U.S. patent application number 15/961094 was filed with the patent office on 2019-10-24 for powertrain with ac brushless starter and sensor/sensorless control method.
This patent application is currently assigned to GM Global Technology Operations LLC. The applicant listed for this patent is GM Global Technology Operations LLC. Invention is credited to Suresh Gopalakrishnan, Lei Hao, Chandra S. Namuduri.
Application Number | 20190323469 15/961094 |
Document ID | / |
Family ID | 68105575 |
Filed Date | 2019-10-24 |
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United States Patent
Application |
20190323469 |
Kind Code |
A1 |
Hao; Lei ; et al. |
October 24, 2019 |
POWERTRAIN WITH AC BRUSHLESS STARTER AND SENSOR/SENSORLESS CONTROL
METHOD
Abstract
An electric starter system includes a brushless alternating
current (AC) starter motor selectively coupled to an engine and
having a rotor with a rotor position. A position sensor generates
measured position signals indicative of rotor position. A
controller is in communication with the sensor. The controller has
sensorless logic, e.g., a BEMF, inductance, or high-frequency
signal injection method, for generating an estimated rotor
position. The controller executes a method in which, below a
threshold speed of the starter motor, the controller calibrates the
sensorless logic using the measured position signals and controls a
torque operation of the starter motor using the measured position
signals. Above the threshold speed, the torque operation is
controlled solely using the estimated rotor position. A powertrain
includes the engine, a transmission, a drive shaft, and a load,
along with the electric starter system.
Inventors: |
Hao; Lei; (Troy, MI)
; Gopalakrishnan; Suresh; (Troy, MI) ; Namuduri;
Chandra S.; (Troy, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GM Global Technology Operations LLC |
Detroit |
MI |
US |
|
|
Assignee: |
GM Global Technology Operations
LLC
Detroit
MI
|
Family ID: |
68105575 |
Appl. No.: |
15/961094 |
Filed: |
April 24, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F02N 15/06 20130101;
H02P 6/182 20130101; F02N 2200/041 20130101; F02N 11/08 20130101;
F02N 2300/102 20130101; F02N 2200/04 20130101; H02P 6/16 20130101;
H02P 6/08 20130101; F02N 2300/104 20130101; F02N 2011/0896
20130101 |
International
Class: |
F02N 11/08 20060101
F02N011/08; H02P 6/08 20060101 H02P006/08; H02P 6/16 20060101
H02P006/16 |
Claims
1. An electric starter system for use with an internal combustion
engine and an alternating current (AC) voltage bus, the electric
starter system comprising: a brushless starter motor electrically
connected to the AC voltage bus and selectively connectable to the
engine in response to a requested engine start event, the brushless
starter motor having a rotor with a rotor position; a position
sensor positioned with respect to the rotor that is configured to
generate measured position signals indicative of the rotor
position; and a controller in communication with the position
sensor and programmed with sensorless logic configured to generate
an estimated rotor position; wherein the controller is configured,
below a threshold speed of the brushless starter motor, to:
calibrate the sensorless logic using the measured position signals;
and control a torque operation of the starter motor during the
requested engine start event using the measured position signals;
and wherein the controller is configured to control the torque
operation of the brushless starter motor above the threshold speed
solely using the estimated rotor position.
2. The electric starter system of claim 1, wherein the measured
position signals form a pulse train having rising and falling
edges, and the controller is configured to determine the angular
position of the rotor by detecting the rising and falling edges of
the pulse train and using a time between the rising and falling
edges.
3. The electric starter system of claim 2, wherein the position
sensor includes a Hall-effect sensor.
4. The electric starter system of claim 2, wherein the position
sensor includes an inductive sensor.
5. The electric starter system of claim 2, wherein the position
sensor includes a reluctance sensor.
6. The electric starter system of claim 1, wherein the sensorless
logic includes a back-electromotive force (BEMF) estimation
technique.
7. The electric starter system of claim 1, wherein the sensorless
logic is an inductance-based estimation technique.
8. The electric starter system of claim 1, wherein the sensorless
logic is a high-frequency signal injection-based estimation
technique.
9. A hybrid sensor/sensorless control method for use with a system
having an alternating current (AC) brushless starter motor
selectively connectable to an internal combustion engine, the
brushless starter motor having a rotor with a rotor position, a
position sensor positioned with respect to the rotor, and a
controller in communication with the position sensor, the method
comprising: below a threshold speed of the starter motor:
generating measured angular position signals using the position
sensor, the measured angular position signals being indicative of
the rotor position of the brushless starter motor; calibrating
sensorless logic of the controller using the measured angular
position signals; and controlling a torque operation the brushless
starter motor below the threshold speed using the measured angular
position signals; and above the threshold speed: generating an
estimated rotor position using the sensorless logic; and
controlling the torque operation of the brushless starter motor
solely using the estimated rotor position.
10. The method of claim 9, wherein the measured angular position
signals form a pulse train having rising and falling edges, the
method further comprising: detecting the rising and falling edges
via the controller; and determining the position and a speed of the
rotor using a time between the rising and falling edges.
11. The method of claim 9, wherein the position sensor includes a
Hall-effect sensor.
12. The method of claim 9, wherein the position sensor includes an
inductive sensor.
13. The method of claim 9, wherein the position sensor includes a
reluctance sensor.
14. The method of claim 9, wherein generating an estimated rotor
position using the sensorless logic includes using a
back-electromotive force (BEMF) estimation technique.
15. The method of claim 9, wherein generating an estimated rotor
position using the sensorless logic includes using an
inductance-based estimation technique.
16. The method of claim 9, wherein generating an estimated rotor
position using the sensorless logic includes using a high-frequency
signal injection-based estimation technique.
17. The method of claim 9, further including a transmission coupled
to the engine, a drive axle coupled to the transmission, and a load
coupled to the drive axle, the method further comprising:
transmitting torque from the engine to the load via the
transmission and the drive axle.
18. The method of claim 17, wherein transmitting torque from the
engine to the load includes transmitting the torque to a set of
drive wheels of a motor vehicle.
19. A powertrain comprising: an internal combustion engine; a
transmission connected to the engine; a drive axle connected to the
transmission; a load connected to the drive axle; and an electric
starter system comprising: a brushless starter motor electrically
connected to an alternating current (AC) voltage bus, the brushless
starter motor being selectively connectable to the engine in
response to a requested engine start event, the brushless starter
motor having a rotor with a rotor position; a position sensor
positioned with respect to the rotor that is configured to generate
measured position signals indicative of the rotor position; and a
controller in communication with the position sensor and programmed
with sensorless logic configured to generate an estimated rotor
position; wherein the controller is configured, below a threshold
speed of the brushless starter motor, to: calibrate the sensorless
logic using the measured position signals; and control a torque
operation of the brushless starter motor during the requested
engine start event using the measured position signals; and wherein
the controller is configured to control the torque operation of the
brushless starter motor above the threshold speed solely using the
estimated rotor position.
20. The powertrain of claim 19, wherein the powertrain is part of a
motor vehicle, and wherein the load is a set of road wheels of the
motor vehicle.
Description
INTRODUCTION
[0001] A powertrain may include an internal combustion engine that
generates engine torque in response to an acceleration request. The
generated engine torque is transmitted to a coupled load via a
transmission, e.g., a planetary gear arrangement or a gearbox. In
some powertrain configurations, a rotor of an electric machine is
selectively coupled to the engine, with motor torque from the
electric machine used to accelerate the engine to a threshold
speed. Such torque assist may be limited to supporting the engine's
cranking and starting function, with the electric machine in such
an application referred to as a starter motor. Alternatively,
torque pulses from the electric machine may be used when the engine
is already running, for instance to temporarily boost engine torque
and/or to reduce driveline noise, vibration, and harshness.
SUMMARY
[0002] An electric starter system is disclosed herein for use with
an internal combustion engine. The starter system includes an
alternating current (AC) brushless starter motor having a rotor
coupled to the engine, one or more position sensors, and a
controller. Control of the starter motor requires accurate
knowledge of the rotor's angular position and speed. To this end,
the controller is configured to execute a hybrid sensor/sensorless
control methodology as described below in controlling a torque
operation of the starter motor.
[0003] In particular, the controller as described herein is
configured to control the torque operation of the starter motor,
i.e., generation and delivery of motor torque to the engine, at
motor speeds below a calibrated threshold speed, such as about 1000
RPM. The controller performs this task using measured angular
position signals from the position sensor(s). Below the threshold
speed, the controller uses the measured angular position signals to
calibrate sensorless logic residing in memory of the controller.
Above the threshold speed, the controller estimates the rotor's
angular position using the sensorless logic alone, i.e., the
controller does not rely on the measured angular position signals
when operating above the threshold speed. The combined use of
measured angular position signals from the position sensor(s) at
low speeds of the starter motor with the exclusive use of a
sensorless logic-based estimated angular position at higher speeds,
i.e., the above-noted "hybrid sensor-based/sensorless" approach, is
intended to achieve a desired power level and improved
flux-weakening control of the starter motor relative to existing
methodologies.
[0004] Various embodiments exist for the position sensors. For
instance, the position sensors may be optionally embodied as
multiplying rotary encoders, digital or analog Hall-effect sensors,
inductive sensors, reluctance sensors, or other incremental
position sensors as described herein.
[0005] Upon starting the engine and while the starter motor rotates
at speeds up to the threshold speed noted above, the angular
position of the rotor is measured in real-time by the controller,
for example using rising and falling edges of the angular position
signals and a time interval between such edges for a Hall-effect
sensor. The sensorless logic is then used to estimate the rotor's
angular position, and an associated rotational speed, at starter
motor speeds above the threshold speed, with the sensorless logic
possibly such techniques as back-electromotive force (BEMF),
inductance, or high-frequency signal injection in various
non-limiting embodiments. Measured angular position of the rotor
from the position sensors is used by the controller to calibrate
and tune parameters of the sensorless logic when the starter motor
operates below the threshold speed. The controller automatically
transitions to the sensorless logic alone once position and speed
estimation by the sensorless logic is stable and calibrated.
[0006] In an example embodiment, a powertrain may include the
engine, a transmission coupled to the engine, the electric starter
system, and the controller.
[0007] A hybrid sensor/sensorless control method is also disclosed
for use with an engine. According to an example embodiment, the
method includes, when the starter motor is operating below a
threshold speed, generating measured angular position signals using
the position sensor(s), with the measured angular position signals
being indicative of the rotor position of the starter motor. The
method further includes, when operating below the threshold speed,
calibrating sensorless logic of the controller using the measured
angular position signals, and then controlling a torque operation
the starter motor using the measured angular position signals. The
method further includes, when operating above the threshold speed,
generating an estimated rotor position/rotor angle using the
sensorless logic and controlling the torque operation of the
starter motor solely using the estimated rotor position.
[0008] The above summary is not intended to represent every
embodiment or aspect of the present disclosure. Rather, the
foregoing summary exemplifies certain novel aspects and features as
set forth herein. The above noted and other features and advantages
of the present disclosure will be readily apparent from the
following detailed description of representative embodiments and
modes for carrying out the present disclosure when taken in
connection with the accompanying drawings and the appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a schematic illustration of an example powertrain
having a polyphase/AC brushless starter motor controlled via a
hybrid sensor/sensorless control approach as set forth herein.
[0010] FIG. 2 is a time plot of example sensor-based angular
position signals usable by the controller of FIG. 1 during a
low-speed portion of an operating range of the starter motor, with
time depicted and rotor position depicted on the horizontal axis
and BEMF for each of three example electrical phases depicted on
the vertical axis.
[0011] FIG. 3 is a flow chart describing a hybrid sensor/sensorless
control method according to a possible embodiment.
[0012] The present disclosure is susceptible to modifications and
alternative forms, with representative embodiments shown by way of
example in the drawings and described in detail below. Inventive
aspects of this disclosure are not limited to the particular forms
disclosed. Rather, the present disclosure is intended to cover
modifications, equivalents, combinations, and alternatives falling
within the scope of the disclosure as defined by the appended
claims.
DETAILED DESCRIPTION
[0013] Embodiments of the present disclosure are described herein.
The various embodiments are examples of the present disclosure,
with other embodiments in alternative forms being conceivable by
one of ordinary skill in the art in view of the disclosure. The
figures are not necessarily to scale. Some features could be
exaggerated or minimized to show details of particular components.
Therefore, specific structural and functional details disclosed
herein are not to be interpreted as limiting, but rather as a
representative basis for teaching one skilled in the art to
variously employ the present disclosure. As those of ordinary skill
in the art will also understand, features illustrated and described
with reference to one of the figures can be combined with features
illustrated in one or more other figures to produce embodiments
that are not explicitly illustrated or described. The combinations
of features illustrated thus serve as representative embodiments
for typical applications. Various combinations and modifications of
the features consistent with the teachings of this disclosure,
however, could be desired for particular applications or
implementations.
[0014] Referring to the drawings, wherein like reference numbers
refer to the same or like components in the several Figures, an
example powertrain 10 is shown schematically in FIG. 1. The
powertrain 10 includes an electric starter system 12 that is
selectively connectable to an internal combustion engine (E) 20.
The engine 20, e.g., a gasoline or diesel engine, ultimately
outputs engine torque to an output shaft 24. The output shaft 24 is
coupled to a transmission (T) 22, which in turn delivers output
torque to a transmission output member 25. The output member 25 in
turn drives a coupled load via one or more drive axles 28, with the
load depicted in FIG. 1 as a set of drive wheels 26 in an example
automotive application. Other applications may be envisioned,
including power plants, robotics, mobile platforms, and non-motor
vehicle applications such as watercraft, marine vessels, rail
vehicles, and aircraft, and therefore the motor vehicle embodiment
of FIG. 1 is intended to be illustrative of the disclosed concepts
without limitation.
[0015] The engine 20 includes a crankshaft 31 coupled to a flywheel
32. When the engine 20 is not running, e.g., after a
fuel-conserving autostop event of the engine 20 at idle or when
cruising with the engine 20 turned off, the electric starter system
12 may be energized via a controller (C) 50 so as to deliver motor
torque (arrow T.sub.M) to the flywheel 32, with the controller 50
being part of the electric starter system 12 in some embodiments or
a separate control device. One possible configuration for achieving
such ends is the use of a solenoid (S) 21. The solenoid 21 may be
disposed between a rotor 19 of a brushless alternating current (AC)
electric machine (M.sub.BL) 18, hereinafter referred to as the
starter motor 18, and a shaft extension 190, possibly with a gear
reduction set (not shown) located between the rotor 19 and the
solenoid 21.
[0016] When the solenoid 21 is energized via starter control
signals (arrow CC.sub.S) from the controller 50, the solenoid 21
linearly translates a pinion gear 33 to the position indicated at
33A, and thus into direct meshed engagement with the flywheel 32
and/or a gear element connected thereto. Once the engine 20 has
started and its internal combustion process sustains a fueling
process, the starter control signals (arrow CC.sub.S) are
discontinued and, as a result, the solenoid 21 is de-energized. The
pinion gear 33 is urged out of engagement with the flywheel 32,
e.g., via a return action of the solenoid 21. Such bi-directional
translation capability of the pinion gear 33 is represented in FIG.
1 by double-headed arrow SS.
[0017] The example electric starter system 12 of FIG. 1 may include
or may be connected to a direct current (DC) battery pack 14, e.g.,
a multi-cell lithium ion, nickel metal hydride, or lead acid
battery pack having positive (+) and negative (-) terminals. The
electric starter system 12 may include a power inverter module
(PIM) 16 that is electrically connected across the positive (+) and
negative (-) terminals of the battery pack 14 via a DC voltage bus
15, e.g., a 12-48 nominal VDC bus in a possible embodiment, as well
as to a polyphase/alternating current (AC) voltage bus 17. Although
omitted from FIG. 1 for illustrative simplicity, the PIM 16, as
will be appreciated by one of ordinary skill in the art, includes
upper and lower semiconductor switching pairs, e.g., IGBTs or
MOSFETs respectively connected to positive (+) and negative (-)
terminals via the DC voltage bus 15, and signal filtering circuit
components which ultimately convert DC power from the battery pack
14 into polyphase power on the AC voltage bus 17.
[0018] In turn, the AC voltage bus 17 is electrically connected to
individual phase windings (not shown) of the starter motor 18. The
starter motor 18 may be variously configured as a surface permanent
magnet machine, an internal permanent magnet machine, a drag-cup or
cage induction machine, a switched reluctance machine, or another
type of brushless motor without limitation. As recognized herein,
brushless motors such as the starter motor 18 may enjoy an extended
operating life with an improved level of speed control precision
relative to certain brush-type motors, among other possible
benefits. A field weakening control strategy may be employed to
further improve control of the power output of the starter motor
18, with such a strategy benefitting from the hybrid
sensor/sensorless approach disclosed herein with reference to FIGS.
2 and 3.
[0019] Because the starter motor 18 of FIG. 1 is an AC machine as
noted above, the controller 50 requires accurate position data to
ensure precise torque control of the starter motor 18, particularly
during a starting function of the engine 20. Thus, at least one
position sensor 36 is positioned with respect to the rotor 19,
e.g., a shaft, hub, or other rotating portion of the starter motor
18 as shown schematically in FIG. 1. The position sensor 36
measures the angular position of the rotor 19 and reports the
measured angular position to the controller 50 as part of a set of
input signals (arrow CC.sub.I). The number of position sensors 36
may vary depending on the application, with as few as one such
position sensor 36 usable in some embodiments.
[0020] With respect to the position sensor(s) 36, as will be
appreciated by one of ordinary skill in the art, a raw angular
position sensor is either incremental or absolute, with a position
signal from an absolute position sensor being proportion to true
position regardless of whether the rotor 19 is stationary or
moving. In contrast, an incremental position sensor detects
positional changes. The finer the resolution of a given position
sensor, the greater its cost. Thus, the cost of a given position
sensor can vary dramatically based on whether the position sensor
is absolute or incremental, and based on the sensing technology
that is used. In some embodiments, therefore, the position
sensor(s) 36 are incremental sensors.
[0021] Within the scope of the present disclosure, a suitable
position sensor 36 for use in the present application is the
multiplying encoder or digital Hall sensors, e.g., using
polymer-bonded, multi-pole magnets, and in which encoder/Hall
pulses and commutation pulses are generated as signal outputs.
Another low-cost sensor usable as the position sensor(s) 36 of FIG.
1 is an analog Hall-effect sensor, e.g., one using neodymium
magnets, or other field-based sensors operable for generating sine
and cosine signals as sensor outputs. Other sensor types generating
similar sine and cosine outputs are inductive-type and
reluctance-type position sensors, both of which forego the use of
magnets in their operation.
[0022] The controller 50, although schematically depicted as a
single controller, may be variously implemented as one or more
control devices collectively managing the example electric starter
system 12 according to a method 100, an example embodiment of which
is depicted in FIG. 3. Multiple controllers may be in communication
via a serial bus, e.g., a Controller Area Network (CAN), or via
discrete conductors. The controller 50 may include one or more
digital computers each having a processor (P), e.g., a
microprocessor or central processing unit, as well as memory (M) in
the form of read only memory, random access memory,
electrically-programmable read only memory, etc., a high-speed
clock, analog-to-digital and digital-to-analog circuitry,
input/output circuitry and devices, and appropriate signal
conditioning and buffering circuitry. The controller 50 may also
store algorithms and/or computer executable instructions in memory
(M), including the sensorless logic 55 described below, and
transmit commands to the electric starter system 12 to enable
performance of control actions according to the present
disclosure.
[0023] The controller 50 is in communication with the engine 20 and
receives, as part of the input signals (arrow CO, signals
indicative of a speed and temperature of the engine 20, as well as
other possible engine operating conditions or parameters. Such
parameters include a starting request of the engine 20, whether
operator-initiated or autonomously generated. The controller 50 is
also in communication with the starter motor 18, and thus receives
signals indicative of current speed, current draw, torque,
temperature, and/or other operating parameters. The controller 50
may also communicate with the battery pack 14 and receive signals
indicative of a battery state of charge, temperature, and current
draw, as well as a voltage across the respective DC and AC voltage
buses 15 and 17. The controller 50 of FIG. 1 is configured to use
the input signals (arrow CO, including the measured position
signals from the position sensor(s) 36, during startup of the
engine 20 and up to a low threshold speed of the starter motor 18,
with the terms "low threshold speed" and "low speed" as used herein
meaning less than about 1000 RPM, i.e., .+-.10%, or less than 1500
RPM in another embodiment.
[0024] Referring to FIG. 2, respective rising and falling edges 41R
and 41F of the measured angular position signals from position
sensor(s) 36 of FIG. 1, embodied as example Hall-effect sensors of
the type described above, are used by the controller 50 to estimate
the current angular position of the rotor 19, and thus to calculate
the current rotational speed of the rotor 19. Once the rotor 19 is
rotating above the calibrated threshold speed, the controller 50
transitions to control of the starter motor 18 solely using the
sensorless logic 55. Between zero speed and the threshold speed,
the controller 50 also uses the measured position data from the
position sensor(s) 36 to calibrate the sensorless logic 55 and
ensure proper convergence of the estimated angular position/speed
with the measured angular position/speed from the position
sensor(s) 36.
[0025] Various embodiments of the sensorless logic 55 may be used
within the scope of the present disclosure. Example approaches
include, but are not limited to, a BEMF-based methodology,
inductance-based methodology, and high-speed signal injection. BEMF
is directly proportional to rotor speed, with BEMF increasing and
resisting motion as the electric machine picks up speed. Thus, once
the rotor 19 begins rotating, it is possible to estimate speed and
position by monitoring BEMF. Signal injection, as the name
indicates, injects a high-frequency carrier signal into the control
voltage to the electric machine, and observes the frequency
response in estimating speed and position. Inductance-based
estimation determines inductance for each voltage phase and, from
this data, estimates position and speed, e.g., by monitoring a
change in phase current during each injected signal pulse. These
and other sensorless approaches will be appreciated by those of
ordinary skill in the art.
[0026] A time plot 40 is shown in FIG. 2 for example sensor-based
position signals usable by the controller 50 of FIG. 1 during the
low-speed portion of an operating range of the starter motor 18,
with time in seconds, t(s), depicted on the horizontal axis along
with angular position (.theta..sub.r) of the rotor 19, and BEMF for
each of three example electrical phases (BEMF A, BEMF B, BEMF C)
depicted on the vertical axis. As shown, traces H.sub.A, H.sub.B,
and H.sub.C correspond to three phases from an example Hall-effect
sensor embodiment of the position sensor(s) 36 shown in FIG. 1.
Thus, FIG. 2 depicts Hall-effect sensor signal correlation to the
measured rotor angle. Other low-cost sensor types would produce a
type-specific trace, and therefore the traces H.sub.A, H.sub.B, and
H.sub.C are intended as illustrative of the disclosed concepts.
[0027] For each electrical phase, each position sensor 36 of FIG. 1
has a corresponding output signal 44A, 44B, and 44C, i.e., traces
H.sub.A, H.sub.B, and H.sub.C, with corresponding rising and
falling edge associated with a given fixed angular position or
rotor angle (.theta..sub.r) of the rotor 19 or other rotatable
portion of the starter motor 18. For instance, for trace H.sub.A
the rising edge 41R corresponds to 0.degree. on a BEMF trace 42A,
and the falling edge 41F corresponds to 180.degree. on a BEMF trace
42A. Likewise, the rising edges 41R of traces H.sub.B and H.sub.C
correspond to 120.degree. and 240.degree., respectively, and the
falling edges 41F of traces H.sub.B and H.sub.C respectively
correspond to 300.degree. and 60.degree..
[0028] The angle difference between two consecutive signal edges is
thus used by the controller 50 to estimate a rotor speed
.omega..sub.r of the rotor 19 at or below a calibrated low speed of
the starter motor 18 of FIG. 1 as follows:
.omega. r = K .pi. 3 t 1 ##EQU00001##
where t.sub.1 is the time period between two closest edges, here
the rising edge 41R of trace H.sub.A and the falling edge 41F of
trace H.sub.C. The variable K is a constant used to convert rotor
speed. For instance, if rotor speed is angular velocity, K=1. If
rotor speed is stated in RPM, then
K = 2 .pi. 60 . ##EQU00002##
[0029] An example method 100 is depicted in FIG. 3 providing hybrid
sensor/sensorless control of a starting operation of the engine 20
within the powertrain 10 of FIG. 1. As part of the present control
strategy, the controller 50 measures the angular position
(.theta..sub.r) of the rotor 19 upon detection of every rising or
falling edge of traces H.sub.A, H.sub.B, and H.sub.C. That is, from
the detected signal edges 41R and 41F the controller 50 is able to
calculate the angular position (.theta..sub.r) of the rotor 19 as
follows:
.theta. r = .omega. r t + k 1 .omega. r 1 - .omega. r 2 t 1 t
##EQU00003##
where .omega..sub.r1 and .omega..sub.r2 are the rotational speeds
at two Hall-effect or other position signal edges defining the time
interval t.sub.1, and k1 is a constant calibration value in the
form of a coefficient of a second order equation. At every signal
edge 41R and 41F, therefore, the controller 50 resets the angular
position (.theta..sub.r) to a real predetermined value.
[0030] As noted above, the controller 50 executes the method 100 in
the overall torque control of the starter motor 18. In general, the
controller 50 is configured to control operation of the starter
motor 18 below a calibrated low threshold speed, e.g., about 1000
RPM or about 1500 RPM in different embodiments, using measured
angular position signals from the position sensor(s) 36. Below such
a threshold speed, the controller 50 uses the measured angular
position signals to calibrate the sensorless logic 55. Above the
threshold speed, the controller 50 determines the position and
speed of the starter motor 18 using the sensorless logic 55
alone.
[0031] FIG. 3 depicts an example embodiment of the method 100 for
hybrid sensor/sensorless control within the powertrain 10 of FIG.
1. After initialization (*) of the controller 50, when the starter
motor 18 has zero speed, the method 100 proceeds to step S102 where
the controller 50 receives raw angular position signals as measured
by the position sensor(s) 36. Other control signals may be received
at step S102, including for instance current and voltage signals
describing a level of power feed to the starter motor 18. The
method 100 then proceeds to step S104.
[0032] At step S104, the controller 50 uses the received angular
position signals from the position sensor(s) 36 of FIG. 1, i.e.,
measured signals, to determine the angular position/rotor position
.theta..sub.r and associated rotor speed .omega..sub.r of the rotor
19 as set forth above with reference to FIG. 2. The method 100 then
proceeds to step S106.
[0033] Step S106 entails estimating the rotor speed .omega..sub.r
and angular position .theta..sub.r using the sensorless logic 55
shown schematically in FIG. 1. As noted above with reference to
FIG. 2, various embodiments of the sensorless logic 55 may be used
within the scope of the present disclosure, e.g., a BEMF-based
methodology, an inductance-based methodology, or a high-speed
signal injection methodology in a few example embodiments. The
method 100 proceeds to step S107 once the rotor speed .omega..sub.r
and angular position .theta..sub.r have been estimated using the
sensorless logic 55.
[0034] Step S107 includes determining, via the controller 50,
whether or not to enable sensorless control of the starter motor
18, i.e., to transition away from use of real-time measurement of
the angular position via the position sensors 36 to real-time
estimation of the angular position using the sensorless logic 55.
Step S107 may entail comparing the speed of the rotor 19 to the
calibrated threshold speed. Step S108 is executed when the
rotational speed .omega..sub.r of the rotor 19 exceeds the
calibrated threshold speed. Below the calibrated threshold speed,
the controller 50 instead executes step S109.
[0035] At step S108, the controller 50 uses the estimated values
from step S106 to control torque output from the starter motor 18
to the engine 20. Typically, this entails delivering the motor
torque (arrow T.sub.M of FIG. 1) to the engine 20 via the flywheel
32 by operation of the solenoid 21, as part of an auto-start
function. However, other operating modes may be envisioned in which
motor torque (arrow T.sub.M of FIG. 1) is delivered to the engine
20 while the engine 20 is running. The method 100 is then complete
(**), starting anew with step S102.
[0036] At step S109, the controller 50 continues to control
operation of the starter motor 18 using the measured angular
position signals from the position sensor(s) 36 of FIG. 1. The
controller 50 determines whether a new or updated position signals
have been received. If so, the controller 50 executes step S110.
Otherwise, the controller 50 proceeds to step S111.
[0037] Step S110 includes calibrating the estimated rotor speed,
West, and the estimated rotor position, .theta..sub.est, using the
position signals from the sensors 36. For instance, the controller
50 may compare the position signals from the sensors 36 to the
estimated values from the sensorless logic 55 and force the
estimated values to converge with the measured values, e.g., in a
closed-loop approach in which variance from the measured values is
treated as error. The method 100 then proceeds to step S111.
[0038] At step S111, the controller 50 determines whether the rotor
speed, .omega..sub.r, as determined at step S104 exceeds a
calibrated threshold. The method 100 proceeds to step S112 when the
rotor speed (.omega..sub.r) exceeds the calibrated threshold speed.
Step S114 is executed in the alternative when the rotor speed
(.omega..sub.r) is less than the calibrated threshold speed.
[0039] At step S112, the controller 50 determines if the estimated
rotor position, .theta..sub.est, has converged. The method 100
proceeds to step S116 when convergence is detected. The method 100
proceeds in the alternative to step S114 when convergence has not
occurred.
[0040] Step S114 includes using the measured rotor position and
speed, i.e., .omega..sub.r and .theta..sub.r, respectively, in the
control of the starter motor 18. The method 100 is finished (**)
with step S114, commencing anew at step S102.
[0041] Step S116 includes enabling sensorless control of the
starter motor 18. In other words, the controller 50 discontinues
using real-time measured position and speed data from the positions
sensor(s) 36 of FIG. 1. Instead, the controller 50 uses the
sensorless logic 55 alone at speeds of the rotor 19 exceeding the
above-noted threshold speed. In this manner, the controller 50 is
able to achieve improved power performance and flux weakening
control of the starter motor 18. Additionally, the added cost of
relatively expensive absolute position sensors is eliminated.
[0042] While some of the best modes and other embodiments have been
described in detail, various alternative designs and embodiments
exist for practicing the present teachings defined in the appended
claims. Those skilled in the art will recognize that modifications
may be made to the disclosed embodiments without departing from the
scope of the present disclosure. Moreover, the present concepts
expressly include combinations and sub-combinations of the
described elements and features. The detailed description and the
drawings are supportive and descriptive of the present teachings,
with the scope of the present teachings defined solely by the
claims.
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