JP2017115633A - Fuel injection control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize combustion at the time immediately after starting purge.SOLUTION: A fuel injection control device for an internal combustion engine 1 includes a fuel injection valve 3 for injecting fuel into a cylinder of the engine 1, and an engine control unit 50 for executing pre-injection before main injection related to the output control of the engine 1 and performing post injection from an expansion stroke to an exhaust stroke after the main injection to make an exhaust temperature high enough to regenerate a proximity NOx catalyst 32 provided in an exhaust pipe 30 while supplying reductant. During a time after starting the post injection but before the passage of a predetermined cycle, the device retards an injection timing for the pre-injection to make a time between the pre-injection and the main injection shorter than that after the passage of the predetermined cycle.SELECTED DRAWING: Figure 1

Description

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

  The exhaust passage of the engine (internal combustion engine) is provided with an exhaust purification device for purifying the exhaust. For example, some exhaust passages of diesel engines are provided with a NOx trap catalyst for reducing and removing NOx as an exhaust purification device. The NOx trap catalyst occludes NOx in exhaust under a lean atmosphere, reduces NOx collected in a rich or stoichiometric atmosphere, and reduces and removes NOx in exhaust.

  For example, Patent Document 1 describes a diesel engine having two NOx trap catalysts in the exhaust passage on the upstream side and the downstream side with a filter interposed therebetween. For these NOx trap catalysts, NOx purge is performed by raising the exhaust temperature by post injection by the in-cylinder injection valve and supplying unburned fuel such as HC or CO as a reducing agent to make a rich atmosphere. Thus, the NOx storage performance is recovered (regenerated).

JP 2015-187402 A

  By the way, in the engine that performs NOx purge by post injection as in Patent Document 1, when the lean operation that is normal operation is switched to the rich operation that performs post injection at the start of NOx purge, the exhaust temperature rise and the reducing agent are changed. When early post-injection is performed with the intention of supply, the in-cylinder temperature is low immediately after the switching of the rich operation, so the misfire of the increased amount of fuel injected from the fuel injection valve or in-cylinder combustion becomes unstable. There is a risk that. Therefore, the operation of the internal combustion engine becomes unstable at the start of the NOx purge, causing fluctuations in torque and noise, which may reduce drivability, and may lead to emission deterioration due to unburned fuel.

  The present invention has been made to solve such problems, and it is an object of the present invention to provide a fuel injection control device for an internal combustion engine that stabilizes combustion immediately after the start of purging.

  In order to achieve the above object, according to the first aspect of the present invention, a fuel injection unit that injects fuel into a cylinder of an internal combustion engine, and fuel is injected by the fuel injection unit before main injection related to output control of the internal combustion engine. An injection control unit that executes pre-injection to be injected, and post-injection by the fuel injection unit in the exhaust stroke from the expansion stroke after the main injection according to the output control of the internal combustion engine to raise the exhaust gas temperature and reduce the reducing agent And a regeneration control unit for regenerating the exhaust purifier provided in the exhaust passage of the internal combustion engine, wherein the injection control unit is configured to perform the post-injection. The time between the preceding injection and the main injection is made shorter than after the predetermined cycle until a predetermined cycle elapses from the start.

Preferably, the injection control unit retards the injection timing of the upstream injection to shorten the time between the upstream injection and the main injection.
Preferably, the fuel injection control device includes a temperature detection unit that detects a temperature of the internal combustion engine, and the injection control unit performs injection timing of the front-stage injection as the temperature of the internal combustion engine decreases. It is good to retard the angle.

Preferably, the injection control unit further advances the injection timing of the main injection as the output torque or rotation speed of the internal combustion engine decreases.
Preferably, the injection control unit performs control so that the time between the preceding injection and the main injection is shorter than after the elapse of the predetermined cycle when the output torque and the rotational speed of the internal combustion engine are in a predetermined range. It should be executed.

  According to the present invention, when the purge is started to regenerate the exhaust purifier, the time between the main injection and the preceding stage injection performed before that is shortened until a predetermined cycle elapses from the start of the post injection. The fuel from the main injection and the fuel from the pre-injection are stacked and burned to increase the in-cylinder temperature, particularly the temperature at the fuel spray orbit, and promote post-injection (early post-injection) to promote diffusion combustion and improve combustibility. Can be improved. Thereby, the combustion stability of the internal combustion engine immediately after the start of the purge can be improved.

It is a schematic structure figure of a diesel engine in an embodiment of the present invention. It is a flowchart which shows the fuel-injection correction | amendment control point in this embodiment. It is an example of the map for water temperature correction coefficient calculation. It is an example of the intake manifold temperature correction coefficient calculation map. It is an example of the map for main injection advance coefficient calculation based on an engine speed. It is an example of the map for main injection advance angle coefficient calculation based on an engine torque.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a diesel engine (an internal combustion engine, hereinafter referred to as an engine 1) to which a fuel injection control device according to an embodiment of the present invention is applied.
The engine 1 is a multi-cylinder direct injection internal combustion engine (for example, a common rail diesel engine) that is mounted on a vehicle as a travel drive source and includes a turbocharger 23. Specifically, high pressure fuel accumulated in a common rail (not shown) is supplied to the fuel injection valve 3 (fuel injection unit) of each cylinder, and from the fuel injection valve 3 to the combustion chamber 4 of each cylinder at an arbitrary injection timing and injection amount. It is configured to be able to inject.

Each cylinder of the engine 1 is provided with a piston 5 that can slide up and down. The piston 5 is connected to the crankshaft 6 via a connecting rod. A flywheel is provided at one end of the crankshaft 6.
An intake port 7 and an exhaust port 8 are communicated with the combustion chamber 4.
The intake port 7 is provided with an intake valve 9 that communicates and blocks the combustion chamber 4 and the intake port 7. Further, the exhaust port 8 is provided with an exhaust valve 10 for performing communication between the combustion chamber 4 and the exhaust port 8 and shutting off.

An intake manifold 11 that distributes the sucked air to each cylinder is provided upstream of the intake port 7 so as to communicate therewith. An exhaust manifold 12 that collects exhaust exhausted from the cylinders is provided downstream of the exhaust port 8.
Between the intake manifold 11 and the exhaust manifold 12, there is provided a high-pressure exhaust gas recirculation passage 15 for returning a part of the exhaust gas to the intake air, that is, introducing high-temperature and high-pressure exhaust gas into the intake air. The high pressure exhaust gas recirculation passage 15 is provided with an exhaust gas recirculation valve 16 that adjusts the amount of high temperature / high pressure exhaust gas that returns to the intake air. The high-pressure exhaust gas recirculation passage 15 is provided with an exhaust gas recirculation cooler 17 that cools the exhaust gas introduced into the intake manifold 11.

  An intake pipe 20 that is an intake passage is connected to the intake manifold 11. An air cleaner that removes dust in the fresh air (not shown) and a turbocharger are sequentially connected to the intake pipe 20 from the upstream side toward the intake manifold 11. 23, an intercooler 25 that cools the intake air that has been compressed by the compressor 24 and has reached a high temperature, and an electronically controlled throttle valve 27 that adjusts the flow rate of the exhaust gas that is introduced from the high-pressure exhaust gas recirculation passage 15. ing.

In the exhaust pipe 30 which is an exhaust passage downstream of the exhaust manifold 12, a turbine 31 of the turbocharger 23, a proximity NOx catalyst 32 (exhaust purifier), and fine particles mainly composed of graphite in the exhaust are arranged in order from the upstream side. It includes a diesel particulate filter 33 that collects and combusts material and an underfloor NOx catalyst 34.
Each of the proximity NOx catalyst 32 and the underfloor NOx catalyst 34 is a NOx trap catalyst (NOx occlusion reduction catalyst) that occludes NOx (nitrogen oxide) in exhaust gas and reduces and purifies it. The proximity NOx catalyst 32 is housed in the same casing 35 as the diesel particulate filter 33 and is disposed in the engine room of the vehicle. The underfloor NOx catalyst 34 is disposed under the floor of the vehicle.

  The casing 35 is provided with an exhaust temperature sensor 40 that detects the temperature of the exhaust gas flowing into the proximity NOx catalyst 32. The intake manifold 11 is provided with an intake manifold temperature sensor 41 (temperature detection unit) that detects the temperature of intake air (intake manifold temperature Ti) flowing into the combustion chamber 4 of the engine 1. Further, the engine 1 is provided with a rotation speed sensor 42 that detects the engine rotation speed r, and a water temperature sensor 43 (temperature detection unit) that detects the engine water temperature Tw.

  The exhaust temperature sensor 40, the intake manifold temperature sensor 41, the rotation speed sensor 42, the water temperature sensor 43, and other various sensors such as an oxygen concentration sensor for detecting the oxygen concentration (air-fuel ratio) of the exhaust, the fuel injection valve 3, and the electronic control Various devices such as the throttle valve 27 and the exhaust gas recirculation valve 16 are electrically connected to an engine control unit 50 (an injection control unit, a regeneration control unit).

  The engine control unit 50 includes an input / output device, a storage device (ROM, RAM, nonvolatile RAM, etc.), a timer, a central processing unit (CPU), and the like. Detection information from each sensor and accelerator operation amount And the like, and the operation control of the various devices is performed by calculating the fuel injection amount, the fuel injection timing, the opening degree of the electronic control throttle valve 27 and the exhaust gas recirculation valve 16 based on the various information. Thus, the operation control of the engine 1 is performed.

  Further, the engine control unit 50 controls the fuel injection valve 3 to perform pre-injection (previous stage) during one cycle centering on main injection related to output control of the engine 1 which is main injection of fuel injection into the cylinder. Injection), after-injection, and post-injection. The pre-injection is performed before the main injection and is performed to improve the ignition performance. After-injection is performed mainly when the engine 1 is at a high rotational speed and high load, and is performed in order to completely burn the fuel that has not been burned out by the main injection. In general, the post injection is performed from the expansion stroke to the exhaust stroke after the after injection. In the present embodiment, exhaust gas temperature rises and CO (carbon monoxide), which is a strong reducing agent, is supplied to the close NOx catalyst 32 provided in the exhaust passage by early post injection in which post injection is performed in the middle of the expansion stroke of the engine 1. NOx purge operation is possible. By this NOx purge operation, NOx stored in the proximity NOx catalyst 32 is reduced and removed, and the proximity NOx catalyst 32 is regenerated.

Further, in the present embodiment, the engine control unit 50 performs fuel injection correction control for correcting the injection timings of the pre-injection and the main injection at the start of the NOx purge operation.
FIG. 3 is a flowchart showing a fuel injection correction control procedure in the NOx purge operation.
This control is repeatedly executed every predetermined time during engine operation.
First, in step S10, various information from the various sensors, specifically, engine rotational speed r, engine torque N (output torque), and information for determining start of NOx purge operation determined in step S20 below are input. Then, the process proceeds to step S20.

  In step S20, it is determined whether or not the NOx purge operation is started. The NOx purge operation is performed after the NOx occlusion amount occluded in the proximity NOx catalyst 32 increases to near the upper limit value of the allowable occlusion amount, or after an interval set in advance by a rotation-torque map or the like, and the catalyst temperature, Starts when conditions such as engine speed, load, in-cylinder air-fuel ratio, intake air amount, etc. are met The NOx occlusion amount can be estimated by a known technique. For example, the NOx occlusion amount may be estimated based on the accumulated operation time of the lean operation in which the engine 1 is operated with the air-fuel ratio lean. If it is determined to start the NOx purge operation, the process proceeds to step S30. When it is determined that the NOx purge operation is not started, this routine is ended (returned).

In step S30, counting of a predetermined cycle cy is started. The predetermined cycle cy is set based on the engine speed r and the engine torque N. The predetermined cycle cy is set to several cycles, for example, and is set so as to decrease as the engine rotational speed r increases and to decrease as the engine torque N increases. Then, the process proceeds to step S40.
In step S40, various information from the various sensors, specifically, the engine speed r, the engine water temperature Tw, the intake manifold temperature Ti, and the engine torque N are input. Then, the process proceeds to step S50.

  In step S50, it is determined whether or not it is a region where fuel injection correction control is performed. The execution region of the fuel injection correction control is determined based on the engine speed r, the engine torque N, and the engine water temperature Tw. The execution region of the fuel injection correction control may be, for example, a predetermined low rotation low torque range in which the engine speed r and the engine torque N are equal to or lower than predetermined values, and the engine water temperature Tw may be set to a predetermined range. Here, the predetermined low rotation low torque range and the predetermined range of the engine water temperature Tw are within a range where NOx purge can be performed and combustion stability decreases immediately after the start of the NOx purge operation. What is necessary is just to set suitably. If it is the execution region of the fuel injection correction control, the process proceeds to step S60. If it is not in the implementation region of the fuel injection correction control, the process proceeds to step S100.

  In step S60, it is determined whether or not a value (Cw × Ci) obtained by multiplying the water temperature correction coefficient Cw and the intake manifold temperature correction coefficient Ci is less than one. The water temperature correction coefficient Cw is calculated using the map shown in FIG. 3 based on the engine water temperature Tw detected by the water temperature sensor 43. As shown in FIG. 3, the water temperature correction coefficient Cw is set to 1 when the engine water temperature Tw is equal to or higher than T2 (for example, 95 degrees Celsius), and is decreased as the engine water temperature Tw is lower than T2. The intake manifold temperature correction coefficient Ci is calculated using the map shown in FIG. 4 based on the intake manifold temperature Ti detected by the intake manifold temperature sensor 41. As shown in FIG. 4, the intake manifold temperature correction coefficient Ci is set to 1 when the intake manifold temperature Ti is equal to or higher than T3 (for example, 80 degrees Celsius), and is set to decrease as the intake manifold temperature Ti decreases from T3. If the product of the water temperature correction coefficient Cw and the intake manifold temperature correction coefficient Ci is less than 1 (Cw × Ci <1), the process proceeds to step S70. If the product of the water temperature correction coefficient Cw and the intake manifold temperature correction coefficient Ci is 1 or more (Cw × Ci ≧ 1), the process proceeds to step S100.

  In step S70, pre-injection correction is performed. The pre-injection correction uses the water temperature correction coefficient Cw and the intake manifold temperature correction coefficient Ci calculated in step S60 with respect to the reference pre-injection interval Pistd (deg) which is the time between normal pre-injection and main injection. It is done. As shown in the following formula (1), a pre-injection interval Pi (deg) which is a time between the pre-injection and the main injection is calculated, and the time (interval) between the pre-injection and the main injection is calculated as the pre-injection. The injection timing of the pre-injection is set so as to be the interval Pi (deg).

When the engine water temperature Tw is less than T2 or the intake manifold temperature Ti is less than T3, Cw × Ci is smaller than 1, and the pre-injection interval Pi (deg) is set to the reference pre-set value set by the base map during normal operation. It becomes a value smaller than the injection interval Pi std (deg), and the pre-injection is changed in the direction of retarding.
Pi (deg) = Pistd (deg) × Cw × Ci (1)
Then, the process proceeds to step S80.

In step S80, main injection correction is performed. In the main injection correction, the main injection advance angle coefficient Cmr based on the engine speed r and the main injection advance angle based on the engine torque N with respect to the reference main injection timing Mstd (deg ATDC) set by the base map during normal operation. This is done using the coefficient Cmt.
The main injection advance coefficient Cmr is calculated using the map shown in FIG. As shown in FIG. 5, the main injection advance coefficient Cmr is set to 1 when the engine rotational speed r is equal to or higher than r1 (eg, 1500 rpm), and is increased as the engine rotational speed r decreases below r1. The The main injection advance coefficient Cmt is calculated using the map shown in FIG. The main injection advance coefficient Cmt is set to 1 when the engine torque N is N1 (for example, 60 Nm) or more, and is set to increase as the engine torque N decreases below N1.

Then, as shown in the following equation (2), the main injection timing M (deg ATDC) is calculated, and the injection timing of the main injection is set based on the main injection timing M (deg ATDC).
It should be noted that when the engine speed r is less than r1 or the engine torque N is less than N1, Cmr × Cmt is greater than 1, and the post injection timing P (deg ATDC) is changed to a direction that advances more than usual.

M (deg ATDC) = Mstd (deg ATDC) × Cmr × Cmt (2)
Then, the process proceeds to step S90.
In step S90, it is determined whether or not the NOx purge operation is continuing. If the NOx purge operation is continuing, the process proceeds to step S100. When the NOx purge operation is not continuing, this routine is ended (returned).

In step S100, it is determined whether or not the counting of the predetermined cycle cy started in step S30 is completed. When the counting of the predetermined cycle cy is completed, this routine is ended (returned). If the predetermined cycle cy has not been counted, the process returns to step S40.
By controlling as described above, in this embodiment, fuel injection correction control is performed until a predetermined cycle cy elapses after the start of the NOx purge operation for performing the post injection.

The fuel injection correction control according to the present embodiment is to retard the pre-injection injection timing so that the interval between the pre-injection and the main injection is shorter than normal.
By the way, immediately after switching from the normal lean operation to the NOx purge operation, the cylinder liner temperature and the in-cylinder temperature are low, and even if early post-injection is performed, the fuel cannot be burned sufficiently immediately after the start, and combustion May become unstable.

  On the other hand, in the present embodiment, the pre-injection and the main injection are reduced by retarding the injection timing of the pre-injection and shortening the pre-injection interval Pi (deg), which is the time between the pre-injection and the main injection. To increase the in-cylinder temperature, especially the temperature in the fuel spray orbit, and promote diffusion combustion at the start of post injection (early post injection) immediately after switching to NOx purge operation, preventing misfire and burning Stability can be improved.

The pre-injection interval Pi (deg) is corrected based on the correction coefficient (Cw, Ci) calculated from the engine water temperature Tw and the intake manifold temperature Ti, and the injection timing of the pre-injection is greatly delayed as the engine temperature decreases. Therefore, the in-cylinder temperature can be further increased, and the combustion stability can be improved more effectively.
Further, when the engine is switched to the NOx purge operation, the main injection is advanced when the engine 1 is running at low speed and low torque. Therefore, the interval between the pre-injection and the main injection is shortened to further increase the in-cylinder temperature. Can be raised.

Further, the fuel injection correction control is performed only when the engine rotation speed r and the engine torque N are within a predetermined low rotation and low torque range. Thus, the fuel injection correction control can be performed only when the in-cylinder temperature is low and the fuel injection correction control is required.
Further, the predetermined cycle cy in which the fuel injection correction control is performed after the start of the NOx purge operation is changed based on the engine rotational speed r and the engine torque N, and the predetermined cycle cy becomes large at low rotation and low torque. The fuel injection correction control is performed for a long time after the start of the NOx purge operation. Since the in-cylinder temperature is unlikely to increase during low rotation and low torque, combustion stability can be ensured by performing the fuel injection correction control for a long time.

  In addition, this invention is not limited to the said embodiment. For example, the advance angle correction of the main injection may not be performed, or the main injection may be retarded conversely at the time of low rotation and low torque. When the main injection is retarded in this way, it is possible to eliminate the shift of the ignition timing of the main injection due to the delay of the pre-injection, so that the ignition timing in the main injection can be unified. In addition, it is possible to prevent the exhaust gas from becoming too rich locally in the cylinder, and to suppress a reduction in exhaust performance and noise.

  In the present embodiment, the exhaust pipe 30 is provided with two NOx trap catalysts, a proximity NOx catalyst 32 and an underfloor NOx catalyst 34, and the fuel injection correction control is performed when the NOx purge is performed on the proximity NOx catalyst 32. The present invention can also be applied when purging (regenerating) a catalyst or filter other than the NOx trap catalyst.

1 engine (internal combustion engine)
3 Fuel injection valve (fuel injection part)
41 Intake manifold temperature sensor (temperature detector)
43 Water temperature sensor (temperature detector)
50 Engine control unit (injection control unit, regeneration control unit)

Claims (5)

A fuel injection section for injecting fuel into the cylinder of the internal combustion engine;
An injection control unit that executes pre-injection in which fuel is injected by the fuel injection unit before main injection related to output control of the internal combustion engine;
Exhaust gas provided in the exhaust passage of the internal combustion engine by increasing the exhaust temperature by performing post injection for injecting fuel from the fuel injection section from the expansion stroke to the exhaust stroke after the main injection related to the output control of the internal combustion engine A fuel injection control device for an internal combustion engine, comprising: a regeneration control unit that performs regeneration of the purifier;
The fuel for the internal combustion engine, wherein the injection control unit shortens the time between the preceding injection and the main injection until the predetermined cycle elapses after the start of the post injection. Injection control device.   2. The fuel injection control of the internal combustion engine according to claim 1, wherein the injection control unit retards an injection timing of the preceding injection and shortens a time between the preceding injection and the main injection. apparatus. The fuel injection control device includes a temperature detection unit that detects the temperature of the internal combustion engine,
The fuel injection control device for an internal combustion engine according to claim 2, wherein the injection control unit retards the injection timing of the pre-stage injection as the temperature of the internal combustion engine decreases.   The said injection control part further advances the injection timing of the said main injection as the output torque or rotational speed of the said internal combustion engine falls, The any one of Claim 1 to 3 characterized by the above-mentioned. A fuel injection control device for an internal combustion engine as described.   The injection control unit executes control to make the time between the pre-stage injection and the main injection shorter than after the elapse of the predetermined cycle when the output torque and the rotational speed of the internal combustion engine are in a predetermined range. The fuel injection control device for an internal combustion engine according to any one of claims 1 to 4.

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