JPH0749023A - Exhaust emission control device for diesel engine - Google Patents

Abstract

PURPOSE:To enable the correct detection of the particulate collecting quantity and the control of the air supply quantity to be conducted without using an exclusive air flow measuring flow sensor in an exhaust emission control device for a diesel engine capable of regenerating a filter during the operation of the engine. CONSTITUTION:The suction pipe 9 of an air pump 8 is connected to the lower reaches of an airflow meter 4. Through an electromagnetic switching valve 7, at the time of computing the collecting quantity, air having passed the airflow meter 4 is sucked into the air pump, while air not passing the airflow meter 4 is sucked into the engine 1. Through an electromagnetic switching valve 11, at the time of computing the collecting quantity, the exhaust of the engine passes filters 15, 16, and at the time of regenerating the filter, the exhaust of the engine 1 does not pass the filter to be the regenerated object.

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. 4, a DPF 32 that collects particulates is provided in the exhaust system of the diesel engine 31, and when the filter is regenerated, the electric heater 34 is energized by the ECU 33 when the engine is stopped to collect the DPF 32. The particulates thus collected are ignited and the air pump 35 is driven to supply combustion air to the DPF 32 to incinerate the particulates collected in the DPF 32. During this regeneration, if the particulate collection amount is too large or the air supply amount for combustion is too large, the heat generation amount of the particulate combustion per unit time increases and the combustion temperature rises. The DPF 32 is cracked or melted. On the contrary, if the particulate collection amount is too small or the air supply amount for combustion is too small, unburned particulates will occur. Therefore, D
In the PF system, it is important to accurately detect the amount of collected particulates and control the supply amount of combustion air.

To detect the amount of collected particulates, the differential pressure sensor 36 detects the differential pressure generated upstream and downstream of the DPF 32, and the volume flow rate of the exhaust gas passing through the DPF 32 is detected to block the DPF 32. Calculate the state,
A general method is to calculate the amount of particulate collection. In order to accurately detect the collected amount of particulates, there is a method of measuring the intake air flow rate of the engine with an air flow meter 37 and converting it into a volume flow rate of exhaust gas.

Further, in order to accurately control the supply amount of combustion air, there is a flow rate feedback method in which the air flow rate is measured by the flow rate sensor 38 and the air pump 35 is driven so as to match the target supply amount. is there.

[0005]

However, the air flow meter 37 for measuring the engine intake air flow rate for accurately detecting the particulate collection amount and the flow rate sensor 38 for measuring the air flow rate for accurately controlling the air supply amount are provided. Both of them are necessary, and the flow sensor 38 is expensive, so that an increase in system cost cannot be avoided.

Therefore, an object of the present invention is to accurately detect the amount of trapped particulate matter and air without using a dedicated air flow rate measuring flow rate sensor in an exhaust purification system of a diesel engine capable of performing filter regeneration during engine operation. An object of the present invention is to provide an exhaust emission control device for a diesel engine that can control the supply amount.

[0007]

The present invention is directed to a filter provided in an exhaust system of a diesel engine for collecting particulates, an air pump for supplying combustion air to the filter, and an intake air of the diesel engine. An intake air flow rate sensor for detecting the intake air flow rate to the diesel engine, a pressure sensor for detecting a pressure difference between the upstream side and the downstream side of the filter, and an upstream side of the filter by the pressure sensor. And the downstream side pressure difference and the intake air flow rate to the diesel engine by the intake air flow rate sensor, the particulate collection amount is obtained, and when the particulate collection amount exceeds a predetermined value, it is necessary to drive the air pump. The amount of air is supplied to the filter and the particulates collected by the filter are burned to regenerate the filter. In a diesel engine exhaust gas purification device including a control circuit, a suction pipe of the air pump is connected to a downstream side of an intake air flow rate sensor in the intake system of the diesel engine, and an intake air flow rate in the intake system of the diesel engine. By providing a first flow path switching valve on the downstream side of the sensor and controlling the first flow path switching valve, the air that has passed through the intake air flow rate sensor is sucked into the diesel engine when calculating the particulate collection amount. The air flow path is formed so that the air that has passed through the intake air flow rate sensor is sucked into the air pump during filter regeneration, and the air that does not pass through the intake air flow rate sensor is drawn into the diesel engine. A second flow path switching valve upstream of the filter in the exhaust system of the diesel engine. However, by controlling the second flow path switching valve, a flow path through which the exhaust gas of the diesel engine passes through the filter is formed when calculating the particulate collection amount, and the exhaust gas of the diesel engine is targeted for regeneration when the filter is regenerated. The gist of the invention is an exhaust emission control device for a diesel engine that forms a flow path that does not pass through the filter.

[0008]

When calculating the amount of trapped particulates, the first flow path switching valve forms an air flow path through which the air that has passed through the intake air flow rate sensor is sucked into the diesel engine, and the second flow path switching valve forms the diesel flow path. A flow path is formed through which engine exhaust passes through the filter. Then, the control circuit determines the particulate collection amount from the pressure difference between the upstream side and the downstream side of the filter by the pressure sensor and the intake air flow rate to the diesel engine by the intake air flow rate sensor. Further, when the particulate collection amount exceeds a predetermined value by the control circuit, it is judged that the filter regeneration time is reached.

When the filter is regenerated, the first flow path switching valve forms an air flow path through which the air that has passed through the intake air flow rate sensor is sucked into the air pump, and the air that does not pass through the intake air flow rate sensor is diesel. An air flow path that is taken into the engine is formed, and the second flow path switching valve forms a flow path in which the exhaust gas of the diesel engine does not pass through the filter to be regenerated. Then, the control circuit obtains the air amount required by the drive of the air pump by the intake air flow rate sensor and supplies it to the filter to burn the particulates collected by the filter to regenerate the filter.

In this way, one intake air flow rate sensor is used both for measuring the intake air flow rate of the engine when calculating the amount of trapped particulates and for measuring the air flow rate for controlling the air pump when regenerating the filter.

The engine is also driven when the filter is regenerated.

[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.

The vehicle is equipped with a diesel engine 1. An intake pipe 2 is connected to the intake side of the diesel engine 1, and an air cleaner 3 is provided at the most upstream part of the intake pipe 2. An air flow meter 4 is arranged in the middle of the intake pipe 2. An intake pipe 5 is branched between the air flow meter 4 and the diesel engine 1 in the intake pipe 2, and an air cleaner 6 is provided at the most upstream part of the intake pipe 5. An electromagnetic switching valve 7 is provided at a branch portion of the intake pipe 5, and the electromagnetic switching valve 7 is a three-way valve. Then, by controlling the electromagnetic switching valve 7, the flow path of the intake pipe 2 or 5 can be selectively switched. That is, the line of the intake pipe 5 is closed by setting the electromagnetic switching valve 7 to the position shown by the solid line in the drawing, and the line of the intake pipe 2 is closed by setting it to the position shown by the broken line in the drawing. There is.

The air flow meter 4 is of the type that measures the mass flow rate. The air pump 8 is for supplying combustion air (secondary air), and its suction pipe 9 is connected between the air flow meter 4 of the intake pipe 2 and the branch portion of the intake pipe 5. .

An exhaust pipe 10 is connected to the exhaust side of the diesel engine 1, and the downstream side of the exhaust pipe 10 is branched into two, has a parallel portion, and further joins on the downstream side. An electromagnetic switching valve 11 is provided at a branch portion of the exhaust pipe 10, and by controlling the electromagnetic switching valve 11, it is possible to switch between a neutral position shown in the figure and three positions for closing any of the branched exhaust pipes 10. Further, an electromagnetic switching valve 12 is provided at the confluent portion of the exhaust pipe 10, and by controlling the electromagnetic switching valve 12, the neutral position shown in the drawing and any one of the converging exhaust pipes 10 can be switched to three positions. .

DPF housings 13 and 14 are provided in parallel with the exhaust pipe 10, and exhaust gas of the diesel engine 1 passes through the DPF housings 13 and 14.
Filters (DPF) 15 and 16 made of ceramic porous material are provided in the DPF housings 13 and 14, and the particulates discharged from the diesel engine 1 are collected by the filters 15 and 16. Furthermore, filter 1
Electric heaters 17 and 18 are provided at the upstream end portions of the electric heaters 5 and 16, and when the electric heaters 17 and 18 are energized, the electric heaters 17 and 18 generate heat to generate particulates collected by the filters 15 and 16. Is ignited.

A muffler 19 is arranged downstream of the confluent portion of the exhaust pipe 10. The discharge pipe 20 of the air pump 8 is the DPF housing 1 in the exhaust pipe 10.
It is connected to the upstream side of 3, 14 via electromagnetic on-off valves 21, 22. That is, the discharge pipe 20 of the air pump 8 communicates with the exhaust pipe 10 on the upstream side of the DPF housing 13 by opening the electromagnetic opening / closing valve 21, and the discharge of the air pump 8 is opened by opening the electromagnetic opening / closing valve 22. Tube 20 and DPF
The exhaust pipe 10 on the upstream side of the housing 14 is communicated.

DPF housing 1 in exhaust pipe 10
Electromagnetic on-off valves 23 and 24 are provided on the downstream side of 3 and 14, respectively.
Atmosphere opening pipe 25 is connected through
5 is open to the atmosphere.

A differential pressure sensor 27 for detecting the differential pressure across the filters 15 and 16 is provided between the upstream side of the branch portion of the exhaust pipe 10 and the downstream side of the merging portion.
Further, an exhaust temperature sensor 28 is arranged on the upstream side of the branched portion of the exhaust pipe 10, and the sensor 28 measures the exhaust gas temperature of the diesel engine 1.

Electronic control unit (hereinafter referred to as ECU)
The electric heaters 17 and 18 are connected to 29, and the ECU 29
The energization of the electric heaters 17 and 18 is controlled according to the control signal from. Further, the ECU 29 is connected to the air pump 8 and the drive of the air pump 8 is controlled according to a control signal from the ECU 29. Further, the ECU 29 is connected to the electromagnetic switching valves 7, 11, 12 and the electromagnetic opening / closing valves 21, 22, 23, 24, and the ECU 29 controls these electromagnetic valves.

The air flow meter 4 and the differential pressure sensor 27 are also provided.
And the exhaust gas temperature sensor 28 are connected to the ECU 29, and the output signals from these sensors are taken into the ECU 29.
In the present embodiment, the air flow meter 4 constitutes an intake air flow rate sensor, the electromagnetic switching valve 7 constitutes a first passage switching valve, and the electromagnetic switching valve 11 constitutes a second passage switching valve. And the differential pressure sensor 27 constitutes a pressure sensor, and E
The CU 29 constitutes a control circuit.

Next, the operation of the exhaust emission control system for a diesel engine constructed as above will be described. The operation of the ECU 29 at the time of particulate collection will be described with reference to the flowchart of FIG. This routine is executed, for example, every one second.

First, the ECU 29 determines in step 100 whether or not reproduction is in progress. If reproduction is in progress, the processing is terminated,
If not being reproduced, the process proceeds to step 101 and thereafter. next,
In step 101, the ECU 29 sets the electromagnetic switching valves 11 and 12 to a neutral state and passes the exhaust gas of the diesel engine 1 through the filter 15 and the filter 16 to collect the particulates in the exhaust gas. Further, the ECU 29 closes the electromagnetic opening / closing valves 21 and 22 to prevent the pressure of the exhaust gas from being applied to the air pump 8 and prevent the exhaust gas from entering. Further, the ECU 29 closes the electromagnetic opening / closing valves 23 and 24 so that the exhaust gas flows into the muffler 19.
Further, the ECU 29 sets the electromagnetic switching valve 7 as shown by the solid line in FIG. 1 so that the total amount of intake air of the diesel engine 1 can be measured by the air flow meter 4.

Next, the ECU 29 calculates the amount of particulate collection in steps 102 to 104.
First, in step 102, the ECU 29 corrects the mass flow rate value G from the air flow meter 4 with the exhaust gas temperature from the exhaust gas temperature sensor 28, and exhaust gas flowing through the filter 15 and the filter 16 as Q = f (G, TEX). It is calculated as the volume flow rate of. This is in consideration of volume expansion due to combustion.

Next, at step 103, the ECU 29 takes in the differential pressure across the filter ΔP from the differential pressure sensor 27. Then, in step 104, the ECU 29 obtains the particulate collection amount PT from the differential pressure ΔP and the exhaust gas flow rate Q as PT = f (ΔP, Q).

In step 105, the ECU 29 determines whether or not the particulate collection amount PT has reached the set value. If the particulate collection amount PT has reached the set value, the regeneration request flag is set in step 106, and the set value is also set. If not reached, the reproduction request flag is cleared in step 107, and the process ends.

Next, the operation of the ECU 29 during reproduction will be described with reference to FIG.
It will be described in accordance with the flowchart of. This routine is executed, for example, every one second. First, the ECU 2
In step 200, it is determined whether or not the reproduction request flag is set, and if it is set, the process proceeds to step 201 and thereafter to perform reproduction control, and if it is not set, the process ends.

At step 201, the ECU 29 increments a counter t for measuring the elapsed playback time.
In step 202, the ECU 29 drives the electromagnetic switching valve 7 to the state indicated by the broken line in FIG. As a result, diesel engine 1
The intake air passes through the air cleaner 6, and the intake air of the air pump 8 passes through the air cleaner 3 and the air flow meter 4 to measure its mass flow rate.

In step 203, the ECU 29 determines whether or not the regeneration elapsed time counter t is smaller than the predetermined time TA, and if it is smaller than the predetermined time TA, the routine proceeds to step 204 and thereafter. The ECU 29 executes the filter 1 in step 204.
The electromagnetic switching valves 11 and 12 are driven to the upper side in FIG. As a result, the exhaust gas from the diesel engine 1 passes only through the filter 16. As a result, the filter 15 is separated from the exhaust gas flow path. And
The ECU 29 drives the electromagnetic on-off valves 21 and 23 to be in the open state, and drives the electromagnetic on-off valves 22 and 24 to be in the closed state. As a result, an air flow path is formed from the air pump 8 through the filter 15 and open to the atmosphere.

Then, in step 205, the ECU 29 energizes the electric heater 17 to ignite the particulates.
Further, in step 206, the ECU 29 reads the air flow rate Qap flowing through the air pump 8 from the signal from the air flow meter 4. Then, in step 207, the ECU 29 obtains a difference e between the target air flow rate Qapr and the actual air flow rate Qap by e = Qapr-Qap.

Then, in step 208, the ECU 29 calculates the drive duty Duty of the air pump 8. The calculation method is, for example, a proportional gain K _P , an integral gain K _I, and a differential gain K _D using error PID feedback control.
Duty (i) = K _P · e (i) + K _I · e _I (i) + K
_D · e _D (i) where e _I (i) = e _I (i-1) + e (i) e _D (i) = e (i) -e (i-1) It As for the subscript of each term, i represents the current time and i-1 represents the previous time.

The ECU 29 executes the step 2 in the step 209.
The drive signal of the air pump 8 is output at the drive duty Duty obtained in 08. That is, in step 205, the electric heater 17 is energized to ignite the particulates collected in the filter 15, and in step 209 the air pump 8 is driven to supply combustion air to the filter 15 to filter the filter. The particulates collected in 15 are incinerated.

In this way, the reproduction control of the filter 15 is performed from the start of reproduction to the predetermined time TA. Then, the ECU 29 proceeds to step 210 when the regeneration elapsed time counter t has passed the predetermined time TA in step 203. The ECU 29 determines in step 210 whether the regeneration elapsed time counter t is smaller than a predetermined time TB (> TA), and if it is smaller than the predetermined time TB, the step 2
Go to 11. The ECU 29 drives the electromagnetic switching valves 11 and 12 downward in FIG. 1 so as to regenerate the filter 16 in step 211. As a result, the exhaust gas from the diesel engine 1 passes only through the filter 15. As a result, the filter 16 is separated from the exhaust gas flow path. Then, the ECU 29 drives the electromagnetic on-off valves 21, 23 to a closed state and drives the electromagnetic on-off valves 22, 24 to an open state. As a result, an air flow path is formed from the air pump 8 to the atmosphere through the filter 16.

Then, in step 212, the ECU 29 energizes the electric heater 18 to ignite the particulates.
After that, the ECU 29 executes the processing of steps 206 to 209 described above. That is, in step 212, the electric heater 18 is energized to ignite the particulates collected in the filter 16, and in step 209 the air pump 8 is driven to supply combustion air to the filter 16 to filter it. The particulates collected in 16 are incinerated.

In this way, the regeneration control of the filter 16 is performed from the predetermined time TA after the start of regeneration to the predetermined time TB. In this way, by switching the air flow path on the downstream side of the air flow meter 4 by the electromagnetic switching valve 7, the diesel engine 1 can be used during particulate collection.
It is possible to accurately detect the amount of collected particulates by measuring the intake air flow rate by the air flow meter 4. Further, at the time of regeneration, the same air flow meter 4 can be used to measure the air flow rate of the air pump 8 to accurately control the air flow rate.

After that, when the regeneration elapsed time counter t has passed a predetermined time TB in step 210, the ECU 29 clears the regeneration start time counter t in preparation for the next time in step 213, and clears the regeneration request flag in step 214. .

As described above, in this embodiment, the intake pipe 9 of the air pump 8 is connected to the downstream side of the air flow meter 4 (intake air flow rate sensor) in the intake system of the diesel engine 1 and the intake system of the diesel engine 1 is connected. An electromagnetic switching valve 7 (first flow path switching valve) was provided downstream of the air flow meter 4. Then, by controlling the electromagnetic switching valve 7, an air flow path is formed in which the air that has passed through the air flow meter 4 is sucked into the teasel engine 1 when calculating the amount of particulate collection, and passes through the air flow meter 4 when regenerating the filter. The air flow path is formed so that the air is sucked into the air pump 8 and the air flow path through which the air that does not pass through the air flow meter 4 is sucked into the diesel engine 1 is formed. Further, an electromagnetic switching valve 11 (second flow path switching valve) is provided on the upstream side of the filter in the exhaust system of the diesel engine 1, and the electromagnetic switching valve 11 is controlled so that when the particulate collection amount is calculated, the diesel switching valve 11 is used. The exhaust gas of the engine 1 forms a flow path that passes through the filter, and at the time of filter regeneration, the exhaust gas of the diesel engine 1 does not pass through the filter that is the regeneration target.

That is, at the time of calculating the amount of collected particulates, the electromagnetic switching valve 7 forms an air flow path through which the air passing through the air flow meter 4 is sucked into the teasel engine, and the electromagnetic switching valve 11 exhausts the diesel engine 1. A flow path is formed through the filter. And E
The CU 29 (control circuit) calculates the amount of particulate collection from the pressure difference between the upstream side and the downstream side of the filter by the differential pressure sensor 27 (pressure sensor) and the intake air flow rate into the diesel engine 1 by the air flow meter 4. Further, when the particulate collection amount of the particulate matter exceeds a predetermined value by the ECU 29, it is determined that the filter regeneration timing is reached.

When the filter is regenerated, the air that has passed through the air flow meter 4 by the electromagnetic switching valve 7 is transferred to the air pump 8.
Is formed into the diesel engine 1 and air that does not pass through the air flow meter 4 is drawn into the diesel engine 1, and the exhaust gas of the diesel engine 1 is regenerated by the electromagnetic switching valve 11. A flow path that does not pass through the filter is formed. Then, the ECU 29 drives the air pump 8 to supply the required amount of air to the filter by the air flow meter 4 and burns the particulates collected by the filter to regenerate the filter.

In this way, one air flow meter 4 is used both for measuring the intake air flow rate of the engine when calculating the particulate collection amount and for measuring the air flow rate for controlling the air pump when regenerating the filter. As a result, it is possible to perform accurate particulate trapping amount detection and air supply amount control without using a dedicated air flow rate measuring flow rate sensor. As described above, by measuring the engine intake air flow rate and the air flow rate of the air pump 8 by the same air flow meter 4, it is possible to suppress an increase in cost without adding an extra flow rate sensor.

The diesel engine 1 is also driven during filter regeneration.

[0042]

As described above in detail, according to the present invention,
An excellent exhaust gas purification device for a diesel engine that can perform filter regeneration when the engine is operating, which can perform accurate particulate collection amount detection and air supply amount control without using a dedicated air flow rate measurement flow rate sensor. Be effective.

[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 an overall configuration diagram of a conventional exhaust emission control device for a diesel engine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Diesel engine 4 Air flow meter as an intake air flow rate sensor 7 Electromagnetic switching valve as a first flow path switching valve 8 Air pump 9 Intake pipe 11 Electromagnetic switching valve as a second flow path switching valve 15, 16 Filter 27 Pressure sensor Differential pressure sensor 29 CPU as a control circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Shoji Morita, 1-1, Showa-cho, Kariya, Aichi Prefecture, Nihon Denso Co., Ltd. (72) Inventor: Takayuki Toya, 1-1, Showa-cho, Kariya, Aichi Nidec Within the corporation

Claims (1)

[Claims] 1. A filter provided in an exhaust system of a diesel engine for collecting particulates, an air pump for supplying combustion air to the filter, an intake system of the diesel engine provided to a diesel engine. An intake air flow rate sensor for detecting an intake air flow rate of the filter, a pressure sensor for detecting a pressure difference between the upstream side and the downstream side of the filter, a pressure difference between the upstream side and the downstream side of the filter by the pressure sensor, and The particulate collection amount is calculated from the intake air flow rate to the diesel engine by the intake air flow rate sensor, and when the particulate collection amount exceeds a predetermined value, the air pump is driven to supply the required air amount to the filter. And a control circuit for regenerating the filter by burning the particulates collected by the filter. In the exhaust purification apparatus over diesel engine, with connecting suction pipe of the pump downstream of the intake air flow rate sensor in the intake system of a diesel engine,
A first flow path switching valve is provided on the downstream side of the intake air flow rate sensor in the intake system of the diesel engine, and by controlling the first flow path switching valve, the intake air flow rate sensor is calculated when calculating the particulate trapped amount. The air that has passed through the intake air flow sensor forms an air flow path that is sucked into the diesel engine, and the air that has passed through the intake air flow rate sensor when the filter is regenerated forms an air flow path that is sucked into the air pump. Forming an air flow path through which air that does not pass through the diesel engine is sucked into the diesel engine, and further, providing a second flow path switching valve on the upstream side of the filter in the exhaust system of the diesel engine. By controlling the valve,
The exhaust gas of the diesel engine forms a flow path that passes through the filter when calculating the particulate collection amount, and the exhaust gas of the diesel engine forms a flow path that does not pass through the filter to be regenerated during filter regeneration. Exhaust gas purification device for diesel engine.