Patent Description:
In the context of engines, especially engines for vehicles such as tanks or automobiles, it is well known to provide a dipstick for checking the level of oil present in the engine crankcase using a dipstick that is secured extending into the crankcase. The level is checked by cleaning the dipstick and inserting it into a passage in the crankcase and then withdrawing it. The oil level of the engine may be immediately determined by looking at the height of oil clingage to the dipstick, which may have markings to indicate the amount of oil associated with the depth of oil.

Systems of that sort require a person to access the dipstick and remove it from the engine and look at it, which may be difficult in various situations.

It is also known to provide sensors that detect the level of oil in an engine and transmit signals indicative of that level. These systems generally require mounting of a sensor in the engine, and it is a complex operation to provide such an electronic system in an engine that is not designed to accommodate the sensor system.

<CIT> shows a dipstick equipped with a transducer as sensor to measure the oil level. However, the oil level measured by the sensor depends on the position of the transducer and may vary with the insertion position and/or rotation of the dipstick. Due to the length of the dipstick and the positioning of the transducers, physical contact between the oil containing vessel and the transducers cannot be excluded during operation, which also interferes with correct measurement results.

It is accordingly an object of the invention to provide an electronic fluid level detection system that overcomes the drawbacks of the prior art.

According to an aspect of the invention, a system comprises a reservoir containing liquid that extends up to a level of the fluid, and a dipstick support structure supporting a dipstick on it so that the dipstick extends into the fluid past the level of the fluid, and so that the dipstick is manually removable from the dipstick support structure by a user. An electrical system is connected with the dipstick, and the electrical system electrically senses the level of the fluid based on an electrical characteristic of the dipstick that varies with the varying level of the fluid when the dipstick extends therein.

According to another aspect of the invention, the reservoir is an engine crankcase containing oil or a fluid mixed with oil, the level of which is detected using a dipstick configured for use in an electronic fluid-level sensor system.

According to another aspect of the invention, a method is provided for sensing liquid in a reservoir, especially oil in an engine crankcase. The method comprises providing a dipstick removably supported so as to extend into the reservoir and into the liquid in an installed position. The dipstick has markings on it that indicate the level of the fluid on visual inspection by a user when the dipstick is removed from the reservoir. An electrical property of the dipstick is electrically detected when the dipstick is placed in the reservoir in the installed position so as to produce an electrical output indicative of the level of the fluid. A comparison of the level of the fluid to a predetermined level is performed electrically, and an alert is output to the user responsive to the comparison indicating that the level of the fluid is below the predetermined level.

According to the invention, the method detects capacitance of the dipstick relative to the reservoir. The detecting of the capacitance comprises repeatedly applying an electrical current to the dipstick until the dipstick is charged, and then cutting the electrical current to the dipstick until the dipstick discharges. This is used to generate an output signal from the repeated charging and discharging that is a waveform with a frequency that is correlated to the level of fluid into which the dipstick extends in the installed position.

According to another aspect of the invention, a use of said system is provided for retrofitting an engine with an electronic liquid or oil level sensor.

According to another aspect of the invention, changing capacitance is used to measure a fluid level based on frequency as an output from the sensor circuit in which a manual dipstick with minor modifications is part of the capacitive fluid level sensing circuit for both remote and manual level checking.

Other objects and advantages of the invention will become apparent from this specification.

The present invention combines the utility of checking liquid levels using a traditional dipstick with the modern convenience of an electronic reporting sensor. The combination of the methods provides redundant operation in case of electronic failure and a traditional method of checking fluid levels for maintainers of the equipment.

<FIG> shows a transmission <NUM> used for a vehicle, comprising a block with a sump <NUM> that is filled with lubricating liquid, usually real or synthetic oil. An access structure <NUM> supports a dipstick structure <NUM> in it that can be removed, and clingage of oil to the dipstick can be viewed to see the level of oil in the crankcase <NUM>. The access structure <NUM> is an opening that, in some cases, also is configured to be an opening for pouring oil into the crankcase.

As best seen in <FIG>, inside the sump <NUM>, the dipstick <NUM> according to the invention is supported by structure that has an access structure <NUM> extending through the housing wall from the exterior where it meets an enlarged perforated tube <NUM> that at its lower end <NUM> is connected with an elongated dipstick tube <NUM> that extends generally to the bottom of the sump <NUM>. The tube <NUM> is open at both ends so it fills up with oil or whatever liquid in the reservoir to the same level as outside of the tube <NUM>. Liquids are allowed to pass through the upper and lower housings or tubes <NUM> and <NUM> to the sump, allowing the maintenance personnel to add fluid at any time by removing the dipstick assembly. The holes in the perforated tube <NUM> allow for oil to be added to the crankcase <NUM> through tube <NUM>.

Referring to <FIG>, a dipstick <NUM> is fixedly attached to the outer dipstick handle <NUM>, which is removably sealed into the access structure <NUM> so as to seal off the access when secured in place. The dipstick extends from the handle <NUM> through the dipstick receiving structure, i.e., tubes <NUM> and <NUM> to a distal end <NUM>.

Referring to <FIG>, the dipstick <NUM> is a flat ribbon-like structure comprising a metal interior <NUM> surrounded by an outer layer <NUM> of electrically-nonconductive material. The interior metal is any sort of conductive metal or other conductive material that is adequately rigid to perform the function of a dipstick, e.g., stainless steel. The outer layer or coating <NUM> is preferably of an electrically non-conductive plastic polymer material that is durable and heat resistant, such as polyimide material, with a thickness sufficient to prevent flow of electrical power at a working voltage of the dipstick sensor, e.g., <NUM> volts.

The dipstick <NUM> functions in traditional manner, in that it may be removed, and a level of fluid in the sump may be checked by a user visually examining the clingage to the outer surface of the dipstick, which may be provided with markings at locations along the length of the dipstick where it contacts fluid when inserted into the housing to show amounts of liquid corresponding to the level of clingage on the dipstick.

The dipstick <NUM> also functions as one side of capacitive sensor pair. The polymer coating <NUM> prevents the metal or steel interior <NUM> of the dipstick from touching the guide tube <NUM> along its curved path. As the oil level inside the sump changes over time, the capacitance between the dipstick steel or metal core <NUM> and the guide housing <NUM> changes as well. The guide tube <NUM> reduces measured oil error due to foaming.

Referring to <FIG>, in the embodiment shown, the dipstick sensor device is configured to be mounted by inserting a two-part cylindrical structure generally indicated at <NUM> into a machined pocket or a bore in and extending through the wall <NUM> of the exterior of the transmission housing <NUM> (shown in phantom) where the conventional dipstick system would extend. As best seen in <FIG>, the manual dipstick bore in wall <NUM>, shown in phantom, normally has an outer cylindrical passage that narrows radially to provide an annular shelf with a narrower concentric cylindrical bore therein extending into and communicating with the interior space of the housing <NUM> The installation may be an original installation or a retro- fit in which the electrical level-sensing system is installed in a block in which only the standard mechanical user-viewed clingage assessment of fluid level is provided. In a retro-fit process, the original mechanical system dipstick structure is removed to leave the bore, and the housings <NUM> and <NUM> are inserted therein.

The two-part cylindrical structure <NUM> includes upper cylindrical housing <NUM> and lower cylindrical housing <NUM>. These structures <NUM> and <NUM> are configured to be received snugly in the bore in the housing.

The lower cylindrical housing <NUM> is sized to fit in and be secured fixedly in the upper wider part of the bore or passage through the wall <NUM> of the crankcase or transmission housing, resting on the annular shoulder of the dipstick bore. Lower housing <NUM> has electrical contacts connected to wires that extend inside the crankcase or housing to the electrical harness and control electronics circuitry of the vehicle. Those may need to be installed in the housing <NUM> in the case of a manual dipstick retrofit process. For example, a hole or passage may be drilled in the housing through which wiring from the dipstick sensor system extends, and sealing the passage so that fluid in the reservoir cannot escape therethrough and so that contaminants cannot enter the reservoir from the outside.

The upper cylindrical housing <NUM> fits into the upper wider bore or passage in wall <NUM> and is secured in it by a screw <NUM> and washer on a bracket <NUM> on the side of the upper cylindrical housing <NUM> that releasably screws into a threaded bore (not shown) in the outer surface of wall <NUM> of the crankcase or transmission housing. An O-ring <NUM> mounted in a groove in the upper cylindrical housing <NUM> seals any gap in the bore in the wall <NUM> around the cylindrical housing <NUM> to keep contaminants out.

The parts of the dipstick assembly are configured so that relatively low-cost, high- reliability components are mounted to the lower housing <NUM> and then connected to the wiring harness of the engine or transmission. As best seen in <FIG>, the outer surface of the upper cylindrical housing <NUM> has a recess <NUM> therein that supports a circuit board strcuture <NUM> fixedly secured to the cylindrical housing <NUM> in the recess <NUM>. In the embodiment shown, the circuit board <NUM> has four electrical spring contacts <NUM> that each mate with and connect electrically to a corrsponding electrcial contact of a set of four plate or tongue contacts <NUM> supported on lower cylindrical housing <NUM> in the bore of the wall <NUM>, and those contacts <NUM> connect to wires leading from the disptick sensor structure to electrical circuitry. The circuit board <NUM> and spring contacts <NUM> are more likely to fail over time than the contacts <NUM> and wires of the lower housing <NUM>, and the circuit board <NUM> and spring contacts <NUM> therefore are mounted to the upper housing <NUM>. The upper housing <NUM> is accessible from outside the engine or transmission exterior, and can be easily removed and repaired without interrupting the main wire harness.

Referring again to <FIG>, the dipstick structure <NUM> comprises a handle <NUM> extending from a cap <NUM> that is configured to fit over the outside upper end of the upper housing <NUM>. The structure includes an elastomeric seal portion <NUM> and a Y-shaped support <NUM> that supports at its lower end the coated metal ribbon-shaped dipstick <NUM>. The seal portion <NUM> is cylindrical and sized to fit into an internal cylindrical passage <NUM> extending through the upper and lower housings <NUM> and <NUM>.

Referring to <FIG> and <FIG>, when the dipstick is closed, the cap <NUM> overlies and covers the open top end of the upper housing <NUM>.

The internal structure and operation of the dipstick structure <NUM> is best seen in <FIG> and <FIG>.

The dipstick <NUM> is connected mechanically and electrically to metallic Y-shaped support <NUM>, which includes a collar plate <NUM>. Collar plate <NUM> has downwardly extending contact arms <NUM> that engage and electrically connect with generally conical contact 5lsecured in the interior passage of upper cylindrical housing <NUM>. Conical contact <NUM> is electrically connected with the circuit board <NUM>. This arrangement electrically links the dipstick <NUM> to the circuitry <NUM>.

The structure also mechanically supports the disptick insulated from electrical contact bewteen the dipstick and any other part of the engine. The coating <NUM> insulates the ribbon- shaped part <NUM> from contact with the tube <NUM>. The Y-shaped support structure <NUM> is held spaced from the surrounding structure so as to avoid elecrtrical contact. Collar plate <NUM> is held between washer <NUM> and inner collar support element <NUM> that extends through a central hole in the collar plate <NUM>.

The cap <NUM> and the outer dipstick structure is secured in place by inserting the dipstick <NUM> into the tube <NUM> and <NUM> through the passage <NUM> in the cylindrical housings <NUM> and <NUM> until cap <NUM> is seated over the upper housing <NUM>. Handle <NUM> is then rotated so as to screw down the structure and seal the assembly. This is accomplished as best seen in <FIG>.

Handle <NUM> is fixed to a central shaft <NUM> that extends centrally through the sealer <NUM>, through a metalic or rigid washer <NUM> and insulator washer <NUM>, and is threaded to screw into a nut <NUM> embedded in collar support element <NUM>. The lower end <NUM> of shaft <NUM> is spaced from the surounding Y-shaped support structure.

Sealing is accomplished by tightening the handle <NUM> by turning it, which screws shaft <NUM> into the nut <NUM>. That compresses the collar support element against the washers <NUM> and <NUM>, which squeezes the elastomeric sealer <NUM> vertically. The sealer <NUM> is configured such that this squeezing causes it to bulge radially outward, sealing the handle structure against the cylindrical inner surface of passage <NUM> in upper housing <NUM>. This structural arrangement ensures that the handle <NUM> that tightens the seal between the upper housing <NUM> and the dipstick seal <NUM> is insulated to prevent anyone touching the handle interfering with an accurate reading.

The diagram of <FIG> illustrates the circuitry of ther circuit board <NUM> that senses the level of fluid or oil that is surrounding the dipstick in the tube <NUM>.

Four electrical contacts <NUM> connect with the circuitry of board <NUM>. One line <NUM> receives a <NUM> volt DC current to power the sensor system. Two contacts <NUM> provide two lines <NUM> that act as a ground "eDipstick_GND" which serves as the cathode for the electrical circuit. The fourth contact connects to a line <NUM> that carries the output signal from the sensor system.

The <NUM>-volt input voltage is passed through a power protection diode circuit <NUM> that prevents spikes or surges from damaging circuit <NUM>. The resulting curent (VP) is transmitted to line <NUM> of resonant digital circuit <NUM>. Resonant digital circuit <NUM> has a line <NUM> connecting electrically to the metal center rod or ribbon <NUM> of the dipstick <NUM>, accomplished by rivets through the wall of the upper housing <NUM> that connect electrically to contact element <NUM>, arms <NUM>, and via Y-shaped structure <NUM> to the dipstick core <NUM>.

The operation of the resonant digital circuit is fairly simple. It applies <NUM> volts of DC current to the dipstick core <NUM> until it has charged the dipstick <NUM> as a capacitor plate in a capacitor defined as the dipstick core <NUM> and the surrounding engine, especially the tube <NUM>. As soon as the capacitor is charged, the voltage is cut and the dipstick core <NUM> discharges the charge back through line <NUM>. As soon as the charge of the insulated disptick is discharged, the circuit again applies the voltage to the dipstick until it is charged again.

This charging and discharging process is repeated continuously, and the resulting electrical output is a series of square waves that have a frequency that is dependent on the capacitance between the dipstick core and the surrounding insulated engine, which varies as the level of liquid or oil in the engine housing changes up or down. That square-wave electrical signal is transmitted via output line <NUM> to a buffer circuit <NUM> that acts to decouple the capacitive dipstick from the output, which is then output via line <NUM> to contact <NUM>. Contact <NUM> is connected with a respective contact <NUM>, which carries the square-wave output signal to the digital circuitry supporting the engine, which determines from the frequency a level of fluid in the engine. The digital circuitry includes a user-visible display device, such as an LCD or CRT screen, and audible alarm systems. If the level of fluid is below a predetermined threshold, a warning is displayed to the user of the vehicle, and a varirety of actions may be taken by the controlling digital system based on the indicated level of fluid in the engine. The circuit board <NUM> processes the signal from the dipstick and ground and returns a signal with a frequency output that can be later converted by software to display the liquid level and/or create an alert if necessary. The circuit board will be potted to enhance reliability after mounted to the upper assembly.

The circuitry <NUM> is also protected by connection therein to transient voltage suppression circuit elements <NUM> and <NUM> that absorb sudden spikes in the signal from the dipstick.

The system of the invention is generally a standardized configuration, so calibration of the capacitance detected to the fluid level should not be required. However, against the possibility of varying capacitances of different individual systems, the system may be calibrated to set the threshold levels of capacitance corresponding to levels of the fluid in the housing <NUM>.

Referring to <FIG>, an alternate embodiment is shown that functions similarly to the above embodiment, but employs a plug structure <NUM> that mechanically or screwingly is secured in a single housing <NUM> secured in the wall <NUM> of the engine. Wires <NUM> connect electrically to the dipstick <NUM>, and sensing of the level of fluid may be done by a circuit remote from the dipstick assembly.

Still another embodiment of a dipstick according to the invention is illustrated in <FIG>. The dipstick <NUM> shown is a metal, usually steel, ribbon or cable supported on the handle structure <NUM>, similar to the previous embodiments. The dipstick <NUM>, instead of being insulated by a coating or complete overmold of polymer insulator, is insulated by an overmold that consists of a series of spaced beads <NUM> on its surface and over its length that keep the dipstick electrically isolated from the surrounding tube <NUM> by preventing actually physical contact between the dipstick <NUM> and the tube <NUM>. Electrical operation and circuitry of the system is the same as or similar to the previous embodiments.

A desirable embodiment of dipstick sensing system for use in a reservoir, such as the engine block crankcase of <FIG> or <FIG>, is shown in <FIG>.

<FIG> shows the overall structure of the dipstick system <NUM>. The system has a cylindrical housing <NUM> that is installed in a cylindrical bore in the reservoir or crankcase of the engine block. A handle <NUM> of the dipstick projects upwardly from a top cap <NUM> of the system and outward from the reservoir. The dipstick <NUM> itself extends downward from the handle <NUM> thorough the housing <NUM> and into the interior of the reservoir. Cable <NUM> carries wires that power the fluid level sensing circuitry and carry an output signal from the circuitry connected with the dipstick. This cable connects with the circuitry in the housing <NUM> from the inside of the reservoir, and extends through the reservoir to an exit aperture through which it can connect with other electronic circuitry of the reservoir or vehicle to provide the signal for electronic monitoring of the fluid level, and for providing an alarm, visible, audible or electrical, when the fluid is lower than a predetermined threshold level.

Perforated upper tube <NUM> is affixed to the bottom of housing <NUM>, and lower tube <NUM> supported on upper tube <NUM> and extends downwardly from the lower narrowed end of upper tube <NUM>. The dipstick <NUM> extends through the upper and lower tubes <NUM> and <NUM> into the reservoir beyond the lower end <NUM> oflower guide tube <NUM>. The fluid or oil in the reservoir is free to flow along the dipstick <NUM> inside tube <NUM>.

Referring to <FIG>, bolt structure <NUM> secures the system <NUM> to the outer surface of the reservoir housing <NUM> by bolt <NUM> which is threadingly secured in a bore in the reservoir housing.

<FIG> shows the interior structure of the dipstick system <NUM>. Cylindrical housing <NUM> is made up of two separate parts, a lower housing <NUM> and an upper housing <NUM>. The two housings <NUM> and <NUM> are both dimensioned to fit snugly in the installation bore <NUM> of the reservoir wall <NUM>. This bore may be specifically provided in a newly manufactured reservoir or engine block so that it is dimensioned to receive the dipstick sensing system <NUM>, or the bore <NUM> may be a bore dimensioned for use with an earlier design of dipstick system, in which case the dipstick outer housing <NUM> is dimensioned for installation in the pre- existing bore <NUM>. Alternatively, a new bore may also be machined out of the reservoir wall <NUM> to receive the system <NUM>. An O-ring seal <NUM> in an annular groove in the upper housing <NUM> is provided to protect the interior of the reservoir <NUM> against infiltration of dirt or contaminants passing between the housing <NUM> and the bore <NUM>.

Handle <NUM> is connected to a central rod or shaft <NUM> that extends through cap <NUM> and through the housings <NUM> and <NUM>. The shaft <NUM> extends through an elastomeric sealing member <NUM> that is generally cylindrical in shape and sealingly contacts inner cylindrical wall <NUM> of upper housing <NUM>. Lower end <NUM> of shaft <NUM> is threaded into holding nut <NUM>, which is embedded in an overmolded isolator body <NUM>. Isolator body <NUM> is of electrically insulating material, preferably plastic, that is resistant to exposure to fluid or oil at high temperatures, such as are encountered in engine crankcases. Particularly preferred for the material of the overmold is VICTREX PEEK (polyaryletheretherketone) material, such as that sold under the designation <NUM>, 450GL30 or 450CA30 by Victrex PLC of Lancashire, U. The isolator body maintains the shaft <NUM> and the handle <NUM> electrically insulated from the dipstick <NUM>, so that someone touching the handle <NUM> does not affect the electronic sensing of the level of fluid in the reservoir.

Isolation body <NUM> engages and supports dipstick connection structure <NUM> and washer <NUM>, which engages a lower surface of sealing member <NUM>, holding member <NUM> between the dipstick connection structure and the cap <NUM>. Sealing member <NUM> is formed of deformable elastomeric insulating material, particularly preferred being fluorosilicone material.

When not in manual use, the user turns handle <NUM> clockwise (the direction indicated "TIGHTEN" on cap <NUM> in <FIG>) to seal the dipstick in the assembly <NUM>. Turning the handle <NUM> in that direction screws shaft <NUM> downward into nut <NUM> in isolation body <NUM>, which vertically compresses sealing member <NUM>, which deforms to bulge radially outward and sealingly press against the inner bore <NUM> of upper housing <NUM>. In this tightened or sealed condition, a force of <NUM> pounds applied to the handle is not enough to withdraw the dipstick assembly from the housing <NUM>.

When the user wishes to withdraw the dipstick, to manually visually check the level of the fluid, or to simply supply more fluid into the reservoir through the opening, the user turns handle <NUM> counterclockwise. This unscrews the end <NUM> of shaft <NUM> upwardly through nut <NUM>, which allows the resilient sealing member <NUM> to expand upward and retract radially inwardly away from the bore wall <NUM>. This allows the user to easily withdraw the dipstick assembly from the housing <NUM>.

The isolation body <NUM> supports metallic dipstick connection structure <NUM>, preferably of stainless steel. The dipstick connection structure <NUM> has a central body with an aperture through which the isolation body <NUM> extends, keeping it electrically apart from shaft <NUM>. The connection structure <NUM> includes a Y-shaped pair of legs 157that extend downwardly and inwardly to connect to and support the metallic dipstick member <NUM>. The connection structure <NUM> also has contact extensions or wings <NUM> that extend outwardly and electrically connect with generally annular conical metallic contact <NUM> in the lower portion of upper housing part <NUM>. This provides an electrical connection to the dipstick <NUM> for fluid-level sensing circuitry in the upper housing <NUM> operating similarly to the circuitry of <FIG> to detect capacitance of the dipstick and output a square wave with a frequency corresponding to the depth of fluid into which the dipstick projects.

<FIG> show the dipstick unit removed from the housing <NUM>. The handle <NUM>, cap <NUM>, and sealing member <NUM> all remain together as the dipstick is withdrawn from the reservoir for viewing of clingage to determine the level of the fluid. The length of the dipstick member <NUM> is coated or covered with an overmold of insulating material that ensures that there is a capacitive spacing between the metal dipstick member <NUM> and the surrounding metallic parts of the reservoir or engine crankcase. This outer layer <NUM> is as shown in <FIG>, and extends down and completely covers the lower end of the dipstick member <NUM>. The insulating material is electrically insulating and also durable enough to survive in the environment of heated oil or other fluid, such as the oil in a crankcase of an operating internal combustion engine. The VICTREX PEEK material identified above is also particularly desirable to use in this overmold <NUM>.

The dipstick <NUM> with its coating of insulation <NUM> has an outer surface to which the fluid or oil in the reservoir clings, and when the dipstick is withdrawn, it is possible to see the level of fluid from the locations to which there is clingage on the dipstick. To aid in visually assessing the fluid level, the outer coating has symbols generally indicated at <NUM> indicating the level of the fluid, and whether adequate fluid is present or needs to be added, as is well known in the art. The symbols or writing and markings may be printed or more preferably are raised surface lettering and marks. In addition, as is well known in the art, the dipstick may be provided with a roughened or patterned portion <NUM> that improves clingage in that area so that the clingage is clearly visible to the user.

<FIG> shows an exploded view of the dipstick assembly of <FIG>. The entire assembly is held together by the threaded nut <NUM> (<FIG>) in isolation body <NUM> screwed on to the threaded lower end <NUM> of shaft <NUM> attached to handle <NUM>.

<FIG> show the structure of the housing <NUM>. Housing <NUM> comprises an upper housing and a lower housing <NUM> and <NUM>, both of which are secured in a cylindrical bore in the wall of the reservoir or engine block.

Upper housing <NUM> supports a bracket <NUM> that bolts on to the outer surface of the reservoir or block (not shown). It has a cylindrical inner bore or passage <NUM> that sealingly receives the resilient sealing member of the dipstick assembly, as described above. Upper housing also has a radially outwardly disposed recess indicated at <NUM> that supports therein circuitry such as that of <FIG> that interrogates or senses electronically the level of fluid in the reservoir from an electrical characteristic of the dipstick when secured in the system, specifically capacitance of the dipstick relative to the surrounding reservoir or engine block or crankcase. This circuitry is preferably in the form of a board <NUM> that is secured to the outward facing recessed surface of the recess <NUM> by a fastening structure, such as rivet <NUM>. Board <NUM> is connected electrically to the annular contact <NUM> (see <FIG>) in lower end of the inner bore <NUM>, which connects the board <NUM> to the dipstick metal member <NUM>.

Upper housing is provided with the board <NUM> because the board is potentially vulnerable and may need replacement, which can be accomplished easily by removing the bolt through bracket <NUM> and swapping out the entire upper housing <NUM> or by repairing the board <NUM> accessible when the upper housing is removed from the reservoir or engine wall.

Lower housing <NUM> is of the same diameter as the upper housing <NUM>, and fits snugly thereagainst when they are installed together, as seen in <FIG>. The lower housing also has an inner passage <NUM> through which the dipstick assembly extends into the reservoir or crankcase. Extending up from lower housing <NUM> is guide protrusion <NUM>, which glidingly fits into a recess in the bottom of upper housing <NUM> to ensure alignment of the housings <NUM> and <NUM> properly when the two housings are placed in the bore of the reservoir.

Alignment is important because the lower housing <NUM> also has contact boards <NUM> and <NUM> extending upwardly. These contact boards <NUM> and <NUM> each has two contacts to respective wires in the cable <NUM>. The contact boards <NUM> and <NUM> are configured so that when the lower housing meets the upper housing <NUM> correctly, electrical contact is made between the wires of the cable <NUM> and the board <NUM>, as is well known in the art of plug-in PC boards. The four wires generally carry DC power for the board <NUM>, provide one or two ground lines, either real ground or local ground, which are used to determine capacitance of the dipstick, and an output line carrying the square wave generated by the capacitance detection circuit used to determine the fluid level, as has been described. The cable <NUM> usually runs through the reservoir or crankcase to connect to electronics that process that output signal to provide alerts to the user when the fluid level is below a predetermined threshold level.

Particularly in a vehicle, there is an extensive electrical harness with indicator lights and displays, and a "low oil" warning light or display can be triggered when a comparison of the sensed level of the oil to one or more predetermined values for levels of the oil indicate that the oil or fluid is low. An audible alarm may also be triggered at the same time, or as an alternative.

In addition, especially where the reservoir is a vehicle engine crankcase, the vehicle may be moved into different orientations at which the detected level of oil may fluctuate without any change in the real amount of oil in the crankcase. That can impact on the reliability of the signal from the dipstick for determining the actual fluid level in the crankcase. To account for this possibility, the vehicle electronics can also electrically detect, using sensors well known in the art, the angle of sloping of the vehicle and its engine, and based on that detected orientation, alter what would otherwise be the reaction to the electrically detected level of fluid. For example, if a high angle of tilt is detected and the level of fluid detected is low, the system may disregard the level detected and not generate an alarm until the vehicle is closer to level. Alternatively, dependent on the angle and direction of tilt of the orientation, the system may adjust the detected value of the level of the fluid to compensate for the tilt before generating an alert to the user.

The embodiment shown is suitable for either installation in a new engine or for retrofit of an existing engine that has only a manual dipstick fluid monitoring system, to provide it with an electrical level sensing system as well.

The dipstick systems shown herein provide for.

The operational principle of the new "dual purpose" dipstick is in part internal capacitance. The level of fluid (oil, for example, but not limited to oil) is sensed by using an outer and inner tube and measuring the electrical capacitance between them as the dielectric (air vs. fluid), which changes with varying fluid level. The measured capacitance is converted into a frequency output, which is used to inform the user (i.e., vehicle driver) of the fluid (transmission oil) level.

In the case of a HNIPT hydromechanical tank transmission, due to variations in oil level from vehicle attitude, monitoring oil level is only possible on level ground. The system includes other sensors and instrumentation that detects orientation of the vehicle and determines adjustments for fore-aft and side-side changes in the orientation of the vehicle that would affect the detected level of fluid in the housing.

An embodiment of the electronic dipstick uses a modification of the existing guide tube and dipstick, with the addition of a circuit board, to perform the electrical detection functions as previous versions. The advantages gained by doing this include:.

Electrical insulation of the dipstick from the guide tube is accomplished by adding plastic overmold along the length of the dipstick. Alternatively, beads can prevent electrical contact between the two parts. At the top of the dipstick, the mounting tube that normally provides a sealing surface for the dipstick is currently made from aluminum. The mounting tube in one system of the invention is replaced by a high-temperature plastic version to further insulate the dipstick.

Electrical contact is made by two spring wipers that are welded to the dipstick that make contact with the inside diameter of the circuit board when the dipstick is secured in the receiving opening of the housing. The circuit board makes contact with the dipstick guide tube through contacts on the lower side of the board that are positioned so as to make contact with the guide.

The overall height of the electrically insulated dipstick is identical to the pre-existing manual dipstick. This means that if an electronic version dipstick is not available for any reason, an earlier, non-electrical dipstick can still be inserted in place of the insulated dipstick of the invention, allowing for manually checking the fluid level.

Additionally, if the insulated dipstick of an electronic level-sensing system of the invention is used in a transmission that has not yet had the contacts etc. of the electronic version installed, manual checking of the level is still available without damage to any components.

It may be understood that while the present specification describes the reservoir of the invention in the general context of the block or crankcase of an engine containing a fluid that is oil or a mixture of oil with another fluid, the present invention may be applied to environments where a dipstick is used to assess the level of a liquid in a container, even liquids with a viscosity that makes them almost a gel, to enable assessment of the level of the liquid in the container by an electrical sensor circuit.

Claim 1:
A fluid level sensing system comprising a capacitive sensor pair including
a dipstick (<NUM>) having an electrically conductive dipstick portion (<NUM>, <NUM>) disposed along at least a portion of a length of the dipstick,
markings thereon configured to enable a user to visually determine a level of a fluid based on clingage of the fluid to a surface of the dipstick when the dipstick is removed from a body of the fluid, and
an electrically nonconductive material (<NUM>) disposed on at least a portion of the electrically conductive dipstick portion, and
a dipstick support structure having an electrically conductive dipstick support structure portion (<NUM>) disposed along at least a portion of the dipstick support structure and disposed parallel to and a non-zero distance from the electrically conductive dipstick portion; and
an electrical system connected to the electrically conductive dipstick portion and the electrically conductive dipstick support structure portion, the electrical system configured to electrically sense an electrical characteristic of an electrical current flowing between the electrically conductive dipstick portion and the electrically conductive dipstick support structure portion, the electrical characteristic corresponding to a length of the capacitive sensor pair having the fluid between the non-zero distance of the electrically conductive dipstick portion and the electrically conductive dipstick support structure portion.