JP2004150319A - Compression ignition type internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce exhaust emission in a wide operation region without deteriorating engine performance and controllability and responsiveness of EGR control by effectively using both a high pressure EGR passage and a low pressure EGR passage. <P>SOLUTION: A diesel engine provided with a turbocharger 2 comprises: a low pressure EGR pipe 12 for recirculating a part of exhaust gas from an exhaust pipe 11 at a downstream side of a turbine 2b of the turbocharger 2 to an intake pipe 5 on an upstream side of a compressor 2a of the turbocharger 2; and a high pressure EGR pipe 17 for recirculating a part of the exhaust gas from an exhaust manifold 10 to an intake manifold 7. Based on a detection signal from an operating condition detection means, EGR and pre-mixed combustion are performed by mainly using high pressure EGR and subsidiarily using low pressure EGR in a low and medium engine speed/low and medium load region, EGR is performed using the low pressure EGR and normal combustion is performed by injecting fuel in the vicinity of compression top dead center in low and medium engine speed/high load region, and EGR is performed using the high pressure EGR and the normal combustion is performed by injecting the fuel in the vicinity of the compression top dead center in a high engine speed/low to high load region. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a compression ignition type internal combustion engine such as a diesel engine provided with a turbocharger.
[0002]
[Prior art]
Conventionally, in a diesel engine for an automobile, a part of exhaust gas is extracted from an exhaust side and returned to an intake side, and combustion of fuel in the engine is suppressed by the exhaust gas returned to the intake side to reduce a combustion temperature. and so as to reduce the generation of NO _X (nitrogen oxides), a so-called exhaust gas recirculation by lowering (EGR: exhaust gas recirculation) is performed.
[0003]
However, possible to reduce of the NO _X by the recirculation of the exhaust gases, since a relation that a trade-off that occurs black smoke by incomplete combustion in the cylinder, from the viewpoint of suppressing the generation of black smoke There is a disadvantage that the amount of exhaust gas recirculation is limited, and it is difficult to significantly reduce NO _{X by} simply recirculating exhaust gas.
[0004]
For this reason, in recent years, in the case of normal diffusion combustion, the fuel injection to be performed near the compression top dead center is performed earlier (for example, 20 to 50 degrees before the compression top dead center), and the fuel is injected into the cylinder. The use of premixed combustion, which promotes premixing of the fuel by prior injection of the fuel and suppresses the generation of black smoke by igniting and burning, has been studied.
[0005]
That is, when such premixed combustion is performed, the combustion is performed in a state where the fuel is dispersed and mixed well and the fuel is evenly diluted. Therefore, the combustion temperature is suppressed to a relatively low level, and the generation of NO _X is reduced. In addition, it is difficult to locally generate a fuel-rich portion, which is effective in suppressing the generation of black smoke.
[0006]
Further, in the diesel engine 100 having a turbocharger 101 as shown in FIG. 3 as the EGR device, a part of the exhaust gas is extracted from an exhaust passage upstream of the turbine 101a of the turbocharger 101, that is, an exhaust manifold 102, and the turbocharger is extracted. The intake passage 101 downstream of the compressor 101b of the turbocharger 101, that is, the high pressure EGR passage 104A that recirculates to the intake manifold 103, and the exhaust passage upstream of the turbine 101a of the turbocharger 101, that is, the exhaust pipe 105, as shown in FIG. Some use a low-pressure EGR passage 104B that extracts a part of the exhaust gas and recirculates the intake passage downstream of the compressor 101b of the turbocharger 101, that is, to the intake pipe 106. In the drawings, 107A and 107B are EGR valves, 108A and 108B are EGR coolers, 109 is an intercooler, and 110 is a VG (variable geometry) nozzle.
[0007]
By the way, a large amount of EGR is required to achieve premix combustion. That is, an EGR rate exceeding 40% is required in the premix combustion application region shown in FIG. However, in a normally used high-pressure EGR path, the EGR amount is determined by the differential pressure (Pti-Pb) between the turbine inlet pressure Pti and the boost pressure Pb, so that when the performance of the turbocharger is improved, the differential pressure decreases ( (Reverse rotation), and a large amount of EGR becomes impossible. That is, in the EGR rate distribution in the high-pressure EGR path in FIG. 5, the EGR rate is 40% even at the maximum. Therefore, it has been considered that a differential pressure is secured by controlling the opening degree of a VG nozzle using a VG (variable geometry) turbocharger to expand the EGR-enabled area. However, it is difficult to secure a large amount of EGR capable of realizing premixed combustion within a range that does not sacrifice power performance even by using the opening control of the VG nozzle.
On the other hand, the low pressure EGR path allows a large amount of EGR because the position of the EGR valve is located upstream of the compressor of the turbocharger. However, even if the EGR valve is rapidly closed, the path to each cylinder is intercooled. For example, when the excess air ratio in each cylinder suddenly decreases as in the case of rapid acceleration, the high EGR state continues for a while in the high pressure EGR path, and black smoke is generated.
Therefore, there is a conventional EGR device using both a high-pressure EGR route and a low-pressure EGR route (for example, see Patent Document 1).
[0010] When the premix combustion is used while recirculating the exhaust gas in the operating state except the high load of the engine, the low pressure EGR path is selected in the operating state of the engine from the high load to the medium load. The low-temperature and low-pressure exhaust gas cooled via an intercooler is recirculated, and when the engine is operating from low load to zero load, the high-pressure EGR path is switched to directly recirculate the high-temperature and high-pressure exhaust gas from the exhaust manifold to the intake manifold. As a result, the problem that misfiring easily occurs in the low-load region of the engine can be solved by the ignition support by increasing the intake air temperature, and good simultaneous reduction of NO _X and black smoke can be realized by using premixed combustion. Things.
[0011]
[Patent Document 1]
JP 2002-21625 A
[Problems to be solved by the invention]
However, in the EGR device disclosed in Patent Literature 1 described above, when the high-pressure EGR path and the low-pressure EGR path are used together, the operating state of the engine requiring a large amount of EGR from low load to zero load. In this case, only the high-pressure EGR path is used, and the shortage is compensated for by controlling the opening of the VG nozzle, so that there is a problem that power performance must be sacrificed. In addition, since the low-pressure EGR path is used in the operating state of the engine from a high load to a medium load, there is also a problem that controllability and responsiveness at the time of rapid acceleration or the like are poor due to an increase in the path length and the intercooler.
[0013]
Accordingly, an object of the present invention is to provide a compression ignition type in which high-pressure EGR paths and low-pressure EGR paths are effectively used to reduce exhaust emissions in a wide operating range without impairing power performance or controllability and responsiveness of EGR control. An internal combustion engine is provided.
[0014]
[Means for Solving the Problems]
In order to achieve the above object, a compression ignition type internal combustion engine according to claim 1 of the present invention is a compression ignition type internal combustion engine equipped with a turbocharger, wherein a part of exhaust gas is extracted from an exhaust passage downstream of a turbine of the turbocharger. A low-pressure EGR path that recirculates to the intake passage upstream of the compressor of the turbocharger, and a high-pressure EGR that extracts a part of the exhaust gas from the exhaust passage upstream of the turbine of the turbocharger and recirculates it to the intake passage downstream of the compressor of the turbocharger. A driving state detection means for detecting an operation state of the engine; and a high-pressure EGR path mainly in the low-medium-speed / low-medium load region based on a detection signal from the operation state detection means. EGR is performed using the EGR path in an auxiliary manner and premix combustion is performed. In addition to performing EGR using the road and injecting fuel near the compression top dead center to perform normal combustion, performing EGR using the high pressure EGR path and fuel near the compression top dead center in the engine high speed / low to high load range. And a control means for performing normal combustion by injecting the EGR gas, thereby effectively using the high-pressure EGR path and the low-pressure EGR path so as to reduce the exhaust emission in a wide operating region.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a compression ignition type internal combustion engine according to the present invention will be described in detail using embodiments with reference to the drawings.
[0016]
[Example]
FIG. 1 is a schematic configuration diagram of a diesel engine showing one embodiment of the present invention, and FIG. 2 is a graph showing segregation of an EGR system.
[0017]
In FIG. 1, reference numeral 1 denotes an engine body of a diesel engine. The engine body 1 has a compression ratio set lower than that of a normal engine, and further includes a VG (variable geometry) turbocharger as a turbocharger 2. The intake air guided from an air cleaner which does not pass through an intake pipe (intake passage) 5 is sent to a compressor 2a of the turbocharger 2, and the intake air pressurized by the compressor 2a is sent to an intercooler 6 where it is cooled. The intake air is further guided from the intercooler 6 to an intake manifold (intake passage) 7 and distributed to each of the cylinders 8 of the engine body 1, which are composed of six in-line cylinders.
[0018]
Further, the exhaust gas discharged from each cylinder 8 of the engine body 1 is sent to a turbine 2b of the turbocharger 2 through an exhaust manifold (exhaust passage) 10, and the exhaust gas driving the turbine 2b is exhausted (exhaust passage). The air is discharged to the outside of the vehicle through the motor 11.
[0019]
An exhaust pipe 11 downstream of the turbine 2b of the turbocharger 2 and an intake pipe 5 upstream of the compressor 2a of the turbocharger 2 are connected by a low-pressure EGR pipe (low-pressure EGR path) 12, and the low-pressure EGR The pipe 12 is equipped with an EGR valve 13 capable of appropriately stopping the recirculation of exhaust gas and adjusting the opening, and an EGR cooler 14 for cooling the recirculated exhaust gas. An exhaust gas purifying device 15 for reducing particulates in exhaust gas is provided upstream of the branch point of the low pressure EGR pipe 12 in the exhaust pipe 11.
[0020]
Further, valves 16a and 16b whose opening degree can be adjusted are provided downstream of the branch of the low-pressure EGR pipe 12 in the exhaust pipe 11 and upstream of the branch of the low-pressure EGR pipe 12 in the intake pipe 5. The valves 16a and 16b are opened. The EGR rate by the low-pressure EGR pipe 12 can be adjusted by adjusting the degree to increase or decrease the pressure at the branch point.
[0021]
The exhaust manifold 10 and the intake manifold 7 are connected by a high-pressure EGR pipe (high-pressure EGR path) 17. The high-pressure EGR pipe 17 has an openable and closable EGR valve so that recirculation of exhaust gas can be stopped appropriately. 18 and an EGR cooler 25 for cooling the exhaust gas to be recirculated. Further, a valve 19 whose opening can be adjusted is provided upstream of the branch point of the high-pressure EGR pipe 17 in the intake pipe 5, and by adjusting the opening degree of the valve 19 to increase or decrease the pressure at the branch point, a high-pressure EGR pipe is provided. 17 so that the EGR rate can be adjusted.
[0022]
Further, the accelerator pedal 20 in the driver's seat is provided with a load sensor 21 for detecting the accelerator opening as a load on the engine body 1, and a crankshaft (not shown) of the engine body 1 uses the rotation of the engine as the engine speed. And a detection signal from both of these sensors, together with a detection signal from an intake air temperature sensor 27 provided in the intake pipe 5, is sent to an electronic control unit (ECU) 23 as control means to be described later. Is to be entered.
[0023]
The electronic control unit 23 is formed of a digital computer, and includes a ROM, a RAM, a CPU (not shown), input / output ports, and the like. A fuel injection signal for commanding a fuel injection timing and an injection amount is output to a fuel injection device (for example, a pressure-accumulation type injection device) 24 for injecting fuel into each cylinder 8, and the EGR valve 13 is provided. , 18, valves 16 a, 16 b, 19, VG nozzle 3, and exhaust brake valve 26 are output with respective opening degree command signals.
[0024]
As shown in FIG. 2, an operating state detecting section (operating state detecting means), a fuel injection control section, and an EGR control section in the electronic control unit 23 provide a high-pressure EGR in an engine low-medium-speed / low-medium load region. EGR is performed using the pipe 17 mainly and the low-pressure EGR pipe 12 as an auxiliary, and the fuel is injected earlier (for example, 20 to 50 ° BTDC) near the top dead center of the compression to perform premixed combustion, and the In the high speed / high load range, the EGR is performed using the low pressure EGR pipe 12 and the fuel is injected near the compression top dead center to perform normal combustion. In the high speed / low to high load range of the engine, the EGR is performed using the high pressure EGR pipe 17. Is performed and fuel is injected near the compression top dead center to perform normal combustion.
[0025]
That is, in the low-medium-speed / low-medium load region of the engine, which is a premixed combustion region requiring a large amount of EGR, the opening of the VG nozzle 3 is reduced to the extent that power performance is not sacrificed, and the EGR valve 18 is fully opened. The valve 19 is controlled to be closed to recirculate as much EGR gas as possible in the high-pressure EGR pipe 17, while the EGR valve 13 is fully opened and the valves 16 a and 16 b are controlled to close so that the low-pressure EGR pipe 12 is closed. To recirculate the shortage of EGR gas.
[0026]
As a result, a sufficient amount of EGR can be ensured without sacrificing power performance in the operating range, and the generation of NO _X and black smoke can be reduced together with the establishment of premixed combustion. .
[0027]
Also, in the low-medium-speed / high-load region of the engine, which is a normal combustion region where the introduction of EGR is severe in the high-pressure EGR pipe 17, the EGR valve 18 is fully closed and the valve 19 is fully opened, while the EGR valve 13 is fully opened. The EGR is performed using the low-pressure EGR pipe 12 by controlling the valves 16a and 16b in the closing direction. At this time, the opening of the VG nozzle 3 is controlled by an opening that emphasizes power performance.
[0028]
As a result, a sufficient amount of EGR can be secured without sacrificing power performance in the operating range, and the generation of NO _X can be reduced.
[0029]
Further, in the high speed, low to high load region of the engine, which is a normal diffusion combustion region having a small EGR rate, the EGR valve 13 is fully closed and the valves 16a and 16b are fully opened, while the EGR valve 18, the valve 19 and the , The VG nozzle 3 is subjected to known λ control (control based on the excess air ratio of EGR) to perform EGR using the high-pressure EGR pipe 17.
[0030]
As a result, in the operating range, since the high-pressure EGR passage 17 in which the distance between the EGR valve 18 and the intake passage 7 is short is used, NO _X (nitrogen oxide) is maintained while maintaining good controllability and responsiveness of the EGR control. Can be reduced.
[0031]
It is needless to say that the present invention is not limited to the above embodiment, and various changes can be made without departing from the spirit of the present invention.
[0032]
【The invention's effect】
As described above, according to the first aspect of the invention, in the low-medium-speed / low-medium load region of the engine, the EGR is performed using the high-pressure EGR path mainly and the low-pressure EGR path as an auxiliary, and the premix combustion is performed. EGR is performed using a low-pressure EGR route in a low-medium-speed, high-load region of the engine, and fuel is injected near the compression top dead center to perform normal combustion. In a high-speed, low-high load region of the engine, a high-pressure EGR route is used. Since control means for performing EGR and injecting fuel near the compression top dead center to perform normal combustion is provided, power performance and EGR control of EGR control are effectively performed by effectively using the high-pressure EGR path and the low-pressure EGR path. Exhaust emission can be reduced in a wide operating range without impairing controllability and responsiveness.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a diesel engine showing one embodiment of the present invention.
FIG. 2 is a graph showing segregation in the EGR system.
FIG. 3 is a schematic configuration diagram of a diesel engine provided with a high-pressure EGR path.
FIG. 4 is a schematic configuration diagram of a diesel engine provided with a low-pressure EGR path.
FIG. 5 is a graph showing an EGR rate distribution of a high-pressure EGR route.
FIG. 6 is a graph showing a premixed combustion application area.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Engine main body 2 Turbocharger 3 VG nozzle 5 Intake pipe (intake passage)
7 Intake manifold (intake passage)
10 Exhaust manifold (exhaust passage)
11 Exhaust pipe (exhaust passage)
12 Low pressure EGR pipe (Low pressure EGR path)
13 EGR valve 14 EGR cooler 15 Exhaust gas purification device 17 High pressure EGR pipe 18 EGR valve 21 Load sensor 22 Crank angle sensor 23 Electronic control unit (ECU)
24 fuel injection device 25 EGR cooler

Claims (1)

In a compression ignition type internal combustion engine equipped with a turbocharger, a low pressure EGR path for extracting a part of exhaust gas from an exhaust passage downstream of a turbine of the turbocharger and recirculating the exhaust gas to an intake passage upstream of a compressor of the turbocharger; A high-pressure EGR path for extracting a part of the exhaust gas from an upstream exhaust passage and recirculating the exhaust gas to an intake passage downstream of the compressor of the turbocharger, and operating state detecting means for detecting an operating state of the engine; On the basis of the detection signal from the means, in the low-medium-speed / low-medium-load region of the engine, EGR is performed using the high-pressure EGR path mainly and the low-pressure EGR path is used as an auxiliary, and premix combustion is performed. In the high load range, EGR is performed using the low pressure EGR path, and fuel is injected near the compression top dead center to perform normal combustion. And control means for performing EGR using a high-pressure EGR path in a high-speed, low to high load region of the engine and injecting fuel near a compression top dead center to perform normal combustion. Compression ignition type internal combustion engine.

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