JPH05125924A - Exhaust purifying device of diesel engine - Google Patents

Abstract

PURPOSE:To reduce regeneration failure of the filter on a filter outer circumferential part, in relation to the exhaust purifying device of a diesel engine. CONSTITUTION:In a filter 1, an end surface heater 5 is provided on one end part thereof, and a plurality of outer circumferencially divided heaters 6a to 6c are provided on the outer circumferencial part thereof, and also temperature sensors 7a to 7c are provided on respective points of the outer circumferential part. At the time of regeneration of the filter 1, electrification of the end surface heater 5 is carried out, but a control circuit 8 heats the outer circumferential part of the filter 1 by means the corresponding outer circumferential divided heaters 6a to 6c and particulates are ignited, for the sake of a part where a particulate ignition temperature can not be achieved according to a filter temperature rising degree detected by respective temperature sensors 7a to 7c.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification device provided in a diesel engine, and more particularly to an exhaust gas purification device provided with a particulate filter composed of a large number of filter cells.

[0002]

2. Description of the Related Art For example, exhaust gas of a diesel engine contains a large amount of exhaust particulates, that is, particulates. Therefore, the exhaust system of the engine has a particulate filter (hereinafter referred to as a filter) for collecting the particulates. Called) is installed.

This filter is composed of a large number of elongated filter cells defined by, for example, a partition wall of a porous ceramic material, one end of each cell is closed by a plug member, and the closing direction is alternated. By arranging the exhaust gas, the exhaust gas flowing in from one of the filter cells passes through the partition wall, enters the adjacent filter cell, and flows out from the open end of the cell. When passing through the partition wall, particulates in the exhaust gas are trapped by the partition wall.

If the amount of particulates accumulated inside the filter increases as the filter is used, the air permeability of the filter is gradually impaired, and the engine performance also deteriorates. Must be regenerated. Here, this filter regeneration processing means heating an electric heater provided near the end face of the filter to ignite and burn particulates in the filter, and at this time, the particulate combustion in the filter is performed. For propagation, a regeneration gas such as air or exhaust gas is introduced.

By the way, in connection with the above filter regeneration,
In the incineration state of the particulates, since the amount of heat released to the outside is large in the outer peripheral portion of the filter, for example, an electric heater is provided on one end face side of the filter, and the particulates are burned from this end face side to the other end face side. In the case of the exhaust gas purifying device, the particulates are likely to remain unburned on the outer peripheral portion of the filter. When such unburned portion gradually expands with each collection, not only the collection efficiency of the filter itself decreases, but also the amount of particulates accumulated at that part increases, so the calorific value if it could be burned May increase and the filter may be melted.

To address the problem of such an exhaust emission control device, for example, in Japanese Unexamined Patent Publication (Kokai) No. 2-123219, in addition to the electric heater having the above-mentioned end face arrangement, the regeneration gas flow direction (or the filter axial direction) is added. An outer peripheral heater is provided for heating the outer periphery of the filter, which is divided into a plurality of parts along the circumference. During regeneration, first, the regeneration gas flow direction, the outermost peripheral heater on the most upstream side is energized, then the end surface heaters are energized, and then sequentially. An exhaust emission control device is disclosed in which the downstream peripheral heater is energized to improve the regeneration of the outer peripheral portion of the filter where the particulate flame is less likely to propagate.

[0007]

By the way, in the actual filter regeneration, there is a large variation in the amount of particulates trapped in each trap and the distribution of traps in the filter, and the particulate unburned state after the filter regeneration. ,
At present, the filter regeneration conditions are different each time.In particular, the combustion of the particulates collected on the outer peripheral portion of the filter is easily affected by the combustion of other parts of the filter, and the combustion mode is different for each regeneration. Change greatly.

However, in contrast to such a regeneration situation, in the regeneration method of the exhaust gas purifying apparatus, since each heater is energized and controlled by a preset energization pattern, for example, the regeneration is performed due to variations in the amount of particulate collection. Even if a partial temperature change is expected in some cases, when each heater is energized under the same energization conditions, the temperature rises excessively in a certain part, or conversely the heating is insufficient. A large amount of unburned residue may occur, resulting in so-called defective reproduction.

In view of the above-mentioned problems of the conventional exhaust emission control device, the present invention has an object to eliminate defective regeneration of the outer peripheral portion of the filter when particulate combustion occurs from one end face side to the other end face side. To do.

[0010]

In order to achieve the above object, according to the present invention, a filter for collecting exhaust particulates is provided in an exhaust passage of a diesel engine, and one end of the filter is regenerated, An end face heater for heating the filter is provided.When the filter is regenerated, the end face heater is operated while supplying regeneration gas from one end of the filter to the other end, and the end face heater is operated from the one end to the other end. In an exhaust emission control device for burning and propagating curates, a plurality of outer peripheral divided heaters electrically divided along the regeneration gas flow direction are provided on the outer periphery of the filter, and the outer peripheral divided heaters are provided in correspondence with each of them. A plurality of temperature detecting means for detecting the filter temperature in the vicinity of the heater is provided, and the temperature is detected according to the temperature detected by each temperature detecting means at the time of filter regeneration. An outer split heater selectively providing the outer peripheral divided heater energization control means for energizing the control.

[0011]

For example, a portion where the filter temperature rises relatively slowly during filter regeneration cannot reach the particulate combustion temperature and is likely to be a regeneration defective portion.

According to the present invention, according to the temperature detected by the temperature detecting means at each point in the vicinity of the outer periphery of the filter, the outer peripheral divided heater assigned to this is energized to the outer peripheral portion of the filter which requires heating, The heater ignites the particulates to prevent defective reproduction.

[0013]

Embodiments of the present invention will be described with reference to the drawings.
1 and 2 show a schematic vertical cross-section of a filter which is a main component of an exhaust emission control device according to the present invention and a perspective external view thereof.

With reference to FIG. 1, reference numeral 1 denotes a filter mounted in the exhaust system of a diesel engine, and solid arrows in the figure show the flow direction of exhaust gas discharged from the engine body. As partially shown in this figure, this filter 1 is composed of a large number of filter cells 3 extending in the exhaust gas flow direction defined by a filter partition wall 2 made of, for example, a porous ceramic material. One end of the cell 3 is always closed by the plug member 4.

The filter 1 is a so-called honeycomb structure in which the filter cells 3 constructed as described above are arranged so that the plug members 4 are alternately arranged with respect to the adjacent cells. Then, it flows into the filter 1 through the filter cell 3a whose left end is opened, passes through the partition wall 2, and flows out to the exhaust gas downstream side from the adjacent filter cell 3b whose right end is opened. The particulates in the exhaust gas adhere to the inner wall of the filter cell 3a when passing through the partition walls 2, so that the particulates are collected by the filter 1.

An end face heater 5 is provided at one end 1a of the filter 1 as an ignition means for burning the particulates thus collected to regenerate the filter. When the filter is regenerated, the end surface heater 5 is energized to generate heat and ignite the particulates in the filter cell 3a. Then, the particulate flame generated near the end face 1a is burned and propagated toward the other end 1b by the filter regeneration gas (for example, secondary air) flowing in the filter 1 in the direction of the arrow at that time point, The particulates in the filter 1 are burned by the burning process.

In the filter 1 constructed as described above, according to the present embodiment, as specifically shown in FIG. 2, the outer periphery of the filter 1 is electrically independent from each other along the filter axis X direction. Three peripheral divided heaters 6a, 6b, 6
c are provided in order. In addition, the outer peripheral heater 6
Three temperature sensors (or thermocouples) 7a, 7b, and 7c that detect the filter temperature of each filter are provided on each filter outer peripheral portion close to a, 6b, and 6c.
The output signals of the sensors are provided so as to correspond to a, 6b, and 6c, and are input to a control circuit (ECU) 8.

As shown in FIG. 2, each outer peripheral heater 6 is divided.
a, 6b, 6c are respectively connected to heater relays 10a, 10b, 10c for controlling on / off of the power supply from the battery 9 by the drive signal from the control circuit 8, and the control circuit 8 is provided with the respective temperature sensors 7a, 7b, 7c. The energization of the outer peripheral divided heaters 6a, 6b, 6c is controlled according to the temperature change state inside the filter detected by. Of course, the above-mentioned end face heater 5 is also connected to the heater relay 11, and the control circuit 8 drives the heater relay 11 so that the end face heater 5 is always energized during filter regeneration.

As described above, when the end face heater 5 is energized and the particulates are ignited at the filter end 1a during filter regeneration, the flame rides on the flow of the regeneration gas and gradually flows toward the other end 1b of the filter. Combustion propagates,
For example, when observing the temperature change at a specific part inside the filter, ideally, it takes some time for the flame to reach after the heater energization is started, and the temperature curve rises relatively rapidly when the flame reaches. For example, as shown in FIG. 3, when the particulate combustible temperature exceeds a certain point (for example, about 600 ° C.), it is ensured that the particulate is burning at least at this point.

However, in the actual filter regeneration, due to the particulate collection distribution, etc., not all such filter parts necessarily draw such an ideal curve and the temperature changes, and when such a curve is not shown. In response to this, the control circuit 8 causes the outer peripheral divided heater 6 to
The energization of a, 6b, and 6c will be controlled.

The energization control in this embodiment will be described below with reference to the operation of the control circuit 8 relating to the energization control of the outer peripheral divided heater 6a. FIG. 4 is a flow chart of energization control of the outer peripheral divided heater 6a which can be started to be executed by the control circuit 8 when, for example, the energization of the end surface heater 5 is started. A similar program for controlling the outer peripheral divided heaters 6b and 6c is stored.

Referring to FIG. 4, first, at step 41, the output signal from the temperature sensor 7a is taken in to detect the filter temperature Ta at the sensor installation location, and the timer counter initialized to 0 at the start of this routine. Increment n.

Next, at step 42, the temperature Ta detected this time is compared with the filter temperature Tab detected last time to determine whether or not the filter temperature is higher than that at the previous time. The filter temperature Tab is also initialized to 0 ° C. at the start of this routine. If it is determined in step 42 that the temperature has risen compared to the previous time (Y
es: including the case where there is no change), the routine next proceeds to step 43, where the temperature Ta detected this time is less than the predetermined temperature a which supports the particulate combustion as shown in FIG. 5 (A). Or not.

If it is determined No in step 43, that is, the temperature is equal to or higher than the predetermined temperature a, and here it is determined that the particulates are burning, the routine skips the following steps and proceeds to step 53, where the timer The counter n and the filter temperature Tab are initialized to 0 respectively, and this routine is ended.

By the way, in general, at the time of filter regeneration, the speed at which the particulate flame propagates inside the filter is
It becomes constant to some extent depending on the size of the filter 1 used, the standard particulate collection amount, or the regeneration gas supply amount. Therefore, for example, in FIG.
As shown in, when the temperature rises gradually, but the rising gradient is gentle, and if it is expected that the above-mentioned predetermined temperature a will not be reached, heating with the outer peripheral divided heater is performed. It is necessary to help raise the temperature.

Therefore, if it is determined Yes in step 43, that is, if the temperature has risen from the previous time and the predetermined temperature a has not yet been reached, then in step 44, the current timer counter value n is the normal value. It is determined whether or not it is less than the timer counter value na corresponding to the time ta (see FIG. 5) required for the temperature increase in the regeneration, and the normal temperature increase time ta has elapsed as shown in FIG. 5 (B). If the temperature has not reached the predetermined temperature a (No), the routine proceeds to step 47 and outputs a signal for turning on the heater relay to heat the corresponding outer peripheral divided heater 7a.

If the temperature rise time ta has not yet elapsed and the temperature is currently raised (Yes), it is necessary to continue temperature detection, so the routine proceeds to step 45, where a certain time (for example, 2 seconds), the process proceeds to step 46, where the temperature Ta detected this time is set to the previous temperature T
After storing as ab, the process returns to step 41 and the temperature is detected again (hereinafter the same).

By the way, returning to step 42 again, when the current temperature Ta becomes smaller than the previous temperature Tab and the filter temperature decreases (No), as shown in FIG. With the heater 5 alone, the peak temperature does not reach the predetermined temperature a and the temperature starts to drop. Therefore, the routine also proceeds to step 47 at this time, and the outer peripheral divided heater 7a is energized.

In step 47, in addition to the heater energization process described above, a process of replacing the temperature Ta detected this time with the previous temperature Tab is performed. Then, in step 48, a predetermined time (for example, 2 seconds) elapses as in step 45. After that, in step 49, the new filter temperature Ta after the start of energization is read and the process of incrementing the timer counter n is executed. In the following step 50, the temperature Ta detected this time is detected in the same manner as in step 43 described above. Is below a predetermined temperature a.

If the result of step 50 is Yes, that is, if the particulate combustible temperature has not yet been reached, the stage before reaching the predetermined temperature a in FIG. 5C and the stage in FIG. 5D.
There are two possible cases in the middle of the slow ascending phase. Therefore, in step 51 following step 50, in order to determine which of the above two cases, the standard temperature rising time tb that can reach the predetermined temperature a under the condition of the auxiliary heating of the outer peripheral divided heater 7a is currently exceeded. It is determined whether or not there is. That is, here, it is determined whether or not the current timer counter n is larger than the timer counter value nb corresponding to the temperature rise time tb, and in the case of Yes, as shown in FIG. However, it is determined that the particulates cannot be ignited, and the process proceeds to step 52 to turn off the power supply to the outer peripheral divided heater 7a to protect the battery.

On the other hand, if No is determined in step 51, it means that it is not yet determined whether the case is (C) or (D) in FIG.
Returning to step 7, processing for continuing energization of the outer peripheral divided heater 7a is performed. Then, by continuing the energization in this way, if it is determined that the predetermined temperature a has been reached at the time when n> nb is not satisfied as shown in FIG.
If it is determined to be o, the process for turning off the heater energization is immediately executed in step 52.

When the heating by the outer peripheral divided heater 7a is completed as described above, the routine proceeds to step 53 as the final processing, and the timer counter n as described above is prepared to prepare for the next filter regeneration to come. Also, the previously detected temperature Tb is initialized to 0, and this routine is ended.

As described above, in this embodiment, the temperature change pattern of the filter portion where the temperature sensor 6a is installed is shown in FIG.
The cases are divided into four cases shown in (A), (B), (C), and (D), and the energization control of the outer peripheral divided heater 7a is executed corresponding to each of the cases, so that the patties collected in this outer peripheral portion are It is possible to achieve appropriate particulate combustion according to the distribution and collection amount of the curate. Further, in this embodiment, as shown in FIG. 5 (D), the battery 9 is stopped in order to stop the energization when a rapid temperature rise is not recognized even when the particulates are ignited by energization of the outer peripheral heater 7a. Can be protected.

The energization control to the outer peripheral divided heater 7a is basically the same in the other outer peripheral divided heaters 7b and 7c as well, and the timers of steps 44 and 51 in the control routine described above are used. Counter na,
Only nb changes. In addition, the number of divided peripheral heaters and the number of temperature sensors according to the present invention are not limited to those in the illustrated embodiment, and may be increased or decreased as necessary.

FIG. 6 is a schematic diagram of a dual filter type exhaust purification device in which the above-mentioned filter is arranged in parallel with the exhaust passage as an example of the exhaust purification device according to the present invention. In the figure, the same elements as those of the apparatus described above are designated by the same reference numerals, and the description thereof will be omitted.

The structure of the apparatus will be briefly described with reference to FIG. 6. Exhaust gas discharged from the engine body 61 is branched from the middle and guided to the two filters 1 arranged side by side. The exhaust gas after collecting the curate merges again and flows to the muffler 62.

On the upstream side of each filter 1, there is provided an exhaust control valve 63 for shutting off the branch passage of the filter 1 to be regenerated when the filter is regenerated. These are negative pressure switching valves which are drive-controlled by the ECU 8. Opening and closing is controlled by the (VSV) 64 and the actuator 65.

Further, between the exhaust control valve 63 and the filter 1, when the filter is regenerated, secondary air as regeneration gas is supplied. Therefore, the electric air pump 66 and the supply destination are connected to each other. A switching valve 67 for determining is provided and each is drive-controlled by the ECU 8. Further, as described above, the end face heater 5, the outer peripheral divided heaters 6a, 6b, 6c and the temperature sensors 7a, 7b, 7c are provided around the filter, and the end face heater 5 is normally operated by the relay 11 when the filter is regenerated. Electric power is supplied, and temperature sensors 7a, 7b, 7c are attached to the outer peripheral divided heaters 6a, 6b, 6c.
Energization control is performed based on the filter temperature detected by.

Although the present invention has been described by taking the dual filter type exhaust gas purification device as an example, the device according to the present invention is not limited to this, and basically, an end face heater is arranged on one side of the filter. When the filter is regenerated, the exhaust gas purification apparatus having any filter can be applied as long as the regeneration gas is supplied from the end heater side. Further, in the embodiment, the exhaust gas purifying device of the forward flow regeneration system, in which the exhaust gas flow direction at the time of particulate collection and the regeneration gas flow direction at the time of filter regeneration are the same, is taken as an example.
Of course, the same can be applied to the exhaust gas purification device of the reverse flow regeneration system.

[0040]

As described above, according to the present invention, when the filter is regenerated, the filter temperature detected at each point in the vicinity of the outer periphery of the filter causes the corresponding outer periphery of the filter to be heated. In order to ensure the ignition of the particulates by energizing the divided heaters, it is possible to optimally regenerate the filter even if there are variations in the particulate collection distribution or the collection amount.

Further, when the filter is regenerated, unnecessary heater energization can be avoided as compared with the conventional exhaust gas purifying apparatus which energizes the outer peripheral divided heater according to a predetermined energization pattern, so that power consumption is reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a partial cross section of a filter that constitutes an exhaust emission control device according to the present invention.

FIG. 2 is a wiring diagram including an external perspective view of the filter of FIG.

FIG. 3 is a diagram showing a temperature change of a certain filter portion during filter regeneration.

FIG. 4 is a flow chart for executing heater energization control of the present invention.

FIG. 5 is a diagram showing each heater energization pattern executed according to the flowchart of FIG. 4, in which (A) shows the case where the outer peripheral divided heater is not operated, and (B) shows the outer peripheral divided heater because the temperature rise is slow. When operating, (C) is a case where the outer peripheral divided heater is energized to cope with the temperature decrease, (D)
(B) and (C) are diagrams showing cases in which energization is stopped because the temperature rise is slow.

FIG. 6 is a schematic configuration diagram of a dual filter type exhaust purification device as an example of the exhaust purification device according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Filter 5 ... End surface heater 6a, 6b, 6c ... Outer periphery division heater 7a, 7b, 7c ... Temperature sensor 8 ... Control circuit

Claims (1)

[Claims] 1. A filter for collecting exhaust particulates is provided in an exhaust passage of a diesel engine, and an end face heater for heating the filter is provided at one end of the filter so that the filter is heated at the time of filter regeneration. In the exhaust gas purification device that operates the end face heater while supplying the regeneration gas from one end to the other end, and burns and propagates particulates from the one end of the filter to the other end side, on the outer periphery of the filter, A plurality of outer peripheral divided heaters electrically divided along the regeneration gas flow direction are provided, and a plurality of temperature detecting means for detecting the filter temperature in the vicinity of the heaters are provided corresponding to the respective outer peripheral divided heaters, Further, the outer peripheral divided heater selectively energizes and controls the outer peripheral divided heater according to the temperature detected by each temperature detecting means during filter regeneration. Exhaust purification apparatus for a diesel engine, characterized in that a charge control unit.