Abstract:
A detachable transmission mechanism for a wheel chair includes a control unit, an engaging unit, a battery unit and a transmission device. The original front wheels of the wheel chair can be detached and the hub and the pivot part are mounted to both the upper and lower frames of the wheel chair. The battery unit can be fixed to the wheel chair under the seat thereof. When a control switch is turned on, the driving wheel can rotate in a forward or a reversed direction with the wheel chair being capable of moving forward or backward. By turning the handle, a follower wheel at the bottom of the wheel chair can be rotated to allow the wheel chair making a turn.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a detachable transmission mechanism for a wheel chair and particularly to an electric transmission mechanism used in a wheel chair with which a used wheel chair can be attached by way of DIY (Do It Yourself) so as to become an electric wheel chair. 
     2. Description of Related Art 
     The wheel chair was specially developed for handicapped or slowly moved aged persons and while a user sits in the wheel chair and pushes both lateral large wheels with both hands actuating grip rings coaxially connecting with the large wheels, the movement of the wheel chair can be obtained purposely. A weak person or a hand-hindered person resulting from illness or wound usually is unable to exert a force to the large wheels so that it is necessary to ask some other persons for gripping the handles at rear side of the wheel chair before the wheel chair can be moved. Hence, the conventional wheel chair has to be assisted by the user himself or any other person in order to meet the basic requirement of movement. 
     Accordingly, the so called electric wheel chair has been developed and the feature of the electric wheel chair is a transmission mechanism is provided under a “h” shaped seat, that is, one of two rear wheels is designed as the driving wheel and the other one rear wheel is the follower wheel so as to constitute a basis of moving forward. Two front wheels are controlled by a stir stem located at the armrests being shifted to front, rear, left or right so that the wheel chair can move toward a direction desired by the user. Although the conventional wheel chair has a good and easily operated control device, there still are following deficiencies: 1) the transmission mechanism of the electric wheel chair has to be driven with the electric power and it becomes unmoved in case of the electric power is depleted and the basic function of manual drive has lost; 2) In order to obtain the effect of speed differential (that is, the inner side rear wheel has a less rotational speed than the outer side rear wheel) for the two rear wheels and to avoid turning over or a risk of being unable to turn during the wheel chair making a turn, a sophisticate speed change box has to be mounted between the two rear wheels so that it increases the complicity of the transmission mechanism of the wheel chair; and 3) due to both the body and the transmission mechanism of the conventional electric wheel chair being made with complication, the production cost thereof is pretty high so that the retail price thereof is much more expensive and is not possible to become prevalent among handicapped and motion hindered persons. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provided a detachable transmission mechanism for a wheel chair. The detachable transmission mechanism includes a control unit, an engaging unit, a battery unit and a transmission device. The original front wheels of the wheel chair can be detached and the hub and the pivot part are mounted to both the upper and lower frames of the wheel chair. The battery unit can be fixed to the wheel chair under the seat thereof. When a control switch is turned on, the driving wheel can rotate in a forward or a reversed direction with the wheel chair being capable of moving forward or backward. By turning the handle, a follower wheel at the bottom of the wheel chair can be rotated to allow the wheel chair making a turn. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention can be more fully understood by reference to the following description and accompanying drawings, in which: 
     FIG. 1 is an exploded perspective view of a detachable transmission mechanism for a wheel chair according to the present invention; 
     FIG. 2 is an exploded perspective view of a manual control device and a driving device according to the present invention; 
     FIG. 3 is a perspective view illustrating the transmission mechanism of the present invention being ready to be assembled to a wheel chair; and 
     FIGS. 4A and 4B are assembled perspective view of the transmission mechanism and the wheel chair shown in FIG. 3 with two different projection angles. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1 through 4A and  4 B, the detachable transmission mechanism for a wheel chair consists of a control unit  1 , an engaging unit  2 , a battery unit  3  and a transmission device  4 . 
     Wherein, the control unit  1  is mainly to provide the entire transmission device  4  the ability to move and turn with a vertical shaft  11  at the top thereof engaging with a handle  12  being held and operated by a user and at the bottom thereof being connected to the engaging unit  2 . The vertical shaft  11  passes through a fixed hub  13  on the frame of the wheel chair so that the vertical shaft is able to rotate. The hub  13  consists of a sleeve  131  contained inside a U-clip  132  and at least one screw  133  can pass through the U-clip  132  and tightened with a nut  134  so that the U-clip  132  can be associated with the screw  133  firmly. A pivot lever  135  is extended from the bottom of the U-clip  132  to be connected to the wheel chair frame. By using a screw  137  passing through a pressing piece  136  and then fixing onto the pivot lever  135 , the frame can be enclosed and held at one lateral side of the wheel chair. 
     Nevertheless, to accommodate body types of different users, the vertical shaft  11  has a function of being adjustably lifted or descended. A plurality of positioning holes  112  are lined up on an outer pipe  111  and the lower part of the outer pipe  111  fits with an inner pipe  113 , which has a button hole  114  at the opening thereof is disposed corresponding to the positioning holes  112 . And a V-shaped elastic strip  115 , inserted into the opening of the inner pipe, has an abrupt button  116  extends outward laterally from the button hole  114  and engages with one of the positioning holes  112  selectively so as to lift the outer pipe  111 . Moreover, a fastener  14  is provided at the joint between the outer pipe  111  and the handle  12  and also the joint between the outer pipe  111  and the inner pipe  113  respectively. By stirring an engaging stem  141  and relatively turning a nut  142 , a loose/tightness effect on a pipe clamp  143  and thus the handle  12  can be adjusted to a suitable angle and provides better comfort during operating the transmission mechanism. Furthermore, a tight fit between the outer pipe  111  and the inner pipe  113  can be obtained instead of becoming loose and disconnected from each other easily. 
     The engaging unit  2  consists of a connecting frame  21  and a fixing base  22 . The connecting frame  21  has a F shape and there are two limit plates  211 ,  212  extending outward from a lateral side thereof with an axial hole  213 ,  214  on each of the limit plates. An axial rod  117  extends downward from the bottom of the inner pipe  113  to pass through the axial holes  213 ,  214 . Furthermore, a joining plate  118  extends laterally from the bottom of the inner pipe  113  and is attached to and fastened to the limit plate  211  with a screw and a nut such that the vertical shaft  11  is supported on top of the connecting frame and thus form a relative movement with the connecting frame. The bottom of the connecting frame  21  has an inversed U-shaped joining part  215 , which is connected to the output unit  42  of the transmission device  4  by a screw rod. 
     The fixing base  22  is disposed between the two limit plates  211 ,  212  and provided with a fitting ring  221  corresponding to the two axial holes  213 ,  214 . A central bore  222  of the fitting ring  221  receives a sleeve  23  and the sleeve  23  is attached with an engaging plate  231  such that the engaging plate and the ring plate  223  can be joined to each other firmly. The sleeve  23  at the upper and the lower end thereof is inserted with a bearing  232  respectively and the axial rod  117  can pass through the bearings  232  for being able to rotate with facility. The axial rod  117  further passes through a washer  233 , a spring  234  and the lower limit plate  212  and then fastened to a connecting piece  235  so as to form a shock absorption system and accommodate to the rugged and rough road surface. In order to join the fixing base  22  to the wheel chair firmly, it is possible to provide a pivotal part, for instance, a base lever  224  and a support  225  extending in a way of being perpendicular to each other but disposed in different levels such that the base lever  224  and the support  225  can be joined to two perpendicular frames underneath the wheel chair respectively. Furthermore, by making use of two urging plates  226  being passed through by a screw  227  and engaging with the base lever  224  and support  225  respectively, the frames can be clamp commonly and the fixing base  22  can be fixed to a lateral side of the wheel chair at the lower part thereof. 
     Further, in order to fix the battery unit  3  in position, please refer to FIG. 3 again. A battery  32  shown is received in a case  31  and the bottom of the case  31  is attached with a lever cap  33  for the support lever passing through. By pressing the knob  34  tightly onto the support lever  225 , this will make the battery unit  3  fixed under the seat of the wheel chair and the contact poles  35  thereof provide the power needed by the transmission device  4 . 
     The transmission device  4  consists of a motor  41 , an output unit  42  and a driving wheel  43 . Wherein, the output unit  42  can be a turbine reducer, a pulley or a gear in practice. Referring to FIG. 2 again, when the motor  41  starts to run, it will make the output shaft  421 , which extends from the output unit  42  laterally to turn in the forward or revered direction according to the operation of a user. Thus, the driving wheel  43 , which is connected to the output shaft, can move forward or backward. The characteristic of the present invention is that the driving wheel  43  is connected with a manual control device  44 , that is, a shaft hole  431  in the driving wheel  43  is inserted with a respective bearing  432  at both ends thereof and an outer flange surrounding the shaft hole  431  provides at least two engaging holes  433 . An engaging groove  422  is provided on the output shaft  421  and extends longitudinally to pass over the two bearings  432  and a follower plate  441 . The follower plate  441  is provided with an engaging bolt  442  and a through hole  443  corresponding to the engaging groove  422  and the engaging hole  433  so that the follower plate  441  can rotate synchronously with the driving wheel  43 . An engaging plate  444  is attached to the outer wall of the follower plate  441 . The engaging plate  444  is pierced with a relay pipe  446  and has an engaging projection  445  corresponding one of the engaging holes  433  so that the engaging projection  445  can pass though and fit with the engaging hole  433  and the engaging plate  444  can rotate with the driving wheel  43 . Furthermore, on the other side of the engaging plate  444 , a spring  447  and a washer  448  are placed one after another for a fixing bolt  449  passing through and being fastened to the output shaft  421 . When the battery  32  in the battery unit  3  is depleted, the driving wheel  43  will not be able to turn. At this moment, the only thing has to be done by the user is to hold and then pull the engaging plate  444  outward along the relay pipe  446 . Under this circumstance, the spring  447  is compressed and the engaging projection  445  is free from both the engaging hole  433  and through hole  443  so that the engaging plate  444  is unable to rotate with the driving wheel  43  and the driving wheel is therefore in a state of no traction. Hence, the user can push the grip ring of the wheel and make the two large wheels at the two lateral sides of the wheel chair to rotate and move forward and the driving wheel  43  is in a state of idling and acts as a driven wheel. 
     Referring to FIGS. 3,  4 A and  4 B again, the detachable transmission mechanism of this invention has been built up as a master structure and a power supply part by way of modularized design. Thus, in case of the detachable transmission mechanism of the present invention being assembled with an existing wheel chair, a small wheel at the front lateral side of the wheel chair has to be removed first and then the pivot lever  135 , base lever  224  and support lever  225  are respectively attached to the upper and lower frame of the wheel chair. Next, both the pressing piece  136  and the urging plate  226  is used for enclosing and holding the frame such that the master structure can be fixed to a lateral side of the wheel chair. After that, the battery unit  3  and the support lever  225  are joined to each other so as to locate the power supply part in position before the assembly job is completed. Hence, once the control switch on the handle  12  is operated, the driving wheel  43  can move forward or backward. In case of making a turn, the user just has to hold and rotate the handle  12  and the driving wheel  43  can turn to another direction extremely conveniently. 
     It is appreciated that the effectiveness of the present invention resides in the transmission mechanism can be associated with an existing wheel chair used in ordinary families, hospitals, nursing home or rehabilitation center and it is not necessary to acquire an expensive electric wheel chair. Moreover, when the power of the battery unit is consumed, adjusting the manual device with hands will make the driving wheel not able to be actuated by the engaging plate and become in a state of idling. The wheel chair is then changed to the manual control and can move by pushing with hands. Furthermore, the present invention does not need complicated design of speed change box and wheel chair frame so that the production cost can be greatly reduced and the goal for popularity and low cost can be reached advantageously and it is impossible for the conventional electrical wheel chair can achieve effectively. Furthermore, the vertical shaft and the handle can be adjusted to lift and turn to accommodate for the build types of different users so that the user can obtain utmost comfort due to human engineering consideration in the present invention. 
     While the invention has been described with reference to the a preferred embodiment thereof, it is to be understood that modifications or variations may be easily made without departing from the spirit of this invention, which is defined by the appended claims.