JPH04350316A - Exhaust gas purifying device for diesel engine - Google Patents

Abstract

PURPOSE:To provide an exhaust gas purifying device in which cracks due to internal temperature differences are not generated during regeneration of filters concerning the exhaust gas purifying device with particulate filters for diesel engines. CONSTITUTION:In an exhaust gas purifying device for diesel engines, filters 3, 4 are vehicle-mounted so that the longitudinal axes 3A, 4A extend nearly perpendicular to the ground G, and electric heaters 9, 10 are arranged on the side of undersurfaces of the filters in order for regenerating gas to flow from below to upward during regeneration of the filters.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is provided in the exhaust system of an internal combustion engine, particularly a diesel engine, to remove solid particles in the exhaust gas.
That is, the present invention relates to a diesel exhaust purification device including a filter for collecting particulates.

0002

2. Description of the Related Art For example, in a diesel engine, exhaust gas contains many particulates which are a source of black smoke due to incomplete combustion. Therefore, in vehicles with such engines, in order to remove particulates from the exhaust gas, particulate filters (particulate filters) made of breathable, heat-resistant materials such as ceramics are used.
Hereinafter, this will be referred to as a filter. ) is installed in the engine's exhaust system.

By the way, as this filter collects particulates, its air permeability gradually deteriorates and eventually it becomes clogged, so when using it,
Depending on the amount of particulates collected by the filter, the filter must be regenerated, that is, the particulates must be incinerated at an appropriate time.

[0004] When regenerating the filter, an electric heater is placed near the end face of the filter on the downstream side of the exhaust gas, as disclosed in, for example, Japanese Patent Laid-Open No. 61-223215. The so-called reverse flow regeneration method, in which the electric heater is energized so that the current flows backwards from the downstream side of the filter to the upstream side of the filter, ignites the particulates, and the flame propagates upstream of the filter along with the flow of exhaust gas. Exhaust purification devices are known.

[0005]

[Problem to be solved by the invention] By the way, the filters of most exhaust purification devices, including the above-mentioned exhaust purification device,
When mounted on a vehicle, it is arranged in a so-called horizontal direction so that its longitudinal axis is approximately parallel to the ground, and the electric heater is also spaced apart from the filter in the horizontal direction.
During regeneration, particulates are ignited from the end face of the filter located in the horizontal direction.

However, in such a horizontally arranged filter, the flame of ignited particulates has a strong tendency to propagate upward from the center of the filter, resulting in a temperature difference between the top and bottom of the filter. This thermal strain causes problems such as cracks occurring within the filter and unburned particulates remaining in the lower part of the filter closer to the ground, resulting in poor regeneration.

SUMMARY OF THE INVENTION In view of these problems with exhaust gas purification devices, it is an object of the present invention to provide a diesel exhaust purification device in which particulate combustion is achieved uniformly over the entire filter during regeneration.

[0008]

[Means for Solving the Problems] To achieve the above object, according to the present invention, a filter for collecting diesel particulates in the exhaust gas is provided in the exhaust system of an engine, and the filter is regenerated by igniting and burning the filter. In a diesel exhaust purification device, a filter regeneration ignition means is provided on the bottom side of the filter to regenerate the filter by igniting the collected particulates, and when the filter is regenerated, the regeneration gas is supplied from below the filter, and the regeneration gas is supplied from above the filter. A diesel exhaust purification device is provided, characterized in that it is provided with means for discharging air from the diesel exhaust gas.

[0009]

[Operation] The arrangement of the filter regeneration ignition means on the bottom side of the filter and the means for supplying regeneration gas from below the filter and discharging it from above allow the flow direction of the regeneration gas to match the direction in which the flame extends, from below the filter. Since it is located upward, it is possible to eliminate bias in the propagation of particulate combustion.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of a diesel exhaust purification device according to the present invention and a vehicle equipped with the same.
M refers to a car (such as a truck), G refers to the ground, and 1
2 is the diesel engine body of this automobile M, and 2 is an exhaust pipe extending from the engine body 1.

In this embodiment, the exhaust pipe 2 branches into two parts in the middle, and particulates in the exhaust gas discharged from the diesel engine main body 1 are collected in the respective exhaust pipe parts 2a and 2b. Approximately cylindrical filters 3 and 4 are housed.

The two exhaust pipes 2a and 2b merge again on the exhaust downstream side from the filter housing portion and extend to a muffler (not shown), but a control circuit (ECU) is installed at this merged portion.
An exhaust switching valve 6 is provided, the operation of which is controlled by a switch 5 and which guides the exhaust gas that has passed through the filters 3 and 4 to the exhaust pipe 2.

In addition, according to this embodiment, the filters 3 and 4
In the exhaust pipes 2a and 2b on the upstream side of the exhaust, the corresponding exhaust pipe 2a or 2b is closed during the regeneration process of the relevant filter.
Exhaust control valves 7a and 7b are provided to prevent exhaust gas from the engine body 1 from being guided to the filters 3 and 4, and their operation is controlled by a control circuit 5.

According to the invention, the above-mentioned filters 3, 4
As is clear from the figure, the filters are arranged in the vehicle M such that the longitudinal axes 3A, 4A of the filters extend substantially perpendicular to the ground G. As a result, during normal particulate collection, the exhaust gas discharged from the engine body 1 flows from the top to the bottom inside the filter, mainly in the exhaust inlet passage 3a where the exhaust control valves 7a and 7b are open. , 4a and near the closed ends (closed by plug members) of the adjacent exhaust outlet passages 3b, 4b (see FIG. 2).

[0015] As a means for periodically burning the particulates collected as described above and regenerating and igniting the filter,
Electric heaters 9 and 10 whose energization from battery B is controlled by a relay 8 that is turned on and off by a control circuit 5 are provided on the lower surfaces of the filters 3 and 4, which are end surfaces on the exhaust downstream side.

In addition, in this filter regeneration, each filter 3 is heated so that the flame of the particulates ignited by the heat of the electric heaters 9 and 10 rises inside the filter.
, 4 is supplied with secondary air as a regeneration gas from below the filter to above. This secondary air is pumped by an electric air pump 11 whose drive is controlled by a control circuit 5.
Air introduction control valves 13a and 13b, which are controlled to open and close by a control circuit 5, are interposed in air introduction pipes 12a and 12b extending from 1 toward the lower surface of each filter 3 and 4, respectively.

Furthermore, exhaust control valves 7a, 7b and each filter 3
, 4, there is a gas discharge pipe 14a for discharging the regeneration gas that has passed through the filter as described above to the outside.
, 14b are connected to the respective exhaust pipes 2a, 2b, and gas release control valves 16a, 16b, which operate in synchronization with the air introduction control valves 15a, 15b, are provided inside each, respectively.

The operation of the diesel exhaust purification system constructed as described above will be briefly explained. First, when collecting particulates, the exhaust control valves 7a, 7b and the exhaust switching valve 6 are operated to fully open the exhaust pipes 2a, 2b.
As a result, the exhaust gas flows through the filter 3 as shown by the dotted arrow in the figure.
, 4 from above to below, and at this time each filter 3, 4
Particulates will be collected inside.

In order to determine when to regenerate the filter, as the amount of particulates collected increases, the filter pressure loss increases. This can be determined by detecting the magnitude of the pressure difference between the front and rear. To regenerate the filter, first close the exhaust control valve 7b and operate the exhaust switching valve 6 to shut off the exhaust pipe 2b downstream of the filter 4, as shown in FIG. 3, the electric heater 10 and the electric air pump 11 are energized, and the air introduction control valve 15b and the gas release control valve 1 are also energized.
The valves 6b are opened to ignite and burn the particulates collected in the filter 4.

When the regeneration process of the filter 4 is completed, in order to regenerate the filter 3, the operations of the above-mentioned control valves and electric heaters are reversed (that is, the exhaust control valve 7b, the air introduction control Valve 15a, gas release control valve 16
When the valve is opened and the electric heater 9 is energized), the particulates collected in the filter 3 are similarly ignited and combusted.

Next, the combustion mode of the particulates in the filter according to the present invention will be explained with reference to FIG. Figure 2 (a
) shows the regeneration gas flow within the filter of the present invention mounted upright on the ground G, and (b) is a simplified conceptual diagram. Further, FIG. 3 shows a related art related to this, in which (a) shows the flow of regeneration gas in a horizontally mounted filter, and (b) shows a conceptual diagram thereof. In addition, in common to these figures, the solid line arrow indicates the flow direction of the regeneration gas (secondary air in this example), and the dotted line arrow indicates the direction of natural convection generated by particulate combustion heat. There is.

As is clear from these figures, in the exhaust gas purification device of the present invention, during filter regeneration, the regeneration gas is supplied from the bottom of the filter near the ground G to the top, so that no gas enters from the exhaust outlet passage. After passing through the filter partition, the exhaust gas flows into the exhaust inlet passage and flows upward as it is, and the direction of movement of the exhaust gas coincides with the direction of natural convection within the exhaust inlet passage where many particulates adhere. This means that the necessary gas flow for flame propagation can be obtained with a small amount of regeneration gas, and uniform combustion of particulates is also achieved in the direction across the filter, so that particulates can be burned inside the filter during combustion. Temperature differences and thermal distortion can be reduced, making it difficult for cracks to occur.

In contrast, in the conventional horizontally disposed filter, the flow of the regeneration gas and the flow of natural convection due to particulate combustion heat are almost perpendicular to each other, as shown in FIG. tends to be in the direction of the composite vector shown in the figure, and therefore, unburned particulates are likely to occur on the downstream side of the regenerating gas below the filter, resulting in poor regeneration, and cracks tend to occur due to filter temperature differences. .

The embodiments of the present invention have been described above by taking as an example an exhaust gas purification device of a backflow regeneration type in which the flow direction of regeneration gas during filter regeneration is opposite to the flow direction of exhaust gas during particulate collection. However, the present invention is not limited to this embodiment, and can also be applied to an exhaust gas purification device using a so-called forward flow regeneration system, in which the flow of regeneration gas and exhaust gas match in the filter. The same effect as described above can be obtained by standing the filter upright and allowing exhaust gas and regeneration gas to flow from the bottom to the top of the filter. Further, although the illustrated embodiment is an exhaust gas purification device in which two filters are arranged side by side, the present invention is of course applicable to a device that purifies exhaust gas with one filter.

[0025] In addition, the above-mentioned embodiments have the following in common:
Since the electric heater is located below the filter, even if the position of the filter changes due to, for example, vehicle vibration, the filter is held by the heater and the gap between the electric heater and the filter does not widen. Another effect is that the ignitability of particulates does not deteriorate.

[0026]

[Effects of the Invention] As explained above, according to the present invention, when the filter is regenerated, the direction in which the particulate flame extends,
In other words, since the direction of natural convection due to particulate combustion heat and the flow direction of the regeneration gas match, it is possible to eliminate bias in the propagation of particulate combustion, and it is possible to perform filter regeneration processing uniformly within the filter and without cracks, with less energy consumption. It can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a partial schematic diagram of a vehicle equipped with a diesel exhaust purification device of the present invention.

FIG. 2 shows the gas flow state during filter regeneration according to the present invention, (a) shows the actual gas flow, and (b) shows its conceptual diagram.

FIG. 3 shows the gas flow state during regeneration of the conventional filter corresponding to FIG. 2, (a) shows the gas flow after the filter is removed;
b) shows its conceptual diagram.

[Explanation of symbols]

3, 4...filter 5...Control circuit 9,10...Electric heater 11...Electric air pump G...ground M...Vehicle 3A, 4A...filter longitudinal axis

Claims (1)

[Claims] Claim 1: In a diesel exhaust purification device that includes a filter that collects diesel particulates in the exhaust gas in the exhaust system of an engine, and regenerates the filter by igniting and burning the particulates, the lower surface of the filter has a filter that collects diesel particulates in the exhaust gas. A diesel exhaust purification system comprising a filter regeneration ignition means for regenerating the filter by igniting particulates, and further comprising a means for supplying regeneration gas from below the filter and discharging it from above the filter during filter regeneration. Device.