Title of Invention	A FUEL LEVEL MONITORING SYSTEM AND A METHOD OF EVALUATING THE DESIRED FUNCTION OF THE FUEL LEVEL MONITORING SYSTEM
Abstract	This invention relates to a fuel level monitoring system for a fuel system having a primary fuel tank (26) and a secondary fuel tank (28), comprising a fuel level sensor (40) that is disposed within said secondary fuel tank (20) and that generate a first signal (FLAGET, FLAGML, FLAGFT); an empty switch (50) that is disposed within said secondary fuel tank (28), that is connected in series with said fuel level sensor (40), and that generates a second signal (FLAGs1) corresponding to a sum of said first and second signals; and a control module (70) that determines a condition of one of said fuel level sensor (40) and said empty switch (50) based on comparisons of said third signal and each of a plurality of signal thresholds (RTHR1,RTHR2,RTHR3), wherein said condition comprises at least one of a fuel level sensor stuck condition and an empty switch stuck condition.

Title of Invention

A FUEL LEVEL MONITORING SYSTEM AND A METHOD OF EVALUATING THE DESIRED FUNCTION OF THE FUEL LEVEL MONITORING SYSTEM

Abstract

This invention relates to a fuel level monitoring system for a fuel system having a primary fuel tank (26) and a secondary fuel tank (28), comprising a fuel level sensor (40) that is disposed within said secondary fuel tank (20) and that generate a first signal (FLAGET, FLAGML, FLAGFT); an empty switch (50) that is disposed within said secondary fuel tank (28), that is connected in series with said fuel level sensor (40), and that generates a second signal (FLAGs1) corresponding to a sum of said first and second signals; and a control module (70) that determines a condition of one of said fuel level sensor (40) and said empty switch (50) based on comparisons of said third signal and each of a plurality of signal thresholds (RTHR1,RTHR2,RTHR3), wherein said condition comprises at least one of a fuel level sensor stuck condition and an empty switch stuck condition.

Full Text	FIELD The present disclosure relates to fuel level monitoring in a vehicle, and more particularly to monitoring a fuel level in a vehicle having primary and a secondary fuel tanks. BACKGROUND The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. Internal combustions engines combust an air and fuel (A/F) mixture within cylinders to produce drive torque. More specifically, the combustion events reciprocally drive pistons that drive a crankshaft to provide torque output from the engine. The fuel is delivered to the engine by a fuel system. The fuel systems of some vehicles include a plurality of fuel tanks. For example, some fuel systems include a primary fuel tank and a secondary fuel tank, wherein each fuel tank includes its own filler neck. The fuel levels within the fuel tanks are monitored and the vehicle operator is informed as to the amount of fuel remaining in each tank. More specifically, a fuel level sensor is provided in each tank. Each fuel level sensor is responsive to the fuel level in the tank and generates a signal based thereon. The amount of remaining fuel is determined based on the signals. Traditional fuel level monitoring control includes rationality diagnostics to determine whether the fuel level sensors are functioning properly. However, the traditional fuel level monitoring control rationality diagnostics are unable to discern between a fuel level signal that is stuck at empty and a fuel tank that has not had any fuel added. In most fuel system designs this is not an issue, because the fuel tank will be refueled on a regular basis. In a dual fuel tank system having separate fueling necks, however, the vehicle operator often decides not to add fuel to the secondary fuel tank for an unspecified amount of time. That is to say that the traditional fuel level monitoring control can not diagnose whether a fuel level is stuck at empty versus resting at empty because no fuel has been added to the secondary fuel tank. SUMMARY Accordingly, the present invention provides a fuel level monitoring system for a fuel system having a primary fuel tank and a secondary fuel tank. The fuel level monitoring system includes a fuel level sensor that is disposed within the secondary fuel tank and that generates a first signal. An empty switch is disposed within the secondary fuel tank and generates a second signal. A control module determines a condition of one of the fuel level sensor and the empty switch based on the first signal, the second signal and a plurality of signal thresholds. In one feature, the control module compares a sum of the first and second signals to each of the plurality of signal thresholds. In other features, the control module sets a condition flag based on the condition. The condition flag indicates one of a fuel tank empty condition, a fuel tank full condition, a normal operating condition, an empty switch stuck condition and a fuel level sensor stuck condition. The control module generates a diagnostic trouble code and initiates an alert when the condition is one of an empty switch stuck condition and a fuel level sensor stuck condition. In another feature, the first signal includes one of a first value, a second value and a third value. In still other features, the fuel level sensor is a variable resistor. The empty switch is connected in electrical series with the fuel level sensor. In yet another feature, the second signal includes one of a first and a second value. Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. ACCOMPANYING DRAWINGS The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. Figure 1 is a functional block diagram of an exemplary vehicle system including a primary and a secondary fuel tank; Figure 2 is a functional block diagram of the primary and secondary fuel tanks; Figure 3 is a schematic circuit diagram of a sensor system implemented in the secondary fuel tank; and Figure 4 is a flowchart illustrating exemplary steps executed by the fuel level detection cross-check control of the present invention. DETAILED DESCRIPTION The following description of the preferred embodiment is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the term module refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, or other suitable components that provide the described functionality. Referring now to Figure 1, an exemplary vehicle system 10 includes an engine 12 having an intake manifold 14 and an exhaust manifold 16. Air is drawn into the intake manifold 14 through a throttle 18. The air is mixed with fuel, and the fuel and air mixture is compressed and ignited within a cylinder 20 to reciprocally drive a piston (not shown) within the cylinder. Although a single cylinder 20 is shown, it is anticipated that the engine can include a plurality of cylinders 20. The piston rotatably drives a crankshaft (not shown) to provide a drive torque output. Fuel is delivered to the engine by a fuel system 22, which includes a fuel regulator 24, a primary fuel tank 26 and a secondary fuel tank 28. The primary and secondary fuel tanks 26, 28 include respective fueling necks 30, 32. Referring now to Figure 2, both the primary and the secondary fuel tanks 26, 28 include a fuel level sensor 40 having a switching unit 42, a float 44 and a lever arm 46. The float 44 is buoyant and floats at the surface of the fuel. As the fuel level increases/decreases, the height of the float 44 relative to the switching unit 42 correspondingly increases/decrease, thereby adjusting a rotational position of the lever arm 46 relative to the switching unit 42. The switching unit 42 includes a variable resistor, the resistance of which is adjusted based on the rotational position of the lever arm 46. For example, if the float 44 is in a high position (H), a first resistance (e.g., 20 Ohms) is provided, if the float 44 is in a mid position (M), a second resistance (e.g., 55 Ohms) is provided, and if the float 44 is in a low position (L) a third resistance (e.g., 230 Ohms) is provided. The secondary fuel tank 28 also includes an empty switch 50 or other resistance device having a float 51 that slides vertically within the empty switch 50, based on the fuel level within the secondary fuel tank 28. Referring now to Figure 3, the fuel level sensor 40 and the empty switch 50 are electrically connected in series to provide a total fuel level signal (SFL). More specifically, the empty switch 50 includes an output point 52, a 5 switch arm 54 and first and second input points 56, 58. The first input point 56 is electrically connected to a resistor 60 having a fixed resistance (R). The second input point 58 is connected to ground. The switch arm 54 connects the output point 52 to one of the first and second output points 56, 58. For example, when the float 51 of the empty switch 50 is at its lowest position (i.e., when the fuel level is below the empty switch 50), the switch arm 54 connects the output point 52 to the first input point 56. In this manner, R is added to the resistance of the fuel level sensor (RFLS). When the float 51 is in its upper most position (i.e., when the fuel level is above the empty switch 50), the output point 52 is connected to the second input point 58 and no additional resistance is added to RFLS. SFL, which is provided as the total resistance of the fuel level sensor 40 and empty switch 50 is sent to a control module 70 (see Figures 1 and 3). The control module 70 executes the fuel level detection cross- check control of the present invention. More specifically, one of a plurality of fuel level condition flags is set based on SFL. The fuel level condition flags include, but are not limited to, an empty tank flag (FLAGET), a first switch stuck flag (FLAGs1) (e.g., indicating that the empty switch 50 is stuck in the empty position), a first or second switch stuck flag (FLAGs1,2) (e.g., indicating that either the empty switch 50 is stuck in its uppermost position or the fuel level sensor 40 is stuck in its lowest (i.e., empty) position), a full tank flag (FLAGFT) and a mid-level flag (FLAGML). The flags are set based on the exemplary truth table below: The control module 70 indicates the fuel level in the secondary fuel tank 28 based on FLAGET, FLAGML or FLAGFT. If FLAGML, in particular, is set, the control module 70 uses a traditional rationality check to determine whether the fuel level sensor 40 is functioning properly. If one of FLAGs1 and FLAGs1,2 are set, the control module 70 sets a diagnostic trouble code (DTC) and illuminates a malfunction indicator lamp (MIL) or other visual or audible device to convey to the vehicle operator that there is a malfunction. Further, because the resistances are added in series, current fuel level reading algorithms are still able to be implemented for fuel level determination and existing in range diagnostics still function correctly. Referring now to Figure 4, exemplary steps executed by the fuel level monitoring cross-check control will be described in detail. The particular flag is set based on a comparison between SFL and a plurality of resistance thresholds. In step 400, control determines whether SFL is greater than or equal to a first resistance threshold (RTHR1) (e.g., 480 Ohms). If SFL is greater than or equal to RTHR1, both switches are functioning properly, control sets FLAGET in step 402 and control ends. If SFL is not greater than or equal to RTHR1, control determines whether SFL is less than RTHRI and greater than or equal to a second resistance threshold (RTHR2) (e.g., 270 Ohms) in step 404. If SFL is less than RTHRI and greater than or equal to RTHR2, the empty switch is not functioning properly, control sets FLAGs1 in step 406 and control ends. If SFL is not less than RTHRI and is not greater than or equal to RTHR2, control continues in step 408. In step 408, control determines whether SFL is less than RTHR2 and greater than a third resistance threshold (RTHR3) (e.g., 230 Ohms). If SFL is less than RTHR2 and is greater than RTHR3, one of the empty switch and the fuel level sensor is not functioning properly, control sets FLAGs1,2 in step 410 and control ends. If SFL is not less than RTHR2 and is not greater than RTHR3. control determines whether SFL is less than or equal to RTHR3 and is greater than or equal to a fourth resistance threshold (RTHR4) (e.g., 20 Ohms) in step 412. If SFL is less than or equal to RTHR3 and is greater than or equal to RTHR4, control sets FLAGML in step 414 and control ends. If SFL is not less than or equal to RTHR3 and is not greater than or equal to RTHR4, control sets FLAGFT in step 416 and control ends. Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims. WE CLAIM 1. A fuel level monitoring system for a fuel system having a primary fuel tank (26) and a secondary fuel tank (28), comprising: a fuel level sensor (40) that is disposed within said secondary fuel tank (20) and that generate a first signal (FLAGET, FLAGML, FLAGFT); characterized by: an empty switch (50) that is disposed within said secondary fuel tank (28), that is connected in series with said fuel level sensor (40), and that generates a second signal (FLAGs1) corresponding to a sum of said first and second signals; and a control module (70) that determines a condition of one of said fuel level sensor (40) and said empty switch (50) based on comparisons of said third signal and each of a plurality of signal thresholds (RTHR1,RTHR2,RTHR3), wherein said condition comprises at least one of a fuel level sensor stuck condition and an empty switch stuck condition. 2. The fuel level monitoring system as claimed in claim 1, wherein said control module sets a condition flag based on said condition. 3. The fuel level monitoring system as claimed in claim 2, wherein said condition flag indicates one of a fuel tank empty condition, a fuel tank full condition, a normal operating condition, an empty switch stuck condition and a fuel level sensor stuck condition. 4. The fuel level monitoring system as claimed in claim 3, wherein said control module generates a diagnostic trouble code and initiates an alert when said condition is one of an empty switch stuck condition and a fuel level sensor stuck condition. 5. The fuel level monitoring system as claimed in claim 1, wherein said first signal comprises one of a first value, a second value and a third value. 6. The fuel level monitoring system as claimed in claim 1, wherein said fuel level sensor is a variable resistor. 7. The fuel level monitoring system as claimed in claim 1, wherein said second signal comprises one of a first and a second value. 8. A method of evaluating a desired functioning of a fuel level monitoring system, comprising: generating a first signal using a fuel level sensor disposed within a fuel tank; generating a second signal using an empty switch disposed within said fuel tank; determining a condition of one of said fuel level sensor and said empty switch based on said first signal, said second signal and a plurality of signal thresholds; and adding said first and second signals; wherein a resultant sum of said first and second signals is compared to each of said plurality of signal thresholds. 9. The method as claimed in claim 8, comprising setting a condition flag based on said condition. 10.The method as claimed in clam 9, wherein said condition flag indicates one of a fuel tank empty condition, a fuel tank full condition, a normal operating condition, empty switch stuck condition and a fuel level sensor stuck condition. 11.The method as claimed in claim 8, wherein said first signal comprises one of a first value, a second value and a third value. 12.The method as claimed in claim 8, wherein said fuel level sensor is a variable resistor. 13.The method as claimed in claim 12, wherein said empty switch is connected in electrical series with said fuel level sensor. 14.The method as claimed in claim 8, wherein said second signal comprises one of a first and a second value. 15.The method as claimed in claim 8, wherein said first and second signals are resistance respectively associated with said fuel level sensor and said empty switch. ABSTRACT TITLE : "A FUEL LEVEL MONITORING SYSTEM AND A METHOD OF EVALUATING THE DESIRED FUNCTION OF THE FUEL LEVEL MONITORING SYSTEM" This invention relates to a fuel level monitoring system for a fuel system having a primary fuel tank (26) and a secondary fuel tank (28), comprising a fuel level sensor (40) that is disposed within said secondary fuel tank (20) and that generate a first signal (FLAGET, FLAGML, FLAGFT); an empty switch (50) that is disposed within said secondary fuel tank (28), that is connected in series with said fuel level sensor (40), and that generates a second signal (FLAGs1) corresponding to a sum of said first and second signals; and a control module (70) that determines a condition of one of said fuel level sensor (40) and said empty switch (50) based on comparisons of said third signal and each of a plurality of signal thresholds (RTHR1,RTHR2,RTHR3), wherein said condition comprises at least one of a fuel level sensor stuck condition and an empty switch stuck condition.

Full Text

FIELD
The present disclosure relates to fuel level monitoring in a
vehicle, and more particularly to monitoring a fuel level in a vehicle having
primary and a secondary fuel tanks.
BACKGROUND
The statements in this section merely provide background
information related to the present disclosure and may not constitute prior art.
Internal combustions engines combust an air and fuel (A/F)
mixture within cylinders to produce drive torque. More specifically, the
combustion events reciprocally drive pistons that drive a crankshaft to provide
torque output from the engine. The fuel is delivered to the engine by a fuel
system. The fuel systems of some vehicles include a plurality of fuel tanks. For
example, some fuel systems include a primary fuel tank and a secondary fuel
tank, wherein each fuel tank includes its own filler neck.
The fuel levels within the fuel tanks are monitored and the
vehicle operator is informed as to the amount of fuel remaining in each tank.
More specifically, a fuel level sensor is provided in each tank. Each fuel level
sensor is responsive to the fuel level in the tank and generates a signal based
thereon. The amount of remaining fuel is determined based on the signals.

Traditional fuel level monitoring control includes rationality
diagnostics to determine whether the fuel level sensors are functioning properly.
However, the traditional fuel level monitoring control rationality diagnostics are
unable to discern between a fuel level signal that is stuck at empty and a fuel
tank that has not had any fuel added. In most fuel system designs this is not an
issue, because the fuel tank will be refueled on a regular basis.
In a dual fuel tank system having separate fueling necks,
however, the vehicle operator often decides not to add fuel to the secondary fuel
tank for an unspecified amount of time. That is to say that the traditional fuel
level monitoring control can not diagnose whether a fuel level is stuck at empty
versus resting at empty because no fuel has been added to the secondary fuel
tank.
SUMMARY
Accordingly, the present invention provides a fuel level
monitoring system for a fuel system having a primary fuel tank and a secondary
fuel tank. The fuel level monitoring system includes a fuel level sensor that is
disposed within the secondary fuel tank and that generates a first signal. An
empty switch is disposed within the secondary fuel tank and generates a second
signal. A control module determines a condition of one of the fuel level sensor
and the empty switch based on the first signal, the second signal and a plurality
of signal thresholds.

In one feature, the control module compares a sum of the first
and second signals to each of the plurality of signal thresholds.
In other features, the control module sets a condition flag based
on the condition. The condition flag indicates one of a fuel tank empty condition,
a fuel tank full condition, a normal operating condition, an empty switch stuck
condition and a fuel level sensor stuck condition. The control module generates
a diagnostic trouble code and initiates an alert when the condition is one of an
empty switch stuck condition and a fuel level sensor stuck condition.
In another feature, the first signal includes one of a first value, a
second value and a third value.
In still other features, the fuel level sensor is a variable resistor.
The empty switch is connected in electrical series with the fuel level sensor.
In yet another feature, the second signal includes one of a first
and a second value.
Further areas of applicability will become apparent from the
description provided herein. It should be understood that the description and
specific examples are intended for purposes of illustration only and are not
intended to limit the scope of the present disclosure.
ACCOMPANYING DRAWINGS
The drawings described herein are for illustration purposes only
and are not intended to limit the scope of the present disclosure in any way.

Figure 1 is a functional block diagram of an exemplary vehicle
system including a primary and a secondary fuel tank;
Figure 2 is a functional block diagram of the primary and
secondary fuel tanks;
Figure 3 is a schematic circuit diagram of a sensor system
implemented in the secondary fuel tank; and
Figure 4 is a flowchart illustrating exemplary steps executed by
the fuel level detection cross-check control of the present invention.
DETAILED DESCRIPTION
The following description of the preferred embodiment is merely
exemplary in nature and is in no way intended to limit the invention, its
application, or uses. For purposes of clarity, the same reference numbers will be
used in the drawings to identify similar elements. As used herein, the term
module refers to an application specific integrated circuit (ASIC), an electronic
circuit, a processor (shared, dedicated, or group) and memory that execute one
or more software or firmware programs, a combinational logic circuit, or other
suitable components that provide the described functionality.
Referring now to Figure 1, an exemplary vehicle system 10
includes an engine 12 having an intake manifold 14 and an exhaust manifold 16.
Air is drawn into the intake manifold 14 through a throttle 18. The air is mixed
with fuel, and the fuel and air mixture is compressed and ignited within a cylinder
20 to reciprocally drive a piston (not shown) within the cylinder. Although a

single cylinder 20 is shown, it is anticipated that the engine can include a plurality
of cylinders 20. The piston rotatably drives a crankshaft (not shown) to provide a
drive torque output. Fuel is delivered to the engine by a fuel system 22, which
includes a fuel regulator 24, a primary fuel tank 26 and a secondary fuel tank 28.
The primary and secondary fuel tanks 26, 28 include respective fueling necks 30,
32.
Referring now to Figure 2, both the primary and the secondary
fuel tanks 26, 28 include a fuel level sensor 40 having a switching unit 42, a float
44 and a lever arm 46. The float 44 is buoyant and floats at the surface of the
fuel. As the fuel level increases/decreases, the height of the float 44 relative to
the switching unit 42 correspondingly increases/decrease, thereby adjusting a
rotational position of the lever arm 46 relative to the switching unit 42. The
switching unit 42 includes a variable resistor, the resistance of which is adjusted
based on the rotational position of the lever arm 46. For example, if the float 44
is in a high position (H), a first resistance (e.g., 20 Ohms) is provided, if the float
44 is in a mid position (M), a second resistance (e.g., 55 Ohms) is provided, and
if the float 44 is in a low position (L) a third resistance (e.g., 230 Ohms) is
provided. The secondary fuel tank 28 also includes an empty switch 50 or other
resistance device having a float 51 that slides vertically within the empty switch
50, based on the fuel level within the secondary fuel tank 28.
Referring now to Figure 3, the fuel level sensor 40 and the
empty switch 50 are electrically connected in series to provide a total fuel level
signal (SFL). More specifically, the empty switch 50 includes an output point 52, a
5

switch arm 54 and first and second input points 56, 58. The first input point 56 is
electrically connected to a resistor 60 having a fixed resistance (R). The second
input point 58 is connected to ground. The switch arm 54 connects the output
point 52 to one of the first and second output points 56, 58. For example, when
the float 51 of the empty switch 50 is at its lowest position (i.e., when the fuel
level is below the empty switch 50), the switch arm 54 connects the output point
52 to the first input point 56. In this manner, R is added to the resistance of the
fuel level sensor (RFLS). When the float 51 is in its upper most position (i.e.,
when the fuel level is above the empty switch 50), the output point 52 is
connected to the second input point 58 and no additional resistance is added to
RFLS. SFL, which is provided as the total resistance of the fuel level sensor 40
and empty switch 50 is sent to a control module 70 (see Figures 1 and 3).
The control module 70 executes the fuel level detection cross-
check control of the present invention. More specifically, one of a plurality of fuel
level condition flags is set based on SFL. The fuel level condition flags include,
but are not limited to, an empty tank flag (FLAGET), a first switch stuck flag
(FLAGs1) (e.g., indicating that the empty switch 50 is stuck in the empty position),
a first or second switch stuck flag (FLAGs1,2) (e.g., indicating that either the
empty switch 50 is stuck in its uppermost position or the fuel level sensor 40 is
stuck in its lowest (i.e., empty) position), a full tank flag (FLAGFT) and a mid-level
flag (FLAGML). The flags are set based on the exemplary truth table below:

The control module 70 indicates the fuel level in the secondary
fuel tank 28 based on FLAGET, FLAGML or FLAGFT. If FLAGML, in particular, is
set, the control module 70 uses a traditional rationality check to determine
whether the fuel level sensor 40 is functioning properly. If one of FLAGs1 and
FLAGs1,2 are set, the control module 70 sets a diagnostic trouble code (DTC) and
illuminates a malfunction indicator lamp (MIL) or other visual or audible device to
convey to the vehicle operator that there is a malfunction. Further, because the
resistances are added in series, current fuel level reading algorithms are still able
to be implemented for fuel level determination and existing in range diagnostics
still function correctly.
Referring now to Figure 4, exemplary steps executed by the fuel
level monitoring cross-check control will be described in detail. The particular
flag is set based on a comparison between SFL and a plurality of resistance
thresholds. In step 400, control determines whether SFL is greater than or equal
to a first resistance threshold (RTHR1) (e.g., 480 Ohms). If SFL is greater than or
equal to RTHR1, both switches are functioning properly, control sets FLAGET in
step 402 and control ends. If SFL is not greater than or equal to RTHR1, control

determines whether SFL is less than RTHRI and greater than or equal to a second
resistance threshold (RTHR2) (e.g., 270 Ohms) in step 404. If SFL is less than
RTHRI and greater than or equal to RTHR2, the empty switch is not functioning
properly, control sets FLAGs1 in step 406 and control ends. If SFL is not less than
RTHRI and is not greater than or equal to RTHR2, control continues in step 408.
In step 408, control determines whether SFL is less than RTHR2
and greater than a third resistance threshold (RTHR3) (e.g., 230 Ohms). If SFL is
less than RTHR2 and is greater than RTHR3, one of the empty switch and the fuel
level sensor is not functioning properly, control sets FLAGs1,2 in step 410 and
control ends. If SFL is not less than RTHR2 and is not greater than RTHR3. control
determines whether SFL is less than or equal to RTHR3 and is greater than or
equal to a fourth resistance threshold (RTHR4) (e.g., 20 Ohms) in step 412. If SFL
is less than or equal to RTHR3 and is greater than or equal to RTHR4, control sets
FLAGML in step 414 and control ends. If SFL is not less than or equal to RTHR3
and is not greater than or equal to RTHR4, control sets FLAGFT in step 416 and
control ends.
Those skilled in the art can now appreciate from the foregoing
description that the broad teachings of the present invention can be implemented
in a variety of forms. Therefore, while this invention has been described in
connection with particular examples thereof, the true scope of the invention
should not be so limited since other modifications will become apparent to the
skilled practitioner upon a study of the drawings, the specification and the
following claims.

WE CLAIM
1. A fuel level monitoring system for a fuel system having a primary fuel tank
(26) and a secondary fuel tank (28), comprising:
a fuel level sensor (40) that is disposed within said secondary fuel tank
(20) and that generate a first signal (FLAGET, FLAGML, FLAGFT);
characterized by:
an empty switch (50) that is disposed within said secondary fuel tank
(28), that is connected in series with said fuel level sensor (40), and that
generates a second signal (FLAGs1) corresponding to a sum of said first
and second signals; and
a control module (70) that determines a condition of one of said fuel level
sensor (40) and said empty switch (50) based on comparisons of said
third signal and each of a plurality of signal thresholds (RTHR1,RTHR2,RTHR3),
wherein said condition comprises at least one of a fuel level sensor stuck
condition and an empty switch stuck condition.
2. The fuel level monitoring system as claimed in claim 1, wherein said
control module sets a condition flag based on said condition.
3. The fuel level monitoring system as claimed in claim 2, wherein said
condition flag indicates one of a fuel tank empty condition, a fuel tank full
condition, a normal operating condition, an empty switch stuck condition
and a fuel level sensor stuck condition.

4. The fuel level monitoring system as claimed in claim 3, wherein said
control module generates a diagnostic trouble code and initiates an alert
when said condition is one of an empty switch stuck condition and a fuel
level sensor stuck condition.
5. The fuel level monitoring system as claimed in claim 1, wherein said first
signal comprises one of a first value, a second value and a third value.
6. The fuel level monitoring system as claimed in claim 1, wherein said fuel
level sensor is a variable resistor.
7. The fuel level monitoring system as claimed in claim 1, wherein said
second signal comprises one of a first and a second value.
8. A method of evaluating a desired functioning of a fuel level monitoring
system, comprising:
generating a first signal using a fuel level sensor disposed within a fuel
tank;
generating a second signal using an empty switch disposed within said
fuel tank;
determining a condition of one of said fuel level sensor and said empty
switch based on said first signal, said second signal and a plurality of
signal thresholds; and
adding said first and second signals;
wherein a resultant sum of said first and second signals is compared to
each of said plurality of signal thresholds.

9. The method as claimed in claim 8, comprising setting a condition flag
based on said condition.
10.The method as claimed in clam 9, wherein said condition flag indicates
one of a fuel tank empty condition, a fuel tank full condition, a normal
operating condition, empty switch stuck condition and a fuel level sensor
stuck condition.
11.The method as claimed in claim 8, wherein said first signal comprises one
of a first value, a second value and a third value.
12.The method as claimed in claim 8, wherein said fuel level sensor is a
variable resistor.
13.The method as claimed in claim 12, wherein said empty switch is
connected in electrical series with said fuel level sensor.
14.The method as claimed in claim 8, wherein said second signal comprises
one of a first and a second value.
15.The method as claimed in claim 8, wherein said first and second signals
are resistance respectively associated with said fuel level sensor and said
empty switch.

ABSTRACT
TITLE : "A FUEL LEVEL MONITORING SYSTEM AND A METHOD OF
EVALUATING THE DESIRED FUNCTION OF THE FUEL LEVEL
MONITORING SYSTEM"
This invention relates to a fuel level monitoring system for a fuel system having
a primary fuel tank (26) and a secondary fuel tank (28), comprising a fuel level
sensor (40) that is disposed within said secondary fuel tank (20) and that
generate a first signal (FLAGET, FLAGML, FLAGFT); an empty switch (50) that is
disposed within said secondary fuel tank (28), that is connected in series with
said fuel level sensor (40), and that generates a second signal (FLAGs1)
corresponding to a sum of said first and second signals; and a control module
(70) that determines a condition of one of said fuel level sensor (40) and said
empty switch (50) based on comparisons of said third signal and each of a
plurality of signal thresholds (RTHR1,RTHR2,RTHR3), wherein said condition
comprises at least one of a fuel level sensor stuck condition and an empty switch
stuck condition.

Documents:

00923-kol-2007-abstract.pdf

00923-kol-2007-assignment.pdf

00923-kol-2007-claims.pdf

00923-kol-2007-correspondence others 1.1.pdf

00923-kol-2007-correspondence others 1.2.pdf

00923-kol-2007-correspondence others 1.3.pdf

00923-kol-2007-correspondence others 1.4.pdf

00923-kol-2007-correspondence others.pdf

00923-kol-2007-description complete.pdf

00923-kol-2007-drawings.pdf

00923-kol-2007-form 1.pdf

00923-kol-2007-form 18.pdf

00923-kol-2007-form 2.pdf

00923-kol-2007-form 3.pdf

00923-kol-2007-form 5.pdf

00923-kol-2007-gpa.pdf

00923-kol-2007-priority document.pdf

923-KOL-2007-ABSTRACT.pdf

923-KOL-2007-AMANDED CLAIMS.pdf

923-KOL-2007-ASSIGNMENT.pdf

923-KOL-2007-CORRESPONDENCE 1.1.pdf

923-KOL-2007-CORRESPONDENCE.pdf

923-KOL-2007-DESCRIPTION (COMPLETE).pdf

923-KOL-2007-DRAWINGS.pdf

923-KOL-2007-EXAMINATION REPORT REPLY RECIEVED.pdf

923-KOL-2007-EXAMINATION REPORT.pdf

923-KOL-2007-FORM 1.pdf

923-KOL-2007-FORM 18.pdf

923-KOL-2007-FORM 2.pdf

923-KOL-2007-FORM 26.pdf

923-KOL-2007-FORM 3 1.1.pdf

923-KOL-2007-FORM 3.pdf

923-KOL-2007-FORM 5.pdf

923-KOL-2007-GRANTED-ABSTRACT.pdf

923-KOL-2007-GRANTED-CLAIMS.pdf

923-KOL-2007-GRANTED-DESCRIPTION (COMPLETE).pdf

923-KOL-2007-GRANTED-DRAWINGS.pdf

923-KOL-2007-GRANTED-FORM 1.pdf

923-KOL-2007-GRANTED-FORM 2.pdf

923-KOL-2007-GRANTED-SPECIFICATION.pdf

923-KOL-2007-OTHERS 1.1.pdf

923-KOL-2007-OTHERS.pdf

923-KOL-2007-PETITION UNDER RULE 137.pdf

923-KOL-2007-REPLY TO EXAMINATION REPORT.pdf

923-KOL-2007-TRANSLATED COPY OF PRIORITY DOCUMENT.pdf

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Patent Number

255040

Indian Patent Application Number

923/KOL/2007

PG Journal Number

03/2013

Publication Date

18-Jan-2013

Grant Date

16-Jan-2013

Date of Filing

27-Jun-2007

Name of Patentee

GM GLOBAL TECHNOLOGY OPERATIONS, INC.

Applicant Address

300 GM RENAISSANCE CENTER, DETROIT, MICHIGAN

Inventors:

#	Inventor's Name	Inventor's Address
1	DOUGLAS J. MOENING	24181 BROADVIEW STREET FARMINGTON, MICHIGAN 48336
2	ERIC M. HALL	3197 TAMARRON DRIVE, ROCHESTER HILLS, MICHIGAN 48309
3	GARY L. ROGERS	4196 N. GALE ROAD, DAVISON, MICHIGAN 48423
4	ZHONG WANG	7050 FOX CHASE LANE, WESTLAND, MICHIGAN 48185
5	SCOT A. KEGEBEIN	5049 MASON ROAD, HOWELL, MICHIGAN 48843

PCT International Classification Number

G01F 23/62; H01H 35/18

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	11/496,971	2006-08-01	U.S.A.