Patent Publication Number: US-6669268-B2

Title: Lost motion mechanism for power liftgate closure system

Description:
This application claims benefit of U.S. Prov. No. 60/332,930 filed Nov. 6, 2001. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a power liftgate assembly for a motor vehicle. More specifically, the invention relates to a power liftgate assembly providing lost motion for manual override. 
     DESCRIPTION OF THE RELATED ART 
     Many motor vehicles including liftgates have the capability of driving the liftgate between its open and closed positions. When operating such an assembly, the operator merely needs to operate a switch and the liftgate latch will release and an electric motor will drive the liftgate between positions. 
     One disadvantage to many systems is the inability to adequately allow the operator the opportunity to manually move the liftgate. More specifically, the motor creates a resistance force that must be overcome in addition to overcoming the force assist struts that aid in maintaining the liftgate in an open position. 
     U.S. Pat. No. 6,283,535 discloses a vehicle liftgate power operating system. The operating system moves a hinged liftgate between its open and closed positions. An electric motor is operatively connected to a rack through a speed reduction device. The rack member is pivotally connected to an arm that is fixedly secured to the liftgate. A rotational force generated by the motor moves the rack axially, which is translated by the arm into a force directed at the liftgate pushing it about its pivot axis to move the liftgate between its open and closed positions. An electromagnetic clutch is required to break the torque transmitted from the motor to an output gear should manual operation of the liftgate be desired or required. The electromagnetic clutch is a heavy and costly item. 
     U.S. Pat. No. 6,142,551 discloses a vehicle liftgate power operating system. This system incorporates two motors that drive two linkages that are connected to the liftgate. The two linkages are arcuate and move through an arcuate path to move the liftgate between open and closed positions. This system does not, however, contemplate the manual movement of the liftgate. 
     U.S. Pat. No. 3,713,472 discloses a linkage system for a liftgate that is operable in a power mode and a manual mode. A drive gear provides power to move the liftgate between its extreme positions. An arcuate slot in the drive gear provides lost motion allowing the liftgate to be operated in manual mode, should it be desired to do so. This reference lacks in that the assembly is too large to be incorporated into the contemporary liftgate systems that require much of the liftgate mechanism to be housed in the headliner of the motor vehicle. 
     SUMMARY OF THE INVENTION 
     A power liftgate assembly is disclosed for moving a liftgate between an open position and a closed position. The liftgate is secured to a motor vehicle having a roof for pivotal movement about a substantially horizontal axis. The power liftgate assembly includes an elongated bracket that is fixedly secured to the roof of the motor vehicle. The elongated bracket extends between first and second ends. A motor is fixedly secured to the elongated bracket. A slide operatively engages the motor. The slide moves along the elongated bracket. An articulated bracket is connected to the slide and moves with the slide. The articulated bracket includes a slot that extends therealong to provide lost motion between the articulated bracket and the slide. An arcuate bracket extends between the articulated bracket and the liftgate for receiving the motion of the articulated bracket and for moving the liftgate in response thereto. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Advantages of the invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
     FIG. 1 is a perspective view of a liftgate mounted to a support structure in its open position and incorporating one embodiment of the invention; 
     FIG. 2 is a perspective view of a portion of one embodiment of the invention with the slide removed therefrom for clarity; 
     FIG. 3 is a side view, partially cut away, of one embodiment of the invention secured to a motor vehicle with the liftgate in the closed position; 
     FIG. 4 is a side view, partially cut away, of one embodiment of the invention secured to a motor vehicle with the liftgate in the open position; and 
     FIG. 5 is an electric schematic view of one embodiment of a control circuit for operating the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, a liftgate  10  is secured to a motor vehicle  12 . The liftgate  10  is shown in an open position in FIG.  1 . The liftgate  10  is hingedly secured to a roof  13  to move from the open position to a closed position where it closes an opening  15  in the motor vehicle  12  that provides access to a passenger compartment therein. Two gas assist struts  14  aid in overcoming the mass forces of the liftgate  10  to move the liftgate  10  to its fully open position as it is shown in FIG.  1 . The gas assist struts  14  are capable of moving the liftgate  10  to its open position once the liftgate  10  is moved away from its closed position a predetermined distance. 
     The inventive mechanism is generally indicated at  16 . While two mechanisms  16  are shown, the description will describe only one mechanism as each is identical to the other. 
     The mechanism  16  is a power liftgate assembly  16 . The power liftgate assembly  16  includes an arcuate bracket  18 . The arcuate bracket  18  extends through an arcuate path between liftgate  20  and linkage  22  ends. The liftgate end  20  is secured to the liftgate  10  whereas the linkage end  22  is secured to a linkage, discussed subsequently. 
     Referring to FIG. 2, the linkage is generally indicated at  24 . The linkage  24  includes an elongated bracket  26  that is secured to a section of the roof  13  of the motor vehicle  12 . The elongated bracket  26  extends between first  25  and second  27  ends. A motor  28  is secured to the first end  25  of the elongated bracket  26 . In the preferred embodiment, the motor  28  is a JOHNSON 60 N-mm motor with a 64:1 gear reduction. The motor  28  operates bidirectionally allowing it to open and close the liftgate  10 . 
     A number of gears  30  translate the output of the motor  28  into rotational motion of a lead screw  32 . The lead screw  32  extends along the elongated bracket  26  and is secured thereto with a bracket  23  that includes a bushing to allow the lead screw  32  to rotate relative to the bracket  23  and the elongated bracket  26 . The number of gears  30  includes two gears  29 ,  31  that each has forty teeth. 
     A drive unit  34  receives the force of the motor  28  and moves along the elongated bracket  26  between the first  25  and second  27  ends. In the preferred embodiment, the drive unit  34  is a drive nut  34  that rides along the lead screw  32  as the lead screw  32  is rotated in one direction or another by the motor  28 . The drive nut  34  is an SAE 660 bronze nut with a mating thread. The drive nut  34  engages a switch  35  identifying the location of a neutral position for the drive nut  34 . The neutral position for the drive nut  34  is the location along the elongated bracket  26  in which the drive nut  34  returns after it operates. The function of the drive nut  34  and its neutral position being discussed in greater detail subsequently. 
     Referring to FIG. 3, the mechanism  16  is fixedly secured to the roof  13  of the motor vehicle  12  with a mounting bracket  33 . The liftgate  10  is partially shown hingedly secured to the roof  13 . An articulated bracket, generally indicated at  38 , extends between the arcuate bracket  18  and a slide  40 . The articulated bracket  38  includes a slot  42  for receiving a portion of the slide  40  therethrough. In the embodiment shown, a roller  44  is shown to extend through the slot  42 . The roller  44  is fixedly secured to the slide  40 . 
     The slot  42  provides lost motion between the motor  28  and the articulated bracket  38 . The slot  42  allows the liftgate  10  to move with respect to the motor  28  without having to overcome forces that are required to move the motor  28 . 
     The slide  40  moves axially along the elongated bracket  26  as the drive nut  34  travels along the lead screw  32 . Two glides  45 ,  47  extend between the slide  40  and the elongated bracket  26  to facilitate the movement of the slide  40  with respect to the elongated bracket  26 . The glides  45 ,  47  are approximately 160 mm long and are manufactured from polyethylene. The glides  45 ,  47  may also have a side that may include self-flushing scallops (not shown). 
     In operation, with the drive nut  34  in its neutral position, the liftgate  10  is manually free as the slide  40  moves freely with respect to the drive nut  34 , depending on the position of the liftgate  10  prior the manual movement. During power closure, the motor  28  causes the drive nut  34  to move linearly away from the liftgate  10 . The drive nut  34  contacts the end of the slot  42  and moves the articulated bracket  38  forward. The liftgate  10  is also moved downward and forward until its latch closes the liftgate  10 . Upon latching, the drive nut  34  travels through the slot  42  back toward its neutral position. 
     During power opening and after the liftgate  10  is unlatched, the motor  28  causes the drive nut  34  to travel away from its neutral position back toward the liftgate  10 . When the drive nut  34  engages the back of the slot  42 , it forces the liftgate  10  to move away from its closed position until the gas assist struts  14  are capable of lifting the liftgate  10  to its open position. Once a liftgate position sensor (not shown) identifies the liftgate  10  is in a position that no longer needs mechanical assistance, the motor  28  is reversed and the drive nut  34  is returned to its neutral position. The drive nut  34  is able to move in a direction away from the liftgate  10  because it is traveling through the slot  42 . 
     During power closing of the liftgate  10 , the drive nut  34  is moved toward the motor  28  freely until it reaches the end of the slot  42 , whereafter it drives the articulated bracket  38  and the arcuate bracket  18  inwardly with respect to the motor vehicle  12 . The motor  28 , again energized with a polarity to create a rotational force in a direction opposite that in which is required to open the liftgate  10 , then drives the liftgate  10  away from its open position toward the closed position. The motor  28  drives the drive nut  34  to move the articulated bracket  38  enough to force the liftgate  10  to a position where the gas assist struts  14  can no longer support the mass of the liftgate  10  and the liftgate  10  falls to its closed position for subsequent latch cinching. 
     Referring to FIG. 5, a control circuit is generally shown at  46 . The control circuit  46  includes the operation of three motors  48 ,  50 ,  52 . The third motor  52  is a latch motor. The latch motor  52  moves the latch (not shown) between latched and unlatched positions. 
     The other two motors  48 ,  50  are actuator motors. The actuator motors  48 ,  50  move the articulated brackets  38  through their respective range of motions. The actuator motors  48 ,  50  are bidirectional and have single pole double throw switches  54 ,  56 ,  58 ,  60  to switch the two actuator motors  48 ,  50  between directions by reversing the direction of current passing therethrough. 
     The control circuit  46  also includes end of travel switches  62 ,  64  that will disengage the actuator motors  48 ,  50  when the slide  40  reaches either of the first  25  or second  27  ends of the elongated bracket  26 . The control circuit  46  also includes a pair of single pole double throw switches  66 ,  68  that identify the location of the drive nut  34  as it moves along the lead screw  32 . The control circuit  46  also includes two operator switches  70 ,  72 . The first operator switch  70  indicates that the liftgate  10  is to be closed whereas the second operator switch  72  indicates that the liftgate  10  is to be opened. 
     The invention has been described in an illustrative manner. It is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the invention may be practiced other than as specifically described.