JP2002168141A - Fuel injection control device of diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel injection control device of a diesel engine capable of reducing a quantity of soot in exhaust gas while suppressing degradation of fuel economy. SOLUTION: The fuel injection control device of the diesel engine includes a fuel injection valve 5 for directly injecting fuel in a combustion chamber 4 of the diesel engine, a main injection control means 36 for controlling main injection injecting fuel from the fuel injection valve at a predetermined time in a periphery of a dead center in a compression stroke, and a post-injection control means 36 for controlling post-injection injecting additional fuel from the fuel injection valve after the main injection. The post-injection control means sets an injection time of the post-injection by referring to a time when a heat generation rate by the main injection is not more than a predetermined value, and in an operating range where the soot generated in combustion by the main injection is more than a predetermined quantity, the post-injection control means increases fuel injection by the post-injection as compared with in the operating range where the quantity of soot is less than the predetermined quantity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection control device for a diesel engine, and more particularly, to a post-injection control means for controlling post-injection in which additional fuel is injected after fuel injection by main injection. A fuel injection control device for a diesel engine.

[0002]

2. Description of the Related Art For the purpose of efficiently purifying NOx contained in exhaust gas of a diesel engine, additional fuel is burned at a predetermined timing following normal fuel injection (main injection) into a combustion chamber. 2. Description of the Related Art A fuel injection control device for a diesel engine that performs post-injection for indoor injection is known (Japanese Patent Application Laid-Open No. 2000-170585).

In the prior application (Japanese Patent Application No. 2000-321699) of the present applicant, which does not correspond to the prior art, the injection timing of post-injection is set based on the end point of diffusion combustion by main injection. There is a statement that soot emission can be effectively reduced.

[0004]

The present invention relates to such a post-injection, and is capable of reducing the amount of soot in exhaust gas while suppressing deterioration of fuel efficiency. It is an object to provide an injection control device.

[0005]

According to the present invention, there is provided a fuel injection valve for directly injecting fuel into a combustion chamber of a diesel engine, the fuel injection valve being provided at a predetermined time near a compression stroke top dead center. Main injection control means for controlling main injection in which fuel is injected from a fuel injection valve, and after the main injection,
Post-injection control means for controlling post-injection in which additional fuel is injected from the fuel injection valve, the post-injection control means based on when the rate of heat generation by the main injection has become a predetermined value or less. In addition to setting the injection timing of the post-injection, the fuel injection by the post-injection is more in the operation region where the soot generated by the combustion by the main injection is equal to or more than a predetermined amount than in the operation region in which the amount of the soot is less than the predetermined amount. And a fuel injection control device for a diesel engine, characterized in that

Here, "increase the fuel injection" means to increase the absolute amount of the post-injection fuel injection or to increase the ratio of the post-injection amount to the main injection amount.

According to such a configuration, in an operation state in which the generation of soot is equal to or more than the predetermined amount, the generation of soot can be suppressed by increasing the post-injection, thereby suppressing the generation and discharge of soot. Further, when the operation state in which the generation of soot is less than the predetermined amount is performed, the post-injection is not increased, so that the fuel efficiency is improved.

In a preferred aspect of the present invention, the post-injection control means increases the fuel injection by the post-injection when the engine is running at a high speed or a high load.

According to such a configuration, in the high rotation or high load region where the generation of soot is increased, the post-injection fuel injection is increased, and the generation of soot is effectively suppressed.

Another preferred embodiment of the present invention is an EG for controlling an EGR means for recirculating a part of exhaust gas to intake air.
The fuel cell system further includes R control means for controlling the EGR amount to reduce the air-fuel ratio (A / F) to a predetermined value or less while the post-injection control means increases the fuel injection.

To reduce NOx in exhaust gas, EGR
It is desirable to increase the rate (the ratio of the EGR amount to the total intake air amount). However, when the EGR rate is increased in this manner, the air-fuel ratio (A / F) becomes rich, and the amount of soot generation increases. Therefore, particularly in an operation region where soot generation increases, the EGR amount is reduced. Control that would greatly increase could not be performed. However, in the above-described configuration, since the generation of soot is suppressed while the fuel injection by the post-injection control unit is increasing, the EGR amount can be controlled to be increased, and both the suppression of soot generation and the reduction of NOx can be achieved.

Another preferred embodiment of the present invention is an EGR control means for controlling an EGR means for recirculating a part of the exhaust gas to the intake air. EGR control means for performing EGR control so that the degree of decrease in the air-fuel ratio with respect to a change in the operating state of the engine toward the load side is smaller than the degree of decrease in the air-fuel ratio in a region where the fuel injection is not increased by the post-injection. Is further provided.

In order to suppress the generation of soot, E is changed according to a change in the operating state to a high rotation or a high load side where soot is easily generated.
The reduction control of the GR rate is usually performed. In this control, even if the operation state shifts to the high rotation or high load side, it is possible to suppress an increase in the generation of soot,
As the rate is reduced, NOx will increase. However, in the above-described configuration, during the increase of the fuel injection by the post-injection control means, the generation of soot is suppressed by the increase of the post-injection, so that the EGR in the state where the fuel injection by the post-injection is not increased is performed. Since the EGR rate can be reduced to a degree smaller than the degree of the rate reduction, that is, the EGR amount can be relatively increased, the reduction of NOx can be realized. still,
In this case, the fuel injection amount increases as the outside of the driving field changes to a high rotation or a high load side, so that the A / F decreases with the change in the operation state. Therefore, A / F
From the point of view, with such a change in driving conditions,
EGR control should be performed so that the degree of decrease in A / F during fuel increase due to post-injection is smaller than the degree of A / F decrease in a region where such increase is not performed. Thereby, both suppression of soot generation and reduction of NOx are compatible.

Another preferred embodiment of the present invention is a pilot injection control means for controlling a pilot injection in which fuel is injected from the fuel injection valve in order to perform premix combustion before a predetermined interval before the main injection. In addition, the fuel cell system further includes a pilot injection control means for controlling the interval to be smaller than when no post-injection is performed during the fuel injection increase by the post-injection control means.

According to such a configuration, since the generation of soot is suppressed while the fuel injection is being increased by the post-injection control means, noise (knock noise) is reduced by shortening the interval between the main injection and the pilot injection. Thus, both suppression of soot generation and noise reduction are achieved.

Another preferred embodiment of the present invention is a pilot injection control means for controlling pilot injection in which fuel is injected from the fuel injection valve in order to perform premix combustion before a predetermined interval before the main injection. During the increase of the fuel injection by the post-injection control means, the degree of the increase in the interval with respect to the change in the operating state of the engine toward the high rotation or the high load side is determined by the increase in the fuel injection by the post-injection. There is further provided pilot injection control means for performing control so as to be smaller than the degree of increase in the absence state.

The interval between the pilot injection and the main injection for suppressing the generation of noise is reduced in accordance with a change in the operation state to a high rotation speed or a high load side where soot is easily generated in order to suppress an increase in soot. Let me be. In such a control, as the operating state changes to a high rotation or a high load side, the generation of soot can be suppressed, but the noise increases. However, in the configuration as described above, during the increase of the fuel injection by the post-injection control means, the generation of soot is suppressed by the increase of the post-injection. By controlling the degree of increase of the interval so as to be smaller than the degree of increase in a state where the fuel injection by the post-injection is not performed, both the suppression of soot generation and the reduction of noise are achieved.

In a preferred aspect of the present invention, the post-injection control means suppresses the fuel injection by the post-injection in a region where the exhaust gas temperature is equal to or higher than a predetermined temperature.

In a region where the exhaust gas temperature is equal to or higher than a predetermined temperature, for example, in a substantially full load or full load region, the exhaust system components are easily thermally degraded by the high temperature exhaust gas.
Further increase in exhaust gas temperature is prevented to avoid thermal damage to exhaust system components.

According to another aspect of the present invention, a fuel injection valve for directly injecting fuel into a combustion chamber of a diesel engine, and fuel is injected from the fuel injection valve at a predetermined time near a top dead center of a compression stroke. Main injection control means for controlling main injection, and post-injection control means for controlling post-injection in which additional fuel is injected from the fuel injection valve after the main injection, wherein the post-injection control means comprises: The injection timing of the post-injection is set on the basis of the time when the heat generation rate by the main injection becomes equal to or less than a predetermined value, and the post-injection is performed in accordance with a change in the operating state of the engine in the direction of high rotation or high load. A fuel injection control device for a diesel engine is provided.

According to such a configuration, the post-injection is increased and the generation of soot is suppressed in accordance with the shift of the operating state of the engine to a high rotation speed or a high load side where the generation of soot increases. In addition, generation and discharge of soot are effectively suppressed. Further, in the region where the generation of soot is small, the post-injection is small, so that the fuel efficiency is improved.

[0022]

Next, preferred embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram illustrating a configuration of a fuel injection control device for a diesel engine according to an embodiment of the present invention.

As shown in FIG. 1, the fuel injection control device includes a diesel engine 1 mounted on a vehicle. The diesel engine 1 has four cylinders 2, 2,.
A piston 3 is disposed in a cylinder constituting each cylinder 2 so as to be able to reciprocate, and a combustion chamber 4 is formed by the piston 3 and the inner peripheral wall of the cylinder. Have been. At substantially the center of the upper surface of the combustion chamber 4, a fuel injection valve (injector) 5 is disposed such that the injection hole at the tip thereof faces the combustion chamber 4. The fuel injection valve 5 is configured to inject fuel directly into the cylinder, that is, into the combustion chamber 4 at a predetermined timing. Further, a water temperature sensor 18 for measuring the temperature of the cooling water (engine water temperature) is provided so as to face a water jacket of the engine 1 (not shown).

Each fuel injection valve 5 is connected to a common common rail (accumulation chamber) 6 for storing high-pressure fuel. High pressure fuel is supplied to the common rail 6 by an injection pump driven after the engine is started by the engine or the motor,
A pressure sensor 6a for detecting an internal fuel pressure (common rail pressure) is arranged, and a high-pressure supply pump 8 driven by a crankshaft 7 is connected. The high-pressure supply pump 8 reduces the fuel pressure in the common rail 6 detected by the pressure sensor 6a to, for example, about 20 MPa during idling operation.
a, and at other times, it is kept at 50 MPa or more.

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 arranged so as to correspond to the outer periphery of the plate. It is configured to generate a pulse signal in response to the passage of the protrusions formed at predetermined angles.

The engine 1 has an intake passage 10 for introducing the intake air filtered by an air cleaner (not shown) into the combustion chamber 4. The downstream end of the intake passage 10 branches via a surge tank (not shown), and is connected to the combustion chamber 4 of each cylinder 2 via an intake port. Further, an intake pressure sensor 10a for detecting a supply pressure supplied to each cylinder 2 in the surge tank is provided.

The intake passage 10 has an air flow sensor 11 for detecting a flow rate of intake air taken into the engine 1 in order from an upstream side to a downstream side, and a turbine 21 described later.
, Which cools the air compressed by the blower 12, and an intake throttle valve 14 which narrows the cross-sectional area of the intake passage 10
Are provided.

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. Is adjusted by the negative pressure control solenoid valve 16 to control the opening degree of the valve. Further, a sensor (not shown) for detecting the opening degree of the intake throttle valve 14 is also provided.

An exhaust passage 20 for discharging exhaust gas from the combustion chamber 4 of each cylinder 2 is connected to the engine 1.
The upstream end of the exhaust passage 20 branches and is connected to the combustion chamber 4 of each cylinder 2 by an exhaust port (not shown). The exhaust passage 20 includes, in order from the upstream side to the downstream side, an O2 sensor (not shown) whose output changes suddenly when the air-fuel ratio of the exhaust gas is substantially the stoichiometric air-fuel ratio, and a turbine rotated by the exhaust flow. 21 and at least NO in the exhaust
A NOx reduction catalyst 22 that reduces and purifies x, and a NOx sensor 19 that detects the concentration of NOx in exhaust gas that has passed through the NOx reduction catalyst 22 are arranged. The NOx purification catalyst that is the NOx reduction catalyst 22 includes a cordierite carrier formed in a honeycomb structure having a large number of through holes extending parallel to each other along the flow direction of the exhaust gas, and a catalyst layer is formed on each of the through hole wall surfaces. It is formed in two layers. Specifically, the catalyst layer is formed by supporting platinum (Pt) and rhodium (Rh) as support materials such as MFI-type zeolite (ZSM5) which is a porous material.

The NOx purifying catalyst 22 converts NOx into a reducing agent when the mixture in the combustion substance 4 is in a lean state and the oxygen concentration in the exhaust gas is high, for example, when the oxygen concentration is 4% or more. And reducing it,
It is configured to purify NOx in exhaust gas.
The NOx purification catalyst 22 functions as a three-way catalyst when the oxygen concentration is low.

The exhaust passage 20 is located at a position upstream of the turbine 21 and is branched and connected to an upstream end of an exhaust gas recirculation passage (EGR passage) 23 for recirculating a part of exhaust gas to the intake side.
The downstream end of the EGR passage 23 is connected to the intake passage 10 at a position downstream of the intake throttle valve 14. EG
At a position near the downstream side of the R passage 23, a negative-pressure operated exhaust gas recirculation amount adjusting valve (EGR valve) 24, whose opening degree can be adjusted, is provided. In this embodiment, a part of the exhaust gas in the exhaust passage 20 is configured to be recirculated to the exhaust passage 10 while the flow rate is adjusted by the EGR valve 24.
The EGR passage 23 constitutes an exhaust gas recirculation (EGR) means 33.

The EGR valve 24 is actuated in the opening direction by a diaphragm 24a while a valve body (not shown) is urged in the closing direction by a spring.
Is linearly adjusted. That is, a negative pressure passage 27 is connected to the diaphragm 24a, and the negative pressure passage 27 is connected to a vacuum pump (negative pressure source) 29 via a negative pressure control electromagnetic valve 28. Is connected to or shuts off the negative pressure passage 27 by a control signal from the ECU 35 described later, whereby the negative pressure for driving the EGR valve is adjusted, and the EGR valve 24 is opened and closed. Further, a lift sensor 26 for detecting the position of the valve body of the EGR valve 24 is provided.

Each fuel injection valve 5, high-pressure supply pump 8, intake throttle valve 14, EGR valve 24, turbocharger 25 and the like are provided with a control unit (Engine Control Uni
t: ECU) 35 is configured to operate in response to a control signal.

On the other hand, the ECU 35 outputs an output signal of the pressure sensor 6a, an output signal of the crank angle sensor 9, an output signal of the air flow sensor 11, an output signal of the water temperature sensor 18,
An output signal of the lift sensor 26 of the GR valve 24, an output signal from an accelerator opening sensor 32 for detecting an operation amount (accelerator opening) of an accelerator pedal (not shown) by a driver of the vehicle, and the like are input. I have.

In this embodiment, the ECU 35 controls the operation of the engine, and controls the main injection in which fuel is injected from the fuel injection valve 5 at a predetermined time near the top dead center of the compression stroke. When the heat generation rate due to the main injection becomes equal to or less than a predetermined value, that is, when the heat generation rate due to the main injection becomes substantially 0 or less, the fuel is injected from the fuel injection valve 5. Post-injection control for controlling post-injection at the timing when the additional fuel starts burning,
Injection control means 3 for performing pilot injection control or the like for controlling pilot injection in which fuel is injected from the fuel injection valve 5 in order to perform premixed combustion by a predetermined interval before main injection.
6 and E for controlling the EGR valve 24 to control the exhaust gas recirculation amount.
GR control means 37 is provided. That is, the injection control means 36 of the present embodiment has functions of a main injection control means, a post-injection control means, and a pilot injection control means.

Next, the fuel injection control executed by the ECU 35 will be described with reference to the flowchart of FIG.

First, in step S1 after the start, data such as a crank angle signal from the crank angle sensor 9, an accelerator opening from the accelerator opening sensor 32, and an intake air amount from the air flow sensor 11 are input. Next, in step S2, the target torque Tr calculated from the accelerator opening is set.
Read from the basic injection quantity map which is set based on the engine speed Ne obtained from the crank angle signal, the read basic fuel injection amount Q _b, a map previously set the injection timing I _b .

Next, at step S3, the injection quantity Q of the post-injection
_fu and the injection timing _Ifu are set. Injection amount Q of post-injection
_{The fu} and the injection timing _Ifu are set by reading an amount corresponding to the target torque Tr and the engine speed Ne from a preset map.

In this map, the post-injection injection amount Q _fu
Increases the fuel injection (amount or rate) by the post-injection when the amount of soot is less than the predetermined amount when the soot generated by the combustion by the main injection is equal to or more than a predetermined amount,
It is set to suppress the generation of soot. Here, the fuel injection amount by the post-injection indicates the absolute amount of fuel injected by the post-injection, and the fuel injection rate by the post-injection indicates a ratio of the injection amount of the post-injection to the injection amount of the main injection.

In the present embodiment, the post-injection amount Q _fu is _calculated as shown in FIG.
As shown in the map, low-speed, low-load region,
It is set so as to gradually increase from a peripheral region such as a full load region toward a high rotation region (for example, 2500 rpm) and a high load region (Z region) indicated by oblique lines. Therefore, when the operating state of the engine is high rotation and high load,
The fuel injection amount _Qfu by the post-injection is increased as compared with other operation states.

In this embodiment, the ratio of the injection amount of the post-injection to the injection amount of the main injection is 10 to 2 at low rotation and low load.
0%, and is increased to 20 to 50% or more at high rotation and high load.

As a modified example, the fuel injection amount Q by the post-injection is also increased in a region where the amount of soot is increased other than at the time of high rotation and high load, for example, at the time of A / F rich, at the time of pilot injection, and at the time of main injection retard. _fu may be increased compared to other operating conditions.

Further, the post-injection may not be executed at the time of low rotation and low load such as idling, and the post-injection may be executed in a region other than at the time of low rotation and low load.

The injection timing _Ifu of the post-injection is set based on the time when the heat generation rate by the main injection is equal to or less than a predetermined value (approximately 0), that is, when diffusion combustion by the main injection is completed. The ignition delay of the post-injection is set so that the combustion of the fuel by the post-injection is started when the rate becomes approximately 0 or less (0.4 or less).
０．７0.7 ms) and the invalid injection time are set on the map.

With this setting, the post-injection is performed when the heat release rate becomes substantially equal to or less than 0, that is, when the diffusion combustion that occurs after the pre-mixed combustion of the main injection fuel in the combustion chamber ends. Will start burning the fuel. For this reason, in the state where the mixing of the soot and oxygen present in the combustion chamber 4 is promoted, the combustion by the post-injection starts, and it is considered that the generation of the soot is reduced.

Further, around the time when the heat generation rate by the main injection becomes substantially 0 or less (in terms of crank angle, preferably ± 10
°, more preferably within ± 5 °), the post-injection injection timing may be set such that combustion by the post-injection starts.

Here, the heat release rate dQ / dθ is calculated according to “Lecture on Internal Combustion Engine” (Fujio Nagao, Yokendo Co., Ltd.)
It is represented as the following equation (1).

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 in-cylinder pressure, and θ is the crank angle.

A 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 the gas temperature, G is the 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 determined by the in-cylinder pressure P ₍ θ ₎ and the stroke volume V
_(Θ) function with _{f (P (θ), V} (θ)) become. When the stroke volume V ₍ θ ₎ is represented based on the bore 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 ₊ Δθ ₎ , V ₍ θ ₊ Δθ ₎ ) − f (P ₍ θ ₎ , V ₍ θ ₎ )] / Δθ (7) Accordingly, if there is in-cylinder pressure data for each crank angle, the heat generation rate can be calculated based on the data.
In the present embodiment, from the heat release rate thus obtained,
Calculates the end time of diffusion combustion (i.e. when the heat generation rate is substantially 0 or less), the injection timing of the post injection time point lag only before the ignition delay time of the post-injection from this end was I _fu Using a map.

The end time of the diffusion combustion varies according to the operating condition of the engine. The end time of the diffusion combustion tends to be delayed as the engine load and the number of revolutions increase. For example, if the engine speed is 2000 rpm and the average effective pressure P
At the time of middle rotation and middle load where e is 0.57 Mpa, as shown in FIG. 4B which is a graph of the result calculated by the above-described method, the fuel that is mainly injected near the compression top dead center of the piston is The heat generation Y by diffusion combustion is substantially the same as the heat generation Y by premix combustion, and the ignition delay τ _f2 (about 0.5 ms) from about 35 ° (CA) after the compression top dead center.
Diffusion combustion ends at time t2, which is delayed only by the delay.

The engine speed is 2500 rpm,
At high rotation and high load where the average effective pressure Pe is 0.9 Mpa, as shown in FIG. 4C, heat generation K due to diffusion combustion is generated for a considerably long time as compared with heat generation Y due to premix combustion, and compression is performed. Time point t3, which is much later than ignition timing τ _f3 (about 0.7 ms) after about 48 ° (CA) after top dead center
It can be seen that diffusion combustion ends.

Further, when the engine speed is 1500 rpm,
At low rotation and low load where the average effective pressure Pe is 0.3 Mpa, as shown in FIG. 4A, it is difficult to distinguish between fuel premixed combustion and diffusion combustion by heat generation. Ignition delay τ _f1 from about 30 ° (CA) after dead center
It can be seen that diffusion combustion ends at a relatively early point in time t1 (about 0.6 ms).

Therefore, in the vicinity of the end of the diffusion combustion, that is, 25 to 35 ° (CA) after the compression top dead center at low rotation and low load, and 33 to 40 after compression top dead center at medium rotation and middle load. It is preferable to set the injection timing so that the post-injection is executed at 45 ° to 48 ° (CA) after the compression top dead center at high rotation and high load.

FIG. 5 is a graph showing the relationship between the post-injection timing and the soot generation amount at each of the low rotation low load, the medium rotation medium load, and the high rotation high load.
It is clear from (a), (b) and (c).

In the present embodiment, as shown by the needle lift amount in FIG.
° (CA) at medium load during rotation
° (CA), at high rotation and high load, 48
° (CA), the post-injection timing is set so that the post-injection is performed, and the diffusion combustion ends in each operating state.
Starting combustion by post-injection at 1, t2, and t3,
The heat generation shown by the dotted line in FIG. 4 is generated.

In other operating states, the injection timing of the post-injection is set on the map so that the combustion by the post-injection starts when the diffusion combustion ends.

FIG. 6 shows the post-injection amount (the ratio to the main injection).
It is a graph which shows the relationship between a soot generation amount. In a low-rotation low-load state with an engine speed of 1500 rpm and an average effective pressure Pe of 0.3 MPa, 30 ° after compression top dead center (CA) so that combustion by post-injection starts at time t1 when diffusion fuel by main injection of fuel ends. )), An experiment was performed to measure the amount of soot generation by changing the ratio (P / T) of the post-injection amount to the main injection amount in the range of 10 to 45%. As shown by the solid line, the ratio of post-injection (P /
The amount of soot generation decreased as T) increased. On the other hand, when the post-injection is performed at 8 ° after the compression top dead center so that the combustion by the post-injection starts before the end of the diffusion combustion,
As shown by the dotted line in FIG. 6B, the soot generation amount increased with an increase in the ratio (P / T) of the post-injection amount.

Further, under the condition that the engine speed is 2000 rpm, the average effective pressure Pe is 0.57 MPa,
35 ° after compression top dead center (C) so that combustion by post-injection starts at time t2 when diffusion fuel by main injection of fuel ends.
FIG. 6 shows a similar experiment in which post-injection was performed in A).
As shown by the solid line in (b), the ratio of post-injection (P /
When the post-injection is performed at 20 ° after the compression top dead center so that the amount of soot generation decreases in accordance with the increase in T) and the post-injection combustion starts before the end of the diffusion combustion, FIG. As shown by the dotted line in b), no significant change in the soot generation amount was observed even when the post injection amount ratio (P / T) increased.

Further, the engine speed is 2500 rpm,
In a high rotation and high load state with an average effective pressure Pe of 0.9 MPa,
48 ° after compression top dead center (C) so that combustion by post-injection starts at time t3 when diffusion fuel by main injection of fuel ends.
FIG. 6 shows a similar experiment in which post-injection was performed in A).
As shown by the solid line in (c), the ratio of post-injection (P /
When the post-injection is performed at 20 ° after the compression top dead center so that the amount of soot generation decreases in accordance with the increase in T) and the post-injection combustion starts before the end of the diffusion combustion, FIG. As shown by the dotted line in c), no significant change in the soot generation amount was observed even when the post injection amount ratio (P / T) increased.

From this, when the post-injection is performed so that the post-injection combustion starts at the time when the diffused fuel by the main injection of the fuel ends, the fuel injection amount _Qfu by the post-injection is increased, so that the soot is reduced. It can be seen that the generation amount is reduced.

FIG. 7 is a graph showing the relationship between the ratio (P / T) of the post-injection amount to the main injection amount and the fuel efficiency. FIG.
(A), (b), and (c) correspond to FIGS.
(B), low rotation low load, medium rotation medium load similar to (c),
6 is a graph of the fuel efficiency measured at a high rotational speed and high load while changing the ratio (P / T) of the post-injection amount to the main injection amount in a range of 10 to 45%. As in FIG. The results of the post-injection performed at 30 °, 35 °, and 48 ° (CA) after the compression top dead center, respectively, so that the combustion by the post-injection starts at time t1 when the diffusion fuel by the main injection of the fuel ends. The dotted lines indicate that the post-injection combustion starts at the point before the end of the diffusion combustion, so that the post-compression combustion starts at 8 ° after the compression top dead center, respectively.
The results of post-injection at 20 ° and 20 ° are shown.

As shown by the solid lines in FIGS. 7 (a), 7 (b) and 7 (c), the post-injection is started so that the combustion by the post-injection starts when the diffusion fuel by the main injection of the fuel ends. If so, the fuel efficiency will deteriorate as the ratio of post-injection to main injection increases. However, in the above-described embodiment, the ratio (P / T) of the post-injection amount to the main injection amount is set to about 20% or less at the time of low rotation and low load and medium rotation and middle load. Have been.

[0066] Then, the program proceeds to step S4, and the injection amount Q _p of pilot injection, and the injection time I _p, is set. In the present embodiment, the injection amount Q _p of pilot injection, for example,
Is a fixed value determined in the range of 30 to 50% of the main injection amount Q _b of the low load. On the other hand, the injection timing _Ip is derived from a predetermined map based on the target torque Tr and the engine speed Ne.

FIG. 8 is a diagram showing a relationship between the map (b) for setting the injection timing _Ip of the pilot injection and the map (a) for setting the injection amount of the post-injection according to the present embodiment. In this drawing, the injection timing _Ip of the pilot injection is indicated by the difference between the pilot injection and the main injection (advance angle: crank angle). As shown by the solid line in FIG. 8B, the injection timing _Ip of the pilot injection according to the present embodiment is different from the injection timing (dotted line) of the pilot injection when the post-injection is not performed. The interval is set to be short.

In the pilot injection, a predetermined amount of fuel is injected prior to the main injection to cause premixed combustion in the combustion chamber, thereby reducing the noise (explosion sound) during combustion by the main injection. It is known that the effect of reducing noise is greater when the injection timing is closer to the injection timing of the main injection. However, when the pilot injection approaches the main injection, the generation of soot tends to increase.In particular, in a region where the generation of soot is remarkable, for example, in a high-speed high-load region, priority is given to suppressing the generation of soot. The injection timing of the injection had to be separated from the injection timing of the main injection.

On the other hand, in this embodiment, since the generation of soot is suppressed by the post-injection, the timing of the pilot injection is set closer to the main injection than in the case where the post-injection is not performed in almost all operation regions. Thus, noise can be reduced, and both generation of soot and noise can be suppressed.

In addition, an operation region (Z region) of high rotation and high load.
In such a case, the setting may be made such that the injection timing of the pilot injection is made later as in the modified example shown by the one-dot chain line and the two-dot chain line in FIG. Accordingly, during the post-injection injection increase (Z region), the operation state is such that the degree of delay of the injection timing of the pilot injection according to the change in the operation state to the high rotation or the high load side is relatively similar. Control is performed so that the fuel injection by the post-injection around the Z region becomes smaller than the degree of delay in a state where the increase is not performed. The reason why the injection timing fluctuates continuously instead of in a stepwise manner in a transition region to a high rotation and high load operation region (Z region) is to avoid a rapid change in sound quality.

In this region, the injection amount (rate) of the post-injection is maximized and the generation of soot is suppressed most. Therefore, even in the region where the generation of soot is large (Z region), the generation of soot is not conventionally performed. The injection timing of the pilot injection, which had to be separated from the main injection in order to give priority to the suppression, is reduced in the degree of separation from the main injection, thereby enabling aggressive noise reduction.

In step S5, the exhaust gas temperature _Tex is input. In the present embodiment, based on the signal from the water temperature sensor 18, the exhaust gas temperature is estimated and the value is input. However, the exhaust gas temperature may be obtained and input by another method such as directly measuring the exhaust gas temperature.

Next, in step S6, the input exhaust gas
Gas temperature T_exIs a predetermined reference temperature T _ex0Higher state
It is determined whether or not the predetermined time has elapsed. Y in step S6
ES, ie exhaust gas temperature T_exIs a predetermined reference temperature T_ex0Yo
Is determined to have continued for a predetermined time,
Proceeding to step S7, the post-injection injection Q_fuSet to 0
To step S8. This is because the exhaust gas temperature is
If the state higher than the value continues for a predetermined time, the exhaust
If the exhaust gas temperature is high due to thermal damage to
In a high-load area that continues for a fixed time, etc.
This is to prevent a rise in exhaust gas temperature. on the other hand,
NO in step S6, that is, the exhaust gas temperature T_exIs the specified group
Quasi-temperature T_ex0Below or the exhaust gas temperature is above the specified value
When it is determined that the high state has not continued for a predetermined time
, The process proceeds to step S8.

In step S8, steps S2, S3,
The fuel injection valve 5 is operated according to the amount and timing set in S4 and S7, and the pilot injection, the main injection, and the post-injection to the combustion chamber are executed.

Next, the exhaust gas recirculation control means 37 of the ECU 35
Will be described with reference to the flowchart of FIG.

First, in step S10, data such as the engine speed and the accelerator opening are input.
Proceeds to 1, based on the accelerator opening and engine speed, for example, from a preset map as shown in FIG. 10, to set a basic target fresh air amount Air _b corresponding to the operating condition of the engine . As a result, the EGR amount (valve opening) is set to decrease as the rotation speed and the load become higher. In the example of FIG. 10, in the idle region shown in oblique lines, is set to be many basic target fresh air amount Air _b than when the load in the engine.
Next, at step 12, a fresh air amount correction value Air _c is set.

[0077] Figure 11 is a fresh air correction amount Air _c setting map (b), shows the relationship between the map of the operating state of the engine (a). Fresh air correction amount Air _c of the present embodiment shown by a solid line in FIG. 11 (b), in the Z region is an operating state of the high-speed and high-load, the result of the EGR control A / F
Is set to be equal to or less than a predetermined value as indicated by a solid line in FIG. Further, the fresh air correction amount Ai of the modified example of the present embodiment shown by a dashed line in FIG.
r _c is also in the Z region is an operating state of the high-speed and high-load, EG
The A / F value as a result of performing the R control is set so as to be equal to or less than a predetermined value, as indicated by a dashed line in FIG.

In FIG. 10, although the EGR amount is set to decrease as the rotation speed and the load become higher, the A / F decreases as the rotation speed and the load become higher as shown in FIG. This is because the total fuel injection amount (pilot injection, main injection, and post-injection) increases as the rotational speed and the load increase.

Further, the fresh air correction amount Ai of another modified example of the present embodiment shown by a two-dot chain line in FIG.
r _c is in the Z region is an operating state of the high-speed and high-load, reduce the degree of the A / F to a change in operating conditions of the engine to a high rotation or a high load side, fuel from after-injection at the periphery of the Z region It is set so as to be smaller than the degree of decrease in the A / F when the injection is not increasing. Also,
The reduction degree of 0, i.e., even after changing the operation state of the engine in a high rotational or high load side, may set the fresh air correction amount Air _c do not change the A / F.

Next, at step S13, a new air amount correction value Air _c is added to the basic target new air amount Air _b to obtain a reference new air amount A.
ir _ref is calculated. As described above, the fresh air amount correction value Ai
Since r _c is a negative value, the basic target fresh air amount is from Air _b is such that the fresh air amount correction value Air _c is subtracted, the value of the basic target fresh air amount Air _b, always fresh air amount Since it is larger than the correction value Air _{c, the} value of the reference fresh air amount Air _ref is a positive value.

[0081] Further, in step S14, from the reference fresh air amount Air _ref, by subtracting the actual fresh air amount Air _real based on the detected value of the air flow sensor 11, to obtain a DerutaAir. The fresh air amount is calculated by the air flow sensor and the intake pressure sensor 10a. In this embodiment, an airflow sensor 11 capable of detecting a backflow is used. According to such an airflow sensor, pulsation due to EGR can be detected when the intake air amount is low, and the fresh air amount can be accurately calculated based on the pulsation.

Next, the routine proceeds to step S15, where ΔAir
The PID control is performed to determine the EGR amount, and step S
At 16, the EGR valve is driven based on the EGR amount to execute the EGR.

The present invention is not limited to the above embodiment, and various changes or modifications can be made within the technical scope described in the claims.

For example, in the above embodiment, the fuel injection control device of the diesel engine which performs the EGR control and the pilot injection is described. However, the present invention may be applied to a fuel injection control device which does not execute these.

In the above embodiment, each of the pilot injection, the main injection, and the post-injection is performed only once. However, the present invention can also be applied to a multi-stage injection.

[0086]

As described above, according to the present invention, there is provided a fuel injection control device for a diesel engine capable of reducing the amount of soot in exhaust gas while suppressing deterioration of fuel efficiency.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a configuration of a diesel engine fuel injection control device according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a fuel injection control executed in an ECU.

FIG. 3 is a graph showing a map for setting an amount of post-injection.

FIG. 4 is a time chart showing a heat generation rate in a combustion chamber.

FIG. 5 is a graph showing a relationship between a post-injection timing and a soot generation amount.

FIG. 6 is a graph showing a relationship between an injection amount of post-injection and fuel consumption.

FIG. 7 is a graph showing a relationship between an injection amount of post-injection and a soot generation amount.

FIG. 8 is a drawing showing a relationship between an injection amount setting map for post-injection and an injection timing _Ip setting map for pilot injection.

FIG. 9 is a flowchart showing EGR control executed in the exhaust gas recirculation control means.

FIG. 10 is a graph showing a specific example of a map for setting a basic target fresh air amount Air _b .

[11] and fresh air correction amount map for Air _c setting is a graph showing the relationship between the map of the operating state of the engine.

FIG. 12 is a graph showing a relationship between an A / F changed by EGR and a map of an operating state of the engine.

[Explanation of symbols]

 1: diesel engine 2: cylinder 5: fuel injection valve 35: ECU 36: injection control means 37: EGR control means

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 41/04 385 F02D 41/04 385D 43/00 301 43/00 301H 301J 301N 301W F02M 25/07 550 F02M 25/07 550A 570 570F 570J F-term (reference) 3G062 AA01 AA03 AA05 BA02 BA04 BA05 BA06 CA07 CA08 DA01 DA02 EA08 EB15 ED01 ED04 ED10 FA02 FA05 FA09 FA13 FA23 GA01 GA04 GA06 GA08 GA14 BA15 GA17 BA21 BA08 CA03 CA04 DA02 DA10 EA04 EA11 EB09 EB13 EC01 EC03 FA07 FA10 FA12 FA20 FA28 FA29 FA37 3G092 AA02 AA06 AA17 AA18 BA05 BA06 BB01 BB06 BB08 BB12 BB13 DB03 DC03 DC09 DC10 DE03S DE05S DG06 EA01 EA02 EA01 EA02 EA01 EA02 EA01 EA02 EA02 GA17 GA18 HA01Z HA06Z HA16Z HB03X HB03Z HD04 X HD04Z HD05X HD05Z HD07Z HE01Z HE03Z HE08Z HF08Z 3G301 HA02 HA04 HA06 HA11 HA13 JA02 JA24 KA09 KA25 LA03 LB11 LC07 MA01 MA11 MA18 NA03 NA04 NA05 NA08 NB03 NB18 NC04 ND05 NE03 NE12 PA01Z PA11Z16PZPD01 PDZ PDZ PDA

Claims (8)

[Claims] 1. A fuel injection valve for directly injecting fuel into a combustion chamber of a diesel engine, and a main injection control for controlling a main injection in which fuel is injected from the fuel injection valve at a predetermined time near a top dead center of a compression stroke. Means for controlling a post-injection in which additional fuel is injected from the fuel injection valve after the main injection. In addition to setting the injection timing of the post-injection based on when the value becomes equal to or less than the value, the operation region in which the amount of the soot is less than the predetermined amount A fuel injection control device for a diesel engine, wherein the fuel injection by the post-injection is increased more than a region. 2. The fuel injection control device for a diesel engine according to claim 1, wherein said post-injection control means increases fuel injection by said post-injection when the engine is at a high speed or a high load. 3. EGR for recirculating a part of exhaust gas to intake air
2. An EGR control means for controlling means, further comprising an EGR control means for controlling an EGR amount to reduce an air-fuel ratio to a predetermined value or less while fuel injection by the post-injection control means is increasing. Or the fuel injection control device for a diesel engine according to 2. 4. EGR for recirculating a part of exhaust gas to intake air
EGR control means for controlling the means, wherein during the fuel injection increase by the post-injection control means, the degree of decrease in the air-fuel ratio with respect to the change in the operating state of the engine toward high rotation or high load is determined by the post-injection. The fuel injection control device for a diesel engine according to claim 1 or 2, further comprising EGR control means for performing EGR control so as to be smaller than a degree of decrease in the air-fuel ratio in a region where the fuel injection is not increased. 5. Pilot injection control means for controlling pilot injection in which fuel is injected from said fuel injection valve in order to perform premix combustion by a predetermined interval before said main injection, wherein said post-injection control means The fuel injection system according to any one of claims 1 to 4, further comprising pilot injection control means for controlling the interval to be smaller than when no post-injection is performed during the fuel injection increase due to the following. A fuel injection control device for a diesel engine as described in the above. 6. Pilot injection control means for controlling pilot injection in which fuel is injected from said fuel injection valve in order to perform premix combustion before a predetermined interval before said main injection, wherein said post-injection control means During the increase in fuel injection, the degree of increase in the interval with respect to a change in the operating state of the engine toward high rotation or high load is smaller than the degree of increase in a region where fuel injection by the post-injection is not increasing. The fuel injection control device for a diesel engine according to any one of claims 1 to 4, further comprising pilot injection control means for controlling the fuel injection. 7. The fuel for a diesel engine according to claim 1, wherein the post-injection control means suppresses fuel injection by the post-injection in a region where the exhaust gas temperature is equal to or higher than a predetermined temperature. Injection control device. 8. A fuel injection valve for directly injecting fuel into a combustion chamber of a diesel engine, and a main injection control for controlling a main injection in which fuel is injected from the fuel injection valve at a predetermined time near a top dead center of a compression stroke. And post-injection control means for controlling post-injection in which additional fuel is injected from the fuel injection valve after the main injection, wherein the post-injection control means has a predetermined heat generation rate by the main injection. A diesel engine, wherein the post-injection timing is set based on the value when the value becomes equal to or less than the reference value, and the post-injection is increased according to a change in the operating state of the engine in the direction of high rotation or high load. Fuel injection control device.