JP4635913B2 - Engine exhaust purification system - Google Patents

Description

  The present invention relates to an exhaust emission control device for an engine, and more particularly, to a technique for preventing a deterioration in exhaust performance by suppressing a decrease in the activity of a catalyst caused by low-temperature exhaust flowing when the engine is restarted.

The following techniques for avoiding deterioration of exhaust performance due to repeated stop and restart of the engine are known. That is, in an engine that constitutes a hybrid drive source of a hybrid vehicle together with a motor generator, the deterioration of the exhaust purification catalyst is detected, and whether or not intermittent operation that repeats stopping and restarting of the engine is repeated is determined based on the detected deterioration. In accordance with the determination result, the engine stop (which is a precondition for restart) is prohibited, and the operation after restart is forcibly maintained (Patent Document 1). This technology is not limited to an engine that constitutes a composite drive source, but can also be applied to an engine that constitutes a drive source of a so-called idle stop vehicle that performs intermittent operation of the engine according to the state of the vehicle.
Japanese Patent Laying-Open No. 2004-124827 (paragraph numbers 0085 to 0088)

  The above-mentioned technology for prohibiting intermittent operation of the engine in accordance with deterioration of the exhaust purification catalyst is an oxygen-excess gas that is swept from the engine during the idling period after the restart until normal ignition and combustion are performed in the hybrid vehicle. In addition, in the idle stop vehicle, after the engine is restarted, it is possible to avoid the occurrence of poor purification of exhaust harmful components discharged from the engine, which tends to become unstable after restarting. That is, according to this technique, it is possible to avoid the progress of catalyst deterioration due to intermittent operation of the engine and the accompanying deterioration of exhaust performance (paragraph numbers 0007 to 0010 of the aforementioned Patent Document 1).

  Recently, a hybrid vehicle that employs a diesel engine as a mechanical drive source has been attracting attention as a carbon dioxide reduction effect that can be expected to be as high as that of a fuel cell vehicle. In this hybrid vehicle, the exhaust of the diesel engine is inherently low temperature, and the temperature of the catalyst does not rise as high as in the case of using a gasoline engine during engine operation. After the engine is cooled and restarted, the catalyst is cooled by the flow of this low-temperature exhaust gas, so that there is a problem that the exhaust performance is deteriorated due to the inactivation of the catalyst. Such a problem of catalyst deactivation due to exhaust cooling is not limited to a diesel engine type but can be a problem even in a hybrid vehicle employing a gasoline engine. However, in the gasoline engine type, the catalyst is kept at a high temperature during engine operation, and high-temperature exhaust gas flows into the catalyst immediately after restarting.

  The present invention suppresses a decrease in the activity of a catalyst in an engine, particularly in a diesel engine whose exhaust temperature is relatively low, due to the exhaust gas cooled in the exhaust pipe while the engine is stopped flowing in along with the restart of the engine. The purpose is to avoid deterioration of exhaust performance.

  The present invention provides an engine exhaust purification device. An apparatus according to the present invention includes an exhaust purification catalyst installed in an exhaust passage, detects engine restart, and responds to detection of restart when the restart is detected. The catalyst is forcibly heated.

  According to the present invention, when the restart of the engine is detected, the catalyst is forcibly heated, so that the exhaust that has remained in the upstream of the catalyst since the previous engine stop and the cooled exhaust gas accompanies the restart. The decrease in the activity of the catalyst due to the inflow can be suppressed, and the active state of the catalyst, that is, the exhaust performance can be maintained after the restart. The present invention is preferably applied to a diesel engine, particularly a diesel engine constituting a composite drive source such as a vehicle together with an electric drive source.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows a configuration of a power transmission system of a hybrid vehicle to which a diesel engine (hereinafter simply referred to as “engine”) 1 according to an embodiment of the present invention is applied. The dotted line indicates the electrical coupling between the elements. The power transmission system includes an engine 1 as a mechanical drive source and two motor generators 2 and 3 as electric drive sources. The motor generators 2 and 3 both function as an electric motor and serve as a generator. Combined with the functions. The engine 1 and the motor generators 2 and 3 constitute a parallel type composite drive source.

  In this power transmission system, the crankshaft of the engine 1 and the rotor of the motor generator 2 are directly connected, and the rotors of the motor generators 2 and 3 are connected to each other via the continuously variable transmission 4. The continuously variable transmission 4 includes an electromagnetic clutch 4a, and connection and disconnection of the engine 1 (and the motor generator 2) with respect to the wheels 6 and 6 are switched by the electromagnetic clutch 4a. When the output of the motor generator 3 and the electromagnetic clutch 4a are engaged, the outputs of the engine 1 and the motor generators 2 and 3 are transmitted to the wheels 6 and 6 through the differential gear 5 to propel the vehicle. The motor generator 2 receives the output from the engine 1 and operates as a generator. On the other hand, when the engine 1 is started (including when it is restarted), the motor generator 2 receives electric power from the battery 81 and operates as an electric motor. 1 cranking is performed. On the other hand, the motor generator 3 receives electric power from the battery 81 and operates as an electric motor to generate a driving force of the vehicle when traveling mainly in a low load region, while operating as a generator during deceleration and braking energy. Is used to generate electricity. The electric power generated by the motor generators 2 and 3 is used for charging the battery 81. The operation of the motor generators 2 and 3 and the switching between engagement and disengagement of the electromagnetic clutch 4a are performed based on a command signal from a hybrid control module (hereinafter referred to as “HCM”) 41 configured as an electronic control unit. The HCM 41 is connected to an engine control module 51 to be described later, and exchanges control information with the engine control module 51.

FIG. 2 shows the configuration of the engine 1. The engine 1 is a sub-chamber type diesel engine and is employed as a vehicle drive source in a high load range. The engine 1 may be a direct injection type.
An air cleaner (not shown) is attached to the introduction portion of the intake passage 11, and dust in the intake air is removed by the air cleaner. A compressor 12a of a turbocharger 12 is installed in the intake passage 11, and the intake air is compressed and sent out by the compressor 12a. The compressed intake air flows into the surge tank 13 and is distributed to each cylinder at the manifold portion.

  In the engine body, a fuel injection valve 21 is installed in the cylinder head for each cylinder. In each cylinder, the fuel injection valve 21 is installed facing a sub chamber formed in the cylinder head, and a command signal from an engine control module (hereinafter referred to as “ECM”) 51 configured as an electronic control unit. Operates based on. The fuel delivered by a fuel pump (not shown) is supplied to the fuel injection valve 21 through the common rail 22 and is injected into the sub chamber by the fuel injection valve 21. In the present embodiment, a glow plug (not shown) is installed facing the sub chamber mainly for stable ignition at the cold start.

  In the exhaust passage 31, a turbine 12b of the turbocharger 12 is installed downstream of the manifold portion. Exhaust gas generated by the combustion is discharged into the exhaust passage 31, and the turbine 12b is driven by the exhaust gas, whereby the compressor 12a rotates. A NOx trap catalyst 32 and a diesel particulate filter 33 are installed downstream from the turbine 12b in order from the upstream side. The NOx trap catalyst 32 traps nitrogen oxide (that is, NOx) in the exhaust gas when the air-fuel ratio of the exhaust gas is leaner than the theoretical value, while the rich air-fuel ratio is lower than the theoretical value. It has the property of releasing trapped NOx when it is in a neutral state. Along with the release of NOx from the NOx trap catalyst 32, the released NOx is purified by the reducing components in the exhaust. On the other hand, the diesel particulate filter 33 collects particulates in the exhaust and removes them from the exhaust. In the present embodiment, an oxidation catalyst component (for example, a noble metal such as Pt) is supported on the NOx trap catalyst 32 and has an oxidation function. The hydrocarbons and carbon monoxide in the exhaust gas on the NOx trap catalyst 32. Can be purified. In addition to the NOx trap catalyst 32, an oxidation catalyst component may be supported on the diesel particulate filter 33. The exhaust of the engine 1 passes through these exhaust purification devices and is then released into the atmosphere.

  The exhaust passage 31 is connected to the intake passage 11 (here, the surge tank 13) by an EGR pipe 35, and the exhaust gas before flowing into the turbine 12b is recirculated to the intake passage 11 through the EGR pipe 35. An EGR valve 36 is interposed in the EGR pipe 35, and the flow rate of exhaust gas recirculated by the EGR valve 36 is controlled. The opening degree of the EGR valve 36 is controlled by an actuator 37.

  The HCM 41 includes a signal from the accelerator sensor 61 that detects the amount of depression of the accelerator pedal, a signal that indicates whether the power is turned on or off from the start key 62, and a shift sensor that detects the shift lever position. 63, a signal indicating on / off of the brake from the brake switch 64, a signal from the vehicle speed sensor 65 for detecting the vehicle speed, a signal from the battery sensor 66 for detecting the remaining capacity of the battery 81, and the like are input. The The HCM 41 executes a predetermined calculation based on the input signal, generates command signals for the motor generators 2, 3 and the continuously variable transmission 4, and generates a start / stop command and an output control command for the engine 1.

  On the other hand, the ECM 51 detects a signal for each unit crank angle or reference crank angle generated by the crank angle sensor 67 (the ECM 51 calculates the rotational speed NE of the engine 1 based on this), and detects the temperature of the engine coolant. A signal from the cooling water temperature sensor 68 to detect, a signal from the catalyst temperature sensor 69 to detect the temperature of the NOx trap catalyst 32, and the temperature in the exhaust pipe upstream of the NOx trap catalyst 32 (downstream of the turbine 12b in this embodiment). A signal from the exhaust temperature sensor 70 to be detected, a signal from the filter temperature sensor 71 to detect the temperature of the diesel particulate filter 33, a signal from the fuel pressure sensor 72 to detect the pressure in the common rail 22, and the like are input. The ECM 51 executes a predetermined calculation based on the input signal and a command from the HCM 41 and generates a command signal for an engine control device such as the fuel injection valve 21. In particular, when the engine 1 is restarted, the ECM 51 performs the following start control in order to suppress deterioration in exhaust performance due to a decrease in the activity of the NOx trap catalyst 32 (specifically, the oxidation catalyst component carried on the catalyst 32). In practice, the fuel component content of the exhaust gas flowing into the catalyst 32 is increased and this is forcibly heated.

  In this embodiment, the start command of the engine 1 is generated by the HCM 41 during acceleration when the accelerator pedal is greatly depressed during traveling by the motor generator 3 in a low load range, and for long-term traveling by the motor generator 3. Is emitted at the time of forced charging or the like when the battery 81 is discharged and the remaining capacity is reduced to a predetermined amount. When the start command is issued, the engine 1 starts as follows. The remaining heat of the glow plug is performed and the engine 1 is cranked by the motor generator 2. After the cranking speed of the engine 1 reaches a stable range by this cranking, the fuel supply is started and the complete explosion is achieved. The supply of fuel at the time of starting is performed only by the fuel injection valves 21 of some cylinders, or by suppressing the fuel injection amount to be small, thereby suppressing the occurrence of vibration associated with the starting of the engine 1.

Hereinafter, control performed by the ECM 51 will be described with reference to flowcharts.
FIG. 3 is a flowchart of the start control routine. This routine is started when the power is turned on by operating the start key 62, and then executed every predetermined time.
In S101, it is determined whether or not an activity determination flag Flag described later is 0. This Flag is normally set to 0, and the NOx trap catalyst 32 has already been deactivated when the engine 1 is restarted by the processing after S102, or is in an active state at the time of restart. It is set to 1 when it is estimated that the activity decreases due to the inflow of exhaust gas, leading to inactivation. When the flag is 0, the process proceeds to S102, and when the flag is 1, the process proceeds to S107.

In S102, it is determined whether a start command has been input. The start command is issued by the HCM 41 as described above. When the start command is input, the process proceeds to S103, and when it is not input, this routine is terminated.
In S103, the coolant temperature TW is read, and it is determined whether or not the read TW is equal to or greater than a predetermined value TW1 for determining that the current start corresponds to a so-called restart. Instead of the cooling water temperature, an elapsed time from the previous engine stop may be adopted, and based on this, it may be determined whether or not the engine is restarted. When it is equal to or greater than TW1, not so much time has elapsed since the previous engine stop, and the process proceeds to S104 as a restart. On the other hand, when it is smaller than TW1, it is determined that the cooling of the engine 1 and the catalyst 32 has sufficiently progressed due to the long-term stop, and this routine is ended. In this case, in the fuel injection control routine, normal starting increase control (in the cold start, the engine 1 is warmed up and the activation of the catalyst 32 is promoted by increasing the fuel injection amount).

In S104, the internal temperature of the catalyst 32 (hereinafter referred to as “catalyst temperature”) Tbed is read. In the present embodiment, the catalyst temperature sensor 69 is installed in the catalyst 32 such that the side surface of the outer shell penetrates from the outside.
In S105, it is determined whether or not the read Tbed is equal to or less than a predetermined value Tbed1 indicating the activation lower limit temperature of the catalyst 32. When it is equal to or less than Tbed1, the process proceeds to S106, and when it is greater than Tbed1, the process proceeds to the activity decrease estimation unit of this routine shown in FIG. Note that Tbed1 corresponds to the “first temperature” of the present invention, and is an activity determination temperature for determining that the activity of the catalyst 32 has been completed in the normal startup increase control at the cold start. Adopted.

In S106, assuming that the catalyst 32 is in an inactive state at the time of restart, the activation determination flag Flag is set to 1, and control for forcibly heating the catalyst 32 is performed.
When it is determined in S101 that the activation determination flag Flag is 1, in S107, the catalyst temperature Tbed is read.
In S108, it is determined whether or not the read Tbed is equal to or larger than a predetermined value Tbed2 larger than the previous Tbed1. When it is equal to or greater than Tbed2, the process proceeds to S109. When it is smaller than Tbed2, this routine is ended, the activity determination flag Flag is held at 1, and forced heating of the catalyst 32 is continued.

In S109, the activation determination flag Flag is set to 0.
Whether or not the NOx trap catalyst 32 (the oxidation catalyst component) is in an active state at the time of restart, is cooled or inactivated by the inflow of exhaust gas accompanying the restart, It is for judging by estimation.
In this activity decrease estimation unit, in S301, the temperature in the exhaust pipe upstream of the catalyst 32 (hereinafter referred to as “exhaust temperature”) Texh is read.

In S302, based on the read Texh, the amount of heat held by the exhaust upstream of the catalyst 32 (in this embodiment, from the exhaust port to the inlet of the catalyst 32) (hereinafter referred to as “exhaust holding heat amount”) Qexh is calculated. . The exhaust holding heat quantity Qexh can be calculated based on the exhaust temperature Texh at the time of restart and the weight of the exhaust.
In S303, the catalyst temperature Tbed is read.

In S304, the amount of heat held by the catalyst 32 (hereinafter referred to as “catalyst holding heat amount”) Qcat is calculated based on the read Tbed. The catalyst holding heat amount Qcat can be calculated based on the catalyst temperature Tbed at the time of restart and the weight of the catalyst 32.
In S305, based on Qexh, Qcat, and Tbed calculated or read as described above, the temperature Test of the catalyst 32 after being lowered by the inflow of exhaust gas is calculated by the following equation (1). The weight of the catalyst 32 is Wc and the specific heat is Cc.

Test = Tbed − ((Qcat−Qexh) / (Wc × Cc)) (1)
In S306, it is determined whether or not the calculated Test is equal to or less than a predetermined value Test1. When it is equal to or less than Test1, the process proceeds to S307, and when it is greater than Test1, the active state of the catalyst 32 is maintained even after restart, and this routine is terminated. The predetermined value Test1 can be set without being related to the previous Tbed1, but in the present embodiment, this is set as the activation lower limit temperature of the catalyst 32 and coincides with Tbed1.

In S307, the activation determination flag Flag is set to 1, and the control for forcibly heating the catalyst 32 is performed.
In the present embodiment, the NOx trap catalyst 32 is forcibly heated by increasing the fuel component content of the exhaust gas flowing into the catalyst 32 and oxidizing the fuel in the exhaust gas on the catalyst 32. For this reason, in this embodiment, an additional fuel injection is performed separately from the normal fuel injection for the purpose of forming engine output. For example, the additional fuel injection is delayed from the normal fuel injection and expanded. By performing it during the stroke, the fuel component content of the exhaust is increased.

  Regarding this embodiment, the NOx trap catalyst 32 and the ECM 51 constitute an “engine exhaust purification device”. That is, S102 in the flowchart shown in FIG. 3 functions as “starting detection means”, S106 in the flowchart and S307 in the flowchart shown in FIG. 5 functions as “catalyst heating means”, and S104 in the flowchart shown in FIG. Is a function as “first temperature detecting means”, S105 in the flowchart is a function as “first activity determining means”, and S305 and 306 in the flowchart shown in FIG. 5 are “second activity determining means”. As a function.

According to this embodiment, the following effects can be obtained.
That is, in the present embodiment, the restart of the engine 1 is detected, and at the time of detecting the restart, the control for forcibly heating the NOx trap catalyst 32 carrying the oxidation catalyst component is performed. Further, it is possible to suppress a decrease in the activity of the catalyst 32 due to the exhaust cooled by receiving the traveling wind or the like while the engine is stopped during the restart, and to suppress the deterioration of the exhaust performance at the restart. In the present embodiment, not only when the catalyst 32 is in an inactive state at the time of restart detection, but also the active state after restart that decreases due to the inflow of low-temperature exhaust gas is determined by estimation. Inactivation can be reliably avoided and good exhaust performance can be maintained. FIG. 6 shows changes in temperatures Tint (≈Texh) and Tbed at the inlet and inside of the catalyst 32 from when the engine is stopped (time t1) to after restart. While the engine temperature is stopped, the inlet temperature Tint rapidly decreases due to the influence of traveling wind and the like, while the internal temperature Tbed is affected by the traveling wind and the like, but is relatively slow because the heat capacity of the catalyst 32 is large. Indicates. For this reason, the internal temperature Tbed is maintained at a high temperature at the time of restart detection (time t2). However, after the restart, the catalyst 32 is cooled by the inflow of low-temperature exhaust gas accompanying the restart. , Decline rapidly. In the present embodiment, forced heating is performed when the catalyst 32 is in an inactive state at the time of restart detection, thereby suppressing a decrease in the activity of the catalyst 32 and promptly recovering the activity. Inactivation of the catalyst 32 can be avoided by performing forced heating when it is estimated that the inactive state is caused by inflow of low-temperature exhaust gas that accompanies restarting, even though the active state is in the active state. . In FIG. 6, curve A shows the most preferable state in which inactivation of the catalyst 32 is avoided by forced heating, and curve B temporarily becomes inactive, but rapid recovery of activity is achieved by forced heating. Shows the state. On the other hand, curve C shows a state in which the active state of the catalyst 32 is recovered as the warm-up progresses without performing forced heating in particular.

  In the present embodiment, the activation state of the catalyst 32 is determined by comparing the catalyst temperature Tbed and the first temperature (= Tbed1) indicating the activation lower limit temperature of the catalyst 32 at the time of restart detection. However, the predetermined temperature is not limited to the activation lower limit temperature. For example, a temperature Tbed3 higher than the lower limit temperature of the catalyst 32 and lower than the normal temperature of the catalyst 32 after the engine 1 is warmed is set, and the catalyst 32 is compared by comparing the catalyst temperature Tbed with this predetermined temperature Tbed3. The active state of is determined. In this case, Tbed3 corresponds to the “second temperature” of the present invention. Note that Tbed3 does not need to coincide with the activation determination temperature for determining the completion of the activation of the catalyst 32 at the time of cold start, and by setting the temperature higher than this, the deactivation of the catalyst 32 is more reliably performed. It can be avoided.

FIG. 4 shows a flowchart of another example of the start control routine. This routine is executed by the ECM 51 every predetermined time. In this flowchart, steps that perform the same processing as in the flowchart shown in FIG. 3 are given the same reference numerals.
In S201, it is determined whether or not a stop command is input. When it is input, the process proceeds to S202, and when it is not input, the process proceeds to S101. The stop command is issued by the HCM 41.

In S202, the temperature in the exhaust pipe upstream of the catalyst 32 (that is, the exhaust temperature Texh) is read as the inlet temperature Tint of the NOx trap catalyst 32, and the read Texh is stored in correspondence with the elapsed time after stopping.
In S203, it is determined whether a start command from the HCM 41 has been input. If it has been input, the process proceeds to S101. If it has not been input, this routine is terminated, and in the next calculation cycle, the inlet temperature Tint is further read in S202 and stored in relation to the elapsed time.

If it is determined in S103 that the current start corresponds to a restart after the determination in S101, a series of inlet temperatures Tint stored in association with the elapsed time after the stop during the engine stop are read out in S204.
In S205, the temperature characteristic of the catalyst 32 is determined based on the read series of Tints. The catalyst temperature characteristic indicates a change in the active state of the catalyst 32 with respect to the inlet temperature Tint, and is determined by correcting the characteristic stored in the ECM 51 in accordance with the detected change in the actual inlet temperature Tint. . This is because there is a difference in the active state (that is, the internal temperature) of the catalyst 32 at a constant Tint when the decrease in the inlet temperature Tint is rapid, such as when the traveling wind is strong, and when the decrease is slow.

In S206, the purification performance value η of the catalyst 32 at the time of restart detection is estimated from the determined catalyst temperature characteristic. This η is a numerical value representing the active state of the catalyst 32. For example, the conversion rate of unburned components such as hydrocarbons is adopted.
In S207, it is determined whether or not the estimated η is equal to or less than a predetermined value η1 corresponding to the performance lower limit value of the catalyst 32. When it is equal to or less than η1, the process proceeds to S106, where the activation determination flag Flag is set to 1, and when it is greater than η1, the process proceeds to the activity decrease estimation unit of this routine. The flow of processing in the activity decrease estimation unit may be the same as that in the flowchart shown in FIG. In the present embodiment, the predetermined value η1 coincides with the purification performance value adopted to determine the completion of the activity of the catalyst 32 during the cold start, and the inlet temperature Tint at which this η1 is obtained is determined by the catalyst 32. There is a difference between the case of being cooled (T1: corresponding to the “third temperature” of the present invention) and the case of being heated (T1 <T2). This is due to the heat capacity of the catalyst 32. FIG. 7 shows the relationship between the inlet temperature Tint and the purification performance value η of the catalyst 32. The curve A shows the temperature when the temperature is lowered, and the curve B shows the value when the temperature is raised.

In S208, the inlet temperature Tint is read.
In S209, it is determined whether or not the read Tint is equal to or higher than a predetermined value Tint2 indicating the inlet temperature T2 at which the performance lower limit value η1 is obtained when the temperature is raised from room temperature. When it is equal to or greater than Tint2, the process proceeds to S109, where the activation determination flag Flag is set to 0. When it is smaller than Tint2, this routine is terminated and Flag is held at 1.

In this example, S203 in the flowchart shown in FIG. 4 has a function as “start detection means”, S202 and 204 in the flowchart have functions as “second temperature detection means”, and S205 to 207 in the flowchart have “ A function as "first activity determination means" is realized.
According to such a configuration, the activation state of the catalyst 32 at the time of cold start is determined based on the inlet temperature Tint, and the activation determination at the time of restart is performed using the temperature sensor employed for this determination. And the number of parts can be reduced.

  In the above, in the activity decrease estimation unit (FIG. 5), the heat amounts Qcat and Qexh that the NOx trap catalyst 32 and the exhaust upstream thereof hold respectively at the time of restart detection are calculated, and based on the difference between these, The active state after restart was estimated (S305, 306). However, the present invention is not limited to this. The difference Δt (= Tbed−Texh) between the catalyst temperature Tbed and the exhaust temperature Texh or the inlet temperature Tint is calculated, and the activated state after restart is calculated based on the calculated Δt. It can also be determined. For example, if Δt is greater than or equal to a predetermined value when restart is detected, it is assumed that the catalyst 32 is cooled by inflow of exhaust gas and reaches an inactive state, and forced heating is performed. is there. Alternatively, forced heating may be performed only when the difference Δt between the detected temperatures Tbed and Texh is equal to or greater than a predetermined value regardless of the active state at the time of restart detection.

Further, in the above, the forced heating of the NOx trap catalyst 32 is performed by increasing the fuel component content of the exhaust gas. However, the present invention is not limited to this, and the temperature of the exhaust gas flowing into the catalyst 32 is increased. This can also be implemented. The forced heating in this case is, for example, by delaying the fuel injection timing by the fuel injection valve 21 from the normal time.
Furthermore, the air-fuel ratio of the exhaust when performing forced heating is preferably adjusted to a value higher than the theoretical value. This is because the internal temperature Tbed of the catalyst 32 at which a constant active state can be obtained is lower when the air-fuel ratio of the exhaust gas is higher than the theoretical value than when it is at the theoretical value. FIG. 8 shows the relationship between the catalyst temperature Tbed and the purification performance value η for each air-fuel ratio of the exhaust gas. The former case is indicated by a curve B, and the latter case is indicated by a curve A.

Furthermore, a gasoline engine other than a diesel engine can be adopted as the engine. The engine is not limited to the composite drive source of the hybrid vehicle, but may be the drive source of the idle stop vehicle.
Furthermore, not only a parallel type composite drive source is configured, but also an engine is used only for driving the generator, and a series type composite drive source is configured to transmit power by operating the motor with the electric power obtained from this generator. May be. Even in such a composite drive source, it is necessary to intermittently operate the engine in response to a power generation request to the generator, and application of the present invention can avoid deterioration of exhaust performance after the engine is restarted.

  Further, the catalyst to be forcibly heated is not limited to being supported on the NOx trap catalyst 32 or the diesel particulate filter 33, but may be configured as a separate body from these exhaust purification devices. The catalyst to be forcibly heated is not limited to the oxidation catalyst, and the present invention can be applied to all catalysts such as a NOx trap catalyst or a reduction catalyst, and in addition, a three-way catalyst.

Configuration of power transmission system according to one embodiment of the present invention Configuration of diesel engine according to the embodiment Flow chart of the activity determination unit of the start control routine The flowchart of the other example of an activity determination part same as the above Flow chart of activity decrease estimation unit of start control routine Changes in temperature at the inlet and inside of the catalyst from engine shutdown to restart Relationship between catalyst inlet temperature and active state Difference in catalyst activation temperature depending on exhaust air-fuel ratio

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Diesel engine, 2, 3 ... Motor generator, 4 ... Continuously variable transmission, 4a ... Electromagnetic clutch, 5 ... Differential gear, 6 ... Wheel, 11 ... Intake passage, 12 ... Turbocharger, 13 ... Surge tank, 21 ... Fuel injection valve, 22 ... common rail, 31 ... exhaust passage, 32 ... NOx trap catalyst, 33 ... diesel particulate filter, 35 ... EGR pipe, 36 ... EGR valve, 41 ... hybrid control module, 51 ... engine control module, 61 ... Accelerator sensor, 62 ... Start key, 63 ... Shift sensor, 64 ... Brake sensor, 65 ... Vehicle speed sensor, 66 ... Battery sensor, 67 ... Crank angle sensor, 68 ... Coolant temperature sensor, 69 ... Catalyst temperature sensor, 70 ... Exhaust gas Temperature sensor 71 ... Filter temperature sensor 72 The fuel pressure sensor.

Claims (12)

An exhaust purification catalyst installed in the exhaust passage;
Start detection means for detecting engine restart when the internal temperature of the catalyst is higher than its inlet temperature;
A catalyst heating means for performing control to forcibly heat the catalyst at the time of restart detection when the restart of the engine is detected by the start detection means;
An exhaust emission control device for an engine comprising: Further comprising first activity determining means for determining an active state of the catalyst when the engine is restarted;
The engine exhaust purification device according to claim 1, wherein the catalyst heating unit heats the catalyst in response to a low activity determination regarding the catalyst by the first activity determination unit when the restart is detected. Further comprising first temperature detecting means for detecting the internal temperature of the catalyst,
The said 1st activity determination means makes the said low activity determination, when the internal temperature detected by the said 1st temperature detection means is below 1st temperature which shows the activity minimum temperature of the said catalyst. The engine exhaust gas purification apparatus according to 2. Further comprising first temperature detecting means for detecting the internal temperature of the catalyst,
The first activity determination unit is a first unit in which an internal temperature detected by the first temperature detection unit is higher than an activation lower limit temperature of the catalyst and lower than a normal temperature of the catalyst after engine warm-up. The engine exhaust gas purification apparatus according to claim 2, wherein the low activity determination is made when the temperature is equal to or lower than 2. Further comprising second temperature detecting means for detecting the inlet temperature of the catalyst,
The first activity determination means is a third temperature at which the inlet temperature detected by the second temperature detection means is lower than the activity determination temperature for determining the completion of activation of the catalyst when the temperature rises from room temperature. The engine exhaust purification device according to any one of claims 2 to 4, wherein the low activity determination is made when: A second activation determination unit that estimates the activation state of the catalyst after the restart, which is reduced by an inflow of exhaust gas accompanying the restart of the engine at the time of restart detection;
The engine according to any one of claims 1 to 5, wherein the catalyst heating unit heats the catalyst in response to a low activity determination related to the catalyst by the second activity determination unit when the restart is detected. Exhaust purification device.   The second activity determination means calculates the amount of heat held by the catalyst when the restart is detected and the amount of heat held by the exhaust upstream of the catalyst when the restart is detected, and based on each calculated amount of heat The exhaust emission control device for an engine according to claim 6, wherein an active state after restart is determined.   The engine exhaust purification apparatus according to any one of claims 1 to 7, wherein the catalyst heating means heats the catalyst by increasing a fuel component content of exhaust gas flowing into the catalyst.   The engine exhaust purification apparatus according to any one of claims 1 to 8, wherein the catalyst heating means heats the catalyst by increasing a temperature of exhaust gas flowing into the catalyst.   The engine exhaust gas purification apparatus according to any one of claims 1 to 9, wherein in the forced heating of the catalyst by the catalyst heating means, the air-fuel ratio of the exhaust gas flowing into the catalyst is adjusted to a value higher than a theoretical value.   The engine exhaust purification apparatus according to any one of claims 1 to 10, wherein the engine is a diesel engine.   The exhaust emission control device for an engine according to claim 11, wherein the engine is a diesel engine constituting a combined drive source with an electric drive source.

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