US2285639A - Impact clutch - Google Patents

Description

' June 9 1942.

' A. AMTSBERG 2,285,639

IMPACT CLUTCH Filed July 5, 1941 2 Sheets-Sheet 2 ATTORNEY Patented June 9, 1942 Y i FFlCE mrAo'r ow'ron Lester A. Amtsberg, Cleveland, Ohio, assignor to Chicago Pneumatic Tool Company, New York,

N. Y., a corporation of New Jersey Application July 3, 1941, Serial No. 400,895 12 Claims. Cl.'192-30.5)

This invention relates to impact clutches by means of which a succession of rotational hammer blows may be imparted through an anvil to a driven member such as a nut or bolt which offers considerable resistance to rotation. It is concerned particularly with the type of impact clutch which comprises pivotally mounted hammer dogs driven by a force which has a component tending to rock the dog toward releasing position. A clutch of' this type is disclosed in applicants co-pending application, Serial No. 305,708, filed November 22, 1939, which contains generic claims covering the present clutch.

An object of the invention is to prolong the usefulness of the clutch parts by reducing wear, particularly between elements tending to be rubbed together under great pressure. Other objects are to strengthen the parts that are susceptible t0. breakage, and to provide a more efli-' cient distribution of forces.

A feature of the invention is a novel form of connection between the hammer dog and its associated driving cam, which allows a reduction in the moment of the declutching force on the dog.

Another feature resides in the novel shape of the impactsurfaces on the hammer dogs and as sociatedanvil, which permits release in response to the reduced declutching moment and which results in efiicient operation under varied conditions.

Another feature is an auxiliary drive between the driving cam and the hammer carrier which limits angular movement of the cam relative to the hammer assembly and prevents drag in of the dogs over the anvil during the first 90 degrees of lost-motion of the hammer assembly.

Other objects and features will appear from the description which follows.

In the accompanying drawings, which illustrate one embodiment of the invention:

Fig. l is a longitudinal section of an impact wrench, the grip handle and motor housing being shown partly in elevation and the upper end of the handle being broken away;

Fig. 2 is a cross section, as indicated by the arrows 2 in Fig. 1, showing the clutch hammer dogs i and the means for pivotally carrying them;

Fig. 3 is a side elevation of a part of the wrench a fragmentary portion of the associated driving cam being illustrated in broken lines;

Fig. 5 is a side elevation of the clutch hammer dog shown in Fig. 4, looking away from the axis 01' revolution of the clutch;

Fig. 6 is a side elevation of the rear portion of the tool head 'or anvil;

Fig. 7 is a cross section through the hammer dogs and anvil, as indicated by the arrows I in Fig. l, the clutch housing being omitted, the dogs being shown in the position they assume immediately following their release from the impact shoulders on the anvil;

Fig. 8 is a view similar to Fig. '7 but with the dogs advanced degrees;

Fig. 9 is a view similar to Fig. 7 with the dogs advanced an additional 90 degrees and at the instant of delivery of an impact;

Fig. 10 is a cross section through the hammer dogs and driving cam as indicated by the arrows m in Fig. 1, theclutch housing being omitted, the hammer dogs being shown in the same posi tion as in Fig. '7; and

Figs. 11 and 12 are views similar to Fig. 10 but with the position of the dogs corresponding to Figs. 8 and 9 respectively.

In Fig. 7 and in Fig. 8, the illustration of the hammer dogs in broken lines is 90 degrees ahead of the position shown in full lines in the same figure. The principal parts of the illustrative clutch are enclosed within a clutch housing is. shown in Fig. 1. This housing is detachably secured in fixed relation to a motor housing 20 and a pistol grip handle 2| by any suitable means such as the usual arrangement of bolts and flanges (not shown)... The front end of the clutch housing is tapered and fluted at 22 to provide another grip portion.

A reversible air motor 23 within the motor housing includes a cylinder or cylinder liner 24 the ends of which abut against end plates 25. The rear end plate has a fiange 26 fitting a recess in the handle member 2| and a peripheral portion fitting the motor housing 2!]. Flange 26 surrounds and supports a ball bearing 21 held between end plate 25 and grip handle 2|. A similar ball bearing 28 is mounted in a flange, projecting forwardly from the front end plate 25. Ball bearings 21 and 28 respectively support rear and front shafts 29 and 30 integral with and projecting from a rotor 3|. The rotor'is of cylindrical shape and is arranged coaxially with its shaft and with the clutch housing ill but eccentric with the cyllnder 24 to provide a crescent shaped chamber between the rotor and cylinder, The rotor is provided with a plurality of radial slots in which blades 32 are mounted for movement with their outer edges in scraping contact with the cylinder to divide the crescent shaped chamber into a series of pockets between the inlet and exhaust ends. A reverse lever 33 controls the direction of flow of compressed air and hence the direction of rotation of motor 23. For a further description of one form of motor which may be employed to drive the clutch of the present invention, reference is made to Amtsberg United States Patent 2,077,733, April 20, 1937.

Positioned centrally of the clutch housing is a rotatable tool head or driven spindle 35 having an elongated shank 36 and having an anvil portion comprising jaws 31 adapted to receive rotational impacts as hereinafter described. Under the usual operating conditions these impacts tend to misalign the tool head axis, as it is practically impossible to manufacture an impact clutch in which both anvil jaws are always struck with the same force at exactly the same instant. Shank 36 of the tool head is supported with a rotating fit in a steel bushing 39. A resilient sleeve 40 made of oil resisting rubber surrounds the bushing and is vulcanized to the outer surface thereof. A synthetic rubber-like material known to the trade as Neoprene is suitable for this pur pose. The synthetic rubber sleeve 40 has a press fit with a counterbore 4! near the front'end of clutch housing I3 and the lower end of the sleeve rests on a shoulder extending between the counterbore and-a bore 42. The bore last mentioned is slightly larger in diameter than the steel bushing 33 and in operation metal-to-metal contact between the bushing and housing is avoided.- The upper end of the resilient sleeve terminates at an annular flange 43 supporting a similar flange on the steel bushing and seated on a shoulder of the clutch housing.

The rear end of the tool head 35 is supported in axial alignment with the steel bushing 39 and with rotor shaft 30 by means which include a pilot shaft 49 seated in complementary recesses in the rotor shaft 30 and tool head.

The hammer assembly surrounds the anvil and extends between two similarly constructed end lates which constitute carriers by which the assembly is revolubly supported. Rear carrier 50 is mounted for oscillatory movement about a bearing surface provided on the rear end of a driving cam splined to the rotor driving shaft 30. A bearing spacer 52 abuts against the rotor bearing 28 at its rear end and the driving cam 51 and hammer carrier 50 at its front end to secure the cam and carrier against rearward axial movement. A thrust plate 53 surrounding the pilot shaft 49 engages the front end of the driving cam and the rear face of the tool head 35 permitting relative rotation therebetween. Forward movement of the carrier 56 is prevented by engagement with projections radiating from the front end of the cam 5| and to be described hereinafter. The front end plate or front carrier 55 for the hammer assembly is mounted for rotary movement relative to the shank 36 of the tool head 35, a bushing 56 being interposed between the carrier and the tool head. The bushing 56 and front carrier 55 abut against a shank spacer 51 and against a thrust washer 58. The shank spacer engages the front of the anvil jaws 31 while the thrust washer seats on the steel bushing 33 whereby the tool head 35 and carriers 50 and 55 are supported against axial thrusts.

A pair of heavy hammer dogs 66, similarly constructed and arranged, are supported for oscilaesaese latory movement about pivot pins 6| which extend through openings in the dogs and carriers, the heads of the pivot pins being retained by the thrust washer 58. A pair of bolts 62 are arranged to pass through openings in the carrier plates and each bolt is surrounded by a spacer sleeve 63 whose ends abut against the carrier plates. The bolts and pivot pins are evenly spaced about the axis of revolution, as illustrated in Fig. 2 and extend parallel to the axis of revolution and cooperate with each other to hold the carriers rigidly in fixed relation to each other and to the pivot pins.

The hammer dogs 60 are capable of delivering torsional impulses to the tool head far in excess of the maximum torque of the motor 23 without resorting to reduction gearing, resilient power accumulators or spring operated clutching mechanism. The hammer dogs are positively guided, after their release from driving relation with the anvil, by complementary surfaces on the dogs and anvil until the striking surface on the hammer dog is properly oriented into the annular path of the stricken surface on the anvil. The impact surfaces are held in engagement until revolution of the hammer assembly has been arrested (relative to the anvil) and the full momentum of the hammer transferred to the anvil as a rotational hammer blow. Upon termination of the blow the hammer dogs are automatically declutched by a novel mechanism including a set of cams between the rotor shaft and the hammer dogs, which will be described hereinafter. The declutching mechanism is designed with a view toward delaying its effectiveness until the contact pressure between the hammer and anvil has been reduced in order to avoid rapid wear that would otherwise result from the rubbing action of the impact surfaces during the concurrent delivery of a blow and movement of the striking surface toward declutched position. v

The reclutching mechanism comprises an internal cam surface 65 on the dog 60, having the general shape of a sector of a cylinder whose center lies on the near side of the axis of revolution of the clutch. This internal cam cooperates with the anvil jaw 31, the periphery of which is a flat surface rounded at the corners and the sides of which constitute impact receiving shoulders or stricken surfaces 61 extending in an approximately radial direction.

Anvil shoulders 61 are driven, sometimes continuously and at other times with a succession of hammer blows, by the impact shoulders 68 which are automatically movable into and out of 'the annular path of shoulders 61. The anvil or tool head 35 also has a'pair of cylindrical surfaces 66 intermediate the jaws 31. Surfaces 66 are concentric with respect to the axis of rotation, and complement the jaws in guiding the dogs 60 while they are rotating ahead of the anvil.

In accordance with a feature of the present invention, the stricken surfaces 61, as well as the striking surfaces 68 at the opposite ends of the dogs 66, are cylindrical. At the time of impact, these cylindrical surfaces are arranged to coincide with the are 69 (Fig. 9) which is concentric with the pivot pin 6|. This permits'the dog to rock about the pivot in the declutching direction without being required to displace pivot 6| relative to the anvil.

Figs. 7, 8 and 9 show how the dog 60 is rocked from one extreme position to the other in a reclutching direction, or clockwise about pivot 6|, as it revolves through degrees, or one cycle,

in a clockwise direction about the axis of the anvil 35. Referring to Fig. 7. which shows the hammer dog 60 just'after it has been declutched, the trailing end of the internal cam 65 rides over or passes near the cylindrical surface 66 without causing any substantial movement in a reclutching direction as the dog moves from the full line to the dotted line position shown in this re. Thereafter the inner cam surface 65 engages the anvil jaw 31 and due to the eccentricity of surface 66 the dog is caused to rock in a reclutching direction. Fig. 8 shows in full lines the position of the dog after 90 degrees of rotation ahead of the anvil and it will be seen that the dog is rocked halfway toward reclutching position. The broken line illustration in Fig. 8 shows the trailing end of the internal cam 65 rubbing over the flat peripheral face of the anvil jaw 31. The dog completes its reclutching or rocking movement shortly prior to the re-engagement of the impact surfaces 61 and 68 and these surfaces are in complete registry at the time of impact. Just before the blow is struck the dog remains at the extremity of its rocking movement due to its inertia and friction. As an additional safeguard against accidental displacement of the hammer dog, it may be so mounted that the center of gravity of the weight 68 is ofiset slightly inward of the center of the pivot 6 I. Thus mounted, the weight is dynamically unstable and tends to remain at one extremity or the other of its rocking movement.

A novel mechanism is provided for declutching I the hammer dog 60 automatically upon termination of the hammer blow delivered between the impact shoulders 68 and 61. In accordance with this invention, the declutching mechanism comprises a central projection II at one end of each of the dogs 68. Driving cam 5| has a pair of projections 12 for each of the associated dogs 60, said projections defining a slot 13 therebetween. Preferably, the driving cam 5| is so designed that I the side walls of slot 13 are parallel, whereby to facilitate the cutting of the slot by a milling operation. Near the open end of the slot, each side wall is cut on a radius of about a quarter inch, the rounded portion providing a cam driving shoulder H. The cam shoulder 14 imparts force to the dog 68 along a line 15 (see Figs. 10 and 12) inward of the pivot pin 6|, thereby tending to rock the dog in a counter-clockwise or declutching direction. This rocking component of motion becomes effective to move the clutch dogs from the engaged position of Figs. 9 and 12 to the released position of Figs. 7 and 10 when the pressure of striking surface 68 against stricken surface 6! is 'suiiiciently reduced to permit relative rubbing action between said surfaces.

Another feature of the present invention re- I sides in a supplementary driving connection between the driving cam 5| and the hammer assembly. A comparison between Figs. 12 and 10 shows that the declutching movement of the dogs 68 is accompanied by a slight rotation of the and longer life of the parts which otherwise would be subjected toa rubbing action.

Preferably the shank -36 of tool head 35 is of sufllcient axial length that advantage may be taken; of the torsional elasticity of the steel. Thus, whena rotational hammenblow is delivered to the rear end of the tool head and the front end is held in engagement with a frozen nut N, the tool head twists slightly. Upon termination of the impact, the shank unwinds causing the hammer dogs 60, carrier members 58, 65

and 6!, driving cam 5| and rotor 3| to rebound as a unit in a direction opposite to the rotary impact. The rebound acts to momentarily relieve the contact pressure between the impact surfaces 61 and 68 thereby facilitating declutching and reducing the rubbing action of the impact shoulders 61 and 68 on each other.

The front end of the shank 36terminates at a socket engaging projection 19 of polygonal cross section fitting a correspondingly shaped opening in wrench socket 811 for the driven bolt or nut N. The end of the tool head and the socket have registering transverse apertures 8| and 82 which receive a locking pin 83. The pin is preferably a rigid cylindrical rod and serves to prevent accidental detachment of the socket from the tool head projection 19, but permits ready removal and replacement of the socket when that is desired. The locking pin is secured by means of an elastic retainer ring, such as rubber band 86, surrounding the pin and seated in an annular groove 81 on the socket member 80.

Briefly summarizing the operation of the illustrative embodiment of the invention let it be assumed that the operator has manipulated the throttle lever (not shown) and reverse lever 33 to admit air to the motor 23 to drive the socket in a clockwise direction, looking forward. shoulder 14 on the driving cam 5| pressesagainst the hammer dog 68 in such a direction that the dog has imparted to it a motion of revolution about the axis of tool head 35 and 'a component of forc which tends to declutch it relative to the anvil jaws 31 on the tool head. The dogs are pivotally mounted on a carrier assembly which includes the carrier plates 50 and 55 and the pivot pins BI and this assembly is carried with the dogs as they revolve. At times the driving force is supplemented by driving shoulders 11 acting direct against the spacer sleeves 63 without imparting a declutching component of force to the dogs. Assuming that the tool head does not immediately partake of the rotation of the hammer assembly, the movement of the dogs relative to the tool head is guided by the cam connection 31, 65, through the positions indicated in Figs. 7, 8 and 9 until the clutch becomes fully meshed, with the impact shoulders 61 and 68 contacting each other over their entire areas. If the resistance to rotation of the driven nut N is relatively slight, the clutch parts may remain for an appreciable time in the Fig. 9 position, all parts revolving in unison due to inertia, centrifugal force, and friction. As the nut N is being driven, the dog may occasionally be declutched to the Fig. 7 position and move into reengagement with an impact. While it is desirable to minimize impacting during the. running up operation on the driven nut, such action is not regarded as highly objectionable.

After the nut N becomes seated, the resistance to further rotation of the nut and consequently of the socket 88, tool head 35 and anvil jaws 31, increases abruptly. The pressure of the driving cam shoulder ll against the hammer dog 60, which is represented by the arrow 15 in Fig. 12 increases with the torque requirement and, when the moment of its force about the pivotal axis 6| overcomes the opposing forces the clutch disengages to the position of Figs. 7 and 10, the dog 60 being moved to its extreme counter-clockwise position relative to pivot 6|.

Immediately following the release of the ham mer assembly from the anvil it starts to revolve clockwise, moving from the full line to the dotted line position of Fig. 7, the trailing end of the internal cam 65 being held in contact with, or closely adjacent to, the cylindrical anvil surface 66 due to the declutching component imparted to the dogs 60 by the cam driving shoulder 14. The declutching component is not effective to press the dog hard against the surface 66 since it is substantially relieved by the auxiliary driving force transmitted between cam shoulder 11 and spacer sleeve 63 which does not tend to rock the dog. Accordingly, this invention reduces the wear on the dogs and anvil during the first part of the lost motion period of the hammer assembly. As the dog approaches the full line position of Fig. 8, it starts to rock about pivot 6| due to the engagement of internal cam 65 with anvil jaw 31, and the auxiliary driving shoulder 'Il ceases to be effective. Rocking movement of the dog continues as the hammer assembly revolves and increases in angular speed as the dog passes beyond the dotted line position of Fig. 8 when the trailing end of the internal cam 65 runs over the flat peripheral face of the anvil jaw 31. By the time the trailing end of the dog moves out of contact with the anvil jaw 31, it has arrived at the extremity of its rocking movement. An instant later the impact shoulder 68 at the front end of the dog strikes the corresponding shoulder 61 on the anvil jaw. The interval of time between the release of the trailing end and the impact at the leading end of the dog is too short to permit any appreciable rocking movement away from the meshing position. Moreover, any tendency to produce such rocking movement would be opposed by friction, inertia and centrifugal force.

It isimportant that rocking movement of the dog be prevented during the time that the blow is delivered as otherwise the impact shoulders 68 and 61 would rub. each other under very great pressure and thereby cause excessive wear. This invention provides improved means for delaying the start of. the rocking movement of the dog in a declutching direction until the full force of the blow has been delivered and the hammer assembly is brought to rest relative to the anvil.

It should be understood that the force of the blowis due to two factors: first, the transfer of kinetic energy previously stored in the hammer assembly, which includes the dogs 60, end plates 50 and 55, and associated connecting pins and spacer sleeves; second, the driving .force bein delivered to the dog by-the cam shoulder I4 concurrently with the delivery of the hammer blow. The factor first mentioned accounts for over 90 per cent. of the force of the blow and is directed, as indicated by the arrow 89 in Fig. 9, along the radius of the curved impact surfaces 61 and 68, whereby the greater part of the force of the blow does not set up any component tending to rock the dog. On the other hand, the friction which it develops prevents rocking movement. The second and minor factor, however, tends to rock the dog since this part of the forceis directed along the arrow 15 of Fig. 12 which is offset from the pivotal axis 6|.

In accordance with this invention, the rocking component of the force transmitted by the cam shoulder 14 is reduced to prevent this force from becoming effective prior to the completion of thedelivery of the hammer blow. This is accomplished by so designin the parts that the arrow 15 is much closer to the pivot 6| than to the center of the driving cam 5|.

After the momentum of the hammer assembly has been absorbed by the anvil, the driving force along the line 15 is effective to rock the dog to the released position shown in Figs. 7 and 10. During the declutching movement of the dog, the motor shaft 30 turns slightly but the carriers 50 and 55 and the associated pins on the hammer assembly remain stationary. It will be noticed that the arrow 15 is somewhat closer to the pivot 8| in Fig. 10 than in Fig. 12. This further reduces the effectiveness of the rocking force on the dog and prevents the dogs from dragging on the anvil during the first part of the lost motion period. As soon as the dogs are declutched, the driving unit is relieved of its load and accelerates to accumulate kinetic energy during a half turn of the motor after which the driving unit is arrested with another impact. The succession of impacts is continued as long as the operator holds the wrench socket in engagement with the torque resisting nut and continues the supply of air to the motor. If the resistance to rotation is moderate the dogs will be declutched before the driving unit comes to a complete rest relative to the wrench casing i9 although the driving unit is arrested at the time of each impact relative to the tool head 35.

The rotating parts of the illustrative embodiment are all symmetrically arranged and it will be understood without further description that the device will operate in the same manner for either direction of rotation. In operation the wrench will ordinarily be used more in one direction than in the other causing the impact shoulder 68 on one side of the hammer in to wear ahead of the impact shoulder on the other side. As shown in Fig. 5, the projection II by which the dog is driven is provided at both ends of the hammer 60 whereby the hammer may be inverted at the time of servicing to equalize wear between impact surfaces 68.

Comparing the present improvement with the illustrative embodiment of applicant's co-pending application, hereinbefore identified, the distinguishing features in general are as follows: first, the provision of the auxiliary driving shoulders 11 engageable with the spacer sleeves 63 to reduce drag of the dogs on the anvil; second, the curved shape of the impact surfaces 81 and 6|; and third, the reversal of the projection and slot connection whereby the slot 13 is provided in the driving cam 5| instead of in the dog 80.

The advantage of the curved impact surfaces 61 and 68 is that the contacting faces are always coincidental independent of small variations in engagement caused by variations in operation and manufacture. Also, in declutching, there is no component force to overcomeas in the case of a flat impact surface.

By providing the slot 13 in the cam 5|, instead of in the dog 60, it becomes possible to select any desired leverage ratio between the cam and dog. Accordingly, the parts may be so designed that the cam shoulder 14 drives along a line (see' arrow 15) as close to the pivot 6| as desired with:

out resulting in any structural weakness as would be the case if a deep slot were provided in the dog. With the declutching force directed close to the pivot 6|, its turning component is reduced to the extent that it barely overcomes friction.

Another advantage obtained in placing the slot in the cam instead of in the dog is that the slot may be larger and the cam driving surfaces I4 may be formed on alarger radius, and therefore will not readily become worn.

The resiliently mounted bushing 12 for the tool head shank 36, and the elastic retainer ring 86 for the locking pin 83 are claimed respectively in copending applications Ser. Nos. 440,173 and 440,174, filed April 23, 1942, both being divisions of application Ser. No. 305,708 aforementioned.

What is claimed is:

1. An impact clutch comprising a rotatable anvil having longitudinally extending jaws, hammer dogs revoluble in a path surrounding the jaws, a revoluble carrier for the dogs, said dogs being pivotally mounted on the carrier for limited rocking movement into and out of the path of the anvil jaws, the pivotal axes extending parallel to the axis of rotation of the anvil, means for driving the dogs, said driving means comprising a driving cam coaxial with and adjacent one end of the anvil, said cam having an open slot associated with each dog, the dog having a pro-= jection within said slot, the side wall of the slot engaging the dog to impart a force thereto extending along a line slightly oifset inwardly from the pivotal axis of the dog, whereby to rock it toward releasing position when the driving cam rotates ahead of the carrier.

2. An impact clutch comprising a rotatable drive shaft, a rotatable anvil coaxial with the drive shaft and arranged with its rear face adjacent the front face of the drive shaft, a driving cam surrounding the drive shaft and keyed thereto, a revoluble carrier assembly supported for rotation on the driving cam and .on the anvil and having longitudinal pivot pins rotatable in a path surrounding the anvil, hammer dogs pivoted on said pins and arranged to rock into and out of clutch engaging relation with the anvil, and a driving connection between the cam and the dogs, said driving connection comprising a projection on the dog extending rearwardly of the anvil, said projection being disposed between two shoulders on the driving cam, each of said shoulders being arranged to drive one of the two. opposite sides of the dog projection, whereby the cam may drive the dog in either direction of rotation, said shoulder being directed to impart a force along a line slightly inward of the pivotal axis of thedog, whereby said force is resolved into a driving and a declutching component.

3. An impact clutchaccording to claim 2 which includes complementary cam elements carried by the dogs and anvil for automatically rocking the dogs into the path of the anvil jaws, such rocking movement causing the rotation of the carrier ahead of the driving cam.

4. An impact clutch comprising a rotatable driving cam, a coaxially rotatable anvil having longitudinally extending jaws arranged in front of the cam, dogs revoluble in a path surrounding the anvil jaws, each dog having-impact shoulders at its opposite ends engageable with and releasable from the jaws and arranged to drive the anvil in either direction of rotation, each dog being mounted on a carrier for limited rocking movement about a pivotal axis extending parallel to the axis of rotation of the anvil, and a driving leasing the dog from the anvil law when the driving cam rotates faster than the carrier.

5. An impact clutch comprising a rotatable anvil having jaws, a coaxially rotatable hammer carrier, hammer dogs mounted on the carrier for rocking movement into and out of the path of the anvil Jaws to deliver a series of impacts to the anvil, a driving cam imparting force to the dogs along a line offset from the pivotal axis, whereby such force has a component tending to rock the dog toward clutch releasing position, and.

means for relieving the dogs of the releasing component of force after they are released fromthe anvil jaws, said relieving means comprising a shoulder on the driving cam engageable with a fixed part of the hammer carrier to limit relative rotation of the driving cam with respect to the carrier.

.6. An impact clutch comprising a revoluble hammer carrier having front and rear end plates and connecting elements therebetween forming a a substantially rigid structure, a coaxially rotatable anvil having longitudinally extending Jaws between the front and rear end plates, hammer dogs supported by the hammer carrier for limited relative pivotal movement about respective axes parallel to the anvil, each dog having an impact shoulder positioned to be moved into and out of the circular path of the anvil jaws in response to the pivotal movement aforesaid, a driving cam at the rear end of the anvil, said driving cam having a driving shoulder engageable with the dogs to transmit torque through the dogs to the carrier, said cam also having an auxiliary driving shoulder engageable at times with one of the connecting elements to impart torque direct to the carrier.

7. An impact clutch according to claim 6 in which the first mentioned driving shoulder is positioned to transmit force to the dog along a line slightly inward of the pivotal axis of the dog,

whereby the driving cam rotates slower than the hammer carrier while the dog is being rocked into impacting relation with the anvil jaws and rotates faster than the carrier while the dog is being released.

8. In an impact clutch, a hammer dog of generally arcuate shap'e, said dog having an inner concave surface and an outer convex surface, approximately radial walls extending between said surfaces, the dog having a bore providing a pivotal support centrally located with respect to the radial walls, front and rear end walls extending in planes perpendicular to the axis of the bore, and a projection extending beyond one of the end walls by means of which the hammer dog is adapted to be driven.

9. A clutch comprising a driven spindle-having longitudinally extending jaws, each provided with shoulders on its opposite sides by means of which the spindle may be driven in either direction, a revoluble carrier, driving dogs each supported by the carrier for limited rocking movement about a pivotal axis parallel to the axis of rotation of the spindle, each dog having at its opposite ends driving shoulders adapted to be rocked into and out of the path of rotation of the jaws, automatically operable declutching means for rocking the dogs toward releasing position while the driving shoulders are in engagement with the driven shoulders, characterized in that the driving and driven surfaces are in the shape of a sector of a cylinder, the axis of which cylinder is coincident with the pivotal axis of the dog, whereby the dog may be rocked to releasing position without displacing its pivotal axis or the associated carrier.

10. A clutch comprising a driven spindle having longitudinally extending jaws, a revoluble carrier, driving dogs each supported by the carrier for limited rocking movement about a pivotal axis parallel to the axis of rotation of the spindle, each dog having a driving shoulder adapted to be rocked into and out of the path of rotation 01' the jaws, automatically operable declutching means for rocking the dogs toward releasing position while the driving shoulders are in engagement with the driven shoulders, characterized in that the driving and driven surfaces are in the shape of a sector of a cylinder, the axis of which cylinder is coincident with the pivotal axis of the dog, whereby the dog may be rocked to releasing position without displacing its pivotal axis or the associated carrier, and whereby to prevent the reaction of the force of the blow from rocking the dog.

11. An impact clutch comprising a revoluble hammer carrier having front and rear end plates and connecting elements therebetween forming a substantially rigid structure, a coaxially rotatable anvil having longitudinally extending Jaws between the front and rear end plates, hammer dogs supported by the hammer carrier for limited relative pivotal movement about respective axes parallel to the anvil, each dog having an impact shoulderpositioned to be moved into and out of the circular path of the anvil Jaws in response to the pivotal movement aforesaid, a driving cam at the rear end of the anvil, said driving cam having a radially open slot associated with each hammer dog,. the dog having a projection extending into the slot, each 0! the opposite side walls of the slot having a driving shoulder engageable with the projection to impart torque thereto, the dog being symmetrically proportioned on opposite sides of the pivotal axis for selective driving in either direction of rotation. v

12. An impact clutch comprising a revoluble hammer carrier having front and rear end plates and connecting elements therebetween forming a substantially rigid structure, a coaxially rotatable anvil having longitudinally extending Jaws between the front and rear end plates, hammer dogs supported by the hammer carrier for limited relative pivotal movement about respective axes parallel to the anvil, each dog having an impact shoulder positioned to be moved into and out of the circular path of the anvil jaws in response to the pivotal movement aforesaid, a driving cam at the rear end of the anvil, said driving cam having a radially open slot associated with each hammer dog, the dog having a projection extending into the slot, one of the side walls of the slot having a driving shoulder engageable with the projection to impart torque thereto, the pressure of the driving shoulder against the dog projection being directed along a line slightly inward of the pivotal axis of the dog, whereby rotation of the driving cam ahead of the carrier rocks the dogs toward clutch releasing position.

' LESTER A. AMTSBERG.

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