Abstract:
An electrical wheelchair includes a chassis to which a frame is pivotally mounted. Two casters are rotatably mounted to the frame. At least a resilient member is arranged between the frame and the chassis for supporting the relative position of the frame with respect to the chassis. The resilient member can be deformed to change the relative position of the frame with respect to the chassis to allow the wheelchair to climb over raised surfaces of different heights. The deformation of the resilient member also stores energy therein which may be released when the wheelchair is about to reach the raised surface for enhancing the wheelchair to move over the raised surface. Further, the resilient member also functions to absorb shock caused by the wheelchair moving down a step-like raised surface.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates generally to an electrical wheelchair, and in particular to an anti-turnover mechanism of an electrical wheelchair for operation safety purposes.  
           [0003]    2. The Related Art  
           [0004]    The improvement of technology and medical care extends life of human beings. The old and the disabled are best benefited from the modern technology and medical care. A lot of different supportive devices have been developed for helping the old and the disabled to transport themselves in an extended area so as to improve their living standard without particular care by other supporting medical personnel. Wheelchairs have been one of the most commonly known supportive devices for the old and the disabled to transport themselves in short distances. However, for those very weak or those having hand or arm injured, they still need other people&#39;s help in moving the wheelchairs.  
           [0005]    Electrical wheelchairs that are equipped with electrical motors allows a person to drive the wheelchair without great effort and thus are particularly suitable for those whose arms are weak or injured. The electrically powered wheelchairs are also advantageous as compared with vehicles equipped with engines powered by fossil fuels for environmental protection.  
           [0006]    The electrical wheelchair comprises two wheels to which electrical motors are mechanically coupled and two front casters for guiding the moving direction of the wheelchair. To ensure a sitter&#39;s safety, the electrical wheelchair is equipped with anti-turnover mechanism, which is usually comprised of two rear casters, to prevent turnover of the electrical wheelchair when moving on an uneven road or surface. Climbing over a step-like raised surface is one of the most commonly seen challenges for the wheelchair moving in the uneven road. In climbing over a step, the front casters are moved to the raised top surface of the step first, while the wheels are still on the lower surface, or in moving down the step, the front casters are moved to the lower surface first with the wheel still positioned on the raised top surface of the step. In both situations, the wheelchair is tilted. For raised surfaces of limited heights, the tilting of the wheelchair is within a range wherein the gravity center of the wheelchair is located in the projected bottom area of the wheelchair and turnover of the wheelchair is prevented. However, for a raised surface of a substantial height, attempting to climb over the step may cause turnover of the wheelchair. Thus, anti-turnover mechanism is required for the electrical wheelchair for safety purposes.  
           [0007]    [0007]FIG. 15 of the attached drawings shows a conventional electrical wheelchair with anti-turnover mechanism. The conventional electrical wheelchair, which is designated with reference numeral  10 , comprises a chassis  12  on which a seat  14  is mounted. Two wheels  16  are mounted on opposite sides of the chassis  12  and are coupled to electrical driving units  18 , which are often electrical motors, to drive the wheelchair  10  forward and/or backward. The motors  18  are fixed in the chassis  12  and are controlled by a control unit  20  that is located in front of the seat  14  for ready access of a sitter of the wheelchair  10 . Two front casters  22  are mounted on the front side of the chassis  12  for smooth movement of the wheelchair  10  and for controlling moving direction of the wheelchair  10 .  
           [0008]    Two rods  24  that are spaced from each other extend rearward from the chassis  12 . A rear caster or anti-turnover roller  26  is rotatably supported by each of the rods  24 . The rear caster  26  is in general not contacting the surface of a road when the wheelchair  10  is moving on a substantially flat road. When the wheelchair is climbing a raised surface which causes the chassis  12  to tilt rearward, the rear casters  26  contact the ground surface and prevent undesired over-tilting situation. Thus turnover of the wheelchair  10  is effectively eliminated.  
           [0009]    Conventionally, the relative position of the rear casters  26  with respect to the chassis  12  is fixed. In other words, the angle of rearward tilting of the chassis  12  that is allowed by the rear casters  26  is limited, determined by the relative position of the rear casters  26  with respect to the chassis  12 . This imposes a constraint to the height of the raised surfaces that the wheelchair can climb.  
           [0010]    Furthermore, the rear casters  26  of the conventional electrical wheelchair  10  are not capable to absorb shock caused by dropping down a step-like raised surface. In moving the wheelchair  10  down a step-like raised surface, the wheels  16  often drop down suddenlyl with the rear casters  26  hitting the top surface of the step. This causes an uncomfortable shock to the sitter of the wheelchair.  
           [0011]    It is thus desirable to have an electrical wheelchair that overcomes the above problems.  
         SUMMARY OF THE INVENTION  
         [0012]    An object of the present invention is thus to provide a wheelchair having an anti-turnover mechanism that allows the electrical wheelchair to climb over raised surfaces of different heights without causing turnover of the wheelchair.  
           [0013]    Another object of the present invention is to provide a wheelchair that is provided with shock absorbing device for absorbing shock caused by moving down a raised surface.  
           [0014]    A further object of the present invention is to provide a wheelchair that is provided with energy storing device that stores energy in an initial phase in climbing a raised surface and releases the energy for helping climbing the raised surface in a final phase of the climbing so as to ensure safe and effective operation of the wheelchair in climbing of the raised surface.  
           [0015]    To achieve the above objects, in accordance with the present invention, there is provided an electrical wheelchair comprising a chassis to which a frame is pivotally mounted. Two casters are rotatably mounted to the frame. At least a resilient member is arranged between the frame and the chassis for supporting the relative position of the frame with respect to the chassis. The resilient member is deformable to change the relative position of the frame with respect to the chassis for allowing the wheelchair to climb over raised surfaces of different heights. The deformation of the resilient member stores energy therein which may be released when the wheelchair is about to reach the raised surface for enhancing the movement of the wheelchair over the raised surface. Further, the resilient member also functions to absorb shock caused by the wheelchair moving down a step-like raised surface. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    The present invention will be apparent to those skilled in the art by reading the following description of preferred embodiments thereof, with reference to the attached drawings, in which:  
         [0017]    [0017]FIG. 1 is a perspective view of an electrical wheelchair constructed in accordance with a first embodiment of the present invention;  
         [0018]    [0018]FIG. 2 is an exploded view of the electrical wheelchair of FIG. 1;  
         [0019]    [0019]FIG. 3 is a side elevational view of the electrical wheelchair of the present invention, showing the wheelchair climbing a step-like raised surface in a first phase;  
         [0020]    [0020]FIG. 4 is a side elevational view similar to FIG. 3 but showing the wheelchair climbing the raised surface in a second phase;  
         [0021]    [0021]FIG. 5 is a perspective view of FIG. 4;  
         [0022]    [0022]FIG. 6 is a side elevational view similar to FIGS. 3 and 4 but showing the wheelchair climbing the raised surface in a third phase;  
         [0023]    [0023]FIG. 7 is a side elevational view of the electrical wheelchair of the present invention, showing the wheelchair moving down the raised surface;  
         [0024]    [0024]FIG. 8 is an exploded view of an electrical wheelchair constructed in accordance with a second embodiment of the present invention;  
         [0025]    [0025]FIG. 9 is a perspective view of an electrical wheelchair constructed in accordance with a third embodiment of the present invention;  
         [0026]    [0026]FIG. 10 is an exploded view of FIG. 9;  
         [0027]    [0027]FIG. 11 is an exploded view of an electrical wheelchair constructed in accordance with a fourth embodiment of the present invention;  
         [0028]    [0028]FIG. 12 is a perspective view of an electrical wheelchair constructed in accordance with a fifth embodiment of the present invention;  
         [0029]    [0029]FIG. 13 is an exploded view of FIG. 12;  
         [0030]    [0030]FIG. 14 is an exploded view of an electrical wheelchair constructed in accordance with a sixth embodiment of the present invention; and  
         [0031]    [0031]FIG. 15 is a perspective view of a conventional electrical wheelchair. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]    With reference to the drawings and in particular to FIGS. 1 and 2, an electrical wheelchair constructed in accordance with a first embodiment of the present invention, generally designated with reference numeral  100 , comprises a chassis  112  on which a seat  114  is mounted to support a person (not shown) sitting on the wheelchair  100 . Two wheels  116  are mounted on opposite sides of the chassis  112  and are driven by electrical driving means  118  for moving the wheelchair  100  forward and/or backward. The electrical driving means  118  can be any means suitable for driving the wheelchair  100  and is an electrical motor in the embodiment illustrated. The motor  118  is fixed in the chassis  112  and is controlled by a control unit  120  that is located in front of the seat  114  for ready access by the person sitting on the wheelchair  100 . Two front casters  122  are mounted to a front side of the chassis  112  for smooth movement of the wheelchair  100  and for controlling moving direction thereof.  
         [0033]    Two spaced, L-shaped rods  128  extend from a rear side of the chassis  112  whereby the rods  128  are substantially opposite to the front casters  122 . Each rod  128  comprises a first, horizontal section  128 A extending from the chassis  122  and a second, vertical section  128 B extending from an end of the first section  128 A in a substantially perpendicular manner. A cross bar  130  extends between and is fixed to the second sections  128 B of the rods  128 . Two through holes  132  are defined in the cross bar  130 . The holes  132  will be further discussed hereinafter.  
         [0034]    The electrical wheelchair  100  comprises an anti-turnover mechanism (not labeled) comprising a frame, generally designated with reference numeral  134  in the drawings. The frame  134  is arranged on the rear side of the chassis  112  and is sized to be received between the rods  128 . The frame  134  comprises two side walls  138  connected together by a plate  136  straddling the side walls  138 . First apertures  140  are respectively defined in the side walls  138  and aligned with each other. The first sections  128 A of the rods  128  define through holes  142  corresponding to the first apertures  140 . A shaft  144  extends through both the holes  142  and the first apertures  140  for pivotally mounting the frame  134  to the chassis  112  whereby the frame  134  is allowed to rotate with respect to the chassis  112 .  
         [0035]    The side walls  138  of the frame  134  define aligned second apertures  146  with a shaft  148  extending therethrough. The shaft  148  has opposite ends (not labeled) extending beyond the side walls  138 . Two rear casters  150  are respectively mounted to the ends of the shaft  148 . The casters  150  serve to prevent the wheelchair  100  from turnover. A collar  152  that is fit over the shaft  148  is provided between each rear caster  150  and the corresponding side wall  138  to reduce wearing and abrasion therebetween and to control distance between the rear casters  150 .  
         [0036]    The rear casters  150  are sized not to contact the ground surface when the wheelchair  100  is moving on a flat surface to enhance the movement of the wheelchair  100 .  
         [0037]    The anti-turnover mechanism further comprises two resilient members  154  which are helical springs in the embodiment illustrated. The resilient member  154  are arranged between the frame  134  and the cross bar  130  of the chassis  112 . The resiliency of the resilient members  154  maintains the relative position between the frame  134  and the chassis  112  while allowing the relative position to be changed by deforming the resilient members  154  so as to change the relative position of the rear casters  150  with respect to the chassis  112 . It is, however, noted that other resilient members can be employed to replace the helical springs shown in the drawings without departing from the scope of the present invention.  
         [0038]    The springs  154  is mounted to the frame  134  and the cross bar  130  in any suitable manner. In the embodiment illustrated, each spring  154  encompasses a rod  156 . The rod  156  has a first end (not labeled) extending through a corresponding one of the holes  132  of the cross bar  130  and is fixed thereto by a pin  160 . The rod  156  has an opposite second end in which a hole  162  extending in a transverse direction is defined for the extension of the shaft  148 . In the embodiment illustrated, a transversely-extending tube (not labeled) is formed on the second end of the rod  156  with the hole  162  defined therein and co-extending therewith. The tube serves to retain the second end of the spring  154 . A slot  164  is defined in the plate  136  for the extension of the rod  156 .  
         [0039]    A collar  166  that is fit over the shaft  148  is arranged between the tubes of the rods  156  for reducing wearing and abrasion between the tubes. It is understood that the provision of the collar  166  is not absolutely necessary in exercising the present invention.  
         [0040]    Also referring to FIGS.  3 - 6 , wherein FIGS. 3, 4 and  6  show three different phases of the operation of the wheelchair  100  in climbing over a step-like raised surface  170  from a lower surface  168 , while FIG. 5 is a perspective view of FIG. 4, when the electrical wheelchair  100  is climbing the raised surface  170  from the lower surface  168 , the front casters  122  contact a side face  171  of the step-like raised surface  170  first and move along the side face  171  up to the raised surface  170 . This causes the chassis  112  and the seat  114  to tilt which in turn causes the rear casters  150  to contact the lower surface  168 .  
         [0041]    As shown in FIGS. 4 and 5, with the front casters  122  moving higher, the chassis  112  is further tilted rearward. This causes deformation of the resilient members  154  in order to change the relative position of the rear casters  150  with respect to the chassis  112  for accommodating the further tilting of the chassis  112 .  
         [0042]    When the front casters  122  eventually reaches the raised surface  170 , further movement of the wheelchair  100  causes the wheels  116  to contact the side face  171  and move upward along the side face  171  as shown in FIG. 6. During the process, the resilient members  154  are maintained in a deformed condition. When the wheels  116  reaches the raised surface  170 , the chassis  112  returns to its non-tilted condition and no force is applied to the resilient members  154 . The resilient members  154  are allowed to spring back to their non-deformed condition. Energy stored in the deformed members  154  is thus released, causing a force acting upon the wheelchair  100  to forcibly drive the wheelchair  100  to the raised surface.  
         [0043]    Further referring to FIG. 7, when the wheelchair  100  is moving down from the raised surface  170  to a lower surface  172 , the wheels  116  are moved toward an edge  173  of the raised surface  170  and drops suddenly to the lower surface  172 . This makes the rear casters  150  hit onto the raised surface  170 , causing a shock to the wheelchair  100 . Due to the resiliency of the resilient members  154 , the shock is absorbed by the deformation of the resilient members  154 . This reduces the discomfort caused by the shock to the person sitting on the wheelchair  100 . When the wheelchair  100  moves forward, the resilient members  154  spring back to their non-deformed condition, releasing the energy stored therein. This helps to quickly drive the wheelchair  100  forward.  
         [0044]    Referring to FIG. 8, an electrical wheelchair constructed in accordance with a second embodiment is shown and is designated with reference numeral  100 ′. The electrical wheelchair  100 ′ of the second embodiment is similar to the electrical wheelchair  100  of the first embodiment with a modification made to the frame of the anti-turnover mechanism. The frame of the electrical wheelchair  100 ′ of the second embodiment is generally designated with reference numeral  190  in the drawings, comprising a rectangular member  192  having opposite side walls  194  connected to each other by opposite end walls (not labeled). First and second apertures  196 ,  198  are defined in the side walls  194  for the extension of the shaft  144 ,  148 , respectively. The remaining parts of the electrical wheelchair  100 ′ of the second embodiment are substantially identical to those of the electrical wheelchair  100  of the first embodiment and bear with the same reference numerals. Thus, no further discussion is needed herein.  
         [0045]    Referring to FIGS. 9 and 10, an electrical wheelchair constructed in accordance with a third embodiment of the present invention, generally designated with reference numeral  200 , is shown. The electrical wheelchair  200  comprises a chassis  212  on which a seat  214  is mounted to support a person (not shown) sitting on the wheelchair  200 . Two wheels  216  are mounted on opposite sides of the chassis  212  and are driven by electrical driving means  218  for moving the wheelchair  200  forward and/or backward. Similar to the first embodiment with reference to FIGS.  1 - 7 , the electrical driving means  218  is any means suitable for driving the wheelchair  200 , such as an electrical motor. The motor  218  is fixed in the chassis  212  and is controlled by a control unit  220  that is located in front of the seat  214  for ready access by the person sitting on the wheelchair  200 . Two front casters  222  are mounted to a front side of the chassis  212  for smooth movement of the wheelchair  200  and for controlling moving direction thereof.  
         [0046]    Two spaced, L-shaped rods  228  extend from a rear side of the chassis  212 . Each rod  228  comprises a first, horizontal section  228 A extending from the chassis  222  and a second, vertical section  228 B extending from an end of the first section  228 A in a substantially perpendicular manner. A cross bar  230  extends between and is fixed to the second sections  228 B of the rods  228 . Two through holes  232  are defined in the cross bar  230 .  
         [0047]    The electrical wheelchair  200  comprises an anti-turnover mechanism (not labeled) comprising a frame  234  arranged on the rear side of the chassis  212  and received between the rods  228 . The frame  234  comprises two side walls  238  connected together by a plate  236  straddling the side walls  238 . First apertures  240  are respectively defined in the side walls  238  and aligned with each other. The first sections  228 A of the rods  228  define through holes  242  corresponding to the first apertures  240 . A shaft  244  extends through both the holes  242  and the first apertures  240  for pivotally mounting the frame  234  to the chassis  212 .  
         [0048]    The side walls  238  of the frame  234  define aligned second apertures  246  with a shaft  248  extending therethrough. The shaft  248  has opposite ends (not labeled) extending beyond the side walls  238 . Two rear casters  250  are respectively mounted to the ends of the shaft  248 . The casters  250  serve to prevent the wheelchair  200  from turnover. A collar  252  that is fit over the shaft  248  is provided between each rear caster  250  and the corresponding side wall  238  to reduce wearing and abrasion therebetween and to control distance between the rear casters  250 .  
         [0049]    The anti-turnover mechanism further comprises two resilient members  254  which, similar to those of the first embodiment, are helical springs arranged between the frame  234  and the cross bar  230 . The resiliency of the resilient members  254  supports the relative position between the frame  234  and the chassis  212  while allowing the relative position to be changed by deforming the resilient members  254  so as to change the relative position of the rear casters  250  with respect to the chassis  212 .  
         [0050]    The springs  254  are mounted to the frame  234  and the cross bar  230  in any suitable manner. For example, each spring  254  encompasses a rod  256 , which has first and second ends (not labeled). A transversely-extending tube (not labeled) is formed on the second end of the rod  256  with a hole  262  defined therein and coextensive therewith for the extension of the shaft  248 . A slot  264  is defined in the plate  236  for the extension of the second end of the rod  256 .  
         [0051]    The anti-turnover mechanism of the electrical wheel  200  further comprises an adjusting plate  276  in which two holes  278  are defined. The first ends of the rods  256  extend through the holes  278  and further extend through the holes  232  of the cross bar  230 . The first end of each rod  256  is fixed to the cross bar  230  by a pin  260 . The resilient members  254  are positioned between the adjusting plate  276  and the frame  234  for retaining the relative position of the frame  234  with respect to the chassis  212  while allowing relative rotation of the frame  234  with respect to the chassis  212 .  
         [0052]    The cross bar  230  further defines an inner-threaded hole  280  engaging a bolt  282 . The bolt  282  has an expanded end portion  284  physically engaging the adjusting plate  276  whereby rotating the bolt  282  changes the distance between the adjusting plate  276  and the frame  234  which in turn changes the amount of deformation of the resilient members  254 . Thus, the resilient members  254  are selectively pre-loaded. The adjusting plate  276  also provides means for compensating fatigue of the resilient members  254 .  
         [0053]    A collar  266  that is fit over the shaft  248  is arranged between the tubes of the rods  256  for reducing wearing and abrasion between the tubes. It is understood that the collar  266  is not absolutely necessary in exercising the present invention.  
         [0054]    The operation of the electrical wheel  200  is substantially identical to that of the electrical wheels  100  and  100 ′. Thus, further description is not needed herein.  
         [0055]    Referring to FIG. 11, an electrical wheelchair constructed in accordance with a fourth embodiment is shown and is designated with reference numeral  200 ′. The electrical wheelchair  200 ′ of the fourth embodiment is similar to the electrical wheelchair  200  of the third embodiment with a modification made to the frame of the anti-turnover mechanism. The frame of the electrical wheelchair  200 ′ of the fourth embodiment is generally designated with reference numeral  290  in the drawings, comprising a rectangular member  292  having opposite side walls  294  connected to each other by opposite end walls (not labeled). First and second apertures  296 ,  298  are defined in the side walls  294  for the extension of the shaft  244 ,  248 , respectively. The remaining parts of the electrical wheelchair  200 ′ of the fourth embodiment are substantially identical to those of the electrical wheelchair  200  of the third embodiment and bear with the same reference numerals. Thus, no further discussion is needed herein.  
         [0056]    Referring to FIGS. 12 and 13, an electrical wheelchair constructed in accordance with a fifth embodiment of the present invention, generally designated with reference numeral  300 , is shown. The electrical wheelchair  300  comprises a chassis  312  on which a seat  314  is mounted to support a person (not shown) sitting on the wheelchair  300 . Two wheels  316  are mounted on opposite sides of the chassis  312  and are driven by electrical driving means  318  for moving the wheelchair  300  forward and/or backward. Similar to the embodiments discussed previously with reference to FIGS.  1 - 11 , the electrical driving means  318  can be any means suitable for driving the wheelchair  300 , such as an electrical motor. The motor  318  is fixed in the chassis  312  and is controlled by a control unit  320  that is located in front of the seat  314  for ready access by the person sitting on the wheelchair  300 . Two front casters  322  are mounted to a front side of the chassis  312  for smooth movement of the wheelchair  300  and for controlling moving direction thereof.  
         [0057]    Two spaced, L-shaped rods  328  extend from a rear side of the chassis  312 . Each rod  328  comprises a first, horizontal section  328 A extending from the chassis  322  and a second, vertical section  328 B extending from an end of the first section  328 A in a substantially perpendicular manner. A cross bar  330  extends between and is fixed to the second sections  328 B of the rods  328 . A through hole  332  is defined in the cross bar  330 .  
         [0058]    The electrical wheelchair  300  comprises an anti-turnover mechanism (not labeled) comprising a frame  334  arranged on the rear side of the chassis  312  and received between the rods  328 . The frame  334  comprises two side walls  338  connected together by a plate  336  straddling the side walls  338 . First apertures  340  are respectively defined in the side walls  338  and aligned with each other. The first sections  328 A of the rods  328  define through holes  342  corresponding to the first apertures  340 . A shaft  344  extends through both the holes  342  and the first apertures  340  for pivotally mounting the frame  334  to the chassis  312 .  
         [0059]    The side walls  338  of the frame  334  define aligned second apertures  346  with a shaft  348  extending therethrough. The shaft  348  has opposite ends (not labeled) extending beyond the side walls  338 . Two rear casters  350  are respectively mounted to the ends of the shaft  348 . The casters  350  serve to prevent the wheelchair  300  from turnover. A collar  352  that is fit over the shaft  348  is provided between each rear caster  350  and the corresponding side wall  338  to reduce wearing and abrasion therebetween and to control distance between the rear casters  350 .  
         [0060]    The anti-turnover mechanism further comprises a resilient member  354  which, similar to the counterpart of the previously-discussed embodiments, is a helical spring arranged between the frame  334  and the cross bar  330 . The resiliency of the resilient member  354  supports the relative position between the frame  334  and the chassis  312  while allowing the relative position to be changed by deforming the resilient member  354  so as to change the relative position of the rear casters  350  with respect to the chassis  312 .  
         [0061]    The spring  354  is mounted to the frame  334  and the cross bar  330  in any suitable manner. For example, the spring  354  encompasses a rod  356  which has first and second ends (not labeled). A transversely-extending tube (not labeled) is formed on the second end of the rod  356  with a hole  362  defined therein and coextensive therewith for the extension of the shaft  348 . A slot  364  is defined in the plate  236  for the extension of the second end of the rod  356 . The first end of the rod  356  extends through the hole  332  of the cross bar  330  and is fixed to the cross bar  330  by a pin  360 .  
         [0062]    A collar  366  that is fit over the shaft  348  is arranged between the tube of the rod  356  and each side wall  338  of the frame  334  for reducing wearing and abrasion therebetween. It is understood that the collars  366  are not absolutely necessary in exercising the present invention.  
         [0063]    The operation of the electrical wheel  300  is substantially identical to that of the electrical wheels  100 ,  100 ′,  200  and  200 ′. Thus, further description is not needed herein.  
         [0064]    Referring to FIG. 14, an electrical wheelchair constructed in accordance with a sixth embodiment is shown and is designated with reference numeral  300 ′. The electrical wheelchair  300 ′ of the sixth embodiment is similar to the electrical wheelchair  300  of the fifth embodiment with a modification made to the frame of the anti-turnover mechanism. The frame of the electrical wheelchair  300 ′ of the sixth embodiment is generally designated with reference numeral  390  in the drawings, comprises a rectangular member  392  having opposite side walls  394  connected to each other by opposite end walls (not labeled). First and second apertures  396 ,  398  are defined in the side walls  394  for the extension of the shaft  344 ,  348 , respectively. The remaining parts of the electrical wheelchair  300 ′ of the sixth embodiment are substantially identical to those of the electrical wheelchair  300  of the fifth embodiment and bear with the same reference numerals. Thus, no further discussion is needed herein.  
         [0065]    Although the present invention has been described with reference to the preferred embodiments with reference to the drawings thereof, it is apparent to those skilled in the art that a variety of modifications and changes may be made without departing from the scope of the present invention which is intended to be defined by the appended claims.