impact wrench

Abstract

The present invention provides an impact wrench that can more effectively alleviate the stress concentrated near the root of the sleeve fitting portion, thereby improving the durability of the anvil. The impact wrench (1) has: a brushless motor (11); a hammer (17) that is arranged on the front side of the brushless motor and rotated by the brushless motor; and a hammer housing (16) that accommodates the hammer. In addition, the impact wrench includes an anvil (4), which has: an arm (25) that is arranged on the front side of the hammer and is struck in the rotation direction by the hammer; a cylindrical portion (30) that is connected to the arm and supported by the hammer housing; a quadrangular prism portion (31) that is arranged on the front side of the cylindrical portion; and an expanded diameter portion (35) that is arranged between the cylindrical portion and the quadrangular prism portion and expands in diameter as it moves from the quadrangular prism portion to the rear. In addition, a concave portion (37) that is continuous in the circumferential direction of the cylindrical portion is formed between the cylindrical portion and the expanded diameter portion of the anvil.

Description

Technical Field

[0001] The present invention relates to an impact wrench which generates intermittent impacts in a rotational direction toward an anvil for assembling a sleeve. Background Art

[0002] As disclosed in Patent Document 1, an impact wrench includes: a spindle to which rotation from a motor is transmitted; a hammer connected to the spindle via a cam and biased forward by a coil spring; and an anvil that engages with the hammer in the rotational direction and protrudes forward. The anvil has a cylindrical portion with a quadrangular prism portion formed at the front end of the cylindrical portion. A sleeve is mounted on the quadrangular prism portion, and a bolt or nut is engaged with the sleeve for tightening. When tightening increases the torque applied to the anvil, the hammer repeatedly engages and disengages with respect to the anvil, thereby generating intermittent impacts in the rotational direction.

[0003] According to this impact wrench, when an impact is generated, the corners of the quadrangular prism portion of the anvil and the inner surface of the square hole of the sleeve strongly contact each other in the rotational direction, thereby generating stress on the anvil. This stress is particularly concentrated near the root of the quadrangular prism portion, which is the part where the shape changes. Therefore, there is a risk of breakage near the root of the quadrangular prism portion over long-term use.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application No. 2007-500607 Summary of the Invention

[0007] However, in the anvil of Patent Document 1, an effort has been made to improve its shape, and the stress concentrated near the base of the quadrangular prism portion is alleviated.

[0008] An object of the present invention is to provide an impact wrench that can more effectively alleviate stress concentrated near the base of a socket fitting portion such as a quadrangular prism portion, thereby improving the durability of an anvil.

[0009] In order to achieve the above-mentioned object, the first invention of the present invention is an impact wrench, characterized in that it includes:

[0010] motor;

[0011] a hammer disposed in front of the motor and rotated by the motor;

[0012] a hammer housing for housing the hammer; and

[0013] anvil,

[0014] The anvil includes: an arm portion, which is arranged on the front side of the hammer and is struck in the rotational direction by the hammer; a cylindrical portion, which is connected to the arm portion and supported by the hammer housing; a sleeve fitting portion, which is arranged on the front side of the cylindrical portion; and an expanded diameter portion, which is arranged between the cylindrical portion and the sleeve fitting portion and expands in diameter as it moves from the sleeve fitting portion toward the rear.

[0015] A concave portion is formed between the cylindrical portion and the enlarged diameter portion of the anvil and is continuous in the circumferential direction of the cylindrical portion.

[0016] In order to achieve the above-mentioned object, the second invention of the present invention is an impact wrench, characterized in that it includes:

[0017] motor;

[0018] a hammer disposed in front of the motor and rotated by the motor;

[0019] a hammer housing for housing the hammer; and

[0020] anvil,

[0021] The anvil includes: an arm portion, which is arranged on the front side of the hammer and is struck in the rotation direction by the hammer; a cylindrical portion, which is connected to the arm portion and supported by the hammer housing; and a sleeve fitting portion, which is arranged on the front side of the cylindrical portion.

[0022] A first recessed portion continuous in the circumferential direction of the cylindrical portion and a second recessed portion arranged behind the first recessed portion and continuous in the circumferential direction are formed between the cylindrical portion and the sleeve fitting portion of the anvil.

[0023] Effects of the Invention

[0024] According to the present invention, by forming the recessed portion, stress concentrated near the base of the sleeve fitting portion can be more effectively alleviated, thereby improving the durability of the anvil. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a partial central longitudinal section of the impact wrench.

[0026] Figure 2 It is a three-dimensional view of the anvil.

[0027] Figure 3A to Figure 3C middle, Figure 3A is a side view of the anvil, Figure 3B is a top view of the anvil, Figure 3C It is the front view of the anvil.

[0028] Figure 4A-4B middle, Figure 4A express Figure 3C The A-A line section, Figure 4B express Figure 3C BB line section.

[0029] Figure 5 This is a perspective view of an anvil according to a modified example.

[0030] Figures 6A to 6C middle, Figure 6A 1 is a side view of the anvil of the modified example. Figure 6B is a top view of the anvil of the modified example, Figure 6C This is a front view of an anvil according to a modified example.

[0031] Figures 7A and 7B middle, Figure 7A express Figure 6C The C-C line cross section, Figure 7B express Figure 6C D-D line section.

[0032] Figure 8 This is a perspective view of an anvil according to a modified example.

[0033] Figures 9A to 9C middle, Figure 9A 1 is a side view of the anvil of the modified example. Figure 9B is a top view of the anvil of the modified example, Figure 9C This is a front view of an anvil according to a modified example.

[0034] Figures 10A and 10B middle, Figure 10A express Figure 9C The E-E line cross section, Figure 10B express Figure 9C F-F line section.

[0035] Explanation of symbols

[0036] 1··Impact wrench, 2··Main body, 3··Handle, 4, 4A, 4B··Anvil, 11··Brushless motor, 13··Spindle, 14··Striking mechanism, 15··Rotating shaft, 17··Hammer, 24··Arm, 30··Cylinder, 31··Quadrangular prism, 32A~32D··Side, 35··Expanded diameter portion, 36··Tongue, 37··Recess, 37A··First recess, 37B··Second recess, 40, 41··Protrusion, 50··Sleeve, A··Axis of anvil, D··Outer diameter of cylinder, d1, d2··Diameter of the deepest part of recess, r1, r2··Radius of the semicircular cross section of recess, C··Circumscribed circle of quadrangular prism, S··The distance between parallel side surfaces, θ1, θ2··Groove angle. DETAILED DESCRIPTION

[0037] Hereinafter, embodiments of the present invention will be described based on the drawings.

[0038] Figure 1 It is a central longitudinal sectional view showing an example of an impact wrench.

[0039] The impact wrench 1 includes a main body 2 and a handle 3. The main body 2 extends in the front-to-back direction, and the handle 3 extends downward from the main body 2. The rear portion of an anvil 4 is housed within the main body 2. The front portion of the anvil 4 protrudes forward from the front end of the main body 2.

[0040] A switch 5 for causing a trigger 6 to protrude forward is provided on the upper portion of the handle 3. A forward / reverse switching button 7 for the rotation direction of the anvil 4 is provided above the switch 5. A light 8 for illuminating the front of the anvil 4 is provided above the trigger 6. A battery assembly portion 9 is formed at the lower end of the handle 3. A battery pack 10 serving as a power source is mounted on the battery assembly portion 9. A controller (not shown) is housed within the battery assembly portion 9.

[0041] Inside the main body 2, from the rear, are a brushless motor 11, a speed reduction mechanism 12, a main shaft 13, and a striking mechanism 14. The brushless motor 11 has a rotating shaft 15. The rotation of the rotating shaft 15 is decelerated by the speed reduction mechanism 12. The decelerated rotation is then transmitted to the main shaft 13.

[0042] The striking mechanism 14 is housed in a hammer case 16 provided at the front of the main body 2. The striking mechanism 14 includes a hammer 17 mounted outside the main shaft 13 and a coil spring 18 for urging the hammer 17 forward.

[0043] The hammer 17 is rotationally coupled to the spindle 13 via balls 19, 19 disposed between the hammer 17 and the spindle 13. Cam grooves 20, 20 are formed on the inner circumference of the hammer 17 and the outer circumference of the spindle 13, into which the balls 19, 19 engage. A coil spring 18 is attached to the outside of the spindle 13 to bias the hammer 17 forward. A pair of claws 21, 21 are provided on the front surface of the hammer 17.

[0044] The anvil 4 is supported by the front cylindrical portion 22 of the hammer case 16. The hammer case 16 is made of aluminum. An iron insert bushing 22a is insert-molded into the front cylindrical portion 22. This secures the insert bushing 22a to the hammer case 16. A metal bearing 23 is press-fitted into the insert bushing 22a. The metal bearing 23 supports the anvil 4 coaxially with the spindle 13. Because the metal bearing 23 is press-fitted into the insert bushing 22a, the anvil 4 can be retained in the hammer case 16 even when the width (axial length) of the insert bushing 22a is small. An oil seal 24 is disposed in front of the metal bearing 23. The oil seal 24 prevents grease from leaking out of the hammer case 16.

[0045] At the rear end of the anvil 4, a pair of arms 25, 25 are radially formed. The arms 25, 25 engage with the claws 21, 21 of the hammer 17 in the rotational direction. There may be more than three arms 25 and claws 21. There may also be one arm 25 and one claw 21. An adjustment shim 26 is provided between the front cylinder 22 and the arms 25, 25. The anvil 4 is positioned forward by the adjustment shim 26. A bottomed hole 27 is formed at the axis of the anvil 4 and starting from the rear end. The small-diameter portion 28 provided at the front end of the spindle 13 is inserted into the rear end of the bottomed hole 27.

[0046] Figure 2 The figure shows a perspective view of the anvil 4 as viewed from the front. In the anvil 4, the front of the arms 25, 25 is a cylindrical portion 30 having a circular cross-section. A quadrangular prism portion 31 is provided in front of the cylindrical portion 30. The cross-section of the quadrangular prism portion 31 perpendicular to the axis A of the anvil 4 is substantially square. The quadrangular prism portion 31 has four side faces 32A, 32B, 32C, and 32D, and four corners 33, 33... located between the side faces 32A to 32D.

[0047] A sleeve 50 is detachably mounted on the quadrangular prism portion 31. The sleeve 50 has a square hole 51 with a substantially square cross-section. A through hole 34 is formed through the quadrangular prism portion 31, perpendicular to the side surfaces 32A and 32C. The purpose of providing the through hole 34 is to allow the sleeve 50's anti-drop pin to pass through.

[0048] An expanded diameter portion 35 is formed on the rear side of the quadrangular prism portion 31. The expanded diameter portion 35 includes four tongues 36 extending rearward from the rear ends of the four side surfaces 32A to 32D of the quadrangular prism portion 31. Each tongue 36 curves and expands radially outward from the anvil 4 as it approaches the rear. The rear end of each tongue 36 has an arc-like shape when viewed from the front. The expanded diameter portion 35 serves as a stopper that limits the rearward movement of the sleeve 50.

[0049] A recess 37 is formed behind the enlarged diameter portion 35 and between the cylindrical portion 30. The recess 37 is annular and continuous in the circumferential direction of the cylindrical portion 30. Figure 3A to Figure 3C and Figure 4A-4B As shown, the cross-sectional shape of the recess 37 is a semicircular shape with a radius r1. The diameter d1 of the deepest part of the recess 37 is formed to be slightly larger than the distance S (width across the sides) between the mutually parallel side surfaces 32A and 32C of the quadrangular prism portion 31. In addition, the diameter d1 is formed to be smaller than Figure 3C The diameter of the circumscribed circle C of the quadrangular prism portion 31 is shown.

[0050] In the recess 37, the groove angle θ1 formed by two tangent lines passing through the front and rear end edges of the cross section ( Figure 4A ) is less than 90°.

[0051] The front end of the bottomed hole 27 at the rear of the anvil 4 stays in the cylindrical portion 30, and its length does not reach the recess 37. That is, the bottomed hole 27 does not overlap with the recess 37 in the radial direction of the anvil 4. Therefore, even if the recess 37 is provided, the strength of the anvil 4 can be maintained.

[0052] A thin-diameter portion 38 is provided in front of the quadrangular column portion 31. The thin-diameter portion 38 is arranged at the front end of the anvil 4. A C-shaped elastic body 39 ( Figure 1 ).

[0053] In the impact wrench 1 constructed as described above, the trigger 6 is pressed in by the hand holding the handle 3. At this point, the switch 5 is turned on, and the brushless motor 11 is driven by power from the battery pack 10. This causes the rotating shaft 15 to rotate, and the spindle 13 rotates at a reduced speed via the speed reduction mechanism 12. Rotation of the spindle 13 causes the hammer 17 to rotate via the balls 19, 19. Rotation of the hammer 17 also causes the anvil 4 to rotate, allowing the socket 50 to tighten a bolt or the like.

[0054] When tightening is performed and the torque of the anvil 4 increases, the hammer 17 retreats against the force of the coil spring 18. That is, the hammer 17 retreats rearward while rotating the balls 19 along the cam grooves 20. Furthermore, when the claws 21, 21 fall off the arms 25, 25, the hammer 17 rotates and advances due to the force of the coil spring 18 and the guidance of the cam grooves 20. As a result, the claws 21, 21 reengage the arms 25, 25, generating a rotational striking force (impact) on the anvil 4. By intermittently repeating this impact, further tightening can be achieved.

[0055] When an impact occurs, stress is generated in the quadrangular prism portion 31 due to the collision between the quadrangular prism portion 31 of the anvil 4 and the inner surface of the square hole 51 of the sleeve 50. However, since a recess 37 is formed between the cylindrical portion 30 and the expanded diameter portion 35, the anvil 4 has a shape in which two shape-changing portions, the quadrangular prism portion 31 and the recess 37, are sandwiched between the expanded diameter portion 35. The shape of the recess 37 is such that the difference between the stress generated in the recess 37 and the stress generated in the quadrangular prism portion 31 does not become large. Therefore, the stress is not concentrated near the root of the quadrangular prism portion 31, but is dispersed toward the recess 37. As a result, breakage is less likely to occur near the root of the quadrangular prism portion 31.

[0056] The specific examples are described below using numerical values. Figure 3ATake the anvil 4 as an example, in which the total axial length L is 49.5 mm, the axial length L1 from the front surface of the arm 25 to the root of the quadrangular prism portion 31 is 24.5 mm, the outer diameter D of the cylindrical portion 30 is 18 mm, and the spacing S between the parallel side surfaces 32A and 32C of the quadrangular prism portion 31 is 12.7 mm.

[0057] In this case, the recessed portion 37 is formed so that the radius r1 of the semicircular cross section is 3.5 mm, the diameter d1 of the deepest portion is 13.4 mm, and the groove angle θ1 is 70°.

[0058] The anvil 4 having the recess 37 and an anvil of a conventional shape with the same dimensions and without the recess 37 were modeled. A moment of 400 Nm was applied to each model to analyze the stress generated at the base of the quadrangular prism portion 31 .

[0059] As a result, it was confirmed that the stress of the anvil 4 having the recessed portion 37 was reduced by approximately 10% compared to the anvil of the conventional shape not having the recessed portion 37 .

[0060] The impact wrench 1 of the above embodiment includes a brushless motor 11 (motor); a hammer 17 disposed in front of the brushless motor 11 and rotated by the brushless motor 11; and a hammer housing 16 that houses the hammer 17. Furthermore, the impact wrench 1 includes an anvil 4 having an arm 25 disposed in front of the hammer 17 and struck in the rotational direction by the hammer 17; a cylindrical portion 30 connected to the arm 25 and supported by the hammer housing 16; a quadrangular prism portion 31 (sleeve fitting portion) disposed in front of the cylindrical portion 30; and an expanded diameter portion 35 disposed between the cylindrical portion 30 and the quadrangular prism portion 31 and increasing in diameter as it moves rearward from the quadrangular prism portion 31. Furthermore, a concave portion 37 is formed between the cylindrical portion 30 and the expanded diameter portion 35 of the anvil 4, extending continuously in the circumferential direction of the cylindrical portion 30.

[0061] According to this configuration, stress concentrated near the base of the quadrangular prism portion 31 can be alleviated, thereby improving the durability of the anvil 4 .

[0062] In particular, the cross section of the recessed portion 37 is semicircular. This allows the recessed portion 37 to have a less distorted shape, thereby suppressing stress generated in the recessed portion 37.

[0063] The diameter d1 of the deepest portion of the recess 37 is smaller than the diameter of the circumscribed circle C of the quadrangular prism portion 31. This allows the recess 37 to be obtained that is effective in relaxing stress.

[0064] The deepest diameter of the recess 37 is larger than the interval S between the parallel side surfaces 32A and 32C of the quadrangular prism portion 31. Thus, even if the recess 37 is provided, the required strength can be ensured.

[0065] However, the diameter d1 of the recess 37 may be the same as the distance S or smaller than the distance S.

[0066] In addition, the diameter d1 may be equal to the diameter of the circumscribed circle C or greater than the diameter of the circumscribed circle C.

[0067] Hereinafter, modification examples will be described.

[0068] The anvil in the above-described embodiment has a structure in which one recess is formed between the cylindrical portion and the enlarged diameter portion. However, a plurality of recesses may be formed.

[0069] Figures 5 to 7A 、 Figure 7B A modified anvil 4A is shown. In this anvil 4A, two recesses are formed in the axial direction of the anvil 4A: a first recess 37A and a second recess 37B. Both recesses 37A and 37B have semicircular cross-sections, with their radii set such that the radius r1 of the first recess 37A is slightly larger than the radius r2 of the second recess 37B. The axial widths of the first recess 37A and the second recess 37B are set to be approximately equal.

[0070] The two recessed portions 37A and 37B partially overlap in the axial direction of the anvil 4A, and an annular protrusion 40 having a diameter smaller than that of the cylindrical portion 30 is formed therebetween.

[0071] The diameters of the deepest portions of the two recesses 37A and 37B are set so that the diameter d1 of the first recess 37A is slightly larger than the diameter d2 of the second recess 37B. Both diameters d1 and d2 are smaller than the diameter of the circumscribed circle C of the quadrangular prism portion 31. Furthermore, both diameters d1 and d2 are set larger than the spacing S between the parallel side surfaces 32A and 32C of the quadrangular prism portion 31.

[0072] In this case, the stress generated in the anvil 4A is also dispersed to the quadrangular prism portion 31, the first recess 37A, and the second recess 37B, and is not concentrated near the base of the quadrangular prism portion 31. Thus, the stress concentrated near the base of the quadrangular prism portion 31 can be alleviated, thereby improving the durability of the anvil 4A.

[0073] Numerical values ​​will be cited to illustrate a specific example. Based on the anvil with the previously mentioned dimensional settings, a model was produced in which the semicircular radius r1 of the first recess 37A was 2.5 mm, the semicircular radius r2 of the second recess 37B was 2.0 mm, the diameter d1 of the deepest portion of the first recess 37A was 13.1 mm, the diameter d2 of the deepest portion of the second recess 37B was 12.8 mm, the axial partial overlap length between the recesses 37A and 37B was 2.5 mm, the groove angle θ1 of the first recess 37A was 45°, and the groove angle θ2 of the second recess 37B was 40°. A moment of 400 Nm was applied to the model, and the stress generated at the root of the quadrangular prism portion 31 was analyzed.

[0074] As a result, it was confirmed that the anvil 4A having the first and second recessed portions 37A and 37B had a stress reduction of approximately 15% compared to an anvil of a conventional shape having no recessed portion.

[0075] In this modified example, a first recess 37A continuous in the circumferential direction of the cylindrical portion 30 and a second recess 37B arranged behind the first recess 37A and continuous in the circumferential direction of the cylindrical portion 30 are similarly formed between the cylindrical portion 30 and the quadrangular prism portion 31. This can alleviate the stress concentrated near the base of the quadrangular prism portion 31, thereby improving the durability of the anvil 4.

[0076] In particular, an annular protrusion 40 having a diameter smaller than that of the cylindrical portion 30 is formed between the first recess 37A and the second recess 37B. This allows the two recesses 37A and 37B to be connected to each other, thereby dispersing stress.

[0077] The first recess 37A and the second recess 37B have the same width in the axial direction of the anvil 4. This allows the stress to be evenly dispersed.

[0078] An expanded diameter portion 35 that expands toward the rear from the quadrangular prism portion 31 is formed between the first concave portion 37A and the quadrangular prism portion 31. This clearly distinguishes the shape-changing portion of the quadrangular prism portion 31 from the shape-changing portion of the first concave portion 37A, thereby improving the stress relaxation effect.

[0079] The cross sections of the first and second recesses 37A, 37B are both semicircular. This allows the first and second recesses 37A, 37B to have minimal shape variation, thereby suppressing stress generated in the recesses 37A, 37B.

[0080] The deepest diameters d1 and d2 of the first and second recesses 37A and 37B are both smaller than the diameter of the circumscribed circle C of the quadrangular prism portion 31. This provides the first and second recesses 37A and 37B that are effective in relaxing stress.

[0081] The deepest diameters d1 and d2 of the first and second recesses 37A and 37B are both larger than the interval S between the parallel side surfaces 32A and 32C of the quadrangular prism portion 31. Therefore, even with the first and second recesses 37A and 37B, the required strength can be ensured.

[0082] but, Figures 5 to 7A 、 Figure 7B In a modified example, the radii r1 and r2 of the first and second recesses 37A and 37B may be equal to each other. The widths of the first and second recesses 37A and 37B in the axial direction may also be equal to each other.

[0083] The diameters d1 and d2 can be set to be equal to each other, the same as the diameter of the circumscribed circle C, or larger than the diameter of the circumscribed circle C.

[0084] The diameters d1 and d2 may be the same as the distance S or smaller than the distance S.

[0085] Figures 8 to 10A 、 Figure 10B Another modified anvil 4B is shown. Similarly, in this anvil 4B, two recesses are formed in the axial direction of the anvil 4B: a first recess 37A and a second recess 37B. However, the axial widths of the two recesses 37A and 37B are different: the first recess 37A is larger than the second recess 37B. Consequently, the radii of the semicircular cross-sections of the two recesses 37A and 37B are different: the radius r1 of the first recess 37A is larger than the radius r2 of the second recess 37B.

[0086] Furthermore, the two recesses 37A and 37B are separated in the axial direction, and an annular protrusion 41 having the same diameter as the cylindrical portion 30 is formed between them. The diameters of the deepest portions of the two recesses 37A and 37B are set so that the diameter d1 of the first recess 37A is slightly smaller than the diameter d2 of the second recess 37B. Both diameters d1 and d2 are smaller than the diameter of the circumscribed circle C of the quadrangular prism portion 31. Furthermore, the diameters d1 and d2 are larger than the spacing S between the parallel side surfaces 32A and 32C.

[0087] In this case, the stress generated in the anvil 4B is dispersed to the quadrangular prism portion 31, the first recess 37A, and the second recess 37B, and is not concentrated near the base of the quadrangular prism portion 31. This can alleviate the stress concentrated near the base of the quadrangular prism portion 31 and improve the durability of the anvil 4B.

[0088] Numerical values ​​will be used to illustrate a specific example. Based on the anvil dimensions previously described, a model was produced in which the semicircular radius r1 of the first recess 37A was 3.0 mm, the semicircular radius r2 of the second recess 37B was 1.0 mm, the diameter d1 of the deepest portion of the first recess 37A was 12.9 mm, the diameter d2 of the deepest portion of the second recess 37B was 13.5 mm, the axial length of the protrusion 41 was 1.3 mm, the groove angle θ1 of the first recess 37A was 45°, and the groove angle θ2 of the second recess 37B was 20°. A moment of 400 Nm was applied to the model, and the stress generated at the base of the quadrangular prism portion 31 was analyzed. The results showed that the anvil 4B with the first and second recesses 37A and 37B showed a stress reduction of approximately 12% compared to an anvil of a conventional shape without recesses.

[0089] In this modified example, a first recess 37A continuous in the circumferential direction of the cylindrical portion 30 and a second recess 37B arranged behind the first recess 37A and continuous in the circumferential direction of the cylindrical portion 30 are similarly formed between the cylindrical portion 30 and the quadrangular prism portion 31. This can alleviate stress concentrated near the base of the quadrangular prism portion 31, thereby improving the durability of the anvil 4.

[0090] In particular, an annular protrusion 41 having the same diameter as that of the cylindrical portion 30 is formed between the first recess 37A and the second recess 37B. This ensures the strength of the vicinity of the two recesses 37A and 37B.

[0091] The first recess 37A and the second recess 37B have different widths in the axial direction of the anvil 4. This ensures the axial length of the cylindrical portion 30 even when a plurality of recesses are provided.

[0092] but, Figures 8 to 10A 、 Figure 10B In the modified example, the diameters d1 and d2 of the first and second recesses 37A and 37B may be set to be equal to each other, or the diameter d1 may be set to be larger than the diameter d2.

[0093] The diameters d1 and d2 may be the same as the diameter of the circumscribed circle C, or may be larger than the diameter of the circumscribed circle C.

[0094] The diameters d1 and d2 may be the same as the distance S or smaller than the distance S.

[0095] Hereinafter, modifications common to the above-mentioned examples will be described.

[0096] The shape of the recessed portion is not limited to the above examples and can be changed as appropriate. The number of recessed portions can be three or more.

[0097] The cross-sectional shape of the recessed portion is not limited to a semicircular shape, and may be a semi-elliptical shape or a V-shaped shape. However, if the shape change is large like a V-shaped shape, stress concentration occurs, and therefore, a shape with a gentle shape change such as a semicircular shape or a semi-elliptical shape is preferred.

[0098] The expanded diameter portion is not limited to the expanded diameter portion including four tongues extending from the side surface of the quadrangular prism portion. For example, the four tongues may be connected to each other in the circumferential direction to form an annular expanded portion (conical portion) with a circular rear end.

[0099] The shapes of the quadrangular prism portion, cylindrical portion, and arm portion may also be changed. The quadrangular prism portion may not have a through hole. In addition, the thin-diameter portion may not be formed.

[0100] The sleeve fitting portion is not limited to a quadrangular prism portion, and may also be in other shapes. For example, it may be a hexagonal prism, an octagonal prism, or other polygonal columns. As long as it can be fitted into the substantially square hole provided in the sleeve in a rotationally fixed state.

[0101] Furthermore, the motor does not need to be a brushless motor, but can be an AC machine that does not use a battery pack.

Claims

1. An impact wrench, characterized in that: include: motor; a hammer disposed in front of the motor and rotated by the motor; A hammer housing for housing the hammer; as well as anvil, The anvil includes an arm portion that is disposed in front of the hammer and is struck in a rotational direction by the hammer; a cylindrical portion connected to the arm portion and supported by the hammer housing; a sleeve fitting portion disposed on the front side of the cylindrical portion; and an enlarged diameter portion, which is disposed between the cylindrical portion and the sleeve fitting portion and which enlarges in diameter as it moves from the sleeve fitting portion toward the rear. A concave portion is formed between the cylindrical portion and the enlarged diameter portion of the anvil and is continuous in the circumferential direction of the cylindrical portion. The sleeve fitting portion is a quadrangular prism portion, and the diameter of the deepest portion of the recess is larger than the interval between the parallel side surfaces of the quadrangular prism portion.

2. The impact wrench according to claim 1, wherein: The cross section of the recess is semicircular.

3. The impact wrench according to claim 1 or 2, characterized in that The diameter of the deepest portion of the recess is smaller than the diameter of the circumscribed circle of the sleeve fitting portion.

4. An impact wrench, characterized in that: include: motor; a hammer disposed in front of the motor and rotated by the motor; A hammer housing for housing the hammer; as well as anvil, The anvil includes an arm portion that is disposed in front of the hammer and is struck in a rotational direction by the hammer; a cylindrical portion connected to the arm portion and supported by the hammer housing; and a sleeve fitting portion, the sleeve fitting portion being arranged on the front side of the cylindrical portion, A first recessed portion continuous in the circumferential direction of the cylindrical portion and a second recessed portion arranged on the rear side of the first recessed portion and continuous in the circumferential direction are formed between the cylindrical portion of the anvil and the sleeve fitting portion. The sleeve fitting portion is a quadrangular prism portion, and the diameters of the deepest parts of the first recess and the second recess are both larger than the interval between the parallel side surfaces of the quadrangular prism portion.

5. The impact wrench according to claim 4, wherein: An annular protrusion having a diameter smaller than that of the cylindrical portion is formed between the first recess and the second recess.

6. The impact wrench according to claim 4, wherein: An annular protrusion having the same diameter as that of the cylindrical portion is formed between the first recess and the second recess.

7. The impact wrench according to any one of claims 4 to 6, characterized in that The first recess and the second recess have the same width in the axial direction of the anvil.

8. The impact wrench according to any one of claims 4 to 6, characterized in that The first recess and the second recess have different widths in the axial direction of the anvil.

9. The impact wrench according to any one of claims 4 to 6, characterized in that An expanded diameter portion that expands in diameter as it moves rearward from the sleeve fitting portion is formed between the first recess and the sleeve fitting portion.

10. The impact wrench according to any one of claims 4 to 6, characterized in that The cross sections of the first concave portion and the second concave portion are both semicircular.

11. The impact wrench according to any one of claims 4 to 6, characterized in that The diameters of the deepest parts of the first recess and the second recess are both smaller than the diameter of the circumscribed circle of the sleeve fitting portion.

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