Impact Wrench Drive

Abstract

An impact wrench having a torsion bar and a latch means which can be manually moved between an inoperative position, wherein the torsion bar limits the torque delivered by the wrench to a fastener, and an operative position, wherein the wrench anvil is connected substantially rigidly to the fastener to deliver an increased torque to the fastener.

Description

BACKGROUND OF INVENTION

This invention relates to the art of rotary impact wrenches and, more particularly, to the type of impact wrench utilizing a torsion bar between the wrench and a fastener driving socket for limiting the amount of torque delivered to a fastener.

Torsion bars are conventionally used with impact wrenches for limiting the amount of torque delivered to a fastener to prevent the impact wrench from overtightening and damaging the fastener, which can easily occur without the use of a torsion bar. For example, impact wrenches with torsion bars are used for both tightening and removing fasteners. In removing fasteners, an occasional fastener will be so tight that the wrench is incapable of removing it using a torsion bar. When this occurs the mechanic must stop the wrench, remove the socket from the torsion bar, remove the torsion bar from the wrench, and replace the socket on the wrench before proceeding to remove the fastener. Thereafter, the torsion bar must again be replaced on the wrench before the mechanic uses it to tighten a fastener. All of this removal and remounting of the torsion bar is an annoyance and an uneconomical waste of a mechanic's time.

SUMMARY OF INVENTION

The principal object of this invention is to solve the foregoing problem by substantially reducing the waste of a mechanic's time using an impact wrench equipped with a torsion bar.

Another important object of this invention is to provide an impact wrench wherein an operator can quickly and easily shift the impact wrench, during the operation of the wrench, between a position driving a fastener solely through a torsion bar and a position wherein the fastener driving socket is rigidly interconnected to the driving anvil of the impact wrench.

In general, the foregoing objects are attained in an impact wrench having an anvil and a hammer mechanism adapted to apply rotary impacts to the anvil, a spindle adapted to be connected to a fastener driving a socket, a torsion bar or other spring resiliently interconnecting the anvil to the spindle, and latch means separate from the torsion bar and operative, in an operative position, to rigidly interconnect the spindle to the anvil for transmitting a much higher value of torque to the spindle than can be transmitted through the torsion bar, with the latch means being easily movable or shiftable by the operator while operating the wrench between the operative position and an inoperative position wherein torque is transmitted solely by the torsion bar.

BRIEF DESCRIPTION OF DRAWING

The invention is described in connection with the drawing wherein:

FIG. 1 is an elevational view of the front end of an impact wrench embodying this invention and having portions cut away and shown in section;

FIGS. 2 and 3 are sections on an enlarged scale taken respectively on lines 2-2 and 3-3 in FIG. 1;

FIG. 4 is an enlarged fragmentary view of FIG. 1 with certain broken-away portions shown in elevation;

FIG. 5 is a curve illustrating the relationship of torque relative to time during both types of operation of the impact wrench, torque being indicated by the vertical coordinate and time being indicated by the horizontal coordinate; and

FIG. 6 is an elevational view similar to FIG. 1 of a second embodiment.

DESCRIPTION OF PREFERRED EMBODIMENT

FIG. 1 shows the front end of a rotary impact wrench 1 including a casing 2 containing a rotary motor (not shown) driving a rotary hammer 3 which, as it rotates, periodically strikes an impact blow to a rotary anvil 4. The anvil 4 includes an integral forwardly extending tube 5 journaled in a bearing 6 mounted in the front end of the impact tool casing 2. The tube 5 surrounds an elongate torsion spring or bar 7 having its rear end 8, which is formed as a square plug, nonrotationally anchored in a corresponding square hole in the anvil 4 so that impact blows received by the anvil 4 from the hammer 3 are transmitted to the torsion bar 7. A transverse pin 9 is mounted in the anvil and extends through the rear end 8 to hold the torsion bar 7 in position in the anvil 4.

The front end 11 of the torsion bar 7 has a square cross section and is adapted to engage a fastener driving socket (not shown) having a square hole for being detachably received on the square front end 11. The use of this type of detachable socket is conventional and well known in the rotary impact wrench art.

When an impact load is being transmitted by the torsion bar 7, the torsion bar limits the amount of torque that can be transmitted to a fastener. This limiting action of the torsion bar 7 is illustrated in FIG. 5 by the curve identified as 12. Initially, when the torque load (indicated by the vertical coordinate) on the fastener is relatively low, the torsion bar will transmit substantially all of the torque applied to it by the impact wrench 1. As the torque load rises, the torsion bar will begin progressively deflecting or winding up under each impact and then rebounding, resulting in a substantial portion of each impact being absorbed by the torsion bar 7 without transmitting it to the fastener. Thus, as noted in curve 12 in FIG. 5, the torque will eventually rise to a maximum limiting value where the torsion bar is incapable of applying additional torque to the fastener even though the wrench is capable of applying a much higher torque load to the fastener when the torsion bar is eliminated. This phenomenon is well known in the impact tool art and is not believed to require further explanation.

In order to apply an increased torque load to a fastener, where desirable, it is necessary to couple the relatively rigid tube 5 of the wrench directly to the front end 11 of the torsion bar 7. It is desirable for the mechanic to be able to do this quickly and easily while the tool remains oriented in his hand in the normal operating position and, preferably, during the operation of the wrench motor. This is accomplished by the subject invention.

The torsion bar 7 contains a series of longitudinally extending spline teeth 14 located adjacent and immediately to the rear of the front end 11 of the torsion bar 7. An annular sleeve 15 is slidably mounted on the forward end of the tube 5 and nonrotatably engages the tube 5 by means of cooperating splines 16 provided on the tube 5 and internal flutes formed on the sleeve 15. The forward end of the sleeve 15 contains a fluted bore 17 which is of reduced diameter relative to the rear portion of the sleeve 15 slidably engaging the tube 5, and is adapted to nonrotatably engage the spline teeth 14 provided on the torsion bar 7, when the sleeve 15 is moved axially forward to the position shown in dotted lines in FIGS. 1 and 4. When the sleeve 15 is in its rearwardly retracted position, shown in solid lines in FIGS. 1 and 4, the fluted bore 17 is free of the spline teeth 14 and the tube 5 is disconnected from the front end of the torsion bar 7.

Means is provided for resiliently urging the sleeve 15 rearwardly on the tube 5. This means includes a longitudinal groove 18 formed in the forward part of the tube 5 and a shoulder 19 facing rearwardly adjacent the front end of the groove 18. A spring 20 is located in the groove 18 and engages the shoulder 19 and a setscrew 21 located in the rear end of the sleeve 15 and extending radially into the groove 18, as shown in FIG. 4. A resilient snapring 22 engages an annular groove provided on the spline teeth 14 to serve as a stop for limiting the forward movement of the sleeve 15 when engaged with the teeth 14, as shown in dotted lines in FIGS. 1 and 4.

In operating the impact wrench 1 during the normal tightening of a fastener, where it is desired to limit the amount of torque delivered to the fastener, a mechanic will use the wrench in the condition shown in solid lines in FIG. 1, wherein the sleeve 15 is retracted to its rearward position and wherein the rearward torque is delivered solely through the torsion bar 7. When the mechanic encounters a fastener requiring the application of an increased torque load, such as when removing a fastener, he simply grasps the sleeve 15 in his free hand, while continuing to hold the wrench in his other hand in the normal manner, slides the sleeve 15 axially forward to engage it with the spline teeth 14, and this can be done while the wrench is operating. This forward movement of the sleeve rigidly connects the anvil 4 to the front end 11 of the torsion bar 7 whereupon substantially all of the torque created by the wrench 1 is delivered to the fastener. In this position, the torque delivered by the wrench to the fastener is characterized by the curve 24 in FIG. 5. The torque delivered to the fastener rises to a point where it ultimately tapers off to a torque limited only by the capabilities of the wrench 1. Once the mechanic has finished with the fastener requiring the increased torque, he simply releases the sleeve 15 whereas the spring 20 returns the sleeve 15 to its rearwardly retracted position whereupon the torsion bar 7 is used for transmitting the torque load in a conventional manner.

SECOND EMBODIMENT

FIG. 6 shows a second embodiment of the invention. In this embodiment the invention is incorporated in an attachment 26 adapted to be releasably mounted on a spindle 27 of a conventional impact wrench 28. In this embodiment, the tube 5 includes a rear end 30 having a socket 31 adapted to cooperatively receive the spindle 27. The rear end 8 of the torsion bar 7 is fixed in the rear end of the tube 5 by a transverse pin 9, in the same manner as shown in FIG. 1. Otherwise, with the exception of being made in the form of an attachment, the second embodiment shown in FIG. 6 is identical with the first embodiment.

While two embodiments of the invention are described and illustrated in detail, this invention is not limited simply to the described embodiments, but contemplates other embodiments and variations which utilize the concepts and teachings of this invention.

Claims

I claim:

1. An impact wrench comprising:

an anvil and hammer mechanism adapted to apply a series of rotary impacts to said anvil;

a spindle adapted to be connected to a fastener driving socket;

a torsion spring resiliently interconnecting said anvil to said spindle and adapted to limit the amount of torque that is transmitted to said spindle from said anvil; and

latch means separate from said torsion spring for rigidly interconnecting said spindle to said anvil in an operative position for transmitting higher values of torque to said spindle from said anvil than can be transmitted by said torsion spring, said latch means being manually movable by the operator while operating the wrench between an inoperative position, wherein torque is transmitted solely by said torsion spring, and said operative position.

2. The impact wrench of claim 1 wherein:

said latch means is axially movable relative to said spindle between said operative and inoperative positions.

3. The impact wrench of claim 2 wherein:

said anvil is connected to a tube extending forwardly around said torsion spring and having a sliding nonrotating engagement with said latch means.

4. The impact wrench of claim 2 wherein:

said latch means includes an axially movable sleeve adapted to engage splines on said spindle and splines connected to said anvil in said operative position.

5. The impact of claim 3 wherein:

said latch means is a sleeve nonrotatably sliding on said tube and includes biasing means urging said sleeve rearwardly to a retracted position where it is disengaged from said torsion spring.

6. The impact wrench of claim 1 wherein:

said torsion spring and latch means is detachable from said anvil.

7. An attachment for an impact wrench having a first driving spindle, said attachment comprising:

a rear end adapted to be connected to said first spindle for transmitting a torque load;

a second spindle adapted to be connected to a fastener driving socket;

a torsion spring resiliently interconnecting said rear end to said second spindle and adapted to limit the amount of torque that is transmitted to said second spindle from said rear end; and

latch means separate from said torsion spring for rigidly interconnecting said second spindle to said rear end in an operative position for transmitting higher values of torque to said second spindle from said rear end than can be transmitted by said torsion spring, said latch means being manually movable by the operator while operating the wrench between an inoperative position, wherein torque is transmitted solely by said torsion spring, and said operative position.

8. The attachment of claim 7 wherein:

said latch means is axially movable relative to said second spindle between said operative and inoperative positions.

9. The attachment of claim 8 wherein:

said rear end is connected to a tube extending forwardly around said torsion spring and having a sliding nonrotating engagement with said latch means.

10. The attachment of claim 8 wherein:

said latch means includes an axially movable sleeve adapted to engage splines on said second spindle and splines connected to said rear end in said operative position.

11. The attachment of claim 9 wherein:

said latch means is a sleeve nonrotatably sliding on said tube and includes biasing means urging said sleeve rearwardly to a retracted position where it is disengaged from said torsion spring.