Abstract:
A torque limiter includes a driving bushing, a clutch spring wound around an outer circumference of the driving bushing, and a housing receiving a driving force via the clutch spring. The housing includes a first catch portion engaged with a first end portion of the clutch spring, and a second catch portion engaged with a second end portion of the clutch spring. The second catch portion is movable with respect to the first catch portion to change an angle between the first and second end portions of the clutch spring.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2007-0040059, filed on Apr. 24, 2007, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present general inventive concept relates to a torque limiter, and particularly, to a torque limiter including a clutch spring. 
         [0004]    2. Description of the Related Art 
         [0005]    A torque limiter is a device that decouples a driving force of a driving unit from a driven unit when a load by the driven unit exceeds a preset range. A torque limiter including a clutch spring has a simple structure, and, thus, the torque limiter is widely used in, for example, cars, electronic products, printers, and duplicators. For example, in a paper feeder for a printer, a torque limiter including a clutch spring is utilized in a power transfer unit for a reverse roller in a paper separator that separates paper sheet by sheet. 
         [0006]      FIGS. 1 and 2  illustrate an example of a conventional torque limiter including a clutch spring. Referring to  FIGS. 1 and 2 , a clutch spring  30  is coupled to a hub  20  receiving a driving force from a driving source (not illustrated). The clutch spring  30  applies a predetermined torque to an outer circumstance of a hub  20 . A driven body (not illustrated) is connected to a housing  10 . The housing  10  includes catch portions  11  and  12  that are engaged with end portions  31  and  32  of the clutch spring  30 . When the hub  20  coupled with the clutch spring  30  is inserted in the housing  10 , both end portions  31  and  32  of the clutch spring  30  are engaged with the catch portions  11  and  12 , respectively. Thereafter, a cap  40  is coupled to the housing  10 . If clearances exist between the end portions  31  and  32  of the clutch spring  30  and the catch portions  11  and  12 , an assembly process may be facilitated, but the torque limiting operation of the torque limiter is delayed by a time period corresponding to the distance that must be traversed by the housing to engage with the clutch spring  30 . To operate the torque limiter without backlash, there must be no clearances between the catch portions  11  and  12  and the end portions  31  and  32  of the clutch spring  30 . Thus, an interval between the catch portions  11  and  12  must be greater than that between the end portions  31  and  32  of the clutch spring  30 . In this case, when the hub  20  coupled with the clutch spring  30  is assembled into the housing  10 , the end portions  31  and  32  of the clutch spring  30  must be spread out so as to be engaged with the catch portions  11  and  12 , which makes the assembly process very inconvenient. 
         [0007]    Because a threshold torque of the torque limiter is dependent upon a coupling force between the clutch spring  30  and the hub  20 , the threshold torque is affected by manufacturing tolerances of the clutch spring  30  and the hub  20 . The torque limiter having the structure illustrated in  FIGS. 1 and 2  does not include a structure for compensating for the manufacturing tolerances of the clutch spring  30  or the hub  20 . Thus, the manufacturing tolerances of the clutch spring  30  or the hub  20  affect the threshold torque. 
       SUMMARY OF THE INVENTION 
       [0008]    The present general inventive concept provides a torque limiter that can be assembled simply and can be adjusted to a selected threshold torque. 
         [0009]    Additional aspects and utilities of the present general inventive concept will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the general inventive concept. 
         [0010]    The foregoing and/or other aspects and utilities of the present general inventive concept may be achieved by providing a torque limiter including a driving bushing; a clutch spring wound around an outer circumference of the driving bushing, and a housing receiving a driving force via the clutch spring, wherein the housing includes a first catch portion engaged with a first end portion of the clutch spring, a second catch portion engaged with a second end portion of the clutch spring, the second catch portion moveable with respect to the first catch portion to change an angle between the first and second end portions and a locking portion locking the second catch portion in one of a plurality of positions. 
         [0011]    The second catch portion may be rotated with respect to the first catch portion. 
         [0012]    One of the plurality of positions may allow the second catch portion to be placed between the first and second end portions of the clutch spring while the clutch spring is in a relaxed state. 
         [0013]    The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing a torque limiter including a driving bushing, a clutch spring wound around an outer circumference of the driving bushing; and a housing receiving a driving force via the clutch spring and including a first housing and a second housing coupled to be movable with respect to each other, and a locking portion locking the second housing in a plurality of positions, wherein the first housing includes a first catch portion engaged with a first end portion of the clutch spring, and the second housing includes a second catch portion engaged with a second end portion of the clutch spring, so that an angle between the first and second end portions of the clutch spring can be changed. 
         [0014]    The first housing may further include a lower housing including the first catch portion, and an upper housing coupled with the lower housing, and the second housing may be coupled rotatably to the upper housing. 
         [0015]    The locking portion may include an adjustment arm provided at the second housing; and a plurality of mounting portions provided in the upper housing and receiving the adjustment arm. 
         [0016]    One of the plurality of mounting portions may allow the second catch portion to be placed between the first and second end portions of the clutch spring. 
         [0017]    The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing a torque limiter including a drive member to receive torque about a rotational axis thereof, a clutch member frictionally coupled to the drive member by an amount of friction proportional to a spread distance between a first end portion and a second end portion thereof, and a housing coupled to the clutch member through a first catch portion and a second catch portion thereof respectively engaging the first end portion and the second end portion of the clutch member, the first catch portion and the second catch portion being displaceable respective one another to establish a selected spread distance between the first end portion and the second end portion of the clutch member and subsequently locked in a relative position respective one another. 
         [0018]    The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing a torque limiter including a cylindrical drive member to receive torque about a rotational axis thereof, a clutch member frictionally coupled to an outer periphery of the drive member by an amount of friction proportional to a spread distance between a first end portion and a second end portion thereof, a cylindrical housing having a longitudinal dimension parallel to the rotational axis and a radial dimension, the housing being coupled to the clutch member through a first catch portion and a second catch portion thereof respectively engaging the first end portion and the second end portion of the clutch member, the first catch portion and the second catch portion being displaceable respective one another to establish a selected spread distance between the first end portion and the second end portion of the clutch member and subsequently locked in a relative position respective one another. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    These and/or other aspects and utilities of the present general inventive concept will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
           [0020]      FIG. 1  is an exploded perspective view illustrating an example of a conventional torque limiter; 
           [0021]      FIG. 2  is a cross-sectional view of  FIG. 1 ; 
           [0022]      FIG. 3  is a perspective view of a torque limiter according to an embodiment of the present general inventive concept; 
           [0023]      FIG. 4  is an exploded perspective view of the torque limiter of  FIG. 3  according to an embodiment of the present general inventive concept; 
           [0024]      FIG. 5  is a detailed view of a mounting part of the torque limiter of  FIG. 3  according to an embodiment of the present general inventive concept; 
           [0025]      FIG. 6  is a detailed view illustrating a mounting part of the torque limiter of  FIG. 3  according to another embodiment of the present general inventive concept; 
           [0026]      FIG. 7  is a perspective view illustrating a coupling state between a driving bushing and a clutch spring in the torque limiter of  FIG. 3  according to an embodiment of the present general inventive concept; 
           [0027]      FIG. 8  is a perspective view illustrating a coupling state between a second housing and an upper housing in the torque limiter of  FIG. 3  according to an embodiment of the present general inventive concept; 
           [0028]      FIG. 9  is a side view of  FIG. 3 , according to an embodiment of the present general inventive concept; 
           [0029]      FIG. 10  illustrates how first and second end portions are related to first and second catch portions before a threshold torque is adjusted by the torque limiter of  FIG. 3  according to an embodiment of the present general inventive concept; 
           [0030]      FIG. 11  illustrates a relationship between first and second end portions and first and second catch portions after a threshold torque is adjusted in the torque limiter of  FIG. 3  according to an embodiment of the present general inventive concept; and 
           [0031]      FIG. 12  illustrates an operation of the torque limiter of  FIG. 3  according to an embodiment of the present general inventive concept. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0032]    Hereinafter, preferred embodiments of the present general inventive concept will be described in detail with reference to accompanying drawings. 
         [0033]    Reference will now be made in detail to the embodiments of the present general inventive concept, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present general inventive concept by referring to the figures. 
         [0034]      FIG. 3  is a perspective view of a torque limiter according to an embodiment of the present general inventive concept, and  FIG. 4  is an exploded perspective view of the torque limiter of  FIG. 3  according to an embodiment of the present general inventive concept. It is to be understood that while a cylindrical embodiment is illustrated and described below, other geometries may be realized without departing from the spirit and intended scope of the present general inventive concept. For example, the embodiment illustrated in  FIGS. 3 and 4  is larger in its longitudinal dimension parallel to the rotational axis than in its radial dimension, however the present general inventive concept may be embodied where the radial dimension is greater than the longitudinal dimension. Other geometries are also possible, as will be apparent to the skilled artisan upon review of this disclosure, and such geometries are intended to fall within the intended scope of the present general inventive concept. 
         [0035]    Referring to  FIGS. 3 and 4 , a exemplary driving bushing  200  is connected to a driving source (not illustrated). A shaft  1  that may be rotated by the driving source (not illustrated) about a rotational axis and may be inserted in an insertion hole  201  of the driving bushing  200 . The insertion hole  201  includes a coupling as a power-connection, such as the groove  202 , between the shaft  1  and the driving bushing  20 . A complementary power-connection, such as a pin  3  inserted into a through hole  2 , is provided on the shaft  1 . In the exemplary coupling arrangement, the shaft  1  is coupled to the driving bushing  200  through the pin  3  placed in the groove  202 , so that the driving bushing  200  is rotated by way of the shaft  1 . 
         [0036]    A clutch member may be frictionally coupled to an outer circumference of the driving bushing  200  to impose a predetermined threshold torque, and is rotated together with the driving bushing  200  under the condition that the threshold torque is not exceeded. The clutch member may be implemented by a clutch spring  300  having first and second end portions  301  and  302 , respectively. It is to be understood that while the clutch spring  300  is illustrated as a coil spring, other devices to impose friction on the driving bushing  200  and to drive the housing  100  are possible without deviating from the spirit and intended scope of the present general inventive concept. 
         [0037]    The housing  100  is coupled to the clutch spring  300  and receives a driving force from the driving bushing  200  through the frictional coupling of the clutch spring  300  with the driving bushing  200 . A driven body (not illustrated) may be connected to the housing  100 . The housing  100  includes first and second catch portions  401  and  402  that are respectively engaged with first and second end portions  301  and  302 . 
         [0038]    The torque limiter according to the current embodiment may be adjusted to a selected threshold torque by increasing or decreasing the friction on the driving bushing  200  by the clutch spring  300 . The threshold torque of the clutch spring  300  can be adjusted by changing an angle, or a spread distance, between the first and second end portions  301  and  302 . To achieve the spread distance in the exemplary embodiment, the second catch portion  402  can be moved with respect to the first catch portion  401  to adjust the threshold torque of the clutch spring  300 . The torque limiter according to the current embodiment of the present general inventive concept further includes a locking portion for locking the second catch portion  402  in a selected one of a plurality of positions. 
         [0039]    Referring to  FIGS. 3 and 4 , the housing  100  may include a first housing  150  and a second housing  400  that can be moved relative to the first housing  150 . The first housing  150  includes the first catch portion  401 , and the second housing  400  includes the second catch portion  402 . According to the current embodiment, as the second housing  400  is rotated with respect to the first housing  150 , the threshold torque of the clutch spring  300  is adjusted. According to the current embodiment, the first housing  150  is divided into a lower housing  110  and an upper housing  120 , and the lower housing  110  includes the first catch portion  401 . The upper housing  120  serves as a cap and is coupled to the lower housing  110 . The upper housing  120  includes an elastic hook  122  as an example of a coupling unit for coupling the upper and lower housings  120  and  110  together. The lower housing  110  includes a complementary coupling portion  112 , which is coupled with the elastic hook  122 , and the upper housing  120  may include a mounting part  130  in which the adjustment arm  410  is inserted. The adjustment arm  410  may extend toward the upper housing  120 . 
         [0040]      FIG. 5  illustrates the mounting part  130  in detail according to an embodiment of the present general inventive concept. The adjustment arm  410  can be locked in a selected one of a plurality of positions of the mounting part  130 , so that a threshold torque can be adjusted in steps. The mounting part  130  may be formed in an arc shape, but may be formed in other shapes in accordance with the particular geometry of the torque limiter implementation. An inner wall  136  of the mounting part  130  may be elastic so that the adjustment arm  410  can be locked in steps when the second housing  400  is rotated. If the upper housing  120  is formed of an elastic material such as plastic, the inner wall  136  is also elastic. In certain embodiments of the present general inventive concept, a thickness (T) of the inner wall  136  may be adjusted to provide an appropriate elastic force, as illustrated in  FIG. 6 , by forming a through hole or slot  137  proximal to the mounting part  130 . Also, in certain embodiments of the present general inventive concept, the width (W) of the mounting part  130  may be greater than the thickness of the adjustment arm  410 , so that when the second housing  400  is rotated, the adjustment arm  410  can be elastically biased into one of a plurality of mounting portions  131 ,  132 ,  133 ,  134 , and  135  within the mounting part  130 . According to the current embodiment, a pair of mounting parts  130  and  130   a  and a pair of adjustment arms  410  and  410   a  are provided, but the present general inventive concept is not limited thereto. One of the plurality of mounting portions  131 ,  132 ,  133 ,  134  and  135  may allow the second catch portion  402  to be positioned between the first and second end portions  301  and  302  of the clutch spring  300  while the clutch spring  300  is in a relaxed state. For example, the position of the mounting portion  131  may be allow both the first catch portion  401  and the second catch portion  402  to be placed between the first and second end portions  301  and  302  of the relaxed clutch spring  300  when the adjustment arm  410  is placed in the mounting portion  131 . 
         [0041]    An assembly process of the exemplary torque limiter of  FIG. 3  will now be described. It is to be understood that the operations of assembly may be performed in a different order than that described below without deviating from the spirit and intended scope of the present general inventive concept. The operations described below also define procedures to adjust the torque threshold of the torque limiter  100 . 
         [0042]    As illustrated in  FIG. 7 , the clutch spring  300  is disposed on an outer circumference of the driving bushing  200 . An inner diameter (D 1  in  FIG. 4 ) of the clutch spring  300  in its relaxed state is smaller than an outer diameter (D 2 ) of the driving bushing  200 . Thus, the clutch spring  300  applies a predetermined frictional force to the outer circumference of the driving bushing  200 , and this frictional force serves to define a threshold torque. Thereafter, the driving bushing  200  and the clutch spring  300  may be inserted in an inner chamber  138  of the lower housing  110 . The first catch portion  401  may be positioned between the first end portion  301  and the second end portion  302  of the clutch spring  300 . Then, the second housing  400  may be inserted on an outer circumference of the clutch spring  300 . The second catch portion  402  may be placed in the internal chamber  138  between the first end portion  301  and the second end portion  302  of the clutch spring  300 . Thereafter, the upper housing  120  may be inserted in the lower housing  110 , surrounding the second housing  400 . The adjustment arm  410  may be inserted in one of the plurality of mounting portions  131 ,  132 ,  133 ,  134 , and  135 . To prevent the clutch spring  300  from being prematurely released when assembling the second housing  400 , the adjustment arm  410  may be inserted, for example, in the mounting portion  131  at an initial assembly stage, as illustrated in  FIG. 9 . As an alternate method, as illustrated in  FIG. 8 , after the second housing  400  is mounted to the upper housing  120 , the upper housing  120  may be coupled to the lower housing  110 . In this case, the second housing  400  and the upper housing  120  may be coupled such that the adjustment arm  410  is inserted in the mounting portion  131 . In certain instances, the second housing  400  and the upper housing  120  may be coupled together without positioning the adjustment arm  410 , and before the coupled second housing  400  and upper housing  120  are coupled to the lower housing  120 , the second housing  400  may be rotated, thereby placing the adjustment arm  410  in the mounting portion  131  at the selected position. The hook  122  may then be coupled to the coupling portion  112 , thereby completing the assembly process of the torque limiter illustrated in  FIG. 3 . As illustrated in  FIG. 10 , when the assembly process is completed, the first and second catch portions  401  and  402  are placed between the first and second end portions  301  and  302  of the clutch spring  300 , and clearances exist between the first and second catch portions  401  and  402  and the first and second end portions  301  and  302 . That is, the first and second catch portions  401  and  402  are spaced apart from the first and second end portions  301  and  302 , respectively. 
         [0043]    Then, the second housing  400  may be rotated to set a threshold torque of the torque limiter to a desired level and to fully engage the first and second catch portions  401  and  402  with the first and second end portions  301  and  302 . The inner diameter (D 3  in  FIG. 4 ) of the second housing  400  may be greater than the outer diameter (D 4  in  FIG. 7 ) of the clutch spring  300  inserted in the driving bushing  200 , and the inner diameter (D 5  in  FIG. 4 ) of the upper housing  210  may be greater than the outer diameter (D 6  in  FIG. 4 ) of the second housing  400 . When so configured, the second housing  400  can be rotated with respect to the upper housing  120 . The lower housing  110  and the upper housing  120  are fixed by the hook  122  being received in the complementary coupling portion  112 , and the second catch portion  402  provides the adjustment capability by being displaceable with respect to the first catch portion  401  when the second housing  400  is rotated. 
         [0044]    For example, if the threshold torque of the torque limiter is set to a desired level by using the mounting portion  133  of the plurality of mounting portions  131 ,  132 ,  133 ,  134  and  135 , as illustrated in  FIG. 11 , the second housing  400  may be rotated to place the adjustment arm  410  in the mounting portion  133 . Then, as illustrated in  FIG. 12 , a spread distance between the first catch portion  401  and the second catch portion  402  (i.e., an angular displacement between the first and second catch portions  401  and  402  by way of the second catch portion  402  being rotated with respect to the first catch portion  401  according to the current embodiment) is changed, and thus the first and second end portions  301  and  302  of the clutch spring  300  are spread out. Thus, the frictional force between the driving bushing  200  and the clutch spring  300  is adjusted to establish the threshold torque. Also, since any clearances between the first and second catch portions  401  and  402  and the first and second end portions  301  and  302  of the clutch spring  300  are closed through the relative displacement of first and second catch portions  401  and  402 , backlash does not occur when the torque limiter is operating. Further, to facilitate the rotation of the second housing  400 , the adjustment arm  410  may extend outwardly beyond an end portion  121  of the upper housing  120  (see  FIG. 3 ). In certain embodiments of the present general inventive concept, the adjustment arm  410  is inline with and extended from the second catch portion  402  to provide an indication from the outside of the housing  100  where the second end portion  302  of the clutch spring  300  is located. 
         [0045]    In the assembly process of the torque limiter according to certain embodiments of the present general inventive concept, the first and second end portions  301  and  302  of the clutch spring  300  can be engaged with the first and second catch portions  401  and  402  simply by placing the first and second catch portions  401  and  402  between the first and second end portions  301  and  302 , without having to spread the first and second end portions  301  and  302  of the clutch spring  300 . After the assembly process is completed, the second housing  400  is rotated to establish the predetermined threshold torque, which makes the assembly process very simple. 
         [0046]    In the structure described above, when the shaft  1  is rotated clockwise or counterclockwise, the housing  100  is rotated clockwise or counterclockwise, thereby driving a driven body connected to the housing  100 . When the shaft  1  is rotated clockwise, the housing  100  is rotated clockwise. When a load is applied by the driven body is sufficient to impose a torque greater than the threshold torque on the housing  100  (e.g., when the housing  100  is abruptly stopped), the driving bushing  200  is rotated clockwise relative to the housing  100 . Then, since the first end portion  301  of the clutch spring  300  is engaged with the first catch portion  401  and the second catch portion  402  continues its movement through friction with the driving bushing  200 , an angle between the first and second end portions  302  rapidly increases, thereby lowering the frictional force of the clutch spring  300  on the driving bushing  200 . Accordingly, slip occurs between the clutch spring  300  and the driving bushing  200 . In this manner, the torque limiter cuts off the power transfer between the driving source and the driven body when a load greater than the threshold torque is applied. A torque less than the threshold torque can be transferred to the load as long as the threshold torque is not exceeded. If a load occurs on the driven body and thus a torque greater than the threshold torque is applied to the housing  100  when the shaft  1  is rotated counterclockwise, the second end portion  302  of the clutch spring  300  is engaged with the second catch portion  402  and the first catch portion  401  continues its movement through friction with the driving bushing  200 . Consequently, an angle between the first and second end portions  301  and  302  increases, and thus slip occurs between the clutch spring  300  and the driving bushing  200 . In this manner, the torque limiter according to an embodiment of the present general inventive concept is operated without backlash. 
         [0047]    According to an embodiment of the present general inventive concept, the torque limiter is configured to allow the adjustment of a threshold torque. In the manufacturing process, dimensional tolerances of the outer diameter D 2  of the driving bushing  200 , and the inner diameter D 1  of the clutch spring  300 , and the angle between the first and second end portions  301  and  302  of the clutch spring  300  can stack up, i.e., individual components may be within tolerance, but the interface between components may be at an extreme of the design range. Consequently, even if the adjustment arm  410  is mounted in, for example, the mounting portion  133 , i.e., a design position, an actual threshold torque of the torque limiter may differ from the design level through a stack-up in tolerances. In this case, according to the torque limiter of the conventional art, the driving bushing  200  or the clutch spring  300  would have to be manufactured again. However, the torque limiter according to an embodiment of the present general inventive concept can easily compensate for a threshold torque error due to manufacturing tolerances by rotating the second housing  400  in a direction that compensates the difference between the design torque threshold and the incorrect torque threshold caused by the tolerance stack up. The adjustment arm  410  can then be mounted in, for example, the mounting portion  132  or the mounting portion  134 . 
         [0048]    According to an embodiment of the present general inventive concept, the torque limiter can obtain threshold torque levels in steps by rotating the second housing  400 . Accordingly, one torque limiter can fulfill the requirements of a plurality of torque applications, where each application has different threshold torque level requirements, so that the torque limiter can be used in various devices. 
         [0049]    The assembly process of the torque limiter is very simple because the first and second catch portions are simply placed between the first and second end portions of the relaxed clutch spring during the assembly process. 
         [0050]    Also, since a relative location of the second catch portion with respect to the first catch portion can be adjusted, a threshold torque can be easily adjusted and thus manufacturing tolerances of the threshold torque can be ameliorated. 
         [0051]    Since the relative location of the second catch portion with respect to the first catch portion can be adjusted, one torque limiter can provide a plurality of threshold torque levels. 
         [0052]    Although a few embodiments of the present general inventive concept have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the general inventive concept, the scope of which is defined in the appended claims and their equivalents.