Patent Publication Number: US-2004040213-A1

Title: Controlled counter balance actuator for a lift-gate

Description:
FIELD OF THE INVENTION  
       [0001] This invention relates to an actuator for a lift-gate and more particularly to a counter balance actuator for a lift-gate.  
       BACKGROUND OF THE INVENTION  
       [0002] Sport utility vehicles and minivans are popular vehicles today. These vehicles include large cargo areas that are accessible via a large opening at the rear of the vehicle. The large opening is usually closed by a lift-gate that is hinged to the rear end of the vehicle roof so as to swing between a generally horizontal open position and a generally vertical closed position.  
       [0003] It is conventional to provide such a lift-gate with a counterbalance system comprising gas springs, that are sometimes called pneumatic struts. The gas springs are pivotally attached to the lift-gate at one end and pivotally attached to the vehicle body at the other end. These gas springs hold the lift-gate in the open position and store energy when the lift-gate is closed in order to assist in the subsequent opening of the lift-gate. A long standing problem with such a counterbalance system is that the moment arm of the gas spring changes substantially as the lift-gate moves from the open position to the closed position due to the geometry of the system. In fact, the change is so great, the counterbalance system is normally designed so that the gas springs go “over-center” near the end of their closing stroke so that the gas springs urge the lift-gate toward the closed position.  
       [0004] This changing moment arm means that considerable manual effort is needed to overcome the “over center” condition and lift the lift-gate to a position where the gas springs produce enough torque to assist in opening the lift-gate and then hold the lift-gate in the open position. The manual opening effort can be reduced by using stronger gas springs. However, it then becomes difficult to close the lift-gate against the resistance of the stronger gas springs. Consequently, various power lift-gate systems have been proposed to assist in the opening and/or closing of the lift-gate. See for instance, U.S. Pat. No. 5,896,703 granted to Kevin W. Wright et al Apr. 27, 1999 for a power lift-gate cable drive and U.S. Pat. No. 6,142,551 granted to Michael Ciavaglia et al Nov. 7, 2000 for a vehicle lift-gate power operating system.  
       [0005] Another proposed solution to the problem is disclosed in the U.S. Pat. No. 6,202,350 granted to Kyle Montgomery et al Mar. 20, 2001 for a power lift device. This patent discloses a lift-gate self closing device in which the lower ends of the gas springs (pneumatic struts) have plates that are pivotally connected to the vehicle body. These plates are rotated in one direction to open the lift-gate via the gas springs and rotated in the opposite direction to close the lift-gate via the gas springs. However, this proposed solution does not deal with the fundamental problem of the changing moment arm of the gas springs as the lift-gate travels between the open position and the closed position.  
       SUMMARY OF THE INVENTION  
       [0006] This invention provides a controlled counter-balance actuator for opening and closing a lift-gate of a sport utility vehicle that deals with the problem of the changing moment arm of the gas springs as the lift-gate travels back and forth between the open and the closed positions. The controlled counter-balance actuator includes a drive unit at each side of the lift-gate having a rotor that is pivotally secured to a body of the vehicle in a fixed position and a gas spring. The gas spring is pivotally secured to the rotor at one end and pivotally secured to the lift-gate at the opposite end. The rotor is indexed angularly by an electric motor so as to rotate from a home position to an open position in one direction or to a close position in an opposite direction. The rotor and the gas spring hold the lift-gate in an open position or a close position when the rotor is in the home position, move an open lift-gate toward the closed position when the rotor is indexed from the home position to the close position, and move a closed the lift-gate toward an open position when the rotor is indexed from the home position to the open position. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0007]FIG. 1 is a perspective view of a rear portion of a sport utility vehicle having a lift-gate, shown in the open position, and a controlled counterbalance actuator of the invention;  
     [0008]FIG. 2 is a side view of the rear portion of the sport utility vehicle of FIG. 1; and  
     [0009]FIG. 3 is a side view of the rear position of the sport utility vehicle of FIGS. 1 and 2 with the lift-gate shown in the closed position. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT  
     [0010] Referring now to the drawings, vehicle  10  has a lift-gate  12  that is attached to the aft end of the vehicle roof by two hinge assemblies. The typical right hand hinge assembly  14  is shown in FIGS. 2 and 3.  
     [0011] Hinge assemblies  14  have hinge portions  16  that are secured to a roof channel of the vehicle  10  and hinge portions  18  that are secured to lift-gate  12 . Hinge portions  18  are attached to hinge portions  16  by pivot pins  20  so that lift-gate  12  pivots about a hinge axis indicated at  21  in FIGS. 2 and 3 from a raised open position shown in FIG. 2 to a closed position shown in FIG. 3. Pivot axis  21  is substantially horizontal and lift-gate  12  is generally permitted to pivot about 90° about hinge axis  21 . However, the range of movement can be varied substantially from one vehicle  10  to another.  
     [0012] Lift-gate  12  is opened and closed by a controlled counter-balance actuator that includes two identical drive units  22  that are installed in the respective generally vertical pillars  23  at the aft end of the sport utility vehicle  10  that define the rear opening that is closed by lift-gate  12 . The typical drive unit  22  is shown in FIGS. 2 and 3.  
     [0013] Each drive unit  22  comprises a rotor  24  that is pivotally secured to the vehicle body in a fixed position and a gas spring  26  that is pivotally secured to the rotor  24  by a pivot pin  25  at one end and pivotally secured to the lift-gate  12  by a pivot pin  27  at the opposite end. Each drive unit  22  is typically mounted beneath the sheet metal or other cover of the associated pillar  23 . The gas spring  26  is typically outside the pillar cover with the pivot pin  25  extending through a slot  29  in the pillar cover to connect the gas spring  26  to the rotor  24  as best shown in FIG. 1. The typical gas spring  26  comprises a cylinder  28  and a plunger or rod  30  that is pushed into the cylinder to store energy by pressuring gas trapped in the cylinder  28 . The pressurized gas then pushes the rod  30  out of the cylinder  28  when the end of the rod  30  is released. The gas spring is shown with the end of the cylinder  28  pivotally secured to the lift-gate  12  and the end of the rod  30  pivotally secured to the rotor  24 . However, the gas spring  26  can be reversed with the rod  30  pivotally secured to lift-gate  12  and the cylinder  28  pivotally secured to rotor  24 .  
     [0014] Rotor  24  is indexable angularly so as to rotate counterclockwise from a home position “H” position to a close position “C” (shown in phantom in FIG. 2) and from the home position “H” clockwise to an open position “O” (shown in phantom is FIG.  3 ). The home position “H”, close position “C” and open position “O” are marked at the pivot  25  in FIGS. 2 and 3.  
     [0015] Rotor  24  is indexed by a reversible electric motor  32  that drives a pinion gear  34  via a reduction gear unit  36 . An electromagnetic clutch  38  is preferably interposed between reduction gear unit  36  and pinion gear  34 . The electromagnetic clutch  38  is normally disengaged so that the reduction gear unit  36  and the electric motor  32  are not back driven when the lift-gate  12  is opened or closed manually.  
     [0016] Pinion gear  34  drives rotor  24  which is preferably attached to or an integral part of a sector gear  40  that has teeth that mesh with the teeth of pinion gear  34 . Drive unit  22  preferably includes a position sensor  42 , such as a resistive or optical sensor, to monitor the position of either the rotor  24  or the lift-gate  12  and provide feed-back to an electronic motor control  44  for electric motor  32  and electromagnetic clutch  38  if one is used. Position sensors and electronic motor controls are well known in the art and thus the position sensor  42  and the electronic motor control  44  are merely illustrated schematically and not shown nor described in detail. Position sensor  42  and electronic motor control  44  are preferably mounted inside the associated pillar  23  for each drive unit  22 .  
     [0017] The controlled counterbalance actuator operates as follows. When the lift-gate  12  is in the open position shown in solid line in FIGS. 1 and 2, the moment arm geometry and the forces of the gas springs  26  are sufficient to hold the lift-gate  12  in the open position where the closing effects of gravity are at or near maximum. To close lift-gate  12 , the electronic motor control in response to a “close” control command energizes the electromagnetic clutch  38  and the electric motor  32  of each drive unit  22  so as to index the sector gear  40  and the rotor  24  attached to it angularly in a counterclockwise direction from the home position “H” shown in solid line in FIG. 2 to the close position “C” shown in phantom in FIG. 2. As rotor  24  rotates counter-clockwise toward the close position “C”, the moment arm of the force of the gas spring  26  decreases so that when rotor  24  reaches the close position “C”, the weight of the lift-gate  12  is sufficient to overcome the total counterbalance forces of the gas springs  26  of all drive units  22  causing the lift-gate  12  to rotate clockwise toward the closed position shown in FIG. 3. The sensor  42  indicates to the electronic motor control  44 , the speed, direction and the position of the lift-gate as it approaches the closed position shown in FIG. 3. This feedback to the electronic motor control  44  energizes the electromagnetic clutch  38  and the electric motor  32  of each drive unit  22  to index the sector gear  40  and the rotor  24  attached to it angularly in a clockwise direction to adjust the position of the rotor  24  between the close position “C” and the home position “H” preferably in such a manner to maintain a near constant speed of counter balance closing. In some instances, it may be desirable to index rotor  24  past the home position “H” toward the open position “O” shown in phantom in FIG. 3. In such instances, the rotor  24  would be returned to the home position “H” after latching and cinching of the lift-gate in the closed position is completed. It should be noted that the pivot pin  25  of gas spring  26  is preferably “over center” when the lift-gate is latched and cinched in the closed position so that the gas spring  26  of each drive unit  22  urges the lift-gate  12  toward the closed position.  
     [0018] To open lift-gate  12 , the lift-gate is unlatched and then, the electronic motor control in response to an “open” control command energizes the electromagnetic clutch  38  and the electric motor  32  of each drive unit  22  so as to index the sector gear  40  and the rotor  24  attached to it angularly in a clockwise direction from the home position “H” shown in solid line in FIG. 3 to the open position “O” shown in phantom in FIG. 3. As rotor  24  rotates clockwise toward the open position “O”, the moment arm of the force of the gas spring  26  moves “over center” and increases so that when rotor  24  reaches the open position “O”, the counterbalance forces of the gas springs  26  of all drive units  22  are sufficient to overcome the weight of the lift-gate  12  causing the lift-gate to rotate counter-clockwise toward the open position shown in FIG. 2. The sensor  42  indicates to the electronic motor control  44 , the speed, direction and the position of the lift-gate as it approaches the open position shown in FIG. 2. This feedback to the electronic motor control  44  energizes the electromagnetic clutch  38  and the electric motor  32  of each drive unit  22  to index the sector gear  40  and the rotor  24  attached to it angularly in a counter-clockwise direction to adjust the position of the rotor  24  between the open position “O” and the home position “H” preferably in such a manner to maintain a near constant speed of counter balance opening. Rotor  24  reaches the home position “H” when lift-gate  12  reaches the open position as shown in solid line in FIG. 2. Under these conditions, the total counterbalance moment of the gas springs  26  of all drive units  22  counterbalance, i.e. equal the gravity moment of the lift-gate  12  which is at or near maximum and the lift-gate  12  is held in the open position.  
     [0019] Sensor  42  can also be used to detect contact between the lift-gate  12  and an obstacle during opening or closure and generate a signal to the electronic motor control  44  to reverse the direction of the rotor and lift-gate.  
     [0020] While the controlled counterbalance actuator of the invention has been described as comprising two identical drive units, in some instances one drive unit may be sufficient although a balanced system with a drive unit at each side of the lift-gate is preferred. Moreover, the drive units need not be identical in every respect although identity or near identity is preferred from an economical stand point.  
     [0021] Moreover the rotors of two drive units can be driven by a single electric motor with one position sensor and one electronic motor control. In other words, many modifications and variations of the present invention in light of the above teachings may be made. It is therefore to be understood that, within the scope of the appended claims, the invention may be practical otherwise than as specifically described.