JP2006194148A - Egr control device for diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an EGR control device for a diesel engine capable of making both of NOx discharge amount and a particulate discharge amount proper. <P>SOLUTION: The EGR control device for the diesel engine has an oxygen concentration detection means 56 arranged on the exhaust passage 30; EGR ratio control means 46, 70 for recirculating a part of an exhaust gas to a suction passage 14 at a combustion stable operation area and controlling the EGR ratio; an engine speed detection means 58; and a vehicle speed detection means 62. The device has a first presumption means 72 for presuming the particulate discharge amount discharged from the engine based on at least engine speed as a first exhaust amount; and a second presumption means 74 for presuming the particulate discharge amount discharged from the engine based on the oxygen concentration as the second exhaust amount. The EGR ratio control means increase the EGR ratio when a ratio of the second exhaust amount to the first exhaust amount falls below a predetermined amount less than 1 at the combustion stable operation area. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an EGR control device for a diesel engine, and more particularly to an EGR control device for a diesel engine that can optimize both NOx emission and particulate emission.

  Conventionally, in a diesel engine, it is known to control the EGR rate in order to appropriately control both the NOx emission amount and the particulate emission amount mainly composed of soot (for example, Patent Document 1). . This technology for controlling the EGR rate is also known to have a trade-off relationship (see FIG. 2) that when the EGR rate is increased, the NOx emission amount is reduced, but the particulate emission amount is increased. .

JP-A-8-86251

  However, even if the EGR valve is controlled with a predetermined control amount due to variations in the entire EGR system and accumulation of carbon in the exhaust gas in the EGR passage, the EGR rate does not reach the target value and NOx emissions There was a problem that it was not possible to adequately optimize both the amount of particles and the amount of particulates discharged. In particular, there has been a serious problem that the EGR rate decreases due to the deposition of carbon or the like in the EGR passage and the amount of NOx increases.

  Accordingly, the present invention has been made to solve the above-described problems of the prior art, and an EGR control device for a diesel engine that can sufficiently optimize both the NOx emission amount and the particulate emission amount. The purpose is to provide.

In order to achieve the above object, the present invention provides an oxygen concentration detecting means that is disposed in an exhaust passage of an engine and detects an oxygen concentration, and recirculates a part of the exhaust gas to the intake passage in the stable combustion operation region and EGR thereof. An EGR control device for a diesel engine, comprising: an EGR rate control means for controlling a rate; an engine speed detection means for detecting an engine speed; and a vehicle speed detection means for detecting a vehicle speed, wherein the engine speed is at least The first estimation means for estimating the particulate emission amount discharged from the engine based on the first emission amount, and the second estimation means for estimating the particulate emission amount discharged from the engine based on the oxygen concentration as the second emission amount When the ratio of the second emission amount to the first emission amount falls below a predetermined value less than 1 in the stable combustion operation region, the EGR rate control means It is characterized by increasing the R ratio.
In the present invention configured as described above, the first estimation means capable of estimating the particulate discharge amount without being influenced by the change in the EGR rate, and the first estimation unit capable of estimating the particulate discharge amount as a value reflecting the change in the EGR rate. The EGR rate control means includes a fine particle discharge amount (second discharge amount) estimated by the second estimation means, and a fine particle discharge amount (first discharge amount) estimated by the first estimation means. Since the EGR rate is increased and corrected when the amount is smaller than that, it is possible to prevent an increase in the NOx amount due to variations in the EGR rate and the like.

In the present invention, preferably, the combustion stable operation region is a steady operation region.
In the present invention configured as described above, since the first emission amount and the second emission amount are compared in the steady operation region, it is possible to improve the estimation accuracy of the particulate emission amount, and as a result, increase the NOx amount. It can prevent more reliably.

In the present invention, preferably, there is further provided target oxygen concentration determination means for determining a target oxygen concentration that eliminates the difference based on the oxygen concentration and the difference between the first discharge amount and the second discharge amount. Then, the EGR rate control means increases the EGR rate so that the oxygen concentration becomes the target oxygen concentration.
In the present invention configured as described above, the EGR rate is corrected so as to eliminate the difference between the first emission amount and the second emission amount, which corresponds to an increase in the NOx amount due to carbon adhesion or the like. As a result, the EGR rate can be increased by the amount to be increased. As a result, the actual amount of NOx can be set to an appropriate value, and the amount of discharged particulates can be prevented from excessively increasing. Further, the target oxygen concentration is determined such that the difference between the first emission amount and the second emission amount is eliminated, and the EGR rate is increased so that the oxygen concentration becomes this target oxygen concentration. It becomes easy to control the increase correction amount to an appropriate amount.

In the present invention, it is preferable to further include a particulate filter provided on the upstream side of the exhaust passage of the oxygen concentration detecting means and capable of collecting fine particles.
In the present invention configured as described above, since the particulate filter is provided on the upstream side of the exhaust passage of the oxygen concentration detecting means, it is possible to prevent fine particles from adhering to the oxygen concentration detecting means. Therefore, the deterioration of the detection accuracy of the oxygen concentration detection unit is prevented, and the estimation accuracy of the second emission amount by the second estimation unit can be increased.

  According to the present invention, it is possible to sufficiently optimize both the NOx emission amount and the particulate emission amount.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
First, an EGR control device for a diesel engine according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a diagram illustrating a configuration of a diesel engine to which an EGR control device according to the present embodiment is applied.
The engine 1 is a multi-cylinder diesel engine. A piston 4 is disposed in each cylinder of the cylinder block 2, and a combustion chamber 8 is formed between the piston 4 and the cylinder head 6. The cylinder head 6 is provided with a fuel injection valve 10. The fuel injection valve 10 is supplied with fuel from a common rail 11 containing high-pressure fuel and injects fuel into the combustion chamber 8.

An intake manifold 18 for introducing air from the air cleaner 12 through the intake passage 14 and the surge tank 16 is connected to the combustion chamber 8. The intake manifold 18 is opened and closed with respect to the combustion chamber 8 by an intake valve 20. The intake passage 14 is provided with an intercooler 22 and an intake throttle valve 24.
The combustion chamber 8 is connected to an exhaust manifold 26 for leading exhaust gas from the combustion chamber 8. The exhaust manifold 26 is opened and closed with respect to the combustion chamber 8 by an exhaust valve 28. An exhaust passage 30 is connected to the downstream side of the exhaust manifold 26, and an oxidation catalytic converter 32 and a particulate filter 34 for purifying the exhaust gas are provided in the exhaust passage 30. The engine 1 is provided with a turbocharger 36, and the compressor 36b provided in the intake passage 14 is rotated by the rotational force of the turbine 36a provided in the exhaust passage 30 to increase the intake pressure. Yes.

  Further, the engine 1 is provided with an EGR device 40 for returning a part of the exhaust gas in the exhaust passage 30 to the intake passage 14. The EGR device 40 controls the EGR rate, the EGR passage 42 that connects the exhaust passage 30 and the intake passage 14, the EGR cooler 44 that cools the exhaust gas that recirculates in the EGR passage 42 to increase the density, and the EGR rate. EGR valve 46. The EGR valve 46 is controlled by a control unit (ECU) 50.

The ECU 50 has an output signal related to the intake air amount A from the air flow sensor 52 provided in the intake passage 14 and an output related to the intake pressure P from the intake pressure sensor 54 provided downstream of the intake throttle valve 24 in the intake passage 14. Signal, an output signal related to the oxygen concentration λ from the O ₂ sensor 56 provided downstream of the particulate filter 34 in the exhaust passage 30, and an output related to the engine speed Ne from the engine speed sensor 58 provided in the cylinder block 2. Signal, an output signal related to the coolant temperature Tw from the coolant temperature sensor 60 provided in the cylinder head 6, an output signal related to the vehicle speed Vs from the vehicle speed sensor 62, an output signal related to the altitude H from the altitude sensor 64, and the accelerator opening. An output signal related to the accelerator opening θ from the sensor 66 is input. That. The ECU 50 determines the required fuel injection amount Q based on the accelerator opening degree θ.

Next, the contents of control by the ECU 50 will be described with reference to FIGS. FIG. 2 is a diagram showing a trade-off relationship between the NOx amount and the particulate emission amount that change depending on the control amount of the EGR rate, and FIG. 3 shows the EGR supply region and the EGR based on the engine speed and the required fuel injection amount. It is a map for determining a rate.
As shown in FIG. 1, the ECU 50 includes an EGR rate control unit 70 that controls the EGR device 40. Here, as shown in FIG. 2, when the EGR rate is increased, the NOx amount and the particulate emission amount are reduced by decreasing the combustion temperature and the NOx amount, while the particulate emission amount is increased and the EGR rate is increased. When it is decreased, there is a trade-off relationship in which the amount of discharged particulates decreases while the amount of NOx increases. In the present embodiment, an EGR rate (target EGR rate) that can optimize (balance) both the NOx amount and the particulate emission amount is determined by a map as shown in FIG. 70 basically determines the control amount of the EGR rate based on the map shown in FIG. FIG. 3 is a map in a substantially steady operation region of the vehicle.

In contrast to the EGR rate determined in FIG. 3, as described above, the actual EGR rate decreases from the target EGR rate and the NOx amount increases from the appropriate value due to variations in EGR rate, carbon adhesion, and the like. There is.
Therefore, in the present embodiment, as will be described in detail later, as shown in FIG. 2, the particulate discharge amount α estimated from the engine speed and the like without being influenced by the change in the EGR rate and the change in the EGR rate are shown. The particulate emission amount β estimated from the reflected oxygen concentration is obtained, and it is determined that the actual EGR rate is lower than the target EGR rate based on the difference between α and β, and the EGR rate is corrected. Yes.

  In the present embodiment, as shown in FIG. 1, the ECU 50 has a first particulate discharge amount estimation unit 72 that estimates the particulate discharge amount α, a second particulate discharge amount estimation unit 74 that estimates the particulate discharge amount β, and α. And β, and the fine particle discharge amount comparison / determination unit 76 that determines whether or not the actual EGR rate is reduced, and the EGR rate is increased and corrected to an appropriate value based on the difference between α and β. And a target oxygen concentration determination unit 78 for calculating a target oxygen concentration for increasing the control amount of the EGR rate by the EGR rate control unit 70 by the estimation units 72 and 74, the comparison determination unit 76, and the determination unit 78. Correction is made so that the actual EGR rate becomes an appropriate value.

Next, specific control contents regarding correction of the EGR rate by the EGR control device of the diesel engine of the present embodiment will be described with reference to FIGS.
FIG. 4 is a flowchart showing the contents of control by the EGR control device of the diesel engine according to the present embodiment, and FIG. 5 is a diagram for estimating the particulate emission amount based on the engine speed and the vehicle speed. 6 is a diagram for estimating the particulate discharge amount based on the oxygen concentration, and FIG. 7 is the same as FIG. 6 for determining the target oxygen concentration for correcting the increase in the EGR rate to an appropriate value. FIG. In the flowchart shown in FIG. 4, S represents each step.

First, as shown in FIG. 4, in S1, the engine speed Ne, the vehicle speed Vs, the oxygen concentration λ, the intake pressure P, the intake air amount A, and the accelerator opening degree θ are read. Further, the EGR amount is calculated from the relationship shown in FIG. Er is obtained, and the required fuel injection amount Q is obtained based on the accelerator opening θ.
Next, from S2 to S4, it is determined whether or not the operating region in which the particulate discharge amount can be accurately estimated, that is, the operating region in which combustion is stable.
Specifically, first, in S2, it is determined whether or not the vehicle speed Vs is equal to or higher than a predetermined vehicle speed. In S3, whether the change rate (acceleration) of the vehicle speed Vs is equal to or higher than 0 and equal to or lower than a predetermined rate, that is, the vehicle. Is in a steady operation state including a slow acceleration state, and in S4, it is determined whether or not it is in the EGR supply region. In S4, it is determined whether or not the engine is in the EGR supply region from the engine speed Ne and the required fuel injection amount Q read in S1 and the map shown in FIG.

In S2 and S3, when the vehicle speed Vs is equal to or higher than the predetermined vehicle speed and is in a steady operation state, it is considered that the combustion is stable. In S4, in the EGR supply region, EGR is considered to be stable. The rate needs to be controlled, and is considered to be a combustion stable region. Therefore, if all the conditions in S2 to S4 are satisfied, the process proceeds to steps S5 and below, and if not all the conditions in S2 to S4 are satisfied, the process does not proceed to steps S5 and below.
In addition to the determinations of S2 to S4, conditions such as that the coolant temperature Tw is equal to or higher than a predetermined temperature and that the altitude H at which the vehicle is traveling are equal to or lower than a predetermined altitude are satisfied, and these conditions are also satisfied. Thus, the fuel stable region may be determined.

  Next, in S5, the first particulate discharge amount estimation unit 72 (see FIG. 1) estimates the particulate discharge amount α. Specifically, using the diagram shown in FIG. 5, the particulate discharge amount α (g / rev) is estimated from the vehicle speed Vs and the engine speed Ne read in S1. The particulate discharge amount α is expressed in units (g / rev), “g” represents the weight of the particulate discharge amount, and “rev” represents the unit rotation of the engine. The vehicle speed Vs may be a value obtained from the engine speed Ne and the gear ratio.

Here, the diagram shown in FIG. 5 is experimentally predetermined for the case where the exhaust gas recirculation actually has the EGR rate shown in FIG. 3, and a plurality of lines are shown in accordance with the engine speed Ne. A figure (only a part is shown in FIG. 5) is defined. In this way, the particulate discharge amount α is estimated based on the vehicle speed Vs and the engine speed Ne, and an ideal value that is not influenced by the actual change in the EGR rate is estimated.
Note that the particulate discharge amount α estimated from the diagram shown in FIG. 5 may be further corrected by either or both of the intake pressure P and the required fuel injection amount Q. That is, the intake pressure P and the required fuel injection amount Q are increased due to an increase in the number of hills and occupants.

Next, in S6, the second particulate discharge amount estimation unit 74 (see FIG. 1) estimates the particulate discharge amount β. Specifically, the amount of particulate discharge β is estimated from the oxygen concentration λ read in S1 using an experimentally predetermined diagram shown in FIG. The particulate discharge amount β is expressed in units (g / exhaust gas kg), “g” represents the weight of the particulate discharge amount, and “exhaust gas kg” is the exhaust gas weight.
Here, when the EGR rate decreases, the particulate discharge amount decreases and the oxygen concentration λ increases (the air-fuel ratio shifts to the lean side). Therefore, according to the diagram shown in FIG. 6, the particulate discharge amount β is estimated as a value reflecting the actual change in the EGR rate.

Here, as described above, the O ₂ sensor 56 (see FIG. 1) is provided on the downstream side of the particulate filter 34 in the exhaust passage 30, so that adhesion of fine particles to the O ₂ sensor 56 can be prevented. I can do it. As a result, deterioration of the oxygen concentration detection accuracy of the O ₂ sensor 56 due to the adhesion of fine particles can be prevented, and the accuracy of estimating the fine particle discharge amount β by the second fine particle discharge amount estimation unit 74 can be increased.
The exhaust gas weight can be calculated by a known method from the intake air amount A (kg), EGR amount Er (kg) detected by the air flow sensor 52, and the value increases as the engine speed Ne increases. Becomes larger. The particulate discharge amount α (g / rev) can be converted into the same unit as the particulate discharge amount β (g / exhaust gas kg) based on the calculated exhaust gas weight.

Next, the process proceeds to S7, where the particulate discharge amount comparison / determination unit 76 (see FIG. 1) compares the particulate discharge amount α estimated in S5 with the particulate discharge amount β estimated in S6, and the actual EGR rate is calculated. It is determined whether or not the target EGR rate is lower than the target EGR rate. That is, when the EGR rate is reduced due to the carbon adhesion or the like described above, the particulate discharge amount β estimated in S6 is smaller than the particulate discharge amount α estimated in S5. It is determined that the rate is lower than the target EGR rate.
Specifically, the integrated values of the estimated values of the particulate discharge amount α and the particulate discharge amount β until YES is determined in S7 are compared, and the ratio of the integrated value of β to the integrated value of α (β / When α) is less than 0.75, it is determined that the EGR rate is actually decreasing. By using the integrated value as described above, it is possible to accurately determine whether or not the EGR rate has decreased. In this embodiment, the unit of the particulate discharge amount α is converted into a unit of the particulate discharge amount β for comparison.

If it is determined in S7 that the actual EGR rate has decreased, the process proceeds to S8, and the target oxygen concentration determining unit 78 (see FIG. 1) performs target oxygen for increasing the EGR rate to an appropriate value. Determine the concentration. Specifically, based on the current oxygen concentration λ (λb) read in S1 and the difference between the particulate discharge amount α and the particulate discharge amount β using the relationship shown in FIG. The target oxygen concentration λa is determined so that the difference disappears. That is, based on the idea that the actual EGR rate is reduced by the difference between the particulate discharge amount α and the particulate discharge amount β, the oxygen concentration λ is set by the amount corresponding to the difference between α and β. The target oxygen concentration λa is determined so that it becomes lower (the air-fuel ratio shifts to the rich side).
In the present embodiment, the difference between α and β is determined from the average values of the particulate discharge amount α and the particulate discharge amount β estimated until YES is determined in S7, so that the correction amount is appropriate. Value. In this embodiment, the unit of the particulate discharge amount α is converted into the unit of the particulate discharge amount β, and the difference between α and β is obtained.

  Next, in S9, the EGR rate control unit 70 (see FIG. 1) corrects the control amount of the EGR valve 46 to be increased with respect to the EGR rate determined in FIG. Specifically, in S9, the value of the EGR rate is gradually increased and the oxygen concentration λ is read, and the EGR rate is increased and corrected until the read oxygen concentration λ becomes the target oxygen concentration λa determined in S8. To do. Thus, if the EGR rate is increased so as to eliminate the difference between α and β, the actual EGR rate becomes a value close to the target EGR rate, and both the NOx amount and the particulate emission amount are optimized (balanced). )

As described above, according to the EGR control device for the diesel engine according to the present embodiment, the particulate emission amount α estimated without being influenced by the change in the EGR rate and the value reflecting the change in the EGR rate are estimated. Since the EGR rate is increased and corrected when the particulate discharge amount β is smaller than the particulate discharge amount α, respectively, the increase in the NOx amount due to the above-described carbon adhesion or the like is prevented. I can do it.
In this embodiment, since the particulate discharge amount α and the particulate discharge amount β are compared in the combustion stable region, particularly in a steady operation state, the estimation accuracy of the estimated value of the particulate discharge amount is increased, and the NOx amount is increased. Can be more reliably prevented.

Further, since the EGR rate is increased and corrected based on the difference between the particulate discharge amount α and the particulate discharge amount β, the EGR rate is increased by an amount corresponding to the increase in the NOx amount due to the above-described carbon adhesion or the like. As a result, the actual amount of NOx becomes an appropriate value, and the particulate discharge amount can be prevented from excessively increasing.
Therefore, according to the present embodiment, it is possible to optimize (balance) both the NOx amount and the particulate emission amount, and to optimize the emission performance of the diesel engine including the EGR device 40.

It is a figure which shows the structure of the diesel engine to which the EGR control apparatus by embodiment of this invention was applied. It is a diagram which shows the trade-off relationship between the NOx amount which changes with the control amount of an EGR rate, and the amount of particulate emission. It is a map for determining an EGR supply area and an EGR rate based on the engine speed and the required fuel injection amount. It is a flowchart which shows the control content by the EGR control apparatus of the diesel engine by this embodiment. It is a diagram for estimating the amount of particulate discharge based on engine speed and vehicle speed. It is a diagram for estimating fine particle discharge | emission amount based on oxygen concentration. FIG. 7 is a diagram similar to FIG. 6 for determining a target oxygen concentration for increasing and correcting the EGR rate to an appropriate value.

Explanation of symbols

1 diesel engine 14 intake passage 30 exhaust passage 32 oxidation catalyst converter 34 particulate filter 40 EGR device 42 EGR passage 44 EGR valve 50 control unit 56 O ₂ sensor 58 engine speed sensor 70 EGR rate control unit 72 first particulate emission amount estimation Unit 74 second particulate discharge amount estimation unit 76 particulate discharge amount comparison determination unit 78 target oxygen concentration determination unit

Claims (4)

An oxygen concentration detecting means disposed in the exhaust passage of the engine for detecting the oxygen concentration;
EGR rate control means for recirculating a part of the exhaust gas to the intake passage in the stable combustion operation region and controlling the EGR rate;
An engine speed detecting means for detecting the engine speed;
A vehicle speed detecting means for detecting a vehicle speed, and an EGR control device for a diesel engine,
First estimation means for estimating a particulate emission amount discharged from the engine based on at least the engine speed as a first emission amount;
Second estimation means for estimating a particulate emission amount discharged from the engine based on the oxygen concentration as a second emission amount,
The EGR rate control means increases the EGR rate when the ratio of the second emission amount to the first emission amount falls below a predetermined value less than 1 in the stable combustion operation region. EGR control device.   The diesel engine EGR control device according to claim 1, wherein the stable combustion operation region is a steady operation region. Furthermore, based on the oxygen concentration and the difference between the first discharge amount and the second discharge amount, there is a target oxygen concentration determination means for determining a target oxygen concentration that eliminates the difference,
The EGR control device for a diesel engine according to claim 1 or 2, wherein the EGR rate control means increases the EGR rate so that the oxygen concentration becomes the target oxygen concentration.   The diesel engine EGR control device according to any one of claims 1 to 3, further comprising a particulate filter provided upstream of the exhaust passage of the oxygen concentration detection means and capable of collecting particulates.

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