Patent Publication Number: US-5298699-A

Title: Rotor for an ignition distributor

Description:
This invention relates to a rotor for an ignition distributor and to a means for securing the rotor to the shaft of an ignition distributor. 
     The rotor of an ignition distributor transfers high voltage from the center electrode of a distributor cap to the outer circumferentially spaced cap inserts that are connected to the spark plugs of an internal combustion engine. The rotor is secured to and driven by the ignition distributor drive shaft and a secure connection must be made between the rotor and the drive shaft Thus, the rotor position is critical for correct firing of the spark plugs. If the rotor works loose from the shaft, spark scatter and crossfiring to an incorrect spark plug can occur. If the rotor vibrates up the shaft, scraping between the distributor cap and the rotor can cause premature failure. 
     It is an object of this invention to provide a secure connection between the rotor and drive shaft of an ignition distributor that does not require fasteners such as screws and does not require fasteners such as metal spring clips. In carrying this object forward, the distributor shaft is provided with an annular groove and with an axially extending slot. The rotor is formed of a molded plastic material. The rotor has a plurality of flexible latch arms the ends of which having latching teeth. When the rotor is pushed onto the end of the shaft, the latch arms are deflected outwardly and when the rotor has been moved to its final assembled position, the latch arm teeth move inwardly into the annular groove on the shaft to lock the rotor from axial movement relative to the shaft. The rotor further has a wall that has an undulated configuration that is defined by circumferentially spaced undulated portions. One of the undulated portions forms a rib that slides into the axial extending slot on the shaft when the rotor is assembled to the shaft to thereby lock the rotor from rotation relative to the shaft and to form a driving connection between the shaft and the rotor. The undulated wall has circumferentially spaced areas that tightly engage the shaft. The undulated wall may be termed a spring wall since it is displaced radially outwardly and develops a spring-like force when the rotor is assembled to the shaft to tightly grip the shaft. 
    
    
     IN THE DRAWINGS: 
     FIG. 1 is a sectional view of an ignition distributor rotor connected to an ignition distributor drive shaft. 
     FIG. 2 is a sectional view taken along line 2--2 of FIG. 1. 
     FIG. 3 is a sectional view of a modified distributor rotor shown connected to a distributor drive shaft. 
    
    
     Referring now to the drawings, the reference numeral 10 designates a metallic drive shaft of an ignition distributor. The shaft 10 has an annular groove 12 and an axially and radially extending slot 14. 
     A rotor generally designated as 16 is shown connected to distributor drive shaft 10. The rotor 16 has a rotor contact supporting portion 18 that carries a metallic rotor contact 20. The rotor 16 further has a lower retaining portion 22 that is used to secure the rotor to the shaft. Portions 18 and 22 are formed of electrical insulating material and can be formed as a one-piece plastic molding from, for example, a polyester plastic molding material. 
     The rotor portion 22 has a continuous axially extending wall designated in its entirety as 24 that extends from portion 18 of the rotor. This wall, as can be seen in FIG. 2, has an undulated or wave-like shape. The wall 24 has undulations 28, 30, 32, 34, 36, 38 and 40 that are U-shaped. The wall 24 further has six circumferentially spaced wall portions each designated as 41. The wall portions 41 connect the undulated wall portions. Each wall portion 41 has an internal arcuate surface 42. The surfaces 42 are in tight engagement with outer arcuate surface portions of the outer cylindrical surface of shaft 10. 
     The rotor has three circumferentially spaced, flexible and resilient latch arms each designated as 44. The latch arms 44 are integral with the portion 18 of the rotor and extend axially therefrom. Each latch arm 44 has a tooth portion 46 that is provided with a surface 48 that engages an annular shoulder or surface 50 that defines the top end of groove 12. When the rotor is pushed onto the shaft, the latch arms 44 extend respectively through undulated portions 28, 32 and 36. 
     It can be seen from FIG. 2 that the undulated portion 40 of wall 24 is located in slot 14. Certain outer surface portions of undulated portion 40 tightly engage inner surfaces portions defining slot 14. The undulated portion 40 can be characterized as a rib that prevents rotation of the rotor relative to the shaft and which forms a driving connection between the shaft and the rotor. 
     The rotor has an internal surface 52 that engages the flat end surface 54 of shaft 10 when the rotor is assembled to the end of shaft 10. The surface 52 can be provided on a radially extending rib. 
     The manner in which the rotor 16 is assembled to the end of shaft 10 will now be described. To assemble the rotor to the shaft the undulated portion or rib 40 is aligned with the slot 14 in shaft 10 and the rotor is then pressed onto the shaft. The undulation or rib 40 has a press-fit with the internal walls of slot 14 so that the walls of undulation 40 tightly engage the walls of slot 14. 
     The outer diameter of shaft 10 is slightly larger than the distance between opposed surfaces 42 on wall 24. Consequently, as the rotor is pressed onto the shaft, portions of wall 24 are deflected or displaced radially outwardly. More specifically, as the rotor is pressed onto the shaft, side wall portions of the undulated portions are deflected away from each other. Using undulated portion 34 as an example of what has just been stated, the side wall portions 34A and 34B will be deflected or moved away from each other as the rotor is pressed onto the shaft. As a result of this, the side walls of the undulated portions tend to develop a spring-like force which tends to force the surfaces 42 into tight engagement with outer surface portions of shaft 10. Further, outer surface portions of side walls 40A and 40B of undulated portion 40 are forced into tight engagement with wall surfaces of slot 14. The spring characteristic of wall 24 therefore causes surfaces 42 to tightly engage outer surface portions of shaft 10. This prevents cocking of the rotor relative to the shaft. 
     As the rotor is pressed onto the shaft, the three flexible latch arms 44 deflect outwardly and the rib or undulated portion 40 tightens against the walls of slot 14. When the surface 52 on the rotor engages the end surface 54 of shaft 10, the latch arms 44 move inwardly due to their resilience causing teeth 46 to enter groove 12 with the tooth surfaces 48 tightly engaging shoulder or surface 50. The latch arms 44 in the latched position prevent the rotor from moving axially relative to shaft 10. Further, the rotor cannot rotate relative to the shaft because of the tight fit between undulation or rib 40 and the walls of slot 14. 
     Referring now to FIG. 3, a modified rotor is illustrated that is formed of two plastic parts that are ultrasonically welded together. In FIG. 3, the same reference numerals have been used as were used in FIG. 1 to identify corresponding parts. 
     In FIG. 3, a plastic part 60 is provided that carries the rotor contact 20. The part 60 is a plastic molded part that can be formed by using a mica-glass filled polyester material that has adequate dielectric properties. 
     The part 60 is secured to a molded retainer part 62 by an ultrasonic annular weld joint 64. The part 62 is formed of a non-glass filled plastic polyester material to maintain flexibility for the latches 44 and wall 24. In this regard, it should be pointed out that the part 62 shown in FIG. 3 does have latches 44 and a wall 24 which are identical to the latches 44 and wall 24 shown in FIGS. 1 and 2. Because of this, only a portion of the latches 44 and wall 24 have been shown in FIG. 3. Further, in regard to FIG. 3, it is to be understood that shaft 10 has a groove, like annular groove 12. 
     The part 62 has a wall 66. A lower surface 68 of the wall 66 engages the end surface 54 of shaft 10. An air space 70 is defined by surfaces on parts 60 and 62. This air space 70 is connected to atmosphere via one or more ports 72. 
     In the rotor of FIG. 3, the part 60 which carries rotor contact 20 has a higher dielectric strength than the part 62. On the other hand, the material of part 62 is more flexible than the material of part 60. Further, both parts have the same polyester base so they therefore can be ultrasonically welded to form the weld joint 64.