the flag is 1 and the operation state is other than the above, If YES to reduce the intake, step H1
Proceeding to 6, the intake throttle amount TH is set according to the value read from the intake throttle map. Further, in step H17, which was determined in step H14 when the idling operation state was determined to be YES, the intake throttle amount TH is set so that the intake throttle valve 14 is fully closed in accordance with the idling operation state.

In step H18 following step H16 or H17, the solenoid valve 16 for negative pressure control is determined based on the intake throttle amount TH set in each step.
To control the opening degree of the intake throttle valve 14. Subsequently, in Step H19, the aforementioned Step H
Based on the gain correction coefficient γ read in either step 10 or step H12, a gain coefficient K for determining the value of the control gain in the EGR valve control is calculated, and then the process returns.

K = K × (1 + γ) Here, the gain correction coefficient γ corresponding to the accelerator return state
When 1 is read, the gain coefficient K is increased from the normal operation state by an amount that the value of γ1 is larger than the value of γ2, and the proportional control gain in the above-described EGR valve control (see FIG. 12) increases. As a result, the operation responsiveness of the EGR valve 24 is improved. In other words, during a period from when the accelerator return state is determined to when the predetermined time elapses, the accelerator operation amount is rapidly changing, and the operation responsiveness of the EGR valve 24 is changed so as not to delay the change. Can be enhanced. The predetermined time may be, for example, a relatively short time (for example, 1 to 2 seconds) corresponding to the shift operation of the manual transmission, and there is no problem even if the convergence of the control deteriorates in the short time.

According to the above-described intake throttle valve control, for example, when the accelerator pedal for starting the vehicle is predicted to be depressed while the engine 1 is in an idling operation state, the intake throttle valve 14 is fully closed. As the differential pressure between intake and exhaust is increased, the opening of the EGR valve 24 is made relatively small (for example, about half open). Then, when the engine 1 shifts from the steady operation state to the acceleration operation state with the start of the vehicle, the intake throttle valve 14 is quickly opened and the EGR is increased with an increase in the fuel injection amount.
Although the valve 24 is also operated to be closed, the delay of the closing operation of the EGR valve 24 can be reduced because the opening degree of the EGR valve 24 is previously reduced as described above. That is, by causing the EGR valve 24 to be fully opened quickly to maximize the amount of intake air, it is possible to reduce the occurrence of smoke when the vehicle starts moving.

(Setting of Fuel Injection Timing) The feature of the present invention is as follows.
In the diesel engine in which the indirect air-fuel ratio control is performed by adjusting the exhaust gas recirculation amount as described above, when the engine 1 shifts from the steady operation state to the accelerated operation state,
In the compression stroke of each cylinder 2, fuel is injected in two stages, early and late (hereinafter referred to as multi-stage injection), and the late injection timing is set earlier than the fuel injection in the steady operation state. I did it.

Specifically, when the engine 1 is in a steady operation state, fuel is supplied from the injector 5 near the compression top dead center of each cylinder 2 (ATDC 4 ° CA in the example) as illustrated in FIG. Injection is performed by one main injection at a time, and particularly in a low-rotation low-load region of the engine 1 (for example, an operation region corresponding to an idling operation state of the engine), as illustrated in FIG. In addition, a pilot injection for injecting a predetermined amount of fuel immediately before the main injection is also performed.

When the operating state of the engine 1 shifts from the steady operating state to the accelerating operating state, the fuel injection from the injector 5 is performed in the middle of the compression stroke of each cylinder 2 as shown in FIG. In the example shown, BTDC 90 °
CA) and the late injection near the compression top dead center are executed separately, and the late injection is advanced so that the end timing is earlier than the main injection in the steady operation state. ing.

Next, the processing procedure of the fuel injection timing control by the ECU 35 will be specifically described with reference to the flowcharts shown in FIGS. This control is executed at every predetermined crank angle in synchronization with the output signal from the crank angle sensor 9 in accordance with a control program stored electronically in a memory, similarly to the intake throttle valve control and the like.

First, as shown in FIG. 21, in steps J1 and J2 after the start, the accelerator opening Acc and the engine speed Ne are respectively detected in the same manner as in the exhaust gas recirculation control and the like. The engine coolant temperature is read based on the output signal, and the fuel injection amount F
And read the common rail pressure CRP (Step J3 ~
J5).

Subsequently, at step J6, it is determined whether or not the engine 1 is in an acceleration operation state (acceleration start?), Similarly to the transient determination in the exhaust gas recirculation control (see FIG. 11). That is, based on the acceleration coefficient α corresponding to the change of the accelerator opening and the injection amount change coefficient β corresponding to the change of the fuel injection amount F, α> 1 or β from the steady operation state of α ≦ 1 and β ≦ 1 > 1, and when it is determined that the vehicle is in the accelerated operation state, the process proceeds to step J7.
Otherwise, that is, if the vehicle is in the steady operation state or continuously in the accelerated operation state, the process proceeds to step J10.

In step J7, the value of the multi-stage injection execution flag Flagsp indicating that it is the period in which the multi-stage injection is performed when the engine 1 shifts to the acceleration operation state is set to 1 (Flagsp =
1) In a succeeding step J8, a counter for measuring a period for performing the multi-stage injection is reset (counter value T
down = Tdown0), and proceeds to step J9. The initial value Tdown0 of the counter is set in advance.

In step J9, based on the output signal from the lift sensor 26 of the EGR valve 24, the EGR valve 24
Is actually moved to the closing side as compared to before the acceleration determination. That is, for example, when the opening of the EGR valve 24 has become smaller than a predetermined value or more than the acceleration determination time in step J6, or when the opening of the EGR valve 24 has become smaller than a predetermined predetermined opening, E
It is determined that the GR valve 24 has been operated to the closed side, ie, YES, and the flow proceeds to step J21 in FIG. 22 to execute the multi-stage fuel injection. On the other hand, when it is determined that the EGR valve 24 has not been closed yet, the process proceeds to step J31 in FIG. 23 to inject the fuel mainly by the main injection near the compression top dead center.

That is, when the operating state of the engine 1 shifts from the steady operating state to the accelerated operating state, EG
After confirming that the R valve 24 has actually been operated to the closing side, multi-stage injection of fuel is started.

On the other hand, in step J10, where it is determined in step J6 that the engine 1 is in the steady operation state or is continuously in the accelerated operation state, the process proceeds to step J10.
It is determined whether or not the value of the multi-stage injection execution flag Flagsp is 1, and if Flagsp = 0 and NO, it is determined that the multi-stage injection is not being performed and the process proceeds to step J31 in FIG.
If sp = 1 and YES, the flow advances to step J11 to count down the counter, and the flow advances to step J12. In this step J12, it is determined whether or not the counter value Tdown has become zero.
If it is determined to be O, it is determined that the period is for performing the multi-stage injection, and the process proceeds to step J9. On the other hand, the counter value Tdown
If = 0 and YES, it is determined that the period for performing the multi-stage injection has ended, the process proceeds to step J13, the multi-stage injection execution flag Flagsp is cleared (Flagsp = 0), and the process proceeds to step J31 in FIG.

That is, after the operating state of the engine 1 shifts from the steady operating state to the accelerated operating state, and the fuel injection mode is switched from the batch injection to the multi-stage injection, until the set time measured by the counter elapses. While the multi-stage injection is continuously performed, if the set time has elapsed, the injection is switched to the batch injection even when the engine 1 is in the accelerating operation state. Thus, not only can the increase in smoke due to the increase in fuel at the start of acceleration be sufficiently suppressed by the multi-stage injection, but also, by switching to the batch injection after the elapse of the set time, deterioration in fuel efficiency due to the multi-stage injection can be suppressed. .

At step J21 in FIG. 22, the fuel injection pulse width Wall corresponding to these values is read from the map on the memory based on the common rail pressure CRP and the fuel injection amount F. This injection pulse width Wall is equivalent to the sum of the two injection pulse widths when the fuel is divided into two stages of early injection and late injection in the compression stroke of each cylinder 2 and multistage injection. Also, the map is:
The optimum value of the injection pulse width Wall corresponding to the change of the common rail pressure CRP and the fuel injection amount F is experimentally obtained and recorded. The injection pulse width Wall becomes longer as the fuel injection amount F becomes larger, and the common rail pressure becomes larger. The higher the CRP, the shorter it is set.

Subsequently, in step J22, based on the injection pulse width Wall obtained in step J21, the pulse width W2 of the late injection is read from the map electronically stored in the memory and determined. This map is obtained by experimentally finding and recording the optimum value of W2 corresponding to the total injection pulse width Wall. As shown in FIG.
In a range where ll is relatively small, it is equal to the wall, while in a range where wall is relatively large, the ratio of W2 is set so as to gradually decrease to finally become about half of the wall. That is, in the accelerated operation state of the engine 1 having a large fuel injection amount, the late injection amount is 2/3 to 1/1 / the total injection amount.
2. As a result, the early injection amount is 1/3 of the total injection amount.
It becomes 1/2.

Subsequently, in step J23, the late injection timing TW2 is read from the injection timing map electronically stored in the memory based on the engine coolant temperature, the common rail pressure CRP, and the like. This injection timing map is
For example, two maps 53a shown in FIGS.
53b. First, a basic map 5 shown in FIG.
In 3a, the basic late injection timing corresponding to the engine water temperature and the engine speed Ne is experimentally determined and recorded. According to the basic map 53a, the basic late injection timing is set to be advanced as the engine water temperature is lower and the engine speed Ne is higher. This is because the ignition delay time of the fuel spray is different if the engine water temperature or the engine speed Ne is different.

The advance angle map 53 shown in FIG.
In b, the optimal advance amount of the late injection timing corresponding to the common rail pressure CRP is experimentally obtained and recorded, and the advance amount of the late injection timing is increased as the common rail pressure CRP is lower. Is set. That is, the late injection timing TW2 is advanced so as to be earlier than the basic injection timing set in the basic map 53a.
The fuel injection state, such as the shape of the fuel spray, deteriorates as the common rail pressure CRP changes depending on P, so that the injection timing is advanced to suppress the generation of smoke. On the other hand, the higher the common rail pressure CRP is, the more the fuel spray penetrates and the easier the fuel adheres to the wall surface of the combustion chamber 4. Therefore, the injection timing is delayed to reduce the wall surface adhesion.

Subsequently, in step J24, the injection pulse width W2 and the injection timing TW2 of the latter injection are set. The injection timing TW2 is a timing to end the fuel injection, and the timing to start the injection is advanced based on the injection timing TW2 as the injection pulse width W2 is longer, while it is delayed as the injection pulse width W2 is shorter. It has become so.

Next, at step J25, the pulse width W2 of the late injection is subtracted from the injection pulse width Wall to calculate the injection pulse width W1 of the early injection. At the next step J26, the injection pulse width W1 is calculated based on the engine coolant temperature and the common rail pressure CRP. Thus, for example, the early injection timing TW1 is read from the injection timing map 54 illustrated in FIG. In the injection timing map 54, the optimum early injection timing corresponding to the engine water temperature and the common rail pressure CRP is experimentally determined and recorded. According to this map 54, the early injection timing is set to be advanced as the engine water temperature is higher and the common rail pressure CRP is lower.

The early injection timing map 54
According to the above, the injection timing TW1 of the early injection, that is, the timing of ending the fuel injection, is set within the range of BTDC 90 ° to 30 ° CA in the compression stroke of the cylinder as illustrated in FIG. That is, since the early injection is performed when the in-cylinder pressure of the combustion chamber 4 is not so high, if the engine water temperature is low, adhesion of the injected fuel to the wall surface of the combustion chamber 4 becomes a problem. Therefore, the injection timing is delayed as the engine water temperature is lower, so that the amount of fuel adhering to the wall surface is reduced. The relationship between the early injection timing TW1 and the common rail pressure CRP is the same as in the advance angle map 53b.

Then, in step J27, the injection pulse width W1 and the injection timing TW1 of the early injection are set, and thereafter, the routine returns.

On the other hand, in step J31 of FIG. 23, the main injection pulse width Wm is read from the same map as that used in step J21 based on the common rail pressure CRP and the fuel injection amount F. The main injection pulse width Wm is for the main injection in which the fuel is collectively injected near the compression top dead center of each cylinder 2. Subsequently, in step J32, the basic map 53 of the injection timing used in step J23 based on the engine coolant temperature and the engine speed Ne.
a (see FIG. 25 (a)), the main injection timing Tm is read, and in the subsequent step J33, the main injection pulse width Wm
And the main injection timing Tm is set, and Step J34
Proceed to. Note that the main injection timing Tm is also a timing at which the fuel injection ends.

Subsequently, in steps J34 and J35, execution determination of pilot injection is performed. That is, in step J34, an area determination map in which the operating area of the engine 1 is set in accordance with the engine speed Ne and the fuel injection amount F is referred to.
Based on the fuel injection amount F and whether the operating state of the engine 1 is in a low-speed low-load operation region corresponding to, for example, the idling operation, it is determined. When the determination is NO, the routine returns without performing the pilot injection. When the determination is YES, the process proceeds to step J36 and proceeds to step J36.
The pilot injection pulse width Wp is read from the map in the same manner as in steps 21 and J31. According to this map, the pilot injection pulse width Wp is about 10% of the main injection pulse width Wm, and is set to be shorter as the common rail pressure CRP is higher.

Subsequently, at step J37, the end timing Tp of the pilot injection is calculated based on the pilot injection pulse width Wp and the injection timing Tm of the main injection.
That is, the pilot injection timing T such that the main injection is started at a predetermined interval after the end of the pilot injection.
Find p. Then, in step J38, the injection pulse width Wp and the injection timing Tp of the pilot injection are set, and then the process returns.

That is, when the engine 1 is in the steady operation state and in the low-load low-speed operation region, the sudden rise of the combustion pressure and the combustion temperature in the premixed combustion of the main injection is alleviated by the pilot injection. As a result, the operating noise of the engine 1 can be reduced.

Step J6 of the flow shown in FIG. 21 constitutes acceleration judging means 35a for judging that the operation state of the engine 1 has shifted from the steady operation state to the acceleration operation state. (Exhaust gas recirculation amount control valve) A closing operation detecting hand 35f is configured to detect that the operation has actually been performed to the closing side.

When the acceleration determining means 35a determines that the operating state of the engine 1 has shifted from the steady operating state to the accelerated operating state in each of the steps J21 to J27 of the flow shown in FIG. To
The fuel injection by the injector 5 is executed in two stages: an early injection in the middle stage of the compression stroke of the cylinder 2 and a late injection near the compression top dead center, which ends earlier than the main injection in the steady operation state immediately before the acceleration determination. Injection timing control means 35
b.

Next, the operation and effect of the control device A according to the first embodiment will be described with reference to FIGS. 28 and 29.

In this embodiment, when the driver of the vehicle depresses the accelerator and the operating state of the engine 1 shifts from the steady operating state to the accelerated operating state, the fuel injection amount is increased in accordance with the accelerator operation. At the same time, in the middle stage of the compression stroke of each of the cylinders 2, fuel of approximately one third or more of the total injection amount in one combustion cycle is early injected. This early-injected fuel is mixed with air by the flow of air in the cylinder 2 and is sufficiently vaporized and atomized.
And gradually reacts with the surrounding oxygen as the cylinder pressure rises. When the temperature of the entire combustion chamber reaches the so-called self-ignition temperature at the end of the compression stroke, the combustion chamber explosively burns. On the other hand, the remaining fuel is injected late in the vicinity of the compression top dead center, and the fuel spray in the latter injection burns rapidly after a very short ignition delay period.

According to the combustion by such multi-stage injection,
First, the fuel spray injected early spreads relatively large and mixes with the air, and is sufficiently vaporized and atomized to burn well, so that the air utilization rate of the combustion chamber 4 becomes extremely high. In addition, the fuel spray gradually transitions to an explosive combustion state while reacting with ambient oxygen, so that premixed combustion after self-ignition does not become excessively violent. That is,
When multi-stage injection is performed, for example, as shown by a solid line in FIG. 28, the in-cylinder pressure P of each cylinder 2 is higher than the case of batch injection before the compression top dead center (TDC) (shown by a broken line in FIG. 28). After that, it rises due to explosive combustion and reaches a peak value, but the peak value is lower than that in the case of batch injection. Moreover, the rise of the combustion pressure becomes gentler than in the case of the batch injection. Therefore, generation of NOx can be significantly reduced.

On the other hand, as a result of the early injection of a large amount of fuel, the fuel injection amount F in one combustion cycle is obtained.
Even if the total amount of the fuel is considerably large, the injection quantity of the latter injection does not increase so much, and the fuel spray of the latter injection is injected into the combustion chamber 4 which is at a high temperature and a high pressure due to the weak combustion of the early injected fuel. It is well mixed with air and is sufficiently vaporized and atomized to burn quickly and well. Further, since the timing of the late injection is earlier than the injection timing in the steady operation state, the mixed state of the fuel and the air is further improved, and the combustion speed is further increased. Therefore,
Although the total amount of fuel injection is considerably large, it is possible to sufficiently suppress the increase in smoke.

In addition, since the fuel spray injected at the latter stage is injected into the combustion chamber in which combustion has already started, even if the injection timing is advanced, the rise of the combustion pressure and combustion temperature is excessive. It does not become steep (see FIG. 2
8). That is, even if the injection timing is set earlier than in the steady operation state, it does not cause a significant increase in the NOx generation amount.

FIG. 29 shows an example of the results of an experiment conducted by the present inventor to confirm the reduction of NOx and smoke due to the multi-stage fuel injection. In the experiment, an in-line four-cylinder direct-injection diesel engine having substantially the same configuration as that of this embodiment was used, and under a constant operating condition of low rotation speed and medium load,
While changing the GR rate within a predetermined range, the NOx concentration and the smoke concentration in the exhaust are measured for each of the multi-stage injection and the batch injection of the fuel. However,
The end timing of the late injection in the multi-stage injection is the same as the end timing of the collective main injection.

According to the figure, when fuel is injected in multiple stages, the NOx concentration is significantly lower than in the case of batch injection, and the EGR rate corresponds to the point X shown in the figure. It can be seen that if the value is lower than the required value, the smoke can be reduced. That is, when it is not necessary to increase the amount of exhaust gas recirculation to the combustion chamber, it is necessary to perform multi-stage injection of fuel and reduce the amount of exhaust gas recirculation to lower the EGR rate, thereby reducing both NOx and smoke. It can be seen that both can be reduced. Therefore, in addition to this, if the timing of the late injection is advanced, the mixed state of fuel and air by the late injection can be further improved, and smoke can be further reduced.

Therefore, according to the diesel engine control apparatus A of this embodiment, when the operating state of the engine 1 shifts from the steady operating state to the accelerated operating state,
The fuel injection amount is increased according to the driver's accelerator operation, and the fuel injection by the injector 5 is performed in two stages, an early stage and a late stage, and the timing of the late injection is immediately before the shift to the accelerated operation state. In the normal operation state. As a result, it is possible to sufficiently suppress the increase in smoke in the exhaust gas while increasing the engine output and reducing NOx. Further, with the increase in the fuel injection amount, EG
The R valve 24 is operated to the closing side, and the intake throttle valve 14 is fully opened to increase the amount of fresh intake air, thereby further increasing the engine output and further suppressing smoke. .

Particularly in the case of this embodiment, the EGR passage 23
The throttle valve 1 is provided in the intake passage 10 upstream of the connection with the
The intake throttle valve 14 is closed by a predetermined amount while the engine 1 is operating at a low rotation speed and a low load so that the negative pressure in the intake passage 10 is increased. Therefore, for example, when the engine 1 shifts to the accelerated operation state when the vehicle starts, the intake air flow resistance in the intake passage 10 is increased by the intake throttle valve 14, so that the amount of intake air to the combustion chamber 4 is particularly insufficient. Therefore, there is a strong possibility that smoke is increased. Therefore, in such a configuration,
As described above, the effect of being able to sufficiently suppress smoke while reducing NOx is extremely effective by the fuel injection divided into two and the late injection timing advance control.

In this embodiment, when the shift of the engine 1 to the accelerated operation state is determined, the lift sensor 2
After confirming the closing operation of the EGR valve 24 based on the output signal from the ECU 6, the multi-stage injection of the fuel is started. That is, immediately after the engine 1 enters the accelerated operation state, the exhaust gas recirculation amount temporarily becomes excessive due to the operation delay of the EGR valve 24. There is a risk that the combustion state will deteriorate and smoke will increase. This is not completely solved even if the operation delay of the EGR valve 24 is reduced by the above-described intake throttle valve control (see FIG. 18). Therefore, EGR
By confirming the closing operation of the valve 24 and starting multi-stage fuel injection, the above-mentioned increase in smoke can be avoided.

(Modification of First Embodiment) As described above, in the first embodiment, when the engine 1 shifts from the steady operation state to the accelerated operation state, the closing operation of the EGR valve 24 is confirmed, and then the multi-stage fuel injection is performed. By starting the injection, it is possible to avoid an increase in smoke caused by an excessive amount of exhaust gas recirculation immediately after the start of acceleration. In contrast, EGR
Instead of detecting the closing operation of the valve 24, the air-fuel ratio of the combustion chamber 4 of the engine 1 may be detected, and whether or not to start the multi-stage injection may be determined based on the detection result.

Specifically, when it is determined in step J6 or J12 of the fuel injection control flow shown in FIG.
6, YES in step J12), and proceeds to step J100 shown in the flow of FIG.
Intake air amount Qi obtained based on the output signal from
Is read, and in subsequent step J101, the actual air-fuel ratio A / F is calculated by dividing the intake air amount Qi by the fuel injection amount F. Subsequently, at step J102, the engine speed
Based on Ne and the actual air-fuel ratio A / F, reference is made to a region determination map 55 as illustrated in FIG.
, It is determined whether the fuel is to be injected in multiple stages or collectively. If YES in the operation region (a) where multi-stage injection is performed, the process proceeds to step J21 in FIG. 22 to execute multi-stage fuel injection, while the other operation region (a).
If the answer is NO, the process proceeds to step J31 in FIG.
Execute fuel batch injection.

[0139] The region determination map 55 indicates the operating regions (A), according to the engine speed Ne and the air-fuel ratio A / F.
(A), where A / F ≧ A /, with respect to the boundary value (set value) A / F * of the air-fuel ratio set so that the value gradually decreases as the engine speed Ne increases. The F * side is an operation area (A) for performing multi-stage fuel injection, and the opposite side is an operation area (A) for collectively injecting fuel. Here, the air-fuel ratio A / F of the combustion chamber 4 is indirectly controlled by adjusting the recirculation amount of the exhaust gas.
The fact that the air-fuel ratio A / F ≧ A / F * in 5 corresponds to the fact that the EGR rate is equal to or less than a predetermined reference value.

That is, for example, if the EGR rate corresponding to the point X in the graph of FIG. 29 is set as the reference value and the air-fuel ratio A / F corresponding to the reference value is set as the boundary value A / F * of the air-fuel ratio, In the operation region (a) in which the multi-stage fuel injection is performed, the EGR rate for each cylinder of the engine 1 is equal to or less than the reference value, and the multi-stage fuel injection can reduce NOx and smoke more than in the case of the batch injection. It corresponds to a suitable operation region. The reason why the boundary value A / F * becomes smaller as the engine 1 rotates at higher rotation speeds is that the intake charging efficiency of the cylinder 2 is reduced in the low rotation speed range of the engine 1 or is low in the high rotation speed range. This is because combustion stability is not impaired even if the EGR rate is increased as compared with the rotation range.

Therefore, according to this modification, similarly to the second embodiment, when the operating state of the engine 1 shifts from the steady operating state to the accelerated operating state, the multi-stage injection of fuel and the advance control of late injection are performed. This is performed and the amount of exhaust gas recirculation is reduced, so that it is possible to sufficiently suppress the increase in smoke while reducing the generation of NOx. Further, the engine output can be increased in accordance with the acceleration operation state of the engine 1.

Further, in this modification, when the engine 1 is in the acceleration operation state, it is confirmed that the air-fuel ratio A / F of the combustion chamber 4 has become equal to or larger than the boundary value A / F *, Since the multi-stage injection is started, when the engine 1 shifts from the steady operation state to the acceleration operation state, if the opening operation of the intake throttle valve 14 is delayed and the intake air amount becomes insufficient,
Alternatively, even if the delay of the closing operation of the EGR valve 24 becomes large and the EGR rate becomes temporarily too high and the air-fuel ratio becomes excessively rich, the multi-stage injection is not performed in such a state. Thus, an increase in smoke immediately after the start of acceleration can be reliably avoided.

(Embodiment 2) FIG. 32 shows a specific processing procedure for setting the early injection timing in Embodiment 2 of the present invention. Since the configuration of the control device A for a diesel engine according to the second embodiment is the same as that of the first embodiment, the same reference numerals are given to the same components as those in the first embodiment, and description thereof will be omitted.

In the control device A according to the second embodiment, as in the first embodiment, when the engine 1 shifts from the steady operation state to the acceleration operation state, the recirculation amount of the exhaust gas is reduced and the fuel is reduced. Is performed and the timing of the late injection is advanced, and in addition, the early injection is further divided into two times.

Specifically, in the control of the fuel injection timing in this embodiment, it is determined that the engine 1 shifts from the steady operation state to the accelerated operation state and is in the period of performing the multi-stage fuel injection (see FIG. 21). After the injection pulse width W2 of the late injection and the injection timing TW2 are set (steps J21 to J24 in FIG. 22) and the early injection pulse width W1 is calculated in the next step J25, the step J41 shown in FIG. Proceed to. In this step J41, it is determined whether or not the magnitude of the early injection pulse width W1 is equal to or greater than a predetermined amount. If NO is determined not to be equal to or greater than the predetermined amount, the process proceeds to step J48, while if YES is determined to be equal to or more than the predetermined amount, the process proceeds to step J42 and step J43 to further reduce the early injection pulse width W1 by the first and second two pulses. It is divided into widths W11 and W12.

That is, first, in step J42, a predetermined division coefficient ε (ε = 0.1 to
0.5) to calculate the first injection pulse width W11,
In a succeeding step J43, the first injection pulse width W11 is subtracted from the early injection pulse width W1 to obtain a second injection pulse width W12.
Is calculated. Then, in a succeeding step J44, based on the engine coolant temperature and the common rail pressure CRP, the same injection timing map 54 as that in the first embodiment is used.
The first injection timing TW11 is read from FIG. 26 (see FIG. 26), and in the subsequent step J45, the injection pulse width W of the first injection
11 and the injection timing TW11 are set.

Subsequently, at step J46, the first injection timing TW11, the second injection pulse width W12, and the preset minimum pulse interval W0 (for example, 100 to 1000)
The second injection timing TW12 is calculated based on (microseconds). That is, the timing delayed from the end timing TW11 of the first injection by the minimum pulse interval W0 and the width W12 of the second injection pulse is defined as the end timing TW12 of the second injection. Then, the process proceeds to a step J47, wherein the injection pulse width W12 and the injection timing TW12 of the second injection are set, and thereafter, the process returns. That is, if the injection amount of the early injection increases and the early injection pulse width W1 becomes larger than a predetermined amount, the early injection is divided into the first and second injections.

On the other hand, if it is determined in step J41 that the early injection pulse width W1 is smaller than the predetermined amount, the early injection is not divided. That is, in steps J48 and J49, as in the case of the first embodiment (steps J26 and J2 in FIG. 22).
7) Read the early injection timing TW1 from the injection timing map 54 based on the engine coolant temperature and the common rail pressure CRP, and read the read early injection timing T
W1 and the early injection pulse width W1 are set, and then the process returns.

Therefore, according to the second embodiment, similarly to the first embodiment, when the operation state of the engine 1 shifts from the steady operation state to the acceleration operation state, the multi-stage injection of fuel and the advance control of late injection are performed. Is performed and the exhaust gas recirculation amount is reduced, so that the increase in smoke can be sufficiently suppressed while the generation of NOx is reduced. Further, the engine output can be increased in accordance with the acceleration operation state of the engine 1.

Further, when the injection amount of the early injection is large, the early injection is performed in two parts, and the mixed state of the early injected fuel and the air can be further improved. This further reduces NOx and smoke.

(Other Embodiments) The present invention is not limited to the above embodiments, but encompasses other various embodiments. That is, the first embodiment
In the multi-stage fuel injection in the first embodiment, the early injection and the late injection are performed once each.
In the above, the early injection is further divided into two times, and the multi-stage injection of three stages in total is performed in the compression stroke. However, the present invention is not limited to this, and the early injection may be performed three times or more. In this case, each early injection is performed in the compression stroke and the BTDC 30
° CA, and the total injection amount of these early injections is 1 / of the fuel injection amount in one combustion cycle of the cylinder.
It is preferable that the number be 3 or more.

In each of the above embodiments, when the engine 1 shifts from the steady operation state to the accelerated operation state, the fuel injection mode is switched from the collective injection to the multi-stage injection until the set time measured by the counter elapses. Is to continuously perform the multi-stage injection, but the invention is not limited to this, while the latter-stage injection is advanced at the beginning of the period in which the multi-stage injection is performed, and then the period of the latter-stage injection is gradually changed to the steady operation state. You may make it return to the same time as time.

Thus, when the engine 1 shifts to the acceleration operation state, first, even if the air-fuel ratio is particularly rich at the beginning of the period of performing the multi-stage injection, priority is given to the advance of the late injection. Smoke can be suppressed. On the other hand, since the air-fuel ratio gradually changes to the lean side during the period in which the above-mentioned multi-stage injection is performed, the timing of the latter-stage injection is returned to correspond to this, so that NOx and smoke can be reduced in a well-balanced manner.

In each of the above embodiments, the engine 1
By controlling the exhaust gas recirculation amount for each cylinder, the air-fuel ratio in the combustion chamber 4 of each cylinder 2 is controlled to be uniform and a target value. However, the present invention is not limited to this. The exhaust gas recirculation amount may be controlled collectively for all of the two. Further, the present invention can be applied to an engine in which exhaust gas recirculation control is not performed, and in that case, it is possible to reduce harmful components in exhaust gas.

In each of the above embodiments, the control device A according to the present invention is applied to the diesel engine 1 provided with the turbocharger 25. Suitable for diesel engines that have not been used.

In each of the above embodiments, the present invention is applied to the direct-injection diesel engine 1 equipped with a common rail fuel injection system. However, the present invention is not limited to this. The present invention is also applicable to a diesel engine in which a unit injector is provided for each cylinder.

[0157]

As described above, according to the control apparatus for a diesel engine according to the first aspect of the present invention, when the engine shifts to the acceleration operation state, one-third or more of the fuel is reduced to 30% before the top dead center of the compression stroke. ° CA before injection, and the remaining fuel is injected earlier than the fuel injection near the compression top dead center immediately before the transition to the accelerated operation state, thereby increasing the air utilization rate in the combustion chamber while premixing combustion. Moderately reduce the rise of combustion pressure and combustion temperature at the time,
The generation of NOx can be reduced, and the fuel can be quickly vaporized and atomized and quickly and satisfactorily burned to sufficiently suppress the increase in smoke. Further, the engine output can be increased corresponding to the acceleration operation.

According to the control apparatus for a diesel engine according to the second aspect of the present invention, when the engine shifts to the acceleration operation state, the exhaust gas recirculation amount is reduced in accordance with the increase in the fuel injection amount, and the fuel injection is reduced. 2. The method according to claim 1, wherein the fuel injection is performed in multiple stages including a first injection ending in the compression stroke of the cylinder and a last injection ending near the compression top dead center earlier than the fuel injection in the steady operation state.
The same operation and effect as those of the described invention can be obtained.

According to the third aspect of the present invention, it is particularly effective to reduce NOx and smoke by multi-stage fuel injection at the time of transition to the acceleration operation state in the low engine speed operation region where the intake charge efficiency is low. .

According to the fourth aspect of the invention, at least one third of the fuel injection amount in one combustion cycle for each cylinder is injected in the compression stroke before 30 ° CA before the compression top dead center. The effect of the second aspect can be sufficiently obtained.

According to the fifth aspect of the present invention, by opening and closing the exhaust gas recirculation amount control valve based on the output signal from the intake air amount sensor, the air-fuel ratio of the combustion chamber of the engine can be highly accurately adjusted to the target value. By performing high-precision air-fuel ratio control and multi-stage fuel injection together, it is possible to achieve both high-dimensional reduction of NOx and smoke in exhaust gas.

According to the sixth aspect of the present invention, high-precision and high-responsive air-fuel ratio control and multi-stage fuel injection are performed in combination to further reduce NOx and smoke in exhaust gas at a higher level. it can.

According to the seventh aspect of the invention, when the engine shifts to the acceleration operation state, the actual closing operation of the exhaust gas recirculation amount control valve is confirmed, and then the multi-stage fuel injection is started to start the acceleration. Immediately after the smoke increase can be avoided.

According to the eighth aspect of the present invention, when the engine shifts to the acceleration operation state, it is confirmed that the actual air-fuel ratio of the combustion chamber has become equal to or higher than the set value, and then the multi-stage fuel injection is started. Thus, the increase in smoke immediately after the start of acceleration can be reliably avoided.

According to the ninth aspect of the present invention, while giving priority to the suppression of smoke in the exhaust gas at the beginning of the acceleration operation of the engine,
Thereafter, both NOx and smoke can be reduced.

According to the tenth aspect of the present invention, in which the intake throttle valve is provided in the intake passage, the effect that NOx can be reduced while suppressing increase in smoke when the vehicle starts moving is particularly effective. become.

According to the eleventh aspect, control of fuel injection timing by injection timing control means can be realized by a so-called common rail type fuel injection system.

According to the twelfth aspect of the present invention, it is possible to suppress overall deterioration of fuel efficiency due to multi-stage fuel injection.

According to the thirteenth aspect, the engine operation noise is reduced by the pilot injection.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an engine according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a part of the turbocharger in a small A / R state (a) or a large A / R state (b).

FIG. 3 is a configuration diagram of an EGR valve and a drive system thereof.

FIG. 4 is a graph showing a relationship between a drive current of the EGR valve and a drive negative pressure (a) or a lift amount (b).

FIG. 5 is an overall configuration diagram of an engine control system.

FIG. 6 is a graph showing a relationship between an air-fuel ratio and a NOx emission amount.

FIG. 7 is a graph showing a relationship between an air-fuel ratio and a smoke value.

FIG. 8 is a diagram showing a basic flow of exhaust gas recirculation and fuel injection amount control.

FIG. 9 is a graph showing a time change of an intake air flow rate of the engine.

FIG. 10 is a flowchart illustrating a calculation procedure of an intake air amount.

FIG. 11 is a flowchart illustrating a procedure of a transient determination process.

FIG. 12 is a flowchart illustrating a procedure for calculating an EGR valve operation amount.

FIG. 13 is a flowchart illustrating a processing procedure of control for giving a preset.

FIG. 14 is a flowchart illustrating a processing procedure of fuel injection amount control during a transition.

FIG. 15 is a graph showing a relationship between a target air-fuel ratio in a steady state, a target air-fuel ratio in a transient state, and a limit air-fuel ratio in a transient state.

FIG. 16 is a flowchart illustrating a procedure for correcting a control gain of the exhaust gas recirculation control.

FIG. 17 is a diagram showing an example of a map in which a gain correction coefficient is set for an intake throttle amount and an engine speed.

FIG. 18 is a flowchart illustrating a processing procedure of intake throttle valve control.

FIG. 19 is a diagram showing an example of a map in which an intake throttle amount with respect to a fuel injection amount and an engine speed is set.

FIG. 20 is a time chart showing timings of multi-stage injection and batch injection of fuel;

FIG. 21 is a flowchart illustrating a first half of a processing procedure of fuel injection timing control performed by the control unit.

FIG. 22 is a flowchart showing a processing procedure in the latter half of fuel injection timing control in the case of multi-stage injection.

FIG. 23 is a flowchart showing a processing procedure in the case of batch injection in the latter half of fuel injection timing control.

FIG. 24 is a diagram illustrating an example of a map in which a late injection pulse width is set with respect to a total injection pulse width of fuel.

FIG. 25A is a diagram showing an example of a basic map in which basic injection timing is set with respect to an engine water temperature and an engine speed, and an example of an advanced angle map in which an advanced amount of injection timing is set with respect to a common rail pressure. (B) of FIG.

FIG. 26 is a diagram showing an example of an injection timing map in which injection timing is set with respect to engine water temperature and common rail pressure.

FIG. 27 is an explanatory diagram showing an area including an end timing of early injection.

FIG. 28 is an explanatory diagram showing a combustion pressure waveform when fuel is injected in multiple stages and a late injection is advanced, in comparison with that when batch injection is performed.

FIG. 29 is a graph showing the relationship between the NOx concentration and the smoke concentration in the exhaust gas when the EGR rate is changed within a predetermined range for each of multi-stage injection and batch injection of fuel.

FIG. 30 is a flowchart showing a procedure for switching to multi-stage fuel injection based on the air-fuel ratio of the combustion chamber in a modification of the first embodiment.

FIG. 31 is a diagram showing an example of a region determination map in which an operation region in which switching to multi-stage fuel injection is performed is set in a modification of the first embodiment.

FIG. 32 is a flowchart illustrating a procedure for setting an injection timing when the early injection is further divided into two injections in the second embodiment.

[Explanation of symbols]

 A Diesel engine control device 1 Diesel engine 2 Cylinder 4 Combustion chamber 5 Injector (fuel injection valve) 6 Accumulation chamber 10 Intake passage (intake system) 11 Air flow sensor (intake amount sensor) 14 Intake throttle valve 23 EGR passage (exhaust recirculation passage) 24) EGR valve (exhaust gas recirculation amount control valve) 35a acceleration determination means 35b injection timing control means 35c injection quantity control means 35d exhaust recirculation control means 35e intake throttle valve control means 35f closing operation detection means 37 target fuel injection amount map 38 target empty Fuel ratio map A / F Air-fuel ratio (reflux amount) A / F * Boundary value of air-fuel ratio (set value) TA / F, KTA / F Target value of air-fuel ratio

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 43/00 301 F02D 43/00 301H 301J 301N F02M 25/07 550 F02M 25/07 550A 550J 570 570B 570F ( 72) Inventor Hideo Hosoya 3-1, Fuchi-machi, Shinchu, Aki-gun, Hiroshima Prefecture Inside Mazda Corporation (72) Inventor Keiji Araki 3-1, Shinchi, Funaka-cho, Aki County, Hiroshima Prefecture F-term (reference) 3G062 AA01 AA05 BA04 BA05 BA06 CA04 CA07 EA05 FA08 GA04 GA05 GA06 GA07 GA08 GA14 GA15 GA21 3G084 AA01 BA13 BA15 BA20 CA04 CA05 DA10 EB08 EB12 EC02 FA00 FA07 FA10 FA11 FA20 FA33 FA38 FA39 3G092 AA02 AA13 AA17 BB03 DC01 BA01 DC EA17 EB01 EB03 FA17 FA18 GA05 GA12 GA17 HA01X HA01Z HA05Z HA0 6X HA06Z HA16X HA16Z HB01X HB01Z HB02X HB02Z HB03X HB03Z HD07X HD07Z HE03Z HF09Z 3G301 HA02 HA11 HA13 JA24 JA25 JA37 KA07 KA08 KA09 KA12 NE11 NA15 NA03 MA01 NA05 MA03 NE23 PA04Z PA07Z PA17Z PB03Z PB08Z PD01A PD01Z PD15A PD15Z PE01Z PE02Z PE03Z PE04Z PE06A PE06Z PE07Z PE08Z PF01Z PF03Z PF04Z

Claims (13)

[Claims] 1. A diesel engine control device, comprising: a fuel injection valve for injecting fuel into a combustion chamber in a cylinder of an engine, wherein at least a fuel injection amount of the fuel injection valve is controlled. Acceleration determination means for determining that the engine has shifted; and when the acceleration determination means determines that the engine has shifted to an accelerated operation state, the fuel injection by the fuel injection valve is performed before 30 ° CA before the compression top dead center of the cylinder. Injection timing control means for performing the injection in multiple stages including an early injection performed in the compression stroke and a late injection performed in the vicinity of the compression top dead center, wherein the early injection is performed by one combustion cycle for each cylinder. In the latter-stage injection, the remaining fuel is injected at a timing earlier than the fuel injection near the compression top dead center immediately before the acceleration determination. Control apparatus for a diesel engine, characterized in that the morphism. A fuel injection valve for injecting fuel into an in-cylinder combustion chamber of the engine; an injection amount control means for controlling a fuel injection amount by the fuel injection valve according to an accelerator operation amount; An exhaust gas recirculation passage for recirculating a part of the exhaust gas, an exhaust gas recirculation amount adjusting valve for adjusting the amount of exhaust gas recirculated in the exhaust gas recirculation passage, and an opening degree of the exhaust gas recirculation amount adjusting valve. An exhaust recirculation control unit that performs feedback control so as to achieve a target value set in accordance with an operation state of the engine. The exhaust gas recirculation control means is operated to close the exhaust gas recirculation amount control valve when the acceleration judgment means judges that the engine has shifted to an acceleration operation state. When the exhaust gas recirculation control is performed by the exhaust gas recirculation control means, and when the transition to the acceleration operation state of the engine is determined by the acceleration determination means, the fuel injection by the fuel injection valve is performed. Injection timing control means is provided for performing the injection in multiple stages including the first injection ending in the compression stroke of the cylinder and the last injection ending earlier than the fuel injection near the compression top dead center immediately before the acceleration determination. A control device for a diesel engine, comprising: 3. The diesel engine according to claim 1, wherein the injection timing control means executes multi-stage fuel injection when the engine is in a low-speed operation range. Control device. 4. The fuel injection control device according to claim 2, wherein the injection timing control means sets at least one third of the fuel injection amount in one combustion cycle for each cylinder to 30 ° C. before compression top dead center.
A control device for a diesel engine, which performs injection in a compression stroke before A. 5. An intake air amount sensor for measuring an intake air amount in an intake passage of an engine according to claim 2, wherein the exhaust gas recirculation control means measures an opening degree of an exhaust gas recirculation amount adjusting valve by the intake air amount sensor. A control apparatus for a diesel engine, wherein feedback control is performed so that an air-fuel ratio of a combustion chamber, which is obtained based on an intake air amount and a fuel injection amount, is a target value. 6. The exhaust gas recirculation control unit according to claim 5, wherein the exhaust gas recirculation control unit has a target air-fuel ratio map in which a target value of an air-fuel ratio corresponding to an operation state of the engine is set. A control device for a diesel engine, comprising a target fuel injection amount map in which a target value of a fuel injection amount corresponding to (i) is set. 7. The apparatus according to claim 2, further comprising a closing operation detecting means for detecting that the exhaust gas recirculation amount control valve has actually been operated to the closing side, and wherein the injection timing control means detects the exhaust gas recirculating amount by the closing operation detecting means. A control apparatus for a diesel engine, wherein a multi-stage fuel injection is started when a closing operation of a control valve is detected. 8. An intake air amount sensor for measuring an intake air amount in an intake passage of an engine according to claim 2, wherein the injection timing control means includes an intake air amount and a fuel injection amount measured by the intake amount sensor. A multi-stage fuel injection control device is configured to start multi-stage fuel injection when the air-fuel ratio of the combustion chamber calculated based on the fuel injection ratio becomes equal to or more than a set value. 9. The fuel injection control device according to claim 7, wherein the injection timing control means sets the last fuel injection timing to a value immediately before the acceleration determination after a predetermined period has elapsed since the engine transitioned to the acceleration operation state. A control device for a diesel engine, which is configured to return to an injection timing. 10. The exhaust gas recirculation passage according to claim 2, wherein the exhaust gas recirculation passage is connected to an intake passage of the engine, and an intake throttle valve is arranged in the intake passage upstream of the connection with the exhaust gas recirculation passage. In a low-speed, low-load operation region of the engine, there is provided intake throttle valve control means for controlling the intake throttle valve to be more closed than the other operation regions. Control device. 11. The diesel engine according to claim 1, further comprising a common rail fuel injection system in which a fuel injection valve is connected to a pressure accumulating chamber for storing fuel in a high pressure state higher than an injection pressure. Engine control device. 12. The injection timing control means according to claim 1, wherein when the engine is in a steady operation state, the fuel injection by the fuel injection valve is collectively executed near the compression top dead center. A control device for a diesel engine, comprising: 13. The injection timing control means according to claim 1, wherein when the engine is in a low-speed low-load operation region in a steady operation state, the fuel injection by the fuel injection valve is performed near a compression top dead center. A control device for a diesel engine, characterized in that it is configured to execute the main injection and the pilot injection immediately before the main injection separately.