Abstract:
An ultrasonic sensor for detecting the presence or absence of an aerated fluid includes a probe having a first solid portion and a second hollow portion. The probe has a closed end at the hollow portion. The solid portion and the hollow portion define an interface therebetween. A transducer element is mounted to the probe at about the solid portion. The transducer element is configured to transmit an ultrasonic signal through the solid portion into the hollow portion and to receive reflections of the ultrasonic signal to determine the presence or absence of a fluid and/or an aerated fluid.

Description:
CROSS-REFERENCE TO RELATED APPLICATION DATA 
       [0001]    This application claims the benefit of priority of Provisional U.S. Patent Application Ser. No. 61/415,214, filed Nov. 18, 2010, the disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    The present invention is directed to a sensing device. More particularly, the present invention pertains to a sensing device used to detect the presence or absence of a fluid even when that fluid is aerated. 
         [0003]    Level sensors are known in the art. Various types of mechanical, electro-mechanical and electrical sensors are known, and the type of sensor used for any given application will depend upon the application 
         [0004]    Fluid level can be determined using, for example, magnetic sensors, float sensors, optical sensors, ultrasonic sensors and the like. Sensors, such as those disclosed in Knowles, U.S. Publication 2010/0024535, and WO 2008/089209, both commonly assigned with the present application, and incorporated herein by reference, use an elongated probe with a transducer operably connected thereto. The transducer is configured to produce compression waves in the probe and circuitry for detecting acoustic energy that is emitted into the liquid when liquid is in contact with the probe. 
         [0005]    While such a probe sensor functions well in certain applications, such as discrete water level detection, it does not function well in fluids that may be aerated. 
         [0006]    Another type of sensor is a double probe sensor in which the transducer and receiver functions are provided in separate elements (e.g., probes). However, aerated fluid detection is problematic here as well, due to the acoustic waves being scattered by the trapped air bubbles, which effectively block the propagation and detection of the waves. 
         [0007]    Accordingly, there is a need for a level sensor that is capable of detecting fluid level in aerated systems. 
       BRIEF SUMMARY 
       [0008]    An ultrasonic sensor is configured for detecting the presence or absence of an aerated fluid. The sensor includes a probe having a first solid portion and a second hollow portion. The probe has a closed end at the hollow portion. The solid portion and the hollow portion define an interface therebetween. 
         [0009]    A transducer element is operably connected to the probe at about the solid portion. The transducer element is configured to transmit an ultrasonic signal through the solid portion into the hollow portion and to receive reflections of the ultrasonic signal to determine the presence or absence of a fluid and/or an aerated fluid. 
         [0010]    The end of the hollow portion is closed, defining closed end. The closed end can be formed by, for example, a cap or a closed-end tube that is press-fit, glued, threaded, a combination of these, or the like. In one embodiment, the transducer element is a compression-type transducer. 
         [0011]    The sensor can include a flange at an end of the solid portion distal from the hollow portion. A temperature sensor can be operably connected to the probe, if desired. 
         [0012]    In one embodiment, the probe is formed as a rod with a lower portion of the rod hollowed. A retaining ring can be disposed on an outer surface of the rod at the interface between the solid portion and the hollow portion. 
         [0013]    The probe can be formed as a rod having a hollowed out bottom portion having a cap thereon. Alternately, the rod can be formed as a multi-section element, in which a solid upper section is joined to a hollowed, closed end lower section, such as by threading, press-fitting or the like. 
         [0014]    The sensor can be positioned in a housing, such that the solid portion of the probe is mounted within the housing and the hollow portion of the probe depends from and is outside of the housing. 
         [0015]    A present probe is formed from aluminum and has a relatively thin wall thickness at the hollow portion. 
         [0016]    These and other features and advantages of the present invention will be apparent from the following detailed description, in conjunction with the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The benefits and advantages of the present invention will become more readily apparent to those of ordinary skill in the relevant art after reviewing the following detailed description and accompanying drawings, wherein: 
           [0018]      FIG. 1  is a perspective sectional view of an ultrasonic liquid sensor in accordance with the principles of the present invention; 
           [0019]      FIG. 2  is a side sectional view of the level sensor; 
           [0020]      FIG. 3  is a side sectional view of an alternate embodiment of the sensor; 
           [0021]      FIG. 4  is a plot of the response spectra in voltage vs. time for the sensor in air (out of fluid); and 
           [0022]      FIG. 5  is a plot of the response spectra in voltage vs. time for the sensor in aerated fluid (hydraulic oil). 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    While the present invention is susceptible of embodiment in various forms, there is shown in the drawings and will hereinafter be described a presently preferred embodiment with the understanding that the present disclosure is to be considered an exemplification of the invention and is not intended to limit the invention to the specific embodiment illustrated. 
         [0024]    Referring now to the figures and in particular to  FIGS. 1 and 2 , there is shown an exemplary embodiment of an ultrasonic level sensor  10  (“sensor”). The sensor  10  includes a rod or probe  12 . The rod  12  includes an upper end  14  which, in the illustrated embodiment includes a grounding flange  16 . It will be appreciated that the grounding flange  16  is intended to facilitate mounting the rod  12  and is not necessary to operation of the sensor  10 . 
         [0025]    The rod  12 , from the upper end  14  (the grounding flange  16 ) to an intermediate portion  18  is solid. The portion  20  of the rod  12  from the opposite or free end  26  to the intermediate portion  18  ring is a hollow portion  20  and defines an interface  22  therebetween the solid  14  and hollow (or lower)  20  portions. The lower portion  20  is closed-off to the environs. Closure can be accomplished by a cap  24  that is positioned on the free end  26  of the hollow portion  20  to maintain the interior of the probe (the hollow portion  20 ) dry. In a present sensor  10 , the rod  12  has a diameter d 12  of about 0.3125 inches ( 5/16 inch) and the hollow portion  20  has a wall  38  thickness t 38  of about 0.030 inches (30 mils) The upper end  14  of the rod  12  remains dry in use, while the lower end  20  is or can be immersed in fluid F. It will be appreciated from the present disclosure that other rod  12  diameters, lengths and hollow portion  20  wall thicknesses and the like can be used to achieve desired characteristics and that such other diameters, lengths and wall thicknesses and the like are within the scope and spirit of the present disclosure. 
         [0026]    The solid portion  14  of the rod  12  is mounted in a housing  28 . The rod  12  can be isolated from the housing  28  by for example, O-rings  30 , a grommet or the like. A transducer  32 , for example, a piezoelectric transducer is bonded to the rod  12 , at about the upper end  14 . In a present sensor  10 , the transducer  32  is mounted to the flange  16 . However, it will be appreciated by those skilled in the art that the transducer  32  can be mounted a various locations on the rod  12 . 
         [0027]    The transducer  32  is of the compression or radial mode type. Electrical circuitry may be positioned in the housing, for example, as part of a circuit board  34  or the like, for providing power and/or signals to and from the sensor  10 . 
         [0028]    In a present sensor a thermistor  36  or other temperature sensor is also mounted at about the upper end  14  of the sensor rod  12 . As illustrated, the thermistor  36  is mounted to the flange  16 . The thermistor  36  can, however, be mounted at other locations within the sensor  10 , which other locations will be appreciated by those skilled in the art. 
         [0029]    In use, extensional (compression) waves are generated by the transducer  32  that propagate through the solid portion  14  of the rod  12  and through the lower or hollow portion  20 . The waves then propagate back up through the lower portion  20  and upper portion  14  to the transducer  32 . In a present sensor  10 , the transducer  32  is excited at frequency of about 208 kHz. It will be appreciated that other excitation frequencies can be used. 
         [0030]    The hollow section  20  is more sensitive to viscous loses due to the lower mass (thin wall  38 ) of that section  20  compared to the solid upper section  14 . In addition, absorption loses at the solid section  14 , for example, due to the O-rings/grommets  30  or mounting to the housing  28 , are less because the solid section  14  is less sensitive than the hollow section  20  (again, due to the lower overall mass of the hollow section  20 ). 
         [0031]    In a present sensor  10 , the rod  12  is formed from aluminum, which, because of is light weight has been found to successfully function in the present sensor  10 . In addition, because aluminum is a good thermal conductor, and the path between the fluid F and the thermistor  36  is short, the temperature of the fluid F is readily determined Those skilled in the art will recognize that other materials can be used, which other materials are within the scope and spirit of the present disclosure. 
         [0032]    An alternate embodiment of the sensor  110  is illustrated in  FIG. 3 . The sensor  110  functions in the same manner as that illustrated in  FIGS. 1-2 . In this embodiment, the rod  112  includes an upper end  114  which includes a grounding flange  116 . This embodiment is a two-piece rod  112  in which the upper end  114  is solid and threads into the lower end  120 . The lower end  120  is a hollow tube having a closed off end  124 . In the illustrated embodiment the lower end  120  is a hollowed out element, for example, a tube having a bore that extends to, but not through the end  124 , thus forming a thin-walled, closed off tube. The upper end  115  of the tube  120  has a thread  125  to mate with the thread  127  on the upper end  114 . Alternately configurations for joining the hollow lower portion  120  with the solid upper portion  114 , such as by press-fit, glue, the illustrated threads or a combination of these, or by other means, will be recognized by those skilled in the art. It will also be appreciated by those skilled in the art that the juncture or joint  129  of the upper  114  and lower  120  sections is within the housing  128  and is thus further protected from infiltration (as by leakage) in that it is above the seals  130  that seal the probe  112  to the housing  128 . 
         [0033]    This embodiment also illustrates a configuration in which the upper end  114  is mounted to the circuit board  134  by springs  135  that extend between, for example, the transducer  132  and the board  134 , the thermistor  136  and the board  134 , and the flange  116  and the board  134 . The springs  135  provide the necessary electrical connections between the transducer  132  and the board  134 , the thermistor  136  and the board  134 , and the flange  116  and the board  134 , and further serve to mount the probe  112  in the housing  128 . The springs  135  provide for electrical and mechanical (physical) isolation of the probe  112  from the housing  128 . 
         [0034]    Functionally, the solid/hollow interface  22 ,  122  provides a wave reflective interface. Due to the rod  12 ,  112  dimensions, the transducer  32 ,  132  receives several reflective passes from this interface  22 ,  122  before the waves from the hollow section  20 ,  120  appear at the transducer  32 ,  132 . As such, in viewing the response time, the response can be viewed in air and in fluid and the response times compared to determine the difference, to eliminate variations in the transducer response due to bonding, temperature, aging and the like. 
         [0035]    It has been observed that the aluminum rod  12 ,  112  coupled with the compression mode type transducer  32 ,  132  provides outstanding aerated liquid or fluid level indication. 
         [0036]    Tests were conducted to determine the effectiveness of the sensor  10  in aerated hydraulic fluid (oil) and air. The hydraulic fluid was a John Deere 20D hydraulic fluid at 95° C. The fluid was aerated by agitating (shaking) the fluid until it appeared as a milky-white fluid. 
         [0037]    The response spectra (voltage vs. time) for in air (out of fluid) and in aerated fluid are shown in  FIGS. 4 and 5 , respectively. As can be seen, the response spectra for the aerated fluid is substantially distinguishable from that in air. The difference at 95° C., which is a worst-case scenario in that the energy losses are essentially due to viscous losses which decrease with temperature, is very pronounced between the aerated fluid and air. 
         [0038]    This, again, is believed to be due to the increased sensitivity of the lower mass (thin-walled  38 ,  138 ) lower portion  20 ,  120  of the rod  12 ,  112 , and the surface area of the rod  12 ,  112  compared to the higher mass upper rod portion  14 ,  114 . It will be appreciated by those skilled in the art that because the sensitivity of the sensor increases with decreased wall  38 ,  138  thickness t 38 , t 138 , and because the sensitivity increases with increased surface area of the probe, generally, a larger diameter d 20 , d 120  a longer hollow section  20 ,  120  and a smaller wall  38 ,  138  thickness t 38 , t 138  will provide a more sensitive and responsive sensor  10 ,  110 . 
         [0039]    Although the present disclosure is directed to a probe  12 ,  112  formed as a rod that is partially hollow and closed (capped) at the hollow free end  26 ,  126  it is anticipated that any of a wide variety of shapes of probes  12 ,  112  that are partially hollow and have hollow/solid interface  22 ,  122  configurations can be used. All such various configurations and shapes are within the scope and spirit of the present disclosure. 
         [0040]    The advantages of the present ultrasonic liquid sensor  10 ,  110  will be appreciated by those skilled in the art. The sensor  10 ,  110  provides a cost-effective assembly and method for determining the presence or absence of an aerated liquid or fluid F in a system. The present sensor  10 ,  110  uses a single probe  12 ,  112  configuration, eliminating the need for double probes and the like. The present sensor  10 ,  110  is easy to install and maintain and can additionally be used to determine other fluid F system characteristics, such as temperature and viscosity. 
         [0041]    All patents referred to herein, are incorporated herein by reference, whether or not specifically done so within the text of this disclosure. In the present disclosure, the words “a” or “an” are to be taken to include both the singular and the plural. Conversely, any reference to plural items shall, where appropriate, include the singular. 
         [0042]    From the foregoing it will be observed that numerous modifications and variations can be effectuated without departing from the true spirit and scope of the novel concepts of the present disclosure. It is to be understood that no limitation with respect to the specific embodiments illustrated is intended or should be inferred. The disclosure is intended to cover by the appended claims all such modifications as fall within the scope of the claims.