Hammer drill with an idling strike prevention mechanism

A hammer drill, comprising:

• a motor for providing drive power for the hammer drill;
• a cylinder fixed in a housing;
• a tool holder coaxially fitted around the cylinder for holding a tool bit in a front thereof;
• a piston reciprocably mounted in the cylinder;
• a striking member reciprocably mounted in the cylinder in front of the piston for imparting hammer blows to the tool bit held in the tool holder;
• an air chamber formed between the piston and the striking member in the cylinder for pneumatically actuating the striking member so that the reciprocating motion of the piston can be transmitted to the striking member;
• a rotation transmission mechanism for transmitting the rotation of the motor to the tool holder so as to rotate the tool holder;
• means forming at least one air port formed in a peripheral wall of the air chamber for pneumatically communicating the inside of the air chamber with the outside of the cylinder;
• and
• an axially movable cylindrical slide sleeve urged in the forward direction by urging means, the slide sleeve being mounted between the cylinder and the tool holder, the slide sleeve being pushed backward together with the tool bit and covering the at least one air port in the peripheral wall of the air chamber during normal operation of the hammer drill, and the slide sleeve being moved forward by the urging means and uncovering the at least one air port during idle operation of the hammer drill, thereby, terminating the pneumatic actuation of the striking member;
• wherein each of the cylinder, the slide sleeve, and the tool holder has at least one air vent formed therein for venting air in the cylinder in front of the striking member to the outside of the tool holder.