JP2012167562A - Diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diesel engine that is reduced in NOemission during a high load without excessively decreasing a combustion temperature by a simple structure.SOLUTION: In the diesel engine 10, a three-way catalyst 90 which is effective in a predetermined air-fuel ratio region near the stoichiometry is disposed on an exhaust conduit 40. The diesel engine includes an engine control device 100 that performs high load control for controlling a fuel injection amount and an intake air amount so that in a high load region where output torque is equal to or higher than a predetermined value, the air-fuel ratio λ is within an effective region of the three-way catalyst 90.

Description

The present invention relates to a diesel engine mounted on a vehicle such as an automobile, to which a reduced NO _X emissions at high load without excessively lowering the combustion temperature with a simple configuration.

In a diesel engine, the generation of nitrogen oxides (NO _X ) becomes a problem because the air-fuel ratio is usually lean and the compression ratio is high compared to a general gasoline engine.
In general gasoline engines, NO _x is treated together with hydrocarbons (HC) and carbon monoxide (CO) using a three-way catalyst that is effective when the air-fuel ratio is almost stoichiometric. In a diesel engine that performs the above, since a large amount of oxygen remains in the exhaust gas, it is usually difficult to apply a three-way catalyst.

As prior art relating to reduction of the NO _X discharged from a diesel engine, for example, by lowering the exhaust gas or recirculation (EGR) to be introduced into the intake side by extracting part of exhaust gases, the compression ratio of the engine, the combustion temperature It is being attempted to reduce this.

Further, for example, Patent Document 1, the NO _X generated during normal operation, NO causes adsorbed on _X absorbent, wherein _the NO _X storage reduction catalyst which is adapted to release during reduction operation to perform post injection, etc. (LNT) is Has been.
Further, Patent Document 2, a urea selective reduction catalyst which processes the NO _X using a urea aqueous solution (SCR) is described.

Japanese Patent No. 2600492 Japanese Patent Laid-Open No. 2001-20724

In the future, there is a demand for further emission reduction of exhaust gas from diesel engines.
However, if the amount of EGR is excessively increased, the oxygen concentration in the engine cylinder decreases and the fuel over-concentration region increases, soot (soot) increases.
Further, if the compression ratio is excessively reduced, startability, engine stability at start-up, exhaust gas, and the like are deteriorated.
Further, when a device such as a NO _X storage reduction catalyst or a urea selective reduction catalyst is added, the structure becomes complicated and the cost increases.
Furthermore, when the NO _X storage reduction catalyst is applied, it is necessary to periodically perform a reduction process by post injection or the like, so that the fuel consumption increases.
In addition, when the urea selective reduction catalyst is applied, a supply infrastructure for the urea aqueous solution is required, and it is necessary to cope with a slip in which ammonia is discharged to the outside.
In view of the above problems, an object of the present invention is to provide a diesel engine with reduced NO _X emissions at high load without reducing excessively the combustion temperature with a simple configuration.

The present invention solves the above-described problems by the following means.
The invention according to claim 1 is a diesel engine in which a three-way catalyst effective in a predetermined air-fuel ratio range in the vicinity of stoichiometry is provided in an exhaust pipe, and an air-fuel ratio in a high load region in which an output torque is a predetermined value or more. Is a diesel engine comprising an engine control device that performs high-load control for controlling the fuel injection amount and the intake air amount so that the fuel consumption is within the effective range of the three-way catalyst.
According to this, the air-fuel ratio can be substantially stoichiometric at high load when the NO _X emission amount increases, and NO _X can be processed by the three-way catalyst.
Thus, EGR amount increases, or excessively promote low compression ratio, without performing the addition of complex and costly post-processing device, such as _the NO _X storage reduction catalyst and urea selective reduction catalyst, NO in the high-load _X emission amount can be reduced.

The invention according to claim 2 includes an EGR device that extracts a part of the exhaust gas from the exhaust pipe and introduces the exhaust gas into the intake pipe, and a throttle valve provided in the intake pipe. The exhaust gas is introduced into the intake pipe by the EGR device when the high load control is executed, and the intake fresh air amount of the engine is reduced by the throttle valve. It is a diesel engine.
According to this, by combining the reduction of the intake fresh air amount by the EGR and the throttle valve to make a substantial stoichiometric state, misfire and increase in soot due to excessive increase in the EGR amount and a decrease in the combustion temperature. Can be prevented.

The invention according to claim 3 is characterized in that the engine control device increases the post fuel injection amount after the main fuel injection during non-execution when the high load control is executed. It is a diesel engine.
According to this, when the air-fuel ratio is lean only by the fresh air throttling and the increase in the EGR amount, the fuel can be stoichiometric by post fuel injection.

The invention according to claim 4 is characterized in that the engine control device delays the fuel injection timing with respect to the non-execution time when the high load control is executed. The diesel engine described in the item.
According to this, the ignition delay time is lengthened, the ratio of diffusion combustion that is likely to generate soot is decreased, the ignition timing is shifted to the expansion stroke side where soot is difficult to generate, and the soot that is likely to increase is enriched when the air-fuel ratio is enriched. The amount of generation can be reduced.

The invention according to claim 5 is arranged in a region closer to the engine than the three-way catalyst in the exhaust pipe, and comes out of the diesel particulate filter that captures particulate matter in the exhaust gas, and the diesel particulate filter. The diesel engine according to any one of claims 1 to 4, further comprising a bypass pipe for bypassing exhaust gas from an inlet side to an outlet side of the three-way catalyst.
According to this, at the time of regeneration of the diesel particulate filter, by bypassing the high-temperature exhaust gas discharged from the diesel particulate filter, it is possible to protect the three-way catalyst and prevent burning or the like.

As described above, according to the present invention, it is possible to provide a diesel engine with reduced NO _X emissions at high load without excessively lowering the combustion temperature with a simple configuration.

It is a figure which shows the structure of the Example of the diesel engine to which this invention is applied. It is a flowchart which shows the high load control of the diesel engine of FIG. It is a graph which shows the correlation with the air fuel ratio (lambda) in a diesel engine, and soot generation amount. It is a graph which shows the correlation with the main injection timing of the fuel in a diesel engine, and a heat release rate log | history.

The present invention, the problem of providing a diesel engine with reduced NO _X emissions at high load without excessively lowering the combustion temperature with a simple structure, provided with a three-way catalyst in the exhaust system, fresh air aperture and strive to NO _X processing by the three-way catalyst performs a stoichiometric operation by EGR, and the injection timing is retarded solved by suppressing the soot generation.

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, an EGR device 60, an oxidation catalyst (DOC) 70, a diesel particulate filter (DPF) 80, a three-way catalyst 90, an engine control unit ( ECU) 100 and the like.

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, 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 exhaust gas aftertreatment devices such as a DOC 70, a DPF 80, and a three-way catalyst 90.

  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 EGR device 60 is intended to recirculate a part of the exhaust gas of the engine 10 extracted from the exhaust pipe 42 into the intake duct 31 for the purpose of reducing the NOx emission amount by suppressing the combustion temperature.
The 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 three-way catalyst 90 in the exhaust pipe 42 and introduces the exhaust gas into an intermediate portion of the intake duct 31 between the air flow meter 33 and the compressor 21 of the turbocharger 20. It is.
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 the traveling wind.

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 (SO ₄ ), 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 three-way catalyst 90 is disposed on the outlet side of the DPF 80 and treats NO _x , CO, and HC in the exhaust gas during stoichiometric operation.
The three-way catalyst 90 includes a catalytic converter in which a noble metal such as platinum, palladium, or rhodium is supported on a carrier such as alumina.
In addition, a bypass line 91 is provided adjacent to the three-way catalyst 90 to bypass the exhaust gas emitted from the DPF 80 to the outlet side of the three-way catalyst 90 without passing the three-way catalyst 90.

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 controls the intake air amount and the fuel injection amount so that the air-fuel ratio becomes a stoichiometric or rich region in a high load region where the driver required torque or the target torque is equal to or greater than a predetermined threshold value, thereby substantially reducing the exhaust gas. and oxygen-free state and subjected to high load control for NO _X treatment with a three-way catalyst 90.
FIG. 2 is a flowchart showing high load control in the diesel engine of the embodiment.
Hereinafter, the steps will be described step by step.

<Step S01: Operation region discrimination>
The ECU 100 detects a driver request torque or a target torque of the engine 10 set based on the driver request torque.
Thereafter, the process proceeds to step S02.

<Step S02: High Load Area Determination>
If the driver request torque or the target torque is greater than or equal to a predetermined threshold value, ECU 100 determines that it is in the high load region and proceeds to step S03.
On the other hand, if the driver request torque or the target torque is less than the threshold value, it is determined that it is not in the high load region, the process returns to step S01, and the subsequent processing is repeated.

<Step S03: Rich control>
The ECU 100 increases the EGR amount by opening the EGR control valve 62 of the EGR device 60 and reduces the intake fresh air amount by reducing the opening of the throttle valve 35, thereby reducing the air-fuel ratio of the engine 10 to the three-way catalyst 90. The enrichment control is performed to enrich the range so as to be within the effective range.
At this time, if the air-fuel ratio is simply enriched to the stoichiometric range, there is a problem that the amount of soot generated increases.
FIG. 3 is a graph showing the correlation between the air-fuel ratio λ and the soot generation amount in a diesel engine.
In FIG. 3, the horizontal axis represents the air-fuel ratio λ, and the vertical axis represents the soot generation amount.
Thus, it can be seen that in the stoichiometric region where the air-fuel ratio λ is close to 1, the amount of soot generated increases rapidly relative to the lean region.

Therefore, in the embodiment, the amount of soot generation is reduced by retarding the fuel injection timing of the main injection.
FIG. 4 is a graph showing the correlation between the fuel main injection timing and the heat release rate history in the diesel engine.
In FIG. 4, the horizontal axis represents the crank angle, and the vertical axis represents the heat generation rate.
As shown in FIG. 4, by retarding the fuel injection timing of the main injection, the ignition delay time can be lengthened, the diffusion combustion rate near the top dead center can be lowered, and the ignition timing can be shifted to the expansion stroke side. it can.
Here, since soot is likely to occur in diffusion combustion near the top dead center and is difficult to occur in combustion in the expansion stroke, the amount of soot generated can be reduced by retarding the fuel injection timing as shown in FIG. It can be effectively reduced.
Thereafter, the process proceeds to step S04.

<Step S04: Determination of Elapsed Time>
The ECU 100 determines whether the time from the start of the enrichment control that is currently being executed has passed a predetermined time. If it has elapsed, the ECU 100 proceeds to step S05, and if not, returns to step S03. The subsequent processing is repeated.

<Step S05: Determination of stoichiometric area>
The ECU 100 detects the current air-fuel ratio λ of the engine 10, and when the air-fuel ratio λ is in a substantial stoichiometric range that is within the effective range of the three-way catalyst 90, the NO _X can be processed by the three-way catalyst 90. It is determined that the state is correct, and a series of processing ends (returns).
On the other hand, if the air-fuel ratio λ is in the lean state and is out of the effective range of the three-way catalyst 90, the process proceeds to step S06.

<Step S06: Post injection execution>
The ECU 100 starts the post injection when the post injection performed following the current main injection is not executed, and increases the injection amount when the post injection is currently being executed.
Thereafter, the process returns to step S05 and the subsequent processing is repeated.

According to the embodiment described above, the following effects can be obtained.
(1) NO _X generation amount is likely to increase during high-load operation, and enriching the air-fuel ratio to substantially stoichiometric state, by treating the NO _X in the three-way catalyst, excessively performed EGR amount increases and the low compression ratio or lowering the combustion temperature Te, NO _X occluding and reducing catalyst, without providing a complicated and expensive post-processing device such as urea SCR, it is possible to reduce the NO _X emissions at high load.
(2) By increasing the EGR amount by the EGR device 60 and reducing the intake fresh air amount by the throttle valve 35 to achieve a substantially stoichiometric state, the EGR amount is excessively increased and the combustion temperature is lowered. Misfire and increase in soot can be prevented.
(3) When only the EGR and the fresh air restriction are still in the lean state, the post-fuel injection amount can be increased to appropriately achieve the substantial stoichiometric state.
(4) When operating in a substantial stoichiometric state, by delaying the injection timing of the main injection, the ignition delay time is lengthened, the ratio of diffusion combustion that is likely to generate soot is reduced, and the expansion stroke side where soot is difficult to generate If the ignition timing is shifted to a rich air / fuel ratio, the amount of soot that tends to increase can be reduced.
(5) By providing the bypass conduit 91 for bypassing the three-way catalyst 90 by the exhaust gas emitted from the DPF 80, the high-temperature exhaust gas discharged from the DPF 80 is bypassed during regeneration of the DPF 80 by after injection or the like. The original catalyst 90 can be protected to prevent burnout and the like.

(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, the EGR device of the embodiment is a low-pressure EGR device that extracts exhaust gas from the discharge side of a turbocharger turbine and various aftertreatment devices and introduces the exhaust gas to the upstream side of the compressor. Not limited to this, high pressure EGR for extracting exhaust gas from the upstream side of the turbine and introducing it to the downstream side of the compressor may be performed.
Further, these low pressure EGR and high pressure EGR may be used in combination.
(2) In the embodiment, the NO _X storage reduction catalyst and the urea SCR are not provided, but these may be provided. In this case, it is possible to reduce the amount of catalyst supported and the fuel consumption required for the regeneration process as compared with the prior art.

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 50 Fuel supply device 51 Supply pump 52 Suction metering solenoid valve 53 Fuel temperature sensor 54 Common rail 55 Fuel pressure sensor 56 in Ekuta 60 EGR 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 Three-way catalyst 91 Bypass line 100 Engine control unit (ECU)
101 accelerator pedal sensor 102 atmospheric pressure sensor

Claims (5)

A diesel engine provided with an exhaust pipe having a three-way catalyst effective in a predetermined air-fuel ratio range in the vicinity of stoichi,
An engine control device that performs high load control for controlling the fuel injection amount and the intake air amount so that the air-fuel ratio is within the effective range of the three-way catalyst in a high load region where the output torque is a predetermined value or more is provided. Diesel engine. An EGR device that extracts a part of the exhaust gas from the exhaust pipe and introduces it into the intake pipe;
A throttle valve provided in the intake pipe line,
The engine control device introduces exhaust gas into the intake pipe by the EGR device when the high load control is executed, and reduces the intake fresh air amount of the engine by the throttle valve. Item 2. The diesel engine according to Item 1. The diesel engine according to claim 2, wherein the engine control device increases the post fuel injection amount after the main fuel injection when the high load control is executed, compared to the non-execution time. The diesel engine according to any one of claims 1 to 3, wherein the engine control device delays a fuel injection timing with respect to a non-execution time when the high load control is executed. A diesel particulate filter that is disposed in a region closer to the engine than the three-way catalyst in the exhaust pipe and captures particulate matter in the exhaust gas;
The diesel engine according to any one of claims 1 to 4, further comprising a bypass pipe for bypassing exhaust gas emitted from the diesel particulate filter from an inlet side to an outlet side of the three-way catalyst. engine.

Images