Abstract:
A pinion stopper arrangement for a starter motor comprises a motor output shaft having a circumferential projection and a coaxial pinion shaft rotatably supported on the output shaft. Two shafts are connected by an over-running clutch having a clutch outer member connected to the output shaft by helical splines and a clutch inner member directly connected to the pinion shaft. An elastic stopper ring is snap fitted between the clutch outer member and the circumferential projection on the output shaft, so that the elastic stopper ring, in cooperation with the circumferential projection on said output shaft, restricts the axial movement of the over-running clutch and the pinion gear relative to the output shaft.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a pinion stopper arrangement for a starter motor which enables to shorten the axial length of the rotary output shaft and to have a stopper with a simple structure. 
     FIG. 1 is a sectional view of a conventional pinion stopper arrangement for a starter motor disclosed in Japanese Utility Model Laid-Open No. 55-53727, and FIG. 2 is a sectional view taken along line II-II of FIG. 1. In FIGS. 1 to 4, an output shaft 2 of an armature 1 to be driven by a magnetic field unit has a large-diameter step portion 2A, and helical splines 3 are formed in the outer periphery of the step portion 2A. 
     To the helical splines 3, a spline tube 5 of a pinion mechanism composed of a pinion 4, the spline tube 5, an over-running clutch 6 is thread-engaged so as to be movable in the axial direction. 
     As best seen in FIG. 4, the output shaft 2 of the armature 1 has formed thereon the large-diameter step portion 2A in which the helical splines 3 are formed and a small-diameter escape portion 2B in which an inner helical splines 5A of the spline tube 5 can be rotated. 
     The length L 1  of the escape portion 2B is longer than the length L 2  of the inner helical spline 5A and has a smaller inner diameter than the helical spline 3. 
     Also, as apparent from FIG. 2, the helical spline 3 is formed by providing the step portion 2A with a plurality of first grooves 2C helically extending over the entire axial length of the large-diamter portion 2A and a plurality of second grooves 2D extending parallel to the first grooves 2C but has shorter length. 
     In the intermediate portion of the step portion 2A, an annular groove 17 is formed, in which a clip 19 as shown in FIG. 3 having inwardly bent portions 18 at a pitch substantially equal to that of the inner helical splines 5A of the spline tube 5 is engaged as shown in FIG. 1. 
     As is well known, the starter motor comprises a shift lever 10, a solenoid switch 12, a plunger 13, a torsion spring 14, a gear case 15, a ring gear 16 and a center plate 20. 
     In the structure as above described, the pinion mechanism is first assembled. After the clip 19 is fitted in the annular groove 17 of the step portion 2A of the output shaft 2, the ridge portions of the inner helical spline 5A of the spline tube 5 of the pinion mechanism are correspondingly positioned with respect to the inwardly bent portions 18 and inserted from the side of the ring gear 16 until the inner helical spline 5A is positioned within the reduced-diameter escape portion 2B of the output shaft 2. Then, when the splines are disengaged from each other, two splined members are rotated relative to each other by an angle corresponding to one ridge. 
     This causes the ridge portion of the helical splines 5A to abut against one end of the clip 19, whereby the pinion mechanism cannot be dislodged from the output shaft 2. 
     Since the pinion stopper mechanism of the conventional starter motor is constructed as above described, the output shaft 2 must have the escape portion 2B for allowing the inner helical splines 5A of the spline tube 5 to be rotated therein, making the axial dimension of the output shaft 2 enevitably large. 
     Also, the second shorter grooves 2D for preventing the movement of the inner helical spline 5A of the spline tube 5 must be formed in the output shaft 2 independently of the first groove 2C, making numbers of the manufacturing steps large and difficult. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of this invention is to provide a pinion stopper arrangement for a starter motor free from the above-discussed problems of the conventional stopper arrangement. 
     Another object of the present invention is to provide a pinion stopper arrangement for a starter motor of which axial dimension of the output shaft is reduced. 
     A further object of the present invention is to provide a pinion stopper arrangement for a starter motor which is simple in structure and easy to manufacture. 
     With the above objects in view, the pinion stopper arrangement for a starter motor comprises an elastic stopper ring disposed between a front end surface of a clutch outer member and a vertical rear end surface of a cicumferential projecting portion mounted on an output shaft. The elastic stopper ring is expanded when it is urged against the circumferential projection on the output shaft to pass over the circumferential projection, but is prevented from returning by passing over again the circumferential projection. According to the present invention, when the pinion drive shaft is driven forward, the clutch outer member of the over-running clutch abuts against the circumferential projection portion of the output rotary shaft through the elastic stopper ring. Therefore, the forward movement of the pinion drive shaft and the pinion relative to to the output shaft can be prevented. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more readily apparent from the following detailed description of the preferred embodiments of the present invention taken in conjunction with the accomapnying drwings, in which: 
     FIG. 1 is a sectional view of the conventional pinion stopper arrangement for a starter motor; 
     FIG. 2 is a sectional view taken along line II--II of FIG. 1; 
     FIG. 3 is a front view of the pinion stopper clip shown in FIG. 1; 
     FIG. 4 is a side view of the shaft helical spline portion of another conventional pinion stopper arrangement for the starter motor; 
     FIG. 5 is a sectional view of one embodiment of the pinion stopper arrangement for a starter motor of the present invention; 
     FIG. 6 is a sectional view showing how the over-running clutch is inserted onto the output shaft of the embodiment shown in FIG. 5; 
     FIG. 7 is an enlarged plan view of the ring-shaped member of the embodiment shown in FIG. 5; 
     FIG. 8 is a sectional view of another embodiment of the present invention; 
     FIG. 9 is a plan view showing how the over-running clutch is inserted onto the output shaft in the embodiment shown in FIG. 8; 
     FIG. 10 is an enlarged plan view of the ring-shaped member of the embodiment shown in FIG. 8; 
     FIG. 11 is a sectional view of still another embodiment of the present invention; 
     FIG. 12 is a plan view showing how the over-running clutch is inserted onto the output shaft in the embodiment shown in FIG. 11; 
     FIG. 13 is an enlarged plan view of the ring-shaped member of the embodiment shown in FIG. 11; 
     FIG. 14 is a sectional view of another embodiment of the present invention; and 
     FIG. 15 is a plan view showing how the over-running clutch is inserted onto the output shaft in the embodiment shown in FIG. 14. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 5 illustrates in section one embodiment of the pinion stopper arrangement for a starter motor of the present invention. In FIG. 5, the arragement comprises an output rotary shaft 21 connected at its rear end (the left end in FIG. 5) to an unillustrated armature rotary shaft of an electric motor for rotation therewith. 
     The output rotary shaft 21 has formed on its outer periphery helical splines 21a which mesh with the helical splines 22a of the over-running clutch 22. 
     A clutch outer member 22b is coupled with a clutch inner member 22c through rollers 23. The clutch inner member 22c is formed integral with the pinion drive shaft 24. A pinon gear 25 is disposed on the front end of the pinion drive shaft 24. 
     Disposed between the pinion drive shaft 24 and the output shaft 21 is a bearing 21b which allows the pinion drive shaft 24 to rotate and axially slide relative to the output shaft 21. 
     According to the present invention, the pinion stopper arrangement comprises an annular circumferential projection or a ring 26 integrally formed on the output shaft 21. The circumferential projection 26 has a bevelled front end surface 26a and a flat rear end surface 26b extending substantially perpendicularly to the axis of the output shaft 21. The circumferential projection 26 has also formed therein a plurality of substantially axially extending grooves 26c for allowing the passage therethrough of the helical splines 22a of the clutch outer member 22b. 
     Also according to the present invention, an elastic stopper ring 27 is placed over the output shaft 21 between the vertical rear end (left end in FIG. 5) surface 26b of the circumferential projection 26 and the front end (right end in FIG. 5) surface 22e of the clutch outer member 22b. This ring-shaped stopper ring 27 is configured as shown in the plan view of FIG. 7. It is seen from FIG. 5 that the elastic stopper ring 27 is made of a spring steel for example and has an inner diameter smaller than the outer diameter of the circumferencial projection 26 and an outer diameter larger than the diameter of the dedendum circle of the helical spline 22a of the clutch outer member 22b. In the illustrated embodiment, the elastic stopper ring 27 is firmly attached to the front end surface 22e of the clutch outer member 22b such as by welding. 
     FIG. 6 is a sectional view showing the manner in which this embodiment of the present invention is assembled. As shown in FIG. 6, the half-assembled over-running clutch 22 is placed and advanced over the output shaft 21 from its front end or from right side in FIG. 6. 
     During this fitting operation, the over-running clutch 22 can be smoothly moved toward the rear end of the output shaft 21 with the helical splines 22a of the clutch outer memeber 22b are mesh with the helical splines 21a of the output shaft 21 as well as the axial grooves 26c formed in the circumferential projection 26 until the elastic stopper ring 27 is brought into contact with the annular ring formed on the output shaft 21. By further forcedly advancing the over-running clutch 22, the elastic stopper ring 27 is forcedly expanded to increase its inner diameter to such an extent that the elastic stopper ring 27 can override the annular ring 26 owing to the sloped or bevelled surface 26a of the annular ring 26 and the elasticity of the stopper ring 27. Once the elastic stopper ring 27 has passed over the annular ring 26, it returns to the original diametrical dimension and is held between the front end surface 22e of the clutch outer member 22b and the rear end surface 26b of the annular ring 26 as shown in FIG. 5. Thus, the clutch outer member 22b and therefore the over-running clutch 22 is prevented from forwardly moving on the output shaft 21. In this context, the elastic stopper ring 27 is a stopper for the over-running clutch 22. 
     The over-running clutch 22 further comprises a ring shaped seal plate 28 held by a cover 29 fitted over the clutch outer member 22b. 
     Another embodiment of the pinion stopper arrangement of the present invention is illustrated in FIGS. 8 to 10, from which it is seen that the pinion stopper arrangement comprises an elastic stopper ring 37 similar to the ring-shaped member 27 of the previous embodiment shown in FIGS. 5 to 7. The elastic stopper ring 37 is different from the elastic stopper ring 27 in that it has a bevelled inner circumferential surface 37a so that the expansion of the elastic stopper ring 37 by the forced advancement over the sloped surface 26a of the circumferentail projection 26 may be easier than that of the previous embodiment. The elastic stopper ring 37 is also different from the elastic stopper ring 27 in that it is not secured such as by welding to the clutch outer member 22b to provide a higher flexibility to the elastic stopper ring 37. In other respects, the arrangement is the same to that of the previous embodiment. 
     FIG. 11 to 13 illustrate still another embodiment of the pinion stopper arrangement of the present invention, from which it is seen that the pinion stopper arrangement comprises an elastic stopper ring 47 similar to the elastic stopper ring 27 of the previous embodiment shown in FIGS. 5 to 7. This elastic stopper ring 47 is made of a relatively hard material such as a spring steel, so that a gap 47c for providing necessary flexibility for overrinding the circumferencial projection 26 is formed in the ring 47. The elastic stopper ring 47 also has an inner bevelled circumferential surface 47a surface 47a and an outer bevelled circumferential surface 47b. The bevelled surface 47a has the same function as the bevelled surface 37a of the elastic ring member 37 shown in FIGS. 8 to 10, and the bevelled surface 47b  is formed to be press-fit by a correspondingly bevelled surface 22d of the clutch outer member 22b. 
     In this embodiment, it is seen that the diameter of the addendum circle of the helical splines 22a of the outer clutch member 22b is larger than the outer diameter of the circumferential projection 36. Therefore, no axial grooves such as those corresponding to the axial grooves 26c provided in the previous embodiments shown in FIGS. 5 to 10 for allowing the passage of the helical splines 22a therethrough is necessary. Thus, the circumferential projection 46 of this embodiment has a continuous outer surface. 
     FIGS. 14 and 15 illustrate another embodiment of the pinion stopper arrangement of the present invention. The arrangement of this embodiment is identical to that shown in FIGS. 11 to 13 except that the inner diameter of the splined clutch outer member 22b is smaller than the outer diameter of the circumferential projection 26 and that the circumferential projection 26 has the axial grooves 26c for allowing the passage of the helical splines 22a fo the clutch outer member 22b. 
     As has been described, the pinion stopper arrangment for a starter motor of the present invention comprises an elastic stopper ring disposed between a front end surface of a clutch outer member and a vertical rear end surface of a cicumferential projecting portion mounted on an output shaft. The elastic stopper ring is expanded when it is urged against the circumferential projection, but is shaft to pass over the circumferential projection, but is prevented from returning by passing over again the circumferential projection. When the pinion drive shaft is driven forward, the clutch outer member of the over-running clutch abuts against the circumferential projection portion of the output rotary shaft through the elastic stopper ring. Therefore, the forward movement of the pinion drive shaft and the pinion relative to to the output shaft can be prevented with a relatively simple structure which can be manufactured and assembled with ease. The axial length of the output shaft can be shortened.