JP2001152853A - Control device for pre-mixed combustion compression ignition engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent pre-ignition of a pre-mixed combustion compression ignition engine. SOLUTION: Fuel is injected in each cylinder of an engine 1 at an intake stroke or a compression stroke, to form pre-mixed fuel gas. The pre-mixed fuel gas is ignited and burned by compression. Excessive increase in burning velocity of the pre-mixed fuel gas causes pre-ignition, resulting in increasing vibrations and a NOX exhaust amount. An electronic control unit(ECU) 30 controls the opening degree of an EGR valve 23 of the engine, so that actual exhaust NOX concentration, detected by an NOX sensor 71 which is arranged in an exhaust passage 3, becomes a target NOX concentration, which is pre- mixed and proper, at a time of pre-mixed combustion. By adjusting an EGR amount according to the actual exhaust NOX concentration, the burning velocity of the pre-mixed fuel gas is controlled to be within a proper range, resulting in preventing the occurrence of pre-ignition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a control device for a homogeneous charge compression ignition internal combustion engine.

[0002]

2. Description of the Related Art In a compression ignition internal combustion engine such as a general diesel engine, combustion mainly comprising diffusion combustion is performed in a combustion chamber. That is, in a diesel engine that performs diffusion combustion, fuel is injected into a high-temperature cylinder whose piston is near compression top dead center. The injected fuel forms fine droplets and evaporates from the droplet surface in high-temperature air to form a combustible mixture around the droplets, and ignites when the ambient temperature exceeds the ignition temperature to form a flame I do. When ignition occurs in the mixture layer around the droplet, fuel evaporation from the droplet is promoted, and the flame around the droplet is maintained. As described above, in the diffusion combustion, the fuel is present on one side and the air is present on the other side with the flame surface interposed therebetween, and a flame is formed at the boundary between these.

However, in the diffusion combustion, the combustible mixture layer formed around the droplet has a continuous air-fuel ratio gradient in which the air-fuel ratio is lowest on the droplet side and becomes higher toward the outside, resulting in a mixed air-fuel ratio. Since combustion occurs at the air-fuel ratio where NO _X is easily generated at the time of combustion of air, the amount of NO _X generated by the combustion is relatively large. Further, since the diffusion combustion flame is generated around the fuel injected from the fuel injection valve, become locally larger flame front in the combustion chamber is formed, the generation of higher becomes more NO _X combustion temperature promote There is a problem that is done. Furthermore, in diffusion combustion, the liquid fuel and air are separated at the flame surface as a boundary, so the liquid fuel is heated in a state where oxygen is insufficient, and it becomes a kind of "steaming" state, and carbon particles are the main component Exhaust smoke is likely to occur.

[0004] In order to solve these diffusion combustion problems, a premixed compression ignition internal combustion engine has also been proposed which performs premixed combustion even in a compression ignition internal combustion engine. In a premixed compression ignition engine, fuel is injected into a cylinder during an intake process or a compression stroke, and mixes with air in the cylinder to form a uniform mixture. This homogeneous air-fuel mixture is compressed with the rise of the piston and the temperature rises, and the entire air-fuel mixture is ignited near the top dead center of the compression stroke, and the combustion proceeds. As described above, in premixed combustion, a flame is generated over the entire air-fuel mixture in the cylinder.However, when viewed microscopically, fine flame particles are dispersed throughout the cylinder, and air flows around the individual flame particles. It has an enclosed shape. Therefore, the flame temperature in the premix combustion is generated in the lower becomes NO _X compared to the diffusion combustion can be suppressed. Further, in premixed combustion, fuel is burned in the presence of a sufficient amount of oxygen in a state of being uniformly mixed with air, so that smoke is less likely to be generated due to lack of oxygen.

An example of such a homogeneous charge compression ignition internal combustion engine is disclosed in, for example, JP-A-10-331690. According to the publication, fine fuel is injected from a fuel injection valve during an intake stroke or a compression stroke of a diesel engine to form a premixed gas in a cylinder, and the premixed gas is ignited near a top dead center in a compression stroke. Like that.

[0006]

However, when premixed combustion is performed in a compression ignition engine, there is a problem that premature ignition or misfire may occur depending on the combustion speed of the air-fuel mixture in the cylinder. For example, in ideal premixed combustion, the in-cylinder mixture formed by the fuel injected in the intake or compression stroke ignites before the top dead center of the compression stroke, continues combustion relatively slowly, and increases the cylinder pressure. It is preferable to reach the maximum pressure immediately after the dead center. However, if the combustion rate of the air-fuel mixture in the cylinder is greater than the range suitable for premixed combustion, the air-fuel mixture ignited before top dead center will burn at once, and the cylinder pressure will rapidly increase before reaching top dead center. It will rise. As described above, if a sudden increase in pressure occurs before the top dead center is reached, so-called premature ignition occurs, as in the case of knocking of a gasoline engine, in which large vibration and noise are generated in the engine. On the other hand, if the combustion speed of the air-fuel mixture in the cylinder becomes lower than the appropriate range, premature ignition does not occur, but the temperature in the cylinder decreases due to the lowering of the piston before the combustion of the air-fuel mixture is completed after the top dead center. There is a problem in that the combustion state of the air-fuel mixture deteriorates, and eventually misfires occur.

In the engine disclosed in Japanese Patent Laid-Open Publication No. Hei 10-331690, fine fuel is injected during the intake stroke or the compression stroke in order to generate premixed combustion. However, the combustion speed of the air-fuel mixture is controlled. I can't. Generally, the combustion speed range in which premixed combustion is established in a compression ignition engine is a narrow range extremely close to the combustion speed at which premature ignition occurs. Further, the vibration and noise of the engine during premixed combustion do not gradually increase as the combustion speed increases, but when the combustion speed exceeds a certain level, premature ignition occurs suddenly and the vibration and noise increase rapidly. For this reason, even if the vibration and noise of the engine are monitored, it is not possible to predict the occurrence of premature ignition, and it is difficult to effectively prevent the occurrence of premature ignition. Therefore, in the same publication, although the above-described premixed combustion is performed at the time of engine low-load operation, premixed combustion is not performed in a medium-high load operation in which the temperature in the cylinder increases, the mixture combustion speed increases, and premature ignition easily occurs. The operation is switched to the same diffusion combustion as a normal diesel engine. Therefore, in the engine of the publication narrows the engine operating region for performing premixed combustion, there is a problem that it is impossible to sufficiently reduce the emissions of the NO _X and smoke in the engine.

In view of the above-mentioned problems of the prior art, the present invention solves the problem of the occurrence of premature ignition by controlling the air-fuel mixture combustion speed within an appropriate range, and performs premixed combustion over a wide operating range. , and its object is to provide a premixed combustion compression ignition internal combustion engine capable of suppressing the increase in the emissions generated and NO _X in the exhaust smoke.

[0009]

According to the first aspect of the present invention, fuel is injected from a fuel injection valve into a combustion chamber to form a premixed mixture of fuel and air in the combustion chamber. the a control apparatus for premixed compression ignition internal combustion engine for igniting the compressed, the premixed compression ignition internal combustion engine, NO _X generation amount by combustion if the combustion rate in the combustion chamber premixture is in the appropriate range There decreased, now the combustion vibration is increased knock with NO _X generation amount as the combustion speed becomes higher than the proper range the combustion chamber premixture is increased occurs, premixed gas combustion speed the proper now misfire occurs such a range as from smaller combustion state with NO _X is reduced further deteriorated, the control device, NO _X sensor for detecting the NO _X in the disposed in the exhaust passage of the engine exhaust When, A combustion control means for changing a burn rate in the combustion chamber premixture, storage means for storing the proper NO _X concentration is concentration of NO _X in the exhaust gas when the engine is operated in a suitable premixture combustion rate And controlling the combustion control means so that the NO _X concentration in the exhaust gas detected by the NO _X sensor matches the stored appropriate NO _X concentration, whereby the premixed gas combustion speed is adjusted to the appropriate level. And a control device for the homogeneous charge compression ignition internal combustion engine that controls the internal combustion engine to fall within the range.

That is, in the first aspect of the present invention, the N
The combustion rate of the air-fuel mixture is controlled by detecting the _OX concentration. With the mixture combustion speed increases concentration of NO _X in the exhaust gas for the flame temperature rises during combustion as it increases, the pre-ignition occurs result in rapid combustion of the mixture and the combustion rate beyond a certain increases I do. On the other hand, NO _X concentration in the exhaust gas for mixture combustion rate conversely decreases overall flame temperature during combustion to be reduced is reduced, so that misfire occurs due to deterioration of the combustion and the combustion rate decreases beyond a certain . Further, NO _X concentration in the exhaust gas is, for example, can be detected directly, such as by placing the NO _X sensor to the engine exhaust passage. Therefore, the present invention focuses on the correlation between the combustion speed and the NO _X in the exhaust gas, detects the NO _X concentration in the exhaust gas, and increases or decreases the combustion speed based on the NO _X concentration, thereby premature ignition. Premixed combustion is performed without causing fire or misfire. That is, the exhaust gas N when the proper premix combustion is performed in advance.
If O _X a range of concentrations measured in the experiments using the actual engine by storing in the storage means, burn rate when the concentration of NO _X in the exhaust gas than the proper NO _X concentration range was higher It can be seen that premature ignition is likely to occur. Therefore, combustion control means in this case performs an operation of lowering the combustion speed, NO _X concentration (i.e. combustion rate) is set to be in a proper range. Also,
Similarly, when the NO _X concentration in the exhaust gas becomes lower than the stored proper range, the combustion speed is reduced, and it is understood that the combustion is likely to deteriorate and misfire is likely to occur. In this case, the combustion control means performs an operation to increase the combustion speed, NO _X concentration is set to be in a proper range. As a result, the air-fuel mixture combustion speed is always controlled to a range in which an appropriate premixed combustion is generated, thereby preventing premature ignition and deterioration of combustion.

The combustion control means increases or decreases the combustion speed by changing conditions that affect the combustion speed of the air-fuel mixture. Conditions that affect the combustion speed include, for example, the amount of exhaust gas recirculated to the engine combustion chamber (EGR gas amount), the amount of intake air drawn into the cylinder (the amount of fresh air), the supercharging pressure of the engine, and the fuel injection. There are timing, number of times, injection amount, compression ratio and the like.

According to the invention described in claim 2, wherein the storage unit stores the proper NO _X concentration in accordance with the engine operating state, the control apparatus further operating condition for detecting the engine operating state comprising means, NO _X concentration in the detected exhaust gas by the NO _X sensor controls the combustion control means so that the proper NO _X density corresponding to the driving state detected in the operation state detection means, according to claim 1 A control device for a premixed compression ignition internal combustion engine according to the first aspect is provided.

That is, in the invention of claim 2, an appropriate NO _X concentration according to the engine operating state is stored in advance, and the combustion control means changes the NO _X concentration in the exhaust gas to the current engine operating state actually detected. The combustion control means is controlled so as to have a corresponding appropriate NO _X concentration. Proper exhaust concentration of NO _X when the premix combustion is being performed, for example, the engine speed varies accordingly if changes the operating state of the fuel injection amount and the like. In the present invention, the appropriate NO _X concentration corresponding to each operation state is stored in advance, and the combustion control means is controlled based on the appropriate NO _X concentration corresponding to the actual operation state during operation. Even when the operating state such as the load changes, proper premixed combustion is always performed.

According to the third aspect of the present invention, the combustion control means includes EGR means for recirculating a part of the engine exhaust gas to the engine combustion chamber, and controls the flow rate of the exhaust gas recirculated to the combustion chamber by the EGR means. A control device for a premixed compression ignition internal combustion engine according to claim 2, wherein the control device controls the premixed gas combustion speed.

That is, according to the third aspect of the invention, the combustion control means controls the air-fuel mixture combustion speed by controlling the flow rate of the exhaust gas (the amount of EGR gas) flowing back to the combustion chamber. The combustion speed of the air-fuel mixture in the cylinder decreases as the oxygen concentration in the cylinder decreases. On the other hand, since the EGR gas is exhaust gas after combustion in the combustion chamber, the oxygen concentration is low. Therefore, the more the EGR gas is supplied to the combustion chamber, the lower the combustion speed of the air-fuel mixture in the cylinder. Therefore, in the present invention, the combustion control means increases the EGR gas amount when the exhaust NO _X concentration increases from an appropriate range, and decreases the EGR gas amount when the exhaust NO _X concentration decreases. As a result, the combustion speed of the air-fuel mixture in the cylinder is always maintained in an appropriate range.

According to a fourth aspect of the present invention, the combustion control means includes intake throttle means for changing an engine intake air amount, and the premixed air is controlled by changing the engine intake air amount by the intake throttle means. 3. The combustion rate is controlled.
A control device for a premixed compression ignition internal combustion engine according to the first aspect is provided.

That is, in the invention of claim 4, the combustion control means controls the combustion speed of the premixed air in the combustion chamber by changing the amount of engine intake air (the amount of fresh air) using the intake throttle means. When the amount of fresh air taken into the engine changes, the amount of oxygen drawn into the cylinder changes. Therefore, the combustion speed is reduced by decreasing the engine intake air amount to decrease the oxygen concentration in the combustion chamber, and conversely, the combustion speed is increased by increasing the engine intake air amount and increasing the oxygen concentration in the combustion chamber. It is possible. Thus, by changing in accordance with the engine intake air quantity to the exhaust NO _X concentration, so burn rate in the combustion chamber mixture is always maintained in a proper range.

According to the fifth aspect of the present invention, the combustion control means includes a supercharging pressure control means for changing an engine intake pressure, and the precharge is performed by changing the engine intake pressure by the supercharging pressure control means. 3. The method according to claim 2, wherein the air-fuel mixture burning rate is controlled.
A control device for a premixed compression ignition internal combustion engine according to the first aspect is provided.

That is, in the invention of claim 5, the combustion control means controls the combustion speed of the premixed air in the combustion chamber by changing the engine intake pressure. For example, in an engine having a supercharger, the engine intake pressure can be adjusted by changing the supercharging pressure. When the engine intake pressure changes, the pressure in the combustion chamber during compression also changes accordingly. For example, the combustion speed of the premixture in the combustion chamber increases as the pressure during combustion increases. Therefore, it is possible to increase the combustion speed by increasing the engine intake pressure and decrease the combustion speed by decreasing the combustion speed. Thus, by changing in accordance with the engine intake pressure in the exhaust NO _X concentration, so burn rate in the combustion chamber mixture it is always maintained in a proper range.

According to the present invention, the combustion control means includes a fuel injection control means for controlling a fuel injection timing from the fuel injection valve, and the fuel injection control means controls the fuel injection in the combustion chamber. A control device for a premixed compression ignition internal combustion engine according to claim 2, wherein the premixed gas combustion speed is controlled by changing a timing.

That is, in the invention of claim 6, the premixed gas combustion speed is changed by changing the fuel injection timing. For example, if the fuel injection timing is advanced, the time from when the fuel is injected to when the temperature in the cylinder rises to the ignition temperature of the fuel in the compression stroke becomes longer, the injected fuel diffuses into the combustion chamber, and the fuel becomes uniform. A dispersed premix is formed. On the other hand, if the fuel injection timing is delayed, the time during which the injected fuel diffuses into the combustion chamber is shortened, and when the combustion chamber temperature rises to the ignition temperature, a portion containing locally high-concentration fuel in the premixture may be reduced. Will be present. When the premixed gas is ignited, a relatively large amount of fuel is burned in the high-concentration portion, so that the flame temperature increases, and the pressure increases near the high-concentration portion. This pressure rise propagates as a pressure wave to the rest of the combustion chamber and adiabatically compresses the surrounding premix. For this reason, when ignition occurs in the high concentration portion, the surrounding premixed gas also starts burning in a chain. That is, if the concentration of the air-fuel mixture formed in the combustion chamber is not uniform, the air-fuel mixture burning speed increases. Conversely, when the air-fuel mixture is formed uniformly and there is no locally high fuel concentration portion, the above-described chain combustion does not occur, and the combustion after fuel ignition becomes relatively slow. Therefore, as the fuel injection timing is advanced and the concentration of the air-fuel mixture formed in the combustion chamber is made uniform, the combustion speed of the air-fuel mixture decreases, and the fuel injection timing is delayed to make the air-fuel mixture concentration uneven. , The combustion speed increases. In the present invention, the combustion speed of the air-fuel mixture in the combustion chamber is always maintained in an appropriate range by changing the fuel injection timing according to the exhaust NO _X concentration.

According to the present invention, the fuel injection control means performs a plurality of fuel injections during one combustion cycle and controls each fuel injection timing and fuel injection amount. 7. The combustion control unit controls the premixed gas combustion speed by changing an injection timing and a fuel injection amount of each fuel injection by the fuel injection control unit.
A control device for a premixed compression ignition internal combustion engine according to the first aspect is provided.

[0023] That is, with the invention of claim 7 performs fuel injection is divided into a plurality of times, the injection amount and is adjusted in accordance with the exhaust NO _X concentration and injection timing of each fuel injection. As described above, the combustion speed of the air-fuel mixture changes depending on the timing at which fuel is injected. Therefore, when the fuel injection is performed a plurality of times during one combustion cycle and the fuel injection timing and the fuel injection amount of each fuel injection are changed, the effect of each fuel injection on the overall mixture combustion speed is more effectively affected. It becomes possible to control it.

According to an eighth aspect of the present invention, the combustion control means includes a compression control means for changing a cylinder compression ratio, and the compression control means changes the cylinder compression ratio to change the premixed gas combustion speed. And a control device for the homogeneous charge compression ignition internal combustion engine according to claim 2 for controlling the internal combustion engine.

That is, in the invention of claim 8, the premixed gas combustion speed is changed by changing the cylinder compression ratio. The cylinder compression ratio can be changed, for example, by changing the engine valve timing. When the cylinder compression ratio changes, both the in-cylinder pressure and the temperature during the compression stroke change. For example, when the compression ratio decreases, the rise in both the temperature and the pressure in the combustion chamber becomes slow, and the premixed gas becomes difficult to burn, so that the combustion speed decreases. Further, when the compression ratio is increased, the temperature and the pressure in the combustion chamber are quickly increased, and the combustion speed of the premixed gas is increased. Therefore, by changing depending cylinder compression ratio in the exhaust NO _X concentration, so burn rate in the combustion chamber mixture is always maintained in a proper range.

[0026]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram illustrating a schematic configuration of an embodiment in which the present invention is applied to an automobile diesel. In FIG. 1, reference numeral 1 denotes a diesel engine main body, 2 denotes an intake passage, 20 denotes a surge tank provided in the intake passage 2, and 21 denotes an intake branch pipe connecting the surge tank 20 and an intake port of each cylinder. In the present embodiment, the intake passage 2 is provided with an intake throttle valve 27 for reducing the flow rate of intake air flowing through the intake passage 2 and an intercooler 26 for cooling intake air. The intake throttle valve 27 includes an actuator 27a of an appropriate type such as a stepper motor, a vacuum actuator, and the like, and an electronic control unit (ECU) 3 described later.
The opening is determined according to the control signal from 0. Intake throttle valve 27
As described later, when the combustion velocity of the premixed air in the combustion chamber of the engine 1 is excessive, the flow rate of the engine intake air (fresh air) flowing through the intake passage 2 is reduced to adjust the combustion velocity to an appropriate range. Can be used.

In FIG. 1, reference numeral 25 denotes an air flow meter provided near the intake port of the intake passage 2. In the present embodiment, an air flow meter 25 such as a hot wire flow meter that can directly measure the weight flow rate of the intake air flowing through the intake passage 2 is used. The air flowing into the intake passage 2 passes through an air flow meter 25, is pressurized by a compressor of an exhaust supercharger (turbocharger) 35, is cooled by an intercooler 26 provided in the intake passage 2, and It is sucked into each cylinder via the branch pipe 21.

Reference numeral 111 in FIG. 1 denotes a fuel injection valve for directly injecting fuel into each cylinder. Each fuel injection valve 111
Is a common accumulator (common rail) for storing high-pressure fuel
115. The fuel of the engine 1 is pressurized by the high-pressure fuel pump 113 and supplied to the common rail 115, and is directly injected from the common rail 115 into each cylinder via each fuel injection valve 111. The diesel engine 1 of the present embodiment performs premix combustion, unlike a normal diesel engine. Therefore, the fuel injection valve 111 injects fuel into the combustion chamber of the engine 1 earlier than during a normal diesel engine (during an intake stroke or a compression stroke).

In FIG. 1, reference numeral 31 denotes an exhaust manifold for connecting an exhaust port of each cylinder to the exhaust passage 3, and reference numeral 35 denotes a turbocharger. The turbocharger 35 includes an exhaust turbine driven by exhaust gas in the exhaust passage 3 and an intake compressor driven by the exhaust turbine. In this embodiment, a variable nozzle 35a is provided at the exhaust inlet of the exhaust turbine. Variable nozzle 3
Reference numeral 5a denotes a nozzle whose opening area can be changed. The nozzle 5a is used to increase the flow velocity of the exhaust gas flowing into the exhaust turbine by narrowing the nozzle opening area when the exhaust flow rate is low and the load is low. Variable nozzle 35a at low engine load operation
, The rotation speed of the exhaust turbine is kept high, so that a decrease in compressor discharge pressure (supercharging pressure) is prevented. The variable nozzle 35a can be used to control the premixed gas combustion speed of the engine 1 by changing the supercharging pressure of the engine 1 as described later. The variable nozzle 35a includes an actuator (not shown) such as a stepper motor and a vacuum actuator, and takes an opening according to a control signal from the ECU 30.

Further, in this embodiment, an EGR device for recirculating a part of the exhaust gas to the intake system is provided. The EGR device includes an EGR passage 33 that connects the exhaust manifold 31 and the intake surge tank 20, an EGR valve 23 disposed on the EGR passage 33, and an EGR valve 23 upstream of the EGR valve 23.
An EGR cooler 45 provided in the R passage is provided. E
The GR valve 23 includes an appropriate type of actuator such as a stepper motor and a vacuum actuator (not shown).
The opening is determined according to the control signal from the ECU 30, and the EGR
EG returning to the intake surge tank 20 through the passage 33
Control the R gas flow rate. In the present embodiment, a relatively large amount of EGR is used in a wide operating range from a low load range to a high load range.
The EGR valve 23 is controlled so that the gas is recirculated. For this reason, in this embodiment, the intake air drawn into each cylinder contains a relatively large amount of EGR gas. Since the EGR gas is high-temperature exhaust gas discharged from the cylinder, if a large amount of the EGR gas is recirculated to the intake air, the intake air temperature rises, and the intake volume efficiency of the engine 1 decreases. In the present embodiment, in order to prevent this, a water-cooled or air-cooled EGR cooler 45 is provided in the EGR passage 33 upstream of the EGR valve 23. In the present embodiment, by using the EGR cooler 45 to lower the temperature of the EGR gas recirculated to the intake system, a large amount of EGR gas can be recirculated without lowering the intake volume efficiency of the engine 1. .

In this embodiment, a well-known type of exhaust purification catalyst 41 such as a three-way catalyst and a particulate filter for collecting particulates in exhaust gas are provided downstream of the exhaust throttle valve in the exhaust passage 3. (DPF) 43 is arranged. The DPF 43 is made of, for example, a metal mesh or a ceramic porous filter, and collects particulates in exhaust gas. In the present embodiment, as the DPF 43,
Any suitable type of known particulate filter can be used.

Furthermore, in the present embodiment, in the exhaust passage of the turbocharger 35 downstream NO _X sensor 71 for detecting the concentration of NO _X in the exhaust gas are provided. NO _X sensor 7
1 will be described in detail later. Further, in this embodiment, the engine 1 is provided with a variable valve timing device 80 that changes the opening / closing timing of at least one of the intake valve and the exhaust valve of each cylinder. Variable valve timing measure 8
For 0, a known type that changes the valve timing by changing the rotation phase of the intake camshaft of the engine 1 with respect to the crankshaft is used, for example. As will be described later, the effective compression ratio of each cylinder can be changed by changing the rotational phase of the camshaft to change the opening / closing timing of the intake valve. Therefore, the variable valve timing device 80 of the present embodiment can be used to change the compression ratio of each cylinder to control the combustion speed of the premixed air in the combustion chamber.

In FIG. 1, reference numeral 30 denotes one electronic control unit (ECU). The ECU 30 of the present embodiment is configured as a microcomputer having a known configuration,
U, RAM, ROM, input port, and output port are connected to each other by a bidirectional bus. ECU 30
Done fuel injection control of the engine 1, besides performing basic control of the rotational speed control or the like, a combustion control for controlling the burn rate in the combustion chamber of the pre-mixture in accordance with the output of the NO _X sensor 71 to be described later in this embodiment ing. The combustion control will be described later.

In order to perform these controls, a signal corresponding to the engine speed NE is input to an input port of the ECU 30 from a speed sensor 55 disposed near the crankshaft of the engine 1, and an air flow meter 25 is provided. And a signal corresponding to the driver's accelerator pedal depression amount (accelerator opening amount) ACCP from the accelerator opening sensor 57 disposed near the engine accelerator pedal. ing. Further, in this embodiment, the exhaust NO _X sensor 71 in the exhaust passage detects the exhaust NO _X
A signal corresponding to the concentration is input to an input port of the ECU 30.

An output port of the ECU 30 is connected to a fuel injection valve 111 of the engine 1 via a fuel injection circuit (not shown), and controls the fuel injection amount and the fuel injection timing from the fuel injection valve 111. Further, the output port of the ECU 30 is connected to the EGR valve 23, the intake throttle valve 27, and the variable nozzle 35a of the turbocharger 35 via a drive circuit (not shown).
The actuators are connected to other actuators to control the respective valve openings. The output port of the ECU 30 is connected to a variable valve timing device 80 via a drive circuit (not shown), and controls the valve timing of the engine 1.

FIG. 2 is a diagram schematically showing the configuration of the NO _X sensor 71 of the present embodiment. In FIG. 2, the NO _x sensor 71 is a solid electrolyte 3 such as zirconia (ZrO ₂ ).
And a first reaction chamber 340 communicating with the exhaust passage through the diffusion control part 335, a second reaction chamber 350 communicating with the first reaction chamber 340 through the diffusion control part 337, and a solid electrolyte. An atmosphere chamber 360 into which the atmosphere as a standard gas is introduced is provided. The diffusion control sections 335 and 337 suppress the inflow of the oxygen component into the first reaction chamber 340 and the second reaction chamber 350 due to the diffusion, respectively.
The reaction chamber can maintain the oxygen concentration difference between the first reaction chamber and the second reaction chamber.

In FIG. 2, reference numeral 341 denotes a first reaction chamber 340.
Reference numeral 342 denotes a platinum electrode (cathode) disposed in the inside, and a similar platinum electrode (anode) provided outside the sensor 71 with the cathode 341 and the solid electrolyte 331 interposed therebetween. Also, the second
The reaction chamber similar platinum electrode 350 is within 350 and NO _X detecting rhodium (Rh) electrode 353, platinum electrode 361 for reference to the air chamber 360 are disposed respectively. An electric heater 370 for heating the solid electrolyte is shown in the figure.

The electrode 341 and the external electrode 342 of the first reaction chamber 340, and the electrode 351 and the external electrode 342 of the second reaction chamber 340.
Function as oxygen pumps for exhausting oxygen in the exhaust gas in the first reaction chamber 340 and the second reaction chamber 350, respectively. When a voltage is applied between the electrodes 341 and 342 and the electrodes 351 and 342 when the solid electrolyte 331 is at a certain temperature or higher, oxygen molecules in the exhaust gas are ionized on the cathodes 341 and 351 and the ionized oxygen molecules are solidified. It moves inside the electrolyte 331 toward the anode 342 and becomes an oxygen molecule again on the anode 342. Therefore, the first reaction chamber 340,
Oxygen in the exhaust gas in the second reaction chamber 350 is exhausted to the outside. In addition, the electrodes 342 and 3
A current proportional to the amount of oxygen molecules moved per unit time flows between 41 and 351. Therefore, by controlling this current, the amount of oxygen discharged from each reaction chamber can be controlled.

In this embodiment, the electrodes of the atmosphere chamber 360 are used.
Between the electrode 341 and the electrodes 341 and 351 in each reaction chamber.
A unit cell is formed. The exhaust in the first and second reaction chambers is oxygen
Because the concentration is lower than the atmosphere, the air in the atmosphere chamber 360
There is a difference in oxygen concentration between exhaust gas in each reaction chamber.
You. Separates the atmosphere chamber 360 from the reaction chambers 340 and 350
If the temperature of the solid electrolyte rises above a certain temperature,
When no voltage is applied between the electrodes, the air
The reaction chamber 34 passes through the solid electrolyte 331 from inside the chamber 360.
Oxygen moves to 0,350. That is, large
The oxygen molecules in the air in the air chamber 360 are ionized on the electrode 361.
And move in the solid electrolyte 331 to reduce the oxygen concentration.
The acid is again applied on the electrodes 341 and 351 of the reaction chambers 340 and 350.
Become elementary molecules. For this reason, the electrode 361 and each electrode 341,
351 between the atmospheric oxygen concentration and the oxygen concentration in each reaction chamber.
A voltage corresponding to the difference is generated. Atmospheric oxygen concentration is one
Is constant, the electrode 361 and each of the electrodes 341 and 351 are
The potential differences V0 and V1 (FIG. 2) are respectively set in the first reaction chamber 340.
And the oxygen concentration of the exhaust gas in the second reaction chamber 351.
You. In the present embodiment, as described above, acid is supplied from each reaction chamber.
Oxygen pump (electrodes 341 and 342,
Electrodes 351 and 342) are provided.
The oxygen pumping rate of the elementary pump depends on the pump voltage between each electrode.
By adjusting the flows Ip0 and Ip1 (FIG. 2),
Oxygen concentration of exhaust gas in the room (that is, voltage V0, V1)
Is controlled to be a predetermined constant value. In this embodiment
Means that the oxygen concentration in the first reaction chamber 340 is, for example, about 1 ppm.
The oxygen concentration in the second reaction chamber 350 is, for example,
The pump currents Ip0, Ip0, Ip0,
p1 is controlled. Therefore, the inside of the second reaction chamber 350
Is maintained in a reducing atmosphere with an extremely low oxygen concentration. one
NO in exhaust_X(NO, NO_Two) By oxygen pump
Is not discharged to the outside, so the discharge in the first and second reaction chambers
Qi NO_XThe concentration is kept the same as the external exhaust. Toko
NO in the second reaction chamber_XThe detection electrode 353 is rhodium
(Rh), so it functions as a reduction catalyst and reduces the atmosphere
NO below_X(NO, NO _Two) To reduce. The atmosphere chamber
360 reference electrode 361 and NO_XWith the detection electrode 353
Since a voltage is applied between them, NO_XDetection electrode 3
On 53, NO → (1/2) N_Two+ (1/2) O_Two, Or N
O_Two→ (1/2) N_Two+ O_TwoReaction occurs and NO _XBy the reduction of
Oxygen is generated. This oxygen is supplied to the electrode 353
Ionized above and headed for the reference electrode 361 of the atmosphere chamber 360
Move through the solid electrolyte 331 and move on the reference electrode 361
Form oxygen molecules. The oxygen concentration in the second reaction chamber 350 is
Because it is extremely low, the solid electrolyte
The total amount of oxygen ions flowing through_XReturn of
It was caused by the cause. That is, in the solid electrolyte
The amount of oxygen ions flowing per unit time is measured in the second reaction chamber.
NO within_XConcentration (NO of exhaust gas in exhaust passage)_XConcentration)
Amount. Therefore, with the movement of oxygen ions,
By measuring the generated current value (Fig. 2, Ip2)
NO of exhaust gas in exhaust passage_XConcentration can be detected
You. NO of this embodiment_XThe sensor 71 detects the current value Ip
2 is converted to a voltage signal, and NO in the exhaust_XDepending on the concentration
It outputs a pressure signal.

[0040] In the present embodiment determines whether pre-mixture combustion speed of the engine 1 based on the exhaust gas NO _X concentration detected by the NO _X sensor 71 is in the appropriate range. Next, a description will be given of the relationship between mixture combustion rate and NO _X generation amount. FIG. 3 is a pressure diagram showing a cylinder pressure change in one combustion cycle of a diesel engine. In FIG. 3, the vertical axis represents the in-cylinder pressure, and the horizontal axis represents the crank angle. FIG.
, Curve N shows the in-cylinder pressure change when fuel injection was not performed, curve C shows the in-cylinder pressure change when conventional diffusion combustion was performed, and curve M shows the case when premixed combustion was performed. , Curve P indicates the in-cylinder pressure change when the combustion speed becomes excessive in premixed combustion and premature ignition occurs.

Since the in-cylinder pressure when fuel injection is not performed is simply compression and expansion associated with the rise and fall of the piston, the in-cylinder pressure change is determined by the compression top dead center (shown by the horizontal axis in FIG. (Shown by TDC). Further, in the case of normal diffusion combustion (curve C), the fuel injected into the cylinder immediately before the compression top dead center ignites, so that the in-cylinder pressure starts increasing immediately before the top dead center and starts after the top dead center. A relatively high value is maintained until the injected fuel has completed combustion.

On the other hand, when the appropriate premixed combustion is performed (curve M), the premixed gas formed in the cylinder ignites before the top dead center, so that the in-cylinder pressure starts to increase. Since the combustion rate is relatively low, the pressure rise is more gradual than in the case of diffusion combustion, and the time until the completion of combustion is relatively long. That is, in the case of premix combustion, the in-cylinder pressure gradually rises to a relatively low value, and this pressure is maintained for a relatively long time.

However, if the combustion speed increases for some reason in the premixed combustion, the premixed gas ignited before the top dead center burns at once as shown in the curve P in FIG. Before it reaches the point, it rises sharply. For this reason, premature ignition in which vibration, noise, and the like due to combustion rapidly increase occurs. FIG. 4 shows in-cylinder heat per unit rotation angle of the crankshaft in the case of conventional diffusion combustion (curve C), appropriate premixed combustion (curve M), and premature ignition (curve P) as in FIG. It is a figure which shows generation | occurrence | production amount (J / CA) (henceforth "heat generation rate"). As shown in FIG. 4, in the diffusion combustion (curve C), the fuel injected near the top dead center burns at a relatively high combustion speed, so that the heat generation rate is high near the top dead center. Further, in premixed combustion (curve M), since the combustion speed of the air-fuel mixture is relatively slow,
The heat release rate curve is also a gentle curve that is lower than that of diffusion combustion. Since the heat release rate can be regarded as the amount of heat generated per unit time, in this case, the diffusion combustion generates a relatively large amount of heat in a shorter time than the premixed combustion. Get higher. For this reason, in the diffusion combustion, NO _X is easily generated by the combustion.

On the other hand, when premature ignition occurs, a large amount of heat is generated in a very short time due to rapid combustion of the premixed gas. For this reason, the heat release rate has an extremely large peak before the top dead center (TDC). As described above, when premature ignition occurs, a large amount of heat is generated in a very short time, so that the in-cylinder temperature and pressure become large values. For this reason, the amount of NO _X generated by combustion suddenly increases.

Generally, the range of the appropriate combustion speed in which proper premixed combustion occurs is relatively narrow. If the combustion speed increases outside this range, premature ignition occurs. Further, when the combustion speed deviates from the proper combustion speed, the in-cylinder temperature during combustion decreases and the NO _X amount decreases, but misfire easily occurs. For this reason, in order to perform premix combustion, it is necessary to maintain the combustion speed in an appropriate range. However, the combustion rate cannot be directly detected, and it has conventionally been difficult to control the combustion rate in an appropriate range. However, as described above, when the combustion speed of the premixed gas increases, the amount of NO _X generated increases due to an increase in cylinder temperature, and when the combustion speed decreases, NO _X
It has been found that the amount generated is reduced.

[0046] Therefore, in this embodiment by using the correlation between the NO _X generation amount and the combustion speed, and controls the burn rate of effectively combustion chamber premixture without detecting the combustion rate directly. Hereinafter, the combustion control of the present embodiment will be described. As described above, there is a correlation between the premixed gas combustion speed and the NO _X generation amount. Thus, for example, the engine is advance measuring the NO _X generation amount when being operated in a proper premix combustion, engine NO _X generation amount in actual operation the proper premix combustion at the time of the NO _X generation If the conditions that affect the combustion rate are controlled so as to obtain the amount, the combustion rate can always be set to an appropriate value for the premixed combustion. In this embodiment, the engine is operated in advance by changing the conditions of the engine speed and the fuel injection amount, and the amount of NO _X generated when proper premixed combustion is performed is measured in the form of the NO _X concentration in the exhaust gas. I have. The actual measurement result is stored in the ROM of the ECU 30 in the form of a two-dimensional numerical map using the engine speed NE and the fuel injection amount _Qfin . In actual operation, ECU 30 detects the exhaust NO _X concentration NO _X sensor 71, the combustion control operation of changing the combustion rate as the NO _X concentration matches the proper exhaust NO _X concentration in the current operating state Do.

FIG. 5 is a flowchart specifically illustrating the above-described combustion control operation. This operation is performed by the ECU 30
Is performed by a routine executed at regular intervals. In the operation of FIG. 5, first, in step 501, the current engine speed NE is read from the speed sensor 55, and the current engine fuel calculated by a fuel injection amount calculation operation (not shown) separately executed by the ECU 30. The value of the injection amount _Qfin is read. In the present embodiment, the ECU 3
0 is the engine 1 read by the accelerator opening sensor 57 separately.
Accelerator pedal depression amount (accelerator opening) ACCP
The fuel injection amount _Qfin is calculated from the relationship previously stored in the ROM based on the engine speed NE and the engine speed NE.

Next, at step 503, the exhaust passage 3
Current exhaust NO _X concentration ANOX from NO _X sensor 71 disposed in is loaded. Further, in step 505, using the values of NE and _Qfin read in step 701, the appropriate premixed combustion is performed under the current operating conditions of NE and _Qfin from the numerical map stored in advance in the ROM. The exhaust NO _X concentration (target NO _X concentration) TNOX is read.

[0049] Then, the actual of the NO _X concentration ANOX from step 507 of the 513 currently, whether it is in the range of TNOX ± alpha is determined (Step 507,51
1). α is the actual N with respect to the target NO _X concentration TNOX
A tolerance of O _X concentration ANOX, is a positive constant value. If the actual NO _X concentration ANOX is larger than the above range, that is, at step 507, ANOX ≧ TNOX +
Since when was α is believed that NO _X concentration because the combustion rate is increased from the appropriate range is increased,
Proceeding to step 509, a combustion speed reduction operation for reducing the premixed gas combustion speed is performed. As a result, the combustion speed is controlled within an appropriate range, and premature ignition due to an increase in the combustion speed is prevented. The operation of reducing the combustion speed will be described later.

When the actual NO _X concentration ANOX is lower than the appropriate range, that is, at step 511,
If there was a TNOX-alpha is now burning rate is NO _X concentration to have lower than the appropriate range is believed to have decreased. Therefore, in this case, a combustion speed increasing operation for increasing the premixed gas combustion speed is performed in step 513 to prevent deterioration of the combustion or misfire due to a decrease in the combustion speed. The combustion speed increasing operation will be described later.

By the above operation, in this embodiment, the premixed gas combustion speed is always controlled to a range in which an appropriate premixed combustion is generated, and the occurrence of premature ignition or deterioration of combustion is prevented. . Next, the combustion speed control operation of the present embodiment, that is, the combustion speed reduction operation of FIG.
9) and the combustion speed increasing operation (step 513) will be described.

Factors that affect the combustion speed of the premixed air in the combustion chamber include, for example, the temperature, pressure, oxygen concentration, fuel injection timing and injection amount of the combustion chamber, and the properties of the fuel (ease of combustion). In this embodiment, the combustion speed control operation is performed by changing these factors that affect the combustion speed. Hereinafter, steps 509 and 513 in FIG.
An example of the operation of decreasing and increasing the combustion speed performed in the above will be described. (1) EGR amount control EGR returning to the surge tank 20 through the EGR passage
Since the gas is exhaust gas after combustion, the oxygen concentration is low. For this reason, when the amount of EGR gas supplied to the combustion chamber is increased, the oxygen concentration in the combustion chamber decreases, and when the amount of EGR gas is reduced, the oxygen concentration in the combustion chamber increases. Also, when the oxygen concentration in the combustion chamber increases, the premixed gas combustion speed increases,
When the oxygen concentration decreases, the premixed gas combustion speed decreases. Therefore, EG in accordance with the exhaust NO _X concentration ANOX
By controlling the opening degree of the R valve 23, it is possible to change the premixed gas combustion speed.

That is, in this case, step 50 in FIG.
In the combustion speed decreasing operation of No. 9, the opening of the EGR valve 23 is increased by a certain amount to increase the amount of EGR gas recirculated to the combustion chamber,
In the combustion speed increasing operation in step 513 of FIG. 5, the EGR valve 23 reduces the opening of the EGR valve 23 by a fixed amount and returns the EGR to the combustion chamber.
Try to reduce the gas volume. As a result, the combustion speed is maintained in an appropriate range. (2) Intake air amount control When the amount of fresh air (intake air amount) taken into the engine decreases, the oxygen concentration in the cylinder decreases. Further, when the amount of intake air drawn into the cylinder as a whole decreases, the in-cylinder pressure during compression also decreases. For this reason, when the intake air amount is reduced, the combustion speed is reduced. Therefore, by controlling the intake throttle valve 27 opening in accordance with the exhaust NO _X concentration ANOX, it is possible to change the pre-mixture combustion rate.

That is, in this case, step 50 in FIG.
In the combustion speed decreasing operation of No. 9, the opening degree of the intake throttle valve 27 is reduced by a certain amount to reduce the amount of fresh air flowing into the cylinder,
In the combustion speed increasing operation in step 513 in FIG. 5, the opening degree of the intake throttle valve 27 is increased by a certain amount so that the amount of fresh air flowing into the cylinder increases. As a result, the combustion speed is maintained in an appropriate range. When the intake air amount control is used together with the above-described EGR control, the control range of the in-cylinder oxygen concentration is further widened, so that adjustment of the combustion speed change becomes easy. (3) Intake pressure control When the engine intake pressure decreases, the in-cylinder pressure at the end of the intake stroke decreases. Therefore, even if the compression ratio is the same, the in-cylinder pressure during the compression stroke decreases. Further, the premixed gas combustion speed decreases as the pressure during combustion decreases. For this reason, it is possible to control the combustion speed by changing the intake pressure. In this embodiment, a turbocharger 35 is provided, and the intake air pressure can be changed by changing the discharge air pressure (supercharging pressure) of the turbocharger. Further, the supercharging pressure can be changed by changing the opening of the variable nozzle 35a of the turbocharger 35. Therefore, by controlling the variable nozzle 35a opening in accordance with the exhaust NO _X concentration ANOX, it is possible to change the pre-mixture combustion rate.

That is, in this case, step 50 in FIG.
In the combustion speed decreasing operation of No. 9, the opening degree of the variable nozzle 35a is increased by a certain amount to reduce the supercharging pressure, and FIG.
In the combustion speed increasing operation of No. 13, the supercharging pressure is increased by reducing the opening of the variable nozzle 35a by a certain amount. As a result, the combustion speed is maintained in an appropriate range. (4) Fuel Injection Timing Control As described above, when the fuel injection timing is advanced, the fuel concentration of the premixture during combustion becomes uniform, so that the combustion speed becomes slow. Further, when the fuel injection timing is retarded, the fuel concentration of the premixture during combustion becomes non-uniform, and the combustion speed increases.

[0056] Therefore, by controlling the fuel injection timing of the fuel injection valve 111 in accordance with the exhaust NO _X concentration ANOX, it is possible to change the pre-mixture combustion rate. That is, in this case, in the combustion speed decreasing operation of step 509 in FIG. 5, the fuel injection timing from the fuel injection valve 111 is advanced by a fixed amount to make the fuel concentration of the premixed gas formed in the cylinder more uniform. In the combustion speed increasing operation of step 513 in FIG. 5, the fuel injection timing from the fuel injection valve 111 is retarded by a fixed amount so that the high fuel concentration portion locally increases in the premixed gas formed in the cylinder. I do. As a result, the combustion speed is maintained in an appropriate range. (5) Fuel injection timing and fuel injection amount control As described above, it is possible to change the combustion speed of the premixed gas by changing the fuel injection timing. As a result, even when fuel injection is performed only once in one combustion cycle, it is possible to control the premixed gas combustion speed in an appropriate range. However, in this case, since the total fuel injection amount needs to be maintained at a value determined from the engine speed and the accelerator opening, there is a possibility that the combustion speed cannot be controlled sufficiently within an appropriate range only by the fuel injection timing. There is. Therefore, in the present embodiment, the fuel injection is performed a plurality of times during one combustion cycle, and the combustion speed is controlled by changing the injection timing and the injection amount of each fuel injection. As described above, by changing the injection timing and the injection amount of each fuel injection, it is possible to freely combine the effects of the respective fuel injections on the combustion speed, so that the degree of freedom in the combustion speed control is improved. I will be.

For example, consider the case where fuel is injected three times during one combustion cycle as shown in FIG. FIG. 6 shows FIG.
Shows the relationship between the in-cylinder pressure (curve M) change during premix combustion and fuel injection. In this case, as shown in FIG.
The fuel injection is performed during the intake stroke, the second fuel injection is performed relatively early in the compression stroke, and the third fuel injection is performed near the top dead center of the compression stroke.

In this case, in the first fuel injection, as the injection timing is advanced, the fuel concentration of the air-fuel mixture finally formed in the cylinder becomes uniform, so that the combustion speed decreases. Also,
Similarly, as the amount of fuel injected by the first fuel injection increases, the amount of fuel dispersed uniformly in the cylinder increases, so that the fuel concentration of the finally formed air-fuel mixture becomes uniform as a whole and the combustion speed decreases. . That is, in the first fuel injection, the combustion speed can be reduced as the injection timing is advanced and the injection amount is increased.

Since the second fuel injection is performed at a relatively late time, the injected fuel burns without sufficiently diffusing into the cylinder. Therefore, when the injection amount of the second fuel injection is increased, the non-uniformity of the fuel concentration of the air-fuel mixture is increased, and the combustion speed is increased. In the second fuel injection, as the injection timing is delayed, the non-uniformity of the fuel concentration of the mixture increases, so that the combustion speed increases.

In the third fuel injection, the remaining fuel of the first and second fuel injections is injected so that the total fuel injection amount becomes a fuel injection amount determined from the engine speed and the accelerator opening. Therefore, the fuel injection amount cannot be set freely. Further, since the third fuel injection is injected after the premixed gas in the combustion chamber near the top dead center has already started combustion, it has no significant effect on the combustion speed, but the fuel injection timing is advanced. Since the fuel injection timing approaches the second fuel injection, the combustion speed increases as in the case where the second fuel injection is retarded.

[0061] Thus 1 when performing three fuel injected into the combustion cycle, for example, the third fuel injection timing is fixed at the top dead center, the first in accordance with the actual exhaust NO _X concentration ANOX and second The fuel injection timing and the fuel injection amount are adjusted. For example, in the combustion speed decreasing operation of step 509 in FIG. 5, the injection timing of the first fuel injection is advanced to increase the injection amount, and the injection timing of the second fuel injection is advanced to decrease the injection amount. As a result, both the first fuel injection and the second fuel injection act in the direction of decreasing the combustion speed. In the operation of increasing the combustion speed in step 513 in FIG. 5, the injection timing of the first fuel injection is retarded to decrease the injection amount, and the injection timing of the second fuel injection is retarded to increase the injection amount. I do. As a result, both the first and second fuel injections act in a direction to increase the combustion speed. (6) Compression ratio control When the cylinder compression ratio decreases, the in-cylinder pressure and temperature during the compression stroke decrease. For this reason, the combustion speed of the premixed gas in the combustion chamber decreases as the compression ratio decreases. Therefore, the combustion speed can be controlled by changing the cylinder compression ratio.

The engine 1 of this embodiment has a variable valve timing device 80 for changing the engine valve timing. When the valve timing changes, the cylinder compression ratio also changes according to the valve timing. For example, if the closing timing of the cylinder intake valve is delayed so that the intake valve is opened halfway through the compression stroke, the intake air sucked into the engine during the intake stroke is discharged to the intake port during the compression stroke. Accordingly, since the substantial compression stroke is started from the time when the intake valve is closed, the cylinder compression ratio is reduced as the intake valve closing timing is delayed. Thus, by controlling the variable valve timing device 80 in accordance with the exhaust NO _X concentration ANOX, it is possible to change the pre-mixture combustion rate.

That is, in this case, step 50 in FIG.
The variable valve timing device 8
Using 0, the engine intake valve timing is retarded by a fixed amount. As a result, the intake valve closing timing is also retarded, so that the cylinder compression ratio decreases and the combustion speed decreases. In the combustion speed increasing operation of step 513 in FIG. 5, the intake valve timing is advanced by a fixed amount. As a result, the cylinder compression ratio increases and the combustion speed increases.

As another method of changing the cylinder compression ratio, for example, there is a method in which a variable volume chamber communicating with each cylinder combustion chamber is provided in an engine cylinder head for each cylinder. A piston is provided in the variable volume chamber so as to be movable in the volume chamber, and the volume of the volume chamber can be made variable by changing the piston position from outside. In this case, it is possible to control the burn rate in the combustion chamber premixture by changing the piston position of the variable volume chamber in accordance with the exhaust NO _X concentration. (7) Fuel property control When the fuel property changes, the premixed gas combustion speed also changes. For example, in the case of a fuel containing a large amount of easily ignitable fuel components, such as cetane, the combustion rate of the air-fuel mixture increases. Therefore, for example, separately from the normal fuel system, a fuel component such as cetane that increases the burning rate is added to the fuel system (for example, the common rail 11 in FIG. 1).
By providing a means for supplying the fuel in 5), it is possible to control the premixed gas combustion speed by changing the property (component) of the fuel injected from the fuel injection valve 111.

In this case, in the combustion speed decreasing operation in step 509 in FIG. 5, the supply rate of the combustion speed increasing component such as cetane mixed with the fuel in the common rail 115 is reduced by a fixed ratio, and the combustion speed increasing operation in step 513 in FIG. Then, an operation may be performed to increase the supply rate of the combustion speed increasing component by a certain ratio. Although the actual operation of the combustion speed control operation has been described above, it is also possible to control the combustion speed to a range in which appropriate premixed combustion can be performed by performing the operations (1) to (7) alone. Is the above (1) to (7)
By using two or more of the above operations in combination, it is possible to more effectively control the combustion rate.

In the above embodiment, the combustion speed of all the cylinders of the engine is uniformly increased or decreased. However, in practice, the range of the combustion speed at which the appropriate premixed combustion is performed may vary from cylinder to cylinder. . Therefore, it is also possible to perform an operation for adjusting the combustion speed to an appropriate range for each cylinder by the method described below. When controlling the combustion speed for each cylinder, the combustion speed is individually adjusted for each cylinder by, for example, a fuel injection timing control or a compression ratio control for each cylinder using a variable volume chamber.

In this case, the ECU 30 operates while the other
While keeping the fuel injection timing and compression ratio of the cylinder constant,
The fuel injection timing of the cylinder is retarded by a certain amount (or cylinder compression
The ratio is increased by a fixed amount). As a result, this cylinder
The premixed gas combustion speed gradually increases, and the exhaust gas from this cylinder
NO_XThe concentration also increases. However, in this case, the cylinder
NO_XIncreased NO even if emissions increase_XIs the other ki
Diluted to exhaust from cylinders, NO in overall exhaust_XThe concentration is
No significant increase, NO_XFrom the output of the sensor,
NO_XIt is difficult to detect a gradual increase in concentration. Place
However, as described above, the premixed gas combustion speed of one cylinder is gradually increased.
Premature ignition in this cylinder at some point
Is generated, and the NO in the exhaust gas from this cylinder_XDark
The degree will be greatly increased. If premature ignition occurs,
NO of exhaust from this cylinder_XConcentrations increase rapidly
Therefore, the overall exhaust after dilution with exhaust from other cylinders
NO_XThe concentration also increases sharply. This one cylinder
Caused by premature ignition _XThe amount of generation is extremely high
NO because it is large_XThe detection can be sufficiently performed by the sensor.

The ECU 30 gradually increases the premixed gas combustion speed of one cylinder as described above, and when the exhaust NO _X concentration detected by the NO _X sensor 71 suddenly increases, the pre-ignition occurs in this cylinder. In addition to determining that the combustion has occurred, the fuel injection timing or the compression ratio of the cylinder is returned to a direction in which the combustion speed decreases by a predetermined amount. The amount of return of the fuel injection timing or the compression ratio is the difference between the fuel injection timing (or the compression ratio) at which premature ignition occurs and the fuel injection timing (or the compression ratio) at which appropriate premixed combustion occurs. Desired. As described above, once the combustion speed at which premature ignition occurs is confirmed, and then the operation of reducing the combustion speed by a certain amount is performed, so that appropriate premixed combustion is performed in this cylinder.

After adjusting the combustion speed of one cylinder to an appropriate value as described above, the ECU 30 repeats the same operation for each of the other cylinders in order for each cylinder to set the combustion speed to an appropriate value. As a result, all the cylinders are adjusted to the appropriate combustion speeds.

[0070]

The invention described in each of the claims prevents the occurrence of premature ignition or deterioration of combustion by controlling the premixed gas combustion speed in an appropriate range in a premixed combustion compression ignition internal combustion engine. However, by making it possible to perform appropriate premixed combustion in a wide operating range, a common effect is achieved in which it is possible to suppress the generation of exhaust smoke and the increase in NO _X emission.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of an embodiment when the present invention is applied to an automobile diesel engine.

FIG. 2 is a diagram illustrating a schematic configuration and an operation principle of a NO _X sensor.

FIG. 3 is a view for explaining changes in in-cylinder pressure during premixed combustion and diffusion combustion.

FIG. 4 is a diagram for explaining a change in in-cylinder heat generation rate between premixed combustion and diffusion combustion.

FIG. 5 is a flowchart illustrating a combustion control operation.

FIG. 6 is a diagram showing fuel injection timing in one embodiment of a combustion control operation.

[Explanation of symbols]

1 ... diesel engine body 2 ... intake passage 3 ... an exhaust passage 23 ... EGR valve 27 ... throttle valve 30 ... electronic control unit (ECU) 35 ... turbocharger 35a ... variable nozzle 71 ... NO _X sensor 80 ... variable valve timing device 111 ... Fuel injection valve

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) F02D 21/08 301 F02D 21/08 301E 3G092 23/02 23/02 C 3G301 41/02 351 41/02 351 41/04 385 41/04 385Z 41/14 310 41/14 310N 310J 41/38 41/38 B 41/40 41/40 C 45/00 320 45/00 320Z F02M 25/07 550 F02M 25/07 550F 570 570B F-term (reference) 3G005 DA02 EA04 EA14 EA16 FA35 GA04 GC05 GC08 GE01 GE09 JA39 JA41 JA42 JB02 3G023 AA05 AB05 AF03 AG03 3G062 AA01 AA05 CA07 CA08 DA01 DA02 EA04 EA11 ED08 FA05 FA12 GA04 GA06 GA15 GA01 GA01 GA46 3G084 AA01 BA05 BA08 BA13 BA15 BA20 BA22 BA23 DA10 EB08 EB12 EC03 FA10 FA13 FA28 FA33 3G092 AA02 AA11 AA12 AA17 AA18 BA02 BB01 BB06 DA08 DB03 DC03 DC09 DD03 DD08 EA01 EA02 EA03 EA04 HA01Z HB01Z HD04Z HE01Z HF08Z 3G301 HA02 HA11 HA13 HA19 JA25 LA03 MA11 MA18 MA26 NE01 NE06 NE11 NE12 PB03Z PD01Z PE01Z PF03Z

Claims (8)

[Claims] A control device for a premixed compression ignition internal combustion engine which injects fuel from a fuel injection valve into a combustion chamber to form a premixed mixture of fuel and air in the combustion chamber and ignites the premixed gas by compression. there, the premixed compression ignition internal combustion engine, the combustion speed in the combustion chamber premixture is NO _X generation amount due to combustion is reduced in the case in the appropriate range, appropriate the combustion speed in the combustion chamber premixture combustion state with NO _X generation amount as from increased range is the combustion vibration as well as increasing now knock increases occurs, NO _X is reduced further as the pre-mixture combustion rate becomes smaller than the appropriate range the There now misfire deteriorated occurs, the control device includes a NO _X sensor arranged in an exhaust passage of the engine for detecting the NO _X in the exhaust gas, a combustion system for changing the burn rate in the combustion chamber premixture Control means, and storage means for storing an appropriate NO _X concentration that is the NO _X concentration in the exhaust gas when the engine is operated at an appropriate premixed gas combustion speed, and is detected by the NO _X sensor. by the concentration of NO _X in the exhaust gas that controls the combustion control means so as to match the proper NO _X concentrations the storage, the premixed compression be controlled so that pre-mixture combustion rate is within the appropriate range the Control device for ignition internal combustion engine. Wherein said storage unit stores the proper NO _X concentration in accordance with the engine operating state, the control device further includes an operation state means for detecting engine operating conditions, by the NO _X sensor The combustion control means is controlled so that the detected NO _X concentration in the exhaust gas becomes an appropriate NO _X concentration corresponding to the operating state detected by the operating state detecting means.
A homogeneous charge compression ignition internal combustion engine according to claim 1. 3. The combustion control means includes EGR means for recirculating a part of the engine exhaust gas to the engine combustion chamber, and controlling the flow rate of the exhaust gas recirculated to the combustion chamber by the EGR means to reduce the premixed gas combustion speed. 3. The control device for a homogeneous charge compression ignition internal combustion engine according to claim 2, which controls. 4. The combustion control means includes intake throttle means for changing an engine intake air amount, and controls the combustion speed of the premixed gas by changing the engine intake air amount by the intake throttle means. 3. The control device for a homogeneous charge compression ignition internal combustion engine according to claim 1. 5. The combustion control means includes a supercharging pressure control means for changing an engine intake pressure, and controls the premixed gas combustion speed by changing the engine intake pressure by the supercharging pressure control means. Item 3. A control device for a premixed compression ignition internal combustion engine according to item 2. 6. The combustion control means includes a fuel injection control means for controlling fuel injection timing from the fuel injection valve,
3. The control device for a premixed compression ignition internal combustion engine according to claim 2, wherein the premixed gas combustion speed is controlled by changing a fuel injection timing in a combustion chamber by the fuel injection control means. 7. The fuel injection control means performs a plurality of fuel injections during one combustion cycle, controls each fuel injection timing and fuel injection amount, and the combustion control means controls the fuel injection control. The control device for a premixed compression ignition internal combustion engine according to claim 6, wherein the premixed gas combustion speed is controlled by changing an injection timing and a fuel injection amount of each fuel injection by means. 8. The combustion control device according to claim 2, wherein the combustion control means includes compression control means for changing a cylinder compression ratio, and controls the combustion speed of the premixed gas by changing the cylinder compression ratio by the compression control means. Control device for a homogeneous charge compression ignition internal combustion engine.