Diesel particulate filter

Abstract: A diesel particulate filter (100) in which a wire net (31c) of electric resistance metal is fastened on a main filter (31) to burn the particulates, collected by the main filter (31), in exhaust gases of a diesel engine, comprising a bypass pipe (11) constituting a sub-filter disposed within a filter case (10), said bypass pipe (11) being provided with an open-close bypass valve (15) in the vicinity of an inlet thereof, a cylindrical main filter (31) made by laminating long fibers of ceramics disposed between said bypass pipe (11) and said filter case (10), a wire net (31c) of electric resistance metal for heating said main filter (31) fastened on one surface of said main filter (31) for receiving the exhaust, and a reinforcing net-like plate (31a) of a heat resistant metal fastened on the other surface of said main filter (31) for releasing the exhaust. A control device for such a particulate filter which comprises means for measuring electric resistance between said wire net (31c) for heating and said reinforcing net-like plate (31a), and control means for driving said bypass valve (15) and said wire net (31c) are so provided that when a resistance value between said wire net (31c) for heating said main filter (31) and said reinforcing net-like plate (31a) is less than a predetermined value and the engine is not in an idling state and gear position of the transmission is in neutral, said bypass valve (15) is opened and said wire net (31c) is energized.

Description: The present invention relates to a diesel particulate filter for collecting and burning particulates in exhaust gases of a diesel engine and a control device therefor. Since the diesel engine employs a heterogeneous combustion in which fuel is injected into air elevated in temperature by heat insulating compression to effect combustion, there existed a problem that less carbon monoxide is contained in exhaust but a large amount of nitrogen oxide (NOx) and particulates (mainly, carbon) are contained. For preventing such particulates from being released into atmosphere, a particulate filter has been developed in which a filter is mounted in an exhaust gas flow passage to filtrate and burn exhaust gases for purification. French patent application publication No. 2600907 discloses an apparatus for burning carbon from an exhaust filter. Accumulated carbon is ignited wherever it builds up sufficiently on a non-conducting filter medium, by passage of electricity through the carbon between electrodes. The electrodes are two wires wound round a fibrous filter medium. US Patent No. 4264344 discloses an exhaust particulate trap for diesel engines comprising a concentric dual bath filter including a tubular outer filter element of high surface area acting as a primary filter, and a tubular mesh-packed secondary filter in a control bypass passage. A normally closed pressure relieve valve opens to permit bypass flow through the secondary filter in order to limit back pressure acting on the primary filter under various operating conditions. The combustion of particulates collected by the filter can be preferably accomplished always during the running of a vehicle. For burning the particulates in a simpler manner, it is desired that the combustion takes place in a state where smoke is hard to generate, for example, when the vehicle is in a stopped state, or in an idling state. However, since, when the combustion takes place, a heater is energized, a considerable amount of power is consumed. In the state where the engine is in an idling state, electric quantities for generation of power are so small that carrying out the combustion of particulates is considerably difficult. The conventional particulate filter had a problem in that filters are arranged in the whole exhaust flow passage, and therefore, when the filter is heated with electric heat, the filter is cooled by exhaust failing to perform satisfactory combustion. Particularly, in the case where the combustion is carried out in the idling state, the temperature of exhaust gases is so low that the filter is difficult to be satisfactorily heated for the reason above. Thus, a problem of an incomplete combustion of particulates is more serious. Further, in the case where the operation of burning particles is let to a driver, there exists an inconvenience that the driver unnecessarily frequently performs the burning operation, and that the driver forgets the burning operation and as a result the filter becomes clogged to bring forth an unexpected situation. The present invention has been accomplished to cope with the foregoing. A first aim of the present invention is not to cool a main filter by exhaust gases when particulates are burned by a main filter even if the engine is operated in any mode; a second aim of the present invention is to detect a clogging of a main filter to automatically perform burning of particulates; a third aim of the present invention is to prevent exhaust gases not filtrated even when particulates are burned from being released into atmosphere; a fourth aim of the present invention is, in the case where a clogging of a main filter extremely progresses, to perform burning of particulates irrespective of any state of the engine and the like; and a fifth aim of the present invention is to provide a means for informing a driver an occurrence of a clogging state when not under environment wherein a clogging of a main filter occurs so that burning is not suitable. This enables a complete combustion of particulates, an automatic combustion of particulates under the managed environment, and enables, when not under environment wherein a clogging of a filter occurs so that burning is not suitable, execution of combustion as soon as moving into a managed yard so as to always maintain a filter in a good state. Accordingly, the present invention provides a particulate filter for a diesel engine comprising a filter case and a main filter disposed in the filter case, the main filter comprising a body of ceramics fibers, and a metal wire for heating said main filter and a reinforcing net-like plate of a heat resistant material on respective opposite surfaces of said body, characterised in that the particulate filter further comprises a sub-filter, the main filter surrounding the sub-filter and the sub-filter comprising a selectively openable bypass valve in the vicinity of an inlet thereof wherein said metal wire is a metal wire net, and sensing means for sensing particulates accumulated on said main filter, said bypass valve being opened in dependence on said sensing means and said wire net for heating being energized to burn the particulates, wherein the main filter is comprised of an inner tube and an outer tube, annular closing plates being connected at the inlet ends of said inner and outer tubes, and between the outlet ends of said inner and outer tubes, and said sub-filter is constituted by a porous metal tube or a porous conductive ceramics tube forming a porous passage, the diameter of the porous passage being larger than that of said main filter. In one preferred embodiment, said sensing means comprise an exhaust pressure sensor disposed in said filter case, and when the exhaust pressure detected by the exhaust pressure sensor exceeds a predetermined value, burning of particulates is initiated. In another preferred embodiment, said sensing means comprise a control device comprising a means for electric resistance between said wire net and said reinforcing net-like plate, and control means for selectively opening said bypass valve and energizing said wire net, such that when a resistance value between said wire net and said reinforcing net-like plate is less than a predetermined value and the engine is not in an idling state and the gear position of the transmission is in neutral said bypass valve is opened and said wire net is energized. Preferably, said control means for driving said bypass valve and said wire net are so provided that when the particulates collected in said main filter are burned and said bypass valve is closed, said sub-filter is energized to burn the particulates collected thereby. In an alternative preferred arrangement said control means for driving said bypass valve and said wire net are so provided that when the electric resistance between said wire net for heating and said reinforcing net-like plate resistance value is less than a predetermined value, and the engine is not in an idling state or the seat belt is not unworn, a filter clogging signal for a vehicle driver is generated and the bypass valve is fully opened. In the particulate filter according to the present invention, a main filter is disposed within a channel of exhaust gases from the internal combustion engine, and a bypass pipe is disposed in the main filter and provided with a bypass valve and a sub-filter. The bypass pipe has substantially the same inside diameter as that of an exhaust pipe. The bypass valve provided on the bypass pipe is opened and the main filter is energized when the collected particulates in the main filter are burned. Since the main filter is energized to burn particulates cooling of the main filter by exhaust gases is suppressed under whatever mode the engine is. Further, in the particulate filter according to the present invention, when the exhaust gas pressure exceeds a first predetermined value, judgement is made by a signal of the exhaust pressure sensor provided on an inlet of the main filter that a clogging caused by particulates occurred. Then a predetermined electric power is automatically applied to a heater to perform burning of particulates in the main filter. Accordingly, it is possible to avoid inconveniences such that excessive burning is carried out, and conversely, a clogging occurs in the main filter because the driver forgets burning. Further, in the particulate filter according to the present invention, particulates (mainly, carbon) are accumulated in an amount in excess of a predetermined value on a resistance element to decrease a value of electric resistance. When the value of electric resistance is less than a predetermined value, judgement is made such that the main filter becomes clogged with particulates. Upon confirmation of an idling state, a predetermined amount of power is automatically supplied to burn particulates. Moreover, when the particulates are burned in the main filter, the exhaust gases are passed through the bypass pipe provided with a sub-filter. It is therefore possible to avoid an inconvenience such that exhaust gases not filtrated during the burning of particulates are released into atmosphere. Preferred embodiments of the present invention will now be described hereinbelow by way of example only with reference to the accompanying drawings, in which: Fig. 1 is a sectional view showing the construction of a diesel particulate filter according to first embodiment of the present invention. Fig. 2 is a flow chart explaining an example of the operation of the diesel particulate filter, shown in Fig. 1. Fig. 3 is a sectional view showing the construction of a diesel particulate filter according to second embodiment of the present invention. Fig. 4 is a sectional view showing the construction of a main filter in the diesel particulate filter, shown in Fig. 3. Fig. 5 is a flow chart explaining an example of the operation of the diesel particulate filter, shown in Fig. 3. An embodiment of the present invention will be described hereinafter with reference to the drawings. Fig. 1 is a sectional view of a particulate filter according to the first embodiment. As shown in Fig. 1, in a particulate filter 100 according to the present embodiment, a cylindrical bypass pipe 11 is disposed in a central portion within a heat resistant steel filter case 10, externally thereof is disposed a cylindrical laminated main filter 12 of a double co-axial tube construction, and further externally thereof is disposed a cylindrical exhaust pipe 13. The main filter 12 is made to be cylindrical in a section like a petal. At a downstream of the bypass pipe 11 is formed a sub-filter 11a. The sub-filter 11a is constituted by a heat resistant metal pipe or a conductive ceramics pipe having a number of irregularly bent pores. In the case where the sub-filter 11a is formed of metal, Fe containing Ni and Cr is used on the surface of which is coated with ceramic. SiC can be used as a ceramic material. In the bypass pipe 11, an inlet portion and a sub-filter portion can be constituted by materials different from each other. Alternatively, the whole bypass pipe 11 be also constituted by the same material. The main filter 12 comprises a heat resistant metal plate bored with a number of holes of air permeability are disposed, a ceramic fiber laminated body formed by superposing long fibers of ceramics which functions as a filter and wire net formed of heat resistant metal using Ni-Cr as main raw material are laminated. The ceramic fiber laminated body and the metal plate are laminated on the heat resistant metal plate and partly fastened. The heat resistant metal plate is positioned at a downstream layer in the exhaust flow. A ceramic net-like construction plate can be used in place of a heat resistant metal plate. Further, a fiber composite body formed of heat resistant metal fiber can be used in place of the ceramic fiber laminated body. Annular closed plates 14 for controlling a flow of exhaust gases are arranged between left end of the bypass pipe 11 and left end of the inner tube of the main filter 12, between left end of the outer tube of the main filter 12 and left end of the exhaust pipe 13, and between right ends of inner and outer tubes of the main filters 12. A bypass valve 15 for controlling passage/interception of exhaust gases is provided in the vicinity of an inlet of the bypass pipe 11. The bypass valve 15 is opened and closed by an actuator 18 through a valve operating arm 16 against of a force of the spring 17. The operation of the actuator 18 is controlled by a controller 19. An exhaust pressure sensor 20 for detecting pressure of exhaust gases on the inlet side is connected to the controller 19. Normally, the bypass valve 15 is closed while particulates are collected by the main filter 12 and exhaust gases do not pass through the bypass pipe 11. Exhaust gases come from the left side in the drawing, and the exhaust gases are fed between outer and inner tubes of the main filters 12, pass through the main filter 12, as shown by the arrows and thence are discharged outside of the main filter 12, as shown by arrows. When the controller 19 receiving output signals of the exhaust pressure sensor 20 judges that the combustion of particulates is necessary from these signals, the bypass valve 15 is opened by the actuator 18, and electric power is applied to the wire net laminated on main filter 12 for a fixed period of time to burn the particulates by the main filter 12. Thereafter, the bypass valve 15 is closed or slightly opened, under which state a small amount of air may flow into the bypass pipe 11, and electric power is applied to the sub-filter 11a to burn the particulates. If a detected value by the exhaust pressure sensor 20 exceeds a given value, an emergency valve is opened, irrespective of the state of the engine and a seat belt, to permit exhaust gases to flow out. Next, an example of operation of the particulate filter according to the present embodiment will be described with reference to Fig. 2. Fig. 2 is a flow chart of assistance in explaining the operation of the particulate filter according to the embodiment. First, in step S1, checking is made whether or not the clogging of the main filter 12 progresses up to a given level or more, that is, checking is made whether or not an exhaust gas pressure P exceeds a predetermined value P1. If exceeding the predetermined value P1, the step proceeds to step S2, otherwise the step returns to step S1. In step S2, checking is made whether or not the clogging of the main filter 12 progresses up to an excessive level, that is, checking is made whether or not an exhaust gas pressure P exceeds a second predetermined value P2 (P1 < P2). If exceeding the predetermined value P2, the step proceeds to step S13, otherwise the step proceeds to step S3. In step S3, checking is made whether or not the engine is in an idling state, that is, whether or not the number of revolutions of the engine is less than a predetermined number. In step S3, if judgement is made that the engine is in an idling state, the step proceeds to step S4, otherwise the step returns to step S1. In step S4, checking is made whether or not seat belt is fastened. If in a "worn" state, judgement is made that the vehicle is running, and the step returns to step S1. If the seat belt is removed, open the bypass valve 15 (step S5) and start to energize the main filter 12 (step S6), after which the step proceeds to step S7. When step S6 is executed, the combustion of particulates is carried out in the main filter 12. Since the bypass valve 15 is opened at this time, an amount of exhaust gases passing through the main filter 12 is reduced, the filter 12 is not cooled by the exhaust gases. Further, since the metal wire net or electric heating element is located at the upstream of the exhaust flow, the whole filter 12 is efficiently heated to enable the combustion without unevenness. Further, since the sub-filter 11a is disposed at the downstream portion of the bypass pipe 11, the exhaust gases not filtrated are not exhausted into atmosphere. In step S7, checking is made whether or not a predetermined time (t1) after starting of combustion has passed. If not, the step returns to step S5. If the predetermined time (t1) has passed, the energization to the main filter 12 is turned off (step S8), and the bypass valve 15 is closed (step S9), after which the step proceeds to step S10 and the energization to the sub-filter 11a is started (step S10. Then the step proceeds to step S11. When step S10 is executed, the combustion of particulates collected in the sub-filter 11a is carried out. At this time, the bypass valve 15 may be slightly opened to supply oxygen to the sub-filter 11a. In step S11, checking is made whether or not the combustion in the sub-filter 11a was carried out for a predetermined time (t2). When a predetermined time has not been passed, the step returns to step S10. If a predetermined time (t2) has passed, the energization to the sub-filter 11a is turned off (step S12), after which the step returns to step S1. In step S2, judgement was made that the clogging of the main filter 12 excessively progressed, the bypass valve 15 is immediately opened (step S13) without checking the state of the engine and the state of the seat belt, and the energization to the main filter 12 is started (step S14) is started, after which the step proceeds to step S15. In step S15, checking is made whether or not a predetermined time (t3) after starting the combustion has passed. If not, the step returns to step S13. If a predetermined time (t3) has passed, the energization to the main filter 12 is turned off (step S16) and the bypass valve 15 is closed (step S17), after which the step returns to step S1. While in the foregoing, a preferred embodiment has been described, it is to be noted that the present invention is not limited to the above-described embodiment but various changes can be made within the scope not changing the gist of the present invention. For example, in the above embodiment, main filters 12 of two coaxially arranged tubes have been employed. However, three or more tubes can be employed. Further, alternatively, after the completion of step S17, cleaning of the sub-filter 11a is carried out for a period of given time, and thereafter the step may return to step S1. Further, instead of carrying out the cleaning of the sub-filter 11a every time the main filter 12 is cleaned, it is so arranged that the sub-filter 11a may be cleaned when times of cleaning of the main filter reached a predetermined value. Fig. 3 is a sectional view of a particulate filter according to a second embodiment. As shown in Fig. 3, in a particulate filter 100 according to the present embodiment, a cylindrical bypass pipe 11 is disposed in a central portion within a steel filter case 10, and externally thereof is disposed a main cylindrical filter 31 including three tubes of different diameter which are coaxially arranged. Fig. 4 is a sectional view of a portion indicated at (A) in Fig. 3 of the main filter 31. As shown in Fig. 4, the main filter 31 comprises a heat resistant metal plate 31a having a number of holes, a ceramics fiber composite 31b formed by placing long fibers of ceramics one upon another and sewing them together and a metal wire net 31c of elecric resistance as Ni-Cr. The ceramics fiber composite 31b performing a filter function is placed between the heat resistant metal plate 31a and the wire net 31c and the wire net 31c is placed in the upstream of the exhaust flow to receive the exhaust into the ceramics fiber compsite 31b. It is to be noted that a ceramics net-like construction can be used in place of the heat resistant metal plate 31a, and a fiber composite formed of heat resistant metal fiber can be used in place of the ceramics fiber composite 31b. Returning to Fig. 3, a bypass valve 15 for controlling passage/interception of exhaust gases is provided in the vicinity of an inlet of the bypass pipe 11. The bypass valve 15 is opened and closed by an actuator 18 through a valve operating arm 16a against a force of the spring 17. The operation of the actuator 18 is controlled by a controller 19. Input into the controller 19 are an output signal of a comparator 32 for comparing a electric resistance value between the wire net 31c (see Fig. 4) as an electric heating element and the net-like metal plate 31a with a reference value, and output signals of an idling sensor 22 which detects the number of revolutions of engine and a seat belt sensor 21 for detecting wearing and unwearing of a seat belt. The controller 19 further controls a supply of electric power to the wire net 31c by a control relay 33. Normally, the bypass valve 15 is closed and thus exhaust gases never pass through the bypass pipe 11. At this time, gases flown from the left side in the drawing are fed between the outer and inner cylidrical filters 31 or between the main filter 31 and the filter case 10, and pass through the main filter 12 as indicated at the arrows and thence are discharged outside of the main filters 31. The controller 19 receives output signals of the comparator 32 for detecting the resistance value between the wire net 31c as a heater provided on the main filter 31 and the metal plate 31a, output signals of the idling sensor 22 and output signals of the seat belt sensor 21 for detecting a neutral position of a gear in a transmission. The resistance value between the wire net 31c and the metal plate 31a gradually decreases as the particulates are accumlated in the ceramics fiber composite 31b. When the controller 19 judges that the combustion of particles is necessary from these signals, the bypass valve 15 is opened by the actuator 18, and a predetermined amount of current is started to feed to the wire net 31c or an electric heat element through the control relay 33 to burn the particulates collected by the main filter 31. Next, an example of operation of the particulate filter according to the present embodiment will be described with reference to Fig. 5. Fig. 5 is a flow chart of assistance in explaining the operation of the particulate filter according to the embodiment shown in Fig. 3. First, in step S21, checking is made whether or not the clogging of the main filter 31 progresses up to a given level or more, that is, checking is made whether or not particulates collected by the wire net 31c reach a predetermined level or more, that is, an electric resistance value R of the wire net 31c is less than a predetermined value Ra. If the value R is less than the predetermined value Ra, the step proceeds to step S22, otherwise the step returns to step S21. In step 22, checking is made whether or nor the engine is in an idling state or the gear position of the transmission is in a neutral state, that is, whether or not the number of revolutions of the engine is less than a predetermined number and the vehicle is in a stopped state. In step S22, if judgement is made that the engine is in an idling state, the step proceeds to step S23, otherwise in step S29, the bypass valve 15 is opened. Then, in step S30, a filter clogging signal is generated, after which the step returns to step S21. The reason why step S29 is provided is that when the combustion of particulates cannot be executed for the reason of the running of vehicle or the like despite the fact that the clogging of the main filter 31 proceeds to a predetermined level or more so that the exhaust gas pressure becomes higher than a the predetermined level, the bypass valve 15 is opened to spread a flow passage of exhaust gases so as not to impair the combustion. Further, step S30 is provided for the reason of informing a driver that since the clogging of the filter occurs, the combustion can be executed quickly as soon as the mode has moved to the combustible situation or environment. Informing means includes a buzzer, a display lamp, etc. In step S23, checking is made whether or not a seat belt is fastened. If the seat belt is fastened, the program step open the bypass valve 15 (step S24), and start energization to the wire net 31c (step S25), and after this, proceeds to step S26. By execution of step S25, the combustion of particles is carried out. At this time, the bypass valve 15 is opened so that the amount of exhaust gases which pass through the main filter 31 is few, thus the main filter 31 is not cooled by the exhaust gases. Further, since the electric resistance element 31c is located at upstream of exhaust flow, the entire filter 31 is efficiently heated to enable even combustion. In step S23, if judgement is made that the seat belt is unworn, the step proceeds to step S30. After a filter clogging signal has generated, the step returns to step S21. In step S25, the electric resistance element 31c is started to be energized, and after this, in step S26, checking is made whether or not a predetermined time (t1) has passed after the start of combustion. When not passed, the step returns to step S24. When passed a predetermined time (t1), the bypass valve 15 is closed (step S27) and the energization to the electric resistance element 31c is turned off (step S28), after which the step returns to step S21. While in the foregoing, a preferred embodiment has been described, it is to be noted that the present invention is not limited to the above. For example, in the above embodiment, though three co-axial filter tubes as the main filter 31 are employed, four or more tubes as the main filters 31 can be employed. As described above, in the diesel particulate filter according to the present invention, a bypass pipe for bypassing exhaust gases when particulate burn is provided within a filter case, and the bypass pipe is also made to have a filter function. Therefore, even if the particulate are burnt in the idling state of engine, the filter is not cooled by the exhaust gases to enable the performance of sufficient combustion. Since the exhaust gases pass through the sub-filter provided on the bypass pipe at this time, the exhaust gases not filtrated are directly not exhausted in the atmosphere. Further, it is so designed that when the clogging occurs in the filter and engine is in the idling state, the particulate are automatically burnt. Therefore, it is possible to prevent the forgetting of combustion or excessive combustion to always maintain the filter in a good state. Further, since the combustion of the particulate is carried out during the idling where a large amount of oxygen are contained in the exhaust gases, the efficient combustion can be obtained. Furthermore, if the clogging of the main filter excessively progresses, screening of the main filter is immediately carried out. It is therefore possible to avoid an engine trouble caused by the clogging of the filter. When the filter is in the clogging state and in the state where the combustion cannot be made, the driver is informed of such information. Then, it is possible to carry out the combustion quickly under the appropriate environment.

Claims: A particulate filter for a diesel engine comprising a filter case (10) and a main filter (12) disposed in the filter case (10), the main filter (12) comprising a body of ceramics fibers, and a metal wire for heating said main filter and a reinforcing net-like plate of a heat resistant material on respective opposite surfaces of said body, characterised in that the particulate filter further comprises a sub-filter (11), the main filter (12) surrounding the sub-filter (11), and the sub-filter comprising a selectively openable bypass valve (15) in the vicinity of an inlet thereof wherein said metal wire is a metal wire net, and sensing means for sensing particulates accumulated on said main filter (12), said bypass valve (15) being opened in dependence on said sensing means and said wire net for heating being energized to burn the particulates, wherein the main filter (12) is comprised of an inner tube and an outer tube, annular closing plates (14) being connected at the inlet ends of said inner and outer tubes, and between the outlet ends of said inner and outer tubes, and said sub-filter (11) is constituted by a porous metal tube or a porous conductive ceramics tube forming a porous passage, the diameter of the porous passage being larger than that of said main filter (12). A particulate filter according to claim 1, wherein said sensing means comprises an exhaust pressure sensor (18) disposed in said filter case (10), and when the exhaust pressure detected by the exhaust pressure sensor (18) exceeds a predetermined value, burning of particulates is initiated. A particulate filter according to claim 1, wherein said sensing means comprise a control device comprising a means for electric resistance between said wire net and said reinforcing net-like plate, and control means for selectively opening said bypass valve and energizing said wire net, such that when a resistance value between said wire net and said reinforcing net-like plate is less than a predetermined value and the engine is not in an idling state and the gear position of the transmission is in neutral said bypass valve is opened and said wire net is energized. A particulate filter according to claim 3, in which said control means for driving said bypass valve and said wire net are so provided that when the particulates collected in said main filter are burned and said bypass valve is closed, said sub-filter is energized to burn the particulates collected thereby. A particulate filter according to claim 3, in which said control means for driving said bypass valve and said wire net are so provided that when the electric resistance between said wire net for heating and said reinforcing net-like plate resistance value is less than a predetermined value, and the engine is not in an idling state or the seat belt is not unworn, a filter clogging signal for a vehicle driver is generated and the bypass valve is fully opened.

Inventors: KAWAMURA HIDEO, KAWAMURA, HIDEO
Applicants: ISUZU CERAMICS RES INST, ISUZU CERAMICS RESEARCH INSTITUTE CO., LTD.
Application year: 1995
Main classification: F01N3
IPC codes: F01N3, F02B3, F01N9