Abstract:
Systems and methods for defrosting sensing components in fluid sensing system. In one embodiment, the invention provides a defrosting system that includes a sensing system. The sensing system includes a sensor operable to sense a characteristic of the fluid in a tank. The defrosting system includes a fluid pickup line spaced apart from the sensor, and a fluid return line. The fluid return line includes an output. The output is positioned to direct fluid onto the sensing system. In one embodiment, the defrosting system further comprises a pipe configured to provide the fluid to a system external to the tank. The fluid is heated by heat generated by the external system and directed onto the sensing system at least partially defrosts fluid contained within the sensing system.

Description:
BACKGROUND 
     The present invention relates to systems for heating a sensor immersed or surrounded by a frozen liquid and, more particularly, to a system for heating a sensor used to sense a liquid to be used with a selective catalytic reluctant diesel emission system. 
     Selective Catalytic Reduction (SCR) is a method of converting diesel oxides of nitrogen (NOx) emissions, by catalytic reaction, into diatomic benign nitrogen gas (N 2 ) and water (H 2 O). In clean diesel engines, an SCR system delivers near-zero emissions of NOx. 
     Diesel Exhaust Fluid (DEF) is used to reduce nitrous oxide (NOx) gases in the exhaust of diesel engines. DEF is a mixture of purified water and urea. In a typical SCR system, DEF is stored in a tank of a vehicle and is injected via one or more injectors into the exhaust at a ratio of about 1:50 to the diesel fuel being burned. The injected urea (in the form of a mist) mixes with the exhaust and breaks down NOx in the exhaust into nitrogen, water, and carbon dioxide. 
     SUMMARY 
     To ensure proper operation of an SCR system it is important to sense the quality and quantity of the DEF fluid. When contaminants such as diesel fuel, water, and ethylene gycol, mix with the DEF, the ability of the DEF to reduce the NOx in the exhaust is diminished. Contaminated DEF may also cause damage to the NOx reluctant system. It is also important that a sufficient amount of DEF be available for use in the SCR system. In or near the tank, one or more sensors are used to sense certain characteristics of the DEF. The sensors may include, but are not limited to: a level sensor for determining a quantity of DEF in the tank; a concentration sensor for determine the quality of DEF in the tank; and a temperature sensor. 
     The DEF is circulated from the tank to the injectors via a pump. Any unused DEF is returned to the tank. DEF freezes at approximately −11° Celsius. If the ambient temperature drops below the freezing point of DEF for a sufficient period of time, the liquid DEF in the tank, the circulation plumbing, and any DEF in or around sensors used to sense or monitor the DEF quality will freeze. When the DEF freezes, the ability of the SCR system is operated is either diminished or eliminated. 
     One method of dealing with the problems associated with freezing of DEF is to locate a heat source near a DEF pickup, which is usually at the bottom the DEF tank. With such a heat source it is possible to thaw DEF near the pickup. However, other portions of the SCR, particularly DEF sensors, may remain frozen or encased in frozen DEF for an extended period of time until convection of heat from the bottom of the tank thaws the DEF in other portions of the SCR system. 
     To overcome some of these problems, one embodiment of the invention provides a system for heating and sensing a fluid in a tank. The system includes a a sensor operable or configured to sense a characteristic of the fluid. The system for heating and sensing fluid in a tank also includes a fluid pickup line configured to take in fluid from the tank. In certain embodiments, the fluid pickup line is space apart from the sensor. A fluid return line configured to return the fluid to the tank. The fluid return line includes an output. The output is positioned to direct fluid onto the sensor. The system may also include a pipe configured to provide the fluid to a system external to the tank, such as an exhaust system. The fluid is heated by heat generated by the external system, and the heated fluid is directed onto the sensor to at least partially defrost fluid contained within and surrounding the sensor. The system may also include a controller configured to receive the sensed characteristic of the fluid, analyze the sensed characteristic of the fluid, and output the analyzed characteristic of the fluid. 
     In another embodiment the invention provides a method for defrosting components in a sensing system and sensing a fluid in a tank of a vehicle system, such as an SCR system. The tank includes a sensing system having a sensor and a controller, a fluid pickup line, and a fluid return line. The method includes taking in fluid from the tank via the fluid pickup line and transporting the fluid outside the tank; returning the fluid to the tank via the fluid return line, and directing the returned fluid onto the sensing system. The method may also include sensing a characteristic of the fluid; analyzing the sensed characteristic of the fluid; and outputting the analyzed characteristic of the fluid. 
     Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating a system for selective catalytic reduction. 
         FIG. 2  is a perspective view of an apparatus for holding and sensing a fluid for use in the system of  FIG. 1 , according to one embodiment of the invention. 
         FIG. 3  is a side view of the apparatus of  FIG. 2 . 
         FIG. 4  is a side view of a sensing system for use in the apparatus of  FIGS. 2 and 3 . 
         FIG. 5  is a block diagram illustrating a control system for the apparatus of  FIGS. 2 and 3 . 
         FIG. 6  is a side view of an apparatus for sensing a fluid for use in the system of  FIG. 1 , according to another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to DEF or UREA based fluids, the details of construction, and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
     Although the invention described herein can be applied to, or used in conjunction with a variety of fluids, embodiments of the invention described herein are described with respect to diesel exhaust fluid (DEF) for use in a selective catalytic reduction system. 
       FIG. 1  illustrates a system  50  for converting diesel oxides of nitrogen (NOx) emissions, by catalytic reaction, into diatomic benign nitrogen gas (N 2 ) and water (H 2 O). In some embodiments, the system  50  includes a selective catalytic reducer (SCR)  60 , a coolant input pipe  70 , a coolant output pipe  75 , a DEF pickup pipe  80 , a DEF return pipe  85 , and a tank or vessel  90 . In operation, the DEF is delivered to the SCR  60  from the tank  90  via the DEF pickup pipe  80 . The SCR  60  uses the DEF to convert the NOx emissions into nitrogen gas and water. Unused DEF is returned to the tank  90  via the DEF return pipe  85 . In the illustrated embodiment, the coolant input pipe  70  and coolant output pipe  75  run through the tank  90  in order to heat the DEF contained within the tank  90 . 
       FIGS. 2 and 3  illustrate an apparatus  100  for sensing and heating a fluid contained within the tank  90 . In some embodiments, the fluid is diesel exhaust fluid (DEF) (i.e., a urea solution, liquid urea, urea, or Adblue™) for use in the system  50 . 
     The apparatus  100  includes a header  105 , a heater loop  110 , a pickup line  115 , a return line  120 , and a sensor system  125 . The header  105  encloses the fluid inside the tank  90 . In some embodiments, a gasket  130  seals the header  105  to the tank  90 . The header  105  includes a plurality of fittings and an electrical connector  135 . In some embodiments, the plurality of fittings include a pickup fitting  140 , a return fitting  145 , a coolant input fitting  150 , and a coolant output fitting  155 . The plurality of fittings provides various paths for fluid to be transported or directed into, out of, and through the tank  90 . The electrical connector  135  provides an electrical connection from the sensor system  125  to an external computer system (e.g., a vehicle&#39;s data bus). 
       FIG. 4  illustrates the sensor system  125 . The sensor system  125  includes a printed circuit board (PCB)  160  and a plurality of sensors. In the illustrated embodiment, the plurality of sensors includes a concentration sensor  165 , a level sensor  170 , and a temperature sensor  175 . In other embodiments, the sensor system  125  may include more or less sensors than shown in the illustrated embodiment. Each of the plurality of sensors is electrically coupled to the PCB  160 . The PCB  160  includes a control system  200  ( FIG. 5 ), which, among other things, provides power to the plurality of sensors, analyzes data from the plurality of sensors; and outputs the analyzed data to other components such as an external computer. 
     The concentration sensor  165  determines a concentration, and thus a quality, of the fluid within the tank  90 . The concentration sensor  165  includes a concentration piezoelectric ultrasonic transducer (PZT)  205  and a concentration reflector  210 . The concentration PZT  205  acts as both a transmitter and receiver. In operation, the concentration PZT  205  generates an acoustic wave signal, which propagates through the fluid toward the concentration reflector  210 . The acoustic wave signal reflects off of the concentration reflector  210  and travels back toward the concentration PZT  205 . The concentration time-of-flight (ToF) of the acoustic wave signal is output to the control system  200 . Although shown in the illustrated embodiment, other embodiments of the apparatus  100  do not include a concentration sensor  165 . 
     The level sensor  170  determines a level, and thus a quantity, of the fluid within the tank  90 . In the illustrated embodiment, the level sensor  170  includes a level PZT  215  and a level focus tube  220 . The level PZT  215  acts as both a transmitter and receiver. Some embodiments also include a float. In the particular embodiment illustrated, the level sensor  170  includes a float  225  located within the level focus tube  220 . Although illustrated as a sphere in  FIG. 4 , the float  225  may be another shape, including but not limited to, a cylinder. The float  225  floats on the surface of the DEF solution contained within the tank  90 . The level PZT  215  generates an acoustic wave signal, which propagates through the fluid contained within the level focus tube  220 . The acoustic wave signal propagates toward the float  225 . The acoustic wave signal reflects off of the float  225 , contained within the level focus tube  220 , and travels back toward the level PZT  215 . In one embodiment not including the float  225 , the level PZT  215  generates an acoustic wave signal, which propagates through the fluid, contained within the level focus tube  220 , toward a surface  227  of the fluid. The acoustic wave signal reflects off of the surface  227  of the fluid and travels back toward the level PZT  215 . The ToF of the acoustic wave signal is output to the control system  200 . 
     The temperature sensor  175  determines a temperature of the fluid within the tank. In one embodiment the temperature sensor  175  is a thermocouple. In another embodiment, the temperature sensor  175  is a thermistor. In yet another embodiment, the temperature sensor  175  is a resistance temperature sensor. In yet another embodiment, the temperature sensor  175  is an infrared temperature sensor. The temperature sensor  175  outputs the sensed temperature to the control system  200 . In some embodiments, the level sensor  170  and the temperature sensor  175  are combined into a combination sensor capable of sensing both a level and a temperature. In other embodiments, the level sensor  170 , the temperature sensor  175 , and the concentration sensor  165  are combined into a combination sensor capable of sensing all three metrics. 
       FIG. 5  shows a block diagram of the control system  200 , which in some embodiments, is contained within the PCB  160  of the sensor system  125 . In some embodiments, the control system  200  includes a plurality of electrical and electronic components that provide power, operation control, and protection to the components and modules within the control system  200  and/or the sensor system  125 . For example, the control system  200  includes, among other things, a controller (such as a programmable microprocessor, microcontroller, or similar device)  250 , a power supply module  255 , and an output driver  260 . The controller  250  includes, among other things, a processor  265  and a memory  270 . The processor  265  is electrically connected to the memory  270 , and executes software instructions which are capable of being stored on the memory  270 . The controller  200  is configured to retrieve from memory and execute, among other things, instructions related to the control processes and method described herein. In other embodiments, the controller  200  includes additional, fewer, or different components. 
     The power supply module  255  supplies a nominal voltage to the control system  200  or other components of the sensor system  125 . In one embodiment, the power supply module  225  supplies a nominal DC voltage. The power supply module  255  is powered by a power source having a nominal voltage and is configured to supply lower voltages to operate circuits and components within the control system  200  or sensor system  125 . 
     The output driver  260  outputs data from the control system  260  to an external controller. The external controller, for example but not limited to, is a vehicle&#39;s data bus which controls the function of the vehicles DEF system. In some embodiments, the output driver  260  is in the form of a digital driver such as J1939 or CAN bus for communicating directly to the external controller. In other embodiments, the output driver  260  generates another suitable analog or digital signal, depending on the needs of the specific application. In some embodiments, the output driver  260  outputs a pulse-width modulated signal. 
     DEF used in an SCR system must be in liquid form. Therefore, the heater loop  110  maintains the DEF contained within the tank  90  at a temperature above the freezing point of DEF (approximately −11° C.). In the illustrated embodiment, warm fluid (e.g., warm engine coolant) is directed through the tank  90  via the heater loop  110  in order to heat the DEF contained within the tank  90 . In such an embodiment, the engine coolant is heated by the vehicle engine and the heated or warmed coolant is used to heat the DEF. Thus, certain embodiments use byproduct heat from the engine to heat the DEF. In this embodiment, warm engine coolant enters the tank  90  through the coolant input fitting  150 , travels through the heater loop  110 , and exits through the coolant output fitting  155 . In another embodiment, the heater loop  110  is an electric heating element which converts electrical energy into heat through the use of a resistance coil. 
     When in liquid form, the DEF contained within the tank  90  is removed from the tank  90 , for use with the SCR system, via the pickup line  115 . The pickup line  115  includes a first end  300  and a second end  305 . The first end  300  is attached to the pickup fitting  140  of the header  105 . The second end  305  is located at the bottom of the tank  90 . In some embodiments, a filter  310  is coupled to the second end  305 . The filter  310  filters the fluid before it is removed from the tank  90 . In operation, the fluid is filtered through the filter  310  before traveling up the pickup line  115 . The filtered fluid then exits the tank  90  through the pickup fitting  140 . The fluid (DEF) is then delivered to the SCR  60  via the DEF pickup pipe  80 . The DEF is then used with the corresponding SCR  60 . 
     Unused DEF is delivered to the tank  90  via the DEF return pipe  85 . The unused DEF is returned inside the tank  90  via the return line  120 . Unused DEF is warmed as a consequence of flowing past various components of the engine via the DEF return pipe  85  from the SCR  60 . The DEF is warmed to a temperature high enough to defrost frozen DEF in the tank  90  and SCR system. The return line  120  includes a first end  315  and a second end  320 . The first end  315  is attached to the return fitting  145  of the header  105 . In order for the sensing system  125  to function properly, the DEF surrounding and within the sensing system  125  must be in liquid form. Thus, the second end  320  of the return line  120  is positioned in a manner that the warmed DEF is directed onto the sensor system  125 . 
     As the warmed DEF is returned to the tank  90 , the warmed DEF sprays onto the sensing system  125 , thus defrosting any frozen DEF surrounding, or within, the sensing system  125 . In some embodiments, the warmed DEF is sprayed at the top of the level focus tube  220 . In such an embodiment, the warmed DEF runs down the level focus tube  220 , thereby defrosting any frozen DEF within and around the level focus tube  220 . The warmed DEF continues down the level focus tube  220  onto the other components of the sensing system  125 , thus defrosting any frozen DEF surrounding, or within, the remaining components of the sensing system  125 . The continual spraying of warmed DEF, via the return line  120 , maintains the DEF sensed by the sensing system  125  in a liquid state. 
     In other embodiments the heater loop  110 ′ has a loop-like configuration.  FIG. 6  illustrates another embodiment of the apparatus  100 . In such an embodiment, the heater loop  110 ′ wraps around the pickup line  115  and the sensing system  125  in the form of a spring or corkscrew (i.e., the heater loop  110 ′ has a spring-like, helix, or screw-like configuration). In such an embodiment, the return line  120  is directed onto the sensing system  125  and functions in a similar manner as discussed above in relation to the other embodiments. 
     In another embodiment of the apparatus  100 , the heater loop  110  is looped into an oblong shape with straight vertical sides, in a form similar to that of a paperclip or paperclip-like. In such an embodiment, the heater loop  110  is located vertically adjacent to the pickup line  115  and the sensing system  125 . In such an embodiment, the return line  120  is directed onto the sensing system  125  and functions in a similar manner as discussed above in relation to the other embodiments. 
     Thus, the invention provides, among other things, a system and method of heating a sensing module. Various features and advantages of the invention are set forth in the following claims.