| 摘要 |
<p>A pneumatic impulse wrench comprises a housing (10) with a motor (12), a pressure air inlet passage (15) with a throttle valve (17), an exhaust air outlet passage (16) connected to the motor (12), an impulse generator (13) coupling the motor (12) to an output shaft (14), and a power control valve (20) located inside the outlet passage (16) and controlled by the back pressure from the motor (12) via a pressure line (27). The power control valve (20) comprises a tubular valve element (21) movably supported on a tube element (25) which is rigidly secured to the housing (10) and forms a part of the pressure line (27) which extends between the inlet passage downstream of the throttle valve (17) and an activation chamber (35) associated with the valve element 21. The valve element (21) is arranged to cooperate with an annular shoulder (22) in the outlet passage (16) to restrict the exhaust air outlet flow as well as the motor speed during low torque running down phase of a screw joint tightening process to thereby avoid a too strong first impulse being delivered after settling of the screw joint. At continued tightening after delivery of the very first impulse the motor load and hence the back pressure from the motor (12) increases whereby the air pressure in the activation chamber (35) forces the valve element (21) away from the shoulder (22) to open up the outlet passage (16) and enable full motor power.</p> |
