JP2007239468A - Exhaust emission control device for engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inhibit deactivation of a catalyst due to inflow of low temperature exhaust gas with accompanying restart of an engine while considering emission control capacity after restart in an engine provided with NOx trap catalyst. <P>SOLUTION: The NOx trap catalyst is forcibly heated and air fuel ratio of exhaust gas in the forcible heating is adjusted to air fuel ratio according to quantity of NOx trapped by the NOx trap catalyst (S403-405) during restart detection. If NOx trap quantity has reached limit trap quantity (=NOX1) of the catalyst, air fuel ratio of exhaust gas is adjusted to theoretical value or value less than that (=λs). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device for an engine, and more specifically, in an engine equipped with a NOx trap catalyst as an exhaust aftertreatment catalyst, the activity of the catalyst is reduced due to low temperature exhaust gas flowing in when the engine is restarted. The present invention relates to a technique for improving the exhaust performance of an engine by suppressing the catalyst while considering the purification ability of the catalyst after restart.

  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 composite drive source of a hybrid vehicle together with a motor generator, the deterioration of the exhaust purification catalyst is detected, and the determination is made based on the detected deterioration that determines whether or not intermittent operation that repeats stop and restart of the engine is performed. According to the result, the engine stop (which is a precondition for restart) is prohibited, and the operation after restart is forcibly maintained (Patent Document 1).

Further, a NOx trap catalyst is known as a catalyst used for the post-treatment of nitrogen oxide (hereinafter referred to as “NOx”) in exhaust gas. This NOx trap catalyst exhibits different properties depending on the air-fuel ratio of the exhaust gas flowing in, and traps NOx in the exhaust when the air-fuel ratio of the exhaust is higher than the theoretical value, while the air-fuel ratio of the exhaust is When it is lower than the theoretical value, trapped NOx is released. The released NOx reacts with the reducing component in the exhaust gas on the catalyst and is reduced.
JP 2004-124827 A (paragraph numbers 0007 to 0010, 0085 to 0088)

  The technique described in Patent Document 1 that prohibits intermittent operation of the engine in accordance with deterioration of the exhaust purification catalyst is swept from the engine during the idling period after the restart until normal ignition and combustion are performed in the hybrid vehicle. This prevents the catalyst from deteriorating due to the inflow of oxygen-excess gas. 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 in exhaust performance. Further, according to this technology, harmful substances exhausted from an engine that tends to become unstable after restart in a so-called idle stop vehicle that performs intermittent operation according to the state of the vehicle, not limited to a hybrid vehicle, The occurrence of poor purification can be avoided.

  By the way, recently, a hybrid vehicle employing a diesel engine as a mechanical drive source has been attracting attention as something that can be expected to have a carbon dioxide reduction effect that is 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 catalyst being deactivated. 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.

  Since the operation of the diesel engine is mainly performed in an oxygen-excess state, the NOx trap catalyst is widely adopted throughout the diesel engine including the one constituting the composite drive source of the hybrid vehicle. As with other catalysts, inactivation at the time of restart is also a problem for NOx trap catalysts. However, this catalyst takes a purification process by trapping, releasing, and reducing NOx. There is a special problem that other catalysts do not have because there is a limit to the amount of trapped NOx that can be stored. In other words, if the amount of NOx trapped by the NOx trap catalyst at the time of restarting has reached the limit, even if the decrease in the activity of the catalyst is suppressed at the time of restarting and the active state can be recovered quickly, NOx Since the trap amount has already reached the limit, the purification capacity cannot be ensured after the restart, and NOx is released without being purified.

  The present invention relates to an engine having a NOx trap catalyst as an exhaust purification catalyst, in particular, a diesel engine having a relatively low temperature of exhaust gas. Suppressing this while considering the purification ability after restart avoids catalyst deactivation or promptly recovers its active state and ensures the purification ability after restart, The purpose is to improve the exhaust performance.

  The present invention provides an engine exhaust purification device. The apparatus according to the present invention includes a NOx trap catalyst. This NOx trap catalyst is installed in the exhaust passage of the engine and traps NOx in the exhaust in an oxygen-excess atmosphere where the air-fuel ratio of the exhaust is higher than the theoretical value, while trapping due to a decrease in the air-fuel ratio of the exhaust. While releasing NOx, the released NOx is reduced. The engine restart is detected when the internal temperature of the NOx trap catalyst is higher than the inlet temperature, and when the restart is detected, the NOx trap catalyst is forcibly heated and the catalyst is forcibly heated. At this time, the air-fuel ratio of the exhaust gas is adjusted to an air-fuel ratio corresponding to the amount of NOx trapped by this catalyst.

  According to the present invention, when the restart of the engine is detected, the NOx trap catalyst is forcibly heated so that it remains upstream of the catalyst from the previous engine stop, and the cooled exhaust gas accompanies the restart. It is possible to suppress a decrease in the activity of the catalyst due to the inflow, to avoid inactivation of the catalyst, or to promptly recover the active state. Further, according to the present invention, the NOx trap amount is taken into consideration when forcing the NOx trap catalyst, and the air-fuel ratio of the exhaust gas is adjusted to the air-fuel ratio according to the NOx trap amount, thereby reducing the activity of the catalyst by forced heating. While suppressing, the purification capability after restart can be secured and the exhaust performance of the engine can be improved. 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 generated by the combustion is discharged into the exhaust passage 31, and the turbine 12b is driven by the exhaust, 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 oxides (i.e., NOx) in the exhaust when the air-fuel ratio of the inflowing exhaust gas is higher than the theoretical value, while the air-fuel ratio of the exhaust gas is the theoretical value (its substantial value). It has the property of releasing trapped NOx when it is lower than this range. 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 elements and is then released into the atmosphere. The relationship between the NOx trap catalyst 32 and the diesel particulate filter 33 is not limited to that shown in the figure, and the diesel particulate filter 33 may be positioned upstream of the NOx trap catalyst 32.

  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 the deterioration of the exhaust performance due to the decrease in the activity of the NOx trap catalyst 32, and raise the temperature of the exhaust gas flowing into the catalyst 32. This is forcibly heated.

  In the present embodiment, the start command for 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 region, or 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 the amount of fuel injection is suppressed 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 NOx trap 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 (hereinafter referred to as “catalyst temperature”) Tbed of the NOx trap catalyst 32 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 S <b> 105, it is determined whether or not the read Tbed is equal to or lower than a predetermined value Tbed <b> 1 indicating the activation lower limit temperature of the NOx trap 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 NOx trap 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, and when it is smaller than Tbed2, this routine is ended, the activation determination flag Flag is held at 1, and the forced heating of the NOx trap catalyst 32 is continued.

In S109, the activation determination flag Flag is set to 0.
The activity decrease estimation unit shown in FIG. 5 is used to determine by estimation whether the NOx trap catalyst 32 is in an activated state at the time of restart, but is cooled and inactivated by the inflow of exhaust gas accompanying the restart. Is.
In this activity decrease estimation unit, in S301, the temperature in the exhaust pipe upstream of the NOx trap catalyst 32 (hereinafter referred to as “exhaust temperature”) Texh is read.

In S302, the amount of heat (hereinafter, referred to as “exhaust holding heat amount”) Qexh held by the exhaust upstream of the NOx trap catalyst 32 (in this embodiment, from the exhaust port to the inlet of the catalyst 32) based on the read Texh. calculate. 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 NOx trap 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 NOx trap 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 lower than Test1, the process proceeds to S307, and when it is higher than Test1, this routine is terminated assuming that the active state of the NOx trap catalyst 32 is maintained even after restarting. 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 NOx trap catalyst 32 is forcibly heated.
FIG. 6 is a flowchart of a fuel injection control routine. This routine is also started when the power is turned on, and is executed every predetermined time.
In S401, it is determined whether or not the activity determination routine Flag is 1. When it is 1, it progresses to S402. On the other hand, when the value is 0, the process proceeds to S406, in which the normal startup increase control is performed at the cold start, and the normal control mainly according to the load is performed in the normal operation after warm-up.

  In S402, the NOx trap amount NOX is read. The NOx trap amount NOX is the amount of NOx trapped by the NOx trap catalyst 32, and is stored in the ECM 51 at the previous engine stop. The NOx trap amount NOX can be calculated based on the accumulated number of revolutions from the previous catalyst regeneration (the exhaust air-fuel ratio is temporarily reduced to release NOx from the catalyst 32). The NOx trap amount NOX can be calculated more accurately by integrating the amount of NOx discharged from the engine 1 per unit revolution.

  In S403, it is determined whether or not the read NOX is greater than or equal to a predetermined value NOX1. When it is equal to or greater than NOX1, the process proceeds to S404, and when it is smaller than NOX1, the process proceeds to S405. NOX1 is used to determine whether or not the NOx trap amount NOX has reached the limit trap amount of the NOx trap catalyst 32 when the engine 1 is restarted. When determining whether or not the catalyst regeneration can be performed during normal operation. It is not necessary to depend on what is adopted (= NOXreg). That is, as the predetermined value NOX1, a special value for determination at the time of restart can be adopted, and in this embodiment, NOX1 is operated in a normal operation in order to provide a sufficient purification capacity after restart. It is set to a value smaller than NOXreg used for judgment at the time.

In S404, the air-fuel ratio λ of the exhaust to be adjusted during forced heating is set to a theoretical value or a predetermined value λs smaller than this.
In S405, the air-fuel ratio λ of the exhaust to be adjusted during forced heating is set to a predetermined value λl (> λs) that is larger than the theoretical value.
In S406, forced heating is performed according to the active state of the NOx trap catalyst 32 at the time of restart. In the present embodiment, this forced heating is performed by increasing the temperature of the exhaust gas flowing into the catalyst 32. For this reason, in the present embodiment, an additional fuel injection is performed separately from the normal fuel injection for the purpose of forming the engine output. For example, the additional fuel injection is delayed from the normal fuel injection and expanded. This is done during the stroke, causing afterburning and raising the exhaust temperature. While the amount of fuel injection by additional fuel injection is varied depending on λ and the exhaust gas is adjusted to an excess oxygen state by λl in principle, when the NOx trap amount NOX reaches the limit trap amount, the intake throttle The intake air amount is decreased by the valve 14 and the injection amount is increased by λs to adjust the air-fuel ratio of the exhaust gas to a theoretical value or a value lower than this.

  Regarding this embodiment, the NOx trap catalyst 32 and the ECM 51 constitute an “engine exhaust purification device”. That is, S102 and 103 in the flowchart shown in FIG. 3 function as “start detection means”, S106 in the flowchart and S307 in the flowchart shown in FIG. 5, and S403 to 406 in the flowchart shown in FIG. The function is realized. Further, S402 in the flowchart shown in FIG. 6 is a function as “NOx trap amount detecting means”, S104 in the flowchart shown in FIG. 3 is a function as “first temperature detecting means”, and S105 in the flowchart is “first”. The function as "first activity determination means" is realized by S305 and S306 in the flowchart shown in FIG.

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 the NOx trap catalyst 32 is forcibly heated when the restart is detected. Therefore, it is possible to suppress the decrease in the activity of the catalyst 32 due to the exhaust gas that has been cooled down flowing in with the restart, and to suppress the deterioration of the exhaust performance during the restart. In this embodiment, when the catalyst 32 is forcibly heated, the NOx trap amount NOX is taken into consideration, and when this reaches the limit trap amount (= NOX1) of the catalyst 32, the air-fuel ratio of the exhaust gas is the theoretical value or lower than this. Since the adjustment is made to the value (= λs), the purification ability of the catalyst 32 after the restart can be secured while suppressing the decrease in the activity of the catalyst 32 by forced heating. In the present embodiment, since the predetermined value NOX1 corresponding to the limit trap amount is set to a relatively small value, the purification capacity after restart is provided with a margin, and the frequency of catalyst regeneration performed during traveling is reduced. be able to. In the present embodiment, not only when the NOx trap 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 of the catalyst 32 can be reliably avoided and the exhaust performance can be maintained satisfactorily. FIG. 7 shows changes in temperatures Tint (≈Texh) and Tbed at the inlet and inside of the NOx trap 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. 7, 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 with the first temperature (= Tbed1) indicating the lower limit activation temperature of the NOx trap catalyst 32 at the time of restart detection. However, the present invention is not limited to this, and a temperature other than the activation lower limit temperature may be employed as the predetermined 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 Tint 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. 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 restart in S103, 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 NOx trap 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 NOx trap 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 NOx 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 NOx trap 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. 8 shows the relationship between the inlet temperature Tint and the purification performance value η of the NOx trap catalyst 32. The curve A shows the temperature when the temperature falls, and the curve B shows the value when the temperature rises.

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 and 103 in the flowchart shown in FIG. 4 function as “start detection means”, S202 and 204 in the flowchart function as “second temperature detection means”, and S205 through S207 in the flowchart. Implements the function as “first activity determination means”.
According to such a configuration, the activation state of the NOx trap 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. This can be done 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 active 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.

In addition to the diesel engine, a gasoline engine can be used 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 operate the engine intermittently in response to a power generation request for the generator, and the exhaust performance of the engine can be improved by applying the present invention.

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 Flow chart of fuel injection control routine Changes in temperature at the inlet and inside of the NOx trap catalyst from engine stop to restart Relationship between NOx trap catalyst inlet temperature and active state

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 (9)

While installed in the exhaust passage of the engine and trapping NOx in the exhaust under an oxygen-excess atmosphere where the air-fuel ratio of the exhaust is higher than the theoretical value, the trapped NOx is released due to the decrease in the air-fuel ratio of the exhaust, A NOx trap catalyst for reducing the released NOx;
Start detection means for detecting restart of the engine when the internal temperature of the NOx trap catalyst is higher than its inlet temperature;
A means for forcibly heating the NOx trap catalyst at the time of restart detection when the engine restart is detected by the start detection means, and when the catalyst is forcibly heated, the catalyst traps the air-fuel ratio of the exhaust gas. Heating control means for adjusting the air-fuel ratio according to the amount of NOx being
An exhaust emission control device for an engine comprising: Further comprising NOx trap amount detection means for detecting the amount of NOx trapped by the NOx trap catalyst as the NOx trap amount;
When the NOx trap amount detected by the NOx trap amount detecting unit is less than a predetermined value as the limit trap amount of the NOx trap catalyst, the heating control unit sets the air / fuel ratio of the exhaust gas to a theoretical value. While adjusting to a high first air-fuel ratio, when the amount of NOx trap is equal to or greater than the predetermined value, the air-fuel ratio of the exhaust gas is adjusted to a second air-fuel ratio lower than the first air-fuel ratio. Item 2. An exhaust emission control device for an engine according to Item 1. A first activity determining means for determining an active state of the NOx trap catalyst when the engine is restarted;
3. The engine exhaust according to claim 1, wherein the heating control unit heats the catalyst in response to a low activity determination regarding the NOx trap catalyst by the first activity determination unit when the restart is detected. Purification equipment. Further comprising first temperature detecting means for detecting the internal temperature of the NOx trap catalyst,
The first activity determination means makes the low activity determination when the internal temperature detected by the first temperature detection means is equal to or lower than a first temperature indicating an activation lower limit temperature of the NOx trap catalyst. The engine exhaust gas purification apparatus according to claim 3. Further comprising first temperature detecting means for detecting the internal temperature of the NOx trap catalyst;
The first activity determination means has an internal temperature detected by the first temperature detection means that is higher than an activation lower limit temperature of the NOx trap catalyst and is higher than a normal temperature of the catalyst after the engine is warmed up. The engine exhaust gas purification apparatus according to claim 3, wherein the low activity determination is made when the temperature is equal to or lower than a low second temperature. Further comprising second temperature detecting means for detecting an inlet temperature of the NOx trap catalyst;
The first activity determination unit is a third mode in which the inlet temperature detected by the second temperature detection unit is lower than the activity determination temperature for determining the completion of the activation of the NOx trap catalyst when the temperature rises from room temperature. The exhaust emission control device for an engine according to any one of claims 3 to 5, wherein the low activity determination is made when the temperature is equal to or lower than a predetermined temperature. A second activity determining means for estimating the NOx trap catalyst activation state after restart, which is reduced by inflow of exhaust gas accompanying engine restart at the time of restart detection;
The said heating control means heats this catalyst corresponding to the low activity determination regarding the said NOx trap catalyst by the said 2nd activity determination means at the time of the said restart detection. Engine exhaust purification system.   The second activity determination means calculates the amount of heat held by the NOx trap 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 the calculated amounts of heat. The engine exhaust gas purification apparatus according to claim 7, wherein the activated state after the restart is determined.   The engine exhaust gas purification apparatus according to any one of claims 1 to 8, wherein the engine is a diesel engine constituting a combined drive source with an electric drive source.

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