Abstract:
An automotive AC generator is provided which includes a rotary shaft and a generator connector jointed to the rotary shaft. The generator connector is designed to establish a mechanical connection between the rotary shaft and a motor connector joined to a drive shaft of the motor for transmitting the drive torque to the rotary shaft. The generator connector is placed to establish eccentricity between an axis thereof and an axis of the motor connector at all times during rotation of the rotary shaft, thereby resulting in a radial load acting on bearings of the rotary shaft in one direction so as to keep a total load on the bearings greater than zero (0) at all the time. This avoids the seizing of the bearings and creeping of a bearing holder.

Description:
CROSS REFERENCE TO RELATED DOCUMENT 
       [0001]    The present application claims the benefit of Japanese Patent Application No. 2006-45364 filed on Feb. 22, 2006, the disclosure of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Technical Field of the Invention 
         [0003]    The present invention relates generally to an improved structure of an automotive AC generator designed to establish a shaft-to-shaft joint with an engine through, for example, a yoke pulley. 
         [0004]    2. Background Art 
         [0005]    Typical automotive AC generators or alternators are designed to be supplied with power from the engine to charge a storage battery or feed electric power to an ignition system of the engine, an in-vehicle lighting system, an in-vehicle air conditioner, an audio system, or other electric components. In recent years, an increased number of devices for augment the comfort of the vehicle or devices designed to meet a variety of regulations such as emission regulations have been mounted on the engine or within the engine compartment. However, there is the need for ensuring spaces within the engine compartment to absorb physical impacts arising from vehicle collisions in order to assure the safety for vehicle occupants, thus resulting in the need for arranging the devices within the engine compartment at high density. The same is true for accessories mounted on the engine. Particularly, the alternators are smaller in size than the other accessories and connected electrically to the body of the engine through flexible wires, so that they have a higher degree of freedom in installation thereof within the engine compartment. The alternators may, therefore, be placed deep within the engine compartment in a shaft-to-shaft connection with the engine. In this case, the alternator is usually disposed in alignment of a rotary shaft with a drive shaft joined to the engine, so that the radial load acting on bearings retaining a rotor of the alternator will be extremely small. This may result in seizing of the bearings arising from a lack of lubricant caused by the slip of rolling elements on rolling contact surfaces of races or creep between a bearing holder and the outer race of the bearing, thus leading to the wear of the bearing within a housing of the alternator. In order to minimize the slip of the rolling elements of the bearing, Japanese Patent First Publication No. 2001-27246 teaches deforming the outer race of the bearing slightly to create a plurality of small gaps between the outer race and the rolling elements each time the outer race or the inner race makes a 360-degree turn, thereby inducing self-rotation of the rolling elements when passing the gaps. 
         [0006]    In order to avoid the creep of the bearing holder, Japanese Patent First Publication No. 11-294469 teaches installing an elastic member such as resin or spring in a groove formed in the outer race of the bearing to elastically create friction between the outer race and the bearing holder to hold the outer race from rotating. 
         [0007]    The former structure requires the need for controlling the configuration of the inner and outer races, that is, the size of the small gaps accurately, thus resulting in an increased difficulty in machining the bearing and an increased production cost of the bearings. Additionally, the size of the gaps depends upon the ambient temperature, therefore, such bearings are unsuitable for the alternators. 
         [0008]    The latter structure is complicate, so that the elastic member fitted on the outer race will cause a disturbance to insertion of the bearing into the bearing holder, thus resulting in increases in assembling steps and production cost of the alternator. 
       SUMMARY OF THE INVENTION 
       [0009]    It is therefore a principal object of the invention to avoid the disadvantages of the prior art. 
         [0010]    It is another object of the invention to provide an improved structure of an automotive AC generator designed to minimize the seizing or creep of bearings without sacrificing production costs and assembling workability thereof. 
         [0011]    According to one aspect of the invention, there is provided an AC generator which may be employed in automotive vehicles. The AC generator comprises: (a) a rotary shaft which is to be rotated by drive torque transmitted from a motor to rotate a rotor to generate AC power; and (b) a generator connector jointed to the rotary shaft. The generator connector is designed to establish a mechanical connection between the rotary shaft and a motor connector joined to a drive shaft of the motor for transmitting the drive torque to the rotary shaft. The generator connector is placed to establish eccentricity between an axis thereof and an axis of the motor connector at all times during rotation of the rotary shaft to exert a physical load on the rotary shaft in a given direction. 
         [0012]    In the preferred mode of the invention, the AC generator also includes a bearing retaining the rotary shaft to be rotatable and an elastic member installed on one of the generator connector and the motor connector. The elastic member is elastically deformed by eccentric rotation of the generator connector and the motor connector to exert the physical load on the bearing as a radial load oriented in a radial direction of the bearing. 
         [0013]    The distance by which the axis of the generator connector is eccentric from the axis of the motor connector may be so selected that when a dynamic load, as produced depending upon the rotor, acts on the bearing, a combination of the radial load and the dynamic load is applied to the bearing at all times only from a preselected direction. 
         [0014]    Specifically, the eccentricity between the generator connector and the motor connector results in the radial load acting on the bearing in one direction so as to keep a total load on the bearing greater than zero (0) at all the time. This avoids the seizing or creeping of the bearing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The present invention will be understood more fully from the detailed description given hereinbelow and from the accompanying drawings of the preferred embodiments of the invention, which, however, should not be taken to limit the invention to the specific embodiments but are for the purpose of explanation and understanding only. 
           [0016]    In the drawings: 
           [0017]      FIG. 1  is a longitudinal sectional view which shows the structure of an alternator according to the invention; 
           [0018]      FIG. 2  is a partially exploded view which shows a joint between the alternator of  FIG. 1  and a coupling of a drive shaft connected to an engine; 
           [0019]      FIG. 3  is a longitudinal sectional view which shows an example of a conventional alternator with a yoke pulley being in alignment with a coupler of a drive shaft; 
           [0020]      FIG. 4  is a longitudinal sectional view which shows an example of a conventional alternator designed to be driven through a belt; 
           [0021]      FIG. 5(   a ) is a view which represents a static load Ps acting on bearings of each of the alternators of  FIGS. 1 ,  3 , and  4 ; 
           [0022]      FIG. 5(   b ) is a view which represents a dynamic load Pf acting on bearings of each of the alternators of  FIGS. 1 ,  3 , and  4 ; 
           [0023]      FIG. 5(   c ) is a view which represents a total load Po acting on bearings of each of the alternators of  FIGS. 1 ,  3 , and  4 ; and 
           [0024]      FIG. 6  is a graph which shows a relation between repulsive force, as produced by an elastic damper installed on a yoke pulley of an alternator, and an eccentric distance between the yoke pulley and a coupler of a drive shaft. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0025]    Referring to the drawings, wherein like reference numbers refer to like parts in several views, particularly to  FIG. 1 , there is shown an AC generator or alternator  1  for automotive vehicles according to the invention which is illustrated, as an example, as having a cooling fan built therein. 
         [0026]    The alternator  1  consists essentially of a rotor  2 , a stator  3 , a brush unit  4 , a rectifier device  5 , an IC regulator  6 , a drive frame  7 , a rear frame  8 , a yoke pulley  9 , and a rear cover  10 . The rotor  2  has a rotary shaft  21  retained at ends thereof by bearings  22  and  23  to be rotatable. 
         [0027]      FIG. 2  is a sectional view which illustrates a joint between a drive shaft  11  and the yoke pulley  9  of the alternator  1 . The yoke pulley  9  is made up of a hollow first cylinder  90 , a second cylinder  92 , and an annular elastic damper  91  made of, for example, rubber. The first cylinder  90  is joined to the shaft  21  of the rotor  2  tightly through a nut  20 . The second cylinder  92  is fitted on the periphery of the first cylinder  90  through the elastic damper  91  for engagement with the inner periphery of a coupler  110  joined to the end of the drive shaft  11 . Specifically, the joint of the drive shaft  11  and the alternator  11  is achieved with the coupler  110  and the yoke pulley  9 . 
         [0028]    The coupler  110  (i.e., the drive shaft  11 ) is in misalignment with the yoke pulley  9 . Specifically, the center or axis of the coupler  110  (i.e., the longitudinal center line of the drive shaft  11 ) is shifted or eccentric from the center or axis of the yoke pulley  9  by a given distance δ (&gt;0). This causes the elastic damper  91  of the yoke pulley  9  to undergo compression in an upper angular range a and expansion in a lower angular range b, as viewed in  FIG. 2 , so that the repulsive force f, as produced by the elastic damper  91 , acts on the yoke pulley  9 . 
         [0029]      FIG. 3  demonstrates an example of a conventional alternator having a yoke pulley  9 ′ joined to the drive shaft  11 . The yoke pulley  9 ′ is in alignment with the drive shaft  11 . Specifically, the distance  6  by which the center of the coupler  110  of the drive shaft  1   1  is eccentric from a front flange  98  of the yoke pulley  9 ′ is zero (0), so that no radial pressure (i.e., the repulsive force f) acts on the yoke pulley  9 ′. 
         [0030]      FIG. 4  demonstrates another example of a conventional alternator equipped with a belt-drive mechanism. The alternator has a V-grooved pulley  13  around which a belt  12  is wrapped while being subjected to a given degree of tension T in dynamic engagement with a crank pulley, an idler, or other devices. The V-grooved pulley  13  is subjected to tension f transmitted from the belt  12 , so that a resulting load oriented in one direction is transmitted to the bearings  22  and  23  through the shaft  21 . 
         [0031]      FIGS. 5(   a ),  5 ( b ), and  5 ( c ) demonstrate physical loads acting on the bearings  22  and  23  of the shaft  21  of three types of alternators: the shaft-driven alternator  1  of this embodiment equipped with the yoke pulley  9  being in misalignment with the drive shaft  11 , the shaft-driven alternator of  FIG. 3  with the yoke pulley  9 ′ being in alignment with the drive shaft  11 , and the belt-driven alternator of  FIG. 4 .  FIG. 5(   a ) represents the static load Ps acting on the bearings  22  and  23  of each of the alternators.  FIG. 5(   b ) represents a dynamic load Pf acting on the bearings  22  and  23  of each of the alternators.  FIG. 5(   c ) represents a total load Po (i.e., the sum of Ps and Pf) acting of the bearings  22  and  23  of each of the alternators. 
         [0032]    The static load Ps added to the bearing  22  and  23  depends upon the external force facting on the pulley  9 ,  9 ′, or  13  and have the value different between the belt-driven alternator of  FIG. 4  and the shaft-driven alternator  1  of this embodiment. Specifically, the value of the static load Ps acting on the belt-driven alternator is the greatest in the three. The value of the static load Ps acting on the shaft-driven alternator of this embodiment is middle in the three. The value of the static load Ps acting on the shaft-driven alternator of  FIG. 3  is zero (0). The dynamic load Pf varies, as illustrated in  FIG. 5(   b ), and is defined by a load parameter P 1 , as determined by the vibration (g) acting on the mass (m) of the rotor  2 , and a load parameter P 2  depending upon an unbalance in rotation of the rotor  2  as a function of the speed of the rotor  2 . 
         [0033]    The total load Po acting on the bearings  22  and  23  of each of the alternators is a combination of the static load Ps and the dynamic load Pf and varies, as illustrated in  FIG. 5(   c ). Specifically, the total load Po on the belt-driven alternator is oriented in one direction at all the time. The total load Po on the shaft-driven alternator of  FIG. 3  is affected by the dynamic load Pf, so that it becomes zero (0) at a time t and is reversed in orientation thereof. This causes the bearings  22  and  23  to undergo irregular radial loads, which leads to concerns about the seizing of the bearing  22  arising from a lack of grease resulting from sliding of rolling elements of the bearing  22  or the creeping wear of the bearing holder  81  of the bearing  23  resulting from a change in orientation of the load on the bearing  23 . 
         [0034]    The shaft-driven alternator  1  of this embodiment is so designed that the static load Ps that is greater than required to cancel the dynamic load Pf is applied to the bearings  22  and  23 , thereby causing the total load Po to be kept oriented in a given direction, like the belt-driven alternator of  FIG. 4 , to avoid the premature seizing of the bearing  22  and the creeping wear of the bearing holder  81 , as described above. 
         [0035]      FIG. 6  shows the repulsive force, as produced by a damper rubber. When the yoke pulley  9  is, as illustrated in  FIG. 2 , arranged eccentrically from the drive shaft  11  in the radial direction thereof by the distance  6 , as selected within an eccentric distance range, as specified in  FIG. 6 , the repulsive force f, as produced by the elastic damper  91 , is transmitted to the bearings  22  and  23  through the yoke pulley  9  and the shaft  21  and acts on the bearings  22  and  23  as desired radial loads which do not become zero (0) at all times. 
         [0036]    Specifically, the eccentricity of the yoke pulley  90  from the coupler  110  (i.e., the drive shaft  11 ) results in the radial loads acting on the bearings  22  and  23  in one direction so as to keep the total load Po on the bearings  22  and  23  greater than zero (0) at all the time. This avoids the seizing of the bearings  22  and  23  and the creep of the bearing holder  81  without the needs for improving the accuracy in machining the bearings  22  and  23  and for installation of elastic members on the outer races of the bearings  22  and  23  which will increase the production cost of the alternator  1  and complicate the assembling of the alternator  1 . 
         [0037]    The eccentric distance δ is so selected based on the mechanical property of the elastic damper  91  as to keep above zero (0) at all times the total load Po, which is a combination of the dynamic load Pf and the radial load produced as a function of the eccentric distance δ, acting on the bearings  22  and  23  from one direction, thereby avoiding the seizing of the bearings  22  and  23  and the creep of the bearing holder  81 . 
         [0038]    While the present invention has been disclosed in terms of the preferred embodiments in order to facilitate better understanding thereof, it should be appreciated that the invention can be embodied in various ways without departing from the principle of the invention. Therefore, the invention should be understood to include all possible embodiments and modifications to the shown embodiments witch can be embodied without departing from the principle of the invention as set forth in the appended claims. For example, the elastic damper  91  may alternatively be attached to the coupler  110  of the drive shaft  11 . An additional damper equivalent to the elastic damper  91  may also be installed to the coupler  110  of the drive shaft  11 .