Abstract:
A float assembly for use in actuating a switch based on the level of a fluid includes a pivot member having a pivot axis and a switching surface. First and second floats are coupled to the pivot member so that at a first fluid level the first and second floats lie on different sides of a vertical line extending through the pivot axis and the switching surface causes the switch to assume a first switching state. At a second fluid level, the first and second floats lie on the same side of the vertical line extending through the pivot axis and the switching surface causes the switch to assume a second switching state.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to float assemblies for sensing fluid levels and, more particularly, to a float assembly for actuating a switch. 
     2. Background Art 
     Conventional float assemblies for actuating a switch based on a fluid level typically include a pushrod that extends upwardly from a float and which moves vertically with the float in response to changes in the fluid level. The pushrod may actuate the switch directly or, alternatively, may actuate the switch via an intermediate lever. 
     In applications where the float assembly controls the operation of a pump, it is desirable to provide switching hysteresis or a control deadband that allows the pump motor to cycle between on and off operational states at an acceptable frequency and duty cycle. As is commonly known, without switching hysteresis, electrical noise or high flow rates into the pumped container may cause the pump motor to cycle rapidly between on and off states when the fluid level is near the switching point. Such rapid cycling of the pump motor can substantially increase power consumption and shorten the life expectancy of the pump motor. It is further desirable to provide a positive (i.e., substantially bounceless) switching action because mechanical bouncing of the switch contacts may cause the pump motor to be turned on and off rapidly despite any switching hysteresis or control deadband and may cause premature wear and failure of the switch contacts. 
     Some conventional float assemblies provide a control deadband by coupling the float pushrod to the switch via a lost motion connection, which allows the vertical displacement of the float to change over a predetermined range of fluid levels without causing any actuation of the switch. Additionally, many of these conventional float assemblies also incorporate an electrical switch having a snap-acting or detent mechanism to provide a positive switching action that eliminates or minimizes contact bounce. 
     In one known configuration illustrated in FIG. 1, a conventional float  10  follows the level of a fluid within a tank  12 . A pushrod  14  extends coaxially from the float  10  and is coupled to the float  10  so that the pushrod  14  follows the vertical displacement of the float  10 . The pushrod  14  passes freely through an opening (not shown) in a lever arm  16  which is coupled to a detent switch  18 . The pushrod  14  includes an upper pushnut  20  and a lower pushnut  22  that define a control deadband therebetween. This control deadband allows the pushrod  14  to move vertically through the lever arm  16  a predetermined distance without actuating the lever arm  16  or the detent switch  18 . 
     At a low fluid level  24 , the pushrod  14  is retracted into the tank  12  so that the upper pushnut  20  pulls the lever arm  16  downward to cause the detent switch  18  to be in one of two switching states. Similarly, at a high fluid level  26 , the pushrod extends out of the tank  12  so that the lower pushnut  22  pushes the lever arm  16  upward to cause the detent switch  18  to be in the other one of the two switching states. 
     While the float assembly shown in FIG. 1 establishes a control deadband so that a pump motor controlled by the detent switch  18  is turned on at one fluid level and turned off at another fluid level, the structure of FIG. 1 is relatively expensive to manufacture because it requires the use of an expensive detent switch. Further, placement of the pushnuts  20  and  22  on the pushrod  14  is labor intensive and tends to be imprecise, leading to a wide variation in the minimum and maximum controlled fluid levels. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, a float assembly includes a carrier rotatable about a pivot axis. The carrier includes an actuation surface which is disposed at an actuating position when the carrier is disposed at a first rotational position and which is moved away from the actuating position when the carrier is rotated away from the first rotational position toward a second rotatable position. 
     The float assembly may further include a pair of spaced floats coupled to the carrier. The floats may be disposed on a certain side of a vertical line extending through the pivot axis when the carrier is disposed at the first rotational position and the floats may be disposed on opposite sides of the vertical line extending through the pivot axis when the carrier is disposed at the second rotational position. 
     The float assembly may be used in combination with a switch having an actuation arm which is moved to a switch actuation position by the actuation surface as the carrier is rotated to the first rotational position and the actuation arm may be biased by a spring to a switch deactuation position as the carrier is rotated toward the second rotational position. 
     In accordance with another aspect of the present invention, a float assembly for actuating a switch based on a level of a fluid includes a pivot member having a pivot axis and a switching surface and first and second floats coupled to the pivot member. At a first fluid level, the first and second floats lie on different sides of a vertical line extending through the pivot axis and the switching surface causes the switch to assume a first switching state and, at a second fluid level, the first and second floats lie on the same side of the vertical line extending through the pivot axis and the switching surface causes the switch to assume a second switching state. 
     In accordance with yet another aspect of the present invention, a float assembly includes a pivot member having a pivot axis and a float coupled to the pivot member. The float provides a first torque to the pivot member in a first direction when the float lies substantially to one side of a vertical line extending through the pivot axis and a second torque in a second direction to the pivot member when the float lies substantially on another side of the vertical line extending through the pivot axis. The float assembly may further include a means for applying a third torque in the second direction to the pivot member to cause the float to move from substantially the one side to substantially the other side of the vertical line through the pivot axis. 
     The invention itself, together with further objects and attendant advantages, will best be understood by reference to the following detailed description, taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic, partial sectional view illustrating a prior art configuration for a float assembly that actuates a switch based on a fluid level; 
     FIG. 2 is an elevational view, partially in section, of a fluid reservoir system incorporating the float assembly of the present invention with a carrier or pivot member in a first position together with a block diagram of a pump and pump motor; 
     FIG. 3 is a view similar to FIG. 2 with the carrier or pivot member in a second position; and 
     FIG. 4 is an isometric view of the carrier or pivot member shown in FIGS.  2  and  3 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The float assembly described herein eliminates the need to use a snap-acting or detent switch and pushnuts, which are commonly used with conventional float assemblies, and instead uses one or more floats mounted on a carrier or pivot member to provide a snap-acting float assembly with hysteresis. Thus, the float assembly described herein may be used to actuate a relatively inexpensive limit switch to control the operation of a pump so that the pump motor is not subjected to rapid cycling between on and off conditions. 
     FIGS. 2 and 3 are views of a fluid reservoir system  50  that controls the level of a fluid between a minimum fluid level  52  and a maximum fluid level  54 . The fluid reservoir system  50  includes a container or tank  56 , a float assembly  58 , a limit switch  60 , a pump motor  62  and a pump  64 . The fluid reservoir system  50  may be, for example, a system that collects condensate (i.e., condensed water vapor) in one location and conveys the collected condensate away from the fluid reservoir system  50 . 
     The pump  64  is driven by the pump motor  62  and is coupled via a fluid conduit  66  to an opening  68  in the tank  56 . The pump motor  62  drives the pump  64  to remove fluid from the tank  56  via the fluid conduit  66  and conveys the removed fluid to an outlet conduit  70 , which carries the removed fluid away from the fluid reservoir system  50 . Preferably, the opening  68  is located below the minimum fluid level  52  to enable the pump  64  to draw fluid from the tank  56  when the fluid level is at or near the minimum level  52  without drawing air into the fluid conduit  66  and the pump  64 . While the pump  64  is configured to remove fluid from the tank  56 , alternative configurations may be used. For example, the pump  64  and the opening  68  may be configured so that the pump  64  adds fluid to the tank  56  via the fluid conduit  66 . Also, the pump  64  and/or motor  62  may be disposed within the tank  56 . 
     The pump motor  62  may be any electrical motor suitable for the particular application of the fluid reservoir system  50 . Additionally, the pump motor  62  may be integral with the pump  64  or may, alternatively, be separate from the pump  64 , in which case the pump motor  62  may be coupled to the pump  64  via a shaft, gear train, magnetic coupling, and/or any other suitable coupling mechanism. 
     The limit switch  60  includes a switch button  72 , a spring biased switch actuation arm  74  that is mounted to the limit switch  60  at a pivot point  76  and which may be moved against the spring bias to depress the switch button  72 , a common terminal  78 , a normally-open terminal  80  and a normally-closed terminal  82 . The common terminal  78  and the normally-open terminal  80  are serially interposed in the path of power supplied to the pump motor  62  so that when the switch button  72  is not depressed, the limit switch  60  is not activated and interrupts the flow of power to the pump motor  62  so that the pump  64  is inactive. 
     As is commonly known, limit switches, such as the limit switch  60 , are relatively inexpensive in comparison to snap-acting and detent switches, which are typically used with conventional float-based fluid level control systems. Although the float assembly described herein may be advantageously used within a fluid level control system (such as the fluid level control system  50  shown in FIGS. 2 and 3) to allow the use of an inexpensive limit switch for the control of a pump motor, conventional snap-acting and detent switches, as well as other types of switches, may nevertheless be used with the float assembly described herein. 
     The float assembly  58  rotates clockwise and counter-clockwise about a pivot axis  84  in response to changes in the fluid level within the tank  56 . The float assembly  58  includes a carrier or pivot member  88 , a lower float  90  disposed on centerline  92 , an upper float  94 , a switching surface  96 , and a pivot member stop surface  98 . The pivot member stop surface  98  contacts a wall  100  of the tank  56  to limit the clockwise rotation of the float assembly  58  and the upper float  94  contacts a tank stop surface  102 , which may be integral to the tank  56 , to limit counter-clockwise rotation of the float assembly  58 . 
     The switching surface  96  acts as a cam surface that converts the angular or rotational position of the float assembly  58  into a vertical displacement of the switch actuation arm  74  and the switch button  72 . Preferably, the switching surface  96  is profiled so that as the lower float centerline  92  moves to the right of a vertical line  104  extending through the pivot axis  84 , the switching surface  96  vertically displaces the switch actuation arm  74  to depress the switch button  72 , thereby activating the limit switch  60 . When activated, the limit switch  60  completes an electrical path between the common and normally-open terminals  78  and  80  which turns the pump motor  62  on so that fluid is removed from the tank  56 . 
     Generally speaking, the pivoting action of the float assembly  58  is determined by the pivot member  88 , the weight and buoyancy (which are a function of density and geometry) of the floats  90  and  94 , and the location of the floats  90  and  94  with respect to the pivot axis  84  and the vertical line  104 . As will be discussed in more detail below, the center of gravity of the pivot assembly  58  lies on or, preferably, to the right of the vertical line  104  as seen in FIGS. 2 and 3. Thus, when the fluid level is below the minimum level  52 , the float assembly  58  rotates to the fully clockwise position to drive the pivot member stop surface  98  against the wall  100 . While the weight and location of the floats  90  and  94  can substantially determine the center of gravity of the pivot assembly  58 , those skilled in the art will recognize that the center of gravity of the pivot assembly  58  is also determined, at least in part, by many other factors including, but not limited to, the materials and geometry of the pivot member  88 . 
     When the fluid level rises to contact one or more of the floats  90  and  94 , the buoyancies of the floats  90  and  94  become dominant in controlling the rotational position of the pivot assembly  58 . In general, the respective buoyant forces and torques provided by the floats  90  and  94  increase in direct proportion to the volume of fluid which is displaced by each of the floats  90  and  94 . 
     The magnitudes and directions of the buoyant torques exerted by the floats  90  and  94  change as the rotational position of the pivot assembly  58  varies. This is due to the fact that the direction and magnitude of the torque developed by each float are dependent upon the angle between the vertical line  104  and a line extending through the pivot axis  84  and the center of the float. Preferably (although not necessarily) the magnitude of the counter-clockwise buoyant torque provided by the upper float  94  increases as the pivot member  88  rotates counter-clockwise from the fully clockwise position to the fully counter-clockwise position. On the other hand, the magnitude of the torque provided by the lower float  90  decreases to zero as the pivot member  84  rotates to bring the lower float centerline  92  into coincidence with the vertical line  104  and increases from zero as the lower float centerline  92  moves to the right of the vertical line  104 . 
     One particularly interesting aspect of the float assembly  58  is that the direction of the buoyant torque provided by the lower float  90  changes abruptly as the lower float centerline  92  crosses the vertical line  104 . Specifically, when the lower float centerline  92  lies to the left of the vertical line  104 , the lower float  90  provides a clockwise buoyant torque and when the lower float centerline  92  lies to the right of the vertical line  104 , the lower float  90  provides a counter-clockwise buoyant torque. As described in more detail below, this abrupt reversal in the direction of the buoyant torque provided by the lower float  90  results in a snap-action pivoting movement for the pivot assembly  58 . 
     The manner in which the above-described torques interact to provide a snap-acting float assembly with hysteresis can be best understood in connection with the following exemplary description of the operation of the fluid reservoir system  50  of FIGS. 2 and 3. Initially, the tank  56  is empty, and because the center of gravity of the pivot assembly  58  lies to the right of the vertical line  104 , the pivot member  58  to rotates fully clockwise to drive the pivot stop surface  98  against the wall  100 . With the float assembly  58  in the fully clockwise position (i.e., with the pivot member stop surface  98  in contact with the wall  100 ), the switching surface  96  is spaced from the switch actuation arm  74  allowing the arm  74  to be biased downwardly so that the switch button  72  is not depressed. As a result, the pump motor  62  and pump  64  are off, and fluid is not removed from the tank  56 . 
     As the fluid level within the tank  56  rises, the fluid first contacts the lower float  90 , which causes the lower float  90  to exert a clockwise buoyant torque on the float assembly  58 , thereby holding the pivot member stop surface  98  firmly in place against the wall  100  (as shown in FIG.  2 ). Further, as the fluid level continues to rise, an increasing proportion of the lower float  90  becomes submerged which increases the clockwise buoyant torque provided by the lower float  90 . When the fluid level rises sufficiently high to completely submerge the lower float  90 , the lower float  90  exerts a maximum clockwise buoyant torque on the pivot assembly  58 . 
     When the fluid level rises to contact the upper float  94 , the upper float  94  begins to provide a counter-clockwise buoyant torque to the pivot assembly  58 . Eventually, when a sufficient portion of the upper float  94  becomes submerged, the counter-clockwise buoyant torque provided by the upper float  94  exceeds the maximum clockwise buoyant torque provided by the lower float  90 . This effect may be achieved in any suitable manner, such as by designing the upper float  94  to have a greater buoyancy than the lower float  90  and/or locating the upper float  94  at a suitable distance from the pivot axis  84  relative to the distance of the lower float  90  from the pivot axis  84 , etc. In any event, further increases in the fluid level cause the pivot assembly  58  to rotate counter-clockwise. When the fluid level rises sufficiently (i.e., to the maximum fluid level  54 ) to cause the lower float centerline  92  to cross the vertical line  104 , the clockwise buoyant torque provided by the lower float  90  abruptly changes direction to become a counter-clockwise buoyant torque which, without any further increase in the fluid level, causes the float assembly  58  to rotate fully counter-clockwise so that the upper float  94  is driven against the tank stop surface  102  (as shown in FIG.  3 ). Additionally, as the lower float centerline  92  crosses to the right of the vertical line  104 , the switching surface  96  displaces the switch actuation arm  74  upward to depress the switch button  72  and activate the limit switch  60 . When activated, the limit switch  60  provides an electrical path between the common and normally-open terminals  78  and  80  to turn the pump motor  62  on, which drives the pump  64  to remove fluid from the tank  56 . 
     As the pump  64  decreases the fluid level within the tank  56  to below the level of the upper float  94 , the float assembly  58  remains rotated fully counter-clockwise with the upper float  94  driven against the tank stop surface  102 . The float assembly remains in the fully counter-clockwise position because the lower float centerline  92  remains to the right of the vertical line  104  and the lower float  90  provides a counter-clockwise buoyant torque that is greater than the clockwise torque provided by the weight of the pivot assembly  58 . As a result, the limit switch  60  continues to provide power to the pump motor  62  and the pump  64  continues to remove fluid from the tank  56 . 
     When the fluid level decreases to about the minimum level  52  (as shown in FIG.  2 ), the counter-clockwise buoyant torque provided by the lower float  90  becomes substantially zero and the clockwise torque provided by the weight of the pivot assembly  58  causes the float assembly  58  to rotate fully clockwise to drive the pivot member stop surface  98  against the wall  100 , thereby allowing the spring biased switch actuation arm  74  to move downward to deactivate the limit switch  60 , which turns off the pump motor  62  so that the pump  64  stops removing fluid from the tank  56 . 
     As can be understood from the above discussion of the operation of the float assembly  58 , the switching surface  96  of the float assembly  58  causes the limit switch  60  to switch between two switching states so that one of the two states turns the pump motor  62  on at the maximum fluid level  54  and the other of the two switching states turns the pump motor  62  off at the minimum fluid level  52 . Thus, the operation of the float assembly  58  provides switching hysteresis that eliminates rapid cycling of the pump motor  62 . Additionally, the float assembly described herein provides a positive detent or snap-action switching action due to the reversal of the direction of the buoyant torque provided by lower float  90  that occurs as the lower float centerline  92  crosses the vertical line  104 . 
     Those skilled in the art will recognize that the floats  90  and  94  may be made from any suitable material providing buoyancy such as, for example, styrofoam. Additionally, the floats  90  and  94  may be approximately spherical in shape or may, alternatively, be of any other shape needed to accomplish the above-described pivoting action in response to a fluid level. In fact, the floats  90  and  94  may be integrated so that the function of the separate floats  90  and  94  is accomplished using a substantially one-piece float. Further, the shape, material, volume, location with respect to the pivot axis  84  and one another, etc. of the floats  90  and  94  may be different, if needed, to provide any desired pivoting action, minimum fluid level, maximum fluid level, etc. Still further, those skilled in the art will recognize that the upper float  94  may be eliminated altogether and instead a lever arm or any other mechanical and/or electromechanical device may be substituted and manually or automatically controlled based on fluid level or some other parameter to apply a torque to the pivot assembly  58  to cause the lower float centerline  92  to cross the vertical line  104 . 
     FIG. 4 is an exemplary isometric view of a pivot member  120  that may be used with the float assembly  58  shown in FIGS. 2 and 3. The pivot member  120  includes barbed fittings  122  and  124  for securely engaging with complementary openings (not shown) in the floats  90  and  94 , shoulder portions  126  and  128 , a pivot bearing  130 , a cam surface  132 , and stops  134  and  136 . Fillets or webs  138  and  140  (and other fillets which are not shown) may be included to strengthen the shoulder portions  126  and  128  to prevent breakage of the barbed fittings  122  and  124  when pressing the floats  90  and  94  onto the barbed fittings  122  and  124 . Preferably, the pivot member  120  is a one-piece structure molded from a thermoplastic material. Alternatively, the pivot member  120  may be a die-cast part or may be fabricated using one or more component pieces from plastics, metals, and/or any other suitable materials. 
     Those of ordinary skill in the art will readily appreciate that a range of changes and modifications can be made to the preferred embodiments described above. The foregoing detailed description should be regarded as illustrative rather than limiting and the following claims, including all equivalents, are intended to define the scope of the invention.