Side mount liquid level sensor with enhanced float travel

A side mount liquid level sensor (10) includes limit arms (100, 102) on the float (80) and limit wings (54, 56) on the switch housing, with the limit wings (54, 56) being spaced vertically from the stem (14) of the housing (11) whereby to allow float (80) to traverse a range of travel that is at least 50% of the vertical depth (D) of the slot (86) of float 80 and advantageously substantially equal to that depth (D). The spacing (58) between wings (54, 56) and stem (14) allows wings (100, 102) to pass therebetween for assembly, but not while sensor (10) is in use.

BACKGROUND OF THE INVENTION
 I. Field of the Invention
 The present invention relates to liquid level sensors such as are mounted
 though the side wall of a liquid container, referred to as side mount
 liquid level sensor assemblies.
 II. Description of Prior Art
 To monitor liquid level in a liquid container, Such as an automobile
 coolant overflow reservoir or windshield washer tank, it has been the
 practice to provide a liquid level sensor mounted to the container. The
 sensor includes a rod-like member or stem about which a float moves
 depending upon the liquid level in the container. A reed switch is held to
 the sensor with a magnet attached to the float moving towards and away
 from the switch to activate and deactivate the switch. Gaining in
 popularity arc so-called side mount liquid level sensor assemblies which
 are mounted through the sidewall of the container such that the stem is
 held in a horizontal disposition. The reed switch is mounted inside the
 stem and the float moves vertically relative to the stem to bring a magnet
 held by the float vertically towards or away from the reed switch.
 One side mount liquid level sensor assembly which has met with good success
 is shown in U.S. Pat. Nos. 5,581,062 and 5,742,999, assigned to the
 assignee hereof, and the disclosures of both of which are incorporated
 herein by reference in their entireties. In the liquid level sensor
 assembly there-shown, a switch housing is provided having a rod-like
 member extending between a mount end and an enlarged disk end, with the
 mount end adapted to be secured through the sidewall of a liquid container
 to hold the rod-like member in a generally horizontally disposition in the
 container. A float, referred to as a buoyant member, has a slot extending
 vertically therethrough between an open end and an oppositely disposed
 closed end. The rod-like member is received in the slot of the buoyant
 member such that the buoyant member can move vertically as the liquid
 level in the container varies. The open end of the slot is sized to
 normally receive the rod-like member therethrough and limit structure
 comprising arms on the buoyant member adjacent the open end and wings
 formed on the adjacent sidewalls of the rod-like member cooperate to
 normally prevent the float from falling away from the rod-like member.
 In order to mount the float to the housing, the float is oriented at a
 ninety degree angle relative to the rod-like member such that the slot may
 pass over the wings and rod from the side. Thereafter, the float is
 rotated ninety degrees to bring the arms into confronting relationship
 with the wings to thereby prevent the float from coming away from the
 housing. This method of assembly has provided great advantages in the
 manufacture of the liquid level sensor assembly.
 The foregoing notwithstanding, some situations have been encountered in
 which the switch does not work properly. In particular, the float is free
 to move vertically over a range of travel between two positions, one where
 the closed end of the slot is against the rod-like member (with the limit
 structures spaced apart) and one where confronting surfaces of the limit
 structures engage. The float moves to and between these positions as the
 fluid level in the container changes, thereby causing the magnet to move
 towards and away from the reed switch. The range of travel in the
 above-described device is about 1/4 inch (or 6 mm). In some instances, it
 has been found that the switch does not reliably change state over that
 range of float travel.
 SUMMARY OF THE INVENTION
 In commercial devices based on the aforementioned patents, the vertical
 depth of the slot has been about 13 mm. Thus, the 1/4 inch or 6 mm range
 of travel available for the float is less than fifty percent (50%) of the
 vertical depth of the slot. Hence, more of the slot depth is available for
 range of travel than is currently being utilized in the above-described
 devices. It is therefore one objective of the present invention to
 increase the amount of the slot depth which is traversed over range of
 travel of the float relative to the rod-like member, to thereby improve
 reliability of the device. It is a further objective of the present
 invention to increase that range of travel in a manner that does not
 interfere with the ability to assemble the float to the stem from the side
 as above-described.
 The present invention provides a side mount liquid level sensor that
 satisfies the above objectives. To this end, and in accordance with one
 feature of the present invention, the limit structure previously
 associated with the rod-like member is moved such that its contact surface
 is spaced vertically away from the stem whereby the arms on the float
 engage the wings after the float has traversed a greater vertical distance
 relative to the rod-like member. In this wax, the limit structure of the
 float and the switch housing are configured such that the float distance
 travel, i.e., the distance the float can traverse, is more than 50% of the
 slot depth, and is advantageously more than 75% thereof. Most
 advantageously, the range of travel is more than 90% of slot depth so as
 to allow the float to traverse a distance substantially equal to the slot
 depth. In a particular embodiment, the range of travel is about 12 mm for
 a 13 mm vertical depth slot, which is thus double the range of travel
 previously achieved as above-described. With the float distance travel
 thus increased, the magnet associated with the float can move towards and
 away from the reed switch over a greater distance to thereby obtain more
 reliable performance.
 In accordance with another feature of the present invention, the vertical
 spacing between the contact surface of the wings and the rod-like member
 is selected to accomplish the limit function without interfering with
 assembly of the float to the housing. To this end, the thickness of the
 float arms is advantageously larger than that vertical spacing so that in
 the normal angular orientation of the float relative to the stem, the
 buoyant member will not come away from the housing and/or the rod-like
 member cannot pass completely out of the slot. By the same token, however,
 the transverse width of the arms is not more than, and is advantageously
 less than, the spacing between the wing contact surfaces and the rod-like
 members so that rotation of the float to a second, different angular
 orientation, such as ninety degrees from the normal angular orientation,
 will allow the arms to pass through the space between the contact surfaces
 of the wings and the rod-like member to facilitate assembly from the side
 as was achieved with the previous device. The spacing is further
 advantageously selected in relation to the diameter of the float so that
 in the normal angular orientation of the float, it will not pass into or
 become lodged in that space.
 By virtue of the foregoing, there is thus provided a side mount liquid
 level sensor that has the advantages of the sensor shown in the
 aforementioned patents, but which has a substantially enhanced float
 travel distance and yet can be assembled from side in the same manner as
 shown in the aforementioned patents. These and other objects and
 advantages of the present invention shall be made apparent from the
 accompanying drawings and the description thereof.

DETAILED DESCRIPTION OF THE DRAWINGS
 With reference to FIGS. 1 and 2, there is shown a side mount liquid level
 sensor 10 in accordance with the principles of the present invention.
 Sensor 10 includes an injection molded plastic (e.g., polypropylene)
 switch housing component 11 comprised of a hollow mount end or support 12
 and a hollow rod-like member 14 extending outwardly from and supported by
 the distal wall 15 of support 12. Formed integral to the distal end 16 of
 rod 14 is an enlarged disc 18 having a diameter slightly less than the
 diameter of support 12 at its proximal end 20. Disc 18 and end 20 are
 sized small enough to be received through a hole 3 in sidewall 5 of a
 liquid container 7 with a grommet G cooperating with proximal end 20 of
 support 12 to mount sensor 10 to sidewall 5 with rod-like member 14 in a
 horizontal disposition within container 7 as shown in FIG. 3.
 Member 14 has a hollow interior with disc 18 sealing off distal end 16
 thereof with proximal end at 15 opening into the interior of support 12.
 Member 14 may be rectangular in cross-section as defined by planar left,
 right, top and bottom sidewalls 22, 24, 26, 28, respectively (see also
 FIG. 5D). Bottom wall 28 may be recessed from the lower edges 30 of left
 and right sidewalls 22, 24 as seen, for example, in FIG. 5D. Also, formed
 on sidewalls 22 and 24 are a pair of vertically oriented projections 36,
 38 (which may be rectangular, semi-circular or triangular in
 cross-section) which define respective planes (not shown) spaced or gapped
 from and parallel to walls 22 and 24 for a purpose to be described
 hereinafter.
 Support 12 is formed with tapered distal cone portion 42 and proximal
 cylinder portion 44, the latter having a diameter slightly smaller than
 the proximal end 46 of cone 42 to provide a lip thereat. The proximal end
 20 of support 12 terminates into an enlarged flange 50 with key 52 (FIG.
 2) and, opposite key 52, triangular locator 53 (FIG. 1), which may be used
 to properly orient sensor 10 for mounting to container 7. Also, formed at
 respective ends 16 and 15 of rod 14, and extending from the adjacent disc
 18 or cone 42, respectively, are a pair of rigid limit wings 54, 56. Wings
 54 extend generally horizontally outwardly from disc 18 towards mount end
 12, and wings 56 extend generally horizontally outwardly from end 12
 towards disc end 18. Wings 54 and 56 each define a contact surface 57.
 Contact surfaces 57 are generally in the same plane which is spaced
 vertically away (above in FIGS. 3 and 4), but paralleled to, the plane
 defined by rod top wall 26 to thus define a space 58 therebetween as
 exemplified in FIGS. 3 and 5D. Each wing 54, 56 is also advantageously
 horizontally or laterally outboard of member 14 as seen in FIG. 1,
 although each pair of wings 54, 56 could be just one such wing 54 or 56,
 respectively. By way of example, wings 54 could be one such wing which
 extends across, but above, rod 14 as if the pair of wings were merged into
 one larger hing. Each wing 54, 56 includes two or more ribs 59 opposite
 surface 57 to rigidify the wing to thereby avoid undue flexure or
 breakage.
 Fitted within the interior of member 14 is a switch, such as normally open,
 0.5 A current switch rated magnetically actuatable reed switch 60 (FIG. 2)
 having its switch contacts 62 extending between ends 16 and 15 along the
 longitudinal axis L of rod 14. Switch 60 may have a sensitivity of between
 10 and 60 ampere turns (AT), and is desirably in the 20-25 AT range. A
 pair of wires 64 electrically connect respective ones of switch contacts
 62 to connector pins 66 held within plastic socket 70 mounted to support
 12. Enclosing switch 60 within rod 14 and securing socket 70 to support 12
 is a potting material (not shown) such as hot melt thermoplastic polyamide
 resin filling the interior of support 12 and gripping a leg (not shown) of
 socket 70 inside support 12.
 Sensor 10 also includes a float or buoyant member 80 injected molded from
 plastic, two examples of which are polypropylene or nylon with an
 endothermic blowing or foaming agent. Member 80 is cylindrical in
 cross-section as defined by generally smooth outer wall 82 defining the
 diameter of float 80, which is advantageously about equal to the diameter
 of disc 18. Wall 82 of float 80 is chamfered inwardly about 15.degree. as
 at 83 at opposite sides 84 of float 12. Formed within member 80 is a slot
 86 which opens into each side 84. Slot 86 also has an open end 88 at wall
 82 and an oppositely disposed closed end 90. Extending between ends 88 and
 90 are planar left and right sidewalls 92, 94 which define a vertical
 depth D of slot 86. Formed at sides 84, and extending horizontally
 outwardly therefrom adjacent open end 88 of slot 86, are a pair of
 projecting limit arms 100, 102 each defining a contact surface 103. Arms
 100, 102 cooperate with wings 54, 56 to limit the movement of float 80
 relative to rod-like member 14 as will be described.
 Float 80 also includes an aperture 106 through outer wall 82 disposed
 opposite slot 86. Aperture 106 is approximately the size of switch
 actuator magnet 108 mounted therein. Magnet 108 may be mounted with its
 north and south poles adjacent respective ones of the ends 84 of member 80
 so as to extend in parallel to the longitudinal axis thereof, although
 other magnet geometries and/or polar arrangements may be used as will be
 appreciated by those skilled in the art. Magnet 108 is held in aperture
 106 such as by melting or otherwise deforming portions of the edge of
 aperture 106 to define tabs 110 overlying magnet 108 to hold same in
 place. Alternatively, magnet 108 may be associated with float 80 in other
 ways, examples of which include insert molding, sonic welding,
 press-fitting, and adhesives. Aperture 106 may open at least partially
 into slot 86 for manufacturability, but not so large as to allow magnet
 108 or rod 14 to pass therethrough. To this end, provided rod 14 cannot
 pass therethrough, end 90 is deemed to be a closed end which thus limits
 relative travel between rod 14 and float 80 to keep rod 14 within slot 86
 thereat.
 Sidewalls 92, 94 of slot 86 are spaced apart (with a slight draft) a
 distance slightly greater than the distance between the planes defined by
 rod-wall projections 36, 38 such that when member 80 is mounted to rod 14,
 member 80 is generally restrained from rotating completely around rod 14
 but has sufficient space therein to be otherwise free to slide vertically
 relative thereto as indicated by arrow 112 in FIG. 5C such that magnet 108
 moves towards and away from reed switch 60 to open or close same as
 appropriate. Also, the spacing provides non-clogging gaps (e.g., slot 84
 is about 0.31 to 0.32 inch wide and the respective projections 36 or 38
 define a distance of about 0.29 inch wide tip-to-tip) between rod
 sidewalls 22, 24 and slot sides 92, 94 which allows for some rotation of
 member 80, i.e., there is a loose fit, to reduce the likelihood of
 sticking or clogging.
 With float 80 mounted to housing 11, i.e., with stem 14 received in slot
 86, and sensor 10 side-mounted to container 7, float 80 is free to move
 vertically between a first position (FIG. 3) and a second position (FIG.
 4). The first position shown in FIG. 3 is representative of a low fluid
 level in container 7 whereas the second position of FIG. 4 is
 representative of a fluid level in container 7 that is above that low
 fluid level, i.e., at a higher fluid level. In the first position,
 rod-like member 14, and particularly top wall 26 thereof, is adjacent
 closed end 90 of slot 86 while open end 88 of slot 86, is spaced away from
 stem 14. In this first position, arm surfaces 103 are spaced out of
 engagement from wing surfaces 57 (FIG. 5C), and magnet 108 is very close
 to switch 60 to actuate same as is well understood in the art.
 In the second position of float 80, surfaces 103 of float limit arms 100,
 102 engage housing limit wing surfaces 57 (FIG. 5D) to limit travel of
 float 80. In this second position, a substantial portion of rod-like
 member 14 may extend out through open end 88 of slot 86 even though still
 considered adjacent thereto. Also, closed end 90 is spaced away from stem
 14, to space magnet 108 well away from switch 60. The switch is thus
 deactivated as is also well understood. Wings 54, 56 and alms 100, 102 are
 advantageously configured to keep rod 14 from coming completely out of
 slot 86 to thereby retain float 80 on stem 14.
 As can be seen by a comparison of FIGS. 3 and 4, the range of travel of
 float 80 is defined between the limits created at the first position by
 the wall 26 and closed end 90 and at the second position by the surfaces
 57 and 103 and can be nearly the entire vertical depth D of slot 86 so as
 to reliably actuate and deactuate switch 60 as magnet 108 moves towards
 and away from switch 60 with variations in liquid level in container 7.
 The range of travel will depend largely on the vertical height of space 58
 between wings 54, 56 and rod-like member 14 on the one hand, and the
 vertical thickness T of arms 100, 102 (FIG. 5C) on the other. The
 thickness T of arms 100, 102 is selected so as to be at least equal to,
 but advantageously slightly greater than, the height of space 58 between
 the planes defined by contact surfaces 57 and the top surface 26 of
 rod-like member 14. As a consequence, and as seen in FIG. 5D, even in the
 second position of float 80, there will be some portion of arms 100, 102
 adjacent to rod-like member 14 so as to prevent float 80 from coming away
 from housing 11 sideways as viewed in FIG. 5B. The thickness of arms 100,
 102 is advantageously selected and the placement of wings 58
 advantageously selected so that the range of travel for a vertical depth D
 is greater than at least 50% of that vertical depth D, advantageously more
 than about 75%, and most advantageously greater than about 90% of the
 vertical depth D in which case the range of travel is substantially nearly
 equal to vertical depth D. In the particular embodiment shown, vertical
 depth D is approximately 13 mm while the range of travel between the first
 and second positions is approximately 12 mm.
 The spacing 58 is also selected to facilitate mounting of float 80 to
 housing 11 with the side approach method of the previously mentioned
 patents, while also avoiding float 80 becoming lodged therein such as with
 chamfered wall 83. To this end, the width W of arms 100, 102 transverse to
 slot depth D is not greater than and is advantageously less than the
 height of space 58 so as to be able to fit therethough for side mounting
 of float 80. The wings 54, 56 arc also positioned, however, so as to
 confront ends 84 of float 80 outside slot 86, irrespective of the position
 of float 80 due to liquid level in the container 7. Thus, the spacing 58
 is also selected to be less than the thickness of float 80 measured along
 side 84 between closed end 90 of slot 86 and adjacent chamfered wall 83,
 such that the end 94 cannot readily pass into or become lodged in a space
 58.
 To mount member 80 to rod 14, member 80 is rotated 90.degree. so that slot
 open end 88 opens towards a sidewall (e.g., right sidewall 24 as seen in
 FIG. 5A) and arms 100, 102 are disposed width-wise relative to spaces 58.
 Member 80 is slid laterally (to the left as indicated by arrow 110 in FIG.
 5A) over rod 14 with arms 100, 102 passing through space 58 (between
 member 14 and wings 54, 56) with slot sidewalls 92, 94 juxtaposed parallel
 to top and bottom walls 26 and 28 of rod 14. As will be appreciated, end
 portions of rod 14 will extend out beyond the sides 84 of buoyant member
 80. Member 14 is then rotated in the direction of arrow 114 as indicated
 in FIG. 5B until slot 86 is vertically oriented with sidewalls 92, 94
 thereof juxtaposed parallel to vertical projections 36, 38 and rod
 sidewalls 22, 24, and magnet 108 is situated above bottom wall 28 of rod
 14, all as seen in FIG. 5C. In this position of member 80, arms 100 and
 102 of buoyant member 80, and particularly faces 103 thereof, extend out
 over and confront wings 54, 56, and particularly faces 57 thereof, as
 above-described.
 As will be readily appreciated, when rod 14 is in its horizontal
 disposition as shown in FIGS. 5C and 5D, buoyant member 80 will move
 vertically (i.e. laterally) relative rod 14 depending upon the level of
 liquid (not shown) around member 80. Consequently, magnet 108 moves
 towards and away from rod 14 and reed switch 60 therein to thus open or
 close switch 60 depending upon the level of the liquid. Switch 60 is
 coupled via connector pins 66 to an electrical circuit (not shown) to
 activate the appropriate indicators.
 Sensor 10 is fully seated in container 7, with magnet 108 at the top of the
 unit, so that member 80 is free to slide up and down and not impact
 against the sidewalls 22, 24 of rod 14. And, as member 80 slides, the gaps
 between slot sidewalls 92, 94 and rod sidewalls 22, 24 are maintained open
 due to vertical projections 36 and 38 so that material cannot become
 lodged therebetween and interfere with operation of sensor 10. Also, a
 projection 138 may be provided on closed end 90 of slot 86 to prevent
 sticking between rod top wall 26 and slot closed end 90. Projection 138
 will also limit the range of travel and so is kept quite small or shallow,
 such as about 1 mm. Support 12 and rod 14 are made relatively short so
 that sensor 10 projects not more than about 47 mm into container 7 to thus
 allow sensor 10 to be used in tight quarters.
 In use, member 80 is mounted to rod 14 from the side as previously
 described. Also, grommet G is slid over rod 14, and member 80 if it is
 already on rod 14, and onto portion 44 of housing 11. Sensor 10 is
 inserted, disc 18 first, into hole 3 of container 7 with magnet 108 on top
 until grommet G and mount end 12 mate snugly into hole 3. Member 80 is
 then free to move vertically relative to rod 14 depending upon the level
 of liquid in container 7. Reed switch 60 is electrically connected via
 pins 66 to appropriate electrical circuitry (not shown) such that the
 relative position of member 80 to rod 14 will control the circuitry.
 Specifically, member 80 travels at least 50% and up to over 90% of slot
 depth D between a first, low liquid level position and a second, higher
 liquid level position. The state of switch 60 indicates to the circuitry
 (not shown) whether or not the liquid level is low.
 By virtue of the foregoing, there is thus provided a side mount liquid
 level sensor with enhanced rang,e of travel without adversely impacting
 the side assembly techniques previously found to provide advantages in
 such sensors.
 While the present invention has been illustrated by the description of an
 embodiment thereof, and while the embodiment has been described in
 considerable detail, it is not intended to restrict or in any way limit
 the scope of the appended claims to such detail. Additional advantages and
 modifications will readily appear to those skilled in the art. For
 example, the thickness or placement of arms 100, 102 and wings 54, 56 may
 be varied so as to adjust the range of travel of float 80. Also, the
 surfaces 57 and 103 need not be planar as shown in the Figures. In use,
 the sensor 10 could be rotated 180.degree. for use such that the second
 position correlates to low liquid level and the first position correlates
 to a high liquid level (with the open end 88 now at the top and magnet 108
 now at the bottom of the sensor). Similarly, fewer than two pairs of arms
 100, 102 might be used such as one arm 100 and one arm 102 confronting
 respective ones of wings 54 and 56. Also, while stem 14 is advantageously
 rectangular in cross-section with planar walls, other cross-sections may
 be utilized as will be readily appreciated by those skilled in the art.
 The float 80 could be mounted in other ways to stem 14, such as over the
 distal end 16 thereof (with a movable or later-attached disk 18), and so
 open end 88 could be closed off such as with an inverted U-shaped cap or
 portion. The cap of portion will extend above the otherwise open end 88
 such that the end may still be considered open to allow a substantial
 portion of rod 14 to extend therethrough in the second position of float
 80. The container 7 may include a recess or pocket in its sidewall 5 as
 shown in the aforementioned patents and/or provided with indicators on
 sidewall 5, which cooperate with key 52 or locator 53 to facilitate proper
 orientation of sensor 10 on mounting to container 7. Alternatively, key 52
 and/or locator 53 may be eliminated. The invention in its broader aspects
 is, therefore, not limited to the specific details, representative
 apparatus and method, and illustrative examples shown and described.
 Accordingly, departures may be made from such details without departing
 from the spirit or scope of the general inventive concept.