JP2013083204A - Diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diesel engine in which an EGR amount is increased without deteriorating a fuel efficiency in a low load region.SOLUTION: The diesel engine 10 includes: a turbo-charger 20 including a turbine 22 driven by exhaust and a compressor 21 driven by the turbine and compressing fresh air; a first EGR device 60 for extracting part of an exhaust gas from an exhaust pipe line 42 on a downstream side of the turbine to introduce the gas into an intake pipe line 31 on an upstream side of the compressor; a second EGR device 90 for extracting part of the exhaust gas from an exhaust pipe line 41 on an upstream side of the turbine to introduce the gas into the intake pipe line on an upstream side of the compressor; and a controller 100 for switching the first EGR device and the second EGR device according to a load condition of the engine.

Description

  The present invention relates to a diesel engine, and more particularly, to an engine in which the amount of EGR (the amount of exhaust gas recirculated) is increased without deteriorating fuel consumption in a low load region.

Engines for automobiles and the like are required to reduce NO _x (nitrogen oxide), which is a harmful substance in exhaust gas.
In particular, in a diesel engine that is often operated with a lean air-fuel ratio, it is difficult to achieve NO _X treatment using a three-way catalyst as in a gasoline engine that is operated in a stoichiometric range, and the combustion temperature it is necessary to reduce the occurrence itself of the NO _X by such inhibition.

As reduction technique of the NO _X discharged from a diesel engine, an exhaust gas recirculation (EGR) is known. EGR is substantially by mixing to be introduced into the combustion chamber fresh air to the exhaust gas said inert gas (combustion air) lowers the combustion temperature to reduce the easy NO _X that occurs during a high temperature technology is there.
As a technique related to such EGR, high-pressure EGR (HP-EGR) is known in which high-pressure exhaust gas upstream of the turbocharger turbine is introduced downstream of the intake-side compressor.

In recent years, it becomes necessary to perform a large amount of EGR than before, such as by strengthening of the NO _X regulations, a turbine downstream of the exhaust gas, the low-pressure EGR introduced into the compressor upstream of the intake channel (LP-EGR) is It is popular.
In the case of such a low pressure EGR, it is possible to increase the amount of EGR by introducing exhaust gas into a relatively low pressure portion upstream of the compressor, and further, the EGR is cooled by an EGR cooler, an intercooler, or the like. It is possible to introduce high-density EGR.

  As a conventional technique related to such high-pressure and low-pressure EGR of a diesel engine, for example, in Patent Document 1, an EGR pipe for low-pressure and high-pressure is provided in the engine, and high-pressure EGR is mainly used in a low, medium-speed and low-load region. It is described that EGR is used as an auxiliary, low pressure EGR is used in low, medium and high load ranges, and high pressure EGR is used at high speeds.

JP 2004-150319 A

In general, when the low pressure EGR is performed, for example, the exhaust pressure (exhaust pressure) is increased by an exhaust pressure adjustment valve that restricts the exhaust line, or the intake pressure is reduced by an intake pressure adjustment valve that restricts the intake line. The introduction pressure of EGR is promoted by increasing the differential pressure on the entry side and exit side of the EGR pipe.
However, when the exhaust pipe and the intake pipe are throttled in this way, the pump loss is worsened and fuel consumption is worsened.
In particular, when a large amount of EGR is performed in a low load region, it is necessary to restrict the exhaust pressure adjusting valve or the like more, and the deterioration of the pump loss becomes remarkable.
The subject of this invention is providing the diesel engine which increased the amount of EGR, without deteriorating a fuel consumption in a low load area | region.

The present invention solves the above-described problems by the following means.
According to a first aspect of the present invention, a turbocharger having a turbine driven by exhaust and a compressor driven by the turbine and compressing fresh air, and a part of exhaust gas is extracted from an exhaust pipe downstream of the turbine. A first EGR device to be introduced into the intake pipe upstream of the compressor, and a part of the exhaust gas is extracted from the exhaust pipe upstream of the turbine, and the inside of the intake pipe upstream of the compressor A diesel engine comprising: a second EGR device to be introduced into the vehicle; and a control unit that switches between the first EGR device and the second EGR device according to a load state of the engine.
According to this, the first EGR device is switched to the second EGR device that EGRs the high-pressure exhaust gas upstream of the turbine at a low load when it is difficult to ensure the EGR amount unless an exhaust pressure adjusting valve or the like is used. Therefore, a large amount of EGR can be performed without increasing the pump loss, and NO _X in the exhaust gas can be reduced without deteriorating the fuel consumption.

  According to a second aspect of the present invention, the control means operates the first EGR device in a predetermined high load region, and operates the second EGR device in a low load region where the load is lower than the high load region. The diesel engine according to claim 1, wherein the diesel engine is operated.

The invention according to claim 3 is the diesel engine according to claim 1 or 2, wherein the second EGR device includes an oxidation catalyst and a diesel particulate filter.
According to this, it is possible to prevent unburned fuel (such as HC) and particulate matter (PM) contained in the exhaust gas from flowing into the compressor and protect the compressor.

The invention according to claim 4 is provided with combustion control means for setting the combustion state of the engine to premixed compression self-ignition combustion in the low load region, and the second EGR device has an oxidation catalyst. Item 3. The diesel engine according to Item 2.
According to this, by using the second EGR device in a soot-free state in which PM is not substantially generated as premixed compression auto-ignition (PCCI) combustion, the compressor can be operated without using a diesel particulate filter (DPF). Protection from unburned fuel and PM.

  As described above, according to the present invention, it is possible to provide a diesel engine with an increased EGR amount without deteriorating fuel consumption in a low load region.

It is a schematic diagram which shows the structure of the Example of the diesel engine to which this invention is applied. It is a figure which shows switching of EGR according to the driving | running state in the diesel engine of an Example.

  The present invention aims to provide a diesel engine having an increased EGR amount without deteriorating fuel efficiency in a low load region, and a first EGR device that performs EGR from the turbine downstream side to the compressor upstream side, and from the turbine upstream side. The problem was solved by switching the second EGR device that performs EGR upstream of the compressor in accordance with the load state of the engine.

Embodiments of a diesel engine to which the present invention is applied will be described below.
FIG. 1 is a schematic diagram illustrating a configuration of a diesel engine according to an embodiment.
The engine 10 includes a turbocharger 20, an intake system 30, an exhaust system 40, a fuel supply device 50, a first EGR device 60, an oxidation catalyst (DOC) 70, a diesel particulate filter (DPF) 80, a second EGR device 90, and an engine control unit. (ECU) 100 is provided.

The engine 10 is, for example, a four-stroke diesel engine used as a driving power source for automobiles such as passenger cars.
The engine 10 includes a crankshaft 11, a piston 12, a cylinder block 13, a head 14, a combustion chamber 15, a glow plug 16, a glow controller 17, and the like.
The crankshaft 11 is an output shaft of the engine 10.
The piston 12 is a member that reciprocates in the cylinder and transmits the combustion pressure to the crankshaft 11 via the connecting rod.
The cylinder block 13 is formed integrally with a cylinder portion in which the piston 12 is accommodated and a crankcase portion in which the crankshaft 11 is rotatably supported.
The cylinder block 13 includes a crank angle sensor 13a and a water temperature sensor 13b.
The crank angle sensor 13a detects the angular position of the crankshaft 11.
The water temperature sensor 13 b detects the cooling water temperature circulating in the water jacket in the engine 10.
The head 14 is provided at the crown-side end of the piston 12 of the cylinder block 13 and includes an intake port, an exhaust port, a valve drive mechanism that opens and closes the intake valve and the exhaust valve, and the like.
The combustion chamber 15 is formed between the crown surface of the piston 12 and the portion of the head 14 facing this.
The glow plug 16 is a preheating device provided in the head 14 with the tip portion exposed in the combustion chamber 15.
The glow controller 17 controls the energization amount to the glow plug 16 according to the control of the ECU 100.

The turbocharger 20 compresses combustion air (fresh air) taken in by the engine 10 using energy of exhaust gas (burned gas) of the engine 10.
The turbocharger 20 includes a compressor 21, a turbine 22, an actuator 23, a negative pressure control valve 24, and the like.
The compressor 21 is a centrifugal compressor that compresses combustion air.
The turbine 22 is provided coaxially with the compressor 21 and is driven by the exhaust gas of the engine 10 and drives the compressor 21. The turbine 22 is of a variable geometry type in which the geometry can be continuously changed by a movable vane provided in nozzles around the turbine wheel.
The actuator 23 is a negative pressure type actuator that drives a movable vane of the turbine 22.
The negative pressure control valve 24 is an electromagnetic valve that introduces a negative pressure from a negative pressure source (not shown) into the actuator 23 according to the control of the ECU 100.
When the actual supercharging pressure is lower than the target supercharging pressure set by the ECU 100, the turbocharger 20 increases the rotational speed of the turbine 22 by closing the movable vane and narrowing the nozzle, Control to increase the pressure is performed.

The intake system 30 introduces combustion air into the engine 10.
The intake system 30 includes an intake duct 31, an air cleaner 32, an air flow meter 33, an intercooler 34, a throttle valve 35, an actuator 36, an intake chamber 37, an intake pressure sensor 38, an intake manifold 39, and the like.

The intake duct 31 is an air flow path that introduces combustion air from the atmosphere and supplies it to the engine 10 via the compressor 21 of the turbocharger 20.
The air cleaner 32 includes a filter element that filters air to remove dust and the like. The air that has passed through the air cleaner 32 is introduced into the compressor 21 of the turbocharger 20 and compressed.
The air flow meter 33 is provided at the outlet of the air cleaner 32 and includes a sensor that detects the air flow rate. The air flow meter 33 includes an intake air temperature sensor for detecting the intake air temperature.

The intercooler 34 is a heat exchanger that cools the air that has exited the compressor 21 of the turbocharger 20 by heat exchange with the traveling wind.
The throttle valve 35 is provided on the downstream side of the intercooler 34 and adjusts the intake air amount of the engine 10.
The actuator 36 opens and closes the throttle valve 35 in response to a control signal from the ECU 100.
The intake chamber 37 is an air chamber into which air that has passed through the throttle valve 35 is introduced, and is connected to an intake port of the engine 10 via an intake manifold 39.
The intake pressure sensor 38 is provided in the intake chamber 37 and detects a pressure in the intake chamber 37 substantially equal to the intake pressure of the engine 10.
The intake manifold 39 is a branch pipe that introduces air from the intake chamber 37 to the intake port of each cylinder of the engine 10.

The exhaust system 40 includes an exhaust manifold 41, an exhaust pipe 42, an exhaust pressure adjustment valve 43, and the like.
The exhaust manifold 41 is a pipe line that collects exhaust gas discharged from the exhaust port of each cylinder of the engine 10 and introduces the exhaust gas into the turbine 22 of the turbocharger 20.
The exhaust pipe 42 is a pipe line that discharges the exhaust discharged from the turbine 22 to the outside of the vehicle. The exhaust pipe 42 is provided with an exhaust gas aftertreatment device such as a DOC 70 and a DPF 80.
The exhaust pressure adjusting valve 43 is provided on the downstream side (exit side) of the DPF 80, and throttles the exhaust gas to improve the exhaust pressure in order to secure the EGR amount when the first EGR device 60 is used.

  The fuel supply device 50 supplies fuel into the combustion chamber 15 of the engine 10. The fuel supply device 50 is a common rail type high pressure fuel injection device including a supply pump 51, a suction metering solenoid valve 52, a fuel temperature sensor 53, a common rail 54, a fuel pressure sensor 55, an injector 56, and the like.

The supply pump 51 includes, for example, an inner cam type pressure feeding system, and pressurizes light oil as fuel and supplies it to the common rail 54.
The intake metering solenoid valve 52 adjusts the fuel intake amount of the supply pump 51 and is driven according to a control signal from the ECU 100.
The fuel temperature sensor 53 detects the temperature of the fuel in the supply pump 51.

The common rail 54 is a pressure accumulator that stores high-pressure fuel discharged from the supply pump 51.
The fuel pressure sensor 55 detects the fuel pressure (fuel pressure) in the common rail 54. The above-mentioned intake metering solenoid valve 52 is adjusted in its opening degree by feedback control using the output of the fuel pressure sensor 55 so that the fuel pressure becomes a predetermined target value set according to, for example, the engine speed and load. The
The injector 56 injects fuel supplied from the common rail 54 into the combustion chamber 15 of each cylinder. The injector 56 has a valve body that is opened and closed by an actuator such as a piezo element or a solenoid, and is opened in response to an injection pulse signal from the ECU 100. The injection timing and injection amount of the injector 56 are controlled by the ECU 100.
The injector 56 performs main injection, pilot injection for injecting a small amount of fuel prior to the main injection, post injection for injecting a small amount of fuel after the main injection, and the like.

The 1EGR device 60, intended to reduce the emissions of the NO _X by suppressing the combustion temperature, part of the exhaust gas of the engine 10 extracted from the exhaust pipe 42 downstream of the turbine 22, the compressor 21 Is also refluxed into the intake duct 31 on the upstream side.
The first EGR device 60 includes an EGR passage 61, an EGR control valve 62, an EGR cooler 63, and the like.
The EGR passage 61 extracts exhaust gas from a region on the outlet side of the DPF 80 in the exhaust pipe 42 and on the upstream side of the exhaust pressure adjusting valve 43, and this is extracted between the air flow meter 33 in the intake duct 31 and the compressor 21 of the turbocharger 20. It is a pipeline introduced into the middle part.
The EGR control valve 62 adjusts the exhaust gas flow rate (EGR amount) of the EGR passage 61 according to the control of the ECU 100.
The EGR cooler 63 cools the exhaust gas flowing through the EGR passage 61 by heat exchange with cooling water.

The DOC 70 is provided in the exhaust pipe 42 and mainly oxidizes hydrocarbons (HC) in the exhaust gas. The DOC 70 is formed by supporting a noble metal such as platinum or palladium or a metal oxide such as alumina on the surface of a ceramic carrier such as a cordierite honeycomb structure.
The DOC 70 is provided with a temperature sensor 71 for detecting the exhaust gas temperature at the inlet portion.

The DPF 80 is provided on the downstream side of the DOC 70 of the exhaust pipe 42 and includes a filter that collects particulate matter (PM) by filtering the exhaust gas. Here, PM includes soot (soot), organic solvent-soluble components (SOF), sulfate (SO4), and the like.
For example, the filter is formed by forming heat resistant ceramics such as cordierite in a honeycomb structure, and sealing a large number of cells serving as gas flow paths at the end face so that the inlet side and the outlet side are staggered. It is a closed type (wall flow type).
The DPF 80 includes a differential pressure sensor 81 that detects a differential pressure between the inlet pressure and the outlet pressure, and a temperature sensor 82 that detects the exhaust gas temperature at the outlet.

The second EGR device 90 reduces a part of the exhaust gas of the engine 10 extracted from the exhaust manifold 41 upstream of the turbine 22 in order to reduce the NO _X emission amount in the low load region of the engine 10. The refrigerant is refluxed into the intake duct 31 via the EGR cooler 63.
The second EGR device 90 includes an EGR passage 91, a DOC 92, a DPF 93, an EGR control valve 94, and the like.
The EGR passage 91 is a pipe line that extracts exhaust gas from the exhaust manifold 41 that is upstream of the turbine 22 and introduces the exhaust gas into an upstream region of the EGR cooler 63 of the EGR passage 61 of the first EGR device 60. The exhaust gas discharged from the EGR passage 91 is cooled by an EGR cooler 63 shared with the first EGR device 60 and then introduced into an intermediate portion of the intake duct 31 between the air flow meter 33 and the compressor 21 of the turbocharger 20.
The DOC 92 is provided in the middle of the EGR passage 91, and mainly oxidizes hydrocarbons (HC) in the exhaust gas.
The DPF 93 is provided on the downstream side of the DOC 92 in the EGR passage 91, and collects PM by filtering the exhaust gas.
The DOC 92 and DPF 93 are provided with a temperature sensor, a differential pressure sensor, and the like that are substantially the same as the DOC 70 and DPF 80 described above.
The EGR control valve 94 adjusts the exhaust gas flow rate (EGR amount) of the EGR passage 91 according to the control of the ECU 100.

The ECU 100 controls the above-described engine 10 and its auxiliary devices in an integrated manner, and includes an information processing device such as a CPU, a storage device such as a ROM and a RAM, an input / output interface, an A / D converter, Peripheral circuits such as timers, counters and various logic circuits are provided.
In addition to the various sensors described above, the outputs of the accelerator pedal sensor 101 and the atmospheric pressure sensor 102 are input to the ECU 100.
The accelerator pedal sensor 101 is request torque detection means for detecting driver request torque by detecting the position of the accelerator pedal operated by the driver.
The atmospheric pressure sensor 102 detects atmospheric pressure in the ambient atmosphere of the vehicle.

  The ECU 100 sets the target torque of the engine 10 according to the required torque set according to the output of the accelerator pedal sensor 101, and based on this, the opening of the throttle valve 35, the fuel injection amount of the fuel supply device 50, and Control timing, fuel pressure, etc.

Further, the ECU 100 also functions as a control unit that performs EGR while switching the first EGR device 60 and the second EGR device 90 described above according to the operating state of the engine 10.
FIG. 2 is a diagram illustrating EGR switching according to the operating state of the engine in the present embodiment.
As shown in FIG. 2, the ECU 100 controls the EGR control valves 62 and 94 of the first EGR device 60 and the second EGR device 90, and in the high load region where the torque of the engine 10 is equal to or greater than a predetermined threshold value, the first EGR device In the low load region where the torque is less than the threshold value, the EGR by the second EGR device 90 is performed.

According to the present embodiment described above, in order to perform a large amount of EGR with the first EGR device 60, the turbine 22 can be used by using the second EGR device 90 in the low load region where the exhaust pressure adjustment valve 43 must be greatly throttled. By extracting a relatively high-pressure exhaust gas from the upstream side and performing EGR to the upstream side of the compressor 21, the amount of EGR can be increased without deteriorating the pump loss.
This makes it possible to reduce the NO _X in the exhaust gas without deteriorating the fuel economy.
Further, by cooling the exhaust gas EGRed by the first EGR device 60 and the second EGR device 90 with the common EGR cooler 63, both EGR gases can be cooled with a simple configuration, and high-density EGR can be performed. The EGR gas is further cooled in the intercooler 34.
Further, the exhaust gas EGR by the first EGR device 60 and the second EGR device 90 passes through the DOCs 70 and 92 and the DPF 80 and 93, thereby preventing unburned fuel and PM from flowing into the compressor 21. 21 can be protected.

(Modification)
The present invention is not limited to the embodiments described above, and various modifications and changes are possible, and these are also within the technical scope of the present invention.
(1) The configurations of the diesel engine and its accessories are not limited to those of the above-described embodiments, and can be changed as appropriate.
For example, in the embodiment, the EGR amount of the first EGR device is ensured by using the exhaust pressure adjusting valve provided in the exhaust pipe, but instead of or in combination with this, the throttle valve provided in the intake pipe line Thus, the EGR amount of the first EGR device may be secured by setting the intake side to a negative pressure.
(2) Although the DOC and DPF are provided in the second EGR device in the embodiment, the combustion of the engine 10 in the low load region where the second EGR device is used is premixed compression auto-ignition combustion (PCCI) by combustion control. In a soot-free state in which PM is not substantially generated, the DPF can be omitted and only the DOC can be provided.
(3) In the embodiment, the common EGR cooler is used in the first and second EGR devices. However, an independent EGR cooler may be provided in each EGR device.

DESCRIPTION OF SYMBOLS 10 Engine 11 Crankshaft 12 Piston 13 Cylinder block 13a Crank angle sensor 13b Water temperature sensor 14 Head 15 Combustion chamber 16 Glow plug 17 Glow controller 20 Turbocharger 21 Compressor 22 Turbine 23 Actuator 24 Negative pressure control valve 30 Intake system 31 Intake duct 32 Air cleaner 33 Air flow meter 34 Intercooler 35 Throttle valve 36 Actuator 37 Intake chamber 38 Intake pressure sensor 39 Intake manifold 40 Exhaust system 41 Exhaust manifold 42 Exhaust pipe 43 Exhaust pressure adjustment valve 50 Fuel supply device 51 Supply pump 52 Suction adjustment solenoid valve 53 Fuel Temperature sensor 54 Common rail 55 Pressure sensor 56 injector 60 first 1EGR device 61 EGR passage 62 EGR control valve 63 EGR cooler 70 oxidation catalyst (DOC) 71 Temperature sensor 80 diesel particulate filter (DPF)
81 Differential pressure sensor 82 Temperature sensor 90 2nd EGR device 91 EGR passage 92 DOC 93 DPF
94 EGR control valve 100 Engine control unit (ECU)
101 accelerator pedal sensor 102 atmospheric pressure sensor

Claims (4)

A turbocharger having a turbine driven by exhaust and a compressor driven by the turbine to compress fresh air;
A first EGR device that extracts a part of exhaust gas from an exhaust pipe downstream of the turbine and introduces the exhaust gas into an intake pipe upstream of the compressor;
A second EGR device that extracts a part of exhaust gas from an exhaust pipe upstream of the turbine and introduces it into an intake pipe upstream of the compressor;
A diesel engine comprising: control means for switching between the first EGR device and the second EGR device in accordance with an engine load state. The control means operates the first EGR device in a predetermined high load region, and operates the second EGR device in a low load region where the load is lower than the high load region. Item 2. The diesel engine according to Item 1. The diesel engine according to claim 1, wherein the second EGR device includes an oxidation catalyst and a diesel particulate filter. Combustion control means for making the combustion state of the engine a premixed compression auto-ignition combustion in the low load region,
The diesel engine according to claim 2, wherein the second EGR device includes an oxidation catalyst.

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