GB2128916A

GB2128916A - Impact mechanism for power driven wrench

Info

Publication number: GB2128916A
Application number: GB08327368A
Authority: GB
Inventors: Michael S Yacobi
Original assignee: Black and Decker Inc
Current assignee: Black and Decker Inc
Priority date: 1982-10-19
Filing date: 1983-10-13
Publication date: 1984-05-10
Also published as: GB8327368D0; FR2534514A1; IT1169855B; IT8323355A0; FR2534514B1; DE3337206A1

Abstract

An output torque maximizing impact wrench has an anvil 26 and output shaft which are driven about an axis of rotation by the intermittent blows to the anvil of an impactor also rotating about the axis. Impacting surfaces 62 on the impactor and impact receiving surfaces 64 on the anvil are generally parallel the axis of rotation but are sufficiently angularly mismatched upon impact as to meet at an angle "A" having a vertex generally parallel the axis of rotation and to locate the effective impact at portions of said impact receiving surfaces radially extreme from the axis of rotation. The wrench preferably utilises an electric motor capable of operation by a low-voltage (eg 120 volt A.C., 12 volt D.C.) power supply. <IMAGE>

Description

SPECIFICATION Impact mechanism for power driven wrench This invention relates to power driven impact wrenches, and more particularly to impact wrenches electrically driven from commonly available power sources, such as 1 20 volt alternating current or 1 2-volt direct current power sources.

Impact wrenches commonly used to drive or remove metal fasteners, such as nuts, bolts, and screws, generally employ an output shaft having one end thereof formed into a fitting attachable to a tool for rotating the fastener. The output shafts in such devices are connected to an anvil which is driven to rotate about an axis by blows received thereon from a power driven impactor rotating about the same axis. Known camming means are used to move the impactor axially away from engagement with the anvil following each impact delivered thereupon, thereby permitting the impactor to continue rotation in the direction dictated by the drive means so as to acquire momentum for its next successive impact upon the anvil.Most such impact wrenches have drive means capable of rotating the impactor in either direction about the axis of rotation; so that the wrench is capable of either tightening or loosening fasteners at the discretion of an operator.

The torque actually delivered to a fastener being rotated by a power driven impact wrench is determined to a large extent by the power of the drive means employed, but is also influenced by the structure and relationship of the surfaces impacting when the impactor and anvil meet. In commercial settings the use of high voltage electric motors in impact wrenches insures that these can deliver more than adequate torque for most tasks in which a power driven impact wrench is required. In homes, however, it is preferred that power tools be capable of operating effectively on conventional 1 20-volt alternating current. In addition there are numerous situations involving vehicular, marine, or field-type maintenance or repair in which the use of power driven impact wrenches would be very beneficial.Frequently in these situations, alternating current is entirely unavailable, and a 1 2-volt direct current power source in the form of an automotive battery is the only energy source from which such a tool may be operated.

Therefore, a need exists for an impact wrench capable of delivering adequate output torque when operated from power sources, such as those providing 120-volt alternating household or 1 2-volt battery supplied current.

An object of the present invention is to produce an output torque maximizing low power impact wrench which is economical to manufacture and therefore widely available to consumers.

In one embodiment of the invention an impact wrench comprises an output shaft having one end thereof formed into a fitting for rotating a tool disposed to engage a fastener, an anvil operatively connected to drive the output shaft, the anvil being disposed to rotate about an axis and comprising two arms aligned radially on opposite sides of the axis, impact receiving surfaces disposed on both sides of both arms of the anvil radially outward from the axis and generally parallel thereto, a drive means, an impactor rotatable by the drive means in either direction about the axis, two lugs projecting from the impactor toward the anvil on opposite sides of the axis, camming means for moving the impactor axially and impacting surfaces on both sides of both lugs of the impactor generally parallel the axis, the impacting surfaces disposed to engage the impact receiving surfaces intermittently when the camming means axially advances the rotating impactor into close proximity with the anvil, the impacting surfaces and the impact receiving surfaces being angularly mismatched upon impact at an angle having a vertex generally parallel to the axis, the angular mismatch being sufficient to place the effective impact of the impactor upon the anvil at portions of the impact receiving surfaces radially extreme from the axis, thereby to increase the torque generated by the impact wrench.

In another aspect of the present invention, in an impact wrench an impact mechanism comprises an anvil disposed to rotate about an axis, the anvil including at least one impact receiving surface disposed radially outward from the axis and generally parallel thereto and an impactor rotating about the axis to intermittently strike the impact receiving surface, the impactor including at least one impacting surface, the impacting surface and the impact receiving surface being angularly mismatched to meet upon impact at an angle having a vertex generally parallel the axis, the mismatch being sufficient to place the effective impact at a portion of the impacting surface radially extreme from the axis, thereby increasing the torque generated by the impact wrench.

The invention will now be described further by way of example with reference to the accompanying drawings, in which: Figure 1 is a partial section of a side view of a power driven impact wrench incorporating the teachings of the present invention.

Figure 2 is an enlarged detail in partial section of a portion of the power impact wrench of Fig. 1; Figure 3 is an enlarged perspective view of the impactor and anvil of Fig. 1 in their assembled relation one with another; Figure 4 is an enlarged top view of the anvil and impactor of the present invention in contact one with another; Figure 5 is a plan view of an anvil embodying one modification of the present invention; and Figure 6 is a plan view of an impactor embodying a second modification of the present invention.

A power drive impact wrench is shown in Fig. 1 which it will be appreciated is indicative of a class of portable power-operated tools within which the teachings of the present invention may be incorporated.

As here embodied, the impact wrench has a generally cylindrical main housing 10 comprising a motor housing 1 2 formed integrally with a transmission housing 14 extending forwardly therefrom. Motor housing 1 2 has a depending portion 1 6 which forms a pistolgrip hand for the tool. An electrical cable 1 8 provides power to a drive means (not shown) contained within motor housing 1 2 and controlled by a trigger 20. The end of power cord 1 8 remote from the impact wrench may be formed into an electrical plug for insertion into an electrical power socket or a pair of clamps for attachment individually to the terminals of a storage battery.

An output shaft 22 emerges from transmission housing 14 generally parallel the longitudinal axis of main housing 10. The end of output shaft 22 exterior transmission housing 14 is formed into a fitting which is attachable selectively to tools designed to rotate metal fasteners, such as nuts, bolts, and screws.

The other end of output shaft 22 is secured or formed within transmission housing 14 to an anvil 26 for rotation there with about an axis coincident with the longitudinal centerline of output shaft 22. Motion of the drive means within motor housing 1 2 is transmitted by gears 28, 30 into rotation of drive shaft 32 about an axis coincident with the axis of rotation of output shaft 22 and anvil 26.

As is most clearly seen in Fig. 2, drive shaft 32 is not rigidly attached to either anvil 26 or output shaft 22. Rather, the end of drive shaft 32 remote from gears 28, 30 of Fig. 1 is formed into a narrow neck portion 34 which is rotatably received in a recess 36 riding against a ball bearing 38 disposed therein.

Thus drive shaft 32 does not directly impart rotational movement to either output shaft 22 or anvil 26 which is securely attached to output shaft 22 in this embodiment by means of a brazing material 40 shown in Fig. 2.

Instead, drive shaft 32 passes through a cam 42 housed within a cylindrical impactor 44 of substantial mass. Rollers 46 upon a pin 48 passing through drive shaft 32 are urged against the surface of cam 42 through the action of spring 50 compressed between a thrust washer 52 attached to the drive shaft 32 and concentric washers 54 bearing against impactor 44. By the known operation of spring 50 and cam 42, impactor 44 rotates with drive shaft 32 and is rendered capable of axial movement in a direction away from anvil 26 when resistance to the rotation of impactor 44 is substantial enough that roller 46 rides up the elevated surface of cam 42 forcing cam 42, and thus impactor 44, axially along drive shaft 32 to the right, as viewed in Figs.

1 and 2.

A clear understanding of how impactor 44 serves to drive anvil 26 in rotation can be derived by reference to Fig. 3, wherein it may be seen that anvil 26 comprises two arms 56 aligned radially on opposite sides of output shaft 22 and the axis of rotation of anvil 26.

In Fig. 2, arms 56 of anvil 26 extended generally parallel and in close proximity to an upper surface 58 of cylindrical impactor 44.

Projecting toward anvil 26 from surface 58 of impactor 44 are two outstanding lugs 60 on opposite sides of the axis of rotation of drive shaft 32. Surfaces 62 of lug 60 which are generally parallel the axis of rotation of drive shaft 32 comprise impacting surfaces which deliver blows to impact receiving surfaces 64 disposed radially outward from and generally parallel to the axis of rotation of anvil 26 on both sides of arms 56.

In operation, drive shaft 32 is capable of rotating the impactor 44 in either direction at the discretion of an operator. Rotation of impactor 44 causes a pair of radially opposite impacting surfaces 62 on lugs 60 to encounter a pair of corresponding impact receiving surfaces 64 on arms 56 of anvil 26. In the resulting impact the momentum of impactor 44 is transferred to anvil 26 and output shaft 22, driving both to rotate. If drive shaft 22 is free to rotate, then impactor 44 and anvil 26 will continue rotating together about a common axis with impacting surfaces 62 and impact receiving surfaces 64 engaged.When output shaft 22 encounters resistance to its rotation, as when a metal fastener being rotated by a tool attached to fitting 24 begins to tighten, the camming means comprising cam 42, spring 50, and washers 52 and 54 move impactor 44 axially away from engagement with anvil 26, thereby permitting impactor 44 to resume rotation in the direction dictated by the drive means and acquire momentum for its next successive impact upon anvil 26.

Impacting surfaces 62 engage impact receiving surfaces 64 again when the camming means returns rotationally driven impactor 44 axially into close proximity with anvil 26.

Through successive intermittent impacts of impactor 44 against anvil 26 the angular momentum of impactor 44 is transferred throughout the shaft 22 to a metal fastener which is gradually tightened or loosened according to the direction dictated by the drive means in motor housing 1 2.

The object of the present invention of maximizing torque output for an impact wrench such as that depicted in Fig. 1 is achieved by orientating impacting surfaces 62 and impact receiving surfaces 64 as to be angularly mismatched by an angle A upon impact, as is shown in Fig. 4. Angular mismatch A between impacting surfaces 62 and impact receiving surfaces 64 is sufficient to place the effective impact of impactor 44 upon anvil 26 at portions of impact receiving surfaces 62 which are radially extreme from the axis of rotation of anvil 26. Thus, the momentum of impactor 44 is delivered to anvil 26 at a longer moment arm from the axis of rotation of anvil 26 than would be the case if impacting surfaces 62 and impact receiving surfaces 64 were to meet flat against each other.

Therefore, angular mismatch A facilitates the generation of maximum torque output from an impact wrench, such as that shown in Fig. 1 When the drive means within motor housing 1 2 is a low power drive means, such as a 120-volt alternating current motor or a 12volt direct current motor, this is a very advantageous result. It has-been found that angular mismatch A need only be sufficiently large to move the effective point of impact radially outward as described above. An angular mismatch A less than or equal to 8 degrees is considered sufficient for such purposes, while the range from one to five degrees is considered more adequate, and the range from two to four degrees is preferred.

Anvil 26 is preferably made of 8620 H hardened steel, while impactor 44 is preferably made of 4320 H hardened steel. Angular mismatch A may be satisfactorily produced in either of two manners. In the first instance, radially opposite pair of impacting surfaces 64 on lugs 60 are broached so as to be generally parallel, while angular mismatch A is produced by setting impact receiving surfaces 62 at an angle A outward from a parallel orientation, as shown in Fig. 5. In an alternative embodiment, radially opposite impact receiving surfaces 62 on the anvil can be oriented generally parallel one with another and angular mismatch A is produced by setting impacting surfaces 64 outward from a parallel orientation, as shown in Fig. 6. While both methods described above have been found to function equally well, the former method is preferred because it minimizes manufacturing costs.

Claims

1. An impact wrench, comprising an impact mechanism having an anvil disposed to rotate about an axis, the anvil including at least one impact receiving surface disposed radially outward from the axis and generally parallel thereto and an impactor rotating about the axis to strike the impact receiving surface intermittently, the impactor including at least one impacting surface, the impacting surface and the impact receiving surface being angularly mismatched to meet upon impact at an angle having a vertex generally parallel the axis, the mismatch being sufficient to place the effective impact a portion of the impacting surface radially extreme from the axis, thereby increasing the torque generated by the impact wrench.

2. A wrench as claimed in claim 1, in which the anvil comprises two arms aligned radially on opposite sides of the axis, the impact receiving surfaces comprise at least one pair of.radially opposite edges of the arms; and the impactor having two lugs projecting therefrom on opposite sides of the axis, the lugs each including at least one impacting surface.

3. A wrench as claimed in claim 2, in which the impact receiving surfaces and the impacting surfaces are substantially perpendicular to the plane of rotation of the anvil and the impactor about the axis.

4. A wrench as claimed in claim 2, in which means are provided for rotationally driving the impactor, impact receiving surfaces being provided on both sides of both of the arms of the anvil, and impacting surfaces being on both sides of both lugs of the impactor, the impacting surfaces being disposed to engage the impact receiving surfaces intermittently when the drive means rotates the impactor in either direction about the axis.

5. A wrench as claimed in claim 4, in which radially opposite impact receiving surfaces are generally parallel and the angular mismatch being as a result of the orientation of the impacting surfaces.

6. A wrench as claimed in claim 4, in which radially opposite impacting surfaces are generally parallel and the angular mismatch is a result of the orientation of the impact receiving surfaces.

7. A wrench as claimed in claim 5 or 6 in which the angular mismatch is less than or equal to eight degrees.

8. A wrench as claimed in claim 5 or 6 in which the angular mismatch is in the range from one to five degrees.

9. A wrench as claimed in claim 5 or 6, in which the angular mismatch is in the range from two to four degrees.

10. An impact wrench, as claimed in any preceding claim, in which an output shaft is provided having one end thereof formed into a fitting for rotating a tool disposed to engage a fastener the anvil being operably connected to drive the output shaft.

11. A wrench as claimed in claim 10, in which the drive means is a 12-volt direct current motor.

1 2. A wrench as claimed in claim 10, in which the drive means comprises a 120-volt alternating current motor.

1 3. An impact wrench constructed and arranged to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.