Abstract:
A fluid level switch for a machine having a fluid reservoir adapted to contain a fluid at an acceptable level. The fluid level switch includes a mounting plate, a float housing, and a float assembly positioned within the float housing. The mounting plate retains first and second contacts. The float housing is configured to receive fluid from the fluid reservoir and the float assembly is movable in response to the level of fluid in the float housing. The float assembly includes a contact member electrically connecting the first and second contacts when the level of the fluid is below the acceptable level. The contact member is coupled to the float for movement with the float and for movement relative to the float.

Description:
BACKGROUND 
   The present invention relates to fluid level sensors, and more specifically to low oil sensors for engines. 
   Fluid level sensors are generally used to determine the level of fluid retained within an enclosure. Some fluid level sensors activate an indicator when the fluid level decreases below a desired fluid level while others automatically shut off the system using the fluid. 
   In operation, fluid level sensors are positioned directly in a fluid reservoir, or within a smaller enclosure in fluid communication with the fluid reservoir. The enclosure maintains a fluid level proportional to the amount of fluid in the reservoir. One example of an application of a fluid level sensor is a sensor for the oil level within the crankcase of an internal combustion engine. The engine requires a desired amount of oil within the crankcase to properly lubricate the engine during operation. If the oil level is too low, the engine can be damaged due to improper lubrication. A fluid level sensor can be used to determine when the oil level within the crankcase is below a desired level. 
   Prior art systems often employ the use of a float within a housing to move with the level of fluid as the level of fluid changes. A sensor or an electrical contact can be positioned in the vicinity of the float and can be used to detect when the level of fluid is not within a desired range. The sensor or contact can communicate the condition of the fluid level through a indicator such as a warning light or by automatically shutting off the device that is using the fluid to operate. For example, the float can complete an electrical connection between a ground and an ignition contact to shut off the engine when the float is in a position indicative of low fluid or complete an electrical circuit for an audible indicator or visual indicator. 
   The use of such a system is generally reliable in shutting off the engine when a low amount of fluid is present. However, signaling a low fluid condition can be inconsistent due to the effect of the vibrations caused by moving parts of the engine, for example. This causes the fluid to move and splash around in the reservoir, thereby causing movement of the float and an unstable contact between the ground and ignition contact. This movement has the potential to prevent the float from grounding the ignition long enough to completely shut down the engine. 
   SUMMARY 
   In some embodiments, the present invention is directed to a low fluid sensor that can be mounted to an engine or other machine to accurately detect a condition of low fluid. The apparatus can include a float contact that compensates for the movement of a float due to splashing of fluid in a reservoir for a system that has moving parts. 
   Using a float contact that is movable relative to the float allows the low fluid sensor to more accurately determine a low fluid condition and limit the incidence of intermittent grounding of the ignition. A movable float contact allows for tolerance or dimensional variations of the contacts. In the case that the contacts are not exactly the same size or height, the moveable plate is still capable of touching all of the contacts simultaneously. Additionally, a movable float contact can remain in contact with the ground and ignition contact even while the float is moving in response to vibrations, because the float contact is weighted and loosely coupled to the float so that the float contact does not move with every slight dip and peak of the float. Instead, the plate will continue to contact the electrical contacts and therefore allow the low fluid indicator to remain in a “shut-off” state until more fluid is added to the system. 
   One embodiment of the present invention is directed to a fluid level switch for a machine having a fluid reservoir adapted to contain a fluid at an acceptable level. The fluid level switch includes a mounting plate, a float housing, and a float assembly positioned within the float housing. The mounting plate retains first and second contacts. The float housing is configured to receive fluid from the fluid reservoir and the float assembly is movable in response to the level of fluid in the float housing. The float assembly includes a contact member electrically connecting the contacts when the level of the fluid is below the acceptable level. The contact member is coupled to the float for movement with the float and for movement relative to the float. 
   Another embodiment of the invention is directed to a fluid level switch for a machine having a fluid reservoir adapted to contain a fluid at an acceptable level. The fluid level switch includes first and second contacts, and a float assembly adapted to be in fluid communication with the fluid reservoir. The float assembly includes a float and a contact member. The float is movable between a raised position when the fluid is at an acceptable level and a lowered position when the fluid is below the acceptable level. The contact member is coupled to the float about at least a portion of the periphery of the contact member. The contact member electrically connects the first and second contacts when the fluid is below the acceptable level. 
   Another embodiment of the invention is directed to a fluid level switch for a machine having a fluid reservoir adapted to contain a fluid at an acceptable level. The fluid level switch includes a float housing, first and second contacts, and a float assembly. The float housing is configured to receive fluid from the fluid reservoir, and the first and second contacts are positioned on a same side of the float housing. The float assembly is positioned within the float housing and includes a float and a contact member. The float is movable between a raised position when the fluid is at an acceptable level and a lowered position when the fluid is below the acceptable level. The contact member is coupled to the float for movement with the float between raised and lowered positions and for movement relative to the float. The contact member electrically connects the first and second contacts in at least one of the raised and lowered condition. 
   Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a fluid level switch according to a first embodiment of the present invention. 
       FIG. 2  is an exploded view of the fluid level switch of  FIG. 1 . 
       FIG. 3  is cross-sectional view taken along line  3 - 3  of  FIG. 1 ; 
       FIG. 4  is a view similar to  FIG. 3  illustrating a float in a tilted condition. 
       FIG. 5  is a perspective view of a fluid level switch according to another embodiment of the present invention. 
       FIG. 6  is a perspective view of a mounting plate according to another embodiment of the present invention. 
       FIG. 7  is an exploded view of a fluid level switch according to another embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   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. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. 
   A fluid level switch  10  of a first embodiment of the present invention is illustrated in  FIG. 1 . The fluid level switch  10  includes a mounting plate  12  fastened to a vertical wall  14  of an engine by mounting screws  16 . Any conventional fastener can be employed to secure the mounting plate  12  to the vertical wall  14  as just described, such as screws, nails, rivets, pins, posts, clips, clamps, inter-engaging elements, and any combination of such fasteners. The mounting plate  12  is L-shaped to include a support portion  18 . As shown in  FIG. 2 , the support portion  18  includes three apertures  20 , however, the number of apertures  20  can vary. 
   As better illustrated in  FIG. 2 , the support portion  18  comprises two electrical contacts  22 ,  24 . The first electrical contact, such as a ground contact  22 , is made from a piece of the support portion  18  that has been bent upwardly a distance from the surface of the support portion  18 , thereby forming an aperture  23 . The second electrical contact is an ignition contact  24  that is made up of a conductive material and that extends through an aperture  26  in the support portion  18 . Although the second contact of the illustrated embodiment is described as being an ignition contact, the second contact in other embodiments can alternatively be any live or hot contact not necessarily electrically connected to the ignition. In the illustrated embodiment, an insulator  28  supports the ignition contact  24  and is press-fit into an aperture  29  of the support portion  18 . However, the insulator  28  can be coupled to the support portion  18  in various ways such as the use of fasteners or molding. The insulator  28  acts to prevent electrical contact between the ground contact  22  and the ignition contact  24 . 
   The fluid level switch  10  also includes a cylindrical float housing  30  with protrusions  32  that line up with the apertures  20  for coupling the float housing  30  to the support portion  18 . The float housing  30  has an open end  34  where the protrusions  32  are located and a closed end  36  having a centrally located aperture  38 . In other embodiments, the aperture  38  could be located anywhere on the closed end to vent for air. A gap or cutout  40  in the float housing  30  provides clearance for the insulator  28  when the float housing  30  is coupled to the support portion  18  and allows for a snap-fit assembly. The insulator  28  is partially located within the float housing  30  to reduce the size of the fluid level switch  10 . The location of the insulator  28  can vary and is not limited to the placement shown in  FIG. 2 . Specifically, the insulator  28  does not have to be located partially within the float housing  30 . 
   A cylindrical float  42  made of a buoyant material is shown in  FIGS. 2 and 3 . The float  42  is held in a retaining member  44  having a cage structure. Both a bottom portion  46  and a top portion  48  of the retaining member  44  are open. The retaining member  44  has a plurality of tabs  50  on the top portion  48  that can retain the float  42  within the retaining member  44 . The float  42  rests on a first lip  52  that includes an outer diameter  54  equal to the upper portion  48  of the retaining member  44  and an inner diameter  55  smaller than that of the float  42 . The first lip  52  thereby supports the bottom  57  of the float  42 . A plate  56  can be positioned between the float  42  and the bottom portion  46  of the retaining member  44 . The plate  56  sits on a second lip  58  on the bottom portion  46  of the retaining member  44 . The second lip  58  is spaced from the first lip  52  a distance D to allow movement of the plate  56  (having a thickness T) relative to the float  42  within the retaining member  44 . The plate  56  is disc-shaped and has apertures  60  for weight adjustment. A centrally located, raised portion  61  of the plate  56  helps to prevent the plate  56  from becoming stuck to the float  42  due to viscous properties of the fluid. The raised portion allows only a small portion of the plate  56  to contact the float  42 . The plate  56 , also referred to as a contact plate, is not limited to the illustrated shape, but can take on a plurality of shapes and sizes such that it can provide electrical communication between two contacts. It is preferable that the plate  56  be more dense than the fluid, however it is not required. In the preferred embodiment, gravity pulls the plate  56  down on the contacts  22 ,  24 . 
     FIG. 3  illustrates the internal structure of the fluid level switch  10 . The plate  56  rests upon the second lip  58  of the retaining member  44 . Between the top of the plate  56  and the bottom  57  of the float  42  is a space  62 . The space  62  allows linear and angular motion of the plate  56  to help improve switching characteristics. The bottom  57  of the float  42  rests upon the first lip  52  of the retaining member  44 , and is held at the top portion  58  of the retaining member  44  by the tabs  50 . In combination, the float  42 , plate  56 , and retaining member  44  define a float assembly  64  ( FIG. 2 ). The float assembly  64  fits within the cylindrical float housing  30 . As shown in  FIGS. 1 and 2 , the protrusions  32  of the float housing  30  engage the apertures  20  to cover contacts  22 ,  24 . The gap  40  in the float housing  30  prevents interference from the insulator  28  when the float housing  30  is coupled to the support portion  18 . 
   A first side of the float housing  30  is defined below the float  42 , and everything located below reference line  63  is considered to be below the float  42 . A second side of the float housing  30  is defined above the float  42 , and everything located above reference line  65  is considered to be above the float  42 . As illustrated in  FIG. 3 , both contacts  22 ,  24  are below the float  42  and on the first side of the housing  30 . 
   One embodiment of the present invention can be located in the crankcase of an engine. The crankcase is a relatively turbulent environment and the level of fluid, such as oil, may fluctuate greatly depending on a number of factors, such as slight tilting or changes to the orientation of the engine and the crankshaft or other moving parts splashing the oil. Other embodiments could be used on pumps, transmissions, or any other machine with moving parts and a fluid reservoir. 
   As illustrated in  FIGS. 1 and 2 , the fluid level switch  10  allows oil to flow into and out of the float housing  30  through the apertures  23 ,  26 ,  38 . The protrusions  32  of the float housing  30  may have apertures  66  as well to allow for fluid flow into the float housing  30 . Since the float  42  is made of a buoyant material, the float  42  will cause the float assembly  64  to rise and fall with the oil level. When oil is added to the engine, the float assembly  64  will rise with the level of the oil. As oil is used in the system, the float assembly  64  will lower with the oil level. 
   As the level of oil nears an undesired low level, the float assembly  64  and hence the plate  56  move increasingly closer to the contacts  22 ,  24 , as shown in  FIG. 3 . When the oil reaches a predetermined level that would be considered a “low oil” condition, the plate  56  touches the contacts  22 ,  24 . Because the plate  56  is more dense than the fluid being monitored, the plate  56  will tend to stay in relatively the same position although the plate  56 , in most situations, is submerged in fluid. As shown in  FIG. 4 , the space  62  between the plate  56  and the float  42  is intended to be large enough to allow the plate  56  to remain in contact with electrical contacts  22 ,  24  even while the float  42  and retaining member  44  move and tilt inside the cylindrical float housing  30  caused by misaligned contacts  22 ,  24  or agitated fluid from normal engine vibration or operation. 
   The illustrated embodiment uses an “engine shutdown” method by grounding the primary ignition current when the plate  56  is touching both contacts  22 ,  24 . For example, the operator of a lawnmower or snow blower can be alerted of such a situation through the engine being shut-off during operation. Upon the operator adding enough oil to the system whereby the plate is not touching either electrical contact  22 ,  24 , the engine can be restarted and regular operation can resume. 
   An alternate design for the fluid level switch  10  uses an “indicator method” to alert an operator of the low oil situation. When the plate  56  touches both contacts  22 ,  24 , an electrical circuit can be completed to alert the operator of a low oil situation through an indicator such as a “low oil” light or a “low oil” alarm or buzzer. When the “low oil” indicator is activated, the operator knows that a low oil situation is occurring. In that case, the operator can choose to continue operating the machine while in a state of low oil and risk damaging the engine, or can add oil until the plate  56  is no longer touching the contacts  22 ,  24 . 
   In the engine shutdown method, a latching module  68  (illustrated in  FIG. 4 ) can be used to prevent intermittent or false shutdown due to switch bouncing caused by engine vibration and turbulence of the fluid surrounding the float assembly  64 . False shutdown occurs when vibration and turbulence of the engine and fluid do not allow the float to ground the ignition long enough to completely shut down the engine. The latching module  68  operates to ground the ignition even after the plate  56  bounces out of contact with the first and second contacts  22 ,  24 . In one embodiment, the latching module  68  includes a capacitor and a silicon controlled rectifier (“SCR”) electrically connected to the capacitor. When the plate  56  electrically connects the first and second contacts (i.e., when the fuel level switch closes), the ignition pulse from the engine&#39;s ignition system charges the capacitor. When the charge of the capacitor reaches a voltage value that is sufficiently high to switch the SCR “on”, the primary winding current is shunted through the SCR to ground, thereby shutting down the engine. The SCR remains “on”, using the energy stored in the capacitor as the engine rotates during coastdown. As long as the SCR is “on”, the primary winding current will remain shunted through the SCR regardless of whether the fluid level switch re-opens due to vibrations. 
   A fluid level switch  110  according to an alternate embodiment of the present invention is illustrated in  FIG. 5 . The fluid level switch  110  is adapted for mounting to a horizontal surface  114  using mounting fasteners  116 . A mounting plate  112  can be fastened to the horizontal surface  114  in the same manner that the first embodiment of the mounting plate  12  can be fastened to a vertical surface  14 . Mounting plate  112  is similar to the support portion  18  as shown in  FIG. 1  and the fluid level switch  110  operates similar to fluid level switch  10 . 
   Another embodiment of a mounting plate  212  is illustrated in  FIG. 6 . The mounting plate  212  is adapted to be fastened to a vertical surface  14  similar to the mounting plate  12  illustrated in  FIG. 1 . The mounting plate  212  has a support portion  218  that comprises three electrical contacts  222 ,  268 ,  24  (shown in  FIG. 2 ). The electrical contacts, such as ground contacts  222 ,  268 , are made from pieces of the support portion  218  that have been bent upwardly a distance from the surface of the support portion  218  thereby forming apertures  223 ,  270 . The electrical contact  24  is made of conductive material and extends through an aperture  226  in the support portion  218 . The mounting plate  212  used with the float assembly  64  is similar to the mounting plates  12 ,  112  illustrated in  FIGS. 1-5 . In other embodiments, the mounting plate  212  can be reconfigured to be fastened to a horizontal surface  114  similar to the mounting plate  112  illustrated in  FIG. 5 . 
   A fluid level switch  310  of another embodiment of the present invention is illustrated in  FIG. 7 . The fluid level switch  310  includes a mounting plate  312  that can fastened to a wall of an engine by inserting fasteners through apertures  316 . The mounting plate  312  includes a support portion  318  that has two electrical contacts  322 ,  368 . The electrical contacts  322 ,  368  can be ground contacts and are made from pieces of the support portion  318  that have been bent upwardly a distance from the surface of the support portion  318  thereby forming apertures  323 ,  370 . 
   The fluid level switch  310  also includes an electrical contact  324  that extends through an aperture  326  in the support portion  318 . The electrical contact  324  can be an ignition contact and is made from a conductive material. The ignition contact extends through the aperture  326  in the support portion  318  such that the ignition contact does not contact the mounting plate  312 . 
   In the illustrated embodiment, a shield  328  supports the ignition contact  324  and is coupled to the mounting plate  312  by the protrusions  332  of the float housing  330 . Specifically, the protrusions  332  of the float housing  330  extend through the apertures  320  of the mounting plate  312  and into apertures  334  of the shield  328  to couple the mounting plate  312  between the float housing  330  and the shield  328 . The shield  328  reduces the effect of oil turbulence within the oil reservoir on the operation of the fuel level switch  310 . Specifically, the shield  328  resists the flow of oil through apertures  323 ,  370  making the operation of the plate  56  and float  42  less affected by the turbulence outside the float housing  330 . The shield  328  is made of an insulating material. In addition, the shield  328  replaces the insulator  28 ,  128  of the previous embodiments ( FIGS. 1-6 ) to support the ignition contact  324  and to prevent electrical contact between the ignition contact  324  and the ground contacts  322 ,  368  and between the ignition contact  324  and the mounting plate  312 . 
   The fluid level switch  310  also includes a float assembly  364  similar to the float assembly  64  of the first embodiment as illustrated in  FIG. 2  except that the protrusions  332  of the float housing  330  are slightly extended to capture the shield  328 . The reference numbers used to describe the float assembly  64  of  FIG. 2  are used to describe the corresponding components of the float assembly  364  in  FIG. 7 . 
   The constructions and aspects described above and illustrated in the drawings are presented by way of example only and are not intended as a limitation upon the concepts and principles of the present invention. As such, it will be appreciated by one having ordinary skill in the art, that various changes in the elements and their configuration and arrangement are possible without departing from the spirit and scope of the present invention as set forth in the claims.