JP4120545B2 - 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.

As shown in Patent Document 1, a filter is provided in an engine exhaust system to purify particulate matter discharged from a diesel engine or the like (hereinafter referred to as “exhaust particulates”), and trapped exhaust particulates are collected at a predetermined interval. An apparatus is known in which the filter is regenerated by oxidation or incineration. The regeneration of the filter is performed by increasing the exhaust temperature by engine control such as retarding the fuel injection timing or secondary injection.
JP-A-5-106427

  When the filter is regenerated, combustion heat is generated due to the combustion of exhaust particulates as the exhaust temperature rises. Especially in a filter with a catalyst, the heat of reaction when HC, CO, etc. in the exhaust is oxidized is also added, so the filter temperature is over 600 ℃ May become hot. When the engine shifts to idle operation under such a high temperature state due to regeneration, even if the regeneration is stopped, the exhaust flow rate flowing through the filter rapidly decreases, and the cooling action by the exhaust decreases, so that the temperature of the filter greatly increases. Such an overheated state causes the filter and the catalyst to deteriorate.

The present invention relates to an exhaust flow rate determination for determining a decrease in an engine exhaust flow rate in an engine exhaust gas purification apparatus having a filter for collecting exhaust particulates of an engine and a filter regeneration control means for increasing exhaust temperature by engine control. And a regeneration suppression unit that suppresses the regeneration for a predetermined time after detecting a decrease in the exhaust flow rate, and the regeneration suppression unit performs the regeneration within a period of time before the detection of the decrease in the exhaust flow rate. The regeneration is suppressed on the condition that the filter temperature is equal to or higher than a predetermined criterion value, and the regeneration is not suppressed when the regeneration is not performed within the period. And

  According to the present invention, even if the exhaust gas flow rate suddenly decreases after shifting from the operation in the regeneration region where the exhaust gas flow rate is relatively large to the low load operation such as idling, the predetermined period from that state Since the exhaust gas temperature control is suppressed, it is possible to prevent the filter from overheating due to the sudden decrease in the exhaust gas flow rate and enhance its durability.

  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 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 the regeneration control for increasing the exhaust temperature by engine control. Means, an exhaust flow rate determining means for determining a decrease in the engine exhaust flow rate, and a regeneration suppressing means for suppressing the regeneration for a predetermined time after detecting the decrease in the exhaust flow rate.

  2 to 4 show a control flow relating to filter regeneration control executed by the control unit 22. These flows are executed periodically at regular intervals. In the following description and the flow, the numbers indicated with the symbol S are processing step numbers.

  FIG. 2 shows the basic operation of the regeneration control. First, in S1, the state of the regeneration prohibition flag R1 is examined. The reproduction prohibition flag R1 is set to 1 when a predetermined prohibition condition is satisfied by the processing of FIG. 3 described later, and is set to 0 when the prohibition condition is released. When R1 = 0, the current routine is terminated without performing the regeneration of the filter 13, and when R1 = 1, the regeneration processing from S102 is executed.

  In the regeneration process, first, an exhaust particulate collection amount (amount deposited on the filter) PM is calculated using the load Q and the rotational speed Ne that are constantly detected in the background as the engine operating state in S102. The load Q uses the fuel injection amount command value as a representative value, and the rotation speed Ne reads the signal of the crank angle sensor 21. There are various known methods for calculating the amount of collected particulate matter. For example, a table in which the amount of exhaust particulate matter (exhaust PM amount) discharged from the engine within a certain period of time according to the load Q and the rotational speed Ne is assigned experimentally in advance. The particulate collection amount PM is obtained by integrating the readings at regular intervals.

  In S103, it is determined whether or not the exhaust particulate accumulation amount PM is greater than or equal to a deposition amount reference value PMn. PMn is a reference value for determining whether or not it is necessary to perform filter regeneration. When PM <PMn, there is no need to perform filter regeneration, so this routine is terminated without doing anything. When PM ≧ PMn, the operation state is determined in S104. This determines which operating point on the map Q and Ne correspond to, for example, as shown in FIG.

  When it is determined in the region determination that the region is a reproducible region, exhaust temperature increase control for filter regeneration is performed for a predetermined time in S105 to S107. Various exhaust temperature rise control methods are known. In the engine system shown in FIG. 1, for example, the intake throttle by the throttle valve 11, the retarded fuel injection timing, the secondary injection, the EGR amount reduction, the variable nozzle Any one of the opening control of 20 is performed to ensure an exhaust temperature of 300 ° C. or higher necessary for fine particle regeneration. In addition to the above, it is also possible to increase the exhaust temperature by increasing the load of auxiliary equipment such as an air conditioner compressor and an alternator.

  By the way, when the regeneration is performed as described above, the temperature of the filter 13 is raised by the combustion action of the exhaust particulates and the like. For this reason, when the operation state of low exhaust flow rate such as idling immediately after regeneration is reached, the temperature of the filter significantly increases as shown in FIG. If regeneration is started while the temperature is rising as described above, the filter temperature further rises as shown by an imaginary line in the figure, and an overheated state may occur, which may cause filter deterioration. In order to avoid such a problem, in the present invention, the low exhaust flow rate state is determined by the processing shown in FIG. 3, and the regeneration prohibition flag R1 is set so that regeneration is temporarily suppressed.

  In FIG. 3, first, a reproduction history within the past t0 time is stored in S201, and then the presence or absence of the reproduction history is determined in S202. If a certain amount of time elapses after the regeneration is completed, the filter temperature decreases during that time. Therefore, even if the regeneration is performed again after the exhaust flow rate has decreased, the filter is less likely to overheat. Therefore, t0 is set as the required filter cooling period, and the presence or absence of regeneration within the time is determined. That is, if there is no playback history within the past t0 time, there is no need to prohibit playback, and thus this routine ends. Note that the regeneration prohibition flag R1 is initially set to 0 by the initialization process when starting the control system. Further, t0 may be given as a map of the bed temperature of the filter 13 and the amount of collected particulates when in the reproducible region, or may be obtained as its moving average value.

  If it is determined in S202 that there is a reproduction history within the time t0, then the temperature Tdpf of the filter 13 is detected in S203. As Tdpf, the bed temperature or inlet temperature of the filter 13 itself is detected. If it is determined in S204 that Tdpf is lower than the predetermined reference temperature T0, it is assumed that there is little risk of filter overheating, and this routine ends.

  If Tdpf ≧ T0 in the determination of S204, then the collected amount PM is calculated in S205. The calculation method of the collection amount PM is as described above. When the amount of collected particulates is small, the generation of combustion heat at the time of regeneration is also small. Therefore, in the determination process of S206, the comparison is made with a predetermined reference value PM0. When PM <PM0, the current routine is terminated.

  If PM ≧ PM0 in the determination of S206, the exhaust flow rate Qex is then calculated in S207. The exhaust flow rate is obtained, for example, by calculation using the engine speed and the fuel injection amount as a function or by searching a table formed in advance using these as parameters. In step S208, Qex is compared with a predetermined reference value Q0. When Qex ≧ Q0 or more, there is little risk of filter overheating, and thus this routine ends. The determination of the low exhaust flow rate state may be made on the condition that the time differential value of the exhaust flow rate Qex is smaller than a predetermined reference value, or may be further added. Or you may make it detect the idle driving | running state detected from the accelerator pedal opening degree etc. as a driving | running state which represents a low exhaust flow volume.

  If Qex <Q0 in the determination of S208, the air-fuel ratio Lambda is compared with a predetermined reference value L0 in S209. The air-fuel ratio is directly detected by an exhaust oxygen sensor or determined from a control command value of the air-fuel ratio control system. Even when the exhaust gas flow rate state is low, when the oxygen concentration in the exhaust gas is low, the temperature rise is also small. Therefore, when the low oxygen concentration state is Lambda <L0, the current routine is terminated.

  When Lambda ≧ L0 in the determination of S209, the regeneration prohibition flag R1 is set to 1 in S210, and then the state of R1 = 1 is maintained until the set time t1 elapses through the processing of S211 to S214. As a result, the filter regeneration by the regeneration control of FIG. 2 is prohibited for t1 time. Therefore, even if the regeneration state is shifted to the operation state again immediately after the low exhaust flow rate as in the idling operation, the filter regeneration is not performed. It is not performed, and overheating of the filter due to regeneration under the conditions can be prevented.

  The regeneration prohibition flag R1 is set to 0 when the set time t1 elapses, and the timer for timing is reset. The set time t1 may be a fixed time, but may be variably set, for example, by a process as shown in FIG. FIG. 4 is a graph in which t1 is set by reading a map set in advance as shown in FIG. 7 based on the relationship between the amount of particulate matter PM remaining in the filter and the inlet temperature. As shown in FIG. 7, t1 is set to be longer as the filter inlet temperature is higher or as the amount of particulate matter in the filter is larger. That is, by setting t1 variably according to the amount of fine particles that cause overheating and the initial temperature condition, the time for suppressing regeneration is minimized and the regeneration efficiency is ensured.

  FIG. 8 shows the effect of the reproduction prohibition control described above. When shifting from the operating state in which regeneration control is being performed to idle operation, regeneration is prohibited for a certain period of time t1 even if the engine is in a recyclable operation region. Since regeneration is permitted after the temperature of the filter 13 is lowered due to the elapse of the regeneration prohibition time t1, the maximum temperature after the start of regeneration is kept low as indicated by the imaginary line.

  In the embodiment, in order to increase the stability of control, regeneration may be prohibited only when the low exhaust flow rate state continues for a certain time or longer in the processing of S207 to S210 of FIG. In the processing of FIG. 4, the regeneration prohibition time t1 may be set so as to increase as the time during which the predetermined low exhaust flow rate state continues is longer. Further, in the above embodiment, regeneration processing from a low exhaust flow rate condition that may cause overheating of the filter is completely prohibited. Good.

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. 6 is a flowchart showing a processing procedure for setting a regeneration prohibition flag R1 used in the regeneration control. The flowchart which shows the process sequence for setting reproduction | regeneration prohibition time. Explanatory drawing about the filter reproducible area | region of an engine. Filter temperature characteristic diagram when regeneration is started in a low exhaust flow rate region. The flowchart which shows the setting process procedure of reproduction | regeneration prohibition time. The filter temperature characteristic figure which shows the effect by this invention.

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 20 Variable nozzle 21 of turbocharger 21 Crank angle sensor 22 control unit

Claims (10)

A filter that collects engine exhaust particulates;
In an engine exhaust purification device, comprising a filter regeneration control means for increasing the exhaust temperature by engine control,
An exhaust flow rate judging means for judging a decrease in the engine exhaust flow rate,
E Bei from detecting a decrease in the exhaust gas flow rate and suppressing reproduction suppressing means the reproduction predetermined time,
The regeneration suppressing means suppresses the regeneration on condition that regeneration is performed within a period of time before a decrease in exhaust gas flow is detected and the temperature of the filter is equal to or higher than a predetermined criterion value. On the other hand, when the regeneration is not performed within the period, the regeneration is not suppressed . The regeneration suppressing means is
The engine exhaust gas purification apparatus according to claim 1, wherein the regeneration is not suppressed when the particulate collection amount of the filter is equal to or less than a predetermined determination reference value. The regeneration suppressing means is
The engine exhaust gas purification apparatus according to claim 1, wherein the regeneration is not suppressed when a decrease in the exhaust gas flow rate is detected and the oxygen concentration in the exhaust gas thereafter is equal to or lower than a predetermined reference value. The engine exhaust gas purification apparatus according to claim 1, wherein the predetermined time during which the regeneration is suppressed is a constant value. 2. The engine exhaust purification system according to claim 1, wherein the predetermined time for suppressing the regeneration is variably set so as to become longer as the catalyst temperature is higher or as the amount of collected particulates of the filter is larger. 2. The engine exhaust gas purification apparatus according to claim 1, wherein the predetermined time for suppressing the regeneration is variably set so as to increase as the time during which the exhaust gas flow rate decreases is longer. The exhaust flow rate determining means includes
The engine exhaust gas purification apparatus according to claim 1, wherein the exhaust gas flow rate is determined to be decreased when the exhaust gas flow rate becomes smaller than a predetermined determination reference value. 2. The engine exhaust gas purification apparatus according to claim 1, wherein the exhaust gas flow rate determination unit determines that the exhaust gas flow rate decreases when a state in which the exhaust gas flow rate is smaller than a predetermined determination reference value continues for a predetermined time or longer. The engine exhaust gas purification apparatus according to claim 1, wherein the exhaust gas flow rate determining means determines that the exhaust gas flow rate is decreased when an idle operation state is detected. The engine control for raising the exhaust temperature is
2. The engine according to claim 1, wherein any one of fuel injection timing control, fuel injection amount control, variable nozzle exhaust turbocharger nozzle opening control, EGR control, intake air amount control, and auxiliary machinery load control is applied. Exhaust purification device.

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