JP2007162548A - Control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device of an internal combustion engine capable of properly setting a boundary for change-over according to a cetane number when changing over a plurality of rich combustion modes according to operation condition. <P>SOLUTION: When enriching control of A/F is performed, a post-injection mode and an EGR increasing mode are changed over according to operation condition and the boundary for change-over of them is varied according to an estimation of the cetane number. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a control device for an internal combustion engine, and more particularly to a control device for switching between a plurality of air-fuel ratio enrichment modes.

The exhaust passage of a diesel internal combustion engine may be provided with a lean NO _X purification catalyst (hereinafter abbreviated as LNC) for reducing and purifying nitrogen oxide (hereinafter abbreviated as NO _X ) in exhaust gas. . In this LNC, when the air-fuel ratio of exhaust gas (hereinafter referred to as exhaust A / F) is higher than a predetermined value (hereinafter referred to as lean), in other words, NO _X taken in when the oxygen concentration is high, When the exhaust A / F is lower than a predetermined value (hereinafter referred to as rich), in other words, when the oxygen concentration is reduced, the exhaust A / F is released and reduced to be harmless.

The LNC is, NO if _X absorption amount increases because the absorbing performance is reduced, timely, exhaust gas reduces the oxygen concentration to increase the CO and HC concentration of the reducing agent by enriching the, whereby NO from LNC _X release is promoted and reduced and purified sufficiently.

As a method for enriching the exhaust A / F, post-injection for injecting a small amount of fuel into the combustion chamber in the expansion stroke (see Patent Document 1), or exhaust for recirculation from the exhaust passage to the intake passage It is known to increase the amount of gas (hereinafter abbreviated as EGR) (see Patent Document 2).
JP 2000-356126 A JP 2003-138970 A

  However, when enriching the exhaust A / F, if post-injection is added, a part of the fuel supplied by post-injection hits the cylinder wall surface, which causes oil dilution that gets mixed into the oil. In some cases, fuel that does not contribute to engine output is injected and fuel efficiency is deteriorated, or that the catalyst is thermally deteriorated by direct contact of mist-like unburned fuel with the catalyst.

  On the other hand, when a large amount of EGR is introduced to enrich the exhaust A / F, the amount of fresh air inflow is relatively reduced. There is a problem in that a large amount of fuel is generated and the fuel injection timing needs to be advanced by an amount corresponding to a decrease in ignitability, resulting in increased combustion noise.

  The present invention has been devised to eliminate such disadvantages of the prior art, and its main object is to improve the exhaust A / F so as not to cause the above-mentioned problems. It is another object of the present invention to provide a control device for an internal combustion engine.

  In order to solve such problems, the present invention provides an intake flow rate control means (intake control valve 5) for controlling the intake flow rate to the combustion chamber of the internal combustion engine, and a fuel injection means (fuel injection) for injecting fuel into the combustion chamber. And a fuel injection control means (included in the ECU 18) for controlling the fuel injection from the fuel injection means to be executed in a plurality of times as main injection and sub-injection in one fuel injection process. An internal combustion engine control device comprising exhaust gas recirculation means (EGR passage 11) for recirculating exhaust gas discharged to the exhaust passage to the intake passage and exhaust gas recirculation amount control means (EGR control valve 13) for controlling the exhaust gas recirculation amount The first air-fuel ratio enrichment means by sub-injection, the second air-fuel ratio enrichment means by exhaust gas recirculation amount, the fuel property estimation means (cetane number map 32), the first air-fuel ratio enrichment means, Second air / fuel ratio Switching means (region discriminating map 33 and selector 34) for switching the execution with the switching means according to the driving situation, and the first air-fuel ratio enrichment means and the second air-fuel ratio enrichment means The switching boundary is changed according to the estimation result of the fuel property.

  According to the present invention, in the low load region where the combustion noise and the amount of smoke generated due to the enrichment of the exhaust A / F do not matter so much, the oil dilution is performed by performing enrichment by increasing the EGR amount. In addition, deterioration of fuel consumption and thermal deterioration of the catalyst can be reduced. Further, in the middle and high load region, the increase in combustion noise and smoke generation can be suppressed by performing the post injection. Then, by changing the boundary line for switching the enrichment control mode according to the cetane number, it is possible to avoid the adverse effects caused by the decrease in ignitability in the case of a low cetane number.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a basic configuration diagram of an internal combustion engine E to which the present invention is applied. The internal combustion engine (diesel engine) E has a mechanical configuration that is not different from that of a known one, and includes a turbocharger 1 with a supercharging pressure variable mechanism. A passage 2 is connected, and an exhaust passage 3 is connected to the turbine side of the turbocharger 1. An air cleaner 4 is connected to the upstream end of the intake passage 2, and an intake control valve 5 for adjusting the flow rate of fresh air flowing into the combustion chamber at an appropriate position of the intake passage 2, and flows in a low rotation speed / low load operation region. A swirl control valve 6 is provided for reducing the cross-sectional area of the road and increasing the intake air flow velocity. At the downstream end of the exhaust passage 3, a three-way catalyst (hereinafter abbreviated as TWC) 7, a filter (hereinafter abbreviated as DPF) 8 for removing particulate matter such as soot, and the LNC 9 described above are provided. The exhaust gas purification device 10 is connected in series in this order along the flow of exhaust gas.

  The swirl control valve 6 and the exhaust passage 3 immediately after the combustion chamber are connected to each other via an exhaust gas recirculation (hereinafter abbreviated as EGR) passage 11. The EGR passage 11 includes a cooler passage 11a and a bypass passage 11b branched via a switching valve 12, and an EGR control valve 13 for adjusting the amount of EGR flowing into the combustion chamber is provided at the junction. .

  The cylinder head of the internal combustion engine E is provided with a fuel injection valve 14 with its tip facing the combustion chamber. The fuel injection valve 14 is connected to a common rail 15 that stores fuel in a predetermined high pressure state, and a fuel pump 17 that is driven by a crankshaft and pumps fuel from the fuel tank 16 is connected to the common rail 15.

  These turbocharger 1 supercharging pressure variable mechanism 19, intake control valve 5, EGR passage switching valve 12 and EGR control valve 13, fuel injection valve 14, fuel pump 17... (Referred to as “abbreviated”) 18 (see FIG. 2).

  On the other hand, as shown in FIG. 2, the ECU 18 includes an intake valve opening sensor 20, a crankshaft rotation speed sensor 21, an intake flow rate sensor 22, a supercharging pressure sensor 23, and an EGR valve disposed at predetermined locations of the internal combustion engine E. Output signals from the opening sensor 24, common rail pressure sensor 25, accelerator pedal operation amount sensor 26, in-cylinder pressure sensor 27, crankshaft rotation angle sensor 28, LNC temperature sensor 29, etc. are input.

  The memory of the ECU 18 stores a map in which control target values for each control object including the optimum fuel injection amount obtained in advance by experiments or the like according to the crankshaft rotation speed and the required torque (accelerator pedal operation amount) are set. Therefore, each part is controlled so that an optimal combustion state is obtained in accordance with the operating state of the internal combustion engine E.

  In the diesel internal combustion engine E, for example, A / F enrichment control is performed during regeneration processing of the LNC 9. In the enrichment control, the EGR increase mode and the post injection mode are selectively executed.

  Post-injection is less susceptible to combustion noise and smoke, and can be executed in all operating areas, but has disadvantages such as oil dilution, fuel consumption deterioration, and catalyst heat deterioration.

  On the other hand, the EGR increase has a demerit that a large amount of smoke is generated in a high load region and combustion noise is deteriorated instead of the demerit of the above-described post injection, and can only be executed in a low load region.

  Therefore, in the present invention, the A / F enrichment control is performed by switching between the EGR increase mode and the post injection mode according to the engine load given by the required torque and the crankshaft rotational speed.

  Also, in the case of a diesel internal combustion engine, even if the fuel injection timing is the same, the actual ignition timing varies depending on the cetane number, and if the cetane number is low, combustion stability will not be improved unless the fuel injection timing is advanced to some extent. On the other hand, if the fuel injection timing is advanced excessively, the rate of increase in pressure increases, which causes a disadvantage that the combustion noise becomes high. Therefore, in the present invention, the cetane number of the currently used fuel is estimated, and the boundary line for switching the A / F enrichment control mode is changed according to the cetane number.

  The control procedure of the present invention will be described below with reference to FIGS.

  First, the injection timing is detected from the operation command signal to the fuel injection valve 14 (step 1), and the actual ignition timing is detected from the signal of the in-cylinder pressure sensor 27 (step 2). These signals and the output of the crankshaft rotation angle sensor 28 are compared by the ignition delay angle calculation means 31 to calculate an ignition delay angle in terms of crankshaft rotation angle (step 3).

  Next, a cetane number corresponding to this ignition delay angle is estimated with reference to a cetane number map 32 (FIG. 5) set in advance (step 4).

  Based on the result, the control mode region discrimination map 33 (FIG. 6) corresponding to the cetane number set in advance is referred to, and the A / F enrichment control mode corresponding to the cetane number of the currently used fuel is switched. The boundary line is read (step 5). Then, it is determined whether the appropriate enrichment control mode corresponding to the current load state is the post injection mode or the EGR increase mode (step 6). Based on this result, either the EGR increase mode or the post injection mode is selected by the selector 34 (steps 7 and 8), and A / F enrichment control is performed.

  Thereby, even if the enrichment control by increasing the amount of EGR is executed, the boundary of the operation region that does not require a significant increase in combustion noise and smoke can be changed. In particular, when using a low cetane fuel, combustion stability cannot be ensured unless the fuel injection timing is advanced to some extent because the ignitability is reduced, and conversely, if the fuel injection timing is advanced too much, the pressure An increase in the increase rate causes an increase in combustion noise. In this case, an increase in combustion noise can be avoided by narrowing the EGR increase mode region.

  It should be noted that the boundary line has a predetermined width so that hunting does not occur in the vicinity of the boundary line during the transition from the EGR increase mode to the post injection mode and when the reverse post injection mode shifts to the EGR increase mode. A hysteresis region is provided.

1 is an overall configuration diagram of an internal combustion engine to which the present invention is applied. It is a block diagram of a control device to which the present invention is applied. It is a block diagram in connection with mode switching control. It is a flowchart in connection with mode switching control. It is a conceptual diagram of a cetane number estimation map. It is a conceptual diagram of a control mode area | region discrimination | determination map.

Explanation of symbols

5 Intake control valve 11 EGR passage 13 EGR control valve 14 Fuel injection valve 18 ECU
32 Cetane number map 33 Area discrimination map 34 Selector

Claims (1)

Intake flow rate control means for controlling the intake flow rate to the combustion chamber of the internal combustion engine, fuel injection means for injecting fuel into the combustion chamber, and fuel injection from the fuel injection means are mainly performed in one fuel injection process. Fuel injection control means for controlling injection and sub-injection to be executed in a plurality of times, exhaust recirculation means for recirculating exhaust gas discharged to the exhaust passage to the intake passage, and exhaust recirculation amount control means for controlling the exhaust gas recirculation amount An internal combustion engine control device comprising:
First air-fuel ratio enrichment means by the sub-injection;
Second air-fuel ratio enrichment means by the exhaust gas recirculation amount;
Means for estimating fuel properties;
Switching means for switching the execution of the first air-fuel ratio enrichment means and the second air-fuel ratio enrichment means in accordance with the operating status of the internal combustion engine,
A control apparatus for an internal combustion engine, wherein a boundary for switching between the first air-fuel ratio enrichment means and the second air-fuel ratio enrichment means is changed according to the estimation result of the fuel property.

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