U.S. patent application number 14/074748 was filed with the patent office on 2015-05-14 for system for controlling overall coasting torque in a hybrid electric vehicle.
This patent application is currently assigned to FORD GLOBAL TECHNOLOGIES, LLC. The applicant listed for this patent is FORD GLOBAL TECHNOLOGIES, LLC. Invention is credited to Rajit JOHRI, Ming Lang KUANG, Wei LIANG, Ryan Abraham McGEE, Xiaoyong WANG, Mark Steven YAMAZAKI.
Application Number | 20150134159 14/074748 |
Document ID | / |
Family ID | 52991108 |
Filed Date | 2015-05-14 |
United States Patent
Application |
20150134159 |
Kind Code |
A1 |
JOHRI; Rajit ; et
al. |
May 14, 2015 |
SYSTEM FOR CONTROLLING OVERALL COASTING TORQUE IN A HYBRID ELECTRIC
VEHICLE
Abstract
A hybrid vehicle is provided that includes an engine, a
reversible electric machine capable of generating and providing
electric power, and a clutch for selectively engaging the engine to
the electric machine. While the vehicle is traveling, an operator
of the vehicle may release ("tip-out") the accelerator pedal,
indicating a desire for a reduction in speed and/or acceleration of
the vehicle. If the clutch is engaged during the tip-out, the at
least one controller is programmed to disengage the clutch and
alter a commanded torque to the electric machine in response to the
tip-out of the accelerator pedal to simulate compression braking of
the engine. If the vehicle is operating in an electric-only mode of
propulsion during the tip-out, and if a state-of-charge of the
battery is relatively high, the controller is programmed to
activate the engine and provide compression torque to the driveline
in response to the tip-out.
Inventors: |
JOHRI; Rajit; (Ann Arbor,
MI) ; YAMAZAKI; Mark Steven; (Canton, MI) ;
WANG; Xiaoyong; (Novi, MI) ; LIANG; Wei;
(Farmington Hills, MI) ; McGEE; Ryan Abraham; (Ann
Arbor, MI) ; KUANG; Ming Lang; (Canton, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FORD GLOBAL TECHNOLOGIES, LLC |
Dearborn |
MI |
US |
|
|
Assignee: |
FORD GLOBAL TECHNOLOGIES,
LLC
Dearborn
MI
|
Family ID: |
52991108 |
Appl. No.: |
14/074748 |
Filed: |
November 8, 2013 |
Current U.S.
Class: |
701/22 ;
180/65.265; 903/902 |
Current CPC
Class: |
B60W 2710/083 20130101;
Y02T 10/6252 20130101; Y02T 10/6286 20130101; Y02T 10/76 20130101;
Y10S 903/902 20130101; B60K 2006/4825 20130101; B60W 10/06
20130101; B60W 10/02 20130101; Y02T 10/60 20130101; B60W 10/08
20130101; B60W 2540/10 20130101; B60W 20/10 20130101; B60W 30/18072
20130101; Y02T 10/62 20130101 |
Class at
Publication: |
701/22 ;
180/65.265; 903/902 |
International
Class: |
B60W 20/00 20060101
B60W020/00; B60W 10/08 20060101 B60W010/08; B60W 10/06 20060101
B60W010/06 |
Claims
1. A hybrid vehicle comprising: an engine; an electric machine
selectively coupled to the engine via a clutch; an accelerator
pedal; and at least one controller programmed to disengage the
clutch and alter a commanded torque to the electric machine in
response to a tip-out of the accelerator pedal to simulate
compression braking of the engine.
2. The hybrid vehicle of claim 1, wherein the at least one
controller is further programmed to command braking torque in the
electric machine in response to the tip-out of the accelerator
pedal.
3. The hybrid vehicle of claim 2, wherein a magnitude of the
braking torque commanded by the at least one controller varies in
response to various tip-outs of the accelerator pedal occurring at
correspondingly various vehicle speeds such that the braking torque
of the electric machine simulates various magnitudes of engine
compression braking at various vehicle speeds.
4. The hybrid vehicle of claim 3, wherein the magnitude of the
braking torque commanded by the at least one controller is
determined from a look-up table as a function of vehicle speed.
5. The hybrid vehicle of claim 1, further comprising a battery
electrically connected to the electric machine for storing electric
power generated by the electric machine, wherein the at least one
controller is further programmed to re-engage the clutch and
activate the engine in response to (i) the accelerator pedal being
non-depressed and (ii) a state of charge (SOC) of the battery
exceeding a SOC threshold.
6. The hybrid vehicle of claim 5, wherein the at least one
controller is further programmed to alter the commanded torque to
the electric machine during vehicle coasting based upon (i) vehicle
speed and (ii) engine torque.
7. The hybrid vehicle of claim 6, wherein the at least one
controller is further programmed to reduce the commanded torque of
the electric machine while a braking torque of the engine is
maintained in response to a reduction of vehicle speed.
8. The hybrid vehicle of claim 6, wherein the at least one
controller is further programmed to increase the commanded braking
torque in the electric machine during vehicle coasting based upon a
decrease of engine torque.
9. The hybrid vehicle of claim 1, wherein the electric machine
includes an output, and wherein the at least one controller is
further programmed to re-engage the clutch and activate the engine
in response to (i) the accelerator pedal remaining non-depressed
and (ii) the output of the electric machine having a rotational
speed above a speed threshold.
10. A system for controlling coasting torque in a hybrid vehicle,
comprising: an engine; an electric machine selectively coupled to
the engine via a clutch; a battery electrically connected to the
electric machine; an accelerator pedal; and at least one controller
programmed to engage the clutch during an electric-only mode of
operation in response to (i) a tip-out of the accelerator pedal and
(ii) a state-of-charge of the battery exceeding a charge
threshold.
11. The system of claim 10, wherein the at least one controller is
further programmed to reduce a braking torque of the electric
machine in response to the engagement of the clutch.
12. The system of claim 11, wherein the at least one controller is
further programmed to alter a rate of decrease of braking torque of
the electric machine while a braking torque of the engine is
maintained in response to a reduction of vehicle speed.
13. The system of claim 11, wherein the at least one controller is
further programmed to increase the braking torque in the electric
machine during vehicle coasting based upon a decrease of engine
torque.
14. The system of claim 11, wherein the at least one controller is
further programmed to alter a rate of decrease of the braking
torque in the electric machine during vehicle coasting based upon
an increase of engine torque.
15. A system for controlling coasting torque in a hybrid vehicle,
comprising: an engine; an electric machine having an output and
selectively coupled to the engine via a clutch; an accelerator
pedal; and at least one controller programmed to engage the clutch
during an electric-only mode of operation in response to (i) a
tip-out of the accelerator pedal and (ii) a rotational speed of the
output of the electric machine being above a speed threshold.
16. The system of claim 15, wherein the at least one controller is
further programmed to decrease a braking torque of the electric
machine in response to the engagement of the clutch.
17. The system of claim 15, further comprising a brake pedal,
wherein a coasting event is defined during a time in which the
accelerator pedal and the brake pedal are non-depressed.
18. The system of claim 17, further comprising a battery
electrically connected to the electric machine for storing electric
power generated therefrom, wherein the at least one controller is
further programmed to engage the clutch during the coasting event
in response to a state of charge of the battery being above a
threshold.
19. The system of claim 15, further comprising a torque converter
having an impeller coupled to the electric machine, wherein the
output of the electric machine is the impeller such that the at
least one controller is programmed to engage the clutch in response
to a rotational speed of the impeller being above the speed
threshold.
20. The system of claim 15, further comprising a battery
electrically connected to the electric machine, wherein a coasting
event of the vehicle begins in response to the tip-out of the
accelerator pedal, and wherein the at least one controller is
further programmed to disengage the clutch to mechanically isolate
the engine from the electric machine during the coasting event in
response to a state of charge of the battery being below a
threshold.
21. The system of claim 15, wherein the at least one controller is
further configured to, subsequent to engaging the clutch, disengage
the clutch in response to a rotational speed of the output of the
electric machine being below the speed threshold.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to a system in a hybrid
electric vehicle for controlling the overall negative torque in the
vehicle while the vehicle is coasting after a tip-out of an
accelerator pedal.
BACKGROUND
[0002] In vehicles that include an internal combustion engine,
compression braking occurs when the vehicle is coasting.
Compression braking is a negative torque supplied by the engine
that slows the vehicle down when the accelerator pedal is released.
Compression braking can be caused by, for example, a
closed-throttle partial-vacuum when there is zero acceleration
request.
[0003] Hybrid electric vehicles (HEVs) include an internal
combustion engine and an electric machine (such as a
motor/generator) that provide power to propel the vehicle. If the
engine "on" and available to immediate propulsion power,
compression braking can be provided by the engine during vehicle
coasting. Due to the presence of the electric machine in the
powertrain, inconsistencies of compression braking may be felt by
an operator of the vehicle during vehicle coasting.
SUMMARY
[0004] According to one embodiment, a hybrid vehicle includes an
engine, an electric machine, and a disconnect clutch for
selectively coupling the engine to the electric machine. An
accelerator pedal is provided. At least one controller is
programmed to disengage the disconnect clutch and alter a commanded
torque to the electric machine in response to a tip-out of the
accelerator pedal in order to simulate compression braking of the
engine. The at least one controller is further programmed to
command braking torque in the electric machine in response to the
tip-out of the accelerator pedal. A magnitude of the braking torque
commanded by the at least one controller varies in response to
various tip-outs of the accelerator pedal occurring at
correspondingly various vehicle speeds such that the braking torque
of the electric machine simulates various magnitudes of engine
compression braking at various vehicle speeds. The magnitude of the
braking torque commanded by the at least one controller is
determined from a look-up table as a function of vehicle speed. A
battery is also provided. The battery is electrically connected to
the electric machine for storing electric power generated by the
electric machine. The at least one controller is further programmed
to re-engage the clutch and activate the engine in response to (i)
the accelerator pedal being non-depressed and (ii) a state of
charge (SOC) of the battery exceeding a SOC threshold. The at least
one controller is further programmed to alter the commanded torque
to the electric machine during vehicle coasting based upon (i)
vehicle speed and (ii) engine torque.
[0005] According to another embodiment, a system is provided for
controlling coasting torque in a hybrid vehicle. The system
comprises an engine, an electric machine selectively coupled to the
engine via a clutch, a battery electrically connected to the
electric machine, and an accelerator pedal. At least one controller
is programmed to engage the clutch during an electric-only mode of
operation in response to (i) a tip-out of the accelerator pedal and
(ii) a state-of-charge of the battery exceeding a charge threshold.
The at least one controller is further programmed to alter a rate
of decrease of braking torque of the electric machine while a
braking torque of the engine is maintained in response to a
reduction of vehicle speed. The at least one controller is further
programmed to alter the rate of decrease of the braking torque in
the electric machine during vehicle coasting based upon an increase
of engine torque.
[0006] In another embodiment, a system for controlling coasting
torque in a hybrid vehicle is provided. The system includes an
engine, an electric machine having an output, and a clutch
selectively coupling the engine to the electric machine. At least
one controller is programmed to engage the clutch during an
electric-only mode of operation in response to (i) a tip-out of an
accelerator pedal and (ii) a rotational speed of the output of the
electric machine being above a speed threshold. A brake pedal is
also provided. A coasting event is defined during a time in which
the accelerator pedal and the brake pedal are non-depressed. A
battery is electrically connected to the electric machine for
storing electric power generated therefrom. The at least one
controller is further programmed to engage the clutch during the
coasting event in response to a state of charge of the battery
being above a state-of-charge threshold.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a schematic illustration of a powertrain of a
hybrid electric vehicle.
[0008] FIG. 2 is a schematic illustration of a control strategy for
controlling an overall coasting torque in the vehicle.
[0009] FIG. 3 is a flow chart of an algorithm for controlling the
overall coasting torque during a coasting event.
[0010] FIG. 4 is a flow chart of another algorithm for controlling
the overall coasting torque during a coasting event.
DETAILED DESCRIPTION
[0011] Embodiments of the present disclosure are described herein.
It is to be understood, however, that the disclosed embodiments are
merely examples and other embodiments can 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
can be combined with features illustrated in one or more other
figures to produce embodiments that are not explicitly illustrated
or described. The combinations of features illustrated 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.
[0012] 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.
[0013] The engine 14 and the M/G 18 are both drive sources for 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 56 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 56 may
provide three phase alternating current (AC) to the M/G 18.
[0014] 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.
[0015] 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 fixed to M/G shaft 30 and
a turbine fixed to a transmission input shaft 32. 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 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 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.
[0016] 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) 50. The gearbox 24 then provides
powertrain output torque to output shaft 36.
[0017] 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.
[0018] 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.
[0019] The powertrain 12 further includes an associated powertrain
control unit (PCU) 50. While illustrated as one controller, the PCU
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.
[0020] The controller communicates with various engine/vehicle
sensors and actuators via an input/output (I/O) interface 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, PCU 50 may communicate signals to and/or from engine 14,
disconnect clutch 26, M/G 18, 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 PCU 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 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, 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), for example.
[0021] Control logic or functions performed by PCU 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 PCU 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.
[0022] 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 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. Based at least upon input from the
pedal 52, the controller 50 commands torque from the engine 14
and/or the M/G 18.
[0023] When the driver releases the accelerator pedal 52, demand
for acceleration falls to zero and the controller 50 does not
command additional acceleration. This action can be referred to as
a tip-out of the accelerator pedal 52. Subsequent to an accelerator
pedal tip-out, the vehicle begins coasting. If the engine 14 is
connected to the M/G 18 via the disconnect clutch 26 during the
coasting, the powertrain 12 experiences a negative torque due to
the engine friction and compression work in the engine 14 without
much (if any) fuel input into the engine 14. This negative torque
can be referred to as engine compression torque, or engine braking
torque. The vehicle begins to slow due to the engine braking until
a creep speed is reached, or until the driver demands additional
acceleration via the accelerator pedal 52.
[0024] Along with the controlling of the accelerator demands, 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.
[0025] 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 torque through the disconnect clutch 26 to
the M/G 18, and then from the M/G 18 through the torque converter
22 and gearbox 24. The M/G 18 may assist the engine 14 by providing
additional power to turn the shaft 30. This operation mode may be
referred to as a "hybrid mode" or an "electric assist mode."
[0026] 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 PCU 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
torque to the shaft 30. This operation mode may be referred to as
an "electric only" operation mode.
[0027] 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 rotational energy from spinning wheels 42 is
transferred back through the gearbox 24 and is converted into
electrical energy for storage in the battery 20.
[0028] It should be understood that the schematic illustrated in
FIG. 1 is merely exemplary and is not intended to be limited. Other
configurations are contemplated that utilize selective engagement
of both an engine and a motor to transmit through the transmission.
For example, the M/G 18 may be offset from the crankshaft 28, an
additional motor may be provided to start the engine 14, 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.
[0029] As previously described, a vehicle (such as the vehicle
illustrated in FIG. 1) may experience engine braking torque due to
compression in the engine when acceleration demands are zero and
the engine is on. In the HEV 10, engine braking due to compression
in the engine 14 is realized in the powertrain 12 only when the
disconnect clutch 26 is at least partially engaged to at least
partially connect the engine 14 to the M/G 18. The amount of engine
compression braking torque experienced in the powertrain 12 is
dependent upon certain operating conditions, such as engine speed.
However, for a given engine speed, the amount of engine compression
braking torque can vary based on several other factors, such as
altitude, engine aging, and engine temperature, and the like that
impact the amount of resistance subjected on the pistons of the
engine during a piston stroke throughout the engine compression
braking event.
[0030] Additionally, in an MHT vehicle, the amount of compression
braking torque in the engine 14 can vary depending on the operating
state of the powertrain. For example, in an electric-only operating
mode, there is no compression braking torque from the engine 14
because it is isolated from the remainder of the powertrain 12. In
a hybrid operating mode, or during times in which the disconnect
clutch 26 is at least partially engaged (such as starting/stopping
of the engine 14), compression braking torque from the engine 14
may sometimes only be partially transferred throughout the
powertrain 12. These changes in engine compression torque can lead
to inconsistent magnitudes of compression braking across various
driving ranges of the vehicle, as well as unpredictable behavior of
the vehicle. For example, when the vehicle is operating in the
hybrid operating mode, the vehicle may experience relatively high
negative torque in response to a tip-out of the accelerator pedal
due to engine compression; however, when the vehicle is operating
in the electric-only mode, the vehicle may experience no negative
torque from the engine.
[0031] According to the present disclosure, a system is provided
that delivers an overall consistent negative torque (or "overall
coasting torque") during a coasting event throughout the
powertrain. In other words, the system provides a consistent
overall coasting torque subsequent to a tip-out of the accelerator
pedal, regardless of the state of the engine. To provide a
consistent overall coasting torque, the controller 50 controls the
M/G 18 to supplement (or substitute for) the engine compression
torque. For example, even when the vehicle is operating in the
electric-only mode, the operator of the vehicle can experience a
negative torque in the powertrain of the vehicle when the vehicle
is coasting similar to the engine compression torque that would
otherwise be experienced if the engine were enabled during a hybrid
operating mode.
[0032] FIG. 2 is a schematic illustration of the overall coasting
torque control strategy according to one embodiment of the present
disclosure. This strategy can be implemented by a controller, such
as the PCU 50, for example.
[0033] A desired overall coasting torque table is stored in a
computer readable storage device that is in communication with the
controller. The desired overall coasting torque increases
negatively as the vehicle speed increases. For example, if a
tip-out event occurs while the vehicle is traveling at 60 mph, the
amount of negative torque desired to be realized throughout the
powertrain 12 is greater than if the tip-out event occurs while the
vehicle is traveling at 30 mph. The desired overall coasting
braking table may be stored in the form of a lookup table. It
should be understood that any amounts of desired overall coasting
torque values can be stored in the lookup table, and the one shown
in FIG. 2 is merely exemplary. For example, the amount of desired
overall coasting torque can be linear and/or constant. In response
to the tip-out event, the processor will determine the vehicle
speed and look up the desired overall coasting torque.
[0034] In response to the tip-out event, the controller also
determines the amount of engine compression torque. This can be
determined, for example, by a torque sensor or other similar
conventional means. The amount of engine compression torque
typically increases with higher vehicle speeds. As previously
described, the amount of engine compression torque may be zero if
the engine 14 is disconnected from the M/G 18.
[0035] The controller then compares the amount of engine
compression torque with the desired overall coasting torque from
the lookup table. The difference between the two is clipped (to
prevent extremely-high and extremely-low readings), and the result
is a commanded motor torque output. The commanded motor torque
output is sent to the M/G 18 for regenerative braking, or electric
braking The desired overall coasting braking is therefore fulfilled
by the combination of the negative torque output by the engine 14
(engine compression torque) and the negative torque output by the
M/G 18 (electric braking)
[0036] FIG. 3 illustrates a flowchart 300 of an example of an
overall algorithm 300 implemented by the controller 50 to command
and control the overall coasting torque. At 302, the controller
determines the beginning of a coasting event. This is indicated by
the release or tip-out of the accelerator pedal 52 as previously
described. Once the coasting event begins, the system controls the
negative torque (regenerative braking) of the M/G 18 to provide a
consistent overall coasting torque that simulates consistent engine
compression braking, as will be described below. The coasting
event, and thus the control strategy, continues until a subsequent
depression of the accelerator pedal, brake pedal, or leveling off
of the vehicle speed.
[0037] At 304, the controller determines whether the engine 14 is
on and/or coupled to the M/G 18 via the disconnect clutch 26. If
the engine 14 is off, then at 306 the commanded negative torque
output to the M/G 18 is a function of vehicle speed. Once the
commanded negative torque output is determined, it is clipped at
308 such that the final negative torque output command sent to the
M/G 18 is within a minimum and maximum threshold. This prevents any
over- or under-delivery of regenerative braking by the M/G 18 that
may harm, for example, the power electronics 56 or the battery
20.
[0038] If the controller determines that the engine 14 is on and
the disconnect clutch 26 is engaged to couple the engine 14 to the
M/G 18, this indicates that the engine 14 is providing compression
braking to the powertrain. Therefore, at 310, the commanded
negative torque output to the M/G 18 is determined as a function of
vehicle speed, less the amount of engine compression torque. The
amount of regenerative braking commanded by the controller to the
M/G 18 is therefore dependent upon the amount of engine compression
torque sustained in the engine 14. The commanded negative torque
output is clipped at 308 to again prevent any over- or
under-delivery of regenerative braking The control system ends at
312 and returns to maintain the overall coasting torque at a
desired amount based upon the changes in vehicle speed, as
indicated by the lookup table.
[0039] FIG. 4 is a flowchart illustrating another exemplary
algorithm 400 implemented by the controller 50 to command and
control the overall coasting torque. The algorithm 400 illustrated
in FIG. 4 is a more detailed algorithm that that of FIG. 3, and
controls the overall coasting torque based on several factors,
including whether the engine 14 is actively providing compression
braking, the state of the disconnect clutch 26, and the state of
charge (SOC) of the battery 20.
[0040] At 402, the controller detects a tip-out of the accelerator
pedal 52. This indicates the start of a coasting event. At 404, the
controller determines whether the disconnect clutch 26 is engaged,
coupling the engine 14 to the M/G 18. This indicates that during a
coasting event, the engine 14 is providing some amount of engine
compression torque. If a determination of NO is made at 404, then
the algorithm proceeds to 406, at which the controller determines
the speed of the vehicle. The controller commands regenerative
braking in the M/G 18 to provide negative torque at an amount based
upon the vehicle speed by utilizing the lookup table, for
example.
[0041] By implementing the system of FIG. 4 as so-far described,
the M/G 18 is the sole source for negative torque in the powertrain
12. When the engine 14 is not providing any compression braking,
the M/G 18 simulates compression braking by providing regenerative
braking at a magnitude that is desirable to effectively simulate
compression braking that occurs in a non-hybrid vehicle, for
example.
[0042] If, however, the engine 14 is providing compression braking
as determined at 404, then the algorithm proceeds to 410. At 410,
the controller determines the SOC of the battery 20 and compares it
to a first SOC threshold (thresh_low). If the SOC is below this
threshold, the SOC of the battery 20 may be low and it is desirable
to recharge the battery 20 through regenerative braking At 412, the
disconnect clutch 26 is disengaged, decoupling the engine 14 from
the M/G 18. This removes any compression braking in the engine 14
from being realized throughout the remainder of the powertrain 12.
With the compression braking being negated, the entire overall
coasting torque can be supplied by regenerative braking in the M/G
18, thereby maximizing the amount of electric charging supplied to
the battery 20 and more efficiently increasing the SOC of the
battery 20. Regenerative braking can supply the necessary negative
torque required to fulfill the desired overall coasting torque
during steps 406 and 408 with the engine 14 disconnected.
[0043] With the disconnect clutch 26 engaged to couple the engine
14 to the M/G 18, if the SOC of the battery 20 is not below the
first SOC threshold at 410, it is not necessarily a priority to
rapidly recharge the battery 20. As such, the engine 14 can remain
coupled to the M/G 18 to supply compression torque during the
coasting event. At 414, the controller determined the vehicle
speed, and utilizes the lookup table at 416 to determine the
desired overall coasting torque. The controller then determines the
amount of compression torque provided by the engine 14, and if
necessary, supplements the engine compression torque with
regenerative braking in the M/G 18 to fulfill the desired overall
costing torque. At 418, similar to step 310, the controller
commands regenerative braking based on the vehicle speed and the
magnitude of engine compression torque. The coasting event, and
thus the control strategy, continues until a subsequent depression
of the accelerator pedal, brake pedal, or leveling off of the
vehicle speed occurs at 420.
[0044] Returning back to the situation in which the disconnect
clutch 26 disengaged (either as determined at step 404 or commanded
at 412) and thus the engine 14 is not providing compression torque,
the SOC of the battery 20 is continuously monitored throughout the
coasting event at 422. If the SOC of the battery 20 is maintained
below a second threshold (thresh_high), the system continues to
meet the desired overall coasting torque by commanding regenerative
braking in the M/G 18 without any compression braking from the
engine 14.
[0045] If, however, the SOC of the battery 20 increases above the
second threshold (thresh_high) at 422, it is determined that the
SOC is too high and additional regenerative braking may be harmful
to the battery 20. In response to the SOC being above the second
threshold, the disconnect clutch 26 is commanded to re-engage to
couple the engine 14 back to the M/G 18 at 424. Fuel may then be
added to the engine to "start" the engine, enabling combustion to
occur in the engine 14. By actuating the disconnect clutch 26, the
engine 14 is enabled to provide compression braking to the
powertrain 12 such that the amount of regenerative braking can be
reduced, inhibiting an overcharge of the battery 20. With
compression braking causing deceleration in the vehicle, the
control system alters its commanded regenerative braking such that
the amount of engine compression torque is compared with the
desired overall coasting torque, with the difference being
commanded by the M/G 18. In other words, after the disconnect
clutch is engaged at 424, the algorithm proceeds to 416. The amount
of regenerative braking is then commanded based on the speed of the
vehicle and the amount of engine compression torque at 418.
[0046] Rather than engaging the disconnect clutch when the SOC is
above the second threshold, it should be understood that the
controller can command friction/hydraulic braking in the vehicle to
meet the desired overall coasting torque. This may provide a better
fuel efficiency in the vehicle as the engine 14 is not needed to be
activated to provide compression braking Friction braking may also
be activated at any time during the control strategy in place of
regenerative braking in the event the SOC of the battery 20 reaches
a charge threshold to prevent overcharging of the battery 20.
[0047] One example of the first threshold is 40% of the maximum
charge of the battery, and one example of the second threshold is
60% of the maximum charge. This provides an optimum battery
operating window of 40%-60%. It should be understood that these
thresholds can vary and can be optimally set for any hybrid
vehicle.
[0048] Instead of (or in combination with) continuously monitoring
the SOC during the coasting event and correspondingly re-engaging
the disconnect clutch 26 based on the SOC being above the second
threshold at 422, the controller can command the disconnect clutch
26 to re-engage based on the rotational speed of the output of the
M/G 18. As previously described, the torque converter 22 includes
an impeller that is connected to the output of the M/G 18.
Rotational speed of the impeller therefore indicates the rotational
speed of the output of the M/G 18. In a scenario in which the M/G
18 is rotating at high speeds during the coasting event, it may be
undesirable to command regenerative braking without the assist of
engine compression due to the maximum limits of the regenerative
braking system. The engine 14 can therefore be recoupled to the M/G
18 via the disconnect clutch 26 in response to the rotational speed
of the impeller being above a rotational speed threshold (e.g.,
2000 RPM) during the coasting event (subsequent to the tip-out of
the accelerator pedal 52). This assures compression braking is
available, and the amount of regenerative braking can be reduced
from what it would otherwise be commanded to provide without the
assist of compression braking in order to fulfill the desired
overall coasting torque. The controller can command the disconnect
clutch 26 to disengage again once the rotational speed falls below
the threshold, whereupon the amount of regenerative braking can be
commanded to sharply increase due to the absence of engine
compression braking
[0049] The embodiments described above explain a system for control
of overall coasting torque of a vehicle by commanding various
outputs by the M/G 18. References have been made to beginning the
control system based upon a tip-out of the accelerator pedal,
indicating the beginning of a coasting event. However, it should be
understood that release of the brake pedal when the vehicle is
stopped can cause the vehicle to creep. Creeping of the vehicle can
also be considered a coasting event, and therefore the algorithms
described above can similarly be activated based upon a tip-out of
the brake pedal.
[0050] The processes, methods, or algorithms disclosed herein can
be deliverable to/implemented by a processing device, controller,
or computer, which can include any existing programmable electronic
control unit or dedicated electronic control unit. Similarly, the
processes, methods, or algorithms can be stored as data and
instructions executable by a controller or computer in many forms
including, but not limited to, information permanently stored on
non-writable storage media such as ROM devices and information
alterably stored on writeable storage media such as floppy disks,
magnetic tapes, CDs, RAM devices, and other magnetic and optical
media. The processes, methods, or algorithms can also be
implemented in a software executable object. Alternatively, the
processes, methods, or algorithms can be embodied in whole or in
part using suitable hardware components, such as Application
Specific Integrated Circuits (ASICs), Field-Programmable Gate
Arrays (FPGAs), state machines, controllers or other hardware
components or devices, or a combination of hardware, software and
firmware components.
[0051] While exemplary embodiments are described above, it is not
intended that these embodiments describe all possible forms
encompassed by the claims. The words used in the specification are
words of description rather than limitation, and it is understood
that various changes can be made without departing from the spirit
and scope of the disclosure. As previously described, the features
of various embodiments can be combined to form further embodiments
of the invention 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 can be compromised to
achieve desired overall system attributes, which depend on the
specific application and implementation. These attributes can
include, but are not limited to cost, strength, durability, life
cycle cost, marketability, appearance, packaging, size,
serviceability, weight, manufacturability, ease of assembly, etc.
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 can be desirable for particular applications.
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