Patent Publication Number: US-2023140002-A1

Title: Cam clutch

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a cam clutch that transmits and interrupts torque between an input shaft and an output shaft. 
     2. Description of the Related Art 
     A cam clutch is primarily composed of a plurality of cams arranged between an inner race and an outer race, a retainer retaining the plurality of cams, and biasing means biasing each of the cams in a direction in which they wedge against the inner race and outer race. 
     Japanese Patent Application Publication No. 2005-106135, for example, discloses a one-way clutch that uses a wire cage as a retainer, which is a wire material with axial portions and circumferential portions forming endless zigzag square U-shaped bends. This retainer retains the cams each set in the space formed by circumferential portions and axial portions in a circumferentially equally spaced manner. 
     SUMMARY OF THE INVENTION 
     Cam clutches with a retainer are often required of different characteristics even in the same size. Sometimes, for example, optimally shaped cams are employed, or the number or arrangement of the cams is changed, in accordance with the transmission torque capacity requirements. This in turn necessitates a change in the design of the retainer. 
     This need to produce purpose-designed retainers in line with the characteristics or size required of the cam clutch was causing issues such as poor versatility of components, and lower productivity and higher production cost due to a difficulty in producing the retainer. 
     In the case where the retainer is formed as a wire cage, an even number of cams are structurally necessary, i.e., there is a limitation on the number of cams. 
     The present invention was made based on the circumstances described above and aims at providing a cam clutch that realizes a reduction in production cost, improves productivity and assemblability, and increases the degree of design freedom. 
     The present invention solves the above problems by providing a cam clutch including: an inner race and an outer race that are coaxial and rotatable relative to each other; a plurality of cams circumferentially arranged between the inner race and the outer race; and positioning members that keep each two adjacent cams at fixed positions relative to each other, the positioning members being configured to link each two adjacent cams such as to be tiltable independently of each other. 
     The cam clutch set forth in claim  1  does not have a retainer and instead positioning members link each two adjacent cams and keep the cams in fixed relative positions. Thus the structure is simple and easy-to-produce, which improves productivity and enables reduction of production costs. This structure also provides high versatility since there is no need to make a purpose-designed retainer. Unlike a cam clutch having a retainer made by a wire cage, there is no limitation on the number of cams, so that a high degree of freedom in design is achieved. 
     According to the configuration set forth in claim  2 , the cam plates and positioning members can be punched from a plate material and the pin holes can be formed at the same time. The simple punching process for the cam plates and positioning members reduces the workload of machining so that productivity can be improved, as well as production costs can be reduced. 
     According to the configuration set forth in claim  3 , a plurality of cam plates are fixed together with two link pins, so that angular alignment of the cams is made easy and the assembling of the cams is facilitated. Moreover, the cams have no redundant (unnecessary) part so that weight reduction can be achieved. 
     According to the configuration set forth in claim  4 , the space between cam plates where the positioning members are disposed can be utilized as the mounting part of the annular spring, and there is no need to form a mounting groove for the annular spring during the production process of the cams. In this respect, too, the workload of machining can be reduced and productivity can be improved, as well as production costs can be reduced. The positioning members doubling as a spring receptacle enable application of a correct biasing force from the annular spring on the cams in an engaging direction so that there is no variation in the extent of engagement of each of the cams. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a plan view illustrating a configuration of one example of a cam clutch according to the present invention viewed from the direction of the rotation axis; 
         FIG.  2    is a perspective view with a cross section along the rotation axis of the cam clutch shown in  FIG.  1   ; 
         FIG.  3    is a cross-sectional view of an axial section along the rotation axis of the cam clutch shown in  FIG.  1   ; 
         FIG.  4    is an exploded perspective view illustrating the configuration of cams in the cam clutch shown in  FIG.  1   ; 
         FIG.  5    is a plan view illustrating the configuration of the cam in the cam clutch shown in  FIG.  1    viewed from the direction of the tilt axis of the cam; 
         FIG.  6 A  is a schematic cross-sectional view illustrating a condition (posture) of the cams in a stand-by state in the cam clutch shown in  FIG.  1   ; and 
         FIG.  6 B  is a schematic cross-sectional view illustrating a condition (posture) of the cams in a freewheeling state in the cam clutch shown in  FIG.  1   . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As shown in  FIG.  1    to  FIG.  3   , the cam clutch  100  according to the embodiment includes: an inner race  110  and an outer race  120  coaxial and rotatable relative to each other; a plurality of circumferentially arranged cams  130  in an annular space between raceways  111  and  121  of the inner race  110  and outer race  120  serving as sprags to transmit and interrupt torque between the inner race  110  and outer race  120 ; and an annular spring  160  biasing each of the plurality of cams  130  toward a direction in which the cams wedge against the inner race  110  and outer race  120 . 
     The plurality of cams  130  are each made up of two cam plates  131  arranged in parallel along the direction of an axis around which the cams tilt, and two link pins  135  extending along the direction of the tilt axis at two circumferentially spaced apart locations and connecting the two cam plates  131  together, as also shown in  FIG.  4   . This design of pairs of cam plates  131  fixed together with two link pins  135  facilitates angular alignment when assembling the cams and improves the assemblability, as well as allows a reduction of material (unnecessary part) of the cams so that a weight reduction can be achieved. 
     In this embodiment, the two link pins  135  are positioned such that the center of gravity G of the cam  130  when assembled is located more toward the engaging direction relative to the normal line H at a contact point C between an outer race engaging surface  133  of the cam  130  and the raceway  121  of the outer race  120 , as shown in  FIG.  5   . 
     While the cam  130  according to this embodiment has two cam plates  131 , the number of cam plates  131  is not limited to two and the cam may have three or more cam plates. If the cams are each made up of three cam plates, for example, the spaces made between two adjacent cam plates can be used as mounting portions for annular springs, i.e., two annular springs can be mounted. Two springs can reliably apply a biasing force suitable for a desirable function. 
     While the cam  130  according to this embodiment is made up of two cam plates  131  connected together by two link pins  135 , the cam plates may be connected together by one link pin  135 , or by three or more link pins  135 . 
     The cam plates  131  have the same outer contour. There is therefore no variation in the extent of engagement of each of the cams  130 , so that frictional loss can be reduced. This also enables improvement of productivity and reduction of production costs. 
     As shown in  FIG.  5   , each cam plate  131  has an inner race engaging surface  132  that makes contact with the raceway  111  of the inner race  110 , and an outer race engaging surface  133  that makes contact with the raceway  121  of the outer race  120 . The inner race engaging surface  132  has a circular arc cross section, for example, and the outer race engaging surface  133  has a curved cross-sectional shape including a circular arc portion with a smaller radius of curvature than the inner race engaging surface  132 . For convenience of explanation,  FIG.  5    illustrates the raceway  111  of the inner race  110  and the raceway  121  of the outer race  120  as parallel flat surfaces. 
     Two pin holes  134  extend through the cam plates  131  in the thickness direction. The two cam plates  131  are fixedly joined by link pins  135  press-fit into the pin holes  134 . 
     This configuration can prevent misalignment of the two cam plates  131  from their positions relative to each other (mismatching postures of the cam plates  131 ), so that the cam plates  131  are unlikely to make engagement in different degrees. The cam plates  131  can be punched from a plate material and the pin holes  134  can be formed at the same time. In this respect, too, the workload of machining can be reduced and productivity can be improved, as well as production costs can be reduced. 
     This embodiment uses columnar link pins  135 , for example, and the pin holes  134  have circular openings with an uniform hole diameter along the thickness direction. The cross-sectional shape of the link pins  135  and the opening shape of the pin holes  134  are not limited to circular. The pins and holes may have any shape as long as they are easy to produce, such as polygonal, elliptical, and oval, for example. Link pins  135  with a polygonal cross section and pin holes  134  with a polygonal opening can reliably provide an anti-rotation function for prohibiting relative rotation of the two cam plates  131 . Columnar link pins  135  need not necessarily have a uniform outside diameter along the axial direction and may include parts that vary in outside diameter. The link pins  135  are separate components from the cam plates  131 . Optionally, the link pins  135  may be formed integrally with one of the cam plates  131 . 
     Each cam  130  is configured to allow an annular spring  160  to be fitted between the two cam plates  131 . Namely, the cam  130  in this embodiment allows a space between cam plates  131  as the mounting part of the annular spring  160 , which obviates the need to form a mounting groove for the annular spring during the production process of the cam  130 , and therefore the workload of machining can be reduced and productivity can be improved, as well as production costs can be reduced. 
     In this embodiment, the annular spring  160  is mounted between the two cam plates  131 . Alternatively, at least one of the link pins  135  may be provided such as to protrude from an outer end face of the cam plate  131 , and the annular spring  160  may be mounted on an outer side in the direction of the tilt axis of the cam plates  131 . 
     The cam clutch  100  in this embodiment uses a ring-like garter spring as one example of the annular spring  160 . As shown in  FIG.  6 A , the garter spring is mounted onto the outer race engaging surfaces  133  of the cams  130  and biases each of the plurality of cams  130  radially inward, imparting a rotational moment M in the engaging direction. The garter spring thus binding the plurality of cams  130  stably retains each cam  130  without variation in their posture (tilt). 
     While the annular spring  160  is mounted such as to bias each of the plurality of cams  130  radially inward in this embodiment, the cam clutch may be configured such that the plurality of cams  130  are each biased radially outward by the annular spring  160 . The annular spring  160  is not limited to a garter spring and may be any spring as long as it biases each of the plurality of cams  130  in a direction in which the cams wedge against the inner race  110  and outer race  120 . 
     The cam clutch  100  described above includes positioning members  140  that keep each two adjacent cams  130  in fixed relative positions, i.e., this configuration does not include a retainer such as a cage ring for retaining the cams  130 . 
     The positioning members  140  are configured to link each two adjacent cams  130  such as to be tiltable independently of each other. 
     The positioning members  140  in this embodiment are a plate-like member that is oval in plan view and provided with two pin holes  141  at locations spaced away along the longitudinal direction. The link pins  135  of each two adjacent cams  130  are each loosely fitted into the pin holes  141  so that the cam plates  131  can tilt relative to the link pins  135 . The cams  130  can therefore move without being obstructed. Thus each two adjacent cams  130  are linked such as to be independently tiltable and kept in fixed relative positions. 
     This configuration realizes a simple and easy-to-produce structure to improve productivity and reduce production costs, as well as provides high versatility because there is no need to make a purpose-designed retainer. Unlike a cam clutch having a retainer made by a wire cage, there is no limitation on the number of cams, so that a high degree of freedom in design is achieved. While an even number, e.g., twenty two, cams  130  are provided in this embodiment, the number of cams  130  can be an odd number, and can be changed as required in accordance with the purpose. 
     The positioning members  140  are disposed between the pairs of cam plates  131  within the outer peripheral edges of the cam plates  131  so as not to touch the inner race  110  and outer race  120 , and configured to make contact with the annular spring  160  and to receive a biasing force from the annular spring  160 . The positioning members  140  doubling as a spring receptacle enable application of a correct biasing force from the annular spring  160  on the cams  130  in an engaging direction so that there is no variation in the extent of engagement of each of the cams  130 . 
     In the cam clutch  100  described above, as shown in  FIG.  6 A , the annular spring  160  imparts a rotational moment M so that the inner race engaging surfaces  132  of the cams  130  are in contact with the raceway  111  of the inner race  110  and the outer race engaging surfaces  133  of the cams  130  are in contact with the raceway  121  of the outer race  120 . That is, all the cams  130  are kept standby so that they can start wedging against the inner race  110  and outer race  120  immediately upon torque input to the inner race  110  or the outer race  120 . 
     For example, when the inner race  110  is rotated in one direction (clockwise in  FIG.  6 A ), the inner race engaging surfaces  132  of the cams  130  make frictional engagement with the raceway  111  of the inner race  110 , and the outer race engaging surface  133  of the cams  130  make frictional engagement with the raceway  121  of the outer race  120  so that torque is transmitted between the inner race  110  and the outer race  120 . 
     On the other hand, when the inner race  110  is rotated in the other direction (counterclockwise in  FIG.  6 B ), the cams  130  tilt against the rotational moment M of the biasing force from the annular spring (not shown in  FIG.  6 B ) by a predetermined centrifugal force, i.e., the centrifugal force lifts up the cams  130  from the inner race  110 . As the inner race engaging surfaces  132  of the cams  130  separate from the raceway  111  of the inner race  110 , the inner race  110  freewheels, i.e., the torque transmission between the inner race  110  and the outer race  120  is interrupted. Wear on the inner race engaging surfaces  132  and outer race engaging surfaces  133  of the cams  130  during high-speed freewheeling can thus be prevented. 
     The positioning members  140  rotate as the cams  130  tilt, since the link pins  135  of each two adjacent cams  130  are each loosely fitted into the pin holes  141 . The positioning members  140  can therefore move smoothly without obstructing the movement of the cams  130  so that a high responsiveness is achieved. 
     While one embodiment of the present invention has been described in detail, the present invention is not limited to the embodiment described above and may be carried out with various design changes without departing from the scope of the present invention set forth in the claims. 
     For example, while each two adjacent cams are connected together by plate-like positioning members in the embodiment described above, the means for keeping each two adjacent cams at fixed relative positions are not limited to plate-like positioning members and may take any form as long as they are capable of linking each two adjacent cams such that the cams can tilt independently. 
     Instead of the link pins that connect two cam plates fixedly together being inserted in the pin holes of the positioning members, cylindrical bushings may be press-fit into the pin holes of the positioning members and the link pins may be loosely fitted in the bushings. 
     Two positioning members may be mounted to each link pin. 
     Instead of the positioning members mounted between two cam plates as in the embodiment described above, at least one of the link pins may be provided such as to protrude from an outer end face of the cam plate, and the positioning members may be mounted on an outer side in the direction of the tilt axis of the cam plates. In such a configuration, stoppers may be provided to prevent the positioning members from coming off. 
     While the cam clutch configuration in the embodiment described above includes biasing means that bias the cams toward a direction in which they wedge against the inner race and outer race, the biasing means may be omitted. In this case, the center of gravity of the cams may be changed as required to cause the cams to make frictional engagement with the inner race and outer race by a centrifugal force. 
     One example has been described above in which the present invention is applied to a one-way cam clutch. The invention is also applicable to a two-way cam clutch having two kinds of cams configured to receive a rotational moment in different directions, for example, or to a cam clutch having an operation mode switching mechanism for forcibly switching the operation modes of the cam clutch.