Title of Invention

AN ENGINE CONTROL SYSTEM AND A METHOD OF REGULATING OPERATION OF AN ENGINE THAT DRIVES A GENERATOR

Abstract An engine control system for an engine that drives a generator includes a temperature sensor that generates a temperature signal and a control module that determines a generator torque based on an engine speed and a generator characteristic. The control module determines a torque correction factor based on the temperature signal and determines a corrected generator torque based on the generator torque and the torque correction factor. Various embodiments of the invention utilize engine speed, system voltage, field winding duty cycle, engine temperature, ambient temperature and/or generator current.
Full Text GP-305932-PTE-CD
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TORQUE ESTIMATION OF ENGINE DRIVEN GENERATOR
FIELD OF THE INVENTION
[0001] The present invention relates to vehicles, and more particularly
to estimating a torque of an engine-driven generator.
BACKGROUND OF THE INVENTION
[0002] Internal combustion (IC) engines generate torque by combusting
a fuel and air mixture. The torque not only provides propulsion force to the
wheels but also drives auxiliary engine loads. For example, the torque is used to
drive loads including, but not limited to, an A/C compressor, a generator or
alternator, a coolant pump, an oil pump and the like. In the event of an
unanticipated load increase, the engine speed decreases and the engine may
stall.
[0003] To prevent engine stall, engine control systems of spark ignited
IC engines maintain a torque reserve by regulating spark timing to a less than
optimal amount. Because this spark advance is sub-optimal for a given fuel/air
rate, the engine produces less torque than at the optimal timing (i.e., minimum
spark for best torque (MBT)). If additional torque is quickly needed to drive an
increased load (i.e., faster than the A/F ratio can be changed), the spark timing is
advanced closer to optimal to produce additional torque for the same air/fuel rate.
Likewise, if less torque is needed, spark timing is retarded further from MBT.
This method, however, results in the engine generally running at sub-optimal
spark timing to maintain the desired torque reserve.
[0004] Another method of preventing engine stall is to regulate the
engine load. For example, the load (i.e., torque) of the generator can be
regulated for idle speed control. In this manner, the engine control system can
maintain the spark timing closer to MBT to reduce fuel consumption at idle.
Reducing the generator load achieves the same result as increasing engine
torque by advancing spark. Tight control the amount of torque load added or
subtracted by the generator is required in order to achieve a combination of

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smooth (i.e., driver transparent) control and improved fuel consumption.
However, traditional methods of estimating generator torque are not sufficiently
accurate to provide the tight control required. For example, traditional methods of
estimating generator torque, when reflected to the engine, can have an error of
approximately +/- 20Nm.
SUMMARY OF THE INVENTION
[0005] Accordingly, the present invention pertains to methods of
accurately estimating the torque of a generator, and is used as part of an engine
control system for an engine that drives a generator. The engine control system
includes a temperature sensor that generates a temperature signal and a
control module that determines a generator torque based on an engine speed
and a generator characteristic. The control module determines a torque
correction factor based on the temperature signal and determines a corrected
generator torque based on the generator torque and the torque correction factor.
[0006] In one feature, the generator characteristic includes a duty cycle
of a field winding of the generator.
[0007] In other features, the generator characteristic includes a field
winding voltage of the generator. The field winding voltage is determined based
on a system voltage and a field winding duty cycle of the generator.
[0008] In still another feature, the control module calculates the
corrected generator torque based on system voltage, generator current and
speed.
[0009] Further areas of applicability of the present invention will
become apparent from the detailed description provided hereinafter. It should be
understood that the detailed description and specific examples, while indicating
the preferred embodiment of the invention, are intended for purposes of
illustration only and are not intended to limit the scope of the invention.

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BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The present invention will become more fully understood from
the detailed description and the accompanying drawings, wherein:
[0011] Figure 1 is a schematic illustration of an exemplary vehicle that
is operated based on the generator torque estimation system according to the
present invention;
[0012] Figure 2 is an electrical schematic of an exemplary generator;
[0013] Figure 3 is a graph illustrating exemplary data points of
crankshaft torque versus field coil duty cycle for multiple operating temperatures;
[0014] Figure 4 is a flowchart illustrating exemplary steps executed by
a generator torque control according to the present invention;
[0015] Figure 5 is a graph illustrating exemplary data points of
crankshaft torque versus torque error for the multiple operating temperatures
achieved using the generator torque control;
[0016] Figure 6 is a graph illustrating exemplary data points of field
winding voltage versus crankshaft torque for multiple operating temperatures;
[0017] Figure 7 is a flowchart illustrating exemplary steps executed by
an alternative generator torque control according to the present invention;
[0018] Figure 8 is a graph illustrating exemplary data points of
crankshaft torque versus torque error for the multiple operating temperatures
achieved using the alternative generator torque control;
[0019] Figure 10 is a graph illustrating exemplary data points of torque
error for multiple samples achieved using the alternative generator torque control;
and
[0020] Figure 9 is a flowchart illustrating exemplary steps executed by
another alternative generator torque control according to the present invention.

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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] 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, and/or other
suitable components that provide the described functionality.
[0022] Referring now to Figure 1, an exemplary vehicle 10 includes an
engine 12, a generator 14 and a transmission 16. The engine 12 produces drive
torque to drive the generator 14 and the transmission 16. More specifically, the
engine 12 draws air into an intake manifold 18 that distributes the air to a cylinder
(not shown) where it is combined with fuel to form an air/fuel mixture. The air/fuel
mixture is combusted to drive a piston (not shown) within the cylinder, thereby
driving a crankshaft 20 to generate drive torque. The combustion process is
initiated be a spark generated by a spark plug (not shown). The timing of the
spark, relative to the position of the cylinder within the piston, can be adjusted
(i.e., retarded or advanced) to regulate exhaust temperature, engine torque and
manifold absolute pressure (MAP).
[0023] The engine 12 and the alternator 14 are coupled via a belt
system 22. The engine 12 and the generator 14 include pulleys 24,26,
respectively, that are coupled for rotation by a belt 28. The pulley 24 is coupled
for rotation with the crankshaft 20 of the engine 12. The engine 12 drives the
generator 14 to generate power used by vehicle systems and/or to recharge an
energy storage device (ESD) 30. The generator 14 includes a variable load on
the engine 12 (TGEN) that is regulated by a voltage regulator (VR) 32. When more
electrical energy is required from the generator 14, the VR 32 increases TGEN,
thereby increasing the amount of engine work. When less electrical energy is
required from the generator 14, the VR 32 decreases TGEN, thereby decreasing
the amount of engine work. During normal engine operation, TGEN is regulated

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based on a standard load control strategy. An exemplary load control strategy is
disclosed in commonly assigned U.S. Pat. Pub. No. US2004/0150375, the
disclosure of which is expressly incorporated herein by reference.
[0024] The transmission 16 can include, but is not limited to, a manual
transmission, an automatic transmission, a continuously variable transmission
(CVT) and/or an automated manual transmission (AMT). Drive torque is
transferred from the engine crankshaft 20 to the transmission 16 through a
coupling device 34. The coupling device 34 can include, but is not limited to, a
friction clutch or a torque converter depending upon the type of transmission
implemented. The transmission 16 multiplies the drive torque through one of a
plurality of gear ratios to drive a driveshaft 36.
[0025] A control module 38 regulates operation of the vehicle 10 based
on the generator torque estimation system of the present invention. The control
module 38 controls engine air flow, fuel injection, spark and alternator load to
regulate engine torque output. A manifold absolute pressure (MAP) sensor 40 is
responsive to the MAP within the intake manifold 18 and generates a MAP signal
based thereon. An engine temperature sensor 42 is responsive to an engine
temperature and generates an engine temperature signal based thereon. It is
anticipated that the engine temperature can be determined from a coolant
temperature and/or an oil temperature of the engine 12. An ambient temperature
sensor 44 is responsive to an ambient temperature and generates an ambient
temperature signal based thereon. It is anticipated that the engine temperature
can be further determined based on the ambient temperature. A speed sensor
46 is responsive to the rotational speed (RPM) of the engine 12 and generates a
speed signal based thereon. An accelerator pedal 48 is a pedal position sensor
50 is sensitive to a position of the accelerator pedal 48. The pedal position
sensor 50 generates a pedal position signal based thereon.

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[0026] Referring now to Figure 2, an exemplary electrical schematic of
the generator 14 and voltage regulator 32 are illustrated. The voltage regulator
includes a control module 60, a transistor 62 and a diode 64. The generator 14
includes a stator having a stator winding 66, a rotor having claw pole halves (not
illustrated) and a field winding 68 and a rectifier 70 having diodes 72. Although
not illustrated, the field windings are enclosed in first and second claw pole
halves, each of which includes a plurality of interleaved tines (e.g., 6 tines per
claw pole half). The rotor is rotatably supported within the stator and is rotatably
driven by the crankshaft 20.
[0027] The voltage regulator 32 is connected to B+ and B- terminals for
both power and voltage sensing. The control module 60 senses the voltage at
B+. If the voltage is too low compared to an internal reference voltage (VREF),
The transistor 62 is turned on to apply a voltage to The field winding 68,
increasing its current. When the transistor is on, the "F" terminal is approximately
0.8V less than the voltage of B+. When the control module 60 senses that the
voltage at B+ is higher than VREF, the transistor 62 is turned off. The current that
is flowing in the field winding circulates through the diode 64 and slowly
decreases. When the transistor is off and the diode 64 is on, the "F" terminal is
approximately 0.8 V less than the voltage at B-. The ratio of the time period
during which the transistor 62 is on (t0N) to the sum of tON and the time period
during which the transistor 62 is off tOFF), is equal to the duty cycle (DC) of the
coil.
[0028] The current in the field winding 68 magnetizes the claw pole
halves of the rotor. The first claw pole half is magnetized to a north pole (N), and
the second claw pole half is magnetized to a south pole (S). The interleaved
tines of the claw pole halves is such that when the rotor is assembled, alternating
N and S poles are provided circumferentially around the rotor. As the rotor
rotates within the stator, a magnetic flux produced by these poles induces an AC
voltage in the windings. In the case of 6 tines per claw pole half, the stator
winding 66 produces 6 AC voltage cycles per rotor revolution. The magnitude of
the AC voltage cycle is proportional to the frequency (i.e., speed of the rotor) and

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the amount of magnetic flux produced by the field winding 68. The more current
in the field winding 68, the more magnetic flux produced by the claw pole halves.
At low field winding current, the relationship is nearly proportional.
[0029] The diodes 72 of the rectifier 70 are arranged in a manner to
efficiently convert the AC voltage produced in the stator winding 66 into DC
voltage and current. However, the voltage produced in the stator winding 66 has
to be sufficiently large for the diodes 72 to become forward biased. For example,
if the battery voltage is 12.6V, it takes about 14.6 volts to begin to forward bias
the diodes 72 and to produce current.
[0030] The generator torque estimation system determines a
temperature-corrected torque TGEN (TGENCORR) based on a duty cycle applied to
the field coil (DCFC), engine speed (RPM) and engine temperature (TEMPENG)-
With reference to Figure 3, exemplary data points were collected for DCFc versus
TMEAS (i.e., the measured torque load on the crankshaft to drive the generator) at
engine idle (e.g., 1800 generator RPM) for multiple ambient temperatures (e.g.,
25°C, 75°C and 125°C). Best fit curves are provided for each temperature data
set. A multi-dimensional look-up table is implemented to determine the best fit
value of TGEN based on engine RPM and DCFC- A torque correction look-up table
is derived based on the temperature data sets and best fit curves. More
specifically, a torque correction factor (TCORR) is determined from the look-up
table based on TEMPENG- TEMPENG is determined based on the coolant
temperature, the oil temperature and/or the ambient temperature. A corrected
generator torque (TGENCORR) is determined based on TGEN and TCORR-
[0031] Referring now to Figure 4, exemplary steps executed by a
generator torque control will be discussed in detail. In step 400, control
determines the engine RPM and in step 402, control determines DCFc- Control
determines TGEN based on RPM and DCFc in step 404. In step 406, control
determines TEMPENG- Control determines TCORR based on TEMPENG in step 408.
In step 410, control calculates TGENCORR as the product of TGEN and TCORR- In
step 412, control regulates operation of the engine based on TGENCORR-

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[0032] Referring now to Figure 5, exemplary data points illustrate the
torque error (TERROR) achieved. More specifically, TERROR is defined as the
difference between the measured generator torque TMEAS and the best-fit curve of
Figure 3. As can be seen, the majority of the exemplary data points lie within +/-
4Nm. This is a significant improvement over the +/- 20Nm error that is achieved
using the traditional method of using a constant value for estimated torque.
[0033] Referring now to Figure 6, an alternative generator torque
estimation system determines TGENCORR based on a field winding voltage (VFw),
engine speed (RPM) and engine temperature (TEMPENG)- VFW is calculated
based on DCFC and a system voltage (VSYS)- VSYS is measured by the control
module 38. Exemplary data points were collected for VFw versus TMEAS (i.e., the
measured torque load on the crankshaft to drive the generator) at engine idle
(e.g., 1800 generator RPM) for multiple ambient temperatures (e.g., 25°C, 75°C
and 125°C). Best fit curves are provided for each temperature data set. A multi-
dimensional look-up table is implemented to determine the best fit value of TGEN
based on engine RPM and VFw- As similarly described above, the torque
correction look-up table is derived based on the temperature data sets and best
fit curves. TCORR is determined from the look-up table based on TEMPENG-
TEMPENG is determined based on the coolant temperature, the oil temperature
and/or the ambient temperature. TGENCORR is determined based on TGEN and
TCORR-
[0034] Referring now to Figure 7, exemplary steps executed by a
generator torque control will be discussed in detail. In step 700, control
determines the engine RPM and in step 702, control determines DCFc- Control
determines VSYS in step 704 and determines VFw based on VSYs and DCFC in step
706. TGEN based on RPM and VFW in step 708. Control determines TEMPENG in
step 710. Control determines TCORR based on TEMPENG in step 712. In step 714,
control calculates TGENCORR as the product of TGEN and TCORR- In step 716,
control regulates operation of the engine based on TGENCORR-

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[0035] Referring now to Figure 8, exemplary data points illustrate
TERROR achieved. Again, TERROR is defined as the difference between the
estimated TMEAS and the best-fit curve of Figure 6. As can be seen, the majority
of the exemplary data points lie within +/- 2Nm. This is a significant improvement
over the +/- 20Nm error that is achieved using the traditional method of
estimating generator torque as a constant value.
[0036] The present invention provides still another alternative generator
torque estimation system. More specifically, a generator current sensor 60 (see
Figure 1) is provided and is responsive to a generator current (IGEN). A curve fit
of generator torque is determined based on engine RPM, VSYS and IGEN to
provide the following relationship:

where ka through kg are calibration constants are obtained by performing a least-
squares curve fit against the test data. This relationship is independent of
temperature because the losses associated with speed and generator current
move in opposite directions versus temperature and therefore, the temperature
effect is minimal.
[0037] Referring now to Figure 9, TERROR is shown for multiple data
points taken across generator RPM, temperature and load ranges. For example,
TERROR was determined from a data set with generator speed varying from 1400
to 10000 RPM (i.e., 420 to 3000 engine RPM), ambient temperature varying from
25 to 125° C, IGEN varying from 10A to 90A and VSYS varying from 12.4V to
15.5V. As can be seen, TERROR is reduced and is within a range of approximately
+/-1Nm.
[0038] Referring now to Figure 10, the steps executed by the second
alternative generator torque estimation system will be described in detail. In
steps 1000, 1002 and 1004, control determines RPM, IGEN and VSYS, respectively.
In step 1006 control calculates TGEN based on RPM, IGEN and VSYS by processing
the above-described equation. Control regulates engine operation based on TGEN
in step 1008.

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[0039] 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.

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CLAIMS
What is claimed is:
1. An engine control system for an engine that drives a generator,
comprising:
a temperature sensor that generates a temperature signal; and
a control module that determines a generator torque based on an engine
speed and a generator characteristic, that determines a torque correction factor
based on said temperature signal and that determines a corrected generator
torque based on said generator torque and said torque correction factor.
2. The engine control system of claim 1 wherein said generator characteristic
includes a duty cycle of a field winding of said generator.
3. The engine control system of claim 1 wherein said generator characteristic
includes a field winding voltage of said generator.
4. The engine control system of claim 3 wherein said field winding voltage is
determined based on a system voltage and a field winding duty cycle of said
generator.
5. The engine control system of claim 1 wherein said control module
regulates operation of said engine based on said corrected generator torque.
6. An engine control system for an engine that drives a generator,
comprising:
a current sensor that generates a generator current signal; and
a control module that calculates a generator torque based on said
generator current signal, an engine speed and a system voltage and that
regulates operation of said engine based on said generator torque.

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7. The engine control system of claim 6 wherein said control module
calculates said generator torque further based on a plurality of calibration
constants.
8. The engine control system of claim 6 wherein said control module
calculates said generator torque by processing an equation.
9. The engine control system of claim 8 wherein said equation is derived
from test data including generator current, engine speed and system voltage.
10. The engine control system of claim 9 wherein said equation is of at least a
second order with respect to speed and is at least second order with respect to
generator current, wherein said equation includes a product of voltage and
current divided by speed.
11. A method of regulating operation of an engine operation that drives a
generator based on a generator torque, comprising:
generating a temperature signal, an engine speed signal and a generator
characteristic signal;
determining a generator torque based on said engine speed signal and
said generator characteristic signal;
determining a torque correction factor based on said temperature signal;
and
calculating a corrected generator torque based on said generator torque
and said torque correction factor.
12. The method of claim 11 wherein said generator characteristic signal is
based on a duty cycle of a field winding of said generator.
13. The method of claim 11 wherein said generator characteristic signal is
based on a field winding voltage of said generator.

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14. The method of claim 13 wherein said field winding voltage is determined
based on a system voltage and a field winding duty cycle of said generator.
15. The method of claim 11 further comprising regulating operation of said
engine based on said corrected generator torque.
16. A method of regulating operation of an engine operation that drives a
generator based on a generator torque, comprising:
generating a generator current signal, an engine speed signal and a
system voltage signal;
calculating a generator torque based on said generator current signal, said
engine speed and said system voltage; and
regulating operation of said engine based on said generator torque.
17. The method of claim 16 wherein said generator torque is calculated based
on a plurality of calibration constants.
18. The method of claim 16 wherein said generator torque is calculated based
on an equation.
19. The method of claim 18 wherein said equation is derived from test data
including generator current, engine speed and system voltage.

An engine control system for an engine that drives a generator includes a
temperature sensor that generates a temperature signal and a control module
that determines a generator torque based on an engine speed and a generator
characteristic. The control module determines a torque correction factor based
on the temperature signal and determines a corrected generator torque based on
the generator torque and the torque correction factor. Various embodiments of
the invention utilize engine speed, system voltage, field winding duty cycle,
engine temperature, ambient temperature and/or generator current.

Documents:

00939-kol-2007-abstract.pdf

00939-kol-2007-assignment.pdf

00939-kol-2007-claims.pdf

00939-kol-2007-correspondence others 1.1.pdf

00939-kol-2007-correspondence others 1.2.pdf

00939-kol-2007-correspondence others 1.3.pdf

00939-kol-2007-correspondence others.pdf

00939-kol-2007-description complete.pdf

00939-kol-2007-drawings.pdf

00939-kol-2007-form 1.pdf

00939-kol-2007-form 18.pdf

00939-kol-2007-form 2.pdf

00939-kol-2007-form 3.pdf

00939-kol-2007-form 5.pdf

00939-kol-2007-priority document.pdf

939-KOL-2007-ABSTRACT 1.1.pdf

939-KOL-2007-AMANDED CLAIMS.pdf

939-KOL-2007-ASSIGNMENT.1.3.pdf

939-KOL-2007-CORRESPONDENCE OTHERS 1.4.pdf

939-KOL-2007-CORRESPONDENCE.1.3.pdf

939-KOL-2007-CORRESPONDENCE.pdf

939-KOL-2007-DESCRIPTION (COMPLETE) 1.1.pdf

939-KOL-2007-DRAWINGS 1.1.pdf

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

939-KOL-2007-EXAMINATION REPORT.1.3.pdf

939-KOL-2007-FORM 1-1.1.pdf

939-KOL-2007-FORM 18.1.3.pdf

939-KOL-2007-FORM 2-1.1.pdf

939-KOL-2007-FORM 26.1.3.pdf

939-KOL-2007-FORM 26.pdf

939-KOL-2007-FORM 3-1.1.pdf

939-KOL-2007-FORM 3.1.3.pdf

939-KOL-2007-FORM 5.1.3.pdf

939-KOL-2007-FORM-27.pdf

939-KOL-2007-GRANTED-ABSTRACT.pdf

939-KOL-2007-GRANTED-CLAIMS.pdf

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

939-KOL-2007-GRANTED-DRAWINGS.pdf

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

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

939-KOL-2007-GRANTED-LETTER PATENT.pdf

939-KOL-2007-GRANTED-SPECIFICATION.pdf

939-KOL-2007-OTHERS.1.3.pdf

939-KOL-2007-OTHERS.pdf

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

939-KOL-2007-REPLY TO EXAMINATION REPORT.1.3.pdf


Patent Number 248999
Indian Patent Application Number 939/KOL/2007
PG Journal Number 38/2011
Publication Date 23-Sep-2011
Grant Date 20-Sep-2011
Date of Filing 29-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 MICHAEL G. REYNOLDS 1179 DORAL COURT TROY, MICHIGAN 48098
2 TOUFIC M HIJAZI 910 BALDWIN DRIVE TROY, MICHIGAN 48098
3 SCOTT J. CHYNOWETH 6522 BENNETT LAKE ROAD FENTON, MICHIGAN 48430
4 MICHAEL LIVSHIZ 2904 LESLIE PARK ANN ARBOR, MICHIGAN 48105
5 CHANDRA S. NAMUDURI 5853 RUBY DRIVE TROY, MICHIGAN 48085
PCT International Classification Number H02P9/04
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 11/468,830 2006-08-31 U.S.A.