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BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an electronically controlled motor-driven system and operating method for powering a liftgate of an automotive vehicle. Although such liftgates are typically used at the rearmost part of vehicles, the present method and system may be employed with liftgates or doors used at a variety of locations on the exterior of an automotive vehicle.  
         [0003]     2. Disclosure Information  
         [0004]     As first used, automotive liftgates were most often manually operated. A pair of gas-filled or spring-loaded struts provided the force required to maintain the liftgate in its uppermost position, as well as assisting the motorist in opening the liftgate. Motor driven liftgates are a relatively new addition to the automotive genre. A motor drive typically powers the liftgate to its uppermost, or fully opened, position. When the liftgate is fully opened, the drive is typically declutched, allowing the gate to be maintained at its uppermost position by means of gas-charged telescoping struts. If however, the liftgate must bear the weight of a significant accumulation of ice, or an accessory such as a bicycle rack, it may be possible in certain cases for the combined weight to overcome the capability of the gas-filled struts, thereby allowing the liftgate to close in an unintended manner.  
         [0005]     Designers of power liftgates have looked at controlling various operating features of the liftgate, such as closing speed under power, and a system for accomplishing this purpose is disclosed in U.S. Pat. No. 6,901,704. The system of the &#39;704 patent does not, however, monitor either the position or unintended movement of the liftgate when it is in its opened position. U.S. Pat. No. 6,719,356 discloses a liftgate operating system having a proximity sensor which is used to stop operation of the liftgate. The system of the &#39;356 patent again, however, does not monitor the liftgate when it is in a fully opened position to assure that the liftgate does not move out of control in an unintended fashion.  
         [0006]     A method and system according to the present invention functions to prevent unintended movement of a liftgate regardless of the condition or load capacity of the telescoping struts normally assigned the task of maintaining the liftgate in an opened position.  
       SUMMARY OF THE INVENTION  
       [0007]     A system for operating an automotive liftgate includes at least one telescopic strut adapted to be positioned between a liftgate and an adjacent door opening panel. As used herein, the term “liftgate” means either a conventional top-hinged tailgate, or a side door for a vehicle which rotates in a generally vertical plane, or yet other closure structures having a significant vertical component in their operating paths. The present system may also be employed with yet other types of automatically operated doors which may be caused by gravity to move unintentionally.  
         [0008]     According to one aspect of the present invention, a motor drive is adapted for positioning the liftgate. The motor drive preferably includes a motor, an actuator powered by the motor, with the actuator being interposed between the motor and a liftgate, and a clutch interposed between the motor and the actuator. A sensor detects movement of the liftgate. A controller connected with the clutch, the motor, and the sensor, operates the motor and the clutch, with the controller commanding the motor drive to place the liftgate in a predetermined position in the event that the sensor detects unintended movement of the liftgate. The sensor may be embodied as an encoder operatively associated with the actuator. The actuator preferably comprises a lead screw driven by the motor, with the encoder counting the revolutions of the lead screw.  
         [0009]     In the event that the actuator&#39;s sensor detects unintended movement of the liftgate, the controller will command the motor drive to close the liftgate. Alternatively, the motor drive may be commanded to maintain the liftgate in an opened position. The latter option is particularly useful when the present system further includes an obstacle sensor, operatively connected with the system controller, for detecting an obstacle in the operating path of the liftgate. As yet another alternative, if an obstacle sensor detects an obstacle in the operating path of the liftgate, the controller may command the motor drive to maintain the liftgate in an existing position.  
         [0010]     A liftgate operating system according to the present invention may further include a load cell interposed between the actuator and the liftgate, with the load cell being operatively connected with the controller. In this configuration, the controller may be programmed to command the motor drive to place the liftgate in a predetermined position in the event that the static force exerted by the liftgate upon the actuator and load cell increases above a predetermined threshold.  
         [0011]     According to another aspect of the present invention, an automotive vehicle having the liftgate and operating system described herein may be used in conjunction with a reverse/park aid, operatively connected with the obstacle sensor, for alerting a motorist in the event that the vehicle is being operated in reverse gear and an obstacle is located behind the vehicle.  
         [0012]     According to yet another aspect of the present invention, a method for operating a power liftgate installed in an automotive vehicle includes the steps of commanding a motor drive to place the liftgate in an open position, and monitoring the time rate of change of position of the liftgate after the liftgate has been opened. In the event that the liftgate begins to move into an unintended position after opening, the motor drive will be commanded to place the liftgate in a predetermined position. The present method may also include the steps of monitoring the operating path of the liftgate for obstacles and commanding the motor drive to maintain the liftgate in a preexisting position if an obstacle is detected in the liftgate&#39;s path.  
         [0013]     According to yet another aspect of the present invention, the present method includes the steps of commanding a motor drive to place the liftgate in an opened position and releasing a motor drive clutch when the open position has been reached, such that the liftgate is supported solely by a plurality of telescoping struts, followed by monitoring of the liftgate&#39;s subsequent position. This method further includes engaging the clutch and commanding the motor drive to place the liftgate in a closed position in the event that the liftgate moves to an unintended position. At the same time, an alarm may be sounded to alert a vehicle operator.  
         [0014]     It is an advantage of a method and system according to the present invention that sensors used with a vehicle&#39;s reverse/park aid system may be used not only to alert a motorist if an obstacle is behind a vehicle and the vehicle is being backed up, but the sensors may also be used to aid in the operation of a powered liftgate, including advising a motorist that an obstacle is adjacent to the liftgate. This will allow the motorist to correct an abnormal condition before the liftgate is cycled.  
         [0015]     It is a further advantage of a method and system according to the present invention that a liftgate may be operated within a defined set of parameters even in the event that a gas-filled telescopic strut becomes incapable of exerting sufficient opening force upon the liftgate.  
         [0016]     It is yet another advantage of the present method and system that this method and system allow increased flexibility regarding usage of remote operating devices with a powered vehicular liftgate.  
         [0017]     It is yet another advantage of the present method and system that this method and system allows for monitoring of movement at the end of a liftgate&#39;s power open operation, regardless of whether a fully opened position is reached. This is important because there are several reasons for terminating power open operation before the normal end of travel is reached.  
         [0018]     Other advantages, as well as objects and features of the present invention, will become apparent to the reader of this specification. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]      FIG. 1  is a perspective view of an automotive vehicle having a powered liftgate according to the present invention.  
         [0020]      FIG. 2  is an internal view of a portion of the vehicle shown in  FIG. 1 , showing mounting and positioning of the present liftgate operating system.  
         [0021]      FIG. 3  illustrates various details of a motor drive and actuating system according to the present invention.  
         [0022]      FIG. 4  is a flowchart illustrating a first mode of operation according to the present inventive method.  
         [0023]      FIG. 5  is a flowchart illustrating a second mode of operation according to the present inventive method. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]     As shown in  FIG. 1 , vehicle  10  has liftgate  14 , which is normally maintained in its fully opened position by means of telescoping struts  18 . Liftgate  14  and struts  18  are both attached at one end to door opening panel  22 . Motor drive  26  is interposed between liftgate  14  and a portion of the body&#39;s D-pillar,  28 .  FIG. 1  also shows a plurality of obstacle sensors,  72 , which are mounted to the rear portion of vehicle  10 . Obstacle sensors  72  are used not only to control operation of liftgate  14 , but may also be employed as part of a reverse/park aid to alert the motorist of obstacles behind vehicle  10 .  
         [0025]      FIG. 2  illustrates the mounting of motor drive  26  to D-pillar  28  and to liftgate  14 . Note that motor drive  26  extends between D-pillar  28  and liftgate  14  in much the same manner as telescoping struts  18  illustrated in  FIG. 1 .  FIG. 2  also shows the mounting locations of actuator  24 , motor  34 , and drive cable  46 .  
         [0026]      FIG. 3  shows various details of motor drive  26 . Controller  30  is connected with motor  34  as well as with load cell  66  and encoder  38 . Motor  34  drives a lead screw,  50 , through clutch  42 , which is also operated by controller  30 . Because motor  34  drives lead screw  50  by means of a spring cable,  46 , freedom of placement of motor  34 , clutch  42  and encoder  38  is allowed. The encoder monitors the rotation of lead screw  50 , so as to allow controller  30  to track the precise location of liftgate  14  at all times. Supported by collar  32  and bearing  36 , lead screw  50  rotates within nut  54 , which is attached to inner tube  58 . As lead screw  50  rotates, nut  54  causes inner tube  58  to move either up or down with respect to outer tube  62 , which is grounded to D-pillar  28 . Load cell  66  is interposed between actuator  24  and liftgate  14  and moves with inner tube  58 . Load cell  66  measures the static force exerted by liftgate  14  upon actuator  24 , and thereby allows load cell  66  and controller  30  to monitor the condition and loading upon struts  18 , as well as allowing load cell  66  to monitor unusual conditions affecting of liftgate  14 , such as a heavy accumulation of ice, or the mounting of accessory equipment upon liftgate  14 . Those skilled in the art will appreciate in view of this disclosure that other types of drive mechanisms other than a lead screw driven machine may be employed to practice the present invention.  
         [0027]     Encoder  38 , as noted above, monitors the location of liftgate  14  by counting revolutions of lead screw  50 . In essence, the signals from encoder  38  may be used by controller  30  to detect the time rate of change of position of liftgate  14 , as described in the following method.  
         [0028]     As shown in  FIG. 4 , beginning at start at block  100 , a software routine within controller  30  moves to block  102  wherein a question is asked regarding whether an obstacle is present behind vehicle  10 , and more precisely, liftgate  14 . If the answer is yes at block  102 , the routine moves to block  104 , wherein liftgate  14  is maintained in its existing position for a period of time sufficient to allow the vehicle operator to clear the path of the liftgate. If, however, the answer is “no” at block  102 , the routine moves to block  106  wherein the liftgate is driven in an opening direction. In block  108 , the routine inquires as to whether liftgate  14  is fully opened. If it is not, the routine continues with block  106 . If however liftgate  14  is completely open at block  108  the routine moves to block  110 , wherein clutch  42  is disengaged. This will allow liftgate  14  to be supported by struts  18 , without the need for any further energization of motor  34 . Thereafter, at block  112 , controller  30  uses encoder  38  and if so equipped, load cell  66  to monitor further movement of liftgate  14 . In essence, encoder  38  and controller  30  perform a time based differentiation of the location of liftgate  14  and thereby determine whether liftgate  14  is moving. If such movement has not been commanded by the motorist, the routine answers yes at block  114 , and moves to block  116 , wherein clutch  42  is engaged and motor  34  is directed to drive liftgate  14  in its closing direction. Then, at block  118  a question is asked as to whether an obstacle is present, as detected by obstacle sensor  72 . If no obstacle is present, the closing process continues at block  120 , wherein a question is asked as to whether the liftgate  14  is fully closed. If liftgate  14  is fully closed, the process ends at block  122 . If however, liftgate  14  is not fully closed at block  120 , the routine continues at block  116 .  
         [0029]     If an obstacle is present at block  118 , the routine moves to block  120 , wherein liftgate  14  is stopped if it is nearing its closed position, for example, or opened once again, if it is not far from its fully opened position. Then, the routine continues with an alert to the motorist at block  121  and ends at block  126 .  
         [0030]     As noted above, the obstacle detection and driver alert componentry described herein, such as sensors  72 , may be beneficially used as part of a reverse/park aid system to alert a motorist when an obstacle is behind a vehicle that is being operated in reverse gear. In this regard, the program steps  118  and  124  may function as part of a park/reverse warning system.  
         [0031]      FIG. 5  illustrates a second mode of operation including the use of load cell  66 . Beginning at block  200 , controller  30  moves to block  202 , wherein a motorist request for liftgate opening is received. At block  204 , the controller drives liftgate  14  in the open direction, while monitoring the load by means of load cell  66 . At block  206  a question is asked regarding the opening status. If the answer at block  206  is “yes”, liftgate  14  is fully open, and the routine moves to block  208 , wherein the actuator load is assessed. If the load, as measured by load cell  66 , is too high at block  208 , the routine moves to block  210 , wherein clutch  42  is engaged and a warning is sounded. Then, after a short time interval, the routine moves to block  222 , wherein the presence of an obstacle is inquired into. If there is no obstacle at block  222 , the routine moves to block  226 , wherein liftgate  14  is closed with actuator  24 . If, alternatively, there is an obstacle, the routine continues with block  224 , wherein a timer, tracking the obstacle, is set. Once the timer times out, the routine moves to block  226 . If an obstacle is detected at block  228 , the routine moves once again to block  204 , where liftgate  14  will be opened. If no obstacle is detected at block  228 , and if liftgate  14  is fully closed at block  230 , the routine ends at block  232 . If, however, the liftgate is not fully closed at block  230 , the liftgate is redirected to close at block  226 .  
         [0032]     Continuing once again with block  208 , if the actuator load is not too high, the routine moves to block  216 , wherein encoder  38  and controller  30  monitor liftgate  14  for further movement. Thus, at block  218 , if liftgate  14  is closing at a speed above a threshold, the routine will continue as before at block  210 . If liftgate  14  is not closing in an unintended manner, the routine looks at a monitor timer at block  220 , and either continues monitoring at block  216 , or ends at block  232 .  
         [0033]     Although the present invention has been described in connection with particular embodiments thereof, it is to be understood that various modifications, alterations, and adaptations may be made by those skilled in the art without departing from the spirit and scope of the invention set forth in the following claims.

Summary:
A system for operating an automotive liftgate includes a motor drive adapted for positioning the liftgate, and at least one telescopic strut positioned between the liftgate and an adjacent body structure. A controller operates the motor drive so as to place the liftgate in a predetermined position, such as a fully closed or fully opened position, in the event that a sensor detects unintended movement of the liftgate.