Note: Descriptions are shown in the official language in which they were submitted.
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~U'l'OMATIC INITI~ION SYSTEM
R~G~NE~ATING A PARTlcur.ATE ~'ILT~R TK~
rl'he invention relates to the technology o~
regenerating a particulate trap used to celnove particu-
lates from the exhaust gases of an automotive internaLco~bustion engine and, more particularly, to the metho(l
and apparatus foc more effectively initia~ing the reyen-
eration cycle. This application is an irnprovement rela
ted to the disclosures, by the same inventors, in co-
pending Canadian patent applications Serial No. 466,695filed October 31, 1984, Serial No. 466,700 filed October 31,
1984, and ~erial No. 467,642 filed November 13, 1984.
~ articulate emissions fcom an engine can be
ceduced with a pacticulate filtec trap and a regeneration
system to eeciodically clean the filter tcap of pacti-
culates by incineration. Generally, durable and accept-
able filter particulate traps have been developed by t~le
art which have included wire mesh (see U.S. patent
3,~99,269~ and, more advantageously, rigid ceramics,
perferably in a honeycomb monolithic cellular wall struc--
ture (see U.S. patents 4,276,0'~1: 4,329,162; and
4,3~0,~03)-
Ceramic monolithic honeycomb celled filtee trapshave shown 60-80% particulate collection e~ficiency ~OL
applications in diesel powered passenger cars and light
and heavy duty trucks. The collection of particulates in
the filter trap results in an increasing exhaust gas back
pressure with mileage accumulation. ~ter a relatively
short driving period, which depends on the filter trap
volume and particulate level entrained in the exhaust gas
flow, the ~ilter trap will requiee regeneration to mini-
mize the loss in fuel economy and performance associated
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1;2S~7~3
with the increased exhaust gas back pressure. ~cyenera-
tion is accomplished by raising the tempera~ure o~ the
particulates on the inlet face o~ the ~ilter trap to
approximatel~ 1200F using a ~uel ~ed burner or electri-
cal heating system.
Previously published schemes used to initiatc
regeneration have all used a manually operated triggeL
which, of course, can lead to inadequate regeneration,
the operator failing to initiate the regeneration systcm
precisely when it is needed. One attempt to p~ovide an
automatic initiation system is disclosed in our Canadian
Patent no. 1,216,200. Such system uses an on-board com-
puter system together with a differential pressure sensor.
The computer memory contains an entire map of the clean
trap back pressure as a function of engine speed, load
(fuel delivery), and exhaust temperature. A differential
pressure sensor is used to provide the actual instantaneous
pressure drop across the trap. This instantaneous trap
pressure drop is compared with the clean trap pressure drop
at the instantaneous engine speed, load, and exhaust tempera-
ture. If the trap pressure drop is greater than the
specified multiple of the clean trap pressure drop, then
regeneration is automatically initiated.
This system is complex and expensive because it
requires a memory of clean trap pressures at various
speed, fuel delivery, and exhaust temperature combina-
tions. It would be of significant technical help if the
- need for an on-board computer could be eliminated while
still providing for an automatic initiation of the
regenerative apparatus according to the needs of the
filter trap.
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The invention is a method and appaLatus ~OL
initiating the energization of a regeneration apparatus
used with a particulate filter trap having a porosity
effective to extract particulates from the exhaust gas
10w of an internal combustion engine.
The method comprises: (a) sensing the actual
pressure drop across the ~ilter trap placed in the flow
of exhaust gases; (b) sensing the actual pressure dcop
across a simulative filter structure also placed in the
flow of exhaust gases, the simulative filter structuce
having a porosity effective to allow the passage of
particulates therethrough; (c) comparing the sensed value
of (a) to the product of the sensed value of (b) and a
reference multiple needed to make the pressure values
equal when the filter trap is free o~ pacticulates, (d)
converting such ratio to an electric signal; and (e)
using the electrical signal to cont~ol energization of the
regeneration apparatus when the signal exceeds an allowable
electric signal limit.
Preferably, the method: (1) conver~s the sensed
pressure to a proportional voltage signal and uses an
allowable limit in the range of 2-8 volts for said elec-
tric signal; (2) carries out conversion of step tc) by
use of pressure transducers and a voltage dividing device
effective to compare voltage signals of each of the
sensed pressures to generate the electrical signal pro
portional thereto; (3) has the filter trap and simulative
filter structure each fabricated from a monolithic cera-
mic honeycomb celled material; and ~4) stations the
simulative filter structure downstream from the ~ er
trap a distance advantageously in the ranye of .2-10
inches.
The apparatus for initiating regeneration com-
prises: (a) a simulative filter structure, in the e.Yhaust
gas flow, having a porosity effective to permit the
passage of substantially all particulates therethrough:
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(b) means to sense the actual pressure drop across the
filter trap and to sense th~ actual pressure drop across
the simulative filter structure; (c) transducer means for
ratioing the actual pressure drop across the filter trap to
the actual sensed pressure drop across the simulative filter
structure multiplied by a reference multiple needed to make
the pressure values equal when the filter trap is free of
particulates and for converting the ratio to an elec~rical
signal; and ~d) ~imit means permitting the electrical signal
to control the energization of the regeneration system when
the voltage ratio exceeds an allowable electrical signal.
The invention is described further, by way of
illustration, with reference to the accompanying drawings,
in which:
E'igure ~ is a schematic diagram of an au~omo~ /e
~ilter trap and cegeneration system employing the princi-
ples of this invention; and
~ 'igure 2 is an enlacged schematic diagcam o~ the
filtec trap, simulative filter structuce, and pcessure
sensor/transducer apparatus used to obtain the automa~ic
initiation of this invention.
In this invention, automatic initiation of the
regenecation apparatus is achieved without an on-board
computer and without sensors to monitoc engine speed,
fuel delivery, and exhaust gas temperatuce. ~ simple,
open channel, cecamic honeycomb celled filter-like struc-
ture C-l is disposed in the exhaust gas flow to simulate
a clean filter trap undec all operating conditions. The
simulative filter structure has a porosity sufficiently
lacge to permit the passage of substantially all
pacticulates therethrough at all times. ~'hus, when the
pressure drop across such simulative filter structure is
sensed and compaced to the actual pressure drop across
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the filter trap, a proportioned signal can be generated
which is indicative of the actual particulatc loadiny in
the filter trap B under any operating condition. When
such signal exceeds an allowable limit, it can be used 1o
initiate or trigger the regeneration cycle. l'he in-
vention provides for a more fail-safe method of
initiation and provides a more simple and economical
initiation system that is easier to ~abricate.
Mel:hod
The method comprises essentially the following
steps (refer to Figure 2).
l. The actual pressure drop (~P trap) across
the ~ilter trap ~3 is sensed by pressure probes 60 and 6l
stationed in the exhaust gas flow and respectively imme-
diately upstream and immediately downstream of the filter
trap body lO. The difference in se~sed pressure by each
of the probes 60 and 61 is compared in pressure trans-
ducer 62 (carried in a control box A-4 contained remote
from the filter trap).
2. The actual pressure drop (~P reference)
across a simulative filter structure C-l, disposed in the
exhaust gas flow (here shown stationed upstream ~rom the
~ilter trap body 10 a distance preferably in the range of
.2-10 inches), is sensed by pressure probes ~4 dnd 60
stationed respectively immediately upstream and down
stream of the structure C-l. The simulative structure
has a porosity effective to allow the passage of substan-
tially all particulates therethrough. The difference in
sens~d pressures by each of the probes 64 and 60 is
compaeed in pressure transducer 65 (also carried in
control box A-4 remote from the filter trap).
3. The pressure drops are converted to propor-
tional voltage signals; the voltage signal for ~P trap is
eatioed or compared to the product of the voltage signal
for the pressure drop ~P reference and a reference multi-
ple (K) determined as the factor necessary to make the
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pressure drop values equal when the filter trap is free
of particulates.
4. This voltage signal ratio is used to conteol
the energi%ation of the regeneeation aeparatus ~ when the
signal exceeds an allowable signal limit. The allowable
limit is preferably in the range of 2-8 volts.
APPara~us
The basic apparatus components, by which the
method is carried out, broadly includes (see ~'igure l): a
regeneration apparatus A comprising an exhaust flow
diverting means A-l, a heating means ~-2, means providing
an oxygen carrying heat transfer medium A-3, and a con-
trol means A-~; a filter trap B; and a regenerative
initiating apparatus C comprising a simulative filter
structure C-1, pressure drop sensors C-2,
transducer/voltage ratioing means C-3, and comparator
means C-4.
The filter trap B has a monolithic cerami~
honeycomb celled body lO suppocted and contained in a
metallic housing 11, the front portion of the housing ~la
guiding the flow of exhaust gases from channel 12 through
the Eront face lOa of the monolithic filter trae. The
monolithic ceramic honeycomb celled body may be similar
to that used for carrying a catalyst material for conver-
sion of gases from a gasoline engine. The monolithicbody contains parallel aligned channels 13 (shown in
Figure 2) constituting the honeycomb cells. l'he ends o~
the channels are alternately blocked with high tempera-
ture ceramic cement at the front and at the rear so that
all of the inlet flow gas must pass through the porous
side walls 16 of the channels 13 before exiting through a
rear opened channel of the filter tcap. The side walls
have a ~orosity small enough and effective to extract
particulates from the exhaust gas flow o~ the internal
combustion engine. This type of monolithic ceramic body
provides very high filtration surface area per unit of
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volume. For example, a ll9 cubic inch filter tcap of
this type with lO0 cells per square inch and .017 inch
wall thickness will provide auproximately 1970 square
inches o filtering surface area, and the filtering
surface area per unit volume for such a filter trap would
be about 16.6 square inches per cubie inch. ~'he channels
are all preferably aligned with the direction o~ the ~low
l/ through the trap. When the pacticulates collect on
the trap, they will nest within the porosity of the walls
which ace spaced along the direction of ~low. Thus,
there can be a generally uniform distribution of
particulates along the length of the trap. Prefecably,
the monolithic structure has an oval cross-section with a
large frontal face lOa of 24-33 square inches, the axes
of the oval preferably have a dimension of ~-5 inches and
'/-8 inehes, respectively.
~ 'he exhaust flow diverting means ~-l o~ the
regeneration apparatus A comprises a bypass channel 1~
defined here as a conduit effective to carry the exhaust
gases from diesel engine exhaust manifold 14 around the
filter trap B. The exhaust flow in channel 12 is divec-
ted from communicating with the ~rontal interior 15 of
the ~ilter trap housing by a diverter valve assembly: the
diverter valve may be a poppet type valve 19 actuated by
a vacuum motor Z0 to move the valve from a normally
biased position, closing off communication with the
bypass channel 18, to an actuated position where the
valve closes off communication with the frontal interior
space 15 oL the filter trap housing. The vacuum motor Z0
is electrically actuated under the con~rol o~ means A-4.
The heating means A--2 comprises essentially one
or more electrical resistance elements 21, and related
~low control elements which are disclosed more fully in
copending Canadian application Serial No. 466,700, invented
by the inventors herein and assigned to the applicant
herein.
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The electrical resistance elements 21 pre~er-
ably are sheathed nickel chcomium wice elements encased
within magnesium oxide powder contained by the sheath.
The elements ace sized to have a resistance heating
capacity sufficient to raise the tempecatuce o~ a low
flow of heat transfer medium to a temperature o~ about
L100F within a period of 1.5-3.5 minutes. The heating
element surface temperatuce itself will reach 1~00~'
during this périod. The elements receive electcica~
lQ energy from an engine driven alternator 22, the supply o~
energy being unregulated to facilitate obtaining t~le
necessacy a~ount of electrical energy. The elements are
characterized by the ability to provide satisfactoLy
heating with 800-1750 watts at 20-80 volts, each element
having a resistance of about 2.4 ohms. Each of the
electrical resistance elements may be preferably con~i-
gured as a spiral, contained in a common plane, extending
transversely accoss the direction of flow of th~ heat
transfer medium. The configured heating elements ace
supeorted in a secure position by ceramic holding sleeve
assembly received in the metallic housing wall lL.
After the heating elements have been heated to
about 1400F (surface temperature), following initiation
of the regenerative cycle, oxygen carrying fluid medillm
(air) is injected by an air pump means A-3 through the
heating means A-2 and the filter trap body 10 to transfec
heat therebetween and support incineration o the parti-
culates in the absence of the diverted exhaust gas. The
air pump means is electronically ac~uated by control
means A-4 at an appropriate time interval.
The control means ~-4 responds to a tcansmi~ted
signal from the initiating apparatus C to actuate several
timed electrical events in sequence. The timed events
include: (1) actuating the vacuum motor 20 to operate the
35 bypass valve 19 substantially simultaneously with the
closing of a circuit to energize the heating elements 21:
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g
(2) closing a circuit to energi%e an air pump motor ~3 of
air pump means A-3 to transmit a supply of air through
conduit 24 to the frontal interior space 15 of the filter
trap after the heater elements have attainéd a su~Lace
temperature of about 1400F; (3) interrupting the supply
of electcical energy to the heating elements after about
one-half of the total oxidizing cycle time has elapsed
(which would translate to about four minutes for a pre-
feeable cycle time of eight minutes hece); and (4) cessa-
tion of the air pump means and deactivation of the diver-
ter valve at the completion of the ull oxidizing cycle
time or when the oxidation of the particulates is stabil-
i~ed and self-sustaining.
The regenerative initiating apparatus comprises
ceramic honeycomb celled structure C-l which is disposed
in the exhaust gas flow upstream from the ceramic honey-
comb celled filter trap B, but preferably closely spaced
to the filter trap. The spacing can be as close as .2
inch, sufficient to permit insertion of a pressure probe
therebetween or as distant as several inches, preferably
up to 10 inches, provided the stcucture A-l is exposed to
only the exhaust gas flow. ~lowever, greater spacing than
10 inches may allow temperature dif~erences between the
exhaust gas passing through the filter trap and through
the simulative structuce to affect accuracy of the sens-
ing system. The simulative filter structuce can be
constructed of the same monolithic structure used to
fabricate the filter trap, but having an open channel
porosity, that is, a porosity which is effective to
permit the passage of substantially all earticulates o
engine exhaust gas therethrough.
The simulative structure may alternatively be
part of a catalytic regeneration fuel burner. Although
illustrated as located upstream from the filter trap, the
structuce can also be located downstream with similar
satisfactocy sensing results. The structure A-l is shown
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as a thick disc spanning across the flow channel section
25 to ensure that all of the exhaust gas ~low passes
therethrough to obtain a reliable pressure dcop reading.
The pressure drop sensors C-2 can ba of conven-
tional construction such as thin tubes which have an open
ended probe (60-61-6~) inserted into the flow which is tG
be sensed. The instantaneous pressure is transmitted
along such probe tube with approximately the speed of
sound to receiving pressure transducer/voltage ratioin~J
means C-3. Probes 60 and 61 are needed to sense the
pressure differential (pressure drop ~P trap) across the
filter trap, and probes 64 and 60 are needed to sense the
pressure drop (~P ceference) across the simulative struc-
ture. The pressure transducers 62 and 65 can be of
conventional capacitancé typé construction ef~ective to
convert a pressure differential to a proportional voltage
output as an electric signal. The voltage signal fcom
t-he transducer 65 is multiplied by a fixed constant value
(determined at the factory) by use of a conventional
voltage multiplier device to ensure chat the ~P trae
and ~P reference are equal when the filter trap is
clean. The multiple factor is prefecably in the range of
10-20, but is dependent on the size of the filter trap,
resolution capabilities of the transducers, and the
degree of porosity in the simulative filter structure.
The multiple factor can be determined by an empirical
cold air flow test at the factory using the actual co~
ponents of the system. Pressure transducers would sepdr-
ately measure ~ trap and ~ reference; if, for example,
trap read 10 and reference was 1.0, then the multiple
factor would be selected as 10. The voltage signals ace
then divided by a conventional electronic device caeable
of dividing two input voltages to ~roduce a cesultant
output voltage which will be indicative of trap parti-
culate loading.
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The divided oc ratioed voltage signal is s(:ruti-
nized by a comparator ci~cuit C-~ to detèrmine i~ it
exceeds a predetermined allowable limit before it is use-l
to control ene~gization o the regenerative apparatus by
cont~ol means A-4. The allowable limit is prefe~ably in
the range of 2-8 volts, which means that the back pres-
sure in the filter trap can be as little as twice the
pressure drop when it is clean, or the back pressure in
the ilter tcap can be as much as eight times the clean
trap back pressure before initiation occurs. I~ an
allowable limit greater than eight times is used ~or
initiation, a dangerous condition may be created, whereby
the exothermic reaction during particulate oxidation may
thermally af~ect some portions of the apparatus.
The transducer/ratioing means C-3 and comparator
ciccuit, as well as the control means ~-4, are located in
a non-hostile environment such as under the dashboard of
the automotive passenger compartment.
Monitoring the re~erence pressure drop across
the open channel ceramic honeycomb structure C-l ~ill
always provide a signal proportional to the clean trap
pressure drop for the instantaneous exhaust flow rate.
Dividing the actual trap pressure drop by the product o~
a constant and the reference pressure drop, will pLovide
an electrical signal proportional to trap loading and
which trap loading signal is independent of engine speed,
fuel delivery, and exhaust temperature. Thus, when the
trap loading is greater than the allowable limit, an
electrical signal will be provided to start the oxidi~in~
3a or regeneration process.
