JP4587012B2 - 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, and more particularly, to a fuel injection control device for a diesel engine that controls post-injection in which additional fuel is injected after fuel injection by main injection.
[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]
In such post-injection, the injection valve does not operate at a desired timing due to deterioration over time, and the timing at which fuel is actually injected from the post-injection valve deviates from the set timing, or the injection of the set post-injection A desired effect such as reduction of wrinkles may not be obtained because the time is shifted from an appropriate time.
[0005]
[Problems to be solved by the invention]
The present invention has been made in view of such a point, and obtains a desired effect by post-injection such as performing post-injection at an appropriate time to efficiently reduce soot in exhaust gas. An object of the present invention is to provide a fuel injection control device for a diesel engine.
[0006]
[Means for Solving the Problems]
According to the present invention,
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 from the intake stroke to the vicinity of the compression stroke top dead center;
After the main injection, the post-injection in which additional fuel is injected from the fuel injection valve is controlled, and the injection timing of the post-injection is controlled so that the combustion of the post-injection starts when the combustion by the main injection ends. Post-injection control means;
Detecting means for detecting a combustion state in the combustion chamber based on detection of an output torque by combustion of post-injection ;
When the post-injection control unit determines that the output torque is equal to or less than a predetermined value based on the output torque generated by the post-injection combustion detected by the detection unit, the post-injection control unit performs the post-injection after the completion of the main injection combustion. Is determined to have started combustion, correction is performed to shift the injection timing of the post-injection to the advance side, and when it is determined that the output torque is greater than a predetermined value, the combustion is performed before the end of combustion by the main injection. It is determined that combustion by injection has started, and correction is performed to shift the injection timing of the post-injection to the retarded side,
A fuel injection control device for a diesel engine is provided.
[0007]
According to such a configuration, since the injection timing of the post-injection is corrected based on the actual combustion state detected by the detection means, the post-injection injection is performed so that the combustion by the post-injection is started at a desired timing. It is possible to obtain a desired effect by post-injection such as soot reduction by feedback correcting the timing. Therefore, for example, even if the operation timing of the injection valve or the optimum post-injection timing of each engine shifts due to deterioration over time, an injection timing that takes this shift into account can be set, and combustion due to post-combustion is compared with main injection. It can be generated at an optimal time.
[0009]
The fact that “combustion by post-injection has started after combustion has ended” means that the valve operation was delayed due to deterioration over time, etc., and the timing at which post-injection was actually performed was later than the setting, This means that the optimal post-injection time is earlier than the set time. In such a case, by performing a correction for shifting the injection timing of the post-injection to the advance side, an injection timing in which this deviation is corrected is set, and combustion by the post-injection occurs at a desired timing.
[0012]
The output torque of the engine during combustion by post-injection reflects the combustion state of combustion by post-injection. That is, if the combustion by the post-injection is started when the combustion by the main injection is completed (that is, at the predetermined timing when the combustion by the main injection is completed), the predetermined torque is generated by the post-injection. When combustion by post-injection starts after completion (that is, after a predetermined timing at which combustion by main injection has ended), predetermined torque is not generated and torque is reduced. In another preferred aspect of the present invention, the post-injection is corrected by estimating the time when the post-injection is actually performed on the basis of the magnitude of the output torque of the engine during combustion by post-injection. Correction that shifts the injection timing of the post-injection to the advance side, assuming that the time when the post-injection was actually performed is delayed from the predetermined time It is carried out.
[0014]
As described above, the output torque of the engine during combustion by post-injection reflects the combustion state of combustion by post-injection. That is, if the combustion by the post-injection has started at the predetermined timing when the combustion by the main injection has ended, the predetermined torque is generated, but the combustion by the post-injection starts before the combustion by the main injection ends (before the predetermined timing) Then, the torque by the main injection is added to the torque by the post injection, and the torque becomes larger than a predetermined value. In another preferred aspect of the present invention, when the detected output torque is larger than a predetermined value, the combustion by the post injection is started before the diffusion combustion by the main injection ends (before the predetermined timing), that is, the post injection is performed. It is determined that the broken timing is too early, and the injection timing of the post injection is shifted to the retard side.
[0015]
In another preferred aspect of the present invention, the degree of correction to the advance side by the post-injection control means is greater than the degree of correction to the retard side.
[0016]
According to such a configuration, hunting can be suppressed, and the existence frequency at the optimal injection timing is increased.
[0017]
In yet another preferred embodiment of the present invention, the post injection control means, the engine speed is high rotation or mean effective pressure Pe above 2500rpm in steady-state operation area of the high load of 0.9 MPa, to perform the correction . In the high-speed or high-load steady operation region, it is easy to detect the combustion state of the engine, so that accurate control is possible.
[0018]
In still another preferred aspect of the present invention, the fuel injection control means performs feedback control so that the engine speed converges to a predetermined speed during idling, and executes the correction during the feedback control. During feedback control performed during idling, since the engine operating state is stable, it is easy to detect the combustion state of the engine, and accurate control is possible.
[0019]
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.
[0020]
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).
[0021]
Each fuel injection valve 5 is connected to a common common rail (pressure accumulation chamber) 6 that stores high-pressure fuel. High pressure fuel is supplied to the common rail 6 by an injection pump driven after the engine is started by an engine or 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.
[0022]
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.
[0023]
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.
[0024]
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.
[0025]
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.
[0026]
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.
[0027]
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.
[0028]
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.
[0029]
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, at a position closer to the downstream side of the EGR passage 23, a negative pressure operation type exhaust gas recirculation amount adjusting valve (EGR valve) 24 capable of adjusting the opening degree is provided. 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 ( EGR) means 33 are configured.
[0030]
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.
[0031]
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.
[0032]
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.
[0033]
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, Post-injection control or the like for controlling the fuel of the post-injection injected from the fuel injection valve 5 to start combustion when the heat generation rate by injection becomes substantially 0 or less (that is, when the combustion by the main injection is completed) And an EGR control means 37 that controls the EGR valve 24 to control the exhaust gas recirculation amount. That is, the injection control means 36 of this embodiment has functions of a main injection control means and a post-injection control means.
[0034]
The ECU 35 is configured to detect the combustion state in the combustion chamber based on torque fluctuation, in-cylinder pressure, and the like, and correct the injection timing of the post-injection by the post-injection control means based on the detection result. Further, the ECU 35 of the present embodiment is configured to perform feedback control (ISC control) for converging the engine speed to a predetermined speed during idling.
[0035]
Next, fuel injection control executed in the ECU 35 will be described along the flowcharts of FIGS. 2A and 2B.
[0036]
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 _b 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. In addition to reading, the injection timing _Ib is read from a preset map.
[0037]
Next, in step S3, it is determined whether or not it is an idle area (ID). In the present embodiment, the engine speed 500 rpm to 1000 rpm and the accelerator opening 0 are set as the idle region, but the idle region may be determined according to other criteria. If YES in step S3, that is, if it is determined that the engine is in the idle region, the current rotational speed Ne (k) is stored in step S4, the average value Ne _ave of the past k rotational speeds Ne is calculated in step S5, and further determines the difference ΔNe by subtracting the current rotational speed Ne _actual average value Ne _ave in step S6. Next, in step S7, the fuel injection correction amount Q _IDC at idling is set from the map based on ΔNe, and in step S8, the fuel injection correction amount Q _IDC is added to the basic fuel injection amount Q _b to obtain the basic fuel injection amount. Set Q _b and proceed to step S9. On the other hand, when it is determined NO in step S3, that is, when not idling, the rotational speed Ne (k) is reset to 0 in step S10, and the process proceeds to step S9.
[0038]
In step S9, the post-injection injection amount Q _fu and the injection timing I _fu are set. The injection amount Q _fu and the injection timing I _fu of the post-injection are 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, the injection amount Q _fu of the post-injection is later than when the amount of soot is less than the predetermined amount in an operation state (high rotation and high load) in which soot generated by combustion by the main injection is a predetermined amount or more. It is set to increase the fuel injection (amount or rate) by injection and suppress the generation of soot. 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 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.
[0041]
Further, as a modified example, the fuel injection amount Q _fu by the post-injection is also changed in a region where there is a lot of soot other than at the time of high rotation and high load, for example, A / F rich, pilot injection execution, main injection retard, etc. It may be increased as compared with the operating state.
[0042]
Furthermore, the state of occurrence of soot using a map for setting the injection amount Q _fu of after-injection regardless may set the injection amount Q _fu of soot injection. Further, the post-injection may not be executed at low rotation / low load such as idling, and the post-injection may be executed in a region other than the low rotation / low load. Further, a configuration may be used in which a map in which the post-injection amount becomes 0 during steady operation is used, and a predetermined value as described later is added to the post-injection amount that is 0 only during predetermined acceleration, and post-injection is executed.
[0043]
The injection timing I _fu of the post-injection is such that the combustion of the fuel by the post-injection is started when the diffusion combustion by the main injection is finished, that is, when the heat generation rate of the combustion by the main injection becomes substantially 0 or less. It is set on the map in consideration of the ignition delay (0.4 to 0.7 ms) of injection and the invalid injection time.
[0044]
By setting in this way, when the heat generation rate becomes substantially 0 or less, that is, when the diffusion combustion of the main injection fuel in the combustion chamber is completed, the combustion of the fuel by the post injection is started. become. 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.
[0045]
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.
[0046]
The heat generation rate dQ / dθ is expressed as the following equation (1) according to “Lecture of Internal Combustion Engine” (Fujio Nagao, Yokendo Co., Ltd.).
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.
[0047]
According to the manual of the combustion analyzer CB566 manufactured by Ono Sokki Co., Ltd., the specific heat ratio K (θ) is expressed based on the following formulas (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)
Here, Cp is constant pressure specific heat, Cv is constant volume specific heat, Ro is gas constant, M is the molecular weight of air, T (θ) is gas temperature, G is gas weight, ap, b, c, d are other constants. is there.
[0048]
From the above formulas (2) to (5), the heat generation rate dQ / dθ shown in the formula (1) is a function f (P (θ), V of the cylinder pressure P (θ) and the stroke volume V (θ). (Θ)). Further, when the stroke volume V (θ) is expressed on the basis of the bore diameter B and the stroke S, it becomes as shown in the following formula (6). Therefore, the heat generation rate dQ / dθ is expressed by the following formula (7). As shown.
V (θ) = (π · B2S / 8) · (1-cos θ) (6)
dQ / dθ = [f (P (θ + Δθ), V (θ + Δθ)) − f (P (θ), V (θ))] / Δθ (7)
[0049]
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 as described above, the post-injection is performed from this end point. A map is used in which the time point before the delay time such as the ignition delay time is the injection timing _Ifu of the post-injection.
[0050]
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. 3B, which is a graph of the results 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 Diffusion combustion ends at time t2 delayed by τ _f2 (about 0.5 ms).
[0051]
In addition, when the engine speed is 2500 rpm and the average effective pressure Pe is 0.9 Mpa, as shown in FIG. 3 (c), diffusion combustion is performed for a considerably long time as compared with heat generation Y by premixed combustion. It can be seen that the heat generation K occurs due to, and diffusion combustion ends at a considerably later time t3 that is delayed from the ignition delay τ _f3 (about 0.7 ms) from about 48 ° (CA) after compression top dead center.
[0052]
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. Although it is difficult, it can be seen that the diffusion combustion ends at a relatively early time t1 that is delayed from the ignition delay τ _f1 (about 0.6 ms) from about 30 ° (CA) after the compression top dead center.
[0053]
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 post-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.
[0054]
This is a graph obtained by experimenting the relationship between the post-injection timing and the amount of soot generated in each of the low rotation and low load, the middle rotation and middle load, and the high rotation and high load, FIGS. 4 (a), (b), ( It is clear from c).
[0055]
In the present embodiment, as shown by the needle lift amount in FIG. 3, 30 ° (CA) after compression top dead center at low rotation and low load, and 35 ° (CA) after compression top dead center at medium rotation. 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 It is set on the map so that the combustion by the post-injection is started at t3 and the heat generation shown by the dotted line in FIG. 4 occurs. 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.
[0056]
Next, in step S11, the fuel injection valve 5 is operated according to the amounts Q _b , Q _fu and the timings I _b , I _fu set in step S2, S8, or S9, and the main injection into the combustion chamber, and Post injection is performed.
[0057]
Next, in step S12, it is determined whether or not it is in a high rotation range (for example, 2500 rpm or more). It is determined whether or not.
[0058]
If YES in step S12 or step S13, that is, if it is determined that the engine is in the high speed range or the high load range, the process proceeds to step S14, where the rate of change Δα of the accelerator opening α is predetermined based on the signal from the accelerator sensor 32. It is determined whether or not it is smaller than the value Δα ₀ , that is, whether or not it is in a predetermined steady operation state.
[0059]
If NO in step S13 or S14, that is, it is determined that the vehicle is not in a high load range or is not in a predetermined steady operation state, it is determined in step S15 whether or not it is an idle region (ID). In the present embodiment, the engine speed 500 rpm to 1000 rpm and the accelerator opening 0 are set as the idle region, but the idle region may be determined according to other criteria. If NO in step S15, that is, if it is determined that the region is not an idle region, the process proceeds to step S16, where the counter n and T ′ (θ) described later are reset and the process returns.
[0060]
If YES in step S14 or step S15, that is, if it is determined that the vehicle is in a predetermined steady operation state or the idle region, the required time Tθ ′ of the predetermined crank period is read in step S17. As the predetermined crank period, for example, 10 ° to 60 ° crank angle (CA) is set from immediately after main injection to 60 ° crank angle (CA), and the required time of this predetermined crank angle is set as the expansion stroke of each cylinder. Every time, it is detected and read by an IC timer or the like. As the required time Tθ ′ is longer, the torque decrease is larger. Therefore, it is possible to detect (estimate) the torque generated by the main injection and the post-injection based on the detected required time Tθ ′. Become.
[0061]
Next, 1 is added to the counter n in step S18, Tθ ′ (n), which is the current Tθ ′, is stored in step S19, and it is determined whether or not the counter n is equal to or greater than a predetermined value n ₀ in step S20. To do. n ₀ is an arbitrary constant, but is selected from the range of 10 to 1000 in this embodiment. If NO is determined in step S20, the process returns. If YES is determined, in step S21, Tθ ′ (n ₁ ) to Tθ ′ (n ₀ ) are averaged to calculate an average value Tθ. .
[0062]
Then clears the counter n at step S22, T.theta in step S23 is a predetermined value T.theta ₀ is determined whether larger. When YES, that T.theta is determined to be greater than a predetermined value T.theta ₀ in step S23, the process proceeds to step S24, the coefficient α is subtracted from the injection timing I _fu injection after being set in step S9, the injection timing of the post injection Correction to shift to the advance side is performed. On the other hand, NO i.e. T.theta in step S23. If it is determined to be equal to or less than the predetermined value T.theta _0, the process proceeds to step S25, the coefficient β is applied to the injection timing I _fu injection after being set in step S9, the post-injection Correction for shifting the injection timing to the retard side is performed. Since there is a relationship of | α |> | β |, the degree of correction toward the advance side is set larger than the degree of correction toward the retard side.
[0063]
FIG. 5 is a graph showing the relationship between the fuel consumption rate at the time of high load and high rotation (2500 rpm, 0.9 Mpa) and the injection timing of post-injection. In this graph, the accelerator opening is selected so that the sum of the torque due to the combustion of the main injection and the torque due to the combustion of the post injection becomes a certain target torque, and the injection timing of the post injection is the injection timing of the main injection. The vertical axis shows the fuel efficiency when the vehicle is moved to the retarded angle side. From this graph, when the injection timing of the post-injection is retarded from about 48 ° (crank angle) after the main injection, which is the set timing of post-injection at the time of high load and high rotation, the fuel consumption rate may deteriorate rapidly Recognize. This means that when the injection timing of the post-injection is retarded from about 48 ° (crank angle) after the main injection, the accelerator opening must be increased in order to produce the target torque. . Therefore, when the injection timing of the post-injection is retarded from about 48 ° (crank angle) after the main injection and the accelerator opening is maintained, the output torque drops.
[0064]
Here, since the torque due to the combustion of the main injection is considered not to be affected by the injection timing of the post-injection, the drop in the output torque is a drop in the torque due to the combustion of the post-injection, and the injection timing of the post-injection is It is considered that the output torque of the engine due to the combustion of the post-injection falls when it is on the retard side from about 48 ° (crank angle) after the main injection.
[0065]
For this reason, when the output torque of the engine during combustion by the post-injection (after) is detected and this value is lower than a predetermined value (Tθ ₀ ), the injection timing of the post-injection is the predetermined time, for example, after the main injection It can be seen that it is on the retard side from about 48 ° (crank angle). For this reason, the injection timing of the post injection is shifted to the advance side by α, and the delay of the post injection is corrected.
[0066]
On the other hand, when the output torque during combustion by the post-injection is equal to or greater than a predetermined value (Tθ ₀ ), the injection timing of the post-injection may be on the advance side from about 48 ° (crank angle) after the main injection. Therefore, the injection timing of post-injection is shifted to the retard side by β to correct “too early” of post-injection.
[0067]
In the present embodiment, by performing the correction to the advance side and the correction to the retard side at all times, control is performed so that the post-injection is performed at an appropriate time.
[0068]
Then, by so-called guard processing in order to prevent extreme retard-advance in step S26, the return map is rewritten to set the injection timing I _fu of after-injection in step S27.
[0069]
When the map is rewritten, for example, when the correction amount (advance angle) of the injection timing I _fu (Ne, Tr) with respect to the rotation speed Ne and the torque Tr is α, the injection timing I _fu (Ne with respect to the rotation speed Ne ₁ and the torque Tr ₁ . ₁ , Tr ₁ ) is corrected by an amount corresponding to the difference in the rotational speed or torque, such as being advanced by (Ne ₁ / Ne) α or (Tr ₁ / Tr) α.
[0070]
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. For example, when the retard is retarded according to the amount of torque change when the post-injection timing is forcibly advanced or retarded, the advance is corrected when the torque decreases greatly, while the decrease in torque is small. When it is (below a predetermined value), control may be performed so as to execute retardation correction (the degree of correction is small).
[0071]
In the above embodiment, it is determined whether or not combustion by post-injection has occurred at a predetermined time based on the torque. However, in the process shown in the flowchart of FIG. Whether or not combustion by post-injection has occurred at a predetermined time may be determined based on the in-cylinder pressure fluctuation.
[0072]
The flowchart in FIG. 6 shows the main part of the process for correcting the injection timing of the post-injection based on the fluctuation of the in-cylinder pressure in the combustion chamber. Since the process is the same as that after step S25 in FIG. 2 after step S25 ′, the processing from step S17 ′ to step S25 ′ will be described here.
[0073]
In step S14 or step S15 of FIG. 2B, if YES, that is, if it is determined that the vehicle is in a predetermined steady operation state or in an idle region, the cylinder pressure trajectory during the predetermined crank period is detected by the cylinder pressure sensor in step S17 ′. As the predetermined crank period, for example, 10 ° to 60 ° crank angle (CA) or the like is set from immediately after main injection to 60 ° crank angle (CA).
[0074]
Next, in step S18 ′, the heat generation rate for each crank angle is calculated.
This calculation is performed, for example, by the method described above. Further, in step S19 ′, when the heat generation by the main injection ends (that is, when the diffusion combustion by the main injection ends), the injection timing I ′ _fu best (n ) Is calculated and stored.
[0075]
Further, in step S20 ′, it is determined whether or not the counter n is greater than or equal to a predetermined value n ₀ . n ₀ is an arbitrary constant, but is selected from the range of 10 to 1000 in this embodiment. Step S20 ', the return when it is determined NO, and when the answer is YES step S21', the average of the values of 'a _fu best (1) I' I to _fu best (n ₀₎ is performed The average value I _fu best is calculated.
[0076]
Next, the counter n is cleared in step S22 ′, and in step S23 ′, it is determined whether or not the current I _fu set in step S9 is greater than I _fu best. If YES in step S23 ′, that is, if it is determined that I _fu is greater than I _fu best, the process proceeds to step S24 ′, where the coefficient γ is added to the post-injection injection timing I _fu set in step S9, and the post-injection Correction is performed to shift the injection to the advance side. On the other hand, if NO in step S23 ′, that is, if it is determined that I _fu is equal to or less than I _fu best, the process proceeds to step S25 ′, and the coefficient δ is subtracted from the post-injection injection timing I _fu set in step S9. Correction is performed so that the post-injection is shifted to the retarded angle side. Since there is a relationship of | γ |> | δ |, the correction degree toward the advance side is set larger than the correction degree toward the retard side.
[0077]
Furthermore, instead of torque fluctuation and in-cylinder pressure, the configuration may be such that the combustion state in the combustion chamber is detected by measuring the combustion light in the combustion chamber and the injection timing of the post-injection is corrected.
[0078]
In the above embodiment, the main injection and the post-injection are each performed only once. However, the present invention can also be applied to those in which these are multistage injections.
[0079]
Further, in the present embodiment, the injection by the main injection is diffusion combustion accompanied by soot generation, but the main injection is performed from the intake stroke to the first half of the compression stroke, and all of the combustion by the main injection is premixed combustion. Even when post-injection is performed to supply HC or the like as a reducing agent to the downstream catalyst, the combustion end timing by main injection is accurately obtained based on torque, in-cylinder pressure, etc. The post-injection timing may be corrected so that an appropriate reducing agent can be supplied on the basis of the combustion end timing thus obtained.
[0080]
In the above embodiment, the combustion state is detected by the output torque and the in-cylinder pressure, but other methods, for example, a method using combustion light in which a laser beam or the like is irradiated into the combustion chamber and detected by a change in its color. Etc. may be used.
[0081]
【The invention's effect】
As described above, according to the present invention, it is possible to obtain a desired effect by post-injection such as performing post-injection at an appropriate time to efficiently reduce soot in the exhaust gas.
[Brief description of 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.
FIG. 2A is the first half of a flowchart showing fuel injection control executed in the ECU.
FIG. 2B is the second half of the flowchart showing the fuel injection control executed in the ECU.
FIG. 3 is a time chart showing a heat generation rate in a combustion chamber.
FIG. 4 is a graph showing the relationship between post injection timing and soot generation amount.
FIG. 5 is a graph showing the relationship between post-injection timing and fuel efficiency.
FIG. 6 is a flowchart showing a part of a modified example of fuel injection control executed in the ECU.
[Explanation of symbols]
1: Diesel engine 2: Cylinder 5: Fuel injection valve 35: ECU
36: Injection control means 37: EGR control means

Claims (4)

A fuel injection valve for directly injecting fuel into the combustion chamber of the diesel engine, and a main injection control means for controlling main injection in which fuel is injected from the fuel injection valve at a predetermined time from the intake stroke to the vicinity of the top dead center of the compression stroke When,
After the main injection, the post-injection in which additional fuel is injected from the fuel injection valve is controlled, and the injection timing of the post-injection is controlled so that the combustion of the post-injection starts when the combustion by the main injection ends. Post-injection control means;
Detecting means for detecting a combustion state in the combustion chamber based on detection of an output torque by combustion of post-injection;
When the post-injection control unit determines that the output torque is equal to or less than a predetermined value based on the output torque generated by the post-injection combustion detected by the detection unit, the post-injection control unit performs the post-injection after the completion of the main injection combustion. Is determined to have started combustion, correction is performed to shift the injection timing of the post-injection to the advance side, and when it is determined that the output torque is greater than a predetermined value, the combustion is performed before the end of combustion by the main injection. It is determined that combustion by injection has started, and correction is performed to shift the injection timing of the post-injection to the retarded side,
A fuel injection control device for a diesel engine. The degree of correction to the advance side by the post-injection control means is greater than the degree of correction to the retard side;
The fuel injection control device for a diesel engine according to claim 1. The post injection control means, the engine speed is high rotation or mean effective pressure Pe above 2500rpm in steady-state operation area of the high load of 0.9 MPa, to perform the correction,
The fuel injection control device for a diesel engine according to claim 1 or 2. The fuel injection control means performs feedback control so that the engine speed converges to a predetermined speed during idling, and executes the correction during the feedback control.
The fuel injection control device for a diesel engine according to any one of claims 1 to 3.

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