JPH0544439A - Exhaust gas purifying device for diesel engine - Google Patents

Abstract

PURPOSE:To decide a collection state of exhaust gas particulate in a filter without locating sensors in an exhaust gas pipe in the vicinity of the front and the rear of the filter arranged below a vehicle. CONSTITUTION:Oxygen concentration O2r in exhaust gas on the upper stream of a filter 21, detected by means of an oxygen sensor 27, is compared with oxygen concentration O2th in a state that exhaust gas particulate is not collected by the filter 21. When the oxygen concentration O2r in exhaust gas is lower than the oxygen concentration O2th by a given value an amount of exhaust gas particulate collected by the filter 21 is high, an exhaust pressure is increased, and an amount of return exhaust gas is increased), it is decided that the above is the regeneration period of the filter 21, and regeneration is carried out.

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, which is provided with an exhaust particulate collection device for capturing exhaust particulates contained in exhaust gas.

[0002]

2. Description of the Related Art A diesel engine contains exhaust particulates such as carbon in its exhaust due to combustion of fuel in a combustion chamber, and if it is directly discharged into the atmosphere, it is not preferable because it causes environmental pollution. In order to prevent this, a method of providing a filter made of porous ceramic or the like in the exhaust passage and collecting exhaust fine particles by allowing the exhaust gas to pass through the filter is well known in the related art. In this case, if the accumulated amount of the collected exhaust particles increases, the exhaust pressure increases and the engine performance is adversely affected. Therefore, the collected exhaust particles are periodically burned and removed by, for example, a heater to perform a filter regeneration operation. Need to do.

When the filter is regenerated, it is necessary to detect the accumulation amount of exhaust particulates and to regenerate the filter when the accumulation amount reaches a predetermined amount. The method for detecting the amount of exhaust particulate matter deposited is based on the differential pressure between the exhaust pressure on the upstream side of the filter and the exhaust pressure on the downstream side thereof (JP-A-63-6).
5113), or a method in which air is supplied to the upstream side of the filter by an air pump and is based on the exhaust pressure at this time (see Japanese Patent Laid-Open No. 63-71511).

[0004]

However, in such a conventional diesel engine exhaust emission control device,
Since the filter is installed in the exhaust passage in the lower part of the vehicle at a position distant from the engine body, the exhaust pressure sensor installed in the exhaust passage near the front and rear of the filter may be damaged by flying stones while the vehicle is running. Therefore, the durability is difficult, and the wiring needs to be routed to the lower part of the vehicle, so that the wiring itself becomes long, which deteriorates the workability of assembly and lowers the reliability.

Therefore, an object of the present invention is to make it possible to determine the collection state of the exhaust particulate collection means without providing sensors in the exhaust passage near the front and rear of the exhaust particulate collection means located in the lower part of the vehicle. There is.

[0006]

In order to achieve the above object, the present invention provides an exhaust particulate collection means for collecting exhaust particulates in exhaust gas provided in an exhaust passage, and the exhaust particulate collection discharged from an engine. Exhaust gas recirculation means for recirculating the exhaust gas upstream of the collecting means to the intake system; oxygen concentration detecting means for detecting the oxygen concentration in the exhaust gas, which is provided in the exhaust passage upstream of the exhaust particulate collection means; The exhaust gas recirculation means detects the concentration detected by the exhaust gas recirculation means, based on the oxygen concentration in the exhaust gas recirculation state, a collection state determination means for determining the collection state of the exhaust particulates to the exhaust particulate collection means It is as a configuration.

[0007]

According to the exhaust emission control device of the diesel engine having the above-mentioned structure, the oxygen concentration detecting means is operated by the exhaust gas recirculation means while the exhaust gas upstream of the exhaust particle collecting means is being recirculated to the intake system. The oxygen concentration in the inside is detected, and the trapped state of the exhaust particulates in the exhaust particulate trapping means is judged based on the detected oxygen concentration. The detected oxygen concentration changes according to the exhaust gas recirculation amount, and the change in the exhaust gas recirculation amount changes the exhaust gas pressure according to the amount of the exhaust gas particles collected by the exhaust gas particle collecting means. Corresponds to changes in the amount of fine particles. Therefore, the collection state determination means can determine the collection state of the exhaust particulate matter collected by the exhaust particulate collection means based on the detected oxygen concentration.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an overall configuration diagram of an exhaust emission control device for a diesel engine showing a first embodiment of the present invention. An exhaust manifold 3 and an intake manifold 5 are connected to the engine body 1 of the diesel engine, an exhaust pipe 7 is connected to the exhaust manifold 3, and an intake pipe 9 is connected to the intake manifold 5.

Exhaust manifold 3 and intake manifold 5
Is connected to an exhaust gas recirculation pipe 11 as exhaust gas recirculation means for recirculating exhaust gas discharged from the engine body 1 to the intake system. The exhaust gas recirculation pipe 11 is provided with an exhaust gas recirculation control valve 13 for adjusting the amount of exhaust gas recirculation. The exhaust gas recirculation control valve 13 is controlled to be opened / closed by a control unit 15 including a collection state determination means composed of a microcomputer or the like. The control unit 15 includes a rotation sensor 17 that detects the rotation speed of the engine body 1 and the engine body 1.
Lever sensor 1 for adjusting the amount of fuel supplied to the
9, the engine speed N shown in FIG. 2 is received.
The exhaust gas recirculation amount Q _th preset by e and the control lever opening C / L is searched to determine the exhaust gas recirculation amount at that time. Here, the exhaust gas recirculation amount Q _th increases as the engine speed decreases and the control lever opening decreases. Further, in an operating region where the engine speed is high and the control lever opening is large (on the right side of the curve A in the figure), the exhaust gas recirculation control valve 13 is closed and the exhaust gas recirculation (EGR) operation is stopped.

At a portion of the exhaust pipe 7 arranged at the lower portion of the vehicle, an adhering trapping type filter 21 or a filter trapping type filter 21 is provided as an exhaust particulate trapping means for trapping exhaust particulates contained in the exhaust gas. Further, an exhaust silencer 23 is provided further downstream thereof. A heater 25 is installed near the exhaust inlet of the filter 21. The heater 25 is
Upon receiving a signal input from the control unit 15, the control unit 15 is heated to oxidatively burn the exhaust particulates collected by the filter 21 to regenerate the filter 21.

An oxygen sensor 27 as an oxygen concentration detecting means for detecting the oxygen concentration in the exhaust is provided near the exhaust manifold 3 of the exhaust pipe 7 on the exhaust upstream side of the filter 21, and the oxygen sensor 27 detects the oxygen concentration. The signal is input to the control unit 15. The control unit 15 is a so-called clean state in which exhaust particulates are not collected by the filter 21, and the exhaust is preset by the engine speed Ne and the control lever opening C / L shown in FIG. Oxygen concentration in O
_2th is compared with the actual oxygen concentration O _2r in the exhaust gas detected by the oxygen sensor 27 to judge the trapped state of exhaust particulates on the filter 21 and to judge the regeneration time. The oxygen concentration in the exhaust gas decreases due to an increase in the exhaust gas recirculation amount recirculated to the intake system. On the other hand, an increase in the exhaust particulates collected by the filter 21 increases the exhaust pressure to increase the exhaust gas recirculation amount. Let Therefore, the oxygen concentration in the exhaust gas decreases as the amount of exhaust particulates collected by the filter 21 increases, and it becomes possible to judge the trapped state of the exhaust particulates according to the oxygen concentration.

Next, the control unit 15 in the exhaust emission control system of the diesel engine constructed as described above.
The control operation will be described with reference to the flowchart shown in FIG.

Engine speed N detected by the speed sensor 17
e and the control lever opening C / L detected by the control lever sensor 19 are read (step S1), and the read operating state is exhaust gas recirculation (EG
It is determined based on FIG. 2 whether or not it is a region where R) is performed (step S2). Here, when it is determined to be in the EGR region (on the left side of the curve A in FIG. 5), the oxygen concentration O _2th in the clean state of the filter 21 corresponding to the operating state at that time is searched from FIG. (Step S3) Further, the oxygen concentration O _2r detected by the oxygen sensor 27 is read (step S4).

Next, the actual oxygen concentration O _2r read above
Is smaller than a value obtained by multiplying the retrieved oxygen concentration O _2th by a constant K1 (step S5), and it is judged whether the exhaust gas recirculation amount exceeds a predetermined amount, that is, whether it is the regeneration time. To do. Since the increase in the exhaust gas recirculation amount is due to the increase in the amount of exhaust particulates collected in the filter 21 and the increase in the exhaust pressure, the increase in the exhaust gas recirculation amount is
This means an increase in the amount of exhaust particulate matter collected in the filter 21. Therefore, in the step S5, O _2th × K1> O
_When the exhaust gas recirculation amount is determined to be _2r and exceeds the predetermined amount, it is determined that the regeneration time of the filter 21 is determined because the amount of exhaust particulates collected in the filter 21 exceeds the predetermined amount.
A drive signal is output to the heater 25 to heat the heater 25,
The exhaust particles that have been collected are oxidatively burned to perform the filter 21.
Is reproduced (step S6). On the contrary, O _2th × K1 ≦
If it is determined to be O _2r , the amount of exhaust particulates collected in the filter 21 is not collected enough to require regeneration, and the process ends.

After the regeneration of the filter 21, the oxygen concentration O _2th is searched again from FIG. 3 (step S7), and the oxygen concentration O _2r detected by the oxygen sensor 27 is read (step S8). This time, the oxygen concentration O _2r is read. _Is a constant K for oxygen concentration O _2th
It is determined whether it is smaller than a value obtained by multiplying 2 (K1 <K2 ≦ 1) (step S9). Where O _2th × K2> O _2r
If it is determined that the actual oxygen concentration O _2r is still low, that is, the exhaust gas recirculation amount is large and the amount of exhaust particles trapped in the filter 21 is large and regeneration is not sufficient, the process returns to step S6 and the filter is returned. 21 playback. vice versa,
When O _2th × K 2 ≦ O _2r , the collected exhaust particulates are considered to be sufficiently regenerated by the heating of the heater 25, and the process ends.

The constant K1 is set to be smaller than the constant K2, for example, 0.7 to 0.8 so that regeneration is performed after the exhaust gas particulate collection amount in the first determination (step S5) becomes sufficient. In the judgment after the regeneration (step S9), the constant K2 is set to about 0.9 to 0.95, which corresponds to the state in which the trapped amount is reduced by the regeneration.

As described above, in the above embodiment, the filter 2 is based on the detection output of the oxygen sensor 27 provided in the exhaust pipe 7.
The state of the amount of collected exhaust particulates in 1 is determined, and the regeneration timing of the filter 21 is determined. Since the oxygen sensor 27 for determining the regeneration timing is attached to the exhaust pipe 7 in a portion arranged in the engine room near the exhaust manifold 3, there is no possibility that the oxygen sensor 27 may be damaged by flying stones while the vehicle is running. In addition, since it is not necessary to route the wiring to the lower part of the vehicle, the wiring itself becomes short, and the workability and reliability of assembly are improved.

FIG. 5 is an overall configuration diagram showing a second embodiment of the present invention. In this embodiment, the amount of exhaust particulates collected in the filter 21 increases, the exhaust gas recirculation amount increases as the exhaust pressure increases, and the oxygen concentration O in the exhaust gas increases accordingly.
_{When 2r} decreases, the exhaust gas recirculation control valve 13 is closed by a predetermined amount to keep the exhaust gas recirculation amount constant at all times, the opening of the exhaust gas recirculation control valve 13 at that time is fed back, and the collection is performed according to the opening. I try to judge the condition. In this case, the control unit 15 includes the engine speed N shown in FIG.
The opening degree As of the exhaust gas recirculation control valve 13 in a state where the exhaust particulates are not collected in the filter 21, which is determined by e and the control lever opening degree C / L, is preset. The other structure is similar to that of the first embodiment.

The control operation of the control unit 15 will be described with reference to the flow charts of FIGS. Here, steps S11 to S14 are the same as steps S1 to S4 in the first embodiment. In the next step S15, the oxygen concentration O _2th retrieved from FIG. 3 is compared with the oxygen concentration O _2r detected by the oxygen sensor 27, and when O _2th > O _2r , that is, the trapped amount increases and the exhaust gas recirculation amount. And the oxygen concentration O in the exhaust gas increases accordingly.
_{When 2r} is _lower than O _2th , the exhaust gas recirculation control valve 13 is closed by a predetermined amount (step S16) to maintain the exhaust gas recirculation amount at a predetermined amount. In step S17, it is determined whether or not O _2th <O _2r (step S17). If O _2th <O _2r , the exhaust gas recirculation control valve 13 is opened by a predetermined amount (step S18) to determine the exhaust gas recirculation amount. Is maintained at a predetermined level.

In this way, after the exhaust gas recirculation control valve 13 is controlled to open and close so as to always maintain the exhaust gas recirculation amount constant according to the oxygen concentration in the exhaust gas, the opening degree Ap of the exhaust gas recirculation control valve 13 at that time is controlled. Is read (step S19). In the step S17, if O _2th <O _2r is not satisfied, that is, O _2th = O
When it is _2r, the process directly proceeds to step S19 to read the opening degree Ap of the exhaust gas recirculation control valve 13. Next, the exhaust gas recirculation control valve 1 in the state without the collection amount set in FIG.
The opening degree As of 3 is read (step S20), and the difference As-Ap between this opening degree As and the read actual opening degree As.
Is determined to be greater than a constant T1 (step S
21).

Here, when As-Ap> T1, the actual opening Ap is smaller than the opening As, that is, the exhaust gas recirculation amount is large, the oxygen concentration is low, and the exhaust gas recirculation control valve 13 is closed large amount. Since the large amount of closing of the exhaust gas recirculation valve means that the amount of trapping is increasing, the heater 25 is operated to regenerate the filter 21 (step S22). After the reproduction, the control operation from step S13 to step S20 is repeated again, and this time, using the constant T2 smaller than the constant T1, it is determined whether As-Ap is larger than the constant T2 (T2 <T1). (Step S23). Where As-
If Ap> T2, the actual opening Ap is smaller than the opening As, and the reproduction is not sufficiently performed. Therefore, the process returns to step S22 to perform the reproduction. When As-Ap ≦ T2, the difference between the actual opening Ap and the opening As is small, and it is concluded that the adhering exhaust particulates have been oxidatively burned favorably and the regeneration has been performed in a predetermined manner, and the process ends.

In the second embodiment, in addition to the effect of the first embodiment, the exhaust gas recirculation control valve 13 is closed by a predetermined amount when the exhaust gas recirculation amount is increased, and opened by a predetermined amount in the opposite case. Since the exhaust gas recirculation amount is always kept constant, it is possible to prevent deterioration of drivability due to an excessive exhaust gas recirculation amount.

[0024]

As described above, according to the present invention, the determination of the collection state of exhaust particulates by the exhaust particulate collection means is performed by determining the oxygen concentration provided in the exhaust passage upstream of the exhaust particulate collection means. The oxygen concentration detecting means for detecting the oxygen concentration is performed based on the oxygen concentration detected by the detecting means. Since it can be installed in the passageway, the oxygen concentration detection means does not have the risk of being damaged by flying stones etc. while the vehicle is running, improving durability, and it is not necessary to route the wiring to the bottom of the vehicle, so the wiring itself becomes shorter. It is possible to improve the assembling workability and reliability.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a characteristic diagram showing an exhaust gas recirculation region and an exhaust gas recirculation amount based on an engine speed and a control lever opening degree.

FIG. 3 is a characteristic diagram showing an oxygen concentration in exhaust gas based on an engine speed and a control lever opening degree.

4 is a flowchart showing a control operation of a control unit in FIG.

FIG. 5 is an overall configuration diagram showing a second embodiment of the present invention.

FIG. 6 is an opening characteristic diagram of the exhaust gas recirculation control valve based on the engine speed and the control lever opening.

7 is a flowchart showing a control operation of the control unit in FIG.

FIG. 8 is a flowchart showing a control operation of the control unit in FIG.

[Explanation of symbols]

 7 exhaust pipe 11 exhaust gas recirculation passage (exhaust gas recirculation means) 13 exhaust gas recirculation control valve 15 control unit (collection state determination means) 21 filter (exhaust particulate collection means) 27 oxygen sensor (oxygen concentration detection means)

Claims (1)

[Claims] 1. Exhaust particulate collection means for collecting exhaust particulates in exhaust gas provided in an exhaust passage, and exhaust gas recirculation for recirculating exhaust gas upstream of the exhaust particulate collection means discharged from an engine to an intake system. Means, an oxygen concentration detection means provided in the exhaust passage upstream of the exhaust particulate collection means for detecting the oxygen concentration in the exhaust gas, and the exhaust gas recirculation means detected by the oxygen concentration detection means performs exhaust gas recirculation. An exhaust emission control device for a diesel engine, comprising: a collection state determination means for determining a collection state of the exhaust particulate matter to the exhaust particulate collection means based on the oxygen concentration in the present state.