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TECHNICAL FIELD 
       [0001]    This disclosure relates generally to truck tailgate lift systems, and more particularly to a dual cable driven power tailgate for a pickup truck or other such vehicle. The described system is robust, allowing compensation for tailgate-vehicle bed misalignment while requiring use of smaller motors, and can be retrofitted to most vehicles without increasing tailgate mass or significantly reducing vehicle bed space. 
       BACKGROUND 
       [0002]    It is known to provide power lift systems for tailgates, for example for pickup trucks. Such systems allow raising and lowering the vehicle tailgate without a user actually having to physically lift/lower the tailgate. This adds a convenience factor, as the user is able to raise/lower the tailgate without, for example, having to set down any packages he or she may be carrying. Still further, such systems aid the physically impaired, who may have difficulty physically raising or lowering a heavy vehicle tailgate. 
         [0003]    However, conventional systems suffer from various disadvantages. They may be complex and require additional components integrated into the tailgate itself, increasing the weight and cost of manufacture of the tailgate. Additionally, conventional tailgates are hinged to pivot at a bottom when raised or lowered. Typically, the latch assemblies for securing the tailgate in the closed position are disposed at the top corners of the tailgate/pickup bed. Conventional powered tailgate systems therefore require significant application of force in order to raise a tailgate and to cause it to latch. Additionally, conventional power tailgate systems lack a mechanism for compensating for tailgate/vehicle bed misalignment. That is, the conventional power tailgate system is required to ensure that each latch operates concurrently. If misalignment of the tailgate/vehicle bed occurs, it is possible that the tailgate will not properly latch to the vehicle bed. 
         [0004]    To solve these and other problems, the present disclosure describes a dual motor tailgate power lift system. Advantageously, the disclosed system provides a simple, robust mechanism to compensate for potential tailgate/vehicle latch misalignment. By the disclosed system design, lesser force is required to latch the tailgate to the vehicle bed than conventional power lift systems. Moreover, the disclosed tailgate power lift system is configured to provide a variety of “down” positions in addition to fully raised or fully lowered, to allow retention of oversized loads that do not allow the tailgate to fully close. 
       SUMMARY 
       [0005]    In accordance with the purposes and benefits described herein, a motor vehicle tailgate power lift system for displacing a motor vehicle tailgate between a closed position and at least one open position is provided, including a first actuator for lengthening and shortening a first stay cable attached to a first tailgate side and a second actuator for lengthening and shortening a second stay cable attached to a second, opposed tailgate side. First and second sensors disposed on a motor vehicle body to which the tailgate is hingedly attached separately detect a latching operation of a first tailgate latch and a second tailgate latch. 
         [0006]    The first actuator and the second actuator each include a motor operatively connected to a cable drum for lengthening and shortening a stay cable, and are disposed on opposed top rear portions of the motor vehicle body. By this configuration, the first stay cable and second stay cable are shortened by spooling onto the respective first and second cable drums whereby the first and second stay cable are oriented substantially horizontally to a plane defined by the motor vehicle body as the tailgate is pulled into a closed, latching position. In turn, the first and second actuators are each controlled to displace the tailgate to a plurality of partially open configurations. In an embodiment, one of the plurality of partially open configurations is a pre-programmed tailgate removal configuration. In another embodiment, one of the actuators is slaved to the other actuator, to ensure that both operate during a particular controlled action. A variety of controllers may be provided for controlling the first and second actuator, including without limitation a controller associated with a tailgate latch handle mechanism, a foot-operated controller, a controller associated with a user key fob, and the like. 
         [0007]    In another aspect, a method for displacing a motor vehicle tailgate between a closed position and at least one open position is provided. The method includes providing first and second actuators as described above for lengthening and shortening stay cables to displace the tailgate between a closed position and at least one open position. The at least one open position may include a pre-programmed tailgate removal position, a partially closed configuration allowing carrying oversized loads in the motor vehicle, and others. 
         [0008]    First and second sensors are provided for independently detecting a latching operation of a first tailgate latch and a second tailgate latch. The first and second sensors may be disposed on the motor vehicle body or on the tailgate. In use, each of the first and second actuators are caused to independently shorten the first stay cable and the second stay cable until each of the first and second sensors independently signals a completed latching operation for each of the first tailgate latch and the second tailgate latch. In embodiments, the first actuator and the second actuator are disposed on opposed top rear portions of the motor vehicle body to which the tailgate is hingedly attached. The first stay cable and second stay cable are shortened by spooling onto respective first and second cable drums driven by first and second motors. As the tailgate approaches the closed position the stay cables are oriented substantially horizontally to a plane defined by the body to pull the tailgate to an upright latching position. One or more controllers may be provided as described above for controlling the first and second actuators to displace the tailgate between the closed position and the one or more open positions. 
         [0009]    In yet another aspect, a motor vehicle tailgate power lift system is provided, including a tailgate having an edge hingedly connected to a motor vehicle body, a first stay cable at a first tailgate side, and a second stay cable at a second tailgate side. A first actuator is provided for lengthening and shortening the first stay cable, and a second actuator is provided for lengthening and shortening the second stay cable to displace the tailgate between the closed position and the at least one open position. A controller is provided for controlling operation of the first and second actuators. A first latch is provided at a first side of the motor vehicle body and a second latch is provided at a second side of the motor vehicle body. A first latch sensor monitors whether the first latch is in a latched or unlatched condition, and a second latch sensor monitors whether the second latch is in a latched or unlatched condition. The controller is responsive to the first and second sensor to operate the first and second actuators when closing the tailgate, thereby adjusting for any tailgate to vehicle body misalignment. 
         [0010]    In the following description, there are shown and described embodiments of the disclosed motor vehicle tailgate power lift system. As it should be realized, the motor vehicle tailgate power lift system is capable of other, different embodiments and its several details are capable of modification in various, obvious aspects all without departing from the armrest device as set forth and described in the following claims. Accordingly, the drawings and descriptions should be regarded as illustrative in nature and not as restrictive. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The accompanying drawing figures incorporated herein and forming a part of the specification, illustrate several aspects of the disclosed tailgate power lift system, and together with the description serve to explain certain principles thereof. In the drawing: 
           [0012]      FIG. 1  is a top view of a pickup truck bed including a tailgate power lift system according to the present disclosure; 
           [0013]      FIG. 2  is a side view of the pickup truck bed of  FIG. 1 , showing various partially open positions of a tailgate; 
           [0014]      FIG. 3  illustrates operation of the tailgate power lift system of  FIG. 1 , with  FIG. 3A  showing the tailgate in the down position and  FIG. 3B  showing the tailgate in the up position; 
           [0015]      FIG. 4  is a top view of a side of the tailgate power lift system of  FIG. 3 , with  FIG. 4A  showing the tailgate in the up position and  FIG. 4B  showing the tailgate in the down position; and 
           [0016]      FIG. 5  illustrates a latch for a pickup tailgate according to the present disclosure including a latching sensor; and 
           [0017]      FIG. 6  shows in electrical block diagram form various elements of and means for controlling the system described in the present disclosure. 
       
    
    
       [0018]    Reference will now be made in detail to embodiments of the disclosed tailgate power lift system, examples of which are illustrated in the accompanying drawing figures. 
       DETAILED DESCRIPTION 
       [0019]    Reference is now made to  FIG. 1  illustrating a tailgate power lift system  10 . The system  10  is adapted to be included in a substantially conventional motor vehicle having a hingedly attached tailgate, or alternatively to be retrofitted to such a vehicle. In the depicted embodiment, the system  10  is incorporated into a pickup truck having a load-carrying bed  12  and a tailgate  14  which is hinged to pivot at a bottom surface thereof for raising and lowering. However, it will be appreciated that the system  10  can be incorporated into any vehicle incorporating such a tailgate  14 . As shown, all or substantially all the system  10  can be disposed within the confines of in a bed  12  sidewall and/or under a bed  12  liner (not shown), thus reducing the profile of the system  10  and avoiding use of the load-carrying space of the vehicle. A further advantage is that while the system  10  is connected to the tailgate  14  as will be described below, the system  10  is otherwise separate from the tailgate  14  and does not add to the tailgate  14  mass. Thus, the system  10  can be connected to any standard, original equipment tailgate  14  provided with a vehicle. 
         [0020]    The system  10  includes a pair of electric drive motors  16  actuating cooperating cable drums  18 . Cable drums  18  rotate to spool/unspool stay cables  20  and so to shorten or lengthen stay cables  20 . As shown in  FIG. 2 , the electric drive motors  16  rotate cable drums  18  in a first direction to unspool and lengthen stay cables  20  and lower the tailgate  14 , and rotate cable drums  18  in a second, opposed direction to spool and shorten stay cables  20  and raise the tailgate  14 . It will be appreciated that the motors  16  can be disposed within a perimeter of the bed  12  and that only cable drums  18  must be exposed from the bed  12 , to allow attachment of the stay cables  20  thereto. Because all of the moving parts of the described system  10  are maintained in the bed  12 , it will also be appreciated that manual raising/lowering of the tailgate  14  without using the described system  10 , removal of the tailgate  14  from the bed  12 , etc. remain possible at the user&#39;s whim. 
         [0021]    A lock ball  22  (see  FIG. 3A ) associated with each stay cable  20  inserts into a slot  24  (see  FIGS. 4A and 4B ) as cable drums  18  unspool stay cables  20  to lower the tailgate  14  to the fully open position (see  FIG. 3A ), preventing further travel of the tailgate  14 . When the tailgate  14  is in the fully closed position, the lock balls  22  are spooled onto the cable drums  18  (see  FIG. 4A ). 
         [0022]    When the tailgate  14  is in the fully lowered, open position ( FIG. 3A ), cables  20  are held at an angle that is similar to that of conventional, non-motorized stay cables (depicted in broken lines) as are known in the art. On the other hand, as motors  16  rotate cable drums  18  to spool stay cables  20  and to raise the tailgate  14  to the closed position, an advantage of the present system  10  is revealed. As can be seen in  FIG. 3B , as the tailgate  14  pivots to the fully upright, closed position (see arrow A) and the top of the tailgate  14  approaches the bed  12 , the stay cables  20  assume a horizontal or near-horizontal configuration as the cables spool onto drums  18  and the tailgate  14  is pressed against a latching mechanism  24 . By this feature, all or substantially all of the latching force is applied in a horizontal direction (see arrow B) compared to the direction that force is applied using a conventional power lift system disposed at the hinged end of tailgate  14 . That is, a “straight pull” of the tailgate  14  into paired latching mechanisms  26  using stay cables  20  increases latching efficiency, because smaller motors  16  can be used to apply the required amount of force to latch tailgate  14  compared to the larger motors that would be required to latch a tailgate  14  using a power system at the hinged end of tailgate  14 . 
         [0023]    In the depicted embodiments, the motors  16  are “smart” electric motors, that is, they are configured for pre-programming or “training” to perform a variety of operations. Such motors are well-known to the skilled artisan in the motor vehicle arts, for example in the sunroof and power side door fields, and so need not be further described herein. Example operations (pre-programmed or operator switch/button actuated) include the fully open and fully closed positions for tailgate  14  as described above. Further, the motors  16  can be programmed to spool the stay cables  20  on drums  18  at a reduced speed as tailgate  14  approaches the fully upright, closed position, to reduce the impact of closing the tailgate  14 . This eliminates any need for pinch strips and/or pinch sensors as are required for conventional power tailgate/door assemblies to ensure that sufficient force is applied to a latching operation. 
         [0024]    In addition, the motors  16  can be configured to spool/unspool stay cables  20  to place tailgate  14  in a variety of partially open configurations (see  FIG. 2 ), or alternatively can be caused to achieve these configurations by inclusion of an operator-usable switch/button (not shown) which causes the motors  16  to spool or unspool the stay cables  20  only as long as the operator is actuating the switch. By this feature, retention of oversized loads that do not allow tailgate  14  to pivot to the fully closed position is possible. 
         [0025]    In the depicted embodiments, two electric “smart” motors  16  are provided, one associated with a left rear portion of the bed  12  and one associated with a right rear portion of the bed  12 . Each motor  16  is responsible for raising/lowering one side of the tailgate  14  by spooling/unspooling stay cables  20 . The motors  16  may be slaved one to the other, that is, when one motor  16  is actuated to spool or unspool stay cable  20 , the other motor follows suit to raise or lower the tailgate  14 . However, each motor  16  operates to latch a side of the tailgate  14  independently. That is, each motor  16  will continue to spool its associated stay cable  20  onto its associated cable drum  18  until its associated latch (described in greater detail below) is fully latched and the tailgate  14  is secured in the closed position. 
         [0026]    Each latching mechanism  26  includes a “tailgate ajar” switch  28  in electrical communication with a motor  16 , by which each motor  16  verifies whether the latching mechanism  26  has latched and tailgate  14  is in the closed position. In the depicted embodiment (see  FIG. 5 ) switch  28  is a simple contact switch. An arm  30  is biased to an “open” position, such as by a spring clip  32 , whenever tailgate  14  is not in the fully closed and latched position. As tailgate  14  approaches the fully closed position, it contacts and biases arm  30  which in turn biases a latching hook  34  forward (see arrow B) to engage a pin (not shown) associated with tailgate  14 . Concurrently, arm  30  biases contact switch  28  (see arrow A) to close the contact, signaling motor  16  that the tailgate  14  is fully closed. Motor  16  then ceases spooling stay cable  20  onto cable drum  18 , thus completing the latching operation. This process occurs independently for each of the two latching mechanisms  26 , thus ensuring that both sides of tailgate  14  are fully latched. Advantageously, by this mechanism any misalignment of the tailgate  14  and the bed  12  which may occur during a tailgate  14  closing operation (for example, one side of the tailgate  14  latching slightly earlier than the other) is automatically compensated for and synching automatic power latches are not required. 
         [0027]    A variety of actuator mechanisms for operating the disclosed system  10  are contemplated. As non-limiting examples (see  FIG. 6 ), an actuator may be incorporated into the tailgate unlatching handle  36 . Alternatively or in addition, a step-latched switch  38  may be included. Also alternatively or in addition, wireless actuators such as lock/unlock buttons may be incorporated into the users&#39; key fob  40 , transmitting a lock/unlock signal to an antenna  42  incorporated into the tailgate  14 . This may be a conventional key fob, a passive entry-passive start (PEPS) actuator, or other such systems. Optionally, pinch strips/optical system/ultrasonic sensors  44  may be included to sense obstructions in the path of tailgate  14  as it is opened and closed in the manner described above. Such mechanisms are known to the skilled artisan, and require no further description herein. 
         [0028]    A body control module (BCM)  46  may be included to provide the motor vehicle with an interactive information, diagnostic, entertainment, and wired/wireless communication system which, as part of its operation, monitors and displays information regarding operation of the presently disclosed system  10 . Such BCMs are described in, for example, U.S. Pat. No. 6,240,347 and marketed as the FORD SYNC system. The BCM  46  may integrate with other vehicle systems. For example, the BCM  46  may communicate by wired means or wireless means, as appropriate, with a vehicle speed sensor  48  to prevent operation of tailgate  14  when the vehicle is in motion (i.e., vehicle speed is greater than 0), when the vehicle transmission is engaged (that is, vehicle transmission is set in “park”), when the BCM  46  cannot locate the PEP key, etc. 
         [0029]    In summary, numerous benefits are provided by the described tailgate power lift system  10 . As should be appreciated, the system provides the advantages of automated raising/lowering of a motor vehicle tailgate  14  without requiring adding mass to the tailgate, and can be retrofitted to existing vehicles. Dual motors  16  which, while slaved together for operation, independently ensure full latching of both sides of tailgate  14  allow automated compensation for any tailgate  14 /bed  12  misalignment encountered during a closing/latching process. In turn, the configuration of system  10  to provide a substantially horizontal configuration of stay cables  20  as tailgate  14  reaches the fully raised and latching position immediately prior to latching allows application of an increased, “straight pull” latching force using a smaller motor than would be possible using a power system at the hinged end of tailgate  14  to raise and lower the tailgate. 
         [0030]    Still more, use of so-called “smart” motors allows a variety of additional operations in addition to fully raising or lowering tailgate  14 . For example, the motors may be pre-programmed for a slower rate of spooling/unspooling of stay cables  20  as the tailgate  14  approaches the fully raised and/or fully lowered position to prevent undue impact and damage. Also, the motors  16  may be pre-programmed or later “trained” to perform a partial raising operation of tailgate  14 , allowing retention of oversized loads. 
         [0031]    The foregoing disclosure has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the embodiments to the precise form disclosed. Obvious modifications and variations are possible in light of the above teachings, and all such modifications and variations are within the scope of the appended claims when interpreted in accordance with the breadth to which they are fairly, legally and equitably entitled.

Summary:
A motor vehicle tailgate power lift system for displacing a motor vehicle tailgate between a closed position and at least one open position includes a first actuator for lengthening and shortening a first stay cable attached to a first tailgate side and a second actuator for lengthening and shortening a second stay cable attached to a second, opposed tailgate side. First and second sensors disposed on a motor vehicle body to which the tailgate is hingedly attached independently detect a latching operation of a first tailgate latch and a second tailgate latch. A controller is responsive to the first and second sensor to operate the first and second actuators when closing the tailgate, thereby adjusting for any tailgate to vehicle body misalignment.