JP2008138619A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device of an internal combustion engine capable of supplying a reasonable quantity of urea aqueous solution by always calculating an appropriate NOx discharge amount regardless of whether regeneration control of a DPF is in execution or not, thereby achieving excellent NOx elimination characteristics, and of preventing wasteful consumption of the urea aqueous solution and slip. <P>SOLUTION: A map in preliminary temperature-raising control according to a process in forced regeneration of a DPF, a map in raising control and a map in lowering control are set, separately from a map in normal control, as a map for calculating an NOx discharge amount, and an NOx discharge amount is calculated from a map according to a current operation state (S4, 16, 18); and the urea aqueous solution is supplied by driving an injection nozzle based on a urea supply amount obtained from the calculated NOx discharge amount (S8). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine (hereinafter referred to as an engine). Specifically, a selective reduction type NOx catalyst (hereinafter referred to as an SCR catalyst) and a particulate matter (hereinafter referred to as PM) are captured in an exhaust passage. The present invention relates to an exhaust emission control device including a diesel particulate filter (hereinafter referred to as DPF).

For example, in an engine equipped with an SCR catalyst in the exhaust passage, an aqueous urea solution is injected as a reducing agent from an injection nozzle disposed upstream of the SCR catalyst in the exhaust passage, and the aqueous urea solution is hydrolyzed by exhaust heat and water vapor in the exhaust gas. The produced NH ₃ (ammonia) is used to reduce NOx in the exhaust gas on the SCR catalyst. In this type of exhaust purification device, when the supply amount of the urea aqueous solution is insufficient with respect to the NOx emission amount of the engine, the NOx purification performance is deteriorated. When the supply amount is excessive, the urea aqueous solution is wasted and the NOx catalyst is passed through. (Slip) will occur, so it is extremely important to supply an aqueous urea solution that is not excessive or insufficient with respect to the NOx emission amount.

Therefore, various measures for the purpose of supplying an appropriate reducing agent have been proposed (see, for example, Patent Document 1). In the technique of Patent Document 1, the EGR gas amount of the engine is controlled to maintain the SCR catalyst at an optimum temperature at which a good purification action is obtained. On the other hand, when the EGR gas amount is corrected to increase by this EGR control, The supply amount is corrected to decrease, and conversely, when the EGR gas amount is corrected to decrease by EGR control, the supply amount of the reducing agent is corrected to increase, thereby achieving an appropriate supply of the reducing agent.
Japanese Patent Laid-Open No. 10-82315

However, the technique disclosed in Patent Document 1 is merely catalyst temperature control and reductant supply control when focusing on a single SCR catalyst. For example, when a DPF is provided together with a filter in the engine exhaust passage, the following 2 will be described. One problem occurs.
That is, as is well known, the DPF that collects PM in the exhaust gas needs to periodically perform regeneration control for raising the temperature of the DPF in order to incinerate and remove the collected PM. For example, engine EGR amount, fuel injection timing, injection pressure change, CO, HC supply to DPF by post injection after main injection, etc. are performed. Compared with normal operation, NOx emission characteristics change significantly. The technique of Patent Document 1 that merely corrects the increase / decrease of the reducing agent supply amount according to the EGR gas amount cannot cope with such a large fluctuation of the NOx emission amount, and during the regeneration control of the DPF, There was a problem that the supply amount would be excessive or insufficient.

  Further, the temperature rise of the DPF at the time of regeneration control also affects the SCR catalyst disposed in the exhaust passage together with the DPF to raise the temperature. For example, the DPF during regeneration control is heated to about 600 ° C. for PM incineration, while the SCR catalyst has an active temperature range of about 250 to 500 ° C. that exhibits good NOx purification performance. If the activation upper limit temperature is exceeded, the NOx purification performance will deteriorate. In the technique of Patent Document 1, since such a situation is not assumed, there is a problem that an excessive reducing agent is supplied with respect to the reduced purification performance of the SCR catalyst.

  The present invention has been made to solve such problems, and the inventions of claims 1 and 2 always calculate an appropriate amount of NOx emission regardless of whether or not the DPF regeneration control is being executed. To provide an exhaust gas purification device for an internal combustion engine that can supply a reducing agent that is free from excess and deficiency, and that can achieve good NOx purification performance, and can prevent wasteful urea or ammonia consumption and slippage. It is in.

  The inventions of claims 3 and 4 can supply an appropriate amount of reducing agent corresponding to the NOx purification performance even when the temperature of the SCR catalyst rises due to the influence of DPF regeneration control. Another object of the present invention is to provide an exhaust purification device for an internal combustion engine that can prevent wasteful urea or ammonia consumption and slippage.

  In order to achieve the above object, according to the first aspect of the present invention, an NOx catalyst for reducing NOx in exhaust gas with urea or ammonia is provided in an exhaust passage of an internal combustion engine, and NOx based on the NOx emission amount obtained from the operating state of the internal combustion engine. An exhaust purification device for an internal combustion engine that determines the supply amount of urea or ammonia to the catalyst and supplies urea or ammonia as a reducing agent from the reducing agent supply means onto the NOx catalyst according to the supply amount. A filter that collects particulate matter in exhaust gas, a filter regeneration means that incinerates and removes particulate matter collected by incineration by heating the exhaust gas, and a filter regeneration according to the operating state of the filter regeneration means The normal control map for calculating the NOx emission amount when the means is not operated, and the NOx emission amount when the filter regeneration means is operated are calculated. Select one of the filter regeneration maps, calculate the NOx emission amount from the operating state of the internal combustion engine based on the selected map, and drive the reducing agent supply means according to the urea or ammonia supply amount obtained from the NOx emission amount Control means for controlling.

  Therefore, the filter regeneration means changes the operating state of the internal combustion engine from that during normal operation when raising the temperature of the filter, for example, by changing the EGR amount of the internal combustion engine, fuel injection timing, injection pressure, adding post injection, etc. The temperature of the filter is raised by supplying temperature, CO, and HC. As a result, when the temperature of the filter is increased, the NOx emission characteristics of the internal combustion engine vary greatly as compared to other normal operations.

  A normal control time map and a filter regeneration time map are set in advance according to the NOx emission characteristics at the time of normal operation and the NOx emission characteristics at the time of temperature rise of the filter, and any one of the control means according to the operating state of the filter regeneration means. A map is selected. Then, the NOx emission amount is calculated from the operating state of the internal combustion engine based on the selected map, and the supply amount of urea or ammonia that is not excessive or insufficient with respect to the NOx emission amount is determined, and urea or ammonia corresponding to the supply amount is determined. It is supplied from the reducing agent supply means to the NOx catalyst and used for NOx reduction.

  Therefore, even if the NOx emission characteristics of the internal combustion engine change significantly depending on the operating state of the filter regeneration means (during normal operation or filter regeneration), the corresponding characteristic map is applied and applied to the calculation of NOx emissions. Therefore, it is possible to supply urea or ammonia without excess or deficiency to the NOx catalyst based on an appropriate NOx emission amount regardless of the operating state of the filter regeneration means. Therefore, it is possible to prevent NOx purification performance from deteriorating due to insufficient supply amount of urea or ammonia, or wasteful urea or ammonia consumption and slipping due to excessive supply amount.

  According to a second aspect of the present invention, in the first aspect, the filter regeneration means raises the filter temperature and lowers the filter temperature so as to keep the filter temperature within a predetermined temperature range when the filter is heated. As the filter regeneration map, at least the NOx emission characteristic map corresponding to the NOx emission characteristic during the ascent control and the descent control time map corresponding to the NOx emission characteristic during the descent control are set and controlled. When the filter regeneration means is in operation, the means selects either the ascending control time map or the descending control time map as the filter regeneration time map according to the execution status of the ascending control and the descending control.

Therefore, when the temperature of the filter is raised by the filter regeneration means, if the temperature rise is insufficient, the particulate matter cannot be incinerated, and if the temperature rises excessively, the filter will be burned out. Thus, the filter temperature is maintained in a temperature range suitable for incineration of particulate matter.
The ascending control and the descending control are both controls during the operation of the filter regeneration means, but the NOx emission characteristics differ due to the difference in the operating state of the internal combustion engine. Ascending control time map and descending control time map corresponding to the NOx emission characteristics are set, and either map is selected according to the execution status of ascending control and descending control, and applied to the calculation of the NOx emission amount. Accordingly, an appropriate NOx emission amount is calculated regardless of the ascending control or the descending control, and it is possible to supply urea or ammonia with no excess or deficiency to the NOx catalyst based on this NOx emission amount.

  According to a third aspect of the present invention, a NOx catalyst for reducing NOx in exhaust gas with urea or ammonia is provided in the exhaust passage of the internal combustion engine, and urea or ammonia is supplied to the NOx catalyst based on the NOx emission amount obtained from the operating state of the internal combustion engine. In an exhaust gas purification apparatus for an internal combustion engine that determines a supply amount and supplies urea or ammonia as a reducing agent from a reducing agent supply means onto a NOx catalyst according to the supply amount, a particulate matter in exhaust gas is provided in an exhaust passage. A filter that collects particulate matter collected by incineration by heating the exhaust gas, a temperature detecting means that detects the temperature of the NOx catalyst, and a filter regeneration means The urea obtained from the NOx emission when the catalyst temperature detected by the temperature detecting means exceeds the NOx catalyst activity upper limit temperature Other process in which a control means for limiting the amount of supply of ammonia, drives and controls the reducing agent supply means in accordance with the supply amount of urea or ammonia after restriction.

  Accordingly, the NOx catalyst disposed in the exhaust passage together with the filter rises in temperature due to the influence of the filter regeneration means when the filter is heated, and the purification performance deteriorates when the activation upper limit temperature is exceeded. Or the supply amount of ammonia becomes excessive. Here, when the temperature of the NOx catalyst exceeds the NOx catalyst upper limit temperature during the operation of the filter regeneration means, the supply amount of urea or ammonia obtained from the NOx emission amount of the internal combustion engine is limited, so that the temperature rises. Thus, an appropriate amount of urea or ammonia corresponding to the purification performance of the NOx catalyst is supplied, and wasteful urea or ammonia consumption or slip due to an excessive supply amount is prevented in advance.

According to a fourth aspect of the present invention, in the third aspect of the present invention, the control means is based on the catalyst temperature detected by the temperature detecting means based on the degradation characteristic of the purification performance with respect to the temperature increase of the NOx catalyst in the vicinity of the preset activation upper limit temperature. The correction amount is calculated, and the supply amount of urea or ammonia is limited based on the correction amount.
Accordingly, the correction amount is calculated based on the reduction characteristic of the purification performance with respect to the temperature increase of the NOx catalyst near the activation upper limit temperature, and the supply amount of urea or ammonia is limited based on this correction amount. A more appropriate amount of urea or ammonia corresponding to the purification performance of the catalyst can be supplied.

  As described above, according to the exhaust gas purification apparatus for an internal combustion engine of the first aspect of the present invention, a map of NOx emission characteristics corresponding to when the filter regeneration means is not operating and when the filter regeneration means is operating is set in advance, and the operating state of the filter regeneration means is set. Accordingly, the map is selected to calculate the NOx emission amount, and the supply amount of urea or ammonia corresponding to this NOx emission amount is supplied to the NOx catalyst. Alternatively, ammonia can be supplied, so that good NOx purification performance can be realized, and wasteful urea or ammonia consumption and slipping can be prevented in advance.

According to the exhaust emission control device for an internal combustion engine of claim 2, in addition to claim 1, the filter regeneration map is subdivided into an ascending control map and a descending control map, and is selected according to the execution state of control. Since the map is applied, the NOx emission amount can be calculated more appropriately, and the supply amount of urea or ammonia can be further optimized.
According to the exhaust gas purification apparatus for an internal combustion engine of the third aspect of the invention, the supply amount of urea or ammonia obtained from the NOx emission amount is limited when the temperature of the NOx catalyst exceeds the activation upper limit temperature when the filter regeneration means is operated. Therefore, it is possible to supply an appropriate amount of urea or ammonia corresponding to the purification performance of the NOx catalyst that has been lowered due to temperature rise, and it is possible to prevent wasteful consumption or slipping of urea or ammonia.

  According to the exhaust emission control device for an internal combustion engine of the invention of claim 4, in addition to claim 3, the supply amount of urea or ammonia is limited based on the correction amount determined from the reduction characteristic of the purification performance with respect to the temperature rise of the NOx catalyst. Therefore, it is possible to accurately supply a more appropriate amount of urea or ammonia corresponding to the purification performance of the NOx catalyst at that time.

Hereinafter, an embodiment in which the present invention is embodied in an exhaust emission control device for a diesel engine will be described.
FIG. 1 is an overall configuration diagram showing an exhaust emission control device for a diesel engine according to this embodiment. The engine 1 is configured as an in-line 6-cylinder engine. Each cylinder of the engine 1 is provided with a fuel injection valve 2, and each fuel injection valve 2 is supplied with pressurized fuel from a common common rail 3 and is opened at a timing according to the operating state of the engine. The fuel is injected into the inside.

  An intake manifold 4 is mounted on the intake side of the engine 1, and the intake passage 5 connected to the intake manifold 4 is opened and closed by an air cleaner 6, a compressor 7a of the turbocharger 7, an intercooler 8, and an actuator 9a from the upstream side. An intake throttle valve 9 is provided. An exhaust manifold 10 is mounted on the exhaust side of the engine 1, and an exhaust passage 11 is connected to the exhaust manifold 10 via a turbine 7b of a turbocharger 7 connected coaxially with the compressor 7a.

  During operation of the engine 1, the intake air introduced into the intake passage 5 through the air cleaner 6 is pressurized by the compressor 7 a of the turbocharger 7, and then distributed to each cylinder through the intercooler 8, the intake throttle valve 9, and the intake manifold 4. These are introduced into the cylinder in the intake stroke of each cylinder. In the cylinder, fuel is injected from the fuel injection valve 2 at a predetermined timing and ignited and burned in the vicinity of the compression top dead center, and the exhaust gas after combustion rotates through the exhaust manifold 10 and then rotates the turbine 7b and then passes through the exhaust passage 11. It is discharged outside.

  On the other hand, the intake manifold 4 and the exhaust manifold 10 are connected by an EGR passage 17, and an EGR valve 18 and an EGR cooler 19 that are opened and closed by an actuator 18 a are provided in the EGR passage 17. During operation of the engine 1, part of the exhaust gas is recirculated as EGR gas from the exhaust manifold 10 side to the intake manifold 4 side according to the opening degree of the EGR valve 18.

  The exhaust passage is composed of a first pipe 33a, an upstream casing 31, a second pipe 33b, a downstream casing 32, a third pipe 33c, and a silencer (not shown) from the upstream side, and the rear end of the silencer is exposed to the atmosphere. It is open. Both the upstream casing 31 and the downstream casing 32 have a substantially cylindrical shape extending in the front-rear direction of the vehicle, and the exhaust purification device of this embodiment is accommodated in the casings 31 and 32 and the second pipe 33b.

  The upstream casing 31 accommodates a pre-stage oxidation catalyst 34 on the upstream side of the interior, and a wall flow type DPF (diesel particulate filter) 35 on the downstream side. As will be described later, the DPF 35 is a PM in exhaust gas. Plays an action to collect (particulate matter). The downstream casing 32 contains an SCR catalyst 36 (selective reduction type NOx catalyst) on the upstream side of the inside, and a downstream oxidation catalyst 37 on the downstream side. As will be described later, the SCR catalyst 36 is in the exhaust gas. It has the effect of purifying NOx.

  In the second pipe 33b, a fin device 38 for generating a swirl flow in the exhaust gas is installed, and a nozzle part temperature sensor 39 and an injection nozzle 40 (reducing agent supply means) are installed on the downstream side thereof, An inlet temperature sensor 41 (temperature detection means) is installed immediately upstream of the SCR catalyst 36. The fin device 38 is constituted by a large number of fins 38a standing on the inner peripheral wall of the second pipe 33b, and each fin 38a makes a swirl flow in the second pipe 33b by forming a predetermined angle with respect to the exhaust flow direction. Wake up. The injection nozzle 40 is configured to be able to arbitrarily inject into the second pipe 33b using a urea aqueous solution fed from a tank (not shown) as a reducing agent.

  On the other hand, the intake throttle valve 9, the exhaust throttle valve 12, the actuators 9a, 12a and 18a of the EGR valve 18, the fuel injection valve 2, the nozzle part temperature sensor 39, the injection nozzle 40, the inlet part temperature sensor 41, etc. The ECU 51 is driven and controlled on the basis of detection information from sensors. For example, the ECU 51 operates the engine 1 by controlling the injection amount, injection pressure, and injection timing of the fuel injection valve 2 based on the operating state of the engine 1 such as the engine speed and load, and opens the EGR valve 18 by the actuator 18a. The EGR reflux amount is adjusted by controlling the degree.

The ECU 51 controls post-injection for forced regeneration of the DPF 35, urea supply from the injection nozzle 40 for NOx purification by the SCR catalyst 36, and so on. The NOx purification action by the SCR catalyst 36 will be described.
The DPF 35 has an action of collecting PM in the exhaust gas. In an operation state where the exhaust gas temperature of the engine 1 is relatively high, NO ₂ is generated from NO in the exhaust gas by the oxidizing action of the pre-stage oxidation catalyst 34, and the NO ₂ The PM collected in the DPF 35 by the oxidation reaction is continuously incinerated and removed, whereby the DPF 35 is regenerated. On the other hand, when the operation state in which such a continuous regeneration action cannot be obtained continues, for example, when the PM accumulation amount obtained from the differential pressure across the DPF 35 reaches a predetermined regeneration start determination value, the exhaust gas is controlled by the control of the engine 1. The temperature is raised and the PM is forcibly removed by incineration (filter regeneration means). This forced regeneration is executed, for example, by changing the EGR amount, fuel injection timing, and injection pressure of the engine 1 or supplying CO and HC onto the DPF 35 by post injection after main injection. Note that CO generated during PM combustion in forced regeneration is oxidized to CO ₂ by the post-stage oxidation catalyst 37.

  The content of forced regeneration will be described in further detail. Forced regeneration is subdivided into three types of control: preliminary temperature rise control, ascent control, and descending control. FIG. 2 is a time chart showing the execution status of forced regeneration of the DPF 35, and this figure shows a process in which the engine 1 shifts from normal operation to forced regeneration. In order to shift from normal operation to forced regeneration, it is necessary to first raise the temperature of the DPF 35. Therefore, in the preliminary temperature rise control, the post-injection amount is suppressed, and then the EGR amount and the fuel injection timing are mainly aimed at raising the temperature of the DPF 35. , Changing the injection pressure. When the DPF temperature rises by continuing the preliminary temperature rise control and reaches the combustion start temperature (500 ° C. in FIG. 2) at which CO and HC can be incinerated on the DPF 35, the control is switched to the rise control and the drop control.

  The ascending control and descending control are mainly aimed at supplying CO and HC required for incineration of PM on the DPF 35 while maintaining the DPF 35 at a combustion temperature suitable for incineration of PM (600 ° C. in FIG. 2). In both controls, CO and HC are supplied by increasing the post injection amount. In addition, the EGR amount, the fuel injection timing, the injection pressure, and the like are set so that the DPF temperature is increased in the increase control and the DPF temperature is decreased in the decrease control.

  When the preliminary temperature increase control is completed, the increase control is first executed to further increase the DPF temperature to the combustion temperature. At this time, the control is switched to the lowering control, and after a predetermined delay until the lowering control is reflected in the DPF temperature, the DPF temperature starts to decrease and decreases to the combustion temperature. At this point, the control is switched to the increase control, and after a predetermined delay until the increase control is reflected in the DPF temperature, the DPF temperature starts to increase and increases to the combustion temperature. The DPF temperature is maintained in the vicinity of the combustion temperature by repeating the above increase control and decrease control alternately.

  Since FIG. 2 shows a case where the engine 1 is in a relatively steady operation, the ascending control and the descending control are continued for substantially the same period. However, the execution status of these controls varies depending on the operating state of the engine 1. For example, during the idling operation in which the exhaust temperature of the engine 1 decreases, the duration of the increase control is naturally extended to increase the DPF temperature, and during the sudden acceleration of the vehicle where the exhaust temperature increases, the duration of the decrease control is naturally increased. As a result, the DPF temperature is lowered, and as a result, the DPF temperature is maintained near the combustion temperature regardless of the engine operating state.

The forced regeneration is terminated when, for example, the PM accumulation amount obtained from the differential pressure across the DPF 35 is reduced to a predetermined regeneration end determination value, but at the end, the control corresponding to the preliminary temperature rise is not executed, The control shifts directly from the ascending control or the descending control to the normal control.
On the other hand, since the SCR catalyst 36 needs to supply NH ₃ (ammonia) for NOx purification, the ECU 51 determines the urea aqueous solution from the injection nozzle 40 based on the operating state of the engine 1 and the detected value of the nozzle temperature sensor 39. The injection amount of the is controlled. The injected urea aqueous solution is hydrolyzed by exhaust heat and water vapor in the exhaust gas to generate NH ₃ , and this NH ₃ reduces NOx in the exhaust gas to harmless N ₂ on the SCR catalyst 36 to purify NOx. On the other hand, surplus NH _{3 at} this time is oxidized to NO by the post-stage oxidation catalyst 37.

A hydrolysis catalyst that acts to hydrolyze urea into NH ₃ may be disposed upstream of the SCR catalyst 36, or an aqueous ammonia solution may be injected from the injection nozzle 40 in place of the aqueous urea solution. Also good.
By the way, as described in [Problems to be Solved by the Invention], in the forced regeneration of the DPF 35, the engine 1 is changed from the normal operation control to the forced regeneration control (specifically, the preliminary temperature increase control, the increase control, and the decrease control). Since the switching is performed, the NOx emission characteristics change significantly with the control status of the engine 1. FIG. 2 schematically shows fuel injection timings T, T1 to T3, injection pressures P, P1 to P3, NOx emission amounts NOx, and NOx1 to NOx3 during normal control and forced regeneration control. Like the fuel injection timings T and T1 to T3 and the injection pressures P and P1 to P3, the NOx emission amounts NOx and NOx1 to NOx3 have a large difference between the controls, and the urea aqueous solution to be inevitably supplied to the SCR catalyst 36. There is also a large gap in the optimum value of, and it is impossible to apply a common urea supply amount. Therefore, in the present embodiment, maps for calculating the NOx emission amount are set in advance corresponding to the NOx emission characteristics in each control (during normal control, preliminary temperature increase control, increase control, and decrease control), and each map Measures are taken to determine the urea supply amount based on the NOx emission amount calculated from (control means).

  In addition, the temperature rise of the DPF 35 during forced regeneration also affects the SCR catalyst 36 located on the downstream side, causing the temperature to rise, the SCR catalyst 36 exceeds the activation upper limit temperature, and the NOx purification performance is reduced. There is a problem that the urea supply amount becomes excessive with respect to performance. Therefore, in the present embodiment, measures are taken to limit the urea supply amount when the SCR catalyst 36 exceeds the activation temperature range (control means).

Two characteristic controls relating to the above urea supply will be described in detail below.
FIG. 3 is a flowchart showing a urea supply control routine executed by the ECU 51. The ECU 51 executes the routine at a predetermined control interval.
First, it is determined in step S2 whether or not the DPF 35 is being forcibly regenerated. If No (No), the process proceeds to step S4, and the normal control time map set corresponding to the NOx emission characteristics during normal control. Based on the above, the NOx emission amount of the engine 1 is calculated. For example, as shown in FIG. 4, the normal control time map is set, and the higher the fuel injection amount q (engine load) or the engine rotational speed Ne, the larger the NOx emission amount is calculated. In the subsequent step S6, the urea supply amount is determined from the calculated NOx discharge amount, the injection nozzle 40 is driven and controlled based on the urea supply amount determined in step S8, and the urea aqueous solution is injected. Then, the routine is terminated.

Basically, the reaction ratio between NH ₃ and NOx produced from urea is naturally determined by a predetermined chemical reaction formula, and therefore NH ₃ derived from NOx emissions can be produced by hydrolysis according to this reaction ratio. Thus, the urea supply amount is determined. Of course, the urea supply amount at this time is a value under the assumption that the SCR catalyst 36 is activated and exhibits normal NOx purification performance. At the time of transition in which the operating range of the engine 1 changes, the NOx emission amount is delayed with respect to changes in the fuel injection amount q and the engine rotational speed Ne. Correction is executed.

  On the other hand, when it is determined that the DPF 35 is being forcibly regenerated in Step S2 (Yes), the process proceeds to Step S10, where it is determined whether the preliminary temperature increase control is currently being performed. When the determination is Yes, the process proceeds to step S12, and the NOx emission amount is calculated based on the preliminary temperature rise control time map (filter regeneration time map) set corresponding to the NOx emission characteristics at the time of the preliminary temperature rise control. The preliminary temperature increase control time map is for calculating the NOx emission amount from the fuel injection amount q and the engine rotational speed Ne in the same way as the normal control time map of FIG. 4, but its characteristics are significantly different from the normal control time map. However, the calculated NOx emissions are different even in the same operation region.

  If the determination in step S10 is No, the process proceeds to step S14, and it is determined whether or not the ascent control is currently being performed. When the determination is Yes, the process proceeds to step S16, and the NOx emission amount is calculated based on the ascent control time map (filter regeneration time map) set corresponding to the NOx emission characteristics during ascent control. When the determination in step S16 is No, the process proceeds to step S18, and the NOx emission amount is calculated based on the descent control time map (filter regeneration map) set corresponding to the NOx emission characteristics during the descent control. . These maps also have different characteristics from the normal control time map and the preliminary temperature increase control time map, and different NOx emission amounts are calculated in the same operation region.

  After calculating the NOx emission amount in any of the above steps S12, 16, and 18, the process proceeds to step S20, and the urea supply amount is determined from the calculated NOx emission amount. Thereafter, the process proceeds to step S22, where the bed temperature Tscr of the SCR catalyst 36 is estimated from the inlet temperature Tin of the SCR catalyst 36 detected by the inlet temperature sensor 41, and the correction amount α ( = 0 to 1.0). It should be noted that a temperature sensor may be provided in the SCR catalyst 36 to directly detect the bed temperature Tscr, or the bed temperature Tscr may be estimated from the operating state of the engine 1.

  FIG. 5 is a characteristic diagram showing the purification characteristics of the SCR catalyst 36 with respect to the bed temperature and the setting state of the correction amount α. The active temperature range in which the SCR catalyst 36 exhibits good NOx purification performance is in the range of about 250 to 500 ° C. If the temperature falls below 250 ° C, which is the lower limit of activity, the purification performance gradually decreases.If the temperature exceeds 500 ° C, which is the upper limit of activity, the purification performance increases as the temperature rises. It gradually decreases and hardly exhibits purification performance below 200 ° C. and above 700 ° C. (corresponding to “reduction characteristics of purification performance” of claim 4 of the present invention).

  Since the upper limit of the temperature range of the SCR catalyst 36 during normal control is less than 500 ° C, there is almost no possibility of exceeding the upper limit temperature of activation. However, when the DPF 35 is heated to around 600 ° C by forced regeneration, it is affected by this. Therefore, the downstream SCR catalyst 36 exceeds the activation upper limit temperature of 500 ° C. Of course, these temperature ranges are merely examples, and it goes without saying that they vary depending on the specifications of the SCR catalyst 36 and the like.

  The calculation process of the correction amount α in step S22 is executed based on the above characteristics of the SCR catalyst 36. The correction amount α is set to 1.0 when the bed temperature Tscr is in the range of 250 to 500 ° C, and is between 500 and 700 ° C. Decreases to 0 at a constant rate of change, and remains at 0 at 700 ° C or higher. Similarly, the correction amount α decreases to 0 at a constant change rate when the bed temperature Tscr is between 250 and 200 ° C., and is maintained at O when the bed temperature is less than 200 ° C. Thus, the correction amount α is set to a value that correlates with the NOx purification performance of the SCR catalyst 36 at that time.

  In the following step S24, the urea supply amount determined in step S20 is multiplied by the correction amount α, and then the process proceeds to step S8 to inject the urea aqueous solution based on the corrected urea supply amount and end the routine. . By multiplying the correction amount α, the urea supply amount is calculated as a value reflecting the NOx purification performance of the SCR catalyst 36. For example, at 250 to 500 ° C. corresponding to the activation temperature range of the SCR catalyst 36, the urea supply amount is set to a value corresponding to the NOx emission amount. The temperature is limited to 0 below 200 ° C. and above 700 ° C., and in the range of 500 to 700 ° C. and 250 to 200 ° C., the value is limited to a value corresponding to the degradation characteristic of the NOx purification performance of the SCR catalyst 36.

Note that the reduction characteristic of the purification performance of the SCR catalyst 36 due to the temperature rise or temperature drop is not limited to the linear constant change rate shown in FIG. However, even in this case, the correction amount α may be set according to the deterioration characteristic.
As described above, according to the exhaust emission control device for the engine 1 of the present embodiment, the NOx emission amount between the normal control and the forced regeneration control in which a large difference occurs in the NOx emission amount due to the control state of the engine 1. A map for calculating the NOx emission amount is set separately for the preliminary temperature rise control, the rise control and the drop control with different NOx emission characteristics in the forced regeneration control. . Accordingly, an appropriate NOx emission amount can be calculated from the map corresponding to the NOx emission characteristic in each control situation, and regardless of the control situation of the engine 1 (regardless of the normal control or the forced regeneration control) based on the calculated NOx emission quantity. Or, even in the forced regeneration control, regardless of the preliminary temperature increase control, the increase control, and the decrease control, it is possible to always supply the urea aqueous solution without excess or deficiency. Therefore, it is possible to prevent the supply amount of the urea aqueous solution from being insufficient and realize a good NOx purification performance, and it is possible to prevent the wasteful consumption and slippage of the urea aqueous solution due to the excessive supply amount.

  Further, when the SCR catalyst 36 deviates from the activation temperature range and decreases the NOx purification performance, the urea supply amount is limited by the correction amount α set based on the decrease characteristic. Not only when the temperature is lower than the lower limit temperature, but also when the SCR catalyst 36 exceeds the upper limit of activation temperature due to the temperature rise of the DPF 35 during forced regeneration, an appropriate amount of urea corresponding to the NOx purification performance degradation characteristics at that time An aqueous solution can be supplied. Therefore, it is possible to prevent wasteful urea aqueous solution consumption and slip due to an excessive supply amount.

  This is the end of the description of the embodiment, but the aspect of the present invention is not limited to this embodiment. For example, in the above-described embodiment, the SCR catalyst 36 is disposed on the downstream side of the DPF 35, but conversely, the DPF 35 may be disposed on the downstream side of the SCR catalyst 36. Even in such a layout, the NOx emission amount of the engine 1 is different between the normal operation and the forced regeneration of the DPF 35, and the temperature of the SCR catalyst 36 increases during the forced regeneration of the DPF 35. Therefore, the measures described in the above embodiment are taken. The same effect can be obtained by executing.

  Further, in the above embodiment, the map for calculating the NOx emission amount at the time of forced regeneration control is subdivided into a preliminary temperature increase control time map, an ascending control time map, and a descending control time map. When only the ascending control and the descending control are executed, the preliminary temperature increase control time map may be omitted and only the ascending control time map and the descending control time map may be applied. Also, the difference in NOx emission characteristics is noticeable between normal control and forced regeneration control. Compared with this, the difference in NOx emission characteristics among the preliminary temperature rise control, ascent control, and descent control is Since the map is relatively small, a single map that averages the characteristics of the preliminary temperature increase control, the ascending control, and the descending control may be applied without subdividing the map during forced attitude control.

1 is an overall configuration diagram illustrating an exhaust emission control device for a diesel engine according to an embodiment. It is a time chart which shows the execution condition of forced regeneration of DPF. It is a flowchart which shows the urea supply control routine which ECU performs. It is a figure which shows the map at the time of normal control for calculating NOx discharge | emission amount from an engine operating state. It is a characteristic view which shows the purification characteristic with respect to the bed temperature of a SCR catalyst, and the setting condition of the correction amount.

Explanation of symbols

1 engine (internal combustion engine)
11 Exhaust passage 35 DPF (filter)
36 SCR catalyst (NOx catalyst)
40 injection nozzle (reducing agent supply means)
41 Inlet temperature sensor (temperature detection means)
51 ECU (filter regeneration means, control means)

Claims (4)

An NOx catalyst for reducing NOx in exhaust gas with urea or ammonia is provided in the exhaust passage of the internal combustion engine, and the supply amount of urea or ammonia to the NOx catalyst is determined based on the NOx emission amount obtained from the operating state of the internal combustion engine. In the exhaust gas purification apparatus for an internal combustion engine that supplies urea or ammonia as a reducing agent from the reducing agent supply means on the NOx catalyst according to the supply amount,
A filter provided in the exhaust passage for collecting particulate matter in exhaust gas;
A filter regeneration means for heating and removing the particulate matter collected by the filter by heating the exhaust gas;
A normal control time map for calculating the NOx emission amount when the filter regeneration means is not operated according to the operating state of the filter regeneration means, and a filter regeneration time map for calculating the NOx emission amount when the filter regeneration means is operated The NOx emission amount is calculated from the operating state of the internal combustion engine based on the selected map, and the reducing agent supply means is provided according to the urea or ammonia supply amount obtained from the NOx emission amount. An exhaust purification device for an internal combustion engine, comprising: control means for driving control. The filter regeneration means alternately executes an increase control for increasing the filter temperature and a decrease control for decreasing the filter temperature in order to keep the filter temperature within a predetermined temperature range when the filter is heated.
As the filter regeneration map, at least an ascending control time map corresponding to the NOx emission characteristic during the ascending control and a descending control time map corresponding to the NOx emission characteristic during the descending control are set,
The control means, when the filter regeneration means is operated, selects either the ascending control time map or the descending control time map as the filter regeneration time map according to the execution state of the ascending control and descending control. The exhaust emission control device for an internal combustion engine according to claim 1. An NOx catalyst for reducing NOx in exhaust gas with urea or ammonia is provided in the exhaust passage of the internal combustion engine, and the supply amount of urea or ammonia to the NOx catalyst is determined based on the NOx emission amount obtained from the operating state of the internal combustion engine. In the exhaust gas purification apparatus for an internal combustion engine that supplies urea or ammonia as a reducing agent from the reducing agent supply means on the NOx catalyst according to the supply amount,
A filter provided in the exhaust passage for collecting particulate matter in exhaust gas;
A filter regeneration means for heating and removing the particulate matter collected by the filter by heating the exhaust gas;
Temperature detecting means for detecting the temperature of the NOx catalyst;
During the operation of the filter regeneration means, when the catalyst temperature detected by the temperature detection means exceeds the upper limit temperature of the NOx catalyst, the supply amount of urea or ammonia obtained from the NOx emission amount is limited, An exhaust emission control device for an internal combustion engine, comprising: a control unit that drives and controls the reducing agent supply unit according to a supply amount of urea or ammonia after the restriction.   The control means calculates a correction amount from the catalyst temperature detected by the temperature detection means on the basis of a reduction characteristic of the purification performance with respect to the temperature rise of the NOx catalyst near the preset activity upper limit temperature, 4. An exhaust gas purification apparatus for an internal combustion engine according to claim 3, wherein the supply amount of urea or ammonia is limited based on the amount.

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