Control Unit For a Power Tool

Abstract

A power tool is provided including a housing, a brushless DC motor housed inside the housing, and a control unit housed inside the housing for controlling an operation of the brushless DC motor. The control unit includes a potting boat having an open portion, a circuit board received within the potting boat through the open portion, power switching elements mounted on the circuit board, a potting compound receiving within the potting boat to substantially surround the circuit board, and a heat sink in thermal communication with the power switching elements. The heat sink has a surface exposed outside the potting compound through the open portion of the potting boat.

1 . A power tool comprising:
 a housing;   a brushless DC motor housed inside the housing; and   a control unit housed inside the housing for controlling an operation of the brushless DC motor, the control unit comprising:
 a potting boat having an open portion; 
 a circuit board received within the potting boat through the open portion; 
 a plurality of power switching elements mounted on the circuit board; 
 a potting compound receiving within the potting boat to substantially surround the circuit board; and 
 a heat sink in thermal communication with the plurality of power switching elements, the heat sink having a surface exposed outside the potting compound through the open portion of the potting boat. 
   
     
     
         2 . The power tool of  claim 1 , wherein the circuit board comprises a power unit, further comprising a control circuit board having a controller mounted thereon. 
     
     
         3 . The power tool of  claim 1 , the plurality of power switching elements are configured as a part of a smart power module (SPM) mounted on the circuit board, the heat sink being mounted over the SPM, the SPM having at least one through-hole arranged for attachment of the heat sink to the circuit board. 
     
     
         4 . The power tool of  claim 1 , further comprising a variable-speed switch assembly including:
 a main body disposed within the potting boat;   a trigger disposed outside the potting boat;   a plunger linearly movable with the trigger with respect to the main body; and   a speed-sensing mechanism housed inside the main body and coupled to the plunger to generate a variable-speed voltage signal based on the position of the plunger.   
     
     
         5 . The power tool of  claim 4 , wherein the potting boat comprises a cut-out portion corresponding to the variable-speed switch assembly. 
     
     
         6 . The power tool of  claim 5 , wherein the plunger links the trigger to the main body through the cut-out portion of the potting boat. 
     
     
         7 . The power tool of  claim 5 , wherein the speed-sensing mechanism is mounted on the circuit board and the cut-out portion of the potting boat facilitates mounting the variable-speed switch assembly on the circuit board. 
     
     
         8 . The power tool of  claim 5 , wherein the cut-out portion includes a groove, and the variable-speed switch assembly includes a tongue fittingly corresponding to the groove to form a labyrinth seal therebetween. 
     
     
         9 . The power tool of  claim 8 , wherein the labyrinth seal is arranged to contain the sealing compound within the potting boat. 
     
     
         10 . The power tool of  claim 5 , wherein the variable-speed switch assembly further comprises at least one output pin connecting the speed-sensing mechanism of the variable-speed switch assembly directly to at least one conductive track on the circuit board. 
     
     
         11 . The power tool of  claim 5 , wherein the heat sink comprises a protruded surface arranged to pass over the variable-speed switch assembly. 
     
     
         12 . A power tool comprising:
 a housing;   a brushless DC motor housed inside the housing; and   a control unit housed inside the housing for controlling an operation of the brushless DC motor, the control unit comprising:
 a potting boat having an open portion; 
 a circuit board received within the potting boat through the open portion; 
 a variable-speed switch assembly including a main body disposed mounted on the circuit board within the potting boat, a trigger disposed outside the potting boat, a plunger linearly movable with the trigger with respect to the main body, and a speed-sensing mechanism housed inside the main body and coupled to the plunger to generate a variable-speed voltage signal based on the position of the plunger; and 
 a potting compound receiving within the potting boat to substantially surround the circuit board, 
 wherein the potting boat comprises a cut-out portion through which the plunger links the trigger to the main body, and 
 wherein the cut-out portion and the variable-speed switch assembly includes a tongue and groove arrangement to form a seal therebetween to contain the potting compound within the potting boat. 
   
     
     
         13 . The power tool of  claim 12 , wherein the cut-out portion includes a groove, and the variable-speed switch assembly includes a tongue fittingly corresponding to the groove to form the seal therebetween. 
     
     
         14 . The power tool of  claim 12 , wherein the seal is labyrinth-shaped. 
     
     
         15 . The power tool of  claim 12 , wherein the control unit comprises a plurality of power switching element and a heat sink in thermal communication with the plurality of power switching elements, the heat sink having a surface exposed outside the potting compound through the open portion of the potting boat.