Patent Publication Number: US-2023143207-A1

Title: Brake device, lever hoist, and ratchet mechanism

Description:
TECHNICAL FIELD 
     The present invention relates to a brake device, a lever hoist, and a ratchet mechanism. 
     BACKGROUND ART 
     A lever hoist is widely used for a work of raising/lowering and pulling a cargo or fixing a cargo by a sling or the like (fastening a cargo). This lever hoist can perform hoisting (winding) and lowering (unwinding) of a chain by operating an operation lever with a hand. An example of the lever hoist is, for example, the one disclosed in Patent Literature 1. In the lever hoist disclosed in Patent Literature 1, the operation lever is operated to drive a drive member, and a drive shaft is rotated via the drive member to rotate a load sheave. This makes it possible to lift a cargo and lower the cargo. Note that the lever hoist is provided with a switching knob, and a switching operation of the switching knob can switch to which of a hoisting direction or a lowering direction a driving force from the operation lever is transmitted. 
     CITATION LIST 
     Patent Literature 
     
         
         {PTL 1} JP 2011-102182 A 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     Incidentally, in the case where the switching knob is switched to the lowering direction side by mistake in hoisting the lever hoist, a brake mechanism may not work any longer. More specifically, if the switching knob is switched to the lowering direction by mistake in a state where a tip of a pawl member is in contact with a tip of a ratchet tooth of a ratchet wheel, the ratchet wheel may start to powerfully rotate by the action of the load of the cargo. 
     If the tip of the pawl member can enter a valley part between the ratchet teeth at a stage of the start of rotation of the ratchet wheel, the rotation of the ratchet wheel can be stopped. However, if the switching knob is switched and the ratchet wheel starts to powerfully rotate in a state where the tip of the pawl member is in contact with the tip of the ratchet tooth, a next ratchet tooth (next tooth) reaches earlier than a time period required for the pawl member to enter the valley part, the pawl member collides with the tip of the next tooth and bounced to cause the same state thereafter, and the tip of the pawl member cannot enter the valley part any longer, failing to stop the rotation of the ratchet wheel. The rotation of the ratchet wheel cannot be blocked with the configuration disclosed in Patent Literature 1. 
     The present invention has been made in consideration of the above circumstances, and has an object to provide a brake device, a lever hoist, and a ratchet mechanism which can block reverse rotation of a ratchet wheel. 
     Solution to Problem 
     To solve the above problem, according to a first viewpoint of the present invention, there is provided a brake device which stops reverse rotation of a drive shaft transmitting rotation to a load sheave around which a chain is wound to prevent reverse rotation of the load sheave, the brake device including: a brake receiver pivotally supported in a non-rotatable manner on the drive shaft and including a flange part and a boss part; a female screw member pivotally supported in a rotatable manner on the drive shaft and screwed to a male screw part provided at an outer periphery of the drive shaft; a ratchet wheel sandwiched between the flange part and the female screw member facing each other, and including ratchet teeth provided on an outer peripheral side and configured to restrict a rotation direction to one direction; a brake plate arranged between the ratchet wheel and at least one of the flange part and the female screw member; and at least one pawl member engaging, on a tip side, with a valley part located between adjacent ratchet teeth, and meshing with the ratchet tooth, wherein the ratchet teeth include tall teeth and short teeth lower in projection height from a rotation center of the ratchet wheel than the tall teeth. 
     Further, in another aspect of the present invention, it is preferable in the above invention that a pair of the pawl members are provided, and the pair of pawl members are arranged at positions symmetric around the drive shaft. 
     Further, in another aspect of the present invention, it is preferable in the above invention that the ratchet wheel is alternately provided with the tall teeth and the short teeth. 
     Further, in another aspect of the present invention, it is preferable in the above invention that a number of the ratchet teeth equal to double an odd number are provided. 
     Further, in another aspect of the present invention, it is preferable in the above invention that a short tooth tip part on a tip side of the short tooth forms a part of an arc. 
     Further, to solve the above problem, according to a second viewpoint of the present invention, there is provided a lever hoist including the brake device according to the above invention, the lever hoist including: an operation lever configured to turn with respect to the female screw member; a switching claw for hoisting attached to the operation lever, and meshing in a hoisting direction with a switching gear integral with the female screw member; a switching claw for lowering attached to the operation lever, and meshing in a lowering direction with the switching gear; and a switching knob provided integrally with the switching claw for hoisting and the switching claw for lowering, and configured to switch with which of the switching claw for hoisting and the switching claw for lowering the switching gear meshes. 
     Further, to solve the above problem, according to a third viewpoint of the present invention, there is provided a ratchet mechanism including a ratchet wheel formed with a plurality of ratchet teeth at an outer periphery and at least one pawl member meshing with the ratchet tooth, to allow rotation of the ratchet wheel only in one direction, wherein the ratchet teeth include tall teeth and short teeth lower in projecting height from a rotation center of the ratchet wheel than the tall teeth. 
     Advantageous Effects of Invention 
     The present invention can provide a brake device, a lever hoist, and a ratchet mechanism which can block reverse rotation of a ratchet wheel even when a switching knob is operated to a lowering direction side by mistake in hoisting. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a front view illustrating an example of a configuration of a lever hoist to which a power transmission device for lever hoist of the present invention is attached. 
         FIG.  2    is a cross-sectional view illustrating the configuration of the lever hoist illustrated in  FIG.  1   . 
         FIG.  3    is an enlarged partial cross-sectional view illustrating the vicinity of a brake device of the lever hoist illustrated in  FIG.  1   . 
         FIG.  4    is a plane view illustrating a ratchet wheel and pawl members of the lever hoist illustrated in  FIG.  1   , and is a view illustrating a state where a number of ratchet teeth equal to double an odd number are provided. 
         FIG.  5    is an enlarged view illustrating the vicinity of the ratchet teeth of the ratchet wheel illustrated in  FIG.  4   . 
         FIG.  6    is a plane view illustrating a ratchet wheel and pawl members of the lever hoist illustrated in  FIG.  1   , and is a view illustrating a state where a number of ratchet teeth equal to double an even number are provided. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a lever hoist  10  according to one embodiment of the present invention will be explained based on the drawings. 
     &lt;Regarding the Overall Configuration of the Lever Hoist&gt; 
     In the following explanation, an X-direction is an axial direction of a drive shaft  25  arranged between a gear box (whose sign is omitted) in which a reduction gear  30  is arranged and a quick-turn grip  60  (hereinafter, referred to as an “idling grip”), an X1 side is a side to which the idling grip  60  is attached, and an X2 side is a gear box side opposite thereto. Further, a Z-direction is a vertical direction (suspension direction; hoisting and lowering direction) in a suspension state of the lever hoist  10 , a Z1 side is an upper side in the suspension state, and a Z2 side is a lower side in the suspension state. 
       FIG.  1    is a front view illustrating an example of a configuration of the lever hoist  10 .  FIG.  2    is a cross-sectional view illustrating the configuration of the lever hoist  10  illustrated in  FIG.  1   . 
     As illustrated in  FIG.  2   , the lever hoist  10  includes a pair of frames  11 ,  12 , and an upper hook  22  is supported on the upper side (Z1 side) of the pair of frames  11 ,  12 . Further, between the pair of frames  11 ,  12 , a load sheave  20  around which a chain C 1  is wound is supported in a rotatable state. The load sheave  20  is integrally molded with a load gear  21  which meshes with a small-diameter gear part  32  of a later-explained reduction gear  30 . Further, the load sheave  20  is formed with an insertion hole  20   a  penetrating in the axial direction (X-direction), and the drive shaft  25  is inserted in the insertion hole  20   a . A male screw part  26  which meshes with a later-explained female screw member  35  is provided on an outer peripheral side in the middle of the drive shaft  25 , and a pinion gear  27  which meshes with a large-diameter gear part  31  of the reduction gear  30  is provided on the other side (X2 side) of the drive shaft  25 . Further, the reduction gear  30  is also integrally provided with the small-diameter gear part  32  which meshes with the aforementioned load gear  21 . 
     Note that a casing  13  is attached to the frame  11  to protect a drive section such as the aforementioned reduction gear  30 , load gear  21  and so on. Further, the aforementioned male screw part  26  meshes with a female screw part  36  of the female screw member  35 . The female screw member  35  is provided, at its peripheral edge portion, with a switching gear  37  capable of meshing with a switching claw  40  at a lower position (Z2 side) in addition to the female screw part  36 . The switching claw  40  is, for example, a ratchet claw which is provided on each of one side and the other side of a later-explained operation lever  50 , and the later-explained operation lever  50  is turned in a state where the switching claw  40  mesh with the switching gear  37  to transmit driving force to the female screw member  35 . 
     Further, a switching knob  45  is attached in a state of being coaxial with the switching claw  40 , and a switching operation of the switching knob  45  can switch in which of a hoisting direction or a lowering direction the driving force to the female screw member  35  is transmitted. For example, when the lower side (Z2 side) of the switching knob  45  is tilted to the left side in  FIG.  1   , the switching claw  40  for hoisting meshes with the switching gear  37 . Thus, when the operation of turning the operation lever  50  is repeated, the switching gear  37  rotates in the hoisting direction but does not rotate in the lowering direction. This corresponds to a hoisting state of the chain C 1 . 
     In addition, as illustrated in  FIG.  1   , a pair of engagement protruding parts  46  are provided on an upper side (Z1 side) of the switching knob  45 . One engagement protruding part  46  of the aforementioned pair of engagement protruding parts  46  engages with a flange part  65  of the idling grip  60  and thereby prevents the idling grip  60  from being pulled out to the one side (X1 side) in the axial direction (X-direction). Therefore, it is possible to keep a state where a not-illustrated urging spring presses a brake mechanism. 
     On the other hand, when the lower side (Z2 side) of the switching knob  45  is tilted to the right side in  FIG.  1   , the switching claw  40  for lowering meshes with the switching gear  37 . Thus, when the operation of turning the operation lever  50  is repeated, the switching gear  37  rotates in the lowering direction but does not rotate in the hoisting direction. This corresponds to a lowering state of the chain C 1 . In addition, the other engagement protruding part  46  engages with the flange part  65  of the idling grip  60  and thereby prevents the idling grip  60  from being pulled out to the one side (X1 side) in the axial direction (X-direction). Therefore, it is possible to keep a state where the not-illustrated urging spring presses the brake mechanism. 
     Further, when the lower side (Z2 side) of the switching knob  45  is located at a neutral position being a position between the hoisting direction and the lowering direction (in this case, the switching knob  45  is located in a direction along the long side direction of the operation lever  50 ), both of the switching claw  40  for hoisting and the switching claw  40  for lowering are brought into a state of not meshing with the switching gear  37 . This brings about a free (idling) state in which even when the operation of turning the operation lever  50  is performed, any of the operations of hoisting and lowering the chain C 1  is not executed. In this event, any of the pair of engagement protruding parts  46  does not engage with the flange part  65  of the idling grip  60 . Therefore, it becomes possible to pull the idling grip  60  out to the one side (X1 side) in the axial direction (X-direction) and to loosen the state where the not-illustrating urging spring presses the brake mechanism. 
     Further, a cam member  55  is attached to the drive shaft  25  in a non-rotatable state with respect to the drive shaft  25 , and a member called the idling grip  60  is attached on a side closer to the one end (X1 side) in the axial direction (X-direction) than the cam member  55  also in a non-rotatable state with respect to the drive shaft  25 . 
     The idling grip  60  is an almost circular handle-shaped portion rotatable together with the drive shaft. On the other side (X2 side) in the axial direction (X-direction) of the idling grip  60 , the flange part  65  is provided. When any of the pair of engagement protruding parts  46  engages with the flange part  65 , the idling grip  60  cannot be pulled out to the one side (X1 side) in the axial direction (X-direction) any longer. Therefore, it is possible to keep the state where the not-illustrated urging spring presses the brake mechanism. 
     During the hoisting and lowering, the idling grip  60  is pressed in toward the other side (X2 side) in the axial direction (X-direction) as illustrated in  FIG.  2   . However, when the switching knob  45  is at the neutral position (neutral state), the idling grip  60  can be pulled out to the one side (X1 side) in the axial direction (X-direction). In the case where the idling grip  60  is pulled out to the one side (X1 side) in the axial direction (X-direction), the pressing force of the urging spring urging the brake mechanism weakens to bring about a brake release state so that the chain  60  can be freely pulled out in any of directions on the hoisting side and the lowering side while gripping the chain C 1  with a hand or the like. 
     &lt;Regarding the Brake Device  70 &gt; 
       FIG.  3    is an enlarged partial cross-sectional view illustrating the vicinity of the brake device  70  of the lever hoist illustrated in  FIG.  1   . As illustrated in  FIG.  2    and  FIG.  3   , the brake device  70  is arranged between the operation lever  50  and the drive shaft  25 . The brake device  70  has a brake receiver  71 , brake plates  72   a ,  72   b , a ratchet wheel  80 , a pawl member  90 , a pawl shaft  91 , a bush  92  and so on as main components. 
     The brake receiver  71  has a flange part  71   a  and a hollow boss part  71   b  (corresponding to a boss part). The flange part  71   a  is a portion provided to be larger in diameter than the hollow boss part  71   b , and can receive the brake plate  72   a.    
     The hollow boss part  71   b  is located on a side closer to the female screw member  35  (X1 side) than the flange part  71   a , and pivotally supports the ratchet wheel  80  via the bush  92 . Note that the inner peripheral side of the hollow boss part  71   b  meshes with the drive shaft  25  by key-coupling, spline coupling, or the like, whereby the drive shaft  25  and the brake receiver  71  integrally rotate. 
     Further, the brake plates  72   a ,  72   b  are pivotally supported on the hollow boss part  71   b  between the flange part  71   a  and the ratchet wheel  80  and between the female screw member  35  and the ratchet wheel  80 , respectively. The brake plate  72   a ,  72   b  is a friction material formed, for example, by sintering or the like a predetermined material. 
     Here, in the case where a load acts on the drive shaft  25  in the lowering direction, the female screw member  35  presses the brake plates  72   a ,  72   b  by a screw fastening action of the female screw member  35  and the brake receiver  71  (flange part  71   a ). This strongly presses the brake plates  72   a ,  72   b , and the brake plates  72   a ,  72   b  strongly press the ratchet wheel  80 . Here, the pawl member  90  is locked on the ratchet wheel  80  to block the rotation of the ratchet wheel  80  in the lowering direction, so that the above strong press brakes the turning of the drive shaft  25  in the lowering direction. 
     Note that when the switching knob  45  is switched to the hoisting direction and the operation lever  50  is operated, the ratchet wheel  80  can rotate in the hoisting direction, so that the turning in the hoisting direction is not blocked by the ratchet wheel  80 . Accordingly, the operation of the operation lever  50  causes the female screw member  35 , the brake plates  72   a ,  72   b , the ratchet wheel  80 , and the brake receiver  71  integrally turn the drive shaft  25 , and its driving force is transmitted to the load sheave  20  via the reduction gear  30  to hoist the chain C 1 . 
     On the other hand, when the switching knob  45  is switched to the lowering direction and the operation lever  50  is operated, the female screw member  35  is rotated by the operation amount to relax the screw fastening action of the brake receiver  71 . Therefore, the brake force with the ratchet wheel  80  is released according to the operation amount of the operation lever  50  (namely, the rotation amount of the female screw member  35 ), so that the brake receiver  71  and the drive shaft  25  turn in the lowering direction. The driving force in the lowering direction is transmitted to the load sheave  20  via the reduction gear  30  to lower the chain C 1 . 
     Further, a ratchet tooth  83  (later explained) provided on the ratchet wheel  80  meshes with a tip part  90   a  of the pawl member  90 . The mesh constitutes a ratchet mechanism which allows rotation in the hoisting direction while preventing the rotation in the lowering direction of the ratchet wheel  80  except when switching the switching knob  45  to the lowering direction and operating the operation lever  50 . 
     Further, as illustrated in  FIG.  3   , the bush  92  is provided on the outer peripheral side of the hollow boss part  71   b  of the brake receiver  71 , and the ratchet wheel  80  is provided on the outer peripheral side of the bush  92 . 
     Further, the pawl shaft  91  is attached to the frame  12 , and the pawl member  90  is turnably supported on the pawl shaft  91 . Further, a coil part  93   a  of a torsion spring  93  is attached to the pawl shaft  91 , and the torsion spring  93  applies an urging force in a direction in which the pawl member  90  is pressed against the ratchet tooth  83  (later explained) of the ratchet wheel  80 . Note that a pair of pawl members  90  are provided and arranged to be point-symmetric with each other about a center axis of the drive shaft  25  in the circumferential direction of the ratchet wheel  80 . 
     &lt;Regarding the Ratchet Wheel  80 &gt; 
     Next, the configuration of the ratchet wheel  80  will be explained.  FIG.  4    is a plane view illustrating the ratchet wheel  80  and the pawl members  90 , and is a plane view illustrating an example of a configuration in which the number of ratchet teeth  83  is equal to double an odd number and illustrating an arrangement of the pawl members  90 . As illustrated in  FIG.  4   , the ratchet wheel  80  is provided with a ring-shaped part  81  in a ring-shape, and the front surface and the rear surface of the ring-shaped part  81  are portions against which the aforementioned brake plates  72   a ,  72   b  are pressed. Note that the aforementioned bush  92  is located in a center hole  82  located at the center of the ring-shaped part  81 , whereby the ratchet wheel  80  is rotatably supported. 
     From the ring-shaped part  81 , the ratchet teeth  83  project toward the outer periphery.  FIG.  5    is an enlarged view illustrating the vicinity of the ratchet teeth  83  of the ratchet wheel  80 . As illustrated in  FIG.  5   , the ratchet teeth  83  include tall teeth  831  and short teeth  832 . A tip portion of the tall tooth  831  (tall tooth tip part  831   a ) of them projects farther to the outside diameter side than a tip portion of the short tooth  832  (short tooth tip part  832   a ). Therefore, the tip part  90   a  of the pawl member  90  at a position where the tip part  90   a  comes into contact with the short tooth tip part  832   a  by the urging force of the torsion spring  93  is located closer to the center side in the radial direction (inside diameter side) than a position where the tip part  90   a  comes into contact with the tall tooth tip part  831   a.    
     Here, in this embodiment, the tall teeth  831  and the short teeth  832  are alternately and adjacently formed, and are provided at regular lengths (pitches) in the circumferential direction. Further, assuming that a space between the tall tooth  831  and the short tooth  832  is a valley part  833 , an inclination angle of a tapered part  831   b  from the valley part  833  toward the tall tooth tip part  831   a  on the tip side of the tall tooth  831  is provided to be equal to an inclination angle of a tapered part  832   b  from the valley part  833  toward the short tooth tip part  832   a  on the tip side of the short tooth  832 . Accordingly, in this embodiment, the short tooth  832  is provided in a form obtained by cutting the tip side of the tall tooth  831 . Note that the short tooth tip part  832   a  of the short tooth  832  may be a part of an arc concentric with the ratchet wheel  80 . However, the short tooth tip part  832   a  may have a shape other than the part of the arc (for example, a linear shape) or may be a part of an arc not concentric with the ratchet wheel  80 . 
     Further, the total number ratchet teeth  83  including the tall teeth  831  and the short teeth  832  is an even number. Here, in the case where the number of the ratchet teeth  83  is the number obtained by doubling an odd number as illustrated in  FIG.  4   , when the tip part  90   a  of one of the pawl members  90  is pressed against the tall tooth  831 , the other pawl member  90  is pressed against the short tooth  832 . Either the one pawl member  90  or the other pawl member  90  is certainly pressed against the short tooth  832 , so that the tip part  90   a  of at least the pawl member  90  pressed against the short tooth  832  certainly collides with (the back of) the tall tooth  831  adjacent thereto when the reverse rotation occurs. This can surely block the reverse rotation of the ratchet wheel  80 . Note that in the configuration illustrated in  FIG.  4   , the number of existing ratchet teeth  83  is 22 in total, but the number of the ratchet teeth  83  may be any number as long as it is the number obtained by doubling an odd number. 
     However, in the case where the total number of the ratchet teeth  83  including the tall teeth  831  and the short teeth  832  is the number obtained by doubling an even number (the number of a multiple of four) as illustrated in  FIG.  6   , when the tip part  90   a  of the one pawl member  90  is pressed against the tall tooth  831 , the other pawl member  90  is also pressed against the tall tooth  831 . Besides, when the tip part  90   a  of the one pawl member  90  is pressed against the short teeth  832 , the other pawl member  90  is also pressed against the short teeth  832 . Also in this case, the tip part  90   a  of the pawl member  90  pressed against the short tooth  832  when the revers rotation occurs certainly collides with (the back of) the tall tooth  831  adjacent thereto, or the interval between the adjacent tall teeth  831  becomes wider than the interval between ratchet teeth at the same height provided at the current ratchet wheel, whereby the tip part  90   a  of the pawl member  90  pressed against the tall tooth  831  can sufficiently block the reverse rotation of the ratchet wheel  80 . Note that in the configuration illustrated in  FIG.  6   , the number of the existing ratchet teeth  83  is 20 in total, but the number of the ratchet teeth  83  may be any number as long as it is the number obtained by doubling an even number. 
     &lt;Regarding the Operation and Effects&gt; 
     The brake device  70  and the lever hoist  10  in the above configuration each includes: the brake receiver  71  pivotally supported in a non-rotatable manner on the drive shaft  25  and including the flange part  71   a  and the hollow boss part  71   b  (boss part); the female screw member  35  pivotally supported in a rotatable manner on the drive shaft  25  and screwed to the male screw part  26  provided at the outer periphery of the drive shaft  25 ; the ratchet wheel  80  sandwiched between the flange part  71   a  and the female screw member  35  facing each other, and including the ratchet teeth  83  provided on the outer peripheral side and configured to restrict the rotation direction to one direction; the brake plate  72   a ,  72   b  arranged between the ratchet wheel  80  and at least one of the flange part  71   a  and the female screw member  35 ; and at least one pawl member  90  meshing with the ratchet tooth  83  and engaging on the tip part  90   a  (tip end side) with the valley part  833  located between the adjacent ratchet teeth  83 , wherein the ratchet wheel  80  is provided with the tall teeth  831 , and the short teeth  832  lower in projection height from a rotation center of the ratchet wheel  80  than the tall teeth  831 . 
     Here, a case where the switching knob  45  is switched to the lowering direction by mistake in a state where the tip part  90   a  of the pawl member  90  is in contact with the tall tooth tip part  831   a  on the tip side of the tall tooth  831  is considered. In this case, by the action of the load of a cargo, the ratchet wheel  80  tries to start to powerfully rotate (reversely rotate). However, the ratchet wheel  80  is provided with the tall teeth  831  and the short teeth  832  as explained above. Therefore, the tip part  90   a  of the pawl member  90  after passing through the short tooth tip part  832   a  of the short tooth  832  collides with the back of the adjacent tall tooth  831 . This can prevent the reverse rotation of the ratchet wheel  80 . 
     Further, in this embodiment, it is preferable that the tall teeth  831  and the short teeth  832  are alternately provided at the ratchet wheel  80 . In this configuration, in the case where the tip part  90   a  of at least one of the pawl members  90  is in contact with the short tooth tip part  832   a  of the short tooth  832 , when the ratchet wheel  80  starts to rotate (reversely rotate), the tip part  90   a  immediately collides with the back of the tall tooth  831  being the next tooth. Besides, in the case where the tip part  90   a  of at least of the pawl members  90  is in contact with the tall tooth tip part  831   a  of the tall tooth  831 , the tip part  90   a  immediately collides with the back of the tall tooth  831  even if the ratchet wheel  80  starts to rotate (reversely rotates) and the tip part  90   a  climbs over the short tooth tip part  832   a . This can prevent the reverse rotation of the ratchet wheel  80  at an early stage. 
     Further, in this embodiment, it is preferable to provide a number of the ratchet teeth  83  equal to double an odd number. In the case of constituting as above, when the tip part  90   a  of the one pawl member  90  is pressed against the tall tooth  831 , the other pawl member  90  is pressed against the short tooth  832 . Certainly pressing either the one pawl member  90  or the other pawl member  90  against the short tooth  832  makes it possible to press the tip part  90   a  of one of the pawl members  90  against the short tooth tip part  832   a  closer to the inside diameter than the tall tooth tip part  831   a  of the ratchet wheel  80  even if the ratchet wheel  80  reversely rotates at a speed higher than expected, thereby surely blocking the reverse rotation of the ratchet wheel  80 . 
     Further, in this embodiment, the short tooth tip part  832   a  on the tip side of the short tooth  832  can be formed to form a part of an arc. In the case of constituting this, the circumferential length of the short tooth tip part  832   a  becomes longer than the circumferential length of the tall tooth tip part  831   a . This makes it possible to make the time during which the tip part  90   a  of the pawl member  90  is in contact with the short tooth tip part  832   a  longer than that with the tall tooth tip part  831   a , thus more surely blocking the reverse rotation of the ratchet wheel  80 . Further, it becomes possible to easily process the short tooth tip part  832   a  using, for example, a machine tool, thus improving the productivity. 
     Modification Example 
     Embodiments of the present invention have been explained above, and the present invention is variously modifiable. Hereinafter, those modifications will be explained. 
     An idling device which switches idling/non-idling by operating the idling grip  60  is explained in the above embodiment, but a lever hoist provided with an idling device by another system such as an automatic idling system may be employed. 
     Further, the case where the brake device  70  is applied to the lever hoist  10  is explained in the above embodiment. However, the above brake device may be applied to a hoisting machine other than the lever hoist, such as a chain block. 
     Further, the case where a pair of pawl members  90  are provided is explained in the above embodiment. However, only one pawl member  90  may be provided, or three or more pawl members  90  may be provided. In the case of three or more pawl members  90  are provided, it is preferable that the pawl members  90  are evenly arranged on the outer peripheral side of the ratchet wheel  80 , and that when one pawl member  90  engages with the valley part located between ratchet teeth adjacent to the tall teeth, at least one of the other pawl members  90  engages with the valley part located between ratchet teeth adjacent to the small teeth. 
     However, it is also possible to arrange a plurality of pawl members  90  not evenly on the outer peripheral side of the ratchet wheel  80 . In this case, it is preferable to arrange them so that that radial forces acting on the pawl shafts  21  of the pawl members  90  become equal. For example, four pawl members  90  may be arranged two by two line-symmetric about a line orthogonal to the drive shaft  25 . Arranging the plurality of pawl members  90  so that the radial forces acting on the pawl shafts  21  become equal disperses the forces acting on the ratchet wheel  80  from the pawl members  90 , resulting in improved durability of the ratchet wheel  80 . Further, the arrangement of the pawl members  90  as above can reduce the imbalance of the force acting on the drive shaft  25  from the ratchet wheel  80 , resulting in improved durability of the drive shaft  25  and members therearound. 
     Further, a pair of pawl members  90  are provided, and the pair of pawl members  90 ,  90  most preferably have the same shape and are arranged at positions point-symmetric about the drive shaft  25 , but the pawl members  90  may have different shapes as long as they are shaped and arranged so that the tip parts  90   a  of the pawl members  90  engage at the same time with the valley parts  83  to be engaged respectively. For example, evenly arranging two or more pawl members  90  on the outer peripheral side of the ratchet wheel  80  makes it possible to disperse the force applied on one pawl member  90  and to reduce the radial force acting on the pawl shaft  91  where the ratchet wheel  80  is arranged. However, the engagement positions of the tip parts  90   a  are actually most preferably point-symmetric positions, and may be positions displaced by an even number of teeth from each other, but the displacement of the engagement positions more than necessary is not preferable because the load applied on the drive shaft  25  increases if the displacement amount becomes large. 
     Further, the brake plate  72  is arranged as a separate body from the ratchet wheel  80  in the above embodiment, but friction members may be formed by burning on both surfaces of the ratchet wheel  80 . 
     Further, the female screw member  35  which presses the ratchet wheel  80  by load torque acting on the drive shaft  25  is configured such that the male screw part  26  of the drive shaft  25  and the female screw part  36  of the female screw member  35  are screwed together in the above embodiment. However, the female screw member  35  may be provided at a separate body (for example, a male screw provided on the outer peripheral portion of a hollow shaft made by extending the hollow boss part  71   b  of the brake receiver  71 ) from the drive shaft  25 , and may be a mechanism which converts the load torque to a thrust force using a cum. 
     Further, the brake device  70  of the lever hoist  10  is explained as an example in the above embodiment, and the present invention can be said to relate to a ratchet mechanism in a wide view of the invention. More specifically, the present invention is a ratchet mechanism including a ratchet wheel formed with many ratchet teeth at an outer periphery and at least one pawl member meshing with the ratchet tooth, to allow rotation of the ratchet wheel only in one direction, wherein the ratchet teeth include tall teeth high in projecting height from a center of the ratchet wheel, and short teeth lower in projecting height from the center of the ratchet wheel. 
     In the ratchet mechanism configured as above, even when the reverse rotation occurs when the tip of the pawl member is located at the tip of the tall tooth or the short tooth, the tip of the pawl member collides at least with the back (slope forming the tall tooth) of a next tall tooth and enters the valley between the ratchet tooth and the ratchet tooth. This can immediately and surely block the reverse rotation of the ratchet wheel. 
     Here, it is preferable that two pawl members are provided at symmetric positions as illustrated in  FIG.  4   . Further, it is preferable that the tall teeth and the short teeth are alternately provided. Further, it is preferable that a number of the ratchet teeth equal to double an odd number are provided. 
     Further, providing two pawl members at the symmetrical positions can eliminate the bias of the stress applied on the ratchet wheel. Further, alternately providing the tall teeth and the short teeth can make the tip of the pawl member collide with the back of the tall tooth located in the immediate vicinity when the reverse rotation occurs. Further, providing a number of the ratchet teeth equal to double an odd number makes it possible that when the tip of one of the pawl members located at the symmetric positions is located at the tip of the tall tooth, the tip of the other pawl member is located at the tip of the short tooth, so that at least the tip of the pawl member located at the tip of the short tooth certainly collides with the back of the adjacent tall tooth when the reverse rotation occurs, thus immediately and surely blocking the reverse rotation of the ratchet wheel. 
     The above ratchet mechanism is applied to the brake device of the lever hoist resisting input torque in one direction as explained, for example, in the above embodiment, and is especially effective for blocking the reverse rotation of the ratchet wheel constituting the brake device. 
     REFERENCE SIGNS LIST 
     
         
         
           
               10  . . . lever hoist,  11  . . . frame,  12  . . . frame,  13  . . . casing,  20  . . . load sheave,  20   a  . . . insertion hole,  21  . . . load gear,  22  . . . upper hook,  25  . . . drive shaft,  26  . . . male screw part,  27  . . . pinion gear,  30  . . . reduction gear,  31  . . . large-diameter gear part,  32  . . . small-diameter gear part,  35  . . . female screw member,  36  . . . female screw part,  37  . . . switching gear,  40  . . . switching claw,  45  . . . switching knob,  46  . . . engagement protruding part,  50  . . . operation lever,  55  . . . cam member,  60  . . . idling grip,  65  . . . flange part,  70  . . . brake device,  71  . . . brake receiver,  71   a  . . . flange part,  71   b  . . . hollow boss part (corresponding to boss part),  72   a  . . . brake plate,  72   b  . . . brake plate,  80  . . . ratchet wheel,  81  . . . ring-shaped part,  82  . . . center hole,  83  . . . ratchet tooth,  90  . . . pawl member,  90   a  . . . tip part,  91  . . . pawl shaft,  92  . . . bush,  93  . . . torsion spring,  93   a  . . . coil part,  831  . . . tall tooth,  831   a  . . . tall tooth tip part,  831   b  . . . tapered part,  832  . . . short tooth,  832   a  . . . short tooth tip part,  832   b  . . . tapered part,  833  . . . valley part, C 1  . . . chain