Pneumatic push-start, torque shut-off screw driver

Claim 2

In a pneumatic screw drive including a rotary air motor and a live air supply chamber, a valve assembly controlling live air flow from the chamber to the motor comprising a valve case having a side inlet port connecting the chamber with the interior of the case for allowing air flow in large volume into thE case, an open-ended slide valve interiorly of the case having a normal condition clear of the port and being movable to a condition closing the port, the slide valve having an internal abutment and having a valve seat opening communicating the interior of the case with the motor, a main valve interiorly of the slide valve having a normal condition closed over the valve seat opening, the main valve being movable relative to the slide valve an initial distance to open condition against the abutment and being movable for a further distance beyond the initial distance in engagement with the abutment to carry the slide valve to its closed condition over the port, and a stem carried by the main valve having a normal clearance condition in an opening of the valve case allowing bleed air from the chamber into the case, the stem having a portion formed with flats movable with the main valve to protrude from said opening as the main valve moves beyond said initial distance so as to allow air flow from the chamber in limited volume into the case.

Claim 3

In a pneumatic screw driver as in claim 1, wherein closing spring means biases the main valve to its normal condition.

Claim 4

In a pneumatic screw driver as in claim 2, wherein means is provided which is effective in response to movement of the slide valve to closed condition to cause the slide valve to be pneumatically retained in said condition.

Claim 5

In a pneumatic screw driver as in claim 3, including first means for moving the main valve against the bias of the closing spring means to the extent of said initial distance and second means for moving the main valve against the bias of the closing spring means over said further distance.

Claim 6

In a pneumatic screw driver as in claim 4, wherein the first means for moving the main valve is a slidable clutch assembly having a pushrod engaged with the main valve.

Claim 7

In a pneumatic screw driver as in claim 5, wherein the second means for moving the main valve over the further distance is a torque responsive cam disengageable overriding driving clutch member having an abutment engaged with the pushrod, and the closing spring means is responsive to the overriding action of the clutch member to return the main valve to its initially moved condition.

Claim 8

In a push-start, torque shut-off screw driving tool including a casing having an internal shoulder, a rotary pneumatic motor, a valve seat, and a main valve to control operating air flow to the motor having a normal condition closed upon the seat, a clutch shaft having rotation with the motor and having relative axial movement, a driving torque releasable cam clutch member carried by the shaft for unitary rotation but having relative axial movement, a driven cam clutch member keyed to the shaft for relative rotation and for axial movement unitary with the shaft, a clutch spring biasing the driving clutch member into clutched engagement with the driven clutch member, the driving clutch member adapted upon delivery of a preset maximum torque to the driven clutch member to disengage axially from the driven clutch member against the bias of the clutch spring while at the same time overriding the driven clutch member for a predetermined degree and then returning under the bias of the clutch spring to reengaged condition, the driven clutch member having a normal condition seated upon the internal shoulder of the casing limiting the extent of axial movement of the clutch shaft away from the motor, bit means carried by the driven clutch member engageable with the work and adapted when pressed upon the work to force the clutch shaft together with the driving and driven clutch members away from the internal shoulder toward the motor, an abutment carried by the driving clutch member, a slide rod extending axially of the tool resting at its bottom end upon the abutment adapted upon axial movement of the clutch shaft together with the driving and driven clutch members to unseat the main valve so as to allow operating air flow to the motor, means responsive to the disengaging and subsequent reengaging action of the driving clutch member to substantially shut off operating air flow to the main valve upon delivery of said maximum torque and then upon said reengagement to finally shut off said air flow to the main valve; and means responsive to removal of the bit means from the work to axially return the clutch shaft together with the reengaged clutch members to normal so as to reseat the driven clutch member upon the internal shoulder and to return the main valve closed upon its seat.

Claim 9

In a push-start, torque shut-off screw driving tool including a casing having an internal shoulder, a rotary pneumatic motor, a valve seat, and a main valve to control operating air flow to the motor having a normal condition closed upon the seat, a clutch shaft having rotation with the motor and having relative axial movement, a driving torque releasable cam clutch member carried by the shaft for unitary rotation but having relative axial movement, a driven cam clutch member keyed to the shaft for relative rotation and for axial movement unitary with the shaft, a clutch spring biasing the driving clutch member into clutched engagement with the driven clutch member, the driving clutch member adapted upon delivery of a preset maximum torque to the driven clutch member to disengage axially from the driven clutch member against the bias of the clutch spring while at the same time overriding the driven clutch member for a predetermined degree and then returning under the bias of the clutch spring to reengaged condition, the driven clutch member having a normal condition seated upon the internal shoulder of the casing limiting the extent of axial movement of the clutch shaft away from the motor, bit means carried by the driven clutch member engageable with the work and adapted when pressed upon the work to force the clutch shaft together with the driving and driven clutch members away from the internal shoulder toward the motor, an abutment carried by the driving clutch member, a slide rod extending axially of the tool resting at its bottom end upon the abutment adapted upon axial movement of the clutch shaft together with the driving and driven clutch members to unseat the main valve so as to allow operating air flow to the motor, means responsive to the disengaging and subsequent reengaging action of the driving clutch member to substantially shut off operating air flow to the main valve upon delivery of said maximum torque and then upon said reengagement to finally shut off said air flow to the main valve; and means responsive to removal of the bit means from the work to axially return the clutch shaft together with the reengaged clutch members to normal so as to reseat the driven clutch member upon the internal shoulder and to return the main valve closed upon its seat.

Claim 10

In a push-start, torque shut-off screw driving tool according to claim 7, wherein the motor is reversible, reversing valve means is provided between the main valve and the motor for directing operating air selectively to the motor so as to drive the motor in either a positive or negative direction.

Claim 11

In a push-start, torque shut-off screw driver according to claim 8, wherein the driven clutch member has a cam engagement with the driving clutch member permitting said overriding disengaging action of the driving clutch member in a positive direction, but blocking it against such action in a reverse direction.