JP2002364437A - Fuel injection controller for diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel injection controller for a diesel engine capable of making exhaust performance and output performance compatible. SOLUTION: A common rail type fuel injection system is applied as a fuel injection system for the diesel engine capable of plural fuel injections per combustion cycle. An ECU 20 calculates an optimum fuel injection quantity from input of various sensors, and controls drive of injectors 14 according to the fuel injection quantity. The ECU 20 divides the fuel injection into main injection and after-injection following the main injection if necessary to execute the fuel injection. The ECU 20 sets a fuel injection quantity (a smoke limit injection quantity QSL) at a smoke limit point wherein smoke concentration rapidly increases. When the injection quantity exceeding the fuel injection quantity at the smoke limit point is required, the ECU 20 executes the main injection with the fuel injection quantity at the smoke limit point, and executes the after- injection by just the exceeding injection quantity after the main injection.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection control device for a diesel engine.

[0002]

2. Description of the Related Art In a diesel engine, it has been known that control for dividing fuel injection into a plurality of injections is effective for improving exhaust performance and output performance. One of such techniques is after injection. .

For example, in Japanese Patent Application Laid-Open No. 62-75051, the smoke concentration is detected by a smoke concentration detector in the exhaust passage of a diesel engine, and the interval between fuel injections is controlled so that the smoke concentration is minimized. . Actually, the increase or decrease of the smoke concentration is determined for each predetermined interrupt,
The injection interval is increased or decreased in accordance with the decreasing tendency of the smoke each time. Thus, the required torque of the engine is maintained while suppressing the smoke concentration to a minimum.

In Japanese Patent Application Laid-Open No. 9-324631, only the first-stage fuel injection is performed in a low / medium-load region of the engine, and the second-stage fuel injection is performed after the first-stage fuel injection in a high-load region. Do. Thus, in all load ranges, smoke and NOx are reduced simultaneously and significantly.

[0005]

However, in the prior arts of the above publications, no consideration is given to the ratio of the fuel amount to be divided into the after injection. Therefore, in practice, either the exhaust performance or the output performance may be impaired.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a fuel injection control device for a diesel engine capable of achieving both exhaust performance and output performance. It is.

[0007]

The present invention is based on the premise that the fuel injection system is capable of performing a plurality of fuel injections per fuel cycle, and the setting means sets the fuel at the smoke limit point where the smoke concentration sharply increases. The injection amount is set.
Also, when an injection amount exceeding the fuel limit at the smoke limit point is required, the injection control means performs the main injection at the fuel injection amount at the smoke limit point, and the excess injection amount is applied after the main injection to the after injection. Is done. Incidentally, the above-mentioned smoke limit point can be defined as a point at which the amount of smoke emission increases rapidly when the injection amount is increased, and is defined by the spray characteristics of the injector and the shape of the combustion chamber.

In this case, since the main injection is performed so that the smoke discharge amount does not exceed the limit point, an excessive increase in the smoke discharge amount can be suppressed. Further, since the required injection amount is supplied to the engine by being divided into the main injection and the after injection, a decrease in the output can be suppressed. Therefore, according to the present invention, it is possible to achieve both exhaust performance and output performance.

According to the second aspect of the present invention, when the required injection amount is smaller than the fuel injection amount at the smoke limit point, the after injection is not performed. In this case, it is possible to correctly determine whether to perform the after-injection.

[0010] The fuel injection amount at the smoke limit point changes depending on the engine speed. Therefore, as described in claim 3, it is preferable to set the fuel injection amount at the smoke limit point according to the engine speed. In this case, since an appropriate injection amount can be set as the fuel injection amount at the smoke limit point, the fuel injection amount for after injection can be divided at an appropriate ratio.

On the other hand, in a diesel engine equipped with an EGR device, the fuel injection amount at the smoke limit point changes according to the EGR amount. Further, since the intake air amount changes depending on the altitude position where the vehicle travels, the fuel injection amount at the smoke limit point changes according to the altitude. Therefore, it is preferable to correct the fuel injection amount at the smoke limit point according to the EGR amount by the EGR device. Alternatively, the fuel injection amount at the smoke limit point may be corrected according to the altitude at which the vehicle travels. With these configurations, the fuel injection amount at the smoke limit point can be accurately obtained, and the control accuracy of the fuel injection can be improved.

According to the present invention, a smoke concentration detector for detecting smoke concentration in exhaust gas is provided in an exhaust passage of a diesel engine, and the smoke concentration detected by the smoke concentration detector is limited to a smoke limit. When the point is reached, the after-injection is performed by the injection control means. Also in such a case, the fuel injection amount for after injection can be divided at an appropriate ratio, similarly to the above-described inventions.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. In the present embodiment,
The present invention is embodied in a common rail fuel injection system for a diesel engine, and in this fuel injection system, a plurality of fuel injections can be performed in one combustion cycle.

FIG. 1 is a diagram showing a system configuration according to the present embodiment. In FIG. 1, a high-pressure pump 11 pressurizes fuel in a fuel tank 10 and discharges high-pressure fuel to a common rail 12. The common rail 12 accumulates high-pressure fuel discharged from the high-pressure pump 11 at a pressure equivalent to the injection pressure. The common rail 12 includes the engine 1
The injectors 14 are connected by the number of three cylinders.
After the high-pressure fuel is once accumulated in the common rail 12,
Injection is supplied from the injector 14 to the engine combustion chamber. Although not shown, a well-known EGR device (exhaust gas recirculation device) is attached to the engine 13.
The EGR amount is adjusted by the opening of the EGR valve.

The ECU 20 is a known electronic control unit having a microcomputer. The ECU 20 includes:
Detection signals are input from a rotation speed sensor 21, an accelerator opening sensor 22, an EGR sensor 23, and an altitude sensor 24, and E
The CU 20 determines the engine speed,
The accelerator opening, EGR amount, and altitude position are calculated. In addition,
The EGR sensor 23 may be embodied as a sensor that detects the lift amount of the EGR valve. However, in addition to the EGR sensor 23, a stepping motor driven E
A GR device that detects the control amount of the stepping motor may be used.

Further, the ECU 20 calculates an optimum fuel injection amount based on each of the detected information, and controls the driving of the injector 14 based on the calculated fuel injection amount. In this case, E
The CU 20 performs the fuel injection by dividing it into a main injection and a subsequent injection as necessary.

Next, the control procedure of the fuel injection will be described with reference to the flowchart of FIG. In the present embodiment, the smoke limit point at which the smoke concentration rapidly increases is checked in advance,
The fuel injection amount of the main injection and the after injection is divided based on the smoke limit point. Here, the smoke emission amount with respect to the fuel injection amount has a relationship as shown in FIG. 3, and the smoke injection amount at the smoke limit at which smoke increases rapidly is referred to as "smoke limit injection amount QSL". FIG.
Is determined by the spray characteristics, the shape of the combustion chamber, and the like. Therefore, the smoke limit injection amount QSL is set for each model of the engine.

When the ECU 20 activates FIG. 2 due to interruption of a predetermined crank angle or the like, first, at step 110
Then, the engine speed and the accelerator opening are determined, and in the following step 120, the target injection amount Qx is calculated from the engine speed and the accelerator opening.

In step 130, a smoke limit injection amount QSL is calculated. In this case, since the smoke limit injection amount QSL changes according to the engine speed, the smoke limit injection amount QSL is calculated based on the engine speed at each time. Specifically, for example, the smoke limit injection amount QSL is calculated using the relationship shown in FIG.

In this case, the smoke limit injection amount Q
SL changes depending on the EGR amount and the altitude position during driving of the vehicle. Therefore, the smoke limit injection amount QSL is corrected based on the EGR amount and the altitude position. That is, at the time of EGR operation,
Even if the injection amount is the same, the smoke emission amount increases compared to when the EGR is not activated.
SL shifts to the decreasing side. The smoke limit injection amount QSL changes according to the EGR amount. In this case, FIG.
Using the relationship (a), a correction term ΔQEGR is calculated according to the EGR amount in each case.

At high altitudes, the intake air amount decreases, and the smoke limit injection amount QSL shifts to a decreasing side. In this case, the correction term ΔQhigh is calculated according to the altitude in each case using the relationship in FIG. In particular, in a non-supercharged engine, since the intake air amount is strongly affected by a change in the atmospheric pressure, a high altitude correction is required.

Then, the correction term ΔQEG calculated as described above
The smoke limit injection amount QSL is corrected using R and ΔQhigh. That is, the smoke limit injection amount Q before correction
The correction terms ΔQEGR and ΔQhigh are added to SL, and the sum is used as the final smoke limit injection amount QSL.

Next, at step 140, it is determined whether or not the target injection amount Qx in each case exceeds the smoke limit injection amount QSL. In the case of Qx> QSL, the effect of smoke reduction by after injection can be expected. Therefore, after injection is performed after main injection, the main injection amount QM
And the after injection amount QA are set. More specifically, in step 150, the main injection amount QM is set to QSL, and the after injection amount QA is set to Qx -QSL. Thus, the shortage of the main injection with respect to the target injection amount Qx is injected by the after injection.

When Qx ≦ QSL, the effect of smoke reduction is not required, so that only the main injection is performed. That is, in step 160, the main injection amount QM = Qx and the after injection amount QA = 0. Finally, at step 170, an injection control signal is calculated and output.

By the above-described fuel injection control, the main injection and the after injection are sequentially performed in the form shown in FIG. In the present embodiment, step 13 in FIG.
0 corresponds to the "setting means" described in the claims,
Step 150 corresponds to the “injection control means”.

According to the embodiment described above, the following effects can be obtained. Smoke limit injection quantity QSL
Since the main injection is performed so as not to exceed (the fuel injection amount at the smoke limit point), an excessive increase in the smoke discharge amount can be suppressed. Further, since the required injection amount is supplied to the engine by being divided into the main injection and the after injection, a decrease in the output can be suppressed. Therefore, according to the present embodiment, it is possible to achieve both exhaust performance and output performance.

Since the smoke limit injection amount QSL is set according to the engine speed, the EGR amount and the altitude position,
The smoke limit injection amount QSL is accurately obtained, and the control accuracy of the fuel injection is improved. In this case, the main injection amount and the after injection amount can be divided at an optimal ratio while reflecting the engine operating conditions.

The present invention can be embodied in the following forms other than the above. In the above embodiment, the EGR correction and the altitude correction were performed when calculating the smoke limit injection amount QSL, but these corrections are not essential, and the invention is embodied without performing at least one of these corrections. It is also possible.

A smoke concentration detector for detecting the smoke concentration in the exhaust gas is provided in the exhaust passage of the diesel engine, and after the smoke concentration detected by the smoke concentration detector reaches the smoke limit point, after-injection is performed. I do. More specifically, for example, a light transmission type smoke concentration sensor is provided in the engine exhaust pipe, and a detection value of the smoke concentration sensor is taken into the ECU 20 as needed. Incidentally, it is considered that the transition of the smoke concentration detection value with respect to the fuel injection amount Q is as shown in FIG. In this case, the ECU 20 recognizes the fuel injection amount when the smoke concentration detection value reaches the smoke limit as the smoke limit injection amount QSL, and sets the main injection amount QM = QSL and the after injection amount QA = Qx-QSL by the injector 14. Control the fuel injection amount. In such a case, as described above, the main injection amount and the after injection amount can be divided at an optimal ratio.

In the above-described embodiment, a specific example of the common rail type fuel injection system has been described. However, any fuel injection system for performing this control may be used as long as fuel injection can be performed a plurality of times per combustion cycle. Is good. That is, the present invention can be embodied in a fuel injection system generally used in a diesel engine, such as an injection system using a distribution type fuel injection pump or an injection system using a unit injector.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an outline of a system according to an embodiment of the invention.

FIG. 2 is a flowchart showing a control procedure of fuel injection.

FIG. 3 is a diagram showing a relationship between a fuel injection amount and a smoke emission amount.

FIG. 4 is a diagram showing a relationship between an engine speed and a smoke limit injection amount.

FIG. 5 is a diagram for setting an EGR correction term and an altitude correction term.

FIG. 6 is a time chart showing a form of main injection and after injection.

FIG. 7 is a diagram showing a relationship between a fuel injection amount and a smoke concentration detection value.

[Explanation of symbols]

 13 ... engine, 14 ... injector, 20 ... ECU.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 43/00 301 F02D 43/00 301H 301N 45/00 310 45/00 310N 312 312P 312Z (72) Inventor Hitoshi Shibata 14 Iwatani, Shimowakaku-cho, Nishio-shi, Aichi Pref. Japan Automobile Parts Research Institute (72) Inventor Showa Kojima 1-1-1, Showacho, Kariya-shi, Aichi F-term (reference) 3G084 AA01 BA13 BA15 DA01 DA10 EA11 EB09 EC01 EC03 FA01 FA10 FA28 FA33 FA37 3G092 AA02 AA06 AA17 BB01 BB13 DC09 EA10 EA11 FA01 FA18 GB06 HA05Z HA06Z HD04Z HD07Z HF08Z 3G301 HA02 HA04 HA13 JA01 JA24 KB05 LB04 NEZZ01 PA11 MA11

Claims (6)

[Claims] 1. A fuel injection system for a diesel engine capable of performing a plurality of fuel injections per combustion cycle, a setting means for setting a fuel injection amount at a smoke limit point at which a smoke concentration increases rapidly, and a fuel injection at a smoke limit point. When an injection amount exceeding the required amount is required, the main injection is performed with the fuel injection amount at the smoke limit point, and the injection control means for after-injection of the excess injection amount after the main injection is provided. Fuel injection control device for diesel engine. 2. The fuel injection control device for a diesel engine according to claim 1, wherein the after-injection is not performed when the required injection amount is smaller than the fuel injection amount at the smoke limit point. 3. The fuel supply system according to claim 1, wherein said setting means sets a fuel injection amount at a smoke limit point according to an engine speed.
3. A fuel injection control device for a diesel engine according to claim 1. 4. An EGR device for recirculating a part of exhaust gas of a diesel engine to an intake system, wherein a fuel injection amount at a smoke limit point is corrected in accordance with an EGR amount by the EGR device. A fuel injection control device for a diesel engine according to any one of the above. 5. A fuel injection control device mounted on a vehicle together with a diesel engine, the fuel injection control device correcting a fuel injection amount at a smoke limit point according to an altitude at which the vehicle travels.
5. The fuel injection control device for a diesel engine according to any one of 4. 6. A smoke concentration detector for detecting smoke concentration in exhaust gas is provided in an exhaust passage of a diesel engine, and when the smoke concentration detected by the smoke concentration detector reaches a smoke limit point, the injection control is performed. The fuel injection control device for a diesel engine according to claim 1 or 2, wherein after-injection is performed by the means.