Abstract:
A ratchet mechanism for a bicycle hub includes a first hub member and a second hub member, wherein the first hub member and the second hub member are rotatable relative to each other. A pawl is supported by the first hub member, a ratchet tooth is supported by the second hub member, and a biasing mechanism is provided for biasing the pawl toward the ratchet tooth. A pawl control mechanism is responsive to relative rotation of the first hub member and the second hub member for allowing the pawl to contact the ratchet tooth when the first hub member and the second hub member rotate relative to each other in one direction and for preventing the pawl from contacting the ratchet tooth when the first hub member and the second hub member rotate relative to each other in an opposite direction.

Description:
BACKGROUND OF THE INVENTION 
     The present invention is directed to bicycle freewheels and, more particularly, to a pawl noise dampening mechanism for a bicycle freewheel. 
     The hub of the drive-side wheel (usually the rear wheel) of a bicycle is sometimes provided with an integrated or separate freewheel. The freewheel is usually equipped with a one-way clutch mechanism so that only unidirectional rotational force is transmitted to the bicycle wheel. One-way clutch mechanisms having various structures are known. One known example is a ratchet mechanism in which engagement between pawls and ratchet teeth is employed. When the chain is driven by the pedals and a cog is rotatably driven, the ratchet mechanism transmits the torque from the ratchet teeth to the pawls and rotatably drives an inner component. The pawls are actuated by pawl springs in such a way as to ensure constant engagement with the ratchet teeth. The ratchet mechanism must possess extremely high strength and shock resistance because considerable torque and impact forces are transmitted from the ratchet teeth to the pawls. 
     When the pedals are stopped or rotated backward, the inner component of the freewheel rotates together with the wheel, creating a rotational movement in relation to the ratchet teeth. Because the inner component has pawls, the pawls and the ratchet teeth move relative to each other. Since the pawls are constantly actuated and pressed against the tooth surfaces of the ratchet teeth by pawl springs, the pawls chatter against the teeth surfaces of the ratchet teeth when performing a rocking movement in conformity with the peaks and valleys of the ratchet teeth. The noise generated by such a ratchet mechanism is unpleasant for the cyclist, and the friction between the pawls and the tooth surfaces of the ratchet teeth wastes energy. The result is that this type of friction wears out the pawls and the tooth surfaces of the ratchet teeth, thus shortening freewheel life. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a bicycle freewheel wherein the engagement between the pawls and ratchet teeth is silent when the bicycle pedals are stopped or rotated backward, and wherein the wear of the pawls and ratchet teeth is reduced. In one embodiment of the present invention, a ratchet mechanism for a bicycle hub includes a first hub member and a second hub member, wherein the first hub member and the second hub member are rotatable relative to each other. A pawl is supported by the first hub member, a ratchet tooth is supported by the second hub member, and a biasing mechanism is provided for biasing the pawl toward the ratchet tooth. A pawl control mechanism is responsive to relative rotation of the first hub member and the second hub member for allowing the pawl to contact the ratchet tooth when the first hub member and the second hub member rotate relative to each other in one direction and for preventing the pawl from contacting the ratchet tooth when the first hub member and the second hub member rotate relative to each other in an opposite direction. 
     The ratchet mechanism may be incorporated in a hub wherein both the first hub member and the second hub member are coaxially and rotatably supported on a hub axle. A plurality of pawls and ratchet teeth may be provided wherein the pawl control mechanism allows at least one of the pawls to contact a corresponding ratchet tooth when the first hub member and the second hub member rotate in the one direction. On the other hand, the pawl control mechanism prevents the pawls from contacting the ratchet teeth when the first hub member and the second hub member rotate relative to each other in the opposite direction. In a more specific embodiment, the first hub member may be formed as an inner cylindrical member and the second hub member may be formed as an outer cylindrical member coaxially supported radially outwardly of the inner cylindrical member. Alternatively, a hub shell may be coaxially and rotatably supported on the hub axle, wherein the hub shell includes an annular component which forms the second hub member. In this case the second hub member is coaxially supported radially outwardly of the first hub member. 
     In any event, the plurality of pawls may be supported to an outer surface of the first hub member, and the plurality of ratchet teeth may be supported to an inner surface of the second hub member. The pawl control mechanism may include an annular cage and a clutch. The annular cage may include a plurality of pawl pressure components, wherein each pawl pressure component is adapted to contact a corresponding pawl. The clutch may coupled to the cage and to one of the first hub member and second hub member so that the pawl pressure components do not interfere with the normal operation of the pawls when the first hub member and the second hub member relatively rotate in the one direction. However, the plurality of pawl pressure components retract their corresponding pawls when the first hub member and the second hub member relatively rotate in the opposite direction. 
     In a more specific embodiment, the clutch may be formed as a circular slide spring having an end coupled to the cage and an outer peripheral surface in contact with the inner surface of the second hub member. When the first and second hub members relatively rotate in the one direction, the slide spring engages the second hub member for moving the pawl pressure components away from engagement with the pawls, thus allowing the pawls to contact the ratchet teeth. On the other hand, when the first and second hub members relatively rotate in the opposite direction, the slide spring engages the second hub member for moving the pawl pressure components to retract the pawls, thus preventing the pawls from contacting the ratchet teeth. This results in silent operation and decreased wear of the ratchet mechanism. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial cross-sectional view of a bicycle hub which incorporates a particular embodiment of a ratchet mechanism including a noise-dampening mechanism according to the present invention; 
     FIG. 2 a  is a partial cross sectional view of an inner cylinder shown in FIG. 1; 
     FIG. 2 b  is a right-side view of FIG. 2 a;    
     FIG. 2 c  is a left-side view of FIG. 2 a;    
     FIG. 3 is a view taken along line III—III in FIG. 1 showing the noise dampening mechanism in an on state; 
     FIG. 4 is a view taken along line III—III in FIG. 1 showing the noise dampening mechanism in an off state; 
     FIG. 5 a  is a front view of a particular embodiment of a cage used in the noise damping mechanism shown in FIG. 1; 
     FIG. 5 b  is a view taken along line Vb—Vb in FIG. 5 a;    
     FIG. 6 is a partial cross-sectional view of a bicycle hub which incorporates an alternative embodiment of a ratchet mechanism including a noise-dampening mechanism according to the present invention; 
     FIG. 7 is a view taken along line VII—VII in FIG. 6 showing the noise damping mechanism in an on state; and 
     FIG. 8 is a view taken along line VII—VII in FIG. 6 showing the noise damping mechanism in an off state. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     FIGS. 1 through 5 illustrate a bicycle hub which incorporates a particular embodiment of a ratchet mechanism including a noise-dampening mechanism according to the present invention. FIG. 1, which is a partial cross section of the outer ring of a rear hub  1 , depicts only a cross section of the portion above the center line. The rear hub  1  is disposed about a horizontally extending hub axle  2 . A hub shell  4  is rotatably supported by means of a left bearing (not shown; positioned on the left side of the drawing) and a right bearing  3  in such a way that rotation about the hub axle  2  is permitted. 
     The hub shell  4  is equipped with a left-side flange (not shown) and a right-side flange  5 . The hub shell  4  is a common standardized component of ordinary shape. The left-side flange and right-side flange  5  are provided with axial spoke insertion holes  6  for inserting the curved portions at the end of spokes (not shown) that extend in radial directions away from the hub axle  2 . 
     An outer ring  7  (also referred to as “the outer”) has a roughly cylindrical shape, and a spline  8  is formed along the outer periphery of the outer ring  7 . A cassette-type multiple sprocket freewheel (not shown) is inserted into and fixed to the spline  8 . Ratchet teeth  11  that form a ratchet mechanism  10  are formed along the inner peripheral surface of the interior opening of the outer ring  7 . In this embodiment, the there are  31  ratchet teeth  11 . In the interior opening of the outer ring  7 , an inner cylinder  20  (also referred to simply as “an inner component”) is inserted and disposed coaxially with the hub axle  2  and the outer ring  7 . The inner cylinder  20  is designed to hold the pawl  30 . 
     FIGS. 2 a ,  2   b , and  2   c  show the structure of the inner cylinder  20 . FIG. 2 a  is a cross section, FIG. 2 b  a right-side view of FIG. 2 a , and FIG. 2 c  a left-side view of FIG. 2 a . As shown in those Figures, five pawl support holes  21  are disposed at regular angular intervals along the outer periphery of the inner cylinder  20 , and the center axes of the pawl support holes  21  are disposed parallel to the center axis of the inner cylinder  20 . The pawl support holes  21 , which are intended to swingably support one end of the pawls  30 , are partially open round holes with an angle of about 240 degrees. The depth of the pawl support holes  21 , that is, the axial length of the pawl support holes  21 , is roughly equal to the length of the pawls  30 . 
     Spring support holes  22  are formed opposite the pawl support holes  21  in pairs with pawl support holes  21 , wherein the center axes of the spring support holes  22  are disposed parallel to the center axes of the pawl support holes  21  and the inner cylinder  20 . The spring support holes  22  are intended to accommodate and support pawl springs  23 . The pawl springs  23  are intended to actuate the tips of the pawls  30  in such a way that they engage the ratchet teeth  11 . In this embodiment, the pawl springs  23  are torsion coil springs in which one end engages one end of the pawls  30 , and the other end comes into contact with the outer peripheral surface of the inner cylinder  20  to actuate the pawls  30  as described above. For this reason, one end of the pawls  30  is inserted into and swingably supported by the pawl support holes  21 , and is actuated by the pawl springs  23  to ensure unidirectional rocking. 
     A support hole  24  is formed in the center of the inner cylinder  20 . The support hole  24  is a through hole for inserting the body fixing bolt  56 . An external thread  57  is formed on the tip of the body fixing bolt  56 , and the inner cylinder  20  is integrally fixed to the hub shell  4  by screwing the external thread  57  into an internal thread  58  formed in the hub shell  4 . 
     A ball rolling surface  25  with a semicircular cross section is formed along the outer periphery of one end of the inner cylinder  20 . A ball rolling surface  26  is also formed on the peripheral surface of the interior opening of the outer ring  7 . Steel balls  31 , which are interposed between the ball rolling surface  26  of the outer ring  7  and the ball rolling surface  25  of the inner cylinder  20 , roll on the ball rolling surface  25  and the ball rolling surface  26 , rotatably &#39;supporting the outer ring  7  on the inner cylinder  20 . 
     Internal serrations  27  are formed at one end of the inner cylinder  20 . The internal serrations  27  are divided into ten equal sections, with the cross-sectional shape consisting of ten semicircular protrusions  28 . The internal serrations  27  are intended to connect the inner cylinder  20  to a serration main body  35 . Serration main body  35  is interposed between the inner cylinder  20  and the hub shell  4 . The serration main body  35  is ajoint for transmitting the rotational torque from the chain to the hub shell  4  via the outer ring  7 , the ratchet mechanism  10 , and the inner cylinder  20 . External serrations  36  for engaging the internal serrations  27  of the inner cylinder  20  are formed along the outer periphery of one end of the serration main body  35 , wherein the peaks and valleys of the external serrations  36  are complementary to the peaks and valleys of the internal serrations  27 , wherein the external serrations  37  are formed along the outer periphery of the other end of the serration main body  35 . The external serrations  37  of the serration main body  35  engage internal serrations  38  formed in the hub shell  4 . The shapes of the external serration  37  and internal serration  38  are similar to those of the aforementioned external serrations  36  and the aforementioned internal serrations  27 , and are therefore not shown. The rotational torque of the freewheel is ultimately transmitted to the hub shell  4  via the outer ring  7 , the ratchet mechanism  10 , the inner cylinder  20 , the internal serrations  27  of the inner cylinder  20 , the external serrations  36  and external serrations  37  of the serration main body  35 , and the internal serrations  38  of the hub shell  4 . 
     A thread  29  is formed along the outer periphery of the other end of the inner cylinder  20 , and an internal thread  41  of a screw cup  40  is screwed onto the thread  29  and fixed to the inner cylinder  20 . The screw cup  40  is therefore integrally fixed to the inner cylinder  20 . A rolling surface  42  is formed on the outer peripheral surface of the screw cup  40 , and a rolling surface  43  is formed on the inner peripheral surface of the interior opening thereof. Steel balls  45  are interposed between the rolling surface  42  of the screw cup  40  and a rolling surface  9  formed on the inner peripheral surface of the interior opening of the outer ring  7 . 
     The outer ring  7  and the inner cylinder  20  can rotate in relation to each other. A cone  50  is screwed into the threaded portion of the hub axle  2 . The cone  50  is also fixed to the hub axle  2  with a lock nut  52 . A rolling surface  51  is formed along the outer peripheral surface of the cone  50 . Steel balls  55 , which are interposed between the rolling surface  43  of the screw cup  40  and the rolling surface  51  of the cone  50 , roll on the rolling surface  43  and the rolling surface  51 . 
     The inner cylinder  20 , serration main body  35 , hub shell  4 , and body fixing bolt  56  are therefore rotatably integrated on the hub axle  2 . As is evident from the description of the above structure, rotating the threaded body fixing bolt  56  makes it possible to fix the outer ring  7 , inner cylinder  20  and serration main body  35  to the hub shell  4  or to detach them from the hub shell  4  as an integral unit when the cone  50  and the steel balls  55  have been removed. The resulting advantage is that these components can be easily replaced. 
     When the outer ring  7  is stopped or rotated backward in the ratchet mechanism  10 , the inner cylinder  20  is rotatably driven by means of the hub shell  4 , so the pawls  30  rotate in relation to the ratchet teeth  11 , and pawl noise is generated by the peaks and valleys on the tooth surfaces of the ratchet teeth  11 , as described above. The pawl noise dampening mechanism  60  is designed to prevent such pawl noise. 
     A cage hole  61  whose diameter is somewhat greater than the size of the ratchet teeth  11  is formed in the inner peripheral surface of the interior opening of the outer ring  7 .The cage hole  61  is disposed in the vicinity of the steel balls  45  along the outer periphery of one end of the pawls  30 . A pawl noise dampening mechanism  60  for dampening pawl noise is inserted into the cage hole  61 . 
     FIGS. 5 a  and  5   b  show a cage  62  that constitutes the pawl noise dampening mechanism  60 . The cage  62  has an annular shape and is made of sheet metal. The cage  62  comprises an annular disk component  63 , pawl pressure components  64 , a slide spring engagement component  65 , and the like. The annular disk component  63  is a portion that forms the main body of the cage  62 , and depressions  66  shaped as radial slots are formed at five locations along the outer periphery thereof. The pawl pressure component  64  in each of the depressions  66  is connected to the annular disk component  63  and is bent at  90  degrees. 
     When the cage  62  is rotated, the inner peripheral surfaces  67  of the pawl pressure components  64  come into contact with the outer peripheral surfaces of the pawls  30 , and the tips of the pawls  30  are turned against the action of the pawl springs  23 , that is, toward the center in the radial direction. The pawls  30  will therefore come into contact with the tooth surfaces of the ratchet teeth  11 . The cage  62  is driven by a slide spring  70  in which friction in one direction of rotation is greater than in the other direction of rotation. 
     The slide spring  70  is made of steel wire and is roughly a full circle. One end of the slide spring  70  is formed into an engagement component  71  bent at about  90  degrees in the radial direction, whereas the other end  72  is free. The engagement component  71  is inserted into a slit  73  between two slide spring engagement components  65 . The outer peripheral surface of the slide spring  70  is pressed against the inner peripheral surface of the cage hole  61  ofthe outer ring  7 . 
     The operation of this embodiment will now be described. 
     The pedaling force of the cyclist drives the left and right crank arms. The drive action is transmitted from the chainwheel via the chain to the sprocket selected by the shifting operation of a multiple sprocket freewheel. This drive action creates a rotational drive force in the outer ring  7 , which is rotated simultaneously with the chainwheel. This rotational drive force is applied to ratchet teeth  11 , which are rotatably driven, and the pawls  30  and the ratchet teeth  11  are rotated in relation to each other in the direction of engagement. This relative rotation causes one of a plurality of the pawls  30  to interlock with and engage the single ratchet tooth  11  that is in the same phase. This engagement allows the outer ring  7  to receive the rotational drive force, and the hub shell  4  to be rotatably driven via the inner cylinder  20  and the serration main body  35 . 
     The above description concerns the operation of the ratchet mechanism  10  that occurs when the bicycle is propelled by pedaling. The operation of the pawl noise dampening mechanism  60  will now be described in detail. For the sake of simplicity, it is assumed that the inner cylinder  20  is stationary. When the pedals and the chain are driven and the outer ring  7  is rotated in the direction of arrow (a) in FIGS. 3 and 4, the inner peripheral surface of the cage hole  61  comes into contact with the outer peripheral surface of the slide spring  70 , so the frictional force acts in the tangential direction on the outer peripheral surface of the slide spring  70 . This action moves aside one end  72  of the slide spring  70 . As a result, the outer ring  7  and the slide spring  70  are rotated as an integral whole. As this integral rotation proceeds, the pawl pressure components  64  of the cage  62  separate from the outer periphery of the pawls  30  and assume a retracted state, as shown in FIG.  4 . Of the five pawls  30  that have different phases, one specific pawl  30  interlocks with the ratchet tooth  11  that has the corresponding angular phase. 
     When the outer ring  7  is rotated backward in the direction of arrow (b), the inner peripheral surface of the cage hole  61  of the outer ring  7  comes into contact with the outer periphery of the slide spring  70 , so the resulting frictional force causes the slide spring  70  and the outer ring  7  to rotate as an integral whole under the action of the frictional force alone. This frictional force is weaker than the frictional force generated during the aforementioned driving action. The rotation of the outer ring  7  in the direction of arrow (b) causes the pawl pressure components  64  of the cage hole  61  to press against the outer periphery of the tips of the pawls  30  in opposition to the action of the pawl springs  23 , disengaging the pawls  30  and the ratchet teeth  11 . In addition, when the outer ring  7  is rotatably driven, the inner peripheral surface of the cage hole  61  and the outer peripheral surface of the slide spring  70  slidably move in relation to each other. The pawl pressure components  64  keep the pawls  30  in a pressed state and prevent the pawls  30  and the tooth surfaces of the ratchet teeth  11  from coming into contact with each other. No pawl noise is thus generated (this state is shown in FIG.  3 ). 
     Although the ratchet mechanism  10  described in the embodiments shown in FIGS. 1-5 above was disposed in the interior opening of the outer ring  7 , it is not always necessary to incorporate the ratchet mechanism  10  into the outer ring  7 . When common sprockets are used, the diameter of the interior opening of the outer ring  7  is limited. More specifically, restrictions are imposed when enhancements are made to strengthen the pawls  30  of the ratchet mechanism  10 , when the number of ratchet teeth  11  is increased and the tooth pitch is reduced, or the like. Accordingly, FIGS. 6 through 8 are views of a bicycle hub which incorporates an alternative embodiment of a ratchet mechanism including a noise-damping mechanism according to the present invention. This embodiment differs from the embodiment shown in FIGS. 1-5 in that the ratchet mechanism  10 ′ is installed at the location of the right-side flange  5 ′ of the hub shell  4 ′. 
     More specifically, the rear hub  1 ′ is disposed about a horizontally extending hub axle  2 ′. A hub shell  4 ′ is rotatably supported by means of a left ball bearing  3 ″ and a right ball bearing  3 ′ in such a way that rotation about the hub axle  2 ′ is permitted. A left-side flange  5 ″ and a right-side flange  5 ′ are integrated into the hub shell  4 ′. The right-side flange  5 ′ of the hub shell  4 ′ in this embodiment is provided with a large-diameter annular component  75 . An annular ratchet tooth main body  80  is linked via a conventionally structured serration  81  in the interior opening of the large-diameter annular component  75 . The ratchet tooth main body  80  is thus fixed in the interior opening of the large-diameter annular component  75 . 
     The ratchet tooth main body  80  is provided with ratchet teeth  11  ′ of the same shape as the ratchet teeth  11  in the embodiment shown in FIGS. 1-5 above. A cage hole  82 , which is the same groove as the cage hole  61  used in the previous embodiment, is formed in the peripheral surface of the inner peripheral hole of the ratchet tooth main body  80 . A noise dampening mechanism  100  comprising a cage  110 , a slide spring  84 , and the like is positioned in this cage hole  82 . The noise dampening mechanism  100  operates on virtually the same principle as in the first embodiment described above, so the detailed description will be omitted, and only the differences will be described. 
     The noise dampening mechanism  100  is fastened with the aid of a fastening ring  83 , which is fixed to the interior opening of the large-diameter annular component  75 , to prevent detachment in the axial direction of the hub axle  2 . In addition, an inner cylinder  20 ′ for swingably supporting the pawls  30 ′ is positioned in the interior opening of the ratchet tooth main body  80 . The pawls  30 ′ are arranged along the outer periphery of the inner cylinder  20 ′. The pawls  30 ′ shown in FIG. 7 are normally actuated by pawl springs  95  (plate springs) to ensure contact with the ratchet teeth  11 ′. 
     Cage stoppers  116  are integrated into the cage  110  of the pawl noise dampening mechanism  100 . The cage stoppers  116  are held stationary by being pressed against the side surfaces  112  of the inner cylinder  20 ′. The cage  110  can move only within a fixed angular range. Pawl pressure components  114  apply pressure to the pawls  30 ′, wherein the pawl pressure components  114  come into contact with the side surfaces  113  of the inner cylinder  20 ′ when the freewheel is driven. The cage  110  is ultimately allowed to move in relation to the inner cylinder  20 ′ only within a fixed angular range. 
     Support inside the interior opening of the inner cylinder  20 ′ is provided by a roller bearing  85 . The roller bearing  85  rotatably supports the inner cylinder  20 ′ and a right-side hub shell  86  in relation to each other. One end of the right-side hub shell  86  is threadably fixed with a screw  87  to the interior opening of the hub shell  4 ′. The right-side hub shell  86  is therefore rotated integrally with the hub shell  4 ′. The right-side hub shell  86  is provided with a cylindrical extension  88 . 
     An inner ring  90  of a ball bearing  89  is fitted around the outside of the extension  88 , and an outer ring  91  of the ball bearing  89  is fitted inside the inner peripheral surface  92  of the interior opening of the outer ring  7 ′. On the other hand, the outer ring  7 ′ is integrally fixed to one end of the inner cylinder  20 ′ with a thread  93 . The result is that the outer ring  7 ′ is rotatably supported on the hub shell  4 ′ with the aid of the roller bearing  85  and the ball bearing  89 , and linkage is provided via the ratchet mechanism  10 ′. 
     A screw cup  40 ′ is fixed to the extension  88  of the right-side hub shell  86 . Because the screw cup  40 ′ comprises a bearing  3 , the hub shell  4 ′ and the right-side hub shell  86  are rotatably supported on the hub axle  2 ′ by the left bearing  3 ″ and the right bearing  3 ′. The structures and functions of the pawl noise dampening mechanism  100  and the pawls  30 ′ of the ratchet mechanism  10 ′ are essentially the same as in the first embodiment described above, so their detailed description will therefore be omitted. 
     The advantages of this embodiment over the embodiment shown in FIGS. 1-5 is that the number of ratchet teeth  11  can be increased, the pawls and the ratchet teeth can be strengthened, and the like. Although a separate inner cylinder  20 ′ was provided in the embodiment shown in FIGS. 6-8, it is also possible to extend the outer ring  7 ′ all the way to the hub shell  4 ′ to form an extension, and to position the pawls  30 ′ in the extension. 
     While the above is a description of various embodiments of the present invention, further modifications may be employed without departing from the spirit and scope of the present invention. For example, there are  31  ratchet teeth  11  and five pawls  30  in the embodiment shown in FIGS. 1-5, and there are  36  ratchet teeth  11  ′ and five pawls  30 ′ in the embodiment shown in FIGS. 6-8. However, clearly neither the number of ratchet teeth  11  or  11 ′ nor the number of pawls  30  or  30 ′ is limited to these numerical values. 
     Thus, the scope of the invention should not be limited by the specific structures disclosed. Instead, the true scope of the invention should be determined by the following claims. Of course, although labeling symbols are used in the claims in order to facilitate reference to the figures, the present invention is not intended to be limited to the constructions in the appended figures by such labeling.