Patent ID: 6085849
Filing Date: 2000-07-11
Classification: B25B

Abstract:
A pneumatic screwdriver comprising:a casing having a connection for a compressed air feed hose;a pneumatic motor positioned within said casing and a drive shaft in driven connection with said pneumatic motor;a control for supplying compressed air from said compressed air feed hose to said pneumatic motor;a member adapted to receive a driving tool and a kinematic coupling between said pneumatic motor and said member; anda torque limiter for said pneumatic motor, operably interposed between said pneumatic motor and said member, for (1) terminating compressed air being supplied to said pneumatic motor and (2) braking said pneumatic motor, in response to torque generated by said pneumatic motor reaching a particular threshold, said torque limiter comprising:a first positive clutch connected to said drive shaft;a second positive clutch connected to said kinematic coupling for driving said member; anda plurality of balls positioned between and retained on respective facing surfaces of said first positive clutch and said second positive clutch;said first positive clutch having a surface opposite to said surface facing said second positive clutch, a compression spring having one end positioned in cooperation with said opposite surface of said first positive clutch;an adjustment plate movably positioned on said drive shaft, a spring guide bearing on said adjustment plate, a second end of said compression spring being positioned on said spring guide, said adjustment plate having a screwthreaded part, a nut screwed onto said screwthreaded part of said adjustment plate for adjusting tension of said compression spring;said first positive clutch including three teeth offset by 120.degree. on said facing surface of said first positive clutch, each of said three teeth having a planar free end surface facing said second positive clutch, each of said teeth being demarcated by two ends, one of said two ends having a steep face and a second of said two ends having a recess, each said recess of said second end of respective ones of said teeth being connected by an inclined ramp to said planar free end surface and being connected by a stepped portion to a steep face of an adjacent one of said teeth, each of said plurality of balls being positioned within a respective one of said recesses;said second positive clutch including three teeth offset by 120.degree. on said facing surface of said second positive clutch and three grooves, each of said three grooves being interposed between respective pairs of said teeth, each of said plurality of balls being guided by a respective one of said grooves, each of said grooves having an ascending slope, a boss in each of said teeth of said second positive clutch, and a slightly inclined slope, each of said teeth of said second positive clutch having a planar free end surface facing said first positive clutch, each of said teeth of said second positive clutch further being demarcated by two ends, one of said two ends having an inclined part and a second of said two ends having a steep face, said teeth of said first positive clutch being disposed asymmetrically relative to said teeth of said second positive clutch;a valve operably connected with said first positive clutch and with said pneumatic motor for terminating compressed air being supplied to said pneumatic motor in response to said first positive clutch and said second positive clutch being spaced apart by said plurality of balls a particular increased amount upon said torque generated by said pneumatic motor reaching a particular threshold;said plurality of balls, in response to increasing torque generated by said pneumatic motor, being moved by said first positive clutch along respective ones of said ascending slopes of said grooves of said second positive clutch to respective ones of said bosses of said grooves of said second positive clutch and, in response to torque generated by said pneumatic motor reaching said particular threshold, said first positive clutch and said second positive clutch becoming spaced apart said particular increased amount, whereby said first positive clutch operates said valve and thereby terminates said compressed air being supplied to said pneumatic motor, said plurality of balls being then moved by said first positive clutch from said bosses of said grooves of said second positive clutch and said planar free end surfaces of said teeth of said first positive clutch being engaged with said planar free end surfaces of said teeth of said second positive clutch for braking said pneumatic motor.