Abstract:
A sensor operable to sense a characteristic of a fluid. The sensor includes a sensing area, a filter, and a transducer. The sensing area is configured to contain the fluid. The filter covers the sensing area. The filter is configured to allow a liquid portion of the fluid to enter the sensing area and substantially prohibit a gas portion of the fluid to enter the sensing area. The transducer is operable to output a pulse of sound through the liquid portion of the fluid contained within the sensing area, receive the reflected pulse of sound, and output a characteristic of the fluid based on the received pulse of sound.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional application of U.S. patent application Ser. No. 14/044,444, filed on Oct. 2, 2013, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    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. 
         [0003]    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. 
         [0004]    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. 
         [0005]    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 
       [0006]    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. 
         [0007]    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. 
         [0008]    Accordingly, in one embodiment, the invention provides a filter, and more specifically, a fluid sensor including a filter. The filter blocks, or inhibits, air bubbles from entering a sensing area of the fluid sensor. The sensing area contains the fluid to be sensed. The fluid is sensed by generating an ultrasonic pulse wave through the fluid contained within the sensing area. The time of flight of the ultrasonic pulse wave travelling the distance of the sensing area and returning to the output point is measured. If air bubbles are embedded within the fluid, the bubbles disperse the ultrasonic signal resulting in the fluid sensor not receiving the echo reflection, and thus no accurate time of flight measurement. These changes cause erratic measurement results or result in no measurement results. 
         [0009]    In another embodiment, the invention provides a fluid sensor for sensing at least one characteristic of a fluid. The fluid sensor includes a sensing area; a sensing element configured to sense a characteristic of fluid located within the sensing area; and a mesh positioned around the sensing area. The mesh is 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 channel while providing an exit, or exhaust, for trapped gas to escape. 
         [0010]    In another embodiment the invention provides a method of preventing gas bubbles in a sensing system for sensing a fluid contained in a tank, where the sensing system includes a sensing area and a sensor. The method includes coupling a mesh to the sensing system, wherein the mesh covers the sensing area; allowing a liquid portion of the fluid to enter and exit the sensing area through the mesh; prohibiting a gas portion of the fluid entering the sensing area; and sensing a characteristic of the fluid contained within the sensing area. 
         [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 and transporting 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 perspective view of one embodiment of a filter shroud. 
           [0018]      FIG. 6  is a perspective view of the filter shroud of  FIG. 5  coupled to the sensing system of  FIGS. 3 and 4 . 
           [0019]      FIG. 7  is a top view of another embodiment of a filter shroud. 
           [0020]      FIG. 8  is a side view of the filter shroud of  FIG. 7 . 
           [0021]      FIG. 9  is a perspective view of the filter shroud of  FIGS. 7 and 8 . 
           [0022]      FIG. 10  is a perspective view of the filter shroud of  FIGS. 7-9  coupled to the sensing system of  FIGS. 3 and 4 . 
           [0023]      FIG. 11  is a perspective view of another embodiment of a sensing system used in the apparatus of  FIG. 1 . 
           [0024]      FIG. 12  is a perspective view of another embodiment of a sensing system used in the apparatus of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    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. 
         [0026]    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.), embodiments of the invention described herein are described with respect to DEF for use in an SCR system. 
         [0027]      FIGS. 1 and 2  illustrate an apparatus  100  for sensing and heating a fluid within a tank  105 . As noted, in some embodiments, the fluid is DEF (e.g., a urea solution, liquid urea, urea, or Adblue™ fluid). The fluid has a liquid portion and a gas portion. In some embodiments, the gas portion represents bubbles of air, or another gas, present in the fluid. 
         [0028]    The apparatus  100  includes a header  110 , a heater loop  115 , a pickup line  120 , a return line  125 , and a sensor 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). 
         [0029]      FIGS. 3 and 4  illustrate the sensor system  130 .  FIG. 3  illustrates a sectional view of the sensor system  130 . 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. 
         [0030]    The concentration sensor  170  determines a concentration, and thus a quality, of the fluid within the tank  105 . The concentration sensor  170  includes a concentration piezoelectric ultrasonic transducer (PZT)  200 , a measurement channel  205 , and a concentration reflector  210 . The concentration PZT  200  is a sensing element configured to act as both a transmitter and receiver. The measurement channel  205  acts as a sensing area for containing a fluid to be sensed. In operation, the concentration PZT  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 PZT  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 . 
         [0031]    The level sensor  175  determines a level, and thus a quantity, of the fluid within the tank  105 . In the illustrated embodiment, the level sensor  175  includes a level PZT  215  and a level sensing tube  220  (e.g., a level focus tube). The level PZT  215  is a sensing element 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. Some embodiments also include a float. In the particular embodiment illustrated, the level sensor  170  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 level PZT  215  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 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 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 PZT  215 . The ToF of the acoustic wave signal is output to the sensor control system. 
         [0032]    The temperature sensor  180  determines a temperature of the fluid within the tank. 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. 
         [0033]      FIG. 5  illustrates a filter, or filter shroud,  250  for prohibiting, or inhibiting, the flow of gas, such as but not limited to, gas bubbles (i.e., gas trapped in a liquid). In some embodiments, the filter  250  includes mesh, or one or more mesh screens,  255  and a frame  260 . In other embodiments, the filter  250  includes only the mesh screens  255 . In some embodiments, the mesh screens  255  are a fine mesh material. In some embodiments, the mesh screens  255  are a synthetic polymer (e.g., nylon, polyethylene, polypropylene, etc.). In other embodiments, the mesh screens  255  are a metallic material. 
         [0034]    The frame  260  couples the filter  250  to the sensor system  130 . The frame  260  includes one or more arms  265 . In some embodiments, the frame  260 , and the arms  265 , are made of a plastic, or plastic like, material. In the illustrated embodiment, the arms  265  are coupled to a housing of the sensor system  130 . In some embodiments, the arms  265  couple to a housing of the level sensing tube  220  of the sensor system  130 . 
         [0035]    In the certain embodiments of the invention, the corollary to a particle is a gas bubble trapped within the fluid. The mesh screens  255  act to prevent the gas bubbles from entering into a sensing area (e.g., the measurement channel  205 , the level sensing tube  220 , etc.), while allowing liquid, or a liquid portion to enter the sensing area or sensing areas. 
         [0036]    In one embodiment, gas bubbles within the fluid having a size larger than an aperture size of the mesh screens  255  are unable to freely pass through the mesh screens  255 . However, a liquid portion of the fluid, can freely pass through the mesh screens  255 , as well as gas bubbles which have a diameter smaller than the aperture size of the mesh screens  255 . It has been found through empirical testing of a DEF tank system that an aperture size of  100  microns reduces the quantity of gas bubbles within a sensing area sufficiently enough to enable continuous measurements by the concentration sensor  170  and/or the level sensor  175 . 
         [0037]      FIG. 6  illustrates the filter  250  coupled to sensor system  130 . In the illustrated embodiment, the filter  250  allows liquid, or a liquid portion of the fluid, to pass through the mesh screens  255  into a sensing area (e.g., the measurement channel  205 , the level sensing tube  220 , etc.), while inhibiting the flow of gas bubbles into the sensing area or sensing areas. In the illustrated embodiment, the mesh screens  255  enclose the measurement channel  205  and one or more inlets of the level sensing tube  220 . In the illustrated embodiment, the mesh screen  255  is held in place by the frame  260 . The frame  260  is coupled to the housing of the sensor system  130  via the arms  265 . In some embodiments, the frame  260  is releasably coupled to the housing of the sensor system  130  via the arms  265 . 
         [0038]      FIGS. 7-10  illustrate another embodiment of the filter  250 ′. The filter  250 ′ includes one or more mesh screens  255 , the frame  260 , and the arms  265 . The filter  250 ′ further includes a chimney  270 . The chimney  270  is configured to exhaust gas, or air bubbles, entrapped in the measurement channel  205 . In some embodiments, the chimney  270  provides an unobstructed path for the gas, or air bubbles, to a location outside the measurement channel  205 . In other embodiments, the chimney  270  includes a component designed to allow one-directional flow of a fluid out of the measurement channel  205 . In some embodiments, the component is a rubber flap. 
         [0039]    In embodiments having a chimney  270 , the gas bubbles which collect within the sensing area or sensing areas, i.e. those bubbles which are smaller than the aperture size of the filter screen, are acted upon by the forces of gravity and convection causing the gas bubbles to flow out of the measurement channel  205  through the chimney  270  in the case of the concentration sensor  170 , or up the level sensing tube  220  in the case of level sensor  175  (i.e., the level sensing tube  220  acts as an exhaust allowing the trapped gas bubbles to flow upward and out). Once bubbles have exited the sensing areas they are free to escape up through the liquid within the tank to a surface of the fluid. 
         [0040]      FIG. 11  illustrates another embodiment of a level sensor  130 ′. In the illustrated embodiment, the level sensor  130 ′ includes one or more mesh screens  255 ′. The mesh screens  255 ′ enclose the sensing areas (e.g., the measurement channel  205 , the level sensing tube  220 , etc.). In such an embodiment, the filter  250  includes only the mesh screens  255 ′. In the illustrated embodiment, the mesh screens  255 ′ are integrated (i.e., molded) into a housing of the level sensor  130 ′. 
         [0041]      FIG. 12  illustrates another embodiment of a level sensor  130 ″. In the illustrated embodiment, the level sensor  130 ″ includes one or more mesh screens  255 ″ enclosing the sensing areas (e.g., the measurement channel  205 , the level sensing tube  220 , etc.) and a chimney  270 ″. In the illustrated embodiment, the mesh screens  255 ″ and chimney  170 ″ are integrated (i.e., molded) into a housing of the level sensor  130 ″. In such an embodiment, the chimney  270 ″ operates as discussed above in relation to chimney  270 . 
         [0042]    Thus, the invention provides, among other things, a sensor system including a filter for preventing gas bubbles from entering the sensor system. Various features and advantages of the invention are set forth in the following claims.