Abstract:
An electromagnetic clutch having an electromagnet, a rotational member mounted to undergo rotation, an armature selectively coupled to the rotational member for rotation therewith when the electromagnet is energized, and a ball bearing rotatably supporting the rotational member. The ball bearing has an inner race, an outer race, and a plurality of balls arranged in a plurality of rows each containing an odd number of the balls. The balls of the ball bearing are disposed between the inner race and the outer race so that each of the balls contacts the inner race at at least one point and contacts the outer race at at least one point.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a ball bearing assembly structure, an electromagnetic clutch having the ball bearing assembly structure, and a gas compressor equipped with the electromagnetic clutch. 
     2. Description of the Related Art 
     In a vane-type gas compressor used for a car air conditioner or the like, a rotary power is transmitted from an engine-crankshaft pulley to a rotor shaft  40  through a belt  60  and electromagnetic clutch  50  as shown in FIG.  1 . 
     The electromagnetic clutch  50  has a ring-shape electromagnet  51 , a prime-mover pulley  5  for passing the magnetic flux of the electromagnet  51 , a plurality of rows of ball bearing  530  (see FIG. 10) for rotatably and coaxially holding the prime-mover pulley  52  to the electromagnet  51 , and a follower armature plate  54  to be attracted or adsorbed to an end surface  52   a  of the prime-mover pulley  52  by the magnetic flux. 
     During engine rotation, the prime-mover pulley  52  and the ball bearing  530  holding the same are rotatively driven at all times by a belt  60 . 
     When operating the gas compressor  1 , the electromagnet  51  of the electromagnetic clutch  50  is energized to attract or adsorb the follower armature plate  54  to an end surface  52   a  of the prime-mover pulley  52  and join the prime-mover pulley  52  and the rotor shaft  40 , thereby rotating the rotor shaft  40 . 
     The ball bearing  530  of the electromagnetic clutch  50  conventionally has used one having an even number of balls  530   a  per row, e.g. fourteen as shown in FIG.  10 . Generally, the ball bearing causes vibration and noise due to rotation. In the case of the ball bearing  530  rotating while undergoing a radial load due to a tension of the belt  60 , vibration and noise considerably occur. Particularly when other vibration and noise levels are lowered during engine idling, the vibration and noise of the ball bearing  530  transmitted to the vehicular compartment is not negligible. 
     The inventor has conducted various experiments and discovered that the one factor of high vibration and noise level is an even number of balls of the ball bearing. In the ball bearing  530  having an even number of balls  530   a  per one row, the balls  530   a  are in a facing relation to have linear-symmetry arrangement between the inner race  530   b  and the outer race  530   c . The deformation and vibration at a regular particular frequency is caused in the inner and outer races. It is to be considered that the vibration as a source also increases noise. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the foregoing problem in the conventional art and provides an electromagnetic clutch low in vibration and noise resulting from a ball bearing assembly of the present invention and a gas compressor with the electromagnetic clutch. 
     In order to solve the foregoing problems in the conventional art, the present invention provides an electromagnetic clutch having a ball bearing assembly having an odd number of balls per row. By providing the odd number of balls, the arrangement of balls will not be in a facing relation. The deformation in the inner and outer races during rotation of the ball bearing while undergoing a radial load is made irregular and complicated, eliminating the deformation and vibration at a regular predetermined frequency and lowering the level of vibration and noise. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal sectional view showing an embodiment of this invention. 
     FIG. 2 is a front view showing a ball bearing of the gas compressor of FIG.  1 . 
     FIG. 3 is a explanatory view showing an empirical value of a relationship between the number of balls of the ball bearing and noise/vibration. 
     FIG. 4A is a plan view and FIG. 4B is side view showing a noise measuring position of a present-invention product and a conventional product in the actual vehicle. 
     FIG. 5A is a plan view and FIG. 5B is a side view showing an installation point of vibrometers for a present-invention product and a conventional product in the actual vehicle. 
     FIGS. 6A and 6B are graphs showing, by comparison, noise levels of the present-invention product and the conventional product. 
     FIGS. 7A and 7B are graphs showing, by comparison, vibration levels of the present-invention product and the conventional product. 
     FIG. 8 is an explanatory view showing a schematic structure of a scroll type gas compressor mounted with an electromagnetic clutch according to the invention. 
     FIG. 9 is an explanatory view showing a schematic structure of a slant plate type gas compressor mounted with the electromagnetic clutch according to the invention. 
     FIG. 10 is a front view of the related art ball bearing used in a gas compressor. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment of this invention will be explained below with reference to FIG. 1 to FIG.  9 . FIG. 1 is a lengthwise sectional view showing an embodiment of this invention, and FIG. 2 is a front view showing a ball bearing of a gas compressor of FIG.  1 . 
     In FIG. 1, the gas compressor  1  is provided with an electromagnetic clutch  50 . The electromagnetic clutch  50  is transmitted with a drive force for rotation from an engine crankshaft through a belt  60  wound over a prime-mover pulley  52  on a prime-mover side thereof. 
     When the electromagnetic clutch  50  is excited, a follower armature plate  54  on a follower side coupled to the rotor shaft  40  is attracted or adsorbed to and coupled or integrated with an end surface  52   a  of the prime-mover pulley  52 , to transmit a rotary power to the rotor shaft  40 . Thus the prime-mover pulley  52  functions as a rotational member which rotates, in a cylinder chamber  2 , the rotor  41  integrated with the rotor shaft  40  and the vanes  42  sliding in radial grooves of the rotor  41  to compress the gas within the cylinder  2 . 
     Incidentally, the compressed gas is discharged to a discharge chamber  3  where it is delivered through a discharge port  3   a  to a piping system such as a car air conditioner, not shown, and returned through a suction port  4   a  to a suction chamber  4 , again being taken into the cylinder chamber  2 . 
     In the electromagnetic clutch  50 , provided is an electromagnet  51  in a ring form fixed on a front cover (frame)  5  of the gas compressor  1 . When the coil  51   a  of the electromagnet  51  is energized, the electromagnetic clutch  50  is excited. The magnetic flux generated by the electromagnet  51  passes through an inside of the prime-mover pulley  52 , to attract the follower armature plate  54  onto the end surface  52   a  of the prime-mover pulley  52 . 
     The prime-mover pulley  52  is rotatably held coaxially to the electromagnet  51  on the frame  5  of the gas compressor  1 , through a ball bearing  53  having a plurality of rows of balls  53   a . More specifically, the inner race  53   b  of the ball bearing  53  is attached on the frame  5  of the gas compressor  1 , and the outer race  53   c  holds the prime-mover pulley  52 . That is, an outer-race-rotating assembling structure is provided by assembling the inner race  53   b  on the side of non-rotatable stator and the outer race  53   c  on the side of a rotatable rotor. This ball bearing  53  is acted upon with, in addition to the load due to the weight of the prime-mover pulley  52 , rotating vibration and the like, a further greater load in a radial direction due to tension, vibration and the like of the belt  60 . 
     The foregoing structure and operation is similar to the gas compressor using an electromagnetic clutch. Next, the featured parts of this invention are explained. 
     The ball bearing  53  has, as shown in FIG. 2, balls  53   a  in an odd number of balls per row, thirteen in this embodiment, arranged nearly equally spaced on a pitch circle p through a retainer (not shown) between the inner race  53   b  and the outer race  53   c.    
     FIG. 3 shows a result of comparison between the vibration and noise on the gas compressor of the invention and the vibration and noise on a conventional gas compressor. In FIG. 3, the invention product is a gas compressor of the invention using the ball bearing  53  having an odd number of balls (thirteen) shown in FIG. 2 on the electromagnetic clutch  50  while the conventional product is a conventional gas compressor using a ball bearing  530  having an even number of balls (fourteen) shown in FIG. 10 on the electromagnetic clutch  50 . 
     The data in FIG. 3 shows respective average values of vibration and noise measured under the same condition on each of five sets manufactured for the invention product and the conventional product. 
     As shown in FIG. 3, where assembling a ball bearing  53  having an odd number of balls of the invention, there is lower in noise level by a little over 5 dB and in vibration level by a little over 0.2 G as compared to the case of assembling a conventional ball bearing  530  having an even number of balls. 
     Next, the invention product and the conventional product were respectively mounted on actual vehicles, thereby conducting a noise measurement test and a vibration measurement test. The measuring conditions in the measurement test are as follows: 
     ambient temperature of 30° C. 
     vehicle halt state (idling state) 
     engine rotational speed Ne=1100 rpm (compressor rotation speed Nc=1400 rpm air conditioner in ON (compressor clutch ON) state. 
     Incidentally, the invention product is a gas compressor of the invention using the ball bearing  53  having an odd number (thirteen) of balls shown in FIG. 2 on the electromagnetic clutch  50  while the conventional product is a conventional gas compressor using the ball bearing  530  having an even number (fourteen) of balls shown in FIG. 10 on the electromagnetic clutch  50 . 
     The noise measuring position is as shown in FIGS. 4A and 4B, wherein the gas compressor  1  is mounted on an engine  72  in an engine room  71  of the vehicle  70  and a microphone (noise meter)  74  for measuring noise is installed in a vehicular chamber  73 . 
     This microphone  74  is set up in a center of the front seat, i.e. at an intermediate position between the driver&#39;s seat and the assistant driver&#39;s seat, at a height corresponding to the human ear. 
     Next, the vibration measuring position is as shown in FIGS. 5A and 5B, wherein the gas compressor is mounted on the engine  72  through a compressor-mounting bracket  72   a , and an acceleration pickup (vibrometer)  75  is mounted on a casing flange  1   a  of the gas compressor  1 . The direction of vibration measurement is set in a front-and-rear direction of the gas compressor  1 . 
     Then, frequency analysis (FFT analysis) is conducted. A result of noise measurement is shown as the invention product in graph of FIG.  6 A and the conventional product in graph of FIG. 6B (frequency on the horizontal axis, noise level on the vertical axis). 
     Meanwhile, a result of vibration measurement by a vibrometer  75  mounted on the gas compressor  1  is shown as the invention product in a graph of FIG.  7 A and the conventional product in a graph of FIG. 7B (frequency on the horizontal axis, vibration level on the vertical axis). 
     Accordingly, as apparent from comparison between the graphs of FIGS. 6A and 6B of concerning the noise measurement result of the present product and the conventional product, the noise level of the conventional product at a frequency 240 Hz conspicuous in noise is 52.53 dB whereas the noise level of the present invention product is 42.49 dB. It can be understood that the noise level decreases by about 10 dB. 
     Meanwhile, comparing the vibration measurement results shown in FIGS. 7A and 7B, the vibration level of the present invention product is −37.98 dB=0.13 G as compared to the vibration level of the conventional product of −28.34 dB=0.38 G. It can be understood that vibration is decreased by 0.2 G or greater. Incidentally, vibration is calculated as 0 dB=10 G by the use of the below calculation formula.                y        [   dB   ]       =         20                 log                     χ        [   G   ]         10        [   G   ]           ⇒     χ        [   G   ]         =         10        [   G   ]       ×     10       y        [   dB   ]       20         =     10         y        [   dB   ]       20     +   1                   [     Formula                 1     ]                                
     Meanwhile, since the sound at about 240 Hz has been conspicuously heard in the vehicular compartment, the other frequencies of sound is guessed negligible. 
     In this manner, the following can be considered as the reason why the noise/vibration level can be reduced between the present invention and the conventional product. 
     In the ball bearing  53  of this invention, the odd number of balls  53   a  are not in a state in which they face each other but the deformation of the inner race  53   b  and outer race  53   c  of the ball bearing  53  is irregular and complicated in form. The deformation/vibration at a regular particular frequency is eliminated to decrease the vibration/noise level. On the contrary, in the conventional ball bearing  530 , the even number of balls  530   a  face each other and are arranged in a linear symmetry. The deformation/vibration at a regular particular frequency is caused in the inner race  530   b , and the outer race  530   c  so that the vibration/noise level is high. 
     The above explained embodiment explained the gas compressor  1  of a rotary vane type provided with the electromagnetic clutch  50  having an odd number of balls in the ball bearing  53 . However, an electromagnetic clutch  50  of the same structure may be mounted on a scroll type gas compressor  80  shown in FIG.  8 . Meanwhile, as shown in FIG. 9, the electromagnetic clutch  50  may be mounted on a slant-plate type gas compressor  90 . 
     The schematic structure and compression operation of the scroll type gas compressor  80  is explained on the basis of FIG.  8 . The scroll type gas compressor in the present embodiment has a scroll type compression chamber arranged in a center. At an electromagnetic clutch side of the compression chamber, a drive section for swiveling a swivel scroll is arranged and a discharge chamber is arranged on an opposite side of the electromagnetic clutch. 
     That is, as shown in FIG. 8, in the scroll type gas compressor  80  the front housing  81  in an inner periphery rotatably supports a rotor  81   b  through a bearing  81   a . The side wall on the opposite side to the electromagnetic clutch  50  side of the front housing  81 , at an outer periphery, is in close contact with one end surface of a fixed scroll housing  82 , forming a front-side side wall of the suction chamber  82   a . Incidentally, the rotor shaft  81   c  provided integral with the rotor  81   b  is integrated with a follower armature plate  54  of the electromagnetic clutch  50 . 
     The fixed scroll housing  82  has a cylindrical outer wall. On the outer wall, the suction port  82   b  is provided. Furthermore, the fixed scroll housing  82  is provided with disc-formed side wall integral with the outer wall and perpendicular to a rotor rotation axis. In this side wall, a fixed scroll  83  in a spiral form is formed. The outermost periphery of the fixed scroll  83  constitutes the suction chamber  82   a.    
     Furthermore, in the front housing  81 , the rotatably supported rotor  81   b  is integrally provided with an eccentric shaft  84  in a position deviated from the rotation axis of the rotor  81   b  in an end on the side opposite to the electromagnetic clutch side. On the eccentric shaft  84 , an eccentric ring  84   a  is fixed to rotatably support the swivel scroll  85  through a needle bearing  84   b.    
     The swivel scroll  85  rotatably supported on the eccentric shaft  84  has a disc-formed side wall and a scroll wall in a spiral form integrally formed rectangular to the side wall. A plurality of crescent-formed compression chambers  86  are formed by the above-mentioned fixed scroll  83  and the swivel scroll  85 . 
     Furthermore, the fixed scroll housing  82  is provided with a discharge port  82   c  to discharge a compressed refrigerant gas and further a discharge valve  82   d  to prevent reverse flow of the refrigerant gas. 
     Further, a rear housing  87  is provided on a back side of the fixed scroll  83 . The rear housing  87 , together with a side wall of the fixed scroll housing  82 , constitutes a discharge chamber  87   a . The rear housing  87  at its outer periphery is provided with a discharge port  87   b  for connection to an external system. 
     Next, explaining the compressing operation of the scroll type gas compressor  80  mounted with the electromagnetic clutch  50  according to the invention is explained. When the electromagnetic clutch  50  is being excited, the follower amateur plate  54  on the follower side connected to the rotor shaft  81   c  is adsorbed to and integrated with the end surface  52   a  of the prime-mover pulley  52 . A rotation force is transmitted from the engine or the like through a belt, to rotate the rotor  81   b  and eccentric shaft  84  through the electromagnetic clutch  50 . 
     Due to rotation of the eccentric shaft  84 , the swivel scroll  85  makes swivel motion. 
     If the swivel scroll  85  starts swivel motion, the suction chamber  82   a  and the compression chamber  86  are repeated of communication and non-communication by the relative movement to the fixed scroll  83 . During communication, the refrigerant gas under low pressure taken through the suction port  82   b  and temporarily reserved in the suction chamber  82   a  is sucked to the compression chamber  86  in the outermost periphery. 
     If the swivel of the swivel scroll  85  proceeds, the suction chamber  82   a  and the compression chamber  86  are shielded of communication, to confine the low-pressure refrigerant gas within the crescent-formed compression chamber  86 . The crescent-formed compression chamber  86  when the swivel of the swivel scroll  85  proceeds is reduced in its volume while changing an angle toward a circumferential direction, moving toward an inner peripheral portion. Simultaneously therewith, the next communication between the suction chamber  82   a  and the compression chamber at the outermost periphery is started thereby continuously carrying out suction and compression of refrigerant gas. 
     When the swivel of the swivel scroll  85  further proceeds, the crescent-formed compression chamber  86  reaches a center of the rotation axis center, and refrigerant gas is push up the discharge valve  82   d  through the discharge port  82   c , discharging to the discharge chamber  87   a . The high-pressure refrigerant gas discharged to the discharge chamber  87   a  is passed through the discharge port  87   b  and discharged to the not-shown system high-pressure piping. 
     In this manner, even if the electromagnetic clutch  50  according to the invention is applied to the scroll type gas compressor  80 , there is the same operation/working effect of lowering the vibration/noise level similarly to the rotary-vane type gas compressor. 
     Next, FIG. 9 shows a schematic structure of a slant plate type gas compressor  90  mounted with the electromagnetic clutch  50  according to the invention. The slant plate type gas compressor  90  in this embodiment is a both slant plate type gas compressor having compression chambers existing in the front and rear of a sandwiched center slant plate to suck, compress and discharge a refrigerant gas by reciprocal motion of a one-bodied piston. 
     The number of compression chambers or pistons is given an arbitrary number depending on a discharge volume required for the compressor. In this example, the pistons are five in the number and there are ten compression chambers in totally in the front and rear. 
     In FIG. 9, the slant plate type gas compressor  90  is first formed, in an outer periphery of the front housing  91 , with a section port  91   a  for connection to a suction-side piping. An annular front suction chamber  91   b  is formed communicating with the suction port  91   a . Meanwhile, an annular front discharge chamber  91   c  is formed on an inner peripheral side of the suction port  91   a . In a end surface on the compression chamber side of the front housing  91 , a disc-formed front valve plate  91   d  is fixed closely. 
     Similarly, the structure of the rear housing  92  has a discharge port  92   a  for connection to a system discharge-side piping and formed such that communicating to the discharge port  92   a , the annular rear discharge chamber  92   b  surrounds an outer periphery of the pin. Furthermore, on an outer peripheral side of the rear discharge chamber  92   b , a rear suction chamber  92   c  is formed that is in a horse&#39;s-hoof form disconnected only in a communication part of the discharge port  92   a  and the rear discharge chamber  92   b . Also, the rear housing  92  at its end surface on the compression chamber side is closely fixed with a disc-formed rear-valve plate  92   d.    
     A cylinder block  93  interposed between the front housing  91  and the rear housing  92  has a front cylinder block  93   a  and a rear cylinder block  93   b  that are pin-coupled through a gasket  93   c . The cylinder block  93  is provided with a suction passage  94   a  communicating between the front suction chamber  91   b  and the rear suction chamber  92   c  and a discharge passage  94   b  communicating between the front discharge chamber  91   c  and the rear discharge chamber  92   b.    
     Furthermore, in the cylinder block  93  is rotatably supported a rotor shaft  95 . The rotor axis  95   a  at a tip of the rotor shaft  95  is integrated with the follower armature plate  54  of the electromagnetic clutch  50  and is rotatively driven by receiving a drive force on the electromagnetic clutch  50  side. 
     The rotor shaft  95  is fixed with a slant plate  96  by a not-shown key or the like. This slant plate  96  at its outer periphery is formed in a size reaching a center of a plurality of pistons  97  radially arranged. The slant plate  96  at its forward and rearward surfaces is slidably holds a semi-spherical shoe  96   a . Through the shoe  96   a , the rotation motion of the slant plate  96  is converted into an axial reciprocal motion of the piston  97 . 
     Incidentally, FIG. 9 shows a state in which the piston  97  is retracted to the rear housing  92  side, in this state the front compression chamber  98  exhibits a maximum volume. 
     Next, explanation is made on the compression operation of a refrigerant gas by the slant plate type gas compressor  90 . The rotation force from the engine or the like is transmitted by the belt or the like, to rotate the rotor axis  95   a , rotor shaft  95  and slant plate  96  through the electromagnetic clutch  50 . 
     By the rotating slant plate  96 , the piston  97  reciprocates in a rotation-axis direction through the shoe  96   a . The piston  97  shown starts to move toward the front chamber  98  simultaneously with rotation of the slant plate  96 . 
     At this time, the refrigerant gas under low pressure sucked from the suction port  91   a  flows into the front suction chamber  91   b  and enters a rear suction chamber  92   c  through the suction passage  94   a . The valve, not shown, of the rear valve plate  92   d  opens toward the piston to suck into a rear compression chamber, also not shown. 
     On the other hand, on a front compression chamber  98  side of the same piston  97 , the low-pressure refrigerant gas stayed in the front compression chamber  98  is compressed by the piston  97 . The compressed refrigerant gas reaches a predetermined high pressure whereupon the valve formed on the front valve plate  91   d  opens to discharge it to the front discharge chamber  91   c . The high-pressure refrigerant gas discharged into the front discharge chamber  91   c  passes the discharge passage  94   c  to enter the rear discharge chamber  92   b , and is discharged toward the system through the discharge port  92   a . Incidentally, the embodiment of the both slant plate type gas compressor was explained above, application is possible for a single-side slant plate gas compressor forming a compression chamber on one of the front side and the rear side. 
     This slant plate gas compressor  90  has the similar effect of reducing the level of noise/vibration because an odd number of ball bearings incorporated in the electromagnetic clutch  50 . 
     It is understood that the ball bearings used in the invention have the similar operation/working-effect if a single-row ball bearing is used but is limited to a ball bearing having a plurality of rows of balls. 
     As explained in detail above, in this invention, because the number of balls per row of the ball bearing for the electromagnetic clutch is an odd number, the level of vibration and noise of the ball bearing during rotation is lowered.