Patent Publication Number: US-7721702-B2

Title: Spark plug having separate housing-mounted electrode

Description:
TECHNICAL FIELD 
   The present disclosure is directed to a spark plug and, more particularly, to a spark plug having a grounded electrode that is separate from the spark plug and mounted to a housing member that receives the spark plug. Background 
   Engines, including diesel engines, gasoline engines, gaseous fuel powered engines, and other engines known in the art ignite injections of fuel to produce heat. The heat from this process may be converted to mechanical and electrical power, or used to increase the temperature of particular engine components. For example, fuel may be injected into a combustion chamber of an engine and ignited by way of a spark plug. The heat and expanding gases resulting from this combustion may be directed to displace a piston or move a turbine blade, both of which can be connected to a crankshaft of the engine. As the piston is displaced or the turbine blade is moved, the crankshaft is caused to rotate. This rotation may be directly utilized to drive a device such as a transmission to propel a vehicle, or a generator to produce electrical power. In another example, the fuel may additionally or alternatively be injected into an exhaust stream and ignited by way of the spark plug. The heat resulting from this combustion may be directed to a particulate laden filtration medium to regenerate the medium, or directed to a catalytic device to improve the operating efficiency of the device. 
   In any of the examples described above, the geometry and orientation of the spark plug relative to the injection of fuel can affect the operation of the associated engine. In particular, if the spark plug geometry and/or orientation are such that an arc is produced at a desired location relative to the injection of fuel, efficient and timely combustion may occur. However, if the spark plug geometry and orientation are such that the arc is produced at an undesired location or the injection of fuel is interrupted or blocked by the spark plug, combustion may occur at an undesired location or timing, or possibly not at all. 
   An example of injecting fuel and igniting the injected fuel with a spark plug is described in U.S. Pat. No. 4,987,738 (the &#39;738 patent) issued to Lopez-Crevillen et al. on Jan. 29, 1991. Specifically, the &#39;738 patent discloses a particulate filter having a burner used to incinerate trapped particulates. The burner includes a fuel injector nozzle for injecting fuel into the burner during regeneration. As the fuel, under pressure, is injected by the nozzle into the burner apparatus, it is atomized by high pressure air. An igniter included within the burner is energized to ignite the air-fuel mixture, and the burning mixture is combined with metered exhaust gas. As illustrated in FIG. 1 of the &#39;738 patent, the igniter includes a typical spark plug having a center electrode and a grounded electrode attached to one side of the spark plug. 
   Although the injector nozzle and igniter configuration of the &#39;738 patent may be suitable in some situations, it may be prone to improper assembly resulting in poor operation of the burner. Specifically, because the ground electrode is attached to one side of the igniter (i.e., the spark plug), an incorrect orientation of the spark plug such as the spark plug being turned to an excessive or insufficient angle could allow the ground electrode to block fuel spray from the injector nozzle. The blockage of fuel spray could adversely effect the resulting combustion. 
   Further, the injector nozzle and igniter configuration of the &#39;738 patent may also be unreliable and prone to unintentional arcing. That is, because the ground electrode is attached to the spark plug and because of space constraints within the burner, the ground electrode may have a relatively small cross section. The small cross section coupled with a large cantilevered distance (i.e., the distance the ground electrode extends from the spark plug) could result in vibration being induced within the ground electrode. This vibration, if significant, could result in damage to the ground electrode and/or unintentional arcing along the length of the ground electrode instead of at the tip of the ground electrode. Further, during operation of the burner, it may be possible for carbon, foreign material, or debris to fill the space between the ground and center electrodes. Without a way to remove this debris, unintentional arcing may occur. 
   The spark plug of the present disclosure solves one or more of the problems set forth above. 
   SUMMARY OF THE INVENTION 
   One aspect of the present disclosure is directed to a spark plug arrangement. The spark plug arrangement may include a body, and a center electrode extending from an end of the body. The spark plug arrangement may further include a mounting member with a bore configured to receive the body, and a grounded electrode extending proximal the center electrode. 
   Another aspect of the present disclosure is directed to a spark plug for use with a mounting member having a grounded electrode. The spark plug may include a body configured for insertion into the mounting member. The spark plug may also include only a positive electrode configured to mate with the grounded electrode. 
   Yet another aspect of the present disclosure is directed to a method of igniting fuel. The method may include injecting fuel into a chamber, and directing air into the chamber. The method may also include grounding a portion of the chamber, and directing current to an electrode to cause an arc between the electrode and the grounded portion of the chamber. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic and diagrammatic illustration of an exemplary disclosed power unit; 
       FIG. 2A  is a cross-sectional illustration an exemplary disclosed regeneration device for use with the power unit of  FIG. 1 ; and 
       FIG. 2B  is pictorial view of the regeneration device of  FIG. 2A . 
   

   DETAILED DESCRIPTION 
     FIG. 1  illustrates a power unit  10  having a common rail fuel system  12 , a purge system  13 , and an auxiliary regeneration system  14 . For the purposes of this disclosure, power unit  10  is depicted and described as a four-stroke diesel engine. One skilled in the art will recognize, however, that power unit  10  may be any other type of internal combustion engine such as, for example, a gasoline or a gaseous fuel-powered engine. Power unit  10  may include an engine block  16  that at least partially defines a plurality of combustion chambers (not shown). In the illustrated embodiment, power unit  10  includes four combustion chambers. However, it is contemplated that power unit  10  may include a greater or lesser number of combustion chambers and that the combustion chambers may be disposed in an “in-line” configuration, a “V” configuration, or any other suitable configuration. 
   As also shown in  FIG. 1 , power unit  10  may include a crankshaft  18  that is rotatably disposed within engine block  16 . A connecting rod (not shown) may connect a plurality of pistons (not shown) to crankshaft  18  so that a sliding motion of each piston within the respective combustion chamber results in a rotation of crankshaft  18 . Similarly, a rotation of crankshaft  18  may result in a sliding motion of the pistons. 
   Common rail fuel system  12  may include components that cooperate to deliver injections of pressurized fuel into each of the combustion chambers. Specifically, common rail fuel system  12  may include a tank  20  configured to hold a supply of fuel, and a fuel pumping arrangement  22  configured to pressurize the fuel and direct the pressurized fuel to a plurality of fuel injectors (not shown) by way of a common rail  24 . 
   Fuel pumping arrangement  22  may include one or more pumping devices that function to increase the pressure of the fuel and direct one or more pressurized streams of fuel to common rail  24 . In one example, fuel pumping arrangement  22  includes a low pressure source  26  and a high pressure source  28  disposed in series and fluidly connected by way of a fuel line  30 . Low pressure source  26  may embody a transfer pump that provides low pressure feed to high pressure source  28 . High pressure source  28  may receive the low pressure feed and increase the pressure of the fuel to the range of about 30-300 MPa. High pressure source  28  may be connected to common rail  24  by way of a fuel line  32 . One or more filtering elements  34 , such as a primary filter and a secondary filter, may be disposed within fuel line  32  in series relation to remove debris and/or water from the fuel pressurized by fuel pumping arrangement  22 . 
   One or both of low and high pressure sources  26 ,  28  may be operably connected to power unit  10  and driven by crankshaft  18 . Low and/or high pressure sources  26 ,  28  may be connected with crankshaft  18  in any manner readily apparent to one skilled in the art where a rotation of crankshaft  18  will result in a corresponding driving rotation of a pump shaft. For example, a pump driveshaft  36  of high pressure source  28  is shown in  FIG. 1  as being connected to crankshaft  18  through a gear train  38 . It is contemplated, however, that one or both of low and high pressure sources  26 ,  28  may alternatively be driven electrically, hydraulically, pneumatically, or in any other appropriate manner. It is further contemplated that common rail fuel system  12  may alternatively embody another type of fuel system such as, for example, mechanical unit fuel injector systems where the pressure of the injected fuel is generated or enhanced within the individual injectors without the use of a high pressure source. 
   Purge system  13  may pressurize a gas and provide this pressurized gas to auxiliary regeneration system  14  for purging and/or combustion purposes. For example, a gas such as compressed air may be directed to auxiliary regeneration system  14  to purge components thereof of residual fuel and/or contaminates. Alternatively or additionally, this purge gas may be directed to mix with fuel and, thereby, aid combustion within auxiliary regeneration system  14 . For these purposes, purge system  13  may include a gas source  44  such as, for example, a compressor, an air pump, or any other suitable source, and a storage reservoir, such as a tank or an accumulator having sufficient volume to complete a purging and/or combusting process with or without operation of gas source  44 . A purge passageway  40  may fluidly connect the components of auxiliary regeneration system  14  to gas source  44  at any upstream location. A check valve  42  may be disposed within purge passageway  40  to ensure that fuel and other contaminates are blocked from flowing through purge passageway  40  to gas source  44 . The flow of purge gas through purge passageway  40  may be controlled by way of a suitable valve arrangement (not shown). 
   Auxiliary regeneration system  14  may be associated with an exhaust treatment device  46 . In particular, as exhaust from power unit  10  flows through exhaust treatment device  46 , particulate matter may be removed from the exhaust flow by wire mesh or ceramic honeycomb filtration media  48 . Over time, the particulate matter may build up in filtration media  48  and, if left unchecked, the particulate matter buildup could be significant enough to restrict, or even block the flow of exhaust through exhaust treatment device  46 , allowing for backpressure within the power unit  10  to increase. An increase in the backpressure of power unit  10  could reduce the power unit&#39;s ability to draw in fresh air, resulting in decreased performance, increased exhaust temperatures, and poor fuel consumption. 
   As illustrated in  FIGS. 2A and 2B , auxiliary regeneration system  14  may include components that cooperate to periodically reduce the buildup of particulate matter within filtration media  48 . These components may include a housing  50 , an injector  52 , and a spark plug  54 . It is contemplated that auxiliary regeneration system  14  may include additional or different components such as, for example, one or more pilot injectors, additional main injectors, a controller, a pressure sensor, a temperature sensor, a flow sensor, a flow blocking device, and other components known in the art. 
   Housing  50  may be an assembly of components that, together, form a combustion chamber  56 . In particular, housing  50  may include a mounting element  58 , a swirler plate  60 , and a can  62 . Swirler plate  60  may be received within mounting element  58 , while can  62  may be connected to a bottom portion of mounting element  58 . 
   Mounting element  58  may receive and fluidly connect fuel injector  52  and spark plug  54  with fuel, air, and coolant. In particular, mounting element  58  may be formed in or connected to an outer wall portion of exhaust treatment device  46 , and include a stepped bore  64  for receiving fuel injector  52 , and a stepped bore  66  for receiving spark plug  54 . Stepped bore  64  may be in communication with common rail fuel system  12  to communicate fuel injector  52  with the pressurized fuel of pumping arrangement  22 , with the compressed air of gas source  44 , and/or with the heat transferring medium of a coolant system (not shown). Each of these systems may have passages that open into stepped bore  64  at different axial locations to communicate their respective fluids therewith. Stepped bore  66  may be in communication with purge system  13  via purge passageway  40 . 
   Swirler plate  60  may be situated to conduct an electrical current to mounting element  58 . That is, swirler plate  60  may be fabricated from an electrical conducting material such as, for example, a stainless steel, and press-fitted into a recess of mounting element  58 . Swirler plate  60 , together with mounting element  58 , may form an air chamber  68 , which may be supplied with compressed air from purge system  13 . It is contemplated that swirler plate  60  may additionally or alternatively be connected to mounting element  58  by way of a snap-ring  70 , a threaded fastener (not shown), welding, or in any other manner known in the art, if desired. 
   Swirler plate  60  may include a through hole  72 , a grounded electrode  74 , and a plurality of annularly disposed air vents  76 . Grounded electrode  74  may be located at a periphery of through hole  72  to interact with spark plug  54 . Air vents  76  may mix air from purge system  13  with injections of fuel inside can  62 . The mixing of air and fuel within can  62  may improve combustion. It is contemplated that air vents  76  may additionally or alternatively be directed to the outer periphery of can  62  for cooling and/or insulating purposes, if desired. 
   Can  62  may embody a tubular member configured to axially direct an ignited fuel/air mixture from auxiliary regeneration device  14  into the exhaust flow of treatment device  46 . In particular, can  62  may include a central opening  78  that fluidly communicates fuel from fuel injector  52  and air from chamber  68  with the exhaust flow. Can  62  may be generally straight and may have a predetermined length set during manufacture according to a desired flame introduction location (the distance that a flame resulting from the ignition of the fuel/air mixture extends from can  62  into the exhaust flow). In one example, this desired introduction location may be about 12 inches from an outlet  80  of can  62 . 
   Injector  52  may be disposed within mounting element  58  and connected to fuel line  32  by way of a fuel passageway  82  and a main control valve  84  (referring to  FIG. 1 ). Injector  52  may be operable to inject an amount of pressurized fuel into can  62  at predetermined timings, fuel pressures, and fuel flow rates. The timing of fuel injection into can  62  may be synchronized with sensory input received from a temperature sensor (not shown), one or more pressure sensors (not shown), a timer (not shown), or any other similar sensory devices such that the injections of fuel substantially correspond with a buildup of particulate matter within filtration media  48 . For example, fuel may be injected as a pressure of the exhaust flowing through exhaust treatment device  46  exceeds a predetermined pressure level or a pressure drop across filtration media  48  exceeds a predetermined differential value. Alternatively or additionally, fuel may be injected as the temperature of the exhaust flowing through exhaust treatment device  46  exceeds a predetermined value. It is contemplated that fuel may also be injected on a set periodic basis, in addition to or regardless of pressure and temperature conditions, if desired. 
   Main control valve  84  (referring to  FIG. 1 ) may include an electronically controlled valve element that is solenoid movable against a spring bias in response to a commanded flow rate from a first position at which pressurized fuel may be directed to common rail  24 , to a second position at which fuel may be directed to auxiliary regeneration system  14 . It is contemplated that main control valve  84  may alternatively be hydraulically or pneumatically actuated in an indirect manner, if desired. 
   Spark plug  54  may facilitate ignition of fuel sprayed from injector  52  into can  62  during a regeneration event. Specifically, during a regeneration event, the temperature of the exhaust exiting power unit  10  may be too low to cause auto-ignition of the particulate matter trapped within exhaust treatment device  46  or of the fuel sprayed from injector  52 . To initiate combustion of the fuel and, subsequently, the trapped particulate matter, a small quantity (i.e., a pilot shot) of fuel from injector  52  may be sprayed or otherwise injected toward the space between spark plug  54  and grounded electrode  74  to create a locally rich atmosphere readily ignitable by spark plug  54 . A spark developed across electrode of spark plug  54  and grounded electrode  74  may ignite the locally rich atmosphere creating a flame, which may be jetted or otherwise advanced toward the trapped particulate matter. The flame jet propagating from injector  52  may raise the temperature within exhaust treatment device  46  to a level that readily supports efficient ignition of a larger quantity (i.e., a main shot) of fuel from injector  52 . As the main injection of fuel ignites, the temperature within exhaust treatment device  46  may continue to rise to a level that causes ignition of the particulate matter trapped within filtration media  48 , thereby regenerating exhaust treatment device  46 . 
   Spark plug  54  may include multiple components that cooperate to ignite the fuel sprayed from injector  52 . In particular, spark plug  54  may include a body  86 , a terminal  88  extending from one end of body  86 , and a center electrode  90  extending from an opposing second end of body  86 . Body  86  may be threadingly received within stepped bore  66 , and separated from center electrode.  90  by an insulating element  92 . Center electrode  90  may be electrically connected to terminal  88 . It is contemplated that terminal  88  may alternatively be integral with center electrode  90  or omitted, if desired. 
   An electrical arc may be generated between center electrode  90  and grounded electrode  74 . That is, center electrode  90  may have a base end  94  operatively fixed to body  86 , a free tip end  96 , and a side portion  98  extending from base end  94  to free tip end  96 . When spark plug  54  is assembled within housing  50 , the free tip end  96  may extend from a first surface  99  of swirler plate  60  through hole  72  past a second surface  100  of swirler plate  60 . Grounded electrode  74  may have a base end  102  connected to the second surface  100  of swirler plate  60  (i.e., integrally formed with swirler plate  60 ), and a free tip end  104 . The free tip end  104  of grounded electrode  74  may extend toward the side portion  98  of center electrode  90 , and terminate at a radial position between the base end  102  and the side portion  98 . The distance between the free tip end  96  and the free tip end  104  may be designed such that, when a charge is directed through terminal  88  to center electrode  90 , an arc may form from the free tip end  96  to the free tip end  104  of grounded electrode  74 . This arc may facilitate ignition of the fuel/air mixture within can  62 . 
   INDUSTRIAL APPLICABILITY 
   The spark plug arrangement of the present disclosure may be applicable to a variety of exhaust treatment devices including, for example, particulate regeneration devices and catalytic warming devices that utilize a spark to ignite a fuel flow. In fact, the disclosed spark arrangement may even be implemented into the primary combustion chambers of an engine to ignite the fuel injected during the typical power-generating cycle. The disclosed spark arrangement may ensure optimal combustion of the fuel flow by minimizing the likelihood of fuel spray blockage and unintentional arcing, while protecting the spark arrangement from residual fuel and contamination. The operation of power unit  10  will now be explained. 
   Referring to  FIG. 1 , air and fuel may be drawn into the combustion chambers of power unit  10  for subsequent combustion. Specifically, fuel from common rail fuel system  12  may be injected into the combustion chambers of power unit  10 , mixed with the air therein, and combusted by power unit  10  to produce a mechanical work output and an exhaust flow of hot gases. The exhaust flow may contain a complex mixture of air pollutants composed of gaseous and solid material, which can include particulate matter. As this particulate laden exhaust flow is directed from the combustion chambers through exhaust treatment device  46 , particulate matter may be strained from the exhaust flow by filtration media  48 . Over time, the particulate matter may build up in filtration media  48  and, if left unchecked, the buildup could be significant enough to restrict, or even block the flow of exhaust through exhaust treatment device  46 . As indicated above, the restriction of exhaust flow from power unit  10  may increase the backpressure of power unit  10  and reduce the unit&#39;s ability to draw in fresh air, resulting in decreased performance of power unit  10 , increased exhaust temperatures, and poor fuel consumption. 
   To prevent the undesired buildup of particulate matter within exhaust treatment device  46 , filtration media  48  may be regenerated. Regeneration may be periodic or based on a triggering condition such as, for example, a lapsed time of engine operation, a pressure differential measured across filtration media  48 , a temperature of the exhaust flowing from power unit  10 , or any other condition known in the art. 
   As illustrated in  FIG. 2 , to initiate regeneration, injector  52  may be caused to selectively pass fuel into exhaust treatment device  46  at a desired rate, pressure, and/or timing. As an injection of fuel from injector  52  sprays into exhaust treatment device  46 , air may be mixed with the fuel via the air vents  76  of swirler plate  60 . As this fuel/air mixture swirls into combustion chamber  56  of can  62 , a current may be directed to center electrode  90  via terminal  88 . As the current builds within center electrode  90 , an arc may form from free tip end  96  of center electrode  90  to free tip end  104  of grounded electrode  74 , thereby igniting the mixture. The ignited flow of fuel and air may then raise the temperature of the particulate matter trapped within filtration media  48  to the combustion level of the entrapped particulate matter, burning away the particulate matter and, thereby, regenerating filtration media  48 . 
   Between and/or during regeneration events, spark plug  54  may be selectively purged of fuel and/or contaminates to ensure proper operation of spark plug  54 . To purge spark plug  54 , purge gas from source  44  may be directed through purge passageway  40 , past check valve  42 , through stepped bore  66 . The purge gas flowing into stepped bore  66  may force any remaining fuel within this bore out into combustion chamber  56 . By removing the fuel and/or contaminates from stepped bore  66 , the likelihood of arcing at a point other than the free tip end  94  of center electrode  90  may be ensured. 
   Because grounded electrode  74  may be attached to housing  50 , proper orientation of spark plug  54  may be ensured. That is, because the orientation of grounded electrode  74  is independent of the angular engagement of spark plug  54  with stepped bore  66 , it may be ensured that grounded electrode  74  is always correctly oriented with respect to fuel injector  52 , regardless of the angular orientation of spark plug  54 . This correct orientation may minimize the likelihood of grounded electrode  74  undesirably blocking fuel spray from fuel injector  52 , and center electrode  90  may always be positioned-correctly between fuel injector  52  and grounded electrode  74 . 
   In addition, because grounded electrode  74  may extend from housing  50  (i.e., from swirler plate  60 ), the likelihood of unintentional arcing may be minimized. Specifically, because grounded electrode  74  may extend from swirler plate  60 , its cantilevered distance may be short. This short cantilevered distance may minimize the amplitude of vibration induced within grounded electrode  74 . By minimizing the induced amplitude vibration, the proper distance between center electrode  90  and grounded electrode  74  may be consistently maintained, thereby minimizing the likelihood of arcing at a point other that the free tip end  96  of center electrode  90 , the likelihood of arcing with an improper current, and/or arcing at an improper timing. Further, the minimized vibration amplitude may correspond with an increased component life of grounded electrode  74 . The increased cross-section of grounded electrode  74  afforded by its connection to swirler plate  60  may further help to reduce the amplitude of vibrations induced therein. 
   It will be apparent to those skilled in the art that various modifications and variations can be made to the spark plug arrangement of the present disclosure without departing from the scope of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the spark plug arrangement disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.