Anvil, hammer and drive assembly for use in impact wrench

Abstract

An anvil configured to be impacted by a hammer in an impact wrench is disclosed. The anvil defines an axis of rotation. The anvil includes an anvil lug having a driven surface engageable with the hammer. The driven surface includes an involute profile. The involute profile is formed by a base cylindrical surface defining a central axis. The central axis is offset relative to a rotational axis of the anvil.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 511,362, filed Jun. 30, 2023, the entire content of which is incorporated herein by reference. Technical Field

[0003] This disclosure relates to tools, and more particularly to power tools. Background Art

[0004] In power tools (e.g., electrically - operated power tools, pneumatic power tools, etc.), a drive assembly is typically employed to transfer torque from a motor to a tool element to operate on a workpiece. In particular, an impact wrench utilizes a drive assembly to convert the continuous rotational motion of an output shaft of a motor into an impact rotational force or an intermittent torque application to the tool element and the workpiece. Thus, impact wrenches are typically used to loosen or remove stuck fasteners (e.g., automotive lug nuts on axle studs) that otherwise cannot be removed or are difficult to remove using manual tools. Such a drive assembly typically includes a hammer and an anvil, the hammer having at least one drive surface and the anvil having at least one, typically flat, driven surface that is oriented generally orthogonally to the longitudinal axis of the anvil.

[0005] The outer corners of the driven surface are typically rounded with a relatively small radius, providing a relatively sharp transition from the driven surface of the anvil to an adjacent end surface. For such a flat driven surface, defects in the shape, size, and symmetry of the anvil may create non - uniform contact between the hammer and the anvil during operation of the impact wrench, which may reduce the efficiency of the impact wrench and / or accelerate wear between the hammer and the anvil.

[0006] Depending on the size and configuration of the impact wrench, a relatively large amount of torque can be transmitted through the drive assembly to the tool element and the workpiece. Thus, relatively high contact stresses often occur at the outer corners of the driven surface during operation of the impact wrench. Summary of the Utility Model

[0007] In some aspects, the technology described herein relates to an anvil configured to be struck by a hammer in an impact wrench, the anvil defining a rotational axis, the anvil including: an anvil lug including a driven surface engageable with the hammer, the driven surface including an involute profile, wherein the involute profile is formed by a base cylindrical surface defining a central axis, and wherein the central axis is offset relative to the rotational axis of the anvil.

[0008] In some aspects, the techniques described herein relate to an anvil, wherein the anvil lug is a first anvil lug, wherein the anvil further includes a second anvil lug positioned opposite the first anvil lug, and wherein the anvil defines an anvil lug diameter from a distal end of the first anvil lug to a distal end of the second anvil lug.

[0009] In some aspects, the techniques described herein relate to an anvil, wherein the follower surface of the first anvil lug is a first follower surface, and wherein the first anvil lug further includes a second follower surface opposite the first follower surface.

[0010] In some aspects, the techniques described herein relate to an anvil, wherein the base cylindrical surface defines a base cylindrical surface diameter, and wherein the base cylindrical surface diameter is greater than the anvil lug diameter.

[0011] In some aspects, the techniques described herein relate to an anvil, wherein the anvil defines an anvil plane that includes a rotational axis, and wherein the anvil is symmetric about the anvil plane.

[0012] In some aspects, the techniques described herein relate to an anvil, wherein the anvil defines an anvil plane that includes a rotational axis, and wherein the central axis is offset relative to the rotational axis in a direction parallel to the anvil plane.

[0013] In some aspects, the techniques described herein relate to an anvil, wherein the anvil defines an anvil plane that includes a rotational axis, and wherein the central axis is offset relative to the rotational axis in a direction perpendicular to the anvil plane.

[0014] In some aspects, the techniques described herein relate to a hammer configured to impact an anvil in an impact wrench, the hammer defining a rotational axis, the hammer including: a body having an inner surface that defines a hammer inner diameter; and a hammer lug that extends inwardly from the inner surface toward the rotational axis, the hammer lug including a drive surface engageable with the anvil, the drive surface including an involute profile, wherein the involute profile is formed by a base cylindrical surface that defines a central axis, and wherein the central axis is offset relative to the rotational axis of the hammer.

[0015] In some aspects, the techniques described herein relate to a hammer, wherein the hammer lug is a first hammer lug, and wherein the hammer further includes a second hammer lug that extends inwardly from the inner surface toward the rotational axis, the second hammer lug being opposite the first hammer lug.

[0016] In some aspects, the techniques described herein relate to a hammer, wherein the hammer defines a hammer plane that includes a rotational axis, and wherein the hammer is symmetric about the hammer plane.

[0017] In some aspects, the techniques described herein relate to a hammer, wherein the base cylindrical surface defines a base cylindrical surface diameter, and wherein the base cylindrical surface diameter is greater than the hammer inner diameter.

[0018] In some aspects, the techniques described herein relate to a hammer in which a central axis is offset relative to a rotational axis in a direction parallel to a hammer plane.

[0019] In some aspects, the techniques described herein relate to a hammer in which a central axis is offset relative to a rotational axis in a direction perpendicular to a hammer plane.

[0020] In some aspects, the techniques described herein relate to a drive assembly for use in an impact wrench, the drive assembly including: a hammer configured to rotate about a rotational axis, the hammer including a body having an inner surface defining a hammer inner diameter and a hammer lug extending inwardly from the inner surface toward the rotational axis, the hammer lug having a drive surface; and an anvil including an anvil lug having a driven surface, wherein the drive surface of the hammer is configured to impact the driven surface of the anvil to transfer torque to the anvil, wherein both the drive surface and the driven surface include an involute profile formed by a base cylindrical surface defining a base cylindrical surface diameter, and wherein the base cylindrical surface diameter is greater than the hammer inner diameter.

[0021] In some aspects, the techniques described herein relate to a drive assembly in which the base cylindrical surface defines a base cylindrical surface axis and in which the base cylindrical surface axis is offset relative to the rotational axis.

[0022] In some aspects, the techniques described herein relate to a drive assembly in which: the driven surface of the anvil lug is a first driven surface, the anvil lug includes a second driven surface opposite the first driven surface, the drive surface of the hammer is a first drive surface, and the hammer includes a second drive surface opposite the first drive surface.

[0023] In some aspects, the techniques described herein relate to a drive assembly in which the first drive surface of the hammer lug is configured to engage the first driven surface of the anvil lug to drive the anvil in a first rotational direction, and in which the second drive surface of the hammer lug is configured to engage the second driven surface of the anvil lug to drive the anvil in a second rotational direction opposite the first rotational direction.

[0024] In some aspects, the techniques described herein relate to a drive assembly in which the hammer lug is a first hammer lug and in which the hammer further includes a second hammer lug extending inwardly from the inner surface toward the rotational axis, the second hammer lug being opposite the first hammer lug.

[0025] In some aspects, the techniques described herein relate to a drive assembly in which the anvil lug is a first anvil lug and in which the anvil further includes a second anvil lug opposite the first anvil lug.

[0026] In some aspects, the techniques described herein relate to a drive assembly, wherein: a hammer defines a hammer plane and is symmetric about the hammer plane, an anvil defines an anvil plane, and the anvil is symmetric about the anvil plane.

[0027] Other features and aspects of the present disclosure will become apparent by considering the following detailed description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a perspective view of a power tool in which a drive assembly including a hammer and an anvil embodying aspects of the present disclosure can be implemented.

[0029] Figure 2 is a cross-sectional view of the power tool taken along line 2-2 Figure 1 and shown with the battery pack of the power tool removed.

[0030] Figure 3 is a cross-sectional view showing a drive assembly according to an embodiment of the present disclosure.

[0031] Figure 4 is Figure 3 a cross-sectional view of the drive assembly at the moment of impact between the hammer and the anvil of the drive assembly.

[0032] Figure 5 is Figure 3 a schematic view of the anvil of the drive assembly showing the origin of an involute profile on the driven surface of the anvil, the involute profile being defined by a base cylinder surface offset relative to the axis of rotation of the anvil.

[0033] Figure 6 is Figure 3 a schematic view of the hammer of the drive assembly showing the origin of an involute profile on the driving surface of the hammer, the involute profile being defined by a base cylinder surface offset relative to the axis of rotation of the hammer.

[0034] Figure 7 is a diagram showing different examples of involute profiles that can be incorporated into the anvil and / or Figure 5 the hammer of Figure 6 the drive assembly.

[0035] FIG. 8 is a schematic view of a prior art anvil showing the origin of an involute profile on the driven surface of the anvil defined by a base cylinder surface centered on the axis of rotation of the anvil.

[0036] FIG. 9 is a schematic view of a prior art hammer showing the origin of an involute profile on the driving surface of the hammer defined by a base cylinder surface centered on the axis of rotation of the hammer.

[0037] Figure 10is a diagram showing different examples of involute profiles defined by a base cylindrical surface centered on the axis of rotation of the anvil of FIG. 8 and / or the hammer of FIG. 9.

[0038] Figure 11 is a diagram comparing involute profiles that embodies aspects of the present disclosure, in which the base cylindrical surface is shifted.

[0039] Before explaining any embodiments of the present disclosure in detail, it should be understood that the present disclosure is not limited in its application to the construction details and component arrangements set forth in the following description or shown in the following drawings. The present disclosure is capable of other embodiments and of being practiced or carried out in various ways. Further, it should be understood that the language and terminology used herein are for the purpose of description and should not be regarded as limiting. Detailed Description

[0040] Figure 1 shows a power tool in the form of an impact wrench 10, which includes an anvil 14 and a tool element 18 coupled to the anvil 14. Although the tool element 18 is schematically shown, the tool element 18 may include a socket configured to engage the head of a fastener (e.g., a bolt). Alternatively, the tool element 18 may include any of a variety of different configurations (e.g., a drill or a bit) for operating on a workpiece. Referring Figure 1 and Figure 2 , the impact wrench 10 includes a housing 22 and a reversible electric motor 26 that is coupled to the anvil 14 to provide torque to the anvil 14 and the tool element 18. The impact wrench 10 also includes a switch (e.g., a trigger switch 30) supported by the housing 22. The illustrated impact wrench 10 includes a rechargeable battery 34. The motor 26 is configured to operate using DC power provided by the battery 34. In some embodiments, the impact wrench 10 may include a power cord extending from the housing 22 for electrically connecting the switch 30 and the motor 26 to an AC power source. As another alternative, the impact wrench 10 may be configured to operate using a different power source (e.g., a pneumatic or hydraulic power source, etc.) other than electricity.

[0041] Referring Figure 2, the impact wrench 10 further includes a gear assembly 38 coupled to the output end of the motor 26 and a drive assembly 42 coupled to the output end of the gear assembly 38. The gear assembly 38 can be configured in any of a variety of different ways to provide a speed reduction between the output end of the motor 26 and the input end of the drive assembly 42. The drive assembly 42 (the anvil 14 can be considered a component thereof) is configured to convert the constant rotational force or torque provided by the gear assembly 38 into an impact rotational force or an intermittent torque application to the tool element 18. In the illustrated embodiment of the impact wrench 10, the drive assembly 42 includes a camshaft 46 coupled to and driven by the gear assembly 38, a hammer 50 supported on the camshaft 46 and axially slidable relative thereto, and an anvil 14. Both the hammer 50 and the anvil 14 define a rotational axis 58 and are rotatable about the rotational axis.

[0042] See Figure 3 and Figure 4 , the hammer 50 includes a body 51 having an inner surface 52 and a pair of hammer lugs 54 that extend inwardly from the inner surface 52 in a direction toward the rotational axis 58. The illustrated pair of hammer lugs 54 are opposite each other. Each of the hammer lugs 54 includes a first drive surface 62a, a second drive surface 62b located on the side of the hammer lug 54 opposite the first drive surface 62a, and a distal end 66 that interconnects the first drive surface 62a and the second drive surface 62b. The distal end 66 can be flat, arcuate, or curved. As will be described in more detail below, the respective first drive surfaces 62a of the hammer lugs 54 can be employed during clockwise or forward rotation of the hammer 50 and the anvil 14, while the respective second drive surfaces 62b of the hammer lugs 54 can be employed during counterclockwise or reverse rotation of the hammer 50 and the anvil 14. Alternatively, the hammer 50 can include only a single hammer lug 54, or include more than two hammer lugs 54. Additionally, in embodiments of an impact wrench incorporating an irreversible motor, each of the drive lugs need only include a single drive surface.

[0043] Continuing to refer to Figure 3 and Figure 4, the anvil 14 includes a body or root 68 and a pair of anvil lugs 70 extending from the root 68 in a direction away from the axis of rotation 58. Each of the anvil lugs 70 includes a first driven surface 74a, a second driven surface 74b located on the side of the anvil lug 70 opposite the first driven surface 74a, and a distal end 78 connecting the first driven surface 74a and the second driven surface 74b to each other. The first drive surface 62a and the second drive surface 62b of the hammer 50 are configured to strike the first driven surface 74a and the second driven surface 74b of the anvil 14, respectively, to transfer torque from the hammer 50 to the anvil 14. The distal end 78 can be flat, arcuate, or curved. As described above, the corresponding first driven surfaces 74a of the anvil lugs 70 can be employed during clockwise or forward rotation of the hammer 50 and the anvil 14, while the corresponding second driven surfaces 74b of the anvil lugs 70 can be employed during counterclockwise or reverse rotation of the hammer 50 and the anvil 14.

[0044] In the illustrated embodiment, both the anvil 14 and the hammer 50 are symmetric. More specifically, the anvil plane 96 extends centrally through each anvil lug 70 and the axis of rotation 58. Thus, the anvil plane 96 contains the axis of rotation 58. The anvil plane 96 defines the plane of symmetry of the anvil 14. The hammer plane 100 extends centrally through each hammer lug 54 and the axis of rotation 58. Thus, the hammer plane 100 contains the axis of rotation 58. The hammer plane 100 defines the plane of symmetry of the hammer 50. In some embodiments, the anvil 14 and the hammer 50 are not symmetric. Thus, the anvil plane 96 may not define the plane of symmetry of the anvil 14, and the hammer plane 100 may not define the plane of symmetry of the hammer 50.

[0045] In the illustrated embodiment of the drive assembly 42, each of the drive surfaces 62a, 62b of the hammer lugs 54 and each of the driven surfaces 74a, 74b of the anvil lugs 70 define an involute profile. More particularly, the involute profiles of each of the driven surfaces 74a, 74b of the anvil lugs 70 and each of the drive surfaces 62a, 62b of the hammer lugs 54 are based on or derived from a hypothetical base cylinder (e.g., hypothetical base cylinder C; Figure 5 and Figure 6 ) offset relative to the axis of rotation 58. The base cylinder C defines a central axis CA that is offset relative to the axis of rotation 58. Refer to Figure 5 , the curvature of the first driven surface 74a is depicted by a point P on a hypothetical taut line or cord as the hypothetical taut line or cord unfolds clockwise (from P0 to P1) from the hypothetical base cylinder C, thereby generating the involute profile CI of the driven surface 74a. The illustrated involute profile CI is formed by setting in the anvil plane 96 ( Figure 3) The point P on is depicted. Then, the involute profile CI is shifted counterclockwise onto the driven surface 74a. The involute profile CI of the second driven surface 74b is generated in a similar manner, except that, from Figure 5 's perspective, the imaginary taut line or cord unwinds counterclockwise from the assumed base cylinder surface C.

[0046] Refer to Figure 6 , the curvature of the first driving surface 62a is depicted by the same point P on the imaginary taut line or cord as the imaginary taut line or cord unwinds counterclockwise from the same assumed base cylinder surface C (from P0 to P1), thereby generating the involute profile CI of the first driving surface 62a. The shown involute profile CI is depicted by the point P provided on the hammer plane 100 ( Figure 3 ). Then, the involute profile CI is shifted clockwise onto the driving surface 62a. The involute profile CI of the second driving surface 62b is generated in a similar manner, except that, from Figure 6 's perspective, the imaginary taut line or cord unwinds clockwise from the assumed base cylinder surface C. The line segment A - P1 ( Figure 5 and Figure 6 ) represents the unwinding length of the imaginary line or cord that is orthogonal to the radius of the base cylinder surface C and the involute at point P1. Although the unwinding length of the imaginary line or cord continuously increases, throughout the unwinding process, it is always orthogonal to the radius of the base cylinder surface C and the involute.

[0047] In embodiments where the anvil 14 and the hammer 50 are not symmetric, the driving surfaces 62a, 62b of the hammer lug 54 and the driven surfaces 74a, 74b of the anvil lug 70 define asymmetric involute profiles. The hammer lug 54 can be asymmetric with respect to the hammer plane 100. The anvil lug 70 can be asymmetric with respect to the anvil plane 96. The curvatures of the driving surfaces 62a, 62b and the driven surfaces 74a, 74b can be depicted using a similar method as discussed previously. However, for example, the driving surfaces 62a, 62b may not be depicted using the same assumed base cylinder surface C. Instead, the first driving surface 62a is depicted from a first assumed base cylinder surface having a first diameter, while the second driving surface 62b is depicted from a second assumed base cylinder surface having a second diameter different from the first diameter. The driven surfaces 74a, 74b can be similarly depicted from assumed base cylinder surfaces having different diameters. In some embodiments, the base cylinder surfaces of different sizes can all be concentric with the rotational axis 58. In other embodiments, the base circles of different sizes can be concentric with each other but not with the rotational axis 58. In still other embodiments, the base circles of different sizes can be neither concentric with each other nor with the rotational axis 58.

[0048] Refer to Figure 5 and Figure 6, the central axis CA of the base cylindrical surface is offset relative to the rotation axis 58 of the drive assembly 42. The shown central axis CA is offset relative to the rotation axis 58 in the first direction along the anvil plane 96 and the hammer plane 100, respectively. More specifically, the shown central axis CA is offset relative to the rotation axis 58 in a direction parallel to the anvil plane 96 and the hammer plane 100, respectively. In some embodiments, the central axis CA may be offset relative to the rotation axis 58 in a second direction perpendicular to the respective planes 96, 100. In other embodiments, the central axis CA may be offset relative to the rotation axis 58 in both the first direction and the second direction. The shown central axis CA extends through one of the anvil lug 70 and the hammer lug 54. In some embodiments, the central axis CA may extend through different portions of the anvil 14 and the hammer 50. In other embodiments, the central axis CA may not extend through any portion of the anvil 14 or the hammer 50.

[0049] Continuing to refer to Figure 5 and Figure 6 , the position of the central axis CA and the diameter 98 of the base cylindrical surface C determine the shape of the involute profile. The central axis CA can be located at any position, and the diameter 98 can be any value to achieve the desired involute profile of the drive surfaces 62a, 62b and the driven surfaces 74a, 74b. In some embodiments, the diameter 98 of the base cylindrical surface C may be greater than the anvil lug diameter ALD ( Figure 5 ) defined by the distal end 78 of the anvil lug 70. Additionally or alternatively, the diameter 98 of the base cylindrical surface C may be greater than the hammer inner diameter HID ( Figure 6 ) defined by the inner surface 52 of the body 51 of the hammer 50. The shown base cylindrical surface C contacts the root 68 at a single point, which is the position of P0. In some embodiments, the base cylindrical surface C may contact the root 68 at two points. In other embodiments, the base cylindrical surface C may not contact the root 68.

[0050] Figure 7Shows a plurality of involute profiles generated by a hypothetical base cylindrical surface C. Root 68 and the hammer inner surface 52 are depicted as defining the lower and upper limits, respectively, of the lengths of the lugs 54, 70. Root 68 defines the lower limit because the anvil lug 70 originates from root 68, and if the hammer lug 54 extends beyond root 68, the drive assembly 42 will not operate. Similarly, the hammer inner surface 52 defines the upper limit because the hammer lug 54 originates from the inner surface 52, and if the anvil lug 70 extends beyond the inner surface 52, the drive assembly will not operate. The dimensions of root 68 and inner surface 52 may be limited by various factors (e.g., the size of the housing 22, the weight of the drive assembly 42, etc.). However, the base cylindrical surface C is not constrained by these same factors because it is hypothetical. Thus, the base cylindrical surface C can be offset relative to the axis of rotation 58 to adjust the involute profile without adjusting the dimensions of root 68 or the hammer inner surface 52. The shown root 68 has a diameter of approximately 21 units (i.e., centimeters, inches, etc.), and the shown inner surface 52 has a diameter of approximately 42 units. The plurality of involute profiles includes a first involute profile I1, a second involute profile I2, and a third involute profile I3. The first involute profile I1 is generated by a first base cylindrical surface (not shown) having a first base circle diameter (e.g., 24 units), the second involute profile I2 is generated by a second base cylindrical surface (not shown) having a second base circle diameter greater than the first base circle diameter (e.g., 50 units), and the third involute profile I3 is generated by a third base cylindrical surface (not shown) having a third base circle diameter greater than the second base circle diameter (e.g., 100 units). In other embodiments, the involute profiles may be generated by hypothetical base cylindrical surfaces having different diameters to achieve a desired involute profile. As Figure 7 seen, the involute profiles I1, I2, I3 extend entirely between the root 68 and the hammer inner surface 52. In other words, the involute profiles I1, I2, I3 can be provided along the entire lengths of the follower surfaces 74a, 74b of the anvil lug 70 and the drive surfaces 62a, 62b of the hammer lug 54.

[0051] The involute profiles of each of the drive surfaces 62a, 62b and the driven surfaces 74a, 74b contribute to distributing the load substantially uniformly over the entire length of each drive surface when each drive surface 62a, 62b engages the corresponding driven surface 74a, 74b. Thus, during operation of the impact wrench 10, the local contact stresses between the hammer lug 54 and the anvil lug 70 are significantly reduced, thereby reducing wear of the hammer 50 and the anvil 14 and increasing the service life of the hammer 50 and the anvil 14. Further, since the contact between the corresponding drive surfaces 62a, 62b and the driven surfaces 74a, 74b is substantially distributed over the entire lengths of the corresponding drive surfaces 62a, 62b and the driven surfaces 74a, 74b, the overall mechanical efficiency of the impact wrench 10 is increased. The contact between the drive surfaces 62a, 62b and the driven surfaces 74a, 74b will produce a "centering" effect on the anvil 14 during operation of the impact wrench 10 (i.e., the force exerted by the hammer 50 on the anvil 14 tends to align the anvil 14 with the axis of rotation 58), thereby further increasing the efficiency of the impact wrench 10.

[0052] In the operation of the impact wrench 10 rotating in the forward or clockwise direction, the operator presses the switch 30 to electrically connect the motor 26 to the power source, thereby causing the motor 26 to operate and drive the gear assembly 38 and the camshaft 46. As the hammer 50 rotates with the camshaft 46, the drive surfaces 62a of the hammer lugs 54 respectively engage the driven surfaces 74a of the anvil lugs 70 to provide an impact in the selected clockwise or forward direction and rotatably drive the anvil 14 and the tool element 18. After each impact, the hammer 50 moves or slides backward along the camshaft 46 away from the anvil 14 such that the hammer lugs 54 disengage from the anvil lugs 70. As the hammer 50 moves backward, the cam balls 82 ( Figure 2 ) located in the corresponding cam grooves 86 in the camshaft 46 move backward in the cam grooves 86. The spring 90 stores a portion of the backward energy of the hammer 50, thereby providing a return mechanism for the hammer 50. After the hammer lugs 54 disengage from the corresponding anvil lugs 70, as the spring 90 releases the energy it has stored, the hammer 50 continues to rotate and move or slide forward toward the anvil 14 until the drive surfaces 62a of the hammer lugs 54 re-engage the driven surfaces 74a of the anvil lugs 70 to cause another impact. In the operation of the impact wrench rotating in the reverse or counterclockwise direction, the drive surfaces 62b of the hammer lugs 54 engage the corresponding driven surfaces 74b of the anvil lugs 70 ( Figure 4 ), in a manner similar to that described above for the forward or clockwise rotation of the impact wrench 10.

[0053] In addition to reducing the local contact stress between the hammer lug 54 and the anvil lug 70, the involute profiles are incorporated on the drive surfaces 62a, 62b of the hammer lug 54 and the involute profiles are incorporated on the driven surfaces 74a, 74b of the anvil lug 70, which also enhances the operating smoothness of the impact wrench 10 by reducing the timing angle A1 during the retraction of the hammer 50 on the camshaft 46 and the passage of the hammer lug 54 past the anvil lug 70. Continuing with reference to Figure 4 , the timing angle A1 is approximately 60 degrees. In other words, when the hammer 50 is in the retracted position along the camshaft 46 and rotating on the anvil 14, the hammer needs to rotate approximately 60 degrees before the hammer 50 can move towards the anvil 14 through the spring 90 to prepare for the next impact or strike between the hammer lug 54 and the anvil lug 70. More particularly, using the Figure 4 orientation of the hammer 50 relative to the anvil 14 shown as a reference, where the drive surface 62b and the driven surface 74b are engaged, the hammer 50 traverses an angle A1 of approximately 60 degrees in the counterclockwise direction when in the retracted position along the camshaft 46, and then the hammer 50 is allowed to resume its extended position to position the drive surface 62a adjacent to the driven surface 74a. Alternatively, the dimensions of the anvil lug 70 and / or the hammer lug 54 can be determined to be reduced in thickness compared to that shown in Figure 4 to further reduce the timing angle A1.

[0054] Figures 8 and 9 show a prior art anvil 114 and a hammer 150. The anvil 114 and the hammer 150 are rotatable about a rotational axis 158. The anvil 114 includes a root 168 and two anvil lugs 170 extending from the root 168 in a direction away from the rotational axis 158. The anvil lugs 170 have driven surfaces 174a, 174b. The hammer 150 includes an inner surface 152 and two hammer lugs 154 extending from the inner surface 152 in a direction towards the rotational axis 158. The hammer lugs 154 have drive surfaces 162a, 162b. The driven surfaces 174a, 174b and the drive surfaces 162a, 162b include involute profiles generated by an assumed base cylindrical surface D. The curvature of the surfaces 174a, 174b, 162a, 162b is depicted by points Q (from Q0 to Q1) in the same manner as the surfaces 74a, 74b, 62a, 62b are depicted by points P. The base cylindrical surface D defines a central axis DA that is the same as the rotational axis 158.

[0055] Figure 10 shows a plurality of involute profiles generated by the assumed base cylindrical surface D and the root 168. The lower limit (i.e., the root 168) and the upper limit (i.e., the inner surface 152 of the hammer) of the lengths of the lugs 154, 170 are shown. The shown root 168 has a diameter of approximately 21 units, and the shown inner surface 152 of the hammer has a diameter of approximately 42 units. The root 168 and the inner surface 152 of the hammer are shown as having the same Figure 7The root 68 and the inner surface 52 of the hammer have the same diameter. The plurality of involute profiles includes a fourth involute profile I4, a fifth involute profile I5, and a sixth involute profile I6. The fourth involute profile I4 is generated by a fourth base cylindrical surface D4 having a fourth base circle diameter (e.g., 24 units), the fifth involute profile I5 is generated by a fifth base cylindrical surface D5 having a fifth base circle diameter greater than the fourth base circle diameter (e.g., 28 units), and the sixth involute profile I6 is generated by a sixth base cylindrical surface D6 having a sixth base circle diameter greater than the fifth base circle diameter (e.g., 31 units). Since the diameters of the shown cylindrical surfaces D4, D5, D6 are greater than the diameter of the root 168, the corresponding involute profiles I4, I5, I6 include unusable lengths. The fourth involute profile I4 includes an unusable fourth length U4 that is equal to the difference between the fourth base circle diameter and the diameter of the root 168 (i.e., approximately 3 units). The fifth involute profile I5 defines an unusable fifth length U5 that is equal to the difference between the fifth base circle diameter and the diameter of the root 168 (i.e., approximately 7 units). The sixth involute profile I6 defines an unusable sixth length U6 that is equal to the difference between the sixth base circle diameter and the diameter of the root 168 (i.e., approximately 10 units). The corresponding involute profiles I4, I5, I6 further include usable lengths defined between the inner surface 152 of the hammer and the corresponding base cylindrical surfaces D4, D5, D6.

[0056] Continuing to refer to Figure 10 , the smaller-diameter base cylindrical surfaces D4, D5, D6 produce corresponding involute profiles with greater curvature. It is desirable to have less curvature along the involute profiles I4, I5, I6 on the follower surfaces 174a, 174b and the drive surfaces 162a, 162b because this results in a smaller pressure angle between the lugs 154, 170. A smaller pressure angle results in a smaller radial force component when the hammer strikes the anvil. The smaller radial force component produces less stress in the hammer lugs 154 and the anvil lugs 170. In other words, it is desirable to maximize the diameters of the base cylindrical surfaces D4, D5, D6. However, as Figure 10As shown, the relatively large diameter base cylindrical surfaces D4, D5, D6 result in relatively large unavailable lengths U4, U5, U6 of the involute profiles I4, I5, I6. It is undesirable to have unavailable lengths along the drive or driven surfaces. The unavailable lengths U4, U5, U6 are filled with linear or non-involute profiles. These fill lengths reduce the contact area between the drive surfaces 162a, 162b and the driven surfaces 174a, 174b. The fill lengths further reduce the cross-section of the hammer lug 154. Accordingly, there is a trade-off between decreasing curvature and increasing unavailable length as the base circle diameter increases. This trade-off exists when the central axis DA of the base cylindrical surface D is the same as the axis of rotation 158 of the anvil 114 and the hammer 150 (Figure 8). Thus, it is highly advantageous for the base cylindrical surface C to be displaced relative to the axis of rotation 58 of the anvil 14 and the hammer 50 ( Figure 5 and Figure 6 ). The displaced base cylindrical surface C allows for a maximized curvature and a minimized unavailable length.

[0057] Figure 11 A comparison between the base cylindrical surface C and the base cylindrical surface D is shown. The diameters of both base cylindrical surfaces C, D are equal to approximately 100 units. The lower limits (i.e., roots 68, 168) and upper limits (i.e., the inner surfaces 52, 152 of the hammer) of the lengths of the lugs 154, 170 are shown. The central axis CA of the shown base cylindrical surface C is offset approximately 40 units relative to the axes of rotation 58, 158, while the central axis DA of the shown base cylindrical surface D is aligned with the axes of rotation 58, 158. The base cylindrical surface C generates an involute profile CI, while the base cylindrical surface D generates an involute profile DI. Since the base cylindrical surfaces C, D have the same diameter, the corresponding involute profiles CI, DI have the same curvature. The involute CI includes an available length set to originate from the lower limit and extend to the upper limit. Thus, the involute profile CI can be set along the entire length of the drive surfaces 62a, 62b on the hammer lug 50 and the driven surfaces 74a, 74b on the anvil lug 70. The involute profile DI cannot be set along any part of the drive surfaces 162a, 162b on the hammer lug 154 or the driven surfaces 174a, 174b on the anvil lug 170 because the involute profile DI originates outside the upper limit. Accordingly, the benefit of displacing the central axis CA of the base cylindrical surface C allows the base cylindrical surface to have a large diameter (e.g., 100 units), resulting in an involute profile with a small curvature while still allowing the involute profile to be set along the entire length of the drive surfaces 62a, 62b and the driven surfaces 74a, 74b.

[0058] The various features and aspects of the present disclosure are set forth in the appended claims.

Claims

1. An anvil configured to be impacted by a hammer in an impact wrench, the anvil defining an axis of rotation, the anvil comprising: an anvil lug including a driven surface engageable with the hammer, the driven surface including an involute profile, characterised in that the involute profile is formed by a base cylindrical surface defining a central axis, and Wherein, the central axis is offset relative to the rotation axis of the anvil.

2. An anvil according to claim 1, characterized in that The anvil lug is a first anvil lug, wherein the anvil further includes a second anvil lug positioned opposite the first anvil lug, and wherein the anvil defines an anvil lug diameter from a distal end of the first anvil lug to a distal end of the second anvil lug.

3. An anvil according to claim 2, characterized in that The driven surface of the first anvil lobe is a first driven surface, and wherein the first anvil lobe further includes a second driven surface opposite the first driven surface.

4. An anvil according to claim 2 or 3, characterized in that The base cylindrical surface defines a base cylindrical surface diameter, and wherein the base cylindrical surface diameter is greater than the anvil lug diameter.

5. An anvil according to any one of claims 1 to 3, characterized in that The anvil defines an anvil plane containing the rotation axis, and wherein the anvil is symmetrical about the anvil plane.

6. An anvil according to any one of claims 1 to 3, characterized in that The anvil defines an anvil plane containing the rotational axis, and wherein the central axis is offset relative to the rotational axis in a direction parallel to the anvil plane.

7. An anvil according to any one of claims 1 to 3, characterized in that The anvil defines an anvil plane containing the rotational axis, and wherein the central axis is offset relative to the rotational axis in a direction perpendicular to the anvil plane.

8. A hammer configured to impact an anvil in an impact wrench, the hammer defining an axis of rotation, the hammer comprising: a body having an inner surface defining an inner diameter of the hammer; as well as a hammer lug extending inwardly from the inner surface toward the rotational axis, the hammer lug including a drive surface engageable with the anvil, the drive surface including an involute profile, characterised in that the involute profile is formed by a base cylindrical surface defining a central axis, and Wherein, the central axis is offset relative to the rotation axis of the hammer.

9. The hammer according to claim 8, characterized in that The hammer lug is a first hammer lug, and wherein the hammer further includes a second hammer lug extending inwardly from the inner surface toward the rotation axis, the second hammer lug opposing the first hammer lug.

10. The hammer according to claim 9, characterized in that The hammer defines a hammer plane containing the axis of rotation, and wherein the hammer is symmetrical about the hammer plane.

11. The hammer according to claim 8, characterized in that The base cylindrical surface defines a base cylindrical surface diameter, and wherein the base cylindrical surface diameter is greater than the hammer inner diameter.

12. The hammer according to claim 10, characterized in that The central axis is offset relative to the rotational axis in a direction parallel to the hammer plane.

13. The hammer according to claim 10, characterized in that The central axis is offset relative to the rotational axis in a direction perpendicular to the hammer plane.

14. A drive assembly for use in an impact wrench, the drive assembly comprising: a hammer configured to rotate about a rotational axis, the hammer comprising a body having an inner surface defining a hammer inner diameter and a hammer lug extending inwardly from the inner surface toward the rotational axis, the hammer lug having a drive surface; as well as an anvil including an anvil lug having a driven surface, wherein the driving surface of the hammer is configured to strike the driven surface of the anvil to transfer torque to the anvil, Characterized in that the driving surface and the driven surface each include an involute profile formed by a base cylindrical surface defining a base cylindrical surface diameter, and Wherein, the diameter of the base cylindrical surface is larger than the inner diameter of the hammer.

15. The drive assembly according to claim 14, characterized in that The base cylindrical surface defines a base cylindrical surface axis, and wherein the base cylindrical surface axis is offset relative to the axis of rotation.

16. The drive assembly according to claim 14, characterized in that The driven surface of the anvil lug is a first driven surface, The anvil lug includes a second driven surface opposite the first driven surface, The driving surface of the hammer is a first driving surface, and The hammer includes a second drive surface opposite the first drive surface.

17. The drive assembly according to claim 16, wherein: The first drive surface of the hammer lug is configured to engage the first driven surface of the anvil lug to drive the anvil in a first rotational direction, and wherein the second drive surface of the hammer lug is configured to engage the second driven surface of the anvil lug to drive the anvil in a second rotational direction opposite the first rotational direction.

18. The drive assembly according to claim 17, wherein: The hammer lug is a first hammer lug, and wherein the hammer further includes a second hammer lug extending inwardly from the inner surface toward the rotation axis, the second hammer lug opposing the first hammer lug.

19. The drive assembly according to claim 18, characterized in that The anvil lug is a first anvil lug, and wherein the anvil further includes a second anvil lug opposite the first anvil lug.

20. A drive assembly according to any one of claims 14 to 19, characterized in that The hammer defines a hammer plane, The hammer is symmetrical about the hammer plane. The anvil defines an anvil plane, and The anvil is symmetrical about the anvil plane.

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