US2720956A - Impact wrenches - Google Patents

Description

Oct. 18, 1955 Filed Oct. 17, 1951 F. B. COOMBES IMPACT WRENCHES 2 Sheets-Sheet l Oct. 18, 1955 a COQMBES 2,720,956

IMPACT WRENCHES Filed OCT 17, 1951 2 Sheets-Sheet 2 United States Patent Oflfice 2,720,956 Patented Oct. 18, 1955 IMPACT WRENCHES Frank B. Coombes, Hale, England, assignor to Holman Brothers Limited, Camborne, Cornwall, England Application October 17, 1951, Serial No. 251,671

Claims. (Cl. 19230.5)

This invention relates to impact wrenches, that is devices of the class in which a succession of rotational hammer blows are imparted through an anvil to a member, such as a nut or bolt, which offers considerable resistance to rotation. More particularly, the invention relates to impact wrenches of the kind in which a driving member, a hammer and an anvil rotate together until the resistance to the rotation of the anvil exceeds the driving torque applied to the hammer, after which the hammer is alternately disengaged from the anvil, the driving member rotating ahead of the hammer and storing energy during the disengaging movement, and re-engaged with the anvil, the stored energy imparting an angular acceleration to the hammer during the re-engaging movement so that it strikes a blow against the anvil upon re-engagement.

In accordance with the present invention the energy for the subsequent acceleration of the hammer is stored by the compression of air or other compressible fluid in a trapped space. This arrangement not only avoids the use of springs or other resilient bodies which are subject to fatigue, but also allows continuous adjustment of the magnitude of the impacts delivered by the hammer to be effected in a very simple manner, namely by varying the initial pressure of the trapped fluid. The nature of the invention will otherwise sufficiently appear from the appended claims when read in the light of the following description of the particular form of impact wrench constructed in accordance with the invention which is shown in the accompanying drawings.

In these drawings:

Figure 1 shows a longitudinal section through the Wrench, the forward end of the wrench being shown at the bottom of the drawing;

Figure 2 is a view similar to Figure l with the parts in difierent relative positions;

Figures 3 and 4 show side elevations of the parts coupling together the driving mem er and the hammer of the wrench in the relative positions which they occupy in Figures 1 and 2 respectively;

Figure 5 shows a ransverse section through the coupling between the hammer and anvil of the wrench;

Figures 6 and 7 are views corresponding respectively to Figures 3 and 4 of a modified coupling between the driving member and the hammer.

Referring to these drawings, a casing 10 accommodates a reversible compressed air motor of conventional design (not shown) or other suitable power means. The motor shaft 11 carries the run wheel 12 of an epicyclic reduction gear, the outer ring of this gear being formed on a member 13 secured between the forward end of casing it) and the rear end of a front casing 14. The planet pinions 15 of the epicyclic gear are carried on a piston member 16, which rotatably supports the forward end of motor shaft 11 and is supported by a bearing 17 within the member 13. Rotation of shaft 11 in either direction causes rotation at a lower speed of the piston member 16, which constitutes thedriving member of the Wrench.

Projecting from the front face of the piston 16 is a spill 16a which extends through a hammer member 18 and is rotatably supported at its front end in an anvil member 19. The anvil is rotatably supported by a bush 20 Within the front end of the casing member 14 and its projecting front end carries a chuck 21 shaped for engagement with the nuts or other parts which it is desired to rotate.

The hammer 18, which is axially movable Within the casing 14, is of double cylindrical form, having a disc portion which is slidable upon the spill 16a and cylindrical portions extending forwardly and rearwardly from the periphery of the disc. The rearwardly extending cylinder engages slidably over the periphery of the piston 16, while the forwardly extending portion carries at its front end a pair of forwardly projecting dogs 22, adapted to engage between a pair of rearwardly extending dogs 23 on the anvil 19 when the hammer 18 is in its forward position (as in Figure l) and to be withdrawn clear of the anvil dogs when the hammer is in its rearward position (as in Figure 2).

Disposed within the front cylindrical portion of the hammer 18 are a pair of annular cams, the rear cam 24 being attached by dowels 25 to the disc portion of the hammer 18, while the front cam 26 fits upon a portion of the spill 16a which is of square or other non-circular ross section, so that it is keyed to the spill and rotates with the driving member 16. This arrangement of the cams makes it a simple matter to remove and replace them if they become worn. The opposed faces of the two annular earns 24, 26 are each formed with two recesses of flattened V form (see Figures 3 and 4) and each pair of opposed recesses in the two cams accommodates a free ball 27.

An axial bore 28 in the motor shaft 11 communicates at its rear end with a source of compressible fluid under pressure, which may conveniently be the air supply of the motor when a compressed air motor is used. Bore 28 is open at its front end to an axial bore 29 in the piston 16 and its spill 16a. A radial bore 30 in the spill connects the axial bore to the trapped space 31 formed between the front face of the piston 16 and the rear face of the disc portion of the hammer 18. 'On the motor side of the radial bore 30, the bore 29 is formed with a valve seat, against which a valve ball 32 is pressed by a spring 33 to close communication between bore 28 and trapped space 31. Spring 33 is accommodated in bore 29 and is stressed by a plug 34, screwthreaded into the front end of the spill bore. It will be appreciated that by adjusting this plug 34, which is accessible through an axial bore in the anvil 19, the pressure of air admitted to the trapped space 31 can be adjusted to any desired value up to that of the air supply to the motor. To minimize escape of air from the trapped space, seals are provided between the piston and the rear cylin drical portion of the hammer at 35, between the spill and the disc portion of the hammer at 36, between the motor shaft and the piston at 37 and between the adjusting plug and the spill at 38.

With the parts in their normal relative positions, as shown in Figures 1 and 3, the hammer 18 is held forward by the pressure of air in the trapped space 31, so that the free balls 27 rest in the bottoms of the recesses in the two annular earns 24, 26 and the hammer dogs 22 project into the spaces between the anvil dogs 23. If the chuck 21 is engaged with a nut and the motor started, the parts remain in their normal relative positions while the nut is being spun freely up its bolt, the driving member 16, hammer 18 and anvil 19 rotating together. When the resistance offered by the nut exceeds a certain limiting value, the anvil and the hammer are held against rotation, but the driving member continues to rotate.

compressing the the trapped space;

The rotation of the front cam 26 (fast to the driving m m er) r la i e to he rear 24. st o. the ham: mer) causes the free balls 27 to roll up the inclined faces of the recesses in the cams 24, 26, as shown in Figu e and. forces the hammer rearwardl ,thereby When the hammer has moved back sufficiently for its dogs 22 to cl ar the anvil dogs 23, the hammer begins to rotate, the dogs 22; passing over. dogs 23 as shown in Figure 2. Immediately the two sets of dogs are clear of one another, the hammer is forced forward by the pressure of air in the trapped space and the hammer dogs 22 re-enter the spaces between the anvil dogs 23. The advance of the rear Cam 24 towards the front cam 26 causes the balls 27 to roll down the, slopes of the cam recesses and accelcrates the hammer to a greater rotational speed than the drivingmember. Accordingly, when the hammer dogs 22 again strike the anvil dogs 23 they impart a substantial impact to thelatter. This cycle of operations is automatically repeated, twice during each revolution of the driving member. The acceleration of the hammerduring its forward movement being dependent upon the pressure in the trapped space 31, the magnitude of the impacts produced can be. adjusted byaltering the setting of the screw plug 34. l a

Therecesses in the cams 24, 26 are made of V shape, with two equal and opposite slopes, so that the wrench will operate in precisely the same way for either direction 'of. rotation. The cam surfacesmay have a constant slope throughout their length, or the slope may vary, so that the rearward movement of the hammer is at first fast and is later slowed down. Instead of making the recesses in the two cams similar in shape, the angle of slope of one cam may be greater than that of the other. Indeed, as shown in Figures 6 and 7, one cam may be replaced by a flat thrust plate 39, all the cam action being contained in one cam 40.

Whatlclaim is: a r

:1. Anirnpact wrench of the type defined comprising a rotatable driving member having a'piston portion and a spilLpoflion extending forwardly from the piston portion, a rotatable and reciprocable hammer having a rear cylindrical portion engaging fluidtight over the piston portion of the driving member, a disc portion engaging fluidnight around the spill portion of the driving member and a front cylindrical portion carrying forwardly projecting dogs, a rotatable anvil coaxial withsaid driving member and carrying rearwardly projecting dogs adapted for engagement by said hammer dogs, a ball track on the forward face of said disc portion of thehammer, a second balltrack spaced forwardly from said first ball'track and secured on said spill portion of the driving member, aplurality of free balls engagedbetween said ball track,

' said driving member'being'formed-with 'a fluid inlet pas sage communicating with the space enclosed between the driving member and'the hammer, a non-return valve in said fluid inlet passage Spring means tending to close said valve and means for adjusting the, pressure exerted onsaid valve by'said spring means.

2. An impact-wrench of the type defined comprising a rotatable driving member, a rotatable anvil coaxial'with the driving member, a hammer disposed between the driving member and the anvil, the hammer and driving member being arranged to enclose between them a fluidtight space, saidhammer being-capable of reciprocating relative to'the drivingmember and the 'anvil'to vary the volume of said space, valve means for admitting compressible fluid under pressure into said space, said valve 4 spill portion extending forwardly from the piston portion, a rotatable and reciprocable hammer having a rear cylindrical portion engaging fluid-tight over the piston portion of the driving member, a disc portion engaging fluid-tight around the spill portion of the driving member and a front cylindrical portion carrying forwardly projecting dogs, an anvil coaxial with the driving member rotatably supported on the forward end of said spill por tion and carrying rearwardly projecting dogs adapted for engagement by said hammer dogs, said driving member being provided with a fluid inlet passage communicating with a fluid-tight space enclosed between said driving member and said hammer, a non-return valve in said fluid inlet passage, spring means tending to close said valve, and manually and externally operable means for adjusting the pressure exerted on said valve by said spring means. V

4. An impact wrench of the type defined comprising a rotatable driving member having a piston portion and a spill portion extending forwardly from the piston portion, a rotatable and reciprocable hammer having a rear cylindrical portion engaging fluid-tight over the piston portion of the driving member, a disc portion engaging fluid-tight around the spill portion of the driving member and a front cylindrical portion carrying forwardly projecting dogs, an anvil coaxial with the driving member rotatably supported on the forward end of said spill por tion of the driving member and carrying rearwardly projecting dogs adapted for engagement by said hammer dogs, said driving member being formed with an axial bore extending throughout its length, a source of commeans preventing fluid escaping from said space when 7 said hammer moves towards said'driving member to decrease the volume of said space, andmanually operable means for adjusting said valve means so as to vary the pressure of the fluidin said space. V

3 An i mpact wrench of the type defined comprising a rotatable driving member having arpiston, portion and a pressible fluid under pressure communicating with the rear end of said axial bore in the driving member, said spill portion being formed with a transverse bore con necting said axial bore of the driving member and a fluidtight space enclosed between said driving member and said hammer, a non-return valvein said axial bore be tween said radial bore and the rear end of said axial bore, spring means in said axial bore forwardly of said valve, and plug means engaging fluid-tight in said axial bore forwardly of said spring means and longitudinally movr able in said axial bore for adjusting the pressure exerted by said spring means on said valve, said anvil being provided with an aperture through which said plug'means are accessible from outside said wrench.

5. An impact wrench of the type defined comprising a rotatable driving member having a piston portion and a spill portion extending forwardly from the piston por tion, a rotatable and reciprocable hammer having a rear cylindrical portion engaging fluid-tight over the piston portion of the driving member, a disc portion engaging fluid-tight around the spill portion of the driving member and a front cylindrical portion carrying forwardly projecting dogs, an anvil coaxial with the driving member rotatably supported on the forward end of said spill por tion of the driving member and carrying rearwardly.

projecting dogs adapted for engagement by said hammer dogs, a ball track on the forward face of said disc portion of the hammer, a second ball track spaced forwardly from said first ball track and secured on said spill portion of the driving member, a plurality of free' balls engaged between said ball tracks, said driving member being formed with an axial bore extending throughout its length, a source of compressible fluid under pressure communi: eating with the rear end of said axial bore in the driving member, said spill portion of the driving member being formed with a radial bore connecting said axialbore with a fluid-tight space enclosed between said driving member and said hammer, a non-return ball valve located in said axial bore between said radial bore and the rear end of the plug is accessible from outside of said wrench for rotation thereof and consequent longitudinal movement of said plug in said axial bore to vary the pressure exerted on said valve by said spring whereby the pressure of the fluid in said space can be varied.

References Cited in the file of this patent UNITED STATES PATENTS Thomas Aug. 30, Jimerson May 30, Worden Aug. 25, Stever Oct. 27, Thomas Jan. 30,

Emery Feb. 19,

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