JP4296585B2 - Fuel injection control device for diesel engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel injection control device for a diesel engine. More specifically, the present invention relates to a fuel injection control for a diesel engine having a post-injection control means for controlling post-injection in which additional fuel is injected after fuel injection by main injection. Relates to the device.
[0002]
[Prior art]
After injecting additional fuel into the combustion chamber at a predetermined timing following normal fuel injection (main injection) into the combustion chamber for the purpose of efficiently purifying NOx contained in the exhaust gas of the diesel engine A fuel injection control device for a diesel engine that performs injection is known (Japanese Patent Laid-Open No. 2000-170585).
[0003]
Further, in the prior application of the present applicant (Japanese Patent Application No. 2000-321699) that does not fall under the prior art, soot emission is set by setting the injection timing of the post-injection based on the end point of the diffusion combustion by the main injection. There is a description that can be effectively reduced.
[0004]
[Problems to be solved by the invention]
The present invention relates to such post-injection, and an object thereof is to provide a fuel injection control device for a diesel engine that can reduce the amount of soot in exhaust gas while suppressing deterioration in fuel consumption. And
[0005]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, a fuel injection valve that directly injects fuel into the combustion chamber of a diesel engine, and fuel is injected from the fuel injection valve at a predetermined time near the top dead center of the compression stroke. Main injection control means for controlling main injection, and post-injection control means for controlling post-injection after which the additional fuel is injected from the fuel injection valve after the main injection, the post-injection control means, The injection timing of the post-injection is set based on when the heat generation rate by the main injection becomes a predetermined value or less, and the operation region where the soot generated by the combustion by the main injection becomes a predetermined amount or more is There is provided a fuel injection control device for a diesel engine, wherein the fuel injection by the post-injection is increased from an operating region where the amount of fuel is less than a predetermined amount.
[0006]
Here, “increasing the fuel injection” refers to increasing the absolute amount of the fuel injection of the post injection or increasing the ratio of the post injection amount to the main injection amount.
[0007]
According to such a configuration, since the generation of soot can be suppressed by increasing post-injection in an operating state where the generation of soot exceeds a predetermined amount, soot generation / discharge is suppressed. Further, when the vehicle is in an operating state where the generation of soot is less than a predetermined amount, the post-injection is not increased, so that the fuel consumption is improved.
[0008]
In a preferred aspect of the present invention, the post-injection control means increases fuel injection by the post-injection when the engine is at a high speed or a high load.
[0009]
According to such a configuration, the fuel injection of the post-injection is increased and the generation of soot is effectively suppressed in a high rotation or high load region where soot is frequently generated.
[0010]
Further, another preferred aspect 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, and controls the EGR amount while the fuel injection is increased by the post-injection control means. EGR control means for setting the air-fuel ratio (A / F) to a predetermined value or less is further provided.
[0011]
In order to reduce NOx in the exhaust gas, it is desirable to increase the EGR rate (the ratio of the EGR amount to the total intake air amount). However, if the EGR rate is increased in this way, the air-fuel ratio (A / F) becomes rich and the amount of soot generated increases. Therefore, particularly in the operation region where soot generation increases, the EGR amount is reduced. Control that greatly increases cannot be performed. However, in the configuration as described above, since the generation of soot is suppressed while the fuel injection by the post-injection control means is increased, the EGR can be controlled to be increased, so that the suppression of soot generation and NOx reduction are compatible.
[0012]
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, and when the fuel injection is increased by the post-injection control means, the EGR control means moves to a higher speed or higher load side. EGR control means for performing EGR control so that the degree of decrease of the air-fuel ratio with respect to the change in the operating state of the engine becomes smaller than the degree of decrease of the air-fuel ratio in the region where the fuel injection increase due to the post-injection is not performed. ing.
[0013]
In order to suppress the generation of soot, it is usually performed to reduce the EGR rate according to a change in the operating state toward the high rotation or high load side where the soot is easily generated. In this control, even if the operating state shifts to the high rotation or high load side, it is possible to suppress the occurrence of soot, but since the EGR rate is decreased, NOx increases. However, in the configuration as described above, during the increase in fuel injection by the post-injection control means, the generation of soot is suppressed by the increase in post-injection, so EGR in a state where the fuel injection by the post-injection is not increased. Since the EGR rate can be reduced to a degree smaller than the rate reduction rate, that is, the amount of EGR can be relatively increased, NOx reduction can be realized. In this case, the fuel injection amount increases as the outside of the driving range changes to the high rotation or high load side, so that the A / F decreases with the change of the operating state. Accordingly, from the viewpoint of A / F, along with such a change in the operating state, the degree of decrease in A / F during the increase in fuel due to post-injection is A in a region where such increase is not performed. Therefore, EGR should be controlled to be smaller than the degree of decrease of / F. Thereby, suppression of soot generation and NOx reduction are compatible.
[0014]
Another preferred aspect of the present invention is pilot injection control means for controlling pilot injection in which fuel is injected from the fuel injection valve in order to cause premix combustion to be performed at a predetermined interval prior to the main injection, Pilot injection control means is further provided for controlling the interval to be smaller than when no post-injection is being performed while fuel injection is being increased by the post-injection control means.
[0015]
According to such a configuration, soot generation is suppressed during fuel injection increase by the post-injection control means, so the noise (knock noise) can be reduced by shortening the interval between the main injection and the pilot injection, Suppression of soot generation and noise reduction are compatible.
[0016]
Another preferred aspect of the present invention is pilot injection control means for controlling pilot injection in which fuel is injected from the fuel injection valve in order to cause premix combustion to be performed at a predetermined interval prior to the main injection, While the fuel injection is being increased by the post-injection control means, the degree of increase in the interval with respect to a change in the operating state of the engine to the high speed or high load side is set in a state where the fuel injection by the post-injection is not increased. Pilot injection control means for controlling to be smaller than the degree of increase is further provided.
[0017]
The interval between the pilot injection and the main injection for suppressing the generation of noise is reduced according to the change in the operating state to the high rotation or high load side where the soot is likely to be generated in order to suppress the increase in soot. Go. In such control, the generation of soot can be suppressed, but the noise increases as the operating state changes to the high rotation or high load side. However, in the configuration as described above, during the increase in fuel injection by the post-injection control means, the generation of soot is suppressed by the increase in post-injection, so that the above-described change in the operating state of the engine toward the high rotation or high load side By controlling the increase degree of the interval to be smaller than the increase degree when the fuel injection by the post-injection is not performed, the suppression of soot generation and the reduction of noise are compatible.
[0018]
In a preferred aspect of the present invention, 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.
[0019]
In areas where the exhaust gas temperature is equal to or higher than the specified temperature, for example, almost full load and full load area, exhaust system parts are subject to thermal degradation due to high-temperature exhaust gas. To prevent thermal damage to exhaust system parts.
[0020]
According to another invention of the present application, a fuel injection valve that directly injects fuel into a combustion chamber of a diesel engine, and a main injection in which fuel is injected from the fuel injection valve at a predetermined time near the top dead center of a compression stroke. And a post-injection control unit that controls post-injection after which the additional fuel is injected from the fuel injection valve, and the post-injection control unit is configured to control the main injection. Set the injection timing of the post-injection based on when the heat generation rate by the engine becomes less than or equal to the predetermined value, and increase the post-injection according to the change of the engine operating state in the high rotation or high load direction A fuel injection control device for a diesel engine is provided.
[0021]
According to such a configuration, since the post-injection is increased and the generation of soot is suppressed in accordance with the transition of the engine operating state to the high rotation or high load side where the generation of soot increases, Generation and discharge are effectively suppressed. Further, the fuel consumption is improved in the region where the generation of soot is less because the post injection is less.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Next, preferred embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of a fuel injection control device for a diesel engine according to an embodiment of the present invention.
[0023]
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... (Only one is shown). In each cylinder 2, pistons 3 are arranged so as to be able to reciprocate. A combustion chamber 4 is formed by the inner peripheral wall of the cylinder. Near the center of the upper surface of the combustion chamber 4, a fuel injection valve (injector) 5 is arranged so that the nozzle 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, 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).
[0024]
Each fuel injection valve 5 is connected to a common common rail (pressure accumulation chamber) 6 that stores high-pressure fuel. A high pressure fuel is supplied to the common rail 6 by an injection pump driven after the engine is started by an engine or a motor, and a pressure sensor 6a for detecting an internal fuel pressure (common rail pressure) is disposed and driven by a crankshaft 7. A high-pressure supply pump 8 is connected. The high-pressure supply pump 8 is configured to maintain the fuel pressure in the common rail 6 detected by the pressure sensor 6a at, for example, about 20 MPa or more during idle operation and 50 MPa or more during other operations.
[0025]
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 so as to correspond to the outer periphery of the plate, and the electromagnetic pickup is disposed on the entire outer periphery of the plate to be detected. A pulse signal is generated in response to the passage of protrusions formed at predetermined angles.
[0026]
The engine 1 also includes an intake passage 10 that introduces intake air filtered by an air cleaner (not shown) into the combustion chamber 4. The downstream end portion of the intake passage 10 branches through a surge tank (not shown), and each is connected to the combustion chamber 4 of each cylinder 2 by an intake port. Further, an intake pressure sensor 10a that detects a supply pressure supplied to each cylinder 2 in the surge tank is provided.
[0027]
In the intake passage 10, an airflow sensor 11 that detects an intake flow rate sucked into the engine 1 in order from the upstream side to the downstream side, a blower 12 that is driven by a turbine 21 to be described later and compresses the intake air, An intercooler 13 that cools the air compressed by the blower 12 and an intake throttle valve 14 that throttles the cross-sectional area of the intake passage 10 are provided.
[0028]
The intake throttle valve 14 is a butterfly valve provided with a notch so that intake air can flow even in a fully closed state. Like the EGR valve 24 described later, the magnitude of the negative pressure that acts on the diaphragm actuator 15. Is adjusted by the negative pressure control solenoid valve 16 so that the opening degree of the valve is controlled. A sensor (not shown) for detecting the opening degree of the intake throttle valve 14 is also provided.
[0029]
An exhaust passage 20 for exhausting 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 is branched and 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 abruptly when the exhaust air-fuel ratio is substantially the stoichiometric air-fuel ratio, and a turbine rotated by the exhaust flow. 21, a NOx reduction catalyst 22 that reduces and purifies at least NOx in the exhaust, and a NOx sensor 19 that detects the NOx concentration in the exhaust gas that has passed through the NOx reduction catalyst 22 are disposed.
The NOx purification catalyst 22 which is the NOx reduction catalyst 22 includes a cordierite carrier formed in a honeycomb structure having a large number of through holes extending in parallel to each other along the exhaust flow direction, and a catalyst layer is provided on the wall surface of each through hole. It is formed in two layers. Specifically, the catalyst layer is formed by supporting platinum (Pt) and rhodium (Rh) using a porous material such as MFI-type zeolite (ZSM5) as a support material.
[0030]
The NOx purification catalyst 22 reacts NOx with a reducing agent when the air-fuel mixture in the combustion product 4 becomes lean and the oxygen concentration in the exhaust gas is high, for example, when the oxygen concentration is 4% or more. In this way, NOx in the exhaust gas is purified by reduction. The NOx purification catalyst 22 functions as a three-way catalyst when the oxygen concentration is low.
[0031]
The exhaust passage 20 is branched and connected to an upstream end of an exhaust gas recirculation passage (EGR passage) 23 that recirculates part of the exhaust gas to the intake side at a position upstream of the turbine 21. 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. Further, a negative pressure actuated exhaust gas recirculation amount adjusting valve (EGR valve) 24 capable of adjusting the opening degree is provided at a position closer to the downstream side of the EGR passage 23. In this embodiment, a part of the exhaust gas in the exhaust passage 20 is recirculated to the exhaust passage 10 while the flow rate is adjusted by the EGR valve 24, and the exhaust gas recirculation (by the EGR valve 24 and the EGR passage 23). EGR) means 33 are configured.
[0032]
In the EGR valve 24, a valve body (not shown) is urged in a closing direction by a spring, and is operated in an opening direction by a diaphragm 24a to linearly adjust the opening degree of the EGR passage 23. 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 an electromagnetic valve 28 for negative pressure control. However, the EGR valve drive negative pressure is adjusted by opening or closing the EGR valve 24 by connecting or blocking the negative pressure passage 27 by a control signal from the ECU 35 described later. Further, a lift sensor 26 that detects the position of the valve body of the EGR valve 24 is provided.
[0033]
Each fuel injection valve 5, high-pressure supply pump 8, intake throttle valve 14, EGR valve 24, turbocharger 25, and the like are configured to operate according to control signals from a control unit (Engine Control Unit: ECU) 35. ing.
[0034]
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 EGR valve 24, a vehicle driver. An output signal from an accelerator opening sensor 32 that detects an operation amount (accelerator opening) of an accelerator pedal (not shown) is input.
[0035]
In this embodiment, the ECU 35 controls the operation of the engine, and includes a main injection control that controls main injection in which fuel is injected from the fuel injection valve 5 at a predetermined timing near the top dead center of the compression stroke, Additional timing injected from the fuel injection valve 5 when the heat generation rate due to the injection becomes a reference value or less, that is, when the heat generation rate due to the main injection becomes substantially 0 or less Pilot control that controls post-injection control that controls post-injection at the timing when fuel starts to burn, and pilot injection that controls fuel injection from the fuel injection valve 5 so that premix combustion is performed prior to the main injection by a predetermined interval An injection control means 36 that performs injection control and the like, and an EGR control means 37 that controls the EGR valve 24 to control the exhaust gas recirculation amount are provided. That is, the injection control means 36 of this embodiment has functions of a main injection control means, a post-injection control means, and a pilot injection control means.
[0036]
Next, fuel injection control executed in the ECU 35 will be described along the flowchart of FIG.
[0037]
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 basic fuel injection amount Q is determined from the basic injection amount map set based on the target torque Tr obtained from the accelerator opening and the engine speed Ne obtained from the crank angle signal. _b And the injection timing I _b Is read from a preset map.
[0038]
Next, in step S3, the injection amount Q of the post-injection _fu And injection timing I _fu Is set. Post-injection injection quantity Q _fu And injection timing I _fu Is set by reading from a map in which amounts corresponding to the target torque Tr and the engine speed Ne are set in advance.
[0039]
In this map, post-injection injection quantity Q _fu Is an operation state in which soot generated by combustion by main injection exceeds a predetermined amount, fuel injection (amount or rate) by post-injection is increased more than when the amount of soot is less than a predetermined amount, so that generation of soot It is set to suppress. Here, the fuel injection amount by post-injection indicates the absolute amount of fuel injected by post-injection, and the fuel injection rate by post-injection indicates the ratio of the post-injection injection amount to the main injection amount.
[0040]
In this embodiment, the amount Q of post-injection _fu As shown in the map of FIG. 3, from the peripheral region such as the low rotation / low load region and the full load region toward the high rotation region (for example, 2500 rpm) and the high load region (Z region) indicated by hatching. Is set to gradually increase. Therefore, when the engine is operating at a high speed and a high load, the fuel injection amount Q by the post-injection _fu Is increased compared to other operating conditions.
[0041]
In the present embodiment, the ratio of the post-injection injection amount to the main injection injection amount is 10 to 20% at low rotation and low load, and is increased to 20 to 50% or more at high rotation and high load.
[0042]
Further, as a modified example, the fuel injection amount Q by the post-injection is also obtained in a region where the soot is increased except 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.
[0043]
Furthermore, the configuration may be such that post-injection is not executed at low rotation / low load, such as idling, but post-injection is executed in a region other than at low rotation / low load.
[0044]
Injection timing I for post injection _fu Is set when the heat generation rate by the main injection is less than a predetermined value (approximately 0), that is, when the diffusion combustion by the main injection is completed, and when the heat generation rate by the main injection becomes approximately 0 or less It is set on the map in consideration of the ignition delay (0.4 to 0.7 ms) of the post injection and the invalid injection time so that the combustion of the fuel by the post injection is started.
[0045]
By setting in this way, when the heat generation rate becomes substantially 0 or less, that is, when the diffusion combustion that occurs after the main injection fuel in the combustion chamber has been premixed and combusted is completed, Combustion will begin. For this reason, it is considered that combustion by post-injection starts in a state where mixing of soot and oxygen present in the combustion chamber 4 is promoted, and so the generation of soot is reduced.
[0046]
Further, the combustion by the post-injection starts near the time when the heat generation rate by the main injection becomes substantially 0 or less (the crank angle is preferably within ± 10 °, more preferably within ± 5 °). You may set the injection timing of post-injection.
[0047]
Here, the heat generation rate dQ / dθ is represented by the following formula (1) according to “Lecture on Internal Combustion Engine” (Fujio Nagao, Yokendo Co., Ltd.).
[0048]
dQ / dθ = A / (K ₍ θ ₎ -1) x [V ₍ θ ₎ ・ (DP ₍ θ ₎ / Dθ) + K ₍ θ ₎ ・ P ₍ θ ₎ ・ (DV ₍ θ ₎ / Dθ)] (1)
Where A is the work equivalent of heat and 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.
[0049]
According to the manual of Ono Sokki Co., Ltd. combustion analyzer CB566, the specific heat ratio K ₍ θ ₎ Is expressed based on the following formulas (2) to (5).
[0050]
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)
Here, Cp is constant pressure specific heat, Cv is constant volume specific heat, Ro is gas constant, M is molecular weight of air, T ₍ θ ₎ Is gas temperature, G is gas weight, ap, b, c, d are other constants.
[0051]
From the above formulas (2) to (5), the heat generation rate dQ / dθ shown in the formula (1) is the in-cylinder pressure P ₍ θ ₎ And stroke volume V ₍ θ ₎ And the function f (P ₍ θ ₎ , V ₍ θ ₎ )become. The stroke volume V ₍ θ ₎ Is expressed based on the bore diameter B and the stroke S as shown in the following formula (6), the heat generation rate dQ / dθ is expressed as the following formula (7).
[0052]
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)
Therefore, if there is in-cylinder pressure data for each crank angle, the heat generation rate can be calculated based on this data. In the present embodiment, the end point of diffusion combustion (that is, the point at which the heat generation rate becomes approximately 0 or less) is calculated from the heat generation rate thus obtained, and the ignition delay time of post-injection and the like are calculated from this end point. The time point before the delay is the post injection time I _fu This map is used.
[0053]
The end time of diffusion combustion changes according to the operating state of the engine, and the end time of diffusion combustion tends to be delayed as the engine load and the rotational speed increase. For example, when the engine speed is 2000 rpm and the average effective pressure Pe is 0.57 MPa, the engine is compressed as shown in FIG. 4B, which is a graph of the result calculated by the method described above. Heat generation Y due to premixed combustion of the main injected fuel near the top dead center and heat generation K due to diffusion combustion at approximately the same level occur, and ignition delay from about 35 ° (CA) after compression top dead center τ _f2 Diffusion combustion ends at time t2 delayed by (about 0.5 ms).
[0054]
In addition, when the engine speed is 2500 rpm and the average effective pressure Pe is 0.9 Mpa, as shown in FIG. 4C, diffusion combustion is performed for a considerably long time compared to heat generation Y by premixed combustion. Heat generation K occurs due to the ignition delay from about 48 ° (CA) after compression top dead center τ _f3 It can be seen that diffusion combustion ends at a considerably late time t3 (approximately 0.7 ms).
[0055]
In addition, when the engine speed is 1500 rpm and the average effective pressure Pe is 0.3 Mpa and the load is low and the load is low, as shown in FIG. 4A, the premixed combustion and the diffusion combustion of the fuel are distinguished by heat generation. Is difficult, but ignition delay τ from about 30 ° (CA) after compression top dead center _f1 It can be seen that the diffusion combustion ends at a relatively early time t1 after being delayed (about 0.6 ms).
[0056]
Therefore, in the vicinity of the end point of the diffusion combustion, that is, 25 to 35 ° (CA) after compression top dead center at low rotation and low load, and 33 to 40 ° (CA) after compression top dead center at medium rotation. ), 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 the time of high rotation and high load.
[0057]
This is a graph obtained by experimenting the relationship between the post-injection timing and the soot generation amount in each of the low rotation and low load, the medium rotation and middle load, and the high rotation and high load. FIGS. 5 (a), 5 (b), ( It is clear from c).
[0058]
In the present embodiment, as indicated by the needle lift amount in FIG. 4, 30 ° (CA) after compression top dead center at low rotation and low load, and 35 ° (CA) after compression top dead center at medium rotation load. At the time of high rotation and high load, the post-injection timing is set so that the post-injection is executed at 48 ° (CA) after the compression top dead center, and the diffusive combustion ends in each operation state, t1, t2, and At t3, combustion by post-injection is started so that heat generation indicated by a dotted line in FIG. 4 occurs.
[0059]
Even 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.
[0060]
FIG. 6 is a graph showing the relationship between the post injection amount (ratio to the main injection) and the amount of soot generated. 30 ° after compression top dead center (CA) so that the combustion by the post-injection starts at the time t1 when the diffusion fuel by the main injection of the fuel is finished in the low rotation and low load state of the engine speed 1500 rpm and the average effective pressure Pe 0.3 MPa. ), The ratio of the post-injection amount to the main injection amount (P / T) was varied in the range of 10 to 45%, and an experiment was conducted to measure the amount of soot generated. As shown by the solid line, the amount of soot generated decreased with an increase in the post-injection ratio (P / T). 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. The soot generation amount increased with an increase in the ratio of the post injection amount (P / T).
[0061]
Also, after the top dead center of compression 35 ° so that the combustion by the post-injection starts at the time point t2 when the diffusion fuel by the main injection of the fuel is finished in the medium rotational load state of the engine speed 2000 rpm and the average effective pressure Pe 0.57 MPa. When the same experiment for performing the post-injection at (CA) was performed, as shown by the solid line in FIG. 6 (b), the amount of soot generated decreased with the increase in the post-injection ratio (P / T), When the post-injection is performed at 20 ° 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. Even when the ratio (P / T) increased, no significant change in the amount of wrinkles was observed.
[0062]
Furthermore, in a high rotation and high load state with an engine speed of 2500 rpm and an average effective pressure Pe of 0.9 MPa, 48 ° after compression top dead center so that combustion by post-injection starts at time t3 when diffusion fuel by main injection of fuel ends. When the same experiment for performing the post-injection in (CA) was performed, as shown by the solid line in FIG. 6 (c), the soot generation amount decreased with the increase in the post-injection ratio (P / T), When the post-injection is performed at 20 ° 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. Even when the ratio (P / T) increased, no significant change in the amount of wrinkles was observed.
[0063]
From this, when post-injection is performed so that combustion by post-injection starts when diffusion fuel by main injection of fuel ends, fuel injection amount Q by post-injection _fu It can be seen that the amount of soot is reduced by increasing.
[0064]
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 consumption rate. FIGS. 7 (a), (b), and (c) are the same as FIGS. 6 (a), (b), and (c), respectively. FIG. 6 is a graph of the fuel consumption rate measured by changing the ratio of the post-injection amount to the main injection amount (P / T) in a range of 10 to 45%, and the solid line is the diffusion due to the main injection of fuel as in FIG. The results of post-injection at 30 °, 35 °, and 48 ° (CA) after compression top dead center are shown so that combustion by post-injection starts at time t1 when the fuel ends, and the dotted line shows diffusion combustion The results of post-injection at 8 °, 20 °, and 20 ° after compression top dead center are shown so that combustion by post-injection starts before the end.
[0065]
As shown by the solid lines in FIGS. 7A, 7B, and 7C, when the post-injection is performed so that the combustion by the post-injection starts when the diffusion fuel by the main injection of the fuel ends. As the ratio of post-injection to main injection increases, the fuel consumption deteriorates. However, in the above-described embodiment, the ratio of the post-injection amount to the main injection amount (P / T) is about 20% or less at low rotation and low load and middle rotation, so that deterioration of fuel consumption in this region is suppressed. Has been.
[0066]
Next, the process proceeds to step S4, and the injection amount Q of the pilot injection _p And injection timing I _p Are set. In this embodiment, the injection amount Q of pilot injection _p Is, for example, the main injection amount Q at low load _b 30 to 50% of the fixed value determined within the range. On the other hand, injection timing I _p Is derived from a predetermined map based on the target torque Tr and the engine speed Ne.
[0067]
FIG. 8 shows the injection timing I of the pilot injection of this embodiment. _p It is drawing which shows the relationship between the map for setting (b) and the injection amount setting map (a) of after-injection. In this drawing, the injection timing I of pilot injection _p Is shown by the difference (advance angle: crank angle) between pilot injection and main injection. Injection timing I of pilot injection of this embodiment _p As shown by the solid line in FIG. 8B, the interval from the main injection is set shorter than the injection timing (dotted line) of the pilot injection when the post injection is not performed.
[0068]
Pilot injection injects a certain amount of fuel prior to main injection to cause premixed combustion in the combustion chamber, aiming to reduce noise (explosive sound) during combustion due to main injection. It is known that the effect of noise reduction is greater when the timing is closer to the injection timing of the main injection. However, since the generation of soot tends to increase when the pilot injection is brought close to the main injection, the pilot gives priority to suppressing the generation of soot, particularly in a region where soot generation is remarkable, for example, in a high rotation high load region. The injection timing of the injection must be separated from the injection timing of the main injection.
[0069]
On the other hand, in this embodiment, since the occurrence of soot is suppressed by the post-injection, the pilot injection timing is set closer to the main injection than in the case where the post-injection is not performed in almost all operation regions. Can be reduced, and both soot generation and noise can be suppressed.
[0070]
Further, in the operation region (Z region) of high rotation and high load, setting is made so that the injection timing of the pilot injection is delayed as in the modified example shown by the one-dot chain line and the two-dot chain line in FIG. Also good. As a result, during the increase in post-injection injection (Z region), the degree of delay in the injection timing of the pilot injection in accordance with the change in the operation state to the high rotation or high load side is a relatively similar operation state. The control is performed so that the fuel injection by the post-injection around the Z region is smaller than the degree of delay when the increase is not performed. The reason why the change in the injection timing continuously changes instead of the step shape in the transition region to the operation region (Z region) of high rotation and high load is to avoid a sudden change in sound quality.
[0071]
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 increased (Z region), priority has been given to the suppression of soot generation. For this reason, the degree of separation of the pilot injection timing, which had to be separated from the main injection, from the main injection is reduced, and active noise reduction is possible.
[0072]
In step S5, the exhaust gas temperature T _ex Enter. In the present embodiment, the exhaust gas temperature is estimated based on a signal from the water temperature sensor 18 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.
[0073]
Next, in step S6, the input exhaust gas temperature T _ex Is a predetermined reference temperature T _ex0 It is determined whether the higher state has continued for a predetermined time. YES in step S6, that is, the exhaust gas temperature T _ex Is a predetermined reference temperature T _ex0 When it is determined that the higher state has continued for a predetermined time, the process proceeds to step S7, where the injection Q of the post-injection _fu Is set to 0, and the process proceeds to step S8. This is because, if the exhaust gas temperature is higher than a predetermined value for a predetermined time, exhaust system parts such as the catalyst are thermally damaged. Therefore, in a high load region where the exhaust gas temperature is high for a predetermined time, post-injection This is to prevent the exhaust gas temperature from rising further without performing the above. On the other hand, NO in step S6, that is, the exhaust gas temperature T _ex Is a predetermined reference temperature T _ex0 When it is determined that the state below or the state where the exhaust gas temperature is higher than the predetermined value is not continued for the predetermined time, the process proceeds to step S8 as it is.
[0074]
In step S8, the fuel injection valve 5 is operated according to the amount and timing set in steps S2, S3, S4, and S7, and pilot injection, main injection, and post injection into the combustion chamber are executed.
[0075]
Next, the EGR control executed in the exhaust gas recirculation control means 37 of the ECU 35 will be described with reference to the flowchart of FIG.
[0076]
First, in step S10, data such as the engine speed and the accelerator opening are input, and the process proceeds to step S11. Based on the accelerator opening and the engine speed, for example, preset values as shown in FIG. From the map, the basic target fresh air volume Air corresponding to the engine operating state _b Set. As a result, the EGR amount (valve opening) is set to be smaller as the rotation speed is higher. In the example of FIG. 10, the basic target fresh air amount Air is higher in the idle region indicated by hatching than in the middle load of the engine. _b Is set to increase. Next, at step 12, the fresh air amount correction value Air _c Is set.
[0077]
FIG. 11 shows the fresh air correction amount Air. _c The relationship between the setting map (b) and the engine operating state map (a) is shown. The fresh air correction amount Air of the present embodiment shown by a solid line in FIG. _c Is set so that the A / F as a result of performing the EGR control in the Z region, which is an operation state of high rotation and high load, is equal to or less than a predetermined value as indicated by a solid line in FIG. . In addition, the fresh air correction amount Air of the modified example of the present embodiment shown by a one-dot chain line in FIG. _c In addition, the A / F value obtained as a result of performing the EGR control in the Z region, which is an operation state of high rotation and high load, is set to be equal to or less than a predetermined value as indicated by a one-dot chain line in FIG. ing.
[0078]
In FIG. 10, although the EGR amount is set so as to decrease as the rotational speed increases, the A / F decreases as the rotational speed increases in FIG. This is because the total fuel injection amount (pilot injection, main injection, and post-injection) increases as the rotational load increases.
[0079]
Furthermore, the fresh air correction amount Air of another modified example of the present embodiment, which is indicated by a two-dot chain line in FIG. _c Indicates that the degree of decrease in A / F with respect to a change in the operating state of the engine to the high speed or high load side in the Z region, which is the operating state of high rotation and high load, indicates that the fuel injection by post-injection around the Z region It is set to be smaller than the degree of decrease in A / F in the state where the increase is not performed. Further, the degree of decrease is 0, that is, the fresh air correction amount Air so that the A / F is not changed even if the engine operating state changes to the high rotation or high load side. _c May be set.
[0080]
Next, in step S13, the basic target fresh air amount Air _b New air amount correction value Air _c Add the standard fresh air volume Air _ref Is calculated. As described above, the new air amount correction value Air _c Is a negative value, so the basic target fresh air amount Air _b To fresh air correction value Air _c May be subtracted, but basic target fresh air volume Air _b Is always the fresh air correction value Air. _c Since it is larger, the standard fresh air amount Air _ref The value of is a positive value.
[0081]
Further, in step S14, the reference fresh air amount Air _ref From the actual fresh air amount Air based on the value detected by the air flow sensor 11 _Fruit Is subtracted to obtain ΔAir. The fresh air amount is calculated by the air flow sensor and the intake pressure sensor 10a. In this embodiment, an airflow sensor 11 that can detect backflow is used. According to such an air flow sensor, pulsation due to EGR can be detected when the amount of intake air is low, and the amount of fresh air can be accurately calculated based on this pulsation.
[0082]
Next, the process proceeds to step S15, PID control is performed on ΔAir, the EGR amount is determined, and in step S16, the EGR valve is driven based on the EGR amount to execute EGR.
[0083]
The present invention is not limited to the above-described embodiments, and various changes or modifications can be made within the scope of the technical matters described in the claims.
[0084]
For example, although the above embodiment is a fuel injection control device of a diesel engine that performs EGR control and pilot injection, the present invention may be a fuel injection control device that does not execute these.
[0085]
Moreover, in the said embodiment, pilot injection, main injection, and post-injection were each performed only once, However, This invention is applicable also to what these are multistage injection.
[0086]
【The invention's effect】
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 consumption.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a configuration of a fuel injection control device for a diesel engine according to an embodiment of the present invention.
FIG. 2 is a flowchart showing fuel injection control executed in the ECU.
FIG. 3 is a graph showing a map for setting the 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 the relationship between post injection timing and 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 an injection amount setting map for post-injection and injection timing I for pilot injection. _p It is drawing which shows the relationship with the map for setting.
FIG. 9 is a flowchart showing EGR control executed in the exhaust gas recirculation control means.
FIG. 10 Basic target fresh air volume Air _b It is a graph which shows the specific example of the map which sets.
FIG. 11 is a fresh air correction amount Air. _c It is a graph which shows the relationship between the map for a setting, and the map of the driving | running state of an engine.
FIG. 12 is a graph showing a relationship between an A / F that changes due to 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

Claims (8)

A fuel injection valve that directly injects fuel into the combustion chamber of a diesel engine;
Main injection control means for controlling main injection in which fuel is injected from the fuel injection valve at a predetermined time near the top dead center of the compression stroke;
A post-injection control means for controlling post-injection in which additional fuel is injected from the fuel injection valve after the main injection;
The post-injection control means sets the injection timing of the post-injection based on when the heat generation rate by the main injection becomes a predetermined value or less, and the soot generated by the combustion by the main injection is not less than a predetermined amount. The fuel injection control device for a diesel engine is characterized in that the fuel injection by the post-injection is increased in the operation region in which the amount of soot is less than the operation region in which the amount of soot is less than a predetermined amount. The fuel injection control device for a diesel engine according to claim 1, wherein the post-injection control means increases fuel injection by the post-injection when the engine is at a high rotation speed or a high load. EGR control means for controlling EGR means for recirculating part of the exhaust gas to the intake air, and during the increase of fuel injection by the post-injection control means, EGR control for controlling the EGR amount to bring the air-fuel ratio below a predetermined value The fuel injection control device for a diesel engine according to claim 1 or 2, further comprising means. EGR control means for controlling EGR means for recirculating part of the exhaust gas to the intake air, and during the increase of fuel injection by the post-injection control means, the engine is operated in response to a change in the operating state of the engine to a high speed or high load side. The EGR control means which performs EGR control so that the decreasing degree of an air-fuel ratio may become smaller than the decreasing degree of the air fuel ratio in the area | region where the fuel injection increase by the said post injection is not performed is provided. The diesel engine fuel injection control apparatus described. Pilot injection control means for controlling pilot injection in which fuel is injected from the fuel injection valve in order to cause premix combustion to be performed at a predetermined interval prior to the main injection, and fuel injection is being increased by the post-injection control means 5. The diesel engine according to claim 1, further comprising pilot injection control means for controlling the interval to be smaller than when no post-injection is performed. Fuel injection control device. Pilot injection control means for controlling pilot injection in which fuel is injected from the fuel injection valve in order to cause premix combustion to be performed at a predetermined interval prior to the main injection, and fuel injection is being increased by the post-injection control means The control is performed so that the increase degree of the interval with respect to the change in the operating state of the engine toward the high speed or high load side is made smaller than the increase degree in the region where the fuel injection by the post injection is not increased. The fuel injection control device for a diesel engine according to any one of claims 1 to 4, further comprising pilot injection control means. The diesel engine fuel injection control apparatus according to any one of claims 1 to 6, 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. A fuel injection valve that directly injects fuel into the combustion chamber of a diesel engine;
Main injection control means for controlling main injection in which fuel is injected from the fuel injection valve at a predetermined time near the top dead center of the compression stroke;
A post-injection control means for controlling post-injection in which additional fuel is injected from the fuel injection valve after the main injection;
The post-injection control means sets the injection timing of the post-injection based on when the heat generation rate by the main injection becomes a predetermined value or less, and changes the operating state of the engine in the high rotation or high load direction. A fuel injection control device for a diesel engine characterized by increasing post-injection in response to

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