JP2002303181A - Fuel injection controller of diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a torque from lowering and the amount of soot from increasing by holding the optimum timing of a post-injection even during the acceleration with an increased variation in suction amount in a diesel engine performing the post-injection with reference to the end time of combustion by main injection. SOLUTION: A suction amount Aire is estimated (S12), a target torque Tr is set (S13), a main injection amount Qm, a main injection timing Im, and a post-injection amount QF are set from the Aire, Tr, and an engine speed, (S14) and a corrected post-injection timing IF by learning is read and set as a basic post-injection timing IFB (S15). The acceleration is judged from the amount of variation (Δα) in the opening of an accelerator (S16) and, during the acceleration, the basic post-injection timing IFB is corrected to advance by an acceleration correction amount IFacc to set the timing as a final post-injection timing IF (S17).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a fuel injection method for a diesel engine mounted on an automobile or the like.

[0002]

2. Description of the Related Art Conventionally, in a diesel engine (direct injection diesel engine) that directly injects fuel into a combustion chamber, a main injection of fuel is performed near a compression top dead center.
It is known that a post-injection (also referred to as post-injection or sub-injection) is performed at a predetermined timing in the first half of the expansion stroke after the main injection. For example, JP-A-2000-170585 discloses that
It describes that the main injection of fuel is performed near the compression top dead center and the sub injection is performed at 10 to 20 ° CA (crank angle) after the compression top dead center.

[0003] In the case of a diesel engine, there is a problem that the exhaust gas temperature is relatively low, so that it is difficult to activate the catalyst device of the exhaust system. To increase the exhaust gas temperature by post-burning to promote catalyst activation,
When a NOx reduction catalyst is provided, in order to increase the supply amount of hydrocarbon (HC) as a reducing agent, fuel is post-injected in an expansion stroke, and HC is increased by post-burning. is there. At this time, in the diesel engine, nitrogen oxides (NO
The task is to improve the purification rate of x),
It is an issue to reduce the amount of soot composed of agglomerates of carbon particles generated in a combustion chamber, and it is required to solve those issues while suppressing an increase in HC and deterioration in fuel efficiency. The above-mentioned Japanese Patent Application Laid-Open No. 2000-170585 aims to reduce soot while suppressing fuel consumption deterioration by performing sub-injection at 10 to 20 ° CA (crank angle) after compression top dead center.

[0004]

However, in the above-mentioned conventional technology, the timing of post-injection is fixed and sometimes deviates from the soot reduction condition which varies depending on the operating state of the engine. It cannot be reduced sufficiently.

[0005] Therefore, based on the end timing of diffusion combustion generated in the combustion chamber by the main injection of fuel near the top dead center of the compression stroke, the fuel is injected so as to start combustion immediately after the end of the main injection combustion. By setting the post injection timing,
In a state where the carbon present in the combustion chamber after the flame spreads is mixed well with the surrounding oxygen, the carbon burns with the post-injected fuel, effectively reducing the emission of soot composed of carbon condensate It has been considered that a fuel injection control device for a diesel engine is configured to perform the above operation.

However, even when the post-injection timing is set on the basis of the end timing of the combustion by the main injection, the end timing of the combustion by the main injection varies depending on the difference in the charged amount. When the engine transient is large, especially during acceleration, the post-injection timing, which is set based on the end of combustion by the main injection, cannot keep up with the change in the combustion end However, there is a problem that the torque decreases and the soot increases.

Although a change in the intake air amount is predicted (estimated) and the injection amount and the injection timing are controlled on the basis of the predicted change in the intake air amount, during the transient state such as acceleration, the estimation is not performed. Since the accuracy is poor, it is difficult to set accurately in response to a change in the intake air amount, and it is impossible to prevent the post-injection timing set based on the combustion end timing from deviating from the optimal timing. Also,
The post-injection timing may shift due to aging or the like. Therefore, learning control is also performed based on parameters (torque fluctuation, oxygen concentration, and the like) that are affected by the execution of the post-injection, but the learning control does not sufficiently follow during transients such as acceleration.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances. In a diesel engine, soot can be effectively reduced by post-injection without inducing torque even at the time of acceleration with a large change in intake air amount. The purpose is to do.

[0009]

The invention according to claim 1 is
Main injection control means for performing main injection of fuel at a predetermined time up to near the top dead center of the compression stroke by a fuel injection valve arranged to directly inject fuel into the combustion chamber; and end time of combustion by the main injection. After the main injection, the fuel injection valve executes the fuel post-injection with the predetermined timing in the first half of the expansion stroke as the basic post-injection timing so that the combustion starts immediately after the combustion by the main injection ends. A fuel injection control device for a diesel engine comprising post-injection control means,
The post-injection control means corrects the basic post-injection timing during engine acceleration, and executes post-injection at the post-correction post-injection timing.

According to this, the combustion is started immediately after the combustion by the main injection is completed, based on the end time of the combustion generated in the combustion chamber by the main injection of the fuel near the top dead center of the compression stroke. By setting the post-injection timing of the fuel, the carbon present in the combustion chamber after the flame has spread is mixed well with the surrounding oxygen, and the carbon is burned together with the post-injected fuel to condense the carbon. Emissions of soot composed of the body will be effectively reduced. Also in the case where the main injection is divided into a plurality of times and the multi-stage injection is performed, the combustion is diffusion combustion, and the emission of soot is reduced by the same action by using the combustion end timing as a reference. When the main injection is performed in the intake stroke, premixed combustion is performed. Even in such a case, diffusion combustion is partially performed. Therefore, similar operation is performed by using the end timing of the diffusion combustion as a reference. This reduces soot emissions.

During acceleration, the basic post-injection timing is corrected, and post-injection is performed at the post-correction post-injection timing. Correct the time, keep the best time,
A decrease in torque and an increase in soot can be prevented.

According to a second aspect of the present invention, in the fuel injection control device for a diesel engine according to the first aspect, when the diesel engine is provided with a turbocharger, the post-injection control means is configured to control the basic injection during engine acceleration. The post-injection timing is configured to be advanced.

In a diesel engine equipped with a turbocharger, the supercharging pressure increases during acceleration, the filling amount increases,
As the oxygen amount increases, the end timing of combustion by the main injection is advanced, and the optimal timing of the post-injection changes to the advance side. Therefore, advance correction of the basic post-injection timing is performed in accordance with such a change in the optimal timing, thereby preventing an increase in soot and preventing a torque reduction particularly at a high rotation or a high load. Can be.

According to a third aspect of the present invention, in the fuel injection control device for a diesel engine according to the second aspect, the post-injection control means corrects the basic post-injection timing after a predetermined period has elapsed from the start of engine acceleration. Make up.

The supercharging pressure does not increase immediately after acceleration, but has a supercharging delay due to the turbo lag. Therefore, the correction timing is shifted in accordance with the delay, thereby coping with the supercharging delay.

According to a fourth aspect of the present invention, when the after-injection control means learns and controls the after-injection timing based on a predetermined operating state parameter affected by the execution of the after-injection,
The fuel injection control device for a diesel engine according to claim 1 is employed.

In this case, in the learning control based on the parameters (torque fluctuation, oxygen concentration, etc.) which are affected by the execution of the post-injection, some erroneous learning is performed due to a change in the operating state of the engine, etc. Although the post-injection timing may slightly deviate from the optimal timing at a setting close to the limit, it is possible to prevent a decrease in torque and an increase in soot even in such a situation.

According to a fifth aspect of the present invention, there is provided a diesel engine fuel injection control device according to the first aspect, further comprising a predicting means for predicting a change in an intake air amount.
Based on the change in the intake air amount predicted by the prediction means,
By the main injection control means and the post injection control means,
The main injection amount and the post injection amount are set.

In this case, a change in the intake air amount is predicted (estimated), and the post-injection is performed at a setting close to the torque reduction limit or the soot increase limit due to wobble when the injection amount is set based on the predicted change in the intake amount. It is possible to prevent a decrease in torque and an increase in soot due to the shift of the timing from the optimal timing.

[0020]

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

FIG. 1 is an overall view of an automotive diesel engine according to an embodiment of the present invention. 1 in the figure
Is an engine body having a plurality of cylinders 2 (only one cylinder is shown in the figure), and a piston 3 is inserted into each cylinder 2 so as to be able to reciprocate. The combustion chamber 4 is partitioned. In the combustion chamber 4 of each cylinder 2, a fuel injection valve 5 is disposed substantially at the center of the upper surface, and fuel is directly injected from the fuel injection valve 5 into the combustion chamber 4 of each cylinder 2 at a predetermined timing. It has become so. Also, a water jacket (not shown) of the engine body 1
A water temperature sensor 18 for detecting the temperature of the cooling water of the engine is provided at a position facing the vehicle.

Each of the fuel injection valves 5 is connected to a common rail 6 for storing high-pressure fuel. In the common rail 6, a pressure sensor 6a for detecting an internal fuel pressure (common rail pressure) is provided. A high-pressure supply pump 8 driven by a shaft 7 is connected. This high-pressure supply pump 8 controls the fuel supply pressure,
The fuel pressure in the common rail 6 detected by the pressure sensor 6a is, for example, about 20 M during the idling operation of the engine.
The pressure is maintained at Pa or higher, and at other times, the pressure is maintained at 50 MPa or higher.

The crankshaft 7 is provided with a crank angle sensor 9 for detecting the rotation angle. The crank angle sensor 9 includes a plate to be detected provided at the end of the crankshaft 7 and an electromagnetic pickup disposed to face the outer periphery of the plate. And outputs a pulse signal by detecting the passage of the projection formed on the substrate.

A downstream portion of the intake passage 10 connected to the engine body 1 branches to a branch portion for each cylinder 2 via a surge tank (not shown), and these branch portions are connected to each other via an intake port. It is connected to the combustion chamber 4 of the cylinder 2. Further, the surge tank is provided with an intake pressure sensor 10a for detecting a pressure of intake air supplied into each cylinder 2.

The intake passage 10 includes, in order from the upstream side thereof, an air flow sensor 11 for detecting a flow rate of intake air taken into the engine body 1, a blower 12 driven by a turbine 21 described later to compress intake air, This prowa 12
Intercooler 13 that cools the air compressed by the
And an intake throttle valve 14 for changing the flow area of the intake air.

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 to be described later, a solenoid valve 16 for negative pressure control is provided. As the magnitude of the negative pressure acting on the diaphragm type actuator 15 is adjusted by
The valve opening is configured to be changed. Further, a sensor for detecting the opening degree of the intake throttle valve 14 is provided at the installation portion of the intake throttle valve 14.

The upstream portion of the exhaust passage 20 connected to the engine body 1 branches into branch portions for each of the cylinders 2, and these branch portions are connected to the combustion chambers 4 of the respective cylinders 2 via exhaust ports. Have been. The exhaust passage 20 includes, in order from the upstream side, a turbine 21 that is rotationally driven by the exhaust gas flow, a NOx reduction catalyst 22 including a NOx reduction catalyst that reduces and purifies at least NOx in the exhaust gas,
NOx in the exhaust gas passing through the NOx purification catalyst 22
A NOx sensor 19 for detecting the concentration is provided.

The NOx purification catalyst 22 comprising the NOx reduction catalyst has a cordierite carrier formed in a honeycomb structure having a large number of through holes extending in parallel with each other along the flow direction of the exhaust gas. 2 catalyst layers on the wall
It is formed in layers. Specifically, platinum (Pt)
And rhodium (Rh) are supported by a porous material such as MFI-type zeolite (ZSM5) as a support material to form the catalyst layer.

The NOx purifying catalyst 22 reduces NOx when the air-fuel mixture in the combustion chamber 4 becomes lean and the oxygen concentration in the exhaust gas is high, for example, when the oxygen concentration is 4% or more. By reacting with the agent and reducing,
It is configured to purify NOx in exhaust gas.
The NOx purifying catalyst 22 has a three-way catalytic function even when the oxygen concentration is low.

The blower 11 disposed in the intake passage 10 and the turbine 21 disposed in the exhaust passage 20
Thus, the turbocharger 25 is configured. The turbocharger 25 is a turbocharger comprising a variable geometry turbo (VGT) having a configuration in which the nozzle cross-sectional area of the exhaust passage 20 changes, and a diaphragm-type actuator 30 for changing the nozzle cross-sectional area; An electromagnetic valve 31 for controlling the negative pressure of the diaphragm type actuator 30 is provided.

An exhaust gas recirculation passage (hereinafter referred to as an EGR passage) 23 for recirculating a part of the exhaust gas to the intake passage 10 is connected to the exhaust passage 20 on the upstream side of the turbine 21. The downstream end of the EGR passage 23 is connected to the intake passage 10 on the downstream side of the intake throttle valve 14. In the EGR passage 23, a negative pressure-operated exhaust gas recirculation amount control valve (EGR valve) 24 configured to be capable of adjusting the valve opening is disposed on the downstream side. Exhaust gas recirculation means 33 is constituted by the EGR passage 23.

The EGR valve 24 is urged in the closing direction by a spring (not shown) of the valve body.
The opening degree of the EGR passage 23 is linearly adjusted by being driven in the opening direction by the diaphragm type actuator 24a. That is, a negative pressure passage 27 is connected to the diaphragm type actuator 24a, and the negative pressure passage 27 is connected to a vacuum pump (negative pressure source) 29 through a solenoid valve 28 for negative pressure control. . The solenoid valve 28 is connected to the negative pressure passage 27.
, The negative pressure for driving the EGR valve is adjusted, and the EGR valve 24 is driven to open and close. A lift sensor 26 for detecting the position of the valve body is provided at the position where the EGR valve 24 is installed.

The fuel injection valve 5, the high-pressure supply pump 8, the intake throttle valve 14, the EGR valve 24, the turbocharger 25 and the like are operated in accordance with a control signal output from an engine control unit (ECU) 35 described later. The operating state is controlled. Therefore, the ECU 35 supplies the output signal of the pressure sensor 6a, the output signal of the crank angle sensor 9, the output signal of the air flow sensor 11, and the water temperature sensor 1
8 and an output signal of an accelerator sensor 32 for detecting an operation amount of an accelerator pedal operated by a driver.

The ECU 35 includes a main injection control means 40 for controlling the injection state of the fuel injected from the fuel injection valve 5 in accordance with the operating state of the engine. A post-injection control means 41 for controlling the fuel injection valve 5 to post-inject fuel and an exhaust gas recirculation control means 39 for controlling the exhaust gas recirculation amount by driving the EGR valve 24 according to the operating state of the engine. Have.

This diesel engine can reduce the soot generated by the main injection by performing the post-injection at a predetermined time after the main injection of the fuel. In this case, an operating state in which the amount of soot discharged from the combustion chamber 4 tends to be large, for example, an operating state in which the engine load is at or above a medium load, or an operating state in which the engine rotational speed is at or above about 2000 rpm Also, in an engine in which a diesel particulate filter (DPF) is installed in the exhaust passage 20, when the purification function is low due to the low temperature condition of the DPF being 300 ° C. or less, the fuel is removed. A predetermined time set based on the end of the diffusion fuel by the main injection (when the engine speed is 1500 rpm
In the above operating state, 30 ° to 60 ° after the top dead center of the compression stroke.
By performing post-injection of the fuel at the time of (° CA), the emission of the soot can be reduced.

The main injection is a fuel injection in which an injection amount corresponding to the required output of the engine or a larger amount is injected at a predetermined time from the intake stroke to the initial stage of the expansion stroke. Since soot is generated when all or part of the fuel is diffused and burned, post-injection of the fuel is performed to reduce the soot. In this case, if the main injection of the fuel is performed at a predetermined time from the vicinity of the compression stroke dead center to the beginning of the expansion stroke, all the fuel becomes diffusion fuel except in the light load state, and in the light load state, both the premixed combustion and the diffusion combustion are performed. Done.

When the main injection of fuel is performed between the intake stroke and the top dead center of the compression stroke, premixed combustion is mainly performed, soot is not generated by this combustion, but the fuel adhering to the combustion chamber wall surface is not generated. In some cases, the fuel is ignited near the top dead center of the compression stroke to cause diffusion combustion to generate soot. In such a case, the soot can be reduced by performing the post-injection of the fuel.

The main injection of the fuel is performed at least two times at a predetermined timing between the intake stroke and the top dead center of the compression stroke and at a predetermined timing between the vicinity of the top dead center of the compression stroke and the beginning of the expansion process. This also includes the case of separately jetting.

As described above, when the fuel is post-injected within the range of, for example, 30 ° to 60 ° (CA) after the main injection of the fuel and after the top dead center of the compression stroke, the combustion At the time when the diffusion combustion that occurs after the pre-mixed combustion of the fuel mainly injected into the chamber 4 ends, the combustion by the post-injection of the fuel is performed. Therefore, the mixing of soot and oxygen present in the combustion chamber 4 at the end of the diffusion combustion is promoted, and combustion is started by post-injection of fuel in a state where ignition is easy, so that generation of soot is reduced. You can do it.

Here, the end timing of the diffusion combustion will be described in detail. This diffusion combustion is obtained based on the heat release rate. According to “Lecture on Internal Combustion Engine” (published by Yokendo Co., Ltd., author Fujio Nagao), the heat release rate is calculated by the following equation (1). expressed.

DQ / dθ = A / (K (θ) −1) × [V (θ) · (dP (θ) / dθ) + K (θ) · P (θ) · (dV (θ) / dθ) ] (1) Here, A is the work equivalent of heat, K (θ) is the specific heat ratio, V
(Θ) is the stroke volume, P (θ) is the cylinder pressure, and θ is the crank angle.

Combustion analyzer CB5 manufactured by Ono Sokki Co., Ltd.
According to the manual of No. 66, the specific heat ratio K (θ) is expressed based on the following equations (2) to (5).

K (θ) = Cp / Cv (2) Cp = ap + b (T (θ) / 100) + c (T (θ) / 100) 2 + d (100 / T (θ)) (3) Cv = Cp− (A · Ro) / M (4) T (θ) = (P (θ) · V (θ) /29.27·G (5) where Cp is constant pressure specific heat, and Cv is constant. Specific heat, Ro is a gas constant, M is the molecular weight of air, T (θ) is gas temperature, G is gas weight, and ap, b, c, and d are other constants.

From the above equations (2) to (5), the heat release rate dQ / dθ shown in the equation (1) is a function f (P (P ()) of the in-cylinder pressure P (θ) and the stroke volume V (θ). θ), V (θ)).
When the stroke volume V (θ) is represented based on the pore diameter B and the stroke S, the following equation (6) is obtained. Therefore, the heat release rate dQ / dθ is expressed by the following equation (7). As shown.

V (θ) = (π · B ² S / 8) · (1-cos θ) (6) dQ / dθ = [f (P (θ + △ θ), V (θ + △ θ))-f (P (θ), V (θ))] / △ θ (7) Therefore, if there is in-cylinder pressure data for each crank angle,
The heat release rate can be calculated based on this.
FIG. 2 shows the heat release rate thus obtained.
As shown in (a) to (c), after the heat generation rate shows a large value in the positive direction according to the combustion by the main injection of the fuel, the heat generation rate becomes 0 according to the end of the diffusion combustion. Therefore, the end point of the diffusion combustion is obtained based on the time point t1 at which the heat release rate becomes substantially zero.

In the present embodiment, normally, the ignition delay set in advance based on the operating state is set so that the combustion by the post-injection is started near the time point t1 obtained in advance as described above. Considering a time (for example, a time of about 0.4 ms to 0.7 ms), a time t at which the heat release rate becomes 0
The post-injection timing is set earlier than 1 by the amount corresponding to the ignition delay time.

The ignition delay time varies according to the engine displacement and the fuel injection pressure.
When the injection pressure is 50MPa ~ 200MPa in the engine of 0cc ~ 3000cc class, 0.4ms ~
It is about 0.7 ms. The ignition delay time is defined as the ignition delay time of the main injection performed at the top dead center of the compression stroke (0.1%).
ms to 0.3 ms) because the post-injection is performed when the in-cylinder temperature after the top dead center of the compression stroke is relatively low.

As the output timing of the injection drive signal to the fuel injection valve, the ignition delay time and the invalid time (drive delay) from the time when the injection valve opening / closing signal is output until the actual injection is started. Time) is also stored in the ECU 35.

For example, while the engine speed is controlled to 2000 rpm, the average effective pressure Pe is 0.57 Mp
When the fuel is mainly injected near the top dead center of the compression process during medium load rotation of the engine controlled at a, the heat release rate in the combustion chamber is determined by the pressure change in the cylinder corresponding to the crank angle and the volume of the cylinder. Based on the change, a graph is obtained by thermodynamically calculating, as shown in FIG. 2 (b), after a delay time Tm of about 0.1 ms has elapsed from the main injection time t0, the main injected fuel At the same time as the heat generation Y due to the premixed combustion and the heat generation K due to the diffusion combustion at substantially the same level, and at the time t1 0.6 ms later than about 35 ° (CA) after the top dead center of the compression stroke. It was confirmed that diffusion combustion was completed.

Therefore, 35 mm after the top dead center of the compression stroke
By performing the post-injection of the fuel at a time point tf of about (CA), the subsequently injected fuel can be burned at the end time point t1 of the diffusion combustion. That is, the time point tf
At time t1 after the ignition delay time (Tf) of about 0.6 ms elapses, the post-injected fuel starts burning and the heat generation amount A increases.

On the other hand, when the engine speed is 2500 r
pm and the average effective pressure Pe is 0.9
As shown in FIG. 2 (c), when the engine controlled to Mpa has a high load and high speed, the heat generation K due to diffusion combustion over a considerably long period of time is larger than the heat generation Y of the premixed combustion of the fuel. This diffusion combustion occurs 47 ° after the top dead center of the compression process.
(CA) Time point t1 which is much later than that by about 0.7 ms
In the compression stroke above the top dead center.
By performing post-injection of the fuel at a time point tf of about 7 ° (CA), the fuel injected thereafter can be burned at the end time point t1 of the diffusion combustion.

The engine speed is controlled to 1500 rpm, and the average effective pressure Pe is set to 0.3 Mpa.
When the engine is controlled at low load and low speed,
As shown in (a), it is difficult to distinguish between the premixed combustion and the diffusion combustion of the fuel based on the heat generation state, but about 0.5 ms later than about 30 ° (CA) after the top dead center of the compression stroke. At a relatively early point in time t1, the diffusion combustion is completed and the heat generation rate becomes 0, so that 30 seconds after the top dead center of the compression stroke,
By performing post-injection of the fuel at a time tf of about (CA), the fuel injected after this can be burned at the end time t1 of the diffusion combustion.

Next, the effect of reducing soot by setting the post-injection timing of the fuel with reference to the end timing of the diffusion combustion will be described. That is, when the engine speed is 150
At 0 rpm, the average effective pressure Pe is controlled to 0.3 Mpa, and at the time of low-load low-speed rotation of the engine, after the main injection of the fuel, the post-injection timing of the fuel is variously changed to reduce the soot generation amount. After conducting an experiment to measure,
As shown in FIG. 3A, after the main injection of the fuel, after the top dead center of the compression stroke, which is considered to be a time point tf advanced from the end time point t1 of the diffusion combustion by the time corresponding to the ignition delay time. It was confirmed that when the post-injection timing of the fuel was set after 30 ° (CA), the generation amount of soot was significantly reduced.

Similarly, when the engine speed is 2000 r.
pm and the average effective pressure Pe is 0.5
An experiment was conducted to measure the amount of soot generation by varying the post-injection timing of the fuel after the main injection of the fuel while the engine was rotating at medium load and controlled at 7 Mpa, and FIG.
As shown in the figure, after the main injection of the fuel, it is considered that the time is advanced to the time corresponding to the ignition delay time from the end time t1 of the diffusion combustion by the time tf.
° (CA) or later, if the fuel injection timing is set,
It was confirmed that the amount of generated soot was significantly reduced.

Further, when the engine speed is 2500 rpm
And the average effective pressure Pe is 0.9 Mp
An experiment was conducted in which the amount of soot generation was measured by changing the post-injection timing of the fuel variously after the main injection of the fuel during the high-load and high-speed rotation of the engine controlled as shown in FIG.
As shown in FIG. 7, after the main injection of fuel, 47 ° after the top dead center of the compression stroke, which is considered to be the time tf advanced from the vicinity of the end time t1 of the diffusion combustion by the time corresponding to the ignition delay time. It was confirmed that when the post-injection timing of the fuel was set after (CA), the amount of generated soot was significantly reduced. In each of the above experimental examples, the engine load was set to be constant, and the ratio of the post-injection amount to the main injection amount of the fuel was set to 20%.

Note that in FIGS. 3A to 3C,
When the post-injection timing is 0 ° (CA), data when only the main injection is executed without executing post-injection of fuel is shown.

The engine speed is controlled to 1500 rpm and the average effective pressure Pe is set to 0.3 Mpa.
When the engine is controlled at a low load and a low speed, the compression stroke is considered to be at a time point tf advanced from the vicinity of the time point t1 of the diffusion combustion by the main injection of the fuel by a time corresponding to the ignition delay time. 30 ° after the point (ATDC) (C
At the time of A), post-injection of the fuel is performed, and the ratio of the post-injection amount to the main injection amount of the fuel (P / T) is variously changed within the range of 10% to 45% to measure the soot generation amount. 4A, the soot generation amount decreased as the ratio (P / T) of the post-injection amount increased, as indicated by the solid line in FIG. On the other hand, when the fuel is post-injected at 8 ° (CA) after the top dead center (ATDC) of the compression stroke, which is considered to be before the time point tf, FIG. As shown by the broken line, the amount of generated soot increased in accordance with the increase in the ratio (P / T) of the post-injection amount.

Further, when the engine speed is 2000 rpm
And the average effective pressure Pe is 0.57M
When the engine is controlled at medium load and medium load, the compression stroke, which is considered to be a time point tf, which is advanced from the vicinity of the end time point t1 of the diffusion combustion by the main fuel injection by a time corresponding to the ignition delay time, is considered. 35 ° after dead center (ATDC)
(CA) and 20 ° C. after the compression stroke top dead center (ATDC), which is considered to be before the time tf.
At the time point A), an experiment was performed to measure the amount of soot generation by post-injecting fuel, and the engine load was controlled to 2500 rpm and the average effective pressure Pe was controlled to 0.9 Mpa. At the time of rotation, 48 ° (CA) after the top dead center (ATDC) of the compression stroke, which is considered to be after the time tf when the angle is advanced by the time corresponding to the ignition delay time from the end time t1 of the diffusion combustion by the main injection of the fuel. ) And at the compression stroke top dead center (ATDC) of 20 ° (CA), which is considered to be before the time tf, an experiment was performed to measure the amount of soot generation by post-injecting fuel. Also in this case, as shown in FIGS. 4B and 4C, the same data as in the case of the low load and low rotation was obtained.

Based on the above experimental data, the post-injection timing of the fuel is set based on the end point of the diffusion combustion generated in the combustion chamber 4 by the main injection of the fuel, and the end point of the diffusion combustion, or the vicinity thereof is determined. By igniting the post-injected fuel, the carbon is effectively mixed by the post-injection of the fuel in a state where the carbon and the oxygen existing in the combustion chamber 4 of the engine are sufficiently mixed according to the end of the diffusion combustion. It can be seen that combustion can be performed, and the amount of soot discharged from the combustion chamber 4 to the exhaust passage 20 can be reduced.

The ratio P of the post-injection amount to the main injection amount is
/ T and the amount of HC, the engine speed is 1
500 rpm and mean effective pressure Pe
At the time of low load and low rotation of the engine controlled to 0.3 Mpa, it is considered to be the time point tf advanced from the vicinity of the end time point t1 of the diffusion combustion by the main injection of the fuel by the time corresponding to the ignition delay time. After the top dead center of the compression stroke (ATD
At 30 ° (CA) of C), the fuel is post-injected, and the ratio (P / T) of the post-injection amount to the main injection amount of the fuel is 10
When an experiment was performed to measure the amount of generated HC by variously changing the amount within the range of% to 45%, as shown by the solid line in FIG. The amount of HC increased with the increase. The dashed line in FIG.
After the top dead center of the compression stroke (ATD
The data when the fuel is post-injected at 8 ° (CA) in C) is shown.

The engine speed is controlled to 2000 rpm, and the average effective pressure Pe is set to 0.57 Mp.
When the engine is controlled to medium load at medium load, the compression stroke, which is considered to be a time point tf which is advanced from the vicinity of the time point t1 of the diffusion combustion by the main injection of the fuel by a time corresponding to the ignition delay time, is considered. 35 ° after dead center (ATDC)
The post-injection of the fuel is performed at the time of (CA), and the ratio of the post-injection amount to the main injection amount of the fuel (P / T) is variously changed within a range of 10% to 45% to measure the generation amount of HC. 5B, the HC amount increased as the ratio (P / T) of the post-injection amount increased, as indicated by the solid line in FIG. 5B. The dashed line in FIG. 5B indicates a 20 ° angle after the top dead center (ATDC) of the compression stroke which is considered to be before the time point tf.
The data when the fuel is post-injected at the time of (CA) is shown.

Further, when the engine speed is 2500 rpm
And the average effective pressure Pe is 0.9 Mp
After the top dead center of the compression stroke, which is considered to be after the time tf at which the ignition is advanced by the time corresponding to the ignition delay time from the end time t1 of the diffusion combustion by the main injection of the fuel at the time of the high load and the high speed controlled by a. At 48 [deg.] (CA) at (ATDC), an experiment was performed to measure the amount of HC generated by post-injecting fuel. As shown by the solid line in FIG. The amount of HC fluctuated with an increase in the ratio (P / T), but did not increase or decrease significantly. The dashed line in FIG. 5 (c) shows data when the fuel is post-injected at a time of 20 ° (CA) after the top dead center (ATDC) of the compression stroke, which is considered to be before the time tf. .

From the experimental results shown in FIG. 5, the amount of fuel injected by the post-injection is set to 15% or more of the amount of fuel injected by the main injection.
It was confirmed that the increase in C) was remarkable.

Since the end point of the diffusion combustion varies according to the load and the number of revolutions of the engine, for example, the heat generation rate by the diffusion combustion becomes zero as shown in FIGS. 2 (a) to 2 (c). The time point t1 can be set by making a map based on various experimental data obtained in the operating state of the engine and reading out the map.

The detection signal of the temperature sensor for detecting the temperature in the combustion chamber 4, the detection signal of the combustion light sensor, or the amount of highly reactive hydrogen or hydrocarbon present in the combustion chamber 4 where the electric charge is biased. Combustion state determining means for determining the diffusion combustion state in accordance with a detection signal of a sensor for detecting the temperature of the fuel, wherein the combustion state determining means determines whether or not the temperature after the main injection of the fuel has become low below a predetermined temperature. By determining whether or not the emission of combustion light has ceased or whether or not the amount of hydrogen or hydrocarbon has sharply decreased, the end point of the diffusion combustion is determined, and the next combustion cycle is determined based on this point. May be configured to set the post-injection timing of the fuel in. Further, the differential value of the value obtained by subtracting the adiabatic expansion temperature from the in-cylinder temperature detected by the temperature sensor is obtained, and the end time of the diffusion combustion is determined by detecting the time when the differential value becomes 0 from the value of-. The determination may be made.

As described above, normally, based on the end time of the diffusion combustion determined based on each operation state of the engine, the vicinity of the end time of the diffusion combustion (±± in crank angle).
5 °), preferably by setting the start timing of the post-injection of the fuel according to the respective operating conditions, so that the post-injection combustion is started immediately after the end of the diffusion combustion. The post-injection of fuel at an optimum time corresponding to the operating state of the engine can effectively reduce the soot emission.

Regarding the relationship between the post-injection timing and the HC amount, when the post-injection timing is set to about 30 ° (CA) after the top dead center of the compression stroke when the engine is running at low load and low speed,
The production amount of HC does not increase remarkably. Similarly, at the time of medium load rotation, 35 ° (CA) after the top dead center of the compression stroke
The HC generation amount does not increase remarkably up to the vicinity, and further, at high load and high rotation, the HC generation amount increases remarkably up to around 45 ° (CA) after the top dead center of the compression stroke. It was confirmed that there was no such thing.

The relationship between the post-injection timing and the fuel efficiency is determined by changing the post-injection timing of the fuel variously when the engine is running at low load, low speed, medium load, medium speed, and high load, high speed. As a result, the fuel consumption rate deteriorates as the post-injection timing of the fuel becomes late, but at low load and low rotation, up to around 30 ° (CA) after the top dead center of the compression stroke,
The fuel efficiency does not deteriorate significantly. Similarly, during the middle load rotation, the fuel efficiency does not significantly deteriorate until around 35 ° (CA) after the top dead center of the compression stroke.
At high load and high rotation, 45 ° (C
Until A), it was confirmed that the fuel efficiency did not significantly deteriorate.

Further, regarding the relationship between the post-injection timing and the NOx amount, the post-injection timing of the fuel is variously changed during low-load low-speed rotation, medium-load medium-speed rotation, and high-load high-speed rotation.
When an experiment for measuring the amount of Ox emission was performed, it was found that at low load and low rotation, N was found around 30 ° (CA) after the top dead center of the compression stroke.
The Ox amount does not increase, the NOx amount does not increase around 35 ° (CA) after the top dead center of the compression stroke during medium load rotation, and the top dead center of the compression stroke even at high load and high rotation. It was confirmed that the NOx amount did not increase around 45 ° (CA) later.

In the diesel engine provided with the turbocharger 25 driven by the exhaust gas to supercharge the intake air, a predetermined amount of the fuel is post-injected after the main injection of the fuel as described above. As a result, the exhaust gas pressure increases, and the supercharging action of the turbocharger 25 is enhanced. As a result, the amount of fresh air introduced into the combustion chamber 4 is increased, the filling amount is increased, the torque is increased, and the oxygen concentration is increased, so that the combustion of carbon remaining in the combustion chamber 4 is promoted, The effect that the generation of soot is effectively suppressed is obtained.

When the amount of intake air increases due to the supercharging action of the turbocharger 25, the end timing of diffusion combustion of the main injected fuel tends to be earlier. Therefore, in the present embodiment, as will be described later, the post-injection timing is corrected during acceleration in accordance with a change in the end timing of diffusion combustion.

Further, in the diesel engine provided with the turbocharger 25, an exhaust gas recirculation means 33 for recirculating a part of the exhaust gas to the intake system is provided, and an exhaust recirculation control means 39 provided in the ECU 35 is provided. When the feedback control is performed so that the recirculation rate of the exhaust gas becomes the target value, the turbocharger 25
When the amount of intake air increases in response to the supercharging effect of, the amount of exhaust gas recirculated to the intake system increases accordingly,
The NOx amount led out from the combustion chamber 4 to the exhaust passage 20 is:
There is an advantage that it is more effectively reduced.

In this embodiment, as described above, the post-injection timing is set such that the combustion is started immediately after the completion of the main injection combustion, based on the end timing of the diffusion combustion by the main injection. Thus, the amount of soot emission can be effectively reduced, and the HC amount does not increase, the fuel efficiency does not deteriorate, and the NOx amount does not increase.

In the present embodiment, the total fuel injection amount including the main injection and the post-injection is set by using a map of the engine speed and the intake air amount. At this time, a change in the intake air amount is predicted ( Estimation), and performs map control based on the predicted change in the intake air amount.

The post-injection control means 41 learns and controls the post-injection timing based on predetermined operating state parameters (torque fluctuation, oxygen concentration, etc.) which are affected by the execution of post-injection.

The post-injection control means 41 sets the post-injection timing based on the end timing of the main injection combustion as described above, but the end timing of the main injection combustion varies depending on the difference in the charged amount. When the engine is in transition with a large change in intake air volume, especially during acceleration, the end timing of combustion by main injection changes, and it is not possible to follow the change. However, since there is a problem that the soot decreases and soot increases, even during acceleration with such a large change in intake air amount, soot can be effectively reduced by post-injection without inducing torque reduction. The basic post-injection timing is corrected, and the post-injection is executed at the post-correction post-injection timing.

FIG. 6 is a flowchart showing the control operation of the fuel injection in the present embodiment. In this control operation, first, in step S11, various data are input, in step S12, an intake air amount estimation process is performed, and in step S13, a target torque Tr is set.

In step S14, Aire, Tr and the engine speed Ne are used as basic settings.
The main injection amount Qm and the post-injection amount Q _F so that the predetermined air-fuel ratio is obtained.
Is set, and the main injection timing Im is set.

[0079] Then, in step S15, reads the injection timing I _F after being learning correction by the routine shown in FIGS. 7 and 8 described later, the injection timing after reading the I
_F is set as the basic post-injection timing _IFB .

[0080] Then, in step S16, the change amount [Delta] [alpha] of the accelerator opening degree, depending on whether greater than a predetermined change amount [Delta] [alpha] _0, it is determined whether the time of acceleration, [Delta] [alpha]> [Delta] [alpha]
When it is ₀ and it is during acceleration, in step S17,
Determining that only advance correction acceleration correction amount I _Facc basic post injection timing I _FB as the injection timing I _F after the final.

[0081] Further, in step S16, the change amount [Delta] [alpha] of the accelerator opening degree, the term predetermined change amount [Delta] [alpha] ₀ or less, in step S18, the injection timing I _F after it final basic post injection timing I _FB .

Then, injection is executed in step S19.

FIGS. 7 and 8 are a part of a flowchart showing a routine of the post-injection timing learning correction. In this routine, first, various data is input in step S21.

Subsequently, steps S22 and S23
And whether the engine is in a steady state,
And whether the post-injection fuel quantity Q _F exceeds the set value Q _FO is determined. Whether the engine is in a steady state rate of change [Delta] [alpha] against time of the accelerator opening degree α is determined by whether it is less than the predetermined set value [Delta] [alpha] _0.

If it is determined in step S22 that the engine is not in the steady state (NO), the process returns to step S21 because it is not in a state suitable for executing the learning correction routine. At this time, the O ₂ concentration smoothing process described later is reset. Further, even if the post-injection fuel quantity Q _F is determined to be less than the set value Q _F0 in step S23 (N
O) Since the state is not suitable for executing the learning correction routine, the process returns to step S21. Post injection fuel quantity Q
When _F is small, O ₂ concentration change in diffusion combustion end timing (decrease) is small, the detection accuracy is because low.

[0086] On the other hand, the engine is judged to be in steady state at the step S22 (YES), and if the post-injection fuel quantity Q _F is determined to be greater than the set value Q _F0 in step S23 (YES), In step S24, an O ₂ concentration smoothing process is performed. The O ₂ concentration smoothing process, all the cylinders (e.g., 4-cylinder) exhaust gas linear O ₂ sensor 17
(The value can be set between 1 and 1000 cylinders).

Next, at step S25, O _{2 for} all cylinders
It is determined whether or not the density smoothing process has been completed. In addition,
O ₂ concentration is relatively slow response, for example, if the engine is a four-cylinder engine, on the basis of the O ₂ concentration of 4 cylinders, the correction value A for the next four-cylinder (step S35~S3
8 is set (can be set between 1 and 1000 cylinders). If it is determined in step S25 that the O ₂ concentration smoothing process for all cylinders has not been completed, (N
O), returning to step S21.

On the other hand, in step S25, O _{2 for} all cylinders
If it is determined that the density smoothing process has been completed (Y
ES), in a step S26, the O ₂ concentration smoothing value is
This is the O ₂ concentration smoothed value O ₂ (n). Subsequently, in step S27, the injection timing I _F after the last correction, are after this injection timing I _F (n).

Next, at step S28, the current O_Twoconcentration
Average value O_Two(N) is the set value O₂₀Whether or not
Is determined. If not exceeded (NO), step S3
1 for O _TwoAfter the density smoothing value is reset, step S
Return to 21. On the other hand, in step S28, the current O_TwoDark
Moderate value O_Two(N) is the set value O₂₀Is determined to exceed
If yes (YES), in step S29, the current O
_TwoDensity smoothing value O_Two(N) to the previous O_TwoDensity smoothing value O
By subtracting 2 (n-1), O_TwoDensity smoothing value
Deviation ΔO_TwoIs calculated. Subsequently, in step S30,
Post-injection timing I for the latest four cylinders_F4 which is one order before (n)
Post-injection timing I for the cylinder_FBy subtracting (n-1)
And the post-injection timing deviation ΔI_FIs calculated.

Thereafter, in step S32, it is determined whether or not the O ₂ concentration smoothing value deviation ΔO ₂ exceeds 0.
Here, if the O ₂ concentration smoothing value deviation ΔO ₂ exceeds 0 (YES), that is, if the O ₂ concentration increases, it is determined in step S33 that the post-injection timing deviation ΔIF is an advanced value. Is determined. And if it is a lead angle value (YES),
In step S35, the predetermined value A is added to the present post-injection timing _IF (n), and the corrected post-injection timing _IF is calculated. In other words, since the O ₂ concentration when the post-injection timing is advanced is rising, the post injection timing I _F is only retarded (retard) A, approaches the diffusion fuel end timing.

On the other hand, if it is not the advance value (NO), that is, if it is the retard value, the predetermined value A is subtracted from the present post-injection timing _IF (n) in step S36, and the corrected post-injection timing is corrected. _IF is calculated. In other words, since the O ₂ concentration when the post-injection timing is retarded is rising, the post injection timing I _F is only advance (advance) A, approaches the diffusion combustion end timing.

On the other hand, if it is determined in step S32 that the O ₂ concentration smoothing value deviation ΔO ₂ is 0 or less (NO),
In other words, when decreasing the O ₂ concentration, whether the post-injection timing deviation [Delta] I _F at step S34 is advance value is determined. If it is the advance angle value (YES), step S3
In step 7, the predetermined value A is subtracted from the current post-injection timing _IF (n), and the corrected post-injection timing _IF is calculated. That is, since the post-injection timing is reduced O ₂ concentration when advanced, the post injection timing I _F is advanced by A, approaches the diffusion combustion end timing. In contrast, step S34
Is not an advance value (NO), that is, if it is a retard value, a predetermined value A is added to the present post-injection timing _IF (n) in step S38, and the corrected post-injection timing _IF is calculated. Is done. In other words, since the O ₂ concentration when the post-injection timing is retarded is reduced, the post injection timing I _F is retarded by A, it approaches the diffusion combustion end timing.

[0093] After the post-injection timing I _F is corrected in this way, I _F guard processing in step S39 is performed. Here, the I _F guard processing, in order to prevent excessive correction (excesses), is a process of the guard so as not to exceed a certain limit there is a post injection timing I _F. Subsequently, in step S40, in preparation for the next routine, the O ₂ concentration moderated value O ₂ (n) is the last of the O ₂ concentration Manashi value O ₂ (n-1)
And the current post-injection timing _IF (n) is moved down to the previous post-injection timing _IF (n-1). After this,
It returns to step S21.

FIG. 9 shows another embodiment of the present invention, in which the accelerator is depressed once during acceleration and the accelerator is returned once the vehicle speed is increased. 9 is a flowchart showing a fuel injection control operation in a case where the acceleration of the post-injection timing is corrected when the value exceeds.

This control operation is performed first in step T11.
Then, various data are input, and in step T12, the intake air amount A
An ire estimation process is performed, and a target torque Tr is set in step T13.

In step T14, Aire, Tr and engine speed Ne are used as basic settings.
The main injection amount Qm and the post-injection amount Q _F so that the predetermined air-fuel ratio is obtained
Is set, and the main injection timing Im is set.

In step T15, the post-injection timing I learned and corrected by the routine shown in FIGS.
Reads the _F, the injection timing I _F after reading that, is set as the basic post-injection timing I _FB.

[0098] Then, in step T16, the variation [Delta] [alpha] of the accelerator opening degree, depending on whether greater than a predetermined change amount [Delta] [alpha] _0, it is determined whether the time of acceleration, [Delta] [alpha]> [Delta] [alpha]
When it is ₀ and it is during acceleration, in step T17,
It is determined whether or not the boost Boost has exceeded a predetermined value Boost _{0. If} it is determined that Boost has exceeded the predetermined value Boost ₀ , the basic post-injection timing I _FB is determined in step T18.
The acceleration correction quantity I _Facc only advance corrected final after what the injection timing is determined as I _F.

In step T16, if the change amount Δα of the accelerator opening is equal to or smaller than the predetermined change amount Δα _0, or if the change amount Δα of the accelerator opening is larger than the predetermined change amount Δα ₀ , the process proceeds to step T17. Boost Boost
Is less than or equal to the predetermined value Boost ₀ , Step T1
The process proceeds to 9, and the injection timing I _F after it is final the basic post-injection timing I _FB.

Then, injection is executed in step S19.

[0101]

As is apparent from the above description, according to the present invention, the fuel injection valve arranged to inject fuel directly into the combustion chamber allows the fuel to be injected at a predetermined time near the top dead center of the compression stroke. In a diesel engine that performs main injection and performs post-injection so that combustion is started immediately after the main injection is completed, with reference to the end time of combustion by the main injection, when the acceleration of the intake air amount is large, In this case, the optimal timing of the post-injection can be maintained to prevent a decrease in torque and an increase in soot.

[Brief description of the drawings]

FIG. 1 is an overall view of a diesel engine according to an embodiment.

FIG. 2 is a time chart showing a change in a heat release rate in a combustion chamber.

FIG. 3 is a graph showing a relationship between a post-injection timing and a soot generation amount.

FIG. 4 is a graph showing a relationship between a ratio of a post-injection amount to a main injection amount and a soot generation amount.

FIG. 5 is a graph showing a relationship between a ratio of a post-injection amount to a main injection amount and an HC amount.

FIG. 6 is a flowchart illustrating a fuel injection control operation according to the embodiment.

FIG. 7 is a part of a flowchart showing a routine of a post-injection timing learning correction.

FIG. 8 is a part of a flowchart showing a routine of a post-injection timing learning correction.

FIG. 9 is a flowchart showing a control operation of fuel injection according to another example of the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine main body 5 Fuel injection valve 20 Exhaust passage 22 NOx purification catalyst 35 Engine control unit (ECU) 40 Main injection control means 41 Post injection control means

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 45/00 340 F02D 45/00 340D 366 366E (72) Inventor Tomoaki Saito 3 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture No. 1 Mazda Co., Ltd. (72) Inventor Akihiro Kobayashi 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Pref. 3G301 HA02 HA11 JA01 JA24 KA12 LB11 MA11 MA19 MA23 MA27 ND02 ND25 PA01Z PE01Z PE03Z PE04Z PE08Z PF03Z

Claims (5)

[Claims] 1. A main injection control means for executing a main injection of fuel at a predetermined time until near a top dead center of a compression stroke by a fuel injection valve arranged to directly inject fuel into a combustion chamber; After the main injection, a predetermined time in the first half of the expansion stroke is set as a basic post-injection timing, based on the end timing of the combustion by the fuel injection valve, so that the combustion is started immediately after the completion of the main injection. A post-injection control device for performing post-injection, the fuel injection control device for a diesel engine comprising: a post-injection control device that corrects the basic post-injection timing during engine acceleration, A fuel injection control device for a diesel engine, wherein a post-injection is executed at an injection timing. 2. The diesel engine according to claim 1, wherein the diesel engine includes a turbocharger, and the post-injection control means is configured to advance the basic post-injection timing during engine acceleration. Diesel engine fuel injection control device. 3. The fuel injection control of a diesel engine according to claim 2, wherein the post-injection control means is configured to execute the correction of the basic post-injection timing after a lapse of a predetermined period from the start of engine acceleration. apparatus. 4. The post-injection control means is configured to perform learning control of the basic post-injection timing based on a predetermined operating state parameter that is affected by execution of post-injection. A fuel injection control device for a diesel engine as described in the above. And a predicting means for predicting a change in the intake air amount, wherein the main injection control means and the post-injection control means use the main injection amount and the post-injection control means based on the change in the intake air amount predicted by the predicting means. The fuel injection control device for a diesel engine according to claim 1, wherein an injection amount is set.