JPH07310530A - Diesel particulate filter - Google Patents

Abstract

PURPOSE:To enable a filter to trap every grain diameter of particulate as the clogging of the filter is prevented from occurring in a short time, and to make the flow of exhaust gas smooth. CONSTITUTION:A bypass pipe serving as a bypass flow passage in burning particulate is arranged at the middle of a filter case 10, and a coarse mesh filter 12, a middle mesh filter 13 and a fine mesh filter 14 are arranged outside the bypass pipe in order. A metal net heater 15 which holds the filter and serves as a heating body in burning the particulate is arranged outside each filter. A controller 22 opens a bypass valve through an actuator 21 in burning the particulate and applys electric current to the metal net heater 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diesel particulate filter which collects and incinerates particulates in exhaust gas of a diesel engine.

[0002]

2. Description of the Related Art Since a diesel engine is a heterogeneous combustion in which fuel is injected into the air heated by adiabatic compression to perform combustion, exhaust gas contains little carbon monoxide, but nitrogen oxides ( There is a problem that a large amount of NOx) and particulates (mainly carbon) are emitted.

As means for coping with this point, a method of reducing particulates themselves generated by using a high pressure pump as a fuel pump and a method of attaching a filter to an exhaust gas passage to filter exhaust gas have been studied. -It is being developed. The former uses a special pump, and the engine itself is extremely expensive. Therefore, expectations are growing for the latter filter method that can achieve low-cost purification of exhaust gas. Here, as a material of the filter body, a ceramic material that can be made to have a large particulate adsorbing power by making it porous or rough has attracted attention. By the way, in the prior art of this type of particulate filter, it has been practiced to filter the particulate with a single type of filter.

[0004]

Exhaust gas is introduced into the exhaust pipe by opening the exhaust valve, and its speed and pressure are constantly changing depending on the number of revolutions and the load condition. Thus, the exhaust pipe is required to discharge the introduced gas to the outside with low resistance. On the other hand, the particulates contained in the exhaust gas of the diesel engine are extremely fine inside the combustion chamber of the engine, and while passing through the exhaust valve and the exhaust pipe, particulates gradually collect and grow into large particles. It is said that the distribution of particle diameters is almost normal distribution, and the distribution state ranges from 2 to 3 μm in the lower part to 30 μm in the upper part with the particle size at the center of 15 μm. When the particulates pass through a porous filter, some of the particulates collide with each other in the vicinity of the inlet and grow into larger particles, and are collected by this filter. However, in the exhaust gas that has reached the filter, it is 30 to 10 above 2 to 3 μm.
It contains particulates with a particle size in the range of 0 μm. However, the conventional particulate filter is a single type of filter that collects particulates having a small particle size, and a fine mesh has been adopted so that the particulates having a small particle size can be collected. Therefore, the filter is heavily clogged, and the gas flow resistance near the inlet of the filter body is increased, which increases the pressure here and hinders smooth discharge of exhaust gas.

The present invention has been made in consideration of such a point, and an object of the present invention is to equalize the pressure in the filter as much as possible so that a smooth flow of exhaust gas can be obtained. To ensure that the particulate collection is efficient and that the filter does not interfere with the exhaust operation of the engine.

[0006]

In order to achieve the above object, according to the present invention, there is provided a diesel particulate filter for filtering exhaust gas of a diesel engine to collect particulates and incinerate them by electric heat. A diesel particulate filter is provided, in which a plurality of filters are installed in a case such that a mesh is gradually fined in a flow path in series from an upstream side to a downstream side.

[0007]

In the particulate filter of the present invention, for example, a plurality of filters such as a coarse mesh filter, a medium mesh filter and a dense mesh filter are installed in series in the flow path in order from the upstream side. .
Therefore, it becomes possible to collect particulates of all particle sizes while avoiding clogging in a short time. Further, since the filter having a coarse mesh is located on the most upstream side, it is possible to prevent the pressure of the exhaust gas from being raised even if the particulates having a large particle size are collected. Furthermore, since the coarse mesh filter has a small diameter and the fine mesh filter has a large diameter, the resistance per unit area of the passing gas becomes large, and the exhaust gas flow velocity becomes small and the dense mesh filter has a large area. Therefore, there is no place where the pressure locally rises, the collection efficiency of particulates increases, and the flow of exhaust gas that does not cause a rapid pressure increase due to collection becomes smooth and efficient filtering becomes possible.

[0008]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a sectional view of a particulate filter according to an embodiment of the present invention. As shown in the figure, in the particulate filter 100 of the present embodiment, a cylindrical bypass pipe 11 is arranged in the center of a steel filter case 10, and a cylindrical filter with a bottom is provided outside thereof. It is arranged in three layers.

That is, in order from the inner side, the coarse filter 1
Two kinds of filters, that is, the second filter 13, the middle filter 13, and the close filter 14 are concentrically installed. This arrangement is referred to as a flow path serial arrangement. Each filter is made of ceramic fiber woven fabric or non-woven fabric formed by weaving porous fibers of SiC ceramics. The coarse filter 12 is made of a large diameter ceramic fiber (20 to 30 μm), and the medium filter is made of a medium diameter ceramic. Due to the fiber (20 to 10 μm), the fine filter has a small diameter ceramic fiber (10 to 5 μm).
μm) is woven in each or a part of the non-woven fabric in which the fiber material is partially locked is laminated.

Outside the filters 12 to 14, a mesh-shaped and cylindrical wire mesh heater 15 and a support 15 'are arranged, and each filter is supported by this heater. An annular terminal 16 is formed at the left and right ends of each wire mesh heater. Instead of the structure in which the filters 12 to 15 are supported by the wire mesh heater 15, each filter and heater are
It can be held in a cylindrical container made of highly rigid porous steel or ceramics.

A cylindrical exhaust guide pipe 17 is installed outside the outermost dense filter 14, and the heat insulating sheet 1 is provided between the exhaust guide pipe 17 and the filter case 10.
8 are arranged. A bypass valve 19 for controlling the flow / cutoff of gas is provided near the inlet of the bypass pipe 11. The bypass valve 19 is operated by the actuator 21.
It is opened and closed via the actuator arm 20. The operation of the actuator 21 is controlled by the controller 22. The controller 22 also supplies electric power to the wire net heater 15 via the terminal 16 during particulate incineration. A hollow truncated cone-shaped inlet guide plate 23 is arranged outside the inlet portion of the bypass pipe 11.

The bypass valve 13 is closed during normal operation, so that exhaust gas does not pass through the bypass pipe. At this time, the gas flowing in from the left side of the drawing is guided by the inlet guide plate 23, and the bypass pipe 1
1 and the coarse filter 12 are introduced into the flow path. Then, the exhaust gas that has flowed in passes through the coarse filter 12, the intermediate filter 13, and the fine filter 14 in this order as shown by the arrow, and is gradually filtered out into fine particulates, and then discharged to the outside of the filter.

If the filter is operated for a long time, the filter will be clogged. This state is detected by the exhaust pressure sensor 25, and in that case, an idling state in which the exhaust gas flow rate of the engine is small is detected, and the controller 22
The bypass valve 19 is opened through the electric power source and the wire mesh heater 15 is supplied with electric power to incinerate particulates (mainly carbon). After a lapse of a predetermined time, power supply is stopped and the bypass valve 19 is closed. The incineration operation of the particulates can be automatically performed by the controller by monitoring the exhaust gas pressure by the controller and assuming that clogging has occurred when the pressure reaches a predetermined pressure. Further, a warning device for clogging may be provided in the driver's seat so that the driver manually incinerates.

The preferred embodiment has been described above.
The present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention. For example, in the embodiment, the filter is installed in three layers, but it may be two layers or four or more layers. Further, the filter may be made of a woven cloth of metal fibers instead of being made of a ceramic fiber woven cloth, or may be made of a layered body of a ceramic fiber woven cloth and a metal fiber woven cloth.

[0015]

As described above, the diesel particulate filter according to the present invention has a filter case in which the upstream side is a coarse filter and the mesh becomes finer toward the downstream side, that is, a plurality of filters are connected in series in the flow path. Since it is arranged, it is possible to efficiently collect particulates of all particle sizes from large particle size to small particle size while preventing clogging in a short time. Like Furthermore, when the coarse mesh filter fiber has a large diameter and the fine mesh filter has a small diameter, the resistance of the passing gas per unit area becomes large and the fine mesh filter has a large area. Therefore, there is also an effect that the flow of the exhaust gas is smooth and smooth filtering is possible without locally increasing the pressure.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of a particulate filter according to an embodiment of the present invention.

[Explanation of symbols]

 10 Filter Case 11 Bypass Pipe 12 Coarse Filter 13 Middle Filter 14 Fine Filter 15 Wire Mesh Heater 16 Terminal 17 Exhaust Guide Pipe 18 Insulation Sheet 19 Bypass Valve 20 Actuator Arm 21 Actuator 22 Controller 23 Inlet Guide Plate 25 Exhaust Sensor 15 'Support

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location F01N 3/02 B 9/00 ZAB Z

Claims (4)

[Claims] 1. A diesel particulate filter that filters exhaust gas of a diesel engine to collect particulates and incinerates them by electroheating, wherein a flow passage is meshed in series in a filter case from an upstream side to a downstream side. The diesel particulate filter is characterized in that the filter is installed in such a manner that it becomes finer. 2. A plurality of cylindrical filters are installed concentrically, a cylindrical bypass pipe is arranged inside the innermost filter, and exhaust gas is discharged when the bypass pipe is closed. The diesel particulate filter according to claim 1, wherein the diesel particulate filter passes in order from the inner filter to the outer filter. 3. Each of the filters is made of a woven or non-woven fabric made of ceramic fibers, the upstream filter is formed of fibers having a larger diameter, and the downstream filter is smaller in diameter and higher in density. 1. The diesel particulate filter according to 1. 4. Each filter has a composite structure characterized in that a wire mesh heater is arranged on the upstream side, and ceramic fibers and a support are superposed.