Monolith diesel exhaust filter with self-regeneration

A self-regenerating diesel engine exhaust particulate filter comprising, in a preferred embodiment, porous ceramic walls defining filter surfaces between adjacent inlet and outlet passages and having electric heating wires in the inlet passages to periodically initiate incineration of collected particulates therein. A movable shield is preferably provided to restrict gas flow through the various passages during their respective periods of incineration so as to provide periodic regeneration with a minimum expenditure of external energy.

TECHNICAL FIELD 
This invention relates to diesel engine exhaust particulate filters and, 
more particularly, to wall-flow monolith-type filters including means for 
self-regeneration through the periodic incineration of particulates. 
BACKGROUND 
As a result of recent efforts to develop practical means for removing 
particulates from diesel engine exhaust gases in automotive vehicles, it 
has been found that wall-flow ceramic monolith filters can provide very 
efficient filtration of diesel exhaust particulates with relatively low 
pressure drop. U.S. Patent application Ser. No. 99,933 filed Dec. 3, 1979 
in the names of Morris Berg, William Johnston and Carl Schaffer and 
assigned to the assignee of the present invention, discloses examples of 
such ceramic monolith filters. 
While such filters have been shown to be highly effective in the collection 
of diesel exhaust particulates, it appears that the volume of particulates 
collectable from diesel engine exhaust products requires that exhaust 
filters be replaced or regenerated at frequent intervals if the size of 
the filter elements is limited to volumes presently considered practical. 
Thus, to avoid the need for frequent servicing of such a system it appears 
desirable to provide means for periodic regeneration of the filter element 
by incineration of the collected exhaust particulates at intervals during 
normal operation of the vehicle. 
To accomplish this, it has been proposed that exhaust gases passing into 
the filter be periodically heated to the particulate ignition temperature. 
A suggested manner of such heating is the method of engine throttling 
proposed in U.S. Patent application Ser. No. 952,710, filed October 19, 
1978, in the names of Otto Ludecke and Theodore Rosebrock, and assigned to 
the assignee of the present invention. However, tests have indicated that 
incineration of particulates in porous wall-flow ceramic monolith filters 
by inlet gas heating would be difficult to initiate and to complete. In 
addition, other proposed methods of heating would apparently require a 
very large expenditure of outside energy. 
SUMMARY 
The present invention provides arrangements for self-regenerating 
monolithic diesel exhaust particulate filters which provide means for 
periodic incineration of particulates with a reasonable expenditure of 
energy. The invention contemplates the provision of individual electric 
heating wires or elements in some or all of the inlet or other passages of 
a monolith filter. The heating wires are selectively energized at periodic 
intervals to initiate and complete incineration of particulates in their 
respective passages and possibly also in adjacent passages. The selective 
operation of the various heating elements limits the amount of electric 
power required and permits, if desired, continuous operation of the 
incineration system to occur sequentially in various portions of the 
element. Preferably, a shield is provided for restricting exhaust flow 
through those passages in which regeneration by incineration is occurring 
so that the heat is more effectively utilized and a reduced expenditure of 
energy is required. 
These and other features and advantages of the invention will be more fully 
understood from the following descripton of certain preferred embodiments, 
taken together with the accompanying drawing.

BEST MODE DISCLOSURE 
Referring now to FIG. 1 of the drawing, numeral 10 generally indicates a 
self-regenerating diesel exhaust particulate filter formed in accordance 
with certain principles of the invention. Filter 10 includes a ceramic 
monolith body 12 having a plurality of interconnecting porous internal 
walls 14. The walls define square cross-sectioned parallel passages, the 
alternate ends of which are plugged by end walls 16, 18 to define a 
plurality of adjacent inlet and outlet passages 20, 22, respectively. In 
the figure, the sizes of the passages are shown greatly enlarged relative 
to the apparent size of the filter body and are intended only to be 
representative of ceramic monoliths of the type described in the 
previously mentioned U.S. Patent application Ser. No. 99,933. 
The filter 10 further includes electric heating means in the form of 
resistance rods or wires 24 for periodically heating and incinerating 
collected particulates on the porous wall surfaces of the inlet passages 
20. These heating rods or wires are arranged to extend longitudinally 
through certain of the inlet passages 20 and to connect at their opposite 
ends with electric conductors 26 and 28 which are respectively connectable 
to the opposite poles of an electric power source, such as a battery (not 
shown). 
If desired, groups of selectively energized heating wires may be arranged 
to extend through all of the inlet passages for individually heating each 
of the respective passages. However, in the arrangement of FIG. 1, the 
wires are shown extending only through alternate rows of the inlet 
passages. It should be understood that suitable switching means may be 
provided to selectively energize any of the groups of heating wires by 
connecting the conductors 26 and 28 of the respective group with the 
battery. 
In operation, the electrically self-regenerating exhaust filter is disposed 
within a suitable housing in the exhaust system of a diesel engine powered 
vehicle. Exhaust gases from the engine are directed into the open ends of 
the inlet passages 20 from which they pass through the porous walls 14 to 
the outlet passages 22, escaping through the open ends thereof to an 
exhaust pipe (not shown). Particulates filtered from the exhaust gases 
collect on surfaces of the porous walls 14 which face into the inlet 
passages and, eventually, the collection of particulates in the respective 
passages build up to a point where gas flow is impeded. 
Self-regeneration of the partially plugged filter is accomplished by 
sequentially energizing the various groups of electric heating wires, one 
group of heating wires being energized at a time in order to limit the 
amount of electrical energy required to a practical value. The energized 
heating wires raise the temperature of their respective inlet passages to 
a value between about 850.degree. and 1500.degree. F. in order to provide 
ignition and complete incineration of the particulates collected on the 
passage walls. 
In the arrangement of FIG. 1, the transfer of heat from the directly heated 
intake passages to the adjacent intake passages through conduction is 
required since all of the passages are not provided with heating wires. 
However, it has been found that such heat transfer is possible within a 
limited area around each heating element. After regeneration of the 
passages surrounding one group of heating wires, the next group of wires 
is energized and the process continues until the whole filter unit is 
regenerated. 
Referring now to FIG. 2 of the drawing, numeral 30 generally indicates an 
alternative embodiment of exhaust filter in accordance with the invention. 
Filter 30 includes a ceramic monolith body 32 constructed in generally the 
same manner as that of the body 12 of FIG. 1. Thus interconnecting porous 
internal walls 34 define parallel passages alternately closed by end walls 
36 and 38 to provide alternate inlet and outlet passages 40 and 42, 
respectively. 
The inlet passages of filter 30 are provided with heating elements in the 
form of rods or wires 44 which connect at the outlet end of the filter 
with conductors 46 connected with a source of electrical power, such as a 
battery 48. 
At the inlet end of the filter, the heating wires 44 terminate near the 
filter face in electrical contacts 50. These contacts are engageable by a 
pie-shaped shield 52 that is mounted on one end of a rotatable shaft 54. 
At its other end the shaft is fixed to a gear 56 that is driven through 
another gear 58 by an electric motor 60. The shaft 54 and pie-shaped 
shielf 52 as well as the motor 60 are connected with the battery 48 which 
provides them with electrical power. 
In use, the filter 30 and its associated components are installed in a 
suitable housing in the exhaust system of a diesel engine-powered vehicle. 
During engine operation, exhaust gas flows from the inlet passages 40 to 
the outlet passages 42 through the porous walls 34, leaving exhaust 
particulates collected on the inlet passage sides of the walls. 
Continuously or periodically during engine operation, the electric motor 60 
is energized to rotate the shield 52 which is charged by the battery 48. 
As the shield rotates, it periodically engages the contacts 50 on the ends 
of various heating wires 44, completing electrical circuits from the 
battery through the shaft 54 and shield 52 to the engaged heating wires 44 
and back to the battery through the grounded conductors 46. Concurrently, 
the shield 52 blocks much of the flow of exhaust gas through the 
particulate inlet passages in which the energized heating wires are 
located. Thus less of the heat generated by the heating wires is carried 
away by flowing exhaust gas and more is absorbed by the passage walls. In 
this way, these collected particulates are more rapidly ignited and 
incinerated with a lesser expenditure of energy. Continued operation of 
the motor rotates the shield around the complete face of the filter 
element, thus sequentially providing for shielded incineration of the 
particulates in all of the inlet passages. 
While the invention has been described by reference to certain specific 
embodiments chosen for purposes of illustration, it should be understood 
that details of construction and form of the illustrated figures are 
intended to only represent some of the many ways in which self-cleaning or 
regenerating exhaust particulate filters may be constructed in accordance 
with the principles of the present invention. Since numerous changes may 
be made without departing from the disclosed principles, it is intended 
that the invention not be limited to the embodiments illustrated, but that 
it have the full scope permitted by the language of the following claims.