FIELD OF THE INVENTION

The present invention relates to a power tool, in particular to an anvil assembly for a power tool and an impact wrench comprising the anvil assembly.

BACKGROUND OF THE INVENTION

An impact wrench is a power tool for securing or loosening a fastening device such as a bolt, nut or screw. In general, motive power is supplied to the impact wrench by electric power or hydraulic motive power and a pneumatic motor. An electric impact wrench is designed to use a series of brief, fierce forces, produced by a swing hammer striking an anvil, to apply a torque; the swing hammer is connected to an output shaft of an electric motor, while the anvil is connected to a drive shaft of the tool.

An existing anvil assembly for a power tool, in particular an impact wrench, is affected by the problem of susceptibility to fatigue failure, resulting in fracture of an anvil assembly bearing component. Fatigue fractures generally begin at a point where a sudden change in geometry occurs, or at a stress concentration point, and gradually increase in size until a critical size is reached. It has been found that in an existing anvil assembly design, stress concentration arises at a transverse hole on a tool clamping head surface. This kind of stress concentration arising at the transverse hole seriously weakens the security of a tool clamping head, thereby increasing the risk of fatigue failure thereof.

For example, CN 10740578 has disclosed a square-head tool clamping head for an impact wrench, comprising an anvil, and a stop bolt for locking a clamped tool element, wherein the stop bolt is locked by means of two locating pins disposed in the drive square head in order to prevent detachment. Thus, it is necessary for two long and narrow holes to be provided running inward from an end face of the drive square head in order to accommodate the locating pins; stress imbalances occur very easily at these two long and narrow holes, causing the drive square head to suffer cracking or even damage, and due to the presence of the holes, the anvil wall is thinned, so the service life is unable to meet customer needs. For the above reasons, there is a need for an anvil assembly for a power tool, in particular an impact wrench, that is capable of reducing stress concentration and fatigue failure at a tool element clamping head.

SUMMARY OF THE INVENTION

The present invention provides an anvil assembly for a power tool, comprising an anvil, on which anvil are provided a drive square head for clamping a tool, and a detent pin for locking a clamped tool element, the detent pin being supported elastically in a recess of the drive square head in such a way as to be moveable perpendicular to a rotation axis (D) of the anvil, characterized in that the detent pin is supported by a U-shaped supporting clip installed in the drive square head.

According to a preferred embodiment of the present invention, the drive square head comprises four substantially flat holding faces extending along a rotation axis (D) and an end face perpendicular to the rotation axis, wherein adjacent holding faces are substantially perpendicular to each other. The recess is disposed in one of the holding faces of the drive square head, and the bottom of the recess is higher than the rotation axis (D) of the anvil. The end face of the drive square head is provided with an opening substantially parallel to the direction of the rotation axis, and the U-shaped supporting clip is disposed in the opening.

According to another preferred embodiment of the present invention, an opening substantially perpendicular to the direction of the rotation axis is provided in another holding face of the drive square head, and the U-shaped supporting clip is disposed in the opening. Preferably, the opening is offset from the rotation axis (D) of the anvil.

According to another preferred embodiment of the present invention, two free ends of the U-shaped supporting clip respectively abut the bottom of the recess and the detent pin. Preferably, a locating slot is provided at the bottom of the recess, and one free end of the U-shaped supporting clip is provided with a locating lug capable of extending into the locating slot. More preferably, the detent pin is constructed to be rotationally symmetric, and a snap-fit structure accommodating another free end of the U-shaped supporting clip is provided at the bottom of the detent pin.

An impact wrench, comprising the anvil assembly as described above for clamping a tool element, in particular an impact wrench socket.

The present invention uses a U-shaped metal clip to support the detent pin in the drive square head, for the purpose of locking a socket of an impact wrench tool element, thereby simplifying the number of components and structure of the anvil assembly. Moreover, due to the fact that a supporting spring and two locating pins for locking the detent pin in the prior art are eliminated, the wall thickness of a detent pin region of the drive square head of the anvil is greatly increased, thereby increasing the sturdiness and durability of the anvil, and furthermore, the elimination of long and narrow locating pin holes also greatly reduces the possibility of the anvil cracking due to excessive local stress. Thus, the anvil assembly for a power tool of the present invention has a simple structure, is easy to manufacture and install, and greatly improves the reliability and durability of the anvil.

In the present invention, the U-shaped supporting clip not only serves the function of locating and supporting the detent pin in an axial direction, but at the same time serves the function of elastically supporting the detent pin in a direction perpendicular to the rotation axis, such that the detent pin protrudes from the holding face of the drive square head in a state of having sprung outwards, and the detent pin is at least partially sunken in the holding face in a state of being pressed inwards. The purpose of the locating slot in the recess is to ensure the position of the U-shaped supporting clip in the opening, so that it will not easily detach from the drive square head. The snap-fit structure on the detent pin makes it easier for the detent pin and the U-shaped supporting clip to be connected together stably and positioned accurately relative to each other.

According to a preferred embodiment of the present invention, the bottom of the recess is higher than the rotation centre of the anvil, and the opening is offset from the rotation centre of the anvil. Thus, viewed from the end face of the drive square head, the opening is offset from the anvil rotation axis, i.e. from the centre of the drive square head; the bottom of the recess is higher than the rotation centre of the anvil, such that the U-shaped supporting clip and detent pin as a whole are located at one side of an anvil rotation centre line, to ensure that the strength and durability of the anvil itself are affected as little as possible. BRIEF DESCRIPTION OF THE FIGURES

The embodiments mentioned can be better understood through the following detailed description while perusing the accompanying drawings. It is emphasized that the various components are not necessarily drawn to scale. In fact, dimensions can be enlarged or reduced at will for the purposes of clear discussion. In the drawings, identical reference labels denote identical elements.

Fig. 1 is a perspective view of a schematic embodiment of the impact wrench of the present invention.

Fig. 2 shows a perspective view of the anvil assembly for a power tool according to the present invention.

Fig. 3 is a front view of the anvil assembly for a power tool according to the present invention shown in fig. 1.

Fig. 4 is a sectional drawing, taken along line A-A, of the anvil assembly for a power tool of the present invention shown in fig. 2. DETAILED DESCRIPTION OF THE INVENTION

An anvil assembly for a power tool and an impact wrench comprising the anvil assembly according to embodiments of the present invention are described below with reference to figs. 1 - 4.

Fig. 1 shows an impact wrench 10, comprising a housing 11, a motor 12, an anvil assembly 13, and a tool element coupled to the anvil assembly. The impact wrench 10 further comprises a switch 14 (e.g. a trigger switch) and the motor; the switch is supported by the housing 11; the switch 12 and motor 12 are electrically connected to an AC power supply. The motor 12 is coupled to the anvil assembly 13 in order to supply torque to the anvil assembly 13 and the tool element. Although the tool element has not been shown schematically, the tool element may comprise a socket configured to mesh with the head of a fastening member (e.g. a bolt). Optionally, the tool element may comprise any number of different structures (e.g. an auger or drill bit) in order to perform work on a workpiece. Optionally, the impact wrench 10 may comprise a battery, and a motor 26 may be configured to rely on a DC power supply provided by the battery for operation. In an additional, optional embodiment, the impact wrench 10 may be configured to use a different energy source other than electric power (e.g. wind power or hydropower) for operation.

Referring to figs. 2 - 4, according to an embodiment of the present invention, the anvil assembly 13 comprises an anvil 1, on which anvil is provided a drive square head 2 for clamping the tool element. Referring to figs. 2 and 3, the drive square head 2 comprises a longitudinal axis, i.e. a rotation axis D when the power tool is operating. Viewed in the direction of the rotation axis D, the drive square head 2 generally has an end face 21 with a substantially square cross-sectional shape, the end face 21 being substantially perpendicular to the rotation axis D. The drive square head further comprises four substantially flat holding faces 20, 20’ extending along the rotation axis D, wherein adjacent holding faces 20, 20’ are substantially perpendicular to each other. The holding faces 20, 20’ together form the generally square cross-sectional shape of the drive square head. Optionally, the cross-sectional shape of the drive square head may be configured in any number of different ways, in order to receive or admit the tool element; the tool element has a hole or slot with a corresponding shape for accommodating the drive square head 2.

A recess 6 is provided in one of the holding faces 20 of the drive square head 2, to accommodate a detent pin 3 for locking a clamped tool element 7. Preferably, the recess 6 is a hole, extending towards the rotation axis D in a such a way as to be substantially perpendicular to the holding face. More preferably, the bottom of the recess 6 is higher than the position of the rotation axis (D). In other words, the recess 6 is located at only one side of the square cross section of the drive square head 2, e.g. an upper half of the square shape. More preferably, the recess 6 is located on a centre line of one holding face 20, at equal distances from two adjacent other holding faces 20’, in order to better resolve the problem of fracture of the drive square head due to uneven stress, and the distance between the recess 6 and the end face 21 should not be too large; the position of the recess 6 is selected rationally according to the size and hardness of the drive square head 2, to ensure the durability of the drive square head.

The detent pin 3 is supported elastically in the recess 6 of the drive square head 2 in such a way as to be moveable perpendicular to the rotation axis D of the anvil 1. The detent pin 3 is supported by a U-shaped supporting clip 4 installed in the drive square head 2. The detent pin 3 has a rounded, preferably hemispherical surface; the surface protrudes from the holding face 20 of the drive square head 2 in a state in which the detent pin 3 has sprung outwards, and is at least partially sunken in the holding face 20 in a state in which the detent pin 3 is pressed inwards.

An opening 5 is provided in the end face 21 of the drive square head in such a way as to be substantially parallel to the direction of the rotation axis D, and the U-shaped supporting clip 4 is disposed in the opening 5. The shape of the opening 5 depends on the shape of the U-shaped supporting clip. For example, the opening 5 may be a blind hole, or a narrow slot. Preferably, the opening 5 extends from the end face to the recess 6. More preferably, the opening 5 is offset from the rotation axis D of the anvil, i.e. a longitudinal axis of the opening 5, whether a blind hole or a narrow slot, does not coincide with the rotation axis D of the anvil. An advantage of the opening 5 being disposed in this way is that the distribution of stress borne by the anvil during operation of the impact wrench is improved, in order to avoid fracture of the drive square head due to stress concentration. In particular, the opening 5 extends to the recess 8 and intersects the bottom of the recess 8; when the bottom of the recess 8 is higher than the rotation axis D, the opening 5 is also higher than the rotation axis D of the anvil, thus the detent pin 3 and U-shaped supporting clip 4 as a whole are close to one side of the square cross section of the drive square head 2, such that the wall thickness of a detent pin region of the drive square head of the anvil is greatly increased, thereby increasing the sturdiness and durability of the drive square head.

Two free ends 41 , 42 of the U-shaped supporting clip respectively abut the bottom of the recess 6 and a lower part of the detent pin 3. The U-shaped supporting clip not only serves the function of locating and supporting the detent pin in an axial direction, but at the same time serves the function of elastically supporting the detent pin in a direction perpendicular to the rotation axis, such that the detent pin protrudes from the holding face of the drive square head 2 in a state of having sprung outwards, and the detent pin is at least partially sunken in the holding face in a state of being pressed inwards. Preferably, a locating slot 7 is provided at the bottom of the recess 6, and one free end 41 of the U-shaped supporting clip is provided with a locating lug 42 capable of extending into the locating slot. The purpose of the locating slot in the recess is to ensure the position of the U-shaped supporting clip 4 in the opening 5, so that it will not easily detach from the drive square head. More preferably, the detent pin 3 is constructed to be rotationally symmetric, and a snap-fit structure accommodating another free end of the U-shaped supporting clip is provided at the bottom of the detent pin. The snap-fit structure on the detent pin makes it easier for the detent pin 3 and the U-shaped supporting clip to be connected together stably and positioned accurately relative to each other.

As stated above, although demonstrative embodiments of the present invention have already been explained herein with reference to the accompanying drawings, the present invention is not limited to the particular embodiments described above; many other embodiments are possible, and the scope of the present invention should be defined by the claims and their equivalent meaning.