JP2009264321A - Combustion control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable premixed combustion without using an external EGR device even in a low temperature state. <P>SOLUTION: A combustion control device of an engine 1 has the external EGR device for recirculating exhaust gas in intake air, by performing premixed combustion operation for igniting via a premixed period after completing fuel injection, and increases an internal EGR quantity by controlling a cam phase variable mechanism 20 so that the valve closing timing of an exhaust valve advances more than the reference timing, when the engine 1 is a predetermined low temperature state in the premixed combustion operation. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a combustion control apparatus for a diesel engine, and more particularly to a combustion control technique during premixed combustion.

In the combustion control of a diesel engine, a premixed combustion operation is known in which fuel injection is completed before the fuel self-ignition timing and ignition is performed thereafter.
At the time of the premixed combustion operation, after the fuel injection is completed, the mixture is sufficiently diluted and homogenized and then ignited, thereby suppressing a local increase in the combustion temperature and reducing the amount of NOx generated.
In order to sufficiently dilute the air-fuel mixture during the premixed combustion operation, there is one that increases the amount of EGR using an external EGR device (Patent Document 1).
JP 2005-291002 A

  However, in a diesel engine, since sulfur oxides and nitrogen oxides in exhaust generally increase in a low temperature state, as described in Patent Document 1 above, in a low temperature state during premixed combustion operation. In some cases, if the amount of external EGR is increased, oxides in the exhaust gas may become sulfuric acid or nitric acid, which may corrode the EGR cooler and the EGR passage constituting the external EGR device. Therefore, the external EGR amount cannot be increased in a low temperature state, and premix combustion may be difficult.

  The present invention has been made to solve such problems, and an object of the present invention is to provide a diesel engine combustion control device capable of premix combustion without using an external EGR device even in a low temperature state. Is to provide.

  In order to achieve the above object, the first aspect of the present invention provides an internal combustion engine having an external EGR device capable of performing a premixed combustion operation in which ignition is performed after completion of fuel injection through a premixed period and circulating exhaust gas to intake air. A combustion control device, variable valve timing means for changing the closing timing of the exhaust valve, and when the internal combustion engine is at a predetermined low temperature during the premixed combustion operation, the closing timing of the exhaust valve is advanced from the reference timing. The variable valve timing means is controlled so as to make an angle, and control means for increasing the internal EGR amount is provided.

Further, in claim 2, the internal combustion engine according to claim 1 is provided with a variable displacement supercharger capable of changing a flow area of the exhaust gas passing through the turbine, and the control means is configured to operate the internal combustion engine during the premixed combustion operation. In the case of a predetermined low temperature state, the variable capacity supercharger is further controlled such that the flow path area is smaller than the reference area.
Further, in claim 3, in claim 1 or 2, the control means is variable so that the closing timing of the exhaust valve is advanced from the reference timing when the internal combustion engine is in a predetermined low temperature state during the premixed combustion operation. The valve timing means is controlled to reduce the oxygen concentration in the cylinder.

  According to the combustion control apparatus for an internal combustion engine of claim 1 of the present invention, when the internal combustion engine is in a predetermined low temperature state during the premixed combustion operation, the valve closing timing of the exhaust valve is advanced from the reference timing and the internal control is performed. Since the EGR amount increases, the EGR amount during intake can be ensured without requiring an external EGR device. Therefore, when the internal combustion engine is in a low temperature state, premixed combustion can be enabled while reliably preventing corrosion due to the inflow of exhaust gas to the external EGR device.

  According to the combustion control apparatus for an internal combustion engine of claim 2 of the present invention, when the internal combustion engine is in a predetermined low temperature state during the premixed combustion operation, the flow area of the exhaust gas passing through the turbine is more than the reference area. Since it decreases, the exhaust resistance increases and the internal EGR rate increases. Therefore, even when the EGR amount is insufficient only by advancing the valve closing timing of the exhaust valve, the EGR amount can be sufficiently secured.

  According to the combustion control apparatus for an internal combustion engine of claim 3 of the present invention, when the internal combustion engine is in a predetermined low temperature state during the premixed combustion operation, the valve closing timing of the exhaust valve is advanced from the reference timing and the cylinder is Therefore, the oxygen concentration in the intake air can be suppressed without requiring an external EGR device, and sufficient premixed combustion can be achieved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an intake / exhaust system of a diesel engine (hereinafter simply referred to as an engine 1) provided with a combustion control device of the present embodiment.
As shown in FIG. 1, the engine 1 includes a turbocharger (variable capacity supercharger) 2 and an EGR system (external EGR device) 3.

  The turbocharger 2 includes a compressor 5 interposed in the intake pipe 4 of the engine and a turbine 7 interposed in the exhaust pipe 6. The turbocharger 2 includes a turbine 7 driven by exhaust of the engine 1. Using the rotational force, the compressor 5 is driven to compress the intake air, thereby increasing the intake air flow rate and improving the output of the engine 1. The turbocharger 2 is a variable capacity turbocharger (VGT), and includes a variable capacity mechanism 8 that changes the inlet area of the turbine 7. The variable capacity mechanism 8 allows the flow rate of exhaust gas passing through the turbine 7 to be changed. By changing, the supercharging effect is controlled. The intake pipe 4 on the downstream side of the compressor 5 is provided with an intercooler 9 for lowering the intake air temperature in order to enhance the supercharging effect by the turbocharger 2.

  The EGR system 3 includes an EGR passage 11 that communicates an exhaust manifold 10 that forms an exhaust pipe on the upstream side of the turbine 7 and an intake pipe 4 on the downstream side of the intercooler 9, and an EGR valve that is provided in the EGR passage 11. By controlling the opening and closing of the exhaust gas 12, a part of the exhaust gas is circulated to the intake side to lower the combustion temperature, thereby suppressing the generation of NOx. The EGR passage 11 is provided with an EGR cooler 13 that lowers the temperature of exhaust gas passing therethrough. A throttle valve 14 is provided in the intake pipe 4 between the EGR cooler 13 and the EGR valve 12.

  The engine 1 is provided with a variable valve timing device that can change the valve timing of the exhaust valve. The variable valve timing device includes, for example, a vane-type cam phase variable mechanism (variable valve timing means) 20 at one end portion of a camshaft that drives an exhaust valve. The opening / closing timing of the exhaust valve is variably controlled by advancing or retarding the phase.

The injector 21 for supplying fuel into the cylinder of the engine 1 is controlled by the controller 30 to control the fuel injection amount and fuel injection timing into the cylinder. The controller 30 has a function of inputting various operating states of the engine 1 and switching the fuel injection by the injector 21 to the normal combustion mode or the premixed combustion mode (premixed combustion operation).
In the normal combustion mode, it is controlled to inject fuel near the compression top dead center of the piston, and additional fuel is supplied even after ignition, so that the amount of fuel supplied into the cylinder increases and high output can be obtained. . In the premixed combustion mode, the fuel injection is controlled to be completed before the fuel self-ignition timing, and after the fuel injection is completed, the mixture is sufficiently diluted and homogenized to ignite, so the local combustion temperature rises. Is suppressed, and the amount of NOx generated is reduced. The normal combustion mode and the premixed combustion mode are switched based on, for example, the engine speed and load.

The intake manifold 15 of the engine 1 is provided with an intake pressure sensor 31 that detects intake pressure and an intake temperature sensor 32 that detects intake temperature. The intake pipe 4 on the upstream side of the compressor 5 is provided with an air flow sensor 33 for detecting the intake flow rate, and the exhaust pipe 6 on the downstream side of the turbine 7 is provided with a λ sensor 34 for detecting the excess air ratio.
In addition to the intake pressure sensor 31, the intake air temperature sensor 32, the airflow sensor 33, and the λ sensor 34, the controller 30 receives various detection information from an engine rotation speed sensor 35 that detects the engine rotation speed. The required EGR rate and the actual EGR rate are calculated, and the EGR valve 12 and the throttle valve 14 are controlled so that the actual EGR rate matches the required EGR rate.

In particular, the controller (control means) 30 of the present embodiment performs control to operate the variable displacement mechanism 8 and the cam phase variable mechanism 20 in the premixed combustion mode.
FIG. 2 is a flowchart showing a combustion control procedure in the premixed combustion mode. This routine is repeatedly executed when the engine 1 is in a low temperature state in the premixed combustion mode. Whether or not the engine 1 is in a low temperature state may be determined based on, for example, the coolant temperature of the engine 1.

As shown in FIG. 2, first, in step S10, it is determined whether or not the above-described actual EGR rate satisfies (or exceeds) the required EGR rate. When the actual EGR rate satisfies the required EGR rate, this routine is returned. If the required EGR rate is not satisfied, the process proceeds to step S20.
In step S20, the cam phase variable mechanism 20 is advanced so that the opening / closing timing of the exhaust valve is advanced (exhaust valve control). Then, the process proceeds to step S30. FIG. 3 is a graph showing the transition of the lift amount of the exhaust valve accompanying the change of the crank angle. As shown in FIG. 3, the opening / closing timing of the exhaust valve is normally set to the valve opening timing just before BDC (bottom dead center) and the valve closing timing just after TDC (top dead center) (reference time). . In this step, the opening / closing timing of the exhaust valve is advanced so that the closing timing of the exhaust valve is earlier than the reference timing, so that it is difficult for exhaust to escape from the cylinder.

In step S30, it is determined whether or not the required EGR rate is satisfied as in step S10. If the required EGR rate is satisfied, this routine is returned. If the required EGR rate is not satisfied, the process proceeds to step S40.
In step S40, the variable capacity mechanism 8 is controlled so as to reduce the inlet area of the turbine 7 (VGT control). Then, this routine is returned. FIG. 4 is a graph comparing the exhaust pressure Pti at the inlet of the turbine 7 and shows when the inlet area of the turbine 7 is reduced (VGT restriction) and when it is not restricted (normal). As shown in FIG. 4, by reducing the inlet area of the turbine 7 in this step, the exhaust pressure on the upstream side of the turbine 7 increases, so that it becomes difficult for the exhaust to escape from the cylinder.

By controlling as described above, in the present embodiment, when the engine 1 is in a low temperature state during premix combustion, the cam phase variable mechanism 20 is controlled so that the closing timing of the exhaust valve is advanced. . Further, in this exhaust valve control, when a sufficient EGR rate for premixed combustion cannot be ensured, the variable displacement mechanism 8 is controlled so as to further reduce the inlet area of the turbine 7.
As described above, when the valve closing timing of the exhaust valve is advanced, it becomes difficult for the exhaust to escape, the internal EGR increases, and the EGR rate in the cylinder increases. Thereby, in this embodiment, when the engine 1 is in a low temperature state, the EGR rate can be increased without using the EGR system 3. Therefore, since the exhaust gas does not flow into the EGR system 3 when the engine 1 is in a low temperature state, corrosion of the EGR cooler 13 and the EGR passage 11 due to sulfur oxides and nitrogen oxides contained in the exhaust gas in the low temperature state can be prevented. At the same time, the premixed combustion can be sufficiently realized by increasing the EGR rate.

Further, in the exhaust valve control, when the EGR rate sufficient to perform the premixed combustion cannot be secured, the VGT control, that is, the inlet area of the turbine 7 is further reduced, which also makes it difficult to exhaust the exhaust gas. The rate can be further increased and sufficiently secured.
In this embodiment, whether or not premixed combustion is possible is determined based on the EGR rate, but the present invention is not limited to this. For example, in the premixed combustion mode, the oxygen concentration in the cylinder is set to the target oxygen concentration. The present invention can also be applied to an engine that is controlled to match the above. Even in such an engine, the oxygen concentration can be lowered by advancing the closing timing of the exhaust valve or reducing the inlet area of the turbine 7, so that the premixed combustion can be sufficiently realized. .

It is a schematic block diagram of the intake-exhaust system of the engine provided with the combustion control apparatus of this embodiment. It is a flowchart which shows the combustion control procedure at the time of a premix combustion mode. It is a graph which shows transition of the lift amount of the exhaust valve accompanying the change of a crank angle. It is the graph which compared the exhaust pressure in the inlet_port | entrance of a turbine.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 2 Variable capacity supercharger 3 EGR system 7 Turbine 20 Cam phase variable mechanism 30 Controller

Claims (3)

A combustion control device for an internal combustion engine, which is capable of a premixed combustion operation that ignites through a premixing period after completion of fuel injection, and includes an external EGR device that circulates exhaust gas to intake air,
Variable valve timing means for changing the closing timing of the exhaust valve;
When the internal combustion engine is at a predetermined low temperature during the premixed combustion operation, the variable valve timing means is controlled to increase the internal EGR amount so that the valve closing timing of the exhaust valve is advanced from the reference timing. Control means;
A combustion control device for an internal combustion engine, comprising: The internal combustion engine includes a variable capacity supercharger capable of changing a flow passage area of exhaust gas passing through a turbine,
When the internal combustion engine is at a predetermined low temperature during the premixed combustion operation, the control means further controls the variable capacity supercharger so that the flow path area is smaller than a reference area. 2. A combustion control apparatus for an internal combustion engine according to claim 1, wherein   The control means controls the variable valve timing means so that the closing timing of the exhaust valve is advanced from the reference timing when the internal combustion engine is at a predetermined low temperature during the premixed combustion operation. The internal combustion engine combustion control apparatus according to claim 1 or 2, wherein the oxygen concentration in the internal combustion engine is reduced.

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