Note: Descriptions are shown in the official language in which they were submitted.
I I I M A
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DUAL FUNCTION HOLDING DEVICE OPERABLE UNDER A
SYSTEM POWER LOSS CONDITION
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Application No.
60/796,473,
filed May 1, 2006, which is incorporated herein by reference.
FIELD OF THE INVENTION
The present invention relates generally to a clutch actuator and, more
particularly, to
a clutclh actuator including a holding device operable to either lock the
clutch actuator to hold
a clutcl:i in an open position, or permit the clutch actuator to move the
clutch to a closed
position.
BACKGROUND OF THE INVENTION
In a vehicle having an electrically actuated clutch, it is desirable to be
able to provide
a fail safe operation mode for the clutch in the event of a power loss, such
as a system power
loss for supplying power to the clutch actuator. In the event of a power loss
when the vehicle
is stationary with the clutch disengaged or open and with the engine running,
it is desirable to
ensure that a power loss does not cause the clutch actuator to engage or close
the clutch,
which imay result in the vehicle lurching forward.
Alternatively, if a power loss occurs when the vehicle is moving and the
electrically
actuated clutch has been disengaged, such as in the middle of a gear shift, it
is desirable for
the clutch to move to an engaged position. For example, when a vehicle is
traveling
downhill, it is desirable to provide engagement of the clutch during a power
loss condition to
connect the drive wheels to the engine in order for engine braking to
facilitate slowing the
vehicle. In such a situation, the clutch must be capable of being actuated to
move from a
disengaged position to an engaged position.
Accordingly, it can be seen that two opposite conditions of the clutch are
required for
a vehicle system power loss condition, depending on the operating state of the
vehicle.
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SUMMARY OF TBE INVENTION
In accordance with one aspect of the invention, an actuator for a clutch is
provided,
the actuator comprising a motor and a drive train receiving a rotational input
from the motor,
where tnovement of the drive train actuates a clutch between engaged and
disengaged
positions. The actuator also includes a holding device for maintaining the
actuator, drive train
stationary at a predetermined position in a first power loss condition and for
releasing the
actuator drive train for movement in a second power loss condition. The motor
is driven by a
rotational output of the drive train in the second power loss condition.
In accordance with another aspect of the invention, an apparatus is provided
in a
vehicle having a power train including a clutch located between an engine and
driven wheels,
the apparatus including an actuator for the clutch, the actuator comprising a
motor and a
power supply for powering the motor. An actuator drive train receives a
rotational input
from the motor, where movement of the drive train actuates the clutch between
engaged and
disengaged positions. A holding device maintains the drive train stationary at
a
predetermined position in a first power loss condition comprising loss of
power from the
power supply when the vehicle is stationary and the clutch is disengaged, and
for releasing
the drive train for movement in a second power loss condition comprising loss
of power from
the power supply when the vehicle is moving and the clutch is disengaged. The
motor is
driven by a rotational output of the drive train in the second power loss
condition.
In accordance with a further aspect of the invention, an actuator for a clutch
is
provided, the actuator comprising a housing, a motor including a stator and a
rotor, a shaft
attached to the rotor of the motor, and a holding device. The holding device
comprises a
body including an electromagnet, where the shaft rotatably passes through the
body. A
holding device rotor is keyed to the shaft for rotational movement with the
shaft, and the
holding device rotor is supported for longitudinal movement relative to the
shaft. An
armature is located between the body and the holding device rotor, where the
shaft passes
through the armature. A spring is located between the body and the armature
for biasing the
armature away from the body to cause the holding device rotor to engage the
housing to
prevent rotational movement of the shaft. A controller is provided for
controlling electrical
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power supplied from a power supply to the motor. The controller includes means
for
responding to at least one of first and second power loss conditions, where
the controller
maintains a control mode for driving the motor in response to the first power
loss condition
and the controller switches to another control mode for generating electricity
from the motor
in response to the second power loss condition.
BRIEF DESCRIPTION OF THE DRAWINGS
While the specification concludes with claims particularly pointing out and
distinctly
claiming the present invention, it is believed that the present invention will
be better
understood from the following description in conjunction with the accompanying
Drawing
Figures, in which like reference numerals identify like elements, and wherein:
Fig. 1 is a system diagram including an electric clutch actuator of the
present
invention;
Fig. 2 is a cross-sectional view of the components of the electric clutch
actuator,
contained within an ECA housing;
Fig. 3 is a cross-sectional view of a clutch that may be controlled with the
electric
clutch actuator;
Fig. 4 is schematic of a portion of a circuit for controlling a motor in the
electric
clutch actuator;
Fig. 5 is a graph of average braking torque and peak phase current of the
motor at
various motor speeds; and
Fig. 6 is a state diagram for controlling the duty cycle switching performed
by the
circuit of Fig. 4 based on measured bus voltage.
DETAILED DESCRIPTION OF THE INVENTION
In the following detailed description of the preferred embodiment, reference
is made
to the accompanying drawings that form a part hereof, and in which is shown by
way of
illustration, and not by way of limitation, a specific preferred embodiment in
which the
invention may be practiced. It is to be understood that other embodiments may
be utilized
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and that changes may be made without departing from the spirit and scope of
the present
invention.
Referring to Fig. 1, a generalized diagram of an electric clutch actuator
(ECA) 10
constructed in accordance with the principles of the present invention is
illustrated. The
ECA 10 is shown diagrammatically incorporated in a vehicle for controlling a
clutch in a
power driveline for the vehicle. The ECA 10 comprises an electronic controller
12 including
controls 14, software 16 connected to the controls 14, and power electronics
18, e.g. field
effect transistors (FETs), controlled by the software 16. The ECA 10 is
connected to the
power circuit for the vehicle including a vehicle battery 20 and vehicle
ignition 22. Signals
from the vehicle power train including signals from a transmission ECU 24, an
engine speed
sensor 26 and other sensors 28 are fed to the ECA 10 as input signals that are
processed by
the ECA 10 for controlling outputs of the controller 12.
The outputs of the electronic controller 12 include voltage outputs for
powering a
stator 30 of a DC brushless permanent magnet motor 32, a holding device 34 for
operating on
a motor rotor 36 of the motor 32, and a sensor circuit board 38 receiving
signals indicative of
the operating state of the motor 32.
The ECA 10 further includes a planetary gear train 40 receiving an output from
the
motor rotor 36. The planetary gear train 40 comprises a gear reducer producing
an output for
controlling actuation of a clutch actuator 98.
Referring to Fig. 2, the above-described components of the ECA 10 are
contained
within an ECA housing 44. The motor 32 includes an outer stationary portion
comprising a
stator stack 46 carrying wire windings 48 to define the stator 30. The motor
rotor 36 is
located inside the stator 30 and comprises permanent magnet sectors acted on
by a magnetic
field of the stator 30 created by current supplied under control of the
controller 12 to produce
rotation. of the motor rotor 36 in a known manner. It should be understood
that although the
present invention is described as incorporating a brushless permanent magnet
motor 32, the
principles described herein may also be implemented using a brushed permanent
magnet
motor.
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The motor rotor 36 is rigidly mounted to a rotor shaft 50 for providing a
rotary output
of the inotor 32. The rotor shaft 50 extends through the holding device 34
including a brake
housing 68 enclosing a holding device rotor 56, an armature plate 60 and a
coil assembly 74.
A splir.ie member 52 is rigidly attached to the motor shaft 50 and comprises
an outer surface
defining a plurality of splines 54. The holding device rotor 56 is supported
on the spline
member 52 and includes an interior surface defining a plurality of splines 58
engaged with
the splines 54 of the spline member 52. The holding device rotor 56 is axially
movable along
the spliine member 52 and is engaged with the spline member 52 for rotation
with the rotor
shaft 50. The armature plate 60 is positioned next to the holding device rotor
56 and includes
an aperture 62 positioned around and out of engagement with the spline member
52.
The coil assembly 74 comprises a body portion 76 mounted to the brake housing
68,
and heli,d in stationary relationship to the brake housing 68 and ECA housing
44. The body
portion 76 includes a first annular region 78 containing an electromagnet
comprising a coil
80, and a second annular region 82 containing a compression spring 84. One end
of the
spring 84 is engaged against an inner surface of the second annular region 82,
and an
opposite end of the spring 84 is engaged against the armature plate 60 to bias
the armature
plate 60 and holding device rotor 56 away from the coil assembly 74. The
armature plate 60
includes an engagement surface 70 for engaging a first contact surface 71 of
the holding
device rotor 56, and the holding device rotor 56 further includes a second
contact surface 72
for engaging a braking surface 73 of the brake housing 68. During a
deactivated state of the
holding device 34, the holding device rotor 56 is biased by the armature plate
60 to cause the
second contact surface 72 to frictionally engage the braking surface 73 and
brake or resist the
holding device rotor 56 and rotor shaft 50 from rotating.
The body portion 76 is preferably formed of a magnetic material, such as a
steel
material, and is insulated from the coi180. Similarly, the armature plate 60
comprises a
magnetic material. The coil 80 is connected to the power electrics 18 for
conducting a
current through the coil 80 to create an electromagnetic field in the body
portion 76 in an
activated state of the holding device 34. During the activated state of the
holding device 34,
the armiature plate 60 is drawn against the force of the spring 84 toward the
body portion 76,
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releasing the holding device rotor 56 from frictional engagement with the
brake housing 68
and releasing the rotor shaft 50 for rotational movement relative to the brake
housing 68.
A sun gear 86 is fixedly attached to an end of the rotor shaft 50 distal from
the motor
32, and a portion of the rotor shaft 50 adjacent the sun gear 86 passes
through and is
supported by a bearing 88 mounted in the body portion 76. The sun gear 86 is
part of the
planetary gear train 40, and provides and input rotational movement to a
plurality of
planetau-y gears in a planetary gear set 90 connected to a series of
additional planetary gear
sets 92, 94. The planetary gear train 40 provides a gear reduction from the
rotor shaft to an
ECA output shaf196, such that the output speed of the output shaft 96 is
substantially slower
than the input speed of the rotor shaft 50 with an accompanying increase in
output torque at
the output shaft 96.
Referring to Fig. 3, the output shaft 96 is connected as an input to the
clutch actuator
98 for a clutch 100. The illustrated clutch 100 comprises a clutch housing 102
connected to a
cranksliaft 103 of an engine (not shown) for driving the clutch housing 102 in
rotational
movement. An intermediate plate 104 and a pressure plate 106 are supported for
rotation
with the clutch housing 102. The clutch housing 102 includes an engagement
surface 108,
the intermediate plate 104 includes a pair of engagement surfaces 110, 112 and
the pressure
plate 106 includes an engagement surface 114. A first driven plate 116 is
located between
the engagement surfaces 108, 110, and a second driven plate 118 is located
between the
engage:ment surfaces 112, 114. The first and second driven plates 116, 118
each include a
respective splined passage 120, 122 for engaging a spline portion 124 of an
input shaft 126.
A release sleeve 128 is supported for axial movement relative to the input
shaft 126
and engages distal ends of release levers 130 mounted for pivotal movement on
the clutch
housing 102. The release sleeve 128 is biased toward an engagement position by
a pressure
spring or springs 132, causing the release levers 130 to press against the
pressure plate 106,
such that the driven plates 116, 118 are clamped between the respective
engagement surfaces
108, 110 and 112, 114 to cause the input shaft 126 to rotate with rotation of
the clutch
housing 102. It should be noted that the clutch 100 is described for
illustrative purposes only
and the present invention is not limited to use with this particular clutch.
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The clutch actuator 98 includes an actuator arm 134 that is rotated with
rotation of the
output shaft 96. An end 136 of the actuator arm 134 is positioned for
engagement with an
outer housing surface 138 of a release bearing 140 that is engaged on the
release sleeve 128.
When the output shaft 96 is rotated counterclockwise, as viewed in Fig. 3, the
end 136 of the
actuator arm engages the outer housing surface 138 to push the release sleeve
128 away from
the clutch housing 102, such that the engagement surfaces 108, 110 and 112,
114 are
disengaged from the driven plates 116, 118 to disengage the clutch 100.
Rotation of the
output shaft 96 in the opposite direction, i.e., in the clockwise direction,
will result in
engagement of the clutch 100.
In order for the clutch 100 to be disengaged or engaged, the holding device 34
must
be activated to permit the output shaft 96 to rotate and move the clutch
actuator 98. In the
event of a system power loss, and in the absence of a supplemental power
supply to the
holding device 34, the output shaft 96 will be locked in its current position
at the time of the
power loss. This would typically be desirable in a first power loss condition
if the vehicle is
stationary with the clutch 100 disengaged, in order to prevent the vehicle
from lurching
forward as a result of the clutch suddenly engaging during a system power
loss. On the other
hand, in a second power loss condition, if the vehicle is moving during a
system power loss
with the clutch 100 disengaged, it would typically be desirable to allow the,
clutch 100 to
engage in order to utilize engine braking to slow the vehicle, particularly if
the vehicle is
traveliiig downhill. As described below, the present invention provides a
control for the
holding device 34 and motor 32 that addresses these two system power loss
conditions.
Referring to Fig. 4, an inverter circuit 142 is illustrated for controlling
current to the
motor :32, which is illustrated as a three-phase permanent magnet brushless
motor that may
be controlled using a pulse width modulation (PWM) control. The circuit 142
includes three
high side FETs Q1, Q3, Q5, and three low side FETs Q2, Q4, Q6 that are
controlled by the
software 16 to effect control of the motor 32. In the first system power loss
condition, where
it is desired to maintain the current position of the clutch 100, such as when
the vehicle is
stationary, the controller 12 operates in a mode where the three low side FETs
Q2, Q4, Q6
are tumed on with 100% duty cycle to short the motor terminals together. If
the motor rotor
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36 is rotating, a back electromotive force will be created across the motor
impedance (i.e.,
the vector sum of resistance and synchronous reactance) as a result of the
shorted tenninals.
The resulting circulating current in the motor windings 48 will generate a
counter-reacting
torque to reduce the back electromotive force. In other words, a braking
torque will be
generated to slow down the motor motion.
Referring to Fig. 5, an example of the average braking torque and peak phase
current
of the motor 32 is illustrated at various motor speeds. The peak current
becomes almost
saturated at high speed due to the synchronous reactance, i.e., motor angular
speed x motor
inductance, of the motor 32. The synchronous reactance dominates over motor
resistance at
high speed, such that the current becomes saturated at high speed.
Accordingly, the effect of
synchronous reactance allows shorting of the three motor terminals even at
high motor
speeds.
The holding device 34 will be deactivated during the first power loss
condition where
it is desired to maintain the current clutch position, and a circuit (not
shown) may be
provided for quickly collapsing the magnetic field generated by the coil
assembly 74 of the
holding device 34. If the motor rotor 36 is still rotating, the motor braking
torque will slow
down the motor rotor 36 to a speed where the holding device rotor 56 will
further brake
rotation. of the motor rotor 36 and hold the rotor shaft 50 against further
rotation. That is, the
holding device rotor 56 will hold the rotor shaft 50 fixed in position to
maintain the output
shaft 96 and actuator 98 in a disengagement position, operating against the
pressure spring
132 to r.naintain the release sleeve 128, and thus the clutch 100, in the
disengagement
position.
in the second system power loss condition where it is desired to move the
clutch 100
from the disengaged to the engaged position, such as when the vehicle is
moving, the
controller 12 operates in a mode where the three low side FETs Q2, Q4, Q6 will
be turned on
to short the motor terminals together for a predetennined braking portion (DB)
of a duty
cycle, and all FETs will be turned off for a remaining regenerative portion
(DR) of the duty
cycle, i.e., during a portion of the duty cycle equal to 1-DB. As described in
further detail
below, during the second power loss condition, provision is made for
activating the holding
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device 34 to release the rotor shaft 50 for rotation for a period of time
sufficient to allow the
clutch 100 to engage. During the period of rotation of the rotor shaft 50,
braking torque will
be applied from the motor 32 during the braking portion of the duty cycle DB,
in a manner
similar to that described for the first power loss condition, and regenerative
energy will be
provided from the motor 32 during the remaining regenerative portion DR of the
duty cycle.
The ECA controller bus includes a controller bus capacitor 144, see Fig. 2,
for
maintaiining a stored amount of energy during normal powered operation of the
ECA
controller 12, and for receiving and storing the regenerative energy from the
motor 32 during
the regenerative portion DR of the duty cycle. The energy stored in the
capacitor 144 is
utilized to provide power to the ECA controller 12 and to the holding device
34 during a
system power loss condition. The capacitor 144 is capable of storing
sufficient energy,
including the additional regenerative energy received from the motor 32, to
maintain the
holding device 34 in the activated state for rotation of the output shaft 96
and clutch actuator
98 to the engagement position for engagement of the clutch 100. That is,
during rotation of
the output shaft 96 and rotor shaft 50, as the clutch 100 moves toward the
engagement
position under the force of the spring(s) 132, the motor rotor 36 will rotate
to produce
regenerative energy supplied to the capacitor during the regenerative portion
DR of the duty
cycle. The regenerative energy will continue to be contributed to any energy
already stored
in the capacitor 144 to maintain the holding device 34 in the activated state,
permitting
continuied rotation of output shaft 96 and clutch actuator 98 until the clutch
100 is fully
engaged at the end of the travel of the release sleeve 128 under the influence
of the stored
energy in the spring(s) 132.
The bus voltage VbõS may be increased or decreased based on the balance
between the
supplied regenerative energy and the amount of power required to activate the
holding device
34 and operate the ECA controller 12. Referring to Fig. 6, a state diagram is
shown for
controlling the duty cycle based on the measured bus voltage, Vbõs. In
particular, the brake
portion DB of the duty cycle is initially set to 0.95 (DR =0.05) at the
beginning of the second
power ]!.oss condition. If Vbõs is greater than 20V, then DB is increased to
0.97 with a
corresponding decrease in the regenerative portion DR of the duty cycle to
0.03. If Vbus falls
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below 18V when DB is set to 0.97, then DB will again be set to 0.95. If VbõS
is greater than
30V wlhen DB is set to 0.97, then DB is increased to 0.99 with a corresponding
decrease in the
regeneirative portion DR of the duty cycle to 0.01. If VbõS falls below 28V
when DB is set to
0.99, then DB is again set to 0.97.
It can be seen that the ECA 10 is capable of meeting the two power loss
conditions
described above. For the power loss condition where the clutch 100 is
disengaged during a
system power loss and the desired action is for the clutch 100 to remain in
its current
positional state, the holding device 134 will move to its power off
deactivated position to
prevent movement of an actuator 98 for the clutch 100. For the power loss
condition where
the clutch 100 is disengaged during a system power loss and the desired action
is for the
clutch 100 to move to an engaged positional state, the ECA motor 32 is used as
a generator to
convert the potential energy of the clutch pressure spring(s) 132 into
electrical energy to
provide energy for powering the holding device 134 to remain activated.
Maintaining the
holding device 134 activated permits the clutch 100 to move to the engaged
position and
thereby allows vehicle engine braking to be used during a power loss of the
system.
While particular embodiments of the present invention have been illustrated
and
described, it would be obvious to those skilled in the art that various other
changes and
modifications can be made without departing from the spirit and scope of the
invention. It is
therefare intended to cover in the appended claims all such changes and
modifications that
are within the scope of this invention.
What is claimed is:
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