GB1574652A

GB1574652A - Impact wrench

Info

Publication number: GB1574652A
Application number: GB775777A
Authority: GB
Original assignee: V N I IPROEKT KONSTRUKT I MEK
Current assignee: V N I IPROEKT KONSTRUKT I MEK
Priority date: 1976-08-23
Filing date: 1977-02-24
Publication date: 1980-09-10
Also published as: SE7703636L; SU810472A1; JPS5326000A; DE2710747C2; DE2710747A1

Description

(54) IMPACT WRENCH (71) We, VSESOJUZNY NAUCHNO-IS SLEDOVATELSKY I PROEKTNO-KONSTRUKT ORSKY INSTITUT MEKHANIZIROVANNOGO I RUCHNOGO STROITELNO-MONTAZHNOGO IN STRUMENTA VIBRATOROV I STROITELNO OTDELOCHNYKH MASHIN, a State Enterprise organised and existing under the laws of the Union of Soviet Socialist Republics (USSR), of 1, Leningradskoe Shosse, Khimiki Moskovskoi oblasti, U.S.S.R., 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: The present invention relates to the tools used for tightening threaded joints, and more specifically, to impact wrenches for torque tightening by delivering a number of rotary blows to a threaded joint.

Torque tightening of threaded joints may be most accurately controlled by the energy methdd. With the employment of impact wrenches, this method consists in that a preset number of rotary blows are delivered to the threaded joint, every blow having the same energy.

At present, it is known to use impact wrenches featuring low blow rate for torque tightening (cf. U.S. Patent No. 3952814). In these impact wrenches, the number of blows is mounted by the operator to put off the impact wrench after a pre-set number of blows are delivered, that is after a predetermined amount of energy is transmitted to the threaded joint.

In case the operator counts the number of blows, human errors may occur associated with rapid fatigue of the operator thus resulting in the need in objective control of tightening of threaded jointS.

Known in the art are impact wrenches having devices for automatically limiting the number of blows to a pre-set number of blows (cf. USSR Inventor's Certificate No.

272173, Cl. B 25 b 21/02) comprising an electrical blow counter which breaks open the supply circuit of the impact wrench motor after a pre-set number of blows are delivered, and the tightening is thus stopped.

It should be, however, noted that the electrical blow counter complicates the electric circuit of the impact wrench because a control circuit is required in addition to the power circuit of the impact wrench. Disadvantages of this counter are also associated with insufficient reliability and durability of a contact setter which is subjected to impact loads during operation, and with difficulties encountered when different types of drive are used for impact wrenches (e.g.

pneumatic or hydraulic drive will require two different supply sources, whereas with the employment of a high-frequency lowvoltage drive, a number of auxiliary devices are required due to increased current in the power circuit, to prevent burning of the setter contacts, whiles the size and weight of the impact wrench should remain within the limits acceptable for hand held power tools).

A device for automatically limiting the number of blows used in a pneumatic wrench (cf. German Patent No. 2119273 C1. 87a, 13) comprises la mechanical adder. This device includes an inertial mass mounted on the rotor shaft for axial movement and acting on a spring-loaded pusher which causes rotation of the adder shaft by means of an overrunning clutch. The adder shaft is connected, by means of bevel gears, to a longitudinal shaft having a freely mounted toothed wheel which is connectible to the longitudinal shaft by means of a friction clutch engageable under the action of cornpressed air fed from a starting device of the tool. The toothed wheel of the longitudinal shaft meshes with a setting gear having a pin engaging a leverage system connected to a cut-off valve after the gear is turned through a pre-set angle.

This device may only be used in pneumatic impact wrenches. In addition, it has involved forced transmitting connections lowering the reliability of operation of the impact wrench.

In any case, disconnection of the drive of an impact wrench for interruption of de livery of blows to a threaded joint substantially complicates the construction of the impact wrench and lowers its reliability.

The main object of the invention is to provide an impact whench in which the device for automatically limiting the number of blows is so constructed as to prevent further axial movement of the hammer after a pre-set number of blows are delivered, without deenergizing the motor.

Another object of the invention is to provide a device for automatically limiting the number of blows and which is independent on the type of impact wrench drive.

Still another object of the invention is to provide an impact wrench having a simple and reliable construction.

In accordance with the present invention, we provide an impact wrench comprising: a housing; a drive; an impact clutch connected to the drive and comprising a hammer which is axially movable for imparting each blow, and a device for automatically limiting to a preset number the blows imparted by the hammer, said device comprising means for setting the number of blows, a movable member directly co-operating with the hammer and displaceable upon every axial displacement of the hammer to permit the axial displacement of the hammer until the pre-set number of blows are delivered, and a counting device engageable with the movable member to be displaced in response to every displacement of the movable member and cooperable with the blow members setting means to preset the number of displacements of the counting device before the movable member is locked against displacement in a position in which it obstructs further axial movement of the hammer.

The movable member is preferably in permanent engagement with the peripheral surface of the hammer, and the hammer has an annular groove on the peripheral surface to receive the movable member.

The movable member is preferably elastically urged against the peripheral surface of the hammer.

The provision of a counting device preventing axial movement of the hammer after the pre-set number of blows are delivered enables the elimination of excessive blows without deenergization of the impact wrench drive, whereby the construction of the impact wrench is simplified and reliability is improved, while one and the same device for automatically limiting the number of blows may be used independent on the type of drive.

It is also noted that the counting device for preventing axial movement of the hammer, and the provision of the movable member permanently engaging the hammer make it possible to use the hammer displacement directly as a signal for actuation of the device thus considerably improving reliability.

The counting device may comprise a latch member which is in permanent engagement with the movable member and which is displaceable together therewith at right angles to the direction of movement of the hammer, and a counting mechanism which is engageable by the latch member and which is displaceable upon every displacement of the latch member for engagement with the blow number setting device after the ultimate blow of the pre-set number of blows is delivered, whereby displacement of the latch member is prevented, and the movable member is locked.

The blow number setting device may comprise a number of radial bores made in an adapter casing secured at right angles to the housing, said bores being along a line extending in parallel with the direction of the hammer movement, and a stop pin inserted into one of the radial bores depending on the pre-set number of blows, the counting mechanism comprises a rod urged by spring away from the stop pin and passing freely through a bore of the movable member, the rod having a plurality of equally spaced annular projections and a cylindrical end portion, and a detent urged by a spring against the rod which is mounted in the movable member to extend at right angle to the direction of the rod movement, the detent having one tapered end for engaging the annular projections of the rod, the other end of the detent protruding from the housing, the latch member is located diametrically opposite to the detent in a bore of the movable member and has a projection which is staggered relative to the detent axially along the rod.

The counting mechanism may comprise a rotatable disc partially received in a recess of the movable member and mounted on a shaft extending at right angles to the direction of the hammer movement, the disc being connected to an adapter casing by means of a torsion spring and having equally spaced teeth-made over a part of its periphery, and a detent urged by a spring against the disc and mounted in the movable member to extend at right angles to the disc, one end of the detent being tapered for engaging the teeth of the disc, the other end protruding from the adapter casing, the blow number setting device comprising a plate fixed to the shaft for rotation together therewith and having a projection at the distal end received between the teeth of the disc depending on the pre-set number of blows, and a fixed stop mounted to the disc, and the latch member is located opposite to the detent in a bore of the movable member and has a projection which is staggered relative to the detent in the direction of rotation ofthe disc.

The blow number setting device may alternatively comprise a plurality of bores made in an adapter casing, said bores being along a line extending at right angles to the hammer movement, and a stop pin inserted into one of the bores depending on the preset number of blows, the counting mechanism comprises a rod extending at right angles to the hammer and urged by a spring theretoward, said rod being provided intermediate its length with a collar and having ratchet teeth over its length which extends from the collar towards the hammer, the number of the teeth being equal to the number of the bores and the spacing of the teeth being equal to the spacing of the bores, said rod also having two diametrically opposed flats at its length with the ratchet teeth, one flat terminating at the collar and the other flat extending over the entire length of the collar, a detent comprising a leaf spring secured to the adapter casing, the distal end of the spring engaging the ratchet teeth of the rod, and a sleeve mounted outside the adapter casing, between the latter and the housing in the region of the collar of the rod, said sleeve being connected to the housing by means of a torsion spring and having a pin received in slots made in the adapter casing, the latch member comprises a leaf spring which is located diametrically opposite to the detent and is secured at one of its ends to the movable member, the other end of the latch member engaging the ratchet teeth of the rod.

The adapter casing is preferably accommodated in a lateral handle of the impact wrench.

Thus, impact wrenches having the device for automatically limiting the number of blows according to the invention enable the transmission of a pre-set amount of energy to a threaded joint, thereby ensuring high quality of tightening job and improving reliability of the impact wrench.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a general view, partially in section, of an impact wrench according to the invention, having a device for automatic limiting to a preset number the blows delivered to a threaded joint by the impact wrench; Fig. 2 is a sectional view on a larger scale of the device for automatically limiting to a preset number the blows delivered to a threaded joint by the impact wrench shown in Fig. 1; Fig. 3 is a sectional view on a larger scale taken along the line III--III in Fig. 2; Fig. 4 is a view taken along the arrow A in Fig. 2; Fig. 5 is a general view partially in section of an impact wrench according to a second embodiment of the invention having a device for limiting to a preset number the blows delivered to a threaded joint by the impact wrench; Fig. 6 is a sectional view on a larger scale of the device for automatically limiting to a preset number the blows delivered to a threaded joint by the impact wrench shown in Fig. 5; Fig. 7 is a sectional view on a larger scale taken along the line VIl-VIl in Fig. 6; Fig. 8 is a sectional view taken along the line VIlI-VIlI in Fig. 6; Fig. 9 is a sectional view taken along the line ix-Ix in Fig. 8 (turned); Fig. 10 is a view taken along the arrow B in Fig. 6; Fig. 11 is a general view, partially in section, of an impact wrench according to a third embodiment of the invention, having a device for automatically limiting to a preset number the blows delivered to a threaded joint by the impact wrench; Fig. 12 is a view, on a larger scale and partially in section, of the device for automatically limiting to a preset number the blows delivered to a threaded joint by the impact wrench shown in Fig. 11; Fig. 13 is a sectional view taken along the line XIII-XIII in Fig. 12; Fig. 14 is a sectional view taken along the line XIV-XIV in Fig. 12; Fig. 15 shows, on a larger scale, movable and latch members of the device of Fig. 12; Fig. 16 is a view, on a larger scale, taken along the arrow C in Fig. 15.

The impact wrenches shown in Figs. 1, 5 and 11 are of a known type and are not described in detail below, and each impact wrench has an adapter casing secured at right angles to housing 1, a drive of any known type (not shown in the drawings), an impact clutch including a hammer 2 which is rotated and axially movable for imparting each blow, and a device 3 for automatically limiting the number of blows to a pre-set number of blows.

The device 3 for automatically limiting the number of blows comprises a blow number setting 4 (Figs. 2, 6, 12), a movable member 5 permanently engaging the hammer 2 and movable upon every axial displacement of the hammer 2 so as to permit the ffea passage of the hammer until a pre-set number of blows are delivered, and a counting device 6 operating in response to every displacement of the movable member 5 to permit its displacement but to lock the movable member against displacement in a position in which it prevents further axial displacement of the hammer after the ulti mate blow of the pre-set number of blows is delivered.

The counting device 6 is in a driving connection with the movable member 5.

The movable member 5 is located next to the peripheral surface of the hammer for movement at right angles to the direction of movement of the hammer 2 and is elastically urged against the peripheral surface of the hammer. The hammer 2 has an annular groove in the peripheral surface thereof to receive the movable member 5 during locking and during axial movement of the hammer 2.

The counting device 6 comprises a latch member 8 and la counting mechanism 9. The latch member 8 permanently engages the movable member 5 and is displaceable together therewith at right angles to the direction of movement of the hammer 2.

The counting mechanism 9 is engageable by the latch member 8 and is displaced upon every one of the number of displacements of the latch member 8 set by the blow number setter 4, whereafter displacement of the latch member 8 is prevented and the movable member 5 is locked.

Specific embodiments of the blow number setter 4 and counting device 6 may be differvent as shown in Figs. 2 to 16.

Thus, in the impact wrench shown in Fig. 2, the device 3 for automatically limiting the number of blows is accommodated in an adapter casing 10 rigidly secured at right angles to the housing 1 by means of screws 11 and 12, the housing 1 having an opening 13 facing the movable member 5.

In this embodiment of the device 3, the movable member 5 comprises a ball 14 received in the annular groove 7 of the hammer, and a slider 15 in contact with the ball 14 and mounted in a sleeve 16 accommodated in the adapter casing 10. A spring 17 disposed between the bottom wall of the sleeve 16 and the slider 15 elastically urges the ball 14, through the slider 15, against the peripheral surface of the hammer 2.

The slider 15 has a bore 18 extending in parallel with the direction of movement of the hammer 2, and two diametrically opposed bores 19 and 20 (Fig. 3) extending at right angles to the bore 18.

The blow number setter 4 (Fig. 2t comprises a plurality of radial bores 21 (Fig.

4) made in the adapter casing 10 along two rows extending in parallel-with the direction of movement of the hammer 2, as shown in Fig. 4, and a stop pin 22 installed in one of the bores 21 depending on the pre-set number of blows. The number of the bores 21 is equal to the maximum number of blows after delivery of which the hammer will be locked.

The counting mechanism 9 (Fig. 2) comprises a rod 23 received 'in the inner space 24 of the adapter casing 10, and a detent 25 which is urged by a spring 36 against the rod 23 and is located in the bore 20 (Fig. 3) of the slider 15 of the movable member 5 to extend at right angles to the direction of movement of the rod 23.

The rod 23 (Fig. 2) is cylindrical and has coaxial upper and lower end portions 26 and 27, respectively, of greater diameter and between which the rod is formed with a plurality of equally spaced collars 28 of the same diameter as the end portions 26 and 27.

The upper end portion 26 is provided for co-operation with the stop pin 22, and the lower-end portion 27 has a collar 29 and a handle 30 protruding from the adapter cas ing through a longitudinal slot 31 therein (Fig. 4) for lifting the rod 23 (Fig. 2) to he upper position in which is bears against the stop pin 22. In the lowermost position, the rod 23 bears against the screw 12.

The rod 23 passes freely through the bore 18 of the slider 15 and is urged by a spring 32 away from the stop pin 22, one end of the spring 32 bearing against the sleeve 16, and the other end thereof against the collar 29.

The detent 25 (Fig. 3) comprises a rod which has, intermediate the length thereof, a collar 33 whereon are two flats preventing rotation of the rod upon axial displacement thereof. The length of the detent 25 is such that one end 34 of the detent protrudes into the bore 18 and the other end protrudes to the exterior through the bore in the bottom wall of the sleeve 16 and is formed thereat with a knob 35.

The detent 25 is urged by the spring 36 which bears with the ends thereof against the bottom wall of the sleeve 16 and collar 33.

The end 34 of the detent 25 is tapered as shown in Fig. 3, and the rod 23 bears against the end 34 through the annular pro jections 28 on the rod 23.

The latch member 8 of the counting de vice 6 comprises an insert mounted in the bore 19 (Fig. 3) of the slider 15 and having a projection 8a radially protruding into the bore 18 as shown in Fig. 3. The latch mem ber 8 is located diametrically opposite to the detent 25, and the projection 8a thereof is staggered relative to the point of the end 34 of the detent 25 axially along the rod 23 as shown in Fig. 2.

With this embodiment of the device 3, axial displacement of the hammer is prevented after a pre-set number of blows are delivered in the following manner.

After the stop pin 22 (Fig. 2) is inserted into that one of the 'bores 21 which corre sponds to the number of blows required to achieve a predetermined tightening force in a threaded joint, and after the rod 23 is brought, by means of the handle 30, to the position shown in Fig. 2 (the spring 32 is compressed, and the end of the detent 25 engages one of the collars 28), the impact wrench drive is started up. As a result, the hammer is axially displaced for imparting a blow after a predetermined rotational speed is achieved. After delivery of each blow, the hammer 2 returns back to the initial position shown in Fig. 2.

During the axial displacement of the hammer 2, the ball 14 of the movable member 5 is forced radially out of the annular groove 7 of the hammer. Accordingly, the slider 15 of the movable member is also displaced in the same direction, together with the detent 25 and latch member 8. Thus, the end 34 of the detent 25 disengages from the collar 28, and the rod 23 is displaced axially under the action of the spring 32 until the same collar 28 engages the projection 8a of the latch member 8.

After the blow is delivered, the hammer 2 returns back into the initial position. At the same time, the movable member 5 and the latch member 8, which are acted upon by the spring 17, and the dete.nt 25, which is acted upon by the spring 36, are also moved radially back into the initial position, and the ball 14 of the movable member enters the annular groove 7 of the hammer. After the latch member 8 disengages from the collar 28, the rod 23 is moved axially until the next collar 28 bears against the tapered end 34 of the detent 25.

Therefore, after the delivery of one blow, the rod 23 is displaced by the amount of one spacing of the collars 28. At every subsequent movement of the hammer (upon every blow), the rod 23 is consecutively displaced by one said spacing. After delivery of the ultimate blow, which is determined by the position of the stop pin 22, the upper end portion 26 of the rod 23 is positioned against the end 34 of the detent 25 to prevent further radial movement of the latter, and hence the displacement of the movable member 5. As a result of the engagement of the latch member 8 with the upper end por tion 26 of the rod 23, the ball 14 cannot leave the annular groove 7 in the hammer and thus obstructs the axial passage of the hammer 2. The hammer 2 cannot be axially displaced for imparting a blow, and the tightening is stopped.

Therefore, after delivery to the threaded joint of a pre-set number of blows required to obtain a predetermined tightening force, the hammer 2 of the impact wrench is automatically locked, and excessive blows are not imparted with the drive still operating.

For tightening the next threaded joint, the drive is stopped, the rod 23 is then brought into the position in which it bears against the stop pin 22, and the drive is started up so that the impact wrench again functions as described above.

When it is necessary to deliver a different number of blows, the detent 25 is moved radially by means of the knob 39 to disengage it from the collar 28 so that the rod 23 is moved under the action of the spring 32 to the lowermost position, and the stop pin 22 is inserted into another bore 21. Then the detent 25 is released to be displaced under the action of the spring 36 to bear against the end face of the upper end portion 26. The rod 23 is then lifted by means of the handle 30 to bear against the stop- pin 22, and the position of the rod is fixed by the detent 25. The impact wrench can be now used for tightening a threaded joint, and the hammer 2 will be locked after the delivery of a pre-set number of blows corresponding to a new position of the stop pin 22 and to another predetermined tightening force, In the impact wrench shown in Figs. 5 and 6, the mechanisms of the device 3 for automatically limiting the number of blows are made in the following manner.

The movable member 5 (Fig. 6) comprises a ball 37 received in the annular groove 7 in the hammer and a slider 38 in permanent contact therewith mounted in a sleeve 39 accommodated in an adapter casing 40 which is secured at right angles to the housr ing 1. The ball 37 is elastically urged, through the slider 38, against the peripheral surface of the hammer 2 by a spring 41 (Fig. 7) which is located between the slider 38 and the bottom wall of the sleeve 39.

A recess 42 is made in the slider 38 to extend in parallel with the direction of the hammer movement, and there are provided two diametrically opposed bores 43 and 44 extending at right angles to the recess 42.

The counting mechanism 9 (Fig. 6) comprises a rotatable disc 45 indented along a portion of the periphery thereof to provide teeth 46 (Fig. 8) which are equally spaced circumferentially of the disc 45, the remaln- ing portion 47 of the disc periphery being uninterrupted.

The disc 45 (Fig. 6) is partially received in the recess 42 of the slider 38 and is mounted on a shaft 48 extending at right angles to the direction of movement of the hammer 2.

The number of the teeth 46 of the disc 45 is equal to the maximum number of blows after the delivery of which the hammer is locked.

As shown in Fig. 6, the shaft 48 is mounted in the adapter casing 40 with the end of the shaft remote from the housing 1 protruding from the casing 40 to the ex terior and having fixed thereon a knob 49.

A torsion spring 50 mountesd about the shaft 48 has one end: secured to- the disc 45 and the other end to the adapter casing 40.

The blow number setter 4 comprises a plate 51 (Fig. 8) which is fixed through one end thereof to the shaft 48 for rotation with the latter, and a stop 52 fixed to the disc 45 (Fig. 6).

The distal end of the plate 51 has a projection 53 which is formed by the bent end of the plate as shown in Fig. 9. The plate 51 is mounted with the projection 53 received between any adjacent teeth of the disc 45 depending on the pre-set number of blows after the delivery of which the hammer should be locked.

Apart from the disc 45, the counting mechanism 9 also includes a detent 54 (Figs.

6 and 7) which comprises a rod mounted in the bore 44 of the slider 38 at right angle to the disc 45, the rod having a tapered inner end 55 for engaging the teeth 46 of the disc 45 and an outer end which protrudes from the sleeve 39 through a hole in the bottom wall thereof and terminates a knob 56.

The detent 54 has a collar 57 whereon are two flats which prevent rotation of the detent during the displacement thereof. The detent 54 is urged by means of a spring 58 one end of which bears against the collar 57 and the other end of which bears against the bottom wall of the sleeve 39.

The latcr member 8 comprises a projection 59 which is- located in the bore 43 of the slider 38 diametrically opposite to the detent 54 in such a manner that the end of the projection 59 is within the recess 42, the end of the projection being staggered relative to the tip of the tapered end 55 of the detent 54 in the direction of rotation of the disc 45.

A pointer 60 is provided on the knob 49 (Fig. 6) and a scale 61 is made on the adapter casing 40 so that a pre-set number of blows may be set up.

A spring 61a is located between the plate 51 and the casing 40.

With the embodiment of the device 3 described with reference to Figs. 5 to 10, the axial displacement of the hammer 2 is prevented after a pre-set number of blows are delivered, in the following manner.

After the projection 53 (Fig. 9) of the plate 51 is placed in one of the indents between the teeth 46 of the disc 45 corresponding to a pre-set number of blows (to a predetermined tightening force of a threaded joint) and after the disc 45 (Fig. 6) and the p]ate 51 are rotated by means of the knob 49 until the plate 51 bears against the sleeve 39 of the movable member 5, the impact wrench drive is started up, and the hammer is axially displaced to deliver a blow after a predetermined rotational speed is achieved.

During the axial displacement of the hammer 2, the ball 37 of the movable member 5 is forced out of the annular groove 7 of the hammer 2 to displace the slider 38 at right angles to the hammer movement and to compress the springs 41 and 58. Concurrently, with the displacement of the slider 38, the detent 54 and the latch member 8 are also moved in the same direction. Thus the tapered end 55 of the detent 54 (Fig. 7) leaves the indent between two adjacent teeth 46 of the disc 45 so that the disc 45 and the plate 51 the rotated by the torsion spring 50 until the end 59 of the latch member 8 enters the indent between the same teeth 46.

After the blow is delivered, the hammer 2 returns back to the initial position; concurrently, the detent 54, which is acted upon by the spring 58, and the movable member 5, which is acted upon by the spring 41, also return back to the initial position so that the ball 37 enters the annular groove 7 of the hammer. Thus, after the latch 8 leaves, together with the movable member 5, the indent between the teeth 46, the disc 45 is rotated until the next tooth 46 bears against the tapered end 55 of the detent 54.

Therefore, after the delivery of one blow, the disc 45 is rotated through one spacing of the teeth 46. The disc will be rotated consecutively every time through one spacing of the teeth upon every subsequent displacement of the hammer 2 (upon every blow).

After the delivery of the ultimate blow which is determined by the position of the plate 51 relative to the disc 45, the uninterrupted portion 47 of the periphery of the disc 45 is positioned under the end 59 of the latch member 8 thus preventing further radial movement of the latter, and the stop 52 bears against the sleeve displaced by the protruding end 56 thereof to disengage the detent 54 from the tooth 46 of the disc 45. The disc 45 is rotated by the spring 50, and the stop 52 bears against the sleeve 39. Then the knob 49 is unscrewed, the projection 53 of the plate 51 is withdrawn from the indent between the teeth 46 by pressing on the shaft 48 and is placed in a new position after appropriately rotating the shaft 48. Then the knob 49 is screwed on the shaft 48 to fix the projection 53 of the plate 51 in the respective indent. The detent 54 is released to be displaced by the spring 58, and the tapered end 55 of the detent enters the indent between the teeth 46 of the disc 45. After the disc 45 is rotated so that the plate 51 bears against the peripheral surface of the sleeve 39, the impact wrench can be used for tightening threaded fasteners, and the automatic locking of the hammer 2 will be effected after the delivery of a pre-set number of blows corresponding to a new position of the plate 51 and to a different predetermined tightening force of threaded joint.

In the impact wrench shown in Fig. 11, the device 3 for automatically limiting the number of blows is accommodated in an adapter casing 62 and the mechanisms of the device are made in the following manner.

The movable member 5 (Fig. 12) comprises a slider 63 having a collar 64 and a ball bearing 65 mounted on an axle 66 and received in the annular groove 7 in the hammer 2, the slider and bearing being accommodated in the adapter casing 62 to extend at right angles to the direction of movement of the hammer 2. The movable member 5 is elastically urged against the hammer 2 by means of a spring 67 having its ends bearing against the collar 64 of the slider 63 and a shoulder of the casing 62.

The blow number setter 4 comprises two series, mutually at right angles, of equally spaced pairs of diametrically-aligned bores 68 made in a cylindrical portion of the casing 62 along a line extending at right angles to the direction of movement of the hammer 2, the number of said pairs of bores in each series being equal to the maximum number of blows, and a stop pin 69 which is inserted into the bores 68 of one of said pairs, depending on the pre-set number of blows.

The counting mechanism 9 comprises a rod 70 extending at right angles to the hammer 2 and urged by a spring towards the hammer, a detent 71 comprising a leaf spring secured at one of its ends to the casing 62, and a rotatable sleeve 72 which is connected to the housing 1 by means of a torsion spring 73.

The rod 70 is provided intermediate its length with a collar 74, the length 70 of the rod, which extends from the collar towards the hammer, being provided with ratchet teeth 75 equal in number to the number of pairs of diametrically-aligned bores 68 in each series. The spacing of the ratchet teeth 75 is equal to the spacing of the bores 68.

The rod 70 is provided with two flats 76 and 77 of different length (Fig. i 3), the flat 77 extending over the length 70a of the rod 70 and terminating at the collar 74, and the flat 76 (Fig. 14) extending over the length 70a of the rod 70 and over the collar 74.

The end of the length 70b (Fig. 12) of the rod 70, at the other side of the collar 74 from the length 70a, is adapted to cooperate with the stop pin 69.

The distal end of the detent 71 engages the ratchet teeth 75 of the rod 70.

The rotatable sleeve 72 is mounted outside the casing 62 and is located between the casing 62 and the housing 1 of the impact wrench opposite to the collar 74 of the rod 70.

The casing 62 has slots 78, 79 (Fig. 14) extending over a part of the peripheral surface of the casing 62 and located opposite to the collar 74 of the rod 70. A pin 80 received in the slots 78 and 79 is fixed to the sleeve 72 to extend along a chord of the sleeve and to engage the flat 76 of the collar 74 for rotation of the rod 70 by turning the sleeve 72.

The sleeve 72 has an internal thread 81 (Fig. 12) through which is screwed into the sleeve 72 a lateral handle 82 of the impact wrench having a rubber sheath 83.

The latch member 8 (Figs. 12 and 15) comprises a leaf spring 84 which is located diametrically opposite to the detent 71. One end of the leaf spring 84 is secured to the slider 63 and the other end engages the teeth 75 of the rod 70.

The slider 63 has flats 85 (Fig. 16) engaging a recess in the housing 1 (not shown) to prevent rotation of the slider.

A return spring 87 is located between the collar 74 of the rod 70 (Fig. 12) and a shoulder 86 of the casing 62.

With the embodiment of the device 3 described with reference to Figs. 11 to 16, axial displacement of the hammer 2 is prevented, after a pre-set number of blows are delivered, in the following manner.

Prior to the beginning of the operation, the lateral handle 82 is unscrewed, and the stop pin 69 is inserted into the pair of diametrically aligned bores 68 which corresponds to a number of blows after the de livery of which the hammer should be automatically locked. After the handle 82 is back in place, the operator sets the impact wrench at the threaded joint by holding it at a handle 88 (Fig. 11) and at the lateral handle 82. All parts of the impact wrench are initially in the position shown in Fig. 12.

After the drive of the impact wrench is started, the hammer 2 is axially displaced in the housing 1. During this displacement loif the hammer 2, the ball bearing 65 is forced out of the annular groove 7 in the hammer and, by acting on the slider 63, causes the displacement of the latch member 8 (leaf spring 84) to compress the spring 67. As a result, the rod 70 of the counting mechanism 9 is displaced by one tooth 75 to compress the return spring 87. During the return stroke of the hammer 2, the slider 63 is displaced by the spring 67, and the ball bearing 65 re-enters the groove 7 in the hammer, and the latch member 8 returns back to the initial position (engages the tooth 75 of the rod 70) under the action ofthe spring 67, while the detent 71 prevents the rod 70 from moving backwards. Then the device 3 functions as described above until the end face of the rod 70 bears against the pin 69 inserted into one of the bores 68.

In this position, the slider 63 cannot be moved due to the engagement of the latch member 8 with the fixed rod 70 so that the ball bearing 65 cannot leave the annular groove 7 in the hammer thus obstructing the axial passage of the hammer and thereby eliminating the possibility of delivery of further blows by the hammer.

Then the operator stops the impact wrench drive, and during the transfer of the impact wrench to the next threaded joint, turns the lateral handle 82. The sleeve 72 is thus rotated to overcome the resistance of the torsion spring 73 so that the pin 80 acts on the flat 76 of the rod 70 to rotate the rod and to disengage it from the latch member 8 and detent 71. As a result, the rod 70 is urged by the return spring 87 towards the hammer 2.

Then the operator releases the handle 82, and the sleeve 72 returns back into the initial position under the action of the torsion spring 73 to bring the rod 70 into the position in which its teeth 74 are located opposite to the detent 71 and latch member 8.

The impact wrench is then ready for operation.

The arrangement of the device 4 in the lateral handle 82 enables reduction in size of the impact wrench.

WHAT WE CLAIM IS:- 1. An impact wrench comprising a housing; a drive; an impact clutch connected to the drive and comprising a hammer which is axially movable for imparting each blow, and a device for automatically limiting to a preset number the blows imparted by the hammer, said device comprising means for setting the number of ,blows, a movable member directly co-operating with the hammer and displace.able upon every axial displacement of the hammer to permit the axial displacement of the hammer until the pre-set number of blows are delivered, and a counting device engageable with the movable member to be displaced in response to every displacement of the movable member and cooperable with the blow number setting means to preset the number of displacements of the counting device before the movable member is locked against displacement in a position in which it obstructs further axial movement of the hammer.

2. An impact wrench as claimed in Claim 1, wherein the movable member is in permanent engagement with the peripheral surface of the hammer, and the hammer has an annular groove on the peripheral surface thereof to receive the movable member.

3. An impact wrench as claimed in Claim 2, wherein the movable member is elastically urged against the peripheral surface of the hammer.

4. An impact wrench as claimed in any one of Claims 1 to 3, wherein the counting device comprises :a latch member which is in permanent engagement with the movable member and which is displaceable together therewith in the direction at right angles to the direction of the hammer movement, and a counting mechanism which is engageable by the latch member and which is displaceable in response to every displacement of the latch member.

5. An impact wrench as claimed in Claim 4, wherein the blow number setting device comprises a plurality of radial bores made in an adapter casing secured at right angles to the housing, said bores being along a line extending in parallel with the direction of the hammer movement, and a stop pin inserted into one of the radial bores depending on the pre-set number of blows, the counting mechanism comprises a rod urged by a spring away from the stop pin and passing freely through a bore of the movable member, the rod having a plurality of equally spaced annular projections and a cylindrical end portion, and a detent urged by a spring against the rod which is mounted in the movable member to extend at right angle to the direction of the rod movement, the detent having one end which is tapered for engaging the annular projections of the rod and the other end protruding frorrt the housing, the latch member is located diametrically opposite to the detent in the bore of the movable member and has a projection which is displaced relative to the detent axially along the rod.

6. An impact wrench as claimed in Claim 4, wherein the counting mechanism comprises a rotatable disc partially received in a recess of . the movable member and mounted on a shaft extending at right angles to the direction of the hammer movement, the disc, being csnnected -to an adapter cas 'ing by a torsion spring and having equally

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. in the housing 1. During this displacement loif the hammer 2, the ball bearing 65 is forced out of the annular groove 7 in the hammer and, by acting on the slider 63, causes the displacement of the latch member 8 (leaf spring 84) to compress the spring 67. As a result, the rod 70 of the counting mechanism 9 is displaced by one tooth 75 to compress the return spring 87. During the return stroke of the hammer 2, the slider 63 is displaced by the spring 67, and the ball bearing 65 re-enters the groove 7 in the hammer, and the latch member 8 returns back to the initial position (engages the tooth 75 of the rod 70) under the action ofthe spring 67, while the detent 71 prevents the rod 70 from moving backwards. Then the device 3 functions as described above until the end face of the rod 70 bears against the pin 69 inserted into one of the bores 68. In this position, the slider 63 cannot be moved due to the engagement of the latch member 8 with the fixed rod 70 so that the ball bearing 65 cannot leave the annular groove 7 in the hammer thus obstructing the axial passage of the hammer and thereby eliminating the possibility of delivery of further blows by the hammer. Then the operator stops the impact wrench drive, and during the transfer of the impact wrench to the next threaded joint, turns the lateral handle 82. The sleeve 72 is thus rotated to overcome the resistance of the torsion spring 73 so that the pin 80 acts on the flat 76 of the rod 70 to rotate the rod and to disengage it from the latch member 8 and detent 71. As a result, the rod 70 is urged by the return spring 87 towards the hammer 2. Then the operator releases the handle 82, and the sleeve 72 returns back into the initial position under the action of the torsion spring 73 to bring the rod 70 into the position in which its teeth 74 are located opposite to the detent 71 and latch member 8. The impact wrench is then ready for operation. The arrangement of the device 4 in the lateral handle 82 enables reduction in size of the impact wrench. WHAT WE CLAIM IS:-

1. An impact wrench comprising a housing; a drive; an impact clutch connected to the drive and comprising a hammer which is axially movable for imparting each blow, and a device for automatically limiting to a preset number the blows imparted by the hammer, said device comprising means for setting the number of ,blows, a movable member directly co-operating with the hammer and displace.able upon every axial displacement of the hammer to permit the axial displacement of the hammer until the pre-set number of blows are delivered, and a counting device engageable with the movable member to be displaced in response to every displacement of the movable member and cooperable with the blow number setting means to preset the number of displacements of the counting device before the movable member is locked against displacement in a position in which it obstructs further axial movement of the hammer.

spaced teeth along a portion of its periphery, and a detent urged by a spring against the disc and mounted in the movable member to extend at right angles to the disc, one end of the detent being tapered for engaging the disc teeth and the other end protruding from the adapter casing, the blow number setting device comprises a plate which is fixed to the shaft for rotation together therewith and has a distal end provided with a projection received between the disc teeth depending on the pre-set number of blows, and a fixed stop mounted to the disc, and the latch member is located opposite to the detent in a bore of the movable member and has a projection staggered relative to the detent in the direction of disc rotation.

7. An impact wrench as claimed in Claim 4, wherein the blow number setting device comprises a plurality of bores made in an adapter casing, said bores being along a line extending at right angles to the hammer movement, and a stop pin inserted into one of the bores depending on the pre-set number of blows, the counting mechanism comprises a rod extending at right angles to the hammer and urged by a spring theretoward, said rod being provided intermediate its length with a collar and having ratchet teeth over its length which extends from the collar towards the hammer, the number of teeth being equal to the number of the bores and the spacing of the teeth being equal to the spacing of the bores, said rod also having two diametrically opposed flats at its length with the ratchet teeth, one flat terminating at the collar and the other flat extending over the entire length of the collar, a detent comprising a leaf spring secured to the adapter casing, the distal end of the spring engaging the ratchet teeth of the rod, and a sleeve mounted outside the adapter casing between the latter and the housing in the region of the collar of the rod, said sleeve being connected to the housing by means of a torsion spring and having a pin received in slots made in the adapter casing, the latch member comprises a leaf spring which is located diametrically opposite to the detent and is secured at one of its ends to the movable member, the other end of the latch member engaging the ratchet teeth of the rod.

8. An impact wrench as claimed in Claim 7, wherein the adapter casing is accommodated in a lateral handle of the impact wrench.

9. An impact wrench substantially as hereinabove described with reference to Figs. 1 to 4 of the accompanying drawings.

10. An impact wrench substantially as hereinabove described with reference to Figs.

5 to 10 of the accompanying drawings.

11. An impact wrench substantially as hereinabove described with reference to Figs.

11 to 16 of the accompanying drawings.