JPH06229228A - Exhaust emission control device for diesel-engine - Google Patents

Abstract

PURPOSE:To provide an exhaust emission control device incorporating oxidizing catalysts and filters, which can effectively purify exhaust components that have not yet been purified during regeneration. CONSTITUTION:During trapping of particulate, exhaust gas flows through oxidizing catalyst 21, 22 located upstream of filters 2, 3 in an exhaust passage, and the filters 2, 3, and during regeneration of the filters, gas to be generated flows through the filters and the catalysts. Accordingly, during the trapping and the regeneration, it is possible to purify exhaust components which has not yet been purified during regeneration of the filters, thereby it is possible to purify exhaust gas with a catalyst having a low capacity.

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 having an exhaust passage provided with a particulate filter for collecting diesel particulates discharged from a diesel engine.

[0002]

2. Description of the Related Art Since the exhaust gas of a diesel engine contains a large amount of exhaust particulates, that is, particulates,
A particulate filter (hereinafter referred to as a filter) for collecting the particulates is usually mounted in the exhaust passage of the engine. Also, this filter
If the amount of particulates that accumulates in the interior increases with use, the air permeability will gradually be impaired and engine performance will also deteriorate.Therefore, a filter such as an electric heater should be used periodically according to the particulate collection amount. Is heated, and at the same time, a so-called filter regeneration process is performed in which regeneration gas (secondary air or the like) for particulate combustion is supplied to burn particulates.

By the way, during such filter regeneration, the particulate combustion gas discharged contains carbon monoxide (CO) and hydrocarbons (HC) generated by incomplete combustion of soot, and further softens. A soluble organic component called (SOF) is also released by being released from the particulates, and if it is discharged outside the vehicle as it is, the surrounding environment may be deteriorated.

To address such a problem, Japanese Patent Laid-Open No. 4-18
Japanese Patent No. 3917 discloses an exhaust gas purifying apparatus which is provided with an oxidation catalyst in a regenerated combustion gas discharge pipe for discharging regenerated combustion gas at the time of filter regeneration, purifies the regenerated combustion gas, and then discharges the purified combustion gas.

[0005]

However, in the above-mentioned exhaust gas purification device equipped with the oxidation catalyst, since the exhaust gas directly flows into the filter at the time of collecting particulates, the exhaust gas purification target device is used as a purification target of the oxidation catalyst. Exhaust components that are unpurified components at the time of filter regeneration,
Since the exhaust gas is discharged all at once when the filter is regenerated, naturally, a high purification capacity is required as an oxidation catalyst for purifying these exhaust components, and there is a problem that the cost of the entire system becomes high.

In view of the above problems, the present invention does not require a high purification capacity with respect to an exhaust purification means such as an oxidation catalyst, and effectively becomes an unpurified component at the time of regeneration. It is an object of the present invention to provide an exhaust gas purification device that can purify air.

[0007]

In order to solve the above-mentioned problems, according to the present invention, a filter for collecting particulates is provided in the exhaust passage of a diesel engine, and a filter is provided according to the amount of particulates collected by the filter. In an exhaust purification device of a diesel engine that heats and regenerates a filter, in the exhaust passage on the exhaust upstream side of the filter,
An exhaust gas purifying means for purifying an exhaust gas component which is an unpurified component at the time of filter regeneration is provided, and at the time of filter regeneration, a gas for regeneration is supplied from a downstream side of the filter toward the filter and the exhaust gas purification means. An exhaust emission control device for a diesel engine is provided, which is provided with means.

[0008]

Since the exhaust gas purifying means is provided in the exhaust passage upstream of the filter rather than the exhaust gas purifying means in the regenerated combustion gas exhaust pipe, the exhaust gas flows from the exhaust gas purifying means to the filter during particulate collection. At this time, the exhaust components that may be unpurified components during filter regeneration can be purified to some extent.

During filter regeneration, the filter is heated and the regeneration gas is supplied from the downstream side of the filter toward the filter and the exhaust purification means, so that the unpurified components are purified by the exhaust purification means.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Below, with reference to the drawings, an exhaust passage of an engine is equipped with two filters, and during filter regeneration, secondary air for regeneration is supplied from the downstream side to the upstream side by a reverse flow regeneration type dual filter type exhaust gas. Taking the example of a purification device,
The present invention will be described. Referring to FIG. 1 showing a schematic configuration of an exhaust emission control device according to the present invention, 1 is a diesel engine main body E
It is an exhaust pipe that guides the exhaust gas from the filters 2 and 3.
The filters 2 and 3 are configured as a honeycomb filter in which plugs are alternately arranged at the ends of a large number of cells in order to collect particulates in the exhaust gas. When collecting particulates, the exhaust gas is upstream. The cells enter from the cells whose ends are open, pass through the partition wall, and then pass out of the filter from the cells whose downstream ends are open.

At the branch portion a from the exhaust pipe 1 to each of the filters 2 and 3, and the confluence portion b from the filters 2 and 3, a first exhaust flow from the engine E is changed when the filter is regenerated.
An exhaust control valve 4 and a second exhaust control valve 5 are provided,
These control valves are driven by the respective actuators 6, 7, and the actuation of the actuators 6, 7 controls the introduction of vacuum into them by a negative pressure switching valve (VSV) 8
The operation is controlled by a control circuit (ECU) 10 that outputs an opening / closing signal to a, 8b, 9a and 9b.

When the corresponding filters are regenerated to the respective branch pipes 1a and 1b on the exhaust upstream side of the merging portion b of the exhaust passage, the secondary air for regeneration is supplied to the filters 2 and 3 to be regenerated.
A secondary air supply pipe 11 is connected, and an electric air pump 12 whose air discharge amount is variably controlled by the ECU 10 is provided at an end portion thereof. Further, in the secondary air supply pipe 11, similar to the second exhaust control valve 7, a supply pipe opening / closing valve 14 that opens and closes the secondary air supply passage from the electric air pump 12 by the VSV 13, and each on the air flow downstream side thereof. A first opening / closing valve 15 and a second opening / closing valve 16 that control the supply of secondary air to the filters 2 and 3 are provided, respectively.

This exhaust gas purification device is constructed as a system for alternately regenerating the filter when the filter is regenerated, and an electric heater that alternately energizes and generates heat at the exhaust gas downstream end of each of the filters 2 and 3 for regenerating the filter. 17, 18 are provided, and the energization ON / OFF of the ECU 10 is controlled. Further, in this exhaust emission control device, in order to detect the filter regeneration timing, that is, the amount of particulates trapped in the filters 2 and 3, the pressure loss value (differential pressure difference) of the entire device is determined by the exhaust pressure before and after the filters 2 and 3. Pressure sensor 1 for detecting
9 is provided, and its output signal is input to the ECU 10.

In addition to the differential pressure sensor 19 described above, the apparatus is provided with an exhaust temperature sensor 20 for detecting the temperature Tin of the exhaust gas flowing through the filters 2 and 3, and the ECU 10 as a parameter indicating the engine operating state. Number of revolutions N
The throttle opening Th, the engine water temperature Thw, the intake air amount Ga, etc. are input. Then, the ECU 10 calculates the particulate collection amount G based on the differential pressure ΔP of the filters 2 and 3 obtained from the differential pressure sensor 19 and the filter inlet gas temperature Tin from the exhaust temperature sensor 20, and this is set to a predetermined trapping amount. When it exceeds the collection predetermined value, it is judged that it is the filter regeneration time.

In the present embodiment, as an exhaust purification means, HC and C in the exhaust gas are provided on the exhaust upstream side of the filters 2 and 3.
Oxidation catalysts 21 and 22 for oxidizing O are arranged. Also,
A regeneration combustion gas discharge pipe 23 for taking in particulate combustion gas (hereinafter referred to as regeneration combustion gas) from the filters 2 and 3 to be regenerated at the time of filter regeneration is connected to each of the branch pipes 1a and 1b on the upstream side thereof. The end of the exhaust pipe 1 is open to the atmosphere as shown in the drawing, or the exhaust pipe 1 on the exhaust downstream side of the muffler 24 provided on the downstream side of the exhaust merging portion b.
Connected to.

Further, like the above-mentioned secondary air supply pipe 11, the regeneration combustion gas discharge pipe 23 has a discharge pipe opening / closing valve 25 for opening and closing the regeneration combustion gas discharge passage, and each filter 2 on the gas flow upstream side thereof. , 3 are provided with a third on-off valve 26 and a fourth on-off valve 27, respectively, and the third on-off valve 26 together with the first on-off valve 15 is controlled by the VSV 28 which is controlled by the ECU 10. 4 on-off valve 27
Are controlled by the VSV 29, which is controlled by the ECU 10 together with the second switching valve 16.

2 and 3 showing the particulate collection operation and the filter regeneration operation of the exhaust gas purification apparatus constructed as described above, in which the exhaust flow at that time is indicated by solid arrows and the regeneration gas flow is indicated by dotted arrows. However, it will be described below. Figure 2
In the particulate collection state shown in (1), the first exhaust control valve 4 occupies the neutral position as shown, and the above-mentioned on-off valves 14 to 16 and 25 to 17 are closed.

As a result, the exhaust gas from the engine E is first branched into two branches at the exhaust branch portion a, and the branch pipes 1a and 1b are respectively branched.
After passing through the oxidation catalysts 21 and 22 and the respective filters 2 and 3, they are joined again at the joining portion b and flow toward the muffler 24 side. In the process of passing through the oxidation catalysts 21 and 22, most of CO and HC in the exhaust gas are oxidatively purified, but the soluble organic components are partially oxidatively purified, and the unpurified components are soot components. While being adsorbed by, it is collected by the filter.

If it is determined that the filter recovery time is reached because the particulate collection amount calculated by the filter pressure loss value ΔP detected by the differential pressure sensor 19 and the operating conditions detected by various sensors exceeds a predetermined value. As a device, first, the ECU 10 is used to start regeneration from the filter 2.
The exhaust control valves 4 and 5 are moved to the positions shown in FIG. 3 by the valve opening signal output from (FIG. 1) to the VSVs 8a, 8b, 9a and 9b.

As a result, the flow of the exhaust gas is deflected toward the filter 3 at the branch portion a, and the oxidation catalyst 22 and the filter 3 are deflected.
After passing through the branch pipe 1b, it flows to the muffler 24 side via the branch pipe 1b, and the exhaust gas purification as described above is continued. On the other hand, on the filter 2 side, the electric heater 17 is energized to heat the filter to ignite the particulates trapped therein and start the operation of the electric air pump 12,
Secondary air as a filter regeneration gas is supplied only to the filter 2. In addition, in the secondary air supply pipe 11,
Only the on-off valve 16 is closed to prevent the outflow of secondary air into the branch pipe 1b and the inflow of exhaust gas into the supply pipe. In the regenerated combustion gas exhaust pipe 23, the exhaust pipe on-off valve 25 and the third open / close valve are provided. The valve 26 is opened and the fourth opening / closing valve 27 is closed, so that the particulate combustion gas discharged from the filter 2 is discharged to the atmosphere as indicated by the dotted line of arrows [VSV 13, 2].
9 (Fig. 1) is ON and VSV30 is OFF;].

At this time, the regenerated combustion gas discharged from the filter 2 contains HC, CO, and soluble organic components generated by incomplete combustion and desorption of soot and soluble organic components. . Such unpurified components at the time of regeneration are converted to stable substances such as CO ₂ and H ₂ O by the oxidation catalyst 21 provided on the downstream side of the regeneration gas flow from the filter ₂ and discharged outside the vehicle. .

The amount of unpurified components discharged from the filter 2 at this time is, to the extent that the total amount of unpurified components discharged from the engine is constant until then, to some extent during particulate collection as described above. Amount of oxidation catalyst 21
Since it has already been purified by, the oxidation catalyst is much lower than in the case where the oxidation catalyst is not provided in the exhaust passage on the upstream side of the filter. Therefore, at this time, even if the capacity and capacity of the oxidation catalyst for purifying the unpurified components are so small. It will be good.

When the particulate combustion in the filter 2 is completed in this way, the apparatus is next operated by the electric heater 1.
8 is energized, the valve positions of the first exhaust control valve 4 and the second exhaust control valve 5 are moved to the positions indicated by the dotted lines in the figure, and the first opening / closing valve 15 and the third opening / closing valve 26 are closed to filter the secondary air this time. Three
Supply to. As a result, this time, the particulates collected in the filter 3 are ignited and burned,
Also at this time, the unpurified components at the time of regeneration are purified by the oxidation catalyst 22 as at the time of regeneration of the filter 2.

The series of filter reproduction processing described above is
For example, the operation is performed in accordance with the operation on / off timing as shown in FIG. 4, so that the particulates collected in the filters 2 and 3 are burned, and the unpurified exhaust components at the time of regeneration are also purified. Become. Although the embodiments of the present invention have been described with reference to the case of the dual flow exhaust gas purifying apparatus of the reverse flow regeneration system, the present invention can naturally be applied to a single filter type apparatus.

FIG. 5 and FIG. 6 show states of a single filter type exhaust purification device in which an oxidation catalyst as exhaust purification means is arranged in the exhaust passage on the exhaust upstream side of the filter provided only during particulate collection and filter regeneration. FIG. 7 is a time chart of secondary air supply and heater energization during regeneration. Throughout these drawings, the same constituent elements as those of the apparatus shown in FIG. 1 are designated by the same reference numerals, and the description of their operation will be omitted.

In this embodiment, however, the functions of the oxidation catalyst 21 and the filter 2 at the time of collecting particulates are exactly the same as those of the previous embodiment, and the exhaust gas bypasses the filter 2 via the bypass pipe 1c. Even when the filter is regenerated, the regenerated combustion gas is discharged while the unpurified component discharged from the filter 2 is purified by the oxidation catalyst 21.

Incidentally, in common with these embodiments described above,
For example, during filter regeneration and when the engine is stopped (when the vehicle is stopped), the radiator cooling fan 31 is operated to blow air toward the outlet of the regenerated combustion gas exhaust pipe 23, as shown in FIG. Alternatively, as shown in FIG. 9, if the dedicated fan 32 is configured to blow air to the tip of the exhaust pipe 23, the regenerated combustion gas can be diluted with a large amount of air, and the peculiar odor contained in the gas can be generated. It can be diffused behind and around the vehicle.

[0028]

As described above, according to the present invention, by providing the exhaust gas purification means in the exhaust passage on the exhaust gas upstream side of the filter, the same exhaust gas purification means can be used at the time of particulate collection and filter regeneration. Since the unpurified components emitted during filter regeneration can be purified, the exhaust purification means can have a smaller capacity than in the past, and the cost of the device can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an exhaust gas purification apparatus of a reverse flow regeneration type dual filter type according to the present invention.

FIG. 2 is a view showing a particulate collection state of the exhaust gas purification device of FIG.

FIG. 3 is a diagram showing a filter regeneration state of the exhaust emission control device of FIG. 1.

FIG. 4 is a timing chart of secondary air supply and heater energization showing filter regeneration conditions of the exhaust gas purification apparatus of FIG.

FIG. 5 is a diagram showing a schematic configuration of a backflow regeneration type single filter type exhaust emission control device according to the present invention and showing a particulate collection state thereof.

6 is a diagram showing a filter regeneration state of the exhaust emission control device of FIG.

FIG. 7 is a timing chart of secondary air supply and heater energization, showing filter regeneration conditions of the exhaust emission control device of FIG.

FIG. 8 is a vehicle-mounted view showing an embodiment of an apparatus in which regenerated combustion gas is diffused by blowing air from a radiator fan.

FIG. 9 is a partial configuration diagram of an apparatus showing an embodiment in which regenerated combustion gas is diffused by blowing air from a dedicated fan.

[Explanation of symbols]

 1 ... Exhaust pipe 2, 3 ... Filter 4 ... First exhaust control valve 5 ... Second exhaust control valve 10 ... Control circuit 11 ... Secondary air supply pipe 12 ... Electric air pump 21, 22 ... Oxidation catalyst

Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location F01N 3/24 ZAB E

Claims (1)

[Claims] 1. An exhaust emission control device for a diesel engine, wherein a filter for collecting particulates is provided in an exhaust passage of a diesel engine, and the filter is heated to regenerate the filter according to the amount of particulates collected by the filter. In the exhaust passage on the upstream side of the exhaust gas, an exhaust gas purifying means for purifying an exhaust gas component which is an unpurified component at the time of filter regeneration is provided, and at the time of filter regeneration, a filter regeneration gas from the downstream side of the filter and the exhaust gas purification means An exhaust emission control device for a diesel engine, characterized in that a regeneration gas supply means for supplying the exhaust gas to the exhaust gas is provided.