U.S. patent application number 09/760503 was filed with the patent office on 2002-07-18 for crankshaft rotation control in a hybrid electric vehicle.
Invention is credited to Downs, Robert Charles, Hoang, Tony T., Richey, Dennis T., Tamai, Goro.
Application Number | 20020093202 09/760503 |
Document ID | / |
Family ID | 25059301 |
Filed Date | 2002-07-18 |
United States Patent
Application |
20020093202 |
Kind Code |
A1 |
Downs, Robert Charles ; et
al. |
July 18, 2002 |
Crankshaft rotation control in a hybrid electric vehicle
Abstract
A method of controlling engine crankshaft motion in a hybrid
electric drive system having an internal combustion engine and a
motor-generator operatively connected to a crankshaft of the engine
is disclosed. The steps include monitoring the crankshaft position,
forecasting a crankshaft stall position; comparing the forecast
stall position with a target range; and if the forecast crankshaft
stall position is outside the target range, operating the
motor-generator to modify the forecast stall position to be within
the target range. These steps properly position the crankshaft for
re-initiating engine start-up. The method further includes the
steps of calculating an effective lube interval time once the
crankshaft speed is zero; comparing the effective lube interval
time to a critical time; and if the effective lube interval time is
greater than the critical time, pulsing the motor-generator to rock
the crankshaft for a pulse time to redistribute a lubricant
film.
Inventors: |
Downs, Robert Charles; (La
Jolla, CA) ; Tamai, Goro; (Warren, MI) ;
Hoang, Tony T.; (Warren, MI) ; Richey, Dennis T.;
(Sterling Heights, MI) |
Correspondence
Address: |
LAURA C. HARGITT
General Motors Corporation
Mail Code 482-C23-B21
P.O. Box 300
Detroit
MI
48265-3000
US
|
Family ID: |
25059301 |
Appl. No.: |
09/760503 |
Filed: |
January 16, 2001 |
Current U.S.
Class: |
290/40R ; 180/60;
180/65.26; 180/65.27; 180/65.28; 180/65.285; 903/917 |
Current CPC
Class: |
Y02T 10/62 20130101;
B60W 10/06 20130101; B60K 6/485 20130101; F02D 2041/0092 20130101;
F02N 2019/008 20130101; F02D 41/009 20130101; F02D 2041/0095
20130101; F01M 5/02 20130101; F02N 19/005 20130101; B60K 2006/268
20130101; Y10S 903/917 20130101; B60W 10/08 20130101; B60W 20/00
20130101; F02N 2019/007 20130101; B60K 6/54 20130101; B60W 10/04
20130101; F02D 41/042 20130101 |
Class at
Publication: |
290/40.00R ;
180/60 |
International
Class: |
B60L 007/00 |
Claims
1. A method of controlling engine crankshaft motion in a hybrid
electric drive system having an internal combustion engine and a
motor-generator operatively connected to a crankshaft of the
engine, comprising the steps of: monitoring the crankshaft
position; forecasting a crankshaft stall position; comparing the
forecast stall position with a target range; and if the forecast
crankshaft stall position is outside the target range, operating
the motor-generator to modify the forecast stall position to be
within the target range.
2. The method of claim 1, wherein the step of operating the
motor-generator further includes one of the following steps:
applying a preloading torque to the crankshaft in the direction of
crankshaft rotation; and applying regenerative braking to slow the
crankshaft to stall within the target range.
3. The method of claim 2, further comprising the steps of: after
operating the motor-generator, monitoring the crankshaft speed; if
the crankshaft speed is zero, comparing the crankshaft stall
position to the target range; and if the crankshaft stall position
is outside the target range, operating the motor-generator to
modify the crankshaft stall position to be within the target
range.
4. The method of claim 3, further comprising the step of: after the
crankshaft speed is zero, calculating an effective lube interval
time; comparing the effective lube interval time to a critical
time; and if the effective lube interval time is greater than the
critical time, pulsing the motor-generator to rock the crankshaft
for a pulse time to redistribute a lubricant film.
5. The method of claim 4, wherein the step of calculating the
effective lube interval time further comprising the steps of:
monitoring engine coolant temperature; monitoring engine oil
pressure; and monitoring how long the crankshaft speed is zero
without motor-generator pulsations.
6. The method of claim 5, further comprising the step of: summing
the pulse times.
7. The method of claim 6, further comprising the step of: comparing
the summed pulse time to a maximum time; and if the summed pulse
time is greater than the maximum time, discontinuing further
pulsing of the motor-generator.
8. A method of controlling engine crankshaft motion for lubrication
redistribution in a hybrid electric drive system having an internal
combustion engine and a motor-generator operatively connected to a
crankshaft of the engine, comprising the steps of: monitoring
crankshaft speed; if crankshaft speed is zero, calculating an
effective lube interval time; comparing the effective lube interval
time to a critical time; if the effective lube interval time is
greater than the critical time, pulsing the motor-generator to rock
the crankshaft for a pulse time to redistribute a lubricant
film.
9. The method of claim 8, wherein the step of calculating the
effective lube interval time further comprising the steps of:
monitoring engine coolant temperature; monitoring engine oil
pressure; and monitoring how long the crankshaft speed is zero
without motor-generator pulsations.
10. The method of claim 9, further comprising the step of: summing
the pulse times.
11. The method of claim 10, further comprising the steps of:
comparing the summed pulse time to a maximum time; and if the
summed pulse time is greater than the maximum time, discontinuing
further pulsing of the motor-generator.
Description
TECHNICAL FIELD
[0001] The present invention relates to a control system for
inducing crankshaft rotation and imposing crankshaft position in a
hybrid electric vehicle.
BACKGROUND OF THE INVENTION
[0002] A hybrid electric vehicle may be powered alternatively or
simultaneously by an internal combustion engine and an electric
motor to maximize fuel economy. The electric motor may be part of
an electric machine, referred to herein as a motor-generator, which
may replace the conventional starter motor and alternator. To move
the vehicle from a stopped position, the motor-generator draws
electrical energy from a battery pack to turn the engine
crankshaft. As vehicle speed increases, fuel and spark are
delivered to initiate engine operation. At a certain vehicle speed
range, the motor-generator may operate as a generator driven by the
engine crankshaft to recharge the battery pack and to supply
electrical power to auxiliary vehicle devices such as fans, radios,
etc.
[0003] When the vehicle is coasting or braking, fuel flow to the
engine may be stopped to improve fuel economy. During fuel-off
deceleration downshifts, the motor-generator may operate as a motor
to synchronize engine and transmission speeds by increasing engine
speed to facilitate a downshift. When the engine is off, the
auxiliary vehicle devices are powered by the battery pack in
cooperation with a DC-DC converter.
[0004] If the vehicle is stalled for a period of time, the engine
oil pressure gradually decreases in the oil feed galleys to the
crankshaft and connecting rod bearings, which may lead to a
degradation of the lubricant film and a pure boundary lubrication
condition. Due to such an increased friction condition,
re-initiating engine start up may require higher torque input from
the electric motor-generator to crank the crankshaft.
[0005] Another mechanism that can affect the torque required to
re-initiate engine start up is the crankshaft angular location
during an engine stall. It is favorable to have the crankshaft rest
with the intake valve open at the cylinder which is in its intake
stroke. If the intake valve closes, the relatively cool inducted
air is expanded by the hot cylinder walls, raising the cylinder
pressure, hence increasing the required torque to rotate the
crankshaft.
[0006] As the engine is cranked, the driver may feel compression
vibration from the engine. The smoothness of the engine cranking is
a function of the rotational position of the crankshaft upon engine
start up since the torque required to rotate the crankshaft
undulates with the in-cylinder pressures.
SUMMARY OF THE INVENTION
[0007] The present invention provides a control method for inducing
crankshaft rotation in a hybrid electric vehicle. The control
method provides the capability of operating an electric
motor-generator to affect at what rotational orientation the
crankshaft will stop, as the crankshaft speed slows to zero.
Further the control method operates the motor-generator to rotate
the crankshaft forward or backwards to a more advantageous
rotational location once the crankshaft speed is zero, prior to
restarting the engine, to minimize the vibration felt by the
driver. The control method determines the crankshaft rotational
location using a crankshaft locational sensing means which may
operate in conjunction with the ignition system.
[0008] The control method also provides the capability of powering
the electric motor-generator to rotate the crankshaft in one or
both rotational directions to redistribute the lubricant film on
the crankshaft bearings. This minimizes the need for greater motor
torque input to restart the engine as the friction level is
maintained and not appreciably increased. The control method
measures the time the engine is stalled as a function of the engine
coolant temperature and oil pressure to determine when power
pulsations to the electric motor are required to "rock" the
crankshaft to re-establish the lubricant film.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a schematic illustration of a hybrid vehicle drive
system;
[0010] FIG. 2 is a cross sectional view of the internal combustion
engine of the hybrid vehicle drive system; and
[0011] FIG. 3 is a flow chart of the control method of the present
invention operational in the drive system of FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0012] With reference to FIG. 1, a hybrid electric vehicle includes
a hybrid drive system, shown generally as 10, having an internal
combustion engine 12, an electric machine referred to herein as a
motor-generator 14, and a multi-speed automatic transmission
16.
[0013] The internal combustion engine 12 may be of conventional
construction as shown in FIG. 2, comprising an engine block 17
having one or more cylinders 18 and a cylinder head 19 mating with
the upper face of the engine block to close off the cylinders. A
piston 20 is housed in each cylinder 18 for reciprocation therein
and is connected to an upper end of a connecting rod 22 by a piston
pin 24. The lower end of the connecting rod 22 is connected to a
throw 26 of a crankshaft 28 by a connecting rod bearing assembly
30. The crankshaft 28 is rotatably supported by upper main bearing
supports in the lower face of the engine block and by lower main
bearing caps bolted to the engine block. An oil pan, not shown,
mounts to the lower face of the engine block and provides an oil
reservoir. An oil pump, not shown, circulates oil from the oil pan
through oil feed galleys in the engine and in particular to
lubricate the interface of the crankshaft 28 to its main bearing
supports and the connecting rod bearing assembly 30.
[0014] The electric motor-generator 14 of the hybrid drive system
10 in FIG. 1 is an electric machine having a stator and a rotor,
both not shown, selectively controlled by controller 31. The
controller 31 is a conventional digital programmable computer with
power electronics. The rotor of the motor-generator is directly
connected to the crankshaft 28 of the engine 12 such as via a
direct drive mechanism 32 shown as a belt and pulley in FIG. 1,
connected to the front end of the engine. This allows the
motor-generator 14 to selectively operate as a starter motor in
supplying a cranking torque to the crankshaft 28 and to operate as
a generator by receiving rotational energy from the crankshaft and
converting it to electrical energy for recharging an associated
battery pack 34. The motor-generator may also be arranged between
the engine and transmission where the stator is mounted to the rear
of the engine block or to the transmission housing and the rotor is
connected to the crankshaft through a clutch assembly or hub.
[0015] A DCDC converter 36 is provided to direct higher voltage
charging power from the motor-generator controller 31 to a lower
voltage vehicle accessory system 38 for powering accessories such
as radios and fans during generator operation.
[0016] The transmission 16 of the vehicle drive system is a
well-known device including gear sets and friction devices operable
to provide a number of drive speed ratios between the engine and
vehicle drive wheels. It may further include a torque converter if
desired. A powertrain control module (PCM) 40 controls the
operation of the engine 12, transmission 16, and motor-generator
controller 31.
[0017] A general control and operating sequence for the hybrid
drive system is described next. Initial vehicle key-up is analogous
to that of a conventionally powered vehicle. The driver turns the
ignition key to the crank state, wherein the controller 31 signals
the motor-generator 14 to draw electrical energy from the battery
pack 34. The motor-generator 14 transfers torque to the engine
crankshaft 28 via the belt drive 32 to crank the engine 12.
[0018] Above a certain engine speed while the engine 12 is
operating, the motor-generator 14 may operate as a generator due to
the rotational input from the crankshaft 28 to recharge the battery
pack 34 and power the vehicle accessory system 38.
[0019] When the driver applies the brake pedal or does not apply
the gas pedal during an extended coast, fuel delivery may stop to
conserve fuel and control emissions. To balance driver-felt
smoothness and fuel economy, the fuel may be cut off one cylinder
at a time as the spark is ramped down. During fuel-off vehicle
coasting, the controller 31 may reverse the motor-generator's
polarity to direct charging current to the battery pack 34 and
decelerate the vehicle by slowing the engine speed. This
motor-generator operation is referred to as "regenerative braking".
When the engine speed drops below a certain speed where compression
pulses may become objectionable to a driver, the PCM 40 shifts the
transmission 16 to an effectively neutral gear thereby stalling the
engine 12. This so called "drop-to-neutral" speed, in the range of
400 to 900 rpm, is chosen to be as low as possible to improve
driveability and may vary based on vehicle deceleration.
[0020] Further, during fuel-off deceleration downshifts, the
motor-generator 14 may operate as a motor to synchronize engine and
transmission speeds as needed. Since an engine idle-air-control
motor, which is conventionally used to match engine and
transmission speeds, has no effect during fuel-off mode, the
motor-generator 14 increases the engine speed for seamlessly
releasing the higher gear clutch and engaging the lower gear
clutch. Downshifts ensure the transmission 16 is in the proper gear
for re-acceleration. If the driver demands acceleration after the
engine speed has dropped below a minimum reference, the
motor-generator 14 may again act as a motor to turn the crankshaft
28, in conjunction with fuel delivery, to restart combustion in the
spinning engine.
[0021] To begin vehicle movement from a vehicle stop, such as at a
traffic light, upon releasing the brake pedal, the controller 31
signals the motor-generator 14 to draw electrical energy from the
battery pack 34. As the motor-generator 14 cranks the crankshaft
28, the vehicle moves forward due to electrical creep drive via the
torque converter or starting clutch, at which time fuel and spark
are delivered to initiate engine combustion. The motor-generator 14
may supplement the torque needed for acceleration supplied by the
engine, especially at lower start-up speeds.
[0022] The smoothness of engine cranking based on compression
vibration felt by a driver during vehicle launch from a fuel-off
stop has been shown to be a function of the initial crankshaft
rotational orientation. The torque required to rotate the
crankshaft fluctuates with in-cylinder pressures. Therefore the
present invention is a method of controlling engine crankshaft
motion to affect the crankshaft stall position. The method provides
two opportunities to modify the crankshaft stall orientation--once
during deceleration, referred to as the Pre-Positioning Control
Cycle, and once the engine has stopped, referred to as the Stall
Positioning Control Cycle.
[0023] To support the Positioning cycles, a means for sensing the
crankshaft rotational orientation is provided. One such locational
sensing means is embodied in a six-tooth encoder wheel about the
crankshaft where a seventh tooth is cut into the crankshaft to
indicate top-dead-center, for example, for two of four cylinders. A
magnetic pickup senses the teeth of the encoder and this
information in conjunction with software monitoring the ignition
cycle can resolve where, in the four-stroke cycle, the engine has
stalled. A second locational sensing means is an optical encoder
requiring an optical sensor to detect the rotational orientation of
the crankshaft.
[0024] The actual desired position of the crankshaft for restart is
based on the specific engine application. For example, the desired
position of the crankshaft in a four cylinder engine may be with a
pair of the pistons within sixty crank degrees before or after
top-dead-center, before the intake valve close position for the
cylinder in its intake stroke. The tolerance for the desired
position is dependent on how sensitive the resolution is for
sensing the crankshaft position. For example, a crankshaft
six-tooth encoder, where the teeth are located at sixty degree
intervals about the crankshaft, can only resolve the position
within a sixty degree window. Properly positioning the crankshaft
may be less critical in engines with more than four cylinders.
[0025] The Pre-Positioning Control method operates to affect the
stalled crankshaft position once the vehicle is decelerating in the
fuel-off mode and the crankshaft speed falls below the "drop to
neutral" speed. An engine stall is commanded (by shifting the
transmission to an effectively neutral gear) and the
motor-generator is commanded to ramp in some regenerative braking
to quickly decrease the engine speed. This assists in preventing
"stumbling run-on" of combustion.
[0026] As shown in FIG. 3A, the Pre-Positioning control method
includes monitoring the crankshaft position via the locational
sensing means. With this data and the deceleration rate of the
crankshaft, the controller forecasts the crankshaft stall position
in block 100. If the forecasted position is within the target
range, then the pre-positioning control method is complete. If the
forecasted position is outside the target range in block 102, then
the controller operates the motor-generator to affect the
forecasted stall position in block 104. This may be accomplished by
either applying a preloading torque in the direction of the
crankshaft rotation to keep the crankshaft from rocking back once
it stops or applying regenerative braking to slow the crankshaft to
the desired position. The motor-generator pre-positioning control
is performed to stall the engine so that the crankshaft position
falls as close to, if not within, the target range.
[0027] The Stall Positioning control method may be initiated after
the Pre-Positioning control has been run or it may be executed
independently. In either case, the Stall Positioning control method
begins when the engine speed is zero in FIG. 3B block 110. Like the
Pre-Positioning method, the controller compares the forecasted
stall position to the target range in block 112. An actual
crankshaft position is not obtainable when the crankshaft is not
rotating. If the forecasted crankshaft position falls outside the
target position range, the controller signals the motor-generator
to draw current from the battery pack, and rotate the crankshaft to
a position within the reference position range in block 114. If the
crankshaft position falls within the reference position range, then
it is properly prepared for minimizing compression vibration upon
vehicle launch from the engine-off state.
[0028] The method of controlling engine crankshaft motion further
includes a Lubrication Redistribution control, which may be
initiated when the engine is stalled in FIG. 3C block 120 and after
the Stall Positioning control cycle. Under certain drive
conditions, the engine may remain stalled for an extended period of
time. Concurrently, the engine oil pump is also inoperative. Oil
pressure gradually drops in the oil feed galleys throughout the
engine, and in particular to the galleys feeding the connecting rod
bearings. During extended stall times, the lubricant film between
the crankshaft and the connecting rod and main bearings may
degenerate leading to a pure boundary lubrication condition. Such a
condition increases the torque needed to crank the engine to
restart it. To maintain the lubricant film at the
crankshaft-bearing interface, the control method of the present
invention operates to power the motor-generator to gently rock,
i.e. rotate, the crankshaft in one or both rotational
directions.
[0029] To determine if the crankshaft needs to be lubricated in
FIG. 3C block 122, the controller calculates an effective lube
interval time. This variable takes into account not only how long
the engine is stalled without active lubrication, but the
controller also checks an engine coolant temperature sensor to
monitor the engine coolant temperature, and an oil pressure sensor
to monitor engine oil pressure. The controller then compares the
effective lubrication interval to a critical time in block 124. For
example, the critical time may be 10 to 20 seconds. If the
effective lube interval is greater than the critical time, then the
crankshaft needs to be rocked to redistribute the lubricant film on
the bearings. In block 126, the controller signals the
motor-generator to draw power from the battery pack and deliver
pulses to rotate the crankshaft, referred to as rocking the
crankshaft. The motor-generator may rotate the crankshaft in both
directions or it may rotate in one direction with the crankshaft
rocking back naturally due to compression reaction forces. To
adequately redistribute the lubrication, the crankshaft need only
be rotated approximately 10 to 60 degrees.
[0030] Preferably the crankshaft returns to its initial position
following the lubrication redistribution cycle as the position may
have already been set by the previous positioning cycle. To ensure
that the crankshaft is returned to its initial position, a locating
wheel on the motor-generator having a finer resolution than the
crankshaft locating wheel may be used to monitor the location of
the motor-generator and therefore the change in position of the
crankshaft during the lubrication redistribution cycle.
[0031] The pulse times of the motor-generator are summed in block
128 and compared to a maximum reference time in block 130. If the
summed pulse time is greater than the maximum time, then the
lubrication cycle is terminated. This is a safety feature to
prevent the risk of battery drain. For example, the maximum time
may be 500 seconds, which would allow 50 motor-generator pulsations
at 10 second intervals. Typically, the engine will be restarted
before the maximum time is reached. If the summed pulse time is
less than the maximum, then the controller continues to monitor the
input variables and run the lubrication redistribution routine
until the engine restart command is given.
[0032] The present invention is for controlling engine crankshaft
motion through the use of the motor-generator operatively connected
to the engine crankshaft. In particular, the method may be used for
positioning the crankshaft for a smoother re-start of the engine
and for re-creating a lubricant film on the crankshaft bearings
when the engine has been stalled for a given period of time.
[0033] The foregoing description of the preferred embodiment of the
invention has been presented for the purpose of illustration and
description. It is not intended to be exhaustive, nor is it
intended to limit the invention to the precise form disclosed. It
will be apparent to those skilled in the art that the disclosed
embodiment may be modified in light of the above teachings. The
embodiment was chosen to provide an illustration of the principles
of the invention and its practical application to thereby enable
one of ordinary skill in the art to utilize the invention in
various embodiments and with various modifications as are suited to
the particular use contemplated. Therefore, the foregoing
description is to be considered exemplary, rather than limiting,
and the true scope of the invention is that described in the
following claims.
* * * * *