US Patent 7815088 Hand-held drive-in tool

A hand-held drive-in tool for driving fastening elements in a workpiece and including a guide (12), a drive-in ram (13) displaceable in the guide (12) for driving a fastening element in, a drive-in unit (30) for driving the drive-in ram (13) and including at least one first drive spring (31) and at least one second drive spring (32) having respectively, opposite first and a second expansion directions (37, 38), and a tensioning device for preloading the drive-in ram (13) and the first drive spring (31).