Abstract:
A compact and lightweight drive mechanism for an electrically powered vehicle such as a wheelchair or a scooter. The compact drive mechanism includes a gearmotor combining a motor and a gearbox. High strength rare earth magnets and a large diameter enable the motor to generate a high torque. Gearmotor efficiency is maximized by placing the motor and gearbox in a direct drive relationship, with the shafts of both motor and gearbox parallel to one another. The compact drive mechanism weighs less than conventional drive mechanisms and occupies less space. The compact drive mechanism therefore improves efficiency and lowers power requirements over conventional systems.

Description:
FIELD OF THE INVENTION 
   This invention relates to drive mechanisms for powered vehicles for the disabled and specifically to an improved drive mechanism for a wheelchair or motor scooter. 
   BACKGROUND OF THE INVENTION 
   Conventional electrically powered wheelchairs are typically powered by motors connected to a separate gearbox. The typical gearbox is a right-angled gearbox. Stopping the wheelchair is accomplished by a brake, which is typically connected externally to the motor. 
   Since the wheelchair must be able to turn in a very tight radius, conventionally powered wheelchairs typically have two drive wheels, which can be rotated independently of one another. Each drive wheel is driven by a gearbox, which in turn is driven by a motor. A brake is typically connected to the outside of the motor. To supply power to the motors, the wheelchair is typically outfitted with one or more batteries. The batteries are typically rechargeable, so that the operator can easily recharge the batteries by simply plugging into a wall electrical outlet. 
   The use of two motors, two gearboxes, an external brake, and the batteries to supply power results in a great demand for space to accommodate all of these components. Typically, a portion of the frame of a conventional wheelchair is reserved for mounting of the batteries and the drive mechanism. The motor, gearbox, and external brake take up a lot of space on a convention wheelchair, leaving little space for installing batteries and other equipment. The gearboxes and motors add to the weight of the wheelchair, increasing the power drain and decreasing the charge of the batteries as the wheelchair is operated. 
     FIGS. 1 and 2  depict a portion of a prior art wheelchair  20  including a frame  22 , drive wheels  24 , batteries  26 , and a drive mechanism  28 . The drive mechanism  28  is a right angle gearmotor  30  comprised of a motor  32  and a gearbox  34 . In powered vehicles for handicapped persons, such as wheelchairs and scooters, the vehicle must include a safety feature that stops the vehicle whenever the vehicle controller is set to the neutral position. Typically, the controller includes a joystick (not shown) that is manipulated by the wheelchair user to control the vehicle. In the conventional wheelchair, a brake  36  mounted external to the motor  32  acts as a safety brake, stopping the rotation of the drive wheels  24  at the appropriate times as the controller is placed in the neutral position. As depicted in  FIGS. 1 and 2 , two right angle gearmotors  30  are typically used in a wheelchair  20 , one to drive each drive wheel  24 . The drive wheels  24  can therefore rotate independently of one another as called for by the controller (not shown). This is to enable the wheelchair  20  to make a tight radius turn, which is necessary in the confined spaces a wheelchair must operate in. 
   As shown in  FIGS. 1 and 2 , the gearmotors  30  on a conventional wheel chair  20  are quite large in size, taking up quite a large area of space on the wheelchair frame  22 . The large area occupied by the conventional gearmotors  30  is to the detriment of the runtime of the wheelchair  20 , as the space occupied by the gearmotors  30  limits the size of the batteries  26  that can be accommodated on the wheelchair frame  22 . As another consequence of using the conventional right angle gearmotors  30 , the large size of the gearmotors  30  translates to a heavier weight further reducing the runtime of the batteries  26 . Typically, the batteries  26  can be recharged from a wall outlet, and any increase in weight of the wheelchair  30  comes at an expense of a reduction in battery life and runtime. 
   As further depicted in  FIGS. 1 and 2 , the safety brake on a conventional wheelchair  20  is an external brake  36  mounted on the end of the motor  32  portion of the gearmotor  30 . Mounting the brake  36  external to the gearmotor  30  further increases the length of the gearmotor  30  and takes up additional space on the frame  22  that could better be used for the batteries  26 . 
   Thus, although the right-angled gearbox and motor with external brake are commonly used as drive mechanisms on wheelchairs, they suffer several disadvantages. Power consumption is high. A large amount of space is required to accommodate a right-angled gearbox. The right-angled gearbox and motor are fairly large, thereby adding a significant amount of weight that will consume power and reduce the efficiency of the drive mechanism. 
   What is needed is a drive mechanism for an electrically powered vehicle that requires less space, is of lower weight, and improves efficiency over conventional drive mechanisms. 
   SUMMARY OF THE INVENTION 
   The invention is a compact and lightweight drive mechanism for an electrically powered vehicle such as a wheelchair or a scooter. The drive mechanism includes a gearmotor combining a motor and a gearbox. Rare earth magnets and a large diameter enable the motor to generate a high torque. Gearmotor efficiency is maximized by placing the motor and gearbox in a direct drive relationship, with the shafts of both motor and gearbox parallel to one another. The drive mechanism weighs much less than conventional drive mechanisms and takes up much less space. The drive mechanism therefore improves efficiency and lowers power requirements over conventional systems. 
   OBJECTS AND ADVANTAGES 
   As a result of providing a brake that is internal to the electric motor, a first advantage is that the overall size of the electric motor is reduced as compared to a conventional motor with an external brake. A further advantage results from the reduction in the footprint or amount of space taken up by the motor and gearbox. By reducing the amount of space required, there is more room for batteries and other essential equipment. 
   Providing a gearmotor including an internal brake provides a further advantage in that the weight of the drive mechanism is reduced. A weight reduction decreases power drain and increases battery life. 
   Placement of the gearbox portion of the gearmotor within the wheel hub of the drive wheels has the advantage of creating additional space on the wheelchair frame. 
   By providing a direct drive between the motor portion and gearbox portion of the gearmotor, overall electrical efficiency is improved over the conventional right-angle motor and gearbox. 
   These and other objects and advantages of the present invention will be better understood by reading the following description along with reference to the drawings. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a prior art wheelchair. 
       FIG. 2  is a top view of the prior art wheelchair of  FIG. 1 . 
       FIG. 3  is a perspective view of a gearmotor that forms part of the drive mechanism of an electrically powered vehicle according to the present invention. 
       FIG. 4  is a side view of the gearmotor of  FIG. 3 . 
       FIG. 5  is a first end view of the gearmotor taken along line  5 — 5  of  FIG. 4 . 
       FIG. 6  is a second end view of the gearmotor taken along line  6 — 6  of  FIG. 4 . 
       FIG. 7  is a sectional view of the gearmotor taken along line  7 — 7  of  FIG. 4 . 
       FIG. 8  is a sectional view of the brake portion of the gearmotor of  FIG. 3 . 
       FIG. 9  is a perspective view of a wheelchair constructed with the drive mechanism according to the present invention. 
       FIG. 10  is a top view of the wheelchair depicted in  FIG. 9 . 
   

   TABLE OF NOMENCLATURE 
   The following is a listing of part numbers used in the drawings along with a brief description: 
   
     
       
             
             
             
           
         
             
                 
                 
             
             
                 
               Part Number 
               Description 
             
             
                 
                 
             
           
           
             
                 
               20 
               prior art wheelchair 
             
             
                 
               22 
               frame 
             
             
                 
               24 
               drive wheel 
             
             
                 
               26 
               battery 
             
             
                 
               28 
               drive mechanism 
             
             
                 
               30 
               right angle gearmotor 
             
             
                 
               32 
               motor 
             
             
                 
               34 
               gearbox 
             
             
                 
               36 
               external brake 
             
             
                 
               40 
               wheelchair 
             
             
                 
               42 
               compact drive mechanism 
             
             
                 
               44 
               frame 
             
             
                 
               46 
               drive wheel 
             
             
                 
               48 
               battery 
             
             
                 
               50 
               compact gearmotor 
             
             
                 
               52 
               motor 
             
             
                 
               54 
               gearbox 
             
             
                 
               56 
               wheel hub 
             
             
                 
               58 
               gearbox shaft 
             
             
                 
               60 
               electrical supply wiring 
             
             
                 
               62 
               keyway 
             
             
                 
               64 
               motor shaft 
             
             
                 
               66 
               gear on motor shaft 
             
             
                 
               68 
               gear on gearbox shaft 
             
             
                 
               70 
               motor end 
             
             
                 
               72 
               gearbox end 
             
             
                 
               74 
               inner cavity 
             
             
                 
               76 
               internal brake 
             
             
                 
               78 
               compression spring 
             
             
                 
               80 
               electromagnet 
             
             
                 
               82 
               controller 
             
             
                 
               84 
               friction disk 
             
             
                 
               86 
               soleplate 
             
             
                 
               88 
               release lever 
             
             
                 
               90 
               rare earth magnet 
             
             
                 
               92 
               walls of motor internal housing 
             
             
                 
                 
             
           
        
       
     
   
   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention is a compact drive mechanism that frees up space, reduces weight, and improves the runtime and efficiency of powered vehicles for the handicapped. 
   Referring to  FIGS. 9 and 10 , a portion of a wheelchair  40  is depicted with the compact drive mechanism  42  of the present invention installed thereon. The wheelchair  40  includes a frame  44 , drive wheels  46 , and batteries  48 . Two compact gearmotors  50  according to the present invention are secured to the frame  44 . The compact gearmotors  50  include a motor  52  and a gearbox  54 . A portion of one drive wheel  46  is broken away to show the gearbox  54 , which is disposed substantially within the wheel hub  56 . 
   As shown in  FIGS. 3 and 4 , the motor  52  and gearbox  54  are joined integrally into a compact gearmotor  50 . A gearbox shaft  58  extends from the gearbox. Electrical current is provided through electrical supply wiring  60  to power the motor  52  and the gearbox  54  reduces the speed of the motor to an appropriate speed for driving the drive wheels (not shown) of the electrically powered vehicle through a direct drive linkage. A keyway  62  is provided on the gearbox shaft  58  for keyed connection to the drive wheel. 
   As shown in  FIG. 7 , a sectional view of the compact gearmotor  50  taken along line  7 — 7  of  FIG. 4 , the gearmotor  50  is a direct drive gearmotor, with the gearbox shaft  58  parallel to the motor shaft  64 . A gear  66  on the motor shaft  64  engages a gear  68  on the gearbox shaft  58 . The gearmotor  50  includes a motor end  70  and a gearbox end  72 . The motor end  70  of the compact gearmotor  50  includes an inner cavity  74  surrounding the motor shaft  64 . A brake  76  is mounted within the inner cavity  74  of the motor  52  and is therefore an internal brake  76 . To improve efficiency of the compact gearmotor  50 , gear  66  on the motor shaft  64  is preferably a helical gear and the gear  68  on the gearbox shaft  58  is preferably a helical gear. 
   With reference to  FIG. 8 , the internal brake  76 , which is contained completely inside the motor  52 , is a friction brake including a compression spring  78 , an electromagnet  80 , a friction disk  84 , a soleplate  86 , and a release lever  88 . The compression spring  78  biases the brake  76  to the brake applied state and the electromagnet  80  when activated releases the brake  76 . 
   With reference to  FIG. 10 , the compact drive mechanism  42  or gearmotor  50  of the present invention is secured to the frame  44  of a wheelchair  40  or other electrically powered vehicle. The gearbox shafts  58  are secured to the respective wheel hubs  56  of the drive wheels  46 . The gearboxes  54  of the compact gearmotors  50  are each disposed substantially within their respective wheel hub  56 . The internal brake  76 , depicted by dashed lines, is within the motor  52 . 
   Typically a controller  82  is provided to enable an operator to control the speed and direction of rotation of the gearmotors  50 . The controller  82  typically includes a run and a stop state. When the controller  82  is placed in the run state, the electromagnet  80  (see  FIG. 8 ) is activated electrically thereby pulling the friction disk  84  away from the soleplate  86  and releasing the brake  76 . In the run state, at the same time that the internal brake  76  is released, the controller  82  causes rotation of the drive wheels  46 . Placing the controller  82  in the stop state cuts power to the electromagnet  80  thereby enabling the compression spring  78  to force the friction disk  84  against the soleplate  86  and apply the brake  76  to stop rotation of the drive wheels  46 . Operation of the present invention is therefore controlled automatically by an operator who manipulates the controller  82 . As a safety feature, whenever the controller  82  is placed in the stop state, the brake&#39;s electromagnet  80 , see  FIG. 8 , is electrically deactivated and the internal brake  76  is applied. The electric motor  52  also includes a manual brake release lever  88  for releasing the internal brake  76  manually when desired, such as when the wheelchair  40  is powered down and it is desired to release the brake for example when the wheelchair  40  is being pushed by a person from one location to another. 
   In an especially preferred embodiment of the compact drive mechanism  42  of the present invention, the motor  52  is a  24  volt DC motor with a speed of rotation preferably between 2,000 and 5,000 rpm. The compact drive mechanism  42  preferably has a step down ratio in speed of rotation of between 50:1 and 8:1. For a 3,000-rpm motor, the gearbox  54  therefore gears the motor down to drive the gearbox shaft  58  at a speed of rotation of between 60 and 375 rpm, depending on the selection of gearbox ratio. 
   Referring to  FIG. 7 , a key advantage of the compact drive mechanism  42  is that the motor  52  is a direct-drive motor. By placing the motor  52  and gearbox  54  in a direct drive relationship, with the gearbox shaft  58  and motor shaft  64  parallel to one another, the efficiency of the gearmotor  50  is maximized and much improved over the right angle drives of conventional motor and gearbox drives. 
   A second key advantage of the compact drive mechanism  42  is that the brake  76  is an internal brake, situated within the motor  52 . By placing the brake  76  within the motor  52 , as shown in  FIG. 7 , the overall length of the motor  52 , as compared to a conventional motor  32  having an external brake  36  (see  FIG. 2 ), is decreased, allowing significant savings in space on the frame of the electrically powered vehicle. As shown in  FIG. 4 , the outer diameter (D M ) of the motor  52  is no greater than 4.5″ and the length (L M ) of the motor  52  is no greater than 3.125″. Although the motor  52  of the present invention is much smaller in length than a conventional motor, the larger diameter and use of rare earth magnets  90  in the motor  52  on the walls  92  of the internal housing enable the motor  52  to develop the high torque that is typically required for an electrically powered vehicle for the handicapped. The motor  52  of the present invention has a nominal power rating of at least ¼ horsepower. 
   A shown in  FIG. 10 , another key advantage of the compact drive mechanism  42  is the compact size of the gearbox  54 . As a result of the reduced size of the gearbox, additional frame space is freed up by disposing the gearbox  54  of the compact gearmotor  50  substantially within the wheel hub  56  of the wheelchair  40 . As shown in  FIG. 4 , the outer diameter (D G ) of the gearbox  54  is no greater than 3.75″ and the length (L G ) of the gearbox  54  is no greater than 4″. 
   With reference to  FIG. 7 , the overall width (W GM ) of the compact gearmotor  50  is no greater than 6.125″ and the overall length (L GM ) of the compact gearmotor  50  is no greater than 7.25″. 
   The compact drive mechanism  42  of the present invention can be used with any electrically powered vehicle for the handicapped, such as a wheelchair or a scooter. For an electrically powered wheelchair according to the present invention, as shown in  FIGS. 9 and 10  herein, the compact drive mechanism  42  would typically include two drive wheels  24  and two compact gearmotors  50 , one compact gearmotor to power each drive wheel. Since a scooter is not required to make sharp turns, typically one wheel is driven, and a scooter according to the present invention would typically include one compact gearmotor connected to a transaxle (not shown) to drive one of the wheels. 
   Having thus described the invention with reference to a preferred embodiment, it is to be understood that the invention is not so limited by the description herein but is defined as follows by the appended claims.