Patent Application
20100154907
The present disclosure relates to pumps for vehicle mounted urea reservoirs.
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 NO2 trapped on the SCR catalyst to form N2 and CO2 and thus reduce pollution of the diesel exhaust.
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'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.
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.
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.
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.
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.
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:
Referring now to
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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.
Referring now to
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.
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.
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.
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.
