Deceleration torque limiter for impact tools

June 9, 1959

H. C. HARRISON ET AL

2,889,902

DECELERATION TORQUE LIMITER FOR IMPACT TOOLS

Filed June 29, 1955

Sheets-Sheet 1

<img file="US2889902A_D0001.tif" />

June 9, 1959

H. C. HARRISON ET AL

2,889,902

DECELERATION TORQUE LIMITER FOR IMPACT TOOLS

Filed June 29, 1955

Sheets-Sheet 2

<img file="US2889902A_D0002.tif" />

2,889,902

Patented June 9, 1959

United States Patent Office along the line 5—5 looking in the direction of the arrows,

Fig. 6 is a vertical elevation, partly in section, of an alternate form of the torque limiting device and mounted ₅ on the hammer,

Fig. 7 is a transverse view of Fig. 6 taken along the li_ne 7—7 looking in the direction of the arrows, and

Figs. 8 and 9 are views similar to Fig. 7 showing the inertia member in different operative positions.

Referring to the drawings, and first to the form of the invention shown in Figures 1 through 6, a conventional impact tool capable of delivering a series of rotary blows in rapid succession for tightening screws, nuts and similar work is shown provided with a preferred form _lg of the torque limiting device. A complete and detailed description of the construction and operation of the impact tool is disclosed in United States Patent No. 2,160,150.

In general, the tool comprises a casing 10 housing a 20 motor 12 connected to rotate a hammer element 14. Positioned in the forward end of the casing 10, and coaxial with the hammer element 14, is an anvil element 16 having a pair of .jaws 18 arranged to engage a similar pair of jaws 20 on the hammer element 14 for trans25 mitting the rotary motion of the hammer 14 to the work (not shown). In the tool shown by way of illustration, the motor 12 rotates continuously during the entire tightening operation, whereas the hammer 14 is rotated continuously during the initial, or “run down,” portion 30 of the tightening cycle and rotated intermittently during the latter, or hammering, portion of the tightening cycle. During the hammering portion of the cycle the hammer 14 is periodically engaged to and disengaged from the anvil 16 to deliver a series of hammer blows in 35 rapid succession on the anvil.

In furtherance to this end the driving connection between a motor driven spindle 22 and the hammer 14 is in the form of a cam comprising inverted V-shaped races 26 for balls 28 which engage the forward surface 40 of an introverted shoulder 30 on the hammer 14. The hammer 14 is normally biased in the fonvard position (as shown in Fig. 1) by means of a spring 32 so that as long as the resistance to rotation of the anvil is relatively low—as for example when the work is relatively 4.5 loose—the hammer will remain engaged to the anvil and will rotate at the speed of the spindle 22. When, however, the resistance to rotation of the anvil reaches some predetermined value, depending on the degree of tightness of the work, the anvil will tend to slow down 50 the speed of rotation of the hammer 14 to a value below that of the speed of rotation of the spindle 22. The rotation of the spindle relative to the hammer 14 cams the balls 28 rearwardly moving the hammer 14 to compress the spring 32 and disengage the hammer jaws 20 55 from the anvil jaws 18. Upon disengagement of the jaws, the hammer is accelerated rotationally at the combined speed of the spindle 22 and the rotational speed imparted to the hammer relative to the spindle 22 by the spring 32 in forcing the hammer forwardly along 60 the cam to move the hammer in position to strike the anvil 16. . ,

Reviewing briefly the operation of the impact tool during a tightening cycle. During the run down portion of the tightening cycle, when the work is relatively 65 loose, the hammer 14 remains engaged to the anvil 16 and these two elements are rotated at the speed of rotation of the spindle 22. As the work is progressively tightened the resistance to rotation of the anvil is proportionally increased, and when this resistance exceeds 70 some predetermined torque, or twisting force, the hammer 14 is cammed out of engagement with the anvil

2,889,902

DECELERATION TORQUE LIMITER FOR IMPACT TOOLS

Henry C. Harrison and Henry Harrison, Port Washington, N.Y., assignors to Ingersoll-Rand Company, New York, N.Y., a corporation of New Jersey

Application June 29, 1955, Serial No. 518,758

Claims. (Cl. 192—.02)

This invention relates to impact tools, and more particularly to a torque limiting device for impact tools of the type adapted to deliver a series of rotational hammer blows in rapid succession to an anvil for rotating a work piece.

In the field of rotary impact tools there has long been a demand for a device for indicating or limiting the amount of torque, or twisting force, applied by the tool to the work, such as screws, nuts and the like. This need arises from the fact that in absence of such a device the degree of tightness—short of maximum torque of the tool—is dependent on the guess of the operator. In most circumstances it is desirable to avoid such guess work, even by an experienced operator, and in some circumstances the degree of tightness of the work must be kept within narrow limits. In the latter instance the operator after using the impact tool to tighten the work to what is believed the proper degree, is required to disengage the tool from the work and then check the tightness of the work by the use of a separate tool, such as a torque wrench.

The present invention eliminates such guess work and the need for a separate tool for checking the degree of tightness of the work by the provision of a torque limiting device responsive to the rate of deceleration of the anvil or hammer during a hammer blow. The operation of the device is correlated with the degree of tightness of the work in that the rate at which the anvil or hammer slows down during a hammer blow is dependent upon the degree of tightness of the work, or more particularly, on the resistance to rotation of the anvil by the work. Thus as the work is progressively tightened by each hammer blow, the hammer and anvil slow down after each hammer blow is struck at a proportionally increased rate. In the present invention an inertia member which is responsive to the deceleration of the anvil is mounted on the anvil or hammer and. operated whenever the rate of deceleration of the anvil exceeds some value corresponding to a predetermined degree of tightness of the work, to shut down the impact tool.

It is accordingly one object of this invention to provide a torque limiting or indicating device for rotary impact tools which is operated in response to the rate of deceleration of the anvil or hammer during a hammer blow whenever the degree of tightness of the work exceeds a predetermined value.

Further objects of this invention will become obvious from the following specification and drawings in which

Fig. 1 is a longitudinal elevation, partly in section, of a rotary impact tool provided with a preferred form of the torque limiter mounted on the anvil,

Fig. 2 is a transverse view taken through Fig. 1 along the line 2—2 looking in the direction of the arrows,

Fig. 3 is a transverse view taken through Fig. 1 along the line 3—3 looking in the direction of the arrows,

Fig. 4 is a side view of Fig. 2,

Fig. 5 is a transverse view taken through Fig. 1

2,889,902

3.

and then quickly accelerated to strike a blow on the anvil 16 to tighten the work. It is to be noted that as the work is progressively tightened the degree of rotation of the anvil 16 resulting. from each hammer blow is progressively decreased for any given speed of the hammer in striking a blow. This means that as the work is progressively tightened the rate of deceleration of the anvil and the hammer during each hammer blow is progressively increased. Accordingly there is a definite relationship between the degree of tightness of the work, or torque applied by the anvil, and the rate of deceleration of the anvil and hammer during a hammer blow. The present invention utilizes this relationship to control the amount of torque applied by the tool to the work.

In the form of the. invention shown in Figures 1 through 6, the torque limiting device is mounted on the anvil element 16. This limiter comprises, in general, an inertia member 34 mounted on the anvil element 16 for movement relative thereto in the direction of the rotation of the anvil and held against movement in the opposite direction by a stop 42. Thus when the anvil decelerates, or slows down, after a hammer blow is struck, the inertia force of the member 34 tends to move it forwardly relative to the anvil. The amount of this force is determined by the mass of the member 34 and the rate of deceleration thereof. Springs 36 are connected to the member 34 and to the anvil 16 (through sleeve 40 and keys 42) which yieldably hold the element against such relative movement so long as the rate of deceleration of the anvil 16 is below a predetermined value. When, however, the rate of deceleration of the anvil element following a hammer blow reaches a value corresponding to a predetermined degree of tightness of the work the inertia force of the member 34 will increase sufficiently to move the inertia member and compress the springs 36. Such relative movement is used to trigger a shut down mechanism to halt the operation of the tool by shutting off the motor 12.

Referring now in greater detail to the construction of the torque limiting device, it comprises the sleeved shaped inertia member 34 rotatably mounted on a sleeve 40 slid. ably, mounted on the forward end portion of the anvil 16. The sleeves 34 and 40 are keyed for rotation with the anvil 16 by means of keys 42 press fitted in the anvil 16 and extending through slots 44 and 46 in the sleeve 40 and the inertia member 34, respectively. Each slot 46 is of considerably greater arcuate length than the width of a key 42 so as to permit limited forward rotational movement of the inertia member 34 relative to the anvil 16.

In the “set” position of the inertia member each of. the keys. 42 abuts the forward, or leading (relative to the direction of the rotation of the sleeve 34), end surface 48 of the slot 46, and the forward, or lower, end of each key 42 rests on a step 50 of considerably less width than the width of the key 42. It is to be noted that the slots 44 are. of sufficient length and the depth of the slots 46 longitudinally forwardly of the steps 50 are of sufficient length that when the steps 50 are disengaged from the keys 42, the sleeves 34 and 40 are free to move longitudinally rearward along the anvil 16.

The inertia member 34 is normally urged in a direction to place the keys 42 in firm engagement with the surfaces 48 and the steps 50 by means of springs 36 received within notches 52 and 54 in the member 34 and sleeve 40, respectively (see Fig. 5). In furtherance to this end it: is to be noted that each spring 36 is mounted in such a way that its longitudinal axis is‘ inclined with respect to the longitudinal axis of the anvil 16. Thus, the force exerted by each spring 36 has a longitudinal component relative to the anvil 16 which tends to force the inertia member 34 longitudinally rearward along the anvil 16 to maintain the keys 42 in engagement with the steps 50. This force also has a tangential component which tends to rotate the inertia member 34 in a direc ⁴ tion opposite to the direction of rotation of the anvil urging the surfaces 48 into firm engagement with the keys 42.

In the form of the invention shown, a compressive 5 force is applied to the spring 36 by applying a longitudinal rearwardly directed force on the sleeve 40. In the embodiment shown this force is applied by the shut down mechanism which comprises a switch mechanism 15® and a trip mechanism 250 connected to be actuated 10 to operate the switch mechanism when the inertia member is tripped. The trip mechanism 250 includes an outer ball race 56 engaged to the sleeve 40 through ballbearings 58 riding in an inner race 60 formed in the sleeve 40. A yoke 62 is pivotally connected at 64 to 15 the outer race 56 and includes a rod 66 extending back along the tool casing 10 and through holes 68 in the tool handle 70. A spring 72 encircling the rod 66 and biased between the handle 70 and a spring retaining nut 74 threaded on the rod 66 urges the rod 66 longitudinally 20 rearward and thereby moves the sleeve 40 to compress the springs 36.

The “set” position of the elements of the torque limiting device is shown in Figures 1 and 6. The sleeve 40 is moved longitudinally rearward on the anvil 16 to a 25 position where the force of the compressed springs 36 equals the operatively directed force exerted by the spring 72. The force of the springs 36 urges the inertia member 34 into engagement with the key 42 positioned on the step 50. During operation of the tool,. the steps 50 30 of the inertia member 34 remain engaged with the keys 42 so long as the maximum inertia force of the member 34 during the slow-down period of the anvil immediately following a hammer blow does not exceed the oppositely directed component forces of the springs 36. When, how35 ever, the work has reached some predetermined degree of tightness, or torque, such that the rate of deceleration of the anvil exceeds a corresponding predetermined value, the inertia force developed by the inertia member 34 will exceed the force exerted by the springs 36 and 40 the member 34 will rotate relative to the anvil disengaging the steps 50 from the keys 42. Such disengagement will permit the springs 36 to acuate the member 34 longitudinally rearward along the anvil thereby releasing the force opposing the spring 72 permitting the rod 66 and sleeve 40 to be actuated longitudinally rearward along the tool. This longitudinal movement of the rod 66 is utilized to actuate switch mechanism 150 to stop the motor 12.

The switch mechanism shown by way of illustration in5θ eludes a pair of conventional electric switches 76 and 78 connected in series in the power supply lines 80 and 82 for the motor 12. The switch 76 mounted on the rearward end portion of the tool housing has a plunger 84 positioned to be actuated by the rearward movement of 55 the rod 66 and open the line 80 to shut down the motor 12. When the rod 66 is reset the switch 76 automatically closes and the second switch 78 is arranged to automatically open—if the trigger 98 is released—the motor power supply circuit to prevent starting the motor. ₆₀ In furtherance to this end a bell-crank 86 is pivotally mounted in the tool handle 70 with the end of one arm 88 positioned in a notch 90 in the rod 66, and the end 92 of the other arm bearing against the plunger 94 of the switch 78. A spring 96 biased between the bellcrank end 92 and the switch 78 constantly urges the crank 86 in a direction to reset the rod 66 and open the switch 73. The crank 86 is rotated in the opposite direction by means of a conventional trigger 98 mounted in the handle 70 to release the rod 66 and close the switch 78.

γθ Reviewing briefly the operation of the torque limiter and assuming the parts are positioned as shown in Fig. 1 with the switch 78 open and the switch 76 closed, the tool is started by depressing the trigger 98, closing the switch 78 to supply power to the motor 12 and.simul75 taneously moving the arm 88 to release the rod 66. As

2.889.902 suming the work to be tightened is relatively loose, the hammer 14 and anvil 16 will remain engaged and work will be rotated at the speed of rotation of the spindle 22. As the work is progressively tightened, the resistance to rotation of the anvil will increase proportionally until it reaches a value at which the spindle 22 will rotate relatively to the hammer 14 thereby camming the hammer 14 longitudinally rearward to disengage the hammer jaws 20 from the anvil jaws 18. Upon such disengagement the hammer 14 will be moved rapidly forward both rotationally and longitudinally to strike a hammer blow on the anvil. The anvil will rotate through a few degrees and stop and the hammer will again be disengaged and accelerated into position to strike another blow against the anvil. This hammering cycle is repeated rapidly so that the anvil is repeatedly accelerated from a stand-still by the hammer blows, and repeatedly decelerated to a stand-still by the resistance to rotation exerted by the work. As the work is progressively tightened the rate of deceleration of the anvil is proportionally increased until it reaches some predetermined value at which the correspondingly increasing inertia force exerted by the member 34 exceeds the oppositely directed force exerted by the springs 36. When this occurs the member 34 will rotate in the clockwise direction, as viewed in Fig. 2, relative to the anvil to disengage the steps 50 from the keys 42 thereby permitting the sleeve 40 to move longitudinally rearward along the anvil 16. The spring 72 then moves the rod 66 longitudinally rearward thereby opening the switch 76 to shut down the tool.

When the operator releases the trigger 98, the spring 96 will rotate the bell-crank 86 in the counterclockwise direction so that the arm 88 engages the notch 90 moving the rod 66 longitudinally forward to reset the torque limiting device. Specifically, such movement of the rod 66 releases the plunger 84 so that the switch 76 is closed, however, the rotation of the crank 86 also releases the plunger 96 to open the switch 78 prior to the closing of the switch 76 thereby precluding starting of the motor 12. Such movement of the rod 66 also resets the other parts of the limiter preparatory to the next tightening operation.

It is to be noted that by merely rotating the nut 74 to adjust the compressive force on the spring 73, the tangential, as well as the longitudinal, component of force on each of the springs 36 is simultaneously adjusted. Accordingly tins varies the amount of inertia force of the member 34 required to trip the limiter. Thus the degree of tightness of the work at which the limiter shuts off the tool may be readily and easily adjusted merely by rotating the nut 74.

Referring now to the alternate form of the invention shown in Figs. 7, 8 and 9 the torque limiting device operates on the same principle as discussed hereinbefore, only in this form of the invention the inertia member is mounted on the hammer.

The impact tool shown in Fig. 7 is identical in construction and operation with that shown in Fig. 1 and accordingly a description of the structure and operation will not be repeated, similar numbers are used to indicate similar parts of the two forms of the invention except that such numbers used on the alternate form are primed.

In this form of the invention the inertia member 100 is shown as a lever mounted on a pivot 114 in a transverse slot 102 formed in a hammer element 14'. The lever is mounted for transverse pivotal movement relative to the hammer and also for longitudinal movement in a direction approximately tangential to the hammer, but is normally held against such longitudinal movement by a spring 108. More particularly, the inertia member 100 in its set position (Fig. 8) is engaged by a step at one end 101 thereof to a pin 104 in the hammer. The spring 108 is connected between the opposite end of the lever 100 and a pin 110 fitted in a slot 112 in the hammer, and urges the end surface 103 of the step into engagement with the pin 104. The axis of the spring 108 is inside the pivot point 114 of the lever 100 such that the spring also exerts a pivotal force on the lever tending to swing the end 101 outwardly and thus urges the side surface 5 106 of the step into engagement with the inside of the pin 110.

It is to be noted that the lever slot 116 for the pivot 114 is somewhat elongated so as to permit limited longitudinal movement of the lever 100 in the direction of 10 rotation of the hammer and approximately tangential to the hammer away from the pin 104 so that the lever 100 may be disengaged from the pin 104. When the rate of deceleration of the hammer exceeds some predetermined value at which the component of inertia force of the lever 15 100 acting in the direction of the slot exceeds the oppositely directed force exerted by the spring 108, the lever 100 will move out of engagement with the pin 104 and will then be rotated about its pivot 114 by the spring 108.

This rotation of the lever 100 is utilized to actuate a 20 shut-down mechanism to halt the operation of the tool. In furtherance to this end a plurality of levers 118 are pivotally mounted at 122 on lugs 120 on the tool casing and extend therethrough to a point adjacent the circumference of the hammer 14'. Each lever 118 is normally 25 positioned with its longitudinal axis inclined relative to the hammer such that inner end points slightly rearward relative to the direction of rotation of the hammer 14'. The reason for this slight inclination is that when the levers 118 are rotated in the direction of the rotation of 30 the hammer 14', the inner ends of the levers will move in a direction toward the hammer 14' to reset the lever 100 as will be explained in detail hereinafter.

In order to insure that the lever 100 will strike the lever 118 whenever the former is released, the width of 35 the inner ends of levers 118 are made at least equal to the maximum longitudinal movement of the hammer 14'.

Any number of levers 118 may be provided, but at least two are required and three as shown is preferable so as to insure that the tool will be shut down shortly 40 after the inertia member 100 is disengaged and early enough in the cycle to prevent the hammer from striking an effective blow thereafter. This assumes that there are only two hammer jaws positioned 180 degrees apart. Where a greater or lesser number of hammer jaws are 45 used then the minimum required number of levers 118 may be increased or reduced accordingly.

In furtherance to the end that movement of the levers 118 stop the hammer, a switch 124 is provided in the motor power circuit which may be actuated directly by 50 a lever 118 (as shown) or by one of the links 126 which connect the outer ends of the levers 118. The links 126 are provided such that movement of any one of the levers 118 results in similar movement of the other levers 118.

It is to be noted that several slots 112 are provided, 55 each slot being positioned at a slightly different angle and distance from the lever 100. Thus by moving the pin 110 into another slot the force exerted by the spring 118 on the lever 100 may be adjusted so that the lever is disengaged at a different degree of tightness of the work. 60 Of course the same effect could be obtained by varying the strength of or tension on the spring without changing its position.

Reviewing the operation of this form of the torque limiting device, it is assumed that the hammer has com65 pleted the run-down period and is now imparting a series of hammer blows to the anvil. During the portion of a hammering cycle that the anvil 16' is being rotated, the hammer remains engaged to the anvil and is accordingly decelerated at substantially the same rate as the rate of 7₀ deceleration of the hammer. This assumes ideal operation, it is recognized that there is normally some rebound of the hammer at each impact, but this does not effect the operation of the torque limiting device. Thus, when the rate of deceleration of the anvil and hammer 75 exceeds some predetermined value corresponding to a

2,889,902 predetermined twisting force applied to the work by the tool, the inertia force of the lever 10® will overcome the force of the spring 108 and the lever 180 will move forwardly disengaging from the pin 104. The lever 100 will then be rotated about its axis 114 so that an edge surface 128 moves into the path of a lever 118. The hammer, in rotating, will move the inertia lever 100 into contact with the lever 118 so that the lever 118 is rotated about its pivot to actuate the switch 124 and shut down the motor. As the lever 118 is rotated about the axis 122, its inner end will move toward the hammer surface so that the inertia lever 100 is pivoted inwardly moving the inner edge surface 13® of the lever into contact with an inclined surface 132 on the pin 104. The lever 100 is cammed longitudinally by the surface 132 to re-engage the shoulder, or side surface, 106 with the pin 104. As the intertia member 100 moves past, or free, of the lever 118, the lever 118 will return to its normal position i.e., with its longitudinal axis inclined with respect to the circumference of the hammer 14' so that the lever 100 can not strike the lever 118.

With the switch arrangement shown by way of illustration it will be necessary, of course, to provide a snap-type switch 124 so that when the switch 124 is actuated by the inertia member 100, the motor will be shut off and will remain shut off although the switch returns to its normal position. This means that the operator will have to depress and release the switch 124 in restarting the tool.

In the forms of the invention shown, the impact tool is driven by an electric motor and the hammer is moved longitudinally to clutch and declutch with the anvil. It is to be understood that the operation of the invention is not limited to the particular form of tool shown, but may be readily adapted to air motor driven tools and tools in which the declutching action occurs in transverse plane.