Joint apparatus of speedometer shaft
BACKGROUND OF THE INVENTION 
     The present invention relates to joint apparatus for a speedometer shaft, specially concerning a joint apparatus providing easy and convenient fitting or repairing of the shaft of a speedometer. 
     Generally, the speedometer shaft is rotated by a cable wire and has a magnet at the top of the shaft. The magnet generates a magnetic flux and is thus inductively coupled with an aluminum cup to provide the electro-force needed to drive the indicator of the speedometer. The speedometer is connected to the speedomoter cable wire by a connection housing underneath the vehicle. The said shaft usually has two bearings to support its rotating and to avoid slipping. Conventionally, one of the two shaft bearings is entirely sealed which will cause problems. For example, the manufacturer needs to use heavy machines to rivet it and the process is complex and costly. Furthermore, it is very difficult to remove the bearing for repairing it. When the speedometer is out of order, the only way to remove the bearing is to destroy it, which will damage other parts. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a joint apparatus which utilizes a plastic material and expands to mount on the rotating shaft easily and rapidly. Besides, the joint element edge provides notches for convenient replacing and mounting. 
     Another object of the present invention is to provide a joint apparatus which offers easy operation and efficient function to avoid conventional defects of the riveted bearings described above. 
     In accordance with this invention, joint apparatus for a speedometer shaft having a connection housing on the base of a speedometer for fixing the cable wire to the speedometer case, said connection housing having an axial aperture to permit the spindle shaft to pass therethrough, the one end of the spindle shaft being a worm gear, and the initial thread of said worm gear having a smooth annular surface to support the said shaft for rotation on the base. The lower part of the axial aperture of the connection housing has a receptacle portion, and the terminal end of spindle shaft has circular tapered recess, which extends beyond the receptacle portion, allows the joint element to be fitted thereto, in the inner wall of the joint element provides a tapered convex edge corresponding to the said circular tapered recess and in the rim wall of the said joint element there are notches, when the joint element joins the shaft the convex edge will mate with the circular tapered recess completely to prevent the joint element from dropping out. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial perspective drawing of a speedometer; 
     FIG. 2 is a sectional drawing taken from A--A direction of FIG. 1; 
     FIG. 3 is a perspective drawing for illustrating the working of the joint apparatus; 
     FIG. 4 is an enlarged drawing of the apparatus in FIG. 3. 
    
    
     DETAILED DESCRIPTION 
     Referring now to FIGS. 1 and 2, a speedometer 1 includes a spindle shaft 3 driven by the cable wire 2 connected to the transmission element (not shown) at top of spindle shaft 3 is a magnet 4. The magnet generates a magnetic flux that couples an aluminum drag cup 5 thereby providing the force needed to move the indicator 6 through an angular displacement as a function of the rotation of the spindle shaft. On the base of speedometer 1 is a connection housing 7 for fixing the cable wire 2 to the speedometer case 11. 
     The afore-mentioned connection housing 7 has an axial aperture 71 to permit the spindle shaft 3 to pass therethrough. At the lower end of the spindle shaft 3, near the magnet 4, is a worm gear 30 which meshes with the driving rod 8 to move the speed register 9. (The contact of the shaft with the rod 8 at the worm gear 30 is not shown). 
     In FIG. 3, the initial thread 301 of the worm gear 30 has a smooth bottom circumference 302. When spindle shaft 3 is inserted through the axial aperture 71, the smooth bottom circumference 302 is held steadily against the rim on the upper end of axial aperture 71 by a joint element 32, enabling the spindle shaft 3 to rotate within the axial aperture 71. Thus, the spindle shaft 3 can only be removed from from the top of the connection housing. 
     The said connection housing 7 which axial aperture 71 has a receptacle portion 72 at its lower part as shown in FIG. 4. The length of the spindle shaft 3 is long enough so that its terminal end extends beyond said receptacle portion 72. 
     The terminal end 31 of the spindle shaft 3 provides a circular tapered recess 311, which is slanting from the shaft rim 312 inward toward the axial center 313 forming a difference Grade x, then extending outwardly and forming a disc 314 on which joint element 32 is installed. 
     The inner wall of said joint element 32 has a tapered edge 33 corresponded to the said circular tapered recess 311. Said convex edge 33 slopes from inner rim of the joint element 32 toward aperture 332, providing a difference grade which corresponds to grade x. That is, when the joint element 32 is attached to the spindle shaft 3, the convex edge 33 will just fit into the circular tapered recess 31 totally to prevent the joint element 32 from dropping out. 
     As shown in FIG. 3, in the rim wall of the joint element 32 has three equal pitch notches 341. When the joint element 32 joints into the shaft 3, the notches will expand outwards by themselves because of the material elastic characteristic of the joint element 32 used. The notches 341 will recover its normal pitch after the convex edge 33 falls into the recess 311. The bottom of the said joint element 32 has a flange 35, the outer diameter of which is received by the receptacle portion 72 of the axial aperture 71. There are marks 351 adjacent each notch 341 on the bottom of the joint element 32. 
     When the joint element is attached to the recess 311 of the shaft 3, it utilizes the match of the grade of convex edge 33 and grade x of recess 311 to assure proper relation of the spindle shaft 3. In addition, when the gearing part of spindle shaft 3 and connection housing 7 or magnet 4 and the parts of spindle shaft 3 breakdown, it is easy and convenient to repair those damaged parts by cutting the joint element 32 apart at the marks 351 on the bottom the joint element 32, then removing the spindle shaft 3. The spindle shaft 3 can then be removed from top of axial aperture 71 easily and won&#39;t destroy other parts of the apparatus.