Abstract:
A spring clutch has a housing containing first and second sleeves surrounding first and second longitudinal spans of a coil spring. A carrier mounting at least one of the sleeves relative to the housing flexes to maintain alignment of axes of the sleeves to control forces on the portion of the spring spanning the gap between the sleeves.

Description:
U.S. GOVERNMENT RIGHTS  
       [0001] The invention was made with U.S. Government support under contract DAAH10-01-2-0032 awarded by the U.S. Army. The U.S. Government has certain rights in the invention. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    (1) Field of the Invention  
           [0003]    This invention relates to power transmission, and more particularly to spring clutches.  
           [0004]    (2) Description of the Related Art  
           [0005]    Overrunning spring clutches are a well developed art. Such clutches make use of the principle that a spring coil will expand if twisted one way about its axis and contract if twisted the other way. In an exemplary clutch, respective portions of a coil spring are positioned within respective sleeves. In a neutral condition, of the spring portion within each sleeve, an end portion is lightly frictional engaged to the sleeve and a remaining portion is slightly radially spaced from the sleeve. When the sleeves rotate relative to each other about their common axis, friction between the sleeves and the associated end portions will tend to twist the spring. If the relative rotation is in the direction which would tend to contract the spring, there will be slippage or overrunning. If the relative rotation is in the opposite direction, the normal forces between the end portions and sleeve will increase and the heretofore spaced portions will expand into frictional engagement with the sleeves thereby resisting the relative rotation. Accordingly, when such a clutch is used to drive an output from an input rotating (absolutely) in a first direction, the clutch permits the output to rotate faster than the input in the first direction. This permits the output to continue to rotate if the input slows or is stopped. Absolute rotation of the input (or both the input and output) in an opposite second direction may be prevented by additional internal or external mechanisms.  
           [0006]    U.S. Pat. No. 5,799,931 (the &#39;931 patent, the disclosure of which is incorporated by reference herein as if set forth at length) discloses an exemplary such spring clutch. In that patent, the spring is formed into a coil by a machining a helical slot in a tubular form (e.g., as distinguished from winding a wire or somehow casting without machining a slot).  
         BRIEF SUMMARY OF THE INVENTION  
         [0007]    Accordingly, in one aspect the invention is directed to a spring clutch apparatus. The spring has a central longitudinal axis and first and second axial ends. First and second sleeves surround first and second longitudinal spans of the spring. A first bearing supports the first sleeve for rotation relative to a housing about a first axis normally coincident with the spring axis. A sleeve carrier at least partially surrounds the second sleeve and has first and second portions and an intermediate portion therebetween. A first portion is secured relative to the housing and the second portion is relatively radially movable relative to the housing with a flexing of the intermediate portion. A second bearing system supports the second sleeve for rotation relative to the sleeve carrier second portion about a second axis coincident with the spring axis and with the first axis when the sleeve carrier intermediate portion is in an unflexed condition. The sleeves engage the spring so that initial relative rotation between the first and second sleeves in a first direction tends to uncoil the spring and bias the spring into firmer engagement with the sleeves. Initial relative rotation between the sleeves in a second direction, opposite the first direction, tends not to uncoil the spring.  
           [0008]    In various implementations, a pinion gear may be unitarily formed with the first sleeve. The first bearing may be positioned radially between the first sleeve and the housing. An arbor may extend through the sleeves and be secured against rotation relative to the second sleeve. The sleeve carrier may have a circumferential array of elongate slots. The slots may extend longitudinally and have relatively wide central portions tapering toward first and second ends. The slots may extend longitudinally and at central portions may be wider than intervening unslotted portions of the carrier. The slots may be through-slots between interior and exterior surfaces of the carrier.  
           [0009]    The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a longitudinal, partially sectional, view of a clutch according to principles of the invention.  
         [0011]    [0011]FIG. 2 is a longitudinal cutaway view of an input housing assembly of the clutch of FIG. 1. 
     
    
       [0012]    Like reference numbers and designations in the various drawings indicate like elements.  
       DETAILED DESCRIPTION  
       [0013]    [0013]FIG. 1 shows a spring clutch  20  having an input housing  22  with a central longitudinal axis  500 . The input housing  22  is itself mounted within a main housing  23  (e.g., a gearbox housing). The clutch receives a driving torque about the axis  500  from an external source (e.g., an engine (not shown)) through an input drive flange  24 . The clutch may transmit a first sense or direction of such torque to an external load (e.g., a helicopter rotor system (not shown)) through an output pinion gear  26 . The clutch advantageously does not transmit substantial torque of an opposite sense. Accordingly, input rotation in a first direction will be transmitted as output rotation, although the output pinion gear may rotate faster in that direction in an overrunning condition. Opposite input rotation (if permitted) will not be so transmitted to the output pinion gear.  
         [0014]    In the illustrated embodiment, the input drive flange  24  drives an arbor shaft  28  via a diaphragm coupling  30 . The arbor shaft has an axis normally coincident with the input housing axis  500 . Specifically, the flange is secured to one end of the coupling while the other end is secured to an outer collar  32 . The outer collar  32  surrounds and engages an upstream or input end collar portion  34  of a sleeve member  35  via interfitting teeth. The collar portion  34  surrounds a portion of the arbor shaft  28  and is secured thereto against relative rotation by a pin  36 .  
         [0015]    The sleeve member  35  further includes a downstream sleeve portion  38  surrounding an upstream portion of a spring  40 . A downstream portion of the spring  40  is surrounded by an upstream sleeve portion  42  unitarily formed with a root collar  44  of the pinion gear  26  downstream thereof. The sleeve portions  38  and  42  and spring each have central longitudinal axes normally coincident with the axis  500 . The illustrated spring  40  has an interior surface  50  surrounding and in facing or contacting close proximity to an exterior surface  52  of a central portion of the arbor. The spring has an exterior surface  54  along its respective upstream and downstream portions in close facing or contacting proximity to interior surfaces  56  and  58  of the sleeve portions  38  and  42 . The spring  40  may be constructed, for example, as in the &#39;931 patent so that when the input flange  24  (and thus the sleeve portion  38 ) is rotated in a first direction about the axis  500  torque and rotation will be transmitted to the pinion gear  26 . When rotated in the opposite direction, such torque and rotation will substantially not be transferred. Similarly, if the pinion gear  26  is externally rotated in the first direction (such as by additional engine input) such rotation will substantially not be transferred to the input flange  24 .  
         [0016]    A series of bearings may mount the various rotatable components for rotation relative to the main and input housings. In the exemplary embodiment, a downstream end portion  60  of the arbor shaft is rotatably mounted relative to the main housing by a duplex ball bearing system  62  mounted in a pocket  64  in the main housing. A downstream portion  66  of the pinion gear root collar  44  is also mounted to the main housing via a roller bearing system  68  in a housing compartment  70  upstream and radially outboard from the compartment  64 . The sleeve portion  42  of the pinion gear is mounted to the input housing  22  via a duplex roller/ball bearing system  72 . In the exemplary embodiment, the outer races of the ball bearing system  72  are held within a downstream portion  80  of a carrier  82 . The downstream portion  80  is mounted by press fit within a downstream compartment  84  of the input housing. The outer races of the bearing system  72  are longitudinally held in place between clips  86  secured to the downstream rim  88  of the input housing and a downstream-facing shoulder portion  90  of the carrier.  
         [0017]    An upstream portion  92  of the carrier carries an outer race of a duplex roller bearing system  94 . The inner race engages the outer surface of the collar portion  34  to rotatably mount the sleeve member  35  to the carrier upstream portion for rotation about an axis of the bearing system  94  normally coincident with the axis  500 . In the exemplary embodiment, there is a radial gap  100  between an outboard surface portion  102  of the carrier upstream portion  92  and an adjacent inboard surface  104  of the input housing  22 . This radial gap permits a limited local radial excursion of the carrier upstream portion  92 , bearing system  94 , collar portion  34  and adjacent arbor portion. The carrier upstream portion  92  includes an upstream end portion  106  separated from a main portion  108  by an intermediate portion  110  having a circumferential array of apertures. A lip seal  112  mounted in an upstream-open compartment  114  of the input housing seals with the outboard surface of the end portion  106 .  
         [0018]    [0018]FIG. 2 shows further details of the carrier  82 . A central portion  120  extends upstream from the shoulder  90  at a slightly smaller diameter than the downstream portion  80 . A second shoulder  122  joins the upstream end of the central portion  120  to the main portion  108  of the upstream portion  92  slightly upstream of a downstream rim thereof. The central portion  120  is made relatively flexible by the inclusion of a circumferential array of longitudinally-extending slots  124  having upstream and downstream ends  126  and  128  respectively. The slots have lengths L and maximum widths W 1  at their longitudinal midpoints. Between each pair of adjacent slots, an unslotted portion  130  provides a longitudinally-extending web or beam between the shoulders  90  and  122 . Near their midpoints, the beams have a width W 2  which, for flexibility, are advantageously smaller than the slot widths W 1 . The carrier may be made flexible by alternate means such as by a general thinning of material in the absence of slots or a local thinning of material (e.g., blind slots).  
         [0019]    The flexibility of the central portion  120  permits a radial and/or angular excursion of the carrier upstream portion  92  (and thus the bearing system  94 , sleeve member  35 , local portion of the arbor  28 , and their locally common axis) relative to the input housing axis  500 . In operation, loads on the pinion gear can produce a combination of flexing of the main housing and input housing, arbor shaft, and pinion gear. Were the outer race of the bearing system  94  rigidly mounted to the input housing without play, the flexing could cause an undesired degree of misalignment of the sleeve portions  38  and  42  causing their local axes and respective longitudinally inboard rims  140  and  142  to become radially and/or angularly misaligned. This misalignment might place substantial stress on the central portion of the spring spanning the gap between the sleeve portions. In the exemplary embodiment, the flexing still transmits a deflection force across the central portion of the spring. However when this force is, in turn, transmitted to the sleeve portion  38 , the carrier central portion flexes, permitting a partial realignment of the carrier portion  38  relative to the carrier portion  40 . Thus transmission of the misalignment to the sleeves is controlled/attenuated as are the misalignment forces encountered by the spring. The magnitude of the radial clearance  100  may limit the range of carrier flexing.  
         [0020]    The clearance  100  may be selected so that a predetermined misalignment may be accommodated without contacting the surfaces  102  and  104 . The clearance should not be so great as to permit overstressing of the carrier central portion  120 . The effective spring rate in flexion of the carrier is influenced by factors such as the slot size and geometry, the number of slots, and the thickness of the local unslotted material. The spring rate may advantageously be selected to be soft or low enough so that expected deflection forces will permit the desired realignment while not being so soft that the system will become dynamically excited during normal operation. The lip seal should have sufficient compliance to accommodate the flexing while maintaining sealing effectiveness to prevent loss of oil.  
         [0021]    One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, in various embodiments or uses, the input and output may be through the arbor rather than the sleeve. Also, the invention may be applied to various spring and clutch configurations both known and yet developed. Details of any particular application (e.g., the environment in which the clutch is used) may influence the structure of such implementation. Accordingly, other embodiments are within the scope of the following claims.