JP4366940B2 - Exhaust purification equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust emission control device for processing exhaust particulates of, for example, a diesel engine.
[0002]
[Prior art]
In order to process exhaust particulates discharged from diesel engines, a filter that collects particulates is placed in the exhaust system, and when a predetermined amount of particulates is deposited on the filter, the filter temperature is raised and deposited on the filter. In this case, the regeneration speed is improved by changing (increasing) the intake fresh air flow rate during the regeneration period of the filter. There is one that realizes improvement in efficiency and shortening of the reproduction period (see Patent Document 1).
[0003]
[Patent Document 1]
JP, 2000-145432, A).
[0004]
[Problems to be solved by the invention]
By the way, it is necessary to prevent particulates from remaining unburned near the end of the filter regeneration process. This is because the following problems occur when unburned residue occurs in the filter.
[0005]
(1) Since the pressure loss of the filter does not disappear completely, the fuel consumption deteriorates.
[0006]
(2) Accumulation of particulates in the unburned part causes an imbalance in the distribution of the deposit, and the durability of the filter decreases due to rapid combustion of that part during the next regeneration process.
The
[0007]
For this reason, it is conceivable to set the target oxygen concentration in the exhaust gas to a high concentration so that particulates do not remain in the filter later in the regeneration process. By applying the conventional device, the intake fresh air flow rate is increased.
[0008]
However, the intake fresh air flow rate has a limit of intake fresh air flow rate (hereinafter referred to as “new air flow rate limit”) that cannot be flowed any further under the operating conditions of the engine at that time. It is not possible to increase the intake fresh air flow rate until it exceeds.
[0009]
In this way, if the intake fresh air flow rate is limited and the target oxygen concentration in the latter stage of the regeneration process cannot be achieved, the regeneration speed cannot be sufficiently increased, the regeneration process time is prolonged, fuel consumption is deteriorated, and part of the particulates There is a possibility that an unburned residue will occur and the durability of the filter may be reduced due to a local abnormal temperature rise during the next regeneration process.
[0010]
Therefore, the present invention aims to bring the filter bed temperature close to the allowable maximum temperature even when the intake fresh air flow rate is limited by the fresh air flow limit.
[0011]
[Means for Solving the Problems]
The present invention provides an exhaust purification apparatus for an engine that includes a filter for collecting particulates in an exhaust passage and performs filter regeneration processing when the filter regeneration timing is reached. High Set to concentration So that the target oxygen concentration can be obtained. Oxygen concentration control And later in the regeneration process The intake fresh air flow is limited by the fresh air flow limit. Therefore, the intake fresh air flow rate to achieve the target oxygen concentration cannot be realized. At this time, it is configured such that control for repeatedly increasing and decreasing the intake fresh air flow rate is performed, or control for fuel injection for increasing the exhaust gas temperature is performed.
[0012]
【The invention's effect】
Late stage of regeneration processing High Set to concentration So that the target oxygen concentration can be obtained. Oxygen concentration control And later in the regeneration process The intake fresh air flow is limited by the fresh air flow limit. Therefore, the intake fresh air flow rate to achieve the target oxygen concentration cannot be realized. In this case, the oxygen concentration is insufficient and the bed temperature of the filter does not rise and the regeneration speed decreases. According to the present invention, the filter is controlled by repeatedly increasing and decreasing the intake fresh air flow rate. The bed temperature can be increased.
[0013]
This is because the exhaust flow that passes through the filter has the function of taking heat away from the filter, and the intake fresh air flow rate starts to decrease from the increase and then suddenly decreases.In other words, if the exhaust flow rate that passes through the filter decreases rapidly, the heat from the filter is lost. This utilizes the fact that the amount of leftover is reduced (reduction of heat loss), and thereby the bed temperature is temporarily raised during the regeneration process of the filter.
[0014]
The bed temperature of the filter can also be increased by controlling the fuel injection for increasing the exhaust temperature.
[0015]
In this way, in the present invention, even if the intake fresh air flow rate is increased so that the target oxygen concentration in the latter stage of the regeneration process is achieved, it is blocked by the new air flow rate limit that is reduced by the operating conditions at that time. Actually, when the intake fresh air flow rate does not increase and the bed temperature during the filter regeneration process decreases, the intake fresh air flow rate is repeatedly increased or decreased, or the fuel injection is controlled to increase the exhaust temperature. Thus, the filter bed temperature can be brought close to the allowable maximum temperature even under operating conditions in which the fresh air flow rate limit becomes smaller in the later stage of the regeneration process, so that particulate unburned residue does not occur in the filter.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the drawings.
[0017]
FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention.
[0018]
In FIG. 1, reference numeral 1 denotes a diesel engine, and a diaphragm type EGR valve 6 that responds to a control pressure from a pressure control valve (not shown) is connected to an EGR passage 4 connecting the exhaust passage 2 and the collector portion 3a of the intake passage 3. I have. The pressure control valve is driven by a duty control signal from the engine controller 31 and thereby obtains a predetermined EGR rate corresponding to the operating conditions.
[0019]
The engine includes a common rail fuel injection device 10. The fuel injection device 10 mainly includes a fuel tank (not shown), a supply pump 14, a common rail (pressure accumulation chamber) 16, and a nozzle 17 provided for each cylinder. The fuel pressurized by the supply pump 14 is accumulated in the pressure accumulation chamber 16. Are once stored, the high pressure fuel in the pressure accumulating chamber 16 is distributed to the nozzles 17 corresponding to the number of cylinders.
[0020]
The nozzle 17 (fuel injection valve) includes a needle valve, a nozzle chamber, a fuel supply passage to the nozzle chamber, a retainer, a hydraulic piston, a return spring, and the like, and a three-way valve (not shown) is interposed in the fuel supply passage to the hydraulic piston. It is disguised. When the three-way valve (solenoid valve) is OFF, the needle valve is seated, but when the three-way valve is turned ON, the needle valve rises and fuel is injected from the nozzle hole at the tip of the nozzle. That is, the fuel injection start timing is adjusted by the switching timing of the three-way valve from OFF to ON, and the fuel injection amount is adjusted by the ON time. If the pressure in the pressure accumulating chamber 16 is the same, the fuel injection amount increases as the ON time increases. Become.
[0021]
The exhaust passage 2 downstream of the opening of the EGR passage 4 is provided with a variable capacity turbocharger 21 in which a turbine 22 that converts heat energy of exhaust gas into rotational energy and a compressor 23 that compresses intake air are connected coaxially. A variable nozzle 24 driven by an actuator 25 is provided at the scroll inlet of the turbine 22. The engine controller 31 allows the variable nozzle 24 to obtain a predetermined supercharging pressure from a low rotational speed range on the low rotational speed side. The nozzle opening degree (tilting state) for increasing the flow rate of the exhaust gas introduced into the turbine 22 is controlled to the nozzle opening degree (fully open state) by introducing the exhaust gas into the turbine 22 without resistance on the high rotational speed side.
[0022]
The actuator 25 includes a diaphragm actuator 26 that drives the variable nozzle 26 in response to the control pressure, and a pressure control valve 27 that adjusts the control pressure to the diaphragm actuator 26. A duty control signal is generated so as to achieve the target nozzle opening, and this duty control signal is output to the pressure control valve 27.
[0023]
In the engine controller 31 to which signals from the accelerator sensor 32, the sensor 33 for detecting the engine speed and the crank angle, the water temperature sensor 34, and the air flow meter 35 are inputted, the target EGR rate and the target supercharging pressure are determined based on these signals. EGR control and supercharging pressure control are performed in a coordinated manner.
[0024]
A filter 41 that collects particulates in the exhaust is installed in the exhaust passage 2. When the accumulated amount of particulates on the filter 41 reaches a predetermined value, the exhaust temperature is raised and the particulates accumulated on the filter 41 are burned and removed.
[0025]
In order to detect the pressure loss of the filter 41 (the pressure difference between the upstream and downstream of the filter 41), a differential pressure sensor 36 is provided in the differential pressure detection passage that bypasses the filter 41.
[0026]
The pressure loss ΔP of the filter 41 detected by the differential pressure sensor 36 is sent to the engine controller 31 together with the filter inlet temperature T1 from the temperature sensor 37 and the filter outlet temperature T2 from the temperature sensor 38, and is mainly composed of a microprocessor. The engine controller 31 that is to perform the regeneration processing of the filter 41 based on these. That is, the period of the regeneration process of the filter 41 is divided into three periods of the first period (time t1), the middle period (time t2), and the second period (time t3) as shown in FIG. The exhaust gas temperature control and the oxygen concentration control in the exhaust gas are performed for each period as follows.
[0027]
The control waveform will be described with reference to FIG. In FIG. 22, the characteristic of the target value of the filter inlet temperature according to the present embodiment is shown by the solid line in the second stage, and the target temperature by the conventional apparatus is also the target value of the filter inlet temperature for comparison in the second stage. The characteristics in the case of being understood are indicated by a one-dot chain line and a broken line. The third stage shows the characteristics of the target oxygen concentration in the exhaust according to the present embodiment.
[0028]
<1> First period: In order to rapidly raise the bed temperature of the filter 41 to the target bed temperature tTbed, the target value tT1 of the filter inlet temperature is set higher than the target bed temperature tTbed, and the target value tT1 is rapidly obtained so as to obtain the target value tT1. Perform temperature rise control.
[0029]
Here, the target bed temperature tTbed is a temperature (for example, 450 ° C. to 650 ° C.) at which the particulates deposited on the filter 41 are self-ignited and burned quickly.
[0030]
Here, as the target value tT1, as shown by the solid line in the second stage of FIG. 22, a temperature much higher than that in the case of the one-dot chain line or the broken line, which is a conventional apparatus, is set. As shown by the solid line at the bottom of FIG. For this reason, the temperature increase according to the present embodiment is referred to as “rapid temperature increase”.
[0031]
However, the target oxygen concentration in the exhaust gas is not determined within the period of the previous period, and therefore oxygen concentration control is not performed (see the third stage in FIG. 22).
[0032]
When the rapid temperature increase control is performed so that the target value tT1 is obtained, the bed temperature of the filter 41 rises and reaches the target bed temperature tTbed, so that the previous period is terminated and the next stage is shifted to the middle period.
[0033]
<2> Middle period: In order to suppress the burning rate of the particulates accumulated in the filter 41, the target oxygen concentration in the exhaust gas is set to a low concentration as shown in the third stage of FIG. Oxygen concentration control (first oxygen concentration control) is performed so that the target oxygen concentration is obtained.
[0034]
In the middle period, the target value tT1 of the filter inlet temperature is switched to the target bed temperature tTbed and maintained. This is to avoid the target bed temperature tTbed being obtained, if the temperature increase control is further continued, the bed temperature is increased beyond the allowable maximum temperature Tmax.
[0035]
When the oxygen concentration control in the exhaust gas is performed so that the target oxygen concentration set to a low concentration is obtained, the combustion proceeds without the particulates accumulated on the filter 41 burning rapidly.
[0036]
<3> Late stage: To completely burn out the particulates remaining in the filter 41 near the end of the regeneration process, the target oxygen concentration in the exhaust is set to a higher concentration than in the middle stage as shown in the third stage of FIG. Oxygen concentration control (second oxygen concentration control) is performed so as to obtain this high concentration target oxygen concentration.
[0037]
Also in the latter period, the target value tT1 of the filter inlet temperature is maintained at the target bed temperature tTbed without changing from the middle period.
[0038]
When the oxygen concentration control in the exhaust gas is performed so that the target oxygen concentration set to a high concentration can be obtained, the regeneration efficiency increases as shown by the solid line in the first stage of FIG. 22 and approaches 100%, which is complete regeneration. .
[0039]
Next, the contents of these controls performed by the engine controller 31 will be described in detail.
[0040]
The flowchart of FIG. 3 is a main routine for performing a reproduction process, and this flow is executed at regular time intervals (for example, every 10 ms).
[0041]
In step 1, the reproduction processing flag is checked. The setting of the reproduction processing flag will be described with reference to the flowchart of FIG.
[0042]
The flow in FIG. 4 is executed at regular intervals (for example, every 10 ms) separately from FIG. In FIG. 4, in step 11, the pressure loss ΔP of the filter 41 is read from the output of the differential pressure sensor 36.
[0043]
In step 12, the reproduction processing flag is checked. The reproduction processing flag is a flag that becomes 1 when a reproduction processing condition described later is satisfied. Since the engine is initially set to zero when the engine is started, the process proceeds to steps 13 and 14 before the regeneration process condition is satisfied, and the regeneration process condition is checked. The establishment of the regeneration process condition is that the pressure loss ΔP of the filter 41 exceeds the regeneration start determination value ΔPHmax and is in the regeneration execution condition.
[0044]
Here, the regeneration execution condition is satisfied, for example, when the operating conditions determined by the engine speed and the fuel injection amount (corresponding to the engine load) are in the regions R1 to R4 shown in FIG.
[0045]
The regeneration execution condition is not satisfied when the vehicle is in the region R5, which is a low load region close to idling or when idling, because the exhaust temperature is originally low during idling, and the filter 41 is used even after post injection and intake throttling This is because the bed temperature cannot be raised to the target bed temperature tTbed.
[0046]
Therefore, when the pressure loss ΔP is equal to or smaller than the regeneration start determination value ΔPHmax or when the engine operating condition is not in the regeneration execution condition, the current process is terminated as it is.
[0047]
When the pressure loss ΔP of the filter 41 exceeds the regeneration start determination value ΔPHmax and the operating condition determined by the engine speed and the fuel injection amount is the regeneration execution condition, it is determined that the regeneration process can be performed, and the process proceeds to Step 15 for regeneration. Process flag = 1.
[0048]
Since the reproduction processing flag = 1 cannot proceed from step 12 to step 13 from the next time, the processing is ended as it is. That is, after the reproduction processing flag is set to 1 in step 15, it remains 1 even when the reproduction processing described later is interrupted (see FIG. 11), and is reset to 0 at the timing of completion of the reproduction processing described later. (See step 31 in FIG. 5).
[0049]
Returning to FIG. 3, when the reproduction process flag = 1 in step 1, the process proceeds to step 2 and subsequent steps to perform the reproduction process. In step 2, a reproduction phase is set. The setting of the reproduction phase will be described with reference to the flow of FIG.
[0050]
The flow of FIG. 5 is for comparing the elapsed time T from the start of the reproduction process with the set times t1, t2, and t3, and setting the first, middle, and second periods of the reproduction phase at regular intervals (for example, 10 ms). Every).
[0051]
In step 21, the reproduction end flag is checked. Since the reproduction end flag is initially set to zero, the process proceeds to step 22 to see the reproduction interruption flag. The playback interruption flag is also initially set to zero, and is a flag that becomes 1 when the playback process cannot be continued before the end of the playback process, as will be described later with reference to FIG.
[0052]
If it is assumed that it is immediately after the start of the reproduction process, the reproduction interruption flag = 0, so that the process proceeds to step 23 to see the reproduction process flag. When the reproduction processing flag = 0, the current processing is terminated as it is.
[0053]
When the reproduction processing flag = 1, the process proceeds to step 24, and the timer value T (initially set to zero) is set.
T = Tz + ΔT (1)
Where ΔT: calculation period (= 10 ms),
Tz: previous value of timer value,
It is incremented by the expression. This timer is for measuring the elapsed time from the start of the reproduction process (that is, the reproduction process time).
[0054]
In steps 25 and 26, each period of the reproduction phase is set as follows based on the timer value T and the set times t1, t2, and t3 (see FIG. 2).
[0055]
(1) When T <t1:
The process proceeds from step 25 to step 27, where the reproduction phase is set to the previous period.
[0056]
(2) When t1 ≦ T <t1 + t2:
Proceeding from step 25 to step 28, the reproduction phase is set to the middle period.
[0057]
(3) When t1 + t2 ≦ T <t1 + t2 + t3:
Proceeding from steps 25 and 26 to step 29, the reproduction phase is set to the latter period.
[0058]
(4) When t1 + t2 + t3 ≦ T:
At this time, it is determined that the reproduction process is completed, and the process proceeds from Steps 25 and 26 to Step 30 to set the reproduction end flag = 1. In order to prepare for the next reproduction process, the reproduction process flag = 0 and the timer value T = 0 are set in steps 31 and 32.
[0059]
The set times t1, t2, and t3 used in step 25 may be constant values, but here, t1 and t2 are set as variable values as follows.
[0060]
FIG. 6 is an example of setting t1 with respect to the actual bed temperature at the start of the regeneration process. In order to regenerate the filter 41, it is necessary to raise the target bed temperature tTbed, which is a temperature at which the particulates accumulated in the filter 41 can self-ignite and burn, but t1 is the target bed temperature from the start of the regeneration process. This is the time until it is raised to tTbed. This time t1 becomes smaller as the bed temperature at the start of the regeneration process becomes higher as shown in FIG. This is because if the bed temperature at the start of the regeneration process is high, the time required to raise the filter bed temperature to the target bed temperature can be shortened.
[0061]
Further, t1 = 0 in the temperature range of tTbed or higher. This is because particulates accumulated on the filter 41 are self-ignited and burned without performing temperature rise control in a temperature range of tTbed or higher, and at this time, t1 is set to zero and the next stage is immediately shifted to the middle stage. Because.
[0062]
Further, the bed temperature at the start of the regeneration process is set to a constant value in a temperature range lower than the predetermined value Ta. This is a constant value because the temperature cannot be increased to the target bed temperature tTbed even if the temperature of the filter 41 is increased in a temperature range lower than Ta.
[0063]
In FIG. 6, the actual bed temperature at the start of the regeneration process on the horizontal axis is determined from the two temperatures T1 and T2 detected by the temperature sensors 37 and 38 provided before and after the filter 41 at the start of the regeneration process.
Tbed = b1 · T1 + b2 · T2 (2)
Where Tbed: the bed temperature at the start of the regeneration process,
b1, b2: constants,
It may be estimated (calculated) by the following formula. In formula (2), b1 and b2 are values determined by experiments.
[0064]
FIG. 7 shows an example of setting t2 with respect to the particulate deposition amount (abbreviated as PM deposition amount in the figure) at the start of the regeneration process. After raising the bed temperature of the filter 41 to the target bed temperature tTbed, the particulates accumulated in the filter 41 are self-ignited and burned. In this case, in a state where the oxygen concentration in the exhaust gas is sufficiently high (predetermined value A on the lean side of the stoichiometric air-fuel ratio in terms of air-fuel ratio), a large amount of particulates accumulated in the filter 41 burns rapidly, As a result, the bed temperature of the filter 41 rises above the allowable maximum temperature Tmax, and the filter 41 may be thermally deteriorated, resulting in a decrease in durability. For this reason, the oxygen concentration is low enough that a large amount of particulate matter accumulated in the filter 41 does not burn suddenly (in terms of air-fuel ratio, the leaner side than the stoichiometric air-fuel ratio, and the predetermined value B on the rich side rather than A above) The time (period) to be maintained at) is t2. This time t2 becomes longer as the particulate deposition amount at the start of regeneration increases.
[0065]
Also, t2 is constant when the particulate deposition amount at the start of regeneration is equal to or greater than the maximum particulate deposition amount pmax.
[0066]
In addition, t2 = 0 is set when the particulate deposition amount at the start of regeneration is a predetermined amount p or less. This is because, in the case of a particulate deposition amount of p or less, the intermediate period is omitted and the process proceeds to the latter period, and even if all of them are burned all at once, the rise in the bed temperature of the filter 41 is small. This is because the maximum allowable temperature Tmax is not reached, so that the middle stage is omitted and the process immediately shifts to the latter stage. That is, the predetermined value p is set in the vicinity of the maximum amount of the particulate accumulation amount in which the bed temperature of the filter 41 does not exceed the allowable maximum temperature in the latter period without passing through the middle period.
[0067]
However, if the regeneration process is started only when a predetermined amount of particulates is deposited, there is no possibility that the particulate deposition amount at the start of the regeneration process is p or less. Therefore, this is considered to be meaningful at the time of resuming the reproduction processing described later. That is, if the regeneration process is interrupted during the middle period, there may be a situation in which the particulate accumulation amount of the filter remains in a state of p or less. At this time, the particulate deposition amount when the regeneration process is resumed is in a state of p or less. become. Therefore, when the particulate deposition amount at the time of resuming the regeneration process is less than or equal to p due to the interruption of the regeneration process during the middle period, the process immediately shifts to the latter stage to perform the oxygen concentration control to the high concentration target oxygen concentration. The reproduction processing period can be shortened.
[0068]
In FIG. 7, the particulate accumulation amount at the start of the regeneration process on the horizontal axis may be calculated by searching a table having the contents shown in FIG. 8 from the pressure loss of the filter at the start of the regeneration process.
[0069]
Returning to FIG. 5, when the reproduction interruption flag = 1 in step 22 (during interruption of reproduction processing), the process proceeds to step 36.
T = Tz−a × ΔT (3)
Where a: predetermined value,
The timer value T representing the elapsed time from the start of the reproduction process is updated by the following formula.
[0070]
This is because the interruption time during the regeneration process is not generally counted as the regeneration processing time, but in the present embodiment, the following behavior is paid to the behavior of the filter bed temperature due to the interruption during the regeneration process. Thus, the timer value T is corrected.
[0071]
(1) First term:
In FIG. 9, if there is no opportunity to interrupt the regeneration process after the regeneration process is started, the actual bed temperature reaches the target bed temperature tTbed at the timing when t1 has elapsed from the start of the regeneration process by the rapid temperature increase control of the present embodiment. .
[0072]
On the other hand, if the regeneration execution condition is not satisfied after the regeneration process is started and the regeneration process (rapid temperature rise control) is stopped, and then the rapid temperature rise control is executed by restarting the regeneration process, the bed temperature is interrupted. The temperature falls below the temperature Tc at the time, rises again from the temperature Td at the time of resuming the regeneration process, and reaches the target bed temperature tTbed (see the one-dot chain line). That is, the time until the target bed temperature tTbed is reached is prolonged from t1 to t1 ′ due to the decrease in the bed temperature accompanying the interruption of the regeneration process. For this reason, when there is an interruption in the reproduction process, it is necessary to wait until t1 ′ and shift to the next stage, the middle period. Even when the reproduction process is interrupted, the transition to the middle period occurs at the timing when t1 has elapsed. Therefore, the transition to the middle period is too early, and the particulates accumulated in the filter in the middle period cannot be burned sufficiently.
[0073]
Therefore, in order to delay the transition to the middle period when the reproduction process is interrupted within the period of the previous period, a positive value is given to the predetermined value a in the above equation (3) to correct the timer value T to be smaller.
[0074]
(2) Medium term:
The interruption of the reproduction process in the middle period is slightly different from the interruption of the reproduction process in the previous period. That is, in the initial stage of the interruption in the middle period, the combustion of the particulates accumulated on the filter 41 is continued for a while by the heat capacity of the filter 41, and the bed temperature is lowered after the combustion is stopped.
[0075]
Therefore, at this time, it is necessary to consider two periods, an initial period during which the particulate combustion continues and an initial period after the initial period when the bed temperature decreases. In this case, in the initial period, Even when the regeneration process is interrupted, the combustion of the particulates continues, and therefore, it is the same as during the regeneration process in the middle period when the regeneration process is not interrupted. For this reason, this initial period of interruption should also be added to the timer value T, otherwise the transition to the latter period will be delayed.
[0076]
Therefore, when the interruption time in the middle period is within the initial period of interruption, the timer value T is set by giving a negative value to the predetermined value a in the above equation (3) in order to speed up the transition to the latter period. Is corrected to the larger side.
[0077]
On the other hand, since the bed temperature decreases during the period of initial interruption, this may be treated in the same way as the interruption of the regeneration process during the previous period.
[0078]
Therefore, in order to delay the transition to the later period when the interruption time in the middle period becomes longer than the period after the initial interruption, the timer value T is given by giving a positive value to the predetermined value a in the above equation (3). Is corrected to the smaller side.
[0079]
(3) Late:
The interruption of the reproduction process during the latter period may be handled in the same manner as the interruption of the reproduction process during the middle period described above.
[0080]
Based on this idea, different values are set for each stage of the reproduction phase as follows in the predetermined value a of the above equation (3) in FIG. 5 and the set predetermined values a1 and a2 are set during interruption. , A3, the timer value T is corrected by the above equation (3).
[0081]
(1) First term (when T <t1):
From step 25, the process proceeds to step 33, and a1 is added to the predetermined value a in preparation for interruption during the previous period.
[0082]
(2) Medium term (when t1 ≦ T <t1 + t2):
From step 25, the process proceeds to step 34, and a2 is set to a predetermined value a in preparation for interruption during the middle period.
[0083]
(3) Late period (when t1 + t2 ≦ T <t1 + t2 + t3):
From steps 25 and 26, the process proceeds to step 35, and a3 is set to a predetermined value a in preparation for interruption during the latter period.
[0084]
The predetermined value a1 is a positive constant value regardless of the interruption time in the previous period as shown in the upper left of FIG. As a result, as shown in the lower left of FIG. 10, the timer value T is corrected so as to become smaller as the interruption time becomes longer than the timer value T when there is no interruption in the previous period (interruption time = 0).
[0085]
On the other hand, the predetermined value a2 (or a3) is a constant negative value during the period (interruption initial period) in which the interruption time is less than the predetermined value tb according to the interruption time in the middle period as shown in the upper right of FIG. When the interruption period exceeds tb (period after the initial period of interruption), it is a positive constant value. In this case, since the temperature drop in the period exceeding tb in the middle period (or later period) is more severe than the temperature drop in the first period, the positive value interval a2 (or a3) is made larger than a1. ing.
[0086]
As a result, as shown in the lower right of FIG. 10, when the interruption time is less than or equal to the predetermined value tb with respect to the timer value T when there is no interruption in the middle period (or later period), the timer value T is corrected to become larger. On the other hand, when the interruption time in the middle period (or later period) exceeds the predetermined value tb, the timer value T is corrected so as to become smaller as the interruption time becomes longer as in the previous period.
[0087]
The actual values of the predetermined values a1, a2, a3, tb and the predetermined value tc in the lower left of FIG. 10 and the predetermined value td in the lower right of FIG. 10 are the heat capacity and heat dissipation characteristics of the filter 41 and the exhaust temperature of the engine 1. It is necessary to experimentally consider the characteristics. In addition, the value of a2 (or a3) needs to be switched between when the interruption time is less than tb and when it is more than tb. For this purpose, the interruption time may be measured by starting a timer from the interruption timing.
[0088]
The flow in FIG. 11 is for setting the reproduction interruption flag used in step 22 in FIG. 5 and is executed at regular intervals (for example, every 10 ms).
[0089]
In step 41, the reproduction interruption flag is checked. Since the regeneration interruption flag is initially set to zero when the engine is started, the routine proceeds to step 42 and the regeneration processing flag is checked. When the reproduction processing flag = 1, the process proceeds to step 43 to check whether the reproduction execution condition is satisfied. When the reproduction execution condition is satisfied, the current process is terminated as it is. However, when the reproduction execution condition is not satisfied, the reproduction process is interrupted to proceed to step 44, where the reproduction interruption flag = 1 is set.
[0090]
Next time from the reproduction interruption flag = 1, the process proceeds from step 41 to step 45 to check the reproduction execution condition. While the reproduction execution condition is not satisfied even during the interruption of the reproduction process, the operation of step 44 is executed to continue the interruption. On the other hand, when the reproduction execution condition is established during the interruption, the operation returns to step 46 to resume the reproduction process again. Advance playback interruption flag = 0.
[0091]
The reproduction interruption flag set in this way is used in step 22 in FIG.
[0092]
Although not shown, the reproduction process is interrupted by the reproduction interruption flag = 1. That is, if the regeneration process is interrupted during the previous period, the rapid temperature increase control of <1> is interrupted, and if the regeneration process is interrupted during the middle period or the latter period, the above <2> or <3> The oxygen concentration control is interrupted.
[0093]
On the other hand, when the reproduction interruption flag becomes zero again, the reproduction process is resumed. That is, if the rapid temperature increase control is interrupted, the interrupted rapid temperature increase control is resumed, and if the oxygen concentration control is interrupted, the interrupted oxygen concentration control is resumed.
[0094]
For this reason, t1 and t2 are reset as follows when the reproduction process is resumed after the interruption.
[0095]
(A) When there is an interruption during the previous period and then the playback process is resumed:
T1 is calculated by searching the table having the contents shown in FIG. 6 from the bed temperature when the regeneration process is resumed, and t2 is obtained by searching the table having the contents shown in FIG. 7 from the particulate deposition amount when the regeneration process is resumed. Then, t1 and t2 are used in place of t1 and t2 that have already been calculated at the start of the reproduction process, and the determination at step 25 in FIG. 5 is performed.
[0096]
(B) When there is an interruption during the middle or later period, and then the playback process is resumed:
The t2 is calculated by searching a table having the contents shown in FIG. 7 from the particulate accumulation amount when the regeneration process is resumed, and this t2 is used in place of the already calculated t2 at the start of the regeneration process. The determination at 25 is performed.
[0097]
In (a) and (b) above, the particulate accumulation amount at the time when the regeneration process is resumed on the horizontal axis in FIG. 7 is calculated by searching a table containing the contents of FIG. 8 from the filter pressure loss at the time when the regeneration process is resumed. To do.
[0098]
When the setting of each stage of the reproduction phase in FIG. 5 is completed in this way, the process returns to FIG. 3. In step 3, it is checked in which stage of the reproduction phase the current processing timing is, and each control is performed as follows. I do. That is, if the previous period, the process proceeds to step 4 where the target value tT1 of the filter inlet temperature is set higher than the target bed temperature tTbed, and the exhaust gas temperature control (rapid temperature rise control) is performed so as to obtain this target value tT1.
[0099]
In the middle period, the process proceeds to Steps 5 and 7, and the target value tT1 of the filter inlet temperature is switched to the target bed temperature tTbed and maintained, and the target oxygen concentration in the exhaust gas is set to a low concentration (first oxygen concentration control). )I do. In the latter period, the process proceeds to Steps 6 and 7, and the target value tT1 of the filter inlet temperature is maintained at the target bed temperature tTbed as in the middle period, and the target oxygen concentration in the exhaust gas is set to a higher concentration than in the middle period (first operation 2 oxygen concentration control).
[0100]
Here, the control in steps 4 to 7 in FIG. 3 will be further described by dividing it into rapid temperature rise control and oxygen concentration control.
[0101]
[1] Rapid temperature rise control:
[1] -1. Rapid temperature increase control method 1:
FIG. 12 shows the control result of the filter inlet temperature according to the present embodiment and how the filter bed temperature changes accordingly. That is, at the start of the regeneration process, a temperature higher than the target bed temperature tTbed is set as the target value tT1 of the filter inlet temperature, and the exhaust gas temperature raising means is obtained so as to obtain this target value tT1 over the entire period of the previous period. Work.
[0102]
When the period (t1) of the previous period ends, the target value tT1 of the filter inlet temperature is switched to and maintained at the target bed temperature tTbed.
[0103]
[1] -2. Rapid temperature rise control method # 2:
FIG. 13 divides the period of the previous period into almost two parts, the first half and the second half. In the first half, a higher temperature than the case of FIG. 12 is set as the target value tT1 of the filter inlet temperature. The target value tT1 is adjusted so as to approach (see the solid line at the bottom). Then, the exhaust gas temperature raising means is operated so as to obtain this target value tT1.
[0104]
As a result, the time required to increase to the target bed temperature tTbed can be reduced from t1 in the case of FIG. 12 to t1 ′, and the overshoot of the bed temperature that has occurred in the case of FIG. 12 can also be prevented. For comparison, FIG. 13 shows the case of FIG. 12 by a broken line.
[0105]
[1] -3. Exhaust temperature raising means:
Since the exhaust temperature varies depending on the fuel injection amount (equivalent to the engine load) and the rotational speed, the entire operation region is roughly divided into five as shown in FIG. 14, and the following is performed according to the exhaust temperature in each divided operation region. By operating the exhaust gas temperature raising means as described above, the target value tT1 of the filter inlet temperature shown in FIG. 12 is realized.
[0106]
Region R1: This is a region near the full load. In this region, the exhaust temperature becomes the target bed temperature tTbed, and the particulates are naturally burned and regenerated without operating the exhaust temperature raising means. Does not work.
[0107]
Region R2: In the regions R2 to R5 on the lower load side than the region R1, the filter inlet temperature T1 does not become the target value tT1, so it is necessary to operate the exhaust gas temperature raising means. For this reason, in the region R2, first, the exhaust temperature is raised by delaying the injection timing (main injection timing) of the fuel injected from the fuel injection device 10 which is the exhaust gas temperature raising means from the normal (before the regeneration process). The filter inlet temperature T1 rises to the target value tT1 due to the delay of the main injection timing.
[0108]
Region R3: This is a region where the filter inlet temperature T1 cannot be set to the target value tT1 only by retarding the main injection timing, and post-injection (injection in the expansion stroke after the main injection) is performed instead of the delay of the main injection timing. Doing so raises the temperature of the exhaust. As a result of post-injection during this expansion stroke, the filter inlet temperature T1 rises to its target value tT1.
[0109]
Region R4: This is a region where the filter inlet temperature T1 cannot be set to the target value tT1 only by post injection, and in addition to post injection, the temperature of the exhaust is raised using an intake throttle device which is another exhaust temperature raising means. By this control, the filter inlet temperature T1 rises to the target value tT1.
[0110]
For this reason, an intake throttle valve 42 (intake throttle device) driven by an actuator 43 is provided at the collector 3a inlet in FIG. The actuator 43 includes a diaphragm actuator 44 that drives the intake throttle valve 42 in response to the control pressure, and a pressure control valve 45 that adjusts the control pressure to the diaphragm actuator 44, and the intake throttle valve 42 opens the target. A duty control signal is generated so as to be closed to a degree, and this duty control signal is output to the pressure control valve 45.
[0111]
When the variable capacity turbocharger 21 and the common rail type fuel injection device 10 are provided as in the present embodiment, these also function as exhaust temperature raising means in the regions R2, R3, and R4, and reach the target value tT1. It is possible to raise the temperature. For example, when the variable nozzle 24 is opened, the work of the turbine 22 is reduced, so that the amount of intake air is reduced and the excess air ratio is reduced, thereby increasing the filter inlet temperature T1. Further, when the common rail pressure is lowered, the injection period is prolonged and the combustion period becomes longer. Then, combustion deteriorates and the engine torque decreases. In order to compensate for this decrease in engine torque, the fuel injection amount increases, thereby increasing the filter inlet temperature T1.
[0112]
Region R5: a low load region where the exhaust gas temperature is originally low as during idling, and in this region, the filter inlet temperature cannot be raised to the target value tT1 by any of the above methods, so the regeneration process is not performed. (The exhaust temperature raising means does not work).
[0113]
On the other hand, the target value tT1 shown in FIG. 13 is achieved by changing the post-injection amount with high sensitivity with time in the regions R3 and R4 shown in FIG. 14 based on the temperature rise control shown in FIG. Can do. For example, by searching a predetermined map (not shown) from the engine speed and load, the base exhaust temperature (exhaust temperature in a state where the exhaust temperature raising means does not work) Tbase, the engine speed and the engine The post injection increase amount ΔPost required to raise the exhaust temperature by 1 ° C. is calculated by searching a map having the contents shown in FIG. 15 from the torque, and these are used.
ΔQp = ΔPost × (tT1−Tbase) (4)
Where tT1: target value of filter inlet temperature,
The additional amount ΔQp of the post injection amount is calculated by the following formula, and this additional amount ΔQp may be added to the post injection amount in the regions R3 and R4 shown in FIG.
[0114]
[2] Oxygen concentration control:
[2] -1. Medium-term oxygen concentration control (first oxygen concentration control):
FIG. 16 shows the relationship between the filter inlet temperature, the exhaust oxygen concentration, and the maximum bed temperature of the filter 41 when the regeneration process is performed in a state where the particulate accumulation amount (PM accumulation amount) is large (that is, in the middle period). The interval between the curves is short due to the large amount of particulate deposit, which indicates that the temperature gradient is steep.
[0115]
Thus, in a state where the particulate accumulation amount is large, the regeneration process of the filter 41 can be performed within the allowable maximum temperature of the bed temperature of the filter 41 by providing the control range of the target oxygen concentration on the low oxygen concentration side.
[0116]
Here, the target oxygen concentration in the exhaust gas is leaner than the stoichiometric air-fuel ratio (for example, an excess air ratio of about 1.5) when converted to an air-fuel ratio. If there is a high concentration of oxygen in a state where the amount of particulate deposition is large, the particulate combustion rate is high and the particulates deposited on the filter 41 burn rapidly, so that the target oxygen concentration in the exhaust gas is suppressed to suppress this. Is set to low oxygen concentration.
[0117]
The reason why the control range of the target oxygen concentration is wide is that the variation and the control delay at the time of transition are taken into consideration.
[0118]
[2] -2. Late oxygen concentration control (second oxygen concentration control):
FIG. 17 shows the relationship between the filter inlet temperature, the oxygen concentration in the exhaust gas, and the maximum bed temperature of the filter 41 when the regeneration process is performed in a state where the particulate accumulation amount is small (that is, the latter stage). When the amount of curated deposition is small, the interval between the curves is widened (the temperature gradient is gentle), and the position of the allowable maximum temperature of the bed temperature is also moving to the right than in the case of FIG.
[0119]
For this reason, in the state where the amount of particulate accumulation is small, the maximum temperature of the bed temperature during the regeneration process of the filter 41 can be kept below the allowable maximum temperature even if the oxygen concentration in the exhaust gas is increased compared to the middle period. In the latter period, the target oxygen concentration is made larger than in the middle period as shown in 1) in the figure. As a result, sufficient oxygen is supplied to increase the burning rate of the particulates, and all of the particulates remaining on the filter 41 can be completely burned out in a short period of time. Further, by increasing the target value tT1 of the filter inlet temperature as shown in 2) in the figure, it is possible to further shorten the regeneration processing time and improve the particulate regeneration efficiency.
[0120]
[2] -3. Control result of oxygen concentration control:
FIG. 18 shows the control target (target oxygen concentration) of the exhaust oxygen concentration according to the present embodiment and the actual change in the exhaust oxygen concentration as a result of the control. As shown in the figure, what was controlled at a low oxygen concentration in the middle period is switched to a higher oxygen concentration in the latter period. It should be noted that the oxygen concentration in the exhaust gas changes drastically in other periods (including the previous period) except for the middle period and the latter period. This is because the oxygen concentration control in the exhaust gas is not originally performed in the other period, and is in a transient state where acceleration and deceleration are repeated.
[0121]
FIG. 18 simply switches the target oxygen concentration in the exhaust gas from the low concentration to the high concentration in two stages. As shown in FIG. 19, the target oxygen concentration is gradually increased in the latter half of the middle period, and the latter period is increased. By smoothly connecting to the target oxygen concentration, it is possible to shorten the regeneration processing period than in the case of FIG.
[0122]
[2] -4. Oxygen concentration control means:
Assuming that the target oxygen concentration in the exhaust gas is tRO2 [%] and the excess air ratio when the target oxygen concentration tRO2 is obtained is the target excess air ratio tλ, the following equation is established.
[0123]
tλ = 21 / (21−tRO2) (5)
However, 21: oxygen concentration in fresh air [%],
In addition, although (5) Formula does not consider the mole increase of the working gas by combustion, in order to improve control accuracy further, this effect can also be put into (5) Formula.
[0124]
Controls for obtaining the target excess air ratio tλ in the equation (5) include intake fresh air amount control and fuel injection control.
[0125]
[2] -4-1. Control of fresh air intake:
If the intake fresh air amount for obtaining the target excess air ratio tλ in equation (5) is tQa, the following equation is established between the fuel injection amount Qf.
[0126]
tQa = Qf × theoretical air-fuel ratio × tλ (6)
Substituting equation (5) into equation (6) yields:
[0127]
tQa = Qa × theoretical air-fuel ratio × 21 / (21−tRO2) (7)
Therefore, the intake fresh air amount is controlled so as to obtain the target intake fresh air amount tQa of the equation (7).
[0128]
In this case, since the operating range that can be covered differs depending on the intake fresh air amount control means as shown in FIG. 20, the oxygen concentration control is performed as follows according to the intake fresh air amount control means.
[0129]
(1) When the intake fresh air amount control means is the variable capacity turbocharger 21:
In the region of R6, R7, R8, the intake fresh air amount is controlled by the variable capacity turbocharger 21. For example, if the opening degree of the variable nozzle 24 is decreased, the rotational speed of the turbine 22 is increased, and the amount of fresh intake air can be increased (the oxygen concentration is increased). Conversely, when the opening degree of the variable nozzle 24 is increased, the rotational speed of the turbine 22 is decreased, and the amount of fresh intake air can be reduced.
[0130]
(2) When the intake air quantity control means is an EGR device:
In the region of R7 and R8, the intake fresh air amount is controlled by the EGR valve 6 (EGR device). For example, if the EGR rate or EGR amount is increased, the intake fresh air amount can be reduced. Conversely, if the EGR rate or EGR amount is decreased, the intake fresh air amount can be increased.
[0131]
(3) When the intake fresh air amount control means is the intake throttle valve 42 (intake throttle device):
In the region R8, the intake fresh air amount is controlled by the intake throttle valve 42. For example, if the intake throttle valve 42 is closed, the amount of fresh intake air can be reduced. Conversely, if the intake throttle valve 42 is returned, the amount of fresh intake air can be increased.
[0132]
[2] -4-2. Control of fuel injection:
If the target fuel injection amount for obtaining the target excess air ratio tλ in the above equation (5) is tQf, the following equation is established between the intake fresh air amount Qa.
[0133]
Qa = tQf × theoretical air-fuel ratio × tλ (8)
When the equations (5) and (8) are solved for the target fuel injection amount tQf, the following equation is obtained.
[0134]
tQf = Qa × (1 / theoretical air-fuel ratio) × (21−tRO2) / 21 (9)
Accordingly, the fuel injection is controlled so as to obtain the target fuel injection amount tQf of the equation (9).
[0135]
In this case, since the operation region that can be covered by the fuel injection control means is different as shown in FIG. 21, the oxygen concentration control is performed as follows according to the fuel injection control means.
[0136]
Region R9: The fuel injection is controlled so as to obtain the target fuel injection amount tQf of equation (9) while retarding the main injection timing.
[0137]
Region R10: The fuel injection is controlled so as to obtain the target fuel injection amount tQf of the equation (9) while performing the post-injection and the retard of the main injection timing. If the post injection amount is increased, the fuel injection amount can be increased (the oxygen concentration can be reduced). Since the post-injection is performed during the expansion stroke of the engine, the injection amount can be increased without much torque increase. The torque increase is controlled by decreasing the main injection amount.
[0138]
Region R11: The fuel injection amount is controlled by the post injection, the intake throttle, and the main injection timing. For example, when the intake throttle is performed, the pumping loss increases, so that the post-injection amount can be increased to compensate for this. Further, the main injection timing at this time is controlled to the advance side than when the injection amount is not controlled.
[0139]
[2] -4-3-3. Feedback control of oxygen concentration in exhaust:
Although the control in [2] -4-1 and [2] -4-2 is open loop control, feedback control can also be performed. For example, the actual intake fresh air amount detected from the output of the air flow meter 35 coincides with the target intake fresh air amount tQa in the equation (7), or the actual fuel injection amount is the target fuel injection in the equation (9). Feedback control is performed so as to match the amount tQf.
[0140]
In addition, a sensor (for example, a wide-range air-fuel ratio sensor) that detects the actual oxygen concentration in the exhaust gas is provided in the exhaust passage 2 so that the actual oxygen concentration in the exhaust gas detected by this sensor matches the target oxygen concentration. Can also be made to perform feedback control.
[0141]
Here, the operation of this embodiment will be described with reference to FIG. 22. From the top, the figure shows the movement of the regeneration efficiency, the target value of the filter inlet temperature, the target oxygen concentration in the exhaust, and the maximum temperature of the filter bed temperature. It is shown as a model. In the first stage, the second stage, and the fourth stage, the case of the present embodiment is indicated by a solid line, while the case of the conventional apparatus is indicated by a dashed line and a broken line.
[0142]
(1) Previous period of regeneration processing:
In the previous period, the target value tT1 (see solid line) of the filter inlet temperature is set higher than in the conventional apparatus (see the dashed line and broken line) as in the second stage, so that the maximum bed temperature of the filter 41 is higher than in the conventional apparatus. The temperature rises rapidly up to the target bed temperature tTbed as at the bottom.
[0143]
(2) Medium-term regeneration process:
(1) Since the target oxygen concentration in the exhaust gas is set to a low concentration side as in the third stage and the combustion rate of the particulates accumulated in the filter 41 is suppressed, the maximum temperature of the filter bed temperature is The allowable maximum temperature is not exceeded (see the bottom solid line), and the durability of the filter 41 is not impaired thereby.
[0144]
(2) There is a method of suppressing the particulate combustion rate by lowering the exhaust temperature, but this particulate combustion rate control method based on the exhaust temperature is controlled by the influence of the thermal inertia of the exhaust and the filter 41. Responsiveness deteriorates. On the other hand, in the present embodiment, since it is not a particulate combustion speed control method based on such exhaust temperature, the influence of exhaust and the thermal inertia of the filter 41 can be eliminated, and control responsiveness is good and control reliability is high.
[0145]
(3) In the particulate combustion rate control method based on the exhaust temperature, when the exhaust temperature is lowered so as to suppress the particulate combustion rate, the bed temperature of the filter 41 is lowered below the target bed temperature. Then, reproduction failure may occur. On the other hand, in this embodiment, since the particulate combustion rate is suppressed by oxygen concentration control while maintaining the target bed temperature, the maximum bed temperature of the filter 41 is the target bed temperature even during particulate combustion. Never fall below temperature. That is, since this embodiment is not a particulate combustion rate control method based on the exhaust temperature, there is no need to lower the bed temperature of the filter 41 below the target bed temperature, thereby preventing regeneration failure due to a temperature drop around the filter.
[0146]
(3) Late stage of regeneration process:
By increasing the target oxygen concentration in the exhaust gas from the middle stage as in the third stage, all the particulates remaining in the filter 41 can be burned out quickly and reliably near the end of the regeneration process. Thus, the reproduction processing time can be shortened and almost complete filter regeneration can be achieved.
[0147]
As a result, the following effects are obtained in this embodiment.
[0148]
(1) Reduction of playback processing time:
The increase in fuel consumption required for the regeneration process can be minimized, and deterioration of fuel consumption can be suppressed. The high temperature maintenance time during the regeneration process is reduced, the thermal deterioration of the filter can be suppressed, the exhaust performance can be improved, and the life can be extended.
[0149]
(2) Realization of complete playback:
Since there is no increase in pressure loss due to unburned particulates, fuel consumption can be prevented from deteriorating. In addition, non-uniform particulate deposition caused by deposition of new particulates on unburned particulates may cause local sudden particulate combustion, which may reduce durability in that part. This can be prevented.
[0150]
Further, according to the present embodiment, t1 (rapid temperature rise control period) is set based on the filter bed temperature at the start of the regeneration process, so t1 is different from the filter bed temperature at the start of the regeneration process. Can be given with high accuracy.
[0151]
Further, according to the present embodiment, the target value of the filter inlet temperature in the first period (rapid temperature rise control period) is initially set higher than the target value of the filter inlet temperature in the middle period and the latter period (oxygen concentration control period). Then, since it is set so that it gradually decreases to the target value of the filter inlet temperature in the middle and latter periods (see FIG. 13), the time required for raising the particulates to the temperature at which they self-ignite can be shortened. In addition, bed temperature overshoot can be prevented.
[0152]
Further, according to the present embodiment, the target oxygen concentration in the exhaust gas is gradually increased toward the target oxygen concentration in the exhaust gas in the later period (second oxygen concentration control period) in the middle period (first oxygen concentration control period). (See FIG. 19), the regeneration processing period can be shortened as compared with the case where the target oxygen concentration in the exhaust gas is switched stepwise.
[0153]
In addition, when the particulate deposition amount at the time of resuming the regeneration process is equal to or less than the predetermined value p, oxygen concentration control targeting the low oxygen concentration (first oxygen concentration control) is omitted and oxygen targeting the high oxygen concentration is targeted. Shifting to concentration control (second oxygen concentration control), even if all the particulates remaining in the filter are burned all at once, the filter bed temperature does not increase so much and the filter bed temperature does not reach the maximum allowable temperature. . That is, according to this embodiment, when the particulate deposition amount at the time of resuming the regeneration process is equal to or less than the predetermined value p due to the interruption of the oxygen concentration control targeting the low oxygen concentration, the oxygen concentration immediately targeting the high oxygen concentration is reached. By shifting to control, the reproduction processing period can be shortened.
[0154]
When the rapid temperature increase control is interrupted, the bed temperature falls below the temperature at the time of interruption, rises again from the temperature at the time of resuming the regeneration process, and rises to a temperature at which the particulates self-ignite. That is, due to the decrease in the bed temperature accompanying the interruption of the rapid temperature rise control, the time until the particulates reach a temperature at which self-ignition is prolonged is longer than the case where there is no interruption. For this reason, when there is an interruption of the rapid temperature increase control, it is necessary to shift to the next stage oxygen concentration control later than when there is no interruption, and there is no interruption even when there is an interruption of the rapid temperature increase control. If the transition to the oxygen concentration control is performed at the same timing as that, the transition to the oxygen concentration control is too early, and the particulates accumulated on the filter cannot be sufficiently burned during the oxygen concentration control period. . On the other hand, according to the present embodiment, when the rapid temperature increase control is interrupted, the timer value T (the elapsed time from the start of the regeneration process) is shortened based on the time when the rapid temperature increase control is interrupted. (See the lower left of FIG. 10), even if the rapid temperature rise control is interrupted, it is possible to shift to oxygen concentration control at an appropriate timing.
[0155]
The interruption during the oxygen concentration control is slightly different from the interruption during the rapid temperature rise control. That is, in the initial stage of interruption during the oxygen concentration control, the combustion of the particulates accumulated on the filter 41 is continued for a while by the heat capacity of the filter 41, and the bed temperature is lowered after the combustion is stopped. Therefore, at this time, it is necessary to consider two periods, an initial period during which the particulate combustion continues and an initial period after the initial period when the bed temperature decreases. In this case, in the initial period, Even when the oxygen concentration control is interrupted, the particulate combustion continues, and therefore, it is the same as during the oxygen concentration control when the oxygen concentration control is not interrupted. For this reason, this initial period of interruption should be added to the elapsed time from the end of the rapid temperature rise control and the elapsed time from the end of the oxygen concentration control (first oxygen concentration control) targeting the low oxygen concentration. If not, the shift to the oxygen concentration control (second oxygen concentration control) targeting a high oxygen concentration is delayed or the end of the regeneration process is delayed.
[0156]
On the other hand, according to the present embodiment, based on the time when the oxygen concentration control targeting the low oxygen concentration is interrupted, the timer value T (the end of the rapid temperature increase control) is stopped until the interruption time reaches a predetermined time tb. Since the timer value T is corrected to become shorter when the interruption time exceeds the predetermined time tb (see the lower right in FIG. 10), the target oxygen concentration is low oxygen concentration. Even if the control is interrupted, it is possible to shift to the oxygen concentration control targeting a high oxygen concentration at an appropriate timing.
[0157]
Further, according to the present embodiment, based on the time when the oxygen concentration control targeting high oxygen concentration is interrupted, the timer value T (from the end of the first oxygen concentration control) until the interruption time reaches a predetermined time tb. Since the timer value T is corrected to be shorter when the elapsed time is longer, and when the interruption time exceeds the predetermined time tb (see the lower right in FIG. 10), oxygen concentration control targeting a high oxygen concentration is performed. Even if it is interrupted, the reproduction process can be terminated at an appropriate timing.
[0158]
Next, FIG. 23 shows the characteristics of the middle and late periods when the horizontal axis represents the intake fresh air flow rate and the vertical axis represents the bed temperature (maximum temperature) of the filter 41. In FIG. 17, the target oxygen concentration was increased in the latter period as in 1) in the figure, but when the setting of the target oxygen concentration in the latter period was shifted to the characteristics shown in FIG. Therefore, the intake fresh air flow rate is increased from a, which is the intake fresh air flow rate at which the target oxygen concentration is achieved, to b, which is the intake fresh air flow rate, at which the target oxygen concentration at the later stage is achieved. That is, by moving the filter 41 to the right along the allowable maximum temperature, the bed temperature during the regeneration process of the filter 41 can be kept close to the allowable maximum temperature (see FIG. 26).
[0159]
Here, the fresh air flow limit is shown in the case where it is on the right side far away from the fresh air flow of b, but in practice the fresh air flow limit varies depending on the operating conditions of the engine and is shown in FIGS. Thus, it may be less than the fresh air flow rate of b. In this case, the fresh air flow rate cannot be moved to the right in the horizontal direction from a to b, and must be moved diagonally downward to c. However, moving diagonally down leaves the maximum allowable temperature, and there is a high possibility that the particulates remaining unburned in the filter 41 will be insufficient to burn out completely. This is because when the bed temperature of the filter 41 decreases, the regeneration speed decreases accordingly (see FIG. 29).
[0160]
More specifically, in the above-described embodiment (first embodiment), it is expected that if the intake fresh air flow rate is increased so as to achieve the target oxygen concentration in the latter period, the intake fresh air flow rate can be realized. However, in practice, the intake fresh air flow rate at which the target oxygen concentration in the later stage is achieved may not be realized depending on the operating conditions (for example, at a low load and high rotation speed).
[0161]
Therefore, if the intake fresh air flow rate that achieves the target oxygen concentration cannot be realized due to the operating conditions, that is, even if the intake fresh air flow rate is increased, the intake fresh air flow rate is not actually increased due to being blocked by the fresh air flow limit. As a result, when the bed temperature during the regeneration process of the filter 41 decreases, the second embodiment repeatedly increases and decreases the intake fresh air flow rate. In the third embodiment, the above [2] -4-2 describes. The exhaust temperature is raised using the control of fuel injection.
[0162]
That is, in the second embodiment, as shown in FIG. 27, at the later stage, the intake fresh air flow rate is first increased to Qc, then the intake fresh air flow rate is decreased to Qd, and the intake new air flow is again returned to Qc. The process of increasing the air flow rate and then reducing the intake fresh air flow rate to Qd is repeated in a short cycle (see the second stage in FIG. 27).
[0163]
As a result, when the intake fresh air flow rate temporarily decreases, the bed temperature of the filter 41 temporarily increases from Tc to Td (see the first stage in FIG. 27). This is because the exhaust flow rate passing through the filter 41 has a function of taking heat away from the filter 41. However, when the intake fresh air flow rate decreases rapidly, that is, when the exhaust flow rate passing through the filter 41 decreases rapidly, the heat from the filter 41 is lost. The amount of leaving is reduced (reduction of heat loss), and this makes use of the fact that the bed temperature during the regeneration process of the filter 41 temporarily rises.
[0164]
For this reason, the bed temperature of the filter 41 is an average value of the temperature Tc when the intake fresh air flow rate is Qc and the temperature Td that rises with a rapid decrease in the intake fresh air flow rate. Therefore, even when the intake fresh air flow rate for achieving the target oxygen concentration in the latter period cannot be realized, the bed temperature of the filter 41 can be brought close to the allowable maximum temperature.
[0165]
In the third embodiment, the bed temperature of the filter 41 can be brought close to the maximum allowable temperature by increasing the exhaust gas temperature.
[0166]
FIG. 28 is for executing the second oxygen concentration control of the second embodiment by the intake fresh air flow rate control, and corresponds to a subroutine of step 6 in FIG. 3 of the first embodiment.
[0167]
In step 51, the actual bed temperature Tbed is compared with the allowable maximum temperature. Here, the actual bed temperature Tbed is obtained by the aforementioned equation (2).
[0168]
When the actual bed temperature Tbed is less than the maximum allowable temperature, the new intake air flow rate is increased even if the intake fresh air flow rate is increased so that the target oxygen concentration in the later stage is achieved, and the new intake air flow rate is actually blocked. This is a case where the air flow rate does not increase and the bed temperature during the regeneration process of the filter 41 is thereby lowered.
[0169]
When the actual bed temperature Tbed is lower than the allowable maximum temperature, the routine proceeds to step 52, where increase / decrease repetitive control of the intake fresh air flow rate is performed.
[0170]
Here, FIG. 27 shows the case where the repetitive increase / decrease control of the intake fresh air flow is executed by the control of the intake throttle valve opening. However, the speed and state for holding the intake throttle valve rapidly decreasing and rapidly increasing, etc. Is determined by matching.
[0171]
On the other hand, if this is not the case, the routine proceeds from step 51 to step 53, where the intake fresh air flow rate is increased so that the target oxygen concentration in the latter period is achieved. This is the case of the first embodiment.
[0172]
As described above, in the second embodiment (the invention described in claim 1), even if the intake fresh air flow rate is increased so that the target oxygen concentration in the later stage is achieved, it becomes smaller depending on the operating conditions at that time. When the intake fresh air flow rate does not actually increase due to being blocked by the fresh air flow rate limit, and the bed temperature during the regeneration process of the filter 41 decreases, the increase or decrease of the intake fresh air flow is repeated, so that Even under operating conditions in which the air flow limit becomes small, the bed temperature of the filter 41 can be brought close to the maximum allowable temperature so that no particulate burnout occurs in the filter 41.
[0173]
Although the flowchart for the third embodiment is not shown, step 52 in FIG. 28 may be replaced with control of fuel injection, and the third embodiment (the invention according to claim 2) is the same as the second embodiment. The effect is obtained.
[0174]
An example of control of fuel injection is post-injection amount increase and post-injection timing retard. These methods may cause oil dilution problems when used in the first stage of regeneration processing when the bed temperature of the filter 41 is not sufficiently increased. However, in the latter stage of the regeneration process in which the bed temperature of the filter 41 is sufficiently raised, there are few restrictions on oil dilution, so this is a more effective method for increasing the temperature. Can be used.
[0175]
The air flow rate increase / decrease repetitive control of the second embodiment and the fuel injection control for increasing the exhaust temperature of the third embodiment can be combined at the same time.
[0176]
The function of the intake fresh air flow rate increase / decrease repetitive control means described in claim 1 is performed by steps 51 and 52 of FIG.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention.
FIG. 2 is a characteristic diagram showing three stages of a reproduction processing period.
FIG. 3 is a flowchart for explaining the entire reproduction process;
FIG. 4 is a flowchart for explaining setting of a reproduction processing flag.
FIG. 5 is a flowchart for explaining setting of a reproduction phase.
FIG. 6 is a characteristic diagram of a set time t1.
FIG. 7 is a characteristic diagram of set time t2.
FIG. 8 is a characteristic diagram of filter pressure loss with respect to particulate deposition amount.
FIG. 9 is a waveform diagram showing the behavior of the filter bed temperature when there is an interruption during the rapid temperature raising control.
FIG. 10 is a characteristic diagram of predetermined values a1, a2, and a3.
FIG. 11 is a flowchart for explaining setting of a reproduction interruption flag.
FIG. 12 is a waveform diagram for explaining a method for setting a target value for the filter inlet temperature in the previous period.
FIG. 13 is a waveform diagram for explaining a method for setting a target value of the filter inlet temperature in the first half of another embodiment.
FIG. 14 is a region diagram for explaining exhaust temperature raising means.
FIG. 15 is a characteristic diagram of an increase in post-injection necessary for raising the exhaust temperature by 1 ° C.
FIG. 16 is a characteristic diagram of the maximum temperature of the bed temperature during the regeneration process when the amount of particulate accumulation is large.
FIG. 17 is a characteristic diagram of the maximum temperature of the bed temperature during the regeneration process when the amount of particulate accumulation is small.
FIG. 18 is a waveform diagram for explaining a method for setting a target oxygen concentration in exhaust gas.
FIG. 19 is a waveform diagram for explaining a method for setting a target oxygen concentration in exhaust according to another embodiment.
FIG. 20 is a region diagram for explaining intake fresh air amount control means;
FIG. 21 is a region diagram for explaining fuel injection control means.
FIG. 22 is a waveform diagram for explaining the function and effect of this embodiment.
FIG. 23 is a characteristic diagram for explaining the second oxygen concentration control of the first embodiment.
FIG. 24 is a characteristic diagram for explaining second oxygen concentration control of the second embodiment.
FIG. 25 is a characteristic diagram for explaining the second oxygen concentration control of the third embodiment.
FIG. 26 is a waveform diagram when the second oxygen concentration control of the first embodiment is performed by the fresh air flow rate increase control.
FIG. 27 is a waveform diagram when the second oxygen concentration control of the second embodiment is performed by fresh air flow rate increase / decrease control.
FIG. 28 is a flowchart for explaining second oxygen concentration control according to the second embodiment;
FIG. 29 is a characteristic diagram showing the relationship between the bed temperature of the filter and the regeneration speed.
[Explanation of symbols]
1 engine
2 Exhaust passage
3 Intake passage
6 EGR valve
10 Common rail fuel injection system
17 Nozzle (fuel injection valve)
21 Variable capacity turbocharger
31 Engine controller
33 Crank angle sensor
36 Differential pressure sensor
37, 38 Temperature sensor
41 Filter
42 Inlet throttle valve

Claims (7)

It has a filter that collects particulates in the exhaust passage,
In the exhaust emission control device of an engine that performs filter regeneration processing when the filter regeneration time comes,
Oxygen concentration control means for controlling the oxygen concentration in the exhaust gas so that a target oxygen concentration set to a high concentration in the latter stage of the regeneration process is obtained;
When the intake fresh air flow rate is limited by the fresh air flow limit at the later stage of the regeneration process and the intake fresh air flow rate for achieving the target oxygen concentration cannot be realized, the control for repeatedly increasing and decreasing the intake fresh air flow rate is performed. An exhaust gas purification apparatus comprising: an intake fresh air flow rate increase / decrease repetitive control means. It has a filter that collects particulates in the exhaust passage,
In the exhaust emission control device of an engine that performs filter regeneration processing when the filter regeneration time comes,
Oxygen concentration control means for controlling the oxygen concentration in the exhaust gas so that a target oxygen concentration set to a high concentration in the latter stage of the regeneration process is obtained;
When the intake fresh air flow rate is limited by the fresh air flow limit at the later stage of the regeneration process and the intake fresh air flow rate for achieving the target oxygen concentration cannot be realized, the control of the fuel injection for increasing the exhaust temperature is performed. An exhaust purification device comprising: a fuel injection control means for performing. It has a filter that collects particulates in the exhaust passage,
In the exhaust emission control device of an engine that performs filter regeneration processing when the filter regeneration time comes,
The filter regeneration process is divided into three periods, the first half, the middle, and the second half. The temperature rise control is performed so that the target value of the filter inlet temperature can be obtained in the first half, and the particulates in the middle Control the oxygen concentration in the exhaust gas so that the target oxygen concentration set to a low concentration can be obtained in order to suppress the burning rate, and the target oxygen concentration set to a high concentration can be obtained in the latter period to burn out the particulates remaining in the filter. Filter regeneration processing means for controlling the oxygen concentration in the exhaust gas,
When the intake fresh air flow rate is limited by the fresh air flow limit in the latter period and the intake fresh air flow rate for achieving the target oxygen concentration cannot be realized, the intake new air flow control for repeatedly increasing and decreasing the intake fresh air flow rate is performed. An exhaust gas purification apparatus comprising: an air flow rate increase / decrease repetitive control means. It has a filter that collects particulates in the exhaust passage,
In the exhaust emission control device of an engine that performs filter regeneration processing when the filter regeneration time comes,
The filter regeneration process is divided into three periods, the first half, the middle, and the second half. The temperature rise control is performed so that the target value of the filter inlet temperature can be obtained in the first half, and the particulates in the middle Control the oxygen concentration in the exhaust gas so that the target oxygen concentration set to a low concentration can be obtained in order to suppress the burning rate, and the target oxygen concentration set to a high concentration can be obtained in the latter period to burn out the particulates remaining in the filter. Filter regeneration processing means for controlling the oxygen concentration in the exhaust gas,
Fuel injection for controlling fuel injection to raise exhaust temperature when the intake fresh air flow rate is limited by the fresh air flow limit in the latter period and the intake fresh air flow rate for achieving the target oxygen concentration cannot be realized. An exhaust purification device comprising a control means.   The exhaust emission control device according to claim 1 or 3, wherein the control for repeatedly increasing and decreasing the intake fresh air flow rate is performed within a range in which a filter bed temperature does not exceed an allowable maximum temperature.   The exhaust emission control device according to claim 2 or 4, wherein the control of fuel injection for increasing the exhaust temperature is performed within a range in which a bed temperature of the filter does not exceed an allowable maximum temperature. When the filter bed temperature is less than the maximum allowable temperature , the intake fresh air flow is always limited by the fresh air flow limit, and the intake fresh air flow for achieving the target oxygen concentration cannot be achieved. The exhaust emission control device according to any one of claims 1 to 4 , wherein the increase and decrease of the fresh air flow rate are repeated .

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