US3331452A

US3331452A - Torque wrench

Info

Publication number: US3331452A
Application number: US397738A
Authority: US
Inventors: Wanner Karl
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1963-09-27
Filing date: 1964-09-21
Publication date: 1967-07-18
Anticipated expiration: 1984-07-18
Also published as: DE1218370B; GB1041808A

Description

July 18, 1967 K. WANNER 3,333,452

TORQUE WRENCH Filed Sept. 21, 1954 Al /v Patented July 18, 1967 3,331,452 TORQUE WRENCH Karl Wanner, Echtcrdingen, Germany, assignor to Robert Bosch G.m.b.H., Stuttgart, Germany Filed Sept. 21, 1964, Ser. No. 397,738 Claims priority, application Germany, Sept. 27, 1963, B 73,666 14 Claims. (Cl. 173-12) The present invention relates to portable power tools and to power machine tools in general, and more particularly to an improved torque wrench or nut runner which may be used to apply or remove nuts, bolts, screws and other types of threaded fasteners.

It is well known to construct an impact wrench in such a way that the fastener which is to be rotated by the anvil maybe driven home with a predetermined minimum force. When the wrench is of the pneumatic type, the magnitude of torque which its anvil may transmit to the fastener depends on fluctuations in the pressure of fluid. A variation of plus or minus 5 p.s.i. is quite serious because the operator is not sure that each of a series of fasteners is driven home with the same force.

It is also known to construct an electric or pneumatic impact wrench in such a way that its motor is antomatically arrested after a predetermined interval of time. Such wrenches are not entirely satisfactory because their action also depends on eventual fluctuations in the supply of power to the motor. Moreover, the elasticity of fasteners which are to be driven home or which are to be removed exerts an undesirable influence on the operation of such impact tools. The same holds true for impact wrenches wherein the anvil is free to rebound, once or more than once, and is automatically reconnected with the motor after each rebounding step.

Accordingly, it is an important object of the present invention to provide a very simple, rugged, compact and highly reliable portable power tool or power machine tool which fully overcomes the above outlined drawbacks of conventional impact wrenches and which is capable of transmitting identical torque to each of a series of bolts, screws, nuts or other types of internally or externally threaded fasteners.

Another object of the invention is to provide a torque wrench of the just defined character whose operation does not depend on the elasticity of the fasteners which are to be rotated by its anvil and wherein the driving torque is independent of any fluctuations in the supply of electrical energy or compressed fluid to its motor.

A further object of the invention is to provide a torque Wrench which may be constructed as a portable or stationary power tool and which may be operated by compressed fluid or by electric current whereby its operation does not depend on the exact nature of power which is required by its motor.

An additional object of the instant invention is to provide a torque wrench or nut runner which may be readily adjusted or modified to transmit to threaded fasteners a torque of desired magnitude, which is constructed and assembled in such a way that its parts are protected from damage or destruction when the resistance offered by its driven parts against further rotation exceeds a maximum permissible value, and which may be operated by skilled, semiskilled or even unskilled persons.

A concomitant object of the invention is to provide a torque wrench whose anvil is arrested in a fully automatic way and at the exact moment when the resistance of the driven parts against further rotation with the motor reaches an exactly predetermined magnitude.

Still another object of my invention is to provide a safety device which insures that not only the driven but also all driving components are positively arrested as soon as the resistance of driven components against further rotation with the driving components reaches a predetermined maximum permissible value.

With the above objects in view, one feature of the present invention resides in the provision of a power tool, preferably of the portable type, which comprises a rotary main shaft, electric or fluid-operated motor means for rotating the main shaft, a rotary torque-transmitting member which is preferably coaxial with the main shaft and is arranged to offer variable resistance against rotation with the main shaft when its head rotates a bolt or another threaded fastener, clutch means forming part of means for drivingly connecting the main shaft with the torque-transmitting member and including a clutch element which is movable axially of the main shaft in opposition to the bias of a spring or the like and in response to increasing resistance offered by the torque-transmitting member against rotation with the main shaft, coupling means for drivingly connecting the main shaft with the clutch element, and a blocking device for holding the clutch element against rotation in response to a predetermined axial displacement of the clutch element such as corresponds to a predetermined resistance offered by the torque-transmitting member against further rotation with the main shaft. The blocking device may comprise a first blocking gear which is fixed to the housing of the power tool and a second blocking gear which is connected to or integral with the clutch element and moves in mesh with the first gear in response to a predetermined axial displacement of the clutch element, i.e., in response to a predetermined resistance offered by the torque-transmitting element against further rotation with the main shaft.

In accordance with another important feature of my invention, the power tool preferably comprises a safety device which automatically arrests the motor means when the blocking device is operative to hold the clutch element against rotation. Such safety device may include an electric switch or a suitable valve, depending upon whether the main shaft is driven by an electric motor or by a fluidoperated motor.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved torque wrench itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawings, in which:

FIG. 1 is an axial section through a portable electric torque wrench which is constructed in accordance with a first embodiment of my invention;

FIG. 2 is a transverse section as seen in the direction of arrows from the line HII of FIG. 1 and illustrates the parts which transmit motion from the main shaft to the anvil;

FIG. 3 is a transverse section as seen in the direction of arrows from the line IIIIII of FIG. 1 and illustrates a portion of the blocking device for the main shaft; and

FIG. 4 is a diagram showing a portion of a modified torque wrench which is provided with an automatic arresting device for the motor.

Referring to the drawings, and first to FIG. 1, there is illustrated a portable electric torque wrench having a susbstantially cylindrical composite housing 10 including a two-piece rear barrel 10a and a front barrel 20 arranged end-to-end with the rear barrel. These barrels are connected with a transverse support in the form of a partition 42, and the rear barrel 10a carries a suitable grip handle 12 provided with a conductor cable 12a leading to a plug (not shown) which may be inserted into an outlet or into another suitable source of D-C or A-C current. The handle 12 carries a normally open main switch or starter switch 13 which is actuated by a finger when the operators hand grips the handle so as to complete the circuit of a universal (D-C or A-C) electric motor 11 which is accommodated in the rear barrel 1001 a tone side of the partition 42. The output shaft 11a of this motor is mounted in bearings 11b and drives a stepdown transmission 14 including a pinion 43 meshing with a gear 43a which is mounted on an intermediate shaft 43b. This intermediate shaft also carries a driver pinion 430 which is rigidly connected thereto and meshes with a driver gear 16 provided at and rigid with the rear end of a hollow drive shaft or main shaft which extends well into the front barrel 20. The gear 43a of the transmission 14 is connected to the intermediate shaft 43b (and hence to the pinion 430) by an overload clutch 45 of any known design, e.g., a suitable friction clutch or slip clutch. The main shaft 15 is rotatable in anti-friction bearings 42a which are mounted in the partition 42 and has a cylindrical projection or tip 17 which is rotatably received in a blind bore 18 machined into the hub 19a of a torque-transmitting anvil 19. This torque-transmitting anvil extends through the apertured front end wall of the barrel 20 and comprises a head or tip 21 of non-circular outline, this head serving to drive a suitable attachment, such as a screwdriver, not shown, by means of which a bolt, screw or another threaded fastener may be driven home with a predetermined force. The anvil 19 is rotatable in a bush 20a provided in the front end Wall of the front barrel 20. The hub 19a comprises a flange-like clutch element 191; which is accommodated in the barrel 20 and is provided with two rearwardly extending

jaws

23, 24. These jaws have inclined faces which engage similarly inclined faces of forwardly extending

complementary jaws

25, 26 forming part of a second clutch element 27 here shown as a substantially cylindrical sleeve which is axially slidably and rotatably telescoped onto the main shaft 15. The sleeve 27 is biased in a direction toward the flange 1917 by a strong prestressed helical expansion spring 28 which operates between an internal shoulder 27:: and the outer end face of the partition 42. The parts 1% and 23-28 together constitute a positiveengagement jaw clutch which invariably tends to rotate the anvil 19 whenever the main shaft 15 rotates.

The driving connection between the main shaft 15 and sleeve 27 further includes a coupling comprising a pair of angularly spaced rollingelements (hereinafter called balls) 30, 31 which are arranged to travel in helical grooves 32 machined in the peripheral surface of the main shaft. One-half of each ball also extends into one of two axial grooves 33 provided in the internal surface of the sleeve 27 and extending rearwardly from the

jaws

25, 26.

The torque wrench further comprises a blocking device for holding the sleeve 27 against rotation when the attach-.

ment rotated by the head 21 offers a predetermined maximum resistance against further rotation. This blocking device may be constructed in a number of ways. FIG. 1 shows a first blocking member in the form of a fixed ring gear 41 which is rigid with the front side of the partition 42 and whose teeth extend in a direction toward the rear end of the sleeve 27. The ring gear 41 may mesh with a complementary blocking member here shown as a second ring gear 40 which is provided at the rear end of the sleeve 27 so that, when the sleeve moves axially and away from the flange 19b to the extent necessary to move the teeth of the gear 40 into actual mesh with the teeth of the gear 41, the anvil 19 is blocked because the

jaws

23, 24 remain in mesh with the

jaws

25, 26 regardless of the axial position of the sleeve 27. The overload clutch 45 is adjusted in such a way that it continues to drive the pinion 430 while the spring 28 undergoes axial compression necessary to allow for axial movement of the ring gear 40 into actual mesh with the fixed ring gear 41; however, once the ring gears 40, 41 are in mesh, i.e., once the blocking device is operative, the overload clutch 45 yields and allows the gear 43a to rotate with reference to the intermediate shaft 43b so that the main shaft 15 comes to a halt.

The torque wrench of FIGS. 1 to 3 is operated as follows:

To start the operation, the user inserts the non-circular head 21 of the anvil 19 into the socket at the rear end of a screwdriver or another suitable attachment which happens to be necessary to drive home a bolt, nut, screw or another threaded fastener. The working end of the attachment is then caused to engage the fastener and the user closes the switch 13 to complete the circuit of the motor 11 while one of his hands grasps the handle 12. The other hand may be used to manipulate the attachment. The motor 11 drives the main shaft 15 via transmission 14 and overload clutch 45 whereby the main shaft rotates the sleeve 27 via

balls

30, 31 and the

jaws

25, 26 rotate the

jaws

23, 24 to drive the anvil 19 so that the fastener engaged by the attachment is gradually driven home or is gradually removed. Initially, a fastener which is to be driven home offers comparatively little resistance against rotation of the anvil 19 so that the spring 28 is free to expand and keeps the

balls

30, 31 in the outer ends of the helical grooves 32. The angular distance between the balls is degrees because the grooves 33 are located diametrically opposite each other.

It is now assumed that the torque wrench of FIGS. 1 to 3 is used for driving home a bolt which is provided with right-hand threads and that the main shaft 15 is driven by the transmission 14 and overload clutch 45 to rotate in a clockwise direction (arrow 22). The

balls

30, 31 are in the positions shown in FIG. 1 and rotate the sleeve 27 in a clockwise direction While the spring 28 remains expanded so that the ring gear 40 is spaced from the fixed ring gear 41, i.e., the blocking device is idle. As long as the spring 28 remains expanded, the sleeve 27 invariably rotates at the exact speed of the main shaft 15. When the resistance of the anvil 19 against further rotation with the main shaft 15 increases, the sleeve 27 begins to move axially toward the partition 42 by simultaneously rotating with reference to the main shaft 15 because the grooves 32 are of helical outline. In other words, the sleeve27 begins to lag behind the main shaft 15 while simultaneously advancing axially in a direction toward the partition 42 to thereby compress the spring 28.-In response to a predetermined maximum resistance of the anvil 19, the sleeve 27 moves its ring gear 40 in actual mesh with the fixed ring gear 41 whereby the anvil 19 is blocked in a fully automatic way because the gear 41 is rigid with the partition 42 which, in turn, is rigid with the housing 10.

Then, and only then, the torque transmitted by the" pinion 43 overcomes the motion transmitting force of the overload clutch 45 so that the main shaft 15 comes to a halt while the motor 11 may but need not continue to rotate. The operator will normally sense when the gear 40 is moved in mesh with the gear 41 and may immediately release the main switch 13 to open the circuit of the motor 11.

It will be readily understood that the motor 11 may be replaced by a fluid-operated motor without in any way departing from the spirit of my invention. The main switch 13 is then replaced by a different starting device, i.e., by a valve which controls the admission of compressed air or another suitable fluid medium to the motor. 7

The front barrel 20 is preferably detachable from the partition 42 so that the spring 28 may be replaced by a weaker or stronger spring, depending on the desired magnitude of driving torque which is to be transmitted to a threaded fastener. This spring 28 may be replaced by a package of dished springs or by another suitable biasing device. Also, the bias of the spring 28 may be increased by placing one or more annular washers against the shoulder 27a of the sleeve 27.

In accordance with a slight modification which is illustrated in FIG. 4, the circuit of the electric motor 111 includes a normally open main switch 113, corresponding to the main switch 13 of FIG. 1, and a normally closed automatic safety switch 147, e.g., a suitable microswitch. The motor 111 drives the main shaft 115 which in turn may drive the sleeve 127 (having jaws 125, 126) in the same way as described in connection with FIG. 1. When the anvil (not shown in FIG. 4 offers such resistance against further rotation that the ring gear 140 actually meshes With the fixed ring gear 141 to block the sleeve 127, a trip 127a of the sleeve opens the switch 147 to disconnect the motor 111 from the source 146 of electrical energy. Thus, the safety switch 147 and the trip 127a replace or supplement in a way the overload clutch 45 of FIG. 1. If the motor 111 is replaced by a fluid-operated motor, e.g., by a pneumatic motor, the switch 147 is replaced by .a normally closed safety valve which opens in response to engagement of the ring gear 140 with the fixed ring gear 141.

It goes without saying that the mechanically operated safety switch 147 may be replaced by another suitable automatic safety device, for example, by a thermoswitch or by an electromagnetic switch which need not be actuated by the sleeve 127 but can respond to increasing power requirements of the motor 111 when the anvil offers a predetermined maximum resistance against rotation. All that counts is to provide a safety device which responds, directly or indirectly, to a predetermined axial movement of the sleeve 27 or 127, namely, to such axial movement which corresponds to a predetermined resistance offered by the anvil against further rotation with the

main shaft

15 or 115.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In a power tool, a rotary shaft; motor means for driving said shaft; a rotary torque-transmitting member arranged to offer variable resistance against rotation with said shaft; means for drivingly connecting said shaft with said torque-transmitting member including a spring-biased clutch element movable axially of said shaft in response to increasing resistance olfered by said torque-transmitting member against rotation with said shaft, coupling means for drivingly connecting said main shaft with said clutch element, and means for drivingly connecting said torque transmitting member with said clutch element independent of the axial position of the latter; and blocking means for holding said clutch element against rotation in response to a predetermined axial movement of said clutch element such as corresponds to a predetermined resistance offered by said torque-transmitting member against further rotation with said shaft. 4

2. In a power tool, particularly in -a portable torque wrench, in combination, a rotary main shaft; motor means for driving said main shaft; a rotary anvil coaxial to and arranged to offer variable resistance against rotation with said main shaft; means for drivingly connecting said main shaft with said anvil including a first clutch element rigid with said anvil, a second clutch element drivingly engaging with said first clutch element and arranged to move axially of said main shaft in response to increasing resistance offered by said anvil against rotation with the .rnain shaft, said clutch elements being constructed and arranged to remain in driving engagement during axial movement of said second clutch element, biasing means for opposing such axial movement of said second clutch element, and coupling means for drivingly connecting said main shaft with said second clutch element; and blocking means for holding said second clutch element against rotation in response to a predetermined axial movement of said second clutch element against the action of said biasing means such as corresponds to a predetermined resistance offered by said anvil to further rotation with said main shaft.

3. In a power tool, a rotary shaft; motor means for driving said shaft; a rotary torque-transmitting member arranged to offer variable resistance against rotation with said shaft; means for drivingly connecting said shaft with said torque-transmitting member including a spring-biased clutch element movable axially of said shaft in response to increasing resistance offered by said torque-transmitting member against rotation With said shaft, and coupling means for drivingly connecting said main shaft with said clutch element, and means for drivingly connecting said torque transmitting member with said clutch element independent of the axial position of the latter; and blocking means for holding said clutch element against rotation in response to a predetermined axial movement of said clutch element such as corresponds to a predetermined resistance oifered by said torque-transmitting member against further rotation with said shaft, said blocking means comprising a fixed blocking member and a second blocking member rigid with said clutch element and movable into and out of blocking engagement with said fixed blocking member.

4. In a power tool, particularly in a portable torque wrench, in combination, a rotary main shaft; motor means for driving said main shaft; a rotary anvil coaxial to and arranged to offer variable resistance against rotation with said main shaft; means for drivingly connecting said main shaft with said anvil including a first clutch element rigid with said anvil, a second clutch element drivingly engaging with said first clutch element and arranged to move axially of said main shaft in response to increasing resistance offered by said anvil against rotation with the main shaft, said clutch elements being constructed and arranged to remain indriving engagement during axial movement of said second clutch element; biasing means for opposing such axial movement of said second clutch element, and coupling means for drivingly connecting said main shaft with said second clutch element; and blocking means for holding said second clutch element against rotation in response to a predetermined axial movement of said second clutch element against the action of said biasing means such as corresponds to a predetermined resistance ofiered by said anvil to further rotation with said main shaft, said blocking means com-- prising a fixed gear and a second gear rigid with said second clutch element and meshing with said fixed gear in response to said predetermined axial movement of said second clutch element.

5. In a power tool, particularly in a portable torque wrench, in combination, a housing; a fixed support in said housing; a main shaft rotatably mounted in said support; motor means for driving said main shaft, said motor means being provided in said housing at one side of said support; a rotary anvil coaxial with said main shaft and provided in said housing at the other side of said support, said anvil having a torque-transmitting head extending from said housing and arranged to offer variable resistance against rotation with said main shaft; means provided in said housing at said other side of said support for drivingly connecting said main shaft with said anvil and including a first clutch element rigid with said anvil, a second clutch element drivingly engaging said first clutch element and arranged to move axially of said main shaft in response to increasing resistance offered by said head against rotation with said main shaft, said clutch elements being constructed and arranged to remain in driving engagement during axial movement of said second clutch element, biasing means for opposing such axial movement of said second clutch element, and coupling means for drivingly connecting said main shaft with said second clutch element; and blocking means for holding said second clutch element against rotation in response to a predetermined axial movement of said second clutch element against the action of said biasing means such as corresponds to a predetermined resistance offered by said head against further rotation with said main shaft, said blocking means comprising a first gear fixedly connected to and located at said other side of said support and a second gear rigid with said second clutch element and meshing with said first gear in response to said predetermined axial movement of said second clutch element.

6. In a power tool, particularly in a portable torque Wrench, in combination, a housing including a pair of barrels arranged end-to-end; a transverse partition fixedly received between said barrels; a main shaft rotatably mounted in said partition; motor means for driving said main shaft; said motor means being provided in said housing at one side of said partition; a rotary anvil coaxial with said main shaft and provided in said housing at the other side of said partition, said anvil having a torque-transmitting head extending from said housing and arranged to offer variable resistance against rotation with said main shaft; means provided in said housing at said other side of said partition for drivingly connecting said main shaft with said anvil and including a first clutch element rigid with said anvil, a second clutch element drivingly engaging said first clutch element and arranged to move axially of said main shaft in response to increasing resistance offered by said head against rotation with said main shaft, said clutch elements being constructed and arranged to remain in driving engagement during axial movement of said second clutch element, biasing means for opposing such axial movement of said second clutch element, and coupling means for drivingly connecting said main shaft with said second clutch element; and blocking means for holding said second clutch element against rotation in response to a predetermined axial movement of said second clutch element against the action of said biasing means such as corresponds to a predetermined resistance offered by said head against further rotation with said main shaft, said blocking means 7 comprising a first gear fixedly connected to and located at said other side of said partition and a second gear rigid with said second clutch element and meshing with said first gear in response to said predetermined axial movement of said second clutch element.

7. In a power tool, a rotary shaft; motor means for driving said shaft; overload clutch means for drivingly connecting said motor means with said shaft; a rotary torque-transmitting member arranged to offer variable resistance against rotation with said shaft; means for drivingly connecting said shaft with said torque-transmitting member including a spring-biased clutch element movable axially of said shaft in response to increasing resistance offered by said torque-transmitting member against rotation with said shaft, coupling means for drivingly connecting said main shaft with said clutch element, and means for drivingly connecting said torque transmitting member with said clutch element independent of the axial position of the latter; and blocking means for holding said clutch element against rotation in response to a predetermined axial movement of said clutch element such as corresponds to a predetermined resistance offered by said torque-transmitting member against further rotation with said shaft, said overload clutch means being arranged to disconnect said shaft from said motor means when said clutch element is held against rotation and in response to further operation of said motor means.

8. In a power tool, particularly in in a portable torque wrench, in combination, a rotary main shaft; motor means for driving said main shaft; means for drivingly connecting said motor means with said main shaft including a transmission driven by said motor means and an overload clutch driven by said transmission and drivingly connected with said main shaft; a rotary anvil coaxial to and arranged to offer variableresistance against rotation with said main shaft; means for drivingly connecting said main shaft with said anvil including a first clutch element rigid with said anvil, a second clutch element drivingly engaging with said first clutch element and arranged to move axially of said main shaft in response to increasing resistance offered by said anvil against rotation with the main shaft, said clutch elements being constructed and arranged to remain in driving engagement during axial movement of said second clutch element, biasing means for opposing such axial movement of said second clutch element, and coupling means for drivingly conmeeting said main shaft with said second clutch element; and blocking means for holding said second clutch element against rotation in response to a predetermined axial movement of said second clutch element against the action of said biasing means such as corresponds to a predetermined resistance offered by said anvil to further rotation with said main shaft, said overload clutch being arranged to disconnect said main shaft from said transmission when said second clutch element is held against rotation with said main shaft.

9. In a power tool, particularly in a portable torque Wrench, in combination a rotary main shaft having a peripheral surface provided with a helical groove; motor means for driving said main shaft; a rotary anvil coaxial to and arranged to offer variable resistance against rotation with said main shaft; means for drivingly connecting said main shaft with said anvil including a first clutch element rigid with said anvil, a sleeve-like second clutch element surrounding said main shaft and having an internal surface provided with a groove, a rolling element having portions received in said grooves, spring means 7 second clutch element with reference to said main shaft,

said jaws being constructed and arranged to remain in engagement with each other during axial movement of said second clutch element; and blocking means for hold ing said second clutch element against rotation in response to a predetermined axial movement of said second clutch element in opposition to the bias of said spring means such as corresponds to a predetermined resistance offered by said anvil against further rotation with said main shaft.

10. In a power tool, particularly in a portable torque wrench, in combination a rotary main shaft having a peripheral surface provided with a helical groove; motor means for driving said main shaft; atrotary anvil coaxial to and arranged to offer variable resistance against rotation with said main shaft; means for drivingly connecting said main shaft with said anvil including a first clutch element rigid with said anvil, a sleeve-like second clutch element surrounding said main shaft and having an internal surface provided with a groove, a rolling element having portions received in said grooves, a prestressed helical spring for biasing said second clutch element toward said first clutch element, and cooperating jaws pr0- main in engagement with each other during axial movement of said second clutch element; and blocking means for holding said second clutch element against rotation' in response to a predetermined axial movement of said second clutch element in opposition to the bias of said spring means such as corresponds to a predetermined resistance offered by said anvil against further rotation with said main shaft.

11. In a power tool, a rotary shaft; motor means for driving said shaft; a rotary torque-transmitting member arranged to offer variable resistance against rotation with said shaft; means for drivingly connecting said shaft With said torque-transmitting member including a springbiased clutch element movable axially of said shaft in response to increasing resistance offered by said torquetransmitting member against rotation with said shaft, and coupling means for drivingly connecting said main shaft with said clutch element, and means for drivingly connecting said torque transmitting member with said clutch element independent of the axial position of the latter; blocking means for holding said clutch element against rotation in response to a predetermined axial movement of said clutch element such as corresponds to a predetermined resistance offered by said torque-transmitting member against further rotation with said shaft; and a safety device for arresting said motor means in response to said predetermined axial movement of said clutch element.

12. A structure as set forth in claim 11, wherein said motor means includes an electric motor and said safety device includes a normally closed electric switch connected in circuit with said electric motor and located in the path of said clutch element to open the circuit in response to said predetermined axial movement of said clutch element.

13. In a portable torque wrench, in combination, a rotary main shaft; universal electric motor means for driving said main shaft; a rotary anvil coaxial to and arranged to olfer variable resistance against rotation with said main shaft; means for drivingly connecting said main shaft with said anvil including a first clutch element rigid with said anvil, a second clutch element drivingly engaging with said first clutch element and arranged to move axially of said main shaft in response to increasing resistance offered by said anvil against rotation with the main shaft, said clutch elements being constructed and arranged to remain in driving engagement during axial movement of said second clutch element, biasing means for opposing such axial movement of said second clutch element, and coupling means for drivingly connecting said main shaft with said second clutch element; and blocking means for holding said second clutch element against rotation in respones to a predetermined axial movement of said second clutch element against the action of said biasing means such as corresponds to a predetermined resistance oifered by said anvil to further rotation with said main shaft.

14. In a power tool, a rotary shaft; motor means for driving said shaft; a rotary torque-transmitting member arranged to offer variable resistance against rotation with said shaft; means for drivingly connecting said shaft with said torque-transmitting member including a rotary element movable in response to increasing resistance offered by said torque-transmitting member against rotation with said shaft, means for drivingly connecting said main shaft With said element and means for drivingly connecting said torque transmitting member with said rotary element regardless of any movement of the latter in response to increasing resistance offered by said torque transmitting member against rotation; and blocking means for hold ing said element against rotation in response to a predetermined movement of said element such as corresponds to a predetermined resistance offered by said torque-transmitting member against further rotation with said shaft.

References Cited UNITED STATES PATENTS 2,778,468 1/1957 Babaian 192-56 2,787,355 4/1957 Dodge 192-18 2,814,277 11/1957 Jimerson 173-12 2,973,067 2/1961 Eddy 173-12 3,030,839 4/1962 Schadlich 173-936 3,162,250 12/1964 Sindelar 173-93.6 3,170,523 2/1965 Short 173-104 3,207,237 9/1965 Wanner 173-935 FRED C. MATTERN, JR., Primary Examiner. L. P. KESSLER, Assistant Examiner.

Claims

14. IN A POWER TOOL, A ROTARY SHAFT; MOTOR MEANS FOR DRIVING SAID SHAFT; A ROTARY TORQUE-TRANSMITTING MEMBER ARRANGED TO OFFER VARIABLE RESISTANCE AGAINST ROTAION WITH SAID SHAFT; MEANS FOR DRIVINGLY CONNECTING SAID SHAFT WITH SAID TORQUE-TRANSMITTING MEMBER INCLUDING A ROTARY ELEMENT MOVABLE IN RESPONSE TO INCREASING RESISTANCE OFFERED BY SAID TORQUE-TRANSMITTING MEMBER AGAINST ROTATION WITH SAID SHAFT, MEANS FOR DRIVINGLY CONNECTING SAID MAIN SHAFT WITH SAID ELEMENT AND MEANS FOR DRIVINGLY CONNECTING SAID TORQUE TRANSMITTING MEMBER WITH SAID ROTARY ELEMENT REGARDLESS OF ANY MOVEMENT OF LATTER IN RESPONSE TO INCREASING RESISTANCE OFFERED BY SAID TORQUE TRANSMITTING MEMBER AGAINST ROTATION; AND BLOCKING MEANS FOR HOLDING SAID ELEMENT AGAINST ROTATION IN RESPONSE TO A PREDETERMINED MOVEMENT OF SAID ELEMENT SUCH AS CORRESPONDS TO A PREDETERMINED RESISTANCE OFFERED BY SAID TORQUE-TRANSMITTING MEMBER AGAINST FURTHER ROTATION WITH SAID SHAFT.