WO2007004471A1

WO2007004471A1 - Control device for diesel engine

Info

Publication number: WO2007004471A1
Application number: PCT/JP2006/312804
Authority: WO
Inventors: Michihiro Hata; Kei Shigahara; Noriyuki Koga; Kazuo Kurata
Original assignee: Mitsubishi Jidosha Kogyo Kabushiki Kaisha
Priority date: 2005-07-05
Filing date: 2006-06-27
Publication date: 2007-01-11
Also published as: JP2007016611A

Abstract

An exhaust gas purification device (50) for purifying exhaust gas from a diesel engine (1) is provided in an exhaust path (30) of the engine (1). In a fuel cutoff state where main fuel injection by a fuel injection valve (4) is stopped, an intake throttle valve (28) is controlled to reduce the amount of inlet air to the diesel engine (1) and an EGR valve (64) is controlled to increase the amount of exhaust gas recirculation to a combustion chamber (6) of the engine (1).

Description

Specification

Diesel engine control device

Technical field

TECHNICAL FIELD [0001] The present invention relates to a diesel engine control device, and more particularly to a technique for maintaining the temperature of an exhaust purification device at an activation temperature.

Background art

[0002] In addition to HC (hydrocarbon), CO (carbon monoxide), NOx (nitrogen oxide), etc., exhaust gas that also emits diesel engine power contains particulate matter (hereinafter referred to as PM). A diesel particulate filter (hereinafter referred to as DPF) that captures PM has been proposed as an exhaust purification means for treating this PM! RU

[0003] In the DPF, it is necessary to remove the PM when the accumulated amount of the captured PM exceeds an allowable amount. As a method for removing the accumulated PM, for example, an oxidation catalyst is provided upstream of the DPF, post-injection in the expansion stroke or exhaust stroke is performed, and the unburned fuel (HC) is oxidized by the oxidation catalyst. There is a method to forcibly remove PM by using the heat of oxidation reaction generated by oxidation.

[0004] In order to perform forced regeneration of DPF by such a method, it is necessary to keep the temperature of the oxidation catalyst inlet at or above the catalyst activation temperature. However, since the exhaust temperature of the diesel engine is relatively low, there is a problem that the temperature of the oxidation catalyst inlet becomes lower than the catalyst activation temperature during idling.

[0005] Therefore, the exhaust throttle valve and the intake throttle valve are fully closed when the engine is in a cold state and idle operation, and the exhaust throttle valve is half-opened and the intake air when the engine is in a cold state and non-idle operation. When the engine is warmed up while the vehicle is running with the engine cold, the technology has been developed, and published in Japanese Patent Laid-Open No. 11-236829 (hereinafter referred to as Patent Document 1). It is disclosed in!

[0006] In the technique disclosed in Patent Document 1 above, the exhaust throttle valve is closed and the intake throttle valve is also closed, so that the engine's pumping loss is greatly increased, and the vehicle operating state is not increased due to excessive engine braking force. If it gets worse! [0007] Further, in a vehicle in which an exhaust gas purification device is provided in the exhaust system, fuel injection is stopped when combustion of a downhill or the like is released, for example, so that fuel injection is stopped and combustion does not occur. In the fuel cut state, combustion is not occurring, but the engine is rotating, so fresh air flows directly into the exhaust passage. For this reason, the heat of the oxidation catalyst and DPF is carried away by fresh air, and the temperature of the oxidation catalyst and DPF decreases rapidly more than during idle operation.

[0008] If the temperature of the acid catalyst or DPF rapidly decreases in this way, forced regeneration of DPF cannot be performed, leading to poor exhaust purification performance, and when combustion is resumed. Since it is necessary to raise the temperature of the acid catalyst again using a large amount of fuel, fuel consumption is deteriorated, which is not preferable.

Disclosure of the invention

[0009] The present invention has been made to solve such a problem, and an object of the present invention is to reduce the temperature of the exhaust purification means that does not deteriorate the vehicle operating state even in the fuel cut state. It is an object of the present invention to provide a control device for a diesel engine that can suppress the exhaust gas and can maintain the exhaust purification performance of the exhaust purification means satisfactorily.

In order to achieve the above-described object, a control device for a diesel engine according to the present invention is provided in a fuel injection means for directly injecting fuel into a combustion chamber, and an intake passage of the diesel engine, and the diesel engine Intake throttle means for adjusting the amount of intake air supplied to the engine, exhaust purification means provided in the exhaust passage of the diesel engine for purifying exhaust gas exhausted from the diesel engine, and the diesel engine An exhaust gas recirculation adjusting means for adjusting the amount of exhaust gas recirculated into the combustion chamber; and a control means for controlling the fuel injection means, the intake throttling means, and the exhaust gas recirculation adjusting means. When in the fuel cut state in which the main fuel injection by the injection means is stopped, the intake throttle means is controlled to reduce the intake air amount and the exhaust gas. The exhaust gas recirculation amount is increased by controlling the air recirculation adjusting means.

That is, in a diesel engine provided with an intake throttle means and an exhaust gas recirculation adjusting means

When the engine is in a fuel cut state, the control means controls the intake throttle means to reduce the intake air amount, and the control means controls the exhaust gas recirculation adjustment means to exhaust the exhaust gas. Increase air reflux.

[0012] Therefore, when the engine is in a fuel cut state, the control means controls the intake throttle means to reduce the intake air amount and suppress the introduction of fresh air into the engine, thereby The removal of heat from the dredging means can be suppressed. At this time, by further increasing the exhaust gas recirculation amount by controlling the control means force S exhaust gas recirculation control means, it is possible to mitigate the increase in the engine's pumping loss due to the suppression of fresh air. Generation of braking force can be prevented.

[0013] Thereby, even if the engine is in a fuel cut state, it is possible to suppress the temperature reduction of the exhaust purification means that would deteriorate the driving state of the vehicle, and the exhaust purification means has good exhaust purification performance. Can be maintained.

[0014] Specifically, in the control device for a diesel engine, the exhaust purification unit includes a particulate filter that captures particulate matter in exhaust exhausted by the diesel engine power, and an upstream of the particulate filter. And an acid catalyst disposed on the side.

[0015] Thereby, it is possible to effectively suppress a temporary decrease in the exhaust purification performance of the diesel engine provided with the continuously regenerating diesel particulate filter.

[0016] Preferably, the control device for the diesel engine performs the expansion stroke or exhaust stroke of the diesel engine by the fuel injection means when the particulate matter accumulation amount in the particulate filter reaches a predetermined amount. The fuel cell further comprises forced regeneration means for forcibly regenerating the particulate filter by forcibly burning and removing the particulate matter captured by the particulate filter by performing the auxiliary fuel injection, and the control means comprises the fuel When the particulate filter is forcibly regenerated by the forced regeneration means in the cut state, the intake throttle means is controlled to reduce the intake air amount, and the exhaust gas recirculation adjustment means is The exhaust gas recirculation amount is increased by control.

That is, when the engine is in a fuel cut state and the particulate filter is forcibly regenerated, the control means controls the intake throttle means to reduce the intake air amount and introduce fresh air. Control and control the exhaust power recirculation control means. By increasing the exhaust gas recirculation amount, the pressure increase in the intake system and exhaust system is reduced.

As a result, the forced regeneration of the particulate filter can be performed satisfactorily.

[0018] Preferably, in the control device for the diesel engine, the control means increases the exhaust gas recirculation amount by the exhaust gas recirculation adjusting means in accordance with an increase in the rotational speed of the diesel engine. .

Thereby, a bombing loss can be reduced more efficiently.

Brief Description of Drawings

FIG. 1 is a schematic configuration diagram of a control device for a diesel engine according to an embodiment of the present invention;

FIG. 2 is a flowchart of a heat retention control routine of the exhaust gas purification device, which is executed by the ECU of the control device of FIG. 1, and

FIG. 3 is a time chart corresponding to the present embodiment, Comparative Example 1 and Comparative Example 2.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

Referring to FIG. 1, there is shown a schematic configuration diagram of a diesel engine control device according to an embodiment of the present invention.

As shown in FIG. 1, the engine 1 is a common rail type diesel engine having a plurality of cylinders. More specifically, the engine 1 supplies high-pressure fuel accumulated in the common rail 2a by the common rail system 2 to the fuel injection valve 4 (fuel injection means) of each cylinder, and the fuel injection valve at an arbitrary injection timing and injection amount. It is configured to be able to inject from 4 into the combustion chamber 6 of each cylinder. FIG. 1 shows a cross section of one cylinder of the engine 1. The other cylinders have the same configuration and are not shown here.

Each cylinder is provided with a piston 8 that can slide up and down, and the piston 8 is connected to a crankshaft 12 via a connecting rod 10. A flywheel 14 is provided at one end of the crankshaft 12, and a crank angle sensor 16 that detects the rotational speed of the crankshaft 12 is provided in the flywheel 14.

[0023] Each combustion chamber 6 communicates with an intake passage 20 and an exhaust passage 30.

Each intake passage 20 has an intake valve 22 that communicates and blocks the combustion chamber 6 and the intake passage 20. Each exhaust passage 30 is provided with an exhaust valve 32 for communicating and blocking between the combustion chamber 6 and the exhaust passage 30.

[0025] The intake passages 20 are gathered together and integrated, and an air cleaner 24 is provided at an upstream end thereof. In the integrated intake passage 20, a turbocharger 40 is provided downstream of the air cleaner 24 to supercharge intake air using exhaust airflow. Specifically, the turbocharger 40 also includes a turbine that rotates by exhaust and a compressor force that rotates in synchronization with the turbine, and the intake passage 20 is connected to a compressor housing that houses the compressor.

[0026] An intake air passage 20 on the downstream side of the turbocharger 40 is provided with an intercooler 26 that cools the supercharged intake air. Further, on the downstream side of the intercooler 26, there is provided an intake throttle valve 28 (intake throttle means) that adjusts the intake air amount by an electromagnetic butterfly rev force.

The intake passage 20 branches downstream of the intake throttle valve 28 and communicates with each combustion chamber 6 as described above.

[0028] On the other hand, after the exhaust passage 30 is assembled and integrated, it is connected to a turbine housing that houses the turbine of the turbocharger 40, and an exhaust purification device 50 is provided downstream of the turbocharger 40. (Exhaust gas purification means) is provided.

[0029] On the upstream side in the exhaust purification apparatus 50, an oxidation catalyst 52 that oxidizes nitrogen monoxide (NO) in the exhaust gas to form nitrogen dioxide (NO) is disposed. Also downstream of the oxidation catalyst 52

2

Is equipped with a diesel particulate filter (hereinafter referred to as DPF) 54 that captures particulate matter (hereinafter referred to as PM) in the exhaust. That is, the oxidation catalyst 52 and the DPF 54 constitute a continuous regeneration type DPF. Further, a temperature sensor 56 for detecting the outlet temperature of the oxidation catalyst 52, that is, the inlet temperature of the DPF 54, is provided at the outlet portion of the acid catalyst 52.

[0030] In addition, an EGR passage is provided so that a portion of the intake passage 20 before branching downstream of the intake throttle valve 28 and a portion of the exhaust passage 30 after collecting upstream of the turbocharger 40 communicate with each other. 60 is provided. Part of the exhaust gas is recirculated as EGR gas from the EGR passage 60 through the intake passage 20 into the combustion chambers 6. [0031] The EGR passage 60 is provided with an EGR cooler 62 that cools the EGR gas, and an electromagnetic EGR valve 64 (exhaust gas) that adjusts the recirculation amount of the EGR gas at the connection portion between the intake passage 20 and the EGR passage 60. A reflux control means) is provided.

[0032] Various devices and various sensors such as the fuel injection valve 4, the crank angle sensor 16, the intake throttle valve 28, the temperature sensor 56, and the EGR valve 64 are ECUs (electronic control units).

70 (Control means) Electrically connected. The ECU 70 controls the operation of various devices based on information from various sensors.

[0033] Furthermore, the ECU 70 is electrically connected to an accelerator sensor 72 that is provided in the vehicle and detects the accelerator opening of the accelerator pedal.

The operation of the diesel engine control device according to one embodiment of the present invention configured as described above will be described below.

[0035] Referring to FIG. 2, in the diesel engine control device according to one embodiment of the present invention, the temperature control routine of the exhaust purification device 50 at the time of fuel cut executed by the ECU 70 at a predetermined control cycle is shown. It is shown in the flowchart, and will be explained based on the flowchart below.

First, in step S1, it is determined whether or not a fuel cut is in progress. That is, it is determined whether or not the main fuel injection for generating torque is stopped, and if the determination result is true (Yes), the process proceeds to step S2.

[0037] In step S2, the rotational speed force of the crankshaft 12 detected by the crank angle sensor 16 is detected, and the engine speed is preset, and whether or not the engine speed is within a predetermined speed. Is determined. If the intake throttle valve is closed at a high speed where the engine speed is higher than the predetermined speed, the bombing loss increases rapidly and excessive engine braking force is generated. This determination is made to prevent the occurrence. If the determination result is true (Yes), the process proceeds to step S3.

[0038] In step S3, it is determined whether or not the engine 1 is performing forced regeneration of the DPF 54. The forced regeneration is performed when the PM accumulation amount exceeds a predetermined amount because PM collected by DPF54 gradually accumulates even if continuous regeneration is performed. Here, PM deposition amount is an example For example, since it correlates with the differential pressure before and after DPF54, that is, the pressure loss of DPF54, and the exhaust flow rate, it is estimated based on a map that defines the relationship between the differential pressure before and after DPF54, the exhaust flow rate, and the PM deposition amount. In forced regeneration, secondary fuel injection is performed in the expansion stroke and exhaust stroke so as not to contribute to the torque generation of the engine 1. The oxidation heat generated when the injected fuel is oxidized on the oxidation catalyst 52 is used. Thus, PM deposited on DPF54 is removed by incineration. Therefore, in this embodiment, the ECU 70 and the fuel injection valve 4 correspond to the forced regeneration means of the present invention.

If the determination result in step S3 is true (Yes), that is, if forced regeneration as described above is performed, the process proceeds to step S4.

[0040] In step S4, the ECU 70 controls the intake throttle valve 28 to be fully closed, and the EGR valve 64 is fully opened to complete the routine in the control cycle.

On the other hand, if any one of the determination results in steps S1 to S3 is false (No), the process proceeds to step S5. In step S5, the ECU 70 performs normal control on the intake throttle valve 28 and the EGR valve 64, and the routine in the control cycle ends.

Here, referring to FIG. 3, there is shown a time chart corresponding to the present embodiment in which the above-mentioned heat retention control is performed, Comparative Example 1 in which the above heat retention control is not performed, and Comparative Example 2 in which the EGR valve is not controlled. Has been.

[0043] As shown in the figure, for example, when the vehicle is traveling downhill and the accelerator pedal is released and the accelerator opening becomes 0, the main fuel injection is stopped and the engine 1 is fuel cut. It becomes a state. Here, in the heat retention control of the present embodiment, when the engine 1 is in the fuel cut state, the intake throttle valve 28 is fully closed and the EGR valve 64 is fully opened.

[0044] In Comparative Example 1 where the intake throttle valve is not fully closed because the engine 1 is running even in the fuel cut state, relatively low temperature fresh air flows directly into the exhaust passage. The heat from the exhaust purification system is taken away. As a result, the inlet temperature of DPF54 drops significantly as shown by the chain line, and quickly falls below the catalyst activation temperature shown by the one-dot chain line. If the sub fuel injection is performed in a state where the temperature is below the catalyst activation temperature, unburned HC is discharged into the atmosphere as it is, so that the sub fuel injection is performed during this catalyst inactive period. Cannot shoot, that is, cannot perform forced regeneration of DPF54.

[0045] On the other hand, as in the present embodiment, the intake throttle valve 28 is fully closed to suppress the introduction of fresh air, thereby suppressing the fresh air flowing into the exhaust passage 30 as it is, and the exhaust purification device 50. The removal of heat from can be suppressed. As a result, the DPF54 inlet temperature does not fall below the catalyst activation temperature, and even when the fuel is cut, secondary fuel injection can be performed to forcibly regenerate the DPF54.

[0046] Further, in Comparative Example 1, when the accelerator pedal is depressed again and the engine 1 returns from the fuel cut state to the fuel supply state, the temperature of the exhaust gas purification device greatly decreases. Until the inlet temperature of the fuel becomes higher than the catalyst activation temperature, sub fuel injection cannot be performed. Therefore, first, the temperature raising control of the exhaust gas purification device must be performed, and extra fuel is consumed.

[0047] On the other hand, in this embodiment, the temperature drop during the fuel cut is small. The inlet temperature of the DPF 54 is sufficiently kept above the catalyst activation temperature! Therefore, it does not consume extra fuel by controlling the temperature rise.

[0048] In Comparative Example 2, the force that causes the intake throttle valve to be fully closed in the fuel cut state is not controlled, and the EGR valve is fully closed. In Comparative Example 2 as described above, by suppressing the introduction of fresh air, the negative pressure of the intake system is further reduced, the bombing loss is increased, and the negative torque, that is, the action of the engine brake increases.

Here, when the intake throttle valve 28 is fully closed and the EGR valve 64 is fully opened as in the present embodiment, the EGR gas is recirculated through the EGR passage 60, thereby Further decompression of negative pressure is suppressed. As a result, generation of excessive engine braking force can be suppressed.

[0050] As described above, in the control apparatus for a diesel engine according to an embodiment of the present invention, even in the fuel cut state, the intake throttle valve 28 is fully closed and the EGR valve 64 is fully opened, so that the vehicle Therefore, it is possible to suppress the temperature reduction of the exhaust purification device 50 without deteriorating the operation state, and to maintain the exhaust purification performance of the exhaust purification device 50 satisfactorily.

[0051] This completes the description of the control device for a diesel engine according to one embodiment of the present invention. However, the embodiment of the present invention is not limited to the above embodiment. For example, an exhaust throttle valve may be provided in the exhaust passage 30 in the above embodiment, and the ECU 70 may be controlled to close the exhaust throttle valve together with the intake throttle valve 28 when in a fuel cut state. By closing the exhaust throttle valve in this way, the exhaust flow is suppressed, and the heat retention effect of the exhaust purification device 50 can be further improved.

Further, in the above embodiment, the ECU 70 controls the intake throttle valve 28 to be fully closed and the EGR valve 64 to be fully open during the forced regeneration of the DPF 54 and the fuel cut state. However, not only during forced regeneration of DPF54 but also during continuous regeneration, ECU 70 controls intake throttle valve 28 to be fully closed and EGR valve 64 to be fully open when the fuel cut state is reached. Also good.

[0054] In the above embodiment, the ECU 70 fully closes the intake throttle valve 28 and fully opens the EGR valve 64 when the fuel is cut. For example, each opening degree is varied according to the engine speed. The ECU 70 may control the intake throttle valve 28 and the EGR valve 64, or the ECU 70 controls the intake throttle valve 28 and the EGR valve 64 so that a specific opening degree is set in advance and the specific opening degree is reached. May be. In this way, by changing the opening according to the engine speed, the bombing loss can be reduced more efficiently.

[0055] In the above embodiment, the acid purification catalyst 52 and the DPF 54 are used as the exhaust gas purification means, but the present invention is not limited to this. Furthermore, the method of forced regeneration is not limited to the method by sub fuel injection, and various known methods can be employed.

[0056] In the above embodiment, the exhaust gas recirculation adjusting means is not limited to the force in which the EGR valve 64 is provided in the EGR passage 60 that connects the intake passage 20 and the exhaust passage 30 as the exhaust gas recirculation adjusting means. Absent. For example, a variable valve mechanism is used to control the so-called internal EGR amount by controlling the opening timing of the intake valve and the closing timing of the exhaust valve and changing the overlap period of intake and exhaust. May be.

Claims

The scope of the claims

[1] Fuel injection means (4) for directly injecting fuel into the combustion chamber;

An intake throttle means (28) provided in the intake passage (20) of the diesel engine (1) for adjusting the amount of intake air supplied to the diesel engine (1);

An exhaust purification means (50) provided in the exhaust passage (30) of the diesel engine (1) for purifying the exhaust discharged from the diesel engine (1);

Exhaust gas recirculation control means (64) for adjusting the amount of exhaust gas recirculated into the combustion chamber (6) of the diesel engine (1);

Control means (70) for controlling the fuel injection means (4), the intake throttle means (28), and the exhaust gas recirculation adjustment means (64),

The control means (70) controls the intake throttle means (28) to reduce the intake air amount when in a fuel cut state in which main fuel injection by the fuel injection means (4) is stopped. A diesel engine control device characterized in that the exhaust gas recirculation amount is increased by controlling the exhaust gas recirculation adjusting means (64).

[2] The exhaust purification means (50) includes a particulate filter (54) for capturing particulate matter in exhaust exhausted from the diesel engine (1), and an upstream side of the particulate filter (54). The diesel engine control device according to claim 1, characterized by comprising an oxidation catalyst (52) disposed.

[3] When the accumulated amount of particulate matter in the particulate filter (54) reaches a predetermined amount, the fuel injection means (4) performs the auxiliary stroke performed in the expansion stroke or exhaust stroke of the diesel engine (1). Forced regeneration means (4, 70) for forcibly regenerating the particulate filter (54) by forcibly burning and removing the particulate matter captured by the particulate filter (54) by performing fuel injection In addition,

The control means (70) is in the fuel cut state, and when the particulate filter (54) is forcibly regenerated by the forced regeneration means (4, 70), the intake throttle means (28) 3. The diesel engine control device according to claim 2, wherein the exhaust air recirculation amount is increased by controlling the exhaust air recirculation adjusting means (64) by controlling the exhaust air amount. The control means (70) increases the exhaust gas recirculation amount by the exhaust gas recirculation control means (64) according to an increase in the rotational speed of the diesel engine (1). A control device for a diesel engine according to claim 1.