JP2002180881A - Combustion controller for diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformize an air-fuel pre-mixture in the application of the compression ignition combusting configuration of a high degree of premix. SOLUTION: In this combustion controller for a diesel engine comprising a fuel injection valve 5 for injecting the fuel into a cylinder 2, and an injection controlling means 39 for allowing the injection of the fuel injection valve 5 in an early period to increase a degree of the premix in an operating condition of a predetermined engine, the fuel for early injection is intermittently injected at predetermined injection stop intervals while divided into several times to properly atomize the fuel and to mix the same with the air.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a combustion control device for a diesel engine.

[0002]

2. Description of the Related Art In general, the combustion modes of engines are roughly classified into premixed combustion and diffusion combustion. Conventionally, spark-ignited engines mainly use the former premixed combustion, and diesel engines use the latter diffusion combustion. Has become the Lord. On the other hand, in recent years, black smoke and NO
In order to simultaneously reduce x (nitrogen oxides), research on a premixed compression ignition combustion system is in progress.

[0003] For example, Japanese Patent Application Laid-Open No. 9-158810 discloses that a total fuel supply amount of 50% in a cylinder at an early stage of an intake stroke.
%, And the main injection of the remaining fuel near the top dead center of the compression stroke. That is, since the lean mixture formed in the cylinder by the preliminary injection contains excess oxygen, the generation of black smoke is reduced, and the combustion gas generated by igniting a part of the mixture becomes internal EGR.
It is stated that the generation of NOx by the main injection is reduced in order to provide the effect. Further, it is described that by controlling the injection amount, the injection timing, or the number of injections of the preliminary injection or the main injection of the fuel, it becomes possible to perform control according to the operating state of the engine.

[0004] Japanese Patent Application Laid-Open No. Hei 10-141124 discloses that a pre-injection of 5% or less of the total supply amount of fuel into a cylinder at an early stage of an intake stroke and a 2 to 15% amount of fuel in a middle or late stage of a compression stroke. After pilot injection of, by performing the main injection of the remaining fuel near the top dead center of the compression stroke, while performing the partial lean premix compression ignition combustion, while suppressing the generation of NOx,
It is described that the emission of black smoke is reduced. If only the homogeneous charge compression ignition combustion system is used, the engine can be operated only in a limited load / rotation range, but by controlling the fuel pre-injection amount and pilot injection amount, the engine can be operated in the full load range. It is stated that can be driven.

In Japanese Patent Application Laid-Open No. 11-93672, a central concave combustion chamber is formed at the center of the top of the piston, and an annular outer concave combustion chamber is formed around the central combustion chamber. By performing the next injection and performing the second injection before the top dead center, a lean premix is formed by the first injection, and a rich mixture is formed in the premix by the second injection. A premixed compression ignition combustion is described.

[0006]

However, although the above-described premixed compression ignition combustion system is effective for simultaneously reducing black smoke and NOx, if the premixed gas has low uniformity, the in-cylinder temperature becomes uneven. As a result, the effect of reducing black smoke cannot be sufficiently obtained, and HC (hydrocarbon) is easily generated due to the formation of an air-fuel mixture that is too thin. Further, there is also a problem that fuel injected early to form a premixed gas adheres to the cylinder wall surface, and the amount of HC emission increases. An object of the present invention is to solve such a problem.

[0007]

SUMMARY OF THE INVENTION Accordingly, the present invention is to improve the uniformity of a premixed gas mixture by employing a multi-stage injection system for fuel injection for forming a premixed gas mixture. is there. Also. According to the present invention, the injection cone angle of the fuel injection valve is adjusted to reduce the adhesion of the early injection fuel to the cylinder wall.

According to a first aspect of the present invention, there is provided a fuel injection valve for injecting fuel into a cylinder, and an intake stroke for increasing a degree of premixing of fuel and air before compression ignition in a predetermined engine operating state. A combustion control device for a diesel engine, comprising: injection control means for causing the fuel injection valve to perform early injection so that at least a part of the fuel is supplied into the cylinder at a predetermined timing from the beginning to near the top dead center of the compression stroke. , Wherein the injection control means operates the fuel injection valve such that the fuel to be early injected is divided into a plurality of injections.

When the early injected fuel is divided into a plurality of injections as described above, the amount of fuel injected in each injection is reduced, which is advantageous for atomization and mixing with air to form a highly uniform lean premixed fuel. can do. As a result, the amount of black smoke generated and the amount of HC generated can be reduced. It is advantageous for the formation of a lean premixed gas that the early injection is performed before 60 ° CA before the top dead center of the compression stroke.

According to a second aspect of the present invention, in the combustion control device for a diesel engine according to the first aspect, the mechanical compression ratio of the engine is 18 or less.

Accordingly, the degree of increase in the temperature in the cylinder during the compression stroke is reduced, which is advantageous in avoiding the early ignition of the lean premixture. In order to reduce the compression ratio, a relatively deep recess (combustion chamber having a large volume) may be formed on the top surface of the piston. The preferred mechanical compression ratio is 10-18, and the more preferred mechanical compression ratio is 12-16.

According to a third aspect of the present invention, in the combustion control apparatus for a diesel engine according to the first or second aspect, the injection cone angle of the fuel injection valve is set to 120 degrees or less. I do.

When the early injection is performed to form a premixed gas, if the cone angle (about 150 degrees) generally used in the conventional diesel engine, the injected fuel is directly blown onto the cylinder wall. And it is easy to adhere there. On the other hand, as in the present invention, the cone angle is set to 12
When the angle is set to 0 degrees or less, the amount of the early-injection fuel adhering to the cylinder wall surface is reduced, which is advantageous in reducing the amount of HC generated.

According to a fourth aspect of the present invention, in the combustion control apparatus for a diesel engine according to the third aspect, the injection cone angle of the fuel injection valve is set such that the total amount of the early-injected fuel is within the recess at the top surface of the piston. Is set to be supplied.

If the entire amount of the early-injected fuel is supplied to the concave portion (combustion chamber) on the top surface of the piston as described above, mixing with air proceeds in the concave portion, so that the fuel does not adhere to the cylinder wall surface. It is easy to vaporize, which is advantageous for reducing the amount of HC generated.

According to a fifth aspect of the present invention, in the combustion control apparatus for a diesel engine according to the first aspect, the injection control means controls the fuel injection so that the number of times of the early injection increases as the engine temperature decreases. Activating the valve.

Therefore, atomization of fuel and mixing with air when the engine temperature is low are promoted, which is advantageous in improving compression ignition performance at a low engine temperature.

According to a sixth aspect of the present invention, in the combustion control apparatus for a diesel engine according to the first aspect, the injection control means controls the fuel injection valve so that the number of divisions increases as the amount of early injected fuel increases. It is characterized by operating.

Even if the amount of early injection fuel increases, the number of divisions increases, so that the fuel injection amount for each injection does not increase, which is advantageous for atomization of fuel and mixing with air.

[0020]

According to the first aspect of the present invention, when early fuel injection is performed to increase the degree of premixing of fuel and air before compression ignition, the fuel is divided into a plurality of times. Since the fuel is injected, it is advantageous for atomization of fuel and mixing with air, and a highly uniform lean premixed gas can be formed, so that the amount of black smoke generated and the amount of HC generated can be reduced.

According to the second aspect of the present invention, since the mechanical compression ratio of the engine is set to 18 or less, the degree of increase in the temperature in the cylinder during the compression stroke is reduced, and the early ignition of the lean premixture is prevented. A decrease in cycle efficiency and an increase in fuel consumption rate can be avoided.

According to the third aspect of the invention, since the injection cone angle of the fuel injection valve is set to 120 degrees or less, the amount of the early injection fuel adhering to the cylinder wall surface is reduced,
This is advantageous for reducing the amount of HC generated.

According to the fourth aspect of the invention, the injection cone angle of the fuel injection valve is set so that the entire amount of the fuel injected at an early stage is supplied into the recess at the top surface of the piston. Mixing with air proceeds in the concave portion (combustion chamber) on the top surface of the piston, and the fuel is easily vaporized without adhering to the cylinder wall surface, which is advantageous for reducing the amount of generated HC.

According to the fifth aspect of the invention, since the number of times of the early injection is increased as the engine temperature decreases, atomization of fuel and mixing with air are promoted, and compression at the time of low engine temperature is performed. This is advantageous in improving ignitability.

According to the sixth aspect of the present invention, the number of divisions is increased as the amount of the early injected fuel is increased. Therefore, even if the amount of the early injected fuel is increased, the atomization and the mixing with air are improved. Therefore, a lean premix having high uniformity can be formed, and the amount of black smoke generated and the amount of HC generated can be reduced.

[0026]

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

FIG. 1 shows the overall configuration of a diesel engine fuel control apparatus according to an embodiment of the present invention, and 1 is an engine body of a multi-cylinder diesel engine mounted on a vehicle. The engine body 1 has a plurality of cylinders 2 (only one is shown), and a piston 3 is inserted into each cylinder 2 so as to be able to reciprocate. An injector (fuel injection valve) 5 is disposed at the approximate center of the top of the cylinder 2 with the injection hole at the tip end facing the cylinder 2. The injection hole is opened and closed at a predetermined injection timing for each cylinder. Then, the fuel is directly injected into the cylinder 2.

Each injector 5 is connected to a common common rail (accumulator) 6 for storing high-pressure fuel.
A high-pressure supply pump 8 driven by a crankshaft 7 is connected to the common rail 6. 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. A crank angle sensor 9 for detecting a rotation angle of the crank shaft 7 is provided.
Is composed of a plate to be detected (not shown) provided at the end of the crankshaft 7 and an electromagnetic pickup arranged to face the outer periphery of the plate, and the electromagnetic pickup is provided around the entire periphery of the plate to be detected. A pulse signal is output in response to the passage of the projections formed at predetermined angles.

Reference numeral 10 denotes an intake passage for supplying intake air (air) filtered by an air cleaner (not shown) into the cylinder 2 of the engine body 1. At a downstream end of the intake passage 10, a surge tank (not shown) is provided. Each passage branched from the surge tank is connected to each cylinder 2 by an intake port. Also, the intake port is designed to generate a relatively strong swirl. For example, a helical port is provided, or an intake port is provided eccentrically to the cylinder so that intake air flows along the cylinder wall surface (tangential port), or a shroud valve is provided. The surge tank is provided with an intake pressure sensor 10a for detecting a supercharging pressure supplied to each cylinder 2.

In the intake passage 10, a hot film type air flow sensor 11 for detecting a flow rate of intake air sucked into the engine body 1 and a compressor 21 driven by a turbine 21 to compress the intake air in order from the upstream side to the downstream side. A blower 12, an intercooler 13 for cooling intake air compressed by the blower 12, and an intake throttle valve (intake air amount adjusting means) 14 for reducing the cross-sectional area of the intake passage 10. The intake throttle valve 14 is a butterfly valve provided with a notch so that intake air can flow even in a fully closed state. Like the EGR valve 24 described later, the magnitude of the negative pressure acting on the diaphragm 15 is negative pressure. The opening degree of the valve is controlled by being adjusted by the control electromagnetic valve 16. Further, the intake throttle valve 14 is provided with a sensor (not shown) for detecting its opening.

An exhaust passage 20 for exhausting exhaust gas from each cylinder 2 is connected to each cylinder 2 via an exhaust manifold. In the exhaust passage 20, a turbine 21 rotated by the exhaust flow is arranged in order from the upstream side to the downstream side.
And a catalyst 22 capable of purifying HC, CO and NOx in the exhaust gas.

An exhaust gas recirculation passage (hereinafter referred to as an EGR passage) 23 for recirculating a part of the exhaust gas to the intake side branches from a portion of the exhaust passage 20 upstream of the turbine 21, and a portion downstream of the EGR passage 23. The end is connected to the intake passage 10 downstream of the intake throttle valve 14. In the middle of the EGR passage 23, a cooler 23a for cooling the recirculated exhaust gas
Is provided. An exhaust gas recirculation amount adjusting valve (intake air amount adjusting means: hereinafter referred to as an EGR valve) 24 whose opening degree can be adjusted is disposed closer to the downstream end of the EGR passage 23 than the cooler 23a. Partly EGR
The gas is returned to the intake passage 10 while the flow rate is adjusted by the valve 24.

The EGR valve 24 is of a negative pressure responsive type, and a negative pressure passage 27 is connected to a negative pressure chamber 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. The negative pressure passage 27 is controlled by a control signal (current) from an ECU 35 described later. By opening and closing 27, 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.

The turbocharger 25 is a VGT (Variable Geometry Turbo), which has a diaphragm 30 attached thereto and a solenoid valve 3 for negative pressure control.
By adjusting the negative pressure acting on the diaphragm 30 by 1, the cross-sectional area of the exhaust gas passage is adjusted.

As shown in FIG. 2, a combustion chamber 4 is formed in the piston 3 of the diesel engine, with the center of the top surface being deeply recessed, whereby the mechanical compression ratio of the engine is reduced to 18 or less. It has been done. In addition, the injection cone angle α of the injector 5 is set to be equal to or less than 120 degrees, and particularly in the present embodiment, the injection cone angle α is set so that the entire amount of the early-injected fuel is supplied into the combustion chamber 4 on the piston top surface. It is set to 90 degrees or less.

Further, the diesel engine is provided with valve adjusting means (variable valve timing means (VVT) or variable valve lift means (VVL)) 36 for changing the opening / closing timing or opening amount of the intake valve. That is,
As shown in FIG. 2, the intake valve 33 for opening and closing the intake port of the engine combustion chamber 4 is provided with an opening / closing timing or opening amount of the valve so that the actual compression ratio of the engine changes according to the operating state of the engine. A solenoid-type valve adjusting means 36 for changing is provided. The exhaust valve 34 that opens and closes the exhaust port of the combustion chamber 4 is provided with a valve mechanism (not shown) that opens and closes the valve at a fixed timing.

Here, the actual compression ratio is the amount of intake air actually compressed in the compression stroke (volume in a standard state) and the top dead center of the compression stroke with respect to the cylinder volume at the compression stroke top dead center. Means the ratio of the sum to the cylinder volume.

Each of the injectors 5, high-pressure supply pump 8, intake throttle valve 14, EGR valve 24, turbocharger 2
5. The valve adjusting means 36 and the like are provided with a control unit (En
A gine control unit (hereinafter referred to as an ECU) 35 is configured to operate according to a control signal from the ECU 35. on the other hand,
The ECU 35 includes an output signal from the crank angle sensor 9 for detecting an engine operating state, an output signal from the air flow sensor 11, and an operation amount (accelerator opening) of an accelerator pedal (not shown) by a driver of the vehicle. An output signal from the accelerator opening sensor 32 to be detected and an output signal from the sensor 18 to detect the engine water temperature are input, and further, an output signal from the pressure sensor 6a, an output signal from the pressure sensor 10a, and an EGR signal. An output signal from the lift sensor 26 of the valve 24 and the like are also input.

The fuel injection amount (fuel supply amount) and the fuel injection timing by the injector 5 are controlled by the fuel injection control means 39 in accordance with the operating state of the engine, and the compression ratio control means 38 controls the valve adjustment means 36. The actual compression ratio of the engine is controlled in accordance with the operation state of the engine, and the common rail pressure, that is, the fuel injection pressure is controlled by the operation of the high-pressure supply pump 8. In addition, the exhaust gas is controlled by the operation of the EGR valve 24. Control of the recirculation amount (intake air amount) and operation control (VGT control) of the turbocharger 25 are performed.

(Fuel Injection Control) The feature of the fuel injection control in this embodiment is that a combustion mode and a combustion mode in which fuel is burned in a state in which the degree of premixing with fuel is high according to the operating state of the engine. The operation of the injector 5 is controlled so as to switch to a combustion mode in which combustion is performed with a low degree of mixing, and multi-stage injection is adopted for early injection for forming a lean premixture.

That is, in the ECU 35, a target torque map in which the optimum value of the target torque is experimentally determined and recorded with respect to the change in the accelerator opening (engine load) and the engine speed, and the target torque, A fuel injection amount map in which an optimum fuel injection amount Qb experimentally determined according to changes in the air amount and the rotation speed is recorded and stored electronically in a memory. Normally, a target torque is determined based on the accelerator opening and the engine speed, and a fuel injection amount Qb is determined based on the target torque, the engine speed, and the intake air amount based on the output signal of the air flow sensor 11, and the fuel injection amount is determined. The excitation time (valve opening time) of each injector 5 is determined based on the amount Q and the common rail pressure detected by the pressure sensor 6a. still,
The fuel injection amount obtained as described above may be corrected according to the engine water temperature, the atmospheric pressure, and the like, and the corrected fuel injection amount may be used as the fuel injection amount Qb.

By the basic fuel injection control as described above, an amount of fuel corresponding to the target torque of the engine 1 (required output to the engine 1) is supplied, and the engine 1 has an average air-fuel ratio in the combustion chamber 4 of the engine 1. Pretty lean (A / F ≧
(18, oxygen concentration of 4% or more). The accelerator opening sensor 32 and the crank angle sensor 9 constitute a required output detecting means for detecting a required output to the engine 1.

In the memory of the ECU 35, the combustion mode of the engine (in other words, the fuel injection mode) is set in accordance with the target torque (or accelerator opening) and the engine speed in the same manner as in the fuel injection amount map. A map is stored electronically, and a combustion mode according to the operating state of the engine is selected from the map based on the target torque of the engine 1 and the engine speed.

That is, FIG. 3 (a) shows an injection mode when a fuel mode is adopted in which the fuel is burned in a state where the degree of premixing is high, and an intake stroke injection for injecting fuel at an early stage of the intake stroke; 60 ゜ CA before the top dead center in the latter half of the compression stroke
By the time, the compression stroke injection for injecting the fuel up to this point and the top injection for injecting the fuel near the top dead center of the compression stroke are performed. In this case, the intake stroke injection and the compression stroke injection are early injections for forming a lean premixture, and each employs multi-stage injection. That is, in this example, the intake stroke injection is a three-split injection, and the compression stroke injection is a two-split injection.

The combustion mode in which the degree of premixing is high is set when the engine temperature is equal to or lower than a predetermined value, the engine speed is equal to or lower than a predetermined value, or the target torque (engine load) is equal to or lower than a predetermined value. Specifically, as shown in FIG.
The operating range in which the degree of premixing is to take the combustion mode is determined by the relationship between the engine speed and the target torque,
The lower the engine temperature, the more the operating region, that is,
The premix zone is expanded to the side where the engine speed is high and to the side where the target torque is high.

As the early injection, either the intake stroke injection or the compression stroke injection may be employed. Further, the early injection amount can be, for example, about 50% of the total injection amount Qb, or it can be several percent or 100% (that is, zero top injection amount).

FIG. 3 (b) shows an injection mode in a combustion mode in which the degree of premixing performed in a region other than the premix zone is low, in which early injection is not performed and compression stroke top dead center is not performed. In the vicinity, a top injection for injecting the entire amount of fuel is performed.

FIG. 5 shows the flow of the fuel injection control. This control is executed for each cylinder in synchronization with the crank angle signal.

At step A1 after the start, necessary data such as a crank angle signal, an air flow sensor output, and an accelerator opening are read. In the following step A2,
A target torque is obtained based on the accelerator opening and the engine speed, and the fuel injection amount Qb is read from the fuel injection amount map based on the target torque, the engine speed and the intake air amount.

In the following step A3, a premix zone is set according to the engine temperature. The engine temperature is estimated based on the supercharging pressure detected by the intake pressure sensor 10a. That is, in this embodiment, the intake pressure sensor 10a
Constitute engine temperature detecting means. Of course, a temperature sensor for detecting the temperature of the intake air is provided in the intake passage to correct the estimated value of the engine temperature based on the supercharging pressure, and further, the intake air amount and the engine water temperature detected by the air flow sensor 11 are taken into consideration. Thus, the estimated value can be corrected.

In the following step A4, it is determined whether or not the operating state of the engine is in the premix zone set in step A3 based on the target torque and the engine speed. If it is the premix zone, the process proceeds to step A5 to divide the fuel injection amount Qb to set the early injection amount (the intake stroke injection amount QL1 and the compression stroke injection amount QL2) and the top injection amount QT, and Timing (intake stroke injection timing I
L1 and the compression stroke injection timing IL2) and the top injection timing IT are set.

Further, since the intake stroke injection and the compression stroke injection employ multi-stage injection, in the step A5, regarding the intake stroke injection, the injection amount QL1 is equally divided by the number of divisions n, and each stage is divided into In addition to setting the injection amount QL1 / n, the injection pause interval Δt1 is set. Also, regarding the compression stroke injection, the injection amount QL2 is equally divided by the division number m to set the injection amount QL2 / m of each stage, and the injection pause interval Δt2
Set. At this time, each of the intake stroke injection and the compression stroke injection is performed by dividing the number of injections n,
m is increased, and the injection pause intervals Δt1, Δt2 are lengthened. In addition, as the number of injections increases, the number of divisions n and m of the injection amount increases, but the injection pause interval is not changed. Of course, as the injection amounts QL1 and QL2 increase, the number of divisions n and m may be increased and the injection pause intervals Δt1 and Δt2 may be increased.

In the following step A6, a multi-stage intake stroke injection at the injection suspension interval Δt1 starting from the timing IL1, the timing I
The multi-stage compression stroke injection at the injection suspension interval Δt2 starting from L2 and the top injection of the injection amount QT at the timing IT are executed.

If the operating state of the engine is not in the premix zone, the process proceeds to step A7 where only top injection is to be performed, the top injection amount QT and the injection timing IT are set, and the process proceeds to step A6 to execute top injection. In this case, Q
T = Qb.

It should be noted that multi-stage injection may be adopted for the top injection in the premixing zone and other zones. In this case, the injection suspension interval is preferably set to, for example, 50 to 1000 μsec.

Therefore, since the multistage injection is adopted for the early injection, the amount of fuel injected each time is reduced, the fuel is easily atomized, and the fuel is easily mixed with the air, and the lean air-fuel mixture is used. Uniformity, suppression of black smoke and NOx generation,
In addition, it is advantageous for suppressing generation of HC. In addition, the intake stroke injection works effectively for vaporizing and atomizing the fuel. Further, since a relatively strong swirl is generated in the cylinder by the swirl generating means of the intake port, the mixing becomes more uniform.

Further, since the early injection is performed in two stages, the intake stroke injection and the compression stroke injection, the intake stroke injection amount is reduced, and the fuel injected in this intake stroke is uniformly dispersed in the cylinder. Can be done. Also, if a large amount of fuel is injected during the intake stroke, a lean mixture having a relatively low air-fuel ratio is formed. Although there is a concern that the fuel injection amount may be small in the intake stroke, it is advantageous in preventing such early ignition and all-in-one combustion. In addition, the fuel injection in the latter half of the compression stroke prevents the cylinder temperature from excessively increasing, thereby preventing early ignition.

When the engine temperature is low, the number n, m of divisions of the early injection increases, and the injection pause interval Δt1,
Since Δt2 becomes longer, atomization of fuel and mixing with air are promoted, and compression ignition performance at low engine temperatures is improved. Also, as the injection amount QL1, QL2 increases, the number of divisions n,
Since m is increased, the atomization of the fuel and the mixing property with the air can be improved, a highly uniform lean premixed gas can be formed, and the amount of black smoke generated and the amount of HC generated can be reduced.

In addition, since the injection cone angle α is set to 90 degrees or less, the entire amount of the fuel injected during the intake stroke and the fuel injected during the compression stroke is supplied to the combustion chamber 4 on the top surface of the piston. Because mixing with air advances in 4,
The fuel is easily vaporized without adhering to the cylinder wall surface, which is advantageous for reducing the amount of HC generated.

(Compression ratio change control) The actual compression ratio of the engine is changed by the compression ratio control means 38 based on the engine temperature and the operating zone of the engine.
It is performed by using. That is, the memory of the ECU 35 stores the opening / closing timing of the intake valve 33,
The optimal timing according to whether or not the premix zone and the engine operating state is set and stored in advance,
Based on this, the opening / closing timing of the intake valve 33 is controlled.

FIG. 6A shows the opening and closing timings of the intake valve 33 and the exhaust valve 34 when the operating state of the engine is in the non-premix zone (during low premix combustion mainly based on diffusion combustion). The opening timing of the intake valve 33 is set to a point when the intake valve 33 is advanced slightly from the top dead center in consideration of an invalid angle at which air is not substantially sucked, and the valve closing timing is determined by the dynamic effect of the intake passage. In order to increase the charging efficiency, the timing is slightly retarded from the bottom dead center of the intake stroke. The retard angle is increased as the engine speed increases.

FIG. 6B shows the opening / closing timing of the intake valve 33 and the exhaust valve 34 when the engine is operating in the premix zone (high premix combustion). As indicated by the solid line, the valve opening timing of the intake valve 33 is advanced from the bottom dead center of the intake stroke (early closing). As a result, the amount of air taken into the cylinder decreases, and the actual compression ratio of the engine decreases. Therefore, an increase in the temperature in the cylinder during the compression stroke is suppressed as compared with the time of the low premix combustion, so that early ignition is prevented, and the generation amount of black smoke and NOx can be reduced.

The closing timing of the intake valve 33 is determined by the timing shown in FIG.
As shown by the dashed line in (b), as the engine speed increases, the angle is retarded. As a result, the degree of utilization of the dynamic effect of the intake passage increases, and the efficiency of charging the cylinder with air increases.
This is advantageous for improving the engine output. In addition, intake valve 3
The valve lift amount (valve opening amount) of No. 3 decreases as the engine load increases, as indicated by the two-dot chain line in FIG. 6B. Therefore, even if the fuel injection amount increases, the actual compression ratio greatly decreases, which is advantageous in preventing early ignition.

In the case where the timing of the early injection for the high premixed combustion mode is the compression stroke, the valve closing timing is changed from the low premixed combustion as shown by the broken line instead of the above-mentioned early closing. May be retarded (slowly closed). In the case of the intake stroke injection, there is a concern that the lean air-fuel mixture is blown back to the intake passage 10 due to the late closing, but in the case of the compression stroke injection, there is no such concern. However, it is necessary to inject fuel after the intake valve 33 is closed.

Further, the intake valve 3 during the high premixed combustion described above.
The opening timing of No. 3 is advanced slightly more than in the case of low premix combustion. As a result, the exhaust gas from the previous combustion remains in the cylinder (internal EGR) and the oxygen concentration in the cylinder decreases, which is advantageous for preventing early ignition and also for reducing NOx.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a diesel engine combustion control device according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a fuel injection control system of the engine.

FIG. 3 is an explanatory diagram of a fuel injection mode of the embodiment.

FIG. 4 is an explanatory diagram of a premixing zone of the embodiment.

FIG. 5 is a flowchart of fuel injection control according to the embodiment;

FIG. 6 is an explanatory diagram of valve timing according to the embodiment.

[Explanation of symbols]

 Reference Signs List 1 diesel engine 2 cylinder 4 combustion chamber 5 injector (fuel injection valve) 10 intake passage (intake system) 11 air flow sensor (intake air amount detecting means) 20 exhaust passage (exhaust system) 23 EGR passage (exhaust recirculation passage) 24 EGR valve (Exhaust gas recirculation amount adjusting means) 33 Intake valve 35 ECU (control unit) 39 Fuel injection control means

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) F02M 61/18 360 F02M 61/18 360J (72) Inventor Naoyuki Yamagata 3-1, Fuchu-cho, Shinchu, Aki-gun, Hiroshima Mazda Stock In-house (72) Inventor Kazushi Kataoka 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima F-term in Mazda Co., Ltd. (reference) 3G066 AA07 AB02 AC09 BA02 BA24 BA26 DA04 DA09 DC01 DC04 DC09 DC18 3G084 AA01 AA04 BA07 BA13 BA15 BA20 BA23 DA02 DA10 EA11 FA08 FA12 FA20 FA29 FA33 FA37 FA38 3G301 HA02 HA11 HA13 HA15 HA17 HA19 JA02 JA24 JA26 MA19 MA26 MA27 MA29 NA08 NC02 NE12 NE15 PA04Z PA07Z PA16Z PA17Z PD03A PD15Z PE01Z PE03Z PE06A PE08Z

Claims (6)

[Claims] A fuel injection valve for injecting fuel into a cylinder;
In a predetermined operating state of the engine, at least a part of the fuel is supplied into the cylinder at a predetermined time from the beginning of the intake stroke to near the top dead center of the compression stroke in order to increase the degree of premixing of the fuel and the air before the compression ignition. A combustion control device for a diesel engine, comprising: an injection control means for causing the fuel injection valve to perform an early injection so that the fuel to be injected early is divided into a plurality of injections. A combustion control device for a diesel engine, wherein the fuel injection valve is operated as described above. 2. The combustion control device for a diesel engine according to claim 1, wherein the mechanical compression ratio of the engine is 18 or less. 3. The combustion control apparatus for a diesel engine according to claim 1, wherein an injection cone angle of the fuel injection valve is set to 120 degrees or less. apparatus. 4. The combustion control device for a diesel engine according to claim 3, wherein the injection cone angle of the fuel injection valve is set such that the entire amount of the early-injected fuel is supplied into the recess on the top surface of the piston. A combustion control device for a diesel engine, which is set. 5. The combustion control device for a diesel engine according to claim 1, wherein the injection control means operates the fuel injection valve such that the lower the engine temperature is, the more the number of divisions of the early injection is increased. Characteristic combustion control device for diesel engine. 6. The combustion control device for a diesel engine according to claim 1, wherein the injection control means operates the fuel injection valve such that the number of divisions increases as the amount of early injected fuel increases. Diesel engine combustion control system.