Note: Descriptions are shown in the official language in which they were submitted.
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POWER DRIVE MECHANISM FOR A MOTOR VEHICLE LIFTGATE
Field of the Invention
The invention relates to power drive mechanisms for power operation of a
vehicle
liftgate.
Background of the Invention
Minivans and recreational vehicles frequently have rear liftgates that are
pivotally
mounted to the vehicle frame at the rear of the vehicle. The liftgate is
pivotally mounted
to the frame by top hinges to allow the liftgate to move between open and
closed
positions. Manually operated liftgates and power operated liftgates are well
known.
Power operated liftgates can be opened and closed manually if a vehicle user
so desires.
Power operated liftgates are typically driven in opening and closing
directions by an
electrical motor that is operatively engagable with the liftgate through a
series of gears.
At least one gear is movably mounted for movement between engaging and
disengaging
positions so that the motor is operatively connected to the liftgate when the
gears are
engaged so the liftgate can be moved in opening and closing directions by the
motor and is
disconnected from the liftgate when the gears are disengaged so the liftgate
can be opened
and closed manually without backdriving the motor. Examples of typical systems
include
United States Patent nos. 5,448,856 and 5,563,483.
The movable gear may have a tendency to move out of engagement when the
motor is either opening or closing the liftgate, depending on the particular
geometry. This
is undesirable because movement of the movable gear can result in gear
slippage and/or in
excessive gear noise.
Summary of the Invention
The disadvantages of the prior art may be overcome by providing a power drive
mechanism in which a gear train can be releasably locked or held in driving
engagement
during power assisted liftgate opening and closing and can be released from
driving
engagement thereafter to give the vehicle user the option of manually opening
or closing
the liftgate without backdriving the drive motor.
According to one aspect of the invention, there is provided a power drive
mechanism for a driving a liftgate for a vehicle. The vehicle has a body
controller
controlling the operation of the power drive mechanism. The liftgate has a
power
operated latch assembly capable of primary and secondary latching engagement
with a
striker on the vehicle to releasably latch the liftgate and capable of power
operated
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unlatching of the latching assembly. The power drive mechanism has a mounting
bracket
mountable on a "D" pillar of the vehicle. A linking arm is pivotally connected
with the
liftgate. A crank arm is pivotally mountable on the mounting bracket and
pivotally
connected with the linking arm. A gear train is pivotally mounted on said
mounting
bracket. A drive motor is mounted to the mounting bracket. The drive motor is
operatively connected with the crank arm through the gear train. The gear
train is
movable between an engaged position and a disengaged position. The engaged
position
effects a driving engagement between the drive motor and the crank arm such
that
energizing the drive motor drivingly rotates the crank arm to responsively
effect opening
and closing of the liftgate. The disengaged position disengages the drive
motor from the
crank arm permitting movement of the crank arm without backdriving the drive
motor.
An actuator is operatively connected with the gear train and is operable to
effect the
movement of the gear train. A holding linkage is operatively connected between
the gear
train and the actuator to maintain the driving engagement once the actuator
moves the gear
train into the engaged position. A switch is mounted on the mounting bracket
and is
switchable in response to movement of the crank arm, indicating open and
closed
conditions of the liftgate. An electronic control unit electrically
communicates with the
body controller, the latch assembly, the drive motor, the switch and the
actuator.
Brief Description of the Drawings
FIG. 1 is a perspective view of a power drive mechanism constructed according
to
the principles of the present invention mounted on a "D" pillar of a
conventional motor
vehicle;
FIG. 2 is a perspective view of the power drive mechanism in isolation showing
an
opposite side of the mechanism from the side shown in FIG. 1;
FIG. 3 is an exploded view of the power drive mechanism;
FIG. 4 is an elevational view of a gear train, a fragment of a crank arm and a
switch of the power drive mechanism in isolation and showing the gear train in
a
disengaged condition, the crank arm in a closed position and the switch in a
full open
position;
FIG. 5 is a view similar to FIG. 4 except showing the gear train in an engaged
condition;
FIG. 6 is a view similar to FIG. 5 except showing the crank arm in an open
position and the switch in a closed position; and
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FIG. 7 is a view similar to FIG. 6 except showing the gear train in a
disengaged
condition.
Detailed Description of the Preferred Embodiment of the Invention
A power drive mechanism, generally designated 10, for power operated opening
and closing of a vehicle liftgate is shown in FIG. 1. The structure of the
vehicle liftgate
(not shown) is conventional and is illustrated in United States Patent nos.
5,448,856 and
5,563,483. A typical vehicle liftgate is pivotally mounted at the rear of a
mini van or
recreational-type vehicle by hinges (not shown) mounted between the top of the
vehicle
liftgate and a portion 11 of the frame 15 of the vehicle. The liftgate has a
conventional
power operated latch assembly (not shown) mounted at a central portion of its
lower edge
that releasably latches to a striker appropriately mounted on the vehicle
frame.
When the latch assembly is released from the striker, the liftgate can be
pivoted
about the hinges from a lowered closed position to a raised open position to
allow access
to the vehicle interior through the rear of the vehicle. Typically, a gas
strut of
conventional construction is mounted between a respective side edge of the
liftgate and an
adjacent, generally vertically extending pillar 17 (each of which is referred
to as a"D"
pillar) of the vehicle frame.
The power drive mechanism 10 of the present invention is mounted on the "D"
pillar 17 of the vehicle on the left side thereof (from the point of view of a
forwardly
facing vehicle occupant) and is operatively engaged with the liftgate to
provide power
operated opening and closing of the same.
The power drive mechanism 10 includes a crank arm 12 that is that is drivable
for
pivotal movement. The crank arm 12 is pivotally mounted to a mounting bracket
14 for
power operated pivotal movement in opening and closing directions with respect
thereto.
The mounting bracket 14 is rigidly secured to an upper portion of the "D"
pillar as shown
in FIG. 1. The mounting bracket 14 is a metal structure preferably made of
diecast zinc or
aluminum, although any metal of suitable strength could be used, and is
secured to the "D"
pillar by conventional fastener such as bolts. The crank arm 12 is preferably
constructed
of stamped metal, the preferred metal being steel. The crank arm 12 is
pivotally mounted
to the mounting bracket 14 by a support structure 21 that extends essentially
in the cross
vehicle direction. The crank arm 12 is secured to the support structure 21 by
rivets 23.
The crank arm 12 is connected with a linking arm 18. One end of a rigid
linking
arm 18 is pivotally mounted to the crank arm 12 and the opposite end of the
linking arm
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18 is pivotally connected to the adjacent side edge of the liftgate. The
pivotal connection
between the linking arm 18 and the liftgate is spaced from the hinges and the
axis of
rotation of the liftgate. Movement of the crank arm 12 in opening and closing
directions
acts through the linking arm 18 to move the liftgate in its opening and
closing directions.
A gear train, generally designated 20, operatively engages the crank arm 12.
The
preferred embodiment of the gear train 20 includes a plurality of gears,
including an
actuator gear 24, inner and outer drive gears 26 and 28, respectively.
A drive motor 34 is operatively connected with the crank arm 12 through the
gear
train 20 and is operable to automatically open and close the liftgate. A motor
gear 22 is
rotatably mounted on the mounting bracket 14 by a shaft 32 that is operatively
connected
in a conventional manner with the drive motor 34 which is preferably a
reversible, high-
torque electrical motor. The drive motor 34 can be electrically energized to
effect bi-
directional rotation of the same.
The actuator gear 24 is rotatably mounted on a bracket assembly 36. The
bracket
assembly 36 includes inner and outer bracket members 38 and 40, respectively,
and the
actuator gear 24 is mounted therebetween by a pin or rivet 42. The bracket
members 38,
40 are preferably made of steel and are rigidly secured together by rivets 39.
The inner drive gear 26 and the outer drive gear 28 are ganged together and
rigidly
secured to a common shaft 44 that is rotatably mounted to the mounting bracket
14 to
allow the gears 26, 28 to rotate with respect to the mounting bracket 14. The
bracket
assembly 36 is pivotally disposed on the central shaft 44 for movement
thereabout
between engaged and disengaged positions. The pivotal movement of the bracket
assembly 36 is independent of the rotational movement of the inner and outer
drive gears
26,28.
The gears 22, 24 within the gear train 20 are disengagable to permit manual
opening and closing of the liftgate without backdriving the drive motor 34.
Pivotal
movement of the bracket assembly 36 about the central shaft 44 with respect to
the
mounting bracket 14 moves the actuator gear 24 in and out of meshing, torque
transmitting engagement with the motor gear 22. When the gears 22, 24 are
disengaged,
the pivotal movement of the crank arm 12 which occurs during liftgate opening
and
closing does not rotate the motor gear which protects the drive motor 34.
A sector gear 30 is rigidly attached to the crank arm 12 by conventional
rivets 37.
The sector gear 30 has a series of teeth on the inside or concave
circumferential edge
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thereof. The outer drive gear 28 is in meshing, torque transmitting engagement
with the
sector gear 30. Rotation of the outer drive gear 28 acting through the sector
gear 30
moves the crank arm 12. The outer gear 28 remains in meshing engagement with
the
sector gear 30 throughout the entire range of pivotal movement of the crank
arm 12.
The pivotal movement of the bracket assembly 36 between engaged and
disengaged positions is controlled by the movement of a U-shaped actuating
link 46 that is
pivotally mounted at the bight portion thereof to the mounting bracket 14
through pin 48.
The actuating link 46 is a metal structure preferably made of steel and has
integral upper
and lower arms 50, 52 extending from a U-shaped body portion 53. The actuating
link 46
is operatively connected to the bracket assembly 36 through a roller 54
rotatably mounted
pin 55 on the upper arm 50. The roller 54 rollingly engages one of first and
second
flanges 56, 58, respectively, integrally formed on an arm of the inner bracket
member 38.
Pin 55 extends through slot 57 which extend parallel to and between flanges
56, 58. The
roller 54 cams against a flange 56 or 58 during pivotal movement of the
actuating link 46
to pivot the bracket assembly 36 with respect to the mounting bracket 14 about
the central
shaft 44 between engaged and disengaged positions.
The actuating link 46 is operatively associated with a holding linkage
comprising a
holding link 60 and an elongated, rigid connecting link 62. Connecting link 62
that is
pivotally mounted between the lower arm 52 and an upper portion of the holding
link 60
by conventional rivets 64. The holding link 60 is operatively associated with
the gear train
20 to maintain the gears 22, 24 in engagement with one another during
automatic
operation of the liftgate. An edge portion of the holding link 60 is pivotally
mounted to an
edge portion of the bracket assembly 36 by a pin 65. The holding link 60 is a
metal
structure preferably made of steel and is provided with a slot 66 that defines
a plurality of
notches therein including an upper releasing notch 68 and a lower holding
notch 70. A
holding pin 72 is rigidly secured to the mounting bracket 14 and is received
within the slot
66. The holding link 60 slidably engages the pin 72 for guiding movement of
the holding
link 60 with respect to the pin 72 between holding and releasing positions.
Movement of the actuating link 46 is effected by an actuator 74, best seen in
FIG.
2, which shows the side of the mounting bracket 14 that is in contact with the
"D" pillar
when the power drive mechanism 10 is mounted in a vehicle. The actuator
comprises a
motor and a gear train which are conventional and are enclosed within an L-
shaped
protective plastic housing 78 mounted on the mounting bracket 14. The actuator
74 is
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operatively connected with the gear train 20 and is operable to engage and
disengage the
gears 22, 24 of the gear train. The actuator includes a conventional
reversible electric
motor and gear train (not shown) that engages a shaft 76 rigidly connected on
the
actuating link 46 that extends through an arcuate slot (not shown) in the
mounting bracket
14. When the motor in the actuator 74 moves the shaft 76, the actuator
assembly 46 pivots
between its engaging and disengaging positions.
An extension spring 88 is mounted between a post 90 on the switch 82 and the
bracket assembly 36 to bias the bracket assembly to disengage from the motor
gear 22
when the vehicle is moving or when the liftgate is being manually opened or
closed.
Operation
Power operation of the power drive mechanism 10 can be controlled
electronically
using conventional electronic control circuitry which is mounted in the
vehicle. The
actuator gear 24 is normally not in meshing engagement with the motor gear 22.
The
control circuitry can be programmed such that when power operated liftgate
opening is
initiated, the actuator 74 and drive motor 34 are energized in sequence. The
actuator 74
moves the actuator gear 24 into engagement with the motor gear 22 and moves
the holding
link 60 into locking relation with the holding pin 72 to releasably hold the
actuator gear 24
and motor gear 22 together during power liftgate movement. The drive motor 34,
acting
through the gear train 20, moves the crank arm 12 in its opening direction.
The circuitry
then disengages the holding link 60 from the holding pin 72 and the moves the
actuator
gear 24 and motor gear 22 out of meshing engagement when the gate is open. The
powered closing operation is essentially the reverse of the opening operation.
During
power operated liftgate closing, the gear holding link 60 holds the actuator
gear 24 and the
motor gear 22 in meshing, torque transmitting engagement to prevent the gears
22, 24
from slipping relative to one another and to reduce or eliminate gear noise.
The basic operation of the power drive mechanism 10 can be understood from
FIGS. 4-7. FIGS. 4-7 show a plurality of structures of the power drive
mechanism 10 in
isolation to show the relative positions thereof prior to and during power
operation. FIG.
4 shows the configuration of the power drive mechanism 10 before power
operated liftgate
opening is initiated by a vehicle user. The system described uses a
conventional key fob
remote control transmitter to initiate powered liftgate opening and closing.
To initiate
power liftgate opening when the liftgate is closed and latched, the vehicle
user actuates the
key fob remote control unit which sends a signal to a body controller located
in the
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vehicle.
In response to the signal generated by the key fob, the body controller sends
an
electronic control signal to a liftgate electronic control unit 80 mounted in
the rear of the
vehicle near the mounting bracket 14. The electronic control unit 80 confirms
that the
latch assembly is latched and the liftgate is closed by detecting the position
of a ratchet
switch and a pawl switch in the latch assembly and of a switch 82 in the power
drive
mechanism 10 and then actuates a motor and clutch assembly (not shown)
associated with
the latch assembly on the liftgate to effect power operated unlatching of the
same to
release the latch assembly from the striker. The electronic control unit 80 is
in electrical
communication with the switch 82 through conventional wires 83. Movement of a
ratchet
and pawl during unlatching toggles the ratchet and pawl switches in the latch
assembly
during unlatching which indicates to the electronic control unit 80 that the
latch assembly
is unlatched.
In response to the switch signals from the latch assembly, the electronic
control
unit 80 energizes the drive motor 34 to cause it to rotate slowly in an
opening direction at
about ten percent of its duty cycle and then, a predetermined amount of time
thereafter
(typically about 30 milliseconds), energizes the actuator motor in the
actuator 74 to cause
it to rotate in a gear engaging direction. The actuator is in electrical
communication with
the electronic control unit 80 through conventional wires 91. The actuator 74
is energized
for a predetermined period of time (typically about 350 milliseconds) which
causes the
actuating link 46 to pivot in a gear engaging direction (clockwise in FIGS. 4-
7).
As the actuating link 46 pivots, the bracket assembly 36, holding link 60, and
connecting link 62 move to mesh the actuator gear 24 into engagement with
motor gear 22
and lock them in meshing engagement as shown in FIG. 5. More specifically, as
the
actuator assembly 46 pivots (clockwise from the point of view in FIG. 4), the
roller 54
cams against the first wall portion 56 of the inner bracket member 38 to pivot
the bracket
assembly 36 about the central shaft 44 (counterclockwise in FIG. 4) and move
the actuator
gear 24 into meshing engagement with the slowly rotating motor gear 22. The
pivotal
movement of the actuating link 46 acting through the connecting structure 62
and the
bracket assembly 36 simultaneously (i.e., simultaneous with the movement of
the bracket
assembly 36) causes the holding link 60 to pivot about pin 65 and thus move
with respect
to the holding pin 72 until the holding pin 72 is disposed generally within
the holding
notch 70 which locks the bracket assembly 36 in place. The actuator gear 24 is
thereby
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locked in meshing engagement with the motor gear 22 until the actuating link
46 is
pivoted in the reverse direction. This configuration of the power drive
mechanism 10 is
shown in FIG. 5.
When the actuation gear 24 is engaged with the motor gear 22, the drive motor
34
drives the gears 22, 24, 26, 28, 30 in an opening direction to cause the crank
arm 12 to
move in its opening direction. It can be appreciated that when the liftgate is
moving in the
opening direction, the holding link 60 is not required to maintain the
actuator gear 24 and
the motor gear 22 in meshing engagement. As the liftgate is opening, the crank
arm 12
pivots about an axis defined by the support structure 21 in a clockwise
direction (from the
point of view of FIGS. 4-6). The inner and outer drive gears 26, 28 rotate in
a clockwise
direction and the actuator gear 24 and motor gear 22 rotate respectively in
counterclockwise and clockwise directions. The forces exerted on the actuator
gear 24
and motor gear 22 tend to move them together as the liftgate opens. Those
skilled in the
art will understand that because the motor gear 22 is rigidly mounted on a
shaft 32 that
extends through and is rotatably disposed within an aperture (not shown) in
the mounting
bracket 14 but is prevented from moving with respect to the mounting bracket
14 in a
direction generally perpendicular to its axis of rotation (i.e., it is
restricted to rotational
movement with respect to the mounting bracket by the sides of the aperture),
and because
the actuator gear 24 is rotatably mounted on rivet 42 which is free to move
with respect to
the mounting bracket 14 (because the bracket assembly 36 on which the rivet 42
is
mounted is pivotally mounted about the central shaft 44), the rotational
movement of the
motor gear 22 in the clockwise direction tends to pivot the bracket assembly
36 in a
counterclockwise direction with respect to the mounting bracket 14, thereby
tending to
move the actuator gear 24 into engagement with the motor gear 22.
As the crank arm 12 moves in the opening direction, the linking arm 18
pivotally
mounted between the crank arm 12 and the left edge of the liftgate, moves the
liftgate
upwardly toward its open position as the gas struts (not shown) elongate. The
structure
and operation of the gas struts is conventional and well known. Each gas strut
includes an
elongated structure that is spring biased to move telescopically out of a
second elongated
structure to provide a spring biased pushing force as the first elongated
structure moves
outwardly. The speed of the outward movement is limited in a well known
manner,
typically by a restricted flow of a gas within the strut. It is well known
that before the
spring biased movement of the gas strut begins, however, the first structure
must be
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moved out of the second member a predetermined distance. The linking arm 18
and crank
arm 12 push the liftgate upwardly during a power gate opening operation almost
the entire
upward range of movement of the liftgate. Because there is only one power
drive
mechanism 10 associated with the liftgate, a large torsional force is applied
to the
mounting bracket 14 during liftgate opening and closing.
As the crank arm 12 moves in the opening direction, the electronic control
unit 80
increases the drive motor 34 power after a predetermined number of revolutions
of the
motor shaft of the drive motor 34 to full duty cycle power and the linking arm
18 moves
the liftgate toward its open position. As the liftgate is opening, the
electronic control unit
80 monitors the Hall effect counts (in a conventional manner) generated by
movement of
the liftgate (or, alternatively, the electronic control unit 80 could be
configured to monitor
the drive motor 34 current) to detect obstructions in the path of the
liftgate. It will be
assumed that no obstructions are encounter as the liftgate opens (or closes).
As the drive
motor 34 rotates in the opening direction, the electronic control unit 80
counts the
revolutions of the drive motor 34 shaft and when a predetermined count is
reached, the
electronic control unit 80 de-energizes the drive motor 34 and the gas struts
(which are
almost fully extended when the drive motor 34 is de-energized) are allowed to
move the
liftgate to its fully open position.
A comparison of FIGS. 5 and 6 shows that as the crank arm 12 moves in a
clockwise direction (from the point of view of FIGS. 4-7) from its fully
closed position
(shown in FIG. 5) to its fully opened position (FIG. 6), the switch 82 is
toggled. More
specifically, as the crank arm 12 is moved to its fully opened position by the
gas struts, a
switch arm 84 rigidly mounted on the crank arm 12 by rivets 85 moves into
contact with a
switch structure 86 of the switch 82 mounted in fixed relation to the mounting
bracket 14
and further movement of the switch arm 84 (and crank arm 12) thereafter
depresses the
switch structure 86 to toggle the switch 82 to indicate to the electronic
control unit 80 that
the liftgate is in the full open position. The electronic control unit 80 in
response
energizes the actuator motor to drive the same in a disengaging direction for
a
predetermined period of time to disengage the actuator gear 24 from the motor
gear 22 and
to move the holding link 60 with respect to the holding pin 72 so that the
holding pin 72 is
disposed in the upper releasing position to allow the actuator gear 24 to move
pivotally
away from the motor gear 22 to the position shown in FIG. 7. The actuator gear
24 is
disengaged from the motor gear 22 when the liftgate is open, thereby allowing
the vehicle
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user to close the vehicle liftgate manually without backdriving the motor. The
liftgate is
held in its fully open position by the gas struts.
The operation of the system to close the liftgate is essentially the reverse
of the
opening operation. When power closing is initiated with the key fob, the
electronic
control unit 80 first energizes the drive motor 34 to rotate in a closing
direction and then
energizes the actuator motor in the actuating link 46 to rotate in the
engaging direction in a
manner similar to that described above. The actuator motor is energized for a
predetermined period of time to engage the actuator gear 24 and motor gear 22
and to
move the holding link 60 simultaneously to its holding position in which the
holding pin
72 is disposed in the holding notch 70. As the liftgate moves in its closing
direction, the
actuator gear 24 and motor gear 22 move in the clockwise and counterclockwise
directions, respectively, and this tends to move them away from each other.
The drive motor 34 moves the vehicle liftgate in the closing direction until
the
latch assembly on the vehicle liftgate impacts the vehicle striker which moves
the ratchet
from an open position to a secondary latched position. Movement of the ratchet
into the
secondary latched position toggles the switch 82 inside the latch assembly
which causes
an electrical signal to be sent to the electronic control unit 80. In response
to this
switching signal, the electronic control unit 80 de-energizes the drive motor
34 and
energizes the actuator motor for rotational movement in its disengaging
direction for a
predetermined period of time to move the actuator gear 24 out of engagement
with the
motor gear 22.
Also in response to the toggling of the switch 82, the electronic control unit
80
energizes the conventional latching motor and the clutch assembly operatively
associated
with the latch assembly to rotate the ratchet to its primary latched position,
thereby
moving the vehicle liftgate into its fully closed and latched position.
It can be appreciated that the actuator gear 24 is normally out of engagement
with
the motor gear 22 so that the vehicle liftgate can be opened and closed
manually without
backdriving the drive motor 34. This reduces wear on the drive motor 34,
thereby
increasing its service life and decreases the amount of manual force the user
has to apply
to the liftgate to open and close the same.
It is to be understood that the foregoing specific embodiment has been
provided to
illustrate the structural and functional principles of the present invention
and is not
intended to be limiting. To the contrary, the present invention is intended to
encompass
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all modifications, substitutions and alterations within the scope of the
appended claims.
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