Fastener driving tool

A fastener driving tool comprising:

• a housing unit having a fastener striking opening located at a bottom of a forward end thereof, a first pivot axle located above and rearwardly of said fastener striking opening, a first fixed axle located below and forwardly of said first pivot axle, and a second fixed axle spaced apart from and located below and rearwardly of said first pivot axle and said first fixed axle;
• a striking member disposed in said housing unit and movable toward and away from said fastener striking opening in an up-down direction, said striking member having an upper portion formed with an engaging slot and a connecting slot below said engaging slot;
• an energy-storing unit disposed in said housing unit and including a torsion spring and a return spring, said torsion spring having a coil sleeved on said second fixed axle to be twistable about said second fixed axle, a force-receiving arm extending forwardly from one end of said coil toward said striking member, a bent arm extending downwardly from one end of said force-receiving arm that is opposite to said coil and then bending inwardly, and a drive arm extending forwardly from the other end of said coil into said connecting hole of said striking member, said force-receiving arm and said drive arm being opposite to each other in the up-down direction, said bent arm being disposed under said drive arm, said return spring being disposed between said bent arm and said housing unit for biasing said bent arm upwardly;
• a locking member having at least one front notched portion rotatably sleeved around said first fixed axle, and a front engaging end detachably engaged to said engaging slot of said striking member;
• a handle unit pivotally mounted on said housing unit for pressing down said force-receiving arm and a rear side of said locking member so as to rotate said locking member relative to said first fixed axle;
• and
• an elastic member disposed between said locking member and said handle unit for biasing said locking member toward said first fixed axle;
• wherein, when said handle unit is pressed down to shift said fastener driving tool from an initial state to an energy-storing state, said force-receiving arm is pressed down by said handle unit, said locking member is driven to rotate relative to said first fixed axle, said front engaging end of said locking member is driven to move said striking member upward and away from said fastener striking opening, said striking member, in turn, drives said drive arm to move upward such that said force-receiving arm and said drive arm move toward each other and said coil stores a biasing force;
• wherein, when said handle unit is pressed down continuously to shift said fastener driving tool from said energy-storing state to a striking state, said front engaging end of said locking member is driven to move upward and rearward so as to disengage from said engaging slot, and said coil is freed to release the stored biasing force such that said drive arm can drive said striking member to move down to said fastener striking opening for performing a fastener striking stroke.