JP4404841B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine, and more particularly to a control device for an internal combustion engine that keeps catalyst temperature and an air-fuel ratio of exhaust gas at predetermined values so as not to cause torque fluctuation.

  In contrast to a gasoline internal combustion engine that uses a spark plug to start combustion of fuel supplied to the combustion chamber, a diesel internal combustion engine that performs self-ignition is extremely important in controlling the fuel injection timing in order to improve combustion efficiency and exhaust properties. is there. In particular, in order to improve the exhaust properties and reduce the combustion noise, it is an important requirement to lower the combustion speed, and it is common to inject fuel in multiple times in one fuel injection process. There are (for example, pilot injection, main injection, post injection, etc.).

On the other hand, a lean NO _X purification catalyst (hereinafter abbreviated as LNC) for reducing and purifying nitrogen oxide (hereinafter abbreviated as NO _X ) in exhaust gas is provided in the exhaust passage of the diesel internal combustion engine. There is. 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.

In such a diesel internal combustion engine, as the exhaust A / F becomes richer in the high rotation speed / high load operation region, the smoke emission amount and the combustion noise increase. To suppress this, In order to perform the regeneration process so that the above-described LNC NO _X absorption amount is not saturated, it is known to perform post injection in which a small amount of fuel is injected into the combustion chamber in the expansion stroke (see Patent Document 1). ).
JP 2001-55946 A

  However, if post-injection is performed without changing the intake flow rate to the combustion chamber during high-speed / high-load operation, the amount of unburned fuel contained in the exhaust increases as the post-injection amount increases. The oxidation reaction in the catalyst provided in the exhaust passage is promoted, and the catalyst temperature rises. If the post-injection amount is increased or decreased to keep the catalyst temperature appropriate, the exhaust A / F does not become an appropriate value, the catalyst regeneration process becomes insufficient, and the fuel consumption deteriorates due to the prolonged time required for the regeneration process. I will.

  On the other hand, in order to set the exhaust A / F to an appropriate value while performing the post injection, it is conceivable to reduce the pilot injection or the main injection. However, as a result, the fuel injection amount contributing to the combustion is reduced. The generated torque will decrease.

  The present invention has been devised to eliminate such disadvantages of the prior art, and its main purpose is to maintain the catalyst temperature and the exhaust A / F at predetermined values while maintaining torque fluctuations during post injection. It is an object of the present invention to provide a control device for an internal combustion engine that can suppress this.

In order to solve such a problem, claim 1 of the present invention provides a fuel injection means (fuel injection valve 14) for injecting fuel into a combustion chamber of an internal combustion engine, and a single fuel injection from the fuel injection means. Fuel injection control means (contained in the ECU 18) for controlling the main injection and sub-injection to be executed in a plurality of times in the fuel injection process, and intake flow rate control means for controlling the intake flow rate to the combustion chamber ( In the control apparatus for an internal combustion engine having the intake control valve 5 and the EGR control valve 13), the intake flow rate control means controls a fresh air flow rate, and the sub-injection is performed in a high load operation region of the internal combustion engine. When the sub-injection is executed, the intake air flow rate supplied to the combustion chamber is changed in response to the change in the injection amount of the sub-injection so that the predetermined exhaust air-fuel ratio is set in advance. control, and the Control of the constant of the exhaust air-fuel ratio, and shall be characterized by being carried out in an environment of naturally aspirated without added boost pressure.
Further, the invention of claim 2 is provided with an exhaust purification device (LNC9), and regeneration processing of the exhaust purification device is performed when the sub-injection is executed.

  According to the present invention as described above, the exhaust A / F can be kept constant by changing the intake flow rate in response to the change in the injection amount of the post-injection. The temperature can be maintained at an appropriate value. Therefore, even if the regeneration process of the LNC is performed at the same time as the exhaust A / F enrichment control in the high rotation speed / high load operation region, the exhaust A / F is maintained at a constant value. It is also possible to avoid the deterioration of exhaust emission and the deterioration of fuel consumption due to.

  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 structure itself 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 apparatus 10 is connected 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. 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 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, the common rail pressure sensor 25, the accelerator pedal operation amount sensor 26, the O ₂ sensor 27, the TWC temperature sensor 28, the 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 according to the load state of the internal combustion engine E.

  In the diesel internal combustion engine E, for example, when the crankshaft rotational speed and the required torque are suddenly increased as in the case of sudden acceleration from constant speed running, the smoke emission amount is reduced by the enrichment of A / F. Since increase and combustion noise may be caused, post injection for injecting auxiliary fuel in the expansion stroke is performed in order to suppress these. Further, in order to effectively use post injection in a high load region, regeneration processing of the LNC 9 is also performed at the same time.

Next, the control procedure of the present invention will be described with reference to FIGS.
A post injection region determination map 31 (FIG. 5) having the crankshaft rotational speed and the required torque (accelerator pedal operation amount) as addresses is searched to determine whether or not the current driving state is the post injection execution region (step). 1). The post-injection region discrimination map 31 has a predetermined hysteresis between the boundary from the non-execution region to the execution region and the boundary from the execution region to the non-execution region. Is prevented from occurring.

  If it is determined that the current state is in the post-injection execution region, the actual LNC temperature at that time is detected by the LNC temperature sensor 29, and the fuel injection is performed so as to maintain a predetermined specified temperature value set in advance. The post injection amount of the valve 14 is feedback controlled (step 2).

  At the same time, the target intake air amount map 32 having the crankshaft rotation speed and the required torque (accelerator pedal operation amount) as addresses is retrieved to obtain the target intake air amount Qair at that time, and a predetermined exhaust A is set in advance. The target intake air amount Qair is corrected by feedback control of the opening degree of the intake control valve 5 and the EGR control valve 13 so as to maintain the specified value of / F (step 3).

  Further, by the fuel injection valve 14, the target injection amount Qinj obtained from the fuel injection amount map 33 of the pilot injection and the main injection having the crankshaft rotational speed and the required torque (accelerator pedal operation amount) as addresses is obtained. The injection amounts of pilot injection and main injection are controlled (step 4).

  On the other hand, if it is determined in step 1 that the current state is in the post-injection non-execution region, post-injection for temperature control of the LNC 9 is stopped (step 5), and the target intake air amount Qair based on the exhaust A / F is Correction control is stopped (step 6). At the same time, the target injection amount Qinj of the pilot injection and the main injection obtained from the injection amount map 33 is corrected so as to maintain a predetermined specified exhaust A / F value (step 7). .

  In this way, the post-injection execution / non-execution region determination map 31 is used to determine the load state of the internal combustion engine at that time, and when it is determined that the post-injection execution region, the temperature of the LNC 9 is maintained at a predetermined value. In response to post injection in which the injection amount is feedback-controlled, the intake air amount flowing into the combustion chamber is corrected and controlled so as to maintain a predetermined exhaust A / F. We are trying to suppress it.

  Since it is difficult to obtain a desired responsiveness in the supercharging pressure control, it is preferable that this control be performed in a natural intake environment in which the supercharging pressure is not substantially applied.

  In addition, the opening degree of the intake control valve 5, the EGR control valve 13, and the fuel injection valve 14 is continuously controlled by duty ratio control or the like.

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 this invention control. It is a flowchart in connection with this invention control. It is a conceptual diagram of a post injection execution / non-execution region discrimination map.

Explanation of symbols

E Internal combustion engine 2 Intake passage 5 Intake control valve 9 LNC
13 EGR control valve 14 Fuel injection valve 18 ECU
31 Post-injection region discrimination map 32 Target intake air amount map 33 Fuel injection amount map

Claims (2)

Control is performed so that fuel injection means for injecting fuel into the combustion chamber of the internal combustion engine and fuel injection from the fuel injection means are executed in a single fuel injection process divided into main injection and sub-injection. An internal combustion engine control device comprising fuel injection control means and intake air flow rate control means for controlling the intake air flow rate to the combustion chamber,
The intake air flow rate control means controls the fresh air flow rate,
The sub-injection is executed in a high load operation region of the internal combustion engine,
When the sub-injection is executed, the intake air flow rate supplied to the combustion chamber is changed in response to the change in the injection amount of the sub-injection, thereby controlling the exhaust air-fuel ratio to be set in advance .
The control apparatus for an internal combustion engine, wherein the control of the predetermined exhaust air-fuel ratio is performed in a natural intake environment where no supercharging pressure is applied .
  2. The control device for an internal combustion engine according to claim 1, further comprising an exhaust purification device, wherein regeneration processing of the exhaust purification device is performed when the sub-injection is executed.

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