GB1593032A - Power tool with torque responsive shutoff mechanism - Google Patents

Description

(54) A POWER TOOL WITH TORQUE RESPONSIVE SHUTOFF MECHANISM (71) We, COOPER INDUSTRIES INC., Ohio corporation, 2700 Two Center Houston, Texas 77002, U.S.A. do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a power tool for driving threaded fasteners and the like, and more specifically to a power tool capable of torquing a fastener to a predetermined value.

Examples of such tools are disclosed in U.S.

Patent No. 3,811,513 to H. Wezel et al and U.S. Patent No. 3,275,116 to P.W. Martin.

Such tools are relatively complex and generally necessitate numerous parts which are subject to continuous wear and breakage due to the engagement and disengagement of a clutch mechanism. As a result, the accuracy of the torque control is short-lived, and maintenance and repair are required frequently.

In a second type of prior tool, a nondisengaging torque sensing mechanism if used which senses the torque on the driven spindle and cuts off power to the tool motor when a predetermined reaction torque is reached.

An example is the tool disclosed in U.S.

Patent No. 3,616,864 to C.A. Sorensen et al.

Tools using the latter type of mechanism are advantageous as compared to the clutch type torque tools in that the clutch mechanism is eliminated including problems and expenses associated therewith. However, in the tool disclosed in U.S. Patent No. 3,616,864 the motor and associated power train remain attached to the fastener driving bit after shutoff of the motor. Accordingly, the kinetic energy in the motor rotor and other power train components tends to overtorque the fastener and introduce scattered torque values from one tool operating cycle to the next. The additional torque cannot be easily predetermined because it is dependent upon the particular fastener and the particular elements which the fastener is joining together.

Thus, the need has arisen for an automatic torquing power tool which eliminates the problem associated with the clutch type torque tool without introducing the inaccuracies which result from the residual kinetic energy of the motor and power train in those systems where rotating bodies remain attached to the drive bit after shutoff of the driving motor.

The present invention provides for an improved torque responsive shutoff mechanism of a power tool which eliminates problems associated with the clutch type torque tools by maintaining the drive motor in engagement with the driven spindle throughout the operation of the tool. Moreover, the present invention eliminates the inaccuracies introduced by the dissipation of kinetic energy of the motor rotor and power train by use of an absorption mechanism between the motor and drive bit.

According to the present invention there is provided a power tool having a rotary motor for driving a rotatable spindle and a torque responsive shutoff mechanism interconnecting said motor and said spindle and being characterized by: a driven member coupled to said spindle; a driving member coupled to said motor, and axially slidable and coaxially rotatable both with and relative to said driven member; means operable upon said axial and rotational movement to absorb residual kinetic energy imparted to said mechanism by said motor; actuating means responsive to predetermined axial movement of said driving member relative to said driven member for shutting off said motor; and, torque transmitting balls engaged with said driving and driven members and forming a torque transmitting connection between said driving and driven members, said balls being disposed in respective grooves formed on a cylindrical portion of one of said members, said grooves being formed as spiral grooves with respect to the axis of rotation of said one member, the arrangement of said balls and said grooves being responsive to a predetermined torque to cause said balls to move along said grooves to force axial and rotational movement of said driving member relative to said driven member to cause said actuating means to shut off said motor followed by further movement of said balls along said grooves.

The grooves in the driven member permit additional rotation and axial translation of the driving member against the bias of a coil spring which biases the driving member into engagement with the driven member, and relative to the driven member after shutoffof the motor for dissipation of residual rotational kinetic energy of the motor rotor and drive elements. In this way, additional torquing forces resulting from the kinetic energy of the motor after shutoff are eliminated.

The invention will be described further by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a longitudinal section view of a pressure fluid operated power tool embodying the present invention; Fig. la is a continuation of Fig. 1 from line a-a; Fig. 2 is an exploded perspective view of the driving and driven members and the driven spindle; Fig. 3 is a planar development of the cylindrical surface of the driven member showing the form of the ball grooves therein; and, Fig. 4 is a section view taken along line 1 4 of or Fig. 1.

Referring to Figs. I and la, a fluid operated power tool comprising a screwdriver is illustrated and generally designated by the numeral 10. In Fig. Ia, the tool 10 includes a motor housing 12 suitably connected to a head portion 14. As may be seen in Fig. 1, the opposite end of housing 12 is suitably connected to a front cover 16.

The housing 12 contains a fluid operated rotary vane motor 22 of a type well known.

The motor 22 includes a rotor 24journaled in bearings 26 and 28. The rotor 24 has an integral stub shaft 30 which is drivingly connected to an elongated shaft 32 by cooperable interfitting splines or the like.

Tool 10 is connected to a power supply, such as a source of pressure fluid (not shown), by means of a connector 40 mounted on head 14. Connector 40 provides fluid flow communication with a passage 42 centrally positioned in the head. A fluid shutoff valve assembly 44 is located in passage 42. The valve assembly 44 includes a valve closure member 46 which, in the closed position, engages a resilient seat 54. The closure member 46 is engageable also with an elongated rod 48. In the position illustrated in Fig. Ia, the closure member 46 is in the unseated or open position permitting the flow of fluid to the motor from passage 42 by way of a passage 72 in the head 14. Pressure fluid supplied to motor 22 is exhausted therefrom through suitable ports, ndtshown.

Referring to Fig. 1, the cover 16 includes a nose 80 having a cylindrical bushing 84.

Bushing 84 rotatably journals a driven spin- dle 86 which in turn drives a removable screwdriver bit 88. The spindle 86 includes a longitudinal hexagonal opening 87 extending partially therethrough to accept a cooperable hexagonal end of the bit 88.

Connected between the spindle 86 and the shaft 30 formed on the motor rotor is a mechanism, generally designated by numeral 100, for transmitting the rotation of motor 22 to the bit 88, sensing the torque exerted by motor 22 on the bit, and effecting shutoff of the motor at a predetermined torque setting.

The mechanism 100 further serves to absorb the residual rotational inertia or kinetic energy of the motor and associated drive train after the motor has been shut off in order to improve the accuracy of the final torque applied to a fastener being driven by the bit 88. The mechanism 100 includes the shaft 32.

The shaft 32 has a longitudinal bore 102 extending along the full length thereof which receives the rod 48. The shaft 32 includes an axial keyway 106 having a ball key 108 disposed therein. The ball key 108 is also drivingly disposed in an axial keyway 110 on a driving member 112 of the mechanism 100.

Thus, rotation of shaft 32 is transmitted to the driving member 112 through the ball key 108. The keyway 110 is long enough to permit some axial movement of the driving member 112 relative to the shaft 32.

Referring to Fig. 2 also, the driving member 112 has an axial bore 114 and three pockets or recesses 116 equally spaced about the circumference of the bore. Each recess 116 is adapted to partially receive a torque transmitting ball 118. The recesses 116 are axially aligned with the longitudinal axis of the tool 10 and open to the end face 113 of the driving member 112.

The mechanism 100 is further characterized by a driven member 120 having a cylindrical portion 122 and an enlarged diameter portion 124 with a transverse slot 126. The slot 126 is adapted to receive an interfitting tang 128 on the spindle 86. The cylindrical portion 122 includes three equally spaced spiral grooves 130 formed on the periphery thereof. The grooves 130 are adapted to receive the balls 118 whereby the driving member 112 may rotatably drive the member 120 and the spindle 86 through the driving connection formed by the balls.

Fig. 3 illustrates a planar development of the cylindrical portion 122 of the driven member and shows the spiral contour of the grooves 130. The grooves 130 each have a portion 132 adjacent the closed end which portion extends a short distance at an angle y with respect to the longitudinal axis of the member 120 which coincides with the longitudinal axis of the tool 10. The portion 132 of a groove 130 merges smoothly by curved surfaces shown with a longer portion 134 which opens to the end face of the cylindrical portion 122 and forms an angle z with the longitudinal axis represented by line 140 shown in Fig. 3. The grooves 130 preferably have an arcuate cross sectional contour for accommodating the balls 118. In a preferred embodiment of the present invention the angles y and z are thirty degrees and seventy degrees, respectively.

Referring again to Fig. 1, the driven member 120 includes an axial bore 141 whereby the member may be disposed around the shaft 32. The member 120 also includes a circumferential recess 142 forming a bearing race in which bearing balls 144 are partially disposed. The balls 144 also ride in a circumferential groove 146 on the shaft 32.

This bearing arrangement aids in supporting the end of the shaft 32 which is remote from the motor shaft 30, and permits rotation of the shaft 32 with respect to the member 120 and the spindle 86.

The shaft 32 has a threaded portion which carries a nut 150 adjustable axially along the shaft. A ring 152 is positioned on shaft 32 at the rearward end of the threaded portion to serve as a stop for the nut. A compression coil spring 154 encircles a shaft 32 between nut 150 and the driving member 112 and serves to bias the driving member 112 toward the driven member 120 while simultaneously biasing the drive balls 118 into the closed end portions 132 of the grooves 130. A ring 158 is fixed to shaft 32 intermediate the nut 150 and driving member 112. A valve control sleeve 160 is positioned on shaft 32 intermediate the ring 158 and member 112. Sleeve 160 has a flange 162.The end of sleeve 160 adjacent ring 158 is sized to closely conform to shaft 32 while the end of the sleeve adjacent flange 162 is formed to a larger inside diameter to provide an angular chamber between shaft 32 and that portion of the sleeve. A compression spring 163 is positioned on shaft 32 between ring 158 and flange 162 to bias the sleeve 160 against member 112. The mechanism 100 is normally biased forward in housing 16 by a compression return spring 180 which acts between ring 152 and motor rotor bearing 26.

Referring to Figs. I to 4, three radial holes 164 extend through shaft 32 to provide a communication channel into bore 102. Located within each hole 164 are two balls 166 which are normally positioned toward the centre of shaft 32 by the close contour portion of sleeve 160 when positioned over holes 164. The rod 48 is of a length such that the shutoff valve 46 may be closed without interrupting the movement of balls 166 into the longitudinal bore 102 when the mechanism 100 is in it forwardmost position as controlled by compression spring 180. Rod 48 is also of a length such that when balls 166 are biased towards the center of shaft 32 to engage the end of the rod the valve 46 may be opened by applying an axial force to bit 88 and moving the spindle 86 and mechanism 100 to the position shown in Fig. 1.This forces shaft 32, balls 166, rod 48, and thus closure member 46, rearward relative to head 14 and valve seat 54. In this way, the closure member 46 is opened to permit pressure fluid to impart rotation to motor 22. Fluid pressure in passage 42 normally biases closure member 46 against seat 54. Thus the valve 44 is normally closed. Prior to commencing an operating cycle of the tool 10 the balls 118 rest in the closed end portions 132 of grooves 130 because compression spring 154 acts on the balls through the driving member 112.

When bit 88 is engaged with a fastener to be driven, an axially directed force is applied to housing 12 by the tool operator moving the mechanism 100 and rod 48 to unseat valve closure member 46. With member 46 open, fluid enters through passage 72 and energizes motor 22. Rotation of the motor rotor 24 is transmitted to shaft 32 and driving member 112. Formed for rotation in the direction of the arrow 60, Fig. 2, the mechanism 100 carries balls 118 nested in the closed ends of grooves 130. The biasing force applied by spring 154 initially prevents movement of the balls 118 up the fast rate riser portion 132 of the grooves 130 and the mechanism 100 rotates to drive spindle 86 and bit 88.

The drive from motor 22 continues to be transmitted through balls 118 until the interacting forces between the balls and grooves 130 overcomes the bias force of spring 154.

When the force increases to the point that the force applied by spring 154 is overcome, balls 118 move along fast rate riser portion 132.

This results in the axial movement of driving member 112 rearwardly away from member 120. Sleeve 160 moves with driving member 112 compressing spring 163. The resulting rearward movement is such that the larger internal bore of sleeve 160 comes into registration with holes 164 as the balls 118 move along the fast rate riser groove portions 132.

Thus balls 166 are now free to move radially outward from the longitudinal bore 102. This permits rod 48 and closure member 46 to move forward under the fluid pressure acting on the latter causing the valve to shut off fluid flow to the motor 22.

The biasing force applied by spring 154 against driving member 112 may be increased or decreased by selectively moving nut 150 toward or away from driving member 112. Thus, by controlling the position of nut 150, the torque value at which balls 118 move to the rearward end of fast rate riser portion 132 to shut off motor 22 may be accurately preselected by the operator of the tool.

Subsequent to the shutoff of motor 22, balls 118 continue to move up the slow rate riser portion 134 with lower but uninterrupted torque imposed between the members 112 and 120. Though torque transmission to the bit 88 continues, it is substantially lowered due to the spiral lead of slow rate riser portions 134 of grooves 130, thus eliminating scattered and variable torque inputs heretofore introduced by the variable levels of kinetic energy in the motor and drive train.

The opposing force of spring 154 increases during movement of balls 118 along slow rate riser portions 134 absorbing the residual kinetic energy of the motor. Ejection of balls 118 out of the grooves 130 is prevented by the ring 158 and the collapse of spring 163 to a solid condition before the balls reach the open ends of the grooves.

After the fluid supply to the motor 22 is shut off and torsional forces relieved, the driving member 112 and balls 118 are driven back along the grooves 130 by springs 154 and 163 to the initial starting position. When the tool is removed from the workpiece, return spring 180 repositions the entire i,lechanism 100. The tool 10 enjoys an improved mechanism which not only provides for accurate torque control due to the kinetic energy absorbing capability but avoids the impact forces and rapid failure of prior art mechanisms. Moreover, the arrangement of the drive balls 118 being operable to move in the continuous curved grooves 130 provides for smoother operation than prior art torque control devices. The arrangement of the driving and driven members, one disposed partially within the other, also provides a more compact mechanism than prior art arrangements.

WHAT WE CLAIM IS: I. A power tool having a rotary motor for driving a rotatable spindle and a torque responsive shutoff mechanism interconnecting said motor and said spindle and being characterized by: a driven member coupled to said spindle; a driving member coupled to said motor, and axially slidable and coaxially rotatable both with and relative to said driven member; means operable upon said axial and rotational movement to absorb residual kinetic energy imparted to said mechanism by said motor; actuating means responsive to predetermined axial movement of said driving member relative to said driven member for shutting off said motor; and, torque transmitting balls engaged with said driving and driven members and forming a torque transmitting connection between said driving and driven members, said balls being disposed in respective grooves formed on a cylindrical portion of one of said members, said grooves being formed as spiral grooves with respect to the axis of rotation of said one member, the arrangement of said balls and said grooves being responsive to a predetermined torque to cause said balls to move along said grooves to force axial and rotational movement of said driving member relative to said driven member to cause said actuating means to shut off said motor followed by further movement of said balls along said grooves.

2. A power tool as claimed in claim 1 wherein: said spiral grooves are, along a first portion thereof, formed along a helix having a first helix angle with respect to said axis, and said grooves include second portions formed at a second helix angle with respect to said axis greater than said first helix angle.

3. A power tool as claimed in claim 2 wherein: said driving member includes an axial bore and recesses in said bore for seating said balls therein, respectively, and said cylindrical portion of said driven member is adapted to be disposed in said bore in said driving member.

4. A power tool as claimed in claim 3, wherein: said means for absorbing said residual kinetic energy comprises a mechanical spring engaged with said driving member and responsive to axial movement thereof for absorbing said residual kinetic energy.

5. A power tool with torque responsive shutoff mechanism substantially as herein described with reference to and as illustrated in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   portion 132 to shut off motor 22 may be accurately preselected by the operator of the tool.

   Subsequent to the shutoff of motor 22, balls 118 continue to move up the slow rate riser portion 134 with lower but uninterrupted torque imposed between the members 112 and 120. Though torque transmission to the bit 88 continues, it is substantially lowered due to the spiral lead of slow rate riser portions 134 of grooves 130, thus eliminating scattered and variable torque inputs heretofore introduced by the variable levels of kinetic energy in the motor and drive train.

   The opposing force of spring 154 increases during movement of balls 118 along slow rate riser portions 134 absorbing the residual kinetic energy of the motor. Ejection of balls 118 out of the grooves 130 is prevented by the ring 158 and the collapse of spring 163 to a solid condition before the balls reach the open ends of the grooves.

   After the fluid supply to the motor 22 is shut off and torsional forces relieved, the driving member 112 and balls 118 are driven back along the grooves 130 by springs 154 and 163 to the initial starting position. When the tool is removed from the workpiece, return spring 180 repositions the entire i,lechanism 100. The tool 10 enjoys an improved mechanism which not only provides for accurate torque control due to the kinetic energy absorbing capability but avoids the impact forces and rapid failure of prior art mechanisms. Moreover, the arrangement of the drive balls 118 being operable to move in the continuous curved grooves 130 provides for smoother operation than prior art torque control devices. The arrangement of the driving and driven members, one disposed partially within the other, also provides a more compact mechanism than prior art arrangements.

   WHAT WE CLAIM IS: I. A power tool having a rotary motor for driving a rotatable spindle and a torque responsive shutoff mechanism interconnecting said motor and said spindle and being characterized by: a driven member coupled to said spindle; a driving member coupled to said motor, and axially slidable and coaxially rotatable both with and relative to said driven member; means operable upon said axial and rotational movement to absorb residual kinetic energy imparted to said mechanism by said motor; actuating means responsive to predetermined axial movement of said driving member relative to said driven member for shutting off said motor; and, torque transmitting balls engaged with said driving and driven members and forming a torque transmitting connection between said driving and driven members, said balls being disposed in respective grooves formed on a cylindrical portion of one of said members, said grooves being formed as spiral grooves with respect to the axis of rotation of said one member, the arrangement of said balls and said grooves being responsive to a predetermined torque to cause said balls to move along said grooves to force axial and rotational movement of said driving member relative to said driven member to cause said actuating means to shut off said motor followed by further movement of said balls along said grooves.
2. 2. A power tool as claimed in claim 1 wherein: said spiral grooves are, along a first portion thereof, formed along a helix having a first helix angle with respect to said axis, and said grooves include second portions formed at a second helix angle with respect to said axis greater than said first helix angle.
3. 3. A power tool as claimed in claim 2 wherein: said driving member includes an axial bore and recesses in said bore for seating said balls therein, respectively, and said cylindrical portion of said driven member is adapted to be disposed in said bore in said driving member.
4. 4. A power tool as claimed in claim 3, wherein: said means for absorbing said residual kinetic energy comprises a mechanical spring engaged with said driving member and responsive to axial movement thereof for absorbing said residual kinetic energy.
5. 5. A power tool with torque responsive shutoff mechanism substantially as herein described with reference to and as illustrated in the accompanying drawings.