Abstract:
A reductant delivery unit having active cooling which is constructed to have sufficient structural robustness, and to improve corrosion resistance of the assembly, where an attack on the base injector is conceivable with the use of incorrect coolant media. The reductant delivery unit has an upper shield, a lower shield connected to the upper shield, and an inner sleeve. The reductant delivery unit also includes a lower sleeve connected to the inner sleeve and the lower shield. A liquid cooling cavity is formed by the connection between the inner sleeve and the lower shield, the lower sleeve and the lower shield, and the lower sleeve and the inner sleeve. Coolant flows into the liquid cooling cavity to provide a cooling function to an injector partially located within the inner sleeve, and a corrugated portion of the lower sleeve transfers heat away from at least a portion of the injector.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates generally to providing active cooling for a reductant delivery unit for an automotive selective catalytic reduction system. 
       BACKGROUND OF THE INVENTION 
       [0002]    New emissions legislation in Europe and North America is driving the implementation of new exhaust after treatment systems, particularly for lean-burn technologies such as compression-ignition (diesel) engines, and stratified-charge spark-ignited engines (usually with direct injection) that are operating under lean and ultra-lean conditions. Lean-burn engines exhibit high levels of nitrogen oxide emissions (NOx), that are difficult to treat in oxygen-rich exhaust environments characteristic of lean-burn combustion. Exhaust after treatment technologies are currently being developed that treat NOx under these conditions. 
         [0003]    One of these technologies includes a catalyst that facilitates the reactions of ammonia (NH 3 ) with the exhaust nitrogen oxides (NOx) to produce nitrogen (N 2 ) and water (H 2 O). This technology is referred to as Selective Catalytic Reduction (SCR). Ammonia is difficult to handle in its pure form in the automotive environment, therefore it is customary with these systems to use a liquid aqueous urea solution, typically at a 32% concentration of urea (CO(NH 2 ) 2 ). The solution is referred to as AUS-32, and is also known under its commercial name of AdBlue. The urea is delivered to the hot exhaust stream and is transformed into ammonia in the exhaust after undergoing thermolysis, or thermal decomposition, into ammonia and isocyanic acid (HNCO). The isocyanic acid then undergoes a hydrolysis with the water present in the exhaust and is transformed into ammonia and carbon dioxide (CO 2 ), the ammonia resulting from the thermolysis and the hydrolysis then undergoes a catalyzed reaction with the nitrogen oxides as described previously. 
         [0004]    In some systems, the reductant delivery unit (RDU) is mounted under the body of the vehicle, downstream of the exhaust line. This results in relatively low temperatures at the SCR catalyst, longer light-off times, and low conversion efficiency of the NOx. Attempts have been made to relocate the SCR catalyst and the RDU injector closer to the engine in order to provide higher temperature exhaust gas for quicker light-off and more efficient conversion of the NOx. 
         [0005]    However, this close placement may result in a high ambient thermal environment for the injector. In this case, active cooling of the injector may be required to prevent excessive heating of the injector tip, and hence of the AUS-32 working fluid. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention is a reductant delivery unit having active cooling which is constructed to have sufficient structural robustness, and to improve corrosion resistance of the assembly, where an attack on the base injector is conceivable with the use of incorrect coolant media. 
         [0007]    In one embodiment the reductant delivery unit has an upper shield, a lower shield connected to the upper shield, and an inner sleeve. An outer surface of the inner sleeve is connected to an inner surface of the upper shield and an inner surface of the lower shield. The reductant delivery unit also includes a lower sleeve having an outer surface, where a portion of the outer surface of the lower sleeve is connected to the inner surface of the inner sleeve, and another portion of the outer surface of the lower sleeve is connected to outer surface of the lower shield. A liquid cooling cavity is formed by the connection between the inner sleeve and the lower shield, the lower sleeve and the lower shield, and the lower sleeve and the inner sleeve. A corrugated portion is formed as part of the lower sleeve, and an injector is partially located within the inner sleeve, and partially located within the lower sleeve. Coolant flows into the liquid cooling cavity to provide a cooling function to the injector, and the corrugated portion of the lower sleeve transfers heat away from at least a portion of the injector. 
         [0008]    A first connection point is formed by the connection between the outer surface of the inner sleeve and the inner surface of the lower shield, a second connection point is formed by a portion of the outer surface of the lower sleeve connected to an inner surface of the inner sleeve, and a third connection point is formed by an area of the outer surface of the lower sleeve connected to the outer surface of the lower shield. 
         [0009]    The injector includes a lower valve body, and a portion of the lower valve body is press-fit into the corrugated portion of the lower sleeve. 
         [0010]    It is an object of the invention to provide delivery of AUS-32 to the engine exhaust for use in SCR exhaust after treatment systems on vehicles via an actively cooled reductant delivery unit (RDU). 
         [0011]    It is another object of this invention to provide active cooling for an RDU from a separate liquid circuit. Although the source of the cooling liquid may be varied, it is within the scope of the invention that engine coolant from an existing engine coolant circuit is used with the RDU of the present invention. 
         [0012]    It is another object of the invention to provide a solution to cooling the exhaust-mount injection units due to extreme high temperature mounting locations. 
         [0013]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0015]      FIG. 1  is a side view of a reductant delivery unit having active cooling, according to embodiments of the present invention; 
           [0016]      FIG. 2  is a sectional side view of a reductant delivery unit having active cooling, according to embodiments of the present invention; and 
           [0017]      FIG. 3  is a sectional view of a reductant delivery unit having active cooling, with several of the internal components removed, according to embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0018]    The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
         [0019]    Referring to the  FIGS. 1-3 , an embodiment of a reductant delivery unit for an automotive selective catalytic reduction (SCR) system with active cooling is shown generally at  10 . The reductant delivery unit  10  includes an outer shell or casing, shown generally at  12 , and the shell  12  includes a retaining cap  14 , which is connected to an upper shield  16 , and a lower shield  18 , which is also connected to the upper shield  16 . The retaining cap  14  and the shields  16 , 18  when connected together form a cavity, shown generally at  20 , in which various components are disposed. 
         [0020]    The cap  14  at least partially surrounds a hydraulic connector  22 . The hydraulic connector  22  has an inlet pipe  24 , and an inlet cup  26 , which in this embodiment are integrally formed together, but it is within the scope of the invention that the inlet pipe  24  and inlet cup  26  may be formed separately. The inlet pipe  24  includes an aperture  28  which extends through the pipe  24  and is in fluid communication with an inner cavity, shown generally at  30 , formed by the inlet cup  26 , best seen in  FIG. 2 . The inner cavity  30  is in fluid communication with an injector, shown generally at  32 , which is disposed within the cavity  20 . 
         [0021]    The retaining cap  14  maintains the inlet cup  26  in place via a weld with the upper shield  16 . The upper shield  16  is constructed so as to minimize heat transfer from the hot ambient environment to the inner volumes of the unit  10  and the AUS-32 fluid passages, particularly during heating transients (e.g., engine drop to idle after a mountain climb pulling a trailer). In so doing, the heat capacity of the upper shield  16  protects against short-term heating of the inner components of the injector  32 . The upper shield  16  is joined to the lower shield  18 , via a laser weld, but also possibly by brazing. 
         [0022]    The injector  32  includes an upper valve body  34 , which is hollow and in fluid communication with the inner cavity  30 . Part of the upper valve body  34  is surrounded by a first seal, which in this embodiment is an upper o-ring  36  which is in contact with the inner wall  38  of the inner cavity  30 , to provide a seal connection between the upper valve body  34  and the inlet cup  26 , ensuring all fluid that flows through the inlet cup  26  passes into the upper valve body  34 . 
         [0023]    The upper valve body  34  is partially surrounded by a housing  40  having a connector  42 . The connector  42  is in electrical communication with a coil  44 , and the coil  44  is part of a solenoid portion, shown generally at  46 . The solenoid portion  46  is part of the injector  32 , and controls the movement of a valve portion, shown generally at  48 , which is also part of the injector  32 . In addition to the coil  44 , the solenoid portion  46  also includes a pole piece  50  surrounded by the coil  44 , and a moveable armature  52 . The pole piece  50  and the armature  52  are substantially hollow such that a return spring  54  is disposed in a cavity, shown generally at  56 , formed by the pole piece  50  and armature  52 . The return spring  54  biases the armature  52  downward when looking at  FIG. 2 , and therefore biases the valve portion  48  toward a closed position. The return spring  54  is located between the armature  52  and a stopper  58 . 
         [0024]    The valve portion  48  includes a tube  60  connected to the armature  52  at a first end, shown generally at  62 , and a ball  64  connected to a second end, shown generally at  66 . The ball  64  is part of a valve, and the valve also includes a valve seat  68 . The valve seat  68  is mounted in the lower end of a lower valve body  70 , and the lower valve body  70  is connected to the pole piece  50 , such that the lower valve body  70  is partially surrounded by the coil  44 . Movement of the ball  64  is controlled by a guide  74 . The guide  74  includes a guide aperture  92  through which the ball  64  moves, and also includes side apertures  76  which the fluid flows through. The valve seat  68  includes a conical-shaped portion  78 , upon which the ball  64  rests when the valve is in the closed position. The valve seat  68  also includes a central aperture  80 , through which the fluid passes as the fluid exits the injector  32 . 
         [0025]    During the operation of the injector  32 , the valve, and more specifically the tube  60  and the ball  64 , are biased by the return spring  54  to contact the valve seat  68 , and therefore keep the valve in a closed position. When the coil  44  is energized, the armature  52  is drawn toward the pole piece  50 . The energizing of the coil  44  generates enough force that the armature  52  overcomes the force of the return spring  54 , and moves towards the pole piece  50 . Because the tube  60  is connected to the armature  52 , and the ball  64  is connected to the tube  60 , the movement of the armature  52  towards the pole piece  50  moves the ball  64  away from the valve seat  68 , opening the valve. When the valve is in an open position, the fluid flows from the aperture  28  through the inner cavity  30 , the upper valve body  34 , pole piece  50 , armature  52 , the tube  60  and out a plurality of exit apertures  72  formed as part of the tube  60 . After the fluid flows out of the exit apertures  72 , the fluid passes through the side apertures  76 , and out the central aperture  80 . 
         [0026]    When the coil  44  is no longer energized, the return spring  54  forces the armature  52  away from the pole piece  50 , and moves the armature  52 , the tube  60  and the ball  64  such that the ball  64  is placed against the conical-shaped portion  78  of the valve seat  68 , placing the valve in the closed position. 
         [0027]    The solenoid portion  46  also includes a casing  82  which at least partially surrounds the coil  44  and the lower valve body  70 . Surrounding part of the casing  82  is a second seal, which in this embodiment is a lower o-ring  84 , and the lower o-ring  84  is surrounded by an inner sleeve  86 . The inner sleeve  86  is disposed within the cavity  20 , and part of the outer surface  88  of the inner sleeve  86  is connected (through the use of a weld) to both the inner surface  90  of the upper shield  16 , and the inner surface  94  of the lower shield  18 . The connection between the outer surface  88  of the inner sleeve  86  and the inner surface  94  of the lower shield  18  forms a first connection point  108 . Part of the lower valve body  70  is also surrounded by a lower sleeve  96 . The lower sleeve  96  includes an outer surface  98 , and part of the outer surface  98  of the lower sleeve  96  is connected to an inner surface  100  of the inner sleeve  86  by a weld or brazing process forming a second connection point  102 . Another area of the outer surface  98  of the lower sleeve  96  is connected to the outer surface  104  of the lower shield  18  by a weld or brazing process to form a third connection point  106 . 
         [0028]    The lower sleeve  96  surrounds a lower end, shown generally at  110 , of the lower valve body  70 . More specifically, the lower sleeve  96  is shaped such that the lower sleeve  96  includes a corrugated portion  112  having ridges which contact the lower end  110  of the lower valve body  70 , such that the lower valve body  70  is press-fit into the lower sleeve  96 . The corrugated portion  112  functions to transfer heat away from the portion of the lower valve body  70  surrounded by the corrugated portion  112 . The connection between the inner sleeve  86  and the lower shield  18 , the connection between the lower sleeve  96  and the lower shield  18 , and the connection between the lower sleeve  96  and the lower shield  18  forms a liquid cooling cavity, shown generally at  114 . 
         [0029]    The lower shield  18  has various contours and shapes, which not only forms the lower end  110  used for connection with the lower sleeve  96 , but also forms the shape of the liquid cooling cavity  114 . There are also two apertures formed as part of the lower shield  18 , into which two hydraulic connectors are fixedly mounted. More specifically, there is an inlet hydraulic connector  116  mounted in a coolant inlet aperture (not shown), and an outlet hydraulic connector  118  mounted in a coolant outlet aperture  120 . The coolant outlet aperture  120  and the coolant inlet aperture are substantially similar, therefore only one is shown. 
         [0030]    The lower shield  18  is joined hermetically to the inner sleeve  86  via laser weld or brazing. The outer surface  88  of the inner sleeve  86  and the inner surface  94  of the lower shield  18  comprise the principal boundary surfaces of the liquid cooling cavity  114 . Liquid is brought to and evacuated from the cavity  114  via the inlet aperture and outlet aperture  120  in the lower shield  18  equipped with hydraulic connectors  116 , 118 , also joined to the lower shield  18 , preferably by brazing. 
         [0031]    The inner sleeve  86  is designed so as to minimize the space between the inside of the inner sleeve  86  and the various injector overmold surfaces. It is also understood that this volume could also be filled with a conductive compound to improve heat transfer to the liquid coolant in the cavity  114 . Additionally, the inner sleeve  86 , lower sleeve  96 , and the lower shield  18  are shaped such that the stress on the connection points  108 , 102 , 106  is minimized. The lower sleeve  96  includes an outwardly extending flange  122  which contacts and connects to the outer surface  104  of the lower shield  18 . More particularly, the lower shield  18  includes an inwardly extending flange  124  which is connected to the outwardly extending flange  122  through a weld or brazing process to form the third connection point  106 . The outer surface  104  is part of the inwardly extending flange  124 . The lower sleeve  96  also includes an upwardly extending flange  126  which contacts and connects to the inner surface  100  of the inner sleeve  86 . In this embodiment, the inner sleeve  86  includes a downwardly extending flange  128  which connects to the upwardly extending flange  126  through a weld or brazing process to form the second connection point  102 . The inner surface  100  of the inner sleeve  86  is part of the downwardly extending flange  128 . 
         [0032]    Mounted to the outer surface of the lower shield  18  is a v-clamp flange  130  which is used for mounting the reductant delivery unit  10  somewhere along the exhaust system. In one embodiment, the reductant delivery unit  10  may be mounted to an exhaust pipe, but it is within the scope of the invention that the reductant delivery unit  10  may be mounted to an exhaust manifold, or other exhaust system component. During the operation of the unit  10 , engine coolant is pumped to the inlet hydraulic connector  116  and flows through the inlet hydraulic connector  116  into the liquid cooling cavity  114 . The coolant then circulates through the liquid cooling cavity  114  and exits the liquid cooling cavity  114  through the outlet hydraulic connector  118 . The coolant is prevented from contacting the solenoid portion  46  of the injector  32  because of the welds at the three connection points  108 , 102 , 106 . This circulation of coolant into and out of the liquid cooling cavity  114  cools the reductant delivery unit  10 , and provides the reductant delivery unit  10  with a more consistent operating temperature. 
         [0033]    The interface with the exhaust line is shown here as one suited for the v-clamp flange  130 . Other mounting configurations are also possible, including flanges with bolts. The v-clamp flange  130  (or other flange configurations) is joined to the lower shield  18 , also preferably by brazing. It is understood that a number of the braze operations could be accomplished simultaneously with one operation. The flanges  130  would then provide suitable surfaces and geometries for implementation of a sealing gasket to prevent exhaust gas leakage through the flange/boss interface. 
         [0034]    An additional advantage of providing the reductant delivery unit  10  with liquid cooling is the unit  10  then has the ability to maintain a constant fluid temperature of the urea, as defined by the liquid cooling circuit. In this way, temperature corrections to adjust for density and viscosity changes in the working fluid can be greatly simplified, or even eliminated, as can be any temperature feedback systems that would be normally required (e.g. coil current measurements). 
         [0035]    When in use, urea solution is fed through the inlet pipe  24 , such that the urea solution passes through the inner cavity  30  and into the upper valve body  34  of the injector  32 . In this embodiment, the inlet pipe  24  is depicted as being substantially perpendicular to the injector  32 , which presents certain packaging advantages for some installations. However, the radial orientation of the inlet pipe  24  may be varied, as well as the axial orientation. In this embodiment, the inlet pipe  24  and the inlet cup  26  are integrated as one piece; however, a two piece construction (inlet pipe  24  and inlet cup  26 ) is also possible which may be advantageous from a construction standpoint. 
         [0036]    The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.