JPH08210123A - Exhaust emission control device for diesel engine - Google Patents

Abstract

PURPOSE: To enable satisfactory flow rate control in the case of setting a plurality of target flow rates for controlling a flow rate of an air pump. CONSTITUTION: An orifice 27 is provided on an air flow passage 24 from an air pump 23, while a bypass flow passage 25 is formed while bypassing the orifice 27. An orifice 28 and an opening/closing valve 26 are provided on the bypass flow passage 25. An ECU 45 senses differential pressure in respect to the orifice based on pressure sensors 40, 41 at the burning regeneration time of filters 9 or 13, and controls the air pump 23 so as to obtain a target flow rate based on the differential pressure. The ECU 45 opens and closes the valve 26 together with variation of the target flow rate for varying a secondary air flow passage. The air pump 23 is controlled according to the orifice characteristic on the respective flow passage.

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 system for a diesel engine equipped with a filter for collecting particulates contained in the exhaust of the diesel engine,
Particularly, it relates to a device for controlling the supply amount of secondary air when the filter is burned and regenerated.

[0002]

2. Description of the Related Art Conventionally, as an exhaust gas purifying device of this type, there is an exhaust gas purifying device disclosed in, for example, Japanese Unexamined Patent Publication No. 4-109919. This exhaust gas purifying device uses particulate matter (particulates, hereinafter referred to as PM) collected by a filter.
Say. ) Is ignited by an electric heater (ignition means) provided on the downstream end face of the filter, and secondary air for combustion is supplied from an air pump to propagate combustion and regenerate the filter.

At this time, in order to perform stable combustion (regeneration), the air pump is controlled so that the differential pressure generated at both ends of the filter becomes constant, and when the combustion progresses, the secondary air flow rate is increased. Sufficient secondary air is supplied to the peripheral portion of the filter where unburned residue is likely to occur. However, in this case, the secondary air flow rate becomes excessively supplied, which may cause cracking and melting damage of the filter. Therefore, in order to perform stable combustion (regeneration), it is necessary to accurately control the secondary air flow rate to a required amount (target flow rate).

Therefore, the applicant of the present application has proposed a method of controlling the secondary air flow rate to a target flow rate (Japanese Patent Application No. 5-2304).
No. 17). This has an orifice in the secondary air flow path,
The differential pressure generated at both ends of the orifice (hereinafter referred to as the orifice differential pressure) is input to a control unit (hereinafter referred to as the ECU), and the characteristic of the orifice differential pressure and the flow rate as shown in FIG. Is called as a map, the secondary air flow rate is calculated from this, and the duty of the air pump is controlled so as to reach the target flow rate. In this way, the secondary air flow rate can be accurately controlled to the target flow rate by feedback control using the orifice differential pressure.

[0005]

However, this method has a problem that the controllable range of the flow rate becomes narrow. This will be described with reference to FIG. Let Q0 be the target value of the secondary air flow rate. Then, the diameter of the orifice is determined in consideration of this target value and the detectable differential pressure value of the orifice, and the orifice characteristic A is determined. However,
It is good when the target value of the secondary air flow rate is only Q0, but when it is necessary to set a large number of target values, for example, the target flow rate is Q
If there are Q1 (<Q0) and Q2 (> Q0) in addition to 0, control at the target flow rates Q1 and Q2 becomes a problem.

That is, if the target flow rate Q1 is controlled under the orifice characteristic A, the flow rate change amount is large with respect to the orifice differential pressure, so that the resolution of flow rate detection is poor and satisfactory control cannot be performed. Further, when the flow rate is controlled to Q2, the resolution is good, but the orifice differential pressure increases and the load on the air pump increases. This increase in load on the air pump causes a problem that the air pump may overheat and fail.

The present invention has been made in view of the above problems. In the feedback control utilizing the above orifice differential pressure,
An object of the present invention is to favorably control the air supply amount when a plurality of target flow rates are set.

[0008]

In order to achieve the above object, in the invention described in claim 1, a filter (9, 13) provided in the exhaust system of the diesel engine (1) for collecting particulates is provided. In an exhaust emission control device for a diesel engine, which comprises an air supply means (23) for supplying air to the filter via an air flow path (100) during combustion regeneration of the filter, an orifice (27, 28, 50-52) having a flow path (24,
25, 56 to 58) is provided with a plurality of branch flow passage parts (200) connected in parallel, and a selection means (26, 104, 107, 53 to 55) for selecting a flow passage in the branch flow passage parts).
A differential pressure detecting means (40, 41, 105, 110) for detecting a differential pressure before and after the branch flow path portion, and the differential pressure detecting means for the flow path selected by the selecting means. The exhaust purification device of a diesel engine is characterized by including control means (106, 111) for controlling the air supply amount by the air supply means based on the detected differential pressure.

According to a second aspect of the present invention, in the exhaust emission control system for a diesel engine according to the first aspect, the control means sets a difference for each of the plurality of flow paths formed by the selection of the selection means. The orifice characteristics (characteristics in FIGS. 4 and 8) showing the relationship between the pressure (P0, P2) and the target flow rate (Q0, Q2 or Q1 to Q5) are stored. The air supply amount is controlled so that the pressure difference detected by the pressure difference detecting means matches.

According to a third aspect of the present invention, in the exhaust emission control system for a diesel engine according to the second aspect, the differential pressure with respect to the target flow rate in each of the orifice characteristics is set to a constant value (P0). It is characterized in that each flow path is configured. The reference numerals and the like in parentheses of the above-mentioned means indicate the correspondence with the concrete means described in the embodiments described later.

[0011]

According to the invention described in claims 1 to 3, a branch flow passage portion, in which a plurality of flow passages having orifices are connected in parallel, is provided in the air flow passage. The flow path is selected, and the air supply amount to the filter is controlled based on the differential pressure before and after the differential pressure branch flow path section with respect to the selected flow path.

Therefore, since a plurality of orifice characteristics can be set by selecting a plurality of flow paths formed, it is possible to perform an appropriate air supply amount control for the target flow rate according to each orifice characteristic.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of an exhaust emission control device for a diesel internal combustion engine. On the intake side of the diesel engine 1, a hot-wire type flow sensor (hereinafter referred to as Ga sensor) 2 for detecting the intake flow rate is provided. Further, a Ne sensor 3 for detecting the rotation speed (Ne) of the diesel engine 1 is provided.

The exhaust pipe 4 of the diesel engine 1 is branched into exhaust pipes 5 and 6, and the exhaust pipe 5 has an exhaust purification device 7 provided therein.
Is provided. The exhaust purification device 7 has a housing 8 connected to the exhaust pipe 5, and a filter 9 made of ceramic porous is installed in the housing 8 to collect PM in the exhaust gas. When the filter is regenerated, the collected PM is ignited by a heating device (electric heater) 10 provided on the upstream end surface of the filter 9 and regenerated by combustion.

On the other hand, similarly to the exhaust pipe 6, the exhaust purification device 1
1 is provided. The exhaust gas purification device 11 has a housing 12 connected to the exhaust pipe 6, and a filter 13 is installed therein. A heating device (electric heater) 14 for igniting the collected PM is also provided on the upstream end surface of the filter 13. Exhaust pipes 15 and 16 are provided downstream of the exhaust purification devices 7 and 11, and the exhaust pipes 17 and 16 join together and are connected to a muffler 18.

Exhaust gas switching valves 32 and 33 are provided at two branch portions of the exhaust pipe. By switching the exhaust gas switching valves 32 and 33, the collection and regeneration states of the filters 9 and 13 are changed. Can be switched alternately. In addition, in FIG. 1, the exhaust gas purification device 11 is in the collecting state, and the filter 13
It collects PM in the exhaust. A pressure sensor 21 is provided in the exhaust pipe 4 via a port 19, and the pressure sensor 21 detects the pressure (front pressure) upstream of the filter 7 or 11. Similarly, the exhaust pipe 17 has a port 2
The pressure sensor 22 is provided via 0, and the pressure (post-pressure) downstream of the filter 7 or 11 is detected by this pressure sensor 22.

Further, a temperature sensor 46 is provided in the exhaust pipe 4, and the temperature sensor 46 detects the exhaust gas temperature (inlet gas temperature) flowing into the filter 7 or 11. Furthermore, temperature sensors 47 and 48 are provided on the downstream side of the filters 7 and 11, and the temperature sensors 47 and 48 are provided.
At 48, the temperature of the exhaust gas discharged from the filters 7 and 11 (exhaust gas temperature) is detected.

Further, when the filter is regenerated by combustion, the filter 9
Alternatively, 13 is provided with an A / P (A / P) 23 for supplying the secondary air through the secondary air flow path 100. An air flow path 24 having an orifice 27 is connected to the discharge side of the A / P 23. Further, a bypass flow passage 25 is connected so as to bypass the orifice 27, and the bypass flow passage 25 is provided with an opening / closing valve 26 and an orifice 28. The flow channel 24 and the bypass flow channel 25 form the branch flow channel section 200.

Ports 29 and 30 are provided at both ends of the branch flow passage portion 200, and pressure sensors 40 and 41 connected to the ports 29 and 30 are used to detect the pressure before and after the branch flow passage portion 200. That is, the pressure before the orifice and the pressure after the orifice are detected. The flow path 24 is connected to the upstream side of the exhaust gas purification devices 7 and 11 via the check valve 38 and the air control valves 34 and 36. In addition, the exhaust emission control device 7, 11
The downstream side of is connected to the secondary air escape passage 31 via the air control valves 35 and 37, and further via the check valve 39, and is finally released to the atmosphere.

In FIG. 1, in order to regenerate the filter 9, A /
P23 to flow path 24 (in some cases, bypass flow path 25
Or, the orifice 27 (or the orifice 28 in some cases)
Also), check valve 38, air control valve 34, exhaust gas purification device 7
The (filter 9), the air control valve 35, the secondary air escape passage 31, the check valve 39, and the air passage for releasing the atmosphere are configured.

The Ga sensor 2, Ne sensor 3, pressure sensors 21, 22, 40 and 41, temperature sensors 46 and 4 described above.
The output signals of 7, 48 are taken into the ECU 45. EC
The U45 is an on-off valve 26, exhaust switching valves 32, 33, air control valves 34, 35, 36, 37, check valves 38, 39 and a semiconductor relay 44 in order to control the collection and regeneration of the filters 9, 13. , 43, 42 to drive the A / P 23 and the electric heaters 10, 14.

Next, in the above structure, the operation is
The calculation process of the CU 45 will be described with reference to the slow chart of FIG. The ECU 45 includes a Ga sensor 2, a Ne sensor 3, pressure sensors 21 and 22, temperature sensors 46, 47, and 4.
The collection amount of the filter on the collection side is calculated from the signal from each sensor of No. 8, and when the collection amount becomes equal to or more than the set value, the regeneration control of the filter is performed. Since the calculation process for calculating the trapped amount is known, the description thereof will be omitted here, and the reproduction control will be mainly described.

The ECU 45 executes step 100 of FIG.
It is determined whether or not t1 time has elapsed since the reproduction control was started. If the time t1 has not elapsed, the heater is controlled (step 101), and after the time t1 has elapsed, the heater is turned off (step 102). Therefore, step 1
At 00 to 102, as shown in FIG. 5, the heater is turned on for t1 time after the start of the regeneration control, and the PM trapped in the filter is ignited.

Next, in step 103, step 100
The same judgment is made. If the time t1 has not elapsed, the opening / closing valve 26 is first opened (step 10).
4). Therefore, passing through the flow path 24 and the bypass flow path 25,
That is, a secondary air flow path passing through the orifices 27 and 28 is formed. The orifice characteristics at this time are shown in Fig. 4.
The orifice characteristic a + b shown in FIG.

In the next step 105, the pressure sensor 4
The differential pressure before and after the orifice is detected by the signals from 0 and 41. The ECU 45 stores the orifice characteristic a + b in a ROM (storage means) as a map, and according to the orifice characteristic a + b, A / A is set so that the differential pressure P2 with respect to the target flow rate Q2 and the orifice differential pressure detected in step 105 match. The duty of P23 is controlled to adjust the secondary air flow rate (step 106). That is, the secondary air flow rate is detected by the orifice differential pressure, and feedback control is performed so as to obtain the target flow rate Q2. Therefore, during the time t1 after the start of the regeneration control, the target flow rate is set to Q2 as shown in FIG.

When the time t1 has elapsed, the opening / closing valve 26 is closed in step 108. This makes 2
The next air passes through the flow path 24, that is, the orifice 27, and the orifice characteristic becomes the orifice characteristic a in FIG. Then, until time t2 has elapsed, step 10 is performed.
The following processing is performed from 9. First, in step 110,
The differential pressure before and after the orifice is detected by the signals from the pressure sensors 40 and 41.

The ECU 45 uses the above-mentioned orifice characteristic a.
Is also stored as a map, and according to this orifice characteristic a, the differential pressure P0 with respect to the target flow rate Q0 and step 110
A / P so that the orifice pressure difference detected by
The secondary air flow rate is adjusted by controlling the duty of 23 (step 111). Therefore, between t1 and t2, the target flow rate is set to Q0 as shown in FIG.

During the reproduction control, that is, until the time t2, the reproduction control counter t is set to the step 10
It is incremented by 7, and this reproduction control counter t
Thus, the elapsed time determination in steps 100, 103 and 109 is performed. Then, when t2 time has elapsed after the start of reproduction, the A / P 23 is turned off in step 112, the reproduction control counter t is cleared in step 113, and the reproduction control is ended.

Thus, in this embodiment, the orifice 27
And a bypass channel 25 provided with an orifice 28 that is opened and closed by an opening / closing valve 26.
And means for detecting the secondary air flow rate by the pressure sensors 40 and 41. Therefore, by opening and closing the opening / closing valve 26, it is possible to provide two orifice characteristics, which allows the secondary air flow rate to be accurately measured in a wide range.
Moreover, the control can be performed without imposing a heavy load on the A / P 23.

In the above embodiment, the bypass passage 28 with the opening / closing valve 26 and the orifice 28 is provided so as to have two orifice characteristics. However, as shown in FIG. Open / close valve 53
By connecting a plurality of flow paths 56 to 58 including in parallel with each other, a combination of the orifices by opening and closing the valves gives orifice characteristics by the factorial of the number of the orifices, and a wide range can be selected by selecting them. The flow rate control may be performed.

Further, the target differential pressure (P0, P2 in FIG. 4) for obtaining the target flow rate may differ for each orifice characteristic. Therefore, as shown in FIG. 8, if the orifices in the respective flow paths are configured so as to obtain the orifice characteristics such that the target differential pressures are all P0 at the respective target flow rates (Q1 to Q5), control for the target differential pressures Will be easier to do.

Each step in the flowchart shown in FIG. 6 is configured as a function realizing means for realizing each function.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an exhaust emission control device showing an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between an orifice differential pressure and a secondary air flow rate.

FIG. 3 is a diagram for explaining a problem when a plurality of target flow rates exist.

FIG. 4 is a characteristic diagram showing orifice characteristics according to an embodiment of the present invention.

FIG. 5 is a timing chart showing operation timings of a heater and an air pump.

6 is a flowchart showing a calculation process of an ECU 45 shown in FIG.

7 is a configuration diagram showing another configuration of the branch flow channel section 200. FIG.

FIG. 8 is a characteristic diagram showing another orifice characteristic.

[Explanation of symbols]

1 ... Diesel engine, 9, 13 ... Filter, 10,
14 ... Electric heater, 23 ... Air pump, 27, 28 ... Orifice, 40, 41 ... Pressure sensor for detecting pressure before and after orifice, 45 ... ECU, 100 ... Air passage, 200 ... Branch passage section.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Keiichi Kato, 1-1, Showa-cho, Kariya city, Aichi Prefecture, Nihon Denso Co., Ltd. (72) Inventor, Naoji Morita, 1-1, Showa-cho, Kariya city, Aichi prefecture Within the corporation

Claims (3)

[Claims] 1. A diesel engine equipped with a filter provided in an exhaust system of a diesel engine for collecting particulates, and an air supply means for supplying air to the filter through an air flow path during combustion regeneration of the filter. In the exhaust emission control device, a branch flow passage unit in which a plurality of flow passages having orifices are connected in parallel is provided in the air flow passage, and a selection unit that selects a flow passage in the branch flow passage unit; Differential pressure detection means for detecting the differential pressure before and after, and the air supply amount by the air supply means based on the differential pressure detected by the differential pressure detection means for the flow path selected by the selection means. An exhaust emission control device for a diesel engine, comprising: control means for controlling. 2. The control means stores an orifice characteristic indicating a relationship between a differential pressure and a target flow rate for each of a plurality of flow paths formed by the selection of the selection means,
2. The exhaust gas of a diesel engine according to claim 1, wherein the air supply amount is controlled so that the differential pressure with respect to the target flow rate and the differential pressure detected by the differential pressure detecting means match according to the orifice characteristic. Purification device. 3. The exhaust gas of the diesel engine according to claim 2, wherein the respective flow paths are configured such that the differential pressure with respect to the target flow rate in the respective orifice characteristics has a constant value. Purification device.