U.S. patent application number 16/928715 was filed with the patent office on 2022-01-20 for vehicle powertrain control system.
The applicant listed for this patent is FORD GLOBAL TECHNOLOGIES, LLC. Invention is credited to Fengyi Chen, Weitian Chen, Yuji Fujii, Bradley Dean Riedle, Yijing Zhang.
Application Number | 20220018403 16/928715 |
Document ID | / |
Family ID | 1000006062703 |
Filed Date | 2022-01-20 |
United States Patent
Application |
20220018403 |
Kind Code |
A1 |
Zhang; Yijing ; et
al. |
January 20, 2022 |
VEHICLE POWERTRAIN CONTROL SYSTEM
Abstract
A vehicle includes a transmission, an engine, a disconnect
clutch, an inertial measurement unit, and a controller. The
transmission has an input shaft and an output shaft. The engine is
configured to generate and deliver torque to the input shaft. The
disconnect clutch is configured to connect and disconnect the
engine from the input shaft. The disconnect clutch is also
configured to crank the engine during an engine start. The inertial
measurement unit is configured to measure inertial forces exerted
onto the vehicle. The controller is programmed to, in response to a
command to adjust a torque of the disconnect clutch to a desired
value that is derived from the inertial forces and a vehicle
velocity, drive the clutch actuator pressure to a value that
corresponds to the desired value.
Inventors: |
Zhang; Yijing; (Canton,
MI) ; Chen; Fengyi; (Dearborn, MI) ; Riedle;
Bradley Dean; (Northville, MI) ; Chen; Weitian;
(Windsor, CA) ; Fujii; Yuji; (Ann Arbor,
MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FORD GLOBAL TECHNOLOGIES, LLC |
Dearborn |
MI |
US |
|
|
Family ID: |
1000006062703 |
Appl. No.: |
16/928715 |
Filed: |
July 14, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F16D 2500/1066 20130101;
F16D 2500/3108 20130101; F16D 2500/50808 20130101; F16D 2500/3024
20130101; F16D 2500/50287 20130101; F16D 2500/70406 20130101; F16D
2500/1026 20130101; F16D 2500/70684 20130101; F16D 2500/70605
20130101; F16D 2500/70668 20130101; F16D 48/066 20130101 |
International
Class: |
F16D 48/06 20060101
F16D048/06 |
Claims
1. A vehicle comprising: a powertrain having, a transmission having
an input and an output, an engine configured to generate and
deliver torque to the input, an electric machine configured to
generate and deliver torque to the input, and a disconnect clutch
configured to connect and disconnect the engine from the input, and
to crank the engine during an engine start; an inertial measurement
unit configured to measure inertial forces exerted onto the
vehicle; and a controller programmed to, in response to a demanded
torque at the output, control the torque at the output based on a
mapped relationship between the inertial forces and a vehicle
velocity, wherein the mapped relationship between the inertial
forces and the vehicle velocity utilizes first, second, third, and
fourth mapping parameters, in response to a command to start the
engine, close the disconnect clutch to start the engine, calculate
the torque of the disconnect clutch based on the controlled torque
at the output and an electric machine torque, and map the
relationship between the torque of the disconnect clutch and a
clutch actuator pressure to derive or adjust a transfer function
that represents the relationship between the torque of the
disconnect clutch and the clutch actuator pressure, and in response
to a command to adjust the torque of the disconnect clutch to a
desired value, adjust the clutch actuator pressure to a value that
corresponds to the desired value according to the transfer
function.
2. The vehicle of claim 1, wherein the controller is configured to
derive or adjust the transfer function utilizing a Kalman
filter.
3. The vehicle of claim 1, wherein the controller is configured to
derive or adjust the transfer function utilizing a recursive least
square method.
4. The vehicle of claim 1, wherein the controller is configured to
derive or adjust the transfer function utilizing a batch mode
regression method.
5. The vehicle of claim 1, wherein the controller is configured to
derive or adjust the transfer function only during engine starts
that correlate with a steady state condition of the vehicle.
6. The vehicle of claim 5, wherein the steady state condition of
the vehicle corresponds to a non-braking condition of the
vehicle.
7. The vehicle of claim 5, wherein the steady state condition of
the vehicle corresponds to a non-shifting condition of the
transmission.
8. The vehicle of claim 5, wherein the steady state condition of
the vehicle corresponds to a pre-determined range of steering
condition of the vehicle.
9. A vehicle comprising: a transmission having an input shaft and
an output shaft; an engine configured to generate and deliver
torque to the input shaft; a disconnect clutch configured to
connect and disconnect the engine from the input shaft, and to
crank the engine during an engine start; an inertial measurement
unit configured to measure inertial forces exerted onto the
vehicle; and a controller programmed to, in response to a command
to adjust a torque of the disconnect clutch to a desired value that
is derived from the inertial forces and a vehicle velocity, drive a
clutch actuator pressure to a value that corresponds to the desired
value.
10. The vehicle of claim 9, wherein the controller is further
programmed to, map the relationship between the torque of the
disconnect clutch and the clutch actuator pressure based on the
inertial forces and the vehicle velocity to derive or adjust a
transfer function that represents the relationship between the
torque of the disconnect clutch and the clutch actuator
pressure.
11. The vehicle of claim 10, wherein the controller is configured
to derive or adjust the transfer function utilizing a Kalman
filter, a recursive least square method, or a batch mode regression
method.
12. The vehicle of claim 10, wherein the controller is configured
to derive or adjust the transfer function during engine starts that
correlate with a steady state condition of the vehicle.
13. The vehicle of claim 12, wherein the steady state condition of
the vehicle corresponds to a non-braking condition of the
vehicle.
14. The vehicle of claim 12, wherein the steady state condition of
the vehicle corresponds to a non-shifting condition of the
transmission.
15. The vehicle of claim 12, wherein the steady state condition of
the vehicle corresponds to a pre-determined range of steering
condition of the vehicle.
16. A vehicle comprising: a transmission having an input and an
output; an engine and an electric machine, each configured to
generate and deliver torque to the input; a disconnect clutch
configured to connect and disconnect the engine from the input, and
to crank the engine during an engine start; an inertial measurement
unit configured to measure inertial forces exerted onto the
vehicle; and a controller programmed to, in response to a demanded
torque at the output, control the torque at the output based on a
mapped relationship between the inertial forces and a vehicle
velocity, in response to a command to start the engine, close the
disconnect clutch to start the engine, calculate the torque of the
disconnect clutch based on the controlled torque at the output and
an electric machine torque, and map the relationship between the
torque of the disconnect clutch and a clutch actuator pressure to
derive or adjust a gain value and an offset value of a transfer
function that represents the relationship between the torque of the
disconnect clutch and the clutch actuator pressure, and in response
to a command to adjust the torque of the disconnect clutch to a
desired value, adjust the clutch actuator pressure to a value that
corresponds to the desired value according to the transfer
function.
17. The vehicle of claim 16, wherein the controller is configured
to adjust the gain value and the offset value utilizing a Kalman
filter, a recursive least square method, or a batch mode regression
method.
18. The vehicle of claim 16, wherein the controller is configured
to derive or adjust the transfer function only during engine starts
that correlate with a non-braking condition of the vehicle.
19. The vehicle of claim 16, wherein the controller is configured
to derive or adjust the transfer function only during engine starts
that correlate with a non-shifting condition of the
transmission.
20. The vehicle of claim 16, wherein the controller is configured
to derive or adjust the transfer function only during engine starts
that correlate with a pre-determined range of steering condition of
the vehicle.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to control systems for
vehicles and vehicle powertrains.
BACKGROUND
[0002] Vehicles may include power generating devices, such as an
engine or an electric motor, that are configured to generate torque
within a powertrain of the vehicle in order to propel the
vehicle.
SUMMARY
[0003] A vehicle includes a powertrain, an inertial measurement
unit, and a controller. The powertrain has a transmission, an
engine, an electric machine, and a disconnect clutch. The
transmission has an input and an output. The engine is configured
to generate and deliver torque to the input. The electric machine
is configured to generate and deliver torque to the input. The
disconnect clutch is configured to connect and disconnect the
engine from the input. The disconnect clutch is also configured to
crank the engine during an engine start. The inertial measurement
unit is configured to measure inertial forces exerted onto the
vehicle. The controller is programmed to, in response to a demanded
torque at the output, control the torque at the output based on a
mapped relationship between the inertial forces and a vehicle
velocity, wherein the mapped relationship between the inertial
forces and the vehicle velocity utilizes first, second, third, and
fourth mapping parameters. The controller is further programmed to,
in response to a command to start the engine, close the disconnect
clutch to start the engine, calculate the torque of the disconnect
clutch based on the controlled torque at the output and an electric
machine torque, and map the relationship between the torque of the
disconnect clutch and a clutch actuator pressure to derive or
adjust a transfer function that represents the relationship between
the torque of the disconnect clutch and the clutch actuator
pressure. The controller is further programmed to, in response to a
command to adjust the torque of the disconnect clutch to a desired
value, adjust the clutch actuator pressure to a value that
corresponds to the desired value according to the transfer
function.
[0004] A vehicle includes a transmission, an engine, a disconnect
clutch, an inertial measurement unit, and a controller. The
transmission has an input shaft and an output shaft. The engine is
configured to generate and deliver torque to the input shaft. The
disconnect clutch is configured to connect and disconnect the
engine from the input shaft. The disconnect clutch is also
configured to crank the engine during an engine start. The inertial
measurement unit is configured to measure inertial forces exerted
onto the vehicle. The controller is programmed to, in response to a
command to adjust a torque of the disconnect clutch to a desired
value that is derived from the inertial forces and a vehicle
velocity, drive the clutch actuator pressure to a value that
corresponds to the desired value.
[0005] A vehicle includes a transmission, an engine, an electric
machine, a disconnect clutch, an inertial measurement unit, and a
controller. The transmission has an input and an output. The engine
and the electric machine are each configured to generate and
deliver torque to the input. The disconnect clutch is configured to
connect and disconnect the engine from the input. The disconnect
clutch is also configured to crank the engine during an engine
start. The inertial measurement unit is configured to measure
inertial forces exerted onto the vehicle. The controller is
programmed to, in response to a demanded torque at the output,
control the torque at the output based on a mapped relationship
between the inertial forces and a vehicle velocity. The controller
is further programmed to, in response to a command to start the
engine, close the disconnect clutch to start the engine, calculate
the torque of the disconnect clutch based on the controlled torque
at the output and an electric machine torque, and map the
relationship between the torque of the disconnect clutch and a
clutch actuator pressure to derive or adjust a gain value and an
offset value of a transfer function that represents the
relationship between the torque of the disconnect clutch and the
clutch actuator pressure. The controller is further programmed to,
in response to a command to adjust the torque of the disconnect
clutch to a desired value, adjust the clutch actuator pressure to a
value that corresponds to the desired value according to the
transfer function.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 is a schematic illustration of a representative
powertrain of a hybrid electric vehicle;
[0007] FIG. 2 is a flowchart illustrating a method of controlling
the torque of the disconnect clutch;
[0008] FIG. 3 is a first example of a series of graphs illustrating
the torque of the disconnect clutch and the pressure of the
disconnect clutch actuator during an engine starting event;
[0009] FIG. 4 is a graph of a non-linear transfer function that
represents the relationship between the torque of the disconnect
clutch and the clutch actuator pressure, which is derived from a
set of recorded data points;
[0010] FIG. 5 is a graph of a linear transfer function that
represents the relationship between the torque of the disconnect
clutch and the clutch actuator pressure, which is derived from a
set of recorded data points;
[0011] FIG. 6 is a second example of series of graphs illustrating
the torque of the disconnect clutch and the pressure of the
disconnect clutch actuator during an engine starting event;
[0012] FIG. 7 is a graph of a non-linear transfer function having a
hysteresis loop that represents the relationship between the torque
of the disconnect clutch and the clutch actuator pressure, which is
derived from a set of recorded data points; and
[0013] FIG. 8 is a graph of a linear transfer function having a
hysteresis loop that represents the relationship between the torque
of the disconnect clutch and the clutch actuator pressure, which is
derived from a set of recorded data points.
DETAILED DESCRIPTION
[0014] Embodiments of the present disclosure are described herein.
It is to be understood, however, that the disclosed embodiments are
merely examples and other embodiments may take various and
alternative forms. 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 merely as a representative basis for teaching one
skilled in the art to variously employ the embodiments. As those of
ordinary skill in the art will understand, various features
illustrated and described with reference to any one of the figures
may 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 provide
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.
[0015] Referring to FIG. 1, a schematic diagram of a hybrid
electric vehicle (HEV) 10 is illustrated according to an embodiment
of the present disclosure. FIG. 1 illustrates representative
relationships among the components. Physical placement and
orientation of the components within the vehicle may vary. The HEV
10 includes a powertrain 12. The powertrain 12 includes an engine
14 that drives a transmission 16, which may be referred to as a
modular hybrid transmission (MHT). As will be described in further
detail below, transmission 16 includes an electric machine such as
an electric motor/generator (M/G) 18, an associated traction
battery 20, a torque converter 22, and a multiple step-ratio
automatic transmission, or gearbox 24. The powertrain 12 includes
power generating components (i.e., engines or electric motors) and
the drivetrain. The drivetrain is the group of components that
deliver power to the driving wheels, excluding the power generating
components. In contrast, the powertrain 12 is considered to include
both the power generating components and the drivetrain.
[0016] The engine 14 and the M/G 18 are both drive sources or
powerplants for the HEV 10 that are configured to propel the HEV
10. The engine 14 generally represents a power source that may
include an internal combustion engine such as a gasoline, diesel,
or natural gas powered engine, or a fuel cell. The engine 14
generates an engine power and corresponding engine torque that is
supplied to the M/G 18 when a disconnect clutch 26 between the
engine 14 and the M/G 18 is at least partially engaged. The M/G 18
may be implemented by any one of a plurality of types of electric
machines. For example, M/G 18 may be a permanent magnet synchronous
motor. Power electronics condition direct current (DC) power
provided by the battery 20 to the requirements of the M/G 18, as
will be described below. For example, power electronics may provide
three phase alternating current (AC) to the M/G 18.
[0017] When the disconnect clutch 26 is at least partially engaged,
power flow from the engine 14 to the M/G 18 or from the M/G 18 to
the engine 14 is possible. For example, the disconnect clutch 26
may be engaged and M/G 18 may operate as a generator to convert
rotational energy provided by a crankshaft 28 and M/G shaft 30 into
electrical energy to be stored in the battery 20. The disconnect
clutch 26 can also be disengaged to isolate the engine 14 from the
remainder of the powertrain 12 such that the M/G 18 can act as the
sole drive source for the HEV 10. Shaft 30 extends through the M/G
18. The M/G 18 is continuously drivably connected to the shaft 30,
whereas the engine 14 is drivably connected to the shaft 30 only
when the disconnect clutch 26 is at least partially engaged.
[0018] The M/G 18 is connected to the torque converter 22 via shaft
30. The torque converter 22 is therefore connected to the engine 14
when the disconnect clutch 26 is at least partially engaged. The
torque converter 22 includes an impeller 29 fixed to M/G shaft 30,
a turbine 31 fixed to a transmission input shaft 32, and a stator
33 that is grounded such that it does not rotate. The torque
converter 22 thus provides a hydraulic coupling between shaft 30
and transmission input shaft 32. The torque converter 22 transmits
power from the impeller to the turbine when the impeller rotates
faster than the turbine. The magnitude of the turbine torque and
impeller torque generally depend upon the relative speeds. When the
ratio of impeller speed to turbine speed is sufficiently high, the
turbine torque is a multiple of the impeller torque. A torque
converter bypass clutch (also known as a torque converter lock-up
clutch) 34 may also be provided that, when engaged, frictionally or
mechanically couples the impeller and the turbine of the torque
converter 22, permitting more efficient power transfer. The torque
converter bypass clutch 34 may be configured to transition between
an opened (or disconnected) state, a closed (or locked) state, and
a slipping state. The rotation of the impeller 29 and the turbine
31 are synchronized when the torque converter bypass clutch 34 is
in the closed or locked state. The rotation of the impeller 29 and
the turbine 31 are non-synchronized when the torque converter
bypass clutch 34 is in the opened state or the slipping state.
[0019] The torque converter bypass clutch 34 may be operated as a
launch clutch to provide smooth vehicle launch. Alternatively, or
in combination, a launch clutch similar to disconnect clutch 26 may
be provided between the M/G 18 and gearbox 24 for applications that
do not include a torque converter 22 or a torque converter bypass
clutch 34. In some applications, disconnect clutch 26 is generally
referred to as an upstream clutch and launch clutch 34 (which may
be a torque converter bypass clutch) is generally referred to as a
downstream clutch.
[0020] The gearbox 24 may include gear sets (not shown) that are
selectively placed in different gear ratios by selective engagement
of friction elements such as clutches and brakes (not shown) to
establish the desired multiple discrete or step drive ratios. The
friction elements are controllable through a shift schedule that
connects and disconnects certain elements of the gear sets to
control the ratio between a transmission output shaft 36 and the
transmission input shaft 32. The gearbox 24 is automatically
shifted from one ratio to another based on various vehicle and
ambient operating conditions by an associated controller, such as a
powertrain control unit (PCU). Power and torque from both the
engine 14 and the M/G 18 may be delivered to and received by
gearbox 24. The gearbox 24 then provides powertrain output power
and torque to output shaft 36.
[0021] It should be understood that the hydraulically controlled
gearbox 24 used with a torque converter 22 is but one example of a
gearbox or transmission arrangement; any multiple ratio gearbox
that accepts input torque(s) from an engine and/or a motor and then
provides torque to an output shaft at the different ratios is
acceptable for use with embodiments of the present disclosure. For
example, gearbox 24 may be implemented by an automated mechanical
(or manual) transmission (AMT) that includes one or more servo
motors to translate/rotate shift forks along a shift rail to select
a desired gear ratio. As generally understood by those of ordinary
skill in the art, an AMT may be used in applications with higher
torque requirements, for example.
[0022] As shown in the representative embodiment of FIG. 1, the
output shaft 36 is connected to a differential 40. The differential
40 drives a pair of wheels 42 via respective axles 44 connected to
the differential 40. The differential transmits approximately equal
torque to each wheel 42 while permitting slight speed differences
such as when the vehicle turns a corner. Different types of
differentials or similar devices may be used to distribute torque
from the powertrain to one or more wheels. In some applications,
torque distribution may vary depending on the particular operating
mode or condition, for example. In another alternative embodiment,
the M/G 18 may be disposed between the gearbox 24 and the
differential 40. In such an alternative embodiment, where the M/G
18 is disposed between the gearbox 24 and the differential, one or
more launch clutches or a torque converter may be disposed between
the engine and the gearbox 24.
[0023] The powertrain 12 further includes an associated controller
50 such as a powertrain control unit (PCU). While illustrated as
one controller, the controller 50 may be part of a larger control
system and may be controlled by various other controllers
throughout the vehicle 10, such as a vehicle system controller
(VSC). It should therefore be understood that the powertrain
control unit 50 and one or more other controllers can collectively
be referred to as a "controller" that controls various actuators in
response to signals from various sensors to control functions such
as starting/stopping engine 14, operating M/G 18 to provide wheel
torque or charge battery 20, select or schedule transmission
shifts, etc. Controller 50 may include a microprocessor or central
processing unit (CPU) in communication with various types of
computer readable storage devices or media. Computer readable
storage devices or media may include volatile and nonvolatile
storage in read-only memory (ROM), random-access memory (RAM), and
keep-alive memory (KAM), for example. KAM is a persistent or
non-volatile memory that may be used to store various operating
variables while the CPU is powered down. Computer-readable storage
devices or media may be implemented using any of a number of known
memory devices such as PROMs (programmable read-only memory),
EPROMs (electrically PROM), EEPROMs (electrically erasable PROM),
flash memory, or any other electric, magnetic, optical, or
combination memory devices capable of storing data, some of which
represent executable instructions, used by the controller in
controlling the engine or vehicle.
[0024] The controller communicates with various engine/vehicle
sensors and actuators via an input/output (I/O) interface
(including input and output channels) that may be implemented as a
single integrated interface that provides various raw data or
signal conditioning, processing, and/or conversion, short-circuit
protection, and the like. Alternatively, one or more dedicated
hardware or firmware chips may be used to condition and process
particular signals before being supplied to the CPU. As generally
illustrated in the representative embodiment of FIG. 1, controller
50 may communicate signals to and/or from engine 14, disconnect
clutch 26, M/G 18, battery 20, launch clutch 34, transmission
gearbox 24, and power electronics 56. Although not explicitly
illustrated, those of ordinary skill in the art will recognize
various functions or components that may be controlled by
controller 50 within each of the subsystems identified above.
Representative examples of parameters, systems, and/or components
that may be directly or indirectly actuated using control logic
and/or algorithms executed by the controller include fuel injection
timing, rate, and duration, throttle valve position, spark plug
ignition timing (for spark-ignition engines), intake/exhaust valve
timing and duration, front-end accessory drive (FEAD) components
such as an alternator, air conditioning compressor, battery
charging or discharging (including determining the maximum charge
and discharge power limits), regenerative braking, M/G operation,
clutch pressures for disconnect clutch 26, launch clutch 34, and
transmission gearbox 24, and the like. Sensors communicating input
through the I/O interface may be used to indicate turbocharger
boost pressure, crankshaft position (PIP), engine rotational speed
(RPM), wheel speeds (WS1, WS2), vehicle speed (VSS), coolant
temperature (ECT), intake manifold pressure (MAP), accelerator
pedal position (PPS), ignition switch position (IGN), throttle
valve position (TP), air temperature (TMP), exhaust gas oxygen
(EGO) or other exhaust gas component concentration or presence,
intake air flow (MAF), transmission gear, ratio, or mode,
transmission oil temperature (TOT), transmission turbine speed
(TS), torque converter bypass clutch 34 status (TCC), deceleration
or shift mode (MDE), battery temperature, voltage, current, or
state of charge (SOC) for example. A pressure transducer may be
utilized to measure a hydraulic pressure applied to a hydraulic
actuator of the disconnect clutch 26.
[0025] Control logic or functions performed by controller 50 may be
represented by flow charts or similar diagrams in one or more
figures. These figures provide representative control strategies
and/or logic that may be implemented using one or more processing
strategies such as event-driven, interrupt-driven, multi-tasking,
multi-threading, and the like. As such, various steps or functions
illustrated may be performed in the sequence illustrated, in
parallel, or in some cases omitted. Although not always explicitly
illustrated, one of ordinary skill in the art will recognize that
one or more of the illustrated steps or functions may be repeatedly
performed depending upon the particular processing strategy being
used. Similarly, the order of processing is not necessarily
required to achieve the features and advantages described herein,
but is provided for ease of illustration and description. The
control logic may be implemented primarily in software executed by
a microprocessor-based vehicle, engine, and/or powertrain
controller, such as controller 50. Of course, the control logic may
be implemented in software, hardware, or a combination of software
and hardware in one or more controllers depending upon the
particular application. When implemented in software, the control
logic may be provided in one or more computer-readable storage
devices or media having stored data representing code or
instructions executed by a computer to control the vehicle or its
subsystems. The computer-readable storage devices or media may
include one or more of a number of known physical devices which
utilize electric, magnetic, and/or optical storage to keep
executable instructions and associated calibration information,
operating variables, and the like.
[0026] An accelerator pedal 52 is used by the driver of the vehicle
to provide a demanded torque, power, or drive command to propel the
vehicle. In general, depressing and releasing the accelerator pedal
52 generates an accelerator pedal position signal that may be
interpreted by the controller 50 as a demand for increased power or
decreased power, respectively. A brake pedal 58 is also used by the
driver of the vehicle to provide a demanded braking torque to slow
the vehicle. In general, depressing and releasing the brake pedal
58 generates a brake pedal position signal that may be interpreted
by the controller 50 as a demand to decrease the vehicle speed.
Based upon inputs from the accelerator pedal 52 and brake pedal 58,
the controller 50 commands the torque to the engine 14, M/G 18, and
friction brakes 60. The controller 50 also controls the timing of
gear shifts within the gearbox 24, as well as engagement or
disengagement of the disconnect clutch 26 and the torque converter
bypass clutch 34. Like the disconnect clutch 26, the torque
converter bypass clutch 34 can be modulated across a range between
the engaged and disengaged positions. This produces a variable slip
in the torque converter 22 in addition to the variable slip
produced by the hydrodynamic coupling between the impeller and the
turbine. Alternatively, the torque converter bypass clutch 34 may
be operated as locked or open without using a modulated operating
mode depending on the particular application.
[0027] To drive the vehicle with the engine 14, the disconnect
clutch 26 is at least partially engaged to transfer at least a
portion of the engine power and/or torque through the disconnect
clutch 26 to the M/G 18, and then from the M/G 18 to shaft 30
(i.e., the impeller of the torque converter 22) and through the
torque converter 22 and gearbox 24. The M/G 18 may assist the
engine 14 by providing additional power and/or torque to turn the
shaft 30 (i.e., the impeller of the torque converter 22). This
operation mode may be referred to as a "hybrid mode" or an
"electric assist mode."
[0028] To drive the vehicle with the M/G 18 as the sole power
source, the power flow remains the same except the disconnect
clutch 26 isolates the engine 14 from the remainder of the
powertrain 12. Combustion in the engine 14 may be disabled or
otherwise OFF during this time to conserve fuel. The traction
battery 20 transmits stored electrical energy through wiring 54 to
power electronics 56 that may include an inverter, for example. The
power electronics 56 convert DC voltage from the battery 20 into AC
voltage to be used by the M/G 18. The controller 50 commands the
power electronics 56 to convert voltage from the battery 20 to an
AC voltage provided to the M/G 18 to provide positive or negative
power and/or torque to the shaft 30 (i.e., the impeller of the
torque converter 22). This operation mode may be referred to as an
"electric only" or "EV" operation mode.
[0029] In any mode of operation, the M/G 18 may act as a motor and
provide a driving force for the powertrain 12. Alternatively, the
M/G 18 may act as a generator and convert kinetic energy from the
powertrain 12 into electric energy to be stored in the battery 20.
The M/G 18 may act as a generator while the engine 14 is providing
propulsion power for the vehicle 10, for example. The M/G 18 may
additionally act as a generator during times of regenerative
braking in which torque and rotational (or motive) energy or power
from spinning wheels 42 is transferred back through the gearbox 24,
torque converter 22, (and/or torque converter bypass clutch 34) and
is converted into electrical energy for storage in the battery
20.
[0030] The battery 20 and the M/G 18 may also be configured to
provide electrical power to one or more vehicle accessories 62. The
vehicle accessories 62 may include, but are not limited to, air
conditioning systems, power steering systems, electric heaters, or
any other system or device that is electrically operated.
[0031] An integrated starter-generator (ISG) 64 may be coupled to
the engine 14 (i.e., may be coupled to the crankshaft 28 of the
engine 14). The ISG 64 may be configured to operate as a motor to
start the engine 14 during an engine start-up event, or to provide
additional torque to the powertrain 12 during vehicle operations.
The ISG 64 may also be configured to receiving torque from the
engine 14 and operate as a generator. The ISG 64 may be selectively
coupled to the engine by a clutch 66, belt 68, and a pair of
pulleys 70. If the ISG 64 is coupled to the engine by a belt 68 it
may be referred to as a belt integrated starter-generator (BISG).
The controller 50 may be configured to transmit signals to the ISG
64 to operate the ISG 64 as either a motor or a generator. The
controller may also be configured to transmit signals to the clutch
66 in order to open or close the clutch 66. The ISG 64 will be
coupled to the engine 14 when the clutch is in a closed state and
decoupled from the engine 14 when the clutch 66 is in an opened
state. The ISG 64 may be configured to provide electrical energy to
charge an accessory battery 72, the traction battery 20, or provide
electrical energy to power the vehicle accessories 62 when
operating as a generator. The accessory battery 72 may also be
configured to power the vehicle accessories 62.
[0032] The controller 50 may be configured to receive various
states or conditions of the various vehicle components illustrated
in FIG. 1 via electrical signals. The electrical signals may be
delivered to the controller 50 from the various components via
input channels. Additionally, the electrical signals received from
the various components may be indicative of a request or a command
to change or alter a state of one or more of the respective
components of the vehicle 10. The controller 50 includes output
channels that are configured to deliver requests or commands (via
electrical signals) to the various vehicle components. The
controller 50 includes control logic and/or algorithms that are
configured to generate the requests or commands delivered through
the output channels based on the requests, commands, conditions, or
states of the various vehicle components.
[0033] The input channels and output channels are illustrated as
dotted lines in FIG. 1. It should be understood that a single
dotted line may be representative of both an input channel and an
output channel into or out of a single element. Furthermore, an
output channel into one element may operate as an input channel to
another element and vice versa.
[0034] It should be understood that the schematic illustrated in
FIG. 1 is merely representative and is not intended to be limiting.
Other configurations are contemplated that utilize selective
engagement of both an engine and a motor to transmit power through
the transmission. For example, the M/G 18 may be offset from the
crankshaft 28, and/or the M/G 18 may be provided between the torque
converter 22 and the gearbox 24. Other configurations are
contemplated without deviating from the scope of the present
disclosure.
[0035] The vehicle 10 also includes an inertial measurement unit
74. The inertial measurement unit 74 is an electronic device that
measures the vehicle's specific force, inertial forces acting upon
the vehicle, angular rate of the vehicle, orientation of the
vehicle, acceleration of the vehicle in multiple directions,
attitude of the vehicle, pitch of the vehicle, etc., using a
combination of accelerometers, gyroscopes, magnetometers and/or
other sensors. The inertial measurement unit 74 may utilize such
sensors along multiple axes to provide an estimation of the
vehicle's orientation in space. The various measurements taken by
the inertial measurement unit 74 may be communicated to the
controller 50.
[0036] It should also be understood that the vehicle configuration
described herein is merely exemplary and is not intended to be
limited. Other non-hybrid, electric, or hybrid vehicle
configurations should be construed as disclosed herein. Other
vehicle configurations may include, but are not limited to,
vehicles powered by an engine only, micro-hybrid vehicles (i.e.,
powered by an engine only that has a start/stop function), series
hybrid vehicles, parallel hybrid vehicles, series-parallel hybrid
vehicles, plug-in hybrid electric vehicles (PHEVs), fuel cell
hybrid vehicles, battery operated electric vehicles (BEVs), or any
other vehicle configuration known to a person of ordinary skill in
the art.
[0037] A wet clutch, which may be controlled by a hydraulic
actuator such as a hydraulic piston, may be utilized in automotive
propulsion systems for various functions such as automatic shifting
of a transmission, disconnecting an engine from the drivetrain, and
starting the engine. A mathematical relationship between pressure
of the hydraulic actuator and the torque of the wet clutch may be
referred to as clutch transfer function. Such a transfer function
may be utilized to control the clutch torque. A linear
approximation of such a transfer function may be utilized by a
vehicle propulsion system to control automatic shifting within the
vehicle transmission and/or to control a clutch-based engine start.
Wet clutch behavior and a corresponding transfer function that is
utilized to control the clutch may be sensitive to engagement
conditions. Wet clutch transfer functions that are observed during
testing of a clutch on a test stand may differ from the transfer
functions observed while operating the same clutch in a vehicle
equipped with non-production instrumentation for studying the
torque of the clutch.
[0038] A wet clutch transfer function behaves linearly under
certain conditions, but not under all conditions, making the use of
linear approximation acceptable under such certain conditions. A
wet clutch transfer function becomes non-linear under other certain
conditions, making the use of linear approximation inaccurate and
less desirable for robust clutch control under such other certain
conditions. Also, a clutch transfer function may vary over a life
of a vehicle and may vary from vehicle to vehicle. The use of an
inaccurate transfer function may affect clutch control robustness
and drivability. Identification and construction of an accurate wet
clutch transfer function in a production vehicle may be difficult
because it requires an accurate determination of clutch torque at
the time of clutch engagement without a specialized torque sensing
device.
[0039] It is desirable to develop a method to adaptively identify a
wet clutch transfer function in a vehicle that applies under all
clutch slip conditions, such as hydrodynamic lubrication, mixed
lubrication, and boundary lubrication, at the time of clutch
engagement without requiring a specialized torque sensing device.
In hydrodynamic lubrication, clutch interface is fully lubricated
with transmission fluid with no physical contact in-between. The
clutch torque is hydrodynamically carried by fluid shearing between
rotating clutch plates. In mixed lubrication, the clutch plates
establish a limited physical contact at their surface asperities,
while partially retaining fluid layer in-between. The clutch torque
is carried by both viscous shear and mechanical friction between
rotating clutch plates. In boundary lubrication, the transmission
fluid is squeezed out from the interface between clutch plates. The
clutch torque is entirely carried by mechanical friction between
rotating clutch plates. The method described herein adaptively
identifies and constructs a clutch transfer function based on the
use of an IMU signal, a.sub.imu, without a specialized torque
sensing device. Such an IMU signal, a.sub.imu, is described in U.S.
patent application Ser. No. ______, Attorney docket number 84274634
(FMC 9738 PUS), filed on ______, which is incorporated by reference
herein in its entirety.
[0040] The clutch transfer function described herein is adaptively
identified and constructed for all lubrication conditions at the
frictional interface based on actual operating conditions at the
time of engagement in a vehicle. The method described herein
includes a mathematical equation to calculate the torque of an
engine disconnect clutch (e.g., disconnect clutch 26) during an
engine start or restart control based on the use of the IMU signal,
a.sub.imu. The engine disconnect clutch torque T.sub.K0(i) is
calculated during engine start and restart events that correspond
to specific conditions that are assumed by the engine disconnect
clutch torque calculation equation. For example, the engine
disconnect clutch torque T.sub.K0(i) is calculated during engine
start or restart events if there is no gear shifting within a
transmission (e.g., gearbox 24) of the vehicle, if there is no
braking of the vehicle, and if the steering angle is less than a
pre-determined threshold.
[0041] The engine disconnect clutch torque T.sub.K0(i) is
calculated at a desired time interval, where i denotes a time step.
The engine disconnect clutch torque T.sub.K0(i) is mapped against
the disconnect clutch actuator pressure P.sub.K0(i) to form a
transfer function data set {T.sub.K0(i), P.sub.K0(i), i=1, 2, . . .
, n} for each engine restart event where P.sub.K0(i) may be
measured or estimated. The transfer function data set may
explicitly represent a hysteresis loop. The transfer function data
set may be binned or assigned to a pre-determined class C.sub.j
(j=1, 2, . . . ) based on operating conditions at the time of
engagement. The pre-determined class C.sub.j (j=1, 2, . . . ) may
be determined based on measured or estimated conditions such as oil
temperature or initial clutch slip speed using onboard temperature
or speed sensors, respectively. The classification of transfer
function data sets may be conducted by the controller 50 or in
cloud computing storage. A mathematical regression may be performed
to determine the transfer function equation for transfer function
data sets in each cluster or class C.sub.j.
[0042] The Transfer function equation may be linear or non-linear.
The transfer function equation may mathematically represent
hysteresis loop. Mathematical regression may be used to determine
the transfer function equation, which may be conducted by the
controller 50 or in cloud computing storage. The mathematical
regression utilized to determine the transfer function equation may
be conducted in a recursive manner or in a batch mode. In a batch
mode, a regression method is applied to a collection of transfer
function data sets in each cluster C.sub.j to fit a linear or a
nonlinear function. In a recursive mode, a method such as recursive
least square method or Kalman filtering is applied to update
constants in the regression equation when a new transfer function
data set becomes available. The transfer function equation
disclosed herein may be used in powertrain control and diagnosis.
The transfer function may be selected during clutch control from
one of the predetermined classes C.sub.j (j=1, 2, . . . ) to match
the operating condition at the time of clutch engagement during
either powertrain control or diagnosis.
[0043] Referring to FIG. 2, a flowchart of a method 100 of
controlling the torque of the disconnect clutch 26 is illustrated.
The method 100 may be stored as control logic and/or an algorithm
within the controller 50 or in cloud computing storage. The
controller 50 may implement the method 100 by controlling the
various components of the vehicle 10. The method 100 begins at
start block 102. Start block 102 may correspond to an engagement of
a vehicle ignition or a "key on" condition that indicates an
operator initiating a new drive cycle for operating the
vehicle.
[0044] The method 100 then moves on to block 104, where it is
determined if an engine start has been initiated. More
specifically, the step at block 104 may determine if an engine
start or restart has been initiated where the disconnect clutch 26
is or will be utilized to start the engine 14. If an engine start
or restart has not been initiated, the method 100 recycles back to
the beginning of block 104. If an engine start or restart has been
initiated, the method 100 moves on to block 106 where it is
determined if the operating or driving conditions of the vehicle
are desirable for calculating the torque of the disconnect clutch
during the engine start or restart. The operating or driving
conditions of the vehicle are desirable for calculating the torque
of the disconnect clutch when the specific conditions that are
assumed by the engine disconnect clutch torque calculation equation
(i.e., equation 1 listed below) are present during the engine start
or restart. For example, the engine disconnect clutch torque may be
calculated during engine start or restart events during operating
or driving conditions, which may be referred to as steady state
conditions, that include the transmission (e.g., gearbox 24)
experiencing no gear shifting, no (i.e., zero) vehicle braking, and
the steering angle being less than a pre-determined threshold
(e.g., the steering angle is less than 10.degree.).
[0045] If the operating or driving conditions of the vehicle are
desirable for calculating the torque of the disconnect clutch
during the engine start or restart, the method moves on to block
108. At block 108, the toque of the disconnect clutch is calculated
according to equations (1) and (2):
T K .times. 0 = T M .times. t .times. r - ( I M .times. t .times. r
+ I impeller ) .times. .alpha. M .times. t .times. r + ( T .times.
R - 1 ) .times. ( .omega. m .times. t .times. r / K ) 2 - T D + I o
.times. u .times. t .times. .alpha. o .times. u .times. t .eta. GR
( 1 ) .times. T D = k 1 + k 2 .times. a i .times. m .times. u + k 3
.times. .nu. + k 4 .times. v 2 ( 2 ) ##EQU00001##
where T.sub.K0 is the torque of the disconnect clutch 26, T.sub.Mtr
is the estimated torque of the M/G 18, I.sub.Mtr is the inertia of
the M/G 18, I.sub.impeller is the inertia of the torque converter
impeller 29, .alpha..sub.Mtr is angular acceleration of the M/G 18,
TR is the torque ratio of the torque converter 22, .omega..sub.mtr
is the angular speed of the M/G 18, K is the K factor of the torque
converter 22, T.sub.D is the torque at the output of the
transmission gearbox 24 (i.e., the torque of output shaft 36),
I.sub.out is the lumped inertia of the transmission (i.e., the
lumped inertia of the torque converter 22 and the gearbox 24),
.alpha..sub.out is the angular acceleration of the transmission
output shaft 36, .eta. is the efficiency of the gearbox 24, GR is
the gear ratio of the transmission at the time of engine restart
(i.e., the gear ratio of gearbox 24), v is linear velocity of the
vehicle, a.sub.imu is the IMU signal, and k.sub.1, k.sub.2,
k.sub.3, and k.sub.4 are the mapping coefficients. It should be
noted that equation (2) and the corresponding variables and
coefficients are disclosed within U.S. patent application Ser. No.
______, Attorney docket number 84274634 (FMC 9738 PUS), which has
been incorporated by reference in its entirety.
[0046] Next, the method 100 moves on to block 110 where the
relationship between the disconnect torque T.sub.K0 and the
disconnect clutch actuator pressure P.sub.K0 are mapped (i.e., the
torque values of the disconnect clutch 26 are mapped to the
corresponding values of the disconnect clutch actuator pressure
P.sub.K0) to derive or adjust the transfer function that represents
the relationship between the disconnect torque T.sub.K0 and the
disconnect clutch actuator pressure P.sub.K0. More specifically at
block 110, the transfer function may be generated via applying a
regression fit to a collection of transfer function data sets that
consist of the mapped values of the disconnect clutch torque
T.sub.K0 and the disconnect clutch actuator pressure P.sub.K0, such
as a recursive least square method, or via applying a Kalman filter
to the mapped values of the disconnect clutch torque T.sub.K0 and
the disconnect clutch actuator pressure P.sub.K0. Multiple transfer
functions may be constructed, specific to a range of operating
conditions, such as transmission fluid temperature. The transfer
function may be a linear function, a non-linear function, a linear
function with a hysteresis loop, or a non-linear function with a
hysteresis loop. Examples of linear and non-linear equations are
illustrated by equations (3) and (4), respectively:
T.sub.k0=C*(P.sub.k0-P.sub.Stroke) (3)
T.sub.K0=F(P.sub.K0) (4)
where P.sub.Stroke is the stroke pressure of the disconnect clutch
actuator (i.e., the pressure required to advance the disconnect
clutch 26 to an initial engagement between the opposing sides of
the disconnect clutch, which may be referred to as the "kiss
point") and C is a gain value of a linear transfer function.
P.sub.Stroke may be referred to as an offset value of a linear
transfer function. F(P.sub.K0) may be a second-order polynomial
function, a power function or an exponential function. F(P.sub.K0)
may be a non-parametric function such as a neural network.
[0047] The transfer function may experience little or no changes
within days or weeks once large amounts of data is collected or if
the data collected is within an allowable variance of the current
values. If new data is an outlier and varies significantly from
other data points, such new data may be ignored and the transfer
function would not be adjusted by such data. Furthermore, the
transfer function may have had initial values that were stored in
the controller 50 after the previous occurrence that the method 100
cycled through block 110 or at the end of a previous drive cycle.
If the transfer function is updated at block 110, the new values of
the transfer function are stored within the controller 50 and may
replace the previous values of the transfer function.
[0048] The transfer function may include fitting several equations
(linear or non-linear) to different clusters of data sets, where
each cluster of data is specific to an operating condition. For
example, a first equation may be fit to a data set that only
includes values of disconnect torque T.sub.K0 mapped to the
disconnect clutch actuator pressure P.sub.K0 during engine starts
where the engine is started during a vehicle acceleration at a
fully warmed transmission fluid temperature, while a second
equation may be fit to a data set that only includes values of
disconnect torque T.sub.K0 mapped to the disconnect clutch actuator
pressure P.sub.K0 during engine starts where the engine is started
at a low transmission fluid temperature.
[0049] Next, the method 100 moves on to block 112, where the
disconnect clutch actuator pressure P.sub.K0 is adjusted to a value
that corresponds with a desired torque of disconnect torque
T.sub.K0 based on the transfer function (whether updated at block
110 or not) in order to drive the torque of the disconnect clutch
26 to such a desired value in response to a command to control the
torque of disconnect torque T.sub.K0 to such a desired value. It
should be noted that if the transfer function includes several
fitting equations that are based on specific operating conditions
of the vehicle, the specific equation fit to such an operating
condition of the vehicle may be applied.
[0050] Next, the method 100 moves on to block 114 where it is
determined if the vehicle ignition has been disengaged, which
corresponds to a "key off" condition that indicates the operator
has turned off the vehicle and has terminated the current drive
cycle. If the vehicle ignition has been disengaged, the method 100
ends at block 116. If the vehicle ignition has not been disengaged,
the method 100 returns to block 104, where the process repeats.
[0051] Returning to block 106, if it is determined that the
operating or driving conditions of the vehicle are not desirable
for calculating the torque of the disconnect clutch during the
engine start or restart, the method 100 moves directly on to 114.
It should be noted that if the answer is "NO" at block 106 and if
there is a command to adjust the torque of the disconnect clutch
T.sub.K0 to a desired value, an unadjusted transfer function that
is stored from a previous drive cycle or from a previous cycle of
the method through block 110 may be applied to control the
disconnect clutch actuator pressure P.sub.K0 in order drive the
torque of the disconnect clutch T.sub.K0 to such a desired value.
It should be understood that the flowchart in FIG. 2 is for
illustrative purposes only and that the method 100 should not be
construed as limited to the flowchart in FIG. 2. Some of the steps
of the method 100 may be rearranged while others may be omitted
entirely.
[0052] Referring to FIG. 3, a series of graphs 200 illustrating the
torque of the disconnect clutch T.sub.K0 and the pressure of the
disconnect clutch actuator P.sub.K0 during an engine starting event
are illustrated. Line 202 represents the torque of the disconnect
clutch T.sub.K0 while line 204 represents the pressure of the
disconnect clutch actuator P.sub.K0. FIG. 3 is an example of an
engine restart event that meets the model assumptions for utilizing
equation (1) to determine the torque of the disconnect clutch
T.sub.K0 (i.e., the operating or driving conditions of the vehicle
are desirable for calculating the torque of the disconnect clutch
during the engine restart as described with respect to block 106 in
FIG. 2). The values of the torque of the disconnect clutch T.sub.K0
are mapped against the clutch actuator pressure P.sub.K0 to
generate transfer function data sets {T.sub.K0(i), P.sub.K0(i),
i=1, 2, . . . , n}. The transfer function data sets {T.sub.K0(i),
P.sub.K0(i), I=1, 2, . . . , n} may then be assigned to a class Cj
based on the operating conditions at the time of the engagement of
the disconnect clutch 26 (i.e., the data sets may be assigned to
clusters of data that are specific to operating conditions and may
be fit to one of several equations within the transfer function
that is specific to such an operating condition as described with
respect to block 110 in FIG. 2). In FIG. 3, the torque of the
disconnect clutch T.sub.K0 may be calculated according to the
equation (1) during the specific time period between A and B. The
period between A and B may be referred to as the first phase of the
engagement or alternatively the "cranking" phase. During the
"cranking" phase, the disconnect clutch 26 begins to crank the
engine 14 at A and continues to increase its torque until B. At or
near B, the engine 14 initiates combustion and begins to generate
its own torque. Following the "cranking" phase, the torque of the
disconnect clutch 26 may be lowered because the clutch torque is no
longer necessary to sustain engine combustion.
[0053] FIG. 4 is a graph 300 of a non-linear transfer function that
represents the relationship between the torque of the disconnect
clutch T.sub.K0 and the clutch actuator pressure P.sub.K0, which is
derived from a set of recorded data points during the "cranking"
phase. More specifically, the dots in FIG. 4 are representative of
mapped data relating the disconnect clutch torque T.sub.K0 against
the clutch actuator pressure P.sub.K0. A regression fit of a
non-linear mathematical equation is applied to the mapped values of
the disconnect torque T.sub.K0 and the disconnect clutch actuator
pressure P.sub.K0 by means of a batch regression method or a
recursive method such as Kalman filter in order to generate the
non-linear transfer function, which is illustrated as line 302.
[0054] FIG. 5 is a graph 400 of a linear transfer function that
represents the relationship between the torque of the disconnect
clutch T.sub.K0 and the clutch actuator pressure P.sub.K0, which is
derived from a set of recorded data points during the "cranking"
phase. More specifically, the dots in FIG. 5 are representative of
mapped data relating the disconnect clutch torque T.sub.K0 against
the against clutch actuator pressure P.sub.K0. A regression fit of
a linear mathematical equation is applied to the mapped values of
the disconnect torque T.sub.K0 and the disconnect clutch actuator
pressure P.sub.K0 by means of a batch regression method or a
recursive method such as Kalman filter in order generate the linear
transfer function, which is illustrated as line 402.
[0055] Referring to FIG. 6, a second example of a series of graphs
500 illustrating the torque of the disconnect clutch T.sub.K0 and
the pressure of the disconnect clutch actuator P.sub.K0 during an
engine starting event are illustrated. Line 502 represents the
torque of the disconnect clutch T.sub.K0 while line 504 represents
the pressure of the disconnect clutch actuator P.sub.K0. FIG. 6 is
a second example of an engine restart event that meets the model
assumptions for utilizing equation (1) to determine the torque of
the disconnect clutch T.sub.K0 (i.e., the operating or driving
conditions of the vehicle are desirable for calculating the torque
of the disconnect clutch during the engine restart as described
with respect to block 106 in FIG. 2). The values of the torque of
the disconnect clutch T.sub.K0 are mapped against the clutch
actuator pressure P.sub.K0 to generate transfer function data sets
{T.sub.K0(i), P.sub.K0(i), =1, 2, . . . , n}. The transfer function
data sets {T.sub.K0(i), P.sub.K0(i); i=1, 2, . . . , n} may then be
assigned to a class C.sub.j based on the operating conditions at
the time of the engagement of the disconnect clutch 26 (i.e., the
data sets may be assigned to clusters of data that are specific to
operating conditions and may be fit to one of several equations
within the transfer function that is specific to such an operating
condition as described with respect to block 110 in FIG. 2).
[0056] Specifically, in FIG. 6, the torque of the disconnect clutch
T.sub.K0 may be calculated according to equation (1) during the
time period between A and C. Engagement of the disconnect clutch 26
may be divided into a first period between A and B and a second
period between B and C. The period between A and B may be referred
to as the first phase while the period between B and C may be
referred to as the second phase. During the first phase, the
disconnect clutch 26 begins to crank the engine 14 at A and the
engine torque continues to increase until B. The first phase may be
referred to as the "cranking" phase. At or near B, the engine 14
initiates combustion and begins to generate its own torque. The
torque of the disconnect clutch 26 then drops during the second
phase between B and C because the clutch torque is no longer
necessary to sustain engine combustion. The second phase may also
be referred to as the "bump off" phase. After the second phase ends
at C, the engine speed (i.e., the speed of the crankshaft of the
engine 14) is matched to the speed the M/G 18 (i.e., the speed of
the rotor of the M/G 18). The torque of the disconnect clutch 26 is
then increased to securely establish engagement between the engine
14 and the M/G 18 and to maintain the synchronized speeds of the
engine 14 and the M/G 18. When the clutch pressure increases and
decreases during a clutch engagement, the corresponding torque
typically exhibits a hysteresis.
[0057] FIG. 7 is a graph 600 of a non-linear transfer function
having a hysteresis loop that represents the relationship between
the torque of the disconnect clutch T.sub.K0 and the clutch
actuator pressure P.sub.K0, which is derived from a set of recorded
data points. More specifically, the dots in FIG. 7 are
representative of mapped data relating the disconnect clutch torque
T.sub.K0 against the against clutch actuator pressure P.sub.K0. A
regression fit of a non-linear mathematical equation is applied to
the mapped values of the disconnect clutch torque T.sub.K0 and the
disconnect clutch actuator pressure P.sub.K0 by means of a batch
regression method or a recursive method such as Kalman filter in
order generate the non-linear transfer function, which is
illustrated as line 602. The transfer function may be represented
by T.sub.K0=F(P.sub.K0) and T.sub.K0 is allowed to possess multiple
values corresponding to one P.sub.K0 in order to generate the
hysteresis loop. The lower portion of line 602 may represent the
data collected during the "cranking" phase while the upper portion
of line 602 may represent the data collected during the "bump off"
phase. The value of the disconnect clutch torque T.sub.K0 may be
determined based on additional information such as the sign of the
rate at which the disconnect clutch actuator pressure P.sub.K0
changes over time (i.e., dP.sub.K0/dt) at the time of clutch
control. The hysteresis behavior may attribute to the lubrication
conditions between the rotating clutch plates. For example, the
disconnect clutch 26 exhibits lower torque level during the
condition where it is slipping according to a hydrodynamic
lubrication condition. The torque of the disconnect clutch 26 tends
to be larger corresponding to the same pressure level during the
condition where the disconnect clutch 26 is slipping according to a
boundary lubrication condition.
[0058] FIG. 8 is a graph 700 of a linear transfer function having a
hysteresis loop that represents the relationship between the torque
of the disconnect clutch T.sub.K0 and the clutch actuator pressure
P.sub.K0, which is derived from a set of recorded data points. More
specifically, the dots in FIG. 8 are representative of mapped data
relating the disconnect clutch torque T.sub.K0 against the clutch
actuator pressure P.sub.K0. A regression fit of a linear
mathematical equation is applied to the mapped values of the
disconnect clutch torque T.sub.K0 and the disconnect clutch
actuator pressure P.sub.K0 by means of a batch regression method or
a recursive method such as Kalman filter in order to generate the
linear transfer function. Two separate linear regressions may be
performed or two separate Kalman filters may be applied, one for
the "cranking" phase and one for the "bump off" phase,
respectively, such that the transfer function is illustrated as an
upper line 702 (for the "bump off" phase) and a lower line 704 (for
the "cranking" phase). The clutch pressure derivative in the time
domain dP.sub.K0/dt can be used to indicate whether a particular
data point belongs to the "cranking" phase or the "bump off" phase.
For example, the "cranking" phase may occur during the condition
where the disconnect clutch 26 is slipping according to a
hydrodynamic lubrication condition while the pressure is initially
rising (i.e., dP.sub.K0/dt>0) and the "bump off" phase may occur
during a condition where the disconnect clutch 26 is slipping
according to a boundary lubrication condition when the pressure
starts decreasing from the peak level (i.e., when
dP.sub.K0/dt<0).
[0059] The words used in the specification are words of description
rather than limitation, and it is understood that various changes
may be made without departing from the spirit and scope of the
disclosure. As previously described, the features of various
embodiments may be combined to form further embodiments that may
not be explicitly described or illustrated. While various
embodiments could have been described as providing advantages or
being preferred over other embodiments or prior art implementations
with respect to one or more desired characteristics, those of
ordinary skill in the art recognize that one or more features or
characteristics may be compromised to achieve desired overall
system attributes, which depend on the specific application and
implementation. As such, embodiments described as less desirable
than other embodiments or prior art implementations with respect to
one or more characteristics are not outside the scope of the
disclosure and may be desirable for particular applications.
* * * * *