Abstract:
A shaft brake mechanism of wind power generator, including a first brake assembly and a second brake assembly independent from each other. The first brake assembly serves to provide braking effect for the shaft of the wind power generator against rotation. The second brake assembly serves to naturally restrain the rotational speed of the shaft from exceeding a nominal upper limit of rotational speed. Accordingly, the wind power generator can still safely operate in a situation that the wind speed exceeds a nominal upper limit of wind speed. Therefore, the wind speed range for the operation of the wind power generator is widened to increase the total power generation capacity thereof.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to wind power generation, and more particularly to a shaft brake mechanism of wind power generator. 
     In wind power generation, as the wind blows, the blades are driven to make the shaft of the generator rotate for converting kinetic energy into electrical energy. However, it is necessary to brake the shaft against rotation in some situations. Conventionally, an electromagnetic brake system is generally used to provide braking effect for the shaft. Such electromagnetic brake system must be continuously powered to keep providing braking effect or stop providing braking effect, allowing the shaft to rotate. As a result, a large amount of electrical energy is consumed for maintaining the function of such electromagnetic brake system. 
     Moreover, as shown in  FIG. 10A , when a wind power generator operates in a condition that the rotational speed exceeds a nominal upper limit t 1 , the safety in operation will be threatened. Therefore, in the case that the wind speed exceeds a nominal upper limit t 2  of wind speed and the rotational speed of the shaft reaches the nominal upper limit t 1 , it is necessary to stop the system. In this case, the total power generation capacity of the wind power generator will be reduced and the natural wind power resource can be hardly fully utilized to cause waste of resource. 
     SUMMARY OF THE INVENTION 
     It is therefore a primary object of the present invention to provide a shaft brake mechanism of wind power generator, in which the electrical power for providing braking effect for the shaft is much less than that of the conventional device. Therefore, the shaft brake mechanism of the present invention has energy-saving effect. 
     It is a further object of the present invention to provide the above shaft brake mechanism of wind power generator, in which a smaller force is input to create a greater output force for providing braking effect for the shaft. Therefore, the shaft brake mechanism of the present invention has power-saving effect. 
     It is still a further object of the present invention to provide the above shaft brake mechanism of wind power generator, which can naturally restrain the rotational speed of the shaft from proportionally increasing with the wind speed. Therefore, the wind power generator can still safely operate in a condition that the wind speed exceeds a nominal upper limit of wind speed. Accordingly, without modifying the nominal upper limit of rotational speed, the nominal upper limit of wind speed can increase to increase total power generation capacity. 
     To achieve the above and other objects, with respect to the energy-saving effect and power-saving effect, the shaft brake mechanism of wind power generator of the present invention includes: a shaft; an annular disc coaxially fixedly fitted around the shaft and synchronously rotatable with the shaft; a clamping section having two first fulcrums and two elongated rock arms each having a first end, a middle section and a second end, the middle sections of the rock arms being respectively pivotally connected with the first fulcrums, the clamping section further having two clamping members respectively pivotally connected with the first ends of the rock arms and rotatable between a clamping position and a releasing position, when positioned in the clamping position, the clamping members tightly abutting against two faces of the disc to brake the disc against rotation, when positioned in the releasing position, the clamping members moving away from the two faces of the disc, a resilient member being bridged between the second ends of the rock arms for resiliently keeping the clamping members in the releasing position; a link section having a second fulcrum and a bar member having a first end, a middle section and a second end, the first end of the bar member being pivotally connected with the second fulcrum, whereby the bar member is rotatable about the second fulcrum between a first position and a second position, the link section further having a push block with a substantially trapezoidal cross section, the push block having two lateral slopes respectively adjacent to the second ends of the rock arms, a middle section of the push block being pivotally connected with the middle section of the bar member, when the bar member is moved to the first position, the push block being urged to move toward the first ends of the rock arms and interpose between the second ends thereof, whereby the two lateral slopes push the second ends of the rock arms away from each other to make the clamping members move to the clamping position, when the bar member is moved to the second position, the push block being moved from between the second ends of the rock arms, whereby the resilient member applies a resilient force to the rock arms to restore the clamping members to the releasing position; and a drive section for supplying power to drive and reciprocally move the bar member between the first position and the second position. 
     With respect to the increase of the nominal upper limit of wind speed without modification of the nominal upper limit of rotational speed, the shaft brake mechanism of wind power generator of the present invention includes: a shaft; a pier having a seat body, a shaft hole being formed through the seat body, the shaft being coaxially rotatably fitted through the shaft hole; a hoof section having an annular base coaxially fitted around and fixedly connected with the shaft, the hoof section further having at least two hoofs each having a pivot shaft, the hoofs being respectively pivotally mounted on the base via the pivot shafts and positioned around the shaft at equal angular intervals, the hoofs being arranged in a pattern centered at an axis of the shaft with the pivot shafts parallel to the axis of the shaft, whereby the hoofs can be pivotally rotated about the pivot shafts between a braking position and a releasing position, at least one resilient member being bridged between the hoofs for resiliently restoring the hoofs from the braking position to the releasing position; and a ring-shaped drum fixedly mounted on the seat body of the pier, the shaft coaxially passing through the drum with the hoofs facing an inner circumference of the drum, the hoofs being synchronously rotated with the shaft, when a centrifugal force applied to the hoofs overcomes resilient force of the resilient member, the hoofs moving from the releasing position to the braking position where the hoofs abut against the inner circumference of the drum, whereby under frictional force between the hoofs and the drum, the shaft is restrained against rotation to prevent rotational speed of the shaft from unlimitedly increasing. 
     The present invention can be best understood through the following description and accompanying drawings, wherein: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective assembled view of a preferred embodiment of the present invention; 
         FIG. 2  is a perspective exploded view of the first brake assembly of the preferred embodiment of the present invention; 
         FIG. 3  is a perspective assembled view of the first brake assembly of the preferred embodiment of the present invention; 
         FIG. 4  is a plane view of the preferred embodiment of the present invention, showing that the first brake assembly releases the shaft; 
         FIG. 5  is a plane view of the preferred embodiment of the present invention according to  FIG. 4 , showing that the first brake assembly is actuated to brake the shaft; 
         FIG. 6  is a perspective exploded view of the second brake assembly of the preferred embodiment of the present invention; 
         FIG. 7  is a perspective assembled view of the second brake assembly of the preferred embodiment of the present invention; 
         FIG. 8  is a sectional view taken along line a-a of  FIG. 7 , showing that the second brake assembly releases the shaft; 
         FIG. 9  is a sectional view according to  FIG. 8 , showing that the second brake assembly naturally brakes the shaft when the rotational speed of the shaft increases; 
         FIG. 10A  is a curve diagram showing that when the wind speed reaches the nominal upper limit t 2 , the shaft is braked and stopped; and 
         FIG. 10B  is a curve diagram showing that without modifying the nominal upper limit of rotational speed of the shaft, the nominal upper limit of operational wind speed increases from t 2  to t 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Please refer to  FIGS. 1 to 9 . According to a preferred embodiment, the shaft brake mechanism  10  of wind power generator of the present invention includes a board-like bed  20 , a first pier  30 , a second pier  40 , a shaft  50 , a first brake assembly  60  and a second brake assembly  70 . 
     The piers  30 ,  40  are side by side disposed on the bed  20 . Each of the piers  30 ,  40  has an upright plate-like seat body  31 ,  41  in which a bearing is inlaid. The bearings of the piers  30 ,  40  have central shaft holes, which are coaxially aligned with each other. 
     The shaft  50  is rotatably fitted through the shaft holes of the bearings and bridged between the piers  30 ,  40 . 
     The first brake assembly  60  provides braking effect for the shaft  50  by means of disc brake technique. The first brake assembly  60  includes an annular disc  61  coaxially fixedly fitted around the shaft  50  between the piers  30 ,  40 . The disc  61  is rotatable with the shaft  50 . The first brake assembly  60  further includes a clamping section  62  for tightly clamping the disc  61  to provide braking effect. The first brake assembly  60  further includes a link section  63  drivable by a drive section  64  for controlling the clamping section  62  to or not to provide braking effect for the shaft  50 . 
     To speak more specifically, the clamping section  62  has a U-shaped support  621  having a horizontal section and two upright sections. The horizontal section of the U-shaped support  621  is fixedly disposed on the bed  20 . Each of the upright sections has a free end serving as a first fulcrum  622 . The clamping section  62  further has two elongated rock arms  623  each having a first end, a middle section and a second end. The middle sections of the rock arms  623  are respectively pivotally connected with the first fulcrums  622 . Two clamping members  624  are respectively pivotally connected with the first ends of the rock arms  623  and rotatable between a clamping position and a releasing position. A resilient member  625  is bridged between the second ends of the rock arms  623  for resiliently keeping the clamping members  624  in the releasing position. To speak more specifically, each clamping member  624  has a clamping plate  6241 . Two linings  6242  are respectively attached to the opposite faces of the clamping plates  6241 . Two pivot blocks  6243  are respectively fixed on the other faces of the clamping plates  6241 . The pivot blocks  6243  are pivotally connected with the first ends of the rock arms  623  via pivot shafts. 
     The link section  63  has a rod-like second fulcrum  631  fixedly disposed on the bed  20 . The link section  63  further has a bar member  632  having a first end, a middle section and a second end. The first end of the bar member  632  is perpendicularly pivotally connected with the second fulcrum  631 , whereby the bar member  632  is rotatable about the second fulcrum  631  between a first position and a second position. The link section  63  further has a board-shaped push block  633  with a trapezoidal cross section. A middle section of the push block  633  is pivotally connected with the middle section of the bar member  632 . Two lateral slopes  6331  of the push block  633  respectively abut against the second ends of the rock arms  623 . Accordingly, when the bar member  632  is moved to the first position, the push block  633  is urged to move toward the first ends of the rock arms  623  and interpose between the second ends thereof. At this time, the two lateral slopes  6331  push the second ends of the rock arms  623  away from each other to make the clamping members  624  move to the clamping position. When the bar member  632  is moved to the second position, the push block  633  is moved from between the second ends of the rock arms  623 . At this time, the resilient member  625  applies a resilient force to the rock arms  623  to restore the clamping members  624  to the releasing position. 
     The drive section  64  has a linear actuator  641  mounted on the bed  20 . The drive section  64  has a power output shaft normal to an axis of the shaft  50 . The drive section  64  has a connection rod  642  having a first end and a second end. The first end of the connection rod  642  is perpendicularly fixedly connected with the power output shaft of the actuator  641 . The second end of the connection rod  642  extends into a slide slot  6321  formed at the second end of the bar member  632  and is slidable within the slide slot  6321 . 
     Accordingly, the drive section  64  can drive the push block  633  of the link section  63  to push and move the clamping members  624  to the clamping position where the linings  6242  tightly abut against two faces of the disc  61 . Under such circumstance, the disc  61  is restrained against rotation to provide braking effect for the shaft  50 . Reversely, the drive section  64  can also drive the push block  633  of the link section  63  to release the rock arms  623  from the push force. At this time, the resilient member  625  pulls the rock arms  623  to restore the clamping members  624  to the releasing position. Under such circumstance, the shaft  50  is permitted to freely rotate again. 
     It should be noted that in the first brake assembly  60 , the link section  63  is a second-class lever in which the point of resistance is between the fulcrum and the point of effort. Therefore, the force applied to the link section  63  by the actuator  641  is always smaller than the force exerted onto the clamping section  62  to provide braking effect for the shaft  50 . Moreover, the push block  633  has two lateral slopes for pushing the rock arms  623 . Therefore, only a little effort is required for providing braking effect for the shaft. In comparison with the conventional technique, the shaft brake mechanism of the present invention has power-saving and energy-saving effect. 
     The second brake assembly  70  includes a hoof section  71  annularly disposed on the shaft  50  and synchronously rotatable with the shaft  50 . The second brake assembly  70  further includes a ring-shaped drum  72  fixedly mounted on the second pier  40  and positioned around the hoof section  71  with the shaft  50  coaxially passing through the drum  72 . The shaft  50  can be restrained against rotation under frictional force between the hoof section  71  and an inner circumference  721  of the drum  72 . 
     To speak more specifically, the hoof section  71  has an annular plate-like base  711  coaxially fitted around and fixed with the shaft  50 . The hoof section  71  further has three hoofs  712  each having a pivot shaft  713 . The hoofs  712  are respectively pivotally mounted on the base  711  via the pivot shafts  713  and positioned around the shaft  50  at equal angular intervals. That is, the hoofs  712  are arranged in a pattern centered at the axis of the shaft  50  with the pivot shafts  713  positioned at 120-degree intervals. The axes of the pivot shafts  713  are parallel to the axis of the shaft  50 . Accordingly, the hoofs  71  can be pivotally rotated between a braking position and a releasing position. A resilient member  714  such as an extension spring is bridged between each two adjacent hoofs  712  for resiliently restoring the hoofs  712  from the braking position to the releasing position. 
     Each hoof  712  has a substantially arc-shaped hoof plate  7121  pivotally disposed on the pivot shaft  713  and a lining  7122  attached to a face of the hoof plate  7121  that faces the inner circumference  721  of the drum  72 . Accordingly, when the hoofs  712  are positioned in the braking position, the linings  7122  tightly attach to and abut against the inner circumference  721  of the drum  72  to apply a dynamic frictional force to the drum  72 . Under such circumstance, the shaft  50  is restrained against rotation. 
     When the hoof section  71  is synchronously rotated with the shaft  50  under wind power, a centrifugal force is created in direct proportion to the rotational speed of the shaft  50 . When the rotational speed of the shaft  50  is approximate to a nominal upper limit t 1 , the centrifugal force will overcome the pulling force of the resilient members  714  to make the hoofs  712  move from the releasing position to the braking position. The higher the rotational speed is, the tighter the linings  7122  abut against the inner circumference  721  and the greater the frictional force is, that is, the greater the resistance against the rotation of the shaft  50  is. Accordingly, the second brake assembly  70  can naturally restrain the rotational speed of the shaft  50  from proportionally increasing with the wind speed. As shown in  FIG. 10B , without modifying the nominal upper limit t 1  of rotational speed, the nominal upper limit of operational wind speed can increase from t 2  to t 3 . Therefore, the operation time of the wind power generator can be prolonged to more efficiently utilize natural resource and increase total power generation capacity of the wind power generator. 
     The above embodiment is only used to illustrate the present invention, not intended to limit the scope thereof. Many modifications of the above embodiment can be made without departing from the spirit of the present invention.