Patent Publication Number: US-9410545-B2

Title: Solid state bilge pump switch

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The application claims the priority benefit of U.S. provisional patent application No. 61/492,622 filed on Jun. 2, 2011, the disclosure of which is expressly incorporated herein in its entirety by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not Applicable 
     PARTIES TO A JOINT RESEARCH AGREEMENT 
     Not Applicable 
     REFERENCE TO APPENDIX 
     Not Applicable 
     FIELD OF THE INVENTION 
     The field of the present invention generally relates to sensors for detecting the presence of fluids for activating a pump, and more specifically, to fluid sensors mounted in boat bilge tanks for activating a bilge pump when bilge fluid reaches a preset level above the bottom of the bilge tank. 
     BACKGROUND OF THE INVENTION 
     Bilge pumps in boats or ships must be activated before accumulating water reaches an excessive level. Early bilge pumps were activated manually or by mechanical switches such as those that have floats with contacts to complete electrical circuits and activate the bilge pumps. These mechanical switches typically performed as desired when initially installed on the boats. However, bilge debris and other contamination built up over time and/or caused corrosion to prevent the mechanical components from moving as intended. Additionally, these mechanical switches had relatively short lives compared to the boats in which they were installed and required replacement. 
     In an attempt to solve these problems with mechanical switches, electronic switches without moving parts were developed. Typically, these electronic switches utilize the conductivity of the water to be sensed with probes to activate the bilge pumps. These electronic switches are susceptible to false alarms, which can b “burn up” the pump motor, and missed detections, which can sink or damage the boat, once contamination in builds up around the probes, sloshing bilge water contacts the switch, and/or there are changing environmental conditions around the switch. 
     Many attempts have been made to solve these problems with electrical capacitive switches. Coated water repellant probes have been used. For example, see U.S. Pat. No. 4,276,454, the disclosure of which is expressly incorporated herein in its entirety by reference. Ultrasonic field detection has been utilized. For example, see U.S. Pat. No. 4,881,873, the disclosure of which is expressly incorporated herein in its entirety by reference. Acoustic transducers have been utilized. For example, see U.S. Pat. No. 4,897,822 , the disclosure of which is expressly incorporated herein in its entirety by reference. Time delays have been utilized. For example, see U.S. Pat. No. 5,404,048 , the disclosure of which is expressly incorporated herein in its entirety by reference. Optical fibers have been utilized. For example, see U.S. Pat. No. 5,425,624 , the disclosure of which is expressly incorporated herein in its entirety by reference. Field effect “touch sensors” have been utilized. For example, see U.S. Pat. No. 7,373,817 , the disclosure of which is expressly incorporated herein in its entirety by reference. While these attempts may have been somewhat successful in reducing false alarms and missed detections, they are either not completely successful or relatively expensive solutions. Accordingly, there is a need for improved bilge pump switches that are less costly and reduce false alarms and missed detections. 
     SUMMARY OF THE INVENTION 
     Disclosed herein are bilge pump switches which overcome at least one of the deficiencies of the prior art. Disclosed is a switch for a bilge pump comprising, in combination, a pair of probes for providing a probe signal indicating the presence of fluid at the probes, a current sensor for providing a sensor signal indicating electric current of the pump, and a controller programmed to energize the pump when a threshold level of the probe signal indicates the presence of fluid and to de-energize the pump when a threshold level of the sensor signal indicates that the pump is not pumping fluid. 
     Also disclosed is a switch for a bilge pump comprising, in combination, a pair of probes for providing a probe signal indicating the presence of fluid at the probes, and a controller programmed to energize the pump when a threshold level of the probe signal indicates the presence of fluid. The controller is programmed to dynamically change the threshold level of the probe signal based on a prior probe signal that indicates changing probe conditions. 
     From the foregoing disclosure and the following more detailed description of various preferred embodiments it will be apparent to those skilled in the art that the present invention provides a significant advance in the technology and art of bilge pump switches. Particularly significant in this regard is the potential the invention affords for providing a reliable and low cost switch. Additional features and advantages of various preferred embodiments will be better understood in view of the detailed description provided below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and further features of the present invention will be apparent with reference to the following description and drawings, wherein: 
         FIG. 1  is a schematic view of a bilge pump system of a boat according to the present invention; 
         FIG. 2  is a perspective view of bilge pump switch of the system of  FIG. 1 ; 
         FIG. 3  is a top plan view of the bilge pump switch of  FIG. 2 ; 
         FIG. 4  is a right-side elevational view of the bilge pump switch of  FIGS. 2 and 3 ; 
         FIG. 5  is a front elevational view of the bilge pump switch of  FIGS. 2 to 4 ; 
         FIG. 6  is a sectional view taken along line  6 - 6  of  FIG. 5 ; 
         FIG. 7  is an fragmented, enlarged view taken along line  7  of  FIG. 6 ; and 
         FIG. 8  is schematic view of an electronic circuit of the bilge pump switch of  FIGS. 2 to 7 . 
     
    
    
     It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred features illustrative of the basic principles of the invention. The specific design features of the bilge pump switch as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes of the various components, will be determined in part by the particular intended application and use environment. Certain features of the illustrated embodiments have been enlarged or distorted relative to others to facilitate visualization and clear understanding. In particular, thin features may be thickened, for example, for clarity or illustration. All references to direction and position, unless otherwise indicated, refer to the orientation of the bilge pump switches illustrated in the drawings. 
     DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS 
     It will be apparent to those skilled in the art, that is, to those who have knowledge or experience in this area of technology, that many uses and design variations are possible for the improved bilge pump switches disclosed herein. The following detailed discussion of various alternative and preferred embodiments will illustrate the general principles of the invention. Other embodiments suitable for other applications will be apparent to those skilled in the art given the benefit of this disclosure. 
     Referring now to the drawings,  FIGS. 1 to 8  illustrate a bilge pump switch  10  according to the present invention. The illustrated bilge switch  10  is mounted at the bottom of a bilge in a boat  14  and is electrically connected to a 12 volt, direct-current bilge pump  16  in order to selectively energize the pump and evacuate the water  17  and other bilge fluids in the bilge  12  of the boat  14 . As best shown in  FIGS. 2 to 7 , the illustrated bilge pump switch  10  includes a protective case or housing  18  , an electronic circuit  20  within the protective case  18 , and a pair of probes  22  electrically connected to the electronic circuit  20  and extending from the protective case  18  to act as a water level sensor. The electronic circuit  20  monitors the water level within the bilge  12  via the two probes  22  and energizes the bilge pump  16  only when the water  17  or other bilge fluids within the bilge  12  reaches the level of the probes  22 . The illustrated electronic circuit  20  also monitors current flow in the bilge pump  16  and shuts off the bilge pump  16  when the bilge  12  is empty of water  17  and other bilge fluids and the bilge pump  16  is not pumping fluid. The illustrated electronic circuit  20  dynamically changes a threshold or trigger signal value for the probes  22  based on changing probe conditions in order to reduce false triggers and enhance the reliability of the bilge pump  16  to control the water level within the bilge  12 . 
     The illustrated case or housing  18  is molded of plastic but it is noted that the protective case  18  can alternatively be formed in any other suitable manner and/or the protective case  18  can alternatively comprise any other suitable material. The illustrated protective case  18  has an upper portion that forms a water-tight sealed interior space or cavity  26  for the electronic circuit  20 . The illustrated bilge pump switch  10  has four electrical wires  28  that exit through a rear wall  29  of the upper portion  24  to electrically connect the electronic circuit  20  within the protective case  18  with the bilge pump  16 . It is noted that alternatively there can be other quantities of wires  28  if desired and/or that the wires  28  can all be located within a single cable sleeve if desired. The illustrated electrical wires  28  are provided with a water-tight grommet  30  to seal the interior cavity  26  of the protective case  18  but alternatively any other suitable manner of sealing the wires  28  can be used. The probes  22  downwardly extend from a bottom wall  32  of the upper portion  24 . The illustrated upper portion  24  forms a downwardly facing recess  34  in which the probes  22  are at least partially located. A wall  36  forming the recess  34  encircles the probes  22  and at least partially protects the probes  22  from sloshing, splashing, and the like of water  17  and other bilge fluids located in the bilge  12 . The recess also at least partially protects the probes  22  from contact with debris floating in the bilge  12  which may damage the probes  22  or cause false readings. The illustrated protective case  18  also has a lower portion  38  downwardly extending from the upper portion  24 . The illustrated lower portion  38  has a horizontally-extending mounting flange  40  at its lower end. The illustrated mounting flange  40  is provided with a pair of openings or holes  42  for receiving mechanical fasteners to mount the bilge pump switch  10  to the bottom or floor of the bilge  12 . It is noted that the bilge pump switch  10  can alternatively be mounted to the bilge  12  in any other suitable manner. The lower portion  38  is sized and shaped to support the upper portion  24  and to position the probes  22  at a desired height above the floor of the bilge  12  at which it is desired to energize the bilge pump  16  to remove the water  17  from the bilge  12 . 
     The illustrated probes  22  comprise stainless steal but any other suitable material can alternatively be utilized. The illustrated pair of probes  22  are vertically extending, parallel, and horizontally spaced apart a suitable distance for providing a signal when the water  17  or other bilge fluid contacts the probes  22  to connect the circuit between the probes  22  to indicate that the water  17  in the bilge  12  has reached the level of the probes  22  in a known manner. The probes  22  are in electrical communication with the electronic circuit  20  (best shown in  FIG. 8 ). 
     As best shown in  FIG. 8 , the illustrated electronic circuit  20  includes a controller or microcontroller  44  and other electrical components (such as, for example, capacitors, resistors, diodes, transistors, relays, and the like) configured to provide the operations and functions described herein. The illustrated controller  44  is a 14-pin, flash based, 8 bit CMOS microcontroller but it is noted that any other suitable type of controller can alternatively be utilized. A suitable microcontroller is part no. PIC16F616/16HV616 available from Microchip technology Inc. of Chandler, Ariz. The electronic components are mounted on at least one circuit board located within the sealed interior cavity  26  of the protective case  18 . 
     The illustrated microcontroller  44  is programmed to supply a one kilohertz, fifty percent duty cycle signal to one of the probes  22  through a conditioning filter and a decoupling capacitor. It is noted that any other suitable duty cycle can alternatively be utilized. The signal occurs at a pre determined interval programmed or embedded in the microcontroller. The microcontroller  44  loops thru a test routine at this interval value to check the status of the probes  22 . If water  17  or other bilge fluids within the bilge  12  is not high enough to cover the probes  22  and provide a signal at or beyond a threshold signal level, the microcontroller  44  enters a sleep state until the predetermined time passes and the loop begins again. However, when water  17  and/or other bilge fluid capable of conducting current covers both of the probes  22  so that a signal at or above the threshold signal level is picked up by the second probe  22 , which is also decoupled thru a capacitor, and the microcontroller  44  enters a test subroutine. This test routine first energizes the bilge pump  16  and measures the current through the bilge pump  16  via a current sensor  46 . The current sensor  46  can be of any suitable type such as, for example a current sensing resistor. Because the current through the bilge pump  16  is proportional to the work being done by the bilge pump  16 , the microcontroller  44  can determine if the bilge pump  16  is pumping water or  17  just spinning in air. It is noted that any other suitable pump value or variable can alternatively be monitored rather than the pump current. A threshold current value indicating the pumping of water is predetermined and programmed or embedded in the microcontroller  44 . If the current through the bilge pump  16  is at or above the threshold current value, the microcontroller  44  permits the bilge pump  16  to continue to operate until the current through the bilge pump  16  drops below this threshold current value as the water  17  and/or other bilge fluid is fully evacuated from the bilge  12 . If the bilge pump  16  is falsely triggered by the probe signal due to high humidity or residual moisture or contamination around the probes  22  as indicated by the current through the bilge pump  16  being below the threshold current value, the microcontroller  44  immediately shuts off the bilge pump  16  and the actual probe signal strength is averaged into the probe threshold signal level. This adjustment of the threshold signal level allows the probe threshold signal level to constantly follow or adjust for any environmental changes or help compensate for any dielectric build up due to dirty liquid coming in contact with the probes  22 . It is noted that the threshold signal level can alternatively be adjusted other any other suitable amount rather than the illustrated averaging. For example, the threshold signal level could be adjusted less than 50% of the difference (such as, for example 25% of the difference) if a slower adjustment is desired or more than 50% of the difference (such as, for example 75% of the difference) if a faster adjustment is desired. 
     It is noted that each of the features and variations of the above disclosed embodiments can be used in any combination which each of the other embodiments. 
     From the foregoing disclosure it is apparent that by monitoring the current draw of the bilge pump  16 , the bilge pump  16  operates only as long as it takes to completely evacuate the bilge  12  of water  17  and other bilge fluids. Prior art bilge pumps operate for a predetermined time period regardless of the capacity of the bilge. Operating for predetermined time periods can result in the pump running dry for long periods and thus reducing the life of the pump. It is also apparent that by keeping a running average of the probe signal strength, the bilge pump switch  10  has the ability to intelligently determine the state of the water level in the bilge  12 . The signal strength can vary due to changing environmental conditions or the accumulation of dirt on the probes  22 . Changing conditions and or dirty probes  22  can result in damage to the bilge pump  16  by running it dry, or the probes  22  not triggering at all resulting in a sinking boat  14 . 
     From the foregoing disclosure and detailed description of certain preferred embodiments, it is also apparent that various modifications, additions and other alternative embodiments are possible without departing from the true scope and spirit of the present invention. The embodiments discussed were chosen and described to provide the best illustration of the principles of the present invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the present invention as determined by the appended claims when interpreted in accordance with the benefit to which they are fairly, legally, and equitably entitled.