Abstract:
A fuel level sender ( 26 ) for signaling liquid fuel level in a fuel tank ( 22 ). An enclosure ( 31 ) forming a hub of the sender provides an interior that is hermetically sealed against intrusion of fuel vapor and liquid. An actuator ( 110, 122 ) is positionable on the enclosure exterior in correlation with liquid fuel level. A movement ( 52 ) within the enclosure interior follows the positioning of the actuator. An electric circuit element ( 62; 86 ) within the enclosure interior is operated by the movement to provide an electric characteristic for transmission through the enclosure to signal liquid fuel level. A bottom reference rod ( 150 ) and stop ( 152 ) position the enclosure circumferentially within its mounting in a fuel pump module to cause the circuit element to signal zero fuel level when the stop is on the tank bottom wall and the actuator is in position corresponding to zero fuel level in the tank.

Description:
REFERENCE TO RELATED APPLICATIONS AND PRIORITY CLAIMS 
   This non-provisional application derives from the following patent applications, the priorities of which are expressly claimed: Non-Provisional application Ser. No. 10/373,955 filed 26 Feb. 2003 claiming the priorities of Provisional Application No. 60/360,337, filed on 26 Feb. 2002, and Provisional Application No. 60/370,058, filed on 4 Apr. 2002; and Provisional Application No. 60/425,770, filed on 13 Nov. 2002. 

   FIELD OF THE INVENTION 
   This invention relates to float-operated senders that are associated with fuel tanks of motor vehicles to transmit a value of a parameter representing the level of liquid fuel in a tank to instrumentation that uses the value to operate a display that presents information related to the level of fuel in the tank to a driver of the vehicle. 
   BACKGROUND OF THE INVENTION 
   One type of sender that is used in motor vehicles comprises a resistor card that is disposed in a fuel tank in a manner that exposes it to whatever fuel is used by the vehicle (gasoline and/or alcohol for example), including fuel additives, sour gas, and/or contaminants. The sender is operated by a float that follows the level of liquid fuel in the tank. As the float assumes different levels within the tank, its motion is transmitted by a float rod, or arm, to a contact arm, causing a contact on the arm to move along a succession of commutator bars extending from locations along the length of a resistor track printed on a resistor card, thereby selecting a portion of the resistor in correlation with the level of the float. The selected portion provides a variable resistance that is electrically connected with instrumentation that operates a fuel gauge that can be observed by the driver. The float rod is mounted for pivotal movement via a bearing, and the float is disposed at an end of the rod opposite the bearing. As the float moves, the rod imparts pivotal motion to the contact arm, causing its contact to move in an arc along the succession of commutator bars, changing the value of the variable resistance as it moves. In that design for a resistive type fuel level sender, the commutator bar contact produces a result similar to a contact moving in an arc along a potentiometer or variable resistor track, changing the value of the variable resistance as it moves. 
   The force that the contact is able to apply against the resistor on the resistor card is important in enabling the sensor to provide a service life that will meet relevant specifications. Over the life of a sender the force that the contact exerts on the resistor may vary for one or more different reasons, such as fuel slosh in the tank and/or looseness in the bearing. The use of a silver palladium alloy as the resistor commutator may reduce the effects of those factors. Nonetheless the contact may at times lose contact with the resistor, creating a momentary open circuit. Events that may cause such open circuits include intrusion of foreign particles between the contact and the resistor, corrosion of the commutator, oxidized fuel coating, and high-G loads experienced by the sender. Momentary open circuits create excess wear on the contact and the resistor commutator. 
   A sender that precludes those undesirable possibilities and that meets certain cost objectives is therefore seen to be a desirable improvement. 
   The durability and accuracy of a fuel sender are also important, especially where a motor vehicle manufacturer warrants a fuel system and/or its components either for legal compliance and/or by competitive considerations. Failure to meet relevant compliance criteria can expose a motor vehicle manufacturer to costly penalties and/or warranty claims. 
   Accordingly, it is believed that a sender that provides both increased durability and accuracy over an extended period would be a significant improvement in the state of the art. 
   U.S. Pat. Nos. 3,739,641 and 4,987,400 describe gauges having magnetically driven senders in which the contacts are housed within sealed enclosures. The gauge of U.S. Pat. No. 3,739,641 is sealed against intrusion of volatile vapors that may accumulate from many sources and might ignite from a spark. An example given is in the bilge of a marine vessel. The gauge of U.S. Pat. No. 4,987,400 is said to be ultrasonically sealed for withstanding at least eight inches of mercury pressure differential. Both patents teach the use of an external magnet driving a magnet internal to the enclosure where the magnet is rotated by a coupling to a float. The enclosure materials are not selected to be highly impermeable to fuel or fuel vapors, only sufficient to prevent spark ignition. 
   Considerations in the prevailing design of motor vehicle fuel systems either tacitly or explicitly mandate that the fuel sender be contained within the fuel tank where it may at times be immersed in liquid fuel. A contact-containing enclosure that is external to a tank, as in U.S. Pat. Nos. 3,739,641 and 4,987,400, is not seen to be suitable for placement in a fuel tank of a motor vehicle where it must withstand immersion in a hostile liquid fuel that can at some times be quite hot and at others, quite cold, and that may contain various contaminants, additives, foreign substances, etc. 
   Accordingly, it is believed that an in-tank fuel sender for a motor vehicle that maintains its accuracy when exposed to liquid fuels, especially liquid fuels like gasoline, over an extended period would be another significant improvement in the state of the art. 
   Prevailing fuel system design practices in the automotive industry employ a fuel pump module that is assembled into a fuel tank, typically through an opening in a top wall of the tank that is subsequently closed. A fuel sender is typically part of the fuel pump module. Certain of the known systems comprise a fixed mounting of the sender in an assembly that is installed in a tank. The assembly has a construction that forces its lower end against a bottom wall of the tank thereby bodily positioning the sender within the tank relative to the bottom wall. 
   Accordingly, an in-tank fuel sender that can be conveniently assembled into fuel pump modules is also seen as desirable. 
   Non-Provisional application Ser. No. 10/373,955, filed 26 Feb. 2003, discloses a novel fuel sender for a motor vehicle fuel tank that possesses features and characteristics that render the sender suitable for in-tank placement in a motor vehicle fuel system where it is exposed to liquid fuel, including convenient mounting on a fuel pump module; that endow the sender with continued accuracy over an extended period, enabling it to comply with increasingly stringent specifications; and that make the sender quite cost-effective considering the increasingly stringent demands that may be imposed on it by motor vehicle manufacturers. 
   The disclosed embodiment of that Application comprises a central hub comprising a sealed enclosure in which a contact arm and a resistor card are disposed. The enclosure is preferably filled with a non-conducting fluid, such as light oil. Force of a contact on the contact arm against a commutator or track on the resistor card will be essentially insensitive to influences, such as particle intrusion and fuel slosh, that otherwise might cause momentary open circuits, with contact-to-resistor card force remaining more consistent over the useful life of the sender. Contact-to-resistor card arcing is unlikely, but any arcing that might occur, such as due to a high-G force, will not be exposed to fuel or fuel vapor. 
   The enclosure is formed by a low permeable casing, or housing, preferably a stainless steel, and a low permeable cover, preferably a non-metallic, fuel-tolerant synthetic material, which may be either transparent or opaque. The housing has a circular back, or rear, wall and a circular perimeter wall that extends forward from and perpendicular to the rear wall. The forward margin of the perimeter wall is crimped over a circular outer edge of the cover to forcefully hold the circular outer margin of the cover against a circular shoulder formed in an intermediate portion of the housing perimeter wall. A sealing gasket that is disposed between the housing shoulder and the cover margin seals the joint between the cover and housing in a manner that prevents both liquid fuel and fuel vapor from intruding into the enclosure interior that is cooperatively formed by the assembled cover and housing. Any method of sealing must take into consideration sealing against fuel vapor, as well as liquid fuel. 
   When installed within a fuel tank, the sender is disposed in an orientation that places a main center axis of the hub enclosure in a desired orientation. The hub is fixedly mounted in any suitable manner, such as by attachment to a wall of a fuel pump module. A movement actuating member that is external to the sealed enclosure and operated by a fuel level float is positionable relative to the central hub in correspondence with fuel level sensed by the float. As the float moves vertically up and down with changing fuel level in the tank, the movement actuating member is correspondingly positioned in relation to the sealed enclosure. 
   The contact arm is positioned by a movement within the interior of the sealed enclosure. The movement is supported within the enclosure for turning about the main center axis and forms one portion of a magnetic circuit whose other portion is formed by the movement actuating member. The movement and the movement actuating member are magnetically coupled such that the movement is forced to turn within the enclosure in correspondence with positioning of the movement actuating member relative to the exterior of the enclosure. In this way the movement is forced to follow the actuating member, and hence follow the level of liquid fuel in the tank. 
   The movement moves the contact arm contact along the commutator, or track on the resistor card to change the resistance that is presented to an electric circuit connected to the sender. In this way, the sender enables the circuit to operate a fuel gauge that indicates to a driver of the motor vehicle the amount of fuel in the tank. 
   The movement provides the source of magnetism, while the movement actuating member comprises a magnetically conductive material. Turning of the movement actuating member causes substantial follower torque to be applied to the movement, thereby causing the movement to follow the turning of the actuating member with low hysteresis. Those features, in conjunction with the isolation of the commutator, its contact, and the resistor from fuel, enable the sender to perform with consistency and accuracy during the course of its useful life. 
   The mounting of in-tank fuel senders in mass-produced automotive vehicle fuel tanks results in some tank-to-tank variation in the distance at which a sender is disposed above a bottom wall of a tank. Even when that distance is fairly well controlled by control of the dimensional tolerances of the parts involved, small differences can give rise to significant differences in accuracy of the reading on a fuel gauge that is presented to the driver. The fuel pump module may also change position within the tank during the life of the vehicle due to various effects such as those caused by impact on the vehicle from an external source. Improvements in accuracy of such readings can be important in mass-produced motor vehicles where such vehicles include trip computers having display features such as “miles to empty”. 
   Various forms of “bottom referencing” have been heretofore proposed. Examples are found in U.S. Pat. Nos. 5,167,156; 5,666,851; and 6,508,121. 
   SUMMARY OF THE INVENTION 
   The present invention relates to a novel in-tank fuel level sender that can alleviate the effect on fuel gauge accuracy of the above-discussed tank-to-tank variations in positioning of the sender from the tank bottom wall. The invention accomplishes this objective by a bottom referencing feature that references the sender to the tank bottom wall. The sender also incorporates the hermetic sealing described in Non-Provisional application Ser. No. 10/373,955 filed 26 Feb. 2003. 
   A general aspect of the invention therefore relates to an in-tank fuel level sender for signaling the level of liquid fuel in a motor vehicle fuel tank. An enclosure forming a hub of the sender provides an interior that is hermetically sealed against intrusion of fuel, both liquid and vapor. An actuator, such as a float rod and float, is positionable on an exterior of the enclosure in correlation with liquid fuel level. A movement within the interior of the enclosure follows the positioning of the actuator. An electric circuit element within the interior of the enclosure is operated by the movement to provide an electric characteristic for transmission through the enclosure to signal the liquid fuel level. The hermetically sealed enclosure is disposed in a mounting, such as in a fuel pump module, for some degree of turning about an axis. A bottom reference rod extends from the enclosure exterior toward the bottom wall of the tank and tends to turn the enclosure in one sense about the turning axis in the mounting. In its installed position in a tank, the sender is disposed such that the bottom reference rod rests on the tank bottom wall at a distance from the turning axis to circumferentially position the enclosure in its mounting about the turning axis. The float rod and float position operate the movement according to the fuel level in the tank. Because of the ability of the enclosure to be positioned in its mounting by the bottom reference rod, the electric characteristic presented by the sender is rendered essentially independent of the distance of the enclosure above the tank bottom wall, thereby essentially removing that distance as an influence on sender accuracy. 
   Another general aspect relates to a method of calibrating such a sender. 
   The foregoing, along with further aspects, features, and advantages of the invention, will be seen in this disclosure of a presently preferred embodiment of the invention depicting the best mode contemplated at this time for carrying out the invention. This specification includes drawings, briefly described below, and contains a detailed description that will make reference to those drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an elevation view of a fuel pump module disposed within a motor vehicle fuel tank and showing a front view of a sender, including a float rod and float, but without the bottom referencing feature. 
       FIG. 2  is an enlarged rear view of the sender of  FIG. 1  by itself, still in elevation, but with the float rod and float omitted and with a hub of the sender rotated counterclockwise a small amount and with an actuating plate of the sender in a different position for illustrative convenience. 
       FIG. 3  is a right side view of  FIG. 2 , looking along line  3 — 3  in  FIG. 2  in the direction of the arrowheads. 
       FIG. 4  is a view in the same direction as  FIG. 2 , but at a stage of fabrication of the sender where a cover is not yet in place, thereby allowing the interior of a movement-containing housing to be seen. 
       FIG. 5  is a right side view of  FIG. 4 , looking along line  5 — 5  in  FIG. 4  in the direction of the arrowheads. 
       FIG. 6  is a view taken generally along line  6 — 6  in  FIG. 4  in the direction of the arrowheads and on a larger scale. 
       FIG. 7  is a cross section view along line  7 — 7  in  FIG. 4  looking in the direction of the arrowheads. 
       FIG. 8  is a view in same direction as the view of  FIG. 2  showing the cover separate from the sender. 
       FIG. 9  is a cross section view as viewed along line  9 — 9  in  FIG. 8  in the direction of the arrowheads. 
       FIG. 10  is a right side view of the cover as viewed along line  10 — 10  in  FIG. 8  in the direction of the arrowheads. 
       FIG. 11  is a rear view of  FIG. 8 . 
       FIG. 12  is an enlarged cross section view as viewed along line  12 — 12  in  FIG. 10  in the direction of the arrowheads. 
       FIG. 13  is a view in the same direction as the view of  FIG. 11  on an enlarged scale showing, by itself, a resistor card that mounts on the cover. 
       FIG. 14  is a plan view of the actuating plate of the sender shown by itself on substantially the same scale as  FIG. 1 . 
       FIG. 15  is a plan view of a retainer of the sender shown by itself on substantially the same scale as  FIG. 1 . 
       FIG. 16  is a view in the same direction as the view of  FIG. 2  showing a magnet return conductor by itself on a slightly smaller scale than  FIG. 2 . 
       FIG. 17  is top view of  FIG. 16 . 
       FIG. 18  is a left side view of  FIG. 16 . 
       FIG. 19  is a view like  FIG. 1 , but with the sender having the bottom referencing feature. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  shows a portion of a fuel pump module  20  that has been placed within a fuel tank  22  through an opening in a top tank wall (not shown) that is subsequently closed. The base of module  20  rests on a bottom wall  24  of tank  22  to set the elevation, within the tank, of a fuel level sender  26  without bottom referencing. 
     FIGS. 2–5  show sender  26  to comprise a non-metallic cover  28  and a metal casing, or housing  30 , that are assembled together to cooperatively form a sealed enclosure  31 . Cover  28  is preferably a fuel-tolerant plastic, either transparent or opaque. Housing  30  is preferably a non-magnetic stainless steel that has been fabricated by drawing sheet stock into the general shape of a cup as shown by  FIG. 7 . The bottom of the cup forms a back, or rear, circular wall  32  and an immediately adjoining circular perimeter wall  34  that extends forward from rear wall  32 . An intermediate portion of wall  34  comprises a circular shoulder  36  that separates a smaller diameter proximal portion  38  of wall  34  from a larger diameter distal wall portion  40  that forms the cup rim. 
     FIGS. 8–12  show cover  28  as essentially a circular disk that has an inner face  42 , an outer face  44 , and an outer margin that comprises a shouldered groove  46  on inner face  42 . The outside diameter of cover  28  is slightly less than the circular inside diameter of distal wall portion  40  of housing  30 . A circular sealing gasket  48  ( FIG. 7 ) is disposed within the housing against shoulder  36 . In preparation for assembly of cover  28  and housing  30 , the housing is disposed with its rear wall facing vertically downward so that the open housing interior faces vertically upward. Such an orientation enables the interior of enclosure  31  to be filled with movement-damping and lubricating fluid, such as a light oil, if desired, by filling housing  30  before cover  28  is assembled to it. 
   Cover  28  is placed over housing  30  with inner face  42  facing and aligned with the open housing interior. The cover is then advanced, i.e. lowered, to fit the cover outer margin within wall portion  40  and seat groove  46  on gasket  48 , thereby closing what would otherwise be the open front of the housing. Wall portion  40  is then rolled over, i.e. crimped, onto outer face  44 , forcing the two parts  28 ,  30  together and compressing gasket  48  in the process to form sealed enclosure  31 . The assembled condition can be seen in  FIGS. 2 and 3  where the sealed joint that has been created endows the enclosure with a circular perimeter ridge  50  that can, if desired, be used for mounting the sender on module  20 . 
   Sender  26  comprises a movement,  52  shown by itself in  FIG. 6 . Movement  52  is housed within enclosure  31  as shown by  FIG. 7 . Movement  52  comprises a magnet  54  magnetized along its length (see  FIG. 4  also) to provide respective North and South poles at opposite rounded tip ends  56 ,  58  respectively of the diameter of the movement. Magnet  54  has flat front and rear faces, giving it a uniform thickness, but it has a narrowing taper in the direction of each tip end. Movement  52  further comprises an electrically conductive contact arm mounting bracket  60  for mounting an electrically conductive contact arm  62  on magnet  54 . An electrically conductive eyelet  64  holds the two parts  54 ,  60  together. 
   Before its association with parts  54 ,  60 , eyelet  64  has a cylindrical shape, but with one end rolled over. Assembly of parts  54 ,  60  is accomplished by placing bracket  60  in front of the front face of magnet  54  with a through-hole  67  in the bracket aligned with a through-hole  65  in magnet  54 , and then inserting the non-rolled-over end of eyelet  64  through the two aligned through-holes so that the non-rolled-over eyelet end protrudes rearward beyond the rear face of the magnet. Through-hole  65  is located at the center of magnet  54 , midway between the magnet&#39;s tip ends  56 ,  58 . The protruding rear end of the eyelet is then rolled over against the margin of through-hole  67  thereby forcing bracket  60  to be held flat against the front face of magnet  54  that is to confront inner cover face  42  in the completed sender. 
     FIG. 4  shows that the length of contact arm mounting bracket  60  is at a right angle to that of magnet  54 .  FIGS. 6 and 7  show that one end of bracket  60  comprises a raised platform  66  to which a flat proximal end  68  of contact arm  62  is affixed, such as by welding in several spots. Contact arm  62  comprises a bend  69  that causes it to extend angularly away from end  68  in overlying relation to bracket  60 . The tip, or distal, end of contact arm  62  comprises an electric contact  70  that can be either an integral formation in the arm, such as a dimple, one or more tines or fingers, or a separate contact element that is affixed to the arm by any suitable process. 
     FIG. 7  shows that rear housing wall  32  comprises an embossment  72  at its center. Embossment  72  is created during the drawing of the cup that forms housing  30 . Embossment  72  is shaped to provide a circular depression, or pocket,  74  on the interior of enclosure  31  and a circular riser  76  on the exterior. Pocket  74  accurately and sturdily seats a circular head  78  of a post  80  so that the post extends within the enclosure along a central main axis  81  that is perpendicular to wall  32  and parallel to and concentric with perimeter wall portions  38 ,  40 . Embossment  72  may be formed in a way that allows post  80  to be assembled to housing  30  by pressing head  78  into pocket  74 . Additional means of attachment, such as welding or the like, may be used as appropriate. 
   As can be appreciated from consideration of  FIG. 7 , movement  52  is associated with housing  30  prior to placement of cover  28 . With post  80  having been assembled to the housing, movement  52  is placed on post  80  by aligning eyelet  64  with the post and moving the two toward each other. Contact arm  62  has an aperture  83  ( FIG. 4 ) that allows post  80  to pass through without interference. The placement of movement  52  on post  80  enables the movement to turn about axis  81 . 
   Cover  28  is a molded synthetic part having several formations that are advantageous for the fabrication and operation of sender  26 . Those formations can be seen in  FIGS. 8–12 . One formation is a shallow depression  82  in inner face  42  for locating a resistor card  84  on which a resistor  86  is disposed. A second formation is a small circular blind hole  88  at the center of face  42  into which the tip end of post  80  locates when the cover is assembled to housing  30 . 
   A third formation shown in  FIG. 12  comprises a shouldered through-hole  90  that provides for a sealed termination of resistor  86  to the exterior of enclosure  31  so that sender  26  can be connected to an electrical system that reads the fuel level signaled by the sender. The termination comprises an electrically conductive rivet  92  that passes through-hole  90 . On the interior of enclosure  31 , a head  94  of rivet  92  bears against an end of resistor  86 . A shank  96  of the rivet extends from head  94 , passing through a hole  95  in resistor card  84 , through hole  90 , and through a hole in the proximal end of an electric terminal  97  that is external to enclosure  31 . An O-ring seal  98  seals the circumference of rivet shank to the wall of hole  90  proximate its shoulder. The distal end  100  of the rivet shank is rolled over to hold the proximal end of terminal  97  flat against a circular pad  102  that is locally raised on cover outer face  44  to complete this third formation in the cover. Terminal  97  comprises a step  104  leading to a blade  106  at its distal end adapted for mating connection with a wiring terminal (not shown) of the electrical system. 
   A fourth formation in cover  28  is a straight ridge  108  on front face  44  lying on a diameter of the cover but stopping short of the perimeter of the cover at both ends. Pad  102  and terminal  97  are disposed to one side of ridge  108 , as shown by  FIG. 8 , with the length of blade  106  running parallel to ridge  108 . Neither terminal  97  nor ridge  108  interfere with crimping of housing  30  to cover  28 . As should be apparent, both terminal  97  and resistor card  84  are assembled to cover  28  prior to attachment of the cover to housing  30 . As will become more apparent later from description of sender calibration, ridge  108  provides a feature for conveniently turning the cover on the housing prior to crimping of the housing to the cover. 
   As cover  28  and housing  30  are being assembled to form enclosure  31 , contact  70  bears against resistor  86  with increasing pressure as the two parts move toward final position. Once the perimeter of cover  28  has engaged gasket  48 , and the housing has been crimped to the cover, the angularly extending portion of arm  62  has been resiliently flexed to cause contact  70  to bear with a desired amount of force against resistor  86 . 
   Riser  76  of embossment  72  provides a bearing on which an actuating plate, or lever,  110  that is shown by itself in  FIG. 14  can turn. Actuating plate  110  is essentially a flat non-magnetic metal plate, having a large end and a small end. The large end comprises a circular through-hole  112 , that when the large end is placed behind and parallel with housing rear wall  32 , and with hole  112  concentric with riser  76 , allows the large end to be disposed against the rear housing wall with the riser fitting closely within hole  112 . A circular retainer  114 , shown by itself in  FIG. 15 , is then placed over the large end of actuating plate  110  to capture the latter on the housing. Riser  76  protrudes through hole  112  just enough to allow the center of retainer  114  to be disposed flat against the riser, and it is there that the retainer is secured by welding to the housing. Consequently, actuating plate  110  is captured on enclosure  31 , but in a manner that allows it to freely turn on the housing riser about axis  81  with no significant looseness. 
   As can be seen in  FIG. 1 , one end of a suitably formed float rod, or arm,  118  is joined to actuating plate  110  in any suitably secure manner, such as welding, at a location spaced radially of housing  30 . A level sensing float  120  is secured on the opposite end of rod  118  to follow the level of liquid fuel in tank  22 . As float  120  moves up and down with changing fuel level, it turns actuating plate  110  about axis  81 , as suggested by arrow  121 . 
   Actuating plate  110  carries a magnet return conductor  122  that is shown by itself in  FIGS. 16–18 . Magnet return conductor  122  comprises a formed metal wire, or rod, of circular cross section that is formed to a shape that provides opposite end segments  124 ,  126  that, when assembled onto actuating plate  110 , overlap, with suitable radial clearance, the exterior of larger diameter portion  40  of housing perimeter wall  34 . Segments  124 ,  126  are parallel with axis  81 , and are located 180° about axis  81 . With segments  124 ,  126  so disposed, magnet  54  aligns between them, with tip end  56  confronting segment  124  and tip end  58  confronting segment  126 . Magnetic flux from one of the magnet poles passes through the non-magnetic housing perimeter wall to the confronting one of the magnet return conductor segments. A yoke portion  127  of magnet return conductor  122  extends between segments  124 ,  126  to provide a return path for magnetic flux from one segment to the other. At the other segment, the flux passes back through the housing wall to the other magnet pole. 
   The circularly contoured perimeter edge of the large end of actuating plate  110  comprises two generally semi-circular notches  128 ,  130  diametrically opposite each other about axis  81 . Those notches locate and seat magnet return conductor  122  on the large end, as shown by  FIGS. 2-5 , so that as actuating plate  110  turns on enclosure  31  about axis  81 , segments  124 ,  126  similarly turn about the same axis. Because magnet  54  continually seeks alignment between segments  124 ,  126 , the motion that actuating plate  110  imparts to magnet return conductor  122  causes movement  52  to follow the actuating plate movement. And because actuating plate  110  follows movement of float  120 , movement  52  is forced to follow the level of liquid fuel in tank  22 . 
   As shown by  FIGS. 11 and 13 , the length of resistor  86  runs along an arc that is generally circular about axis  81 . Rivet  92  establishes electrical connection of one end of resistor  86  to terminal  97 . Movement  52  is effective to position contact  70  along resistor  86  at various distances from rivet head  94  in correspondence with fuel level. The amount of resistance present between rivet  92  and contact  70  corresponds to the level of fuel sensed by float  120 . Contact  70  is electrically connected to ground via grounding of contact arm  62  to housing  30  through bracket  60  and eyelet  54 , with eyelet  54  being urged into contact with housing rear wall  32  by the magnetic attraction to return conductor  127  and by the force by the resiliently flexed contact arm  62  to keep the rolled-over eyelet end at the rear face of magnet  54  in continual contact with wall  32 , even as movement  52  turns within enclosure  31 . 
   Grounding of housing  30  is accomplished through a conductive electric terminal  132  ( FIGS. 1–5 ) that is affixed to the exterior of housing perimeter wall portion  40 . An intermediate portion  133  of the terminal is curved for conformance to the housing perimeter wall where it is affixed to the housing in any suitable manner such as welding. At one end the terminal has an upturned blade  134 , and at the other end, a short upturned tab  136 . Blade  134  is adapted for mating connection with a wiring terminal (not shown) of the electrical system. Blade  134  presents an interference to magnet return conductor segment  126  for limiting circumferential travel of actuating plate  110  in the clockwise direction, as viewed in  FIGS. 2 and 4  when abutted by that segment. Tab  136  presents an interference to segment  124  for limiting circumferential travel of actuating plate  110  in the counterclockwise direction when abutted by that segment. 
   Turning of movement  52  within enclosure  31  can be damped and lubricated by filling the interior with a light oil, thereby immersing movement  52  and resistor  86  in a fluid medium, as mentioned earlier. Calibration of sender  26  occurs after cover placement, but before the housing is crimped onto the cover. 
   Calibration is performed with the aid of suitable equipment. First, before attaching float rod  118  to actuating plate  110 , the resistance measured between terminals  132  and  97  must be properly correlated with the position of actuating plate  110 . The proper resistance can be set for extra close tolerance for a low fuel signal point, such as empty, by holding actuating plate  110  at a particular position about axis  81  referenced to terminal  132 , turning the cover via ridge  108  to obtain the proper resistance, and then crimping housing  30  to cover  28 , as described above, to prevent cover turning. With this calibration, proper orientation of the sender in a fuel tank, or on a fuel module, uses terminal  132  as the reference. With the resistance having been properly correlated with actuating plate position, float  120  is placed at the low fuel, or other, level, actuating plate  110  is turned to provide the corresponding resistance across terminals  132 ,  97 , and the opposite end of float rod  118  is secured to actuating plate  110 , such as by welding. 
   When sender  26  is installed in a fuel tank, float  120  will move up and down with changing fuel level. As a result, rod  118  turns actuating plate  110 , and hence magnet return conductor  122 , on enclosure  31  about axis  81 . Movement  52  tracks return conductor  122  to correspondingly position contact  70  along resistor  86 , causing resistance between terminals  97  and  132  to indicate the fuel level. The arrangement of various parts in the particular embodiment of sender  26  illustrated here provides that contact  70  is essentially midway along the arcuate length of resistor  86  when actuating plate  110  and magnet return conductor  122  are midway between limits of travel constrained by blade  134  and tab  136 . When the fuel level falls to empty, the moving parts of sender  26  assume the solid line position shown in  FIG. 1  where segment  124  is close to tab  136 . When the fuel level rises to full, they assume the broken line position where segment  126  is close to blade  134 . The travel allowed by blade  134  and tab  136  assures that contact  70  remains on resistor  86  for all positions of actuating plate  110 . Hence, when the tank is empty, resistance between terminals  97  and  132  will be at its minimum reading; when the tank is full, resistance will be at maximum reading. A reverse of the resistance signal can be developed by making contact from terminal  95  to the far end of resistor  86  via a printed circuit buss bar on resistor card  84 . 
   It is believed that the sender that has been described herein provides significant improvements in performance and durability that are quite cost-effective. The magnet can be economically fabricated by known magnet fabrication technology, magnet molding technology in particular being contemplated. The metal parts, such as the housing, actuating plate, and the contact arm and its mounting bracket can be fabricated from conventional materials using conventional metalworking techniques. The cover can be molded by conventional molding techniques to include the various features described. 
   Tight dimensional tolerances in a mass-produced bent wire part may be costly to achieve. Dimensional tolerances for the formed wire magnet return conductor  122  however need not be especially strict. It is the precision in stamping notches  128 ,  130  in the perimeter of actuating plate  110  that enable conductor  122  to have less strict tolerance because it is the notches that will control the locations of end segments  124 ,  126 . Yoke portion  127  need merely allow member  122  to expand from its free unstressed state to spread end segments  124 ,  126  sufficiently apart to enable them to fit over actuating plate  110  so that when the wire is thereafter allowed to relax, the energy that has been imparted to the wire by expanding it will result in the yoke portion exerting retention force on the end segments urging them into the respective notches and thereafter keeping them in place in the notches. To the extent that such retention force may be considered insufficient, member  122  may be mechanically secured to actuating plate  110  by any suitable means, such as welding, or providing features in the actuating plate that are deformed or bent onto member  122 . 
   It is possible to minimize movement hysteresis and maximize movement accuracy by making the radius of curvature of each magnet tip end  56 ,  58  equal to the radius of curvature of the outside diameter of the wire forming magnet return conductor  122 . 
   The movement damping provided in the inventive sender may be especially desirable for significantly attenuating the effect of float flutter on the resistance output of the sender. 
     FIG. 19  illustrates a fuel pump module in a tank as in  FIG. 1 , but with the sender having the bottom referencing feature. Except for the bottom referencing feature, sender  26  in  FIG. 19  is like sender  26  in previous Figures. The hermetically sealed enclosure  31  is disposed in a mounting in a fuel pump module  20 , for some degree of turning about a generally horizontal axis that is substantially coincident with axis  81 . 
   A bottom reference rod  150  extends from the enclosure exterior toward bottom wall  24  of tank  22 . A proximal end of rod  150  is formed for fitting to and joining with wall portion  40  of casing  30 . A stop  152  is mounted on the distal end of rod  150 . Rod  150  and stop  152  form a lever whose weight acts to turn enclosure  31  in a clockwise sense about axis  81  when immersed in liquid fuel. Enclosure  31  is mounted in pump module  20  to allow for at least some degree of turning about axis  81  within its mounting. 
   In installed position shown in  FIG. 19 , sender  26  is disposed such that stop  152  rests on tank bottom wall  24  at a distance from axis  81 . The rod of the rod and stop create a moment arm that circumferentially positions enclosure  31  in its mounting on module  20  about axis  81 . Float rod  118  and float  120  operate the movement  52  according to the fuel level in tank  22 . 
   Because of the ability of enclosure  31  to be positioned in its mounting by bottom reference rod  150  and stop  152 , the electric resistance presented by the sender when float  120  is at a zero fuel level corresponding to the tank being empty is rendered essentially independent of the distance of enclosure  31  above tank bottom wall  24 . This essentially removes that distance as an influence on the sender&#39;s accuracy in indicating the empty level, and inherently enhances the sender accuracy as fuel level approaches empty, the most critical part of the range for the driver. 
   While a presently preferred embodiment has been illustrated and described, it is to be appreciated that the invention may be practiced in various forms within the scope of the following claims.