Abstract:
A fluid sensor for sensing at least one characteristic of a fluid. The fluid sensor including a sensing area; a sensing element configured to sense a characteristic of a fluid located within the sensing area; and a shroud having a textured area. The shroud configured to allow a liquid portion of the fluid to enter and exit the sensing area, and substantially prohibit a gas portion of the fluid to enter the sensing area.

Description:
BACKGROUND 
       [0001]    The present invention relates to systems for sensing a fluid. More particularly, embodiments of the invention relate to mechanisms and techniques for reducing interference in measurements caused by air bubbles (e.g., a gas trapped in a liquid) in fluid level and concentration sensors. 
         [0002]    Fluid level and fluid concentration sensing is important in a number of vehicle applications including, for example, the sensing of Diesel Exhaust Fluid (DEF) used in a selective catalytic reluctant diesel emission-control 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). DEF is used in the process. In clean diesel engines, an SCR system delivers near-zero emissions of NOx. 
         [0003]    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. 
         [0004]    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. Fluid level is representative of the amount or quantity of fluid and concentration is one characteristic that is representative of the quality of the fluid. 
       SUMMARY 
       [0005]    It has been recently observed that DEF fluid in an SCR system can become aerated (i.e., mixed with air in such a way that bubbles of air are entrained in the fluid). Aeration can occur, for example, during rapid filling or refilling of a tank or reservoir for DEF fluid. Aeration can also occur during severe vibration, fluid sloshing violently within the tank, or may be present in the return flow of the DEF fluid if a pump of the SCR system ingests air. Similar aeration can occur in other fluids as well, including but not limited to, gasoline fuel, diesel fuel, engine oil, hydraulic fluid, and transmission fluid. 
         [0006]    Generally, accurate fluid measurements require a homogeneous fluid from which to measure the speed of sound. When the fluid is aerated the path of the ultrasonic sound waves are dispersed by the presence of air bubbles. This interference of the sound waves causes a loss in the reflected echo (i.e., no speed of sound measurement) and thus a loss of accurate fluid measurements. 
         [0007]    Accordingly, in one embodiment, the invention provides a fluid sensor for sensing at least one characteristic of a fluid. The fluid sensor including a sensing area; a sensing element configured to sense a characteristic of a fluid located within the sensing area; and a shroud having a textured area. The shroud allows a liquid portion of the fluid to enter and exit the sensing area, and substantially prohibits a gas portion of the fluid to enter the sensing area. 
         [0008]    In another embodiment the invention provides a method of preventing gas bubbles in a sensing system for sensing a fluid contained in a tank. The sensing system including a sensing area and a sensor. The method including coupling a shroud to the sensing system, wherein the shroud has a textured area; separating a liquid portion of the fluid and a gas portion of the fluid via the textured area; allowing the liquid portion of the fluid to enter and exit the sensing area; prohibiting the gas portion of the fluid entering the sensing area; and sensing a characteristic of the fluid contained within the sensing area. 
         [0009]    In another embodiment, the invention provides a sensor operable to sense a characteristic of a fluid. The sensor including a sensing area configured to contain a fluid; a textured area covering the sensing area; and a transducer. The textured area allows a liquid portion of the fluid to enter the sensing area, and substantially prohibits a gas portion of the fluid to enter the sensing area. The transducer outputs a pulse of sound through the liquid portion of the fluid contained within the sensing area, receives the reflected pulse of sound, and outputs a characteristic of the fluid based on the received pulse of sound. 
         [0010]    In another embodiment, the invention provides a shroud configured to overlay a sensor for sensing at least one characteristic of a fluid. The shroud includes a main body including a top portion and a bottom portion; a leg coupled to the bottom portion an exterior portion; and an interior portion including a textured area. The textured area directs a liquid portion of the fluid toward a sensing area of the sensor, and directs a gas portion of the fluid away from the sensing area of the sensor. 
         [0011]    It should be observed that the invention is applicable to a variety of fluids, including but not limited to, gasoline fuel, diesel fuel, engine oil, hydraulic fluid, and transmission fluid, all of which are known to foam during sloshing and heavy vibration conditions. 
         [0012]    Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a side view of an apparatus for sensing a fluid. 
           [0014]      FIG. 2  is a perspective view of the apparatus of  FIG. 1 . 
           [0015]      FIG. 3  is a sectional view of a sensing system used in the apparatus of  FIGS. 1 and 2 . 
           [0016]      FIG. 4  is a perspective view of the sensing system of  FIG. 3 . 
           [0017]      FIG. 5  is a top perspective view of a boot or shroud. 
           [0018]      FIG. 6  is a bottom perspective view of the shroud of  FIG. 5 . 
           [0019]      FIG. 7  is a perspective view of the shroud of  FIG. 5  coupled to the sensing system of  FIG. 3 . 
           [0020]      FIG. 8  is a side view of the shroud of  FIG. 5  coupled to the sensing system of  FIG. 3 . 
           [0021]      FIG. 9  illustrates one embodiment of a tortuous path of the shroud of  FIG. 5 . 
           [0022]      FIG. 10  illustrates another embodiment of a tortuous path of the shroud of  FIG. 5 . 
           [0023]      FIG. 11  illustrates another embodiment of a tortuous path of the shroud of  FIG. 5 . 
           [0024]      FIG. 12  illustrated an example of operation of the shroud of  FIG. 5 . 
           [0025]      FIG. 13  is a perspective view of the shroud of  FIG. 5  coupled to the sensing system of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    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 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. 
         [0027]    Although the invention described herein can be applied to, or used in conjunction with a variety of fluids, fuels and oils (e.g., gasoline fuel, diesel fuel, engine oil, hydraulic fluid, transmission fluid, etc.) and systems (e.g., fuel level, liquid level, concentration measurement, etc.), embodiments of the invention described herein are described with respect to DEF for use in an SCR system. 
         [0028]      FIGS. 1 and 2  illustrate an apparatus  100 , such as a fluid sensor, for sensing a fluid within a tank  105 . In the particular embodiment shown, the apparatus  100  also includes a heater. The heater has certain benefits, but is not required in all embodiments. As noted, in some embodiments, the fluid is DEF (e.g., a urea solution, liquid urea, urea, or Adblue™ fluid). The fluid may have a liquid portion and a gas portion. In some embodiments, the gas portion includes bubbles of air, or another gas, present in the fluid as a result, for example, from sloshing in a tank that mixes air in the fluid. 
         [0029]    The apparatus  100  includes a header  110 , a heater loop  115 , a pickup line  120 , a return line  125 , and a sensor module or system  130 . The header  110  encloses the fluid inside the tank  105 . In some embodiments, a gasket  135  seals the header  110  to the tank  105 . The header  110  includes a plurality of fittings and an electrical connector  140 . In some embodiments, the plurality of fittings include a pickup fitting  145 , a return fitting  150 , a coolant input fitting  155 , and a coolant output fitting  160 . The plurality of fittings provides various paths for fluid to be transported or directed into, out of, and through the tank  105 . The electrical connector  140  provides an electrical connection from the sensor system  130  to an external computer system (e.g., a vehicle&#39;s data bus). 
         [0030]      FIGS. 3 and 4  illustrate the sensor system  130 .  FIG. 3  illustrates a sectional view of the sensor system  130 . The sensor system  130  include a top portion  131  and a bottom portion  132 . The sensor system  130  includes a printed circuit board (PCB)  165  and a plurality of sensors (i.e., sensing elements). In the illustrated embodiment, the plurality of sensors includes a concentration sensor  170 , a level sensor  175 , and a temperature sensor  180 . In other embodiments, the sensor system  130  may include more or less sensors than shown in the illustrated embodiment. Each of the plurality of sensors is electrically coupled to the PCB  165 . In some embodiments, the PCB  165  includes a sensor control system, 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. 
         [0031]    The concentration sensor  170  is a concentration sensing element for determining a concentration, and thus a quality, of the fluid within the tank  105 . The concentration sensor  170  includes a concentration ultrasonic transducer  200 , a measurement channel  205 , and a concentration reflector  210 . The concentration transducer  200  is a sensing element configured to act as both a transmitter and receiver. In some embodiments, the concentration transducer  200  is a piezoelectric transducer. The measurement channel  205  acts as a sensing area for containing a fluid to be sensed. In operation, the concentration transducer  200  generates an acoustic wave signal, which propagates through the fluid, contained within the measurement channel  205 , toward the concentration reflector  210 . The acoustic wave signal reflects off of the concentration reflector  210  and travels back toward the concentration transducer  200 . The concentration time-of-flight (ToF) of the acoustic wave signal is output to the sensor control system of the sensor system  130 . Although shown in the illustrated embodiment, other embodiments of the apparatus  100  do not include a concentration sensor  170 . 
         [0032]    The level sensor  175  is a level sensing element for determining a level, and thus a quantity, of the fluid within the tank  105 . In the illustrated embodiment, the level sensor  175  includes a level transducer  215  such as but not limited to a piezoelectric transducer, a level sensing tube  220  (e.g., a level focus tube), and a level sensing receiving tube  221  configured to receive the level sensing tube  220  and couple the level sensing tube  220  to the sensor system  130 . The level transducer  215  is configured to act as both a transmitter and receiver. The level sensing tube  220  acts as a sensing area for containing a fluid to be sensed. In some embodiments, the level sensing tube  220  is a figure-eight level sensing tube having two tubes coupled together in such a fashion such that the level sensing tube  220  resembles the number eight when viewed from direction A ( FIG. 1 ). Some embodiments of the level sensor  175  may also include a float. In the particular embodiment illustrated, the level sensor  175  includes a float  225  located within the level sensing tube  220 . Although illustrated as a sphere in  FIG. 3 , 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  105 . The transducer generates an acoustic wave signal, which propagates through the fluid contained within the level sensing 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 sensing tube  220 , and travels back toward the level transducer  215 . In one embodiment not including the float  225 , the transducer generates an acoustic wave signal, which propagates through the fluid, contained within the level sensing tube  220 , toward a surface  227  of the fluid. The acoustic wave signal reflects off of the surface of the fluid and travels back toward the level transducer  215 . The ToF of the acoustic wave signal is output to the sensor control system. 
         [0033]    The temperature sensor  180  is a temperature sensing element for determining a temperature of the fluid within the tank  105 . In one embodiment the temperature sensor  180  is a thermocouple. In another embodiment, the temperature sensor  180  is a thermistor. In yet another embodiment, the temperature sensor  180  is a resistance temperature sensor. In yet another embodiment, the temperature sensor  180  is an infrared temperature sensor. The temperature sensor  180  outputs the sensed temperature to the sensor control system. In some embodiments, the level sensor  175  and the temperature sensor  180  are combined into a combination sensor capable of sensing both a level and a temperature. In some embodiments, the concentration sensor  170  and the temperature sensor  180  are combined into a combination sensor capable of sensing both a concentration and a temperature of the fluid. In other embodiments, the level sensor  175 , the temperature sensor  180 , and the concentration sensor  170  are combined into a combination sensor capable of sensing all three metrics. 
         [0034]      FIGS. 5-8  illustrate a boot or shroud  250  for prohibiting, or inhibiting, the flow of bubbles (i.e., air or other gas trapped in liquid). The shroud  250  overlays the top portion  131  of the sensor system  130 . The shroud  250  may be made from rubber or a similar pliable material. In the illustrated embodiment, the shroud  250  is substantially “L” shaped having a main body  255  and a leg  260 . The main body  255  has a top portion  265  and a bottom portion  270 . The leg  260  is coupled to the main body  255  at the bottom portion  270 . 
         [0035]    The shroud  250  further has an interior portion  275  and an exterior portion  280 . The interior portion  275  of the shroud  250  includes a textured area  285 . The textured area  285  causes the fluid to follow one or more tortuous paths. The one or more tortuous paths are configured to direct bubbles within the fluid (a gas portion of the fluid), away from the one or more sensing areas (i.e., the measurement channel  205 , the level sensing tube  220 , etc.), while a liquid portion of the fluid is directed toward the one or more sensing areas. 
         [0036]    The illustrated embodiment of the shroud  250  also includes a chimney  290  having a vent  295 . The chimney  290  is configured to exhaust an entrapped gas portion (i.e., entrapped gas bubbles) from the one or more sensing areas. Because the entrapped gas portion is less dense than the liquid and because of convection the gas portion flows out of the one or more sensing areas through the chimney  290 . Once the gas portion has exited the sensing areas, the gas portion is free to escape up through the fluid within the tank  105  to a surface of the fluid. 
         [0037]      FIG. 9  illustrates one embodiment of the textured area  285 . In some embodiments, the textured area  285  covers the entire interior portion  275  of the shroud  250 . In other embodiments, the textured area  285  partially covers the interior portion  275  of the shroud  250 . In the illustrated embodiment, the textured area  285  includes a plurality of micro-vents  300  in order to direct the gas portion away from the sensing areas. 
         [0038]      FIG. 10  illustrates another embodiment of the textured area  285 . In the illustrated embodiment, the textured area  285  includes a plurality of micro-cavities  305  in order to direct the gas portion away from the sensing areas. 
         [0039]      FIG. 11  illustrates another embodiment of the textured area  285 . In the illustrated embodiment, the textured area  285  includes a plurality of raised dots, or stipples,  310  in order to direct the gas portion away from the sensing areas. 
         [0040]    In another embodiment, the textured area  285  includes a combination of one or more of a plurality of micro-vents  300 , a plurality of micro-cavities  305 , and a plurality of raised dots  310 . In another embodiment, the textured area  285  is similar to a sand-blasted texture, or the texture of sand paper. 
         [0041]      FIG. 12  illustrates one example of operation of the fluid in one embodiment of the textured area  285 . As the fluid enters the sensor system  130 , the textured area  285  forces the fluid to follow one or more tortuous paths  315 , thereby directing the gas portion  320  in a first direction  325 , away from the sensing area, while directing the liquid portion  330  in a second direction  335 , towards the sensing area. The gas portion  320  and the liquid portion  330  are first separated as a result of the textured area  285 . The gas portion  320  is then directed in the first direction  325 , away from the sensing area, because the density of the gas portion  320  is less than the density of the liquid portion  330 . Thus, the gas portion  320  flows upward (e.g., the first direction  325 ) away from the sensing area. The liquid portion  330  is then directed in the second direction  335 , to the sensing area, as a result of gravity. 
         [0042]    In the illustrated embodiment of  FIGS. 5-8 , the shroud  250  further includes a port or receptacle  340 . In the embodiment show, the receptacle  340  is a dual-opening port configured to receive the level sensing tube  220  and couples the level sensing tube  220  to the level sensing receiving tube  221  of the sensor system  130 . In some embodiments, the receptacle  340  includes a plurality of striations (e.g., ridges)  345  configured to promote coupling of the bottom portion of the level sensing tube  220  to the level sensing receiving tube  221  of the sensor system  130 . 
         [0043]    In the illustrated embodiment of  FIGS. 5-8 , the shroud  250  further includes a retainer. The retainer is configured to hold the shroud  250  onto the sensor system  130 . The retainer may include a toe clip  350 . The toe clip  350  is configured to capture a toe  355  of the sensor system  130  in order to retain the shroud  250  onto the sensor system  130 . 
         [0044]    As illustrated in  FIG. 13 , the retainer may further include a strap  360 . The strap  360  extends from a first side  365  of the shroud  250 , wraps around a bottom portion  132  of the sensor system  130 , and releasably attaches to a second side, opposite the first side, of the shroud  250 . In the illustrated embodiment, the strap  360  includes a buckle  370  for releasably attaching the strap  360  to the second side of the shroud  250 . 
         [0045]    Thus, the invention provides, among other things, a shroud for a fluid sensing system. Various features and advantages of the invention are set forth in the following claims.