JP2008175194A - Control device for internal combustion engine - Google Patents

Abstract

In a control device for an internal combustion engine provided with an EGR device, fluctuations in combustion of the engine due to addition of fuel into exhaust gas are suppressed.
In a control device for an internal combustion engine, a DPF is provided on the exhaust passage and downstream of the turbine, and from the downstream side of the exhaust purification device on the exhaust passage to the upstream side of the compressor on the intake passage. An EGR device is provided. Further, fuel is added to the exhaust gas reaching the DPF by a fuel addition valve. The fuel added to the exhaust gas reacts with oxygen in the exhaust gas purification device to generate carbon dioxide, and the exhaust gas containing carbon dioxide is returned to the intake side as EGR gas. Therefore, if the fuel addition timing varies, the carbon dioxide concentration or oxygen concentration in the intake air also fluctuates due to fluctuations in the carbon dioxide concentration or oxygen concentration in the exhaust gas, causing combustion fluctuations in the internal combustion engine. Therefore, the fuel addition device adds fuel in synchronization with the crank angle in each cycle of the internal combustion engine during operation of the exhaust gas recirculation device. Thereby, combustion fluctuation is suppressed.
[Selection] Figure 2

Description

  The present invention relates to an internal combustion engine control device including an exhaust gas recirculation passage for recirculating exhaust gas from an exhaust passage to an intake passage.

  An exhaust purification device having a NOx catalyst that stores nitrogen oxide (NOx) in exhaust gas and reduces and purifies NOx stored by supplying fuel as a reducing agent is known (see Patent Document 1). Patent Document 1 describes that fuel addition as a reducing agent is performed at a predetermined crank angle position at which an exhaust valve of an internal combustion engine opens.

  Further, in an internal combustion engine such as a diesel engine, exhaust gas recirculation (EGR: Exhaust Gas Recirculation) that suppresses the generation of NOx by returning a part of the exhaust gas from the exhaust passage to the intake passage and lowering the combustion temperature in the engine. ) The device is known. Patent Document 2 describes an example of a diesel engine equipped with an EGR device that circulates exhaust gas from a position downstream of the catalyst in the exhaust passage to the intake side.

JP 2002-106332 A Japanese Patent Laid-Open No. 2001-234772

In the technique of Patent Document 1, when a plurality of fuel additions are performed, each fuel addition is performed at a predetermined crank angle. However, fuel is not added in every cycle of the internal combustion engine, and a cycle in which fuel is added and a cycle in which fuel is not added are mixed. For this reason, the air-fuel ratio of the exhaust repeats lean and rich, and the CO ₂ concentration in the EGR gas sent to the intake side fluctuates, so the combustion state of the internal combustion engine fluctuates.

  The present invention has been made in view of the above points, and an object of the present invention is to suppress combustion fluctuations of the engine due to the addition of fuel into exhaust gas in a control device for an internal combustion engine including an EGR device.

  In one aspect of the present invention, a control device for an internal combustion engine is provided on a downstream side of the turbine on the exhaust passage and a turbocharger having a compressor provided in the intake passage and a turbine provided in the exhaust passage. An exhaust gas purifier, an exhaust gas recirculation device for circulating exhaust gas from a position downstream of the exhaust gas purification device on the exhaust passage to a position upstream of the compressor on the intake air passage, and exhaust gas flowing through the exhaust gas purification device The fuel addition device adds fuel in synchronization with the crank angle in each cycle of the internal combustion engine during operation of the exhaust gas recirculation device.

  The above control device for an internal combustion engine can be preferably applied to, for example, a diesel engine including a turbocharger. An exhaust purification device such as a DPF or NOx occlusion reduction catalyst is provided on the exhaust passage and downstream of the turbine. Further, a device for circulating the exhaust gas such as an EGR device is provided from the downstream side of the exhaust purification device on the exhaust passage to the upstream side of the compressor on the intake passage. Further, a fuel addition device is provided for adding fuel to the exhaust gas that reaches the exhaust gas purification device. This fuel addition is performed for the purpose of PM regeneration of DPF, rich spike of NOx storage reduction catalyst, and the like.

  In the above configuration, the fuel added to the exhaust gas reacts with oxygen in the exhaust gas purification device to generate carbon dioxide, and the exhaust gas containing carbon dioxide is returned to the intake side as EGR gas. Therefore, if the fuel addition timing varies, the carbon dioxide concentration or oxygen concentration in the exhaust gas fluctuates, so that the carbon dioxide concentration or oxygen concentration in the intake air also fluctuates, causing combustion fluctuations in the internal combustion engine. Therefore, the fuel addition device adds fuel in synchronization with the crank angle in each cycle of the internal combustion engine during operation of the exhaust gas recirculation device. As a result, the carbon dioxide concentration or oxygen concentration in the exhaust gas is made uniform, so the carbon dioxide concentration or oxygen concentration in the intake air is also made uniform, and combustion fluctuations can be suppressed.

  In one aspect of the control device for an internal combustion engine, the fuel addition device adds fuel each time the crank angle of the internal combustion engine reaches a predetermined crank angle. In this case, fuel addition may be performed a plurality of times during the cycle of the internal combustion engine.

  In a preferred example, the exhaust purification device is a particulate matter removal device, and the fuel addition device raises the temperature of the particulate matter removal device and regenerates it by adding fuel.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

[Device configuration]
FIG. 1 is a block diagram showing a schematic configuration of a control device 100 for an internal combustion engine according to an embodiment of the present invention. In FIG. 1, solid arrows indicate the flow of intake and exhaust, and broken arrows indicate control signals.

  In FIG. 1, an internal combustion engine control device 100 includes an in-line four-cylinder diesel engine as the internal combustion engine 10. Each cylinder of the internal combustion engine 10 is connected to an intake manifold 11 and an exhaust manifold 12. The internal combustion engine 10 includes a fuel injection valve 15 provided in each cylinder, and a common rail 14 that supplies high-pressure fuel to each fuel injection valve 15, and the fuel is in a high-pressure state on the common rail by a fuel pump (not shown). Supplied in. The crank angle sensor 18 detects the crank angle of the internal combustion engine 10 and supplies a detection signal S2 to the ECU 7.

  In an intake passage 20 connected to the intake manifold 11, an air flow meter 21 that measures the amount of air flowing into the internal combustion engine 10, a throttle 22 valve, a compressor 23 a of a turbocharger 23, and an intercooler 24 that cools intake air. Is provided. On the other hand, a turbine 23 b of a turbocharger 23 and a DPF (Diesel Particulate Filter) 30 are provided in the exhaust passage 25 connected to the exhaust manifold 12.

  In addition to the fuel injection valve 15 provided for each cylinder, a fuel addition valve 17 for injecting unburned fuel is provided in the exhaust manifold 12. In this embodiment, the fuel addition valve 17 is used to regenerate particulate matter (PM) that accumulates in the DPF 30 on the exhaust passage 25. That is, fuel is added to the exhaust gas by the fuel addition valve 17 to raise the temperature of the DPF 30, and the PM collected in the DPF 30 is burned and processed.

  The control device 100 for an internal combustion engine includes an EGR device (hereinafter referred to as a “low pressure loop EGR device”) that extracts EGR gas from the downstream side of the turbocharger. Specifically, as shown in the figure, an EGR passage 35 that connects a position downstream of the DPF 30 on the exhaust passage 25 and a position upstream of the compressor 23a of the intake passage 20 is provided. The EGR passage 35 is provided with an EGR cooler 36 that cools the EGR gas and an EGR valve 37 that controls the amount of EGR gas.

  Each element of the control device 100 for the internal combustion engine is controlled by the ECU 7. Specifically, the ECU 7 controls the opening degree of the throttle valve 22 by sending a control signal S1 to the throttle valve 22. The ECU 7 sends a control signal S3 to the fuel injection valve 15 to control the fuel injection amount, and sends a control signal S4 to the fuel addition valve 17 to control the fuel addition timing and the fuel addition amount. Further, the ECU 7 sends a control signal S5 to the EGR valve 37 to control its opening. The ECU 7 also controls other components of the control device 100 for the internal combustion engine, but description of portions that are not particularly related to the present embodiment is omitted.

[PM regeneration processing]
Next, the PM regeneration process of the DPF 30 according to the present embodiment will be described. The DPF 30 is composed of, for example, a ceramic porous filter and collects PM in the exhaust. However, since the collected PM accumulates on the filter, if the PM is continuously collected, the filter is clogged. Therefore, when a certain amount of PM is deposited on the filter, it is necessary to add fuel to the exhaust gas passing through the DPF 30 to raise the exhaust gas temperature, and to burn and remove the PM deposited on the DPF 30. This process is called “PM regeneration”.

  In the present embodiment, fuel addition for PM regeneration is performed by the fuel addition valve 17. Specifically, the ECU 7 sends a control signal S4 to the fuel addition valve 17 to inject a predetermined amount of fuel when PM regeneration is necessary. The PM regeneration is performed when a predetermined amount or more of PM is deposited on the DPF 30. The amount of PM accumulated in the DPF 30 can be estimated based on, for example, the difference in exhaust pressure before and after the DPF 30. When the estimated amount of accumulation exceeds a predetermined value, the ECU 7 determines that there is a PM regeneration request, and PM regeneration Process. Various known methods can be applied to the method for detecting the amount of accumulated PM, conditions for performing PM regeneration, and the like.

  In the PM regeneration process, the ECU 7 first calculates a necessary fuel addition amount and performs fuel addition from the fuel addition valve 17 a plurality of times. 2A and 2B show examples of fuel addition timing in the PM regeneration process.

FIG. 2B shows an example in which fuel addition is performed regardless of the cycle of the internal combustion engine. One cycle of the internal combustion engine corresponds to a crank angle (CA) of 720 degrees. In the example of FIG. 2B, a cycle in which fuel addition is performed and a cycle in which fuel addition is not performed are mixed. Further, even in the cycle in which fuel addition is performed, the timing of fuel addition in one cycle (that is, the crank angle when fuel addition is performed) varies. By adding the fuel, hydrocarbon (HC) in the fuel and oxygen (O ₂ ) in the exhaust gas react to generate carbon dioxide (CO ₂ ), so that the CO ₂ concentration in the exhaust gas increases after the fuel addition. Since this exhaust gas is returned to the intake side as EGR gas, the CO ₂ concentration in the intake air also increases. As in the example shown in FIG. 2B, when the fuel addition timing is varied, the CO ₂ concentration in the intake air varies, so that the combustion state of the internal combustion engine varies.

On the other hand, FIG. 2 (A) shows the fuel addition timing according to the present embodiment. In this embodiment, when PM regeneration is performed and the EGR device is operating, fuel addition is performed at the same crank angle in each cycle of the internal combustion engine. That is, the fuel addition is synchronized with the crank angle of the internal combustion engine, and the fuel addition is performed at a predetermined crank angle (hereinafter referred to as “X degree”) among crank angles 0 to 720 degrees corresponding to one cycle of the internal combustion engine. Is implemented. Thus, while the fuel addition is continuously performed, the CO ₂ concentration in the exhaust gas becomes constant, and the CO ₂ concentration in the intake air also becomes constant as shown in FIG. Therefore, since fluctuations in the CO ₂ concentration in the intake air are eliminated, fluctuations in the combustion state can be prevented.

  In the example of FIG. 2A, fuel is added once during one cycle of the internal combustion engine. In this case, fuel addition is performed at intervals of 720 degrees of crank angle. However, in the present invention, the interval of the crank angle at which fuel is added (hereinafter referred to as “fuel addition cycle”) is not limited to 720 degrees. For example, when fuel is added twice during one cycle of the internal combustion engine, the fuel may be added at every crank angle of 360 degrees. In this case, in the above example, in each cycle of the internal combustion engine, fuel addition may be performed when the crank angle is X degrees and (X + 360) degrees. Similarly, the fuel addition timing interval may be further shortened, and fuel addition may be performed every crank angle of 180 degrees.

  Next, the fuel addition cycle will be examined. Theoretically, it is preferable to add fuel at every crank angle of 180 degrees since one fuel addition is performed for one explosion of the internal combustion engine. However, as a practical problem, there is a limitation due to the accuracy of the injection amount from the fuel addition valve 17. The fuel injection valve can accurately control the injection amount when the injection amount is sufficiently large, but if the injection amount is small, the error of the injection amount per one time becomes large and the accuracy of the injection amount decreases. is there. Therefore, in theory, it is desirable to add fuel at every crank angle of 180 degrees, but the injection amount per time is the minimum injection amount that can maintain the accuracy of the injection amount (hereinafter referred to as “minimum injection amount”). .) When smaller, it is preferable to perform fuel injection every 360 degrees or 720 degrees so that the amount of fuel added per time is equal to or greater than the minimum injection amount. Thus, it is preferable to determine the fuel addition cycle in consideration of the ability and accuracy of the fuel addition valve in practice.

  FIG. 3 is a flowchart of the fuel addition process according to the present embodiment. In this example, it is assumed that one fuel addition is performed at a timing of crank angle = X degrees during one cycle of the internal combustion engine. That is, the addition cycle is a crank angle of 720 degrees.

  First, the ECU 7 determines whether or not there is a PM regeneration request (step S101). As an example, as described above, for example, the PM accumulation amount in the DPF 30 is detected or estimated, and when a predetermined accumulation amount is exceeded, it is determined that there is a PM regeneration request. If there is no PM regeneration request (step S101; No), the process ends.

  On the other hand, when there is a PM regeneration request (step S101: Yes), the ECU 7 calculates the fuel addition amount per time (step S102). A method for calculating the fuel addition amount will be described below. The target temperature for raising the temperature of the DPF 30 for PM regeneration is determined in advance, and the ECU 7 stores this. The ECU 7 detects or estimates the current temperature of the DPF 30 by, for example, detecting the temperature of the DPF 30 or the exhaust gas temperature flowing into the DPF 30 using a temperature sensor. Then, a difference between the current temperature of the DPF 30 and the target temperature, that is, a temperature increase amount ΔT for increasing the temperature of the DPF 30 is calculated. Then, the required energy for raising the temperature of the DPF 30 is obtained by the following equation (1), and the fuel addition amount per time is calculated by the equation (2).

(Required energy) = (Air flow rate during addition cycle) × (temperature increase ΔT) × specific heat (1)
(Fuel addition amount) = (Required energy) / (Heat generation amount by unit amount of fuel) (2)
When the fuel addition amount per time is calculated in this way, the ECU 7 refers to the detection signal S2 from the crank angle sensor 18 and when the crank angle reaches a predetermined fuel injection crank angle (X degrees) (step S103; Yes), a control signal S4 is sent to the fuel addition valve 17 to perform fuel addition (step S104). Then, the ECU 7 determines whether or not the DPF 30 has reached the target temperature (step S105), and ends the process when the target temperature has been reached. On the other hand, when the DPF 30 does not reach the target temperature, the process returns to step S103 and the fuel addition is repeated.

As described above, in the present embodiment, in the PM regeneration process, fuel is added at the timing of a predetermined crank angle in each cycle of the internal combustion engine in synchronization with the crank angle, so the CO ₂ concentration in the exhaust gas Can be made constant. As a result, the CO ₂ concentration circulating to the intake side by the EGR device can also be kept constant, and combustion fluctuations of the internal combustion engine can be prevented.

[Modification 1]
In the above embodiment, the control device 100 for the internal combustion engine includes only the low-pressure loop EGR device. Instead, it is also possible to apply the present invention to a control device for an internal combustion engine that includes both a low pressure loop EGR device and a high pressure loop EGR device. An example of such a control device for an internal combustion engine is shown in FIG.

  In FIG. 4, the upstream position of the turbine 23 b in the exhaust passage 25 and the downstream position from the intercooler 24 in the intake passage 20 are connected by an EGR passage 31. The EGR passage 31 is provided with an EGR valve 33 for controlling the EGR amount. The EGR device having the EGR path upstream of the turbocharger is hereinafter referred to as a “high pressure loop EGR device”.

  The present invention is basically effective when applied to a control device for an internal combustion engine having a low-pressure loop EGR device. However, even in a control device for an internal combustion engine having only a high-pressure loop EGR device, the added fuel is There is room for application to a configuration that can be mixed into the intake air through EGR gas.

[Modification 2]
In the above embodiment, fuel is added to the exhaust by the fuel addition valve 17 for PM regeneration of the DPF 30. In contrast, in a control device for an internal combustion engine having a NOx occlusion reduction type catalyst in the exhaust passage, the air-fuel ratio of the exhaust gas is temporarily made rich, and fuel is added to the exhaust gas in order to reduce the NOx occluded in the catalyst. (Generally referred to as “rich spikes”). The present invention can also be applied to the case where fuel is added to the exhaust for such a purpose. That is, when performing the rich spike, the ECU 7 may add fuel at a predetermined crank angle timing in synchronization with the crank angle in each cycle of the internal combustion engine, as shown in FIG.

1 is a schematic block diagram of a control device for an internal combustion engine according to an embodiment. It is a figure which shows the example of a fuel addition timing. It is a flowchart of a fuel addition process. It is a schematic block diagram of the control apparatus of the internal combustion engine which concerns on a modification.

Explanation of symbols

7 ECU
10 Internal combustion engine
17 Fuel addition valve 20 Intake passage 23 Turbocharger 25 Exhaust passage 30 DPF
31, 35 EGR passage 33, 37 EGR valve

Claims (3)

A control device for an internal combustion engine,
A turbocharger having a compressor provided in the intake passage and a turbine provided in the exhaust passage;
An exhaust gas purification device provided downstream of the turbine on the exhaust passage;
An exhaust gas recirculation device that circulates exhaust gas from a position downstream of the exhaust purification device on the exhaust passage to a position upstream of the compressor on the intake passage;
A fuel addition device for adding fuel to the exhaust gas flowing through the exhaust purification device,
The control device for an internal combustion engine, wherein the fuel addition device adds fuel in synchronization with a crank angle in each cycle of the internal combustion engine during operation of the exhaust gas recirculation device.   2. The control device for an internal combustion engine according to claim 1, wherein the fuel addition device adds fuel each time the crank angle of the internal combustion engine reaches a predetermined crank angle.   3. The exhaust gas purification device is a particulate matter removal device, and the fuel addition device raises the temperature of the particulate matter removal device and regenerates it by adding fuel. Control device for internal combustion engine.

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