JP2006183581A - Combustion control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To minimize degradation in fuel economy and increase in HC or smoke even if a cetane number of fuel used is fluctuated, when an exhaust temperature is increased or an air-fuel ratio is enriched by combined injection. <P>SOLUTION: An operational status, a status of an exhaust emission control device and the cetane number of the fuel used are respectively detected. When the combined injection constituted of preliminary injection for controlling preliminary combustion generated near a top dead center and retard combustion started after the completion of the preliminary combustion is performed based on detection result of the operational status and the status of the exhaust emission control device, the fuel injection is controlled to control at least one of the preliminary combustion and the retard combustion based on the cetane number. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a combustion control device for an internal combustion engine.

Conventionally, as disclosed in Patent Document 1, in a fuel injection device of a diesel engine, when urging the temperature of the exhaust gas to increase the activity of a catalyst or the like, the fuel injected from the fuel injection valve is Divided injection is known in which injection is performed divided into a plurality of times in the vicinity of the compression top dead center of the cylinder. In addition, it is also known to increase the fuel injection amount (enrich the air-fuel ratio) in order to increase the exhaust temperature while satisfying the required torque of the engine.
JP 2000-320386 A

  However, in the apparatus described in Patent Document 1, when the exhaust temperature is raised or the air-fuel ratio is made rich, the fuel is injected into the flame of the initially injected fuel so that the combustion of the separately injected fuel continues. It is necessary to inject. In this case, the fuel injected after the second time is likely to be mainly combustion by diffusion combustion, and particularly when the exhaust temperature is raised or the air-fuel ratio is made rich, the load (fuel injection amount) of the internal combustion engine increases. It has been a big problem to perform combustion control (fuel injection control) so as not to increase smoke as much as possible.

  Therefore, as proposed in Japanese Patent Application No. 2003-193310, Japanese Patent Application No. 2003-279629, Japanese Patent Application No. 2003-282723, and Japanese Patent Application No. 2003-284325, the applicant of the present application at least once near the top dead center. Performs fuel injection control (composite injection) to generate the required torque by combustion consisting of pre-combustion that is performed and retarded combustion (main combustion) that is started after pre-combustion is completed, and exhaust temperature without deteriorating smoke It was made possible to meet demands for increasing the temperature or enriching the air-fuel ratio.

  However, in the case of combined injection, the purpose is to obtain the required output and exhaust gas temperature rise by pre-combustion near top dead center and retarded combustion started after the pre-combustion is completed. Compared to the case where the same amount of fuel is injected, the fuel injection period is extended and delayed as a whole, so the success or failure of preliminary combustion by split pre-injection is greater than the success or failure of retard combustion by subsequent split retard injection. It is easy to influence, and there is a strong tendency that the influence of the change in the ignitability of the fuel is particularly large as compared with the combustion by the normal fuel injection.

By the way, it is well known that the fuel properties and characteristics of fuels in the current market generally vary depending on the manufacturer, region, or season, and in particular, the cetane number that regulates ignitability also varies. is there.
For this reason, when the fuel having a relatively low cetane number is used and the ignitability of the fuel in the preliminary injection is lowered (the ignition delay period becomes longer), the retarded combustion becomes very slow and the combustion becomes unstable. As a result, since the fuel is increased as compared with the case of the normal fuel injection, there is a tendency that the deterioration of the fuel consumption and the increase of HC, which is an unburned fuel component, increase.

Conversely, when a fuel having a relatively high cetane number is used to improve the ignitability (the ignition delay period is shortened), the ratio of diffusion combustion in the entire combustion increases. As a result, since the fuel is increased as compared with the case of the normal fuel injection, the smoke is increased.
That is, when the cetane number of the fuel to be used fluctuates, it has been a big problem to control the combustion so that the influence on the entire combustion generated through the composite injection is not amplified compared to at least the case of the normal fuel injection.

  In light of this situation, the present invention is based on the fact that when the exhaust gas temperature is increased or the air-fuel ratio is enriched by combined injection, even if the cetane number of the fuel used fluctuates, the fuel consumption deteriorates, the HC increases, or the smoke The purpose is to minimize the increase of.

  Therefore, in the present invention, in an internal combustion engine provided with an exhaust purification device in an exhaust passage, a fuel injection device capable of directly injecting fuel into a combustion chamber of the internal combustion engine and capable of performing injection by dividing fuel injection into two or more, Normal combustion by fuel injection performed near the top dead center based on the detection results of the operating state and exhaust purification device state, detecting the operating state of the internal combustion engine, the state of the exhaust purification device, and the cetane number of the fuel used Or a combined injection comprised of a pre-injection for controlling the pre-combustion that occurs near the top dead center and a retard injection for controlling the retarded combustion that is started after the pre-combustion is completed. When at least one of these injections is performed and combined injection is performed, the combustion of at least one of preliminary combustion and retarded combustion is controlled based on the cetane number To control the fuel injection.

  According to the present invention, when the exhaust gas temperature is increased by the combined injection or the air-fuel ratio is enriched, even if the cetane number of the fuel used fluctuates, the deterioration of fuel consumption, the increase of HC, or the increase of smoke is minimized. It is possible to limit to the limit.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram of an engine system provided with a combustion control device for an internal combustion engine according to the present invention, and is an example of a diesel engine using light oil as fuel as an internal combustion engine.
In FIG. 1, 1 indicates a diesel engine (hereinafter simply referred to as “engine”), and 3 indicates an exhaust passage of the engine 1.

  An exhaust outlet passage 3a constituting an upstream portion of the exhaust passage 3 of the engine 1 is connected to a turbocharger turbine 3b. In the exhaust passage 3 downstream of the turbocharger turbine 3b, NOx in the exhaust is trapped when the exhaust air-fuel ratio is lean, and the trapped NOx is desorbed and purified when the exhaust air-fuel ratio is rich, for exhaust purification. A NOx trap catalyst 16 is disposed. The NOx trap catalyst 16 has a function of previously supporting an oxidation catalyst (noble metal) to oxidize inflowing exhaust components (HC, CO).

  Further, a diesel particulate filter (hereinafter referred to as “DPF”) 17 is disposed downstream of the NOx trap catalyst 16 as a filter for collecting PM (Particulate Matter) which is exhaust particulate. The DPF 17 is also preloaded with an oxidation catalyst (noble metal) and has a function of oxidizing the inflowing exhaust components (HC, CO). Note that the NOx trap catalyst 16 and the DPF 17 may be disposed in reverse, or may be configured integrally by supporting the NOx trap catalyst on the DPF.

As an exhaust gas recirculation device, an EGR passage 4 for recirculating a part of the exhaust gas is provided between the intake collector 2c and the exhaust outlet passage 3a of the intake passage 2, and the opening is continuously increased by a stepping motor. A controllable EGR valve 5 is interposed.
The intake passage 2 is provided with an air cleaner 2a at an upstream position, and an air flow meter 7 for detecting the intake air amount Qair and a compressor 2b of a supercharger are disposed downstream thereof, and the compressor 2b and the intake collector 2c In between, an intake throttle valve 6 that is driven to open and close by an actuator (for example, a stepping motor type) is interposed.

  The fuel injection device 10 of the engine 1 is a well-known common rail fuel injection device, and generally includes a supply pump 11, a common rail (accumulation chamber) 14, and a fuel injection valve 15 provided for each cylinder. After the fuel pressurized by the supply pump 11 is temporarily stored in the common rail 14 via the fuel supply passage 12, the high-pressure fuel in the common rail 14 is distributed to the fuel injection valve 15 of each cylinder.

  The common rail 14 is provided with a pressure sensor 34 and a temperature sensor 35 in order to detect the pressure and temperature of the fuel in the common rail 14. Further, in order to control the fuel pressure in the common rail 14, a part of the fuel discharged from the supply pump 11 is returned from the overflow passage (not shown) to the fuel supply passage via the pressure control valve 13. The pressure control valve 13 changes the flow path area of the overflow passage according to the duty signal from the engine control unit 30. Thereby, the substantial fuel discharge amount from the supply pump 11 to the common rail 14 is adjusted, and the fuel pressure in the common rail 14 is controlled.

  The fuel injection valve 15 is an electronic injection valve that is opened and closed by an ON-OFF signal from the engine control unit 30, and directly injects fuel into the combustion chamber by the ON signal and stops fuel injection by the OFF signal. The fuel injection valve 15 can divide the fuel injection into two or more times by receiving the ON-OFF signal from the engine control unit 30 a plurality of times. The fuel injection amount increases as the period of the ON signal applied to the fuel injection valve 15 increases, and the fuel injection amount increases as the fuel pressure of the common rail 14 increases.

Further, a water temperature sensor 31 for detecting the cooling water temperature Tw is attached to an appropriate position of the engine 1 as representative of the temperature of the internal combustion engine.
The engine control unit 30 includes a signal from the water temperature sensor 31 (cooling water temperature Tw), a signal from the crank angle sensor 32 for crank angle detection (a crank angle signal serving as a basis for the engine speed Ne), and a crank angle sensor 33 for determining the cylinder. Signal (cylinder discrimination signal Cy1), a signal of the pressure sensor 34 for detecting the fuel pressure of the common rail 14 (common rail pressure Pcr), a signal of the temperature sensor 35 for detecting the fuel temperature (fuel temperature Tf), and an accelerator pedal corresponding to the load A signal (accelerator opening (load) Acc) of the accelerator opening sensor 36 that detects the amount of depression of the air flow meter 7 and a signal (intake air amount Qair) of the air flow meter 7 are input.

  Further, a catalyst temperature sensor 37 for detecting the temperature of the NOx trap catalyst 16 (catalyst temperature T1), an exhaust pressure sensor 38 for detecting the exhaust pressure (P1) on the DPF 17 inlet side of the exhaust passage 3, and the temperature of the DPF 17 (DPF temperature T2). ) And an air / fuel ratio sensor 40 for detecting an exhaust air / fuel ratio (L: hereinafter referred to as “λ”) at the outlet side of the DPF 17 in the exhaust passage 3. Has been entered. However, the temperature of the NOx trap catalyst 16 and the temperature of the DPF 17 may be indirectly detected from the exhaust temperature by providing an exhaust temperature sensor on the downstream side thereof.

Based on these input signals, the control unit 30 controls the fuel injection amount to the fuel injection valve 15 and the fuel injection command signal to the fuel injection valve 15, the opening degree command signal to the intake throttle valve 6, and the EGR valve 5. The opening command signal etc. of is output.
Here, the control unit 30 regenerates the DPF 17 by burning and removing the PM collected and accumulated in the DPF 17, desorbing and purifying NOx trapped in the NOx trap catalyst 16, and sulfur (S) coverage of the NOx trap catalyst 16. Exhaust gas purification control including removal of poison and the like is performed, and the exhaust gas purification control will be described in detail below.

16 to 32 are flowcharts of the exhaust purification control executed by the control unit 30.
First, it demonstrates along the flow of FIG.
This control mode is a basic control mode for exhaust purification.
In S1, various sensor signals are read, the intake air amount Qair, the cooling water temperature Tw, the engine speed Ne, the cylinder discrimination signal Cy1, the common rail pressure Pcr, the fuel temperature Tf, the accelerator opening (load) Acc, the catalyst temperature T1, and the DPF. The inlet exhaust pressure P1, the DPF temperature T2, and the exhaust air / fuel ratio λ are detected.

  In S2, the cetane number of the fuel (light oil) used is detected. The detection of the cetane number is performed, for example, as disclosed in Japanese Patent Application Laid-Open No. 2004-239229 (Japanese Patent Application No. 2003-031832) filed by the present applicant. First, the actual fuel supply weight Gmain is obtained from the intake air flow rate Qair detected by the air flow meter 7 and the exhaust air / fuel ratio λ detected by the air / fuel ratio sensor 40. Next, the actual specific gravity Gfuel is obtained based on the actual fuel supply weight Gmain and the actual fuel injection amount (fuel supply amount) Qmain by the fuel injection valve 15. Then, a standard specific gravity (specific gravity at a reference temperature, for example, a standard temperature of 20 ° C.) Gstd is obtained from the actual specific gravity Gfuel and the fuel temperature Tf, and the cetane number of light oil is obtained using the standard specific gravity Gstd as a parameter.

  In S3, the warm-up / cold-down state of the exhaust system NOx trap catalyst 16 is determined. When the catalyst temperature T1 is lower than T52 (about 220 ° C.), which is a predetermined temperature at which stable activity can be obtained, it is determined that the engine is in the cold state, and the control proceeds to the catalyst warm-up promotion control mode shown in FIG. When it is determined that the catalyst temperature T1 is equal to or higher than the predetermined temperature (catalyst temperature ≧ T52), that is, the warm-up state (after completion of warm-up), the process proceeds to S4.

  In S4, the NOx deposition amount trapped and deposited on the NOx trap catalyst 16 is calculated. For example, it may be estimated from the integrated value of the engine speed Ne as in the calculation of the NOx absorption amount described in Japanese Patent No. 2600492 on page 6, or may be estimated from the travel distance. When the integrated value is used, NOx desorption reduction purification of the NOx trap catalyst 16 (hereinafter simply referred to as NOx desorption reduction purification) is completed (NOx desorption reduction purification is simultaneously performed by performing sulfur poisoning release). The total value is reset at the same time.

In S5, the amount of sulfur deposited on the NOx trap catalyst 16 due to sulfur poisoning is calculated. Here, similarly to the calculation of the NOx accumulation amount, it may be estimated from the integrated value of the engine speed Ne and the travel distance. When the integrated value is used, the integrated value is reset when the sulfur poisoning release of the NOx trap catalyst 16 (hereinafter simply referred to as sulfur poisoning release) is completed.
In S6, the PM accumulation amount collected and accumulated in the DPF 17 is calculated as follows, for example. When the amount of accumulated PM in the DPF 17 increases, the exhaust pressure on the DPF inlet side naturally increases. Therefore, the exhaust pressure sensor 38 detects the exhaust pressure P1 on the DPF inlet side, and the current operating state (engine speed Ne, load Acc) The PM accumulation amount is estimated by comparison with the reference exhaust pressure at. Note that the PM accumulation amount may be estimated by combining the engine rotational speed integrated value or travel distance from the previous DPF regeneration and the exhaust pressure. When using the integrated value, the integrated value is reset when the regeneration of the DPF 17 is completed.

In S7, it is determined whether or not a reg flag indicating that DPF regeneration is in progress is set. If the reg flag = 1, it is determined that the DPF regeneration is in progress, and the process proceeds to the DPF regeneration control mode shown in FIG.
In S8, it is determined whether or not a desul flag indicating that sulfur poisoning is being released is set. When the desul flag = 1, the process proceeds to the sulfur poisoning release control mode of FIG.

In S9, it is determined whether or not the sp flag indicating that the rich spike control mode for NOx desorption reduction purification is being set is set. When the sp flag = 1, the process proceeds to a rich spike control mode shown in FIG.
In S10, it is determined whether or not a rec flag is set indicating that the control mode is in the prevention of melting damage after DPF regeneration and sulfur poisoning is released. When the rec flag = 1, the process proceeds to a flaw prevention control mode shown in FIG.

In S11, it is determined whether or not an rq-DPF flag indicating that a DPF regeneration request has been issued is set. When the DPF regeneration request is issued and the rq-DPF flag = 1, the process proceeds to the flow of FIG. 21 described later, and the priority of regeneration when the DPF regeneration request is issued is determined.
In S12, it is determined whether or not an rq-desul flag indicating that a sulfur poisoning release request has been issued is set. When the sulfur poisoning release request is issued with the rq-desul flag = 1, the flow proceeds to the flow of FIG. 22 described later, and the priority of regeneration when the sulfur poisoning release request is issued is determined.

In S13, it is determined whether or not an rq-sp flag indicating that a rich spike request for NOx desorption reduction purification has been issued is set. If the rich spike request has been issued and the rq-sp flag = 1, the process proceeds to the flow of FIG. 23 described later, and it is determined in S701 that the sp flag is set to 1 to shift to the rich spike control mode.
In S14, it is determined whether or not the PM accumulation amount of the DPF calculated in S6 has reached a predetermined amount PM1 and the DPF regeneration time has come (PM accumulation ≧ amount PM1).

If it is determined that the PM accumulation amount ≧ PM1, that is, the DPF regeneration timing, the flow proceeds to the flow of FIG. 24, and the rq-DPF flag is set to 1 in S801 to issue a DPF regeneration request.
In S15, it is determined whether or not the sulfur accumulation amount of the NOx trap catalyst 16 calculated in S5 has reached a predetermined amount S1 and the sulfur poisoning release time has come (sulfur accumulation amount ≧ S1).
If it is determined that the sulfur accumulation amount ≧ S1, that is, the sulfur poisoning release timing, the flow proceeds to the flow of FIG. 25, and the rq-desul flag is set to 1 in S901 to issue a sulfur poisoning release request.

In S16, it is determined whether or not the NOx accumulation amount of the NOx trap catalyst 16 calculated in S4 has reached a predetermined amount NOx1 and the NOx desorption reduction purification time has come (NOx accumulation amount ≧ NOx1).
When NOx accumulation amount ≧ NOx1 and NOx desorption purification timing is determined, the flow proceeds to the flow of FIG. 26, and the rq-sp flag is set to 1 in S1001, and a NOx desorption purification request (rich spike request) is issued.

From S14 to S16, it is detected whether or not the state of the exhaust purification device (NOx trap catalyst 16, DPF 17) is either normal or other time. The time other than that means a DPF regeneration request, a NOx desorption regeneration request, a sulfur poisoning release request, or an activity enhancement request (warm-up promotion request).
In S17, normal basic control of the engine 1 is performed because there is no need for DPF regeneration, sulfur poisoning cancellation, rich spike, and DPF meltdown prevention.

Next, the control mode of DPF regeneration in FIG. 17 will be described.
This control mode is started when the PM accumulation amount reaches the predetermined amount PM1, the rq-DPF flag = 1, and the reg flag = 1 is received in accordance with the flow of FIG.
In S101, it is determined whether or not the DPF temperature (T2) is already equal to or higher than a target upper limit value T22 (about 650 ° C.) for DPF regeneration. If the DPF temperature is equal to or greater than T22 in S101, the process proceeds to S109, and the fuel injection is maintained or switched to the normal injection mode. That is, if the operating condition of the engine 1 is a high load and high rotation condition, the temperature reaches a temperature at which the DPF 17 can be regenerated without increasing the exhaust temperature, so that the DPF 17 is regenerated naturally (referred to as self-regeneration). In such a case, it is not necessary to raise the temperature, and conversely, if the temperature is raised, the temperature becomes too high and the DPF 17 is regenerated suddenly, which may lead to a situation such as cracking or melting. ing.

  If the DPF temperature is less than T22 in S101, the process proceeds to S102, and it is determined whether or not the DPF temperature T2 is equal to or higher than a target lower limit T21 (about 600 ° C.) for DPF regeneration. If the DPF temperature is less than T21 in S102, that is, if it is less than the regeneration lower limit temperature, the routine proceeds to S103, where the fuel injection is switched to the combined injection (Div L) of the present invention that realizes combustion with an emphasis on short-time temperature rise. The injection amount is corrected to increase again, and the process proceeds to S104.

If the DPF temperature is greater than or equal to the regeneration lower limit temperature in S102, that is, if the regeneration lower limit temperature or higher, the routine proceeds to S110, and combustion that places importance on minimizing fuel consumption deterioration and HC and smoke increase without deteriorating combustion stability is performed. The process proceeds to S104 after switching to the combined injection (Div S) of the present invention to be realized.
Here, the composite injection performed in the present invention will be described. The combustion is used for DPF regeneration, sulfur poisoning release, NOx desorption reduction purification (rich spike), and catalyst (including oxidation catalyst) warm-up promotion.

When the DPF is regenerated, it is necessary to control the exhaust λ between 1.1 and 1.4 and to control the DPF temperature T2 to about 600 ° C. or higher (the upper limit temperature is about 650 ° C.).
Further, when releasing sulfur poisoning, it is necessary to make the exhaust λ stoichiometric and to control the catalyst temperature T1 to 600 ° C. or higher (the upper limit temperature is about 700 ° C. to prevent thermal deterioration of the catalyst).
When performing NOx desorption reduction purification (rich spike), the exhaust λ is made rich (about 0.8), and the temperature of the NOx trap catalyst is at least about 200 ° C. (sufficient activity is obtained). Therefore, it is necessary to control the temperature to about 220 ° C. or higher.

  In order to establish DPF 17 regeneration, sulfur poisoning release, etc. in a diesel engine that is normally operated with lean combustion, it is essential to achieve a low exhaust λ at a high exhaust temperature or a high exhaust temperature. It is necessary to reduce the in-cylinder working gas amount by reducing the intake air from the lean operation state. However, if the amount of working gas is reduced, the compression end temperature in the cylinder will decrease, so that combustion becomes unstable at the same injection setting as normal lean combustion, and misfire will occur in extreme cases, so output control of the engine 1 It is difficult to realize a high exhaust temperature and a low exhaust λ.

Therefore, in Patent Document 1, the main fuel injection amount is increased to satisfy the required torque of the engine and the exhaust temperature is raised, and the fuel is supplied a plurality of times (2 to 3 times) near the compression top dead center of each cylinder. The injection period is divided and the injection period is extended so as not to deteriorate the combustion stability, thereby realizing high exhaust temperature and low exhaust λ.
However, in such divided injection control, unlike the normal injection pattern (single-stage injection) as shown in FIG. 2, the required output and exhaust gas temperature increase are obtained by the entire combustion that occurs through multiple fuel injections. This is because the overall fuel injection period is extended and delayed as compared with the case of normal fuel injection, so when the exhaust temperature is raised or the air-fuel ratio is made rich, the combustion of the separately injected fuel In order to continue, it is necessary to inject the next fuel into the flame of the first injected fuel, and the success or failure of the previously injected fuel has a great influence on the success or failure of the next injected fuel. . That is, in the split injection, the entire combustion caused by multiple fuel injections is easily influenced by the cetane number of the fuel, and a fuel having a relatively low cetane number (indicated as a low CN fuel in the figure, the same applies hereinafter) is used. Then, the combustion becomes very slow, the combustion becomes unstable, and the fuel consumption deteriorates and the HC of the unburned fuel component increases. On the other hand, when a fuel having a relatively high cetane number is used, the proportion of diffusion combustion in the entire combustion increases and the increase in smoke increases.

  For this reason, the applicant of the present patent application in Japanese Patent Application No. 2003-193310 (filed on July 8, 2003), Japanese Patent Application No. 2003-279629, Japanese Patent Application No. 2003-282723, Japanese Patent Application No. 2003-284325, etc. Proposed fuel injection control (composite injection) that embodies combustion consisting of pre-combustion performed once and retarded combustion started after the pre-combustion is completed, and raising the exhaust temperature without deteriorating smoke Alternatively, the air-fuel ratio enrichment request can be realized.

  However, even in the case of this combined injection, as in the case of the split injection in Patent Document 1, the entire fuel injection period is extended and delayed as compared with the case of the normal fuel injection. The success or failure of the preliminary combustion by injection tends to have a great influence on the success or failure of the retard combustion by the subsequent divided retard injection, and the influence of fluctuations in the cetane number of the fuel tends to be larger than the combustion by the normal fuel injection. Therefore, when a fuel having a relatively low cetane number is used, the combustion becomes very slow, the combustion becomes unstable, and the fuel consumption deteriorates and the HC of the unburned fuel component increases. On the contrary, when a fuel having a relatively high cetane number is used, the ratio of diffusion combustion in the entire combustion increases, and the increase in smoke increases.

Therefore, in the composite injection of the present invention, as shown in FIGS. 3 and 4, when the exhaust temperature is raised or the air-fuel ratio is made rich, optimal composite injection control is performed according to the level of the cetane number of the fuel used. In this way, stable combustion was always realized.
Specifically, when a fuel having a high cetane number is used and ignition is promoted, injection control is performed so as to relatively suppress ignitability.

  In FIG. 3, as Example 1, the fuel used has a high cetane number, the fuel injection period (MP period, MR period) for pre-combustion and retarded combustion is unchanged, and pre-combustion in standard cetane fuel In addition, the fuel injection start timing difference ITC P and ITCR R with respect to the fuel injection start timing for retarded combustion is set to ITC P> ITCR, and ΔIT is reduced. In this case, the combustion pattern is indicated by a broken line.

As Example 2, the fuel used has a high cetane number, MP period decreased, MR period increased, ΔIT unchanged, and injection pressure increased. In this case, the combustion pattern is indicated by a dotted line.
In addition, when the fuel having a low cetane number is used and the ignition is retreated, the injection control is performed so as to relatively promote the ignition.

FIG. 4 shows a case where the fuel used has a low cetane number, the MP period is unchanged, the MR period is unchanged, ITC P> ITCR, and ΔIT are expanded as Example 3. In this case, the combustion pattern is indicated by a broken line.
As Example 4, the fuel used has a low cetane number, MP period increased, MR period decreased, ΔIT unchanged, and injection pressure decreased. In this case, the combustion pattern is indicated by a dotted line.

  Further, as shown in FIG. 10, the fuel injection timings of the divided preliminary injection and the divided retarded injection in the composite injection are variably controlled based on the cetane number of the fuel. The amount is made larger than the retard amount of the divided retard injection. As a result, the ignition combustion of the fuel in the divided pre-injection can be reliably or stably performed. As a result, the fuel combustion start timing (heat generation timing) and the combustion in the divided retard injection can be stabilized.

  Then, as shown in FIG. 12, the fuel injection amount ratio between the divided preliminary injection and the divided retarded injection in the composite injection is variably controlled based on the cetane number of the fuel. Decrease the injection amount ratio. In other words, the fuel injection amount ratio of the split retard injection is increased as the cetane number is higher. As a result, the temperature rise in the combustion chamber obtained by the ignition combustion of fuel in the split pre-injection can be set low when the cetane number is high, and conversely high when the cetane number is low. (Heat generation time) and combustion can be stabilized.

Furthermore, as shown in FIG. 11, at least when performing the combined injection, the fuel injection pressure is increased (the cetane number correction value is increased) as the cetane number of the fuel is higher. Thus, the diffusion of the injected fuel is promoted when the cetane number is high, and conversely, it is suppressed when the cetane number is low, and ignition combustion is stabilized.
As a result, combustion by combined injection is stabilized, and high exhaust temperature and low exhaust λ can be realized without deteriorating fuel consumption, increasing HC, or increasing smoke emission.

  In order to quickly complete the regeneration of the DPF 17 and the release of sulfur poisoning, it is desirable to achieve the target high exhaust temperature and low exhaust λ in a short time. Therefore, in the initial stage of the regeneration control of the DPF 17 or the initial stage of the sulfur poisoning release control, as shown in FIG. 6, the total fuel injection amount differs depending on the exhaust temperature or the temperature of the exhaust purification device. By performing the composite injection (Div S and Div L described in detail in FIGS. 29 and 30 described later), the target high exhaust temperature and low exhaust λ can be reached in a short time. This will be described in detail later.

In S104, the exhaust λ is controlled to a target value according to a flow described later, and then the process proceeds to S105.
Here, as described above, the target value (1.1 to 1.4) of the exhaust λ when the DPF 17 is regenerated varies depending on the PM accumulation amount. The purpose of this is to prevent the DPF 17 from burning out due to excessive temperature rise because the PM re-combustion becomes more active as the PM deposition amount increases. For this reason, as shown in FIG. As the amount increases, the target λ is set smaller to lower the oxygen concentration, thereby suppressing the PM reburning rate.

In S105, it is determined whether or not a predetermined time t dpreg has elapsed since the start of regeneration of the DPF 17. If the predetermined time has elapsed, the PM accumulated in the DPF 17 has been removed by combustion, and the process proceeds to S106.
In S106, since the regeneration control of the DPF 17 is completed, the divisional injection according to the present invention is switched to the normal injection, the temperature rise of the exhaust gas is stopped, and the heating of the DPF 17 is stopped. In normal injection, combustion is performed by fuel injection performed near top dead center.

In S107, the reg flag is set to 0 to indicate completion of regeneration control of the DPF 17, and the process proceeds to S108.
In S108, the rec flag is set to 1 in order to enter the control mode for preventing DPF melting damage. When the regeneration control of the DPF 17 is completed, if there is PM unburned in the DPF 17, if the exhaust λ is suddenly increased, the unburned PM is reburned at once and the DPF 17 has a sudden temperature. This is performed in order to avoid a rare danger that the DPF 17 melts due to an increase.

Next, the control mode for canceling sulfur poisoning in FIG. 18 will be described.
This control mode is started when the sulfur accumulation amount of the NOx trap catalyst reaches the predetermined value S1 and the rq-desul flag = 1, and in response to this, the desul flag = 1 is established by the flow of FIG.
In S201, it is determined whether or not the temperature T1 of the NOx trap catalyst 16 has already exceeded the target upper limit value T42 (about 700 ° C.) for releasing sulfur poisoning. When NOx trap catalyst temperature ≧ T42 in S201, the process proceeds to S211 to maintain or switch the fuel injection to the normal injection mode. That is, if the operating conditions of the engine 1 are high load, high rotation conditions, etc., the NOx trap catalyst 16 is naturally released from sulfur poisoning because it reaches a temperature at which sulfur poisoning can be released without raising the exhaust temperature. Temperature is obtained. In such a case, it is not necessary to raise the temperature, and conversely, if the temperature is raised, the temperature becomes too high and there is a possibility that the thermal deterioration of the NOx trap catalyst 16 is promoted. If NOx trap catalyst temperature <T42 in S201, the process proceeds to S202.

  In S202, it is determined whether or not the NOx trap catalyst temperature T1 is equal to or higher than a target lower limit T41 (about 600 ° C.) for releasing sulfur poisoning (catalyst temperature ≧ T41). If NOx trap catalyst temperature ≧ T41 in S202, that is, if it is less than the sulfur poisoning release lower limit temperature (catalyst temperature <T41), the process proceeds to S203, and the combustion of the present invention that realizes combustion particularly focusing on short-time temperature rise is realized. Switch to combined injection (Div L) and proceed to S204.

When NOx trap catalyst temperature ≧ T41 in S202, that is, when the temperature T1 of the NOx trap catalyst 16 is equal to or higher than the sulfur poisoning release lower limit temperature T41, the routine proceeds to S212, the combustion stability is not deteriorated, the fuel consumption is deteriorated and the HC Then, the process proceeds to S204 after switching to the combined injection (Div S) of the present invention that realizes combustion focusing on minimizing the increase in smoke.
In S204, the exhaust λ is controlled stoichiometrically. That is, after setting the target λ to stoichiometric and controlling according to the flow described later, the process proceeds to S205.

In S205, it is determined whether or not a predetermined time t desul has elapsed in the sulfur poisoning release control mode. If the predetermined time has elapsed, the sulfur poisoning has been released, and the process proceeds to S206.
In S206, since the sulfur poisoning release control is completed, switching from the divided injection according to the present invention to the normal injection is performed, the temperature increase of the exhaust gas temperature is stopped, the heating of the NOx trap catalyst 16 is stopped, the process proceeds to S207, and the exhaust λ Release control.

Then, the process proceeds to S208, the desul flag is set to 0 to indicate the completion of the sulfur poisoning release control, and the process proceeds to S209.
In S209, in order to enter the control mode for preventing DPF melting, the rec flag is set to 1, and the process proceeds to S210.
Here, although the sulfur poisoning release control is not aimed at the regeneration of the DPF 17, if PM is deposited on the DPF 17 at the stage when the sulfur poisoning release control is completed, the sulfur poisoning release control is performed under such a high temperature condition. If the exhaust λ is suddenly increased, PM accumulated in the DPF 17 may be recombusted at once, causing a rapid temperature rise of the DPF 17 and causing the DPF 17 to melt. In order to avoid such a risk, the DPF melt damage prevention control is performed even after the sulfur poisoning release control is completed.

In S210, the sp flag is set to 0. This is because when the sulfur poisoning release control is performed, the NOx trap catalyst 16 is exposed to stoichiometry for a long time, so that NOx desorption reduction purification is also performed at the same time. Therefore, when a NOx desorption reduction purification request (rich spike request) has been issued, the rq-sp flag is set to 0 in order to cancel it.
Next, the control mode of the rich spike (NOx desorption reduction purification) of FIG. 19 will be described.

This control mode is started when the NOx accumulation amount of the NOx trap catalyst 16 reaches the predetermined value NOx1 and becomes rq-sp flag = 1, and in response to this, the sp flag = 1 is established by the flow of FIG. 21 or FIG. The
In S301, the exhaust λ is controlled to be rich. That is, the target λ is set to be rich (λ <1) and controlled according to a flow described later, and then the process proceeds to S302.

In S302, it is determined whether or not a predetermined time t spike has elapsed in the rich spike mode. When the predetermined time has elapsed, since NOx is desorbed and purified from the NOx trap catalyst 16, the process proceeds to S303.
In S303, since the rich spike control is completed, the exhaust λ control is canceled to release the rich operation, and the process proceeds to S304.

In S304, the sp flag and the rq-sp flag are set to 0 to indicate the completion of NOx desorption reduction purification.
Next, the control mode for preventing melting in FIG. 20 will be described.
This control mode is started when the regeneration of the DPF 17 or the sulfur poisoning release of the NOx trap catalyst 16 is completed and the rec flag is set to 1 according to the flow of FIG. 17 or FIG.

  In S401, the exhaust λ is controlled to a target value, for example, λ <1.4. This is because immediately after DPF regeneration or sulfur poisoning is released, the DPF 17 is still in a high temperature state, and when the exhaust λ is leaned rapidly, the remaining or accumulated PM in the DPF 17 is reburned at once and the DPF 17 is rapidly This is to avoid such a danger by controlling the exhaust λ to λ <1.4 and lowering the oxygen concentration since the DPF 17 may be melted due to a temperature rise.

In the melt prevention control mode, it is necessary to lower the exhaust gas temperature, and as described in the flow of FIG. 17 or FIG. 18, the fuel injection is returned to the normal injection instead of the divided injection according to the present invention.
After the exhaust λ is controlled to the target value in S401, in S402, it is determined whether or not the DPF temperature T2 has become lower than a predetermined temperature T3 (for example, 500 ° C.) that does not induce a rapid re-combustion of PM. When the DPF temperature is equal to or higher than the predetermined temperature T3 (DPF temperature ≧ T3), the exhaust λ control is continued.

If it is lower than T3, melting of the DPF 17 can be avoided even if the normal lean state is restored, so the routine proceeds to S403 and the exhaust λ control is canceled.
Then, the process proceeds to S404, and the rec flag is set to 0 to indicate the end of the melting prevention control mode.
Next, the regeneration priority order determination flow at the time of the DPF regeneration request shown in FIG. 21 will be described.

This control mode is started when a DPF regeneration request (rq-DPF flag = 1) is issued. In this flow, the regeneration priority order when a DPF regeneration request and a sulfur poisoning release request (rq-desul flag = 1) or a NOx desorption reduction purification request (rq-sp flag = 1) occur simultaneously. It prescribes about.
In S501, after the DPF regeneration request is issued, it is determined by the same method as S15 whether or not the sulfur accumulation amount reaches the predetermined value S1 and the sulfur poisoning release timing is reached.

When the sulfur accumulation amount ≧ S1, the process proceeds to S901 in the flow of FIG. 25, and the rq-desul flag = 1 is set, and a sulfur poisoning release request is issued. In this case, the priority order is determined by the regeneration priority order determination flow at the time of the sulfur poisoning release request shown in FIG.
When the sulfur deposition amount does not reach the predetermined value S1 (sulfur volume amount <S1), the process proceeds to S502.

In S502, it is determined whether the rq-sp flag = 1, that is, whether the NOx desorption reduction purification request (rich spike request) of the NOx trap catalyst 16 is issued.
If a NOx desorption reduction purification request is issued in S502, the process proceeds to S506, and if not, the process proceeds to S503.
In S503, after the DPF regeneration request is issued, it is determined by the same method as S16 whether or not the NOx accumulation amount in the NOx trap catalyst 16 has reached the predetermined value NOx1 and the NOx desorption reduction purification time has come.

When NOx accumulation amount ≧ NOx1, the process proceeds to S1001 in the flow of FIG. 26, where the rq-sp flag = 1 is set, and a NOx desorption reduction purification request (rich spike request) is issued.
When the NOx accumulation amount does not reach the predetermined value NOx1 (NOx accumulation amount <NOx1), only the DPF regeneration request is issued. In this case, the process proceeds to S504.
In S504, the DPF regeneration and sulfur poisoning release possible region shown in FIG. 5 (the temperature rise margin is relatively small in the region other than the low rotation and low load, and the exhaust performance deteriorates even when the composite injection according to the present invention is performed. It is determined whether or not the allowance is an area that does not exceed the allowable value. In the case of the DPF recyclable region (sulfur poisoning releasable region), the process proceeds to S505, where the reg flag = 1 is set and the process proceeds to regeneration of the DPF 17.

If it is determined in S502 that the rq-sp flag = 1, the DPF regeneration request and the NOx desorption reduction purification request are issued simultaneously. In this case, the process proceeds to S506.
In step S506, it is determined whether or not the engine operating condition is a condition (for example, a steady condition) with a small NOx emission amount. If the amount of NOx emission is small, it is desirable to give priority to regeneration of the DPF 17 that greatly affects the operability because there is almost no deterioration of the exhaust in the tail pipe even if the regeneration of the NOx trap catalyst 16 is somewhat delayed. . Accordingly, in this case, the process proceeds to S507.

On the other hand, it is desirable to prioritize regeneration of the NOx trap catalyst 16 in order to prevent exhaust deterioration in the tail pipe under conditions where the amount of NOx emission is large (for example, acceleration conditions). Therefore, in this case, the process proceeds to S508, where the sp flag = 1 is set, and the process proceeds to NOx desorption reduction purification (rich spike).
In S507, it is determined whether or not the DPF temperature is equal to or higher than a predetermined temperature T6 (for example, about 450 ° C.). When starting the temperature rise, if the DPF temperature is lower than the predetermined temperature T6 (DPF temperature <T6), it takes time until the DPF 17 reaches the regenerative temperature even if the temperature rise is started. Since there is a concern about deterioration of NOx in the pipe, it is desirable to give priority to regeneration of the NOx trap catalyst 16. Accordingly, also in this case, the process proceeds to S508, where the sp flag = 1 is set, and the process proceeds to NOx desorption reduction purification (rich spike).

If it is determined in S507 that DPF temperature ≧ T6, the process proceeds to S504 and 505 described above in order to prioritize regeneration of the DPF 17.
Next, the regeneration priority determination flow at the time of the sulfur poisoning release request shown in FIG. 22 will be described.
This control mode is started when a sulfur poisoning release request (rq-desul flag = 1) is issued. This flow defines the regeneration priority when a sulfur poisoning release request (rq-desul flag = 1) and a NOx desorption purification request (rq-sp flag = 1) occur at the same time.

In S601, after the sulfur poisoning release request is issued, it is determined by the same method as in S14 whether or not the PM accumulation amount reaches the predetermined value PM1 and the DPF regeneration time has come.
When the PM accumulation amount ≧ PM1, the process proceeds to S801 in the flow of FIG. 24, and the rq-DPF flag = 1 is set and a DPF regeneration request is issued. In this case, the priority order is determined by the regeneration priority order determination flow at the time of the DPF regeneration request shown in FIG.

When the PM accumulation amount does not reach the predetermined value PM1 (PM accumulation amount <PM1), the process proceeds to S602.
In S602, it is determined whether or not the catalyst temperature is equal to or higher than a predetermined temperature T7 (for example, about 450 ° C.). If it is equal to or higher than the predetermined temperature T7, the process proceeds to S603.
In S603, it is determined whether or not it is a DPF regeneration and sulfur poisoning release possible region shown in FIG. In the case of the sulfur poisoning releasable region (DPF reproducible region), the process proceeds to S604, and the desul flag = 1 is set, and the process shifts to sulfur poisoning cancellation.

If it is determined in S602 that the catalyst temperature has not reached the predetermined temperature T7 (catalyst temperature <T7), it takes time to reach the temperature at which sulfur poisoning can be released even if the temperature increase is started. Since there is a concern about deterioration of NOx in the tail pipe, it is desirable to give priority to NOx desorption reduction purification, and in this case, the process proceeds to S605.
In S605, it is determined whether or not the rq-sp flag = 1, that is, whether the NOx desorption reduction purification request has been issued. If so, the process proceeds to S607, where the sp flag = 1 is set to NOx desorption reduction purification (rich). (Spike).

If the rq-sp flag = 0 in S605, that is, if the NOx desorption reduction purification request is not issued, the process proceeds to S606.
In S606, after the sulfur poisoning release request is issued, it is determined by the same method as S16 whether or not the NOx accumulation amount reaches the predetermined value NOx1 and the NOx desorption reduction purification time has come.
When NOx accumulation amount ≧ NOx1, the process proceeds to S1001 in the flow of FIG. 26, and an rq-sp flag = 1 and a NOx desorption reduction purification request (rich spike request) are issued.

Next, the control mode for promoting catalyst warm-up in FIG. 27 will be described.
This control mode is executed when the catalyst temperature is lower than T52 (about 220 ° C.) in S3.
In S1101, it is determined whether the catalyst temperature has reached T51 (about 200 ° C.), which is the lower limit of the activation temperature. If the catalyst temperature has reached T51 (catalyst temperature ≧ T51), the process proceeds to S1102, and if it has not reached (catalyst temperature <T51), the process proceeds to S1103.

In S1102, since the catalyst 16 has reached a temperature at which activity can be obtained (when split injection Div L has been performed so far), combustion that places importance on minimizing fuel consumption deterioration and increasing HC and smoke By switching to the divided injection Div S that realizes the above, the early warm-up promotion operation of the catalyst 16 is switched to the normal warm-up promotion operation.
In S1103, since the catalyst temperature T1 is not yet a temperature at which the activity can be obtained, the split injection Div L that realizes the combustion with an emphasis on short-time temperature rise is performed, and the early warm-up promotion operation is performed.

FIG. 28 is a flowchart of the normal fuel injection control mode.
In S1201, a reference fuel injection amount Qstd is calculated. As shown in FIG. 5, the reference fuel injection amount Qstd is stored in advance in the computer control unit as map data corresponding to the accelerator opening Acc and the engine speed Ne, and the accelerator opening Acc and the engine speed at that time are stored. Obtained from the number Ne.

  In S1202, the reference fuel injection timing IT std is calculated. As shown in FIG. 7, the reference fuel injection timing IT std is stored in advance in the computer control unit as map data corresponding to the reference fuel injection amount Q std (or may be the accelerator opening Acc) and the engine speed Ne. , From the reference fuel injection amount Qstd calculated in S1201 and the engine speed Ne at that time.

  In S1203, a reference fuel injection pressure IP std is calculated. As shown in FIG. 8, the reference fuel injection pressure IP std is also stored in advance in the computer control unit as map data corresponding to the reference fuel injection amount Q std (or the accelerator opening Acc) and the engine speed Ne. It is obtained from the reference fuel injection amount Q std calculated in S1201 and the engine speed Ne at that time.

  In S1204, the fuel injection timing is corrected according to the cetane number of the fuel (shown as CN correction in the figure). The cetane number correction of the fuel injection timing is corrected so that the fuel injection timing is retarded as the cetane number of the fuel used at that time shown in FIG. 10 is higher. Then, the higher the cetane number of the fuel, the larger the retardation amount of the divided preliminary injection is made larger than the retard amount of the divided retard injection. As a result, the ignition combustion of the fuel in the divided pre-injection can be performed reliably or stably. As a result, the combustion start timing (heat generation timing) and the combustion of the divided retard injection are stabilized.

In addition, since the appropriate values of the injection start timing of normal injection and the injection start timing of divided preliminary injection in combined injection are substantially the same time (temperature) in the compression stroke, cetane number correction between normal injection and split preliminary injection The value (IT CN) is preferably the same as described below.
(IT std ← IT std + IT CN)
In S1205, the fuel injection pressure is corrected according to the cetane number of the fuel. The cetane number correction of the fuel injection pressure is performed so that the fuel injection pressure is decreased as the cetane number of the fuel used at that time shown in FIG. 11 is higher.

It is desirable that the fuel injection pressure in the composite injection is the same as the normal fuel injection pressure as described below.
(IP std ← IP std + IP CN)
In step S1206, the fuel injection valve 15 is driven (opened) so that the fuel injection amount Q std is obtained from the corrected fuel injection timing IT std and the fuel injection pressure IP std.

FIG. 29 is a control flowchart of the composite injection (Div S) of the present invention that realizes combustion with an emphasis on minimizing fuel consumption deterioration and increasing HC and smoke.
In S1301, by multiplying the total fuel injection amount Q DivS and the divided preliminary injection amount ratios Ratio P and Ratio R of the respective divided injection amounts (the preliminary injection amount QS Pre and the retarded injection amount QS Ret) as follows, The preliminary injection amount QS Pre and the retard injection amount QS Ret are calculated.

(QS Pre ← Q DivS × Ratio P)
(QS Ret ← Q DivS x Ratio R)
The combined total injection amount Q DivS is obtained from the accelerator opening Acc and the engine speed Ne at that time, for example, as in the case of obtaining the normal injection amount Q std, but AA, BB, C in FIG. As shown in FIG. 6, the −C cross section is set to be increased with respect to the normal injection amount Q std.

The fuel increase limit is desirably set so as not to exceed the fuel injection amount at the full load from the viewpoint of keeping the load on the engine 1 in an appropriate state.
Further, as a method of obtaining the combined total injection amount Q DivS, the increase ratio with respect to the normal injection amount Q std is previously stored in the computer control unit as map data in advance corresponding to the accelerator opening Acc and the engine speed Ne, A method of multiplying the injection amount Q std by the increase ratio may be used.

  Further, the combined total injection amount Q DivS is divided to inject the respective divided injection amounts (preliminary injection amount QS Pre and retarded injection amount QS Ret). As shown in FIG. 13, as the load (based on the fuel injection amount Q, which may be either Q std or Q DivS) increases, the split preliminary injection amount ratio (Ratio P) increases and conversely splits. The retard injection amount ratio (Ratio R) is set to decrease. By setting the injection amount ratio in this way, the premixed combustion can be strengthened as the combustion mode as the load increases, so that an increase in smoke can be suppressed.

  Further, as shown in FIG. 14 in the DD cross section of FIG. 5, as the engine speed Ne increases, the divided preliminary injection amount ratio (Ratio P) gradually increases, and conversely the divided retard injection amount ratio. (Ratio R) is set so as to decrease gently. This is because the temperature also increases as the engine speed Ne increases, and in this case as well, the ratio of the premixed combustion is increased, and the combustion is terminated relatively quickly to suppress the deterioration of the fuel consumption.

In S1302, the respective injection start timings (preliminary injection start timing ITS Pre and retard injection start timing ITS Ret) in the combined injection Div S are calculated, and the process proceeds to S1303.
Note that the retard interval dIT S (ΔIT shown in FIGS. 2 to 4) is, for example, a load (fuel injection) as shown by a solid line in FIG. 9 at the BB cross section in FIG. 5 (or FIGS. 7 and 8). The retard interval dIT S is set to increase as the quantity Q is used as a reference, but either Q std or Q DivS may be increased.

(ITS Pre ← IT std)
(ITS Ret ← ITS Pre-dIT S)
By setting the fuel injection timing in this way, it is possible to suppress an increase in diffusion combustion accompanying an increase in load (the ratio of diffusion combustion to premixed combustion can be made appropriate), so that an increase in smoke can be suppressed. it can.

In S1303, the reference fuel injection pressure IP std is calculated as in S1203, and the process proceeds to S1304.
In S1304, each fuel injection amount (preliminary injection amount QS Pre and retard injection amount QS Ret) is corrected with a correction value corresponding to the cetane number of the fuel used at that time shown in FIG. Proceed to That is, in the preliminary injection, the preliminary fuel injection amount is decreased by decreasing the fuel injection amount ratio correction amount (Ratio CNP) as the cetane number of the fuel is higher. On the other hand, in the retarded injection, the retarded injection amount is increased by increasing the fuel injection amount ratio correction amount (Ratio CNR) as the cetane number is higher.

(QS Pre ← QS Pre × Ratio CNP)
(QS Ret ← QS Ret × Ratio CNR)
As a result, the temperature rise in the combustion chamber obtained by the ignition combustion of fuel in the preliminary injection can be set low when the cetane number is high, and conversely, it can be set high when the cetane number is low. Timing) and combustion can be stabilized.

  In S1305, each fuel injection start timing (ITS Pre and ITS Ret) is corrected with a correction value corresponding to the cetane number of the fuel used at that time shown in FIG. 10, and the process proceeds to S1306. That is, in the preliminary injection, the retard amount of the fuel injection timing is made larger than the retard amount of the divided retard injection as the cetane number of the fuel is higher. As a result, the ignition combustion of the fuel in the divided pre-injection can be reliably or stably performed. As a result, the fuel combustion start timing (heat generation timing) and the combustion in the divided retard injection can be stabilized.

(ITS Pre ← ITS Pre + IT CN)
(ITS Ret ITS Ret + IT CNR)
In S1306, the reference fuel injection pressure IP std is corrected with a correction value corresponding to the cetane number of the fuel as in S1205, and the process proceeds to S1307.
(IP std ← IP std + IP CN)
In S1307, the fuel injection valve 15 is driven so that the respective divided injection amounts (QS Pre and QS Ret) can be obtained at the corrected fuel injection start timings (ITS Pre and ITS Ret) and the fuel injection pressure IP std. (Valve open) Control.

FIG. 30 is a control flowchart of combined injection (Div L) that realizes combustion with an emphasis on short-time temperature increase according to the present invention.
In addition, description is abbreviate | omitted about the part which is functionally the same as divided injection (Div S).
In S1401, the total injection amount Q Div L and the respective divided injection amounts (the preliminary injection amount QL Pre and the retarded injection amount QL Ret) are calculated.

(QL Pre ← Q Div L × Ratio P)
(QL Ret ← Q Div L × Ratio R)
The combined total injection amount Q Div L is obtained from the accelerator opening Acc and the engine speed Ne at the same time as in the case of obtaining the normal injection amount Q std or the combined injection amount Q Div S, for example, as shown in FIG. Thus, the fuel injection amount is set to be further increased from the normal injection amount Q std or the composite injection amount Q Div S.

In S1402, the respective injection start timings (preliminary injection start timing ITL Pre and retard injection start timing ITL Ret) in the combined injection Div L are calculated, and the process proceeds to S1403.
The retard interval dIT L is set so that the retard interval also increases because the injection amount is increased as compared with the combined injection Div S, as indicated by the dotted line in FIG.

(ITL Pre ← IT std)
(ITL Ret ← ITL Pre-dIT L)
In S1403, the reference fuel injection pressure IP std is calculated as in S1203 or S1303, and the process proceeds to S1404.
In S1404, each fuel injection amount (preliminary injection amount QL Pre and retard injection amount QL Ret) is corrected with a correction value corresponding to the cetane number of the fuel used at that time shown in FIG. Proceed to

(QL Pre ← QL Pre × Ratio CNP)
(QL Ret ← QL Ret × Ratio CNR)
In S1405, each fuel injection start timing (ITL Pre and ITL Ret) is corrected with a correction value corresponding to the cetane number of the fuel in the same manner as in S1305, and the process proceeds to S1406.
(ITL Pre ← ITL Pre + IT CN)
(ITL Ret ← ITLRet + IT CNR)
In S1406, the reference fuel injection pressure IP std is corrected with a correction value corresponding to the cetane number of the fuel in the same manner as in S1205 or S1306, and the process proceeds to S1407.

(IP std ← IP std + IP CN)
In S1407, the fuel injection valve 15 is driven so that the respective divided injection amounts (QL Pre and QL Ret) can be obtained at the corrected fuel injection start timings (ITL Pre and ITL Ret) and the fuel injection pressure IP std ( (Open valve) control.
FIG. 31 is a flowchart of the exhaust λ control.

In step S1501, the target air amount Q airt is calculated from the target λ and the fuel injection amount. As described above, the target λ is set in accordance with each of DPF regeneration, sulfur poisoning release, NOx desorption reduction purification, DPF erosion prevention, etc. It is set in accordance with the injection (Div S or Div L).
Then, the process proceeds to S1502, and the EGR valve 5 or the intake throttle valve 6 is controlled so as to obtain the target air amount Qairt. At this time, the actual air amount Q air detected by the air flow meter is compared with the target air amount Q air, and feedback control is performed so that Qair = Qairt.

FIG. 32 is a flowchart of engine basic control.
The basic engine control is executed when the DPF regeneration, the sulfur poisoning release, the NOx desorption reduction purification, and the DPF meltdown prevention control are not necessary as described above.
In S1601, it is determined whether or not the catalyst warm-up promotion control mode is being executed. If the catalyst warm-up is being promoted, the process proceeds to S1603.

If the catalyst warm-up is not being promoted in S1601, the process proceeds to S1602, the fuel injection is switched to the normal injection (or the normal injection is maintained), and the process proceeds to S1603.
In step S1603, normal EGR control, that is, operation control of the EGR valve 5 or the intake throttle valve 6 set in advance according to the warm-up state of the engine 1, the rotational speed, and the load is performed so as to obtain the target exhaust performance. Execute.

  According to this embodiment, in the internal combustion engine 1 having the exhaust gas purification device (NOx trap catalyst 16, DPF 17) in the exhaust passage 3, fuel can be directly injected into the combustion chamber of the internal combustion engine 1, and fuel injection is performed twice or more. The fuel injection device 10 that can be divided and injected, the operating state detection means (S1) that detects the operating state of the internal combustion engine 1, and the exhaust purification device state detection means (S4) that detect the states of the exhaust purification devices 16 and 17 To S6), the cetane number detection means (S2) for detecting the cetane number of the fuel being used, and the fuel to be performed in the vicinity of the top dead center based on the detection results by the operating state detection means and the exhaust purification device state detection means Normal injection for controlling normal combustion by injection (S109, S211), or preliminary injection for controlling preliminary combustion that occurs near top dead center, and a retarder that is started after completion of preliminary combustion When at least one of the combined injection (S103, S110, S203, S212) composed of retarded injection for controlling the combustion of the gas and performing the combined injection, the preliminary combustion is performed based on the cetane number. Or fuel injection control means (S1301 to S1307, S1401 to S1407) for controlling fuel injection so as to control at least one of the retarded combustion. For this reason, when exhaust gas temperature is increased or the air-fuel ratio is enriched by combined injection, even if the cetane number of the fuel used fluctuates, fuel consumption deterioration, HC increase, or smoke increase are minimized. It is possible.

  Further, according to the present embodiment, the fuel injection control means detects the normal state by the exhaust purification device state detection means (S105, S205), the operation state detected by the operation state detection means (S1), Based on the cetane number detected by the cetane number detection means (S2), normal injection is performed (S1201 to S1206), while the exhaust gas purifier state detection means is not normal (during DPF regeneration request, NOx desorption regeneration request) When the sulfur poisoning release request or the activity enhancement request (warming-up promotion request) is detected, the operating state (for example, the rotational speed Ne) detected by the operating state detection means and the cetane number detection Based on the cetane number detected by the means, combined injection is performed (S1307, S1407). For this reason, an appropriate combined injection can be performed according to the operating state and the cetane number.

  Further, according to the present embodiment, the fuel injection control means has a higher cetane number based on the cetane number detected by the cetane number detection means when it is detected by the exhaust gas purification apparatus state detection means to be other than normal time. The fuel injection pressure is increased (S1306, S1406, FIG. 11). For this reason, the diffusion of the injected fuel is promoted when the cetane number is high, and conversely, it is suppressed when the cetane number is low, and ignition combustion is stabilized.

  Further, according to the present embodiment, the fuel injection control means is configured to perform preliminary injection in combined injection based on the cetane number detected by the cetane number detection means when the exhaust purification device state detection means detects that it is not normal. Among the fuel injection timings with the retard injection, at least the fuel injection timing of the preliminary injection is retarded as the cetane number is higher (S1305, FIG. 10). For this reason, the ignition combustion of the fuel in preliminary injection can be performed reliably or stably.

  Further, according to the present embodiment, the fuel injection control means detects the fuel injection timing other than the normal time by the exhaust gas purification apparatus state detection means, and the higher the cetane number of the fuel injection timings of the preliminary injection and the retarded injection in the combined injection, When retarding, the retard amount of the preliminary injection is made larger than the retard amount of the retarded injection (S1305, FIG. 10). For this reason, the ignition combustion of the fuel in the preliminary injection can be performed reliably or stably, and the fuel combustion start timing (heat generation timing) and the combustion in the retard injection can be stabilized.

  Further, according to the present embodiment, the fuel injection control means detects the cetane number detection ratio of the fuel injection amount between the preliminary injection and the retarded injection in the composite injection when the exhaust purification device state detection means detects that it is other than the normal time. Control is performed based on the cetane number detected by the means (S1304, 1404, FIG. 12). For this reason, it is possible to stabilize the combustion start timing (heat generation timing) and combustion of the fuel in the retard injection according to the cetane number.

  Further, according to the present embodiment, the fuel injection control means controls the fuel injection amount ratio between the preliminary injection and the retarded injection in the composite injection based on the cetane number, which is detected by the exhaust gas purification device state detection means other than the normal time. In this case, the higher the cetane number, the lower the fuel injection amount ratio of the preliminary injection (S1304, 1404, FIG. 12). For this reason, the temperature rise in the combustion chamber obtained by the ignition combustion of fuel in the split pre-injection can be set low when the cetane number is high, and conversely, it can be set high when the cetane number is low. Generation time) and combustion can be stabilized.

  Further, according to the present embodiment, the fuel injection control means detects the operation state (accelerator opening degree Acc, engine speed) detected by the operation state detection means when the exhaust gas purification apparatus state detection means detects that it is not normal. Ne), the fuel injection amount (total injection amount Q Div L, preliminary injection amount QL Pre, retard injection amount QL Ret) of the composite injection is increased and corrected with respect to the normal fuel injection amount Q std (S1301, S1401, FIG. 5, FIG. 6). For this reason, it can be set as an appropriate fuel injection amount according to an operation state.

  Further, according to the present embodiment, the fuel injection control means is detected by the exhaust purification apparatus state detection means at times other than normal, and the temperature within the exhaust purification apparatus (catalyst temperature T1, DPF temperature T2) is the first predetermined upper limit. When the temperature is lower than the temperature (S101, S201) and the lower limit second predetermined temperature (S102, S202) or higher (S102, S202), the fuel injection amount of the composite injection is corrected to increase with respect to the normal fuel injection amount Qstd (S1301). When the temperatures T1 and T2 in the purification device are lower than the second predetermined temperature (S102, S202), the fuel injection amount of the combined injection is increased (S1401). For this reason, when the temperature in the exhaust purification apparatus is equal to or higher than the second predetermined temperature and lower than the first predetermined value temperature (T21 ≦ DPF temperature <T22 or T41 ≦ catalyst temperature <T42), the combustion is stabilized by the combined injection Div S. Therefore, it is possible to realize combustion that places importance on minimizing deterioration in fuel consumption and minimizing increase in HC and smoke. On the other hand, when the temperature in the exhaust purification device is lower than the second predetermined temperature (DPF temperature <T21 or catalyst temperature <T41), combustion with an emphasis on short-time temperature rise can be realized by the composite injection Div L. .

  Further, according to the present embodiment, the fuel injection control means detects the fuel injection amount of the combined injection based on the temperature in the exhaust purification apparatus based on the temperature inside the exhaust purification apparatus, and is detected by the exhaust purification apparatus state detection means. When the increase correction is made with respect to the amount, the fuel injection interval (retard interval) in the composite injection is expanded when the increase correction is made (S1302). For this reason, since the increase in diffusion combustion accompanying the increase in load can be suppressed (the ratio of diffusion combustion and premixed combustion can be made appropriate), the increase in smoke can be suppressed.

  Further, according to the present embodiment, the fuel injection control means detects the load while the operating state detection means detects at least one of the load (fuel injection amount Q, accelerator opening Acc) or the rotational speed Ne of the internal combustion engine. As the engine speed increases or the rotational speed increases, the fuel injection amount ratio (Ratio P) of the preliminary injection is increased at least at any of these times (S1301, S1401, FIGS. 13 and 14). For this reason, the preliminary injection amount ratio (Ratio P) can be increased and the retard injection amount ratio (Ratio R) can be decreased, and the premixed combustion can be strengthened as the combustion mode as the load increases. An increase in smoke can be suppressed.

  Further, according to the present embodiment, the fuel injection control means determines the fuel injection timing of normal injection based on the cetane number detected by the cetane number detection means when it is detected as normal time by the exhaust gas purification device state detection means. The higher the cetane number, the more retarded (S1204). For this reason, the ignition combustion of the fuel in the preliminary injection can be performed reliably or stably, and the combustion start timing (heat generation timing) and combustion of the fuel in the retard injection can be stabilized.

Further, according to the present embodiment, the exhaust gas purification device includes at least one of the collection filter (DPF) 17 or the NOx trap catalyst 16 that collects exhaust particulates in the exhaust gas. For this reason, at least one of exhaust particulates or NOx can be reduced.
Further, according to the present embodiment, in the state other than the normal state detected by the exhaust gas purification device state detecting means, the exhaust temperature is raised and the exhaust particulates accumulated on the collection filter are burned and removed to regenerate the collection filter 17. When the regeneration filter is requested to regenerate (S14, S801), and when the regeneration of the NOx trap catalyst 16 is performed to enrich the exhaust air-fuel ratio and desorb and purify NOx trapped in the NOx trap catalyst 16 (S13, S701). When the NOx trap catalyst 16 is requested to detoxify the sulfur adsorbed on the NOx trap catalyst 16 by raising the exhaust temperature (S15, S901), the exhaust temperature is raised to increase the activity of the exhaust purification device. It includes at least any one state of the activity enhancement request to increase (S1601). Therefore, it is possible to determine when to recover the exhaust purification capability of the exhaust purification device from these states.

System configuration diagram of a diesel engine equipped with the combustion control device of the present invention Characteristic diagram showing the relationship between fuel injection system and combustion mode (heat generation rate) Characteristics chart of compound injection of the present invention Characteristics chart of compound injection of the present invention Characteristic diagram showing the relationship between accelerator opening, engine speed and required fuel injection amount, and possible region for DPF regeneration and sulfur poisoning release Characteristic diagram showing the relationship between normal injection amount and combined total injection amount Characteristic diagram showing the relationship between fuel injection amount, engine speed and fuel injection timing Characteristic diagram showing the relationship between fuel injection amount, engine speed and fuel injection pressure The figure for demonstrating the setting of the injection timing in compound injection Diagram for explaining injection timing correction by cetane number Diagram for explaining correction of injection pressure by cetane number The figure for demonstrating the setting of the compound injection quantity ratio in compound injection The figure for demonstrating the setting of the compound injection quantity ratio in compound injection The figure for demonstrating the setting of the compound injection quantity ratio in compound injection Diagram for explaining exhaust λ setting during DPF regeneration Flow chart showing basic control mode of exhaust purification Flow chart showing control mode of DPF regeneration Flow chart showing control mode of sulfur poisoning release Flow chart showing control mode of rich spike (NOx desorption reduction purification) Flow chart showing control mode for preventing melting The flowchart which shows the reproduction | regeneration priority determination processing at the time of a DPF reproduction | regeneration request | requirement The flowchart which shows the reproduction | regeneration priority determination processing at the time of sulfur poisoning cancellation | release request Flow chart for shifting to rich spike control mode Flow chart for requesting DPF regeneration Flow chart for requesting removal of sulfur poisoning Flowchart for requesting a rich spike Flow chart showing catalyst warm-up promotion control mode Flow chart showing normal injection control mode Flow chart showing the composite injection control mode (Div S) Flow chart showing the composite injection control mode (Div L) Flow chart showing exhaust λ control mode Flow chart showing basic engine control mode

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Diesel engine 2 Intake passage 3 Exhaust passage 5 EGR valve 6 Intake throttle valve 7 Air flow meter 10 Fuel injection device 16 NOx trap catalyst 17 DPF
30 Engine control unit

Claims (14)

In an internal combustion engine provided with an exhaust purification device in an exhaust passage,
A fuel injection device capable of directly injecting fuel into a combustion chamber of an internal combustion engine and capable of dividing the fuel injection into two or more injections;
An operating state detecting means for detecting an operating state of the internal combustion engine;
An exhaust purification device state detection means for detecting the state of the exhaust purification device;
Cetane number detection means for detecting the cetane number of the fuel used;
Based on the detection results by the operating state detection means and the exhaust purification device state detection means,
Ordinary injection that controls normal combustion by fuel injection near the top dead center,
Alternatively, at least one of the combined injection constituted by the preliminary injection for controlling the preliminary combustion generated in the vicinity of the top dead center and the retarded injection for controlling the retarded combustion to be started after the completion of the preliminary combustion is performed. Done
A fuel injection control means for controlling fuel injection so as to control at least one of the preliminary combustion and the retarded combustion based on the cetane number when performing the combined injection;
A combustion control device for an internal combustion engine, comprising: The fuel injection control means includes an operation state detected by the operation state detection means and a cetane number detected by the cetane number detection means when the exhaust purification device state detection means detects normal time. Based on normal injection,
Combined injection is performed based on the operating state detected by the operating state detecting unit and the cetane number detected by the cetane number detecting unit when the exhaust gas purifying device state detecting unit detects that it is not normal. The combustion control apparatus for an internal combustion engine according to claim 1.   The fuel injection control means increases the fuel injection pressure as the cetane number is higher based on the cetane number detected by the cetane number detection means when the exhaust gas purification device state detection means detects that it is not normal. The combustion control device for an internal combustion engine according to claim 1 or 2, wherein   The fuel injection control means determines whether the pre-injection and the retarded injection in the combined injection are based on the cetane number detected by the cetane number detection means when the exhaust gas purification apparatus state detection means detects that it is not normal. The combustion control device for an internal combustion engine according to any one of claims 1 to 3, wherein at least the fuel injection timing of the preliminary injection is retarded as the cetane number increases.   When the fuel injection control means is detected by the exhaust gas purification device state detection means at a time other than the normal time, and the fuel injection timing of both the preliminary injection and the retarded injection in the combined injection is delayed as the cetane number increases. 5. The combustion control device for an internal combustion engine according to claim 4, wherein the retard amount of the preliminary injection is made larger than the retard amount of the retard injection.   The fuel injection control means detects the fuel injection amount ratio between the preliminary injection and the retarded injection in the combined injection by the cetane number detection means when the exhaust purification device state detection means detects that it is not normal. 6. The combustion control apparatus for an internal combustion engine according to claim 1, wherein the control is performed based on the cetane number.   The fuel injection control means detects cetane when the exhaust gas purification device state detection means detects a fuel injection amount ratio between preliminary injection and retarded injection in the combined injection based on a cetane number. 7. The combustion control apparatus for an internal combustion engine according to claim 6, wherein the fuel injection amount ratio of the preliminary injection is decreased as the value is higher.   The fuel injection control means sets the fuel injection amount of the combined injection at a normal time according to the operation state detected by the operation state detection means when the exhaust gas purifier state detection means detects that it is other than the normal time. The combustion control device for an internal combustion engine according to any one of claims 1 to 7, wherein an increase correction is made with respect to the fuel injection amount.   The fuel injection control means is detected by the exhaust purification apparatus state detection means at a time other than normal time, and when the temperature in the exhaust purification apparatus is lower than the first predetermined temperature at the upper limit and equal to or higher than the second predetermined temperature at the lower limit. The fuel injection amount of the composite injection is corrected to be increased with respect to the fuel injection amount at the normal time, and the fuel injection amount of the composite injection is increased when the temperature in the exhaust emission control device is lower than the second predetermined temperature. A combustion control device for an internal combustion engine according to any one of claims 1 to 8.   The fuel injection control means is detected by the exhaust purification device state detection means to be other than normal time, and the fuel injection amount of the combined injection is increased with respect to the normal fuel injection amount based on the temperature in the exhaust purification device. 10. The combustion control device for an internal combustion engine according to claim 1, wherein when correcting, the fuel injection interval in the combined injection is increased when the increase correction is performed.   The fuel injection control means detects at least one of the load and the rotational speed of the internal combustion engine by the operating state detection means, and at least one of these increases as the detected load increases or the rotational speed increases. The combustion control device for an internal combustion engine according to any one of claims 1 to 10, wherein the fuel injection amount ratio of the preliminary injection is sometimes increased.   The fuel injection control means sets the fuel injection timing of normal injection to a high cetane number based on the cetane number detected by the cetane number detection means when the exhaust purification device state detection means detects normal time. The combustion control device for an internal combustion engine according to any one of claims 1 to 11, wherein the angle is retarded as much as possible.   The internal combustion engine according to any one of claims 1 to 12, wherein the exhaust gas purification device includes at least one of a collection filter or a NOx trap catalyst that collects exhaust particulates in exhaust gas. Combustion control device. The state other than the normal state detected by the exhaust gas purification device state detecting means is
When the regeneration filter is requested to regenerate the collection filter by burning and removing the exhaust particulate accumulated on the collection filter by raising the exhaust temperature,
A request for regeneration of a NOx trap catalyst that enriches the exhaust air-fuel ratio and desorbs and purifies NOx trapped in the NOx trap catalyst;
A NOx trap catalyst detoxification request for detoxifying sulfur adsorbed on the NOx trap catalyst by raising the exhaust temperature; and
At the time of an activity enhancement request to raise the exhaust temperature and increase the activity of the exhaust purification device,
The combustion control device for an internal combustion engine according to claim 13, wherein at least one of the states is included.

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