Abstract:
An external lift for a scooter includes a load sensor actuated by rotation of the platform as a load is applied anywhere on the platform, a lock mechanism for preventing the platform from rotating in a loaded and raised position, and a lock mechanism for preventing the platform from rotating in an unloaded and raised position. A pair of shoes on a hold down prevent a scooter from leaving the lift unintendedly. The lift includes a fixed post and a moveable post. A roller coupled to the moveable post engages a small ramp on the end of the fixed post, thereby further stabilizing the lift and increasing the lifting capacity.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to a scooter lift for a vehicle and, in particular, to an improved external lift for loading and transporting a scooter safely.  
           [0002]    A variety of small motorized scooters have been developed to carry a seated person through areas intended for pedestrian traffic. These scooters are battery powered, ride on either three or four small wheels, and are relatively compact but can be rather heavy because of the battery and electric motor. Unlike powered or unpowered wheelchairs, motorized scooters are usually not driven into a van or other vehicle with a person seated on the scooter. Rather, a lift is provided for attaching a scooter to the vehicle for traveling long distances. Such lifts are either external, as illustrated in U.S. Pat. No. 5,011,361 (Peterson) and U.S. Pat. No.5,567,107(Bruno), or internal. External lifts typically have a fold-down platform for receiving a scooter. An internal lift is essentially a small derrick mounted in the rear portion of a van. This invention relates to an external lift having an improved load sensor and improved carriage.  
           [0003]    External lifts typically include a horizontal square steel tube that fits within the receiver of a trailer hitch on a vehicle. A vertical post is welded to the tube and the rest of the lift is attached to the post in a series of joints. For example, an adjustable sleeve is attached to the vertical post to enable vertical adjustment of the platform. A lift mechanism is attached to the sleeve and to a horizontal hinge. The platform is attached to the movable part of the hinge, about which the platform rotates. There is a problem in that the joints flex or twist as loads are applied. The result is a constant rattling as one drives down the road, whether a scooter is loaded or not, particularly if not.  
           [0004]    Any mechanical system subjected to vibration has a frequency at which energy is preferentially absorbed, i.e. a resonant frequency. It has been found that the combination of vehicle, lift, and scooter may have a resonant frequency at frequencies less than 10 Hz, particularly less than 1 Hz. Encountering the right source of vibration depends heavily upon the suspension of the vehicle and the type of road, which are difficult to predict. However, under rare but favorable conditions, a resonance can be set up that increases in amplitude enough to throw a scooter from a lift during transport, even with the hold-down typically used to clamp the scooter to the platform.  
           [0005]    A problem with any external lift is the fact that, when loaded with a scooter, a considerable weight is being added a long distance behind the rear wheels of a vehicle. Particularly for smaller vehicles, wherein the weight of the scooter is a greater fraction of the total weight of the vehicle, any instability in the load adversely affects the handling of the vehicle. The effect is very much one of “the tail wagging the dog.” However picturesque the metaphor, the effect can be quite unsettling for a driver and, perhaps, unsafe.  
           [0006]    It is known in the art to incorporate a load sensor into the platform, e.g. as disclosed in the Peterson patent. A problem with load sensors of the prior art is that the sensor is activated by a wheel of the scooter. Thus, the sensor is not just exposed to the elements but is exposed to dirt, stones, and whatever other debris may be adhering to the wheels of the scooter.  
           [0007]    Another problem with sensors of the prior art is that the sensor mechanism includes a long coupling past the hinge about which the platform rotates. Because the sensor is located at or near ground level, in order for a wheel to roll over the sensor, the coupling mechanism is also exposed to dirt, mud, and damage. If the platform is lowered over uneven ground or ground strewn with rocks, twigs, or other debris, the treadle for the sensor may be supported and not depress when the wheel of a scooter rolls over the sensor. Finally, load sensors of the prior art typically sense a load at a small location. If a child stands on the lift, it is not likely that the child will stand on the load sensor. Thus, a child could actuate the lift and have the platform fold up with the child on it.  
           [0008]    In view of the foregoing, it is therefore an object of the invention to provide an external scooter lift with a load sensor that senses a load anywhere on the scooter platform.  
           [0009]    Another object of the invention is to provide a load sensor that is protected from the wheels of a scooter.  
           [0010]    A further object of the invention is to provide a lift that minimizes motion of the platform during transport.  
           [0011]    A further object of the invention is to minimize adversely affecting the handling of a vehicle loaded with an external scooter.  
           [0012]    Another object of the invention is to prevent resonance effects in scooter lifts.  
           [0013]    A further object of the invention is to secure a scooter to a lift even if the vehicle carrying the scooter is bounding down a road.  
         SUMMARY OF THE INVENTION  
         [0014]    The foregoing objects are achieved in this invention in which an external lift for a scooter includes a load sensor actuated by rotation of the platform as a load is applied, a lock mechanism for preventing the platform from rotating in a loaded and raised position, and a lock mechanism for preventing the platform from rotating in an unloaded and raised position. The load sensor is attached to the hinge that enables the platform to rotate and includes a first plate coupled to the frame of the lift, a second plate coupled to the platform and approximately parallel with the first plate when the platform is horizontal. A compression spring separates the first plate from the second plate, whereby said platform is supported in an approximately horizontal position by the spring. A load on said platform causes the separation of the first plate from the second plate to decrease. The change is separation is sensed and an interlock is opened to prevent rotation of the platform as the platform is raised. A pin through the hinge prevents the platform from rotating in a raised position. A pair of shoes on a hold down prevent a scooter from leaving the lift unintendedly. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    A more complete understanding of the invention can be obtained by considering the following detailed description in conjunction with the accompanying drawings, in which:  
         [0016]    [0016]FIG. 1 is a perspective view of a stroller lift attached to the rear of a vehicle;  
         [0017]    [0017]FIG. 2 is a detail perspective of a load sensor constructed in accordance with the invention located adjacent the platform of the scooter lift;  
         [0018]    [0018]FIG. 3 is a detail of the catch used for tilting the platform;  
         [0019]    [0019]FIG. 4 is a detail of the load sensor;  
         [0020]    [0020]FIG. 5 is a perspective view illustrating a load lock constructed in accordance with the invention;  
         [0021]    [0021]FIG. 6 is an end view of the bar used as the hinge pin for the platform; and  
         [0022]    [0022]FIG. 7 is a perspective view of a hold down constructed in accordance with the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]    [0023]FIG. 1 illustrates a scooter lift constructed in accordance with the invention mounted on the rear of vehicle  11  by a trailer hitch. Platform  12  pivots about hinge  13  from a vertical to a horizontal position, and back, as indicated by double ended arrow  14 . Steel tube  16  is welded to a horizontal steel tube (not shown in FIG. 1) that fits within the receiver for the trailer hitch on vehicle  11 . Sliding post  17  fits within tube  16  and is driven by a suitable source of power (not shown) to raise or lower platform  12 , which is mechanically coupled to the lower end of the sliding post.  
         [0024]    Load sensor  19  is attached to the rear of hinge structure for supporting platform  12 . Referring to FIG. 2, load sensor  19  includes first plate  21  and second plate  22  that operate somewhat like the pivoting jaws of pliers to compress load spring  24 . First plate  21  is welded or otherwise attached to beam  25 , which is welded or otherwise suitable attached to sliding post  17 . Second plate  22  is attached to the platform and coupled to first plate  21  by spring  24 . Spring  24  is preferably a coil spring and is compressed between the first plate and the second plate when the platform is rotated to a horizontal position. Spring  24  provides a sufficient restoring force that it can not be completely compressed by the weight of the platform. Strictly speaking, the torque of the platform about the hinge is opposed by the torque from load spring  24 . Although a single spring is shown, more than one spring can be used to counter the torque from the platform. The upper end of spring  24  is attached to first plate  21  by bolt  25 . The load sensor is protected from the wheels of a scooter by fence  27 , which also guides the wheels of a scooter onto track  29 .  
         [0025]    The platform for a scooter rotates to a vertical position for travel, unless a scooter is on the platform. Referring to FIG. 3, whether or not the platform rotates depends upon whether or not pin  31  on the end of lever  32  engages slot  34  at the end of arm  35 . If pin  31  engages slot  34 , then the platform rotates as it is raised. If pin  31  does not engage slot  34 , then the platform remains horizontal as it is raised.  
         [0026]    Lever  32  is movable and rotates about a shaft at the lower end thereof. In FIG. 4, shaft  41  extends along the rear of the platform from within load sensor  19  almost to post  17 . Lever  32  (FIG. 3) is attached near one end of shaft  41 . The other end of shaft  41  is journaled in support bracket  44 , which is attached to plate  22 . Angle iron is welded or otherwise suitably attached to shaft  41  to form tab  45  extending away from the long dimension of the shaft. Return spring  46  applies a torque to shaft  41 , turning lever  32  into position for pin  31  to engage slot  34 . Adjustable stop  47  is attached to plate  21  above tab  45 . The adjustable stop, tab, and shaft provide an indication of the separation of plates  21  and  22 .  
         [0027]    If a torque greater than the torque due to the platform is applied to the system, then plates  21  and  22  move toward each other, spring  24  is further compressed, and tab  45  engages adjustable stop  46 . When adjustable stop  47  engages tab  45 , a torque is applied to shaft  41 , opposing return spring  46  and pivoting arm  32  away from engagement between pin  31  and slot  34 . A weight anywhere on the platform causes further compression of spring  24  and, therefore, prevents the platform from being rotated as it is raised. In one embodiment of the invention, as little as thirty pounds on the platform was sufficient to prevent the platform from rotating as it was raised.  
         [0028]    Mechanical stops  48  and  49  prevent spring  24  from being unduly compressed. That is, plates  21  and  22  move enough to cause arm  32  (FIG. 3) to move out of alignment but not enough to cause the platform to droop.  
         [0029]    [0029]FIG. 5 illustrates a scooter lift constructed in accordance with another aspect of the invention in which the platform is locked to prevent rotation during transport. The hinge about which platform  12  rotates includes steel tube  51  enclosing bar  54 . Tube  51  is welded to upper plate  21  and to sliding post  17  (FIG. 3). Platform  12  is welded to bar  54 . In accordance with this aspect of the invention, tube  51  includes hole  57  aligned with pin  58 . Pin  58  is attached to tube  16  and, therefore, is fixed or stationary relative to platform  12 . Bar  54  include at least one bore, such as bore  61  in FIG. 6. Preferably bore  61  extends through bar  54 . When platform  12  is raised horizontally, pin  58  enters hole  57  and engages bore  61 , thereby preventing platform  12  from rotating.  
         [0030]    Second bore  62  through bar  54  is provided to receive pin  58  for transporting the lift with platform  12  in a vertical position. The bores are not necessarily at 90° as illustrated in the drawings but may be at some other angle to accommodate the position of platform  12  after rotation. It has been found that the lock mechanism shown in FIG. 5 has the added advantage of changing the resonant frequency of the system such that undue bouncing of the scooter is avoided.  
         [0031]    In accordance with another aspect of the invention, which further provides a much stronger lift without greatly affecting the weight of the lift, U-shaped steel ramp  73  is attached to the lower end of post  74  for engaging wheel  75 . Bracket  71 , attached to the upper end of post  74  is subject to great strain when a load is placed on platform  12 . Wheel  75  rides on ramp  73  to support the lower end of tube  16 , greatly increasing the weight that can be lifted safely.  
         [0032]    [0032]FIG. 7 illustrates a hold down constructed in accordance with the invention in which a pair of laterally displaced feet are used hold down the scooter. Hold down  70  includes tube  71  welded or otherwise securely attached to tube  16 . Tube  71  is approximately horizontal and receives one end of arm  72 , which is preferably a bent, solid bar of steel. Arm  72  rotates within tube  71  to provide an up or down motion to the free end of the arm. Tube  73  is welded to the free end of arm  72  and tube  74  fits within tube  73  with a spring (not shown) to provide a resilient connection to foot  75 , which is mounted on one end of tube  74 . Along the length of arm  72  a second telescoping pair of tubes is welded to provide connection to foot  79 . Feet  75  and  79  are preferably attached to tubes  74  and  78  by a mechanism that will allow some movement of the feet about at least two axes. As shown in the FIG. 7, foot  79  is attached by a ball and socket joint. Other mechanisms could be used instead.  
         [0033]    Feet  75  and  79  are separated along arm  72  by 5-10inches or more. The result is that the feet are laterally displaced, i.e. separated from side to side across a scooter. Preferably, the feet straddle longitudinal axis  81  of a scooter (not shown). Thus positioned, the feet prevent the scooter from rolling about longitudinal axis  81  during transport. To some extent, hold down  70  also prevents the scooter from rolling on its wheels. What is of concern here is rolling in the sense of the one of the motions of roll, pitch, and yaw.  
         [0034]    The invention thus provides an external scooter lift with a load sensor that senses a load anywhere on the scooter platform yet the load sensor is protected from the wheels of a scooter. The invention further provides a more rugged lift by locking the platform in place for transport, thereby minimizing motion of the lift during transport, and by supporting the sliding post while the platform is raised or lowered, thereby minimizing flexing of joints and major components of the lift. The displaced feet on the hold down further prevent unwanted motion of the scooter during transport. The result is noticeably better handling of a vehicle carrying the scooter, particularly in smaller vehicles, no resonance effects, and a quieter ride.  
         [0035]    Having thus described the invention, it will be apparent to those of skill in the art that various modifications can be made within the scope of the invention. For example, either pin  58  or bores  61  and  62  or all of them can be cylindrical or tapered. Instead of bolts  48  and  49  as stops, one could use a plate welded to the rear of plate  21 . Such a plate would not only engage plate  22  along its entire length, rather than in just one or two places, it would also provide an enclosure for the load sensor. On the other hand, such a plate is fixed, requiring some adjustment in spring  24  to allow for variations in manufacture. A torsion spring or leaf spring can be used instead of a coil spring for spring  25 . A torsion spring can be used for all or part of shaft  41 . If the platform is locked only in the horizontal position, then means must be provided to move pin  58  out of position when the platform is in a vertical position. Pieces that are welded can be made as a single piece. Ancillary apparatus, such as a pawl and catch mechanism for operating the hold-down, is not shown but would be part of a scooter lift incorporating this invention. Such mechanisms are known in the art. One could provide feet on separate arms but this is needlessly complicated. Spring  24  operates in compression but could be made to operate in expansion by reversing the connections of plates  21  and  22  (attaching plate  21  to bar  54  and attaching plate  22  to tube  51 ) but this is not preferred. The particular construction of the hinge about which the platform rotates is not critical to the invention. For example, either a single bar or a segmented bar can be used and either the bar or the sleeve can be attached to the frame. Motive power for the lift is commercially available from several sources and, other than being able to lift four hundred pounds vertically a distance of eighteen inches, is not critical.