JPH07317530A - Exhaust emission control device of diesel engine - Google Patents

Abstract

PURPOSE:To provide an exhaust emission control device for diesel engine, which can control the secondary air amount for putting the filter temp. in a certain desired range. CONSTITUTION:A filter 5 to collect particulates is provided in the exhaust pipe 2 of a diesel engine 1. An electric heater 6 is installed in the secondary air upstream part about the filter 5, and a temp. sensor 14 is furnished at the end of the secondary air upstream part within the filter 5. An ECU 17 calculates the particulate collecting amount from the temp. of exhaust gas and the engine speed. and when the collecting amount exceeds the specified value, the EPU ignites the particulates collected by the filter 5 and starts the supply of the secondary air so that the burn-out of the collected particulates is started, and controls the secondary air amount thereafter on the basis of the temp. of the filter upstream given by the temp. sensor 14 at the time of the filter regeneration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust emission control device for a diesel engine.

[0002]

2. Description of the Related Art D as a measure against black smoke in diesel engines
A PF (diesel particulate filter) system is adopted. As shown in FIG. 9, the exhaust system of the diesel engine 31 is provided with a filter 32 for collecting particulates, and the pressure sensor 33 detects the pressure on the upstream side of the filter 32 and the pressure sensor 3 is used.
4, the pressure on the downstream side of the filter 32 is detected, and the ECU 3
5 calculates the amount of particulates trapped in the filter 32 from the pressure difference between the upstream side and the downstream side of the filter 32, and when a certain amount or more of particulates are trapped, the filter clogging is eliminated. Burn the collected particulates. As a method of this filter regeneration, the ECU 35
By energizing the electric heater 36 at the filter 32
The particulates trapped in the filter 32 are ignited, the electromagnetic valve 37 is opened, and the electric air pump 38 is driven to supply secondary air (oxygen) to the filter 32. It was supposed to incinerate curates.

Further, as disclosed in Japanese Patent Application Laid-Open No. 60-1317, it is also practiced to calculate the particulate collection amount from the engine operating state. However, the accuracy of calculating the amount of collected particulates in the filter from the operating state of the diesel engine is inferior to the case of calculating the amount of collected particulates from the differential pressure across the filter. Therefore, as disclosed in Japanese Patent Laid-Open No. 59-101518, a temperature sensor is provided in the center of the filter in the flow direction of the secondary air, and the filter temperature is measured during regeneration to measure the secondary air. By controlling the amount by feedback, combustion is performed within a predetermined filter temperature range to avoid melting loss, unburned residue, etc. of the filter.

[0004]

However, since a temperature sensor is provided in the center of the filter in the direction of flow of the secondary air and the secondary air amount is feedback-controlled, the temperature at the flame portion can be accurately measured. I couldn't. In other words, the secondary air in the filter is ignited at the upstream end and the flame moves toward the downstream, but the temperature sensor is located at the center of the moving direction of the flame, so the combustion temperature (filter temperature) is accurate. Could not be measured, and it was difficult to control the amount of secondary air within the desired filter temperature range.

Therefore, an object of the present invention is to provide an exhaust emission control device for a diesel engine, which makes it possible to control the amount of secondary air to bring it into a desired filter temperature range.

[0006]

According to a first aspect of the present invention, there is provided a filter provided in an exhaust system of a diesel engine for collecting particulates, and a secondary air supply means for supplying secondary air to the filter. An ignition means provided on the upstream side of the secondary air in the filter, a temperature sensor provided on an upstream end of the secondary air in the filter, and detects the operating state of the diesel engine. Operating state detecting means, a trapping amount calculating means for calculating the trapped amount of particulates in the filter from the operating state of the diesel engine by the operating state detecting means, and trapping of particulates by the trapping amount calculating means. When the collected amount is equal to or more than a predetermined value, the particulate matter collected by the filter by the ignition means is ignited and the secondary air supply means is also provided. More secondary air is started to start incineration of the particulates collected in the filter, and the desired filter temperature range is set thereafter based on the temperature of the filter upstream portion by the temperature sensor at the time of starting the filter regeneration. The exhaust gas purifying device for a diesel engine, which is provided with a control means for controlling the amount of secondary air for

According to a second aspect of the present invention, when the control means in the first aspect of the invention starts regeneration and the temperature upstream of the filter by the temperature sensor exceeds the upper limit value, the secondary air supply is stopped. After that, measure the stop time until it falls below the lower limit value, start the supply of secondary air when it falls below the lower limit value, and measure the supply time until it exceeds the upper limit value.
The gist is an exhaust emission control device for a diesel engine in which the supply of secondary air during the supply stop time and the supply of secondary air during the supply time are alternately repeated.

According to a third aspect of the present invention, in the diesel engine according to the first aspect of the present invention, the trapping amount calculating means has a correcting means for correcting the trapping amount of particulates according to the temperature of the filter during regeneration. The exhaust gas purifying device of is the gist.

[0009]

In the first aspect of the invention, the collection amount calculating means calculates the collection amount of particulates in the filter from the operating state of the diesel engine by the operating state detecting means. The control means ignites the particulate matter collected in the filter by the ignition means and supplies the secondary air by the secondary air supply means when the collected amount of the particulate matter by the collected amount calculation means becomes equal to or more than a predetermined value. Starts to incinerate the particulates trapped in the filter, and controls the secondary air amount to reach the desired filter temperature range thereafter based on the temperature of the filter upstream part by the temperature sensor at the start of filter regeneration. To do. That is, at the time of regeneration, the temperature of the flame portion at the start of regeneration is detected by the temperature sensor, and the secondary air amount is controlled based on the temperature to bring it into a desired filter temperature range thereafter.

According to a second aspect of the present invention, in addition to the operation of the first aspect of the invention, the secondary air is supplied when the control means starts regeneration and the temperature upstream of the filter by the temperature sensor exceeds the upper limit value. Stop, then measure the stop time until it falls below the lower limit, start the supply of secondary air when it falls below the lower limit, measure the supply time until it exceeds the upper limit, and then the supply stop time The secondary air supply stop and the secondary air supply for the supply time are alternately repeated. Therefore, it becomes possible to reliably bring the filter temperature within the predetermined range during regeneration.

According to the invention described in claim 3, in addition to the operation of the invention described in claim 1, the correcting means corrects the trapped amount of particulates by the temperature of the filter at the time of regeneration. As a result, it becomes possible to more accurately determine the trapped amount of particulates.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an overall configuration diagram of an exhaust emission control device for a diesel engine.

A diesel engine 1 is mounted on a vehicle, and the diesel engine 1 is supplied with high-pressure fuel from a column fuel injection pump and injected in a combustion chamber. The exhaust pipe 2 of the diesel engine 1 is provided with a housing 4 of an exhaust emission control device 3. The housing 4 communicates with the exhaust pipe 2, and exhaust gas of the diesel engine 1 passes through the housing 4. A filter (D
PF) 5 is provided, and the particulate matter discharged from the diesel engine 1 is collected by the filter 5. In this embodiment, a porous ceramic material (cordierite) is used as the filter 5. Further, an electric heater (heat wire) 6 as an igniting means is provided at the upstream end of the filter 5, and the electric heater 6 generates heat when the electric heater 6 is energized to generate particulates collected by the filter 5. Is ignited.

A secondary air supply pipe 7 is branched on the upstream side of the housing 4 in the exhaust pipe 2, and an electromagnetic valve 8 is arranged in the middle of the secondary air supply pipe 7. The electromagnetic valve 8 is for preventing exhaust gas from flowing back to the secondary air supply path during normal operation. A discharge side of an electric air pump 9 as a secondary air supply means is connected to the tip of the secondary air supply pipe 7. An air cleaner 10 is provided on the intake side of the electric air pump 9.
The air pump 9 is equipped with an electric motor, and the air pump 9 is driven by supplying electric power to the electric motor. Then, when the electromagnetic valve 8 is opened, the secondary air is sucked into the secondary air supply pipe 7 through the air cleaner 10 by the drive of the electric air pump 9 and is supplied into the exhaust pipe 2 of the diesel engine 1. ing. as a result,
The particulates collected in the filter 5 burn and the filter is regenerated.

An electric heater 6 is connected to the power source 11 to form a power source circuit. A bipolar transistor 12 is arranged in the middle of the power supply line. Then, by controlling the ON / OFF of the bipolar transistor 12, the energization of the electric heater 6 can be controlled.

An electric air pump 9 is connected to the power source 11 to form a power circuit. A bipolar transistor 13 is arranged in the middle of the power supply line. By controlling the on / off of the bipolar transistor 13, the electric motor of the electric air pump 9 can be drive-controlled.

A temperature sensor 14 is provided at the upstream end of the filter 5 so that the internal temperature of the filter 5 can be detected. The temperature sensor 14 can detect the internal temperature of the filter at the initial stage of regeneration. That is, the electric heater 6 ignites from the upstream side of the filter 5 and the filter 5
It is possible to measure the filter temperature at the start of combustion when the fuel is burned to the downstream side.

An exhaust gas temperature sensor 15 as an operating condition detecting means is attached to the exhaust pipe 2, and the sensor 15 detects the exhaust gas temperature. Further, the diesel engine 1 is provided with an engine speed sensor 16 as an operating condition detecting means.

An electronic control unit (hereinafter referred to as an ECU) 17 as a collection amount calculation means, a control means and a correction means 17
Is mainly composed of a CPU and various memories. EC
U17 is connected to the base terminal of the bipolar transistor 12, and the ECU 17 controls ON / OFF of the bipolar transistor 12. The ECU 17 is connected to the base terminal of the bipolar transistor 13, and the ECU 17 controls the bipolar transistor 13 to be turned on / off.

Further, a temperature sensor 14, an exhaust gas temperature sensor 15 and an engine speed sensor 16 are connected to the ECU 17, and the ECU 17 inputs signals from these sensors 14, 15, 16 to input the temperature of the filter 5 and the exhaust gas. Gas temperature,
Detects engine speed.

Further, the ECU 17 is connected to the electromagnetic valve 8 and controls the opening / closing of the electromagnetic valve 8. Further, the ECU 17 controls the bipolar transistors 12 and 13 and the electromagnetic valve 8 to regenerate the filter 5 by burning the particulate matter collected in the filter 5 when the amount of collected particulate matter Pmq described later becomes a predetermined value or more. It is like this.

Next, the operation of the exhaust emission control system for a diesel engine constructed as above will be described. The ECU 17 executes the processing shown in FIG. 2 every predetermined time. This process is to calculate the amount Pmq of trapped particulates in the filter 5. Here, the particulate collection amount Pmq is defined by the particulate collection weight per unit volume of the filter 5.

In step 101, the ECU 17 reads the correction coefficient a _{n according} to the filter temperature at the time of regeneration. The initial value of the correction coefficient a _n is "1". A method for _obtaining the correction coefficient a _n will be described later.

Then, in step 102, the ECU 17 obtains the particulate emission rate k ₂ determined by the engine operating conditions. This particulate emission rate k ₂ is
It refers to the particulate discharge weight per unit time, and more specifically, the particulate discharge weight is the filter 5
It is defined by the particulate discharge weight per unit volume of. This particulate emission rate k ₂ is generally determined by the engine operating conditions, and the particulate emission rate k ₂ should be integrated using the map of the particulate emission rate k ₂ measured in advance on the target engine (Fig. 4). Thus, the particulate collection amount Pmq can be obtained. That is, since the particulate emission rate k ₂ is determined by the engine speed and the engine load, the engine speed is detected by the engine speed sensor 16 and the engine load is detected by the exhaust gas temperature sensor 15. Here, instead of the exhaust gas temperature by the exhaust gas temperature sensor 15, the detection element corresponding to the engine load may be the accelerator opening by the accelerator opening sensor or the rack position by the rack position sensor in the column fuel injection pump.

The map of the particulate emission rate k ₂ shown in FIG. 4 is obtained by previously obtaining the particulate emission rate k ₂ according to the engine speed and the exhaust gas temperature.
The ECU 17 uses the k ₂ map to determine the particulate emission rate k ₂ from the engine speed and exhaust gas temperature at that time.
Ask for.

The ECU 17 determines in step 103 the correction coefficient a.
Multiply _n by the particulate discharge rate k ₂ . further,
ECU17 updates the particulate collection amount Pmq by adding the previous particulate collection amount Pmq the multiplied value of the correction coefficient a _n and particulate emission rate k ₂ at step 104 (= a _n · k ₂₎ . By repeating such a process, the particulate discharge rate k ₂ is integrated, and the particulate collection amount Pmq is calculated.

FIG. 3 shows a learning process of the correction coefficient a _n performed every time reproduction is completed. That is, by collecting the particulate emission rate k ₂ , the particulate collection amount P
When mq is calculated, there are variations between engines and fuel injection pumps, and accuracy cannot be reduced because it cannot follow changes over time, environmental changes (intake air temperature, humidity), and the like. Such a decrease in detection accuracy hinders stable regeneration, and there is a possibility that the filter 5 may be melted and unburned. Therefore, the maximum temperature T of the upstream portion of the filter at the initial stage of regeneration
_Since the relationship between _MAX and the amount of particulate collection is as shown in FIG. 5, the maximum temperature T of the upstream portion of the filter at the initial stage of regeneration is T.
Correct with _MAX .

The ECU 17 uses the temperature sensor 14 to obtain the filter maximum temperature T _MAX during the regeneration period each time the filter 5 is regenerated. And the ECU
In step 17, when the maximum temperature T _MAX at the upstream end in the filter 5 at the initial stage of regeneration exceeds 900 ° C. in step 201, the correction coefficient a _n is learned and corrected to a large value of “0.01” in step 202. As a result, the particulate collection amount Pmq for the next collection is corrected to a larger value. Therefore, the amount of trapped substance at the start of regeneration is lowered and the regeneration temperature is lowered.
Further, the ECU 17 determines in steps 201 and 203 that the maximum temperature T _MAX at the upstream end in the filter 5 at the initial stage of regeneration is 800.
If the temperature does not exceed ℃, in step 204 the correction coefficient a
Learning correction is performed on _n to a small value of "0.01". as a result,
The particulate collection amount Pmq at the next collection is corrected to a smaller value. Therefore, the amount of trapped material at the start of regeneration increases and the regeneration temperature rises.

The operation of the ECU 17 during reproduction will be described with reference to the flowchart of FIG. The process of FIG. 6 is a routine executed at a predetermined time (for example, every 1 second).
First, while the diesel engine 1 is operating, the ECU
In step 300 of FIG. 6, it is determined whether or not 17 is the regeneration time. That is, when it is determined that the particulate collection amount Pmq is less than the predetermined value and regeneration is not necessary, this routine is ended. On the other hand, when the particulate collection amount Pmq becomes equal to or larger than the predetermined value and the regeneration is required, the regeneration is started.

When the regeneration is started when the diesel engine 1 is stopped, the ECU 17 opens the electromagnetic valve 8 in step 400 so that air (oxygen) can be supplied from the electric air pump 9. Further, the ECU 17
In step 500, the bipolar transistor 12 is turned on to drive (energize) the electric heater 6. Also, the ECU 1
In step 600, 7 controls the bipolar transistor 13 to drive the electric air pump 9 to supply secondary air. That is, by energizing the electric heater 6, the particulates collected in the filter 5 are ignited,
The electric air pump 9 is driven to incinerate the particulates collected by the filter 5 to regenerate the filter.

The details of the control of the air pump 9 in step 600 of FIG. 6 are shown in FIG. This process will be described with reference to the time chart of FIG. In the regenerating process, the correction coefficient a _n is not completely corrected at the beginning of the system startup, and the detection accuracy is not high in the method of obtaining the particulate trapped amount from the engine operating state. The temperature may deviate from the expected value. Therefore, the filter regeneration temperature is controlled within a predetermined range by detecting the filter temperature at the initial stage of regeneration and adjusting the secondary air flow rate so as to reach a predetermined temperature.

The ECU 17 determines in step 601 whether the filter temperature T _f measured by the temperature sensor 14 has reached 900 ° C. If it has not reached 900 ° C., the air pump 9 is turned on in step 602. By repeating steps 601 and 602, the temperature of the filter 5 rises (see FIG. 8).
Before t1).

When the filter temperature T _f reaches 900 ° C. (timing t1 in FIG. 8), the ECU 17 shifts from step 601 to step 603 and the air pump 9
Is turned off and the off time TM1 of the air pump 9 is measured. Then, the ECU 17 determines in step 604 whether the filter temperature T _f has reached 800 ° C.
If not, the process returns to step 603. By repeating steps 603 and 604, the temperature of the filter 5 decreases and the off time TM1 of the air pump 9 is measured (t1 to t2 in FIG. 8).

After that, when the filter temperature T _f reaches 800 ° C. (timing of t2 in FIG. 8), the ECU 17 shifts from step 604 to step 605 and the air pump 9
Is turned on and the on-time TM2 of the air pump 9 is measured. Then, the ECU 17 determines in step 606 whether the filter temperature T _f has reached 900 ° C.
If the temperature is not ℃, the process returns to step 605. By repeating steps 605 and 606, the temperature of the filter 5 rises and the ON time TM2 of the air pump 9 increases.
Is measured (t2 to t3 in FIG. 8).

When the filter temperature T _f reaches 900 ° C. (timing of t3 in FIG. 8), the ECU 17 shifts from step 606 to step 607 and the air pump 9
Is turned off, and in step 608, step 6
It is determined whether or not the off time TM1 measured in 03 has elapsed, and if it has not elapsed, the process returns to step 607. When the temperature of the filter 5 is reduced by repeating steps 607 and 608 and the off time TM1 elapses (timing t4 in FIG. 8), the ECU 17 shifts from step 608 to step 609 to turn on the air pump 9. Further, the ECU 17 executes step 6 in step 610.
It is determined whether or not the on-time TM2 measured in 05 has elapsed, and if it has not elapsed, the process returns to step 609. When the temperature of the filter 5 rises due to the repetition of steps 609 and 610 and the on-time TM2 elapses (timing of t5 in FIG. 8), the ECU 17 shifts from step 610 to step 611. ECU17 is step 61
In step 1, it is determined whether or not a predetermined time has passed since the secondary air control was started, and if the predetermined time has not passed, step 60
Returning to step 7, the processes of steps 607 to 611 described above are repeated.

The ECU 17 terminates the regeneration process when a predetermined time has elapsed since the secondary air control was started in step 611. As described above, in the present embodiment, the electric heater 6 is provided on the upstream side of the secondary air in the filter 5, and the temperature sensor 14 is provided at the upstream side end of the secondary air in the filter 5, and the temperature sensor 14 starts regeneration. The temperature of the upstream portion of the filter at that time is used to control the amount of secondary air for achieving the desired filter temperature range thereafter. As a result, at the time of regeneration, the temperature of the flame portion at the start of regeneration is detected by the temperature sensor 14, and the secondary air amount thereafter is controlled based on the temperature to obtain a desired temperature range for the filter. It is possible to control the amount of secondary air, and it is possible to avoid melting damage, unburned residue, etc. of the filter 5. That is, since the measurement point of the filter internal temperature is at the upstream end in the filter 5, combustion starts when the electric heater 6 ignites from the upstream side of the filter 5 and burns to the downstream side of the filter 5. The filter temperature at that time can be measured and reflected in the subsequent regeneration.

More specifically, regeneration is started and the temperature
Filter T upstream temperature T _fIs the upper limit (900
Temperature), the secondary air supply is stopped and the lower limit value thereafter
Measure the stop time TM1 until it falls below (800 ° C),
When the temperature falls below the lower limit (800 ° C), supply of secondary air is started.
Supply time TM2 until the upper limit (900 ° C) is exceeded
Of the secondary air during the supply stop time TM1
The supply is stopped and the supply of secondary air during the supply time TM2
I tried to repeat each other. Therefore, when playing back, filter
The temperature can be brought exactly within the predetermined range.

Here, the upper limit value is set to 900 ° C. and the lower limit value is set to 800 ° C. within the range of 1000 ° C. which is the heat resistant temperature of cordierite which is the material of the filter to 600 ° C. which is the ignition temperature of the particulates. This is for burning.
The upper and lower temperatures are 900 ° C and 800 ° C.
However, it is possible to set an appropriate numerical value depending on the material of the filter.

Further, the correction coefficient a _n is learned by the temperature inside the filter for each regeneration to correct the trapped amount of particulates, so that the measurement accuracy can be improved and the reliability can be improved. .

In the present embodiment, the engine speed and the exhaust gas temperature (or the accelerator opening, the rack position of the column fuel injection pump) are used as factors for obtaining the particulate collection amount from the engine operating state. However, a throttle opening sensor for detecting the throttle opening provided in the intake system of the diesel engine may be used, and the point is that it is possible to obtain the particulate collection amount from the engine operating state. .

[0041]

As described above in detail, according to the invention described in claim 1, it is possible to control the amount of secondary air for controlling the desired filter temperature range. .

According to the invention of claim 2, claim 1
In addition to the effects of the invention described in (1), the filter temperature can be reliably kept within a predetermined range during regeneration. According to the invention of claim 3, in addition to the effect of the invention of claim 1,
The collected amount of particulates can be obtained more accurately.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an exhaust emission control device for a diesel engine of an embodiment.

FIG. 2 is a flowchart for explaining the operation.

FIG. 3 is a flowchart for explaining an operation.

FIG. 4 is a map for obtaining a particulate emission rate k ₂ .

FIG. 5 is a graph showing the relationship between the collection amount and the maximum temperature of the upstream portion of the filter at the start of regeneration.

FIG. 6 is a flowchart for explaining the operation.

FIG. 7 is a flowchart for explaining the operation.

FIG. 8 is a time chart for explaining the operation.

FIG. 9 is an overall configuration diagram of a conventional exhaust emission control device for a diesel engine.

[Explanation of symbols]

1 ... Diesel engine, 2 ... Exhaust pipe, 5 ... Filter,
6 ... Electric heater, 9 ... Air pump, 14 ... Temperature sensor,
15 ... Exhaust gas temperature sensor, 16 ... Engine speed sensor, 17 ... ECU

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshimi Muramatsu 1-1, Showa-cho, Kariya city, Aichi Nihon Denso Co., Ltd. (72) Inventor Katsuyuki Tamai 1-1-chome, Showa town, Kariya city, Aichi Incorporated (72) Inventor Mori Oki 1-1-1, Showa-cho, Kariya, Aichi Prefecture

Claims (3)

[Claims] 1. A filter provided in an exhaust system of a diesel engine for collecting particulates, a secondary air supply means for supplying secondary air to the filter, and an upstream side of the secondary air in the filter. Igniting means provided in, a temperature sensor provided at the upstream end of the secondary air in the filter, an operating state detecting means for detecting the operating state of the diesel engine, by the operating state detecting means A collection amount calculation means for calculating the collection amount of particulates in the filter from the operating state of the diesel engine, and the collection amount of particulates by the collection amount calculation means becomes a predetermined value or more, by the ignition means The particulate matter trapped in the filter is ignited and the secondary air is started to be supplied by the secondary air supply means to fill it. Start the incineration of the particulates collected in the ta,
Exhaust of a diesel engine, comprising: a control unit that controls the amount of secondary air for setting a subsequent desired filter temperature range based on the temperature of the filter upstream portion by the temperature sensor at the start of filter regeneration. Purification device. 2. The control means stops the secondary air supply when the temperature upstream of the filter by the temperature sensor exceeds the upper limit value by starting regeneration, and then measures the stop time until the temperature falls below the lower limit value. When the value falls below the lower limit value, the supply of secondary air is started, and the supply time until the upper limit value is exceeded is measured.
The exhaust emission control device for a diesel engine according to claim 1, wherein the supply of the secondary air during the supply stop time and the supply of the secondary air during the supply time are alternately repeated. 3. The exhaust gas purification device for a diesel engine according to claim 1, wherein the trapping amount calculation unit has a correcting unit that corrects the trapped amount of particulates according to the temperature of the filter during regeneration.