Note: Descriptions are shown in the official language in which they were submitted.
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HYDRAULIC CLOSURE SYSTEM FOR A MOTOR VEHICLE AND
METHOD FOR OPERATING SAME
BACKGROUND OF THE INVENTION
The present invention relates to a
hydraulic closure system for a motor vehicle and
method for operating the same.
Sport utility vehicles and minivans have
become very popular with automobile consumers and
their popularity continues to grow. Such vehicles,
because of their size, afford passenger and cargo
space, as well as ease of ingress and egress, not
afforded by cars.
Minivans and sport utility vehicles are
typically equipped with a liftgate, also referred to
as a cargo door or closure, usually located at the
back of the vehicle. Typically, a liftgate is
pivotally attached by hinges to the top of a cargo
opening defined by an opening frame. The liftgate
is opened by pivoting it upwardly and outwardly from
the cargo opening.
In conventional liftgates, pneumatic
~~actuators~~ or ~~cylinders~~ containing compressed gas
are provided on each side of the liftgate, one end
of each being attached to the liftgate, the other
end of each being attached at opposite sides of the
opening frame. When the liftgate is closed and
latched, the actuators are contracted and the gas
within the actuators is compressed. When the
liftgate is unlatched, the stored energy provided by
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the compressed air in the pneumatic actuators forces
the liftgate to open partially, thus "popping" the
gate. The liftgate must then be manually lifted .
while the actuators continue to exert an outward
force on the liftgate that assists the manual
opening of the liftgate. Eventually, the liftgate
is manually lifted to a position at which the
geometric relation of the actuators with respect to
the center of gravity of the liftgate is such that
moment arm associated with the lifting action
becomes sufficiently large that the remaining energy
in the actuators can take over the lifting movement
of the liftgate and bring the liftgate and retain
the liftgate in the fully opened position. More
particularly, the pivoting dynamics of a liftgate
are a function of the force exerted by the pneumatic
actuators, the distance between the line of action
of the actuators and the liftgate pivot axis, the
weight of the liftgate, and the distance between the
liftgate center of gravity and the liftgate pivot
axis. The first two factors affect the upward
moment acting on the liftgate due to the force of
the actuators and last two factors affect the
downward moment acting on the liftgate due to its
own weight. The lengths of the actuator and the
force of the gravity moment arms vary through the
arcing movement of the liftgate. Therefore, the
upward and downward acting moments also vary with
position of the liftgate.
From the above it can be appreciated that
conventional liftgates are designed with what is
known in the art as an "overcenter condition." With
this condition, the "center position" of movement is
a position in the path of the liftgate in which the
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downward acting movement is equal to the upward
acting moment. When the liftgate is moved below
this position, the downward acting moment becomes
greater than the upward acting moment and the
liftgate will travel the remainder of the downward
path under the force of its own weight.
Alternatively, when the liftgate is moved above this
position, the upward acting moment becomes greater
than the downward acting moment and the liftgate
will travel the remainder of the upward path under
the force of the actuators.
Because of the size and weight of
conventional liftgates is substantial, manual
opening and closing can be awkward and cumbersome,
especially if one's hands are full, for example,
with groceries and/or small children.
To overcome the aforementioned
difficulties encountered with vehicle liftgates, it
has been proposed in U.S. Patent No. 5,147,106 to
Bartelt et al. to provide a rear vehicle gate with
hydraulically powered automatic opening and closing
capabilities. A hydraulic pump is connected to
hydraulic actuators which are attached to the rear
gate and to the rear gate opening. The actuators
are extended to open the gate and contracted to
close the gate by fluid flow from the pump. A
problem associated with a hydraulic liftgate system
such as that in Bartelt, however, relates to what is
known as "hydraulic lock." That is, when the pump
is off or malfunctioning, the rear gate cannot be
closed manually, since hydraulic fluid is not
permitted to flow through the system in desired
fashion. In addition, manual closing of the
liftgate cannot override the power closure during
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automated power opening and/or closing during
operation of the hydraulic pump. Another .
disadvantage present in a system such as that
disclosed in Bartelt is that both automatic opening ,
and closing require operation and wear of the pump.
Another system proposed in Q.S. Patent No.
4,858,981 to Post provides a rear vehicle gate that
is opened by hydraulic power. The gate is lifted by
the hydraulic actuators under pressure from a
hydraulic pump. However, automated closure is not
provided.
For maximum convenience and efficiency,
there is a need for a hydraulic liftgate system that
provides both automatic opening and closing of the
liftgate, while providing flexibility by permitting
manual override of the automated system to permit
manually generated closing of the liftgate, and
while also conserving pump wear and tear by storing
energy input to the system during closure of the
liftgate, which energy can be subsequently used to
open the liftgate.
An object of the present invention is to
fulfill the needs expressed above. In accomplishing
this object, a hydraulic closure system is provided
for use in a motor vehicle and is constructed and
arranged to cooperate with a closure opening defined
by an opening frame of the motor vehicle body. The
system comprising a closure constructed and arranged
to be pivotally mounted on the opening frame for
movement between a closed position in which the
closure closes the closure opening and an opened
position in which the closure is oriented to permit
access through the closure opening. A latching
structure is constructed and arranged to latch the
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closure in the closed position and to unlatch the
closure to permit the closure to move from the
closed position to the opened position. And a
manually overridable power control system, including
. 5 at least one hydraulic actuator assembly, a
motorized hydraulic pump, and a biased energy
storage system, is constructed and arranged to
enable automatic opening and closing of the closure
and to permit manual closing of the closure. The at
l0 least one hydraulic actuator assembly is coupled at
one end thereof to the closure and is coupled at an
opposite end thereof to the opening frame. The at
least one hydraulic actuator assembly includes a
cylinder and a piston rod assembly, and the piston
15 rod assembly includes a piston and a rod member
connected to the piston. The piston is moveable
within the cylinder in slidably sealed relation with
inner walls of the cylinder, and the rod member
extends outwardly from a rod extension end of the
20 cylinder. The piston rod assembly is moveable
between an extended condition in which the rod
member has a relatively large extent thereof
extending outwardly from the rod extension end of
the cylinder so as to create a distance between the
25 opposite ends of the at least one hydraulic actuator
assembly sufficient to maintain the closure in the
opened position and a contracted condition in which
the rod member has a relatively smaller extent
thereof extending outwardly from the rod extension
30 end of the cylinder in comparison with the extended
condition to create a distance between the opposite
' ends of the at least one hydraulic actuator assembly
that enables the closure to be disposed in the
' closed position. The biased energy storage system is
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constructed and arranged to store energy therein,
and applies a biasing force to the at least one
hydraulic actuator assembly sufficient to move the
closure from the closed position to the opened
position and maintain the closure in the opened
position when the energy stored therein is expended.
The motorized hydraulic pump is operable to input
energy to the at least one hydraulic actuator
assembly to effect the closing of the closure by
creating hydraulic fluid flow in one direction with
respect to the cylinder on a first side of the
piston to force the piston away from the rod
extension end of the cylinder and move the at least
one hydraulic actuator assembly against the biasing
force from the extended condition to the contracted
condition and the closure from the opened position
to the closed position. The biased energy storage
system is constructed and arranged to store a
portion of the energy input to the at least one
hydraulic actuator assembly by the motorized
hydraulic pump when the closure is moved by
operation of the pump from the opened position to
the closed position. The biased energy storage
system is constructed and arranged to expend energy
stored therein on a second side of the piston when
the closure is unlatched and thus apply said biasing
force to move the piston toward the rod extension
end of the cylinder and hence create hydraulic fluid
flow in an opposite direction with respect to the
cylinder on the first side of the piston and thereby
move the at least one hydraulic actuator assembly
from the contracted condition to the extended
condition and move the closure from the closed ,
position to the opened position and maintain the
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closure in the opened position. The manually
overridable control system constructed and arranged
to permit manually generated movement of the closure
from the opened position to the closed position to
force the piston away from the rod extension end of
the cylinder and move the at least one hydraulic
actuator assembly against the biasing force from the
extended condition to the contracted condition to
create hydraulic fluid flow in the one direction
with respect to the cylinder on the first side of
the piston when the pump is in an inoperative state.
The biased energy storage system is further
constructed and arranged to store a portion of
energy input to the at least one hydraulic actuator
assembly by the manually generated movement of the
closure from the opened position to the closed
position to enable the energy storage system to
subsequently move the closure from the closed
position to the opened position when the stored
. 20 energy is expended.
It is desirable to provide a liftgate
having powered closing capability with an obstacle
detection device that detects an obstacle
interfering with proper closure of the liftgate and
terminates the powered closing when the obstacle is
detected A proposal described in Bartelt '106
includes a tape switch mounted along the door frame
which will shut off the hydraulic system if an
obstacle comes into contact with the tape. A
disadvantage associated with this proposal is that
the system will only be shut down when and if the
obstacle contacts the tape, which is mounted on the
door frame.
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There is a need for an obstacle detection
mechanism for a hydraulic liftgate system that
promptly detects an obstacle interfering with
closure of the liftgate regardless of the location
at which the obstacle contacts the liftgate. It is
another object of the present invention to fulfill
this need. In accordance v~ith this object, the
present invention provides a hydraulic closure
system for use in a motor vehicle and constructed
and arranged to cooperate with a closure opening
defined by an opening frame of the motor vehicle
body. The hydraulic closure system comprises a
closure constructed and arranged to be pivotally
mounted on the opening frame for movement between a
closed position in which the closure closes the
closure opening and an opened position in which the
closure is oriented to permit access through the
closure opening. A latching structure is
constructed and arranged to latch the closure in the
closed position and to unlatch the closure to permit
the closure to move from the closed position to the
opened position. At least one hydraulic actuator
assembly is coupled at one end thereof to the
closure and coupled at an opposite end thereof to
the opening frame and includes a cylinder and a
piston rod assembly. The piston rod assembly
includes a piston and a rod member connected to the
piston, the piston being moveable within the
cylinder in slidably sealed relation with inner
walls of the cylinder. The rod member extends
outwardly from a rod extension end of the cylinder.
The piston rod assembly is moveable between an
extended condition in which the rod member has a
relatively large extent thereof extending outwardly
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from the rod extension end of the cylinder so as to
create a distance between the opposite ends of the
at least one hydraulic actuator assembly sufficient
to maintain the closure in the opened position and
a
contracted condition in which the rod member has a
relatively smaller extent thereof ex=~nding
outwardly from the rod extension end of the cylinder
in comparison with the extended condition to create
a distance between the opposite ends of the at least
one hydraulic actuator assembly that enables the
closure to be disposed in the closed position. An
automated closure opening system is constructed and
arranged to effect automatic movement of the closure
from the closed position to the opened position when
the latching structure in unlatched. A motorized
hydraulic pump is constructed and arranged to input
energy to the at least one hydraulic actuator
assembly to effect automatic movement of the closure
from the opened position to the closed position by
creating hydraulic fluid flow with respect to the
cylinder on a first side of the piston to force the
piston away from the rod extension end of the
cylinder and move the at least one hydraulic
actuator assembly from the extended condition to the
contracted condition and the closure from the opened
position to the closed position. An obstacle
detection mechanism comprises a pressure transducer
constructed and arranged to monitor hydraulic
pressure resulting from the hydraulic fluid flow
created on the first side of the piston by operation
of the motorized hydraulic pump. The obstacle
' detection mechanism is constructed and arranged to
detect an obstacle interfering with the automatic
- . movement of the closure from the opened position to
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the closed position by operation of the motorized
hydraulic pump based upon the hydraulic pressure
monitored by the pressure transducer and to
terminate operation of the motorized hydraulic pump
when the interfering obstacle is detected.
The amount of force needed to open a
liftgate against the force of gravity depends on the
inclination or the declination of the vehicle, as
the geometric orientation of the liftgate will
affect the line of action of the gravitational force
and gravitational moment arm relative to the
geometry of the liftgate and actuators.
Conventional liftgates having pneumatic actuators
for assisting in opening the liftgate and prior
proposals for hydraulically powered rear gates
include no compensation for vehicle inclination or
declination. While the system could be designed
with a high pressure level so as to be able to open
the liftgate under any inclination or declination,
this will lead to unnecessary stress in components
under pressure a.n circumstances when such high
pressures are not required, and may cause opening of
the liftgate at a rate that is faster than desired
when the particular inclination or declination is
favorable for opening.
It is an object of the present invention
to overcome the deficiencies in the prior art noted
above. In accordance with this object, the present
invention provides a hydraulic closure system for
use iri a motor vehicle and constructed and arranged
to cooperate with a closure opening defined by an
opening frame of the motor vehicle body., the
hydraulic closure system comprises a closure
constructed and arranged to be pivotally mour~ted on
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the opening frame for movement between a closed
position in which the closure closes the closure
opening and an opened position in which the closure
is oriented to permit access through the closure
opening. A latching structure is constructed and
arranged to latch the closure in the closed position
and to unlatch the closure to permit the closure to
move from the closed position to the opened
position. At least one hydraulic actuator assembly
is coupled at one end thereof to the closure and
coupled at an opposite end thereof to the opening
frame and includes a cylinder and a piston rod
assembly. The piston rod assembly includes a piston
and a rod member connected to the piston, the piston
being moveable within the cylinder in slidably
sealed relation with inner walls of the cylinder.
The rod member extends outwardly from a rod
extension end of the cylinder. The piston rod
assembly is moveable between an extended condition
in which the rod member has a relatively large
extent thereof extending outwardly from the rod
extension end of the cylinder so as to create a
distance between the opposite ends of the at least
one hydraulic actuator assembly sufficient to
maintain the closure in the opened position and a
contracted condition in which the rod member has a
relatively smaller extent thereof extending
outwardly from the rod extension end of the cylinder
in comparison with the extended condition to create
a distance between the opposite ends of the at least
one hydraulic actuator assembly that enables the
closure to be disposed in the closed position. A
biased energy storage system.is constructed and
arranged to expend energy stored therein on a first
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side of the piston when the closure is unlatched to
move the piston toward the rod extension end of the
cylinder and thereby move the at least one hydraulic
actuator assembly from the contracted condition to
the extended condition and move the closure from the
closed position to the opened position and maintain
the closure in the opened position. A vehicle level
detection and compensation system includes vehicle
level detector constructed and arranged to detect
inclination or declination of the motor vehicle.
The vehicle level detection and compensation system
is constructed and arranged to control the amount of
energy stored in the biased energy storage system
based upon a detected inclination or declination of
the vehicle as detected by the vehicle level
detector so that the energy stored in the biased
energy storage system is commensurate with an amount
of energy required to move the closure from the
closed position to the opened position for the
detected inclination or declination.
The effectiveness of an automated closure
system which utilizes stored energy to open the
closure may be adversely effected by the inability
to maintain proper fluid pressure (either liquid or
hydraulic fluid pressure) in the system. For
example, in a closure which incorporates a charge of
compressed gas, the pressure within the system may
fluctuate due to fluctuations in temperature.
Particularly, temperature increases will increase
the pressure of the compressed gas, while
temperature decreases will decrease the pressure of
the compressed gas. Also hydraulic systems maybe
subject to pressure fluctuations due to other
causes, such as system leaks
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There is a need to provide a hydraulic
liftgate or closure system that employs stored
- energy for opening the closure, and that monitors
and maintains a sufficient amount of stored energy
- 5 to open the closure. It is an object of the present
invention to fulfill this need.
In accordance with this object, the
present invention provides a hydraulic closure
system for use in a motor vehicle and constructed
and arranged to cooperate with a closure opening
defined by an opening frame of the motor vehicle
body. The system comprises a closure constructed
and arranged to be pivotally mounted on the opening
frame for movement between a closed position in
which the closure closes the closure opening and an
opened position in which the closure is oriented to
permit access through the closure opening. A
latching structure is constructed and arranged to
latch the closure in the closed position and to
unlatch the closure to permit the closure to move
from the closed position to the opened position. At
least one hydraulic actuator assembly includes a
cylinder and a piston rod assembly, and the piston
rod assembly includes a piston and a rod member
connected to the piston, the piston being moveable
within the cylinder in slidably sealed relation with
inner walls of the cylinder. The rod member extends
outwardly from a rod extension end of the cylinder.
The piston rod assembly is moveable between an
extended condition in which the rod member has a
relatively large extent thereof extending outwardly
' from the rod extension end of the cylinder so as to
create a distance between the opposite ends of the
- at least one hydraulic actuator assembly sufficient
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to maintain the closure in the opened position and a
contracted condition in which the rod member has a
relatively smaller extent thereof extending
outwardly from the rod extension end of the cylinder
in comparison with the extended condition to create
a distance between the opposite ends of tie at least
one hydraulic actuator assembly that enables the
closure to be disposed in the closed position. A
biased energy storage system is constructed and
arranged to expend energy stored therein on a first
side of the piston when the closure is unlatched to
move the piston toward the rod extension end of the
cylinder and thereby move the at least one hydraulic
actuator assembly from the contracted condition to
the extended condition and move the closure from the
closed position to the opened position and maintain
the closure in the opened position. An energy
monitoring device is constructed~and arranged to
monitor the amount of energy stored in the biased
energy storage system. And an energy control system
is in communication with the energy monitoring
device and is constructed and arranged to control
the amount energy stored in the biased energy
storage system so that the amount of energy remains
within a predetermined range so that the amount of
energy remains commensurate with the energy required
to move the closure from the closed position to the
opened position.
It is a further object of the present
invention to provide an automated hydraulic closure
system in which automatic closure of the closure by
operation of a motorized hydraulic pump can be
commenced in response to manually generated movement
of the closure from the opened position toward the
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closed position for a prescribed distance in more
than a prescribed time.
It is another object of the invention to
provide a system which contemplates any hydraulic
S system with manual override. In accordance with
this object, the present system provides a hydraulic
closure system for use in a motor vehicle and
constructed and arranged to cooperate with a closure
opening defined by an opening frame of the motor
vehicle body. The system comprises a closure
constructed and arranged to be mounted on an upper
portion of the opening frame and pivoted for
movement about a horizontal axis between a closed
position in which the closure closes the closure
opening and an opened position in which the closure
is oriented to permit access through the closure
opening. An electrically operated latching
structure is constructed and arranged to latch the
closure when the closure is moved to the closed
position and to unlatch the closure in response to a
first electrical signal to permit the closure to
move from the closed position to the opened
position. A manually overridable power control
system includes at least one hydraulic actuator
assembly which couples the closure with the closure
opening and is capable of effecting movement of the
closure between the opened and closed positions in
response to hydraulic fluid flow generated by the
manually overridable power control system. The
manually overridable power control system is
constructed and arranged to effect hydraulic fluid
flow that causes the at least one hydraulic actuator
assembly to move the closure from the closed
position to the opened position when the latching
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structure is unlatched in response to the first
electrical signal, and to effect hydraulic fluid
flow that causes the at least one hydraulic actuator
assembly to move the closure from the opened .
position to the closed position in response to a
second electrical signal. A remote control device
is provided. An electrical controller responsive to
selective activation of the remote control device is
provided to generate the first electrical signal to
unlatch the latching structure and thereby permit
the manually overridable power control system to
effect hydraulic fluid flow that causes the at least
one actuator to move the closure from the closed
position to the opened position. The electrical
controller is responsive to selective activation of
the remote control device to generate the second
electrical signal so that the manually overridable
power control system effects hydraulic fluid flow
that causes the at least one hydraulic actuator
assembly to move the closure from the opened
position to the closed position. The manually
overridable power control system also permits
manually generated movement of the closure from the
opened position to the closed position.
A still further object of the invention is
to provide methods for operating a hydraulic closure
system for a motor vehicle, which methods accomplish
each of the objects noted above.
In accordance with a first method of
operating the hydraulic closure system for a motor
vehicle, the method comprises opening the closure by
activating a remote control device to unlatch the
closure and to effect hydraulic fluid flow which .
causes the at least one hydraulic actuator assembly
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to move the closure from the closed position to the opened position. The
method
further comprises closing the closure by optionally (a) activating the remote
control
device to effect hydraulic fluid flow which causes the at least one hydraulic
actuator
assembly to move the closure from the opened position to the closed position,
or (b)
manually engaging the closure and providing manually generated movement of the
closure to move the closure from the opened position to the closed position.
Manually generated movement of said closure activates a hydraulic pump
effecting
said fluid flow to cause said at least one hydraulic actuator assembly to move
said
closure from said opened position to said closed position if said manually
generated
movement of said closure moves said closure from said opened position toward
said
closed position for a prescribed distance in more than a prescribed time.
In accordance with a second method of operating the hydraulic closure system
for a motor vehicle, the method comprises actuating a remote control device to
effect
15 flow of hydraulic fluid in communication with the at least one hydraulic
fluid actuator
assembly, moving the closure from the opened position toward the closed
position in
response to the flow of the hydraulic fluid in communication with the at least
one
hydraulic fluid actuator assembly, detecting a level of hydraulic fluid
pressure of the
hydraulic fluid in communication with the at least one hydraulic fluid
actuator
assembly, and terminating the flow of hydraulic fluid in response to a
detected level
of hydraulic fluid pressure outside of a prescribed range to terminate
movement of the
closure from the opened position toward the closed position.
In accordance with a third method of operating the hydraulic closure system
for a motor vehicle, the method comprises utilizing energy stored in the
hydraulic closure system to move the closure from
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the closed position to the opened position when the
closure is unlatched, increasing the amount of
energy stored in the hydraulic closure system if the
amount of energy stored is less than a prescribed
range of energy, thus maintaining the amount of
energy stored in the hydraulic closure system within
the prescribed range of energy, and decreasing the
amount of energy stored in the hydraulic closure
system if the amount of energy stored is more than
the prescribed range of energy, thus maintaining the
amount of energy within the prescribed range of
energy.
These and other objects of the present
invention will become more apparent during the
course of the following detailed description and
appended claims. The invention may best be
understood with reference to the accompanying
drawings wherein an illustrative embodiment is
shown.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a perspective view of a motor
vehicle employing a hydraulic power liftgate in
accordance with the principles of the present
invention.
FIGURE 2 is a hydraulic system schematic
of the hydraulic power liftgate in accordance with
the principles of the present invention.
FIGURE 3 is an electrical schematic of the
electrical control system of the hydraulic power
liftgate in accordance with the principles of the
present invention.
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DETAILED DESCRIPTION OF THE INVENTION
' FIGURE 1 is a perspective view of the rear
portion of a minivan, generally indicated at 10,
which employs a hydraulic power liftgate, or
closure, in accordance with the principles of the
present invention. The minivan 10 comprises a main
body 12, which has a rearward liftgate opening or
door aperture 13 defined by a rearward opening frame
14. A liftgate, generally indicated at 16, is
pivotally mounted on an upper horizontal portion of
opening frame 14 by a pair of laterally spaced
hinges 18 (only one being shown in FIGURE 1).
A hydraulic actuator assembly, preferably
in the form of a pair of hydraulic actuators 20, is
interconnected between the liftgate 16 and the
opening frame 14, with the lower end of each being
pivotally connected at respective opposite vertical
portions of opening frame 14, and with the upper end
of each being pivotally connected at respective
adjacent opposite upper interior portions of the
liftgate 16. More specifically, as shown in FIG. 2,
each hydraulic actuator 20 comprises a piston rod
assembly 22 and cylinder member 24. Each piston rod
assembly 22 includes a rod member 25 having a distal
portion thereof extending outwardly from a rod
extension end 27 of the cylinder member 24, and
hydraulic fluid sealing member or piston 28 disposed
in slidably sealed relation with the inner walls of
the cylinder 24. The distal end 26 of each rod
member 25 is pivotally connected with an upper
' interior portion of the liftgate 16, and the
opposite end of the rod member 25 is connected with
the hydraulic fluid sealing member or piston 28
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within the cylinder member 24(see FIGURE 2). Each
cylinder member 24 has its lower end 30 pivotally
connected on respective opposite vertical portions
of the door opening frame 14. _
It will be appreciated by those skilled in
the art that the orientation of the actuators 20
disclosed above is merely illustrative, and that any
particular configuration of the hydraulic actuators
that would accomplish the opening and closing
function is possible. For example, it is possible
to provide only a single actuator 20. The present
invention further contemplates that the actuators
may be inverted so that the distal end 26 of rod
members 25 are connected with the door opening frame
14 and the ends 30 of the cylinder members 24 are
connected with the liftgate 16.
A hydraulic pump assembly 32 is mounted
beneath the vehicle floor 34 and provides hydraulic
fluid through hydraulic lines, generally indicated
at 36, to the hydraulic actuators 20. The hydraulic
pump assembly 32 functions to provide hydraulic
fluid to the hydraulic actuators 20 as needed to
cause such cylinders to automatically close the
liftgate 16.
A latching structure, preferably in the
form of a pair of electrically operated latching
mechanisms 40, is provided to latch and unlatch the
liftgate to and from the closed position. The
latching mechanisms 40 are provided at opposite
lower interior portions of the liftgate 16 and are
cooperable with associated striker members 42 (only .
one being shown in FIGURE 1) mounted on the opposite
vertical portions of the opening frame 14. When the
liftgate 16 is closed, each power latching mechanism
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40 latches with the associated striker member 42 to
secure the liftgate 16 in_its closed position.
- Shown in FIGURE 2 is a hydraulic system,
generally indicated at 100, in accordance with the
- 5 principles of the present invention. From FIGURE 2
it can be appreciated that the hydraulic lines 36
include a hydraulic liftgate pull-down line 106 and
a hydraulic liftgate lift line 108. As shown, the
pull-down line 106 is divided into two hydraulic
line segments 102 proximate the hydraulic actuators
20. Each of the segments 102 are connected in fluid
communication with a respective upper chamber 31 of
the cylinder member 24 of one of the associated
actuators 20. Similarly, the lift line 108 is
divided into two hydraulic line segments 104
proximate the actuators 20. The segments 104 are
each connected in fluid communication with a
respective lower chamber 29 of the cylinder member
24 of one of the associated actuators 20. The
segments 102 of line 106 are in fluid communication
with the chambers 31 at positions above that which
can be attained by sealing members 28, while
segments 104 of lift line 108 are in fluid
communication with the associated chambers 29 at
positions below that which can be attained by
sealing members 28.
The hydraulic pump assembly 32 preferably
includes a bi-directional hydraulic pump 114 and a
D.C. electric motor 115 for actuating the pump 114.
The pump 114 preferably is connected between the
pull-down line 106 and lift line 108, and is capable
of individually pressurizing each of said lines with
hydraulic fluid withdrawn from the fluid reservoir
118. More specifically, in a preferred embodiment
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of the present invention as schematically
represented in FIGURE 2, the right side of the
hydraulic pump 114 is connected with pull-down line
106, while the left side of the pump 114 is
connected with lift line 108.
Preferably disposed within the pull-down
line 106 is a pull-down pressure transducer 110,
which measures hydraulic pressure in the pull-down
line 106.
The pull-down line 106 further includes a
pull-down valve 112, which preferably comprises a
two position three-way valve, disposed between the
bi-directional hydraulic pump 114 and the upper
chambers 31 of hydraulic actuators 20 for
controlling the flow of hydraulic fluid
therebetween. The pull-down valve 112 is shown as
being biased by a conventional valve spring,
symbolically indicated at 116, into its normal
(rest) position. In this position, the pull-down
valve 112 permits fluid communication between the
upper cylinder chambers 31 and a hydraulic fluid
reservoir 118. When the pull-down line 106 is
pressurized by the right side of hydraulic pump 114,
pressurization in the dashed hydraulic valve pilot
line 122 of pull-down valve 112 shifts the pull-down
valve 112 to the right, against the force of valve
spring 116, so as to permit hydraulic fluid to flow
from the hydraulic pump 114 to the upper cylinder
chambers 31, while cutting off communication between
the upper chambers 31 and the hydraulic fluid
reservoir 118.
It should be appreciated that, although
there are several schematic representations of the
hydraulic fluid reservoir 118 in FIGURE 2, this is
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done solely for the convenience of illustration, as
the hydraulic system 100 in actuality comprises only
- a single common hydraulic fluid reservoir 118.
Disposed in the pull-down line 106 between
. 5 the right side of hydraulic pump 114 and the pull-
down valve 112 is a pull-down pressure relief valve
124. Preferably, a flow restrictor 120 is disposed
between the pull-down pressure relief valve 124 and
the pull down valve 112. The pressure relief valve
124 is spring biased, by a valve spring,
schematically indicated at 126, into a normally
closed position. Pressure relief valve 124 will
shift against the bias of valve spring 126 when the
dashed hydraulic valve pilot line 130, which is
subject to the pressure in pull-down line 106, is
pressurized to unacceptably high levels. Opening of
valve 124 will enable the hydraulic fluid in the
pull-down line 106 between pull-down valve 112 and
pump 114 to drain into hydraulic fluid reservoir 118
thus relieving any excess fluid pressure. The
pressure relief valve 124 is not intended to be
opened during the normal course of operation of the
hydraulic system 100, but is intended to function as
a safety valve that opens only in the event of
overpressurization of the pull-down line 106 by pump
114. Thus, pressure relief valve 124 is set to open
at a greater pressure than the pressure required to
move pull-down valve 112 to the right against the
force of spring 116.
The pull-down line 106 also includes a
pull-down suction line check valve 134 disposed in a
~ direct line between the right side of hydraulic pump
114 and the hydraulic fluid reservoir 118. The
check valve 134 functions as a one-way valve that
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permits the right side of hydraulic pump 114 to
withdraw hydraulic fluid from the reservoir 118 to
be discharged from the left side of pump 114 but
prevents hydraulic fluid from being discharged from
the right side of hydraulic pump 114 directly into
the hydraulic fluid reservoir therethrough.
Preferably, a filter 136 is provided between the
check valve 134 and the hydraulic fluid reservoir
118 to prevent contamination of the hydraulic lines
and or pump.
The lift line 108 incorporates a biased
energy storage system, preferably in the form of a
gas-charged hydraulic fluid accumulator assembly
140, and preferably the type of accumulator having a
diaphragm 141 separating a charge of compressed gas
143 from the hydraulic fluid in the hydraulic system
100. The compressed gas 143 applied a biasing force
that pressurizes the hydraulic fluid in the lift
line 108. Although a gas-charged accumulator is
preferred a spring-loaded accumulator or energy
storage system may also be used. In a spring-loaded
system, a spring applies a biasing force on a
diaphragm or piston to exert pressure on the
hydraulic fluid in the lift line 108. The biased
energy storage system is used to store and release
energy and is preferably capable of providing a
relatively constant pressure (approximately ~ 5%)
which is exerted on the volume of hydraulic fluid
that is in the hydraulic lift line circuit. The
accumulator assembly 140 is maintained in fluid
communication with the lower chambers 29 of the
cylinder members 24 through lift line 108.
Accordingly, the accumulator assembly provides a
biasing force tending to urge extension of the
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hydraulic actuators 20 and thus to urge the closure
or liftgate toward the opened position. Disposed
between the accumulator assembly 140 and the lower
.chambers 29 is a flow restrictor 142, which limits
the speed at which hydraulic fluid can travel to the
lower cylinder chambers 29 from the accumulator
assembly 140. A bypass check valve 144 functions as
a one-way valve that bypasses the flow restrictor
142 so that the travel of hydraulic fluid to the
accumulator assembly 140 from the lower chambers 29
is not limited by the flow restrictor 142. A lift
line pressure relief valve 146 is biased by a valve
spring, schematically illustrated at 148, into a
normally closed position. ~ The pressure relief valve
146 functions to drain hydraulic fluid into the
hydraulic fluid reservoir 118 in the event of
overpressurization of the accumulator assembly
and/or lower cylinder chambers 29 in a manner to be
described later.
A lift line check valve 150 is a one-way
valve disposed in the lift line 108 that prevents
flow of hydraulic fluid from the accumulator
assembly 140 and the lower cylinder chambers 29
towards the pump 114 or fluid reservoir 118, but
permits flow in the opposite direction.
Another lift-line pressure relief valve
152 is preferably provided between the hydraulic
pump 114 and the check valve 150, and functions as a
safety valve to relieve overpressurization in this
portion of lift line 108. Pressure relief valve 152
is set to open at a higher pressure than pressure
relief valve 146 and will be opened only in the
event that the pump exceeds the maximum allowable
operating pressure. This safety pressure relief
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valve 152 can optionally be omitted (upon
integration of relief valve 146 and check valve 150
into the pump body).
A lift line check valve 154 is preferably
provided between the left side of the hydraulic pump
114 and the hydraulic fluid reservoir 118 and
functions as a one-way valve to prevent flow of
hydraulic fluid discharged from the left side of
hydraulic pump 114 directly into the reservoir 118,
while permitting fluid to be withdrawn from the
hydraulic fluid reservoir 118 by the left side of
pump 114 to be discharged from the right side of
pump 114. Filter 136 prevents cross contamination
between the hydraulic fluid reservoir 118 and the
remainder of the hydraulic circuit, especially the
hydraulic pump 114.
Preferably, a lift line pressure
transducer 156 communicates with the lift line 108
and constantly measures the common pressure in the
accumulator assembly 140 and the lower cylinder
chambers 29. When the transducer 156 detects that
the measured pressure is less than a predetermined
level, the transducer 156 will send a signal to the
system electronic control module 200 (See FIGURE 3),
which in turn sends a signal to pump motor 115 to
cause the pump 114 to pressurize the lift line 108,
accumulator assembly 140, and lower chambers 29. As
will be appreciated from FIGURE 2, controller 200
performs all system logic operations.
The operation of the present invention
will now be described generally.
When the liftgate 16 is in its closed
position, the energy stored in the accumulator
assembly 140 in the form of compressed gas is
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sufficient to move the liftgate from the closed
position to the opened position. To open the
' liftgate, the latching mechanisms 40 must first be
unlatched. The latching mechanisms 40 may be
unlatched either by manual movement of an outside
release handle on the liftgate, or automatically
upon receiving a signal from the'controller 200.
The controller 200 will generate the appropriate
signal to open the latching mechanisms 40 when the
l0 controller receives an input signal which is
generated upon manual actuation of a remote control
device, such as electrical switch 202 (See FIGURE 3)
hardwired within the vehicle or a wireless remote
(such as a conventional infrared device). Upon
release of the electrically powered latching
mechanisms 40, the hydraulic fluid is permitted to
flow from the accumulator assembly 140 and into the
cylinder members 24. The hydraulic energy stored
within the accumulator 140 will be expended by
expansion of the gas 140 and movement of the
diaphragm 141 against the hydraulic fluid in line
108 to cause fluid flow within chambers 29. As a
result, it can be appreciated that the stored energy
of the compressed gas is utilized to exert a biasing
force by fluid pressure upon one side of sealing
members 28. Once the latching structure is
unlatched, the biasing force causes the sealing
members 28 to move upwardly within the cylinder
members 24. Upward movement of sealing members 28
will cause the respective rod members 25 to extend
outwardly relative to the cylinder members 24 and
' the lower chambers 29 to expand linearly. It can be
thus appreciated that the pressure maintained in the
accumulator assembly 140 and lower chambers 29 is
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sufficient to cause the piston rod assemblies 22 to
be moved outwardly against the weight of the
liftgate 16 to lift the liftgate 16 to its fully
opened position and maintain the liftgate 16 in its
fully opened position in a passive manner.
Particularly, it can be appreciated that this
lifting action is accomplished without resort to any
pumping action of the hydraulic pump 114.
It should be appreciated that the liftgate
according to the present invention does not have an
"overcenter" condition as the biasing force applied
by the accumulator 140, or other energy storage
system, constantly urges the liftgate into an opened
position from any position at which the liftgate is
released.
As lower cylinder chambers 29 expand
linearly, the fluid in the contracting upper
cylinder chambers 31 is drained via pull-down line
106 through the normally positioned hydraulic pull-
down valve 112, and into the hydraulic fluid
reservoir 118. In a preferred embodiment, the lift
line pressure transducer 156 performs continuous
measurement of the pressure in the lift line 108
between the check valve 150 and the accumulator 140.
If at any time during operation, or otherwise, the
pressure in the accumulator assembly 140 and the
lower chambers 29 are below a predetermined pressure
that is set according to the pressure necessary for
properly lifting the liftgate 16, the transducer 156
will send an electrical signal to the electronic
control module 200, which in turn sends a signal to
actuate the pump motor 115. As a result, the right
side of pump 114 will withdraw hydraulic fluid from
the reservoir 118 through the filter 136 and the
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check valve 134, and then discharge such hydraulic
fluid from the left side thereof past the check
- valve 150 and into the accumulator assembly 140 and
lower cylinder chambers 29. The pump 114 will
continue to function in such fashion until the
transducer 156 detects that the pressure within
accumulator assembly 140 and lower cylinder chambers
is equal to or greater than the predetermined
pressure.
It is contemplated, however, according to
the most basic principles of ~ze present invention
that lift line 108 may not be connected to pump 114.
In this arrangement, the liftgate is opened solely
by the energy stored in the accumulator assembly 140
and pump 114 may be a single direction pump
connected to the pull-down line 106 only.
To close the liftgate by hydraulic power,
the remote control device, such as hardwired motor
vehicle electric switch 202 (SEE FIG. 3) or wireless
remote, is actuated and sends a signal to the
controller 200, which in turns sends a signal to
pump motor 115 to actuate pump 114. The pump 114
inputs energy to the hydraulic actuators 20 when the
left side of the hydraulic pump 114 withdraws
hydraulic fluid from the hydraulic fluid reservoir
118 through the filter 136 and check valve 154, and
the right side of the pump pressurizes the pull-down
line 106. Hydraulic fluid pressure in valve
activation pilot line 122 moves the pull-down valve
112 to the right in FIGURE 2 against the force of
valve spring 116. Hydraulic fluid is thus pumped
through valve 112 and discharge into the upper
cylinder chambers 31. Pressurization of chambers 31
forces sealing members 28 downwardly into the
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respective cylinder members 24 to withdraw the
piston rod assemblies 22 into the respective
cylinder members 24 and thereby pull liftgate 16
closed. As upper cylinder chambers 31 are expanded,
the respective lower cylinder chambers 29 are
compressed. The fluid expelled by the compression
of the lower cylinder chambers 29 is forced back
past check valve 144 into the accumulator assembly
140 at relatively constant pressure. It should be
noted that under normal operating conditions, the
fluid volume within the lower cylinder chambers 29
and the accumulator assembly are not disturbed by
valves or the pump.
It can be appreciated that the relatively
constant pressure in accumulator assembly 140 is at
all times applied to cylinder chamber 29 side of
sealing member 28. This results in the biasing
force tending to urge the piston rod assemblies 22
to extend from their respective cylinder members 24
and thus tending to urge the liftgate into its open
position. When the liftgate is closed, it is closed
against this biasing force, and the movement of
fluid into the accumulator as a result of the
liftgate being closed restores potential energy to
the accumulator assembly 140 by action of the
diaphragm further compressing the charge of
compressed gas 143.
After the liftgate 16 is latched closed at
the end of travel, pump 114 is turned off, and the
pull-down valve 112 returns to its normal position
as shown in FIGURE 2. Subsequently, hydraulic fluid
pressure within the upper chambers 31 is permitted
to drain through pull-down valve 112, and into
reservoir 118. After such drainage, the hydraulic -
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pressure in the accumulator 140 and lower chambers
29 will be sufficiently greater than the pressure in
the upper chambers 31 to enable the cylinders 20 to
automatically lift the liftgate 16 when subsequently
unlatched.
It is contemplated that lift line 108 and
pull down line 106 may be switched so that they
connect to chambers 31 and 29, respectively, and
pump 114 would be a vacuum pump and the biased
energy storage system would store a energy in the
form of a vacuum instead of a pressure. The
liftgate 15 then closed by operation of the vacuum
pump to create a vacuum in chamber 29 sufficient to
contract the actuators and effect closing of the
door. This vacuum energy is stored in the energy
storage system in the form of a constant vacuum.
When the door is unlatched and chamber 29 is opened
to atmospheric pressure, the vacuum energy applied
to chamber 31 is sufficient to effect extension of
the actuators and thus opening of the liftgate.
Specific features of the invention will
now be described.
Manual Override Feature
In the preferred embodiment of the present
invention, the hydraulic system 100 provides a
manually overridable power control system which
includes at least one hydraulic actuator 20, the
motorized hydraulic pump 32, and the biased energy
storage system preferably in the form of the
accumulator 140. The manually overridable power
control system permits the liftgate 16 to be
manually opened or closed at any time after the
- power latching mechanisms 40 have been unlatched
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from their respective striker members 42, without
the possibility of hydraulic lock preventing such
manually generated movement. For example, when the
liftgate 16 is in the opened position, it is
possible to close the liftgate manually rather than '
by using the pumping action of hydraulic pump 114.
It is to be understood that the present invention
contemplates that the liftgate can be moved manually
by manual engagement of the liftgate for the entire
distance from the opened position to the closed
position, or alternatively manually engaged for a
brief instance and then released after being moved
with sufficient speed to cause the momentum of the
liftgate to carry the liftgate to the closed
position at which the liftgate is slammed shut. In
both instances, the manual movement is manually
generated. Thus, the term "manually generated"
movement as used herein refers to both types of
manual movement.
When the liftgate 16 is manually forced
downwardly from its opened position, the rod
assemblies 22 are forced into their respective
cylinder members 24, and the fluid within the lower
cylinder chambers 29 is forced through lift line
108, past the check valve 144 (bypassing flow
restrictor 142), and into the accumulator assembly
140. The fluid expelled by the compression of the
lower cylinder chambers 29 is forced back into the
accumulator assembly at relatively constant pressure
so the energy put into the hydraulic liftgate system
while manually closing the liftgate is stored by the
accumulator assembly 140. Any excess pressure that
builds in the lower chambers 29 or accumulator
assembly 140 will be drained via lift line pressure
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relief valve 146. As the upper cylinder chambers 31
are expanded during this manually forced movement of
- the rod assemblies 22, hydraulic fluid is withdrawn
from the hydraulic fluid reservoir 118 through the
pull-down valve 112 and replenished in the upper
cylinder chambers 31:
During opening of the liftgate 16, manual
assistance can also be performed. More
specifically, while the hydraulic pressure
accumulated within accumulator assembly 140 and the
lower cylinder chambers 29 function to automatically
open the liftgate 16 when it is unlatched, it is
possible to expedite the opening of the liftgate by
manually pulling it upwardly. During this movement,
hydraulic fluid is drawn from the accumulator
assembly 140 by the expanding lower cylinder
chambers 29 while hydraulic fluid within the upper
cylinder chambers 31 is expelled through the pull-
down valve 112 and drained into the hydraulic fluid
reservoir 118. Opening is expedited because fluid
is both forced into lower chamber 29 by accumulator
assembly 140 and drawn into lower chamber 29 by the
expanding volume of chamber 29 due to the manually
assisted upward movement of the liftgate. Fluid is
drawn into lower chamber 29 and forced from upper
chamber 31 at a rate determined by the additional
manual force exerted.
During pump-activated closing of the
liftgate 16, it is preferred that the closing
operation can be expedited or assisted in similar
fashion. In this instance, hydraulic fluid in the
lower cylinder chambers 29 is forced into
accumulator 140 at a rate determined, at least
- initially before the flow capacity of the fluid
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system is achieved, by the additional manual force
exerted. Similarly fluid is drawn into upper ,
cylinder chamber 31 at a rate more rapid than that
provided by operation of the pump alone. The ,
additional fluid is drawn from reservoir 118 through
check valve 134.
A hydraulic control system according to
the most basic principles of the present invention
need not be provided with check valve 134. Without
check valve 134, manually assisted closure during
power operation of the pump is not achieved.
Nevertheless, manual closure of the liftgate while
the pump is in an inoperative state (i.e., either
inactivated or malfunctioning) is still possible, as
pull down valve 112 permits hydraulic flow. That
is, when pump 114 is in an inoperative state, pull
down valve 112, disposed in its normal position,
will permit fluid from reservoir 118 into chambers
31 during manual closing.
In addition, at any time during the
automated opening or closing of the liftgate, the
liftgate can be manually stopped and forced into an
opposite direction to its motion. Manual stoppage
of the liftgate 16 when the liftgate is being
hydraulically closed will cause the pump 114 to
automatically turn off. This will be more fully
appreciated by reference to the obstacle detection
feature, described in the next section.
Another advantage of the manual override
feature is that it permits the hydraulic system 100
to operate in a completely manual mode at any time .
by simply disabling the motor 115 to hydraulic pump
114, for example, by activating a switch 204 _
provided within the vehicle (See FIGURE 3) or a
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wireless remote. In addition, this feature is also
greatly advantageous in that it permits complete
- manual operation in the event of pump or battery
failure .
Obstacle Detection Feature
During power closure of the liftgate 16,
the hydraulic system 100 is preferably capable of
detecting an obstruction, and, in response to such
detection, the pump motor 115 is shut off to
terminate the pumping operation of the hydraulic
pump 114. More specifically, as pump 114
pressurizes the upper cylinder chambers 31, an
obstacle detection mechanism, preferably in the form
of the pull-down pressure transducer 110
continuously measures the pressure in pull-down line
106 between the pump 114 and upper chambers 31. The
force exerted on the liftgate 16 by an obstacle can
be derived from the pressure in the pull-down line
106. When the pull-down transducer 110 detects a
pressure above a predetermined threshold level as
determined by the electronic control module 200,
thus indicating that an obstacle is preventing
proper expansion of upper chambers 31 and liftgate
closure, the electronic control module 200 will send
a signal to pump motor 115 to terminate operation of
the hydraulic pump 114. The system of this
embodiment a.s also preferably provided with a biased
energy storage system, such as accumulator assembly
140, so that at this point, the hydraulic system
will function in the manual mode, and the pressure
. within the accumulator assembly 140 will be expended
and the pressure within the lower cylinder chambers
- 29 will become greater than the pressure in upper
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chambers 31. As a result, the piston members 22
will be driven upwards and the liftgate 16 will
automatically move passively, and with minimal
force, into its opened position.
Preferably, the predetermined threshold
pressure that controller 200 compares against the
pressure in pull-down line 106 as measured by the
pull-down pressure transducer 110 is made to be a
function of the position of the liftgate 16. More
specifically, as the position of the liftgate
changes, so will the pressure within the pull-down
line 106, and the controller 200 takes this into
account when determining whether an obstacle exists.
There are three major factors which contribute to
the change in pressure in the pull-down line 106
with respect to the liftgate position.
First, it can be appreciated that, at
varying positions of the liftgate, there will be
varying gravitational moment acting on liftgate 16
that assist the pull-down operation. For example,
due to the position of the center of gravity of the
liftgate 16 relative to its hinged connection 18 to
the vehicle body, there will be significantly
greater gravitational moment assisting closure of
the liftgate when it is in the fully opened position
(horizontal) than when the liftgate is almost closed
(vertical).
Second, when the liftgate is in its fully
open position, the perpendicular distance from the
line of action of each rod assembly 22 to the pivot
axis of the liftgate 16 is approximately maximized.
This forms a relatively large moment arm for
movement of the liftgate. On the other hand, when
the gate is nearing its closed position, the
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perpendicular distance from the line of action of
each rod assembly 22 and the pivot axis of the
liftgate 16 is substantially smaller, and the moment
arm for movement of the liftgate is substantially
reduced.
Third, when the liftgate is being closed,
and the lower cylinder chambers are compressed,
pressure builds within the accumulator assembly 140,
which pressure opposes the hydraulic forces provided
by the hydraulic pump 114 to effectuate closure. It
is thus desirable to continuously adjust the
obstacle detection threshold pressure values to
effectuate sensitive and consistent obstacle
detection actuation forces at the liftgate.
To account for the varying pressure in the
pull-down line 106 with respect to the liftgate
position, one of the cylinders 20 is equipped with
linear potentiometer 206 (See FIGURE 3) or a similar
position feedback device on the liftgate that is
calibrated to determine the relative position of the
liftgate. The position feedback device 206 sends a
signal to the main controller 200. By correlating
the pressure measured by the pull-down pressure
transducer 110 with the relative position of the
liftgate 16 as measured by the position feedback
device 206, the controller is capable of determining
whether the pressure within the pull-down line is
within a predetermined range for the relative
position of the liftgate 16. If the controller
determines that the pressure within the lift line
106 is greater than the predetermined range, thus
indicating that an obstacle is in place, the
controller will send a signal to the pump motor 115
to disable the pump, and the hydraulic system 100
37
CA 02215340 2005-09-06
will then assume the manual mode of operation.
In a preferred embodiment of the present invention, the obstacle detection
feature is disabled during the liftgate's last few millimeters of downward
travel so that
the hydraulic system does not mistake the engagement of the liftgate with the
opening
frame as the detection of an obstacle. This ensures that that hydraulic fluid
continues
to be pumped into the actuators 20 at the very end of the closure cycle in
order to
accomplish final sealing and latching of the liftgate in the closed position.
The obstacle detection feature can, of course, be configured so that the
predetermined threshold pressure is a constant value that corresponds to the
highest
pressure expected to be encountered in the pull-down line during closure.
As alternative arrangements, obstacle detection can be determined by changes
in electrical current draw in the hydraulic pump motor 115, and the liftgate
position
can be derived from the volumetric flow of hydraulic fluid within the
hydraulic
system. In addition, because the speed of the liftgate opening and closing is
relatively
constant, the liftgate position can be approximated as a function of time.
As an additional obstacle detection feature, a pressure sensitive strip or
tape
switch 208 is employed along the periphery of the door opening frame 14, as is
known to those of skill in the art. When an obstacle contacts this sensitized
strip, a
signal is sent to the electronic control module 200, which in turn shuts off
the
hydraulic pump motor 115. This
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obstacle detection feature is independent of the
liftgate position.
Imt~ulse Touch Start Feature
The hydraulic liftgate assembly in
accordance with the present invention preferably
includes an impulse touch start feature. This
feature enables the operator to begin hydraulic
power closure of the liftgate 16 by simply manually
moving the fully opened liftgate 16 downwardly only
a small distance, after which the hydraulic pump
motor 115 is automatically activated so that the
hydraulic pump 114 pressurizes the upper cylinder
chambers 31 to complete the lowering of the liftgate
16. More specifically, the aforementioned position
feedback device 206 sends a signal to the electronic
control module 200, which in turn calculates the
time at which the liftgate 16 reaches a
predetermined position of movement. Preferably, the
hydraulic pump motor 115 will be automatically
activated only if the liftgate 16 reaches the
predetermined position in more than a predetermined
period of time. In other words, if the liftgate I6
is manually moved relatively slowly so that it
reaches such predetermined position only after the
predetermined amount of time, the electronic control
module 200 will send a signal to the pump motor 115
to actuate the pump and begin automated liftgate
pull-down. On the other hand, if the operator
intends to manually close the liftgate through the
entire range of closing motion, the operator should
move the liftgate with sufficient speed (either by a
fast initial swing and release of the liftgate or by
rapid manual movement of the liftgate while the
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liftgate continues to be manually engaged) so that
it reaches the predetermined position prior to the
predetermined time. In such instance, the
electronic control module 200 will not actuate the
motor 115 of the hydraulic pump 114, and the
liftgate 16 will be closed in the manual mode.
As noted above with respect to the
obstacle detection feature, as an alternate
arrangement the position of door travel can be
derived from volumetric flow of hydraulic fluid,
rather than utilizing the position feedback device.
Additionally, the impulse touch start feature may be
achieved by manually depressing the pressure
sensitive strip affixed to the periphery of the door
aperture or door frame. In this case, the switch
sends an electrical signal to the electronic control
module 200, which in turn initiates the closing
cycle of the door. After a very brief predetermined
amount of time, the tape switch reverts back to its
original mode of operation: obstacle detection.
The impulse touch start closing feature is
to be used in conjunction with an automated liftgate
or closure opening system that effects automatic
movement of the closure from the closed position to
the opened position. While in the preferred
embodiment this closure opening system takes the
form of the aforementioned energy storage system,
and in particular the accumulator assembly 140, the
present invention contemplates that other closure
opening systems can be used to automatically move
the closure from the closed position to the opened
position in response to an electrical signal (e. g.,
generated by a remote control device) without the
need to manually engage and move the closure itself.
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For example, the motorized hydraulic pump could be
used to reverse the direction of hydraulic fluid
- flow in comparison with the closing direction, or an
automated mechanical spring operated system could be
used.
Level Compensation Feature
As noted with respect to the obstacle
detection feature, the gravitational moments acting
on the liftgate 16 are influenced by the relative
position of the liftgate. It can be appreciated
that these forces will be further influenced by the
relative incline or decline of the surface upon
which the vehicle rests. For example, with the
vehicle facing a relatively steep decline (e.g., 17
degrees with respect to horizontal), and with the
liftgate 16 in the closed position, the
gravitational forces that need to be overcome to
initially open the liftgate will be greater in
comparison with when the vehicle is on a level
surf ace .
To accommodate for the particular incline
or decline of the vehicle, the hydraulic liftgate
includes a level detection and compensation system
having a level detector 210 (See FIGURE 3)that sends
a signal to the controller 200. The controller, in
turn, generates a control signal to appropriately
adjust the lift line 108 pressure (pressure in the
accumulator circuit) provided to the hydraulic
actuators 20 for opening the liftgate. A pendulum
switch, mercury switch or equivalents thereof can be
used as the level detector for determining the
incline or decline of the vehicle.
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Thus, with the liftgate 16 closed, and the
vehicle disposed at a relatively large decline, the
accumulator assembly 140 will be pressurized to a
greater extent (in comparison to when the vehicle is
level) in order to compensate for the additional
forces that will be necessary to open the liftgate
16. Level compensation allows the system to adjust
the working pressures such that the optimal force
balances are achieved at all times and hence the
physical stresses on the vehicle and manual
operating efforts are minimized.
To increase the pressure in the lift line,
i.e., to store additional energy in the accumulator
140 in order to accommodate a steep decline, in the
preferred embodiment the controller 200 activates
motor 115 so that pump 114 provides additional
hydraulic fluid to the lift line 108. Alternatively,
a pneumatic pump in communication with the
accumulator may pump additional air into the charge
of compressed air 143. On the other hand, where the
biased energy storage device constitutes a
compressed spring device, such as a spring-loaded
accumulator, in communication with hydraulic fluid
in the lift line, the amount of energy stored in the
device can be adjusted by varying the amount
compression in the spring.
In the preferred embodiment, to release
energy from the system, an energy releasing device,
preferably in the form of pressure relief valve 146,
in communication with the lift line, can be
employed. As an alternative to pressure relief ,
valve 146, a solenoid valve, air operated valve,, or
any other type valve that can be electronically ,
controlled rather than pressure controlled is used.
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The electronically controlled valve is electrically
connected to control module 200. This adds
- flexibility to the system, and allows the pressure
within the system to be regulated as a function of
S incline/decline or any other parameter for that
matter.
As another alternative for the energy
releasing device that releases energy from the
system, the pump 114 can be particularly constructed
and arranged in the system 100 to withdraw fluid
from the lift line at the appropriate time to draw
energy out of the system.
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It should be appreciated from the above
that the vehicle level and compensation system
controls the amount of energy stored in the biased
energy storage system based upon the detected
inclination or declination of the vehicle as
detected by the vehicle level detector so that the
amount of energy stored in the biased energy storage
system when the closure is in the closed position is
within a range that is generally commensurate with
the amount of energy required to move the closure
from the closed position to the opened position for
the detected inclination or declination. Although
possible, it is not necessary for the amount of
energy stored in the biased energy storage system to
vary in direct proportion or relation to the amount
of energy required to move the closure from the
closed position to the opened position. Rather, the
present invention contemplates broadly that the
amount of energy stored in the biased energy storage
system is to be increased by the level detection and
compensation system when the more energy is needed
to open the liftgate and decreased by the level
detection and compensation system when less energy
is needed to open the liftgate.
2S I should be further appreciated that the
level compensation feature of the present invention
is advantageous in its use with the biased energy
storage system and the lift line. Therefore,
powered automatic closing capability, which is
provided in the preferred embodiment of the present
invention, need not be provided to reap the benefits
of the level compensation feature.
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Temperature Comr~ensation Features
Hydraulic pressure in the accumulator
assembly 140, as well as the rest of the lift line
circuit will vary in proportion with temperature.
This is due to the temperature dependency of gasses
according to Boyle~s law of ideal gasses (PV = nRT).
It can be appreciated, therefore, that at very cold
temperatures, the pressure within accumulator
assembly 140 may become significantly lower, to the
extent that the pressure therein is insufficient to
pressurize the lower cylinder chambers 29 to the
extent necessary to lift the liftgate 16 to a fully
open position.
To accommodate for this possibility, a
device for monitoring the amount of energy stored in
the biased energy storage system and lift lines,
preferably in the form of pressure transducer 156
provided in the lift line, continuously monitors the
stored energy level in the biased energy storage
system. An energy control system is also provided
to adjust the amount of energy stored in the biased
energy storage system based on the amount of energy
stored therein as detected by-the energy monitoring
device. The different mechanisms by which the
amount of stored energy can be adjusted are
discussed above. Motorized hydraulic pump 114 and
pressure relief valve 146 are, however, preferred.
In the preferred embodiment, when the
controller 200 receives a signal from the pressure
transducer 156 indicating that the pressure within
the lower cylinder chambers 29, the accumulator
assembly 140, and the hydraulic line therebetween is
below a predetermined pressure for the particular
' vehicle inclination, (in a system which preferably
CA 02215340 1997-09-12
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combines temperature compensation with level
compensation) the controller 200 will generate a
signal to energize pump motor 115. As a result, the
hydraulic pump 114 will withdraw hydraulic fluid
from the hydraulic fluid reservoir 118 and
pressurize the accumulator assembly 140 and the
lower cylinder chambers 29 until they meet or exceed
the predetermined pressure as detected by transducer
156. This procedure is accomplished whether the
vehicle is running or idle.
On the other hand, at relatively high
temperatures, the pressure within the accumulator
assembly 140 and the lower cylinder chambers 29 may
be higher than what is desirable. In this instance,
pressure will be relieved through the lift line
pressure relief valve 146, which is set to relieve
pressure at a predetermined level. It can thus be
appreciated that the pressure within the accumulator
assembly 140 and the lower cylinder chambers 29 is
maintained within a predetermined range at all
times. It should be noted that the lift line
pressure relief valve 146 may be substituted with a
solenoid, air operated, or other type electronically
controlled valve that can be controlled
electronically through the control module 200 in
order to facilitate a more flexible temperature
compensation feature. In other words, the pressure
at which the valve will open and close can be varied
in accordance with incline/decline or any other
desired parameter.
Because the upper cylinder chambers 31
freely drain and withdraw fluid to and from the
hydraulic fluid reservoir 118 via hydraulic pull-
down valve 112 (in the normal condition), there is
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no need for temperature compensation in this portion of the hydraulic system.
When
the system is idle, the pull-down line is essentially at atmospheric pressure.
The energy monitoring device and control system have been described as
useful for accommodating for fluctuations in the ambient temperature. It
should be
appreciated, however, that the critical function of the energy monitoring
device and
control system is to minimize undesired fluctuations in the amount of energy
stored in
the energy storage system. While undesired energy level fluctuations can be
attributed
to changes in temperature, such fluctuations can be attributed to other
causes, such as
system leaks, as well.
It should be further appreciated that the temperature compensation feature of
the present invention is advantageous in its use with the biased energy
storage system
and the lift line. Therefore, powered automatic closing capability, which is
provided
in the preferred embodiment of the present invention, need not be provided to
reap the
benefits of the temperature compensation feature.
It will be realized that the foregoing preferred specific embodiment of the
present invention has been shown and described for the purposes of
illustrating the
functional and instructional principles of this invention and are subject to
change
without departure from such principles. Therefore, this invention includes all
modifications encompassed within the spirit and scope of the following claims.
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