Abstract:
A belt driven mechanism which may be employed to transmit engine torque to an automotive electric rotary accessory such as an alternator. The belt driven mechanism is equipped with bearings disposed between a pulley around which a belt is wound and a torque output rotor. The belt driven mechanism also includes a coil spring mechanism having a length with a first and a second end portion to establish transmission of torque between the pulley and the rotor. Each of the first and second end portion has a plurality of points of attachment to a corresponding one of the pulley and the rotor, thereby distributing a mechanical load acting on the pulley or the rotor into fractions. This avoids local exertion of the load on the bearings, thereby prolonging the service life and ensuring the reliability of operation of the bearings.

Description:
CROSS REFERENCE TO RELATED DOCUMENT 
       [0001]    The present application claims the benefit of Japanese Patent Application No. 2007-3704 filed on Jan. 11, 2007, 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 a belt driven mechanism which may be mounted passenger automobiles or autotrucks to transmit torque of a crankshaft of an engine to auxiliaries or accessories, and more particularly to such a belt driven mechanism designed to ensure the stability of operation of bearings and improve the service life thereof. 
         [0004]    2. Background Art 
         [0005]    Usually, a rotary electric accessory mounted in automobiles such as an alternator is driven by the engine power through a belt. A change in angular velocity of a crankshaft of the engine causes the rotary electric accessory to fail to follow rotation of the crankshaft, thus resulting in slippage of the belt which will lead to mechanical noises and reduction in service life of the belt. In order to avoid this problem, Japanese Patent First Publication No. 6-207525 teaches a serpentine belt driven mechanism which has a coil spring disposed between a pulley around which the belt is wound and an armature assembly of the alternator to permit the pulley and the armature assembly to rotate relative to each other elastically. 
         [0006]    The serpentine belt driven mechanism, as taught in the above publication, encounters the problem in that torque acting on an end of the coil spring results in concentration of load on a single point on the pulley which is transmitted to two bearings disposed on both sides of the pulley. This will result in decreases in service life and reliability of operation of the bearings. Depending upon mechanical properties of the coil spring, an excessive load may be exerted by the end of the coil spring on the bearings through the pulley, so that the bearings produce reactive force and decreases in service life thereof. In order to alleviate this drawback, large-sized bearings may be used, but requiring the need for increasing the size of peripheral components, which results in an increase in entire manufacturing cost of the serpentine belt driven mechanism. 
       SUMMARY OF THE INVENTION 
       [0007]    It is therefore a principal object of the invention to avoid the disadvantages of the prior art. 
         [0008]    It is another object of the invention to provide an improved structure of a belt driven mechanism equipped with bearings which is designed to decrease the degree of mechanical load locally exerted on the bearings to increase the service life and improve the reliability of operation thereof. 
         [0009]    According to one aspect of the invention, there is provided a belt driven mechanism which may be employed to transmit engine torque to an automotive electric rotary accessory such as an alternator. The belt driven mechanism comprises: (a) a pulley to be rotated by a belt; (b) a rotary member; (c) bearings disposed between the pulley and the rotary member to permit the pulley and the rotary member to rotate relative to each other; and (d) a coil spring mechanism having a length with a first and a second end portion to establish transmission of torque between the pulley and the rotary member. The first end portion has a plurality of first points of attachment to the pulley. The second end portion has a plurality of second points of attachment to the rotary member. The first points are located away from each other in a circumferential direction of the coil spring mechanism. The second points are located away from each other. 
         [0010]    Specifically, each of the coil spring mechanism is joined to one of the pulley and the rotary member at a plurality of points, thereby distributing a mechanical load acting on the pulley or the rotary member into fractions. This avoids local exertion of the load on the bearings, thus prolonging the service life and ensuring the reliability of operation of the bearings. This also permits peripheral components in the belt driven mechanism to be reduced in size and the entire manufacturing cost to be decreased. 
         [0011]    In the preferred mode of the invention, the coil spring mechanism may be made up of a plurality of coil springs assembled to extend around an axis of rotation of the rotary member in a spiral fashion. Each of the coil springs is joined at one of opposed ends thereof to the pulley and at the other end thereof to the rotary member. 
         [0012]    The coil springs may be laid to overlap each other in an axial direction thereof. 
         [0013]    The coil springs may alternatively be laid to overlap each other in a radius direction thereof. 
         [0014]    The coil spring mechanism may alternatively be made of a single coil spring with the first and second end portions. The first end portion has a plurality of ends which are located away from each other in a circumferential direction of the coil spring and attached at the first points to the pulley. Similarly, the second end portion has a plurality of ends which are located away from each other in the circumferential direction of the coil spring and attached at the second points to the rotary member. 
         [0015]    The first points may be located at an equi-angular interval away from each other in the circumferential direction of the coil spring mechanism. Similarly, the second points may be located at an equi-angular interval away from each other in the circumferential direction of the coil spring mechanism. 
         [0016]    The coil spring mechanism may be so designed that mechanical loads identical in degree with each other are exerted on the first points or the second points. 
         [0017]    At least one of the pulley and the rotary member may have formed integrally therewith a support portion by which a corresponding one of the first and second portions of the coil spring mechanism is supported at one of groups of the first points and the second points are supported. 
         [0018]    At least one of the pulley and the rotary member may alternatively have secured thereto a support portion by which a corresponding one of the first and second portions of the coil spring mechanism is supported at one of groups of the first points and the second points are supported. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    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. 
           [0020]    In the drawings: 
           [0021]      FIG. 1  is a longitudinal sectional view which shows a belt driven mechanism according to the first embodiment of the invention; 
           [0022]      FIG. 2(   a ) is a top view which shows an assembly of coil springs installed in the belt driven mechanism of  FIG. 1 ; 
           [0023]      FIG. 2(   b ) is a side view which shows the assembly of coil springs, as illustrated in  FIG. 2(   a ); 
           [0024]      FIG. 2(   c ) is a bottom view of  FIG. 2(   b ); 
           [0025]      FIG. 3  is a side view which shows the first modification of an assembly of coil spring installed in the belt driven mechanism of  FIG. 1 ; 
           [0026]      FIG. 4(   a ) is a top view which shows the second modification of an assembly of coil springs installed in the belt driven mechanism of  FIG. 1 ; 
           [0027]      FIG. 4(   b ) is a side view of  FIG. 4(   a ); 
           [0028]      FIG. 5  is a side view which shows a coil spring to be installed in the belt driven mechanism of  FIG. 1  according to the second embodiment of the invention; 
           [0029]      FIG. 6  is a top view which shows a coil spring to be installed in the belt driven mechanism of  FIG. 1  according to the third embodiment of the invention; and 
           [0030]      FIG. 7  is a top view which shows a coil spring to be installed in the belt driven mechanism of  FIG. 1  according to the fourth embodiment of the invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0031]    Referring to the drawings, wherein like reference numbers refer to like parts in several views, particularly to  FIG. 1 , there is shown a belt driven mechanism  100  according to the first embodiment of the invention which is designed to transmit torque of a crankshaft of an internal combustion engine (not shown) to a shaft  200  connected to an electric rotary accessory (not shown) such as an alternator mounted in the automotive vehicle. The belt driven mechanism  100  includes generally a rotor  10 , an inner  12 , a pulley  20 , bearings  30  and  32 , and an assembly of coil springs  81  and  82 . 
         [0032]    The rotor  10  is to be joined to the shaft  200  so that it rotates together with the shaft  200 . The rotor  10  has formed in an inner periphery thereof an internal thread  10   a  which makes a joint with the shaft  200  firmly. 
         [0033]    The pulley  20  has formed in an outer periphery thereof a plurality of V-grooves around which a belt (not shown) is wound which extends from the crankshaft of the engine. The pulley  20  also has formed on an inner periphery thereof an annular flange  22  which protrudes inwardly. The flange  22 , as can be seen in  FIG. 1 , has formed on one of opposed surfaces a pair of recesses in which ends  81 -A and  82 -A of the coil springs  81  and  82  are fitted, respectively, to retain the coil springs  81  and  82 . The two recesses are located at an angular interval of 180° away from each other in the surface of the flange  22 . The belt driven mechanism  100  works to transmit torque of the crankshaft of the engine from the pulley  20  to the rotor  10  through the coil springs  81  and  82 . 
         [0034]    The bearings  30  and  32  are located away from each other in alignment with an axis of rotation of the belt driven mechanism  100  between the pulley  20  and the rotor  10 . The bearing  30  is fit at an outer periphery of an outer ring thereof on an inner periphery of a portion of the pulley  20  which is located farther away from an opening of the belt driven mechanism  100  into which the shaft  200  is to be inserted and at an entire inner periphery of an inner ring thereof on an outer periphery of the inner  12 . The inner  12  is made of an annular member separate from the rotor  10  and fit on a portion of the outer periphery of the rotor  10  which is located farther away from the opening of the belt driven mechanism  100  into which the shaft  200  is to be inserted. The inner  12  has a pair of recesses in which the other ends  81 -B and  82 B of the coil springs  81  and  82  are fitted and which are located at an angular interval of 180° away from each other. 
         [0035]    The bearing  32  is located closer than the bearing  30  to the opening the opening of the belt driven mechanism  100  into which the shaft  200  is to be inserted. The bearing  32  is fit at an outer periphery of an outer ring thereof on the inner periphery of the pulley  20  and at an inner periphery of an inner ring thereof on the outer periphery of the rotor  10 . A cover  14  is secured to an open end of the belt driven mechanism  100 . The cover  14  is made of a hollow cylindrical member having formed therein a hole  16  through which the shaft  200  is to be inserted. The cover  14 , as can be seen from the drawing, has an annular extension  140  which is fit in the inner periphery of the bearing  32  to cover the outer end of the bearing  32 . 
         [0036]    The coil springs  81  and  82  are disposed to make a mechanical connection between the pulley  20  and the inner  12 . Each of the coil springs  81  and  82  is, as described above, retained at one of the ends thereof by the flange  22  formed integrally with the pulley  20  and at the other end thereof by the inner  12  secured to the rotor  10 . 
         [0037]      FIGS. 2(   a ),  2 ( b ), and  2 ( c ) illustrate an assembly of the coil springs  81  and  82 . One of the ends of the coil spring  81  and one of the ends of the coil spring  82  are, as clearly illustrated in  FIG. 2(   a ), diametrically opposed to each other, that is, located at an angular interval of 180° away from each other around a longitudinal center line of the assembly of the coil springs  81  and  82  (i.e., an axis of rotation of the belt driven mechanism  100 ). Similarly, the other end of the coil spring  81  and the other end of the coil spring  82  are, as clearly illustrated in  FIG. 2(   c ), diametrically opposed to each other, that is, located at an angular interval of 180° away from each other around the longitudinal center line of the assembly of the coil springs  81  and  82 . The coil springs  81  and  82  are identical in configuration, spring constant, and thickness with each other. If the thickness of each turn of the spiral assembly of the coil springs  81  and  82  is defined as H, the thickness of each turn of the coil springs  81  and  82  is H/2. The coil springs  81  and  82  are shifted by 180° to each other in the spiral direction. 
         [0038]    As described above, the joint of the pulley  20  and the rotor  10  is achieved by attaching the ends of the coil springs  81  and  82  to the flange  22  of the pulley  20  and the inner  12  fitted on the rotor  10 , thereby causing loads F 1 , F 3 , F 2 , and F 4  exerted by either of the pulley  20  or the rotor  10  on the ends  81 -B,  82 -B,  81 -A, and  82 -A of the coil springs  81  and  82  be distributed to two places of each of the bearings  30  and  32  located 180° away from each other. Therefore, when the pulley  20  has undergone a change in angular velocity arising from a change in rotation of the crankshaft of the engine, and a rotary body such as a rotor of an automotive alternator which has a greater inertia and is connected to the shaft  200  continues to rotate, an excessive load is not exerted locally on the bearings  30  and  32  in the circumferential direction thereof which are disposed between the pulley  20  and the rotor  10 . This results in an increase in service life of the bearings  30  and  32  and ensures the stability of operation thereof, which eliminates the need for increasing the size of the bearings  30  and  32  in order to avoid the deterioration thereof and permits peripheral components to be reduced in size or manufacturing cost. 
         [0039]    The coil springs  81  and  82  are, as described above, assembled together around the axis of rotation of the rotor  10  and joined at the ends  81 -A and  82 -A to the pulley  20  and at the other ends  81 -B and  82 -B to the rotor  10 . Specifically, the coil springs  81  and  82  are identical in shape and laid to overlap each other in the form of a spiral. Such assembling is usually easily, thereby improving the service life of the bearings  30  and  32  and ensuring the reliability of operation thereof. 
         [0040]    The ends  81 -A and  82 -A or  81 -B and  82 -B of the coil springs  81  and  82  are affixed to each of the pulley  20  and the rotor  10  at an interval of 180° away from each other in the circumferential direction of the coil springs  81  and  82 . In other words, the ends  81 -A and  82 -A or  81 -B and  82 -B of the coil springs  81  and  82  secured to each of the pulley  20  and the rotor  10  are symmetrical about the longitudinal center line of the assembly of the coil springs  81  and  82 , thereby distributing the load acting on either of the pulley  20  or the rotor  10  into fractions to be exerted on the bearings  30  and  32  in the circumferential direction thereof, which also results in an increase in service life, ensures the stability of operation thereof, and permits peripheral components to be reduced in size or manufacturing cost. Use of the same size of the coil springs  81  and  82  causes the physical load acting between the ends  81 -A and  82 -A or  81 -B and  82 -B of the coil springs  81  and  82  and either of the pulley  20  or the rotor  10  at two points located 180° away from each other to be oriented in opposite directions as a couple of forces exerted on the bearings  30  and  32  evenly, thus further increasing the service life, ensuring the stability in operation thereof, and permitting the peripheral components to be reduced in size or manufacturing cost. 
         [0041]    The joints of the ends  81 -A and  82 -A of the coil springs  81  and  82  to the pulley  20  are made at the flange  22  formed integrally with the pulley  20 , thereby resulting in a decrease in discrete component parts of the belt driven mechanism  100 . Additionally, the inner  12  to which the other ends  81 -B and  82 -B of the coil springs  81  and  82  to the inner  12  are joined is made as a part separate from the rotor  10  and mechanically attached to the rotor  10 , thus permitting the rotor  10  to be machined to have a simple structure. 
         [0042]    The flange  22  may alternatively be formed as a part separate from the pulley  20  and fit on the inner periphery of the pulley  20 . The rotor  10  may alternatively be machined to have an annular protrusion formed integrally on the outer periphery thereof as the inner  12 . 
         [0043]      FIG. 3  illustrates the first modification of the assembly of the coil springs  81  and  82 . 
         [0044]    The coil springs  81  and  82  are, unlike the ones of  FIGS. 2(   a ) to  2 ( c ), assembled at intervals away from each other. The coil springs  81  and  82  are extend coaxially with the axis of rotation of the rotor  10  (i.e., the pulley  20 ) and have ends opposed diametrically to each other in the same manner as described above. 
         [0045]      FIGS. 4(   a ) and  4 ( b ) illustrate the second modification of the assembly of the coil springs  81  and  82 . 
         [0046]    The coil springs  81  and  82  are laid not to overlap each other in the axial direction of the assembly and wound coaxially with each other. In other words, the coil spring  81  is, as can be seen from  FIG. 4(   a ), extends inside the coil spring  82  and laid to overlap the coil spring  82  in the radius direction of the assembly. It is advisable that the width and/or the thickness of either or both of the coil springs  81  and  82  be regulated to bring load (i.e., torque) acting on the ends of the coil spring  81  into agreement with that acting on the ends of the coil spring  82 . 
         [0047]    While the coil springs  81  and  82 , as illustrated in  FIGS. 2(   a ) to  2 ( c ), are identical in size or type with each other, but they may alternatively be designed to have diameters different from each other and assembled so that they partially overlap in the axial direction of the assembly. 
         [0048]    The coil springs  81  and  82 , as illustrated in  FIGS. 4(   a ) and  4 ( b ), are laid in direct contact with each other. Specifically, the coil spring  81  has an outer periphery abutting on an inner periphery of the coil spring  82 , but however, either or both of them may be altered in inner or outer diameter to have an air gap therebetween. Alternatively, the coil springs  81  and  82  of  FIGS. 4(   a ) and  4 ( b ) may be shifted vertically (i.e., the axial direction of the assembly) to have the ends thereof, like in  FIG. 3 , aligned with each other in the radius direction of the assembly. 
         [0049]      FIG. 5  illustrates the second embodiment of the invention. 
         [0050]    Instead of the coil springs  81  and  82 , a coil spring  83  is used in the belt driven mechanism  100 , as illustrated in  FIG. 1 . The coil spring  83  is designed to have a pair of ends  83   a  and  83   b  formed at one end side thereof and a pair of ends  83   c  and  83   d  formed at the other end side thereof. The ends  83   a  and  83   b  are diametrically opposed to each other. Specifically, the end  83   a  is formed on a portion of the coil spring  83  which is located 180° away from the end  82   a.  Similarly, the ends  83   c  and  83   d  are diametrically opposed to each other. Specifically, the end  83   c  is formed on a portion of the coil spring  83  which is located 180° away from the end  82   d.  The end  83   a  is aligned with the end  83   d  in an axial direction of the coil spring  83 . Similarly, the end  83   b  is aligned with the end  83   c  in the axial direction of the coil spring  83 . 
         [0051]      FIG. 6  illustrates the third embodiment of the invention. 
         [0052]    Instead of the coil springs  81  and  82 , a spring assembly  90  is used in the belt driven mechanism  100  of  FIG. 1 . The spring assembly  90  is made up of three coil springs  91   a,    91   b,  and  91   c  which are assembled in a manner similar to that in  FIGS. 2(   a ) to  2 ( c ). Specifically, the coil springs  91   a  to  91   c  are laid to overlap each other in the axial direction of the spring assembly  90  to have three ends  92   a,    92   b,  and  92   c  located 120° away from each other at each end side in a circumferential direction of the spring assembly  90  so that loads acting on the ends  92   a  to  92   c  may be identical with each other. The spring assembly  90  may alternatively be made up of four or more coil springs. 
         [0053]      FIG. 7  illustrates the fourth embodiment of the invention. 
         [0054]    Instead of the coil springs  81  and  82 , a spring assembly  105  is used in the belt driven mechanism  100  of  FIG. 1 . The spring assembly  105  is made up of three coil springs  105   a,    105   b,  and  105   c  which are assembled in a manner similar to that in  FIGS. 4(   a ) and  4 ( b ). Specifically, the coil springs  105   a  to  105   c  has diameters different from each other and are laid in contacting abutment in the radius direction of the spring assembly  105  to have three ends  106   a,    106   b,  and  106   c  located 120° away from each other at each end side in a circumferential direction of the spring assembly  105  so that loads acting on the ends  106   a  to  106   c  may be identical with each other. The spring assembly  105  may alternatively be made up of four or more coil springs. 
         [0055]    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.