Patent Publication Number: US-8973895-B2

Title: Electromagnetically controlled injector having flux bridge and flux break

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is continuation-in-part of U.S. application Ser. No. 13/164976, filed Jun. 21, 2011, which is a continuation-in-part of U.S. application Ser. No. 13/023870, filed Feb. 9, 2011, which claims the benefit of U.S. Provisional Application No. 61/303,146, filed Feb. 10, 2010. The entire disclosures of each of the above applications are incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to injector systems and, more particularly, relates to an injector system for injecting reagent, such as an aqueous urea solution, into an exhaust stream to reduce oxides of nitrogen (NO x ) emissions from diesel engine exhaust. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. Lean burn engines provide improved fuel efficiency by operating with an excess of oxygen, that is, a quantity of oxygen that is greater than the amount necessary for complete combustion of the available fuel. Such engines are said to run “lean” or on a “lean mixture.” However, this improved or increase in fuel economy, as opposed to non-lean burn combustion, is offset by undesired pollution emissions, specifically in the form of oxides of nitrogen (NO x ). 
     One method used to reduce NO x  emissions from lean burn internal combustion engines is known as selective catalytic reduction (SCR). SCR, when used, for example, to reduce NO x  emissions from a diesel engine, involves injecting an atomized reagent into the exhaust stream of the engine in relation to one or more selected engine operational parameters, such as exhaust gas temperature, engine rpm or engine load as measured by engine fuel flow, turbo boost pressure or exhaust NO x  mass flow. The reagent/exhaust gas mixture is passed through a reactor containing a catalyst, such as, for example, activated carbon, or metals, such as platinum, vanadium or tungsten, which are capable of reducing the NO x  concentration in the presence of the reagent. 
     An aqueous urea solution is known to be an effective reagent in SCR systems for diesel engines. However, use of such an aqueous urea solution involves many disadvantages. Urea is highly corrosive and may adversely affect mechanical components of the SCR system, such as the injectors used to inject the urea mixture into the exhaust gas stream. Urea also may solidify upon prolonged exposure to high temperatures, such as temperatures encountered in diesel exhaust systems. Solidified urea will accumulate in the narrow passageways and exit orifice openings typically found in injectors. Solidified urea may also cause fouling of moving parts of the injector and clog any openings or urea flow passageways, thereby rendering the injector unusable. 
     In addition, if the urea mixture is not finely atomized, urea deposits will form in the catalytic reactor, inhibiting the action of the catalyst and thereby reducing the SCR system effectiveness. High injection pressures are one way of minimizing the problem of insufficient atomization of the urea mixture. However, high injection pressures often result in over-penetration of the injector spray plume into the exhaust stream, causing the plume to impinge on the inner surface of the exhaust pipe opposite the injector. Over-penetration also leads to inefficient use of the urea mixture and reduces the range over which the vehicle can operate with reduced NO x  emissions. Only a finite amount of aqueous urea can be carried on a vehicle, and what is carried should be used efficiently to maximize vehicle range and reduce the need for frequent replenishment of the reagent. 
     Several known reagent injectors include a solenoid valve for metering the supply of reagent into the exhaust stream. Typically, a magnetic moveable member of the valve is urged to translate between open and closed positions as an electromagnet is selectively energized and deenergized. The electromagnets of many prior injectors include multiple flux leakage areas resulting in a poorly defined magnetic circuit. Control of the reagent valve may not be optimized using these types of magnetic circuits. The amount of reagent actually dispensed within the exhaust system may vary from a target rate of reagent injection resulting in inefficient use of the onboard reagent. The time required for the valve to cycle from a closed condition, to an opened condition, and back to a closed condition, may be larger than desired due to the magnetic circuit arrangement. 
     Further, aqueous urea is a poor lubricant. This characteristic adversely affects moving parts within the injector and requires that relatively tight or small fits, clearances and tolerances be employed between adjacent or relatively moving parts within an injector. Aqueous urea also has a high propensity for leakage. This characteristic adversely affects mating surfaces requiring enhanced sealing resources in many locations. 
     It may be advantageous to provide an improved electromagnetically controlled injector having a well defined magnetic circuit to improve reagent injection control. 
     Methods and apparatus of the present disclosure provide the foregoing and other advantages. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     An injector for injecting a reagent includes an axially translatable valve member positioned within a housing. An electromagnet is positioned within the housing and includes a cylindrically-shaped coil of wire. The valve member moves between a seated position and an unseated position in response to energizing the electromagnet. A flux sleeve passes through the coil and includes two magnetic portions interconnected by a non-magnetic portion. Each of the magnetic portions is aligned with transverse planes defined by the ends of the cylindrical coil. The non-magnetic portion is axially positioned between the transverse planes. 
     An injector for injecting a reagent includes an axially translatable valve member positioned within a housing. An electromagnet is positioned within the housing and includes a coil of wire circumscribing at least a portion of the valve member. The valve member moves between a seated position and an unseated position in response to energizing the electromagnet. A flux frame surrounds the coil. The frame includes first and second radially extending portions axially spaced apart from one another and extending along substantially parallel planes positioned on opposite sides of the coil. A flux sleeve includes two magnetic portions interconnected by a non-magnetic portion. Each of the magnetic portions is intersected by one of the planes in which the radially extending flux frame portions lie to define flux bridges. The non-magnetic portion is surrounded by the coil and axially positioned between the parallel planes to define a flux break. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is a schematic depicting an exemplary exhaust aftertreatment system including an electromagnetically controlled reagent injector having a flux bridge and flux break in accordance with the teachings of the present disclosure; 
         FIG. 2  is a perspective view of the electromagnetically controlled reagent injector; 
         FIG. 3  is an exploded perspective view of the reagent injector; and 
         FIG. 4  is a cross-sectional view taken through the injector depicted in  FIGS. 2 and 3 . 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. 
     It should be understood that although the present teachings may be described in connection with diesel engines and the reduction of NO x  emissions, the present teachings may be used in connection with any one of a number of exhaust streams, such as, by way of non-limiting example, those from diesel, gasoline, turbine, fuel cell, jet or any other power source outputting a discharge stream. Moreover, the present teachings may be used in connection with the reduction of any one of a number of undesired emissions. For example, injection of hydrocarbons for the regeneration of diesel particulate filters is also within the scope of the present disclosure. For additional description, attention should be directed to commonly-assigned U.S. Patent Application Publication No. 2009/0179087A1, filed Nov. 21, 2008, entitled “Method And Apparatus For Injecting Atomized Fluids”, which is incorporated herein by reference. 
     With reference to the FIGS., a pollution control system  8  for reducing NO x  emissions from the exhaust of a diesel engine  21  is provided. In  FIG. 1 , solid lines between the elements of the system denote fluid lines for reagent and dashed lines denote electrical connections. The system of the present teachings may include a reagent tank  10  for holding the reagent and a delivery module  12  for delivering the reagent from the tank  10 . The reagent may be a urea solution, a hydrocarbon, an alkyl ester, alcohol, an organic compound, water, or the like and can be a blend or combination thereof. It should also be appreciated that one or more reagents can be available in the system and can be used singly or in combination. The tank  10  and delivery module  12  may form an integrated reagent tank/delivery module. Also provided as part of system  8  is an electronic injection controller  14 , a reagent injector  16 , and an exhaust system  18 . Exhaust system  18  includes an exhaust conduit  19  providing an exhaust stream to at least one catalyst bed  17 . 
     The delivery module  12  may comprise a pump that supplies reagent from the tank  10  via a supply line  9 . The reagent tank  10  may be polypropylene, epoxy coated carbon steel, PVC, or stainless steel and sized according to the application (e.g., vehicle size, intended use of the vehicle, and the like). A pressure regulator (not shown) may be provided to maintain the system at predetermined pressure setpoint (e.g., relatively low pressures of approximately 60-80 psi, or in some embodiments a pressure of approximately 60-150 psi) and may be located in the return line  35  from the reagent injector  16 . A pressure sensor may be provided in the supply line  9  leading to the reagent injector  16 . The system may also incorporate various freeze protection strategies to thaw frozen reagent or to prevent the reagent from freezing. During system operation, regardless of whether or not the injector is releasing reagent into the exhaust gases, reagent may be circulated continuously between the tank  10  and the reagent injector  16  to cool the injector and minimize the dwell time of the reagent in the injector so that the reagent remains cool. Continuous reagent circulation may be necessary for temperature-sensitive reagents, such as aqueous urea, which tend to solidify upon exposure to elevated temperatures of 300° C. to 650° C. as would be experienced in an engine exhaust system. 
     Furthermore, it may be desirable to keep the reagent mixture below 140° C. and preferably in a lower operating range between 5° C. and 95° C. to ensure that solidification of the reagent is prevented. Solidified reagent, if allowed to form, may foul the moving parts and openings of the injector. 
     The amount of reagent required may vary with load, exhaust gas temperature, exhaust gas flow, engine fuel injection timing, desired NO x  reduction, barometric pressure, relative humidity, EGR rate and engine coolant temperature. A NO x  sensor or meter  25  is positioned downstream from catalyst bed  17 . NO x  sensor  25  is operable to output a signal indicative of the exhaust NO x  content to an engine control unit  27 . All or some of the engine operating parameters may be supplied from engine control unit  27  via the engine/vehicle databus to the reagent electronic injection controller  14 . The reagent electronic injection controller  14  could also be included as part of the engine control unit  27 . Exhaust gas temperature, exhaust gas flow and exhaust back pressure and other vehicle operating parameters may be measured by respective sensors. 
     With reference now to  FIGS. 2-4 , reagent injector  100  will be further described. Reagent injector  100  includes an outer injector body  102  having an outer body upper section  102   a  and an outer body lower section  102   b . Outer body lower section  102   b  may include a deformable portion  103  that is crimped to outer body upper section  102   a . An elongated inner lower body  104  may be received within at least one of outer body upper section  102   a  and outer body lower section  102   b . Elongated inner lower body  104  defines a cylindrical central bore  106  in fluid communication with an orifice plate  108  to define at least one exit orifice  110  that passes completely through the orifice plate  108 . 
     Orifice plate  108  may be coupled to and retained within outer body lower section  102   b  using an orifice plate holder  112 . Orifice plate holder  112  may be integrally formed with inner lower body  104 , if desired. Alternately, orifice plate holder  112  is formed separately, as shown in the FIGS., to include a reduced diameter portion  114  spaced apart from an inner wall  116  of outer body lower section  102   b . A supply fluid passageway  118  is formed therebetween. Reduced diameter portion  114  is hollow and receives a reduced diameter end portion  120  of inner lower body  104 . Plate holder  112  may be fixed to inner lower body  104  and outer body lower section  102   b  via a process such as electron beam welding. Orifice plate holder  112  also includes a central bore  124  coaxially aligned with central bore  106  and having a smaller inner diameter than central bore  106 . A plurality of passageways  125  extend through plate holder  112  to fluidly interconnect passageway  118  with a cavity  126  formed between reduced diameter end portion  120  and central bore  124 . 
     A valve member  130  is slidably mounted within central bore  106 . Valve member  130  includes an elongated pintle  132  having a conically shaped first end  134  and an opposite second end  136 . Conical end  134  is selectively engageable with valve seat  140  to define a sealed and closed position of valve member  130  when seated. An unsealed, opened position exists when pintle  132  is unseated from valve seat  140 . Valve seat  140  surrounds exit orifice  110 . The valve seat may be conically or cone-shaped as shown to complement the shape of conical end  134  of pintle  132  to restrict the flow of reagent through orifice  110 . Depending on the application and operating environment, pintle  132  and orifice plate  108  may be made from a carbide material, which may provide desired performance characteristics and may be more easily and cost-effectively manufactured. In addition, limitations or disadvantages associated with other materials may be avoided, such as those associated with manufacturing complex part shapes. Carbide may provide additional advantages, such as insensitivity to brazing temperatures that may range from 870-980° C., as opposed to carbon steels and tool steels, which may distemper. Carbide may also provide an increased surface hardness when compared to the hardness achievable with most other steels. Carbide may also be advantageous with regard to overall wear resistance. 
     A pintle head  142  is fixed to end  136  of pintle  132 . Pintle head  142  is slidably positioned within an enlarged bore  144  of inner lower body  104 . A running-class slip fit between pintle head  142  and bore  144  provides an upper guide for valve member  130 . A lower valve member guide is formed at the sliding interface between central bore  124  and pintle  132 . Based on this arrangement, valve member  130  is accurately aligned with valve seat  140  and exit orifice  110 . 
     A bottom surface  150  of pintle head  142  is spaced apart from a surface  152  of inner lower body  104  to define a cavity  154  in fluid communication with cavity  126  via a passageway  158  defined as a portion of central bore  106  that is not occupied by pintle  132 . A passageway  160  extends through pintle head  142  to define a portion of a reagent return passageway. 
     A pole piece  164  having a first end  166  is sized to be received within bore  144 . First end  166  of pole piece  164  is fixed to inner lower body  104  using a process such as electron beam welding. An opposite second end  168  of pole piece  164  is sealingly fitted within a bore  172  formed in outer body upper section  102   a . A seal  176  separates an inlet passageway  178  from an outlet passageway  180  within outer body upper section  102   a . Elongated pole piece  164  includes a central bore  184  extending therethrough. Central bore  184  is coaxially aligned with central bore  106 . A counterbore  188  inwardly extends from second end  168  of pole piece  164  that is coaxially aligned with a counterbore  190  extending into pintle head  142 . A compression spring  194  is positioned within counterbores  188 ,  190  to urge valve member  130  into engagement with seat  140 . 
     An electromagnet assembly  200  is positioned within outer body upper section  102   a  as depicted in the FIGS. Electromagnet assembly  200  may include a plastic material  201  overmolded to encapsulate the other components of electromagnet assembly  200  therein. Electromagnet assembly  200  includes a coil of wire  202  wrapped around a bobbin  204 . A two-piece flux frame  207  includes a first frame half  208  fixed to a second flux frame half  210  positioned to circumferentially surround wire  202  and bobbin  204 . Pintle head  142  is constructed from a magnetic material such as 430 stainless steel such that electrical energization of coil  202  produces a magnetic field urging pintle head  142  toward pole piece  164 . End  134  of pintle  132  becomes disengaged from seat  140  to allow reagent to flow through exit orifice  110 . Coil  202  may be energized via access to a receptacle  211 , for example, in response to a signal from electronic injection controller  14 . Electronic injection controller  14  receives sensor input signals and determines when reagent is to be injected into the exhaust stream to provide selective catalytic reduction of NO x  emissions. 
     Controller  14  also defines the reagent injection duration and reagent injection rate. Depending on the engine operating condition, load, ambient air temperature, exhaust temperature, and other factors, it may be desirable to control injector  100  to deliver a relatively wide range of reagent injection rates. To achieve this goal, it may be desirable to minimize the total time associated with moving pintle  132  from a seated position, to an open position, and returned to the seated position. Accurate control of the position of pintle head  142  may be achieved by providing a well defined magnetic circuit. 
     Flux frame half  210  includes a radially extending portion  214  generally extending along transverse line  216 . Pintle head  142  includes an enlarged diameter portion  218  intersected by line  216 . Both flux frame half  210  and pintle head  142  are made from a magnetic material. To further define the magnetic circuit, inner lower body  104  is constructed from a non-magnetic material such as 304 stainless steel. A portion of inner lower body  104  through which line  216  crosses includes a minimum cross-sectional thickness to minimize any interruption in magnetic flux. 
     A fluid sleeve assembly  220  is depicted as a three-piece assembly having a first flux bridge collar  224  and a second flux bridge collar  226  interconnected by a flux break  228 . Fluid sleeve assembly  220  is shaped as an elongated hollow cylindrical member sized and positioned to define a portion of inlet passage  178 . First and second seals  232 ,  234  assure that pressurized reagent continues to travel through inlet passage  178  and does not enter electromagnet assembly  200 . Each of flux bridge collars  226  and  224  are substantially the same including a counterbore with a first reduced inner diameter  238  and a second larger inner diameter  240 . The external surface of each flux collar is also stepped including a cylindrical surface  242  having a larger outer diameter than a second cylindrical surface  244 . Flux break  228  is a substantially right circular cylinder having an inner surface  248  engaged and fixed to each reduced diameter outer surface  244 . Outer surface  242  engages or is very minimally spaced apart from walls  252  and  254  that define circular apertures extending through flux frame halves  210 ,  208 . Inner cylindrical surface  238  of flux bridge collar  224  is sized to closely fit inner lower body  104  and minimize any air gap through which line  216  intersects. 
     Inner cylindrical surface  238  of flux bridge collar  226  is sized to cooperate with an enlarged diameter portion  260  of pole piece  164 . Flux frame half  208  includes a radially inwardly extending portion  264  extending along a line  266 . Enlarged diameter portion  260  and flux bridge collar  226  are axially positioned to be aligned with line  266  and provide a magnet circuit pathway across injector  100 . Flux frame halves  208  and  210  are constructed from a magnetic material such as 1018 low carbon steel. Flux bridge collars  224  and  226  are constructed from ferritic 430 stainless steel. Pole piece  164  is made from ferritic 430 stainless steel or a similar magnetic material. Pintle head  142  may be made from ferritic 430 stainless steel. Flux break  228  is made from non-ferritic and non-magnetic  304  stainless steel as is inner lower body  104 . Constructing the previously described components from magnetic and non-magnetic materials as well as closely positioning the magnetic materials adjacent to one another along lines  216  and  266  greatly improves the magnetic circuit performance associated with electromagnet assembly  200 . Benefits may include the use of a smaller coil wire, a lesser number of turns of wire, and a reduced quantity of electric current to provide an improved electromagnetic actuator having lower cost, reduced size and mass. Increased control regarding the position of valve member  130  is also realized. It should also be appreciated that the transverse planes defined by the ends of cylindrical wire coil  202  may be interpreted as part of the magnetic circuit as well as the planes containing lines  216  and  266 . At least one of these transverse planes cuts through pintle head  142 , flux bridge collars  224 ,  226  and enlarged diameter pole piece portion  260 . 
     A reagent fluid path is defined within injector  100  when pintle  132  is in the closed position. The fluid path provides for circulation of fluid through injector  100 . More particularly, the reagent fluid path extends from an inlet  270  of outer body upper section  102   a  through an inlet filter  268  and inlet passageway  178  including a gap between an outer surface of pole piece  164  and outer body upper section  102   a , through fluid sleeve assembly  220 , fluid passageway  118 , the paths formed in plate holder  112  through cavity  126 , passageway  158 , passageway  160 , central bore  184 , outlet passageway  180 , a restrictor orifice  272 , an outlet filter  274 , to exit outlet  278 . Typically, reagent entering inlet  270  is at a first relatively cool temperature compared to the exhaust passing through exhaust system  18  in close proximity to orifice  110 . The recirculation of reagent through injector  100  transfers heat from orifice plate  108  and orifice plate holder  112 . The recirculation of reagent also assists in transferring heat from coil  202  because bobbin  204  is placed in close contact with fluid sleeve assembly  220  through which reagent flows. 
     When coil  202  is electrically energized, a magnetic field is generated and pintle head  142  is urged against the biasing force of spring  194  to unseat pintle end  134 . Pressurized reagent located within cavity  126  passes between pintle  132  and seat  140  and through exit orifice  110  to inject reagent into an exhaust stream flowing through exhaust system  18 . Electromagnet assembly  200  may be controlled by any number of methods including pulse width modulation to open and close exit orifice  110  at a predetermined frequency. 
     Furthermore, the foregoing discussion discloses and describes merely exemplary embodiments of the present disclosure. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that various changes, modifications and variations may be made therein without departing from the spirit and scope of the disclosure as defined in the following claims.