Abstract:
An injector for injecting a reagent includes an electromagnet and an axially translatable valve member positioned within a housing. The valve member is moveable from a seated position to an unseated position in response to energizing the electromagnet. The valve member includes a hollow tube including a curled end having a reduced diameter sized to allow a ball to partially extend beyond the tube end but not pass through the tube. The tube includes an inwardly extending detent restricting the ball from movement within the tube. A pintle head is fixed to the tube and positioned proximate the electromagnet.

Description:
FIELD 
       [0001]    The present disclosure relates to injector systems and, more particularly, relates to an injector system for injecting a reagent, such as an aqueous urea solution, into an exhaust stream to reduce oxides of nitrogen (NO x ) emissions from diesel engine exhaust. 
       BACKGROUND 
       [0002]    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 ). 
         [0003]    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. 
         [0004]    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 may involve 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 may 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. 
         [0005]    Some reagent injection systems are configured to include a pump, a supply line and a return line such that aqueous urea is continuously pumped to minimize solidification and also transfer heat from the injector to the aqueous urea stored at a remote location. Some injectors are equipped with moveable members including a hollow tube to provide a return flow path for reagent that has not been injected. The hollow tubes may be welded to valve bodies having conically-shaped ends engaging a valve seat. The valve bodies are typically complex components constructed from high alloy metals. Relatively expensive electron beam or laser welding may be required to fix the tube to the valve body. While relatively complex injector valve members have functioned properly in the past, these components may be relatively costly, complex and sizeable. Accordingly, it may be desirable to provide an improved injector system including a reagent injector having an improved pintle assembly. 
       SUMMARY 
       [0006]    This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
         [0007]    An injector for injecting a reagent includes an electromagnet and an axially translatable valve member positioned within a housing. The valve member is moveable from a seated position to an unseated position in response to energizing the electromagnet. The valve member includes a hollow tube including a curled end having a reduced diameter sized to allow a ball to partially extend beyond the tube end but not pass through the tube. The tube includes an inwardly extending detent restricting the ball from movement within the tube. A pintle head is fixed to the tube and positioned proximate the electromagnet. 
         [0008]    A method of constructing a reagent injector includes providing a substantially cylindrical tube having a first end and an opposite second end. An inner diameter of the tube is reduced at the first end. A ball is inserted into the tube at the second end. The ball abuts an inner surface of the tube at the reduced diameter first end such that a portion of the ball extends outside of the tube beyond the first end. The tube is crimped to form a radially inwardly protruding detent to restrict the ball from moving toward the second end. A pintle head is coupled to the second end of the tube. 
         [0009]    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 
         [0010]    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. 
           [0011]      FIG. 1  is a schematic depicting an exemplary exhaust aftertreatment system including an electromagnetically controlled reagent injector constructed in accordance with the teachings of the present disclosure; 
           [0012]      FIG. 2  is a perspective view of a reagent injector constructed accordance to the teachings of the present disclosure; 
           [0013]      FIG. 3  is a cross-sectional view taken through the injector; 
           [0014]      FIG. 4  is a cross-sectional exploded view of the injector; 
           [0015]      FIG. 5  is a fragmentary partial exploded perspective view of the injector; 
           [0016]      FIG. 6  is a sectional perspective view of a valve member of the injector; and 
           [0017]      FIG. 7  is an enlarged fragmentary sectional view of the injector. 
       
    
    
       [0018]    Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
       DETAILED DESCRIPTION 
       [0019]    Example embodiments will now be described more fully with reference to the accompanying drawings. 
         [0020]    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. Pat. No. 8,047,452, issued Nov. 1, 2011, entitled “Method And Apparatus For Injecting Atomized Fluids”, which is incorporated herein by reference. 
         [0021]    With reference to the Figures, 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 . 
         [0022]    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. 
         [0023]    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. 
         [0024]    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. 
         [0025]    With reference now to  FIGS. 2-7 , reagent injector  100  will be further described. Reagent injector  100  includes an injector body  102  having an upper section  102   a  and a lower section  102   b . A flux frame  104  interconnects upper section  102   a  and lower section  102   b . A seal  106  is provided at an interface between the upper and lower sections. Lower section  102   b  may include a deformable portion  108  that is crimped to flux frame  104  at a retaining groove  109 . 
         [0026]    An electromagnet assembly  110  is positioned within upper section  102   a  as depicted in the Figures. Electromagnet assembly  110  includes a coil of wire  112  wrapped around a bobbin  114 . Flux frame  104  includes an end wall  116  adjacent bobbin  114  and a cylindrical wall  118  surrounding electromagnet assembly  110 . 
         [0027]    A pole piece  122  is received within a bore  124  of upper section  102   a . Pole piece  122  extends through bobbin  114 . A bore  128  extends through pole piece  122  to provide a return flow path for injected reagent as will be described in greater detail. A seal  130  is positioned between upper section  102   a  and pole piece  122 . An orifice  132  is positioned within bore  128  to restrict the rate of reagent flow therethrough. 
         [0028]    A valve member  138  is slidably positioned within a bore  140  extending through lower section  102   b . Valve member  138  is constructed as an elongated pintle including a stainless steel cylindrical tube  142 . A hardened steel ball  144  is fixed to an end  146  of tube  142 . Ball  144  is selectively engageable with a valve seat  148  provided on an orifice plate  150 . Orifice plate  150  may be coupled to and retained within a recess  152  of lower section  102   b . Orifice plate  150  includes an orifice  154  through which pressurized reagent may flow when valve member  138  is moved from its seated position. When valve member  138  is in the seated or closed position, ball  144  sealingly engages seat  148  such that reagent may not pass through orifice  154 . A spring  156  is positioned within bore  128  of pole piece  122  to urge valve member  138  toward the seated position. Valve member  138  is moveable to an unseated, open position where ball  144  is spaced apart from seat  148 . Valve seat  148  surrounds orifice  154  and may be conically or cone-shaped. 
         [0029]    A pintle head  158  is fixed to an end  159  of tube  142  opposite end  146 . Pintle head  158  is slidably positioned within a counterbore  160  formed in pole piece  122 . A running-class slip fit between pintle head  158  and bore  160  provides a guide for axial movement of valve member  138 . Another running-class fit may exist between tube  142  and bore  140  to provide another guide for aligning valve member  138  with seat  148 . Pintle head  158  may be stamped from a magnetic metal sheet. 
         [0030]    Valve member  138  may be rapidly and economically constructed by beginning with a substantially straight walled cylindrical tube. End  146  of tube  142  is mechanically deformed to curl the tube wall radially inwardly. This process step locally reduces an inner diameter of tube  142 . The new reduced inner diameter is sized to restrict ball  144  from passing therethrough while also allowing a portion of the ball to extend beyond end  146  such that the spherical surface of ball  144  may contact seat  148 . 
         [0031]    After end  146  of tube  142  is curled, ball  144  is inserted into tube  142  from end  159 . Ball  144  is urged into contact with an inner partially spherically-shaped surface  168  of tube  142 . At this time, tube  142  is further mechanically deformed in a crimping process where several circumferentially spaced apart detents  170  inwardly protrude to contact ball  144 . After the crimping process has been completed, ball  144  is retained at a fixed location between curved surface  168  and detents  170 . The present process avoids the costs and possible complications relating to other mechanical fastening processes including welding. 
         [0032]    To continue the manufacturing process step of valve member  138 , a portion  174  of tube  142  is necked down to have a reduced diameter. Tube  142  is cut to a predetermined overall length. Pintle head  158  is placed over portion  174  and placed in engagement with a stop  182  located at a transition between reduced diameter portion  174  and the adjacent portion of tube  142  having its original larger outer diameter. A bore  184  extending through pintle head  158  may be sized to engage reduced diameter portion  174  in a press-fit manner. After pintle head  158  has been assembled to tube  142 , end  159  of tube  142  is flared, crimped or otherwise mechanically deformed to provide an enlarged diameter flange  186  to trap pintle head  158  between stop  182  and flange  186 . Pintle head  158  may include a recess  187  in receipt of flange  186 . A plurality of radially extending apertures  188  are drilled through tube  142 . Apertures  188  are axially positioned at a location in communication with a reservoir  192  positioned in lower section  102   b.    
         [0033]    An inlet tube  194  is fixed to lower section  102   b  and provides a path for pressurized reagent to enter injector  100 . A filter  195  is mounted within inlet tube  194 . A passageway  196  extends through lower section  102   b  placing pressurized reagent provided from inlet tube  194  in communication with slots  198  of orifice plate  150 . Slots  198  urge pressurized reagent to swirl and exit orifice  154  when valve member  138  is in the open position. Passageway  196  is in communication with a passage  202  that is in turn in communication with reservoir  192 . As such, a return flow path for pressurized reagent that does not exit orifice  154  is provided. In particular, reagent flows through inlet tube  194 , passageway  196 , passage  202 , reservoir  192  and apertures  188  to enter tube  142 . Pressurized reagent flows through tube  142 , bore  128 , orifice  132  and exits injector  100  through an outlet  204 . 
         [0034]    A receptacle  210  of upper section  102   a  includes a terminal  212  in electrical communication with coil  112 . When coil  112  is electrically energized, a magnetic field is generated. Pintle head  158  is drawn toward pole piece  122  to move valve member  138  from the seated position to the unseated, open position. Pressurized fluid is injected into exhaust conduit  19 . 
         [0035]    It should be appreciated that the lightweight, easily manufacturable valve member previously described may also be used with any number of other injectors having different configurations than the injector depicted in the Figures. In addition to the manufacturing advantages previously presented, the valve member including a crimped pintle may facilitate the use of a reduced diameter tube in view of the inventive ball retention method. The corresponding bore in which the valve member slides may also be reduced in size such that the injector assembly may also exhibit reduced size and weight. 
         [0036]    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.