Power transmission mechanism

Abstract

A power transmission mechanism has a first rotary body, a second rotary body and an elastic body. The second rotary body is located coaxially with the first rotary body. The first rotary body is operatively connected to the second rotary body through the elastic body for transmitting torque. The elastic body has a plurality of elastic members so as to stepwise change an elastic coefficient of the elastic body in accordance with the value of the torque.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a power transmission mechanism that transmits torque from a drive rotary body to a driven rotary body.

[0002] Japanese Unexamined Patent Publication No. 10-267047 discloses this type of power transmission mechanism. In the above prior art, a fixed pawl of a pulley engages with a turn pawl pivotally supported by a boss which is located coaxially with the pulley, thereby enabling power (torque) transmission between the fixed pawl and the turn pawl.

[0003] The turn pawl is pressed against the fixed pawl by a plate spring mounted on the boss. In the constitution, when excessive torque is applied between the pulley and the boss, the turn pawl tends to pivot against the elastic force of the plate spring. Thereby, the turn pawl disengages from the fixed pawl. Thus, power transmission between the pulley and the boss is blocked. In this state, the turn pawl is maintained by the pressing force of the plate spring so as not to be capable of engaging with the fixed pawl. Thereby, the turn pawl and the fixed pawl are prevented from engaging with each other again.

[0004] In the prior art, the plate spring is used such that a torque limit function in the power transmission mechanism is attained twice or more. However, the plate spring is not used for restraining resonance.

SUMMARY OF THE INVENTION

[0005] The present invention addresses a power transmission mechanism that is capable of restraining resonance of the drive rotary body and the driven rotary body. The power transmission mechanism also functions as a damper.

[0006] According to the present invention, a power transmission mechanism has a first rotary body, a second rotary body and an elastic body. The second rotary body is located coaxially with the first rotary body. The first rotary body is operatively connected to the second rotary body through the elastic body for transmitting torque. The elastic body has a plurality of elastic members so as to stepwise change an elastic coefficient of the elastic body in accordance with the value of the torque.

[0007] The present invention also has a following feature. A compressor is operatively connected to an external drive source. The compressor includes a compression mechanism and a power transmission mechanism. The compression mechanism has a drive shaft for compressing fluid. The power transmission mechanism has a pulley, a receiving member and an elastic member. The pulley is operatively connected to the external drive source. The receiving member is connected to the drive shaft. The pulley is operatively connected to the receiving member through the elastic body for transmitting torque. The elastic body has a plurality of elastic members so as to stepwise change an elastic coefficient of the elastic body in accordance with the value of the torque.

[0008] Furthermore, the present invention has a following feature. A rotary machine includes a rotary mechanism and a power transmission mechanism. The rotary machine has a rotary shaft. The power transmission mechanism includes a first rotary body, a second rotary body and an elastic body. The second rotary body is connected to the rotary shaft. The first rotary body is operatively connected to the second rotary body through the elastic body for transmitting torque. The elastic body has a plurality of elastic members so as to stepwise change an elastic coefficient of the elastic body in accordance with the value of the torque.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The features of the present invention that are believed to be novel are set forth with particularity in the appended claims. The invention together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:

[0010] FIG. 1 is a cross-sectional view illustrating a variable displacement compressor that has a power transmission mechanism of a first preferred embodiment according to the present invention;

[0011] FIG. 2A is a front view illustrating a pulley and a receiving member of the first preferred embodiment;

[0012] FIG. 2B is a partial cross-sectional view taken along line I-I in FIG. 2A;

[0013] FIG. 3 is a front view illustrating the pulley and the receiving member of the first preferred embodiment;

[0014] FIG. 4 is a graph illustrating load torque as function of a relative rotational angle of the first preferred embodiment;

[0015] FIG. 5 is a graph illustrating the amplitude of torque variation as function of a rotational speed of the first preferred embodiment;

[0016] FIG. 6 is a front view illustrating a pulley and a receiving member of the first preferred embodiment;

[0017] FIG. 7 is a partial enlarged view illustrating a power transmitting arm and a roller of the first preferred embodiment;

[0018] FIG. 8A is a front view illustrating a pulley and a receiving member of the second preferred embodiment;

[0019] FIG. 8B is a cross-sectional view taken along line II-II in FIG. 8A;

[0020] FIG. 9 is a front view illustrating a pulley and a receiving member of the third preferred embodiment;

[0021] FIG. 10 is a partial enlarged view illustrating a power transmitting arm and a roller of the third preferred embodiment;

[0022] FIG. 11A is a front view illustrating a pulley and a receiving member of the fourth preferred embodiment;

[0023] FIG. 11B is a cross-sectional view taken along line III-III in FIG. 11A;

[0024] FIG. 12 is a partial enlarged view illustrating a plate spring and an engaging pin of the fourth preferred embodiment;

[0025] FIG. 13 is a front view illustrating a pulley and a receiving member of another embodiment;

[0026] FIG. 14 is a front view illustrating a pulley and a receiving member of another embodiment; and

[0027] FIG. 15 is a front view illustrating a pulley and a receiving member of another embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] A first preferred embodiment of a variable displacement compressor according to the present invention will now be described with reference to FIGS. 1 and 2. A left side of FIG. 1 is referred to as a front end and a right side of FIG. 1 is referred to as a rear end.

[0029] As shown in FIG. 1, the variable displacement compressor (hereinafter, referred to as the compressor) C includes a cylinder block 11, a front housing 12, which is secured to the front end of the cylinder block 11, and a rear housing 14, which is secured to the rear end of the cylinder block 11 with a valve plate assembly 13 arranged between the cylinder block 11 and the rear housing 14.

[0030] The cylinder block 11, the front housing 12 and the rear housing 14 form a compressor housing.

[0031] A crank chamber 15 is formed in a space encompassed by the cylinder block 11 and the front housing 12. A drive shaft 16 is rotatably supported in the crank chamber 15. In the crank chamber 15, a lug plate 17 is secured to the drive shaft 16 so as to rotate integrally with the drive shaft 16.

[0032] The front end of the drive shaft 16 is connected to an engine E of a vehicle, which is an external drive source, through a power transmission mechanism PT. The crank chamber 15 accommodates a swash plate 18. The swash plate 18 is supported so as to slide along the drive shaft 16 and so as to incline with respect to the drive shaft 16. A hinge mechanism 19 is located between the lug plate 17 and the swash plate 18. Thus, the swash plate 18 rotates integrally with the lug plate 17 and the drive shaft 16 through the hinge mechanism 19 and inclines with respect to the direction of an axis L of the drive shaft 16 while sliding in the direction of the axis L.

[0033] A plurality of cylinder bores 20 (only one cylinder bore is shown in FIG. 1) is formed through the cylinder block 11 and is located around the drive shaft 16. Each of the cylinder bores 20 receives a single-headed piston 21 that reciprocates in the cylinder bores 20. Front and rear openings of each cylinder bore 20 are closed by the valve plate assembly 13 and the piston 21. In each cylinder bore 20 a compression chamber is defined. The volume of each compression chamber is varied in accordance with reciprocating movement of the associated piston 21. Each piston 21 is connected to the outer periphery of the swash plate 18 through a pair of shoes 22. Thus, when the swash plate 18 rotates integrally with the drive shaft 16, the shoes 22 convert the rotation of the swash plate 18 to the reciprocating movement of each piston 21.

[0034] The valve plate assembly 13 and the rear housing 14 form a suction chamber 23 and a discharge chamber 24. Corresponding to each cylinder bore 20, the valve plate assembly 13 includes a suction port 25, a suction valve 26 that selectively opens and closes the suction port 25, a discharge port 27 and a discharge valve 28 that selectively opens and closes the discharge port 28. Each suction port 25 connects the associated cylinder bore 20 to the suction chamber 23. Each discharge port 27 connects the associated cylinder bore 20 to the discharge chamber 24.

[0035] When each piston 21 moves from the top dead center to the bottom dead center, refrigerant gas flows from the suction chamber 23 to the associated cylinder bore 20 through the associated suction port 25 opened by the suction valve 26. When the piston 21 moves from the bottom dead center to the top dead center, the refrigerant gas is compressed to a predetermined pressure in the associated cylinder bore 20 and is discharged to the associated discharge chamber 24 through the associated discharge port 27 opened by the discharge valve 28.

[0036] In the compressor C, the pressure in the crank chamber 15 is varied by an electromagnetic control valve CV, thus adjusting the inclination angle of the swash plate 18 to a certain value between a maximum value (a state shown in FIG. 1) and a minimum value. When the inclination angle of the swash plate 18 relative to the plane perpendicular to the axis L is the closest to 90.degree., the inclination angle then is minimum. When the swash plate 18 inclines to an angle that is the remotest from the minimum inclination angle, the inclination angle then is maximum.

[0037] The crank chamber 15 connects with the suction chamber 23 through a bleed passage 29. The discharge chamber 24 connects with the crank chamber 15 through a supply passage 30. The electromagnetic control valve CV is located in the supply passage 30. A controller, which is not shown in the drawings, adjusts the opening degree of the control valve CV in order to adjust the amount of high-pressure refrigerant gas flowed from the discharge chamber 24 to the crank chamber 15 through the supply passage 30. The pressure in the crank chamber 15 is determined based on a balance between the amount of refrigerant gas flowing into the crank chamber 15 and the amount of refrigerant gas flowing from the crank chamber 15 to the suction chamber 23 through the bleed passage 29. As the pressure in the crank chamber 15 varies, pressure differential applied to the piston 21 between the crank chamber 15 and the cylinder bores 20 varies. Thereby, the inclination angle of the swash plate 18 varies, with a consequence of the stroke of each piston 21, or the displacement of the compressor C, is adjusted.

[0038] As shown in FIGS. 1 and 2, a support cylinder 31 extends from the front end of the front housing 12, and encompasses the front end of the drive shaft 16. A pulley 32, or a first (drive) rotary body, includes a cylindrical belt receiving portion 32a and an annular base portion 32b. A belt 33 connects with an output shaft of the engine E, and winds around the belt receiving portion 32a. The base portion 32b extends radially inward from the inner side of the belt receiving portion 32a. The support cylinder 31 rotatably supports the pulley 32 through a bearing 34 at the base portion 32b. That is, the pulley 32 is located coaxially with the axis L of the drive shaft 16, and rotates relative to the drive shaft 16.

[0039] A receiving member 35, or a second (driven) rotary body, is secured to the front end of the drive shaft 16 and rotates integrally with the drive shaft 16. The receiving member 35 includes a cylindrical member 35a and a disk-like hub 35b. The cylindrical member 35a is fitted around the front end of the drive shaft 16. The hub 35b engages with the front end of the cylindrical member 35a. Although not illustrated, a structure such as a spline engagement structure and a key structure engages the drive shaft 16 with the cylindrical member 35a and also engages the cylindrical member 35a with the hub 35b to block rotation relative to the drive shaft 16.

[0040] A plurality of support pins 36 (four in the present embodiment) is fixedly fitted to the rear end of the hub 35b adjacent to the outer periphery. The support pins 36 are located around the axis L at predetermined intervals (every 90 degrees in the present embodiment). A cylindrical sleeve 37 is fitted around each support pin 36 through appropriate force. When each sleeve 37 receives certain strength of rotational force, each sleeve 37 rotates relative to the respective support pin 36.

[0041] A plurality of engaging pins 38 (four in the present embodiment) is fixedly fitted to the front end of the base portion 32b of the pulley 32. The engaging pins 38 are located around the axis L at predetermined intervals (every 90 degrees in the present embodiment). Each engaging pin 38 engages with respective cylindrical roller 39, or a rolling component to rotatably support the cylindrical roller 39. The rollers 39 are located outward from the sleeves 37 of the hub 35b (outer side of the pulley 32).

[0042] As shown in FIGS. 2A and 2B, first power transmitting arms 41 and second power transmitting arms 42 are made of plate springs and are located between each sleeve 37 and the associated roller 39. The first power transmitting arms 41 and the second power transmitting arms 42 each are arranged by turns at predetermined intervals (every 180 degrees in the present embodiment or two arms each). The proximal portion of each of the arms 41 and 42 fixedly winds around the sleeve 37. The arms 41 and 42 interconnect each sleeve 37 and the associated roller 39, while passing by along the outer side of the respective rollers 39 (outer side of the pulley 32), and curve toward the center of the pulley 32 (toward the axis L). Each roller 39 is located radially outward from the corresponding sleeve 37 and is shifted clockwise from the sleeve 37, as shown in FIG. 2A.

[0043] The distal ends of the arms 41 and 42 each extend radially outward from the roller 39 of the corresponding engaging pin 38. The arms 41 and 42 are also curved in a radially inward direction of the pulley 32 (toward the axis L) along the circumferential surface of the corresponding roller 39. That is, engaging recesses 41a and 42a are respectively formed near the distal ends of the arms 41 and 42 to engage with the corresponding roller 39. In other words, the arms 41 and 42 of the receiving member 35 engage with the corresponding roller 39 of the pulley 32 at the engaging recesses 41a and 42a, respectively. Thereby, power transmission between the receiving member 35 and the pulley 32 is permitted. Further, the receiving member 35 connects with the pulley 32 so as to rotate relative to the pulley 32 in the range of a predetermined angle.

[0044] The power of the engine E is transmitted to the pulley 32 through the belt 33, and then is transmitted to the receiving member 35 through the rollers 39 of the pulley 32 and the arms 41 and 42 engaging with the corresponding rollers 39. Thus, the power is transmitted to the drive shaft 16 of the compressor C.

[0045] In the first preferred embodiment, in a state that power is not transmitted from the pulley 32 to the receiving member 35, such as upon a stop of the engine E, when the pulley 32 starts to rotate clockwise in FIG. 2A, the power transmission is performed only by the first transmitting arms 41. Upon power transmission, the engaging recess 41a of each first power transmitting arm 41 elastically deforms due to the corresponding roller 39, which engages with the engaging recess 41a. In this state, as load torque T between the pulley 32 and the receiving member 35 becomes large, the amount of elastic deformation of each first power transmitting arm 41 is increased. In addition, the relative rotational angle .theta. between the pulley 32 and the receiving member 35 increases.

[0046] When the load torque T reaches a predetermined value, the relative rotational angle .theta. also reaches a predetermined value. Thereby, the engaging recess 42a of each second power transmitting arm 42 engages with the corresponding roller 39 as shown in FIG. 3. Thus, not only the first power transmitting arms 41 but also the second power transmitting arms 42 transmit torque. In this state, the engaging recess 42a of each second power transmitting arm 42 deforms due to the corresponding roller 39, which engages with the engaging recess 42a. Then, the amount of elastic deformation of each first power transmitting arm 41 is further increased as compared with the power transmission only by the first power transmitting arms 41.

[0047] As shown in FIG. 4, a graph shows the load torque T, which is applied to an elastic body constituted by the arms 41 and 42, as a function of the relative rotational angle .theta..

[0048] In the graph, the value of the relative rotational angle .theta. is zero when the pulley 32 and the receiving member 35 are arranged such that the rollers 39 engage with the respective engaging recesses 41a and the first power transmitting arms 41 are not deformed by the respective rollers 39 (the load torque is not applied between the pulley 32 and the receiving member 35).

[0049] Also, in the graph, an angle value .theta. a indicates the predetermined angle value, where the power transmission only by the first power transmitting arms 41 and the power transmission by both the power transmitting arms 41 and 42 switch to each other.

[0050] In the present embodiment, hysteresis arises between the load torque T and the relative rotational angle .theta. due to friction generated between the engaging pins 38 and the rollers 39. That is, the graph forms a closed area A1. When the value of the relative rotational angle .theta. is the predetermined angle .theta. a, the minimum value and the maximum value of the load torque T are torque values Ta1 and Ta2, respectively.

[0051] Also, in the graph, an angle value .theta.b is the maximum value .theta.b of the relative rotational angle .theta. for permitting the power transmission by both the arms 41 and 42. In other words, the angle value .theta.b is the maximum value .theta.b of the relative rotational angle .theta. for permitting a state that both the engaging recesses 41a and the engaging recesses 42a engage with the corresponding rollers 39, respectively. When the value of the relative rotational angle .theta. is the angle value .theta.b, the value of the load torque T is torque value Tb.

[0052] When the value of the relative rotational angle .theta. is continuously increased in the range of zero to .theta.a, exclusive of .theta.a, the value of the load torque T tends to slowly increase from zero toward the torque value Ta2. In this case, only the first power transmitting arms 41 of the elastic body operate, and then an elastic coefficient ka of the elastic body is expressed by Ta2/.theta.a.

[0053] When the value of the relative rotational angle .theta. is continuously increased in the range of .theta.a to .theta.b, the value of the load torque T tends to increase from the torque value Ta2 to the torque value Tb more extremely than the load torque T corresponding to the value of the relative rotational angle .theta. in the range of zero to .theta.a, exclusive of .theta.a. In this case, both the arms 41 and 42 of the elastic body operate, and then an elastic coefficient kb of the elastic body is expressed by (Tb-Ta2)/(.theta.b-.theta.a).

[0054] That is, the elastic body is constituted by a plurality of elastic members (both the arms 41 and 42) such that the elastic coefficient k of the elastic body switches from the elastic coefficient ka to the elastic coefficient kb or from the elastic coefficient kb to the elastic coefficient ka in accordance with the value of load torque T. In other words, the elastic body is constituted such that the elastic coefficient k stepwise switches. The elastic coefficient kb is larger than the elastic coefficient ka. The elastic coefficient ka is predetermined to such an extent that vibration generated by compressor C is effectively dampened in the range of a relatively low rotational speed at which the engine E is practically frequently used.

[0055] When the value of the relative rotational angle .theta. is continuously decreased in the range of .theta.a to .theta.b, the value of the load torque T tends to extremely decrease from the torque value Tb to the torque value Ta1. When the value of the relative rotational angle .theta. is continuously decreased in the range of zero to .theta.a, the value of the load torque T tends to decrease toward zero more slowly than that of the load torque T corresponding the value of to the relative rotational angle .theta. in the range of .theta.a to .theta.b.

[0056] In the present embodiment, the elastic coefficient of only the second power transmitting arm 42 is predetermined to be larger than the elastic coefficient ka of only the first power transmitting arm 41. Accordingly, the elastic body constituted by both the arms 41 and 42 is determined such that differential between the elastic coefficient ka in the range of zero to .theta.a, exclusive of .theta.a (corresponding to the range of zero to Ta2, exclusive of Ta2) and the elastic coefficient kb in the range of .theta.a to .theta.b (corresponding to the range of Ta2 to Tb) is further increased as compared with the case that the elastic coefficient ka of only the first power transmitting arm 41 and the elastic coefficient of only the second power transmitting arm 42 are equal to each other.

[0057] Since each of the arms 41 and 42 has a different elastic coefficient, each of the arms 41 and 42 has a different natural frequency. That is, the second power transmitting arm 42 has more natural frequency than the first power transmitting arm 41.

[0058] When the drive shaft 16 is rotated, compressive reaction force of the refrigerant and reaction force generated due to reciprocating movement of the piston 21 are transmitted to the drive shaft 16 through the swash plate 18 and the hinge mechanism 19. Thereby, twist vibration arises on the drive shaft 16. The twist vibration generates variation of the load torque or torque variation. The torque variation causes resonance between the compressor C and an external rotational machine such as a vehicle engine E and an accessory, which is operatively connected to the compressor C through the pulley 32 and the belt 33. The torque variation arises to increase and reduce torque values substantially by an equal amplitude relative to its average torque value. The average value of torque is substantially constant regardless of the value of the rotational speed V of the drive shaft 16. In the present embodiment, the elastic body is tuned such that an intermediate value between the torque value Ta1 and the torque value Ta2 or (Ta1+Ta2)/2 is equal to the average value of torque.

[0059] Also, a peak of the amplitude of the torque variation arises when the natural frequency of the elastic body is equal to the frequency of the twist vibration of the drive shaft 16. The frequency of the twist vibration of the drive shaft 16 is proportional to the rotational speed V of the drive shaft 16.

[0060] As shown in FIG. 5, a graph shows the amplitude of torque variation as a function of the rotational speed V with reference to the arms 41, the arms 42 and the elastic body constituted by both the arms 41 and 42. The amplitude of the torque variation means an amount of torque variation relative to the average value of torque. Curved lines C1, C2 and C3 indicate the amplitude of the torque variation as a function of the rotational speed V, respectively when the power transmission is performed by the arms 41, the arms 42, and the elastic body constituted by both the arms 41 and 42.

[0061] As shown by the curved line C1, while the power is transmitted only by the first power transmitting arms 41, the peak of the amplitude of torque variation arises relatively at a low rotational speed. This is because the elastic coefficient of the first power transmitting arm 41 is relatively low and the natural frequency of only the first power transmitting arm 41 is relatively small.

[0062] As shown by the curved line C2, while the power is transmitted only by the second power transmitting arms 42, the peak of the amplitude of torque variation arises relatively at a high rotational speed. This is because the elastic coefficient of the second power transmitting arm 42 is relatively high and the natural frequency of only the second power transmitting arm 42 is relatively large.

[0063] In the present embodiment, the power transmission by the elastic body is constituted such that the power transmission only by the first power transmitting arms 41 and the power transmission by both the arms 41 and 42 switch to each other at the value Va of a slightly lower rotational speed than the rotational speed of the drive shaft 16 which generates the twist vibration of the frequency that is equal to the natural frequency of only the first power transmitting arm 41 while the value of the rotational speed V is continuously increased from zero.

[0064] Also, the power transmission by the elastic body is constituted such that the power transmission by both the arms 41 and 42 and the power transmission only by the first power transmitting arms 41 switch to each other at the value Vb of a slightly lower rotational speed than the rotational speed of the drive shaft 16 which generates the twist vibration of the frequency that is equal to the natural frequency of the elastic body constituted by both the arms 41 and 42 while the value of the rotational speed V is continuously increased further from the rotational speed Va. That is, when the value of the rotational speed V is continuously increased in the range of zero to Va, exclusive of Va, or in the range of from Vb, the elastic body is constituted such that only the first power transmitting arms 41 operate. When the value of the rotational speed V is continuously increased in the range of Va to Vb, exclusive of Vb, the elastic body is constituted such that both the arms 41 and 42 operate. This is performed by predetermining both the arms 41 and 42 and so forth such that the value of torque differential (Ta1-Ta2)/2 between the torque values Ta1 and Ta2, and the average value of torque (Ta1+Ta2)/2 of the torque variation is equal to the amplitude of torque variation corresponding to the values Va and Vb of rotational speed.

[0065] As shown by the curved line C3, while the elastic body has the value of the rotational speed V in the range of zero to Va, exclusive of zero and Va, the value of the relative rotational angle .theta. is less than the angle value .theta.a. Thereby, the curved line C3 indicates a similar property to the curved line C1. While the value of the rotational speed V is continuously increased from zero, when the natural frequency of the elastic body and the frequency of twist vibration of the drive shaft 16 approach each other, and when the amplitude of torque variation is increased and then becomes equal to the value of the torque differential (Ta1-Ta2)/2 (corresponding to the value Va of the rotational speed), the load torque T reaches the torque value Ta2. At this time, the curved line C3 is different from the curved lines C1 and C2. That is, the curved line C3 indicates the property of cooperative operation of both the arms 41 and 42. That is, the amplitude of torque variation of the elastic body begins to tend to decrease when the value of the rotational speed V reaches Va. The amplitude of torque variation shown by the curved line C3 decreases such an extent that the amplitude of torque variation shown by the curved line C3 becomes lower than the amplitude of torque variation of only the second power transmitting arms 42 shown by the curved line C2. In other words, the load torque T of the curved line C3 indicates closer value to the average value of torque of the torque variation than those of the curved line C1 and the curved line C2. In this state, since the value of the load torque T varies in the area A1 shown by the graph in FIG. 4, the arms 41 and 42 of the elastic body continuously cooperatively operate.

[0066] While the value of the rotational speed V is continuously increased further, when the natural frequency of the elastic body cooperatively operated by both the arms 41 and 42 and the frequency of twist vibration of the drive shaft 16 approach each other, and when the amplitude of torque variation is increased and then exceeds the value of the torque differential (Ta1-Ta2)/2 (corresponding to the value Vb of the rotational speed), the load torque T becomes less than the torque value Ta1. At this time, the relative rotational angle .theta. becomes less than the angle value .theta.a. That is, the power transmission by the elastic body is changed from the power transmission by both the arms 41 and 42 to the power transmission only by the first power transmitting arms 41. In other words, the amplitude of torque variation of the elastic body begins to tend to decrease when the value of the rotational speed V reaches Vb. The amplitude of torque variation shown by the curved line C3 decreases so as to indicate the property of the amplitude of torque variation of only the first power transmitting arm 41 shown by the curved line C1. Accordingly, in the power transmission mechanism PT of the present embodiment, the amplitude of torque variation is effectively decreased in the range of a relatively low rotational speed at which the engine E is practically frequency used and even in the range of a relatively high rotational speed at which durability of the engine E is affected.

[0067] In the present embodiment, when the load torque T varies to such an extent that the engine E is not affected, or when the load torque T is the torque value Tb or less, at least one of the engaging recesses 41a and the engaging recesses 42a, engage with the corresponding rollers 39. Thereby, the power transmission is continued from the engine E to the drive shaft 16.

[0068] However, as shown in FIG. 6, if the load torque T applied to the compressor C exceeds the torque value Tb due to a problem such as deadlocking, the elastic force of both the arms 41 and 42 cannot hold engagement between the arms 41 and 42, and the corresponding rollers 39. At this time, each roller 39 is disengaged from the corresponding arms 41 and 42. This blocks the power transmission from the pulley 32 to the receiving member 35. Accordingly, the engine E is prevented from being affected due to the load torque T which exceeds the torque value Tb.

[0069] When each roller 39 is disengaged from the corresponding arms 41 and 42, the pulley 32 freely rotates relative to the receiving member 35. At this time, each roller 39, which is attached to the pulley 32, contacts the back surface (an opposite surface to the surface on which the engaging recess 41a of the first power transmitting arm 41 and the engaging recess 42a of the second power transmitting arm 42 are formed) of the adjacent arms 41 and 42 on the path of the movement of the rollers 39. That is, force that pivots the arms 41 and 42 around the support pins 36 is applied due to the contact between the arms 41 and 42, and the corresponding rollers 39. The arms 41 and 42, together with the associated sleeves 37 that securely support the arms 41 and 42, are pivoted clockwise around the support pin 36 in FIG. 7. Thereby, the arms 41 and 42 are held at positions retreated from the corresponding roller 39. In FIG. 7, only the first power transmitting arm 41 is illustrated while the second power transmitting arm 42 is omitted.

[0070] As described, each sleeve 37 is fitted around the associated support pin 36 through appropriate pressure. Therefore, even if an external force (for example, force generated by vibration of the vehicle) acts on each sleeve 37, the arms 41 and 42 are securely held at the position retreated from the corresponding roller 39. This prevents noise and vibration from being otherwise caused by repeated hitting of the rollers 39 and the corresponding arms 41 and 42.

[0071] When the torque variation generates in a state that the power is transmitted between the pulley 32 and the receiving member 35, the contact between the engaging recesses 41a, the engaging recesses 42a and the rollers 39 is repeatedly varied at a position. That is, the pulley 32 repeatedly alternates clockwise movement and counterclockwise movement relative to the receiving member 35 in the range of a predetermined angle value. This damps the variation of the transmission torque between the pulley 32 and the receiving member 35.

[0072] In the present embodiment, the compressor C is constituted so as to vary displacement. The load torque T can be varied in accordance with the displacement. The above described predetermined value of the power transmission mechanism PT for restraining the resonance is determined so as to correspond to the displacement while the compressor is normally driven.

[0073] In the first preferred embodiment, the following advantageous effects are obtained.

[0074] (1) The elastic body is constituted by a plurality of elastic members such as the arms 41 and 42 such that the elastic coefficient k of the elastic body changes in accordance with the load torque T. The change of the elastic coefficient of the elastic body enables prevention against resonance between the pulley 32 and the receiving member 35 and reduction of the magnitude of the resonance in such a state that the power transmission mechanism PT has a function as a damper.

[0075] Also, the elastic body is constituted such that the elastic coefficient k of the elastic body switches from the elastic coefficient value ka to the elastic coefficient value kb in accordance with the value of the load torque T. That is, the elastic body is constituted such that the value of the elastic coefficient k stepwise changes. Therefore, the value of the elastic coefficient k definitely changes. As the constitution of the first preferred embodiment is compared with the constitution that the elastic coefficient continuously changes, prevention against the resonance and reduction of the magnitude of the resonance are more securely performed.

[0076] (2) The elastic body is constituted such that the number of operative elastic members (the arms 41 and 42) increases in accordance with increase of the value of the load torque T. The increase of the number of operative elastic members enables the value of the elastic coefficient k of the elastic body to stepwise increase.

[0077] (3) The elastic body is constituted such that the first power transmitting arms 41 operate first and then the second power transmitting arms 42 operate. That is, the elastic members (the arms 41 and 42) start to transmit the torque in order of increasing the elastic coefficient. At this time, the elastic coefficient k of the elastic body can be greatly increased by a stage. Accordingly, prevention against the resonance and reduction of the magnitude of the resonance are further securely performed.

[0078] (4) Both the arms 41 and 42 are made of plate springs. Therefore, the elastic member is easily formed. Accordingly, cost can be reduced.

[0079] A second preferred embodiment according to the present invention will now be described below. In the second preferred embodiment, the constitution of the pulley 32 and the receiving member 35 of the first preferred embodiment is changed and the other aspect is constituted in a similar manner to the first preferred embodiment. Accordingly, the same reference marks of the first preferred embodiment is applied to substantially the same components of the second preferred embodiment and overlapped explanation is omitted.

[0080] As shown in FIG. 8A, a plurality (four in the second preferred embodiment) of support pins 36 is fixed to a hub 50a constituting a main body of a receiving member 50 functioning as a second (driven) rotary body. A power transmitting arm 52 functioning as an elastic member made of plate spring is arranged between each support pin 36 and the corresponding roller 39 formed on a pulley 51 functioning as a first (drive) rotary member.

[0081] Still referring to FIG. 8A, the power transmitting arm 52 is constituted in a similar manner as the first power transmitting arm 41 and the second power transmitting arm 42 of the first preferred embodiment. That is, a proximal portion of the arm 52 is securely wound around the sleeve 37 which is not shown in FIG. 8A and the distal portion of the power transmitting arm 52 has a engaging recess 52a which can engage with the corresponding roller 39. In other words, the receiving member 50 is connected to the pulley 51 such that the receiving member 50 rotates relative to the pulley 51 in the range of a predetermined angle. In this state, power or torque is transmittable from the pulley 51 to the receiving member 50.

[0082] In the present embodiment, an arcuate recess 53 is formed between the support pins 36 on an outer circumference of the hub 50a. Thus, the hub 50a has a plurality (four in the embodiment) of support arms 54 that extends radially outwardly. The support pin 36 is fixed to each of the radial outward portions of the support arms 54.

[0083] As shown in FIGS. 8A and 8B, an engaging pin 55 is erected so as to extend parallel to the axis L on an annular base portion 51b that extends inward from the inner circumferential surface of a cylindrical belt receiving portion 51a of the pulley 51. The distal end of the engaging pin 55 is chamfered to form the shape of a conical support. Thereby, a slope 55a is formed.

[0084] In the present embodiment, in such a state that power is not transmitted from the pulley 51 to the receiving member 50, when the pulley 51 starts to rotate clockwise with respect to FIG. 8A, the power is transmitted only by the power transmitting arms 52. In this state, as the value of the load torque T applied between the pulley 51 and the receiving member 50 increases, the amount of elastic deformation of the power transmitting arm 52 is increased. In addition, the value of the relative rotational angle .theta. between the pulley 51 and the receiving member 50 is increased.

[0085] When the load torque T increases and reaches a predetermined value, the relative rotational angle .theta. reaches a predetermined value. At this time, the support arm 54 contacts a surface of the slope 55a of the engaging pin 55. Thereby, power is transmitted not only by the rollers 39 and the corresponding power transmitting arms 52 but also by the engaging pin 55 and the support arm 54.

[0086] In this state, the support arm 54 is elastically deformed toward an extending direction of the engaging pin 55 (upward in FIG. 8B) by the surface of the slope 55a. That is, the support arm 54 functions as an elastic member which is elastically deformed in such a state that the center of the support arm 54 is supported. The elastic coefficient of only the support arm 54 or a ratio of the variation of load torque T to the variation of the relative rotational angle .theta. upon the power transmission between the pulley 51 and the receiving member 50 being performed only by the support arm 54 is predetermined to be even larger than the elastic coefficient kc of only the power transmitting arm 52. In a state that the support arm 54 is elastically deformed by the engaging pin 55, the amount of elastic deformation of the power transmitting arms 52 is further increased as compared with the case that the power is transmitted only by the power transmitting arms 52.

[0087] In the present embodiment, the power transmitting arm 52 and the support arm 54 constitute an elastic body. The value of the elastic coefficient k of the elastic body is predetermined to kd in a state that both the power transmitting arms 52 and the support arm 54 operate.

[0088] The elastic body is constituted by a plurality of elastic members (both the power transmitting arms 52 and the support arm 54) such that the value of the elastic coefficient k of the elastic body switches between kc and kd in accordance with the value of the load torque T. That is, the elastic body is constituted such that the value of the elastic coefficient k of the elastic body stepwise changes

[0089] In the present embodiment, the power transmission by the elastic body is constituted such that the power transmission only by the power transmitting arms 52 and the power transmission by both the power transmitting arms 52 and the support arm 54 switch to each other at the value Vc of a slightly lower rotational speed than the rotational speed of the drive shaft 16 which generates the twist vibration of the frequency that is equal to the natural frequency of only the power transmitting arms 52 while the value of the rotational speed V is continuously increased from zero.

[0090] Also, the power transmission by the elastic body is constituted such that the power transmission by both the power transmitting arms 52 and the support arm 54 and the power transmission only by the power transmitting arms 52 switch to each other at the value Vd of a slightly lower rotational speed than the rotational speed of the drive shaft 16 which generates the twist vibration of the frequency that is equal to the natural frequency of the elastic body constituted by both the power transmitting arms 52 and the support arm 54 while the value of the rotational speed V is continuously increased further from the value Vc of the rotational speed. That is, when the value of the rotational speed V is continuously increased in the range of zero to Vc, exclusive of Vc, or in the range of from Vd, the elastic body is constituted such that only the power transmitting arms 52 operate. When the value of the rotational speed V is continuously increased in the range of Vc to Vd, exclusive of Vd, the elastic body is constituted such that both the power transmitting arms 52 and the support arm 54 operate.

[0091] In the second preferred embodiment, the following advantageous effects are obtained. In addition, the effects (1) and (2) of the first preferred embodiment is also obtained.

[0092] (5) The elastic body is constituted such that the power transmitting arms 52 operate first and then the support arm 54 operates. That is, the elastic members such as the power transmitting arms 52 and the support arm 54 start to transmit the torque in order of increasing the elastic coefficient. At this time, the value of the elastic coefficient k of the elastic body is relatively greatly increased by a stage. Accordingly, prevention against the resonance and reduction of the magnitude of the resonance are further definitely performed.

[0093] Also, in the second preferred embodiment, the value of the elastic coefficient of only the support arm 54 is predetermined to be even larger than that of the elastic coefficient kc of only the power transmitting arms 52. At this time, the natural frequency of the elastic body constituted by both the arms 52 and 54 can be further increased. Accordingly, the practical rotational speed of the compressor C can be expanded in the range of a relatively high rotational speed.

[0094] (6) Since the power transmitting arms 52 are made of plate springs, the power transmitting arms 52 are easily formed. Thereby, cost can be reduced.

[0095] (7) The support arm 54 or a part of the hub 50a is applied as an elastic member. As the constitution of the elastic body of the second preferred embodiment is compared with that of the elastic body of the first preferred embodiment, the other kinds of elastic member for attaching to the hub 50a can be reduced. In the second preferred embodiment, only the power transmitting arms 52 are attached to the hub 50a. Also, for example, in the case that the power transmitting arm 52 of the second preferred embodiment has the same constitution as the first power transmitting arm 41 of the first preferred embodiment, maximum value for enabling to transmit power from a pulley to a receiving member is increased. This is because the number (four) of the second power transmitting arms 52 is more than that (two) of the first power transmitting arms 41. On the contrary, in the case that the maximum value for enabling to transmit the power is predetermined to be equal between the first preferred embodiment and the second preferred embodiment, the number of the power transmitting arms 52 for attaching to the hub 50a can be reduced.

[0096] A third preferred embodiment according to the present invention will now be described below. In the third preferred embodiment, the constitution for supporting the power transmitting arm of the first preferred embodiment is changed and the other aspect is constituted in a similar manner to the first preferred embodiment. Accordingly, the same reference marks of the first preferred embodiment is applied to substantially the same components of the third preferred embodiment and overlapped explanation is omitted.

[0097] In the present embodiment, as shown in FIG. 9, a proximal portion of each of first power transmitting arms 60 and second power transmitting arms 61 functioning as elastic members made of plate springs is attached to a support pin 36 of a receiving member 35 through a sleeve 37 which is not shown in the drawing. That is, a plurality (two in the present embodiment) of elastic members is supported by each support pin 36. The arms 60 and 61 are each arranged between the support pin 36 and the roller 39 corresponding to the support pin 36.

[0098] Both the arms 60 and 61 are arranged such that the first power transmitting arm 60 is at an inner circumferential side of a hub 35b (on the side of the roller 39) and the second power transmitting arm 61 is at an outer side of the hub 35b while a part of the first power transmitting arm 60 and a part of the second power transmitting arm 61 are layered. The first power transmitting arm 60 which is arranged at the inner circumferential side directly can engage with the corresponding roller 39 of a pulley 32 at an engaging recess 60a which is a distal portion of the first power transmitting arm 60 in a similar manner as both the arms 41 and 42 of the first preferred embodiment. When load torque T is not applied between the pulley 32 and the receiving member 35, an engaging recess 61a of a distal portion of the second power transmitting arm 61 which is arranged at the outer circumferential side is formed such that a predetermined clearance is interposed between the back surface of the engaging recess 60a and the inner circumferential surface of the engaging recess 61a.

[0099] Thereby, the receiving member 35 and the pulley 32 are connected to each other in the range of a predetermined angle so as to relatively rotate while being capable of transmitting power (torque) from the pulley 32 to the receiving member 35. An elastic coefficient of only the second power transmitting arms 61 is predetermined to be larger than an elastic coefficient ke of only the first power transmitting arms 60.

[0100] In the present embodiment, in a state that power is not transmitted from the pulley 32 to the receiving member 35, when the pulley 32 starts to rotate clockwise in FIG. 9, the power transmission is performed only by the first transmitting arms 60.

[0101] As the load torque T increases in the state, the amount of elastic deformation of the first power transmitting arms 60 increases. Thereby, the relative rotational angle .theta. between the pulley 32 and the receiving member 35 is increased. When the value of the relative rotational angle .theta. increases and reaches the value of a predetermined angle, as shown in FIG. 10, the distal portions of the first power transmitting arms 60 contact the engaging recesses 61a of the second power transmitting arms 61. Thereby, the power is transmitted not only between the rollers 39 and the first power transmitting arms 60 but also between the rollers 39 and the second power transmitting arms 61 through the first power transmitting arms 60. In this state, while the second power transmitting arms 61 are elastically deformed, the amount of elastic deformation of the first power transmitting arms 60 is further increased as compared with the state that the power is transmitted only by the first power transmitting arms 60.

[0102] The arms 60 and 61 constitute an elastic body. The elastic coefficient k of the elastic body is predetermined to kf in a state that both the arms 60 and 61 operate.

[0103] The elastic body is constituted by a plurality of elastic members (both the arms 60 and 61) such that the value of the elastic coefficient k of the elastic body switches between ke and kf in accordance with the value of the load torque T. That is, the elastic body is constituted such that the value of the elastic coefficient k of the elastic body stepwise changes.

[0104] In the present embodiment, the power transmission by the elastic body is constituted such that the power transmission only by the first power transmitting arms 60 and the power transmission by both the arms 60 and 61 switch to each other at the value Ve of a slightly lower rotational speed than the rotational speed of the drive shaft 16 which generates the twist vibration of the frequency that is equal to the natural frequency of the first power transmitting arm 60 while the value of the rotational speed V is continuously increased from zero.

[0105] Also, the power transmission by the elastic body is constituted such that the power transmission by both the arms 60 and 61 and the power transmission only by the first power transmitting arms 60 switch to each other at the value Vf of a slightly lower rotational speed than the rotational speed of the drive shaft 16 which generates the twist vibration of the frequency that is equal to the natural frequency of the elastic body constituted by both the arms 60 and 61 while the value of the rotational speed V is continuously increased further from the value Ve of the rotational speed. That is, when the value of the rotational speed V is continuously increased in the range of zero to Ve, exclusive of Ve, or in the range of from Vf, the elastic body is constituted such that only the first power transmitting arms 60 operate. When the value of the rotational speed V is continuously increased in the range of Ve to Vf, exclusive of Vf, the elastic body is constituted such that both the arms 60 and 61 operate.

[0106] If the load torque T is excessive due to a problem, the elastic force applied to both the arms 60 and 61 cannot hold engagement between the elastic body and the rollers 39. At this time, the rollers 39 are disengaged from the elastic body. This blocks the power transmission from the pulley 32 to the receiving member 35.

[0107] In the third preferred embodiment, the following advantageous effects are obtained. In addition, the effects (1) through (4) of the first preferred embodiment are also obtained.

[0108] (8) The elastic body is constituted such that a plurality of elastic members is supported by each support pin 36 of the receiving member 35. In this case, a space for placing each of the arms 60 and 61 is effectively used.

[0109] A fourth preferred embodiment according to the present invention will now be described below. In the fourth preferred embodiment, the constitution of the pulley 32 and the receiving member 35 of the first preferred embodiment is changed and the other aspect is constituted in a similar manner to the first preferred embodiment. Accordingly, the same reference marks of the first preferred embodiment are applied to substantially the same components of the fourth preferred embodiment and overlapped explanation is omitted.

[0110] As shown in FIGS. 11A and 11B, a hub 70a constitutes a main body of a receiving member 70 functioning as a second (driven) rotary body. The hub 70a is integrally formed with a plurality (two in the present embodiment) of cylindrical engaging projections 71 that extends along the axis L rearward at equal intervals (at an angle of 180 degree in the present embodiment).

[0111] An engaging recess 73 is formed on an annular base portion 72b that extends toward the axis L from the inner circumferential surface of a cylindrical belt receiving portion 72a of a pulley 72 functioning as a first (drive) rotary body so as to receive the rear end of the engaging projection 71.

[0112] In the engaging recess 73, a pair of first plate springs 74a and a pair of second plate springs 74b functioning as a plurality of elastic members are juxtaposed among them. Each of the first plate springs 74a and the second plate springs 74b is arranged symmetrically and parallel with respect to an imaginary line that links the center of the pulley 72 and the center of the engaging recess 73 when the pulley 72 is seen at the front side. In other words, in the recess 73, the first plate springs 74a are arranged so as to sandwich the imaginary line at the inner side and the second plate springs 74b are arranged so as to sandwich the imaginary line at the outer side. Both ends of each first plate spring 74a and each second plate spring 74b are supported in grooves which are formed in the inner wall of the recess 73 so as to be inserted. The first distance between the first points for supporting both ends of each first plate spring 74a is predetermined to be longer than the second distance between the second points for supporting both ends of each second plate spring 74b.

[0113] Each engaging projection 71 is inserted between the first plate springs 74a in the corresponding recess 73. In this case, each engaging projection 71 engages with the first plate springs 74a to directly contact each other.

[0114] The receiving member 70 and the pulley 72 are connected so as to enable relative rotation with each other in the range of a predetermined angle since the engaging projection 71 engages with the elastic body. In addition, power (torque) is transmittable from the pulley 72 to the receiving member 70. The elastic coefficient of each second plate spring 74b is predetermined to be larger than an elastic coefficient ki of each first plate spring 74a.

[0115] In the present embodiment, in a state that power is not transmitted from the pulley 72 to the receiving member 70, when the pulley 72 starts to rotate with respect to the receiving member 70, the power is transmitted only by the first plate springs 74a.

[0116] As the load torque T increases in the state, the amount of elastic deformation of the first plate spring 74a increases. Thereby, the relative rotational angle .theta. between the pulley 72 and the receiving member 70 is increased. When the relative rotational angle .theta. increases and reaches the value of a predetermined angle, as shown in FIG. 12, the first plate springs 74a which are elastically deformed by the associated engaging projection 71 contact the associated second plate springs 74b. Thereby, power is transmitted not only by the engaging projections 71 and the corresponding first plate springs 74a but also by the engaging projections 71 and the corresponding second plate springs 74b through the corresponding first plate springs 74a.

[0117] In the above state, the second plate spring 74b is elastically deformed. In addition, the amount of elastic deformation of the first plate spring 74a is further increased as compared with the state that the power is transmitted only by the first plate springs 74a. The elastic coefficient k of the elastic body is predetermined to kj in a state that both the plate springs 74a and 74b operate.

[0118] The elastic body is constituted by a plurality of elastic members (both the plate springs 74a and 74b) such that the elastic coefficient k of the elastic body switches between the value of coefficient ki and the value of coefficient kj in accordance with the value of the load torque T. That is, the elastic body is constituted such that the elastic coefficient k of the elastic body stepwise changes.

[0119] In the present embodiment, the power transmission by the elastic body is constituted such that the power transmission only by the first plate springs 74a and the power transmission by both the plate springs 74a and 74b switch to each other at the value Vg of a slightly lower rotational speed than the rotational speed of the drive shaft 16 which generates the twist vibration of the frequency that is equal to the natural frequency of only the first plate spring 74a while the value of the rotational speed V is continuously increased from zero.

[0120] Also, the power transmission by the elastic body is constituted such that the power transmission by both the plate springs 74a and 74b and the power transmission only by the first plate springs 74a switch to each other at the value of Vh a slightly lower rotational speed than the rotational speed of the drive shaft 16 which generates the twist vibration of the frequency that is equal to the natural frequency of the elastic body constituted by both the plate springs 74a and 74b while the rotational speed V is continuously increased further from the rotational speed Vg. That is, when the value of the rotational speed V is continuously increased in the range of zero to Vg, exclusive of Vg, or in the range of from Vh, the elastic body is constituted such that only the first plate springs 74a operate. When the value of the rotational speed V is continuously increased in the range of Vg to Vh, exclusive of Vh, the elastic body is constituted such that both the plate springs 74a and 74b operate.

[0121] In the fourth preferred embodiment, the following advantageous effects are obtained. In addition, the effects (1) and (2) of the first preferred embodiment are also obtained.

[0122] (9) The elastic body is constituted such that the first plate springs 74a operate first and then the second plate springs 74b operate. That is, the elastic members such as the plate springs 74a and 74b start to transmit the torque in order of increasing the elastic coefficient. At this time, the elastic coefficient k of the elastic body is relatively greatly increased by a stage. Accordingly, prevention against the resonance and reduction of the magnitude of the resonance are further definitely performed.

[0123] (10) The elastic members (both the plate springs 74a and 74b) are made of plate springs. Therefore, the elastic members are easily formed. Accordingly, cost can be reduced.

[0124] (11) In the recess 73, the pair of first plate springs 74a and the pair of the second plate springs 74b are arranged so as to sandwich the imaginary line respectively at the inner side and the outer side while each engaging projection 71 is inserted between the pair of first plate springs 74a in each recess 73. In the fourth preferred embodiment, the rotational direction of the pulley 72 is not limited to one direction. Therefore, the power can be transmitted not only clockwise in FIG. 11A but also counterclockwise in FIG. 11A.

[0125] (12) In the fourth preferred embodiment, the elastic coefficient of each first plate spring 74a and each second plate spring 74b can be varied by adjusting respectively the first distance between the first points for supporting both ends of the first plate spring 74a and the second distance between the second points for supporting both ends of the second plate spring 74b. In this case, material of each first plate spring 74a and each second plate spring 74b can be used in common.

[0126] In the present invention, the following alternative embodiments are also practiced.

[0127] In the first preferred embodiment, in a state that the relative rotational angle .theta. has not reached the predetermined angle value .theta.a, the second engaging recess 42a of the second power transmitting arm 42 and the corresponding roller 39 are constituted such that the second engaging recess 42a does not engage with the corresponding roller 39. Even in a state that the value of the relative rotational angle .theta. has not reached the predetermined angle value .theta.a, however, the second engaging recess 42a of the second power transmitting arm 42 and the corresponding roller 39 may be constituted so as to engage with each other by joining the proximal portion of the second power transmitting arm 42 to a support portion formed on the hub 35b so as to enable pivotal movement about the support portion and movement in a circumferential direction of the hub 35b. In this case, as shown in FIG. 14, an engaging pin 81 formed on the proximal portion of the second power transmitting arm 42 may be inserted through an oblong hole 80 which is formed on the hub 35b as a support portion. Also, as shown in FIG. 15, a pin 83 erected on the hub 35b as a support portion may be inserted through an oblong shaped portion 82 which is formed at the proximal portion of the second power transmitting arm 42.

[0128] In the second preferred embodiment, the engaging pin 55 of the pulley 51 and the support arm 54 of the receiving member 50 enable engagement with each other. However, an engaging pin formed on a receiving member and an elastic member of a pulley (such as the annular base portion 51b) may enable engagement with each other.

[0129] In the third preferred embodiment, each of the arms 60 and 61 transmits the torque between the common engaging pin 38 and the common roller 39. As shown in FIG. 13, however, each of the arms 60 and 61 may transmit the torque between the respective engaging pin 38 and the respective roller 39 by adding another engaging pin 38 and another roller 39. In this case, layered area between the arms 60 and 61 can be reduced. Therefore, a hysteresis arisen from wear generated between the arms 60 and 61 can be reduced.

[0130] In the fourth preferred embodiment, each of the plate springs 74a and 74b is placed on the pulley 72 and each engaging projection 71 is formed on the receiving member 70. However, the power transmission may be performed by engaging an engaging projection formed on the pulley 72 with plate springs placed on the receiving member 70.

[0131] In the fourth preferred embodiment, each of the plate springs 74a and 74b is supported at both ends of the plate springs 74a and 74b as lateral support plate springs. However, each of the plate springs 74a and 74b may be supported only at one end of each plate spring.

[0132] In the first and third preferred embodiments, when the excessive load torque T is applied between the pulley 32 and the receiving member 35, the power transmission between the pulley 32 and the receiving member 35 is blocked. However, the function for blocking the power transmission may be omitted.

[0133] In the first through third preferred embodiments, the proximal portion of each of the arms 41, 42, 52, 60 and 61 is supported by the receiving members 33 and 35 while the distal portion of each of the arms 41, 42, 52, 60 and 61 engages with the pulleys 32 and 51. However, the proximal portion of each of the arms 41, 42, 52, 60 and 61 may be supported by the pulleys 32 and 51 while the distal portion of each of the arms 41, 42, 52, 60 and 61 engages with the receiving members 33 and 35.

[0134] In each of the above-described embodiments, each of the elastic members 41, 42, 52, 60, 61, 74a and 74b is constituted of plate springs. However, the elastic members 41, 42, 52, 60, 61, 74a and 74b may be constituted of material other than plate spring as long as the material has elasticity. For example, the pulley may be connected to the receiving member through a coil spring or a wire spring.

[0135] In each of the above-described embodiments, when the pulley starts to rotate in a state that load torque T is not applied, it is desired that the elastic coefficient of each of the elastic members 41, 52, 60 and 74a which transmits torque first and the elastic coefficient of each of the elastic members 42, 54, 61 and 74b which transmits torque secondly have relatively great difference. When the above elastic coefficients has relatively great difference, the natural frequency introduced by the elastic coefficient of only one elastic member and the natural frequency introduced by the elastic coefficient in a state that both elastic members transmits torque have relatively great difference. That is, range of practical rotational speed of the drive shaft 16 is expanded.

[0136] In each of the above-described embodiments, it is predetermined such that the elastic coefficient of each of the elastic members 41, 52, 60 and 74a which transmits torque first is smaller than that of each of the elastic members 42, 54, 61 and 74b which transmits torque secondly when the pulley starts to rotate in a state that load torque T is not applied. However, it may be predetermined such that the elastic coefficient of each of the elastic members 42, 54, 61 and 74b which transmits torque secondly is equal to or smaller than the elastic coefficient of each of the elastic members 41, 52, 60 and 74a which transmits torque first.

[0137] In each of the above-described embodiments, the elastic body is constituted such that the elastic coefficient of the elastic body varies by two stages. However, the elastic body may be constituted such that the elastic coefficient of the elastic body varies by three stages or more by increasing the number and the kind of the elastic members.

[0138] The compressor C is not limited to a single-headed piston type compressor whose single-headed piston compresses refrigerant. The compressor C may be a double-headed piston type compressor whose double-headed piston compresses refrigerant in the cylinder bores formed at front and rear sides with respect to a crank chamber.

[0139] The compressor C whose cam plate wobbles while supported relatively rotatably by the drive shaft 16 may be applied in place of the constitution that the swash plate 18 functioning as the cam plate integrally rotates with the drive shaft 16. For example, a wobble plate type compressor may be applied.

[0140] The compressor C may be a fixed displacement type compressor whose piston stroke is unchangeable.

[0141] In all the above embodiments, the present invention is applied to the piston type compressor whose piston moves reciprocally. However, the present invention may be applied to a rotary type compressor such as a scroll type compressor which is disclosed in Japanese Unexamined Patent Publication No. 11-324930.

[0142] In all the above embodiments, the present invention is applied to a compressor. However, the present invention may be applied to a rotary machine provided with a rotary shaft which is connected to a receiving member so as to integrally rotate with the receiving member as long as twist vibration arises on the rotary shaft.

[0143] In all the above embodiments, a sprocket and a gear may be applied as the drive rotary body.

[0144] In all the above embodiments, the present invention is applied to the compressor for compressing refrigerant. However, the present invention may also be applied to a compressor for compressing air or fluid.

[0145] The present examples and preferred embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein but may be modified within the scope of the appended claims.

Claims

What is claimed is:

1. A power transmission mechanism comprising; a first rotary body; a second rotary body located coaxially with the first rotary body; and an elastic body through which the first rotary body is operatively connected to the second rotary body for transmitting torque, the elastic body having a plurality of elastic members so as to stepwise change an elastic coefficient of the elastic body in accordance with the value of the torque.

2. The power transmission mechanism according to claim 1 wherein the number of the elastic members engaging with the rotary bodies increases as the value of the torque increases.

3. The power transmission mechanism according to claim 1 wherein the elastic members have at least a first elastic member and a second elastic member having different elastic coefficients from each other and start to engage with the rotary bodies in order of increasing the elastic coefficients of the elastic members as the value of the torque increases.

4. The power transmission mechanism according to claim 1 wherein the elastic members are made of plate springs.

5. The power transmission mechanism according to claim 1 wherein the first rotary body has a main body which functions as the elastic member by engaging with a part of the second rotary body.

6. The power transmission mechanism according to claim 1 wherein the first rotary body has a support portion for supporting a plurality of the elastic members.

7. The power transmission mechanism according to claim 6 wherein the second rotary body has a plurality of engaging portions, and wherein the distal ends of the elastic members supported by the support portion engage with different engaging portions, respectively.

8. The power transmission mechanism according to claim 6 wherein at least a part of each of the elastic members is layered.

9. The power transmission mechanism according to claim 1 wherein the elastic body is connected to the first rotary body and is capable of engaging with the second rotary body.

10. The power transmission mechanism according to claim 1 wherein the first rotary body is a drive rotary body and the second rotary body is a driven rotary body.

11. A compressor operatively connected to an external drive source, the compressor comprising: a compression mechanism having a drive shaft for compressing fluid; and a power transmission mechanism including; a pulley operatively connected to the external drive source, a receiving member connected to the drive shaft, and an elastic body through which the pulley is operatively connected to the receiving member for transmitting torque, the elastic body having a plurality of elastic members so as to stepwise change an elastic coefficient of the elastic body in accordance with the value of the torque.

12. The compressor according to claim 11 wherein a piston type compressor is applied.

13. The compressor according to claim 12 wherein the piston type compressor is a single-headed piston type compressor.

14. The compressor according to claim 11 wherein a variable displacement type compressor is applied.

15. A rotary machine comprising: a rotary mechanism having a rotary shaft; and a power transmission mechanism including; a first rotary body, a second rotary body connected to the rotary shaft, and an elastic body through which the first rotary body is operatively connected to the second rotary body for transmitting torque, the elastic body having a plurality of elastic members so as to stepwise change an elastic coefficient of the elastic body in accordance with the value of the torque.