Patent Application
20060042379
The present invention relates generally to fuel sensors for vehicles and, more particularly, to a sealed fuel level sensor for a vehicle.
It is known to provide a fuel level sensor in a fuel tank of a vehicle to sense or indicate a level of fuel in the fuel tank. Examples of such fuel level sensors are disclosed in U.S. Pat. No. 5,746,088 and U.S. Pat. No. 6,021,668. Typically, the fuel level sensor includes a ceramic resistor card operatively connected to structure for a fuel module and a wiper assembly pivotally connected to the structure for engaging the resistor card. The wiper assembly has one end connected to a float arm and float to rotate the wiper assembly relative to the resistor card based on a level of fuel in the fuel tank.
Currently, thick film ceramic fuel level sensors have been open and exposed to fuel in the fuel tank. These fuel level sensors typically employ silver (Ag) based conductive inks (Ag, Pd, Pt) and high content Ag contacts (Paliney6, Ag/Ni). These materials function properly in fuels that contain moderate sulfur levels or that are low in alcohol content. These materials have also allowed manufacturers to produce a cost effective fuel level sensor.
Fuel level sensors that are open and exposed to fuels have always been susceptible to solid contaminates, for example sand, which can cause the sensor output to produce opens. As sulfur levels in fuels are reduced, what remains are smaller, more reactive compounds. Sulfination is a chemical reaction between Ag and sulfur. Natural aging of the ink/contact interfaces of the fuel level sensor exposes the silver in these components to sulfurs, producing a thin lacquer contamination. Silver based fuel level sensors produce opens or a shift in resistance when exposed to this extremely reactive fuel.
Also, as refineries introduce fuels with higher levels of alcohol, silver based fuel level sensors that are open or exposed to this fuel are more susceptible to plating, galvanic, or dendritic growth. Galvanic growth is a plating process which forms an insulating layer between the contacts and a working surface of the conductive ink, no matter if the materials are Ag based or Noble metals. Given enough powered exposure time, the output of the fuel level sensor will produce an open. Dendritic growth is a silver migration that will short out segments of the resistor of the fuel level sensor.
Therefore, it is desirable to provide a fuel level sensor that does not expose inks or contacts to the fuel. It is also desirable to provide a fuel level sensor that has the ability to use lower cost Ag based materials. Thus, there is a need in the art to provide a fuel level sensor that meets these desires.
Accordingly, the present invention is a sealed fuel level sensor for a fuel tank including a frame having a cavity therein and a variable resistor disposed in the cavity and operatively supported by the frame. The sealed fuel level sensor also includes a wiper disposed in the cavity for rotation relative to the variable resistor and for contacting the variable resistor. The sealed fuel level sensor includes a cover connected to the frame to enclose the cavity and a float arm extending through the cover and connected to the wiper. The sealed fuel level sensor further includes a float connected to the float arm such that the float moves the float arm and the wiper relative to the variable resistor as a level of fuel increases and decreases in the fuel tank.
One advantage of the present invention is that a sealed fuel level sensor is provided for a fuel tank of a vehicle. Another advantage of the present invention is that the sealed fuel level sensor encloses a wiper and sensor card via a cover and seal at a frame interface. Yet another advantage of the present invention is that the sealed fuel level sensor has the ability to use lower cost Ag based materials as compared to less reactive materials like Gold (Au). Still another advantage of the present invention is that the sealed fuel level sensor can function in a dry environment, either minimizing or preventing exposure of the inks or contacts to fuel.
Other features and advantages of the present invention will be readily appreciated, as the same becomes better understood, after reading the subsequent description taken in conjunction with the accompanying drawings.
Referring to the drawings and in particular
Referring to
The sealed fuel level sensor 10 also includes a variable resistor comprising a ceramic resistor card 48 operatively connected to the frame 28. The ceramic resistor card 48 has at least one bus portion (not shown), preferably a resistive bus portion (not shown) and a conductive bus portion (not shown) spaced from the resistive bus portion. The ceramic resistor card 48 also has a solder pad (not shown) at one end of the resistive bus portion and a solder pad (not shown) at one end of the conductive bus portion. The resistive bus portion extends over a predetermined angle, for example approximately sixty-five degrees (65°), to provide a variable resistance corresponding to the fuel level in the fuel tank 12. It should be appreciated that the conductive bus portion is a common ground. It should also be appreciated that the solder pads provide connection points to be described.
The ceramic resistor card 48 is generally planar and rectangular in shape. The ceramic resistor card 48 is made of a ceramic material. The bus portions and solder pads are made of a conductive ink where contacts to be described ride on and are formed in generally arcuate pathways. The conductive ink is made of an alloy of silver (Ag). It should be appreciated that the conductive ink is known in the art.
The ceramic resistor card 48 is disposed in the cavity 34 of the frame 28 and abuts the base wall 30. The ceramic resistor card 48 is secured in place by a hold down projection 50 extending from the base wall 30 and into the cavity 34. The projection 50 has a generally inverted “L” cross-sectional shape and the ceramic resistor card 48 is disposed between the projection 50 and the base wall 30. It should be appreciated that the ceramic resistor card 48 is also secured by a suitable mechanism such as soldering at 51.
The sealed fuel level sensor 10 includes at least one, preferably a plurality of terminals 52 operatively supported by the frame 28. The terminals 52 are made of a conductive material. The terminals 52 are generally rectangular in shape. The terminals 52 are insert molded to the frame 28 and extend longitudinally from one end of the frame 28. The terminals 52 are electrically connected to the solder pads of the ceramic resistor card 48. It should be appreciated that the terminals 52 are connected by wires 54 (
The sealed fuel level sensor 10 includes a cover 56 to enclose the cavity 36 of the frame 28. The cover 56 has a base wall 58 extends radially and has a generally circular shape. The base wall 58 also includes an aperture 60 extending axially therethrough and communicating with the cavity 36. The cover 56 includes a side wall 62 being generally annular and extending generally perpendicular from the base wall 58. The side wall 62 is disposed in the groove 38 of the frame 28 and secured thereto by a suitable mechanism such as press-fitting. The side wall 62 may include a chamfer 64 on an outer portion thereof. The side wall 62 may also include a projection 66 extending radially and axially. The projection 66 is disposed in a slot 68 of the second side wall 34 of the frame 28 to locate the cover 56 relative to the frame 28. The cover 56 is made of a plastic material and formed as a monolithic structure being integral, unitary and one-piece. It should be appreciated that, in another embodiment, the cover 56 may allow a limited amount of fuel to enter the cavity 36.
The sealed fuel level sensor 10 includes a seal 70 disposed between the cover 56 and the frame 28. The seal 70 is generally annular and circular in cross-sectional shape. The seal 70 is of an o-ring type and made of an elastomeric material. The seal 70 is disposed in the groove 38 of the frame 28 between the side wall 62 of the cover 56 and the first side wall 32 of the frame 28.
The sealed fuel level sensor 10 also includes a bushing 72 disposed in the aperture 62 of the base portion 58. The bushing 72 has a shaft portion 73 extending axially. The shaft portion 73 is generally cylindrical in shape and has an aperture 74 extending axially therethrough. The aperture 74 has a groove 76 extending circumferentially about one end to receive a retainer (not shown) to prevent a float arm 82 to be described from exiting the aperture 74 of the bushing 72. The bushing 72 includes a lip seal portion 78 extending outwardly from the shaft portion 73. The lip seal portion 78 is generally planar in shape and extends outwardly past the aperture 62 of the cover 56. The lip seal portion 78 includes a pair of posts 80 extending axially and spaced radially to limit movement of the float arm 82. The bushing 72 is made of a conductive metal such as brass. The bushing 72 is formed as a monolithic structure being integral, unitary, and one-piece. It should be appreciated that the one-piece lip seal and bushing allows for ease of assembly. It should also be appreciated that the bushing 72 forms a seal around the float arm 82 while still allowing a wiper to be described to move freely in a dry environment.
The sealed fuel level sensor 10 includes a float arm 82 connected to the bushing 72. The float arm 82 is made of a metal material, preferably a plated cold rolled steel. The float arm 82 is a rod that is bent with one end disposed in a cavity (not shown) of a float 84 and another end disposed in the aperture 74 of the bushing 72. The sealed fuel level sensor 10 includes a float 84 (
Referring to
The wiper assembly 86 includes a wiper 94 connected to the shaft 88 for contacting the ceramic resistor card 48. The wiper 94 has a base 96 that is generally arcuate in shape and connected to the shaft 88. The wiper 94 also has at least one, preferably a plurality of contact flex arms 98 formed by slots (not shown) spaced laterally and extending longitudinally therein. The contact flex arms 98 extend longitudinally and downward at an angle from the base 96. The contact flex arms 98 and base 96 are formed from a non-Noble metal such as copper. The contact flex arms 98 and base 96 are integral, unitary and formed as one-piece. The wiper 94 is preferably insert molded into the shaft 88 to retain the wiper 94 thereto. The wiper 94 also includes at least one, preferably a plurality of or multiple contacts (not shown) near a free end of each contact flex arm 98. It should be appreciated that the wiper 94 is operatively supported by the shaft 88. It should also be appreciated that the contact flex arms 100 flex or deflect relative to the base 98.
In operation, the sealed fuel level sensor 10 is operatively connected to the fuel reservoir 22 of the fuel pump module 14 inside the fuel tank 12. Fuel inside the fuel tank 12 causes the float 84 to rise to the top thereof. The wiper 94 engages the bus portions of the ceramic resistor card 48. The contacts engage the bus portions and the contact flex arms 98 create a shorting bar between resistive and conductive paths on the ceramic resistor card 48 to provide a predetermined resistance when an electrical signal is sent by a controller (not shown) via the electrical connector 18 to indicate the level of fuel in the fuel tank 12. As the fuel level increases or decreases in the fuel tank 12, the float 84 is raised or lowered to rotate the wiper assembly 86 relative to the frame 28 via the float arm 82. As the wiper assembly 86 rotates, the wiper 94 rotates across the bus portions and the contacts move to different portions thereof to vary or provide a different predetermined resistance to indicate the level of fuel in the fuel tank 12. It should be appreciated that the wiper 94 has the ability to function in a five-volt (5 v), ten milliamp (10 mA) system.
The present invention has been described in an illustrative manner. It is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation.
Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the present invention may be practiced other than as specifically described.
