REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority to U.S. provisional patent application No. 60/799,698, which was filed May 11, 2006 and is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention relates to a drive unit for use with a liftgate of a motor vehicle. More particularly, the invention relates a liftgate drive unit having an integral motor and biasing member assist.  
       BACKGROUND OF THE INVENTION  
       [0003]     Automotive vehicles typically include a cargo space and an entrance formed in a vehicle wall providing access to the cargo space. Some vehicles, such as sport utility vehicles or vans, also typically include a liftgate, which covers the entrance in a closed position and which movable to an open position to allow access to the cargo space through the entrance. Liftgates can be made to swing about the hinges between the closed and open positions. In the latter case, it is known to provide a dampener or strut to bias and hold the liftgate toward the open position. It is also known to provide an actuator for automatically moving the liftgate between the closed and open positions. It remains desirable to design a compact drive unit that integrates a strut and an actuator that is compact in size while maintaining or exceeding the performance of conventional struts and actuators.  
       SUMMARY OF THE INVENTION  
       [0004]     According to one aspect, a drive unit is provided for driving a liftgate of a motor vehicle between closed and open positions. The drive unit includes an outer tube having an end configured to couple the drive unit to one of the liftgate or the motor vehicle. The drive unit also includes an inner tube having an end configured to couple the drive unit to the other of the liftgate or the motor vehicle. The inner tube is telescopically engaged with the outer tube. The inner tube is movable between a retracted position and an extended position relative to the outer tube. An actuator is operative for actuating the inner tube relative to the outer tube between the retracted position and the extended position and causing movement of the liftgate between closed and open positions, respectively. The motor drive is housed within the outer tube. A biasing member is connected between the outer tube and the inner tube. The biasing member biases the inner tube relative to the outer tube and assists actuation of the inner tube toward the extended position.  
         [0005]     According to another aspect, a drive unit is provided for driving a liftgate of a motor vehicle between closed and open positions. The drive unit includes an extendable strut for movement between retracted and extended positions corresponding with the closed and open positions of the liftgate, respectively. The drive unit includes a screw drive for extending the extendable strut. The drive unit also includes a motor and gear set for actuating the screw drive, wherein the motor and gear set are supported by the extendable strut.  
         [0006]     According to another aspect, a drive unit is provided for driving a liftgate of a motor vehicle between closed and open positions. The drive unit includes an extendable strut for movement between retracted and extended positions corresponding with the closed and open positions of the liftgate, respectively. The drive unit includes a screw drive for extending the extendable strut. The drive unit also includes a motor and gear set defining an epicyclic transmission for actuating the screw drive, wherein the motor and gear set are supported by the extendable strut. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     Advantages of the present 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:  
         [0008]      FIG. 1  is an exploded perspective view of a liftgate drive unit according to the present invention;  
         [0009]      FIG. 2  is a partial sectional view of the transmission of the liftgate drive unit of the present invention;  
         [0010]      FIG. 3  is a sectional view of the liftgate drive unit in both the retracted and extended positions;  
         [0011]      FIG. 4  is a perspective view of the liftgate drive unit in the retracted position;  
         [0012]      FIG. 5  is a perspective view of the liftgate drive unit in the extended position;  
         [0013]      FIG. 6  is an environmental view of the liftgate drive unit attached to a vehicle;  
         [0014]      FIG. 7  is an exploded perspective view of the liftgate drive unit according to another embodiment of the invention; and  
         [0015]      FIG. 8  is a cross sectional view of the liftgate drive unit of  FIG. 7 , illustrating a retracted position in solid lines and an extended position in dotted lines.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]     Referring to  FIG. 1 , there is shown a liftgate drive unit  10  according to one embodiment. The liftgate drive unit  10  includes an outer tube  15  extending between a first end  20  and a second end  25 . The outer tube  15  includes a hollow interior  30 . The liftgate drive unit  10  also includes an inner tube  35  that is telescopically disposed within the outer tube  15 . It should be realized that the term tube as used through out the specification and claims may indicate cross sectional shapes other than round, such a square rectangular, asymmetrical or other cross sectional shapes. A motor assembly  40  associated with the outer tube  15  may be disposed within the hollow interior  30  of the outer tube  15  and is operatively coupled to the inner tube  35  for telescopically moving the inner tube  35  relative to the outer tube  15 . It should be appreciated that the motor may be positioned outside of the hollow interior  30  of the outer tube  15 , but may be co-lineal with the inner tube  35 .  
         [0017]     A biasing member in the form of an assist strut  45  may be positioned parallel to the outer tube  15  and is connected at one end to the outer tube  15  and at another end to the inner tube  35  for assisting telescopic movement of the inner tube  35  relative to the outer tube  15 . As can be seen in the figures, the assist strut  45  is positioned outside of the outer tube  15  to allow for relatively simple servicing and replacement by simply removing the attachment to the inner and outer tubes  35 ,  15  and then replacing the assist strut  45  with another and then thereby reattaching.  
         [0018]     Referring to  FIGS. 1 and 2 , there is shown the motor assembly  40  and transmission assembly  50  of the liftgate drive unit  10  in accordance with one aspect of the invention. The motor assembly  40  may have an electrical motor  55  including a driveshaft  60  extending from the motor  55 . An electrical wire and connector  65  is attached to the motor  55  for providing an electrical power source. In one aspect, the electrical wire may include a grommet  70  sealing to the vehicle body sheet metal and to the motor assembly  40 , as shown in  FIG. 1 . The grommet protects of the wire and directs a routing of the wire.  
         [0019]     The driveshaft  60  extending from the motor  55  is linked with the transmission assembly  50 . The transmission assembly  50  is epicyclic and includes a housing  75  in which the various transmission components are disposed. The housing  75  includes an end cap  80  for retaining and providing correct axial spacing of the transmission components within the housing  75  and allowing passage of the driveshaft  60  of the electric motor  55 . The drive shaft  60  may extend in any manner from the motor  55 , but in one aspect it extends co-lineally with respect to the inner tube  35 . The driveshaft  60  from the electric motor  55  is coupled to a pinion gear  85 .  
         [0020]     Surrounding the pinion gear  85  is a first set of planetary gears  90 . The first set of planetary gears  90  is disposed on shafts  95  extending from a first carrier plate  100  on a first side  105  of the carrier plate  100 . The second side  110  of the first carrier plate  100  includes a pinion gear  115 . The pinion gear  115  on the first carrier plate  100  is surrounded by a second set of planetary gears  120 . The second set of planetary gears  120  is disposed on shafts  125  formed on a first surface  130  of a second carrier plate  135 . A second side  140  of the second carrier plate  135  includes a spline engagement feature  140  for linking with a drive screw  150 , as will be discussed in more detail below. In one aspect, the transmission assembly  50  components may be made of plastic, composite or other suitable materials including metal, and powdered metal. As stated above, the motor assembly  40  and the transmission assembly  50  may be disposed within the outer tube  15  of the liftgate drive unit  10 . Disposing the motor and transmission assemblies  40 ,  50  within the outer tube  15  provides an improved packaging of a liftgate drive unit  10 . While the transmission assembly  50  has been described as having first  90  and second  120  sets of planetary gears, various numbers of planetary gears may used by the present invention to achieve the design characteristics of various vehicle liftgates.  
         [0021]     As referenced above, the liftgate drive unit  10  may include a drive screw  150  linked with the transmission assembly  50 . The drive screw  150  extends from a first end  155  to a second end  160  with a corresponding spline feature  165  formed on the first end  155  for linking with the spline feature  145  formed on the second surface  140  of the second carrier plate  135 . The drive screw  150  also includes a bearing assembly  170  for supporting the drive screw  150  within the hollow interior  30  of the outer tube  15  providing free rotation of the drive screw  150  within the outer tube  15 . The bearing assembly  170  includes a bearing housing  175  including first and second housing members  180  that receive first and second bearing members  185  that are disposed on opposing faces  190  formed on a first end  155  of the drive screw  150 . The portion of the drive screw  150  extending from the first end  155  toward the second end  160  is disposed within the inner tube  35 . The drive screw  150  includes a drive nut  195  that is positioned about a circumference of the drive screw  150 . The drive nut  195  is received within a drive nut sleeve  200  having a corresponding shape to the drive nut  195  such that the drive nut  195  is prevented from rotating relative to the drive screw  150 . In this manner, the drive nut  195  is allowed to travel up and down the drive screw  150 . The drive nut sleeve  200  is coupled to a drive nut housing  205 . The drive nut housing  205  includes a portion  210  that extends within the inner tube  35  such that the drive nut  195  is attached or retained relative to the inner tube  35  at a first end of the inner tube  35 . In one aspect, the drive screw  150  may be a lead screw, a ball screw or any other screw drive mechanism.  
         [0022]     As described above, the drive screw  150  extends from the first end of the inner tube  35  through the inner tube  35  toward the second end of the inner tube  35 . Also as stated above, the inner tube  35  is positioned within the outer tube  15  for telescopic movement of the inner tube  35  relative to the outer tube  15 . The second end of the outer tube  15  includes a bushing  215 , seal  217  and end cap  220 . The bushing  215 , seal  217  and end cap  220  provide for the inner tube  35  to penetrate allowing telescopic movement of the inner tube  35  relative to the outer tube  15 . Additionally, the inner tube  35  includes an end cap  235  attached to the second end of the inner tube  35 . The end cap  235  includes an attachment portion  240  formed thereon to provide for connecting the assist strut  45  such that it runs on an outside of the outer tube  15 . Additionally, the first end of the outer tube  15  may include a similar end cap  242  again providing for an attachment portion  245  to attach the assist strut  45  such that it runs outside of the outer tube  15 .  
         [0023]     The liftgate drive unit  10  may also include a travel sensor switch assembly  250  disposed within the outer tube  15 . The travel sensor switch assembly  250  may be disposed within a flat section  255  formed on the outer tube  15 . The travel sensor switch assembly  250  is electrically coupled to the motor  55  to allow for regulating the power to the motor when the inner tube  35  has traveled a predetermined distance relative to the outer tube  15 . In one aspect, the travel sensor switch is a Hall effect sensor. The Hall effect sensor detects the presence of a magnet  255  associated with the drive nut housing  205  indicating when the inner tube  35  has traveled a desired distance relative to the outer tube  15 .  
         [0024]     In use, the liftgate drive unit may be attached at one end to a liftgate of a vehicle and at another end to the body of a vehicle, as shown in  FIG. 6 . In one aspect, the end of the liftgate drive unit  10  having the motor assembly  40  is attached at an upper portion  300  of a liftgate opening  310  to the vehicle. In this manner, the electrical wire  65  or harness may be routed through a roof  315  of the vehicle. The routing through the roof  315  simplifies the electrical connection to the motor assembly  40 , as well as improves the positioning of the wire harness within the liftgate opening  310  compared to prior art designs. The opposing end of the liftgate drive unit is attached to the liftgate  320 . The electric motor  55  can receive a signal providing an electrical current thereby rotating the drive shaft  60  attached to the motor  55 . The drive shaft  60  in turn is coupled to the first pinion gear  85  which in turn rotates the first set of planetary gears  90 , causing the first carrier plate  100  to rotate and thereby drive the pinion  115  on the second side  110  of the first carrier plate  100 . The second set of planetary gears  120  is driven by the pinion gear  115  on the first carrier plate  100 ; thereby driving the second carrier plate  135  which is connected to the drive screw  150  via a spline or other connection, as described above. Rotation of the drive screw  150  causes the drive nut  195  to travel up and down the drive screw  150 . As stated above, the drive nut  195  is retained by a drive nut sleeve  200  and drive nut housing  205  that is connected to the inner tube  35 . Therefore, travel of the drive  195  nut up and down the drive screw  150  causes longitudinal movement of the inner tube  35  relative to the outer tube  15 . A magnet  255  disposed on the drive nut housing  205  triggers a Hall effect sensor and a travel sensor switch indicating when the inner tube  35  has traveled a desired distance relative to the outer tube  15 . A signal may then be sent to the motor  55  shutting off the driving power.  
         [0025]     The assist strut  45  may be coupled to the liftgate drive unit  10  via the end cap  240  disposed on the first end of the outer tube  15  and the end cap  235  connected to the second end of the inner tube  35 . The assist strut  45  aids an operator when opening a liftgate of a vehicle by providing an additional force should the electric drive not be utilized.  
         [0026]     Once the inner tube  35  has moved to the desired position relative to the outer tube  15  such that a liftgate is in the opened position, the liftgate drive unit  10  is now in the extended position. The liftgate drive unit may then be returned to a retracted position by rotating the motor  55  in an opposing direction, or if the motor  55  is not utilized an operator may exert a force on a liftgate; thereby back driving the electric motor  55  through the transmission assembly  50 .  
         [0027]     In another embodiment, a clutch may be positioned between the transmission assembly  50  and the drive screw  150  such that the drive screw  150  will be back driven separately from the motor and transmission assemblies  40 ,  50 . The clutch may be a roller type mechanical or an electromagnetic clutch or may be a lead screw clutch that travels up and down a drive screw as disclosed in U.S. patent application Ser. Nos. 11/406104 and 60/732,735 which are herein incorporated by reference.  
         [0028]     In  FIGS. 7 and 8 , another embodiment is shown wherein like parts are indicated by like prime numerals. The construction of the drive unit  10 ′ is substantially the same as in the previously described embodiments. The biasing member in this embodiment, however, is provided in the form of a pair of springs, where one of the pair of springs is an inner spring  47  and the other of the pair of springs is an outer spring  49 . The inner spring  47  is coaxially mounted along an outer surface of the inner tube  35 ′. The outer spring  49  extends over the inner spring  47  in a concentric manner and is also generally coaxial with the inner tube  35 ′. The springs  47 ,  49  are compressed between the end cap  220 ′ and a second end cap  51  fixedly secured to the second end of the inner tube  35 ′ for continuously biasing the inner tube  35 ′ in the direction of the arrow indicated in  FIG. 8 .  
         [0029]     In use, the liftgate drive unit  10 ′ of this embodiment has one end coupled to a liftgate of a vehicle and another end coupled to the body of a vehicle. The description of the operation of the drive unit from the previous embodiments, particularly with regard to the actuation of the inner tube relative to the outer tube between the retracted and extended positions is similar to that already described. As best shown in  FIG. 8 , the springs  47 ,  49  are compressed between the end cap  220 ′ and the second end cap  51  so as to assist in the opening of the liftgate by forcing the inner tube  35 ′ axially apart from the outer tube  15 ′. This is particularly useful during manual actuation of the liftgate when the electric motor  55 ′ of the drive unit  10 ′ is not utilized. Additionally, the springs  47 ,  49  also decrease a force needed from the actuator to power open the liftgate.  
         [0030]     It should be appreciated that the biasing member may be provided in the form of one or more springs. If more than one spring is used, the springs may be arranged other than as shown in the illustrated embodiment. For example, the springs may be arranged end to end rather than nested, as illustrated. The springs may also be the same or differ in terms of size and/or spring constant. All of these factors in general depend on the desired amount of assist and the design characteristics of various vehicle liftgates.  
         [0031]     The invention has been described in an illustrative manner. It is, therefore, to be understood that the terminology 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. Thus, within the scope of the appended claims, the invention may be practiced other than as specifically described.
A drive unit is provided for driving a liftgate of a motor vehicle between closed and open positions. The drive unit includes an outer tube having an end configured to couple the drive unit to one of the liftgate or the motor vehicle. The drive unit also includes an inner tube having an end configured to couple the drive unit to the other of the liftgate or the motor vehicle. The inner tube is telescopically engaged with the outer tube. The inner tube is movable between a retracted position and an extended position relative to the outer tube. An actuator is operative for actuating the inner tube relative to the outer tube between the retracted position and the extended position and causing movement of the liftgate between closed and open positions, respectively. The motor drive is housed within the outer tube. A biasing member is connected between the outer tube and the inner tube. The biasing member biases the inner tube relative to the outer tube and assists actuation of the inner tube toward the extended position.