JP2679456B2 - Exhaust gas cleaning device for diesel engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diesel engine exhaust gas cleaning device provided with a filter for collecting exhaust particulates.

[0002]

2. Description of the Related Art Exhaust particulates such as carbon are contained in the exhaust gas of a diesel engine, and it is not preferable to discharge the particulates into the atmosphere as they are because they cause environmental pollution. In order to prevent this, a method in which a filter is provided in the exhaust passage of the engine and exhaust gas is passed through this filter to collect exhaust particulates,
Well known from the past. In this case, the exhaust particulates adhere to the vicinity of the exhaust gas inflow part of the filter and gradually accumulate, but if the deposition amount increases, the exhaust pressure increases and the engine performance is adversely affected. It is necessary to periodically perform a regeneration process of a filter that removes by burning or the like.

[0003] As a filter regeneration process, there is a process of burning exhaust particulates by an electric heater provided immediately before the filter, or a process of igniting fuel injected from a fuel injection valve to burn the exhaust particulates. To determine when to burn the exhaust particulates, that is, to determine when to regenerate the filter, the differential pressure between the exhaust pressure on the upstream side of the filter and the exhaust pressure on the downstream side of the filter was measured, and this differential pressure exceeded a prescribed value. There is a method of utilizing the exhaust pressure such as when the regeneration time is set (see Japanese Patent Laid-Open No. 60-67713).

[0004]

By the way, when the amount of exhaust particulates deposited near the exhaust gas inflow portion of the filter increases, the deposited exhaust particulates depart from the adhering portion and diffuse inside the filter depending on operating conditions. Internal diffusion phenomenon occurs. When the internal diffusion phenomenon occurs, the exhaust pressure on the upstream side of the filter decreases, and as a result, the exhaust pressure difference between the upstream side and the downstream side of the filter decreases, but the exhaust particulates adhering at this time are the exhaust inflow side of the filter. It does not diffuse uniformly from the surface, and there is a portion where exhaust particulates remain on the filter surface without locally diffusing.
The internal diffusion phenomenon here means that when exhaust particulates adhering to the surface of the filter diffuse inside, a soluble organic substance such as hydrocarbon (SO
It also includes the removal of exhaust particulates adsorbed on the SOF due to the oxidation of F).

FIG. 13 shows a variation in the exhaust pressure difference P between the upstream side and the downstream side of the filter and the corresponding exhaust particulates (P
(CT) deposition weight, respectively. According to this, when the internal diffusion occurs, the exhaust pressure on the upstream side of the filter sharply decreases, so the exhaust pressure difference P sharply decreases, and the accumulated weight of the exhaust particulates causes the internal diffusion. It can be seen that it is gradually accumulated for each. FIG.
15 and FIG. 15 show the exhaust particulate PCT attached to the filter F.
However, a cross-sectional view shows a change in the filter when exhaust gas flows from the left side to the right side in the figure and diffuses. FIG.
The state in which the exhaust particulate PCT is accumulated on the exhaust inflow side surface of the filter F (the differential pressure across the filter increases) and the exhaust particulate PCT diffuses inside (the differential pressure across the filter decreases) is shown. Shown in FIG.
Is increased in the amount of internal diffusion of exhaust particulates into the filter F by repeating the above internal diffusion, and diffuses in the left side state (increase in differential pressure across the filter) in which a partial clogging G is generated. It shows a state in which G further diffuses into the inside and changes to the right side state (decrease in differential pressure across the filter) where the deposition amount gradually increases.

In this way, when the internal diffusion is repeated,
Exhaust particulates are locally deposited such as a clogging G. Therefore, as in the above-described conventional example, a method of simply detecting the exhaust pressure difference before and after the filter to determine the deposition amount is used. Since the amount of fine particles cannot be accurately determined, the determination of the filter regeneration time is erroneous. So, for example, if filter regeneration is delayed,
The trapped amount becomes too large, which causes the exhaust pressure to rise, which deteriorates drivability and causes problems such as poor combustion and shortened filter life.

Therefore, an object of the present invention is to accurately grasp the time when the exhaust particulates collected by the filter are burned to regenerate the filter.

[0008]

In order to achieve the above object, the present invention is, as shown in FIG. 1, a filter 3 provided in an exhaust passage 1 of an engine for collecting exhaust particulates in exhaust gas, and this filter. Regenerating means 5 for regenerating the filter 3 by burning the exhaust particulate matter collected in the filter 3, and differential pressure detecting means 15 for detecting the differential pressure between the exhaust passages on the upstream and downstream sides of the filter 3. A flow coefficient calculating means 23 for calculating a flow coefficient of the exhaust gas passing through the filter 3 under a reference operating condition set in advance in a low load / low speed region of the engine, and the engine based on the calculated flow coefficient. Of the estimated differential pressure of the filter 3 and the actual differential pressure detected by the differential pressure detection means 15 are the estimated differential pressures calculated by the differential pressure detection means 15 and the estimated differential pressure calculation means 31. Predetermined value than The filter 3 when it on small
Internal diffusion determining means 33 for determining that the exhaust particulates adhering to the filter have separated from the adhered portion, and regeneration timing for determining the regeneration timing of the filter 3 by the regeneration means 5 based on the internal diffusion determination by the internal diffusion determining means. And a judging means 37.

[0009]

According to the exhaust gas cleaning device for a diesel engine constructed as described above, the operating condition of the engine is the standard operation set in advance in the low load low rotation region where the exhaust particulates adhering to the filter 3 are difficult to separate. When the condition is met, the flow coefficient calculating means 23 calculates the flow coefficient of the exhaust gas passing through the filter 3 at this time. Then, when the operating state of the engine fluctuates thereafter and becomes a high load or a high rotation state, the internal diffusion determination means 33 causes the estimated differential pressure calculation means 31 to calculate the estimated differential pressure based on the flow coefficient and the differential pressure. The actual differential pressure detected at this time by the detection means is compared, and when the actual differential pressure becomes smaller than the estimated differential pressure by a predetermined value or more, the exhaust particulates adhering to the filter 3 adhere to the adhering portion. Therefore, the regeneration timing determining means 37 determines that it is the regeneration timing of the filter 3 based on this internal diffusion determination.

[0010]

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

FIG. 2 is an overall configuration diagram showing an exhaust emission control device for a diesel engine according to an embodiment of the present invention. A filter 3 made of porous ceramic or the like is provided in the exhaust passage 1 of the diesel engine. As the exhaust gas passes through the filter 3, exhaust gas particles such as carbon particles in the exhaust gas are collected by being attached to the filter 3.

When the amount of exhaust particulates collected by the filter 3 increases and the filter 3 reaches the regeneration time, an electric heater 5 as a regeneration means provided immediately before the filter 3 is energized to generate exhaust particulates. To burn.

A first exhaust passage 7 is provided upstream of the filter 3.
Is provided in the exhaust passage 11 on the downstream side of the filter 3, and the second pressure sensor 13 is provided in the exhaust passage 11 on the downstream side of the filter 3. The detected values of these pressure sensors 9 and 13 are input to a filter front-rear differential pressure detection circuit 15 as a differential pressure detection unit that detects a differential pressure between the exhaust pressure on the upstream side of the filter 3 and the exhaust pressure on the downstream side of the filter 3. It

The operating condition judging circuit 17 for judging the operating condition of the diesel engine comprises a rotation sensor 19 for detecting the engine speed Ne and a load sensor 2 for detecting the engine load Q.
In response to the detection signal of 1, the engine speed Ne and the engine load Q are sequentially output to the flow coefficient calculation circuit 23 as the flow coefficient calculation means. The standard operating condition setting circuit 25 sets a standard operating condition with a high operating frequency in the low load and low engine speed region of the engine. The exhaust flow rate calculation circuit 27 is based on the rotation sensor 1 described above.
9 and the detection signal of the load sensor 21, the flow rate Qexh is searched from the exhaust flow rate map shown in FIG. 3 based on the engine speed Ne and the engine load Q.

The flow coefficient calculating circuit 23 is provided before and after the filter when the engine speed Ne and the engine load Q input from the operating condition judging circuit 17 become the standard operating conditions set by the standard operating condition setting circuit 25. The differential pressure P of the filter 3 detected by the differential pressure detection circuit 15 and the exhaust flow rate calculation circuit 27
Based on the exhaust flow rate Qexh obtained by

(Equation 1) Is calculated by The calculated flow coefficient K is a flow coefficient in a state where exhaust particulates adhering to the vicinity of the exhaust inflow portion of the filter 3 are not separated, and are input to the flow coefficient storage circuit 29 and stored therein.

The estimated differential pressure calculation circuit 31 as the estimated differential pressure calculation means has a flow rate coefficient K stored in the flow rate coefficient storage circuit 29 and the exhaust flow rate Qexh calculated by the exhaust flow rate calculation circuit 27.
Based on the above, the estimated differential pressure between the upstream side exhaust pressure and the downstream side exhaust pressure of the filter 3 under conditions other than the standard operating condition is sequentially calculated and obtained. As shown in FIG. 4, the internal diffusion determination circuit 33 serving as the internal diffusion determination means has the estimated differential pressure calculation circuit 3 as shown in FIG.
The estimated differential pressure P_th obtained by 1 and the actual differential pressure P detected by the differential pressure detection circuit 15 before and after the filter are sequentially compared to obtain the difference ΔP = P_th-P. Here, the estimated differential pressure P
When there is no difference ΔP between _th and the actual differential pressure, or when the difference ΔP is smaller than the predetermined value RefP obtained by the exhaust flow rate Qexh based on the map shown in FIG. 5, almost no exhaust particulate matter is present in the filter 3. Since the exhaust particles are not accumulated, or the exhaust particles accumulated on the filter 3 are slightly diffused, it is determined that the internal dispersion in which the exhaust particles are aggregated to some extent and separated from the adhering portion does not occur. It The state in which the exhaust particulates deposited on the filter 3 are slightly diffused in a slight amount means that the amount of the exhaust particulates gradually deposited from the exhaust gas on the filter 3 and the amount of the exhaust particulates diffused from the adhering portion near the exhaust inflow portion to the inside of the filter 3. In addition, the amount of exhaust particulates leaving the filter 3 due to self-ignition or the like becomes almost equal, and the so-called filter 3 is self-sustaining, in which the deposition and removal of the exhaust particulates in the filter 3 are well balanced. Say.

On the contrary, the estimated differential pressure P_th and the actual differential pressure P
If the difference ΔP is more than a predetermined value, it means that the exhaust particles of a predetermined amount or more have separated from the adhering portion in the vicinity of the exhaust gas inflow portion of the filter 3 and diffused into the inside of the filter 3. It is determined that it has occurred. The state in which this internal diffusion occurs will be described in more detail. In FIG. 6, the filter 3 is in a fresh or regenerated state in which exhaust particulates are hardly adhered, and in such a state, it is estimated that the actual differential pressure P is obtained. It is almost the same as the differential pressure P_th,
And both are low pressure overall. When the exhaust gas passes through the filter 3 in such a state, and the exhaust particulates in the exhaust gas gradually adhere to the vicinity of the exhaust gas inflow portion of the filter 3, as shown in FIG. Pressure P_th
Becomes high pressure as a whole. However, in this state,
Since the amount of exhaust particulate adhered has not yet reached the predetermined amount, internal diffusion does not occur even when the exhaust flow rate increases, and the actual differential pressure P and the estimated differential pressure P_th do not differ greatly. Then, as shown in FIG. 6, when the amount of exhaust particulates adhering to the vicinity of the exhaust inflow portion of the filter 3 further increases and reaches a predetermined amount, internal diffusion does not occur if the exhaust flow rate is small, Although the actual differential pressure P and the estimated differential pressure P_th are substantially equal to each other, when the exhaust gas flow rate is increased, exhaust particulates are separated from the adhering portion and start diffusing into the filter 3, so that the estimated differential pressure P_th is exhausted. While it increases as the flow rate increases, the actual differential pressure P does not increase above a certain value. Therefore, the difference Δ between the estimated differential pressure P_th and the actual differential pressure P
When P is equal to or larger than the predetermined value, it can be determined that a predetermined amount of exhaust particulate has separated from the adhering portion of the filter 3 near the exhaust inflow portion and diffused into the filter 3.

When the internal diffusion determination circuit 33 determines internal diffusion, the internal diffusion pattern analysis circuit 35 stores the number of times of internal diffusion, and the internal diffusion pattern analysis circuit 35 uses the internal diffusion to filter the filter 3.
The accumulated accumulation value PCT is obtained by integrating the amount of exhaust particulates that diffuse inside and remain inside the filter 3 as they are. As shown in FIG. 7, the accumulated accumulation value PCT is obtained by adding the accumulated accumulation value PCT- _{1 up} to the time of the previous internal diffusion, and the adhered accumulation amount ΔPCT which is the amount of exhaust particulate newly adhering after the previous internal diffusion. , Which is obtained by subtracting the diffusion removal amount ΔB, which is the amount of exhaust particulates not carried by the filter 3 during internal diffusion and carried away with the exhaust gas (PCT = PC
T _-1 + ΔPCT-ΔB). Here, the deposition amount ΔPCT of the exhaust particulates newly attached to the filter 3 between the internal diffusion and the next internal diffusion can be obtained by the flow rate coefficient K based on the map shown in FIG. The diffusion removal amount ΔB of exhaust particulates carried away along with the exhaust during diffusion is estimated differential pressure P_th based on the map shown in FIG.
And the actual differential pressure can be obtained by the difference ΔP and the exhaust flow rate Qexh.

The regeneration timing determining circuit 37 as a regeneration timing determining means is used when the number of times of internal diffusion stored in the internal diffusion pattern analyzing circuit 35 reaches a predetermined number or more, or when the accumulated accumulation obtained by the internal diffusion pattern analyzing circuit 35. When the value PCT is equal to or higher than a predetermined value, or when the differential pressure P of the filter 3 detected by the differential pressure detection circuit 15 before and after the filter is equal to or higher than a predetermined value, it is determined that the regeneration time of the filter 3 is reached, and the electric heater 5 is activated. Is energized to burn and remove the exhaust particulates adhering to the filter 3.

Next, the control operation in the exhaust gas purification device of the diesel engine configured as described above will be described with reference to FIGS.
1 and FIG. 12 will be described.

First, the engine speed Ne detected by the rotation sensor 19 is read (step 101), the engine load Q detected by the load sensor 21 is read (step 103), and the exhaust flow rate Qexh is read from the map shown in FIG. The differential pressure P detected by the search and the differential pressure detection circuit 15 before and after the filter is read (step 107). Then, the flow coefficient calculating circuit 23 determines whether the operating condition signal input from the operating condition determining circuit 17 is the reference operating condition set in the reference operating condition setting circuit 25 (step 109), and the reference is set. Flow rate coefficient K
To

(Equation 2) (Step 111), and the flow coefficient storage circuit 2
It is stored in step 9 (step 113).

If it is determined in step 109 that the operating condition is not the reference operating condition, the estimated differential pressure calculation circuit 31 calculates the estimated differential pressure P_th (step 115). Estimated differential pressure P
The calculation of _th is based on the exhaust flow rate Qexh obtained by the search in step 105 and the flow coefficient K stored in the flow coefficient storage circuit 29 at this time, and P_th = (Qex
h / K) ² . After calculating the estimated differential pressure P_th,
The internal diffusion determination circuit 33 obtains a difference ΔP between the estimated differential pressure P_th and the actual differential pressure P at this time detected by the differential pressure detection circuit 15 before and after the filter, and the difference ΔP is obtained from the map shown in FIG. It is determined whether the pressure is equal to or higher than the predetermined pressure RefP retrieved (step 117).

When the actual differential pressure P is smaller than the estimated differential pressure P_th and the difference ΔP is equal to or larger than the predetermined value RefP, it is determined that internal diffusion has occurred, the internal diffusion counter is incremented (step 119), and reproduction is performed. The timing determination circuit 37
It is determined whether or not the internal diffusion counter is equal to or more than a predetermined value (step 121), and if it is equal to or more than the predetermined value, it is determined to be the reproduction time (step 123). Step 121
When it is determined that the internal diffusion counter has not reached the predetermined value or more, the amount of adhered deposition ΔP is determined from the map shown in FIG.
The CT is read (step 125), the diffusion removal amount ΔB is read from the map shown in FIG. 9 (step 127), and the accumulated deposition value PCT is calculated by PCT = PCT ₋₁ + ΔPCT−ΔB (step 129). It is determined whether the accumulated accumulation value PCT is a predetermined value or more (step 131), and if it is the predetermined value or more, it is determined that the regeneration time is reached (step 12).
3). Further, when it is determined in step 117 that the difference ΔP between the actual differential pressure P and the estimated differential pressure P_th is less than the predetermined value RefP, and when it is determined in step 131 that the accumulated accumulation value PCT is less than the predetermined value. Determines whether the actual differential pressure P is equal to or higher than a predetermined value (step 133), and if it is equal to or higher than the predetermined value, it is determined to be the regeneration time (step 123). this is,
When the engine operating condition is low load and low rotation, the exhaust flow rate Qexh becomes small as shown in the map of FIG. 3, and when the exhaust flow rate Qexh is small, as shown in FIG. Even if the amount of exhaust particulate adhering to has reached a predetermined value or more, internal diffusion does not easily occur, so
This is for determining the regeneration timing when only such an operation at low load and low rotation is continuously performed for a long time based only on the actual differential pressure P.

When it is judged at step 123 that the regeneration time has come, the filter 3 is regenerated. When the regeneration operation of the filter 3 is determined to be the regeneration time (step 135), the electric heater 5 is energized to heat the electric heater 5 (step 137) as shown in the flowchart of FIG. Exhaust particles are burned and removed,
When the regeneration of the filter 3 is completed (step 139), the number of internal diffusions and the accumulated accumulation value PCT in the internal diffusion pattern analysis circuit 35 are cleared (step 141).

As described above, according to the present embodiment, the regeneration time of the filter 3 is set to the time when the internal diffusion occurs a predetermined number of times or more, or the estimated cumulative value PCT of the exhaust particulates becomes the predetermined value or more. Even when the locally accumulated portion of exhaust gas particles generated by repeated internal diffusion remains, the regeneration timing of the filter 3 can be accurately determined.

In this embodiment, a filter of the type that adheres and collects exhaust particulates is used, but the present invention is not limited to this type of filter,
For example, the regeneration time of the filter can be more accurately determined by using it in a filter that may cause an internal diffusion phenomenon, such as a filter having an open honeycomb structure supporting a catalyst.

[0027]

As described above, according to the present invention, the flow rate coefficient of the filter is obtained under the operating condition which is the reference set in advance in the low load and low speed range of the engine, and the estimation is performed based on this flow rate coefficient. When the actual differential pressure becomes smaller than the differential pressure before and after the filter by a predetermined value or more, it is determined that the exhaust particulates adhering to the filter have separated from the adhering part and internal diffusion has occurred. Since the regeneration time of the filter is determined, it is possible to accurately determine the regeneration time of the filter even if the locally accumulated portion of exhaust particulates caused by repeated internal diffusion remains.

[Brief description of the drawings]

FIG. 1 is a diagram corresponding to claims of the present invention.

FIG. 2 is an overall configuration diagram showing an exhaust gas purification device for a diesel engine according to an embodiment of the present invention.

FIG. 3 is an exhaust flow characteristic diagram according to engine speed and engine load.

FIG. 4 is an explanatory diagram showing a relationship between an actual differential pressure P and an estimated differential pressure P_th and an exhaust gas flow rate.

FIG. 5 is a diagram showing a relationship between a pressure difference RefP that is a reference for generating internal diffusion and an exhaust flow rate.

FIG. 6 is an explanatory diagram showing a relationship between a differential pressure of a filter and an exhaust gas flow rate corresponding to an adhered state of exhaust particulates.

FIG. 7 is an explanatory diagram showing the relationship between the differential pressure of the filter and the exhaust particulate deposition weight.

FIG. 8 is an explanatory diagram showing the relationship between the deposition amount ΔPCT of exhaust particulate newly adhering to the filter between internal diffusion and the next internal diffusion and the flow coefficient.

FIG. 9 is an explanatory diagram showing a relationship between the diffusion removal amount ΔB of exhaust particulates carried away with exhaust during internal diffusion and the differential pressure of the filter.

10 is a flowchart showing a control operation for determining a regeneration timing in the exhaust gas purification device of FIG.

FIG. 11 is a flowchart showing a control operation for determining a regeneration timing in the exhaust gas purification device of FIG.

FIG. 12 is a flowchart showing a control operation of a reproduction operation.

FIG. 13 is an explanatory diagram showing fluctuations in the exhaust pressure difference P between the upstream side and the downstream side of the filter and the accumulated weight of exhaust particulates in the conventional example.

FIG. 14 is a cross-sectional view showing changes in the inside of the filter when exhaust particulates attached to the surface of the filter on the exhaust inflow side diffuse internally.

FIG. 15 is a cross-sectional view showing the inside of the filter when the exhausted particles have diffused inward, and the further generated clogging part has diffused inward.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 exhaust passage 3 filter 5 electric heater (regeneration means) 15 differential pressure detection circuit before and after filter (differential pressure detection means) 23 flow coefficient calculation circuit (flow coefficient calculation means) 31 estimated differential pressure calculation circuit (estimated differential pressure calculation means) 33 Internal diffusion determination circuit (internal diffusion determination means) 37 Reproduction timing determination circuit (reproduction timing determination means)

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-59-134317 (JP, A) JP-A-60-67713 (JP, A) JP-A-63-295815 (JP, A) JP-A-1- 142211 (JP, A) JP-A-4-203414 (JP, A) JP-A-63-65113 (JP, A) JP-A-1-253522 (JP, A) Actual development Sho-63-138414 (JP, U) Actual Kaihei 3-25810 (JP, U)

Claims (2)

(57) [Claims] 1. A filter provided in an exhaust passage of an engine for collecting exhaust particulates in exhaust gas, a regeneration means for burning the exhaust particulates collected by the filter to regenerate the filter, and an upstream of the filter. Pressure detection means for detecting the pressure difference between the exhaust passages on the downstream side and the downstream side, and the flow rate coefficient of the exhaust gas passing through the filter under a reference operating condition set in advance in the low load and low rotation region of the engine. A flow rate coefficient calculating means for calculating the above, a presumed differential pressure calculating means for calculating an estimated differential pressure of the filter in a high load or high rotation region of the engine based on the calculated flow coefficient, and the differential pressure detecting means. When the actual differential pressure detected by the filter becomes smaller than this estimated differential pressure by a predetermined value or more, it is determined that the exhaust particulates adhering to the filter have separated from the adhering portion. An exhaust gas purification device for a diesel engine, comprising: disconnection means and regeneration timing determination means for determining regeneration timing of the filter by the regeneration means based on the internal diffusion determination of the internal diffusion determination means. 2. The internal diffusion determination means adds the newly deposited amount of exhaust particulates to the deposited amount of exhaust particulates after having been separated from the filter, and when the amount of exhaust particulates after this addition becomes a predetermined amount or more. The exhaust gas purification device for a diesel engine according to claim 1, wherein it is determined that the exhaust particulate has separated from the adhered portion.