Liftgate counterbalance system

Information

  • Patent Grant
  • 6341809
  • Patent Number
    6,341,809
  • Date Filed
    Wednesday, December 13, 2000
    24 years ago
  • Date Issued
    Tuesday, January 29, 2002
    23 years ago
Abstract
A vehicle liftgate has a counterbalance system comprising a first link pivotally connected to the vehicle body. A second link is pivotally connected to the first link at one end and to the liftgate at the opposite end. The counterbalance system includes a compression spring that is attached to the first link via a pulley. The compression spring stores energy when the liftgate is closed to assist in subsequent opening of the tailgate. The liftgate may be closed manually or with power assistance.
Description




FIELD OF THE INVENTION




This invention relates to vehicles, such as sport utility vehicles, having a liftgate for access to a cargo compartment and more particularly to a counterbalance system for the liftgate.




BACKGROUND OF THE INVENTION




Vehicles that have liftgates usually include a counterbalance system that stores energy when the lift gate is closed with the stored energy then being used to assist in the subsequent lifting of the liftgate to an open position. A common liftgate counterbalance system uses a pair of gas springs that are pivotally attached to opposite sides of the lift gate at one end and to the vehicle body at the opposite end.




A drawback with gas springs is that the gas springs are sensitive to variations in ambient temperature. This results in the use of gas springs that resist closure of the liftgate with considerable force on hot days. For instance, the gas spring or springs must be strong enough to open the liftgate on the coldest day (usually assumed to be −40° C.) Such gas springs increase closing resistance substantially on the hottest day (usually assumed to be 80° C.) Therefore considerable effort must be used to close the liftgate or a very large electric motor used in the case of a power operated system.




Liftgates that have two or more gas springs for a counterbalance system are common. These gas springs generally occupy a position in which their axes is substantially parallel to the liftgate so that the gas springs are hidden when the liftgate is closed. In this closed position the moment arm of the gas springs is quite small. With such systems the liftgate may move about one-third of its total travel range before the ga cylinders exert sufficient force to open the liftgate further without the application of an independent lifting force. There are even some systems in which the gas springs pass over center and bias a liftgate toward a closed position when the liftgate is closed. With these self-closing systems a liftgate may need to be more than one-third open before the gas springs will open the liftgate further. Thus the geometry of the gas spring counterbalance system itself increases the drawback of gas spring counterbalance system.




Decklids have been counterbalanced with steel coil springs for many years. A decklid when open, with spring relaxed has the gravity moment at its minimum. As the decklid is closed the gravity moment and the spring output both increase. With spring and gravity moment tracking together, counterbalancing a decklid is straightforward. The difficulty with counterbalancing a liftgate, in comparison to a decklid is that with the liftgate in the open position, and the counterbalance spring relaxed, the gravity moment is near its maximum. This means that when the spring is at its minimum output the load from the liftgate is maximum. The converse is also true. When the spring is at a maximum output the liftgate has its smallest gravity moment. Thus coil spring counterbalance systems for decklids are not well suited for liftgates.




SUMMARY OF THE INVENTION




The counterbalance system of this invention uses a compression spring or springs as an alternate for gas springs in a liftgate application and thus provides a liftgate counterbalance system that is not sensitive to variations in ambient temperature. The counterbalance system of the invention also has an improved geometry and changing mechanical advantage for applying the compression spring forces of the counterbalance system to assist in opening the liftgate.











BRIEF DESCRIPTION OF THE DRAWINGS




The presently preferred embodiment of the invention is disclosed in the following description and in the accompanying drawings, wherein:





FIG. 1

is a perspective end view of a vehicle equipped with a liftgate and a counterbalance system in accordance with the invention;





FIG. 2

is a side view of the vehicle of

FIG. 1

showing details of the counterbalance system with the liftgate in the open position, and





FIG. 3

is a side view of the vehicle of

FIG. 1

showing details of the counterbalance system with the liftgate in the closed position.











DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT




Referring now to the drawings, vehicle


10


has a liftgate


12


that is attaches the aft end of the vehicle roof by two hinge assemblies. A portion of a typical right hand hinge assembly


14


is shown in

FIGS. 2 and 3

. Hinge assemblies


14


have hinge portion that are secured to a roof channel of the vehicle


10


and hinge portions that are secured to liftgate


12


. The vehicle hinge portions are attached to the liftgate hinge portions by pivot pins


16


so that liftgate


12


pivots about a substantially horizontal hinge axis


18


at the aligned centerlines of pivot pins


16


from an open position shown in

FIG. 2

to a closed position shown in FIG.


3


. Liftgate


12


is generally permitted to pivot about 90° about the substantially horizontal axis


18


defined by pivot pins


16


. However, the range of movement can be varied substantially from one model of vehicle to another.




Liftgate


12


is opened and closed manually or by a suitable power operating system and includes two identical counterbalance units


22


that are installed in the aft end of the vehicle body. Counterbalance units


22


are laterally spaced from each other and near the respective vertical body pillars


23


at the aft end of vehicle


10


, commonly referred to as the D pillars, that define the width of the rear opening that is closed by liftgate


12


. The typical counterbalance unit


22


is shown in greater detail in

FIGS. 2 and 3

.




Each counterbalance unit


22


comprises a first link


24


that is pivotally connected to a body portion of the vehicle by a first hinge pin


25


at or near the D pillar


23


. A second link


26


is pivotally connected to the first link


24


adjacent one end by a second hinge pin


27


and pivotally connected to the vehicle liftgate


12


adjacent an opposite end by a third hinge pin


29


. The first and second links


24


and


26


form an obtuse angle when liftgate


12


is open as shown in FIG.


2


and an acute angle when liftgate


12


is closed as shown in FIG.


3


.




Each counterbalance unit


22


includes a coil shaped compression spring


28


that is disposed in a tubular housing


30


that is fixed the vehicle body, preferably at or near the D pillar


23


. The upper end of the compression spring


28


abuts an upper annular flange


32


of the housing


30


. Each counterbalance unit


22


includes a pulley having a flexible tension member


34


that is connected to the lower end of the coil shaped compression spring


28


. Tension member


34


extends through the open center of the coil shaped compression spring


28


axially and out a concentric hole in an upper annular wall


32


of housing


30


. Tension member


34


then continues upward and wraps around a roller


36


that is part of the pulley. Roller


36


revolves around an axis


37


that is substantially parallel to and spaced below the hinge axis


18


of the liftgate


12


defined by pivot pins


16


. Tension member


34


is then attached to link


24


near the hinge pin


27


connecting links


24


and


26


. The tension member


34


may be made of any flexible material and preferably is a steel cable.




The operation of the counterbalance system is as follows. When liftgate


12


is in the open position as shown in

FIGS. 1 and 2

, the coil shaped compression spring


28


is in an expanded state as shown in FIG.


2


. Spring


28


is preferably slightly compressed when liftgate


12


is open to take up any lash in hinge assemblies


14


or the counterbalance units


22


due to manufacturing tolerances. The liftgate


12


is moved manually with the assistance of gravity to the closed position shown in FIG.


3


. During closure the assistance of gravity initially increases and then decreases substantially as liftgate


12


approaches the closed position shown n

FIG. 2

due to the changing moment arm. As liftgate


12


is moved manually to the closed position, tension member


34


pulls the lower end of compression spring


28


up compressing spring


28


and storing energy in the compressed spring


28


as shown in FIG.


3


. This stored energy reaches a maximum when liftgate


12


is closed and assists in a subsequent opening the liftgate


12


. When the closed liftgate


12


shown in

FIG. 3

is opened, the compressed spring


28


expands and rotates link


24


counterclockwise about hinge pin


25


as viewed in

FIG. 3

from the closed position shown in

FIG. 3

to the open position shown in FIG.


2


. Link


24


simultaneously rotates link


26


clockwise about the hinge pin


29


connecting link


26


to liftgate


12


. This increases the angle between links


24


and


26


and the distance between the hinge pins


25


and


29


causing liftgate


12


to pivot counterclockwise about the hinge axis


18


from the closed position shown in

FIG. 3

to the open position shown in FIG.


2


.




The counterbalance system


22


may also be power operated by providing a drive roller


38


between the upper end of housing


30


and roller


36


that is driven by a suitable motor, such as an electric motor (not shown). In the case of power operation, the liftgate


12


is moved from open position of

FIGS. 1 and 2

to the closed position of

FIG. 3

by controlling the motor to rotate drive roller


38


counterclockwise as shown in

FIG. 2

to drive tension member


34


up which compresses spring


28


and allows liftgate


12


to close under the influence of gravity. The liftgate


12


is then capable of being opened as described above or with the assistance of the motor driven roller


38


being driven clockwise.




With a counterbalance system, it is also preferably to locate drive roller


38


between roller


36


and compression spring


28


and to locate roller


36


so that the flexible tension member or cable


34


is forced against drive roller


38


for good driving engagement.




While the tension member


34


is illustrated as being attached to the first link


24


near the hinge pin


27


, the tension member


34


may be connected to either link


24


or


26


, the precise location of the attachment being determined by the physical characteristics of the vehicle and the lifting assistance that is desired.




In other words, while the present invention has been described as carried out in a specific embodiment thereof, it is not intended to be limited thereby but is intended to cover the invention broadly within the scope and spirit of the appended claims.



Claims
  • 1. A counterbalance system for a vehicle liftgate that is pivotally attached to an aft end of a vehicle roof for pivotal movement about a hinge axis between a generally horizontal open posit ion and a closed generally vertical position, the counterbalance system storing energy during closure of the vehicle liftgate for assisting subsequent opening of the liftgate, the counterbalance system comprising:a first link pivotally connected to a body portion of the vehicle by a pivot member, a second link pivotally connected to the first link adjacent one end and pivotally connected to the vehicle liftgate adjacent an opposite end, a compression spring abutting a body portion of the vehicle at one end, and a tension member connected to an opposite end of the spring at one end and to one of the first links and the second links at the opposite end whereby the spring stores energy when the liftgate is closed and releases the stored energy upon subsequent opening of the liftgate to assist in the subsequent opening of the liftgate, and a drive roller that engages the tension member to drive the tension member downwardly to store energy to assist in opening the liftgate.
  • 2. A counterbalance system for a vehicle liftgate that is pivotally attached to an aft end of a vehicle roof for pivotal movement about a hinge axis between a generally horizontal open position and a closed generally vertical position, the counterbalance system storing energy during closure of the vehicle liftgate for assisting subsequent opening of the liftgate, the counterbalance system comprising:a first link pivotally connected to a body portion of the vehicle by a pivot member, a second link pivotally connected to the first link adjacent one end and pivotally connected to the vehicle liftgate adjacent an opposite end, a compression spring abutting a body portion of the vehicle at one end, and a tension member connected to an opposite end of the spring at one end and to one of the first links and the second links at the opposite end whereby the spring stores energy when the liftgate is closed and releases the stored energy upon subsequent opening of the liftgate to assist in the subsequent opening of the liftgate wherein the tension member is flexible and wraps around a roller that is located between the hinge axis and the pivot member.
  • 3. The vehicle as defined in claim 2 wherein the counterbalance system includes a pulley and the tension member is a cable that is part of the pulley.
  • 4. The vehicle as defined in claim 3 wherein the pulley includes the roller that is located between the hinge axis and the pivot member.
  • 5. The vehicle as defined in claim 4 whereina drive roller engages the tension member to drive the tension member downwardly to store energy to assist in opening the liftgate, and the drive roller is below the roller of the pulley.
  • 6. A vehicle having a counterbalance system for opening and closing a vehicle liftgate that is pivotally attached to an aft end of a vehicle roof for pivotal movement between an open position and a closed position about a hinge axis, the counterbalance system having at least one drive unit, comprising:a first link pivotally connected to a body portion of the vehicle at one end, a second link pivotally connected to an opposite end of the first link at one end and pivotally connected to the vehicle liftgate at an opposite end of the second link, a roller located between the hinge axis and the first end of the first link, a compression spring disposed in a housing attached to the body portion of the vehicle, the compression spring having an end proximate the roller abutting an end wall of the housing, and a cable having a first end connected to an opposite remote end of the spring, the cable having a second end connected to one of the first links and the second links at the opposite end after the cable wraps around the roller whereby the spring stores energy when the liftgate is closed and releases the stored energy upon subsequent opening of the liftgate to assist in the subsequent opening of the liftgate.
  • 7. The vehicle as defined in claim 6 wherein the cable is connected to the first link.
  • 8. The vehicle as defined in claim 6 further including a drive roller that engages the cable to drive the cable downwardly to assist in opening the liftgate.
  • 9. The vehicle as defined in claim 6 further including a drive roller that is located between the roller and the compression spring and that engages the cable to drive the cable downwardly to assist in opening the liftgate.
US Referenced Citations (3)
Number Name Date Kind
4601446 Opsahl Jul 1986 A
4765026 Dochnahl Aug 1988 A
6120080 Hori et al. Sep 2000 A