U.S. patent application number 15/967910 was filed with the patent office on 2019-11-07 for temperature control strategy for electric starter system with polyphase brushless starter motor.
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 | 20190338745 15/967910 |
Document ID | / |
Family ID | 68276565 |
Filed Date | 2019-11-07 |
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United States Patent
Application |
20190338745 |
Kind Code |
A1 |
Hao; Lei ; et al. |
November 7, 2019 |
TEMPERATURE CONTROL STRATEGY FOR ELECTRIC STARTER SYSTEM WITH
POLYPHASE BRUSHLESS STARTER MOTOR
Abstract
An electric starter system is usable with a powertrain having an
engine with a flywheel. The starter system includes a brushless
starter motor having a machine temperature, and a solenoid operable
for translating a pinion gear into meshed engagement with the
flywheel and the starter motor in response to a requested engine
start event. A controller has temperature regulation logic that
includes a proportional-integral torque control loop. Execution of
a method embodied by the logic, in response to the requested engine
start event when the machine temperature exceeds a first
temperature, causes the controller to determine a required starting
torque of the starter motor using the control loop. The controller
causes the starter motor to transmit the required starting torque
to the engine at a level that reduces the machine temperature below
the first temperature.
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: |
68276565 |
Appl. No.: |
15/967910 |
Filed: |
May 1, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F02N 15/06 20130101;
H02P 29/60 20160201; H02P 6/182 20130101; H02P 21/16 20160201; H02P
21/34 20160201; H02P 21/26 20160201; F02N 2200/045 20130101; F02N
2300/106 20130101; F02N 11/0851 20130101; F02N 11/106 20130101;
F16F 15/30 20130101; F02N 2011/0896 20130101; F02N 2300/104
20130101 |
International
Class: |
F02N 11/10 20060101
F02N011/10; F02N 11/08 20060101 F02N011/08; H02P 21/16 20060101
H02P021/16 |
Claims
1. An electric starter system for use with an internal combustion
engine having a flywheel, the electric starter system comprising: a
brushless starter motor having a machine temperature; a pinion
gear; a solenoid operable for translating the pinion gear into
meshed engagement with the flywheel to thereby connect the
brushless starter motor to the flywheel in response to a requested
engine start event; and a controller programmed with temperature
regulation logic having a proportional-integral (PI) torque control
loop; wherein execution of the temperature regulation logic by the
controller in response to the requested engine start event when the
machine temperature is greater than a first temperature, causes the
controller to determine a required starting torque of the brushless
starter motor, via the PI torque control loop, at a level that
reduces the machine temperature below the first temperature, to
command the solenoid to translate the pinion gear into the meshed
engagement with the flywheel, and to command delivery of the
required starting torque by the brushless starter motor to the
engine.
2. The electric starter system of claim 1, wherein the controller
is configured to abort the requested engine start event via the PI
torque control loop when the machine temperature is greater than a
second temperature that exceeds the first temperature.
3. The electric starter system of claim 1, wherein the brushless
starter motor is electrically connected to a power inverter module
(PIM), and wherein the controller is further configured to generate
or command pulse width modulation of the PIM to provide the
required starting torque at the level that reduces the machine
temperature below the first temperature.
4. The electric starter system of claim 1, further comprising at
least one temperature sensor positioned on or within the brushless
starter motor and configured to measure the machine
temperature.
5. The electric starter system of claim 1, where in the controller
includes a state observer operable for estimating the machine
temperature in real time.
6. The electric starter system of claim 1, wherein the PI torque
control loop uses a q-axis current command, a d-axis current
command, a q-axis feedback current value, and a d-axis feedback
current as inputs, applies an integral gain indexed or referenced
by the machine temperature, and generates a q-axis voltage command
and a d-axis voltage command to the starter motor as outputs.
7. The electric starter system of claim 6, wherein the PI torque
control loop also includes a flux linkage block that calculates a
back electromotive force of the starter motor as a product of an
angular speed and a flux leakage value of the starter motor, the
flux leakage value being based on the machine temperature, and
wherein the controller is configured to calculate the q-axis
voltage command using the back electromotive force.
8. A powertrain comprising: an internal combustion engine having a
flywheel; a transmission coupled to the engine; a load coupled to
the transmission; and an electric starter system that includes: a
brushless starter motor having a machine temperature; a pinion
gear; a solenoid operable for translating the pinion gear into
engagement with the flywheel and the brushless starter motor in
response to a requested engine start event; a pair of current
sensors operable for measuring a corresponding pair of phase
currents into the brushless starter motor; and a controller in
communication with the pair of current sensors and programmed with
temperature regulation logic, the temperature regulation logic
including a proportional-integral (PI) torque control loop; wherein
execution of the temperature regulation logic in response to the
requested engine start event, when the machine temperature is
greater than a first temperature, causes the controller to
determine a required starting torque of the starter motor using the
PI torque control loop, and further causes the controller to
transmit a torque command to the starter motor to cause the starter
motor to transmit the required starting torque to the engine at an
adjusted level that reduces the machine temperature below the first
temperature.
9. The powertrain of claim 8, wherein the load is a set of drive
wheels.
10. The powertrain of claim 8, wherein the controller is configured
to abort the requested engine start event via the temperature
regulation logic when the machine temperature is greater than a
second temperature that is higher than the first temperature.
11. The powertrain of claim 8, wherein the brushless starter motor
is electrically connected to a power inverter module (PIM), and
wherein the controller is further configured to generate or command
pulse width modulation of the PIM to reduce the machine temperature
below the first temperature.
12. The powertrain of claim 8, further comprising at least one
temperature sensor positioned on or within the starter motor and
configured to measure the machine temperature.
13. The powertrain of claim 8, where in the controller includes a
state observer operable for estimating the machine temperature in
real time.
14. The powertrain of claim 8, wherein the PI torque control loop
uses a q-axis current command, a d-axis current command, a q-axis
feedback current value, and a d-axis feedback current value as
inputs, applies an integral gain indexed or referenced by the
machine temperature, and generates a q-axis voltage command and a
d-axis voltage command to the starter motor as outputs.
15. The powertrain of claim 8, wherein the PI torque control loop
also includes a flux linkage block that calculates a back
electromotive force of the starter motor as a product of an angular
speed and a flux leakage value of the starter motor, the flux
leakage value being based on the machine temperature, and wherein
the controller is configured to calculate the q-axis voltage
command using the back electromotive force.
16. A method for regulating temperature of an electric starter
system having a brushless starter motor, the method comprising:
detecting, via a controller, a requested engine start event of an
internal combustion engine in which a solenoid translates a pinion
gear into meshed engagement with the brushless starter motor and a
flywheel of the engine; determining a machine temperature of the
brushless starter motor using the controller; in response to the
requested engine start event when the machine temperature is
greater than a first temperature, determining a required starting
torque of the starter motor using a proportional-integral torque
control loop of the controller, the required starting torque being
a value that limits an output power level of the starter motor to a
level sufficient for reducing the machine temperature below the
first temperature; and transmitting a torque command to the starter
motor to cause the starter motor to transmit the required starting
torque to the flywheel of the engine via the pinion gear.
17. The method of claim 16, further comprising: aborting the
requested engine start event via the controller when the machine
temperature is greater than a second temperature that is higher
than the first temperature.
18. The method of claim 16, further comprising determining, via the
controller, a q-axis current command, a d-axis current command, a
q-axis feedback current value, and a d-axis feedback current value
as control inputs to the proportional-integral torque control loop,
applying an integral gain indexed or referenced by the machine
temperature, and generating a q-axis voltage command and a d-axis
voltage command to the starter motor via the controller as control
outputs.
19. The method of claim 18, further comprising: using a flux
linkage block of the PI control loop to calculate a back
electromotive force of the starter motor as a product of an angular
speed and a flux leakage value of the starter motor, the flux
leakage value being based on the machine temperature; and
calculating the q-axis voltage command using the back electromotive
force.
20. The method of claim 16, including at least one temperature
sensor connected to or within the starter motor, wherein
determining a machine temperature of the brushless starter motor
includes directly measuring the machine temperature via the at
least one temperature sensor.
Description
INTRODUCTION
[0001] Powertrains, power plants, and other systems 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 power transmission arrangement,
e.g., one or more planetary gear sets. In some powertrain
configurations, an electric machine referred to as a starter motor
may be used to support a cranking and starting function of the
engine, such as when automatically restarting the engine after a
fuel-conserving engine auto-stop event. A rotor of the starter
motor may be connected to an engine crankshaft, such as via a
meshed gear engagement with a flywheel. Motor torque from the
starter motor is thereafter used to accelerate the engine to a
threshold starting speed. The starter motor is then disconnected
from the engine once the engine has started and is able to sustain
a threshold idle speed.
SUMMARY
[0002] An electric starter system is disclosed herein. The electric
starter system, which is configured for use with a powertrain or
other system having an internal combustion engine, includes a
solenoid, a translatable pinion gear, and a polyphase brushless
starter motor having a rotor and a ring gear. The brushless starter
motor is selectively connectable to a flywheel of the engine via
operation of the solenoid in response to a requested engine start
event. Translation of the pinion gear by action of the solenoid
places the pinion gear in meshed engagement with the ring gear and
the flywheel. In this manner, motor torque from the starter motor
is delivered to the flywheel via rotation of the interposed pinion
gear.
[0003] The electric starter system also includes an electronic
controller. One or more temperature sensors may be optionally
connected to the brushless starter motor, such as to a pair of
phase windings and/or a lamination slot or other physical structure
of the brushless starter motor. The temperature sensors output
electronic signals indicative of a temperature level of the
brushless starter motor, with the temperature referred to herein as
the machine temperature. Alternatively, a state observer residing
within the controller or in a separate control device may be used
to estimate the machine temperature in real time.
[0004] The controller is configured to regulate temperature of the
starter motor by automatically limiting the starter motor's output
power, and thus its motor torque, based on machine temperature. To
do this, the controller is programmed with proportional-integral
(PI) control logic forming a torque control loop. Heat within the
starter motor tends to increase when the starter motor operates at
a combination of low speed and high torque. The
low-speed/high-torque operating mode is typically present during an
automatic restart event of the engine. Thus, the controller uses a
temperature-profiled methodology to regulate the machine
temperature during such a low-speed/high-torque operating mode.
[0005] Execution of temperature regulation logic in response to the
requested engine start event ultimately causes the controller to
determine a required starting torque of the starter motor, and to
transmit a torque command to the starter motor to cause the starter
motor to transmit the required starting torque to the engine. The
required starting torque has a value that, via operational of the
programmed logic, automatically limits output power of the starter
motor based on the machine temperature, thereby maintaining the
machine temperature within a permissible range.
[0006] Within the disclosed PI control loop, integral gain is
affected by machine temperature, and therefore the integral gain in
the control loop is automatically modified as machine temperature
changes. The integral gain may be, in various embodiments, a
1.sup.st order function of machine temperature or determined by
accessing a lookup table populated or referenced by machine
temperature. Rotor flux within the starter motor is likewise
closely related to machine temperature, and therefore is also
considered as a control parameter within the control loop. As with
the integral gain, rotor flux may be determined mathematically or
via a lookup table. Additionally, as terminal voltage of the
starter motor varies with changing machine temperature, such a
value may also be used by the controller in the overall control of
the starter motor.
[0007] In a possible embodiment, an electric starter system
includes a brushless starter motor having a machine temperature, a
solenoid operable for translating a pinion gear into meshed
engagement with a flywheel of an engine to thereby connect the
brushless starter motor to the flywheel in response to a requested
engine start event, and a controller. The controller is programmed
with temperature regulation logic having a PI torque control
loop.
[0008] Execution of the temperature regulation logic by the
controller in response to the requested engine start event, when
the machine temperature is greater than a first temperature, causes
the controller to determine a required starting torque of the
brushless starter motor, via the PI torque control loop, at a level
that reduces the machine temperature below the first temperature.
The controller also commands the solenoid to translate the pinion
gear into the meshed engagement with the flywheel, and to command
delivery of the required starting torque by the brushless starter
motor to the engine.
[0009] The controller may abort the requested engine start event
via the PI torque control loop when the machine temperature is
greater than a second temperature that exceeds the first
temperature.
[0010] The brushless starter motor may be electrically connected to
a power inverter module (PIM). In such an embodiment, the
controller may be configured to generate or command pulse width
modulation of the PIM to provide the required starting torque at
the level that reduces the machine temperature below the first
temperature.
[0011] The electric starter system may include at least one
temperature sensor positioned on or within the brushless starter
motor and configured to measure the machine temperature.
Alternatively, the controller may include a state observer operable
for estimating the machine temperature in real time.
[0012] The controller, via the PI torque control loop, may use a
q-axis current command, a d-axis current command, a q-axis feedback
current value, and a d-axis feedback current value as inputs, apply
an integral gain indexed or referenced by the machine temperature,
and generate a q-axis voltage command and a d-axis voltage command
to the starter motor as outputs.
[0013] The PI torque control loop may also include a flux linkage
block that calculates a back electromotive force (back-EMF) of the
brushless starter motor as a product of an angular speed and a flux
leakage value of the starter motor, with the flux leakage value
being based on the machine temperature. The controller is
configured in such an embodiment to calculate the q-axis voltage
command using the back-EMF.
[0014] A powertrain is also disclosed herein. An embodiment of the
powertrain includes an internal combustion engine having a
flywheel, a transmission coupled to the engine, a load coupled to
the transmission, and the electric starter system.
[0015] A method is also disclosed for regulating temperature of an
electric starter system having a brushless starter motor. The
method may include detecting, via a controller, a requested engine
start event of an internal combustion engine in which a solenoid
translates a pinion gear into meshed engagement with the brushless
starter motor and the engine. The method may also include
determining a machine temperature of the brushless starter motor
using the controller. In response to the requested engine start
event when the machine temperature is greater than the first
temperature, the method may further include determining a required
starting torque of the starter motor using a PI torque control loop
of the controller. The required starting torque is a value that
limits an output power level of the starter motor to a level
sufficient for reducing the machine temperature below a first
temperature. The controller then transmits a torque command to the
starter motor to cause the starter motor to transmit the required
starting torque to the flywheel of the engine via the pinion
gear.
[0016] 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
[0017] FIG. 1 is a schematic illustration of an example powertrain
having a polyphase brushless starter motor whose machine
temperature is used in a proportional-integral (PI) torque
control/feedback loop during an engine auto-start event as set
forth herein.
[0018] FIG. 2 is a plot of electrical current and rotational speed
performance values of the starter motor shown in FIG. 1, with
electrical current and rotational speed depicted on the vertical
axis and time depicted on the horizontal axis.
[0019] FIG. 3 is a schematic logic flow diagram describing an
exemplary implementation of temperature regulation logic usable
with the electric starter system of FIG. 1.
[0020] FIG. 4 is a flow chart describing an example embodiment of a
method for regulating machine temperature of the starter motor
shown in FIG. 1, particularly during an engine start event.
[0021] 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
[0022] 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 may 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 a given one of the figures may be combinable with
features illustrated in one or more other figures in order 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.
[0023] Referring to the drawings, wherein like reference numbers
refer to the same or like components in the several Figures, a
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 electric
starter system 12 includes and/or is controlled via a controller
(C) 50. The controller 50 is configured to execute a temperature
regulation method 100 in the overall control of a torque operation
of a polyphase/alternating current (AC) brushless electric machine,
hereinafter referred to as brushless starter motor (M.sub.BL) 18.
Thus, torque feedback control of the starter motor 18 is
automatically performed by the controller 50 in order to regulate
the temperature of the brushless starter motor 18 in the manner set
forth below.
[0024] The brushless starter motor 18 may be variously configured
as a surface permanent magnet machine, an internal permanent magnet
machine, a drag-cup 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.
[0025] The engine 20, which may be embodied as a gasoline or diesel
engine, ultimately outputs engine torque to an output shaft 24. The
output shaft 24 may be coupled to a transmission (T) 22, such as
via a hydrodynamic torque converter or clutch (not shown). The
transmission 22 may be embodied as one or more planetary gear sets,
a gear box, or a continuously-variable arrangement, ultimately
delivers output torque at a suitable gear or speed ratio 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 beneficial applications for the
powertrain 10 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.
[0026] The engine 20 of FIG. 1 also includes a crankshaft 31 that
is mechanically coupled to a flywheel 32. When the engine 20 is not
running, such as after a fuel-conserving auto-stop event of the
engine 20 or when cruising with the engine 20 turned off, the
electric starter system 12 may be electrically energized in
response to starter control signals (arrow CC.sub.S) from the
controller 50 so as to selectively command delivery of motor torque
(arrow T.sub.M) to the engine 20 via the flywheel 32.
[0027] A solenoid (S) 21 may be included as part of the electric
starter system 12 for this purpose. The solenoid 21 according to an
exemplary embodiment is disposed between a rotor 19 of the
brushless 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. Alternatively, a fixed ring gear (not shown) may
be coupled to the rotor 19, with the solenoid 21 translating a
pinion gear 33 into and out of engagement with the flywheel 32 and
such a ring gear. A position sensor 36, e.g., a Hall-effect sensor,
multiplying rotary encoder, inductive sensor, or reluctance sensor,
may be used to measure and output an angular position (arrow
P.sub.19) of the rotor 19, which the controller 50 may use to
determine an angular position and rotational speed of the rotor
19.
[0028] In a possible embodiment, when the solenoid 21 is energized
in response to the starter control signals (arrow CC.sub.S), the
solenoid 21 linearly translates the pinion gear 33 to the position
indicated at 33A, and thus into direct meshed engagement with
mating teeth or splines on the flywheel 32 and/or a gear element
connected thereto. Once the engine 20 has started and runs at a
speed sufficient to sustain its fueling and internal combustion
process, the starter control signals (arrow CC.sub.S) are
discontinued. As a result of this action, the solenoid 21 is
de-energized. The pinion gear 33 is then urged out of engagement
with the flywheel 32 via 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.
[0029] 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 the DC voltage
bus 15, e.g., a 12-48 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
includes semiconductor switching pairs, e.g., MOSFETs, which are
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.
[0030] In turn, the AC voltage bus 17 is electrically connected to
individual phase windings internal to the brushless starter motor
18. Phase current sensors 13 may be positioned on two or more phase
windings or leads of the brushless starter motor 18 as shown, with
measured phase currents (arrow I.sub.PH) transmitted to the
controller 50. The starter motor 18 may be configured such that a
calibrated back electromotive force results for a given performance
range, e.g., 3-5V at 6000 RPM, or other values ensuring that
sufficient motor torque (arrow T.sub.M) is available for starting
the engine 20, e.g., 5-7 Nm within parameters of the DC voltage bus
15.
[0031] In accordance with the present disclosure, the controller 50
of FIG. 1 is configured to regulate machine temperature of the
brushless starter motor 18 within a permissible temperature range
during and after conducting an automatic start event of the engine
20. To this end, at least one temperature sensor 11 may be
positioned within the starter motor 18 and configured to measure
and transmit a temperature signal (arrow T.sub.18) indicative of
the machine temperature. The temperature sensor 11, for instance a
thermocouple or a thermistor, may be positioned at an end-turn of a
given phase winding (not shown) of the starter motor 18. Another
temperature sensor 11 may be positioned within a lamination slot
(not shown) of the starter motor 18. Alternatively, the temperature
sensors 11 may be omitted in favor of a real-time estimated
temperature, e.g., via a state observer of the controller 50.
However the machine temperature is ultimately determined, the
machine temperature is used as part of a set of input signals
(arrow CC.sub.I) to the controller 50.
[0032] The controller 50 may be variously implemented as one or
more control devices collectively managing the motor torque (arrow
T.sub.M) from the brushless starter motor 18 within the example
electric starter system 12, with the controller 50 performing this
task using temperature regulation logic 150L according to a method
100, an example of which is shown as 150L 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 underlying algorithms or code embodying
the method 100 described below, and transmit commands to the
electric starter system 12 to enable performance of certain control
actions according to the present disclosure.
[0033] The controller 50 is in communication with the engine 20 and
also receives, as part of the input signals (arrow CC.sub.I),
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 brushless 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. In addition to
transmitting a torque request to the starter motor 18 via the
starter control signals (arrow CC.sub.S), the controller 50 also
transmits output signals (arrow CC.sub.O) to the engine 20 and
transmission 22 and motor control signals (arrow CC.sub.M) to the
starter motor 18 as part of the overall operating function of the
controller 50.
[0034] Referring to FIG. 2, a representative time plot 40 is shown
for rotational speed N.sub.18 of the brushless starter motor 18,
i.e., trace 42, and for machine current IDC, i.e., trace 44. Speed
in RPM and current in amps (A) are depicted on the vertical axis,
with time in seconds, i.e., t(s), depicted on the horizontal axis.
The brushless starter motor 18 of FIG. 1 is located in proximity to
the engine 20, and thus temperature around the brushless starter
motor 18 is subject to substantial variation under normal operating
conditions. Depending on the severity, such temperature variation,
absent the present method 100, may result in inconsistent
performance of the brushless starter motor 18 and/or difficulty
starting the engine 20.
[0035] Additionally, heat tends to be generated early in a starting
sequence when the brushless starter motor 18 is operating at low
speeds and high torque levels, e.g., 0-7000 RPM. That is, from
t.sub.0 to t.sub.1 in FIG. 2, the starter motor 18 is at zero
speed, such that no current flows through the starter motor 18 and
no heat is generated. Cranking of the engine 20 commences at
t.sub.1 with a rapid increase in current feed to the phase windings
of the brushless starter motor 18 of FIG. 1, as indicated by the
rapidly rising trajectory of trace 42 and the peak current of trace
44, with a large amount of heat generated. Cranking of the engine
20 of FIG. 1 continues between t.sub.1 and t.sub.2 until the engine
20 starts. The starter motor 18 is then turned off at t.sub.2, with
the rotational speed N.sub.18 (trace 42) thereafter decaying as the
starter motor 18 is turned off and the solenoid 21 disengages the
pinion gear 33 of FIG. 1.
[0036] The controller 50 is programmed to consider and compensate
for undesirable temperature effects due to rising machine
temperature within or around the brushless starter motor 18 of FIG.
1. Phase windings of the starter motor 18 are typically constructed
of copper, which is an element having a temperature coefficient of
0.393 percent (%) per degree Celsius (.degree. C.). Thus, the
internal resistance of conductive portions of the starter motor 18
varies by 0.393% for every 1.degree. C. change in the machine
temperature. Since the machine temperature can easily vary anywhere
between -40.degree. C. and 180.degree. C. during normal operation
of the electric starter system 12 of FIG. 1, the controller 50 uses
the logic 150L detailed in FIG. 3 to compensate in real time for
such temperature changes.
[0037] As shown in FIG. 3, the temperature regulation logic 150L
may have, as different inputs, a commanded quadrature axis/q-axis
current (I.sub.q) and a direct axis/d-axis current (I.sub.d) needed
to achieve a required torque and rotational speed of the brushless
starter motor 18, feedback currents (I.sub.q,FB) and (I.sub.d,FB),
and integrator scales (V.sub.q,SC) and (V.sub.d,SC). As understood
in art of synchronous electric machines, in a rotating d-q frame of
reference the d-axis coincides with an axis of the rotor 19. The
q-axis is perpendicular to the d-axis. The controller 50 is thus
configured to transmit a d-axis and q-axis current command to the
starter motor 18 in order to control a torque operation of the
starter motor 18.
[0038] The feedback currents (I.sub.q,FB) and (I.sub.d,FB) may be
calculated by the controller 50 in real time. For instance, two
phase currents, such as for phases A and B, are measured via the
current sensors 13 shown in FIG. 1 and transmitted to the
controller 50. The controller 50 then transforms the measured phase
currents into the corresponding feedback current (I.sub.q,FB) or
(I.sub.d,FB). For instance, the controller 50 may perform a
stationary-to-synchronous frame transformation, i.e., a Cartesian
"ABC" frame to a rotating machine "dq" frame transformation.
[0039] The integrator scales (V.sub.q,SC) and (V.sub.d,SC) are
values that may also be calculated by the controller 50 of FIG. 1.
For instance, with a maximum d-axis control voltage being a
predicted value, or a preset value such as between 0.9 to 0.97 of a
peak phase voltage, then the maximum q-axis control voltage may be
calculated by the controller 50, i.e.;
Vq= {square root over (V.sub.S.sup.2-V.sub.d.sup.2)}
where V.sub.q is the maximum q-axis control voltage, V.sub.d is the
maximum d-axis control voltage, and V.sub.S is the peak phase
voltage. If the maximum d-axis control voltage (V.sub.d) exceeds
the peak phase voltage, i.e., if V.sub.d>V.sub.S, then the
derivative scale
V d , sc = V S V d . ##EQU00001##
However, when the maximum q-axis control voltage V.sub.q exceeds
the peak phase voltage V.sub.S, then the integrator scale
V q , sc = V S V q . ##EQU00002##
Otherwise, the integrator scale V.sub.q,sc is equal to 1. Both the
output voltage limitation and integrator scale (V.sub.q,sc) use the
peak phase voltage (V.sub.S). However, peak phase voltage (V.sub.S)
varies with machine temperature. For a low-voltage starter motor 18
such as a 12V starter motor, the phase voltage drop due to cable
and battery, e.g., a 1V difference between a cold and hot engine
20, has a significant impact. The controller 50 therefore employs
the following compensation to minimize the temperature effect:
V.sub.S=V.sub.B-I.sub.PH(R.sub.C+R.sub.B)
where V.sub.B is the voltage of battery pack 14, I.sub.PH is the
phase current on the AC voltage bus 17, R.sub.C is the resistance
of a length of cable connecting the battery pack 14 to the PIM 16,
and R.sub.B is the internal resistance of the battery pack 14, with
R.sub.C and R.sub.B both being temperature dependent values.
[0040] As shown in FIG. 3, the illustrated logic 150L may include a
q-axis control loop 150q and a d-axis control loop 150d, with the
control loops 150q and 150d being cross-coupled as set forth below.
In the q-axis control loop 150q, a q-axis feedback current
(I.sub.q,FB) is subtracted from a q-axis current command (I.sub.q)
at node 45 to generate an adjusted q-axis current command 46. The
adjusted q-axis current command 46 is then fed into a temperature
independent proportional gain block (Kpq) 54 and an integrator
block
( 1 S ) ##EQU00003##
52. The output of proportional gain block 54 is fed into a
saturation block 58, which in turn applies calibrated upper and
lower limits to the output of the proportional gain block 54. This
limited voltage value (V.sub.1) is fed into another summation block
64.
[0041] The output of the integrator block 52 is fed, along with the
integrator scale (V.sub.q,SC) noted above, into a limiter block
152. Like the saturation block 58 described above, the limiter
block 152 in the integral loop of the depicted q-axis control loop
150q applies upper and lower limits to the output of the integrator
block 52. The output of integrator block 52, along with the
integrator scale (V.sub.q,SC), are multiplied together at
multiplier block 55, with this result processed through separate
integral gain blocks 56 and 57. The integrator gain block 57 is a
cross-coupled gain block that is independent of machine
temperature, while the integrator block 56 is a
temperature-dependent gain value, with both values possibly
extracted from a lookup table in memory (M) of the controller 50 or
calculated by the controller 50 using the processor (P) of FIG.
1.
[0042] The output (trace 60) of temperature-independent integrator
gain block 57 is fed into node 161 as a cross-couple term into the
d-axis control loop 150d. At the same time, the output of
integrator gain block 56 is added to another cross-coupled term
that is output (trace 160) from the d-axis control loop 150d as
explained below. The sum at node 61 is fed into the summation node
164 as another voltage value V.sub.2 and added to the limited
output of saturation block 58, i.e., the voltage value V.sub.1
noted above.
[0043] An additional input to the summation block 64 is a
temperature-dependent terminal voltage value calculated by the
controller 50 to properly compensate for temperature effects on
magnetic flux density of the starter motor 18. Magnetic flux
density varies by about 30% over a typical operating temperature
range of the starter motor 18. For instance, at -40.degree. C. the
flux density may be about 1.29, decreasing to 1 at about
180.degree. C. Since flux linkage is directly related to magnetic
flux density, the controller 50 is configured to compensate
directly for such temperature-based changes in the flux linkage,
doing so at flux linkage block 62.
[0044] That is, by using flux linkage block 62, the controller 50
multiples the product of the angular speed of the rotor 19 of
brushless starter motor 18 (see FIG. 1), i.e., N.sub.18 of FIG. 1,
and k, i.e., a flux leakage constant extracted from a lookup table
based on machine temperature, or calculated in real time based on
changes in machine temperature. Thus, the flux linkage block 62
determines the product of angular speed and flux linkage to
generate, as a third voltage value V.sub.3, the back-electromotive
force (back-EMF) of the starter motor 18.
[0045] The final output voltage of summation block 64, i.e.,
V.sub.1+V.sub.2+V.sub.3, may be used by the controller 50 as the
synchronous q-axis control voltage (Vq). The controller 50 may
control internal switching operation of the PIM 16 of FIG. 1 in
order to apply the synchronous q-axis control voltage (V.sub.q) to
the brushless starter motor 18, as will be appreciated by one of
ordinary skill in the art.
[0046] FIG. 3 also depicts implementation for the d-axis. That is,
the feedback current (I.sub.d,FB) is subtracted from the d-axis
current command (I.sub.q) at node 145 to generate an adjusted
d-axis current command 146. The adjusted d-axis current command 146
is fed into a temperature-independent proportion gain block (Kpd)
154 and an integrator block
( 1 S ) ##EQU00004##
152. The output of the proportional gain block 154 is then fed into
a saturation block 158, which applies calibrated upper and lower
limits to the output of the proportional gain block 154. This
limited voltage value (V.sub.4) is fed into a summation block
164.
[0047] The output of the integrator block 152 is fed, along with
the derivative scale (V.sub.d,SC) noted above, into a limiter block
252, which applies upper and lower limits to the output of the
integrator block 152. The output of integrator block 152, along
with the derivative scale (V.sub.d,SC), are multiplied together at
multiplier block (X) 155, with this result processed through
separate integral gain blocks 156 and 157. Gain block (Kidc) 157
is, like block 57 in the q-axis control loop 150q, a cross-coupled
gain block that is independent of machine temperature. Block 156
applies a temperature-dependent gain value, with the gains of
blocks 156 and 157 possibly being extracted from a lookup table
stored in memory (M) of the controller 50 or calculated by the
controller 50. The output (trace 160) of integrator gain block 157
is then fed into node 61 of the q-axis control loop 150q. At the
same time, the output (trace 60) of block 57 within the q-axis
control loop 150q is subtracted from the output of block 156 within
the d-axis control loop 150d at node 161. The difference at node
161 is fed into summation node 164 as another voltage value
V.sub.5, and added at summation node 164 to the limited output of
saturation block 158, i.e., the voltage value V.sub.4.
[0048] The final output voltage of summation block 164 within the
d-axis control loop 150d, i.e., V.sub.4+V.sub.5, is thereafter used
by the controller 50 as the synchronous d-axis control voltage
(V.sub.d). The controller 50 may control internal switching
operation of the PIM 16 of FIG. 1 in order to apply the synchronous
d-axis control voltage (V.sub.d) to the brushless starter motor 18,
as will be appreciated by one of ordinary skill in the art.
[0049] FIG. 4 is a flow chart describing a possible embodiment of
the method 100 for regulating machine temperature of the brushless
starter motor 18 shown in FIG. 1. Normally, the starter motor 18
will include stator windings and a permanent magnet or a conductive
bar within the rotor 19. The permitted operating temperature of the
starter motor 18 is largely determined by the material properties
of such hardware components. Therefore, the controller 50 shown in
FIG. 1 is configured to automatically limit the machine temperature
via active torque control of the starter motor 18 so as to protect
the hardware components of the starter motor 18 from undesirable
temperature effects, particularly when operating under
low-speed/high-torque operating conditions.
[0050] Beginning at step S102 of FIG. 4, upon initialization (**)
of the controller 50 of FIG. 1, the controller 50 determines the
machine temperature, e.g., via direct measurement using the
temperature sensors 11 to output the temperature signal (T.sub.18),
or via estimation using a state observer. The method 100 proceeds
to step S104 when the machine temperature has been determined.
[0051] Step S104 includes comparing the machine temperature
determined at step S102 to a first temperature, i.e., a first
calibrated threshold (CAL1). The first temperature may be a maximum
operating temperature short of a higher shutdown temperature limit,
as detailed in step S106, e.g., at an upper end of a normal
permissible operating temperature range. The method 100 proceeds to
step S106 when the machine temperature exceeds the first
temperature. The method 100 is otherwise finished *** when the
machine temperature is less than the first temperature.
[0052] At step S106, the controller 50 next compares the
temperature signal (T.sub.18) or an estimated variant thereof,
indicative of the machine temperature, to a second temperature,
i.e., a second calibrated threshold (CAL2), corresponding to a
maximum permissible machine temperature. The second temperature may
correspond to a maximum temperature above which the performance
and/or structural integrity of the starter motor 18 is likely to be
compromised. The method 100 proceeds to step S108 when the machine
temperature from step S102 exceeds the second temperature. The
method 100 otherwise proceeds to step S110.
[0053] At step S108, the controller 50 enforces a condition in
which the motor torque (T.sub.M) that is commanded from the
brushless starter motor 18 is set to zero. Effectively, execution
of step S108 aborts or prevents further execution of an auto-start
event of the engine 20 in order to protect the hardware of the
electric starter system 12 of FIG. 1. Coupled with this control
action, the controller 50 may record a diagnostic code in its
memory (M) indicative of the aborted auto-start event, and may take
other actions such as alerting an operator of the powertrain 10 of
FIG. 1 with a text message and/or indicator signal. The method 100
is then finished (***).
[0054] Step S110 includes commanding a level of machine power
(P.sub.M) from the starter motor 18 of FIG. 1 at a limited level,
i.e., P.sub.M=LIM. Step S110 may include applying a multiplier to a
normal power level of the brushless starter motor 18, with the
multiplier possibly being extracted by the controller 50 from a
lookup table indexed or reference by machine temperature, or by a
delta temperature relative to a starting temperature.
[0055] Using the method 100 described above in conjunction with the
electric starter system 12 of FIG. 1, PI control as descried above
may be implemented by a control loop in which particular attention
is paid to temperature effects on the brushless starter motor 18 of
FIG. 1. An integral gain applied within the context of FIG. 3 is
temperature-dependent, with temperature effects on rotor flux and
machine resistance also considered. Ultimately, the controller 50
selectively limits output power of the starter motor 18 during an
auto-start event of the engine 20, using the above-described
factors, so as to protect the constituent hardware of the electric
starter system 12.
[0056] 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.
* * * * *