US3315754A

US3315754A - Torque limiting apparatus

Info

Publication number: US3315754A
Application number: US412023A
Authority: US
Inventors: Holdo Jan Kristian; Westerlund Bengt Arvid
Original assignee: Atlas Copco AB
Current assignee: Atlas Copco AB
Priority date: 1964-11-18
Filing date: 1964-11-18
Publication date: 1967-04-25
Anticipated expiration: 1984-04-25
Also published as: NL6515000A; BE672512A

Description

A ril 25, 1967 J, K. HOLDO ETAL 3,315,754

TORQUE LIMITING APPARATUS Filed Nov. 18, 1964 Armmw United States Patent 3,315,754 TORQUE LTMETING APPARATU Jan Kristian Hoido, Stockholm, and Bengt Arvid Westerinnd, Klinten, Sweden, assignors to Atlas Copco Aktiebolag, Nacka, Sweden, a corporation of Sweden Filed Nov. 18, 1964, Ser. No. 412,023 16 Claims. (Cl. 173-12) This invention relates generally to torque limiting apparatus for limiting the maximum torque transmitted from a rotary driving motor to an element rotated by the motor. More specifically the invention relates to torque limiting apparatus applicable to power wrenches of the rotary as well as of the impacting type.

In many technical applications, such as for example in tightening down threaded fasteners during assembly of machine or structural elements, control of the final torque applied to the fasteners is important for the provision of uniform tightening and maximum strength in the connection. Normally the rotated element such as the tool shaft or head of a power Wrench, rotates rapidly at the beginning of the tightening operation but then slows down gradually with increased resistance to rotation until the drive is interrupted when the desired final torque has been reached. Similarly in power wrenches of the impacting type the tool head together with the fastener during the continuously repeated blows turns a certain angle for each blow and this angle decreases successively from blow to blow with increasing tightness. In rotary as well as impact tightening the angle of displacement per unit of time of the tool shaft, tool head or fastener thus evidently is a measure for the torque applied to the fastener and can be used for purposes of limiting the final torque to a predetermined value.

It is an object of the invention to provide a simple and eflicient torque limiting apparatus for controlling the final or maximum torque transmitted from a driving motor to an element rotated thereby which apparatus measures the angular displacement per unit of time of the rotated element and cuts off the supply of power to the motor when the angular displacement per unit of time has decreased to a predetermined value. A further object of the invention is to provide a torque limiting apparatus of the above character in which the measuring is performed continuously by pneumatic means and the cut off of power is controlled by means responsive to the behaviour of the pneumatic measuring means.

The above and other objects of the invention will become obvious from the following description and from the accompanying drawings in which two embodiments of the invention are illustrated by way of example. It should be understood that these embodiments are only illustrative of the invention and that various modifications may be made within the scope of the claims without departing from the scope of the invention.

In the drawings FIG. 1 is a longitudinal sectional view through a power wrench incorporating the apparatus according to the invention; FIG. 2a is a sectional view on the line 22 in FIG. 1; FIG. 2b is a sectional view through a modified embodiment of the automatic control valve forming part of the wrench shown in FIG. 1; FIG. 2c is a measuring instrument coupled to a line connecting the elements shown in FIGS. 2:: and 2b; FIG. 3 shows a sectional view on the line 33 in FIG. 1.

In the figures the numeral designates a rotary pressure fluid driven power wrench which may be of any suitable conventional type with or without impact action. For purposes of illustration has been chosen an impact wrench similar to the one disclosed in US. patent application Ser. No. 184,013, now Patent No. 3,179,219 to Kardn but the invention is not restricted to power wrenches of that particular type. Accordingly, there is provided in the housing 11 of the power wrench 10 a reversible rotary air motor 12 having radial driving vanes 13 on a rotor 14, the rotational direction of which is controlled by the usual reversing valve 15. The reversing valve 15 and motor 12 are supplied with compressed air through a passage 16 controlled by a control valve 17 which can be operated manually by a trigger 18 on the handle 19 of the power wrench 10. An air-nipple 20 upstream of the control valve 17 receives compressed air from a supply hose, not shown, connected thereto. The rotor 14 of the air motor 12 is coupled for rotating a hammer 21 journalled in the housing 11. The hammer 21 is supported at its rear end on a splined projection of the rotor 14 while its forward end slides on the tool shaft or anvil 22 of the power wrench. The rear end of the shaft 22 is supported inside of the hammer 21 While its middle portion is journalled in the front end of the housing 11. The outer end of the shaft 22 has the usual square end 23 for removably carrying tools engageable with the fasteners to be driven. As described in full detail in the above-mentioned patent an impact dog 24 pivotally journalled inside of the hammer 21 delivers impacts to the shaft 22 when the latter meets sufiicient resistance to rotation. The impact dog 24 is moved to impact delivering position. FIG. 3, by a cam 25 on the shaft 22 cooperating with the trailing edge of the impact dog 24, while a torsion spring 26 extending centrally and longitudinally of the Wrench 10, in the position depicted in FIG. 3 cooperates with a pin 49 on the impact dog 24 so that the leading edge thereof is pivoted out of engagement with the shaft 22 and the impact dog 24 will be able to rotate in unison with the hammer 21 around the arrested shaft 22 for producing the next impact.

The apparatus for limiting the application of torque to the fasteners driven by the power wrench 10 includes an automatic control valve 27 in a valve case 31 upstream of the manual control valve 17. The valve 27 is a fiat disk valve cooperating with a circular valve seat 28 in the passageway 29 connecting the nipple 20 with the manual control valve 17. The automatic control valve 27 has a projecting piston end 3!} which is slidably but tightly received in a bore in the valve case 31 whereby the control valve 27 is guided in its movements between a cut-off and an open position. Adjacent the piston end 36 in the valve case 31 there is provided an air chamber or reservoir 32 in which one end of a helical spring 33 bears against the face of the piston end 30. The opposite end of the spring 33 is supported by a washer 34, the axial position of which in the chamber 32 can be adjusted by means of a set screw 35, which extends through the wall of the valve case 31 and is in threaded engagement therewith. From the passageway 29 a branch passage 36 leads to the chamber 32. The air flow through the passage 36 can be controlled by a needle valve 37.

The chamber 32 is connected to the forward end of the power wrench 10 by a conduit 38 communicating with a bore 39 disposed preferably perpendicularly to the surface of the shaft 22. The bore 3? is provided in a fitting 4t), FIG. 2a, connected to the housing 11 as by screws 41. A nozzle body 42 is slidable in the bore 39 and has an O-ring therearound for providing tightness between the nozzle 42 and the bore 39. The nozzle 42 is preferably made of plastic material offering small frictional resistance to sliding motion against metal and sliding in collector brush manner on the periphery of the shaft 22. A bore 43 extends axially through the nozzle 42. A helical spring 44 is interposed between a shoulder in the bore 39 and the nozzle 42 for urging the latter against the shaft 22.

A series of axial grooves 45 are provided in evenly spaced disposition circumferentially on the

shaft

22 and 3 the portion thereof forming the path of movement of the nozzle 42 during rotation of the shaft 22. Between the grooves 45 peripheral boom portions 46 of the shaft 22 remain undisturbed.

The passage 16 upstream of the reversing valve 15 is connected by a conduit 50 to the chamber 32 in the valve case 31. A spring pressed check valve 51 opening for flow in the direction from the chamber 32 to the passageway 16 is provided in the conduit 50 and the valve case 31.

A bleed hole 52 is provided in the valve disk of the automatic control valve 27 whereby air can bleed past the valve 27 in the cut-off position thereof.

In operation let it be assumed that the fastener to be driven is rotated by the air motor 13 over the rotor 14, the hammer 21, the impact dog 24, the shaft 22, the square end 23 and a tool, not shown, carried thereby. Compressed air is delivered to the nipple 20 past the seat 28 of the automatic control valve 27 in the open position thereof and past the manual control valve 17 to the passageway 15 and on to the reversing valve 15 and the motor 12 for rotating the vanes 13 thereof. Simultaneously herewith a certain quantity of air is branched from the passageway 29 via the branch passage 36 and the needle valve 37 to the chamber 32 and thence via the conduit 38 to the bore 43 of the nozzle 42.

During initial rotation of the shaft 22 as well as during the first rapidly repeated impacts of the hammer 21 and dog 24 against the shaft 22, the grooves 45 thereon will pass the bore 4-3 with a high angular velocity and with the needle valve 37 set at a lesser flow rate than issuing from the bore 43, no pressure rise will occur in the chamber 32 since the grooves 45 passing the nozzle 42 in rapid succession obviously act to keep the bore 43 substantially open to atmosphere. However, with increasing resistance to rotation of the fastener, that is to say with increasing torque, the angle of displacement produced by each separate impact successively decreases. With the hammer 21 normally delivering a substantially constant number of impacts per time unit this obviously means that the total angular displacement per unit of time of the shaft likewise decreases. Thus the boom portions 46 on the shaft 22 between the grooves 45 will take a longer time to pass the bore 43, thereby offering a successively increasing obstruction to the flow therethrough with increased torque. This obstruction causes a rise of pressure in the chamber 32, whereby a force tending to close the automatic control valve 27 is imposed on the face of the piston end 30. This force is added to the force exerted by the helical spring 33 but both these forces are counteracted by the pressure acting on the valve 27 in the passageway 29. By adjustment of the set screw 35 and of the needle valve 37 the spring force and the air flow branched to the chamber 32 are set to such values that the automatic valve will be moved to the cutoff position by the pressure built up in the chamber 32 at the right moment corresponding to the desired torque in the fastener.

The valve disk of the automatic control valve 27 is disposed at a relatively small distance from the seat 28 in the open position of the valve 27 in such manner as to create a pressure differential across the valve disk assisting in closing the valve 27 at the desired instant with a snap action. The compressed air trapped in the passage 16 expands upon closing of the automatic valve 27 through the air motor 12. The falling pressure in the passage 16 results in that the check valve 51 in the conduit 50 is opened whereupon the chamber 32 is exhausted to atmosphere via the motor 12. As long as the operator keeps the trigger 18 depressed and the manual control valve 17 is open, air leaking from the passageway 29 through the bleed hole 52 in the valve 27 will likewise leak out to atmosphere through the passage 16 and the motor 12 so that the automatic control valve 27 will remain closed. If the trigger 18 is released, whereby the valve 17 is closed, the air issuing through bleed hole 52 will rapidly equalize the pressures at opposite sides of the valve disk of the valve 27, whereupon the pressure in the passageway 29 will return the valve 27 to open position against the action of the spring 33. The chamber 32 is exhausted to the atmosphere by the conduit 50 and the motor 12 or by the conduit 38 when one of the grooves 45 registers with the bore 43 in the nozzle 42. The opening force acting on the valve 27 is therefore not counteracted by pressure in the chamber 32. The power wrench It) is thus again in starting position and ready for the next tightening cycle.

In the above described operation limiting of the torque was performed during impact action of the power wrench. The present apparatus is, however, equally suited for limiting the torque also during purely rotary action of the wrench to which the apparatus is applied. In FIG. 1, for example, by suitably releasing the set screw 35 and by adjusting the needle valve 37 to suitably increase the flow area of the passage 36, torque limiting will be possible during rotation, provided the internal driving friction between the hammer 21, the dog 24 and the shaft 22 is sufficiently high to allow transmission of torque within certain limits without impacting taking place. With increased resistance the rotation will slow down gradually and the decrease in the number of grooves 45 passing the bore 43 per unit of time will cause pressure to build up in the chamber 32 until the automatic control valve 27 is closed at the pressure value in the chamber 32 corresponding to the desired torque. The operation will be identical when the present apparatus is applied to rotary power wrenches of other type.

The modified automatic control valve shown in FIG. 2b has an axial central passage 53 through the piston end 30 and through a tubular extension 54 coaxially thereon. The extension 54 is tightly but slidably received in a partition 55 forming the rear wall of the air chamber 32 in the valve case 56. Through a nipple 57 screwed to the valve case 56 and disposed coaxially with the automatic valve 27 compressed air enters from the supply hose, not shown, and passes along the central passage 53 through radial apertures 58 to the rear of the valve disk included in the automatic valve 27. The bleed hole 52 is in this instance provided centrally in the valve disk. The action of the automatic valve 27 depicted in FIG. 2b is identical with the operation of the valve in FIG. 1 except for the compressed air being supplied axially through the valve 27 past the chamber 32. The helical spring 33 bears against the partition 55 and cannot be adjusted since no set screw is provided therefor. As before a needle valve 37 provides a means for adjusting the desired maximum torque at which the power to the tool is to be cut off.

A pressure gauge 59 may be connected to the conduit 38 whereby adjustment of the torque limiting apparatus is made more easy when using the spring 33 for pressure adjustments. The gauge 59 can also be used for indicating the moment at which the operator has to interrupt the supply of power purely manually for reaching the desired value of the final torque. However, such manual control, during which the automatic valve 27 can be omitted or made inoperative, depends heavily upon the skill of the operator and is undesirable in production work. Furthermore the pressure gauge 59 obviously can be used as an indicator of the angular velocity of the shaft 22. In such case the disk of the automatic valve 27, FIG. 2b, will be omitted so that driving air constantly can pass to the driving motor of a rotary shaft 22 arranged as indicated in FIG. 2a. By the aid of a tachometer the readings on the gauge 59 can be calibrated to indicate the angular velocity of the shaft 22 whereby the device according to FIGS. 2a-2c can be used for direct measurement of angular velocity.

What we claim is:

1. A torque limiting apparatus comprising in combination a rotary motor, a member connected to said motor for being rotated thereby, means for measuring the angular displacement per unit of time of said member, and automatic means for cutting of the supply of power to said motor, said measuring means operative upon the decrease of said angular displacement per unit of time to a predetermined value to cause actuation of said automatic mfieans whereby the supply of power to said motor is cut 0 2. In an apparatus for limiting the maximum torque transmitted from a compressed air driven motor to an element rotated thereby the combination which comprises said motor and element, an air line connected to said motor for supplying compressed air thereto, a drive shaft connected between said motor and element, pneumatic measuring means cooperating with said shaft in a manner to build up a pressure in said means which inrreases with decreasing angular displacement per unit of time of said shaft, a valve in said air line for cutting off the air supply to said motor, and means connected to said valve and operative upon the development of a predetermined pressure in said measuring means to cause actuation of said valve whereby the supply of air to said motor is cut off.

5. A power wrench comprising a housing, a rotary motor in said housing, a tool head connected to said motor for being rotated thereby and protruding from said housing, a shaft included in said tool head, a series of axial grooves in evenly spaced disposition circumferentially on said shaft, a nozzle nonrotatably supported in said housing and having an outlet orifice adjacent the periphery of said shaft and traversing said grooves and the portions of said shaft therebetween during rotation of said tool head, said portions obstructing flow through said orifice when in registry therewith, a passageway communicating with said nozzle and orifice, means for constantly supplying air under pressure to said passageway at a lesser rate than issuing through said orifice when said orifice registers with said grooves, and automatic means responsive to the development of a predetermined pressure in said passageway as a result of the obstruction offered by said portions during rotation of said tool head and shaft for automatically cutting ofl. the supply of power to said motor.

4. A power wrench as set forth in claim 3 in which said nozzle is axially slidably supported in said housing and in which there are provided means for biasing the end of said nozzle carrying said orifice into sliding contact with said shaft and said portions thereon.

5. A power wrench as set forth in claim 3 in which there is provided an adjustable valve in said air supply means for adjustably controlling the air supply to said passageway.

6. A portable pneumatic power wrench comprising a rotary air motor, a shaft driven by said motor, a first passageway for supplying said motor with air under pressure for rotating said shaft, a valve seat in said first passageway, an automatic control valve in said first passageway upstream of said seat and movable between open and seated positions to admit or cut off the supply to said motor, resilient means urging said valve to seated position, a first surface on said valve exposed to pressure in said first passageway for maintaining said automatic valve in open position against the action of said resilient means, a second passageway branched ofi from said first passageway at a point upstream of said valve seat, a second surface on said valve opposed to said first surface and communicating with said second passageway, said second surface responsive to the development of a predetermined pressure in said second passageway for combining its action with the action of said resilient means to move said valve to seated position, and pneumatic means connected to said second passageway and receiving air under pressure therefrom, said pneumatic means being responsive to decrease of the angular displacement per unit of time of said shaft to a predetermined value for developing said predetermined pressure in said second passageway in order 6 to move said automatic valve to seated position and thereby to stop said motor.

'7. A power wrench as set forth in claim 6 in which said automatic valve in the open position thereof is disposed in such proximity to said seat as to create a pressure differential across said valve for placing an additional bias on said valve towards said seated position thereof during operation of said motor.

8. A power wrench as set forth in claim 6 having a manually operable control valve in said first passageway downstream of said seat, said control valve being movable between open and closed positions to admit or cut off the air supply to said motor, there being provided a bleed passage in parallel with said automatic valve in the closed position thereof for pressure equalization at opposite sides of said seat and for resetting said automatic valve to open position when said manually operable valve is closed.

9'. A power wrench as set forth in claim 8 including a communication for connecting said second passageway with said first passageway at a point between said control valve and said motor, and a check valve in said communication for relieving the pressure in said second passageway when said manually operable valve is closed.

16'. A power wrench as set forth in claim 6 in which there are provided means for adjusting the bias of said resilient means exerted upon said automatic valve.

11. An impact wrench comprising a housing, a rotary air motor in said housing, a rotatable hammer in said housing connected to said motor, an anvil shaft rotatably journalled in said housing and carrying a tool head at one end thereof, said tool head protruding from said housing and having means thereon connectable to a threaded fastener to be driven, means for transmitting rotational blows from said hammer to said anvil shaft in response to said shaft meeting sufficient resistance to rotation of said fastener, said blows causing successively decreasing angular displacements of said anvil shaft with increasing resistance of said fastener, a passageway for supplying air under pressure to said motor for operating the same, an automatic valve controlling said passageway and movable between open and closed positions to admit or cut ofi the supply of air to said motor, and means responsive to the angular displacements per unit of time of said anvil shaft decreasing to a predetermined value for effecting the movement of said valve to closed position to stop said motor.

22. An impact wrench as set forth in claim 11 comprising a series of axial grooves in evenly spaced disposition circumferentially on said shaft, a nozzle nonrotatably su ported in said housing and having an outlet orifice adjacent said shaft for traversing said grooves and the portions of said shaft therebetween as a consequence of said angular displacements, said portions being in such proximity to said nozzle when in. registry therewith as to obstruct flow through said orifice, a second passageway communicating with said nozzle and orifice, means for supplying air under pressure to said second passageway at a lesser rate than issuing through said orifice when said orifice registers with said grooves, and means responsive to the development of a predetermined pressure in said second passageway as a result of the obstruction offered by said portions during consecutive angular displacements of said shaft for effecting the movement of said valve to closed position to stop said motor.

13. An impact wrench as set forth in claim 12 in which said second passageway is branched ofi? from said first passageway upstream of said automatic valve and said means for supplying air to said second passageway is an adjustable valve.

14. An impact wrench as set forth in claim 12 in which said second passageway includes an air reservoir chamber.

15. A device for measuring the angular velocity of a shaft rotated by power comprising a rotary shaft, a series of grooves in evenly spaced disposition circumferentially on said shaft, a nozzle non-rotatahly supported adjacent said shaft and having an outlet orifice supported to traverse said grooves and the portions of said shaft therebetween during rotation of said shaft, said portions obstructing flow through said orifice when in registry therewith, a passageway communicating with said nozzle and orifice, means for constantly supplying fluid under pressure to said passageway at a lesser rate than issuing through said orifice when said orifices register with said grooves, and a pressure gauge connected to said passageway to respond to pressure fluctuations therein thereby to indicate the angular velocity of said shaft and its fluctuations with rotational resistance.

16. A measuring device as set forth in claim 15 in which said nozzle is axially slidably supported in said housing and in which there are provided means for bias- 8 ing the end of said nozzle carrying said orifice into sliding contact with said shaft and said portions thereon.

References fitted by the Examiner UNITED STATES PATENTS 3,136,326 9/1964 Bryant 7352l 3,195,655 7/1965 Karden 17312 3,216,252 11/1965 Chapmen et al 73521 PQREIGN PATENTS 1,104,233 4/1961 Germany.

1,176,405 8/1964 Germany.

FRED C. MATTERN, In, Primary Examiner.

L. P. KESSLER, Assistant Examiner.

Claims

1. A TORQUE LIMITING APPARATUS COMPRISING IN COMBINATION A ROTARY MOTOR, A MEMBER CONNECTED TO SAID MOTOR FOR BEING ROTATED THEREBY, MEANS FOR MEASURING THE ANGULAR DISPLACEMENT PER UNIT OF TIME OF SAID MEMBER, AND AUTOMATIC MEANS FOR CUTTING OF THE SUPPLY OF POWER TO SAID MOTOR, SAID MEASURING MEANS OPERATIVE UPON THE DECREASE OF SAID ANGULAR DISPLACEMENT PER UNIT OF TIME TO A PREDETERMINED VALUE TO CAUSE ACTUATION OF SAID AUTOMATIC MEANS WHEREBY THE SUPPLY OF POWER TO SAID MOTOR IS CUT OFF.