JP2010121505A - Fuel injection control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel injection control device capable of performing post injection control excellent in transient response. <P>SOLUTION: The fuel injection control device for an internal combustion engine 1 executing post injection contributing to exhaust gas temperature rise after main injection contributing engine output, includes an exhaust gas temperature rise request generating means 10 generating an exhaust gas temperature rise demand, a temperature estimation means 10 estimating an inside-cylinder temperature or an exhaust gas temperature in an exhaust gas passage on the upstream side of an exhaust gas purification catalyst at exhaust valve open timing, and an injection control means 10 setting the injection timing and the injection quantity of the main injection and the post injection. The injection control means 10 sets the injection quantity and the injection timing of the post injection based on the inside-cylinder temperature or the exhaust gas temperature in the exhaust gas passage at the exhaust valve open timing when the temperature rise in exhaust gas is requested. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to fuel injection control of an internal combustion engine, and more particularly to fuel injection control for raising the exhaust temperature.

  Fuel injection control is known in which post injection is performed after main injection in order to raise the temperature of an exhaust purification catalyst for an internal combustion engine for activation, regeneration, and the like.

For example, if the catalyst temperature is detected and the catalyst is above the activation temperature, the post injection timing is retarded to increase the HC emission amount. If the catalyst temperature is below the activation temperature, the post injection timing is advanced to increase the exhaust temperature. Japanese Patent Application Laid-Open No. H10-228688 discloses control for raising the value.
JP 2004-169595 A

  However, when the post injection timing is changed, the exhaust temperature first changes, and the catalyst temperature changes due to the change in the exhaust temperature. That is, there is a delay between the change of the post injection amount and the change of the catalyst temperature. For this reason, in the control method of Patent Document 1 that controls the post-injection timing based on the catalyst temperature, there is room for improvement in the temperature rise of the catalyst during the transition when the catalyst temperature changes.

  Therefore, an object of the present invention is to provide a control device for an internal combustion engine that is excellent in raising the temperature of a catalyst.

  An internal combustion engine fuel injection control apparatus according to the present invention is an internal combustion engine fuel injection control apparatus capable of performing post-injection contributing to exhaust gas temperature increase after main injection contributing to engine output. Temperature rise request generation means, temperature estimation means for estimating the in-cylinder temperature at the exhaust valve opening timing or the exhaust temperature in the exhaust passage upstream of the exhaust purification catalyst, and the injection timing and injection amount of main injection and post injection The injection control means, and when there is a request to increase the exhaust temperature, the injection control means sets the injection amount and the injection timing of the post injection according to the in-cylinder temperature at the exhaust valve opening timing or the exhaust temperature in the exhaust passage. To do.

  According to the present invention, it is possible to estimate the in-cylinder temperature at the exhaust valve opening timing or the exhaust temperature in the exhaust passage upstream of the exhaust purification catalyst, and perform post injection control excellent in raising the temperature of the catalyst.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a system configuration diagram of a diesel engine to which the present embodiment is applied.

  1 is a diesel engine body, 2 is a fuel injection valve for each cylinder, 3 is a common rail for storing high-pressure fuel, 4 is an intake collector, 5 is an intake passage, 11 is an exhaust passage, 10 is a control unit for performing various controls, 14 Is a transmission that transmits the driving force of the diesel engine body 1 to the drive shaft. The transmission 14 may be a stepped transmission or a continuously variable transmission.

  The fuel injection device of this system is a so-called common rail fuel injection device. That is, the fuel increased in pressure by the high-pressure pump 9 is stored in the common rail 3, and each fuel injection valve 2 opens and closes according to an injection signal from the control unit (ECU) 10. Inject into.

  An intake passage 5 is connected to an intake collector 4 connected to each intake port of the diesel engine main body 1. An air flow meter 15 for detecting an intake air amount from the upstream side is connected to the intake passage 5, in order to pressurize intake air. The compressor 6a of the turbocharger 6 and an intercooler 7 that cools the pressurized air to a high temperature are installed.

  A turbine 6b of the turbocharger 6, a NOx catalyst 12 that adsorbs NOx in the exhaust, and an exhaust trap (DPF) 13 that collects particulates (PM) in the exhaust are arranged in the exhaust passage 11 from the upstream side. The

  The exhaust valve that connects / disconnects the communication between the inside of the cylinder and the exhaust passage 11 is driven by a variable valve mechanism that can variably control at least the opening / closing timing.

  An EGR passage 21 that branches from the exhaust passage 11 upstream of the turbine 6b and is connected to the intake collector 4 is provided. An EGR valve 22 is provided in the EGR passage 21 and is recirculated into the intake air according to operating conditions. Control the amount of exhaust.

  The ECU 10 receives detection signals from an engine speed sensor 16 that detects the engine speed and an accelerator opening sensor 17 that detects the opening of the accelerator pedal. Based on these, fuel injection control, opening control of the EGR valve 22, opening control of the intake throttle valve 8, estimation of the PM accumulation amount in the DPF 13, and the like are performed. Further, it is determined whether or not a request for raising the exhaust temperature is required, and if there is a request for raising the exhaust temperature, control is performed to change the post injection timing and the exhaust valve opening timing as will be described later.

  Next, fuel injection control will be described. FIG. 2 is a flowchart of the fuel injection control executed by the ECU 10. This flowchart is repeatedly executed every short time of about 10 ms, for example.

  In step S10, the engine speed NE detected by the engine speed sensor 16 and the accelerator opening Vn detected by the accelerator opening sensor 17 are read.

  In step S20, the required injection amount Q is calculated by map search based on the required torque calculated from the accelerator opening degree Vn and the engine speed NE. Here, for example, as shown in FIG. 3, a map is used in which the required torque is plotted on the vertical axis and the engine rotational speed NE is plotted on the horizontal axis, and the main injection amount decreases as the low load and the low rotation increase. .

  In step S30, it is determined whether there is an exhaust gas temperature increase request. If there is an exhaust gas temperature increase request, the process proceeds to step S40, and if not, the process proceeds to step S140. For example, it is determined that there is an exhaust gas temperature increase request when it is a DPF regeneration time or a poisoning release time. Whether it is a DPF regeneration time or a poisoning release time is determined by a method similar to a generally known method.

  In step S40, the target main injection amount and the target main injection timing are determined from the required injection amount Q and the injection amount corresponding to the exhaust gas temperature increase request. The injection amount in response to the exhaust gas temperature increase request decreases as the exhaust gas temperature decreases from a low load and low rotation to a high exhaust temperature and a high load and high rotation.

  In step S50, based on the main injection amount, the main injection timing, the fuel injection pressure, and the actual air amount detected by the air flow meter 15, the exhaust valve opening timing (at the time of EVO) is determined by a simple method as described below. The in-cylinder temperature Tin-cyl is calculated.

  First, the in-cylinder pressure history during the cycle is obtained based on the air amount, and the heat generation rate is obtained based on the target main injection amount, the target main injection timing, the fuel injection pressure, and the like.

  The heat generation rate is a value indicating what rate the fuel burns with respect to the change in the crank angle.

  FIG. 4 is a diagram showing the in-cylinder pressure history and the heat generation rate. The horizontal axis represents the crank angle [deg. ATDC], the vertical axis represents in-cylinder pressure [MPa] and heat generation rate [J / deg].

  As shown in FIG. 4, after the intake valve is closed, the in-cylinder pressure increases due to the piston being raised. When the fuel is injected, heat is generated by further burning the fuel. The position where the heat generation rate rises corresponds to the combustion start position. When combustion ends, the heat generation rate becomes zero, and the in-cylinder pressure decreases as the piston descends.

  Next, as shown in FIG. 5, the in-cylinder temperature history with respect to the crank angle is obtained from the in-cylinder pressure history and heat generation rate, and the gas state equation, and the in-cylinder temperature during EVO is calculated.

  For calculating the in-cylinder pressure history and the heat generation rate, and the in-cylinder temperature during EVO based on these, a known method, for example, a method disclosed in Japanese Patent Application Laid-Open No. 2007-247487 can be applied.

  In step S60, it is determined whether or not the in-cylinder temperature Tin-cyl at the time of EVO is lower than a predetermined temperature T1 (first temperature). If low, the process proceeds to step S70, and if high, the process proceeds to step S100.

  The predetermined temperature T1 sets a temperature at which the post-injected fuel can be partially oxidized in the cylinder. That is, if the temperature is such that partial oxidation is not possible, the process proceeds to step S70, and if possible, the process proceeds to step S100.

  In step S70, an EVO advanceable range is calculated. The EVO advanceable range refers to an EVO range in which the required engine load determined from the operating state can be ensured on the advance side with respect to EVO during normal operation. For example, the range is from EVO to EVOI in FIG.

  In step S80, the EVO is advanced to the most advanced position within the EVO advanceable range, and in step S90, the post injection timing is set to a state in which the exhaust valve is open after EVO. Thereby, the post-injected fuel is sent to the NOx catalyst 12 and the DPF 13 together with the high-temperature exhaust gas.

  In step S100, it is determined whether or not the in-cylinder temperature Tin-cyl is lower than a predetermined temperature T2 (second temperature). If low, the process proceeds to step S110, and if high, the process proceeds to step S130. Here, the predetermined temperature T2 is, for example, the activation temperature of the NOx catalyst 12, which is higher than the predetermined temperature T1.

  In step S110, the post injection timing is set immediately after the main combustion (combustion of the main injected fuel) is completed. Thereby, the partial oxidation of the post-injected fuel is performed.

In step S120, EVO is set to post injection timing or during post injection.
As a result, oil dilution by post-injected fuel can be prevented, and the exhaust temperature has risen to some extent, so that partial oxidation of the fuel is also performed in the exhaust passage 11 to the NOx catalyst 12. For this reason, the time required for exhaust gas temperature raising can be shortened. Further, when the cold machine is started, the activation of the NOx catalyst 12 and the DPF 13 is promoted, and the generation of unburned HC can be suppressed.

  In step S130, the post injection timing is set to a time after EVO. As a result, post injection is performed while the exhaust valve is open, and the fuel injected by the post injection is effectively sent to the NOx catalyst 12 and the DPF 13, and the temperature rise of the exhaust is promoted. Note that the same effect can be obtained even if post-injection is set during so-called valve overlap in which both the intake valve and the exhaust valve are open.

  In step S140, operation is performed with the target main injection amount and the target main injection timing set as in the case of a general engine.

  The in-cylinder temperature region, valve timing, and post injection timing in the above control are summarized as shown in FIGS. As shown in FIG. 6, the in-cylinder temperature Tin-cyl is divided into three regions: a region I below the predetermined temperature T1, a region II above the predetermined temperature T1 and below the predetermined temperature T2, and a region III above the predetermined temperature T2. It is done.

  FIG. 7 is a diagram illustrating an example of EVO and post-injection timing in regions I to III.

  In region I, the EVO timing is advanced from normal EVO to EVOI which is the most advanced in the EVO advanceable range, and post-injection is performed in the crank angle region ITi after EVOI.

  In region II, post injection is performed in the crank angle region ITii after the end of main combustion, and EVO is also set within this range.

  In region III, post-injection is normally performed during the crank angle region ITiii after EVO, or during the valve overlap period.

  The post injection amount is determined according to the temperature increase request. Therefore, the region III having a relatively high temperature is smaller than the region I and the region II. On the other hand, in the region I, the in-cylinder temperature Tin-cyl at the time of EVO is lower than that in the region II, but the post injection amount is small. This is because in the region I where the in-cylinder temperature Tin-cyl at the time of EVO is relatively low, the fuel is difficult to be partially oxidized and the NOx catalyst 12 is not activated. This is to prevent an increase in HC emissions.

  Note that the exhaust temperature Texh in the exhaust passage 11 upstream of the NOx catalyst 12 may be calculated instead of the in-cylinder temperature Tin-cyl during EVO.

  As described above, according to the present embodiment, the following effects can be obtained.

  (1) In a fuel injection control device for an internal combustion engine capable of performing post injection for raising the temperature of exhaust after main injection, when there is a request for raising the temperature of exhaust gas, an in-cylinder temperature Tin-cyl or NOx catalyst at the time of EVO Since the post-injection injection amount and the injection timing are set depending on which of the temperature regions I to III the exhaust temperature Texh in the exhaust passage 11 upstream of 12 belongs to in advance, the responsiveness is excellent Post injection can be controlled.

  (2) In-cylinder temperature Tin-cyl or exhaust temperature Texh is calculated based on the actual intake air amount, main injection timing and main injection amount, and EVO timing, so that post-injection control with excellent responsiveness is performed. It is possible to accurately estimate the temperature required for the operation.

  (3) When there is an exhaust gas temperature increase request and the in-cylinder temperature Tin-cyl or the exhaust gas temperature Texh belongs to the region I, the EVO is advanced and the post injection timing is set after the EVO. Post injection is performed while exhausting the exhaust gas, so that the temperature rise of the exhaust gas and the activation of the NOx catalyst 12 can be promoted, and the discharge of unburned HC can be suppressed.

  (4) When there is an exhaust temperature increase request and the in-cylinder temperature Tin-cyl or the exhaust temperature Texh belongs to the region I, from a crank angle set in advance during an expansion stroke to a crank angle corresponding to EVO during normal operation Therefore, the fuel injected by the post injection is partially oxidized in the cylinder or the exhaust passage 11. As a result, the temperature rise of the exhaust gas and the activation of the NOx catalyst 12 can be promoted, and the discharge of unburned HC can be suppressed.

  (5) Furthermore, since the EVO is advanced to either the post injection start timing or the post injection timing, oil dilution by post injection can be suppressed.

  (6) When there is an exhaust temperature increase request and the internal temperature Tin-cyl or the exhaust temperature Texh belongs to the region III, post injection is performed after EVO or during the valve overlap period, that is, the NOx catalyst is activated. In this state, post-injection is performed in a state where the exhaust valve is opened and the exhaust flow rate is high, so that the fuel is efficiently guided to the NOx catalyst 12 and the DPF 13, and the temperature rise of the exhaust is promoted.

  (7) Since the temperature T1 is set to a temperature at which the fuel can be partially oxidized in the cylinder or in the exhaust passage 11 upstream of the NOx catalyst 12, the temperature of the exhaust passage 11 is preferentially raised at a temperature lower than T1, Above T1, partial oxidation of the fuel in the exhaust passage 11 is possible.

  (8) Since the temperature T2 is set to the activation temperature of the NOx catalyst 12, the temperature of the NOx catalyst 12 is preferentially raised at a temperature lower than T2, and the temperature rise of the exhaust gas by combustion in the NOx catalyst 12 can be promoted at T2 or higher. It becomes.

  A second embodiment will be described.

  In this embodiment, the system configuration is the same as that of the first embodiment, but part of the post injection control is different.

  FIG. 8 is a flowchart showing a control routine of post injection control according to this embodiment. Since steps S270 to S290 are different from the flowchart of FIG. 2, only this portion will be described.

  In step S270, a retardable range of the main injection timing is calculated. The main injection retardable range is a range of the main injection timing that can ensure the required engine load that is retarded from the main injection timing during normal operation and determined from the operating state.

  In step S280, the main injection timing is set within the retardable range calculated in step S270.

  In step S290, the post injection timing and the injection amount are set. Here, a timing earlier than a predetermined injection timing and injection amount set in advance and a small injection amount are set. The predetermined injection timing set in advance is, for example, an injection timing at which misfire occurs due to combustion by post injection. On the other hand, the predetermined injection amount set in advance is, for example, an injection amount that causes misfire when post injection is performed.

  That is, when post-injection is performed, the injection timing and the injection amount are set so that the fuel injected by post-injection can be combusted in the cylinder. Note that post injection may be prohibited.

  As described above, in the present embodiment, the following effects can be obtained.

  When there is an exhaust gas temperature increase request and the in-cylinder temperature Tin-cyl or the exhaust gas temperature Texh belongs to the region I, the main injection is retarded, and post injection is performed at an injection timing and an injection amount that does not inhibit or cause misfire. The exhaust gas temperature in the exhaust passage 11 is raised to promote the exhaust gas temperature rise and the activation of the NOx catalyst 12, and the unburned HC emission can be suppressed.

  The present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made within the scope of the technical idea described in the claims.

1 is a configuration diagram of a system to which a first embodiment is applied. It is a flowchart which shows the control routine of the post injection control of 1st Embodiment. It is a request | requirement injection quantity map. It is a figure which shows the log | history with respect to the crank angle of a cylinder internal pressure and a heat release rate. It is a figure which shows the log | history with respect to the crank angle of exhaust temperature. It is a figure which shows an in-cylinder temperature range. It is a figure which shows the post injection timing and the exhaust valve opening timing. It is a flowchart which shows the control routine of the post injection control of 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Diesel engine body 2 Fuel injection valve 3 Common rail 4 Intake collector 5 Intake passage 6 Turbocharger 7 Intercooler 8 Inlet throttle valve 9 High pressure pump 10 Control unit (ECU)
11 Exhaust passage 12 NOx catalyst 13 DPF
DESCRIPTION OF SYMBOLS 14 Transmission 15 Air flow meter 16 Engine speed sensor 17 Accelerator opening sensor 21 EGR passage 22 EGR valve

Claims (9)

In a fuel injection control device for an internal combustion engine capable of performing post injection contributing to exhaust gas temperature increase after main injection contributing to engine output,
Exhaust temperature increase request generating means for issuing an exhaust temperature increase request;
Temperature estimating means for estimating the in-cylinder temperature at the exhaust valve opening timing or the exhaust temperature in the exhaust passage upstream of the exhaust purification catalyst;
Injection control means for setting the injection timing and the injection amount of the main injection and the post injection;
With
When there is an exhaust temperature increase request, the injection control means sets the post-injection injection amount and the injection timing according to the in-cylinder temperature at the exhaust valve opening timing or the exhaust temperature in the exhaust passage. A fuel injection control device for an internal combustion engine.   The injection control means calculates the in-cylinder temperature at the exhaust valve opening timing or the exhaust temperature in the exhaust passage based on the actual intake air amount, the main injection timing and injection amount, and the exhaust valve closing timing. The fuel injection control device for an internal combustion engine according to claim 1, wherein: Variable valve means capable of changing at least the closing timing of the exhaust valve,
When there is a request to increase the exhaust temperature, if the in-cylinder temperature at the exhaust valve opening timing or the exhaust temperature in the exhaust passage is lower than a preset first temperature, the variable valve means closes the exhaust valve. 3. The fuel injection control device for an internal combustion engine according to claim 1, wherein the timing is changed to an advance side, and the injection control means sets the injection timing of the post injection after the exhaust valve closing timing. At least variable valve operating means capable of changing the closing timing of the exhaust valve is provided,
When there is a request to increase the exhaust temperature, if the in-cylinder temperature at the exhaust valve opening timing or the exhaust temperature in the exhaust passage is lower than a preset first temperature, the main injection timing is controlled by the injection control means. Is changed to the retard side, or the exhaust valve closing timing is changed to the advance side by the variable valve means, and the post injection is prohibited by the injection control means, or the post injection is set from the preset injection timing. 3. The fuel injection control device for an internal combustion engine according to claim 1, wherein the fuel injection control is performed at an earlier timing and with an injection amount smaller than a preset injection amount.   When there is a request to increase the exhaust temperature, if the in-cylinder temperature at the exhaust valve opening timing or the exhaust temperature in the exhaust passage belongs to a region that is equal to or higher than the first temperature and lower than a preset second temperature, The injection control means sets the post-injection timing so as to perform the post-injection from a preset time during an expansion stroke to an exhaust valve closing timing when there is no request for the exhaust gas temperature increase. Item 5. The fuel injection control device for an internal combustion engine according to Item 3 or 4.   6. The fuel injection control device for an internal combustion engine according to claim 5, wherein the variable valve mechanism advances the exhaust valve closing timing to either a post injection start timing or a post injection timing.   When there is a request to increase the exhaust temperature, if the in-cylinder temperature at the exhaust valve opening timing or the exhaust temperature in the exhaust passage is equal to or higher than the second temperature, the injection control means The fuel injection control device for an internal combustion engine according to claim 5 or 6, wherein the post injection timing is set so that post injection is performed during a valve overlap period.   8. The first temperature according to claim 3, wherein the first temperature is a temperature at which the fuel injected by the post injection can be partially oxidized in a cylinder or in an exhaust passage upstream of the exhaust purification catalyst. A fuel injection control device for an internal combustion engine according to one.   The fuel injection control device for an internal combustion engine according to any one of claims 5 to 8, wherein the second temperature is an activation temperature of the exhaust purification catalyst.

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