WO 2007/045970 PCT/IB2006/002914
METHOD AND SYSTEM FOR SHUTTING DOWN
AN ENGINE IN A HYBRID VEHICLE
Background of the Invention
Field of the Invention
[0001] The present invention relates to a hybrid vehicle and to a method and system for
shutting down an engine in a hybrid vehicle to improve the noise, vibration and harshness
("NVH") characteristics of the engine shutdown event.
Description of the Related Art
[0002] The motor vehicle industry is actively working to develop alternative powertrain
systems in an effort to improve vehicle fuel economy and reduce the level of pollutants
exhausted into the air by conventional powertrain systems equipped with internal combustion
engines. Significant development efforts have been directed to electric and fuel-cell vehicles.
Unfortunately, these alternative powertrain systems currently suffer from several limitations and,
for all practical purposes, are still under development. However, "hybrid" vehicles, which
typically include an internal combustion engine and an electric motor and/or generator, offer a
compromise between traditional internal combustion engine powered vehicles arid full electric
powered vehicles.
[0003] Hybrid vehicles are generally classified as either series hybrid vehicles or parallel
hybrid vehicles. In a series hybrid vehicle, a generator is driven by the mechanical output of an
internal combustion engine. The output of the generator may be combined with the output of a
vehicle battery to drive an electric motor, which in turn drives the vehicle.
[0004] Parallel hybrid vehicles, on the other hand, are usually driven directly by the
mechanical output of the internal combustion engine. However, when the vehicle must be
accelerated or decelerated at a rate that cannot be accomplished by the internal combustion
engine alone, the electric motor-generator, which is mechanically connected to the internal
combustion engine, operates as an electric motor (on acceleration) or as an electric generator (on
deceleration) to meet the required rate of acceleration or deceleration through the combined
output of the internal combustion engine and the electric motor-generator.
[0005] In certain hybrid vehicle configurations, the engine is shut down periodically during
vehicle operation when power is not required to conserve fuel and reduce emissions. During
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engine shutdown, the pumping processes within the engine result in torque disturbances and
engine crankshaft speed oscillations that adversely effect the smoothness of the engine shutdown
event. Noise, vibration and harshness associated with the shutdown event is generally
undesirable since it may be perceived by the vehicle occupant.
Summary of the Invention
[0006] A method is provided for shutting down an internal combustion engine in a hybrid
vehicle that includes a motor and a generator operatively connected to an engine crankshaft. In
an embodiment, the method includes the steps of reducing compression in at least one engine
cylinder and operating the motor or generator to influence motion of the engine crankshaft
during engine shutdown to attenuate oscillations in and expedite reduction of engine crankshaft
speed. A system for shutting down a hybrid vehicle internal combustion engine is also provided.
Brief Description of the Drawings
[0007] Embodiments of the invention will now be described, by way of example, with
reference to the accompanying drawings, wherein:
[0008] FIG. 1 is a schematic illustration of a hybrid vehicle powertrain including a system
for shutting down an internal combustion engine according to an embodiment of the present
invention;
[0009] FIG. 2 is a schematic illustration of a hybrid vehicle powertrain including a system
for shutting down an internal combustion engine according to another embodiment of the present
invention;
[0010] FIG. 3 is a graphical illustration of engine speed during engine shutdown in a prior art
powertrain;
[0011] FIG. 4 is a graphical illustration of engine speed during engine shutdown in a hybrid
powertrain as provided by an embodiment of the present invention; and
[0012] FIG. 5 is a graphical illustration of engine speed and motor-generator torque during
engine shutdown in a hybrid powertrain as provided by an embodiment of the present invention.
Detailed Description
[0013] Referring to FIG. 1, an exemplary hybrid vehicle powertrain 10 is shown, which
utilizes a method and system for shutting down an internal combustion engine according to an
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embodiment of the present invention. As illustrated in FIG. 1, hybrid powertrain 10 includes an
engine 12, such as a diesel or gasoline-fueled internal combustion engine, an electric or hydraulic
motor-generator 14, and an engine and/or motor-driven power transmission mechanism 16. In
FIG. 1, hybrid powertrain 10 operates as a parallel hybrid powertrain system, permitting motor-
generator 14 to drive power transmission mechanism 16 alone or in combination with engine 12
to provide motive power to a vehicle drive-axle 18. An optional clutch 20 may be positioned
between engine 12 and motor-generator 14 to selectively couple or uncouple engine 12 from
motor-generator 14 and/or power transmission mechanism 16. In this manner, motor-generator
14 is operatively connected to an engine crankshaft 21 and may be selectively operated to
influence motion thereof.
[0014] The energy required to operate motor-generator 14 is supplied by an energy source
22, including, without limitation, a battery, a bank of batteries or a hydraulic accumulator. As an
example, energy source 22 will be described herein below as a battery for storing the electrical
energy needed to power an electric motor-generator 14. It will also be appreciated that motor-
generator 14 may function as a generator to convert powertrain energy into electrical energy,
which may be used to charge energy source 22 and/or power various electrical components in the
vehicle.
[0015] Operation of hybrid powertrain 10 is controlled by a controller 26, such as a
microprocessor-based electronic control unit. Controller 26 may include or be linked to one or
more sub-controllers (not shown), such as a battery controller, for controlling operation of one or
more individual powertrain components. Controller 26 may also communicate with a vehicle
engine controller (not shown), which may also be contained in the same unit. Controller 26 may
be linked to one or more vehicle sensors (not shown), such as conventional engine or crankshaft
speed sensors, which provide data, such as engine or crankshaft speed, to controller 26 for
utilization in controlling motor-generator 14. As described in an embodiment of the invention
below, controller 26 may receive signals from the sensors, and based upon the received signals,
control operation of motor-generator 14 during engine shutdown to influence motion of
crankshaft 21.
[0016] In an embodiment, engine 12 includes a compression reducing device 28.
Compression reducing device 28 may include, without limitation, an engine brake or hydraulic
valve actuation system that controls actuation of an engine valve(s) independent of the
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crankshaft position. In an embodiment, compression reducing device 28 is mounted on, or
within, the engine overhead, and is adapted to change the opening timing of the engine intake
and/or exhaust valves to reduce compression in at least one engine cylinder (neither shown). In
this manner, the cylinder pressure and, accordingly, the torque applied to engine crankshaft 21
by the compressed cylinder contents, may be selectively reduced. In a particular configuration,
compression reducing device 28 is configured to continuously open at least one engine intake
valve during engine shutdown.
[0017] The hybrid powertrain system configuration shown in FIG. 1 is provided for
reference only and is not intended to limit the scope of the present invention. As shown in FIG.
2, for example, hybrid powertrain 10 may also be configured with a motor 30 that is separate and
distinct from a generator 32. Motor 30 and generator 32 may be operatively connected to engine
crankshaft 21 by a power splitting device 34, such as a planetary gearset and the like, which
permits hybrid powertrain 10 to operate in a serial or parallel manner.
[0018] A method and system for shutting down an internal combustion engine 12 in a hybrid
vehicle according to an embodiment of the present invention will now be described with
reference to FIGS. 3-5. In an embodiment, when a command to shutdown internal combustion
engine 12 is received by controller 26, controller 26 is configured to selectively operate
compression-reducing device 28 to reduce the compression in at least one cylinder of the engine
and, accordingly, to reduce the torque applied to crankshaft 21. For example, compression-
reducing device 28 may open at least one engine intake valve during the engine shutdown event,
thereby reducing or eliminating the cylinder pressure and corresponding torque applied to rotate
crankshaft 21. Controller 26 may operate compression-reducing device 28 to open the intake
valves in any number of engine cylinders to achieve the desired engine cylinder decompression.
Controller 26may also be configured to operate compression-reducing device 28 during the
entire engine shutdown event or only during some finite portion of the engine shutdown event.
[0019] During the engine shutdown event, controller 26 is also configured to operate motor-
generator 14, or motor 30 and generator 32 independently when not integrally packaged as
shown in FIG. 2, to influence motion of engine crankshaft 21. In an embodiment, motor-
generator 14 may be operated to apply a predetermined torque to engine crankshaft 21, or a
target torque profile that varies with respect to time, to influence motion of engine crankshaft 21.
Torque may be applied to crankshaft 21 by virtue of motor-generator 14 operating as a generator,
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whereby mechanical energy removed from crankshaft 21 is converted to electrical energy by
motor-generator 14 and stored in energy source 22. The torque profile may be substantially
synchronized with the engine crankshaft speed during engine shutdown. The predetermined
torque or target torque profile may be pre-programmed into controller 26 and referenced during
the engine shutdown event to generate a command for operation of motor-generator 14 or may
be determined in a closed-loop manner relying on data received from the vehicle sensors.
[0020] Operation of the present invention will be further appreciated with reference to
FIGS. 3-5. FIG. 3 illustrates engine speed during engine shutdown in a prior art powertrain.
Oscillations in engine speed that contribute to noise, vibration and harshness in the powertrain
are visible in the engine speed graph, particularly near the end of the engine shutdown event as
the engine crankshaft slows to a stop. By contrast, FIG. 4 graphically illustrates engine speed
during engine shutdown according to an embodiment of the present invention. By reducing
compression in at least one engine cylinder and operating motor-generator 14 to influence
motion of engine crankshaft 21 during engine shutdown, the oscillations visible in FIG. 3 are
attenuated and crankshaft speed reduction is expedited.
[0021] FIG. 5 overlays motor-generator torque with the engine speed graph of FIG. 4. In
the embodiment illustrated in FIG. 5, controller 26 determines the required torque in a closed-
loop manner based on data received from vehicle sensors, such as the engine or crankshaft speed
sensors, with the objective of slowing the motor-generator speed to zero revolutions per minute
("RPM"). At T0, engine is operating at approximately 1030 RPM and motor-generator 14 is
applying no torque to crankshaft 21. At approximately T1.1, engine 12 is commanded off and
controller 26 operates motor-generator 14 as a generator to apply its maximum torque (e.g.,
about 420 Nm) to remove energy from crankshaft 21. The mechanical energy removed from
crankshaft 21 is converted to electrical energy by motor-generator 14 and stored in energy source
22, thereby increasing the energy source's state-of-charge. At approximately T2.1, controller 26
operates motor-generator 14 to apply torque generally proportional to engine crankshaft speed.
Gradually reducing the torque applied to crankshaft 21 inhibits motor-generator 14 from
applying such as significant amount of torque that engine 12 is cranked backwards after coming
to rest.
[0022] Alternatively, motor-generator 14 may be operated at a predetermined speed or
according to a target speed profile that varies with respect to time during engine shutdown. In an
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embodiment, for example, motor-generator 14 may be commanded to operate at zero revolutions
per minute so that motor-generator 14 removes energy from crankshaft 21 during shutdown. In
another embodiment, controller 26 may be configured to alternatively operate motor-generator
14 as a motor and a generator, or motor 30 and generator 32 in their individual capacity, to
actively dampen oscillations in engine crankshaft speed during engine shutdown. In this manner,
positive torque may be applied to crankshaft 21 by virtue of motor-generator 14 operating as a
motor and negative torque may be applied crankshaft 21 by virtue of motor-generator 14
operating as a generator.
[0023] The present invention has been particularly shown and described with reference to the
foregoing embodiments, which are merely illustrative of the best modes for carrying out the
invention. It should be understood by those skilled in the art that various alternatives to the
embodiments of the invention described herein may be employed in practicing the invention
without departing from the spirit and scope of the invention as defined in the following claims.
It is intended that the following claims define the scope of the invention and that the method and
apparatus within the scope of these claims and their equivalents be covered thereby. This
description of the invention should be understood to include all novel and non-obvious
combinations of elements described herein, and claims may be presented in this or a later
application to any novel and non-obvious combination of these elements. Moreover, the
foregoing embodiments are illustrative, and no single feature or element is essential to all
possible combinations that may be claimed in this or a later application.
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CLAIMS
What is claimed is:
1. A method for shutting down an internal combustion engine (12) in a hybrid vehicle that
includes at least one of a motor (30) and a generator (32) operatively connected to an engine
crankshaft (21), the method comprising the steps of:
reducing compression in at least one engine cylinder; and
operating the motor (30) or the generator (32) to influence motion of the engine
crankshaft (21) during engine (12) shutdown to attenuate oscillations in and expedite reduction
of engine crankshaft speed.
2. The method of claim 1, wherein the reducing step further includes opening at least one
engine valve.
3. The method of claim 1, wherein the reducing step further includes reducing compression
in at least one cylinder until compression is substantially eliminated.
4. The method of claim 1, wherein the motor (30) and the generator (32) are integrally
packaged as a motor-generator (14).
5. The method of claim 1, wherein the operating step includes operating the motor (30) or
the generator (32) to apply a predetermined torque to the engine crankshaft (21) or a target
torque profile that varies with respect to time.
6. The method of claim 5, wherein the torque profile is substantially synchronized with the
engine crankshaft speed during engine shutdown.
7. The method of claim 1, wherein the operating step includes operating the motor (30) or
the generator (32) at a predetermined speed or according to a target speed profile that varies with
respect to time.
8. The method of claim 7, wherein the predetermined speed is approximately zero
revolutions per minute.
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9. The method of claim 8, wherein the operating step includes alternatively operating the
motor (30) and the generator (32) to actively dampen oscillations in engine crankshaft speed
during engine shutdown.
10. The method of claim 1, wherein the hybrid powertrain system (10) further includes a
clutch (20) between the engine (12) and the motor (30), and the method further includes the step
of activating the clutch (20) to connect the motor (30) to the engine (12) prior to the operating
step.
11. A method for shutting down an internal combustion engine (12) in a hybrid vehicle that
includes a motor (30) and a generator (32) operatively connected to an engine crankshaft (21),
the method comprising the steps of:
reducing compression in at least one engine cylinder; and
operating the generator (32) to remove energy from the engine crankshaft (21) during
engine shutdown, wherein the operating step includes operating the generator (32) to apply a
predetermined torque load to the engine crankshaft (21) or a target torque load profile that varies
with respect to time, or operating the generator (32) at a predetermined speed or according to a
target speed profile that varies with respect to time.
12. The method of claim 11, wherein the motor (30) and generator (32) are integrally
packaged as a motor-generator (14).
13. A system for shutting down a hybrid vehicle internal combustion engine (12) that
includes at least one engine cylinder and a crankshaft (21), the system comprising:
an engine cylinder compression-reducing device (28);
at least one of a motor (30) and a generator (32) operatively connected to the engine
crankshaft (21) and adapted to influence motion of the engine crankshaft (21) during engine
shutdown; and
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a controller (26) configured to selectively operate the compression-reducing device (28)
to reduce compression in at least one engine cylinder and to selectively operate the motor (30) or
the generator (32) to influence motion of the engine crankshaft (21) during engine shutdown.
14. The system of claim 13, wherein the reducing step further includes opening at least one
engine valve.
15. The system of claim 13, wherein the controller (26) is configured to reduce compression
in at least one cylinder until compression is substantially eliminated.
16. The system of claim 13, wherein the motor (30) and the generator (32) are integrally
packaged as a motor-generator (14).
17. The system of claim 13, wherein the controller (26) is configured to operate the motor
(30) or the generator (32) to apply a predetermined torque to the engine crankshaft (21) or a
target torque profile that varies with respect to time.
18. The system of claim 17, wherein the torque load profile is substantially synchronized
with the engine crankshaft speed during engine shutdown.
19. The system of claim 13, wherein the controller is configured to operate the motor (30) or
the generator (32) at a predetermined speed or according to a target speed profile that varies with
respect to time.
20. The system of claim 19, wherein the predetermined speed is approximately zero
revolutions per minute.
21. The system of claim 13, wherein the controller (26) is configured to selectively operate
the motor (30) or the generator (32) in a closed-loop manner.
22. The system of claim 13, wherein the controller (26) is configured to alternatively operate
the motor (30) and the generator (32) to actively dampen oscillations in engine crankshaft speed
during engine shutdown.
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23. The system of claim 13, wherein the hybrid powertrain system (10) further includes a
clutch (20) between the engine (12) and the motor (30), and wherein the controller (26) is
configured to activate the clutch (20) to connect the motor (30) to the engine (12) prior to the
operating the motor (30).
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A method is provided for shutting down an internal combustion
engine (12) in a hybrid vehicle that includes a motor (30) and a
generator (32) operatively connected to an engine crankshaft
(21). The method includes the steps of reducing compression in
at least one engine cylinder and operating the motor (30) or
generator 32) to influence motion of the engine crankshaft (21)
during engine shutdown to attenuate oscillations in and expedite
reduction of engine crankshaft speed. A system for shutting down
a hybrid vehicle internal combustion engine (12) is also provided.