Abstract:
A bush cutting machine including an automatic braking mechanism having a brake drum formed integrally with a clutch case which houses a centrifugal clutch. When the number of rotations of a clutch drum decreases, at least two braking members press against the brake drum, whereby the clutch drum stops rotating, and a cutting blade also stops rotating automatically.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to an improvement in a brake for stopping rotation of cutting blades of bush cutting machines.  
         BACKGROUND OF THE INVENTION  
         [0002]    A brake for a bush cutting machine is disclosed, for example, in Japanese Utility Model Laid-Open Publication No. SHO-51-53248 entitled “Rotary Cutter Stopping Device for Bush Cutting Machine”, or in Japanese Utility Model Laid-Open Publication No. SHO-51-99039 entitled “Safety Device for Bush Cutting Machine”.  
           [0003]    The rotary cutter stopping device of SHO-51-53248 has a pair of brake shoes provided on an outer periphery of a driven shaft, cam plates mounted to press the respective brake shoes. When grip of a brake lever is released, the cam plates are rotated by springs, pressing the brake shoes against the outer periphery of the driven shaft, thereby stopping the rotary cutter. The above rotary cutter stopping device, however, requires an operator&#39;s constant operation of the brake lever, which is troublesome, when stopping the rotary cutter. Further, the device requires such components as a brake lever and wires, increasing the number of components and thereby increasing the production cost.  
           [0004]    The safety device of SHO-51-99039 has brake linings provided proximately to an outer periphery of a clutch drum. When grip of a brake lever is released, the brake linings come into contact with the clutch drum, and a motor is stopped in response to a signal from a movable contact, thereby stopping the rotary cutter. This safety device, however, requires an operator&#39;s constant operation of the lever, which is troublesome, when stopping the motor and the rotary cutter, deteriorating its operability. Further, the device has a rod connected to a linkage, extended through a clutch housing, a construction which requires the consideration of dust- and water-proofing of the through hole. Further, the device requires such efforts as checking and adjustment of the tensioning of the linkage connected to the lever, which efforts are troublesome.  
         SUMMARY OF THE INVENTION  
         [0005]    It is therefore an object of the present invention to provide a bush cutting machine with improved drive operability and improved dustproof and waterproof properties, which can be produced at a relatively low cost.  
           [0006]    According to an aspect of the present invention, there is provided a bush cutting machine which comprises: a motor; a centrifugal clutch designed to establish drive connection when a number of rotations of an output shaft of the motor exceeds a predetermined value; a blade driving shaft for transmitting a torque; a cutting blade mounted to a distal end of the blade driving shaft; the centrifugal clutch comprising a clutch drum provided on the blade driving shaft, a centrifugally pivotal member provided on the output shaft of the motor and housed in the clutch drum, and a clutch case connected to a motor housing for enclosing the pivotal member and the clutch drum; and an automatic braking mechanism housed in the clutch case and comprising a brake drum formed integrally within the clutch case, at least two centrifugal braking members pivotally mounted to the clutch drum in such a manner as to expand by a centrifugal force proportionate to the number of rotations of the clutch drum, and resilient members for biasing the braking members to the brake drum, whereby the braking members are brought into abutting engagement with the brake drum with decrease in the number of rotations of the clutch drum.  
           [0007]    With the automatic braking mechanism thus installed in the clutch case, it becomes possible to make the braking members abut against the braking drum in accordance with the reduced number of rotations of the clutch drum. When the number of rotations decreases, the braking members press against the braking drum, whereby the clutch drum instantaneously stops rotating and the blade driving shaft and the cutting blade also stop. Thus, the operator does not need to manually control a brake lever to stop the blade driving shaft, leading to improved operability. Further, with the automatic braking mechanism installed in the clutch case, it is no longer necessary to provide in the clutch case a through hole for a wire or a rod for braking. This further leads to the advantage that dustproof and waterproof properties are improved. Furthermore, with the automatic braking mechanism installed in the clutch case, the need for mounting such components as a brake lever or a wire is eliminated, resulting in reduced production cost.  
           [0008]    Desirably, the braking members are disposed around the brake drum in equidistantly spaced relation to each other, and the resilient members are provided to extend between adjacent two of the braking members. As a result, the weight of the braking members and the weight of the resilient members can be evenly distributed, thereby preventing unbalanced rotation. The braking members are synchronized to improve the braking properties. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    A preferred embodiment of the present inventing will be described in detail below, by way of example only, with reference to the accompanying drawings, in which:  
         [0010]    [0010]FIG. 1 is a side view showing use of a bush cutting machine according to the present invention;  
         [0011]    [0011]FIG. 2 is a detailed view of portion  2  of FIG. 1;  
         [0012]    [0012]FIG. 3 is a sectional view taken along line  3 - 3  in FIG. 2;  
         [0013]    [0013]FIG. 4 is a cross-sectional view taken at portion  4  of FIG. 2; and  
         [0014]    [0014]FIGS. 5A and 5B are functional diagrams of the bush cutting machine according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0015]    Referring initially to FIG. 1, when cutting bush, a bush cutting machine  10  according to the present invention is hung from a shoulder of an operator M via a hanging belt or shoulder strap  11  with a controller  12  gripped. Reference numeral  13  denotes a cutting blade for cutting bush.  
         [0016]    As shown in FIG. 2, the bush cutting machine  10  has a motor  21 , a centrifugal clutch  23  designed to establish drive connection when the number of rotations of a crankshaft  22 , serving an output shaft of the motor  21 , exceeds a predetermined value, a blade driving shaft  24  for transmitting a rotational force or torque to the cutting blade  13  shown in FIG. 1, and an automatic braking mechanism  25 .  
         [0017]    The centrifugal clutch  23  has a clutch drum  31  provided on the blade driving shaft  24 , a centrifugally pivotal member  32  (See FIG. 4) provided on the crankshaft  22  of the motor  21  and housed in the clutch drum  31 , and a clutch case  34  connected to a motor housing  33 , enclosing the pivotal member  32  and the clutch drum  31 .  
         [0018]    The automatic braking mechanism  25  has a brake drum  35  formed integrally within the clutch case  34 , centrifugal braking members  36  pivotally mounted to the clutch drum  31  such that they expand by a centrifugal force proportionate to the number of rotations of the clutch drum  31 , and resilient members  37  (See FIG. 3) biasing the braking members  36  to the brake drum  35 . The braking mechanism  25  is installed in the clutch case  34 . Reference numeral  38  denotes a stopper.  
         [0019]    The motor  21  has a cylinder  41 , a piston  42 , a crankshaft  22 , and an ignition plug  43 . Reference numeral  44  denotes a fuel tank,  45  an oil tank, and  46  a starter.  
         [0020]    The clutch drum  31  has a tubular transmitting portion  47 , a disc-shaped connecting portion  48  formed integrally with one end of the transmitting portion  47 , and a connecting shaft  49  (See FIG. 4) mounted to the connecting portion  48 .  
         [0021]    As shown in FIG. 3, the two braking members  36 ,  36  are disposed around the brake drum  35  with a distance or interval L left therebetween, while the resilient members  37 ,  37  are extended between the adjacent braking members  36 ,  36 .  
         [0022]    Serration  49   a  is formed centrally of the connecting shaft  49 . Serration  24   a  is formed on the blade driving shaft  24 . The serration  49   a  is in meshing engagement with the serration  24   a.    
         [0023]    Each braking member  36  has an arc-shaped body  51 . One end  52  of the body  51  is formed with a bearing  53  and a first hooking aperture  54 . The other end  55  is formed with a second hooking aperture  56 . An engaging portion  57  is formed in the middle, curved to the brake drum  35 . A friction member  58  is attached to the engaging portion  57 . Spindles  59  are attached to the connecting portion  48  of the clutch drum  31 . The bearing  53  is mounted to the spindle  59 . Reference numeral  61  denotes a retaining ring.  
         [0024]    As shown in FIG. 4, the clutch case  34  includes a bearing support  62  provided on the inner surface of the brake drum  35 , supporting the connecting shaft  49  via bearings  63 ,  63 .  
         [0025]    The member  32  of the centrifugal clutch  23  swings when the number of rotations of the crankshaft  22  exceeds a predetermined value, abutting at one end  64  against the transmitting portion  47 , thereby contacting the clutch drum  31 .  
         [0026]    Now, an operation of the above-mentioned bush cutting machine will be described with reference to FIG. 5A and FIG. 5B.  
         [0027]    In FIG. 5A, the automatic braking mechanism  25  of the bush cutting machine presses the braking drum  35  with the braking members  36 ,  36  as shown by arrows {circle over (1)}, {circle over (1)}. This is the state wherein the motor stops. For the cutting operation, the motor is started, increasing the number of its rotations.  
         [0028]    Turning to FIG. 5B, with increase in the number of rotations of the motor, the number of rotations of the clutch drum  31  of the centrifugal clutch  23  increases. Then, the braking members  36 ,  36  skid over the braking drum  35  with the other ends  55 ,  55  swung by a centrifugal force about the spindles  59 ,  59  supporting the bearings  53 ,  53 , in directions shown by arrows {circle over (2)}, {circle over (2)} against the forces of the resilient members  37 ,  37 , thus causing the friction members to move away from brake drum  35 . As a result, the number of rotations is further increased, allowing the blade driving shaft  24  to rotate as shown by arrow {circle over (3)}. At this time, the swung braking members  36 ,  36  abut against stoppers  38 ,  38 , stably maintaining the maximally expanded state.  
         [0029]    Conversely, when the number of rotations of the motor is reduced, the other ends  55 ,  55  are returned to their original positions, as shown in FIG. 5A, by forces F, F of the resilient members  37 ,  37 , and the friction members  58 ,  58  of the braking members  36 ,  36  are pressed against the brake drum  35  as shown by arrows {circle over (1)}, {circle over (1)}, thereby causing the clutch drum  31  and hence the blade driving shaft  24  to instantaneously stop rotating.  
         [0030]    Since the automatic braking mechanism  25  in which, in correspondence with the reduced number of rotations of the clutch drum  31  of the centrifugal clutch  23 , the braking members  36 ,  36  abut against the brake drum  35 , is thus installed in the clutch case  34 , manual braking control for stopping rotation of the blade driving shaft  24  is no longer required, thereby improving the driving operability of the machine.  
         [0031]    Further, with the automatic braking mechanism  25  installed in the clutch case  34 , it is no longer necessary to provide a through hole in the clutch case  34  for allowing passage of such components as a wire and a rod, thus improving dustproof and waterproof properties of the machine.  
         [0032]    Still further, with the automatic braking mechanism  25  installed in the clutch case  34 , it is no longer necessary to provide such components as a control lever and a wire for a braking operation, thereby reducing the number of components and hence the production cost.  
         [0033]    In addition, since the two braking members  36 ,  36  are disposed around the brake drum  35  in an equidistantly spaced relation to each other and the resilient members  37 ,  37  are provided to extend between the adjacent braking members  36 ,  36 , it becomes possible to evenly distribute the weight of the components around the rotational center, thereby preventing unbalanced rotation.  
         [0034]    Moreover, since the two braking members  36 ,  36  are provided around the brake drum  35  in an equally spaced relation to each other and the resilient members  37 ,  37  are provided to extend between the adjacent braking members  36 ,  36 , it becomes possible to render the resulting machine compact and to achieve synchronization of the braking members  36 ,  36 . This leads to reliable braking.  
         [0035]    In the embodiment discussed above in relation to FIG. 2, the brake drum  35  is formed in the clutch case  34 . Alternatively, the brake drum may be formed at any other fixed portion.  
         [0036]    Although two braking members are provided around the brake drum  35 , the number of such members may be greater.  
         [0037]    The present disclosure relates to the subject matter of Japanese Patent Application No. 2000-381407, filed Dec. 15, 2000, the disclosure of which is expressly incorporated herein by reference in its entirety.