CA1251743A - Automatic initiation system for regenerating a particulate filter trap - Google Patents

Abstract

ABSTRACT
A method and apparatus is disclosed for initiat-ing the energization of a regenerative apparatus used with a particulate filter trap having a porosity effec-tive to extract particulates from the exhaust gas flow of an internal combustion engine. The method comprises: (1) sensing the actual pressure drop across the filter trap and sensing the pressure drop across an open channel simulative filter structure: (2) converting the pressure drops to proportional voltages and ratioing the voltage of the filter trap pressure drop to the product of a constant and the voltage of the simulative filter struc-ture pressure drop; and (3) using the resultant voltage ratio to control the energization of the regeneration apparatus when the output exceeds a predetermined allow-able limit, e.g., 2-B volts. The apparatus employs a simulative filter structure fabricated of the same mono-lithic honeycomb celled ceramic as is the filter trap, except that the structure has a controlled porosity effective to permit the passage of substantially all particulates in the gas flow therethrough.

Description

~L25~ 3 ~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 ,,'' ~

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.

~253a7~3 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:
;

~S~L7~3 (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 ~2~4~

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 125~ 3 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 ~25~7~3 , 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.

r . . .

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:

~2~ 3 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 ~S~L3 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.

:~L25~7'~3 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.

Claims (9)

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

1. A method of initiating the energization of a regeneration apparatus used with a particulate filter trap having a porosity effective to extract particulates from the exhaust gas flow of an internal combustion engine, said method comprising:
(a) sensing the actual pressure drop across said filter trap placed in the flow of exhaust gas:
(b) sensing the actual pressure drop across a simulative filter structure also placed in the flow of said exhaust gas flow, said simulative filter structure having a porosity effective to allow the passage of particulates therethrough;
(c) comparing the sensed value of (a) to the sensed value of (b) multiplied by a reference multiple needed to make the pressure values equal when the filter trap is free of particulates;
(d) converting the ratio of step (c) to an electric signal; and (e) using said electric signal to control the energization of said regeneration apparatus when said signal exceeds an allowable electric signal limit.

2. The method as in Claim 1, in which said allowable limit is in the range of 2-10.

3. The method as in Claim 1, in which said conversion of step (d) is carried out by use of a pres-sure transducer elective to compare each of said sensed pressures and to generate an electrical signal propor-tional thereto.

4. The method as in Claim 1, in which said filter trap and said simulative filter structure are each comprised of a monolithic ceramic honeycomb celled material,

5. The method as in Claim 1, in which said simulative filter structure is placed in the exhaust gas flow downstream from said filter trap.

6, An apparatus for initiating the energization of a regeneration system used with a particulate filter trap having a porosity placed to extract particulates from the exhaust gas flow of an internal combustion engine, comprising:
(a) a simulative filter structure in said exhaust gas flow and having a porosity effective to allow the passage of substantially all particulates therethrough;
(b) means to sense the actual pressure drop across said filter trap and to sense the actual pressure drop across said simulative filter structure;
(c) transducer means for ratioing the actual sensed pressure drop across said filter trap to the actual sensed pressure drop across said 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 electric signal: and (d) limit means permitting said electric signal to control the energization of said regeneration system when said signal exceeds an allowable electric signal limit.

7. The apparatus as in Claim 6, in which limit means permits energization when said signal is in the range of 2-10.

8. The apparatus as in Claim 6, in which both said filter trap and simulative filter structure are comprised of a monolithic ceramic honeycomb celled material.

9. The apparatus as in Claim 6, in which said simulative filter structure is placed in the exhaust gas flow downstream from said filter trap.