Abstract:
A clutch mechanism for coupling and uncoupling an electric motor and leadscrew has dog-clutch gears that can be engaged by a linear actuator, bell crank, and linkage shaft. Uncoupling force due to narrowed dog teeth are resisted by the alignment of the linkage shaft with the central portion of the bell crank.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/069,953, filed Oct. 29, 2014, which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Field of the Invention 
         [0003]    This patent is directed to a clutch mechanism between a leadscrew and an electric motor for driving the leadscrew. It is particularly useful for enabling the manual opening of sliding plug doors on a public transit vehicle, such as a passenger bus. Such sliding doors are driven to open and close by alternate rotation of the leadscrew. 
         [0004]    Description of Related Art 
         [0005]    Sliding plug doors for transit vehicles are described in detail in U.S. Pat. No. 6,032,416 entitled “Transit Vehicle Door” assigned to the same assignee as the present invention. 
         [0006]    As can be understood from the above-referenced prior art patent, outside sliding plug doors on a transit vehicle are actuated by use of an electric motor coupled to a leadscrew and nut drive usually through a gearbox. The leadscrew and nut drive a door carriage mounted on a linear slide. The disadvantage of this system is that when the doors need to be opened manually, such as in an emergency, the motor and gearbox are not decoupled from the leadscrew. Therefore, the door or doors can only be back driven while forcing turning of the leadscrew. This requires a strong manually applied force. 
         [0007]    It is an advantage according to this invention to provide a clutching mechanism inserted between the output of the electric motor and gearbox and the leadscrew facilitating the emergency manual opening of the sliding doors. 
       SUMMARY OF THE INVENTION 
       [0008]    Briefly according to this invention, a clutch mechanism between the rotatable output shaft of an electric motor fixed to a base and a leadscrew rotatably journaled to the base comprises a leadscrew gear, a drive gear mounted to rotate with the output shaft of the electric motor, axially slidable dog-clutch gear directly or indirectly driving the leadscrew, said axially slidable dog-clutch gear having a plurality of dog teeth axially extending away from the leadscrew and circumferentially spaced on the face of the axially slidable dog-clutch gear, said face being perpendicular to the rotating axis of the gear, said axially slidable dog-clutch gear having gear teeth on the circumference for engaging the gear teeth on the leadscrew gear, a axially fixed dog-clutch gear for engaging or disengaging the slidable dog-clutch gear, said fixed dog-clutch gear having a plurality of dog teeth axially extending toward the leadscrew and circumferentially spaced on the face of the fixed dog-clutch gear, said face being perpendicular to the rotating axis of the gear, said fixed dog-clutch having gear teeth on the circumference for engaging the gear teeth on the drive gear, a bell crank being rotatably mounted to the base, said bell crank having extensions in at least two radial directions, a linear actuator having a shaft extending from a first end thereof, said linear actuator being pivotally mounted to the base at the other end, said linear actuator having a biasing means for extending the shaft when not powered, the shaft of the linear actuator being pivotally connected to an extension of the bell crank, and a linkage shaft pivotally connected at one end to an extension of the bell crank and connected via a universal joint connection at the other end to the slidable dog-clutch. When the linear actuator is unpowered, the linkage shaft due to the biasing means in the linear actuator forces the disengagement of dog teeth on the dog-clutch gears enabling the emergency manual opening of the sliding doors. 
         [0009]    Preferably, the dog teeth on the dog-clutch gears have planar contact faces that taper radially toward the axis and also in the direction of the axis, the dog teeth thus narrowing moving away from the face of the dog-clutch gears to facilitate disengagement. 
         [0010]    Preferably, the linkage shaft and the linear actuator shaft are pivotally connected to the bell crank angularly spaced more than 90 degrees and less than 180 degrees such that at one stop position when the dog-gears are coupled, the axis of the linkage shaft passes centrally through the bell crank, and in a second position when the dog-gears are uncoupled, the axis of the linkage shaft pass through an outer edge of the bell crank. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Further features and other objects and advantages will become clear from the following detailed description made with references to the drawings in which: 
           [0012]      FIG. 1  shows a pair of bi-parting doors in a wall of a transit vehicle according to the prior art with a direct connection between the electric motor and the leadscrew; 
           [0013]      FIG. 2  shows, for a single door, a motor, leadscrew, support rod and hangers, door hangers and lock assembly according to the prior art with a direct connection between the electric motor and the leadscrew; 
           [0014]      FIG. 3  is a perspective view of gears comprising the clutch mechanism between the leadscrew and electric motor according to this invention; 
           [0015]      FIG. 4  is a view showing the entire clutch mechanism according to this invention including the linear actuator, bell crank, and linkage shaft in the coupled position; and 
           [0016]      FIG. 5  is a view showing the entire clutch mechanism according to this invention in the uncoupled position. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0017]      FIG. 1  shows, by way of background, a transit vehicle door system, generally designated  10 , for covering and uncovering an aperture  12  for ingress and egress of passengers in a wall  14  of a transit vehicle  16 . The door system  10  has a first door  20  mounted for movement in a first door closing direction  22  to a first door closed position at least partially covering aperture  12  and for movement in a first door opening direction  26  to a first door open position at least partially uncovering aperture  12 , the first door opening direction  26  being opposite to the first door closing direction  22 . 
         [0018]      FIGS. 1 and 2 , by way of background, show door  20  suspended from a rod  40  by sliding connections  42  on a first door outer hanger  44  and a first door inner hanger  46 , rod  40  being oriented about in a longitudinal direction of the transit vehicle  16 . Rod  40  is suspended from a rod hanger  48 . Contacting surfaces of rod  40  and sliding connections  42  of door hangers  44  and  46  should be smooth and preferably include low friction materials. 
         [0019]    Door system  10  also has a second door  30  connected to a drive leadscrew  60  for longitudinal movement opposite to the first door  20 , the second door  30  moving in a second door closing direction  32  to a second door closed position at least partially covering aperture  12  when first door  20  moves in the first door closing direction  22 , and second door  30  moving in a second door opening direction  36  to a second door open position at least partially uncovering aperture  12  when first door  20  moves in the first door opening direction  26 . The second door closing direction  32  is generally opposite to the first door closing direction  22  and the second door opening direction  36  is generally opposite to the first door opening direction  26 . Hence, the first door  20  and the second door  30  cooperate to cover and uncover the aperture  12 , as shown in  FIGS. 1 and 2 . A leadscrew  60  includes a nut assembly (not shown) for the first door  20  and a nut assembly (not shown) for the second door  30 . The nut assemblies turning on the leadscrew interconnect with the respective doors to carry the doors to the open or closed positions depending on the rotation direction of the leadscrew driven by an electric motor  66 . 
         [0020]    Referring now to  FIG. 3 , a clutch mechanism  70  is positioned between a rotatable output shaft  68  of the electric motor  66  fixed to a base and the leadscrew  60  rotatably journaled to the base. The base is either the vehicle wall  14  or a structure fixed relative to the vehicle wall. 
         [0021]    A leadscrew gear  71  has a plurality of wide gear teeth  72  spaced on the circumference. The leadscrew gear is mounted to rotate with the leadscrew. 
         [0022]    A drive gear  73  has a plurality of gear teeth  74  spaced on the circumference, said drive gear mounted to rotate with the output shaft  68  of the electric motor  66 . 
         [0023]    An axially fixed dog-clutch gear  75  directly or indirectly drives the leadscrew. The fixed dog-clutch gear  75  has a plurality of dog teeth  76  axially extending away from and circumferentially spaced on the face of the fixed dog-clutch gear. The face is perpendicular to the rotating axis of the gear. The fixed dog-clutch gear  75  has gear teeth  77  on the circumference for engaging the gear teeth  74  on the drive gear  73 . 
         [0024]    An axially sliding dog-clutch gear  78  is secured axially slidable relative to the base for engaging or disengaging the fixed dog-clutch gear  75 . The slidable dog-clutch gear  78  has a plurality of dog teeth  79  axially extending and circumferentially spaced on the face of the slidable dog-clutch gear. The face is perpendicular to the rotating axis of the gear. The slidable dog-clutch  78  has gear teeth  80  on the circumference for engaging the wide gear teeth  72  on the lead screw gear  71 . 
         [0025]    The sliding dog-clutch gear  78  and the fixed dog-clutch gear  75  are attached to a sliding shaft and fixed axle, respectively. They rotate due to bearings affixed between them and the shaft or axle. 
         [0026]    Referring now to  FIGS. 4 and 5 , a bell crank  50  is rotatably mounted to the base. The bell crank has extensions in at least two radial directions. A linear actuator  52  has a shaft  53  extending from a first end of the actuator. The linear actuator  52  is pivotally mounted at an extension  51  to the base at the other end. The linear actuator  52  has a biasing means, for example, a coil spring  53   a,  for extending the shaft  53  out of the actuator when not powered. The actuator shaft  53  is pivotally connected to the extension  51  of the bell crank  50 . The actuator  52  may be powered, for example, by an electrical solenoid. When the actuator is unpowered, the biasing means extends shaft  53 . 
         [0027]    A linkage shaft  54  is pivotally connected at one end to an extension  55  of the bell crank  50  and connected via a universal joint  57  at the other end to the second dog-clutch gear  78 . Thus, when the linear actuator is unpowered, the linkage shaft  54  due to the biasing means in the linear actuator extends the shaft  53  and rotates the bell crank  50  withdrawing the linkage shaft  54  forcing the disengagement of dog teeth on the first dog-clutch gear  75  and the second dog-clutch gear  78  enabling the manual opening of the door. 
         [0028]    According to a preferred embodiment, the dog teeth on the dog-clutch gears have planar contact faces that taper radially toward the axis and also in the direction of the axis. The dog teeth thus narrow moving away from the face of the dog-clutch gears to facilitate disengagement. However, as the dog teeth on both dog-clutch gears meet on a plane inclined to the direction of motion, there exists a small axial force urging separation of the dog-clutch gears. 
         [0029]    According to another preferred embodiment, the linkage shaft  54  and the linear actuator shaft  53  are pivotally connected to the bell crank  50  angularly spaced more than 90 degrees and less than 180 degrees about the axis of the bell crank  50  such that at one stop position as shown in  FIG. 4  when the dog-gears are coupled, the axis of the linkage shaft  54  passes centrally through the bell crank  50 . In a second position when the dog-gears are uncoupled, as shown in  FIG. 5 , the axis of the linkage shaft  54  passes near an outer edge of the bell crank  50 . The bell crank has a third extension  56  engaging a stop fixed to the base when the bell crank  50  has rotated to the coupled position. 
         [0030]    In the coupled position, an uncoupling force transmitted through the linkage shaft  54  thus can apply a very small, if any, moment force to rotate the bell crank  50 . On the other hand, in the coupled position, the moment force exerted though the actuator shaft  53  to resist uncoupling is maximum. 
         [0031]    Having thus described our invention with the detail and particularity required by the Patent Laws, what is desired protected by Letters Patent is set forth in the following claims.