Power-operated Impact Wrench Or Screwdriver

Abstract

A portable power-operated impact wrench, screwdriver or the like rotary tool, provided with inertia means which causes increased disengagement movement of the hammers from the anvils to interrupt the power to the tool at a predetermined maximum torque by movement of the inertia means in a longitudinal direction of the tool away from the hammers against the action of a compression spring which is adjustable to vary the maximum torque developed by the tool.

Description

The invention relates to portable power operated impact wrenches, screwdrivers and like rotary impact tools of the kind comprising relatively movable anvil and hammer members with means for automatically causing them to become engaged and disengaged as required in the operation of the tool, and is an improvement in or modification of the invention described and claimed in the specification of British Pat. No. 1180771, which consists in a power-operated impact wrench, screwdriver or like rotary tool of the kind comprising relatively movable hammer and anvil members with means for automatically causing them to become engaged and disengaged cyclically, characterized in that there is provided inertia means coupled to the hammer member by resilient means in such manner that, at values of torque below a predetermined value, the inertia means is constrained by the resilient means from moving relative to the hammer means, while at the predetermined value of torque the inertia means moves relative to the hammer means and thereby acts upon the said automatic means to increase the amount of disengagement movement of the members and operates control means to interrupt a supply of power to the tool.

In the embodiment described and illustrated in the specification of our British Pat. No. 1180771 the spring means for applying pressure of predetermined value to the inertia member is a torsion cylinder with axial slots in the wall thereof, and it has been found that the torsion cylinder is difficult and expensive to manufacture, and it is therefore proposed to provide for a linear motion of the inertia means instead of a rotary motion, thereby making it possible to use a spring which operates in a rectilinear manner instead of using a torsion spring.

The invention consists in a power-operated impact wrench, screwdriver, or like rotary tool as claimed in our British Pat. specification No. 1180771, characterized in that the inertia means is supported upon and moves axially of the hammer member to operate control means to interrupt the supply of power to the tool.

The invention further consists in a power-operated tool as set forth in the preceding paragraph in which the inertia means is urged in a direction of the hammers by the resilient means to rest upon an abutment at values of torque below a predetermined value, while at the predetermined value of torque the inertia means moves away from the abutment against the action of the spring by cam means upon the hammer member and the inertia means.

The invention still further consists in a power-operated tool as set forth in the preceding paragraph in which the cam means acts to move the inertia means relative to the hammer member due to relative rotational movement of the inertia means and the hammer member at the instance of impact of the hammers upon the anvils.

The invention still further consists in a power-operated tool as set forth in the preceding paragraph in which the cam means comprises ramped surfaces upon the inertia means and the hammer member and a ball between and resting upon the ramp surfaces.

The invention still further consists in a power-operated tool as set forth above in which the resilient means is adjustable to vary the maximum torque developed by the tool.

The accompanying drawings show, by way of example only, one embodiment of the invention in which,

FIG. 1 is a part longitudinal section part elevation of the tool;

FIG. 2 is a section on the line 2--2 of FIG. 1;

FIG. 3 is a section on the line 3--3 of FIG. 1;

FIG. 4 is a section on the line 4--4 of FIG. 1;

FIG. 5 is a section on the line 5--5 of FIG. 1;

FIG. 6 is a section on the line 6--6 of FIG. 1;

While FIG. 7 is a side elevation of the junction between a relative longitudinal moving parts of the hammer member.

The tool illustrated is of the pistol grip type, and comprises a motor portion 1, a gear portion 2, a torque control and a hammer and anvil portion 3, a head portion 4 and a pistol grip portion 5.

The motor 6 is of the pneumatic vane type and is of conventional design, the shaft 7 of which is supported in bearings 8 and 9. The shaft 7 drives the planetary gears 10, the output of which drives the shaft 11 at a reduced speed by way of the enlarged part 12 of the shaft 11.

The passage of air from a flexible hose connected to the connector 13 in the pistol grip portion 5 is controlled by a master valve 14, and passes up the passage 15 to forward direction of push button control valve 16 and a reverse direction push button control valve 17, from whence the air passes by channels, not shown, to the appropriate parts of the motor 6, to drive it in either direction.

In order that the supply of air to the motor may be interrupted by the torque control means, hereinafter described, for the forward direction of rotation of the motor and not in the reverse direction of the motor, there is provided a passage 18, connected at the upper end to a pressure release valve 19, and at its lower end to the valve 14, and also to the rear of the valve 16 by the passage 20. When the pressure release valve 19 is opened by the longitudinal movement of the rod 21, then any air under pressure in the passage 18 is released to atmosphere, and the valve 14 closes, due to the difference in pressure thus created across it, and the motor stops.

The tool holder 22 in the head portion 4 of the tool, is adapted to receive a wrench, screwdriver or other rotary tool, and is held for rotation in a bearing 23 in the outer casing 24, and is provided with an axial bore which receives the end 25 of the shaft 11, and is provided with a thrust ball 26.

The tool holder 22 has a pair of anvils 27 (see also FIG. 2) formed integral therewith, which are rotatable intermittently when struck by the continually rotating hammers 28. The hammer members are for convenience of manufacture constructed in two parts, the outer ring 29 carrying the hammers 28, located longitudinally on the inner ring 30 by the balls 40, but free to move circumferentially thereon for a purpose to be described later.

The inner surface of the inner ring 30 is provided with spiral ramped surfaces which are engaged by a pair of balls 31, which also engage in grooves in the surface of the shaft 11, so that, when the hammers 28 are retarded by the anvils 27, the shaft 11, which is continually rotating urges the balls to roll up the ramps upon the inner ring 30 and urge the latter in an axial direction of the shaft 11, to compress the helical spring 32, thereby allowing the hammers 28 to become disengaged from the anvils 27, to pass over them and then re-enter between the anvils to repeat the cycle of operation.

The ramps on the inner ring 30 and the grooves in the shaft 11 are of a V-shape in elevation, and therefore symmetrical about a plane passing through the axis of rotation, and the hammering cycle therefore takes place in a similar manner in either direction of rotation of the tool.

In order that the pressure relief valve 19 shall be operated when a torque greater than a predetermined maximum is applied by the tool to a nut or screw and the motor stopped, an inertia cylinder 33 is keyed to the inner ring 30 by the keys 34 in the keyway 35, and seeing that they make a sliding fit therein, the inertia cylinder 33 can move longitudinally against the action of the dished annular springs 36, but is unable to move circumferentially in relation to the inner ring 30.

The opposed faces of the ends of the outer ring 29 and the inertia cylinder 33 are provided with conical depressions 37, which each house a ball 38, so that, at the instant the hammers strike the anvils, the outer ring 29 is caused to rotate around the inner cylinder 30 to a few degrees and due to the action of the balls 38 moves the inertia cylinder 33 longitudinally to the inner cylinder 30 and compresses the spring 36. The energy used in compressing springs 36 is returned by their resilience and the rebound causes the hammer member to move a greater distance longitudinally than would be the case for torques below the predetermined maximum torque. The mass of the inertia cylinder and the strength of the springs are chosen to fall within the desired range of maximum torques to be developed by the tool.

In order for the maximum predetermined torque to be varied, the abutment member 39 is movable longitudinally at the inner ring 30 to vary the compression of the springs 36 by means of a bevel-toothed wheel 41 having a screw threaded axial bore 42 on a screw thread on an extension 43 of the inner ring 40. The casing 24 is provided with a bore 44 through which a tool 45 may be passed and engaged with the teeth on the toothed wheel 41 to rotate it. The tool is provided with a projection which engages with a small bore 46 in the abutment member 39.

The abutment member 39 is prevented from rotating on the extension 43 of the inner ring 29 by a key 48, but which allows longitudinal movement when the value of torque is adjusted. The toothed wheel is locked at each setting by an arcuate spring 49, which is engaged to release it by pressure upon the tool 45 engaged in the bore 47. The bore 44 for the tool is closed by a screw threaded plug 50 when not in use.

The rear end of the extension 43 of the inner ring 30 is provided with an abutment 51 which engages the end of the rod 21 when the inner ring oscillates longitudinally the extra amount caused by the torque reaching the predetermined level of torque, and pressing upon the ball 19 opens the valve and stops the motor.

The torque control means only operates in the one direction of rotation, for example, when tightening up a nut, or screw, as it is not necessary when the tool rotates in the opposite direction to release a nut or remove a screw.

It can be appreciated from the above description the tool is relatively simple in form and has few moving parts, which renders it robust, and that the degree of torque applied by the tool is readily adjustable as to its maximum value.

It is to be understood that the above description is by way of example only, and that details for carrying the invention into effect may be varied without departing from the scope of the invention claimed.

Claims

I claim:

1. In a power-operated impact wrench, screwdriver or like rotary tool of the kind comprising relatively movable hammer and anvil members with means for automatically causing them to become engaged and disengaged cyclically, and in which there is provided inertia means coupled to the hammer member by resilient means in such manner that, at values of torque below a predetermined value, the inertia means is constrained by the resilient means from moving relative to the hammer means, while at the predetermined value of torque the inertia means moves relative to the hammer means and thereby acts upon the said automatic means to increase the amount of disengagement movement of the members and operates control means to interrupt a supply of power to the tool, the improvement comprising in that at the values of torque below the said predetermined value, the inertia means rests against the hammer member under the action of the resilient means, while at the predetermined value of torque, the inertia mans moves away from the hammer member against the action of the resilient means to increase the amount of disengagement of the hammer and anvil members.

2. A power-operated tool as claimed in claim 1 in which the hammer member is provided with an abutment against which the inertia member rests, while the resilient means is a spring which urges the inertia means against the abutment at values of torque below the said predetermined value, while at the predetermined value of torque the inertia means moves away from the abutment by cam means upon the hammer member and the inertia means.

3. A power-operated tool as claimed in claim 2 in which the cam means acts to move the inertia means away from the hammer member due to relative rotational movement of the hammer member and the inertia means at the instant of impact of the hammers upon the anvils.

4. A power-operated tool as claimed in claim 3 in which the cam means comprises ramped surfaces upon the inertia means and the hammer member, and a ball between and resting upon the ramped surfaces.

5. A power-operated tool as claimed in claim 1 in which the resilient means comprises a plurality of dished annular rings mounted coaxial of the axis of rotation of the hammer member.

6. A power-operated tool as claimed in claim 5 in which the dished annular ring remote from the inertia means rests against an abutment which is movable towards and away from the inertia means to adjust the resilient means to vary the predetermined value of torque.