ROTARY IMPACT TOOL

A rotary impact tool includes an anvil that receives rotational impact force from a hammer of an impact mechanism. A driver cover covers the impact mechanism. A bearing is press fitted into and fixed to the driver cover to hold the anvil. A bearing separation restricting component restricts separation of the bearing from the driver cover. The bearing separation restricting component is hidden inside the driver cover and is invisible from an outer surface of the driver cover.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2015-047243, filed on Mar. 10, 2015, the entire contents of which are incorporated herein by reference.

FIELD

The present invention relates to a rotary impact tool and, more particularly, to a bearing that holds an anvil of a rotary impact tool.

BACKGROUND

Japanese Laid-Open Patent Publication No. 2010-76022, the entire contents of which are incorporated herein by reference, discloses a prior art rotary impact tool. The rotary impact tool includes an anvil that is held by a bearing. The bearing is press fitted into and fixed to a driver cover, which covers an impact mechanism that includes a hammer, which strikes the anvil. The impact mechanism coverts the rotational output of an electric motor to rotational impact force that rotates an output shaft. The rotary impact tool tightens or loosens a fastener with a bit coupled to the output shaft, such as a Phillips screwdriver bit.

SUMMARY

The anvil is rotationally supported by a bearing which is press fitted into and fixed to the driver cover. Vibration produced when the hammer strikes the anvil may separate the bearing from the driver cover. Separation of the bearing from the driver cover results in the loss of a clearance that rotates the anvil and the hammer in a lubricative manner. This impedes lubricative rotation of the anvil and the hammer.

In a referential example shown inFIG. 5, a linear pin94is used to restrict separation of a bearing93. More specifically, a driver cover91includes a pin hole92that is orthogonal to a rotary axis. The pin hole92extends from the outer surface of the driver cover91to the inner surface (wall surface of cylindrical bore) of the driver cover91. The outer circumferential surface of the bearing93includes a socket95, which receives the pin94. When assembling the rotary impact tool, the bearing93is press fitted into the driver cover91along the rotary axis. Then, the pin94is inserted into the pin hole92from the outer side of the driver cover91. The distal end of the pin94is press fitted into the socket95of the bearing93. The pin94restricts separation of the bearing93from the driver cover91. Finally, the driver cover91is covered with a protector96to hide the head of the pin94. If the head of the pin94were visible from the driver cover91, this would deteriorate the outer appearance of the rotary impact tool. The protector96improves the design of the rotary impact tool and hides the pin94. However, the protector96increases the number of components.

It is an object of the present invention to provide a rotary impact tool that restricts separation of the bearing and improves the design without increasing the number of components.

One aspect of the present invention is a rotary impact tool including an anvil, a bearing, a driver cover, and a bearing separation restricting component. The anvil receives rotational impact force from a hammer of an impact mechanism. The bearing holds the anvil. The driver cover covers the impact mechanism. The bearing is press fitted into and fixed to the driver cover. The bearing separation restricting component is configured to restrict separation of the bearing from the driver cover. The bearing separation restricting component is hidden inside the driver cover and is invisible from an outer surface of the driver cover.

The present invention provides a rotary impact tool that restricts separation of the bearing and improves the design without increasing the number of components.

DETAILED DESCRIPTION OF THE EMBODIMENTS

One embodiment of a rotary impact tool will now be described.

Referring toFIG. 1, a rotary impact tool11is a portable power tool that can be held with a single hand. The rotary impact tool11is used as, for example, an impact driver or an impact wrench. The rotary impact tool11includes a housing12, which serves as an outer shell. The housing12includes a barrel13and a grip14, which extends downward from the barrel13. A trigger lever28is supported by the grip14.

The barrel13accommodates a motor15, which serves as a rotational drive source. The motor15includes an output shaft16that extends toward the distal end (right end as viewed inFIG. 1) of the barrel13. The motor15is a DC motor such as a brush motor or a brushless motor. An impact mechanism17is coupled to the output shaft16of the motor15.

In a low-load state, the impact mechanism17reduces the speed of the rotation produced by the motor15and generates a high-torque rotational output. In a high-load state, the impact mechanism17generates rotational impact force from the rotation produced by the motor15. In the illustrated example, the impact mechanism17includes a reduction mechanism18, a hammer19, an anvil20, and an output shaft21. The reduction mechanism18reduces the rotation speed of the motor15by a predetermined reduction ratio. The rotation of which the speed is reduced and the torque is increased by the reduction mechanism18is transmitted to the hammer19. The hammer19strikes the anvil20. The striking of the anvil20rotates the output shaft21. The output shaft21and the anvil20may be integrated into a single component. Alternatively, the output shaft21may be a component that is separate from and coupled to the anvil20.

The hammer19is rotatable relative to a drive shaft22, which is rotated by the reduction mechanism18, and movable along the drive shaft22. A coil spring24is arranged between the reduction mechanism18and the hammer19. The coil spring24urges the hammer19toward the anvil20. The hammer19is normally in contact with the anvil20in the axial direction due to the elastic force of the coil spring24. The hammer19includes hammer heads19a, which abuts against radially outer portions of the anvil20that define anvil claws20awhen the hammer19rotates. The rotation of the drive shaft22, the speed of which has been reduced by the reduction mechanism18, causes the hammer heads19ato abut against the anvil claws20ain the circumferential direction and rotate the anvil20integrally with the hammer19. This rotates the output shaft21.

A chuck13aprojects from the distal end (right end as viewed inFIG. 1) of the barrel13. A bit23is attached to the chuck13a. The chuck13a, which is rotated integrally with the output shaft21, rotates the bit23. The load applied to the output shaft21increases as the bit23tightens a fastener, such as a bolt (not shown), and when the bit23loosens a fastener. When a predetermined amount of force or greater acts between the hammer19and the anvil20, the hammer19compresses the coil spring24and moves rearward (leftward as viewed inFIG. 1) along the drive shaft22. When the hammer heads19aof the hammer19are disengaged from the anvil claws20aof the anvil20, the hammer19rotates freely. As the hammer19rotates freely, the urging force of the coil spring24returns the hammer19to the position where the hammer19is engageable again with the anvil20. As a result, the hammer19strikes the anvil20. The output shaft21receives a large load when the hammer19strikes the anvil20. The load is repetitively applied whenever the hammer19rotates freely relative to the anvil20against the urging force of the coil spring24. In this manner, the rotary impact tool11tightens or loosens a fastener such as a bolt.

A torque sensor25is coupled to the output shaft21of the rotary impact tool11. The torque sensor25may be a strain sensor that detects the strain of the output shaft21. The torque sensor25detects the strain of the output shaft21, which corresponds to the rotational impact force (impact torque) applied to the output shaft21, and outputs a torque detection signal, which has a voltage corresponding to the strain. The torque detection signal is provided via a slip ring26, which is arranged on the output shaft21, to a control circuit40, which controls the motor15.

The control circuit40is arranged on, for example, a circuit board27in the grip14. The circuit board27may include a drive circuit50that supplies the motor15with drive current under the control of the control circuit40. A battery pack29is attached in a removable manner to the lower end of the grip14.

The circuit board27is connected to a rechargeable battery30in the battery pack29by power lines31, connected to the motor15by power lines32, and connected to the torque sensor25(slip ring26) by a signal line33. Further, the circuit board27is connected to a trigger switch (not shown) that detects operation of the trigger lever28.

A bearing61that holds the anvil20and a structure that restricts separation of the bearing61will now be described.

In the example shown inFIG. 2, the anvil20is a one-piece component integrated with the output shaft21. The anvil20is supported in a rotatable manner by the bearing61near the distal end of the barrel13(refer toFIG. 1) of the housing12. The bearing61is press fitted into and fixed to a driver cover62, which forms the barrel13. The driver cover62covers the impact mechanism17including the hammer19. The driver cover62may be a one-piece member.

Referring toFIG. 2, the rotary impact tool11has a rotary axis AX. The anvil20rotates about the rotary axis AX. An elastic component, which may be a C-shaped spring65, extends around the rotary axis AX.

As shown in the enlarged view ofFIG. 3, the driver cover62has an inner circumferential surface that is a wall surface of a cylindrical bore. The inner circumferential surface includes a first groove63that extends in the circumferential direction. The bearing61has an outer circumferential surface including a second groove64that extends in the circumferential direction. The first groove63cooperates with the second groove64to form a void that receives the C-shaped spring65. The C-shaped spring65is arranged in the void in a slightly deformed state, or nearly non-deformed state, in which the interval between the two ends of the C-shaped spring65is narrowed. The elastic force that widens the interval between the two ends abuts the C-shaped spring65against the bottom surface of the first groove63and positions the driver cover62. In this state, the C-shaped spring65occupies a portion of the second groove64. More specifically, when cutting the C-shaped spring65along a plane orthogonal to the rotary axis AX, the outer half of the C-shaped spring65is located in the first groove63, and the remaining inner half of the C-shaped spring65is located in the second groove64.

The C-shaped spring65is used in a strongly deformed state and a lightly deformed state, which is a state between the strongly deformed state and a non-deformed state. For example, the C-shaped spring65is in the strongly deformed state just before the bearing61is completely press fitted into the driver cover62, and the C-shaped spring65is in the lightly deformed state when the bearing61is completely press fitted into the driver cover62. In the illustrated example, the C-shaped spring65is completely accommodated in the second groove64when in the strongly deformed state and accommodated in both of the first groove63and the second groove64when in the lightly deformed state. The outer portion of the C-shaped spring65presses the bottom surface of the first groove63outward in the radial direction. The inner portion of the C-shaped spring65is accommodated in the second groove64. A gap extends between the inner portion of the C-shaped spring65and the bottom surface (deepest portion) of the second groove64.

The bearing61is press fitted into the driver cover62as described below.

First, the bearing61is press fitted into the driver cover62with the C-shaped spring65accommodated in the second groove64of the bearing61in the strongly deformed state. When the second groove64is aligned with the first groove63, the bearing61is completely press fitted into the driver cover62. Simultaneously, the C-shaped spring65is released from the strongly deformed state in the void formed by the two grooves63and64and shifted to the lightly deformed state. This restricts separation of the bearing61from the two grooves63and64. The first groove63of the driver cover62corresponds to a first recess or an outer recess, and the second groove64of the bearing61corresponds to a second recess or an inner recess. The C-shaped spring65corresponds to a bearing separation restricting component. The C-shaped spring65may be referred to as a non-linear or curved elastic component. The grooves63and64may each be a curved groove or an annular groove.

The operation of the rotary impact tool11will now be described.

The motor15produces rotation when a user operates the trigger lever28. The impact mechanism17converts the rotation of the motor15to a rotational impact force applied to the anvil20of the output shaft21. The rotational impact force from the impact mechanism17rotates the output shaft21including the anvil20. The rotational impact force generates vibration that may act to separate the bearing61, which holds the anvil20, from the driver cover62in the axial direction (leftward direction indicated by arrow inFIG. 4).

In the present example, however, the C-shaped spring65, which is located between the bearing61and the driver cover62, does not allow the bearing61to move in the axial direction. This restricts separation of the bearing61from the driver cover62. As a result, a fastener such as a bolt may be tightened and loosened in a desirable manner with the anvil20appropriately held by the bearing61.

The C-shaped spring65is hidden inside the driver cover62and is invisible from the outer surface of the driver cover62. Thus, the present example does not use a protector to cover the driver cover62.

The above embodiment has the advantages described below.

(1) The C-shaped spring65restricts separation of the driver cover62from the bearing61. Further, the C-shaped spring65is hidden inside the driver cover62and is invisible from the outer surface of the driver cover, and there is no need for a protector. This allows for design improvements. Thus, separation of the bearing61is restricted and the design is improved without increasing the number of components.

(2) When arranging the C-shaped spring65in the void formed by the first groove63and the second groove64, the first groove63positions the C-shaped spring65. Further, the C-shaped spring65is arranged over the first groove63and the second groove64. This restricts separation of the bearing61.

(3) When the task for press fitting and fixing the bearing61to the driver cover62is completed, the C-shaped spring65is simultaneously shifted to the lightly deformed state, or nearly non-deformed state, to prevent separation of the bearing61. This improves the coupling efficiency of the bearing61.

(4) The bearing61is not shortened in the axial direction and has a sufficient length that obtains a wide area of contact with the anvil20and reduces friction of the bearing61. This obtains the desired bearing performance.

(5) The bearing61is not longer than necessary. Thus, the driver cover62and, consequently, the barrel13do not increase the entire length of the rotary impact tool11.

(6) Separation of the bearing61is limited while improving the design and obtaining the desired bearing performance without increasing the entire length of the rotary impact tool11.

The depths of the first groove63and the second groove64may be adjusted so that the C-shaped spring65is completely accommodated in the first groove63in the strongly deformed state. In this case, when the bearing61is completely press fitted into the driver cover62, the C-shaped spring65simultaneously shifts to a lightly deformed state and is accommodated in both of the first groove63and the second groove64to restrict separation of the bearing61from the driver cover62.

When the bearing61is completely press fitted into the driver cover62, it is preferred that the C-shaped spring65be simultaneously shifted to the lightly deformed state. Instead, the C-shaped spring65may be shifted to a non-deformed state. In this case, the depths of the first groove63and the second groove64are set to hold the C-shaped spring65at the desired position.

The first recess in the inner circumferential surface of the driver cover62is not limited to a single groove. The inner circumferential surface may include more than one groove arranged in the axial direction. Alternatively, a plurality of non-continuous recesses may be arranged in the rotational direction. In this case, the outer circumferential surface of the bearing61includes second recesses opposing the first recesses, and a bearing separation restricting component is arranged in each void formed by the opposing recesses.

It is preferred that the bearing separation restricting component be an elastic component such as the C-shaped spring65to facilitate coupling. However, a different bearing separation restricting component such as a snap ring may be used.

The structure of the rotary impact tool11may be changed as required.

The invention is not limited to the foregoing embodiments and various changes and modifications of its components may be made without departing from the scope of the present invention. Also, the components disclosed in the embodiments may be assembled in any combination for embodying the present invention. For example, some of the components may be omitted from all components disclosed in the embodiments. Further, components in different embodiments may be appropriately combined. The scope of the present invention and equivalence of the present invention are to be understood with reference to the appended claims.