Alternator having driving pulley with end flanges

An alternator for use in an automobile is driven by an internal combustion engine. The alternator includes a pulley that is coupled to a rotating shaft of the engine via a driving belt such as a poly-V belt. Plural pulley grooves to be engaged with the driving belt are formed on the pulley between a front flange and a rear flange. A projected surface of a front frame is located around the outer periphery of the rear flange, so that the driving belt is correctly positioned between the front and the rear flanges, guided by the projected surface. Two overlaps in the axial direction between the pulley and the front frame are formed to reduce an amount of water entering into the alternator through a gap between the pulley and the front frame.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims benefit of priority of Japanese Patent Application No. 2004-327599 filed on Nov. 11, 2004, the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an alternator for use in an automotive vehicle, and more particularly to such an alternator having a driving pulley with end flanges.

2. Description of Related Art

Generally, an alternator for use in an automobile is driven by an engine via a driving belt coupled to a pulley of the alternator. When a so-called poly-V belt having plural V-shaped projections is used as the driving belt, the poly-V belt has to be correctly positioned relative to plural pulley grooves formed on the pulley. That is, the plural V-shaped projections of the driving belt have to be engaged with the plural pulley grooves, so that the V-belt is correctly positioned in the axial direction within a width of the pulley. For this purpose, a pulley having end flanges formed at both axial ends of the pulley is proposed, as exemplified in JP-B2-3509292.

It is not easy, however, to make end flanges having a relatively large diameter, especially when the pulley is made of a steel plate by stamping. If the diameter of the flanges is not sufficiently large, the poly-V belt may not be correctly positioned relative to an axial width of the pulley. Further, water may enter into a bearing of the alternator through an axial gap between the pulley and an axial end of a bearing holder. The bearing may be damaged with the water, and thereby noises may be generated and a life of the alternator may be shortened.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an improved alternator having a pulley with end flanges, wherein a poly-V belt is correctly positioned around the pulley and an amount of water entering into the alternator is reduced.

The alternator includes a frame composed of a front frame and a rear frame, a stator fixedly contained in the frame, a rotor rotatably supported in the frame inside the stator and a pulley connected to the rotor at an front side of the frame. A rotating shaft of an engine and the pulley are coupled by a driving belt (such as a poly-V belt) to drive the alternator by the engine. The pulley has a cylindrical shape and includes plural pulley grooves to be engaged with projections formed on an inner surface of the driving belt, a first flange formed at an front end of the pulley and a second flange formed at a rear end of the pulley. The diameter of the second flange is made larger than the outer diameter of the pulley grooves and smaller than the diameter of the first flange. A projected portion is circularly formed on a front end of the frame so that the projected portion is positioned at a radial outside of the second flange. Windows for sucking cooling air into the frame are formed at a radial outside of the projected portion.

A gap L1between the inner diameter of the projected portion and the diameter of the second flange is made smaller than a thickness (in the radial direction) of the driving belt. A front end surface of the projected portion is positioned at a front side of a rear end of the second flange, thereby making an overlap L2therebetween. A front end surface of the projected portion is positioned at a front side of a rear end surface of the pulley, thereby making another overlap L3therebetween.

Since the gap L1is smaller than the thickness of the driving belt, and since the front end surface of the projected portion is positioned in a front side of the rear end of the second flange, the driving belt can be correctly positioned between two flanges, guided by the front end surface of the projected portion even if the diameter of the second flange is not sufficiently large. Since there are two overlaps L2and L3between the front frame and the pulley, an amount of water entering into a bearing in the front frame is reduced. Since the cooling air sucking windows are formed radially outside of the projected portion, cooling air smoothly flows into the frame.

Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiment described below with reference to the following drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the present invention will be described with reference to accompanying drawings. As shown inFIG. 1, an alternator1is composed of a rotor2, a stator3, a frame formed by a front frame4and a rear frame5, a brush device6, a rectifier7, a voltage regulator8, a pulley9and other associated components. The pulley9is positioned at a front side of the alternator1, while components such as the brush device6are positioned at a rear side of the alternator1. The front side and the rear side are indicated inFIG. 1with an arrow.

The rotor2includes a pair of rotor cores22,23firmly connected to a rotor shaft24and a rotor winding21wound on the rotor cores22,23. Each rotor core22,23has a boss connected to the rotor shaft24and six claw-shaped poles. A cooling fan25for sucking cooling air in the axial direction and blowing the sucked cooling air in axial and radial directions is connected to a front surface of the front rotor core22. Another cooling fan26(a centrifugal fan) for sucking cooling air in the axial direction and blowing the sucked cooling air in the radial direction is connected to a rear surface of the rear rotor core23. The cooling fans25,26are connected to respective rotor cores22,23by welding or the like.

A pair of slip-rings27,28are formed at the rear end of the rotor shaft24, and brushes61,62held in the brush device6slidably contact the slip-rings27,28. Excitation current is supplied to the rotor winding21from the rectifier7through the brushes61,62and the slip-rings27,28.

The stator3is composed of a cylindrical stator core31and stator winding32disposed in slots formed in the stator core31. The stator winding32forms a three-phase armature winding. The rectifier7rectifies three-phase alternating current generated in the stator winding32into a direct current output. The rectifier7is composed of heat-sink plates and rectifier elements mounted on and soldered to the heat-sink plates.

The frame composed of the front frame4and the rear frame5contains therein the stator3and the rotor2. The stator3is fixedly contained in the frame, and the rotor2is rotatably supported in the frame inside the stator3. The stator3is sandwiched between the front frame4and the rear frame5, and both frames4,5are connected to each other with bolts34inserted into four supporting portions420formed at equal intervals around the outer periphery of the frames4,5.

The voltage regulator8controls the output voltage, which otherwise changes according to rotational speed and loads of the alternator1, to a substantially constant level. The pulley9is connected to the front end of the rotor shaft24with nut81, and the rotor2is driven by an engine via a driving belt coupling the engine to the pulley9. The brush device6, the rectifier7and the voltage regulator8mounted on the rear side of the rear frame5is covered with a rear cover82.

Now, a structure of the pulley9and the front end of the front frame4will be described in detail with reference toFIGS. 2 and 3. The front flame4includes a bearing holder400in which a bearing36is contained. A collar29is sandwiched between the rear end surface of the pulley9and an inner ring of the bearing36, and the pulley9is firmly connected to the rotor shaft24by fastening the nut81.

The pulley9is made of a steel plate, for example, by stamping. The cylindrically shaped pulley9includes plural pulley grooves91, a first flange92formed at the front end and a second flange93formed at the rear end of the pulley9. The outer diameter ΦB of the second flange93is lager than the outer diameter of the pulley grooves91and smaller than the outer diameter ΦA of the first flange92. Plural projections formed on the inside surface of the driving belt100engage with the plural grooves91. The width of the driving belt100is correctly positioned between the first flange92and the second flange93, guided by both flanges92,93.

A projected portion41is circularly formed on the front end of the front frame4and positioned outside of the second flange93. A gap L1between the outer diameter ΦB of the second flange93and the inner diameter of the projected portion41is made smaller than a thickness (in the radial direction) of the driving belt100. It is preferable to make the gap L1considerably smaller than the thickness of the driving belt100, taking into consideration that the driving belt100is made of a material having a certain resiliency. For example, the gap L1is made smaller than 3 mm. Windows42for introducing cooling air into the frame are made at a radial outside of the projected portion41.

As shown inFIG. 3, the front end surface41aof the projected portion41is positioned at a front side of the rear end surface93aof the second flange93. In other words, there is a small overlap L2in the axial direction between the rear end surface93aof the second flange93and the front end surface41aof the projected portion41. The rear end surface9aof the pulley9is positioned at a rear side of the front end surface41aof the projected portion41. In other words, there is a small overlap L3in the axial direction between the rear end surface9aof the pulley9and the front end surface41aof the projected portion41.

The outer diameter ΦB of second flange93is smaller than the outer diameter ΦA of the first flange92. Therefore, when the driving belt100is coupled to the pulley9, the driving belt100may not be properly guided by the second flange93and may shift toward the front frame4. If this happens, the rear side of the driving belt100contacts the front surface41aof the projected portion41and is properly guided to a correct position. The gap L1is smaller than the thickness of the driving belt100, and there is the overlap L2between the rear end surface93aof the second flange93and the front end surface41aof the projected portion41. Therefore, the side of the driving belt100surely interferes with the front end surface41aof the projected portion41if the driving belt100shifts toward the front frame4when coupling the driving belt100to the pulley9. In this manner, the driving belt100is always correctly positioned between the first flange92and the second flange93.

Since there is the overlap L3between the front end surface41aof the projected portion41and the rear end surface9aof the pulley9, water is prevented from easily entering into the bearing36when the alternator1is mounted on an automobile so that the rotor shaft24becomes parallel to the horizontal direction. Thus, an amount of water entering into the bearing36is reduced. Since the projected portion41is formed at a radial inside of the cooling air sucking windows42, the projected portion41does not interfere with a cooling airflow entering into the windows42, rather the cooling airflow is properly guided by the projected portion41.

The present invention is not limited to the embodiment described above, but it may be variously modified. For example, the pulley9may be made by machining or forging though it is explained that the pulley9is made of a steel plate by stamping in the above embodiment. While the present invention has been shown and described with reference to the foregoing preferred embodiment, it will be apparent to those skilled in the art that changes in form and detail may be made therein without departing from the scope of the invention as defined in the appended claims.