Cap structure for pulley-fixing nut of vehicle-use electric rotating machine

The cap structure includes a nut engaged with a bolt end portion formed in an end of a rotating shaft of a vehicle-use electric rotating machine to fix a pulley. The nut has a polygonal outer periphery including a step portion projecting radially outward at an axial position closer to a seating surface of the nut than an axial center of the nut. The cap structure further includes a cap for covering the nut and the bolt end portion engaged with the nut and protruding from the nut. The cap is made of casting resin so as to have a polygonal inner periphery and an annular claw portion, the number of sides of the polygonal inner periphery being equal to a natural number-multiple of the number of sides of the outer periphery of the nut.

This application claims priority to Japanese Patent Application No. 2012-164841 filed on Jul. 25, 2012, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a cap structure for a pulley-fixing nut of a vehicle-use electric rotating machine mounted on a vehicle such as a passenger car or a truck

2. Description of Related Art

Generally, a vehicle-use electric rotating machine, which is mounted on a vehicle to be driven through a belt or to drive various auxiliaries through a belt, includes a pulley for transmitting a driving force between the belt and the rotor of the vehicle-use electric rotating machine. The pulley is fixed to an end of the rotating shaft of the rotor by tightening a nut. It is preferable to rust-proof the end of the rotating shaft after the pulley is fixed using the nut to improve marketability of the vehicle. However, plating or antirust-coating the end of the rotating shaft after tightening the nut increases the manufacturing cost substantially.

It is known to put a cap on the end of the rotating shaft after tightening the nut so that the end of the rotating shaft becomes resistant to rust, or at least rust which has occurred on the end of the rotating shaft becomes invisible. For example, refer to Japanese Utility Model Application Laid-open No. S57-172920. This Application describes that a rust-preventing cap, which covers both the outer periphery of such a nut and the end of a bolt engaging with the nut, is fixed by fitting projections formed in the inner periphery of the cap to the thread portion of the bolt.

However, using the rust-preventing cap involves a problem that, in a case where the bolt end portion protruding from the nut is not sufficiently long, it is not possible to sufficiently fit the projections formed in the inner periphery of the cap to the thread portion of the bolt. In such a case, if a longer bolt is used so that the bolt end portion protruding from the nut is sufficiently long, it is possible to fix the rust-preventing cap. However, in this case, it becomes difficult to reduce the size of the vehicle-use electric rotating machine including the rust-preventing cap, and the size of the rust-preventing cap itself has to be increased.

In addition, since the rotating shaft of the vehicle-use electric rotating machine rotates at a high speed and accordingly the nut also rotates at the high speed, there is a concern that the rust-preventing cap may come off because of decrease of the fixing force between the projections of the rust-preventing cap and the thread portion of the bolt, which is caused by the centrifugal force, a force in the rotational direction caused by variation of the rotational speed, and environmental stress (high vibration and high temperature).

SUMMARY

An exemplary embodiment provides a cap structure for a pulley-fixing nut of a vehicle-use electric rotating machine having a pulley driven by a belt including:

a nut engaged with a bolt end portion formed in an end of a rotating shaft of the electric rotating machine to fix the pulley, the nut having a polygonal outer periphery including a step portion projecting radially outward at an axial position closer to a seating surface of the nut than an axial center of the nut; and

a cap for covering the nut and the bolt end portion engaged with the nut and protruding from the nut, the cap being made of casting resin so as to have a polygonal inner periphery and an annular claw portion, the number of sides of the polygonal inner periphery being equal to a natural number-multiple of the number of sides of the outer periphery of the nut, an inner diameter of an axial end of the annular claw portion being smaller than an outer diameter of the step portion of the nut.

According to the exemplary embodiment, there is provided a cap structure for a pulley-fixing nut of a vehicle-use electric rotating machine having a pulley driven by a belt, in which a cap can be firmly attached to a nut engaged with a bolt formed in an end of the rotating shaft of the vehicle-use electric rotating machine, and accordingly can be prevented from coming off while the vehicle-use electric rotating machine is in operation, irrespective of the length of a part of the bolt protruding from the nut.

Other advantages and features of the invention will become apparent from the following description including the drawings and claims.

PREFERRED EMBODIMENTS OF THE INVENTION

A vehicle-use alternator1including a pulley-fixing nut cap structure according to an embodiment of the invention is described with reference toFIGS. 1 and 2. The alternator1includes a stator2, a rotor3, a brush device4, a rectifier5, a frame6, a rear cover7, a pulley8and a cap9.

The stator2includes a stator core21, a three-phase stator winding23wound around slots formed at even intervals in the stator core21. The rotor3has a structure in which a field winding31formed by winding an insulated copper wire in a cylindrical and concentric shape is sandwiched by two pole cores32each having a plurality of magnetic claw portions fixed to a rotating shaft33. The end surfaces of the pole cores32are fitted with cooling fans34and35, respectively, by welding or the like.

The brush device4is provided for generating an excitation current to be supplied from the rectifier5to the field winding31. The rectifier5rectifies a three-phase AC voltage outputted from the stator winding23to generate a DC voltage.

The frame6houses the stator2and the rotor3in such a state that the rotor3is rotatable around the rotating shaft33, and the stator2is fixed outside the pole cores32of the rotor with a gap therebetween. The rear cover7is for covering and protecting the brush device4, the rectifier5and an IC regulator12which are disposed outside the frame6.

The pulley8is coupled to an engine (not shown) through a belt to receive a driving force from the engine. The pulley8is fixed to the front end portion of the rotating shaft33of the rotor3by tightening a nut36on a bolt end portion33ain this front end portion as a male thread formed. The cap9, which is made of casting resin, covers the nut36fixing the pulley8, and a part of the bolt end portion33aprotruding from the nut36. The cap9is provided for preventing foreign matter from adhering to the nut36or the bolt end portion33a, and trapping rust which has occurred in these portions. The cap9is devised so as not to come off after being fitted.

The vehicle-use alternator1is configured such that the rotor3rotates in a predetermined direction when a rotational force is transmitted from the engine to the pulley8through the belt. By applying an excitation voltage to the field winding31of the rotor3to excite the claw portions of the pole cores32, a three-phase AC voltage is induced in the stator winding23, and a DC power is outputted from the output terminal of the rectifier5.

Next, the nut36and the cap9are explained in detail. As shown inFIGS. 3 and 4, the nut36includes an outer periphery360of a polygonal shape (a hexagonal shape in this embodiment) and a seating surface361. The outer periphery360includes a step portion362radially projecting at a seating surface-side position. Here, the term “seating surface-side position” means a position between the axial center position363(seeFIG. 4) of the nut36and the seating surface361. It is preferable that the step portion362is closer to the seating surface361than the axial center position363. The step portion362has a circular ring shape with no discontinuity or unevenness in the circumferential direction. The diameter of the end portion at the side of the seating surface361of the outer periphery360is smaller than the outer diameter (seeFIG. 4) of the step portion362. The shape of this end portion may be the same polygonal shape as the outer periphery360. Alternatively, this end portion may be formed in a shape of a cylinder shape whose diameter is smaller than that of the step portion362.

As shown inFIGS. 5 to 7, the outer periphery of the cap9is formed in a stepped shape including a first cylindrical portion91and a second cylindrical portion92. The first cylindrical portion91corresponds to the outer periphery360of the nut36. The second cylindrical portion92corresponds to the bolt end portion33aprotruding from the nut36.

The cap9includes a polygonal inner periphery93the number of whose sides is equal to a natural number-multiple of the number of the sides (six in this embodiment) of the outer periphery360of the nut36, and an annular claw portion94having an inner diameter of b (seeFIG. 6) smaller than the outer diameter of a of the step portion362of the nut36. In this embodiment, the number of the sides of the polygonal inner periphery93is equal to 12 (twice the number of the sides of the outer periphery360of the nut36). The polygonal inner periphery93and the claw portion94are formed corresponding to the first cylindrical portion91.

The claw portion94is circumferentially divided into a plurality of split claw portions94a. Each of the split claw portions94ais formed with a slit95extending from the opening of the first cylindrical portion91in the direction parallel to the center axis of the cylindrical portion91. Since the distal end of each split claw portion94aprojects radially inward, the thickness of each split claw portion94ais thinner at its proximal end and thicker at its distal end. The thinner proximal ends of the split claw portions94acorrespond to the step portion362of the nut36when the cap9is fitted to the nut36. The thicker distal ends of the split claw portions94acorrespond to the end of the outer periphery360of the nut36at the side of the seating surface361when the cap9is fitted to the nut36.

As shown inFIG. 5, there is provided a guide portion97at the boundary between each adjacent two of the sides of the polygonal inner periphery93. The guide portion97is formed by making a dent in the adjacent two sides, which has a shape of a triangular sidewall which widens toward the end of the cap9. In this embodiment, since the number of the sides of the polygonal inner periphery93is 12, the number of the guide portions97is 12. Here, as shown inFIGS. 8A and 8B, since the number of the sides of the outer periphery360of the nut36is 6, it is possible that the polygonal inner periphery93of the cap9contacts the outer periphery360of the nut36at either one of two groups of six 60-degree spaced points which are shifted by 30 degrees from each other in the circumferential direction. Accordingly, the cap9can be positioned in place by turning the cap by 30 degrees at most. Further, positioning operation of the cap can be done automatically by the provision of the guide portions97.

According to the vehicle-use alternator described above, since the nut36for fixing the pulley8is formed with the step portion362, and the cap9is retained by engagement between the claw portion94thereof and the step portion362of the nut36, the cap9can be reliably fixed irrespective of the length of the bolt end portion33aprotruding from the nut36. Since the inner periphery93of the cap9is formed in the polygonal shape, the cap9can be prevented from turning relative to the nut36. Since the cap9is fixed by engagement between the claw portion94thereof and the step portion362of the nut36, the cap9can be prevented from coming off the nut36irrespective of its circumferential position.

There is provided the guide portion97at the boundary between each adjacent two of the sides of the polygonal inner periphery93, the guide portion97being formed by making a dent in the adjacent two sides so as to have a triangular sidewall which widens toward the end of the cap9. Accordingly, since the cap9can be positioned in place at the time of fitting the cap9to the nut36without concern of the circumferential position of the cap9, it is possible to automate the procedure of fitting the cap9at a low cost.

The claw portion94is circumferentially divided into a plurality of the split claw portions94a, the thickness of each split claw portion94ais thinner at the proximal end thereof and thicker at its distal end thereof. Accordingly, the cap9can be fitted to the nut36with a small force because the claw portion94can be easily engaged to the step portion362of the nut36by slightly deforming the cap9.

Since each of the outer peripheries91and92of the cap9is formed in a cylindrical shape, the wind noise generated when the cap9rotates at a high speed together with the pulley8can be substantially reduced. More specifically, the outer periphery of the cap9is formed in the stepped shape including the first cylindrical portion91corresponding to the outer periphery360of the nut36and the second cylindrical portion92corresponding to the bolt end portion33aprotruding from the nut36. This makes it possible to reduce the weight and material cost of the alternator1by reducing the amount of necessary resin material and also to improve the reliability of the alternator1because the centrifugal force generated when the cap9rotates together with the pulley8can be reduced.

It is a matter of course that various modifications can be made to the above described embodiment as described below. In the above embodiment, the number of the sides of the outer periphery360of the nut36is 6. However, it is possible to use a nut having an outer periphery the number of whose sides is other than 6. In the above embodiment, the number of the sides of the polygonal inner periphery93of the cap9is 12 (twice the number of the sides of the outer periphery360of the nut36). However, it may be equal to the number of the sides of the outer periphery360multiplied by a natural number other than 2 (1 or 3, for example).

The above embodiment relates to the cap structure of a nut for fixing a pulley of a vehicle-use alternator. However, the present invention is applicable to a cap structure of a nut of an electric rotating machine used as other than a vehicle-use alternator.