EP0303754A1

EP0303754A1 - Exhaust filter for compression ignition engines

Info

Publication number: EP0303754A1
Application number: EP87850250A
Authority: EP
Inventors: Hergart Anders
Original assignee: Unikat AB
Current assignee: Unikat AB
Priority date: 1987-08-21
Filing date: 1987-08-21
Publication date: 1989-02-22

Abstract

The invention relates to an exhaust filter for compression ignition engines. The filter is mounted in a heat-insulating enclosure (10, 11) and is separated into two or more individual and identical substantially cylindrical filter bodies (21) each of which is enclosed by a surrounding metal sheet envelope (23) and is mounted between apertures (25) in partitions (12, 14) defining an inlet chamber (13) and an outlet chamber (15), respectively, in the heat-insulating enclosure.

Description

The invention relates to an exhaust filter for compression ignition engines, having a heat-insulating enclosure and substantially vertically extending parallel passages some of which are connected as inlet passages to an inlet chamber at the bottom and others are connected as outlet passages to an outlet chamber at the top, said passages being separated by porous walls coated with a catalyst, an electric heater for generation of the filter being provided in the inlet chamber below the inlet passages.
A filter of this kind is described in the Swedish patent specification 8400084-3 (publication No. 439,949). It is regenerated by burning catalytically at a sufficiently high temperature any soot coating accumulated in the filter and comprising substantially coal particles separated from the exhaust gas of the compression combustion engine during operation thereof. Such regeneration of the filter takes place automatically when the engine is operated at high power output and thus at high exhaust gas temperature, by the exhaust gas providing the necessary temperature, and when the engine is not operating, by supplying external energy via the electric heater so as to maintain the necessary temperature.
In the embodiment of the prior art filter described in the patent specification referred to above there is a risk that relatively colder portions exist at the periphery of the filter in spite of the enclosing heat insulation provided. Thus, a decreased catalyst action will be obtained at the filter periphery particularly at the inlet side of the filter such that it cannot be avoided that there is obtained a more permanent peripheral soot coating at the inlet side of the filter. The purpose of the invention is to overcome this drawback and to provide a filter wherein the regeneration is more effective, and this is achieved by the filter of the invention having obtained the characterizing features of claim 1.
It has been found that by constructing the filter in this way there is obtained the further advantage that the filter provides a substantial noise silencing. Moreover, the filter can easily be designed for a specific engine power output by including in the filter a proper number of identical filter components.
For explanation of the invention in more detail reference is made to the accompanying drawings in which

FIG. 1 is a vertical sectional view of a filter of the invention in one embodiment thereof,
FIG. 2 is a plan view of the filter in FIG. 1,
FIG. 3 is a side view of the filter in FIG. 1 as seen from the inlet side,
FIG. 4 is an enlarged axial sectional view of a filter component forming part of the filter in FIG. 1,
FIG. 5 is a fragmentary enlarged axial sectional view illustrating the mounting of the filter component.
FIG. 6 is a side view, partly a vertical cross-sectional view, of another embodiment of the filter of the invention,
FIG. 7 is a plan view, partly a cross-sectional view along line VII-VII in FIG. 6, of the filter shown therein, and
FIG. 8 is an end view, partly a vertical cross-sectional view, of the filter in FIG. 6.

The filter illustrated in the drawings comprises a housing 10 having inner walls of steel sheet and outer walls e.g. of aluminium, a heat insulation 11 being provided between said walls. In the housing there is defined by means of a lower flat metal sheet partition wall 12 an inlet chamber 13 and by means of an upper flat metal sheet partition wall 14 an outlet chamber 15. The inlet chamber has a flanged connection socket 16 to be connected to the exhaust pipe of the engine, and the outlet chamber has a flanged connection socket 17 to be connected to the exhaust pipe including the silencer. The inlet chamber may have a further connection socket having a valve so as to be connected over said valve to the exhaust pipe including the silencer such that the filter can be short-circuited if there should be a need of doing so at a failure. In the inlet chamber two electric heaters 18 are provided having connection boxes 19 outside the housing 10.
Between the two partition walls 12 and 14 four filter elements 20 as shown in FIG. 4 are provided. Each of said elements consists of a cylindrical monolitic porous filter body 21 e.g. of the type made by Corning Glass Filter, forming a number of mutually parallel passages 22 which extend axially between opposite end faces of the filter body and are separated by the porous filter material. However, the passages are alternatingly plugged at one and the other end face of the filter body to provide an exhaust gas flow as indicated by arrows. A metal sheet envelope 23 is clamped around the filter body with a ceramic mat 24 located between the filter body and the envelope, said mat being partially compressed. The mat compensates for differences in thermal expansion of the filter body and the metal sheet envelope, respectively, and moreover forms a protection and a heat insulation around the filter body.
The filter elements 20 are mounted between circular apertures 25 in the partitions 12 and 14 by the envelope 23 projecting slightly axially from the filter body at the ends thereof, being welded to the edges of said apertures. In the space defined between the partitions 12 and 14 a heat insulating material 26 is provided around the filter elements 20. In the passages opening into the inlet chamber 13 the filter bodies 21 are coated with a catalyst for soot combustion, and in the passages opening into the outlet chamber 15 said bodies are coated with a catalyst for CO and CH combustion.
In the manner described in the Swedish patent specification 8400084-3 soot collected in the inlet passages of the filter body is burnt off by catalytic combustion when the engine is operating thanks to the fact that the exhaust gas then generates the necessary temperature in the filter bodies. However, when the engine is not operating, the necessary temperature is obtained by external heat energy supplied by means of the heaters. In the inlet conduit to the socket 16 or even in the socket proper an air inlet controlled by a solenoid valve may be provided said solenoid valve being energized to open the air inlet when the heaters are energized. In that case air will be drawn through the filter bodies from the air inlet by chimney action, and this air is sufficient for burning off soot coating, if any, when the engine is not operating. However, more air may be supplied if necessary through the air inlet by connecting said inlet to an air accumulator or a compressor.
The filter of the invention combines three functions: particle separation, catalytic exhaust cleaning and noise silencing. As far as the particle separation is concerned, the filter is so effective that the exhaust gas discharged from the filter is sufficiently clean to be mixed with the inlet air of the engine in a manner known per se in order to reduce the NOX content, necessitating that the exhaust gas does not contain particles which can be detrimental to the engine. With regard to the particle separation the filter is self-regenerating. The catalytic exhaust cleaning is obtained at the down stream end of the filter where CO and CH are burnt catalytically. The noise silencing as such is not sufficient so as to make the conventional silencer superfluous but provides a substantial improvement of the noise silencing.
In the embodiment described four filter elements 20 are provided but depending on the output power of the engine to which the filter is to be connected a greater or lower number of filter elements may be provided in a suitable configuration. Filters for different output power values thus can be designed by using a suitable number of identical filter elements 20.
In the embodiment of the filter shown in FIGS. 6-8, the inlet chamber 13 is defined by a semicylindrical tray 27 and the lower partition 12, which is secured to the tray at flanged end walls 28 to cover the open top of the tray. One end wall is provided with the inlet connection socket 16 and the other end wall is provided with a socket 29 for mounting an electric heater (not shown) in the inlet chamber in a similar way as shown in FIG. 1. The outlet chamber 15 is defined by an inverted semi-cylindrical tray 30, having flanged end walls 31 and an outlet connection socket 32, and the upper partition 14 which is secured to the tray at the end walls to cover the open bottom of the tray 30.
Two filter bodies 21 of the type shown in FIG. 4 but having no mat and no envelope which is clamped around it, are mounted between the partitions 12 and 14. Each filter body is housed in a cylindrical tube 33 forming a spacer between the partitions which are tied together by means of bolts 34 and nuts 35 with the tubes clamped therebetween. The filter bodies are located between circular flat gaskets 36 of an elastic material, which are compressed between the partitions and the end surfaces of the filter body such that the filter body is securely positioned within the surrounding tube. Thus, it will be seen that the inlet and outlet units of the filter are secured together by means of the tie bolts with the filter bodies mounted therebetween. Apertures 37 in the partitions register with the filter bodies.
The filter has an outer casing 38 comprising two halves as indicated in FIG. 8, and as in the embodiment described with reference to FIGS. 1-5 the body formed by the inlet and outlet units and the tubes therebetween shall be covered by heat insulating material enclosed by the casing, which can be secured to the flanged end walls by screws or other fasteners which allow the casing to be easily removed for inspection or replacement of the filter bodies. An important advantage of the embodiment in FIGS. 6-8 is that the filter bodies can be easily replaced if they crack or break.

Claims

1. Exhaust filter for compression ignition engines having a heat-insulating enclosure (10, 11) and substantially vertically extending parallel passages (22) some of which are connected as inlet passages to an inlet chamber (13) at the bottom and others are connected as outlet passages to an outlet chamber (15) at the top, said inlet and outlet passages being separated by porous walls coated with a catalyst, an electric heater (18) for regeneration of the filter being provided in the inlet chamber below the inlet passages, characterized in that the filter is separated into two or more individual and identical substantially cylindrical filter bodies (21) each of which is enclosed by a surrounding metal sheet envelope (23), and that each filter body is mounted between apertures (25) in partition walls (12, 14) defining the inlet chamber and the outlet chamber, respectively.

2. Filter as in claim 1 wherein a heat-insulating material (26) is provided between said partition walls (12, 14) in the spaces between the filter elements (21).

3. Filter as claimed in claim 1 or 2 wherein the envelope (23) of each filter body is clamped around the curved surface of the filter body, a ceramic mat (24) being positioned between the envelope and the filter body.

4. Filter as claimed in claim 3 wherein the envelope (23) is attached to the edges of said apertures (25).

5. Filter as claimed in claim 1 or 2 wherein the filter body (21) is received by a metal tube (33) and wherein the inlet and outlet chambers are defined by separate units which are tied together against the ends of the tubes located as spacers therebetween, resilient gaskets being positioned between the end surfaces of the filter body and said units.