JP4370942B2 - Engine exhaust purification system - Google Patents

Description

  The present invention relates to an exhaust emission control device for an engine, and more particularly, to improvement of a regeneration processing technique for a filter that collects particulate matter in engine exhaust.

In order to purify particulate matter discharged from diesel engines, etc. (hereinafter referred to as “exhaust particulates”), a filter is provided in the engine exhaust system, and the captured exhaust particulates are oxidized or incinerated at predetermined intervals to regenerate the filter. Devices that do this are known.
JP-A-6-58137

  In the past, many methods using an electric heater have been proposed for the treatment of exhaust particulate captured by a filter, but in recent years the exhaust temperature has been raised by engine control such as retarding the fuel injection timing or secondary injection. Things are attracting attention in terms of structure, reliability and cost. However, in the conventional processing method based on engine control, regeneration is not performed during idle operation where the amount of generated heat is low in order to avoid deterioration of fuel consumption. Therefore, excessive exhaust particles accumulate in the filter when idle operation continues for a long time. There was a risk of doing so.

  In the present invention, as a reference value for starting filter regeneration by engine control, in addition to the first accumulation amount reference value for starting regeneration in a high-load engine operating state, a second accumulation amount larger than this is set. A reference value is set, and filter regeneration is started when the particulate accumulation amount becomes equal to or greater than the second accumulation amount reference value in an engine operating state with a low load such as when idling.

  In an operation state with a high load, filter regeneration is performed by increasing the exhaust gas temperature when the amount of exhaust particulate accumulation reaches or exceeds the first accumulation amount reference value, and the accumulation of exhaust particulate is suppressed. On the other hand, when an operation state with a low load continues, such as during idling, filter regeneration is started only when the accumulation amount of exhaust particulates becomes equal to or higher than a second accumulation amount reference value that is higher than the first accumulation amount reference value. The

  As described above, the reference value for starting engine control for filter regeneration is set stepwise according to the engine operating state, thereby reducing the chance of exhaust gas temperature rise that tends to deteriorate fuel consumption during low-load operation. In addition, accumulation of exhaust particulates can be suppressed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an example of an engine system to which the present invention can be applied. In the figure, reference numeral 1 denotes an engine body, 2 denotes an intake passage, and 3 denotes an exhaust passage. A fuel injection valve 4 and a fuel injection pump 5 are attached to the engine body 1. An air cleaner 6, an air flow meter 7, a compressor 9 of an exhaust turbocharger 8, an intercooler 10, and a throttle valve 11 are interposed in the intake passage 2 from the upstream side. A turbine 12 of an exhaust turbocharger 8 and a filter (DPF) 13 for collecting exhaust particulates are interposed in the exhaust passage 3 from the upstream side. Reference numerals 14 and 15 are temperature sensors for detecting the inlet temperature and the outlet temperature of the filter 13, respectively, and 16 is a pressure sensor for detecting the pressure difference between the front and rear of the filter 12. Reference numeral 17 denotes an EGR passage that communicates the intake passage 2 and the exhaust passage 3, and an EGR valve 18 and an EGR cooler 19 are interposed in the middle thereof. The exhaust turbocharger 8 includes a variable nozzle 20 that can adjust the flow rate of the exhaust gas flowing into the turbine 12. A crank angle sensor 21 detects the engine speed and the crank position.

  Reference numeral 22 denotes a control unit, which is composed of a microcomputer comprising a CPU, a memory and its peripheral devices. The control unit 22 controls the fuel injection timing, the fuel injection amount, the throttle valve opening, the EGR amount, the variable nozzle opening, and the like based on the signals from the various sensors, and calculates the particulate accumulation amount of the filter 13. It functions as a regeneration control means for raising the exhaust gas temperature by means of quantity calculation and engine control.

  FIG. 2 shows a flow of filter regeneration control executed by the control unit 22. This flow is executed periodically at regular intervals. In the following description and the flow, the numbers indicated with the symbol S are processing step numbers.

  In this control, first, the exhaust particulate accumulation amount PM1 is calculated using the load Q and the rotational speed Ne that are constantly detected in the background as the engine operating state in S1. The load Q uses the fuel injection amount command value or the accelerator pedal opening as a representative value, and the rotation speed Ne reads the signal of the crank angle sensor 21. Various methods for calculating the amount of accumulated particulates are known. For example, as shown in FIG. 3, the amount of exhaust particulates (exhaust PM amount) discharged from the engine within a predetermined time Δt1 according to the load Q and the rotational speed Ne is shown. By experimentally creating the assigned table and accumulating the readings at regular intervals, for example, PM1 = PM1 (i) = PM (i-1) + f (Q, Ne) A particulate deposition amount PM1 is obtained. Here, PM (i-1) is the amount of fine particle accumulated previously calculated in step S1. PM1 (i) is the current amount of particulate deposition. The PM discharge rate f (Q, Ne) is the amount of particulate matter discharged from the engine within a certain time Δt1. The fixed time is a time interval in which step S1 is repeated. The PM discharge rate f (Q, Ne) is determined based on the engine load Q and the engine speed Ne by looking up the map of FIG. PM (i-1) is set to the initial value PM0 at the start of the control routine. If the control routine starts after the filter has been completely regenerated (after step S10), the initial value PM0 is zero. If the control routine starts after the filter has been regenerated incompletely (after step S8), the initial value PM0 is not zero.

  In S2, it is determined whether or not the exhaust particulate deposition amount PM1 is equal to or greater than the deposition amount reference value PMn. PMn is a first criterion value for determining whether or not it is necessary to perform filter regeneration. When PM <PMn, there is no need to perform filter regeneration, and the process returns to the beginning without doing anything. When PM ≧ PMn, the average operating state is determined in S3. In order to ensure the stability of the control, for example, the average value of the operation state (Q, Ne) for the past 5 minutes is calculated, and it is determined which point on the map as shown in FIG. .

  If it is determined in the region determination that the region is a low load region including the idle (A region in FIG. 4), then in S4, the accumulation amount PM2 in the low load region is determined by the same table retrieval method as that for PM1. The calculation is made according to the operating state, and the result obtained by adding this to PM1 in S5 is newly set as PM1.

  In S6, it is determined whether or not the current operation state is maintained in the low load region (A region in FIG. 4). If it is maintained, the PM1 is compared with the second deposition amount reference value PMe in S7. As shown in FIG. 5, PMe is set to a value that is larger than the first reference value PMn and smaller than the allowable maximum deposition amount Pmax of the filter 13. For example, PMe is set to 90% of Pmax, and PMn is set to 70% of Pmax. The allowable maximum deposition amount Pmax is a deposition amount at which engine trouble occurs due to clogging of the filter, or a deposition amount at which fine particles are discharged outside through the filter. If PM1 <PMe in this determination, the process returns to S4, and calculation of PM2 and update of PM1 are repeated as long as the load is in the low load region.

  When PM1 ≧ PMe is satisfied in the determination of S7, a balance point reproduction process (BPT reproduction process) is performed in S8. The BPT regeneration process is a control that does not increase or decrease the amount of particulates deposited on the filter 13 remaining when the regeneration mode (S8) is entered. This is because it is impossible to burn all the fine particles accumulated on the filter 13 by, for example, continuous running for 5 minutes in an operation mode with a lot of low vehicle speed running, so the amount of fine particles deposited on the filter 13 is not increased. The current state is maintained so as not to decrease, and when the vehicle speed enters the high speed side regeneration mode (S10), all the fine particles accumulated on the filter 13 are burned out by continuous running for 5 minutes, for example. To do.

  Specifically, when the regeneration process is started and the exhaust temperature is raised to a target value (about 400 ° C.), the fine particles deposited on the filter 13 are gently burned. On the other hand, particulates in the exhaust gas flow into the filter 13 during the regeneration process and accumulate on the bed of the filter 13. Therefore, the amount of fine particles flowing into the filter 13 is adjusted (reduced) so that the amount of fine particles that flow into the filter 13 and accumulate on the bed matches the amount of fine particles that disappear from the bed due to combustion.

  In FIG. 2A, S11, 12, and 13 are flowcharts of the BPT reproduction process. In S11, the exhaust temperature is raised to the target value (set to about 400 ° C.) using the temperature raising means. As the temperature raising means, those for controlling the main injection, those for retarding the main injection timing, those for performing the intake throttle (intake amount control), those for increasing the post injection amount of fuel, those for retarding the post injection timing, The nozzle opening degree control and EGR control of the variable nozzle exhaust turbocharger can be considered. Further, it is conceivable to increase the load of auxiliary equipment such as an air compressor and an alternator (auxiliary equipment load control) as a temperature raising means. In the BPT regeneration, the deterioration of the fuel consumption accompanying the exhaust temperature increase control can be suppressed to the minimum.

  In S12, the smoke reduction operation is performed, and in S13, it is checked whether or not the differential pressure across the filter 13 has increased. If the differential pressure across the filter 13 increases, it is determined that the amount of particulate that flows into the filter 13 and accumulates on the bed exceeds the amount of particulate that disappears from the bed due to combustion, and returns to S12 to continue the smoke reduction operation. .

  Here, the smoke reduction is another expression of the particulate reduction, and if the differential pressure across the filter 13 increases, the smoke reduction operation is performed, so that the particulate accumulation amount of the filter 13 remaining when entering the regeneration mode is You can make it neither increase nor decrease.

  Means for performing the function of S12 (smoke reduction operation means) are those that reduce the EGR amount, those that reduce the pilot injection amount (in the case of a diesel engine), those that increase the pilot injection interval, immediately upstream of the intake port It can be considered that the swirl strength is increased by closing the swirl control valve at the position.

  Further, in order to determine whether or not the differential pressure across the filter has increased in S13, for example, the following may be performed. That is, the differential pressure before and after the filter 13 immediately after entering the regeneration mode is detected by the differential pressure sensor 16 and stored in the memory, and then the actual differential pressure before and after the filter detected by the differential pressure sensor 16 is detected. If the actual pressure difference across the filter increases when the actual pressure difference across the filter increases above this memory value, conversely, if the actual pressure difference across the filter is less than or equal to this memory value, the difference across the filter It may be determined that the pressure has not increased.

  On the other hand, if it is determined in the operation region determination of S3 or S6 that the region is a high load region, a regeneration processing subroutine in the high load region of S10 is executed. This is because, for example, in the B region with a relatively low load shown in FIG. 4, quantitative regeneration is performed in order to suppress deterioration in fuel consumption, and in the C region where the load is higher and the amount of heat of exhaust is large, the burden of fuel consumption for regeneration is small. Therefore, complete regeneration is continued until the accumulated particulates disappear. The region D is a natural regeneration region where an exhaust temperature sufficient for regeneration can be obtained without performing exhaust gas temperature control.

  In this control, in the operation region judgment processing (S6) in the low load region, the transition is made to the regeneration processing at the time of high load in the instantaneous operation state, thereby responding to the transition to the high load operation state with high regeneration efficiency. Thus, the reproduction can be performed promptly. After the high load regeneration process is completed, the process returns to the beginning of the process of FIG. 2 again, and the regeneration process according to the amount of accumulated particulates and the operation region is repeated.

  The exhaust emission control device of the present invention can be used as an exhaust emission control device for automobile engines such as diesel engines.

1 is a schematic diagram of an engine system to which the present invention can be applied. The flowchart which shows the process sequence of the reproduction | regeneration control which concerns on one Embodiment of this invention. The flowchart which shows the process sequence of BPT reproduction | regeneration processing. Explanatory drawing of the table for the accumulation amount calculation used by the said reproduction | regeneration control. Explanatory drawing of a driving | operation area | region. Explanatory drawing of the reference value of accumulation amount.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine main body 2 Intake passage 3 Exhaust passage 4 Fuel injection valve 5 Fuel injection pump 7 Air flow meter 8 Exhaust turbocharger 9 Compressor 11 Throttle valve 12 Turbine 13 Filter 17 EGR passage 18 EGR valve 18
20 Variable nozzle of turbocharger 21 Crank angle sensor 22 Control unit

Claims (8)

A filter that collects engine exhaust particulates;
Means for detecting engine operating conditions including load;
A deposition amount calculating means for calculating a particulate deposition amount of the filter based on an engine operating state;
Filter regeneration control means for raising the exhaust temperature by engine control,
The regeneration control means has a first accumulation amount reference value for starting regeneration in a high-load operation state, and a second accumulation amount reference value for starting regeneration in an idle operation state, and the second The engine exhaust gas purification apparatus, wherein the accumulation amount reference value is set to be larger than the first accumulation amount reference value. The reproduction control means includes
The engine exhaust gas purification apparatus according to claim 1, wherein an idle operation state and a predetermined low load operation state are set as an operation state to which the second accumulation amount reference value for starting regeneration is applied. The reproduction control means includes
The balance point regeneration in which the amount of particulates flowing into the filter and depositing and the amount of particulates disappearing by combustion is made to coincide with each other in a low-load operation state where the second deposition amount reference value is applied. The engine exhaust gas purification apparatus as described. The reproduction control means includes
The exhaust emission control device for an engine according to claim 1 or 2, wherein complete regeneration is performed in a high-load operation state to which the first accumulation amount reference value is applied. The reproduction control means includes
Which deposition amount reference value is to be applied is determined based on a result obtained by averaging the operation state for a predetermined time. However, during regeneration based on the second deposition amount reference value, the operation state is the first deposition amount reference. 5. The engine exhaust gas purification apparatus according to claim 4, wherein the engine control system immediately shifts to regeneration control based on the first accumulation amount reference value when a high load operating state to which the value is to be applied is entered. The engine control for raising the exhaust temperature is
3. The fuel injection timing control, the fuel injection amount control, the nozzle opening control of the variable nozzle exhaust turbocharger, the EGR control, the intake air amount control, and the auxiliary machinery load control are applied to any one of claims 1 and 2. The engine exhaust gas purification apparatus as described. The reproduction control means includes
The engine exhaust purification device according to claim 1 or 2, wherein the engine operating state is determined based on a load and an engine speed. The accumulation amount calculating means includes:
The exhaust emission control device for an engine according to claim 1 or 2, wherein the accumulation amount is calculated by referring to a table that gives the particulate accumulation amount from the engine load and the rotational speed.

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