Abstract:
Multiple storage tanks and multiple valves that open simultaneously allow gas charges stored at superatmospheric pressure in the tanks to simultaneously discharge and form a single substantial percussion pulse that dislodges particulate matter from a diesel particulate filter.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates devices and methods for mechanically removing trapped particulate matter from diesel particulate filters (DPF&#39;s) that are used in diesel engine exhaust systems.  
       BACKGROUND OF THE INVENTION  
       [0002]     A known system for treating exhaust gas passing through an exhaust system of a diesel engine comprises a diesel oxidation catalyst (DOC) associated with a diesel particulate filter (DPF). The combination of these two exhaust gas treatment devices promotes chemical reactions in exhaust gas and traps diesel particulate matter (DPM) as exhaust flows through the exhaust system from the engine, thereby preventing significant amounts of pollutants such as hydrocarbons, carbon monoxide, soot, SOF, and ash, from entering the atmosphere.  
         [0003]     While an engine is running, the existence of certain conditions enables regeneration of a DPF to be initiated. Various techniques are available for developing temperatures sufficiently high to initiate regeneration and thereafter control on-going regeneration. Regeneration is essentially a chemical process that burns off trapped DPM. For any of various reasons, not all trapped DPM may be burned off by regeneration. Moreover, the burning of trapped DPM may contribute to the build-up of ash, a non-combustible particulate.  
         [0004]     Consequently, it may be either necessary or desirable to occasionally use a mechanical, rather than a chemical, process to remove particulate matter, such as DPM and/or ash, from a DPF. The use of compressed air has been proposed as one way to remove the particulate matter.  
         [0005]     Compressed air is an appropriate medium because it is readily available in service facilities and shops and it is environmentally friendly.  
         [0006]     Cleaning a DPF by compressed air has involved certain manual operations such as removing the actual filter module from a casing and manually manipulating a compressed air nozzle across a face of the module. Dislodged matter is ejected from an opposite face and collected in some type of collector for subsequent disposal.  
         [0007]     In light of this background, it is believed that improvements in the mechanical cleaning of diesel particulate filters would enjoy commercial acceptance. For example, a cleaning device and method that would minimize the amount of labor required would be beneficial. Likewise, a device and method that could clean a diesel particulate filter more thoroughly would be desirable. The ability to satisfactorily clean a diesel particulate filter without having to remove the actual filter module from its casing also would have obvious advantages.  
       SUMMARY OF THE INVENTION  
       [0008]     It has been discovered that a device that provides a succession of compressed air pulses, or percussion pulses, can provide improvements for mechanically cleaning the trapping medium of a diesel particulate filter.  
         [0009]     The pulses can be created from an available compressed air source, such as shop air, using a novel DPF cleaning device in accordance with principles of the present invention. The device comprises at least one storage tank and an associated valve.  
         [0010]     While general principles of the device are not dependent on any particular number of storage tanks and valves used to create percussion pulses, one particular embodiment of the inventive device comprises multiple storage tanks and multiple valves that open simultaneously to allow gas charges stored at superatmospheric pressure in the tanks to simultaneously discharge and form a single substantial percussion pulse.  
         [0011]     It has been discovered that for developing percussion pulses effective to dislodge trapped particulates from a diesel particulate filter trapping medium, the total cost of multiple smaller valves is less than that of a single larger valve that would produce comparable pulses.  
         [0012]     One generic aspect of the present invention relates to a method for dislodging trapped particulate matter from a diesel particulate filter.  
         [0013]     The method comprises a) charging a storage tank with a gas to superatmospheric pressure; b) placing a face at one end of a flow path through a trapping medium of the diesel particulate filter in communication with the superatmospheric gas charge in the storage tank via a gas flow path containing a valve that is selectively operable to a closed condition closing the flow path and to an open condition opening the flow path and that comprises a diaphragm to which the superatmospheric gas charge in the storage tank is applied to provide force for unseating a valve element from a seat when the valve operates from closed condition to open condition; c) operating the valve from closed condition to open condition to allow the gas charge in the storage tank to discharge through the gas flow path and the flow path through the trapping medium and maintaining the open condition long enough to allow a majority of the gas charge to discharge; and d) repeating steps a), b), and c).  
         [0014]     Another generic aspect relates to a device for mechanically removing trapped particulate matter from a diesel particulate filter that is used in a diesel engine exhaust system.  
         [0015]     The device comprises: a storage tank capable of being charged with a gas to superatmospheric pressure; a flow path containing a valve that is selectively operable to a closed condition closing the flow path and to an open condition opening the flow path for delivering a charge of gas from the storage tank to a face at one end of a flow path through a trapping medium of the diesel particulate filter when the valve operates from closed condition to open condition; the valve comprising a diaphragm to which the superatmospheric gas charge in the storage tank is applied to provide force for unseating a valve element from a seat when the valve operates from closed condition to open condition; and an operator for operating the valve from closed condition to open condition, and maintaining open condition long enough, to allow a majority of the gas charge in the storage tank to discharge through the gas flow path and the flow path through the trapping medium.  
         [0016]     The foregoing, along with further features and advantages of the invention, will be seen in the following disclosure of a presently preferred embodiment of the invention depicting the best mode contemplated at this time for carrying out the invention. This specification includes drawings, now briefly described as follows. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  is a diagram, partly in cross section, of a portion of one embodiment of cleaning device that embodies principles of the invention.  
         [0018]      FIG. 2  is a diagram, partly in cross section, of a portion of another embodiment of cleaning device that embodies principles of the invention.  
         [0019]      FIG. 3  is an enlarged cross section view taken along line  3 - 3  in  FIG. 2 .  
         [0020]      FIG. 4  is a perspective view of still another embodiment of cleaning device that embodies principles of the invention.  
         [0021]      FIG. 5  is a schematic diagram representative of  FIG. 4 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]      FIG. 1  shows a first embodiment of DPF cleaning device  10  comprising a receiver  12  for holding a trapping medium  14  of a DPF during cleaning, a collector  16  for collecting particulate matter dislodged from trapping medium  14  during cleaning, and a portion of a percussion air pulse delivery system  18  for delivering percussion air pulses to medium  14  to dislodge trapped particulate matter.  
         [0023]     Medium  14  has a cylindrical shape that fits inside a casing (not shown in  FIG. 1 ) of the DPF, and hence  FIG. 1  shows medium  14  having been removed from the casing. Medium  14  has opposite end faces  20 ,  22 , one of which is an inlet and the other of which is an outlet. As engine exhaust gases flow through an engine exhaust system, they enter the DPF casing through an inlet port and then pass through a flow path in medium  14  between the end faces, with medium  14  trapping DPM in the process. After having passed through the medium, the treated exhaust exits the casing through an outlet port.  
         [0024]     Receiver  12  comprises a conical shaped inner wall  24 . One end of medium  14  is inserted upright into receiver  12  through the wider open end  26  of wall  24  to place the perimeter of the medium at end  22  in abutment with wall  24 . The narrower open end  28  of wall  24  opposite end  26  is communicated to an entrance  30  of collector  16  through a passageway  32 .  
         [0025]     Air pulse delivery system  18  comprises a device for creating percussion air pulses that are capable of dislodging trapped particulate matter from medium  14 .  FIG. 1  shows only the portion of system  18  that directly associates with medium  14 . That portion comprises a movable conduit  34  that includes a conical nozzle  36  at one end. The opposite end that is not shown connects to the device that creates the percussion pulses.  
         [0026]     For cleaning medium  14 , nozzle  36  is placed against end face  20  and moved manually across the end face while percussion pulses are delivered through conduit  34  and nozzle  36 . To prevent particulates from being blown into the air from end face  20 , an encasement bag  38  is associated with conduit  34  and medium  14 . Bag  38  comprises a flexible, imperforate sleeve of suitable material. One end of the sleeve is sealed around the outside of conduit  34  and the opposite end around the outside of medium  14 . The size and flexibility of the sleeve allow the user to manipulate the nozzle over the entire end face of the medium as percussion air pulses are delivered.  
         [0027]     The percussion pulses enter the flow path through medium  14  where DPM is trapped. The percussion forces act to dislodge the trapped matter and carry it through the medium to the other end face where they are further conveyed via passageway  32  to collector  16 .  
         [0028]     Collector  16  may be any suitable collection device that will hold the dislodged particulates until time of disposal. One example is a passive device such as a container or bag that is appropriately vented without allowing escape of particulates. Another example is an active device such as a vacuum that aids in drawing particulates into itself.  
         [0029]      FIGS. 2 and 3  show another embodiment that is substantially similar to that of  FIG. 1 . One difference is that the trapping medium  14  is supported generally horizontally by a saddle that is shown to comprise two separate, spaced apart saddle elements  40 . The saddle elements comprise tapered walls  42  on which the sidewall of medium  14  rests at opposite sides of an imaginary vertical plane through the axial centerline of the medium.  
         [0030]     In this instance the collector  16  is shown as a flexible bag that is open at one end for fitting over an end face of the medium. Where the bag overlaps the medium, a band  44  seals the bag to the medium to prevent escape of particulates coming out of that end during cleaning. Medium  14  is held secure in the saddle by strapping it in place using one or more straps  46 , as shown in  FIG. 3 . Bag  38  is not specifically shown in  FIG. 2 .  
         [0031]     The use of tapered walls  42  and conical wall  24  allow a single cleaning device to be used to clean trapping media having different diameters and lengths.  
         [0032]     The complete percussion air pulse delivery system  18  is shown by  FIGS. 4 and 5 . The disclosed embodiment comprises three air storage tanks  50 , three valves  52 , and various pipes and fittings. Tanks  50  store charges of air in suitable volume and at suitable superatmospheric pressure to enable suitable percussion air pulses to be delivered to medium  14 . Tanks  50  are each 12″ long by 4″ in diameter. They are capable of safely holding air at pressures in excess of 125 psi, which is a typical storage pressure.  
         [0033]     Any suitable air source can be used to charge tanks  50 , such as shop air. In typical automotive service facilities shop air is readily available at sufficiently high pressure, but as the inventor has found, not in sufficient volume to create percussion pulses suitable for dislodging trapped particulates from a DPF.  
         [0034]     Shop air is delivered to tanks  50  via charging ports  54 . Each charging port  54  comprises a respective fitting connected in a respective pipe running between a respective tank and the inlet port of a respective valve  52 .  
         [0035]     Each valve  52  further comprises a respective outlet port that is communicated to a respective inlet of a fitting  56  that has a 4″ diameter outlet  58 . It is through outlet  58  that the percussion pulses are delivered to medium  14 .  
         [0036]     For developing percussion pulses, valves  52  must be capable of opening simultaneously and almost instantly. A valve that is capable of doing so is described in U.S. Pat. No. 5,520,366 “Rapid Pulse Delivery Diaphragm Valve”, the entirety of which is incorporated herein by reference. Such a valve is normally closed and comprises a solenoid that is actuated by electricity to open the valve. The valve has a diaphragm that is held seated on a valve seat closing the valve when the solenoid is not actuated. When the solenoid is actuated, the hold on the seat is released. Fast opening of the valve is accomplished by using the pressure of air present at the valve inlet to lift the diaphragm off the seat.  
         [0037]     U.S. Pat. No. 5,520,366 says that the valve is used to create a reverse jet pulse for shaking dust off dust collection filter bags. While the compressed air source is not described in detail, it is understood from the patent that the solenoid does not remain energized long enough to allow the compressed air source to lose any significant pressure.  
         [0038]      FIG. 5  shows a pressure switch  60  that senses air pressure in tanks  50  as the tanks are being charged from the shop air supply with valves  52  closed. When a predetermined pressure is reached, such as 125 psi for example, the switch trips. This completes an electric circuit to each solenoid  62  of each valve  52 , causing each valve to open. With the valves opening essentially simultaneously and instantly, the stored charges in the tanks are suddenly released through valves  54  and into fitting  56  to form a combined percussion pulse that is delivered through outlet  58 .  
         [0039]      FIG. 4  shows a DPF being cleaned using the device that has just been described. Here, the trapping medium remains inside a casing  64 . A short hose  66  is fit over outlet  58  and an outlet port of casing  64  and held clamped at each place by a respective hose clamp  68  so that the percussion pulse can propagate through the casing outlet port and into the interior of the casing. There, it is constrained to continue through the trapping medium, dislodging trapped particulates in the process. After passing through the trapping medium, the pulse exits the casing through an inlet port  70  and carries dislodged particulates into a collection bag  72 .  
         [0040]     As the compressed air charges are released from the tanks and propagate through the device to form the pulse that passes through the DPF, energy is gradually lost and the intensity of the pulse dissipates. As a cautionary measure, a relief valve may be placed ahead of the DPF to vent excess pressure that might be unsuitable for application to the DPF.  
         [0041]     Pressure switch  60  is a commercially available device that has an adjustment feature allowing the pressure at which it closed to be set to any desired pressure within a range of pressures. One example of representative range is 20 psi to 120 psi. At lower settings, DPF cleaning device  10  delivers weaker pulses more rapidly; at higher settings, more powerful pulses less frequently. Switch  60  opens at some pressure lower than the pressure at which it closes to provide for a majority of the superatmospheric charges in the tanks to discharge and form a percussion pulse. The pressure at which the switch opens should be somewhat greater than atmospheric pressure to assure switch opening.  
         [0042]     While a presently preferred embodiment of the invention has been illustrated and described, it should be appreciated that principles of the invention apply to all embodiments falling within the scope of the following claims.