CA1260407A - Regenerative filter trap system with apparatus for diverting the exhaust gas flow - Google Patents

Abstract

ABSTRACT
A system is disclosed for extracting parti-culates from the exhaust gas flow flow an internal com-bustion engine for an automobile by the use of a filter trap stationed adjacent a heat controlled zone of the automobile, and which system periodically cleanses the filter trap of the particulates. The system has an apparatus which channels the flow of the exhaust gas between a condition where the exhaust gas is carried through at least a portion of the filter trap for an extraction mode and a condition where the exhaust gas is diverted away from said portion of the filter trap during a cleansing mode of said portion. The apparatus com-prises: (a) walls defining a primary flow channel for normally guiding said exhaust gases through at least a portion of said filter trap, the walls comprise a roof juxtaposed said zone: (b) means defining a diversion flow channel for diverting the exhaust gases away from said portion during the cleansing mode, the diversion flow means being superimposed on the roof of said walls to normally insulatingly separate the primary flow channel from said zone; and (c) flow diverter means for directing the flow of exhaust gases through said primary flow channel and through the diversion flow channel.
The walls defining the primary flow channel Comprises a tube with an expanding conical inlet section, the tube having a cross-section with a height no greater than substantially one-half of its horizontal dimension, the top of the tube forming said roof. The roof pre-ferably extends horizontally and the diversion flow channel is defined by a wall extending across the roof to form the diversion flow channel therebetween.

Description

i2~07 REGENERATIVE FILTER TRAP SYSTEM WITH
APPARATUS FOR DIVERTING THE EXHAUST GAS FLOW

The invention relates to the technology of using filter traps for extracting particulates from the exhaust gases of an internal combustion engine and, more particularly, to an improved apparatus for channeling the exhaust gases to a given zone of the particulate collection and away from such zone during regeneration. This application is an improvement related to co-pending Canadian patent application Serial No. 466,695 filed October 31, 1984 directed to apparatus that permits electrically energized regeneration to take place with less electrical energy input, and to co-pending Canadian patent application Serial No. 466,700 filed directed to an electrical heating assembly, both by the same inventors.
Particulate emissions from an engine can be reduced with a particulate filter trap and a regeneration system to periodicaily clean the filter trap of particulates by incineration. Generally, durable and acceptable filters for particulate traps have been developed by the art, which have included wire mesh (see U.S. Patent 3,499,269) and, more advantageously, rigid ceramics, preferably in a monolithic honeycomb cellular wall structure (see U.S. patents 4,276,071;
4,329,162; and 4,340,403).
It is important that the filter trap be cleansed periodically during vehicle operation. The prior art has heretofore envisioned that such filter traps can be cleansed by a variety of proposals, all of which have included ~ raising the temperature of a gas flow through ~:~

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Patents 4,167,852; 4,211,675 and 3,499,269), or have included heating a separate heat transfer medium, such as air, by electrical means or by fuel fed burners (see U.S. Patents 4,270,936; 4,276,066; 4,319,896 and Japanese Patent 55-19934).
During vehicle operation, the exhaust gas flow emanating from the engine operation presents a significant heated gas flow having a pressure in the range of 2-15 pounds and a temperature in the range of 200-1150F. The exhaust gas flow typically is laminar as it passes along a tubular exhaust pipe. An important strategy to achieve reliable regeneration, disclosed in applicants' copending U.S. application Serial No.
463,688, is to divert the exhaust flow away from at 20 least a first portion of the filter trap while such first portion is cleansed of the particulates that may have collected there. During such exhaust gas flow diversion, several problems have become evident with respect to providing a diverting apparatus, such 25 problems include: (a) insulating the filter trap from the vehicle particularly during regeneration; (b) minimizing the overall height of the filter trap assembly and bypass passage, while eliminating the need for other exhaust treating devices such as a muffler;
30 and ~c) assuring economical construction with ease of assembly. It would be desirable if an apparatus for channelling exhaust gas flow could be devised which solves the above-listed problems.
In accordance with the present invention, there is 35 provided a system for extracting particulates from the exhaust gas flow from an internal combustion engine for an automobile having a heat-controlled zone, comprising (a) a filter trap stationed adjacent the heat B controlled zone of the automobile; (b) means for , .

lZ~V;~(~7 periodically thermally cleansing the filter trap of the particulates; (c) walls defining a primary flow channel for normally guiding the exhaust gases through at least the portion of the filter trap, the walls comprising a roof juxtaposed the heat controlled zone; (d) means defining a diversion flow channel for diverting the exhaust gases away from the primary flow channel, the diversion flow means being superimposed on the roof of the walls to normally insulatingly separate the primary flow channel from the heat controlled zone; and (e) flow diverter means for directing the flow of exhaust gases selectively through either the primary flow channel for a particulate extraction mode, or through the diversion flow channel during a cleansing mode of the filter trap.
Preferably the walls defining the primary flow channel comprises a tube with an expanding conical inlet section, the tube having a cross-section with a height no greater than substantially one-half of its horizontal dimension, the top of the tube forming the roof.
Advantageously, the tube may be formed with a cross-section defined as the outer periphery of two spaced circular sections connected by rectangular section. The roof of the tube preferably flat extending horizontally and the diversion flow channel is defined by a generally flat wall extending over and across the roof to form the diversion flow channel therebetween.

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V ~V7 Preferably, the means for defining the diversion flow channel comprises a single ply, U-shaped wall ex-tending across the roof and having a cross-section area with a width to height ratio in the range of 5/1 to 20/1.
Preferably, the means defining the diversion flow channel comprises baffles to muffle the sound of gas flow therethrough during the cleaning mode, the filter trap functioning to muffle gas flow sounds during the extraction mode.
The invention is described further, by way of illustration, with reference to the accompanying drawings, in which:
Figure I is a schematic illustration of an automotive diesel engine and exhaust flow including the improved apparatus embodying the principles of this invention;
Figure 2 is an enlarged elevational view of the filter trap and flow control means effective to channel the exhaust gas between various operative modes;
Figure 3 is a top view of the apparatus of Figure 2;
Figure 4 is a sectional view taken substantially along line 4-4 of Figure 2; and Figure 5 is a longitudinal sectional view of a portion of the housing for the filter trap taken along line 5-5 of Figure 4.
The apparatus employed channels the flow of the exhaust gas between a condition where the exhaust gas is carried through the filter trap for an extraction mode and a condition where the exhaust qas is bypassed around the filter trap for a trap cleaning mode. The bypassed flow of exhaust gas is channeled as a generally flat layer along the roof of the filter trap housing to serve as a thermal insulation body between the heated filter trap during regeneration and the heat controlled zone of ~'.
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12~()40'7 the automobi le . To o~nhance l:he use oL the bypas~l~d exhau~t gas as an insulation barriec, the filt~r trdE) is pcovided with a cross-section having a height substantially less than the horizontal dimension; co enhance the use of the apparatus as a substitute to~ the conventional sound muffler on ~he a~tomobile, the bypa:is channel has ba~fles to secve as a muftlec during the cleaning mode while the ~iltec trap serves as a muf~le~
during the extraction mode.
Turning to E'igure 1, the system with which this invention is associa~ed comprises a diesel enyine ~
having intake and exhaust mani~olds 10 and 11, d long wi~h a dciven output membec 12. The stream o exhaust gases is cacried fcom the exhaust manifold 11 o~ the engine by an exhaust channel l3 leading away from t.he engine. 'rhe exhaust channel typically is of a circular cro~s-section promoting streamlined oc laminac flow o~ the exhau~3~
gases, ~'he eiltration system C is interposed in the exhaust channel 13 and includes a eiltec trap C l, a heating means C-2, and a means C-3 for displacing flow o~
exhaust gases with another oxygcn carrying eluid medium during an oxidation cycle of ~he particulates in the filter trap. The displacing means particularly in~ludes an ayparatus 20 for channeling exhaust gas ~low between a condition where the exhaust gas is directed through the particulate filter trap for an extraction mode and a condition where the exhaust gas is divected away from at least a first poetion of the particulate filter tcap during a thermal cleansing mode Oe the ~irst portion.
The sy~tem further includes electrical contcol means C-4 which broadly includes means 21 for initiating the oxi dizing cycle and an electronic timer or control 22 eOr regulating the sequence of electrically actuated events o~ the oxidizing cycle.
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The filtec trap C-~ is a monolithic ceLamic honeycomb cellular structure 15 suppor~ed and contained in walls 23, a metallic housing. The front portion 35 of 5 the housing guides the 10w of exhaust gases through the front ~ace 15a o~ the monolith and the trailing poction 14b of the housing guides the flow of exhaust gases from the filter trap. The trap is stationed adjaccnt a heat controlled zone 43 of the automobile by being hung imrned-iately beneath the passenger compartment. ~he ~ront ~aceof the ~ilter trap has an area which is greater than the cross-sectional area of ~he exhaust pipe 13 by a ratio o~
8:1 to 20:1. The monolithic ceramic honeycomb cellular stcuctuce may be similac to ~tructures used for catalytic 15 convecsion o~ gases fcom a gasoline engine. The mono-lithic structuee contains parallel aligned open channel~
16 constituting the honeycomb cell structure; the ends of the channels are alternately blocked with hiyh tem-pecature ceramic cement at the front and the rear so that 20 all of the inlet flow of gas must pass through the porous side walls 16a of the channels before exiting from the filtec trap. This type of monolithic cecamic structuce provides very high filtration sucface area per unit of volume. For examele, a 119 cubic inch filter trap of 25 this type, with 100 cells per square inch and .017 inch wall thickness, will provide approximately 1970 squace inches of filtering surface area, and the filtering surface area per unit volume or such a filtec tcap would be ab~ut 16,6 square inches per cubic inch. The channels 30 are all aligned with the center line of the exhaust ~; flow, When the earticulates collect on the trap they will nest within the eorosity of the side walls which then will space the particulate collection along the ~ direction of flow. Thus, there will be a general uniform 5 ~ 35 di~tcibution of the pa~ticulates along the length of the ~ tcap, ,"~ ~
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lZ~ 7 Heating Means The heating means C-2, which is disclosed more fully in co-pending application Serial No. 466,700 assigned to the applicant herein, has a heater element assembly comprising resistance elements which are continuous sheathed stainless steel nichrome resistor elements, the elements being configured in a helical fashion, much in the fashion of heating coils for a surface heating unit of a stove, and extend transversely across the flow. The resistance elements are energized by a power supply derived from the battery or alternator of the engine.
The heater element assembly also comprises foraminous plates which function as a flow diffuser, slowing down the flow for better heat transfer. The plates present a screen or grid effect which has at least a 40% open area. A flow mask or disc may also be interposed between the plates and the heating elements to guide the oxygen carrying heat transfer medium (such as air) to a peripheral location along the outer rim of the filter front face. Thus, when the transfer medium flow is sufficiently heated, ignition of the oxidizable particulates will take place substantially along the outer radial region and thus proceed both axially as well as radially inwardly as migration of the flame front proceeds through the particulate collection in the device. The airflow mask blocks off approximately 50% of the filter frontal area which will be at the central region of the flow.
The element assembly may lastly comprise a catalyzed wire mesh located as a foraminous blanket immediately downstream of the heater elements; the mesh is woven and carries a catalyst coating which is a low sulphate S02 active catalyst such as Pt/Rh on ceria

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(see U.S. application Serial No. 466,700. The catalyzed wire mesh functions as a uniform heat transfer medium as well as to lower the temperature required to incinerate or ignite the particulate collection, when there is a significant amount of hydrocarbon occluded in the col-lected soot or particulates, thereby minimizing power requirements and lowering energy consumption. The cata-lyzed wire mesh also functions to collect small amounts of hydrocarbon soot during exhaust gas filtration, which soot is easily ignited and operates to transfer ignition to the particulate collection.
The power supply for the electrical resistance elements may be derived from the alternator of the engine, which alternator should have dual functions, one function being used during regeneration of the filter trap.
Alternatively, an auxiliary alternator may be utilized, driven by a pulley system which in turn is driven by the output member of the engine and may be selectively engaged only during the regeneration period.
An air Pump 63, when energized, drives a flow of air through a tube 64 into and through the heating means and filter when the exhaust gas has been bypassed. The supply of air acts as a heat transfer medium and a supplier of oxygen to ignite and sustain the oxidation cycle.
Exhaùst Gas Channeling Means The apparatus 20 for channeling exhaust gas flow provides for a condition when the exhaust gas is carried into and through the particulate filter trap for an extraction mode, and a condition where the exhaust gas is bypassed away fr~m at least a first portion of the particulate filter trap during a thermal cleansing mode of the particulate portion. Such apparatus 20 comprises walls 23 defining a primary flow channel for guiding the exhaust gases through at least a portion of the filter trap C-l and preferably the entire trap. The walls 23 .

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126~ 7 ~o~m d tub~ enclosing an itlterllal space 2~ which has a cross~section ~lattened along at least the uppe~ side or roof 42 of the tube (see Figure 4). The tube here i5 shown to enclose an internal s~ace having a cross--section with a height 2~ no greater than two-thirds that oC thc width 25, and is particularly defined as ~he outec periphery of two spaced circular sections 26-Z7 connected by a rectangular section 28. The ceramic filter trap C-L
has a cross-section which is designed to snuggly fit within the interior of such primary wall configurati~n.
As shown in Figure 5, the structure 15 of the filtec trap . i5 suppocted within such primary walls 23 by way of WiLe mesh bands 29 wrapped around the ceramic body from i~s front to substantially near the trailing end of the filter trap. The wire mesh bands provide a cushioned su~)~ort within the housing and are inserted in such a manner as to abut against the modified L~rings 30 with a seal ring 31 therebetween. About the trailing pt)rtion 15c of the outer eeriphery of the ceramic filter, is-packed fiberglass rope 32: the rope space is sealinglyclosed by a complimentary L-shaped ring 33, again having a sealing ring 34 compressed therebetween.
The walls Z3 for the primary flow channel define an expanding conical section 35 proceeding from a con--nection 36 to the exhaust pipe 13, such expanding conicalsection 35 providing or a slowing down of the exhaust gas flow prior to entering the filter trap and thereby improving the filtering function. The ratio between the diameter 37 of the throat section at the immediate 3Q entrance to the conical section 35 and the diameter 38 of the frontal section ~Sa of the filter trap is about 1:2 to 1:3.
The apparatus 20 further comprises means defin-ing a diversion flow channel 39 or bypass for the exhaust 35 gases during the thermal cleaning mode. The exhaust gases in channel 39 are diverted away from the trap oc _, "': ~: '-, ' :;

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roo~ 42 of the walls 23 to normally insulatingly separate the primary flow channel from the zone 43. Such ~eans compcises a single ply metallic wall 40 which i.s ~orme~
as an inverted U-section hav;ng its edges 41 sealinyly attached to substantially the extreme ends or edges o~
the flattened roof 42 of the primary walls. The divec-sion flow channel 39 is thereby given a ccoss-section which is effective to function as a thermal insulating air space between the controlled or protected t~mpecdtuLe zone 43 of the automobile and the filter trap C-l.
Prefeeably, the height of such diversion channel 39 provides a width (44) to height (45) catio in the Lanqe of 5/l to 20tl. It is a general requirement for auto-motive vehicle design for catalyst conversion device~that an air space of about l-l/2 inches must be de~ined between the controlled zone of the vehicle and the cata-lytic device itself. Here, such l-l/2 inches of space is occupied by the bypass channel 39, which normally con 2Q tains no gas flow during normal filtec mode operation of the aeparatus. The entire height or silhouette of the filtering system is minimized, thereby making maximum use of the normally required insulation space and deploying it for another purpose.
The diversion flow also contains bafEles 80 Which serve to mufele the sound of the exhaust gas ~low therethrough during the cleaning mode, the filter trap functioning to muffle the sound of exhaust gas ~low during the extraction mode.
The apparatus 20 further comprises means 46 for controlling the diversion of the flow of exhaust gases either through the expanding &ection 35 of the primaey flow channel or through the diversion channel 39. Means , ~ ~
46 particularly comprises a flow diverter member having a pair of valve seats 48 and 49, each seat lying within a :~ plane aligned with the center line of the flow 50 of the , i,~

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12~ 7 e~haust gases. Each valve sedt i~ spaced f~om the other a distance no greater than one inch. rrhe Elow diversion me.lns 46 further comprises a flow diveLtiny valve Sl having a substantially ~lat valve head Sla lying within a plane also aligned with the center line of the exhaust flow 50 and operative to move linearly between a seated position against each of said cespective valve seal.s 48-49. The member is advantageously fabrica~ed as a casting. In an alternative arrangement, the v~lve s~eln can be biased to the dicection of flow at an anqle of about 30-50. The parting plane between casting uarts defining the valve seats will be midway between the valve seats which are aligned with the direction of flow at an angle of 30-60. In this arrangement, the pressu~e of the flow assists opening and closing of the valve head.
The diverter valve 51 in Figure 2 is o~ a poppet design, wherein the valve head 51a, which is of a flat coniguration having its edges provided with a pair of inverted conical sections, is normally biased to eosi~ion against a first of the valve seats (here 4~) to permit the filtration mode. ~n actuator 52, when energized;
~ - moves the valve head 51a to a second position, s~ated ; against the other valve seat (here 49), foe flow through - the bypass channel 39. The actuator 52 of the valve may comprise a vacuum motor effective to apply a orce of ;~ about 15-45 pounds.
:, Electrical Control Means The electrical control means C-4 has the ini-tiator 21, preferably comprised of two pressure sensors /~ 3a or transducers 60 and 61. Sensor 61 is located to sen~e ; the back pressure immediately upstream of the front of the filter trap device which corrolates with the degree ~; of pacticulate collection in the filter. Sensor 60 is ,, ~ placed in an open channel ceramic honeycomb struc- ture ~ 35 62 located considerably up~tream from the filter itself, i~ ~

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L Z -the latte~ containing a porosity which i5 much lacge~
than that oL the ~ilter tcap itself so that none o~ the particuLates will become en~Lapped within the open channel honeycomb ceramic. The pressure sensor 60 loca-ted in or adjacent this honeycomb structure will sense apressuee simulating a clean filter trap. The sensors are each of the capacitance type with a measuLable voltaye output that is a function of the sensed back pressure.
The voltage output is conveyed to an electronic colllpara-10 tor device in the control box 22: the two voltage sigrare ~atioed in the comparator device. When the ratio exceeds a predetermined set maximum, a signal is then relayed within the control box to initiate the regen-ecation or oxidizing cycle. Monitoring the reference 15 pressure drop across the open channel c~ramic honeycomb structure 62 will always provide a signal proportional to the clean trap pressure drop for the instantaneous ex-haust flow rate. Dividing the actual trap pressure dcop by a constant multiplied by the reference pressure drop 20 will provide an electcical signal proportional to the trap loading, which is independent of engine speed, engine load, and exhaust temperature. Thus, when the trap loading is greater than the allowable limit, an electrical signal will be provided to initiate the 25 regeneration process.
The control box 22 has an electronic timer which, when it receives a signal from the comparator, will actuate several timed electrical events in se-quence. The timed events include the following: (l) the 3Q actuator to open bypass channel 39 is energized sub-s~tantially simultaneously with the connection of the heating elements to a power source; (2) the air pump means 63 is actuated to transmit a supply of air to the internal space 24 when the heating coils reach 1400F;
35 (3) disconnecting the power supply from the heater ele-ments at about one-half of the total oxidiziny cycle .

V~07 time; and (4) cessation of the ai.r pump means and de~cti-vation of the divertec valve at the completion of the full oxidizing cycle time oc when oxidation is stable and self-sustaining.

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Claims (7)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A system for extracting particulates from the exhaust gas of an internal combustion engine for an automobile having a heat controlled zone, comprising:
(a) a filter trap stationed adjacent said heat controlled zone of the automobile;
(b) means for periodically thermally cleansing said filter trap of particulates;
(c) walls defining a primary flow channel for normally guiding said exhaust gases through at least a portion of said filter trap, said walls comprising a roof juxtaposed said heat controlled zone;
(d) means defining a diversion flow channel for diverting the exhaust gases away from said primary flow channel, said diversion flow channel being superimposed on the roof of said walls to normally insulatingly separate said primary flow channel from said zone; and (e) flow diverter means for directing the flow of exhaust gases selectively through either said primary flow channel for a particulate extraction mode, or through said diversion flow channel during a cleansing mode of said filter trap.

2. The apparatus as in claim 1, in which said walls defining said primary flow channel comprise a tube having a cross-section with a height no greater than substantially one-half of its horizontal dimension, the top of said tube forming said roof being juxtaposed to said zone.

3. The apparatus as in Claim 1, in which said walls defining said primary flow channel comprises a tube having a cross-section defined as the outer periphery of two spaced circular sections connected by a rectangular section.

4. The apparatus as in Claim 1, in which said walls defining a primary flow channel provide a generally horizontally extending flat wall defining said roof, and said means defining a diversion flow channel comprises a generally flat wall extending over and across said roof to form said diversion flow channel therebetween.

5. The apparatus as in Claim 1, in which said walls defining said primary flow channel comprise an expanding conical inlet section, with the outlet of said conical inlet section being greater than the cross-sectional area of the exhaust gas inlet by a ratio of 8:1 to 20:1.

6: The apparatus as in Claim 1, in which said means defining said diversion flow channel comprises a single ply, U-shaped wall extending across said roof to form said diversion flow channel therebetween, said diversion flow channel having a cross-sectional area with a width to height ratio of 5/1 to 20/1.

7. The apparatus as in Claim 1, in which said means defining said diversion flow channel comprises baffles for muffling the sound of gas flow therethrough during the cleaning mode, said filter trap functioning to muffle gas flow sounds during the extraction mode.