Abstract:
A urea storage system comprising a storage tank for a urea solution is provided. The system comprises a heated reservoir, a channel connecting the storage tank to the heated reservoir and a pump for drawing urea from the heated reservoir. A second pump including an actuator comprising a memory shape metal for drawing urea from the storage tank to the heated reservoir is also provided.

Description:
[0001]    The present disclosure relates to pumps for vehicle mounted urea reservoirs. 
       BACKGROUND OF THE INVENTION 
       [0002]    Urea selective catalyst reaction (SCR) systems treat diesel exhaust to reduce tailpipe emissions. A urea and water solution is injected into the exhaust stream. Hydrolysis converts the solution to ammonia upstream of a SCR catalyst converter. The ammonia reacts with NO 2  trapped on the SCR catalyst to form N 2  and CO 2  and thus reduce pollution of the diesel exhaust. 
         [0003]    At temperatures below −11° C., the urea solution freezes into solid ice. A thermal heating system thaws the solid ice into liquid solution. A pump transports the thawed solution to an injector that is in the exhaust stream. In order to provide adequate operation during cold weather, a predetermined amount of the urea solution must be proximate the heater and the pump&#39;s pickup tube. This is accomplished by using a reservoir within the urea solution storage tank. The reservoir holds the heater and the predetermined amount of urea. The solution level within the reservoir is typically even with the solution level within the remainder of the storage tank unless a pump and check valve system is employed. The pump and check valve system pumps solution from the storage tank into the reservoir, thereby raising the solution level within the reservoir to above the solution level in the remainder of the storage tank. A check valve prevents the solution from draining out of the reservoir and back into the storage tank. 
         [0004]    Present designs do not have pumps due to cost and reliability issues related to freezing and thawing of the urea solution. Meeting legislated emission requirements is not a problem if the storage tank is full of solution when it freezes. However, if the solution level in the storage tank is low, such as 25% full, the solution level in the reservoir is not sufficient to supply the amount of urea demanded until the outer tank thaws, which may not be sufficient to provide urea to the exhaust treatment system. 
       SUMMARY OF THE INVENTION 
       [0005]    A urea storage system comprising a storage tank for a urea solution is provided. The system comprises a heated reservoir a channel connecting the storage tank to said heated reservoir and a pump for drawing urea from the heated reservoir. A second pump including an actuator comprising a memory shape metal for drawing urea from the storage tank to the heated reservoir is also provided. 
         [0006]    The invention also contemplates a method of pumping urea solution in a urea storage system. The method provides a urea storage tank and aurea reservoir fluidly connected to the storage tank. A pump, including an actuator is interposed between the storage tank and the reservoir. The method comprises moving the actuator to a first position by energizing a shape memory metal attached to the actuator and moving the actuator to a second position by de-energizing the shape memory metal attached to said actuator of said pump. Finally, the method comprises decompressing a spring in contact with said actuator. 
         [0007]    The present invention provides a simple mechanism for pumping urea solution in applications where urea is subject to freeze/thaw cycles. Such applications include motor vehicles that are subject to ambient temperatures below the freezing point of the urea solution. The simplicity of the disclosed pumping mechanism is tolerant of frozen urea solution and provides a method of quickly thawing frozen urea for maintaining liquid urea for exhaust treatment. The present invention resumes pumping when the urea solution within it has been sufficiently heated to return to a liquid state. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the drawings in which: 
           [0009]      FIG. 1  is a functional block diagram of one embodiment urea of a solution storage system in accordance with the present invention; 
           [0010]      FIG. 2  is a pictorial of the pump and reservoir, partially in cross-section, in accordance with the present invention; 
           [0011]      FIG. 3  is a functional block diagram of the pump in accordance with the present invention; and 
           [0012]      FIG. 4  is a pictorial view of the reservoir partially in cross-section, in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    Referring now to  FIG. 1 , a functional block diagram is shown of a urea storage system  10 . Storage system  10  includes a storage tank  12  that contains a urea solution  14 . Urea solution  14  can be refilled via a filler opening  16 . Storage tank  12  includes a reservoir  18 . Reservoir  18  contains a portion of solution  14  within a volume that can be heated by a heater  20 . A pump  22  pumps solution  14  into reservoir  18 . The level of solution  14  can therefore be higher than the solution level in tank  12  providing a pressure load in reservoir  18  that is greater than the pressure head within tank  12 . A check valve  24  prevents solution  14  from draining out of reservoir  18  and returning to storage tank  12 . Another pump  26  transports solution  14  from reservoir  18  to a urea injection system that injects solution  14  into the engine exhaust stream. 
         [0014]    Referring now to  FIG. 2 , one of several embodiments is shown of reservoir  18 . Reservoir  18  includes a level sensing tube  30  that contains a printed circuit board (PCB)  32 . PCB  32  includes electronic circuitry that senses the position or height of a level sensing float  34 . Level sensing tube  30  contains PCB  32  and guides level sensing float  34  which is concentric to tube  30  and rides circumferentially thereon. Level sensing tube  30  also serves as a cylinder which houses pump  22  therein at a bottom portion  31  of tube  30 . Heater  20  heats urea solution in the proximity of level sensing tube  30  and at the bottom of reservoir  18 . 
         [0015]    Referring now to  FIG. 3 , a functional block diagram is shown of pump  22 . PCB  32  is secured within level sensing tube  30  at an upper end  33 . A shape memory metal, shown as shape memory wire  40  is disposed within upper end  33  and is adapted to expand and contract based on temperature. As shown, a first end  41  of shape memory wire  40  attaches to a piston  42 . Piston  42  includes a sealing ring  43  about the circumference of piston  42  and in contact with the inner circumference of bottom portion  31  of tube  30 . A second end  43  of shape memory wire  40  attaches to PCB  32  through a strain limiting spring  44 . Spring  44  is employed to limit strain in shape memory wire  40 . However, it will be appreciated that any elastic member capable of conducting electricity can be substituted. In addition, strain limiting spring  44  is shown as being connected between PCB  32  and shape memory wire  40  at a second end  43 ; however, it will be appreciated that spring  44  may also be connected at the first end  41  of shape memory wire  40 , between shape memory wire  41  and piston  42 . 
         [0016]    PCB  32  is connected to a power source and includes electrical terminals  46  and  50 , extending therefrom, that selectively provide electrical energy. The electrical energy is communicated to shape memory wire  40  via strain-limiting spring  44  connected to terminal  46  and a wire lead  48 . Wire lead  48  communicates between the bottom end of shape memory wire  40  and terminal  50 . Charging shape memory wire  40  with electrical energy causes it to heat up. As shape memory wire  40  is heated it contorts, causing its axial length to shrink. The contortion causes piston  42  to axially traverse along the length of level sensing tube  30  and bear against a spring  52  disposed within bottom portion  31  of tube  30 . A first end  53  of spring  52  bears against an upper end  55  of piston  42 , while a second end  57  of spring  52  bears against the lower portion  59  of PCB  32 . Since the spring constant “K” of spring  52  is less than the spring constant “K” of strain limiting spring  44 , then the contortion and resulting axial reduction in length of shape memory wire  40  causes piston spring  52  to deflect first. When the electrical energy is cycled off, the shape memory wire  40  cools, indeed can be quickly cooled by the urea solution  14  in reservoir  18  that surrounds sensing tube  30 . Upon cooling, the axial length of memory wire  40  expands, allowing piston spring  52  to push piston  42  downward to the bottom of its stroke within bottom portion  31  of tube  30 . 
         [0017]    Referring now to  FIG. 4 , where a partial view of reservoir  18  is shown, a partially circumferential channel  37  is formed by the bottom of reservoir  18  to allow urea solution  14  to enter a first chamber  29 . Specifically, reservoir  18  comprises a cylindrical bottom portion  118  with a bottom end wall  119  and a cylindrical upper portion  120  capped at both ends with a lower end wall  121  and with an upper end wall  123  (shown in  FIG. 2 ). Cylindrical bottom portion  118  is concentric with cylindrical upper portion  120  and has a larger diameter, such that the outer diameter of upper portion  120  fits within the inner diameter of bottom portion  118  to form circumferential channel  37 . Lower end wall  121  is spaced above end wall  119  to form the first chamber  29 . 
         [0018]    After urea solution  14  flows from tank  12  to reservoir  18  through circumferential channel  37  a first check valve  60 , shown as an umbrella valve through lower end wall  121  is configured to allow urea solution  14  to flow from first chamber  29  and enter a cavity  129  formed in level sensing tube  30  by the upstroke of piston  42 . After cavity  129  has been filled with urea solution  14  by the upstroke of piston  42 , shape memory wire  40  can be de-energized and allowed to cool. Thereafter, piston spring  52  forces piston  42  in a downward stroke. A second check valve  62 , also an umbrella valve, is configured to pass urea solution  14  from level sensing tube  30  to an interior portion  70  of reservoir  18  as piston  42  continues its downward stroke into cavity  129 . It will be appreciated that the flow rate of the urea solution  14  into interior portion  70  is adjustable. For example, by adjusting the stroke of piston  42 , the area of the head of piston  42 , and/or the reciprocating frequency of piston  42  as controlled by the energizing and de-energizing of memory wire  40 , the flow rate into reservoir  18  can be matched to any specified criteria. 
         [0019]    Once urea solution  14  has been pumped into the interior portion  70  of reservoir  18 , it forms a pressure head therein that is greater than the pressure head of tank  12 , within which reservoir  18  is positioned. The positioning of heater  20  near lower end wall  121  of reservoir  18  allows interior portion  70  to be quickly and efficiently heated, thus quickly thawing urea solution  14  when heater  20  is energized. Therefore, pump  26  can draw liquid urea solution  14  via a draw pipe  45  connected to pump  26  soon after heater  20  is energized. Level sensing float  34  floats on urea solution within interior portion  70 . As described above, PCB  32  senses the level of float  34  for purpose of energizing memory wire  40  to insure reservoir  18  contains a sufficient amount of urea solution  14  in preparation for the next freeze/thaw cycle. In addition float  34  may also be used as a urea solution  14  level signal to activate pump  26 . 
         [0020]    Pump  22  is very simple, requires minimal power, is very compact, inexpensive and has very few moving parts. Pump  22  is robust to the expansion and contraction of the urea solution as it freezes and thaws. The memory shape wire  40  drive system for piston  42  allows the urea solution  14  to freeze and expand without damaging pump  22 . It will be appreciated by those skilled in the art that the displaced volume provided by piston  42  and level sensing tube  30  may also be provided by bellows, a diaphragm, or the like that are actuated by a shape memory wire  40  and counter spring equivalent to spring  52 . In addition, it will be understood by one skilled in the art that any type of pressure relief valve may be substituted for the umbrella check valves  60  and  62  disclosed herein. 
         [0021]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.