JP2010112192A - Exhaust emission purifying apparatus for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce an emission amount of an emission component such as HC to the atmosphere while suppressing the deterioration of fuel consumption caused by a rich spike when a catalyst temperature is high. <P>SOLUTION: An exhaust emission purifying apparatus includes a catalyst 32 for purifying exhaust emission having an exhaust emission function installed in an exhaust emission passage 31 of an internal combustion engine 1, a catalyst temperature detecting means 66 for detecting a temperature of the catalyst 32, an activation determination means 51 for determining whether or not the catalyst 32 is activated based on detected values of the catalyst temperature detecting means 66, and a control means 51 for selecting and executing either an exhaust emission temperature rising mode which gives priority to a raising exhaust emission temperature as an operating mode of an engine, or an exhaust emission component reducing mode which gives priority to a reducing exhaust emission component based on a determination result of the activation determination means 51. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to control of an internal combustion engine, and more particularly to control for early activation of an exhaust purification catalyst while preventing a decrease in exhaust performance.

  A catalyst for purifying exhaust gas is provided in the exhaust passage of the internal combustion engine. Since the catalyst does not exhibit a sufficient purifying action unless the temperature exceeds the activation temperature, it is necessary to activate the catalyst immediately after starting the engine in order to ensure the exhaust performance at the time of cold start.

As a means for activating the catalyst, a method is known in which the exhaust gas temperature is raised by making the air-fuel ratio richer than during normal operation (rich spike). In Patent Literature 1, when an oxidation catalyst that traps and oxidizes unburned carbide (HC) discharged from a diesel engine is activated early, the calorific value due to oxidation of HC in the oxidation catalyst is used, and the calorific value due to oxidation. The idea of reducing the amount of increase in exhaust temperature, that is, the degree of enrichment, is disclosed by that amount. According to this, it is possible to reduce the HC emission amount while suppressing the deterioration of fuel consumption by reducing the rich spike amount.
JP 2005-2852 A

  However, the method of Patent Document 1 has a problem that when the amount of HC trapped in the oxidation catalyst reaches the HC adsorption limit, the amount of HC released into the atmosphere (TPHC) increases.

  Therefore, an object of the present invention is to provide an exhaust emission control device that reduces the exhaust amount of exhaust components such as HC into the atmosphere while suppressing deterioration of fuel consumption due to rich spikes when the temperature of the catalyst is raised.

  An exhaust purification device for an internal combustion engine according to the present invention includes an exhaust purification catalyst having an exhaust purification function interposed in an exhaust passage of the internal combustion engine, catalyst temperature detection means for detecting the temperature of the catalyst, and detection of the catalyst temperature detection means. Activation determining means for determining whether the catalyst is activated based on the value. Then, based on the determination result of the activation determination means, select either the exhaust temperature raising mode that prioritizes raising the exhaust temperature or the exhaust component reduction mode that prioritizes reducing exhaust components as the engine operation mode Control means to be executed.

  According to the present invention, since the operation mode is switched according to the active state of the catalyst, for example, the purification performance has hysteresis with respect to the temperature as in the case of an oxidation catalyst, and after the catalyst is activated, compared with the time of temperature increase. If the purification performance can be exhibited even at a low exhaust temperature, the temperature is not increased unnecessarily, and the deterioration of the fuel consumption performance can be suppressed. Furthermore, by executing the exhaust component restriction mode, the amount of exhaust components discharged into the atmosphere can be reduced.

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

  FIG. 1 is a diagram illustrating a configuration of a diesel engine to which the present embodiment is applied.

  An air flow meter 12 and an intake air temperature sensor 65 are installed in the intake passage 11, the intake air amount is measured by the air flow meter 12, and the intake air temperature is measured by the intake air temperature sensor 65. The intake air that has passed through the air flow meter 12 flows into the surge tank 13 and is distributed to each cylinder in the manifold portion. An intake throttle valve 14 and an EGR valve 42 that operate in response to a signal from an electronic control unit (hereinafter referred to as “ECU”) 51 are set upstream of the surge tank 13. The intake throttle valve 14 controls the intake air amount, and the EGR valve 42 controls the EGR amount that recirculates from an exhaust passage 31 described later.

  An injector 21 is installed on the cylinder head of the engine 1 so as to face the upper center of the combustion chamber. The fuel delivered by a fuel pump (not shown) is supplied to the injector 21 at a predetermined pressure via the common rail 22 and is injected into the combustion chamber by the injector 21.

  In the exhaust passage 31, an HC adsorption catalyst 32 is installed downstream of the manifold portion. HC is removed from the exhaust gas by the HC adsorption catalyst 32, for example, after the start of the engine 1 in which the HC adsorption catalyst 32 is in a low temperature state. When the operation is continued and the exhaust gas temperature rises, NOx in the exhaust gas reacts with HC adsorbed on the HC adsorption catalyst 32, NOx is reduced, and HC is processed. A catalyst temperature sensor 66 for detecting the catalyst temperature is installed in the HC adsorption catalyst 32, and an exhaust gas temperature sensor 61 for detecting the exhaust gas temperature is installed downstream of the HC adsorption catalyst 32.

  The exhaust passage 31 is connected to the intake passage 11 by an EGR pipe 41. The EGR pipe 41 is provided with an EGR valve 42 that operates in response to a signal from the ECU 51, and an appropriate amount of exhaust gas according to the opening of the EGR valve 42 is recirculated to the intake passage 11.

  In addition to the intake air amount detection signal of the air flow meter 12 and the exhaust gas temperature detection signal of the exhaust temperature sensor 61, the ECU 51 includes a coolant temperature detection signal from the water temperature sensor 62, a crank angle detection signal from the sensor 63 (the ECU 51 Based on this, the engine speed Ne is calculated.), The accelerator opening detection signal from the sensor 64, the fuel pressure detection signal from the fuel pressure sensor 65, the intake air temperature detection signal from the intake air temperature sensor 65, and the catalyst temperature sensor 66. The catalyst temperature detection signal is input.

  FIG. 2 is a flowchart of the catalyst temperature increase control executed by the ECU 51.

  In step S100, the bed temperature Tbed of the oxidation catalyst 32 is read based on the detection signal of the catalyst temperature sensor 66.

  In step S101, it is determined whether or not the bed temperature Tbed is equal to or lower than the first activation temperature T1. If the temperature is equal to or lower than the first activation temperature T1, the process proceeds to step S102, and if not, the process proceeds to step S108. The first activation temperature T1 is an activation temperature when the oxidation catalyst 32 is activated by raising the temperature from the inactive state.

  In step S102, it is determined whether or not the bed temperature Tbed is equal to or lower than the second activation temperature T2. If the temperature is equal to or lower than the second activation temperature T2, the process proceeds to step S103. Otherwise, the process proceeds to step S105. The second activation temperature T2 is a lower limit temperature of the active region of the oxidation catalyst 32 that has already been activated. As shown in FIG. 3, the purification performance of the oxidation catalyst 32 has hysteresis with respect to temperature, and the first activation temperature T1 is lower than the second activation temperature T2.

  In step S103, the first flag Flg1 indicating whether or not it is in the active state is set to zero, that is, inactive.

  In step S104, a temperature raising mode to be described later is executed.

  In step S105, it is determined whether or not the first flag Flg1 is zero. If it is zero (inactive state), the process proceeds to step S103. If it is one (active state), the process proceeds to step S106.

  In step S106, mode selection control described later is executed.

  In step S107, it is determined whether or not the second flag Flg2 is zero. The second flag Flg is an E.D. O. Since it is 1 in the E reduction mode and zero in the temperature raising mode, the process proceeds to step S104 when it is zero, and to step S109 when it is 1.

  On the other hand, if the bed temperature Tbed is higher than the first activation temperature T1 in step S101, the process proceeds to step S108, the first flag Flg is set to 1, and the process proceeds to step S109.

  Next, the temperature raising mode executed in step S104 will be described.

  FIG. 4 is a flowchart showing a control routine in the temperature raising mode.

  In step S200, the target main injection timing tMainIT of fuel is set to tMainIT1 that is retarded from the injection timing in the warm-up state.

  In step S201, the target air-fuel ratio tLamb is set to Lamb1 that is richer than the lean air-fuel ratio in the warm-up state.

  In step S202, a target intake throttle valve opening TVO calculation described later is executed.

  In step S203, a target EGR valve opening tAEGR calculation described later is executed.

  Note that it is not always necessary to both enrich the target air-fuel ratio and retard the main injection timing tMainIT, and at least one of them may be performed. Further, instead of retarding the main injection timing tMainIT, so-called post-injection, in which fuel injection is performed again after main injection, may be performed.

  Here, the target intake throttle valve opening TVO calculation executed in step S202 and the target EGR valve opening tAEGR calculation executed in step S203 will be described with reference to FIGS.

  FIG. 5 is a flowchart of the target intake throttle valve opening TVO calculation. This routine is executed every 20 ms, for example.

  In step S300, the engine speed Ne, the fuel injection amount Qf, and the target excess air ratio tLamb are read.

  In step S301, the target intake air amount tQac is calculated by equation (1).

    tQac = tLamb × 14.6 × Qf (1)

  In step S302, the target filling rate tQh0 is calculated by equation (2).

tQh0 = tQac ÷ (VCE # × ROU #) (2)
VCE # is the displacement per cylinder, and ROU # is the air density.

  In step S303, the table in FIG. 7 is searched based on the target filling rate tQh0, and the target air flow rate ratio tADNV is read out.

  In step S304, the target opening area tAtvo is calculated by the following equation (3) based on tADNV and Ne. The total displacement is VOL #.

    tAtvo = tADNV × Ne × VOL # (3)

  In step S305, the table shown in FIG. 8 is retrieved by tAtvo, and the target intake throttle valve opening TVO is set.

  FIG. 6 is a flowchart of the target EGR valve opening tAEGR calculation. This routine is executed every 20 ms, for example.

  In S400, the engine speed Ne, the fuel injection amount Qf, and the target intake air amount tQac are read. In S401, the map shown in FIG. 9 is searched using Ne and Qf, and the target EGR rate Megr is read. In S402, the target EGR gas amount tQec is calculated by the following equation (4) based on tQac and Megr. In S403, the table shown in FIG. 10 is retrieved by tQec, and the target EGR valve opening tAEGR is set.

    tQec = tQac × Megr (4)

  Next, the E.D. O. The E reduction mode will be described.

FIG. O. In step S500 showing the control routine in the E reduction mode, the target main injection timing tMainIT of fuel is set to tMainIT2 which is a value on the advance side of the target main injection timing tMainIT1 set in step S200 of FIG.

  In step S501, the target air-fuel ratio tLamb is set to Lamb2, which is leaner than Lamb1 set in step S201 of FIG.

  It should be noted that the target main injection timing tMainIT and the target air-fuel ratio tLamb set in steps S500 and S501 are such that the exhaust gas temperature becomes such that the HC emission amount decreases based on the HC emission weight calculated during mode selection control described later. Set to.

  Note that it is not always necessary to perform both leaning of the target air-fuel ratio and advancement of the main injection timing, and at least one of them may be performed.

  Steps S502 and S503 are the same as steps S202 and S203 in FIG.

  Next, the mode selection control executed in step S106 in FIG. 2 will be described.

  FIG. 12 is a flowchart showing a control routine of mode selection control executed in step S106 of FIG. In this control, when the bed temperature Tbed is between T2 and T1, the temperature rise control or the E.P. O. This is for selecting which one of the E reduction control is performed.

  In step S600, the bed temperature Tbed of the oxidation catalyst 32 is read based on the detection signal of the catalyst temperature sensor 66.

  In step S601, the purification rate η of the oxidation catalyst 32 is estimated based on the bed temperature Tbed. As an estimation method, an engine operation test is performed in advance, the relationship between the bed temperature Tbed and the purification rate η is mapped, and this is searched.

  In step S602, the engine speed NE, torque Trq, and intake air amount rQac are read. The engine speed NE is read based on the crank angle sensor 63 and the intake air amount rQac is read based on the detection signal of the air flow meter 12. The torque Trq is calculated based on the fuel injection amount.

  In step S603, E. is the amount of exhaust gas discharged from the engine 1. O. Detect gas emissions and HC concentration in exhaust gas. Further, the catalyst space velocity SV is calculated.

  E. O. The gas discharge amount is calculated by adding the intake air amount Qac and the fuel injection amount Qf (gas flow rate converted value after combustion). As for the HC concentration, an engine operation test is performed in advance to grasp the HC concentration under each operation condition, and the information is stored in a map and searched. It may be detected using an oxygen concentration sensor. These E.I. O. The HC emission weight in the exhaust is calculated by multiplying the gas emission amount and the HC concentration.

  The catalyst space velocity SV is a passing gas amount per fixed time with respect to the catalyst capacity, and is calculated by the equation (5).

SV = rQac / Vcat (5)
Vcat: catalyst capacity

  In step S604, the reaction rate is estimated by searching the map of FIG. 13 using the catalyst space velocity SV and the bed temperature Tbed. FIG. 13 is a reaction rate estimation map created in advance based on experiments or the like. The vertical axis represents the bed temperature Tbed and the horizontal axis represents the catalyst space velocity SV. The reaction rate increases as the SV decreases and increases as Tbed, and decreases as the SV increases as the SV decreases.

  In step S605, the reaction rate and E.E. O. The mode determination flag Flg2 is set by searching the map of FIG. 14 using the gas discharge amount. In FIG. O. Emission gas, horizontal axis is reaction rate, low reaction rate, low to medium E. O. For gas emissions, see E. O. E. The reduction mode (Flg2 = 1), otherwise the temperature increase mode (Flg2 = 0).

  Using the flag set here, the determination in step S107 of FIG. O. E. Perform one of the reduction modes.

  According to the temperature raising control described above, the temperature raising mode is executed at the time of cold start to quickly raise the temperature of the oxidation catalyst 32. O. E. A reduction mode is executed to prevent an increase in HC emissions. Since the purification performance of the oxidation catalyst 32 has a hysteresis with respect to temperature, once it reaches the activation temperature T1, the higher temperature side becomes the active region from T2 lower than T1. Therefore, when the temperature reaches T2 to T1 after the activation temperature T1 is reached, E.I. O. In order to reduce the HC emission amount, the temperature increasing mode or O. E. Select and execute one of the reduction modes.

  FIG. O. It is a figure which shows the relationship between HC discharge | emission amount and exhaust temperature, and excess air ratio (lambda). Note that the heating mode and E.I. O. E. As described in the description of the reduction mode, the main combustion injection timing is relatively retarded when the excess air ratio λ is rich, and relatively advanced when lean.

  In both cases where the excess air ratio λ is rich and lean, the E.C. O. HC emissions increase. However, at a temperature Ta or lower, the excess air ratio λ is E.E. O. When the amount of HC emission is small and the temperature is higher than the temperature Ta, conversely, when the excess air ratio λ is rich, the E.C. O. HC emissions are reduced.

  Thus, E.I. O. E. In the reduction mode, control is performed so that the exhaust temperature is equal to or lower than Ta and the excess air ratio λ is lean, and in the temperature increase mode, control is performed so that the exhaust temperature is higher than Ta and the excess air ratio λ is rich. Thus, the catalyst temperature can be raised without excess or deficiency without deteriorating the exhaust performance. In addition, since the hysteresis of the purification rate with respect to the temperature is taken into consideration, the temperature is not increased unnecessarily, and thereby the fuel efficiency is not deteriorated.

  As described above, according to the present embodiment, the following effects can be obtained.

  (1) Based on whether or not the oxidation catalyst 32 is activated, the exhaust temperature raising mode or E.E. O. E. Since any one of the reduction modes is selected and executed, it is possible to suppress deterioration in fuel consumption performance due to useless temperature rise, and to reduce the amount of HC emissions into the atmosphere.

  (2) The temperature increase mode is selected from the start of the engine until the oxidation catalyst 32 is activated, and within the active region once activated, the temperature rises based on at least one of the purification performance of the oxidation catalyst 32 or the HC emission amount. Temperature mode or E.I. O. E. Since one of the reduction modes is selected, the oxidation catalyst 32 can be activated early. Furthermore, the exhaust component discharged from the engine 1 can be adjusted to an amount corresponding to the purification performance of the oxidation catalyst 32.

  (3) The temperature raising mode includes enrichment of the excess air ratio that changes the excess air ratio in the rich direction, retarded injection timing that changes the main injection timing of the fuel in the retarded direction, and post-injection that injects fuel after the main injection. The exhaust component reduction mode is an operation mode in which at least one of the above is performed, and the exhaust component reduction mode is the lean air excess ratio that changes the excess air ratio in the lean direction, and the injection timing that changes the main injection timing of the fuel in the advance direction. This is an operation mode in which at least one of advancement is performed. Thereby, the oxidation catalyst 32 can be activated at an early stage without deteriorating the exhaust performance.

  The present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made within the scope of the technical idea described in the claims. For example, even in a configuration provided with a NOx purification catalyst such as a NOx occlusion reduction type catalyst or a NOx direct reduction type catalyst in place of the oxidation catalyst 32, a similar temperature increase mode and E.P. O. By switching the E reduction mode, it is possible to raise the temperature of the NOx purification catalyst while reducing the NOx emission amount. However, E.I. O. E. The excess air ratio λ in the reduction mode is made rich unlike the case of the oxidation catalyst 32.

It is a block diagram of the system to which this embodiment is applied. It is a flowchart which shows the control routine for catalyst temperature rising. It is a figure which shows the relationship between a purification rate and catalyst temperature. It is a flowchart of temperature rising mode control. It is a flowchart of target intake throttle valve opening calculation. It is a flowchart of target EGR valve opening calculation. It is a target air flow rate ratio tADNV table. It is a target intake throttle valve opening degree table. It is a target EGR rate table. It is a target EGR valve opening degree table. E. O. It is a flowchart of E reduction mode control. It is a flowchart of mode selection control. It is a reaction rate map. It is a map for mode determination flag setting. E. O. It is a figure which shows the relationship between HC discharge | emission amount and exhaust temperature, and excess air ratio (lambda).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 11 Intake passage 12 Air flow meter 13 Surge tank 14 Intake throttle valve 21 Injector 22 Common rail 31 Exhaust passage 32 Oxidation catalyst 41 EGR passage 42 EGR valve 51 Electronic control unit (ECU)
61 exhaust gas temperature 62 water temperature sensor 63 crank angle sensor 64 accelerator opening sensor 65 intake air temperature sensor 66 catalyst temperature sensor

Claims (6)

An exhaust purification catalyst interposed in an exhaust passage of the internal combustion engine and having an exhaust purification function;
Catalyst temperature detecting means for detecting the temperature of the catalyst;
Activation determining means for determining whether or not the catalyst is activated based on a detection value of the catalyst temperature detecting means;
Based on the determination result of the activation determination means, the engine operation mode is selected from either an exhaust temperature raising mode that prioritizes raising the exhaust temperature or an exhaust component reduction mode that prioritizes reducing exhaust components. Control means to be executed,
An exhaust emission control device for an internal combustion engine, comprising:   The control means selects the temperature raising mode from the start of the engine until the exhaust purification means is activated, and is based on at least one of the purification performance of the catalyst or the exhaust component within the active region once activated. 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein either the temperature raising mode or the exhaust component reduction mode is selected.   The exhaust purification device for an internal combustion engine according to claim 1 or 2, wherein the catalyst is an oxidation catalyst. The temperature increase mode includes an excess air ratio enrichment that changes the excess air ratio in the rich direction, a retarded injection timing that changes the main injection timing of the fuel in the retarded direction, and a post-injection that injects fuel after the main injection. An operation mode in which at least one of them is performed;
The exhaust component reduction mode is an operation mode in which at least one of lean air excess ratio that changes the excess air ratio in the lean direction and injection timing advance that changes the main injection timing of the fuel in the advance direction is performed. An exhaust emission control device for an internal combustion engine according to claim 3.   The exhaust gas purification apparatus for an internal combustion engine according to claim 1 or 2, wherein the catalyst is a NOx purification catalyst. The temperature increase mode includes an excess air ratio enrichment that changes the excess air ratio in the rich direction, a retarded injection timing that changes the main injection timing of the fuel in the retarded direction, and a post-injection that injects fuel after the main injection. An operation mode in which at least one of them is performed;
The exhaust component reduction mode includes at least one of enrichment of the excess air ratio, retarding the injection timing for changing the main injection timing of the fuel in the retarded direction, and increasing EGR gas for increasing the EGR gas amount. 6. The exhaust emission control device for an internal combustion engine according to claim 5, wherein the operation mode is an operating mode.

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