Abstract:
Providing a pulley unit with a reduced diameter, stable operating characteristics, and that is simple and readily removable from an engine is accomplished by a one-way clutch disposed between a pulley and a shaft body that are concentrically arranged. A shaft defines a shaft attachment space at a position which is not overlapped by rollers contained in the one-way clutch in an axial direction. The shaft body is attached to the shaft at the shaft attachment space. The shaft body, disposed inside the rollers in a radial direction, does not have a through hole, but rather, has a non-through structure.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
         [0001]    This application is based on and incorporates herein by reference Japanese Patent Application No. 2000-356175 filed on Nov. 22, 2000 and Japanese Patent Application No. 2001-214314 filed on Jul. 13, 2001.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Technical Field of the Invention  
           [0003]    The present invention relates to a pulley unit including a one-way clutch.  
           [0004]    2. Description of Related Art  
           [0005]    Various accessories mounted on a vehicle engine are attached to a belt driven by an engine&#39;s crankshaft. However, when an accessory such as an alternator is connected to the crankshaft of the engine, and rotated synchronistically with the crankshaft, the following problem occurs. That is, when a rotational speed of the crankshaft is reduced, alternator power generation is also reduced. Conventionally, to avoid such a problem, a pulley unit containing a one-way clutch is used for a vehicle alternator so as to improve power generation efficiency when the rotational speed of the crankshaft is reduced.  
           [0006]    [0006]FIG. 8 is a related art, cross-sectional view showing a conventional pulley unit containing a one-way clutch. As shown in FIG. 8, the conventional pulley unit includes a pulley  200 , a shaft body  210  and a one-way clutch  220 . The pulley  200  and the shaft body  210  are concentrically disposed, and the one-way clutch  220  is disposed in a space therebetween at a middle position in an axial direction. The one-way clutch  220  is composed of an outer ring  222  fixed to the pulley  200 , an inner ring  224  fixed to the shaft body  210 , and plural cylindrical rollers  226  sandwiched between the outer ring  222  and the inner ring  224 . The outer ring  222  and the inner ring  224  define a plurality of wedge-shaped spaces therebetween in a circumferential direction. The rollers  226  are disposed in these wedge-shaped spaces, thereby constructing the one-way clutch  220  for transmitting rotational driving force only in a single direction.  
           [0007]    The one-way clutch  220  is switched using this type pulley unit between a locked condition (driving-force transmitting condition) and a free condition (driving-force interrupting condition) in accordance with a revolution speed difference between a rotor of the vehicle alternator, integrated to the shaft body  210 , and the pulley  200 . Thus, a driving force can be transmitted and interrupted between the rotor and the pulley  200 . Two bearings  230  are provided at both ends of the one-way clutch  220  in its axial direction, respectively, so as to smooth any relative rotational operation between the rotor and the pulley  200  and to undertake a load added from the belt.  
           [0008]    In the above conventional pulley unit, the shaft body  210 , provided inside the one-way clutch  220  in its radial direction, defines an attachment through hole at its center. The pulley unit is attached to a shaft of an accessory using this attachment through hole. Therefore, when water hits an end surface of the pulley unit used in a state where the pulley unit is attached to the crankshaft, the water enters between the shaft body  210  and the shaft. Then, portions covered with the water rust, and it is difficult to remove the pulley unit from the shaft. Water, hitting the end surface of the pulley unit, is generally prevented from entering the pulley unit by a cap covering the end surface of the pulley unit. However, because of this arrangement, the number of components must be increased making an attachment process complicated, thereby increasing production costs.  
           [0009]    It has been considered that a diameter of a pulley unit be reduced to increase a rotational speed of the accessory. The conventional pulley unit shown in FIG. 8 defines the attachment through hole at its center, and the one-way clutch  220  is provided outside the attachment through hole. Therefore, the conventional pulley unit has a complicated structure in its radial direction, and the diameter of the pulley unit is difficult to reduce.  
           [0010]    There are screw portions, each provided on the shaft and a surface defining the attachment through hole, inside the one-way clutch  220  in its radial direction. When the pulley unit is attached to the shaft, the screw portions are clamped to each other so that the shaft body  210  is deformed outside in its radial direction by a clamping force in its axial direction by force received from the screw portions. Therefore, the shape of the plural wedge-shaped spaces, provided in the one-way clutch  220  in its circumferential direction, where the plurality of rollers  226  are contained, changes. As a result, the one-way clutch  220  sometimes does not operate in a normal, stable fashion.  
           [0011]    [0011]FIG. 3 is a related art, cross-sectional view that exemplifies a case where the cam surface  224   a  is deformed in the radial direction in a conventional pulley unit. As shown, the wedge angle of the wedge-shaped space, formed between the outer ring  222  and the inner ring  224 , controls the position of roller  226  and changes the wedge-shaped space from a wedge angle θ 1 , at which the cam surface is not deformed, to a wedge angle θ 2 , at which the cam surface is deformed. Therefore, the rotational speed at which either the lock or free state switches, varies in accordance with the degree of deformation, thereby degrading operational stability.  
         SUMMARY OF THE INVENTION  
         [0012]    The present invention has been made in view of the above problems, and an object is to provide a pulley unit with a diameter that can be reduced, whose operation can be stabilized, and that is readily removable after being used, without increasing current production costs.  
           [0013]    In order to solve the above problems, a pulley unit of the present invention includes a one-way clutch disposed between a pulley and a shaft body which are arranged concentrically. In the pulley unit, further, the one-way clutch includes a roller contained in a wedge-shaped space. The shaft body includes a shaft attachment portion, by which the shaft body is integrated to the shaft, at a position which is not overlapped with the roller in an axial direction. Since the shaft attachment portion is not provided inside the roller in a radial direction, a radial cross-sectional structure of the pulley unit can be simplified at this portion, and a diameter thereof can be reduced.  
           [0014]    Preferably, the shaft attachment portion is a female screw portion clamped to a male screw portion provided on an outer surface of the shaft. Generally, the pulley unit is required to be clamped or fixed to the male screw portion of the shaft by a large force so as to prevent falling and circular movement of the pulley unit. In the pulley unit, since the female screw portion is not formed inside the roller in a radial direction, a wedge-shaped space around the roller is not deformed by a clamping force generated in an axial direction at a clamping time by force received from the male screw portion of the shaft, thereby stabilizing operation of the one-way clutch.  
           [0015]    The above shaft attachment portion, having a recessed shape, is provided on an end surface of the shaft body, and preferably, the shaft body is formed in a non-through structure, that is, the shaft body defines a non-through hole. Therefore, when water strikes the end surface of the pulley unit, it is prevented from entering the clamped portion between the shaft and the shaft body, thereby preventing rust from forming. Accordingly, the pulley unit can be readily removed from the vehicle after being used without increasing production cost, and using a cap and the like.  
           [0016]    Preferably, the above shaft body includes a projection-shaped screwing portion, by which the shaft body is clamped to the shaft, on an end surface at an opposite side of the shaft attachment portion. Since the screwing portion is not required to be provided inside the shaft body, a diameter of the shaft body can be reduced by a diameter of the screwing portion, thereby further reducing a diameter of the pulley unit.  
           [0017]    Preferably, the above shaft body is formed by fixing, to each other, a member where the one-way clutch is formed facing the roller, and a separate member having the shaft attachment portion. When the shaft attachment portion is a separate member, heat treatment for improving abrasion resistance is permitted only for the member where the one-way clutch is formed. Therefore, production equipment costs can be reduced while heat treatment time is shortened, thereby reducing production costs.  
           [0018]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    [0019]FIG. 1 is an axial cross-cross-sectional view showing a pulley unit according to an embodiment of the present invention;  
         [0020]    [0020]FIG. 2 is a cross-sectional view taken along lineII-II in FIG. 1;  
         [0021]    [0021]FIG. 3 is a related art explanation view showing a change of a wedge angle when an inner member (shaft body) is deformed;  
         [0022]    [0022]FIG. 4 is a cross-sectional view showing a pulley unit containing rollers in pocket spaces defined by an inner surface of a pulley;  
         [0023]    [0023]FIG. 5 is an axial cross-sectional view showing a pulley unit including a projection-shaped screwing portion;  
         [0024]    [0024]FIG. 6 is an axial cross-sectional view showing another pulley unit including a projection-shaped screwing portion;  
         [0025]    [0025]FIG. 7 is an axial cross-sectional view showing another pulley unit where a shaft attachment space and cam surfaces are provided separately from each other; and  
         [0026]    [0026]FIG. 8 is a related art, axial cross-sectional view showing a conventional pulley unit with a one-way clutch. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]    Hereinafter, detail description will be made on a pulley unit according to an embodiment of the present invention with reference to the drawings.  
         [0028]    [0028]FIG. 1 is an axial cross-sectional view showing a pulley unit  1  according to the embodiment, and FIG. 2 is a cross-sectional view taken along lineII-II in FIG. 1.  
         [0029]    As shown in FIGS. 1 and 2, the pulley unit  1  according to the present embodiment includes a pulley  10 , a shaft body  12 , a one-way clutch  20  and two bearings  30 ,  32 . The pulley  10  and the shaft body  12  are concentrically disposed, the one-way clutch  20  is disposed in an annular space therebetween, and the two bearings  30 ,  32  are disposed in the one-way clutch  20  at both sides in its axial direction.  
         [0030]    The pulley  10  includes a wave-shaped groove on its periphery, and a belt is wrapped around the wave-shaped groove. The pulley  10  is rotated by a crankshaft of a vehicle engine by using the belt. The shaft body  12  is a cylindrical member, and it is fixed to a shaft of a vehicle accessory (e.g., a shaft of a vehicle alternator)  40 .  
         [0031]    The shaft body  12  includes plural cam surfaces  13  each having a curved shape at its outside portion in its circumferential direction. The plural cam surfaces  13  and an inner surface  10   a  of the pulley  10  define plural pocket spaces, and a roller  26  and a coil spring  28  are contained in each pocket space. The coil spring  28  has a substantially rectangular cross-section, and it presses the roller  26  in a circumferential direction and in a single direction.  
         [0032]    A clutch cam portion including a wedge-shaped space, of which width in a radial direction is gradually reduced in the circumferential direction, is provided in the pocket space. The roller  26  is pressed to a narrower side (lock side) of the wedge-shaped space by the coil spring  28 . The one-way clutch  20  is composed of the pocket spaces, the rollers  26  and the coil springs  28 .  
         [0033]    The shaft body  12  defines a shaft attachment space  14 , at which the shaft body  12  is attached to the shaft  40 , at a position which is not overlapped with the rollers  26  in its axial direction. Specifically, the shaft body  12  defines the shaft attachment space  14  at one end in a recess shape, and a female screw portion  14   a  is formed on an inner surface defining the shaft attachment space  14 . The female screw portion  14   a  is screwed to a male screw portion  40   a  formed on an outer surface of the shaft  40  around its tip, so that the pulley unit  1  is attached to the shaft  40 . A screwing tool is inserted into a screwing space  16  which is defined on the shaft body  12  at the other end thereof, and it is screwed at a predetermined screw torque, so that screwing work is performed.  
         [0034]    The pulley unit  1  according to the present embodiment has such structure. Next, operational situations will be described.  
         [0035]    (1) When a revolution speed of the pulley  10  is higher than that of the shaft body  12 :  
         [0036]    Each roller  26  of the one-way clutch  20  moves to the radially narrower side or portion of each wedge-shaped space. Therefore, each roller  26  is sandwiched between each cam surface  13  and the inner surface  10   a  of the pulley  10 , so that the shaft body  12   a  and the pulley  10  become locked when they are integrally rotated. Accordingly, they become integral with each other, and synchronistically rotate.  
         [0037]    (2) When the revolution speed of the pulley  10  is lower than that of the shaft body  12 , or when the pulley  10  is rotated in an inverse direction from a rotational direction of the shaft body  12 :  
         [0038]    Each roller  26  of the one-way clutch  20  moves to the radially wider side or portion of each wedge-shaped space. Therefore, each roller  26  is released from the state where it is sandwiched between each cam surface  13  and the inner surface  10   a , so that the shaft body  12  and the pulley  10  come into a free state in which they can be individually rotated. Accordingly, transmittance of rotational driving force from the pulley  10  to the shaft body  12  is interrupted, so that the shaft body  12  maintains its rotational speed by a rotational inertia force of the rotor.  
         [0039]    In consideration of a case where the above pulley unit  1  is used for a vehicle alternator, the power generation efficiency can be improved by maintaining a high revolution speed of the rotor irrespective of revolution speed fluctuation of an engine crankshaft connected to the pulley unit  1  through the belt. That is, when the revolution speed of the crankshaft is increased, the one-way clutch  20  comes into the lock state, so that the shaft body  12  and the pulley are synchronistically rotated. Then, when the rotational speed of the crankshaft is decreased, the one-way clutch  20  transitions to the free state, so that the shaft body  12  maintains its rotational speed by the rotational inertial force irrespective of the decreased rotational speed of the pulley  10 .  
         [0040]    In such a case where the pulley unit  1  is clamped and fixed to the shaft  40 , the clamping force is required to be increased so that an axial force of one ton or more is applied to the female screw portion  14   a  so as to prevent falling and circular movement of the pulley unit  1 . Therefore, the shaft body  12  is deformed on an outer periphery in its radial direction by this axial force. In the pulley unit  1  according to the present embodiment, however, the female screw portion  14   a  of the shaft body  12  is formed at the position which is not overlapped with the rollers  26  of the one-way clutch  20  in the axial direction of the shaft body  12 . That is, there is not the female screw portion  14   a  inside the cam surfaces  13 , which is an inside contact surface for the rollers  26 , in the radial direction of the shaft body  12 . Therefore, since the cam surfaces  13  are not affected by this deformation around the female screw portion  14   a , a wedge angle of each wedge-shaped space is maintained at a predetermined angle. Thus, action of each roller  26  of the one-way clutch  20  is stabilized in both, the lock and free states, and a revolution speed at which these two states is switched is stabilized, thereby ensuring functional stabilization of the one-way clutch  20 .  
         [0041]    In a case where the cam surface is deformed in the radial direction in such a conventional pulley unit, as shown in the related art of FIG. 3, the wedge angle of the wedge-shaped space changes from a wedge angle θ 1 , at which the cam surface is not deformed, to a wedge angle θ 2  at which the cam surface is deformed. To elaborate, FIG. 3 exemplifies a case where the cam surface  224   a  is deformed in the radial direction. As shown, the wedge angle of the wedge-shaped space, formed between the outer ring  222  and the inner ring  224 , controls the position of roller  226  and changes the wedge-shaped space from a wedge angle θ 1 , at which the cam surface is not deformed, to a wedge angle θ 2 , at which the cam surface is deformed. Therefore, the rotational speed at which either the lock or free state switches, varies in accordance with the degree of deformation, thereby degrading operational stability.  
         [0042]    The shaft body  12  of the pulley unit  1  according to the present embodiment defines two non-through holes (shaft attachment space  14  and screwing space  16 ), that is, it has a non-through structure. Even when water strikes the end surface of the shaft body  12  where the screwing space  16  is provided, water does not enter between the shaft  40  and the female screw portion  14   a , thereby preventing rust generation therebetween. Thus, after an installed vehicular accessory is used, the pulley unit  1  can be readily removed from the vehicle for maintenance or the like. Additionally, a cap or similar cover, for covering the end surface of the shaft body  12  to prevent rust generation on the female screw portion  14   a , is not required. Therefore, the number of components is not increased, and attachment processes are not complicated, thereby preventing production costs from increasing. Additionally, since the shaft attachment space  14  is not provided inside of the rollers  26  of the one-way clutch  20  in its radial direction, the radial cross-sectional structure can be simplified at this portion, thereby reducing a diameter of the pulley unit  1 .  
         [0043]    The present invention can be modified in several ways without limiting the invention to the above embodiment. In the above embodiment, the rollers  26  are contained in the pocket spaces defined by an outer surface of the shaft body  12  shown as the cam surfaces  13 . However, the pocket spaces can be defined by an inner surface of the pulley  10  as the cam surfaces.  
         [0044]    [0044]FIG. 4 is a cross-sectional view showing a pulley unit  1 A containing rollers  126  in pocket spaces defined by an inner surface of a pulley  110  as cam surfaces  110   a . As shown in FIG. 4, the pulley unit  1 A includes the pulley  110 , a shaft body  112 , a one-way clutch  120  and two bearings (not shown). The pulley  110  and the shaft body  112  are concentrically disposed, the one-way clutch  120  is disposed in an annular space therebetween, and the two bearings are disposed in the one-way clutch  120  at both end sides in its axial direction.  
         [0045]    The pulley  110  includes plural cam surfaces  110   a  each having a curved shape at its inside in its circumferential direction. The plural cam surfaces  110   a  and an outer surface  112   a  of the shaft body  112  define plural pocket spaces, and a roller  126  and a coil spring  128  are contained in each pocket space. The coil spring  128  has a substantially rectangular cross-section, and it presses the roller  126  in a single, circumferential direction. The pocket space forms a clutch cam portion including a wedge-shaped space of which width in a radial direction is gradually reduced in the circumferential direction. The roller  126  is pressed to a narrower side (the locking side) of the wedge-shaped space by the coil spring  128 . The one-way clutch  120  is composed of the pocket spaces, the rollers  126  and the coil springs  128 . Although the screwing space  16 , having a recess shape, is provided in one end surface of the shaft body  12  in the above embodiment, a screwing portion having a projection shape can be provided in place of the screwing space  16 .  
         [0046]    [0046]FIG. 5 is an axial cross-sectional view showing a pulley unit including a projection-shaped screwing portion  16   a . The shaft body  12   a  includes a projection-shaped screwing portion  16   a  on its end surface, and an outer diameter of the shaft body  12   a  is partially reduced at a portion adjacent to the rollers  26  and the bearing  30  at the tip side (side of the screwing portion  16   a ), thereby reducing a diameter of the entire pulley unit  1 .  
         [0047]    [0047]FIG. 6 is an axial cross-sectional view showing another pulley unit including a projection-shaped screwing portion  16   a . The structure shown in FIG. 6 is identical to the structure shown in FIG. 5 in a viewpoint where the projection-shaped screwing portion  16   a  is formed on the end surface of the shaft body  12   b . The structure in FIG. 6 is different from the structure in FIG. 5 in a viewpoint where the outer diameter of the shaft body  12   b  is partially reduced at a portion adjacent to the rollers  26  and both bearings  30 ,  32 , thereby reducing a diameter of the entire pulley unit  1 . Although the pulley unit according to the present invention is applied to a vehicle alternator as an example in the above embodiment, it can be applied to an accessory other than the vehicle alternator, such as a compressor, a water pump and a cooling fan for an air conditioner.  
         [0048]    Although the shaft body  12 , the shaft attachment space  14  and the cam surfaces  13  are integrally provided in the above embodiment, they can be provided separately from each other as shown in FIG. 7, and they can be integrally fixed to each other by press-fitting and the like. In this case, heat treatment for improving abrasion resistance is allowed to be performed only for a member  120  having cam surfaces constituting a one-way clutch. Therefore, heat capacity becomes small, and heat treatment time is lessened, thereby reducing a heat treating apparatus required for heat treatment and ultimately reducing production costs.  
         [0049]    The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.