U.S. patent application number 10/174425 was filed with the patent office on 2003-12-18 for optical fuel level sensor.
Invention is credited to Forgue, John R., Gilmour, Daniel A..
Application Number | 20030230141 10/174425 |
Document ID | / |
Family ID | 29733585 |
Filed Date | 2003-12-18 |
United States Patent
Application |
20030230141 |
Kind Code |
A1 |
Gilmour, Daniel A. ; et
al. |
December 18, 2003 |
OPTICAL FUEL LEVEL SENSOR
Abstract
An optical fuel level sensor for providing an electronic signal
representative of the fuel level within a fuel tank, generally
comprising a waveguide body, a photo source, and a photo receiver.
The waveguide body can either be of a dual-tapered or single-taper
shape and includes numerous tiered facets, which are angled
surfaces located on the outer periphery of the waveguide. When the
fuel level within the fuel tank is above a particular tiered facet,
light that impinges that facet will refract out of the waveguide,
conversely, when the fuel level is below that facet, impinging
light will be reflected back into the waveguide such that it is
received by the photo receiver. In this manner, the fuel level
sensor is able to utilize the reflected light received by the photo
receiver to provide an electronic signal representative of the fuel
level. Furthermore, a calibration feature may be included which
provides calibration information indicating when the fuel level has
reached a known, predetermined level.
Inventors: |
Gilmour, Daniel A.; (West
Hartford, CT) ; Forgue, John R.; (Cheshire,
CT) |
Correspondence
Address: |
REISING, ETHINGTON, BARNES, KISSELLE, P.C.
P O BOX 4390
TROY
MI
48099-4390
US
|
Family ID: |
29733585 |
Appl. No.: |
10/174425 |
Filed: |
June 18, 2002 |
Current U.S.
Class: |
73/290R |
Current CPC
Class: |
G01F 23/2927 20130101;
Y10S 250/902 20130101 |
Class at
Publication: |
73/290.00R |
International
Class: |
G01F 023/00 |
Claims
1. An optical fluid level sensor for use with a fluid vessel,
comprising: a waveguide capable of conducting light and having an
outer periphery that includes a plurality of tiered facets, each of
said tiered facets being capable of both reflecting light
internally within said waveguide and refracting light out of said
waveguide according to the presence of fluid against said tiered
facet, said waveguide also including a calibration feature located
at a predetermined position, a photo source capable of emitting
light into said waveguide, and a photo receiver capable of
receiving light from said waveguide, wherein said sensor is capable
of utilizing the light received by said photo receiver to provide
an electronic fluid level signal representative of a fluid level
within the vessel and wherein said sensor is further capable of
providing calibration information in an electronic signal that
identifies when the fluid level reaches said predetermined
position.
2. An optical fluid level sensor as defined in claim 1, wherein
said sensor is a fuel level sensor.
3. An optical fluid level sensor as defined in claim 1, wherein
said photo source and said photo receiver are located at an end of
said waveguide.
4. An optical fluid level sensor as defined in claim 1, wherein
each of said tiered facets is capable of internally reflecting
light within said waveguide when said facet is located at an axial
position above the fluid level and is capable of refracting light
out of said waveguide when said facet is immersed within the
fluid.
5. An optical fluid level sensor as defined in claim 1, wherein
said calibration feature includes a tiered facet having a different
size than other tiered facets.
6. An optical fluid level sensor as defined in claim 1, wherein
said calibration feature includes a longitudinal segment located
between adjacent tiered facets, said longitudinal segment having a
different length than other longitudinal segments.
7. An optical fluid level sensor as defined in claim 1, wherein
said calibration feature includes a reflective element capable of
reflecting light originating from said photo source to a second
photo receiver.
8. An optical fluid level sensor as defined in claim 1, wherein
said tiered facets comprise first and second sets of opposing
angled surfaces, with each of said first and second sets extending
along an opposite side of said outer periphery.
9. An optical fluid level sensor as defined in claim 8, wherein
said calibration feature includes a first angled surface of said
first set and a second angled surface of said second set, said
first and second angled surfaces having a different size than other
angled surfaces of said first and second sets.
10. An optical fluid level sensor as defined in claim 8, wherein
said calibration feature includes a first longitudinal segment
located between adjacent angled surfaces of said first set and a
second longitudinal segment located between adjacent angled
surfaces of said second set, said first and second longitudinal
segments having a different length than other longitudinal segments
of said first and second sets.
11. An optical fluid level sensor as defined in claim 8, wherein
said calibration feature includes a reflective element capable of
reflecting light originating from said photo source to a second
photo receiver.
12. An optical fluid level sensor as defined in claim 1, wherein
said waveguide has a tapered first axial end and a tapered second
axial end.
13. An optical fluid level sensor as defined in claim 12, wherein
said photo source and said photo receiver are located at a position
approximately equidistant from said first and second tapered axial
ends.
14. An optical fluid level sensor as defined in claim 13, wherein
said photo source is capable of internally emitting light within
said waveguide in directions generally towards said first and
second axial ends and said photo receiver is capable of receiving
light from within said waveguide in directions generally from said
first and second axial ends.
15. An optical fluid level sensor as defined in claim 1, wherein
said electronic signal containing said calibration information is
included within said electronic fluid level signal.
16. An optical fluid level sensor as defined in claim 1, wherein
said electronic signal containing said calibration information is a
separate signal from said electronic fluid level signal.
17. A fuel level sensing system for use with a fuel tank,
comprising: a power source having an output for providing an
electrical power signal, an optical fuel level sensor mounted
within the fuel tank, said sensor comprising: a waveguide capable
of conducting light and having an outer periphery that includes a
plurality of tiered facets, each of said tiered facets being
capable of both reflecting light internally within said waveguide
and refracting light out of said waveguide according to the
presence of fluid against said tiered facet, said waveguide also
including a calibration feature located at a predetermined
position, a photo source capable of emitting light into said
waveguide, a photo receiver capable of receiving light from said
waveguide, and a signal output for providing an electronic fuel
level signal, wherein said sensor is capable of utilizing the light
received by said photo receiver to provide said fuel level signal
which is representative of the fuel level within the fuel tank and
wherein said sensor is further capable of providing calibration
information in an electronic signal, and an interface electronics
unit having a first input coupled to said signal output of said
sensor for receiving said fuel level signal and a second input
coupled to said power source output for receiving said power
signal, wherein said electronics unit is capable of utilizing said
fuel level signal to determine the fuel level within the fuel tank
and wherein said electronics unit is capable of receiving and
utilizing said calibration information to calibrate said sensor
with reference to said predetermined position.
18. An optical fluid level sensor for use with a fluid vessel,
comprising: a waveguide capable of conducting light and having a
tapered first axial end, a tapered second axial end, and an outer
periphery that includes a plurality of tiered facets, each of said
tiered facets being capable of both reflecting light internally
within said waveguide and refracting light out of said waveguide
according to the presence of fluid against said tiered facet, a
photo source located at a position approximately equidistant from
said first and second axial ends and being capable of emitting
light into said waveguide in a first direction generally towards
said first axial end and in a second direction generally towards
said second axial end, and a photo receiver located at a position
approximately equidistant from said first and second axial ends and
being capable of receiving light from within said waveguide from
said first and second directions, wherein said sensor is capable of
utilizing the light received by said photo receiver to provide an
electronic fluid level signal representative of a fluid level
within the vessel.
19. An optical fluid level sensor as defined in claim 18, wherein
said sensor is a fuel level sensor.
20. An optical fluid level sensor as defined in claim 18, wherein
each of said tiered facets is capable of internally reflecting
light within said waveguide when said facet is located at an axial
position above the fluid level and is capable of refracting light
out of said waveguide when said facet is immersed within the
fluid.
21. An optical fluid level sensor as defined in claim 18, wherein
said waveguide includes a calibration feature located at a
predetermined position such that said sensor is capable of
providing calibration information in an electronic signal that
identifies when the fluid level reaches said predetermined
position.
22. An optical fluid sensor as defined in claim 21, wherein said
calibration feature includes a tiered facet having a different size
than other tiered facets.
23. An optical fluid level sensor as defined in claim 21, wherein
said calibration feature includes a longitudinal segment located
between adjacent tiered facets, said longitudinal segment having a
different length than other longitudinal segments.
24. An optical fluid level sensor as defined in claim 21, wherein
said calibration feature includes a reflective element capable of
reflecting light originating from said photo source to a second
photo receiver.
25. A fuel level sensing system for use with a fuel tank,
comprising: a power source having an output for providing an
electrical power signal, an optical fuel level sensor mounted
within the fuel tank, said sensor comprising: a waveguide capable
of conducting light and having a tapered first axial end, a tapered
second axial end, and an outer periphery that includes a plurality
of tiered facets, each of said tiered facets being capable of both
reflecting light internally within said waveguide and refracting
light out of said waveguide according to the presence of fuel
against said tiered facet, a photo source located at a position
approximately equidistant from said first and second axial ends and
being capable of emitting light into said waveguide in a first
direction generally towards said first axial end and in a second
direction generally towards said second axial end, a photo receiver
located at a position approximately equidistant from said first and
second axial ends and being capable of receiving light from within
said waveguide from said first and second directions, a signal
output for providing an electronic fuel level signal, and an
interface electronics unit having a first input coupled to said
signal output of said sensor for receiving said fuel level signal,
and a second input coupled to said power source output for
receiving said power signal, wherein said sensor is capable of
utilizing the light received by said photo receiver from said first
and second directions to provide said fuel level signal which said
electronics unit utilizes to determine the fuel level within the
fuel tank.
26. An optical fuel level sensor for use with a fuel tank,
comprising: a waveguide capable of conducting light and having a
tapered first axial end, a tapered second axial end, an outer
periphery that includes a plurality of tiered facets, each of said
tiered facets being capable of both reflecting light internally
within said waveguide and refracting light out of said waveguide
according to the presence of fuel against said tiered facet, said
waveguide also including a calibration feature located at a
predetermined position, a photo source located at a position
approximately equidistant from said first and second axial ends and
being capable of emitting light into said waveguide in a first
direction generally towards said first axial end and in a second
direction generally towards said second axial end, and a photo
receiver located at a position approximately equidistant from said
first and second axial ends and being capable of receiving light
from within said waveguide from said first and second directions,
wherein said sensor is capable of utilizing the light received by
said photo receiver from said first and second directions to
provide an electronic fuel level signal representative of a fuel
level within the fuel tank and wherein said sensor is further
capable of providing calibration information in an electronic
signal that identifies when the fuel level reaches said
predetermined position.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to an optical fluid level
sensor, and more particularly, to an optical fuel level sensor
capable of providing fuel level and calibration information via
electronic signals.
BACKGROUND OF THE INVENTION
[0002] Various types of fuel level sensors have been employed for
the purpose of providing fuel level information, particularly in
the automotive industry. One such fuel level sensor involves a
light conducting waveguide having a photo source and photo
receiver, wherein light emanates from the photo source and impinges
upon a series of tiered facets located at various depths within the
tank. Those facets located above the current fuel level inwardly
reflect the light so that it is returned to the photo receiver,
while those facets located below the current fuel level outwardly
refract the light such that it is never received by the photo
receiver. Thus, the sensor is capable of generating an electronic
signal representative of the amount of light received by the photo
receiver, wherein the amount of light received corresponds to a
particular fuel level.
[0003] One problem associated with these optical fuel level sensors
is that they may experience a long-term drift, or measurement
shift, that impacts the accuracy and stability of the sensor's
readings. Changes to the photo source output, photo receiver input,
or other associated circuitry could be incorrectly interpreted as a
change in fuel level. Such a phenomenon is not uncommon for sensor
components, and the drifting is typically accelerated by exposure
to extreme temperatures and other harsh environmental
conditions.
[0004] Furthermore, optical fuel level sensor designs such as those
discussed above, typically utilize a photo source and receiver
located at one axial end of the waveguide. Locating the photo
source and receiver at either the very top or the very bottom of
the waveguide increases the distance that light must travel,
particularly when the fuel tank is completely empty or completely
full. For example, when the fuel tank is empty, optical fuel level
sensors having photo sources and receivers located at their upper
most axial end must emit light from the top of the waveguide such
that it travels the entire length of the waveguide, reflects off a
dry facet located near the waveguide's lowermost end, and then
travels back up the length of the waveguide to the photo receiver.
Thus, the light has traveled a total distance roughly equivalent to
twice the axial length of the waveguide. The greater the distance
that light must travel, the greater the opportunity for signal
loss, which can cause the photo receiver to report inaccurate
readings.
[0005] Therefore, it is a general object of the present invention
to provide an optical fuel level sensor that minimizes the effects
of long-term drift and signal loss. Features aimed at minimizing
those effects may include one or more of the following: a
calibration feature, a center mounted photo source and receiver,
and an optical fuel level sensor having two tapered axial ends.
SUMMARY OF THE INVENTION
[0006] The above noted shortcomings of prior art fuel level sensors
are overcome by the present invention which provides an optical
fluid level sensor for use with a fluid vessel, comprising a
waveguide, a photo source, and a photo receiver. The waveguide is
capable of conducting light and has an outer periphery that
includes a plurality of tiered facets, each facet is capable of
both reflecting light internally within the waveguide and
refracting light out of the waveguide depending upon whether or not
fluid is in contact with that facet. The waveguide also includes a
calibration feature located at a predetermined position. The photo
source emits light into the waveguide and the photo receiver
receives light exiting the waveguide. The optical fluid level
sensor uses the light received by the photo receiver to provide an
electronic fluid level signal representative of a fluid level
within the vessel, and the sensor further provides calibration
information in an electronic signal that identifies when the fluid
level reaches the predetermined position. This fluid level sensor
can also be implemented as part of a fuel level sensing system to
be used with a fuel tank. In addition to the optical sensor, the
fuel level sensing system includes a power source having an output
for providing a power signal and an interface electronics unit. The
interface electronics unit includes a signal input for receiving
the electronic fuel level signal and is coupled to the sensor for
receiving the calibration information. Furthermore, the interface
electronics unit utilizes the fuel level signal to determine the
fuel level within the fuel tank, and utilizes the calibration
information to calibrate the sensor with respect to the
predetermined position.
[0007] In accordance with yet another aspect of the present
invention, there is provided an optical fluid level sensor for use
with a fluid vessel, the sensor comprises a waveguide, a photo
source, and a photo receiver. The waveguide conducts light and has
a tapered first axial end, a tapered second axial end, and an outer
periphery that includes a plurality of tiered facets. Each of the
tiered facets reflects light internally within the waveguide and
refracts light out of the waveguide according to the presence of
fluid against the tiered facet. The photo source is located at a
position approximately equidistant from the first and second axial
ends and emits light into the waveguide in a first direction
generally towards the first axial end and in a second direction
generally towards the second axial end. Similarly, the photo
receiver is located at a position approximately equidistant from
the first and second axial ends and receives light from within the
waveguide from the first and second directions. The sensor utilizes
the light received by the photo receiver to provide an electronic
fluid level signal representative of a fluid level within the
vessel. This fluid level sensor can also be implemented as part of
a fuel level sensing system to be used with a fuel tank. In
addition to the optical sensor, the fuel level sensing system
includes a power source for providing a power signal and an
interface electronics unit for receiving a fuel level signal from
the optical sensor. The sensor utilizes the light received by the
photo receiver from the first and second directions to provide the
interface electronics unit with the fuel level signal which the
interface electronics unit utilizes to determine the fuel level
within the fuel tank.
[0008] An advantage of this invention is that it provides an
optical fuel level sensor which can offset the affects of long term
drift of sensor components through the use of a calibration
feature. Also, the accuracy of the sensor is increased and the size
can be decreased by utilizing a dual-tapered waveguide design
having a photo source and receiver mounted near the center of the
waveguide. Thus, the optical fuel level sensor of the present
invention can be made more accurate and economical to manufacture
than other designs that provide fuel level sensing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] These and other objects, features, and advantages of the
present invention will be apparent from the following detailed
description of the preferred embodiments, appended claims, and
accompanying drawings in which:
[0010] FIG. 1 is a block diagram of a fuel level sensing system,
including a first embodiment of the optical fuel level sensor of
the present invention,
[0011] FIG. 2 is an enlarged view of the optical fuel level sensor
seen in FIG. 1,
[0012] FIG. 3 is an enlarged view of the lower portion of the
optical fuel level sensor seen in FIG. 2,
[0013] FIG. 4 is an enlarged view of the lower portion of a second
embodiment of the optical fuel level sensor of the present
invention having a calibration feature,
[0014] FIG. 5 is an enlarged view of the lower portion of a third
embodiment of the optical fuel level sensor of the present
invention having a calibration feature, and
[0015] FIG. 6 is an enlarged view of the lower portion of a fourth
embodiment of the optical fuel level sensor of the present
invention having a calibration feature.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0016] With reference to FIG. 1, there is shown a fuel level
sensing system 10 that measures and displays the relative fuel
level within a fuel tank, and generally comprises a power source
12, a fuel tank 14, an optical fuel level sensor 16, a sensor
interface electronics (SIE) unit 18, and a fuel gauge 20. The power
source, which is typically 12 volts, includes an output terminal
for providing the SIE with an electrical power signal. The optical
fuel level sensor provides the SIE unit 18 with an electronic fuel
level signal indicative of the current fuel level. The SIE unit
interprets that signal and is capable of performing a wide variety
of processing functions, such as controlling a warning light for
low fuel level indication, controlling fuel system devices, and
performing sensor calibration functions. The SIE generates an
electronic output signal that is sent to the fuel gauge or
instrument panel computer, which in turn visually informs an
operator of the current fuel level.
[0017] It should be noted, the fuel level sensing system 10 is not
specifically limited to the configuration just described. For
instance, the optical fuel level sensor could be directly connected
to the fuel gauge, such that the amount of current or voltage
associated with the fuel level signal would drive the fuel gauge as
an ammeter or voltmeter, respectively. Also, the SIE could be
incorporated into either the sensor or the fuel gauge itself,
rather than being a separate, stand-alone device. Furthermore, the
fuel level signal could be either digital or analog, and can be
processed according to one of any number of techniques commonly
known in the art for processing electronic signals.
[0018] Referring now to FIG. 2, a first embodiment of optical fuel
level sensor 16 of the present invention is seen in further detail,
and comprises a waveguide body 30, a first axial end 32, a second
axial end 34, a plurality of tiered facets 36, a photo source 38,
and a photo receiver 40. Waveguide body 30 is made from an
optically conductive material, such as Ultem.TM. from General
Electric, and is of an elongated shape having two tapered axial
ends. The upper portion of the waveguide body, that is the segment
extending from the center section 42 to first axial end 32, is
essentially a mirror image of the lower portion of the waveguide
body, which is the segment extending from the center section to
second axial end 34. The length of the waveguide varies, depending
upon the specific fuel tank or fluid vessel in which it is to be
installed. The width of waveguide body 30 is greatest towards
center section 42 and tapers as one moves towards either of the two
axial ends.
[0019] The tiered facets 36 are angled transition surfaces located
between adjacent longitudinal waveguide segments 44, and are
capable of both reflecting and refracting light according to an
optical phenomena commonly known as total internal reflection.
There can either be multiple layers of tiered facets, as seen in
FIG. 2, wherein different layers are located at different depths
within the waveguide, or there can be a single layer of tiered
facets, as seen in FIGS. 3-6. By having multiple layers, more
tiered facets can be located on the outer periphery of the
waveguide, thus improving the resolution of the sensor. The
longitudinal waveguide segments extend in a direction generally
parallel to the longitudinal axis of the waveguide, which happens
to also be the direction in which light emitted from light source
38 travels. Because the longitudinal segments are generally
parallel to these light paths, they do not provide an impinging
surface for the light to impact. The tiered facets 36, on the other
hand, are angled with respect to the direction of light emitted
from the light source and, therefore, provide a light reflecting
surface. Whether or not light from photo sources 38, which impinges
tiered facets 36, will reflect back into the waveguide body or
refract out of the waveguide, depends on the fuel level within the
fuel tank.
[0020] The light source can be an IR LED or any other suitable type
of light source capable of emitting light in a first direction
which is generally towards first axial end 32 (as represented by
the solid arrows) and in a second direction which is generally
towards second axial end 34 (represented by broken arrows). Light
source 38 emits a wide light path having a width W (seen in FIG.
3), such that light emitted in the first direction impinges
multiple tiered facets 36 located at different axial positions
within the upper portion of the waveguide, and light emitted in the
second direction impinges multiple tiered facets located at
different axial position in the lower portion of the waveguide. If
the light source emitted a single, narrow ray of light, only a
single tiered facet would be struck and the sensor would be unable
to take an accurate reading. Additionally, light emitted from the
photo source passes through curved optical devices 46, such as
Winston reflectors, which direct an increased portion of the total
light emitted towards the first and second axial ends. This
increased portion of light is needed to compensate for losses
attributable to the long light path from the center of the
waveguide to each of its extreme axial ends. Such compensation is
less required for the light which strikes the tiered facets closest
to the photo source. Photo receiver 40 is a photo-optical receiver
capable of receiving light and producing an electronic signal
indicative of the intensity of the light received. Although not
seen in FIG. 2, optical fuel level sensor 16 has a power signal
input for receiving an electrical power signal from power source 12
and a signal output for providing an electronic fuel level signal
indicative of the fuel level within the fuel tank.
[0021] In operation, optical fuel level sensor 16 is able to
produce an electronic fuel level signal representative of the fuel
level within the fuel tank by directing photo source 38 to emit a
quantity of light within waveguide body 30, measuring the portion
of emitted light that is reflected back to photo receiver 40, and
generating the fuel level signal based upon the measured amount of
reflected light. Referring now to FIG. 3, which is an enlarged view
of the lower portion of the sensor seen in FIG. 2 (with only a
single layer of tiered facets), there is seen a plurality of light
rays 50 being emitted from photo source 38. As previously
mentioned, it is important that the photo source emit a light path
having a width W such that the path is wide enough to strike the
multiple tiered facets 36 located at different axial positions.
Alternatively, the photo source could emit a plurality of
individual parallel light rays each designed to strike a different
tiered facet, as long as all of the tiered facets are impinged. As
the light rays emanate from the photo source they pass through
curved optical device 46, such that an increased portion of the
rays are focused towards second axial end 34. As seen in FIG. 3,
those light rays 50 which strike tiered facets 36 located at axial
positions above the fuel level (F.L.) are reflected back into the
waveguide at an angle that is approximately perpendicular to the
axial length of the waveguide. After being reflected, those rays
extend across the width of the waveguide and strike an opposing
tiered facet 36' located at an equivalent axial position as the
facet originally impinged. Tiered facets 36' are angled such that
light reflected from them travels again in a direction generally
parallel to the axial length of the waveguide and strikes photo
receiver 40. The reflection off of the tiered facets 36 and 36'
arises due to the optical phenomenon known as total internal
reflection. That is, the ratio of the index of refraction of the
waveguide to the index of refraction of the material located on the
other side of the interface (air when the fluid level is below the
impinged facet and fuel when the fluid level is above the impinged
facet) determines whether or not the light will be reflected back
into the waveguide or refracted out of the waveguide. The waveguide
is composed of an optically conductive material chosen such that
its index of refraction will allow for reflection when the
surrounding environment is air, but will refract when the
surrounding environment is fuel. Thus, light rays 50 which strike
tiered facets 36 located at axial positions below the fuel level
(F.L.) do not reflect back into and across the waveguide as the
higher impinging light rays do, rather, they strike the tiered
facet and refract out of the waveguide and into the fuel tank. This
process of emitting and receiving light according to the fuel level
is conducted in both the upper and lower portions of the waveguide,
even though only the lower portion is seen in FIG. 3. Following
reception of the reflected light, photo receiver 40 produces an
electronic fuel level signal indicative of the fuel level. That
signal may simply be an electronic signal whose voltage is
representative of the amount of light received by the photo
receiver. In such a case, the SIE could process the signal by using
commonly known filtering techniques, and could drive a fuel gauge
or other instrumentation with the filtered signal.
[0022] Referring now to FIG. 4, there is seen a second embodiment
of the optical fuel level sensor 16 of the present invention having
a calibration feature 60, wherein the calibration feature is used
to produce electronic calibration information for offsetting any
long term drift effect in the sensor circuitry. The structure and
operation of this second embodiment is largely the same as the
first embodiment seen in FIG. 3, however, in addition to having a
photo source 38, photo receiver 40, tiered facets 36, 36', this
embodiment also includes calibration feature 60. The calibration
feature includes a pair of longitudinal waveguide segments 62, 62'
and a pair of opposing tiered facets 64, 64', wherein longitudinal
waveguide segments 62, 62' are of a longer length than the adjacent
waveguide segments; the ones shown in FIG. 4 are of a longer
length, however, waveguide segments having a shorter length could
be used as well. Tiered facets 64, 64' are essentially the same as
those previously discussed.
[0023] In operation, light rays 66 are emitted from photo source 38
such that they pass through curved optical device 46 and strike a
plurality of tiered facets located at different axial positions
within the waveguide. When the fuel tank is full such that the fuel
level (F.L.) is at an axial position above the uppermost tiered
facet seen in FIG. 4, all of the tiered facets below the photo
source are submersed in fuel and thus refract light out of the
waveguide. Consequently, the photo receiver does not receive any of
the light emitted from the photo source. As the associated engine
is operated, fuel is being drawn from the fuel tank to supply the
combustion process, thus causing the fuel level to decrease within
the fuel tank. Each time the fuel level recedes past an axial
position having a pair of tiered facets, thus leaving them above
the fuel level, photo receiver 40 receives an increased amount of
light. In this manner, the various fuel levels that the sensor is
capable of measuring are discrete levels; the more axial positions
having tiered facets the greater the resolution of the sensor. For
instance, when the fuel level recedes to an axial position lower
than the uppermost tiered facet seen in FIG. 4 such that the tiered
facet is fully exposed, a light ray which strikes that facet will
now be reflected to the photo receiver. Thus, the photo receiver
will recognize that the fuel level has subsided a certain amount
due to the presence of the newly reflected light ray. Further
recession of the fuel level causes additional tiered facet pairs to
become exposed, thereby reflecting new rays of light to the photo
receiver in addition to those rays already being reflected by
tiered facet pairs located at axial positions above. Because
calibration feature 60 has a much longer axial segment 62 than
those separating other adjacent tiered facets, it takes longer for
the fuel level to recede the entire axial length of longitudinal
segment 62. The increased amount of time it takes for the photo
receiver to recognize the transition from the discreet fuel levels
above and below calibration feature 60, relative to the other
amounts of time between discreet levels, is the basis for the
calibration information used by the SIE.
[0024] Once the SIE is aware that the calibration feature has been
encountered, regardless of the fuel level readings being conveyed
by the sensor, the SIE knows that the fuel level is at a
predetermined position coinciding with the permanent position of
the calibration feature, a position which is constant and not
affected over time. In this embodiment, the sensor provides the SIE
with calibration information embedded within the electronic fuel
level signal. One method of processing this information involves
the SIE measuring the rate of change of the fuel level by recording
the amount of time between successive fuel level readings. Thus,
when the SIE records the noticeably longer amount of time needed
for the fuel level to recede down the increased length of axial
segment 62, it will be alerted that the fuel level is currently at
a position corresponding with the permanent predetermined position
of the calibration feature. Accordingly, the SIE can immediately
calibrate the sensor by offsetting the entire error between the
current reading and the known predetermined position, or the SIE
can gradually calibrate the sensor by offsetting it over a period
of time so as to not produce sudden, erratic changes in the fuel
level reading. Additionally, the SIE can use the natural movement
of the fuel within the fuel tank to calculate the rate of change of
the signal from the photo receiver. By recording and storing the
signal level at which the discontinuity in the rate of change
occurs, a correction factor can be determined which can then be
applied to the signal from the photo sensor, thus, canceling any
cumulative error. Also, the SIE can be designed to receive an
electronic signal indicating the current fuel consumption rate of
the engine, such as a throttle position signal. This information
allows the SIE to take into account the fact that the periods of
time between successive fuel levels can be affected by the rate at
which the engine is consuming fuel. Additional features and methods
for processing the fuel level signal and the calibration
information exist, and can be used without departing from the scope
of the present invention.
[0025] Referring now to FIG. 5, there is seen a third embodiment of
the fuel level sensor of the present invention having a calibration
feature 70. Like the optical fuel level sensor seen in FIG. 4 and
discussed above, this third embodiment includes a calibration
feature 70 which includes a pair of tiered facets 72, 72' located
at a predetermined axial position within the fuel tank. The tiered
facets 72, 72' have enlarged reflective surface such that they are
capable of reflecting more light than the typical tiered facets 36,
36'. Thus, when the fuel level recedes to an axial position low
enough to expose the enlarged facets 72, 72', an increased amount
of light is received by photo receiver 40.
[0026] In operation, as the fuel level within the fuel tank
recedes, it exposes tiered facets located at various axial
positions that were previously submersed. Each time a new pair of
tiered facets is exposed, an additional portion of the total light
emitted from the photo source is received by the photo receiver. As
long as tiered facets 36, 36' are uniform in size and other
reflective characteristics, the discreet amount of light received
by the photo receiver per facet pair is generally the same.
However, when the calibration feature 70 reflects light to the
receiver, its enlarged surface area allows it to reflect a greater
amount of light than the typical tiered facet 36, 36', thereby
affecting the electronic fuel level signal being sent to the SIE.
Similarly to the embodiment seen in FIG. 4, the sensor of FIG. 5
provides the electronic calibration information, which is the
increased strength compared to previous signals, within the
electronic fuel level signal. Thus, the SIE is able to determine
when the fuel level is at a known, predetermined axial position by
the increased amount of light received by photo receiver 40, which
is reflected in the calibration information produced by the sensor.
As previously discussed, the SIE can either immediately correct any
disparity that may exist between the current fuel level reading and
the predetermined calibration position, or it may gradually correct
the error over a period of time.
[0027] In reference to FIG. 6, a fourth embodiment of the present
invention is seen and includes a calibration feature 80. Embedded
within the waveguide body 30, or affixed to the waveguide surface,
such that it is able to reflect light being conducted within the
waveguide, is calibration feature 80. The calibration feature 80
includes a pair of tiered facets 82, 82', a reflective element 84,
and an additional photo receiver 86. Other than light reflected
from reflective element 84, the additional photo receiver does not
receive light from any other source. Thus, the SIE knows when the
fuel level is at a known, predetermined level by the reception of
an electronic signal indicating the presence of light at the
additional photo receiver.
[0028] In operation, when the fuel level within the fuel tank
recedes to an axial position lower than the pair of tiered facets
82, 82', light from the photo source reflects off of facet 82,
strikes and reflects off of reflective element 84, and is
transmitted to additional photo receiver 86. The reception of light
by the additional photo receiver causes that receiver to provide
the SIE with an additional electronic signal, a signal containing
calibration information which alerts the SIE that the fuel level
within the tank has reached a predetermined level. In this manner,
it is possible for the fuel level sensor to provide the SIE with
separate electronic signals, one being a fuel level signal provided
by photo receiver 40, and the other being an electronic signal
carrying calibration information provided by additional photo
source 86.
[0029] Thus far, the embodiments seen in FIGS. 3-6 have each been
described as only a lower portion of an overall fuel level sensor;
the upper portion not being seen. It is worth noting, each of those
embodiments could also represent an entire fuel level sensor, that
is, a fuel level sensor having a single tapered axial end, as
opposed to the double tapered axial end previously seen and
discussed.
[0030] It will thus be apparent that there has been provided in
accordance with the present invention an optical fuel level sensor
for use in a fuel tank associated with an internal combustion
engine which achieves the aims and advantages specified herein. It
will of course be understood that the foregoing description is of a
preferred exemplary embodiment of the invention and that the
invention is not limited to the specific embodiment shown. Various
changes and modifications will become apparent to those skilled in
the art. For instance, the fuel level sensor could be constructed
such that light rays striking a tiered facet located at an axial
position above the fuel level would be refracted out of the
waveguide, while those light rays striking tiered facets located
below the fuel level would be reflected into the waveguide. Also,
the optical fuel level sensor could easily be adapted to measure
the level of fluids other than fuel. Furthermore, the SIE could
process the electronic signals sent by the sensor according to any
of a number of different methods. All such variations and
modifications are intended to come within the spirit and scope of
the appended claims.
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