Abstract:
An impact wrench includes a hammer, an anvil and a rotor driven by a motor, the hammer being swingeable in either direction with respect to the rotary axis of the rotor, the hammer resting on the anvil in a spring-loaded state so as to enable the hammer to line up with the axis of the anvil, the hammer including means for engaging itself with the inside surface of the rotor, whereby the hammer produces impacts at fixed intervals and transmits the same to the anvil.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an impact wrench for use in fastening or unfastening bolts or nuts, and more particularly, to an impact wrench for such use, having an improved rotor system capable of producing impacts at fixed intervals and transmitting the same to the bolt or nut to be fastened or unfastened, in which harsh noises are not caused. 
     A conventional impact wrench has a hammer carried on a rotor driven by a motor, which hammer is caused to rotate in association with the rotor during which the hammer repeats its engagement and disengagement with an anvil, which has a recess to meet the hammer, thereby transmitting impacts thereto. However, this has drawbacks as follows: 
     As the centrifugal force varies with the peripheral speed of the rotor, the strength of the impact differs from impact to impact. In addition, a lubricant oil is unevenly circulated, and is likely to gather at unnecessary parts at the high speed of the rotor. As a result, necessary parts remain unlubricated. What is more, harsh noises are produced each time the hammer hits the anvil, which causes the problem of noise pollution. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     The present invention aims at solving the problems pointed out with respect to the conventional impact wrench, and has for its object to provide an improved impact wrench having an improved arrangement of a rotor, a hammer and an anvil whereby impacts are produced at fixed intervals to fasten or unfasten bolts or nuts. 
     Another object of the present invention is to provide an improved impact wrench capable of producing impacts without causing harsh noise. 
     Other objects and advantages will become more apparent from the following description when taken in connection with the accompanying drawings which show, for the purpose of illustration only, one embodiment in accordance with the present invention. 
     According to the present invention, an impact wrench includes a hammer, an anvil and a rotor driven by a motor, the hammer being swingeable in either direction with respect to the rotary axis of the rotor, the hammer resting on the anvil in such a spring-loaded state as to enable the hammer to line up with the axis of anvil, the hammer including means for engaging itself with the inside surface of the rotor, whereby the rotor transmits its motion to the hammer. 
    
    
     BRIEF EXPLANATION OF THE DRAWINGS 
     FIG. 1 is a vertical cross-section through an impact wrench according to the present invention; 
     FIG. 2 is a vertical cross-section taken along the line A--A in FIG. 1; 
     FIGS. 3 to 7 are cross-sectional views showing the movements of a rotor, a hammer and an anvil included in the embodiment of FIG. 1; 
     FIG. 8 is a vertical cross-section through a modified version of the embodiment; and 
     FIG. 9 is a vertical cross-section taken along the line B--B in FIG. 8. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1 a casing 1 is provided with a handle 2 into which a compressed air is introduced in a known manner to rotate a pneumatic motor 4 in the clockwise or anti-clockwise direction through the operation of a trigger 3 and a changeover-valve (not shown). The pneumatic motor 4 has a rotating shaft 6 to which a cylindrical rotor 5 is spline-connected so as to effect a unitary rotation. As best shown in FIGS. 2 and 3, the cylindrical rotor 5 has a cylindrical inside wall surface 5a on which a lengthwise projection 7 is formed. The projection 7 is defined by recessed sides 7a and 7b, and continuous to round grooves 8a and 8b at its foot. The cylindrical inside wall surface 5a has a round recess 9, which is formed by cutting away the front portion of the projection 7 such that its round surface is on the same curve with the bottoms of the grooves 8a and 8b as shown by dotted lines in FIGS. 3 and 4. 
     An anvil 10 is rotatively provided in the casing 1. In the illustrated embodiment the anvil 10 has a head 10a, a body 10b and a tail 11, wherein the body 10b having a relatively large diameter than that of the head 10a, is fully accommodated in the cylindrical rotor 5. The tail 11 is rotatively inserted in a supporting recess produced in a rear section 5b of the cylindrical rotor 5. The head 10a is adapted to hold a socket (not shown) for supporting a bolt or a nut. 
     The body 10b of the anvil 10 has a slot 12 axially formed to receive a hammer 13, which slot is semi-circular in cross-section as shown in FIGS. 2 to 4. The hammer 13 is rotated in the slot 12 in the clockwise or in the anti-clockwise direction as described below. 
     The hammer 13 has a semi-circular bottom to meet the semi-circular inside surface of the slot 12. The depth of the hammer 13 which sinks in the slot 12 must be carefully decided; its optimum state is shown in FIG. 2 in which opposite side ridges 13a and 13b of the hammer are not engaged in the slot 12, positioning on the plane crossing the diameter of the cylindrical rotor 5 at right angle. The hammer 13 has a top ridge 14 axially projecting. The top ridge 14 is adapted to keep contact with the cylindrical inside surface 5a except when it passes through the region of the recess 9. When the top ridge 14 is in contact with the cylindrical inside surface 5a, the hammer as a whole rotates as shown in FIGS. 3 and 4, and one of the side ridges 13a or 13b comes into engagement with the cylindrical inside surface 5a and slides thereon. As the rotor 5 rotates, the side ridge 5a or 5b continues to slide on the cylindrical inside surface 5a until it comes into engagement with the recessed side 7b or 7a, depending upon the clockwise or the anti-clockwise rotation. The anvil 10 has an internal space 15 which is formed by boring in the bottom of the slot 12. The internal space 15 accommodates a spring 18, which is connected at one end to a pin 17 provided integral with the hammer 13 and at the other end to a pin 16, thereby exerting a pull on the hammer 13. 
     A typical example of the operation will be explained: 
     The pneumatic motor 4 is rotated, for example, in the clockwise direction by operating the trigger 3 and the changeover-valve (not shown). As shown in FIG. 3, the cylindrical rotor 5 is rotated in the clockwise direction with respect to the hammer 13. At this stage, the hammer 13 is caused to swing or tilt against the spring 18 in the clockwise direction, with the side ridge 13a sliding on the cylindrical inside surface 5a. As the rotor 5 is further rotated, the side ridge 13a reaches the round groove 8b as shown in FIG. 4, and as it is still further rotated, the side ridge 13a comes into engagement with the recessed side 7b. In this way the motion of the rotor 5 is transmitted to the anvil 10 through the hammer 13. 
     The engagement of the projection 7 with the hammer 13 takes place during one rotation of the rotor 5. Even when the side ridge 13a of the hammer 13 is free from the cylindrical inside surface 5a of the rotor 5 while passing in the region of the round groove 8b, the top ridge 14 keeps contact with the cylindrical inside surface 5a, thereby enabling the hammer 13 to maintain its tilted posture. When the top ridge 14 is free from the cylindrical inside surface 5a, the other side ridge 13a in turn comes into engagement with the cylindrical inside surface 5a as shown in FIG. 5, thereby enabling the hammer 13 to keep its tilted posture. 
     In these situations the spring 18 gives no influence on the rotation of the anvil 10, because its tension is previously designed not to exceed the sum of the centrifugal force exerting on the hammer 13 due to the rotation of the rotor 5 and the frictional force occurring between the recessed side 7b and the side ridge 13a or 13b. As a result, the engagement of the hammer 13 with the projection 7 is effectively maintained, thereby securing a continuous associated rotation of the rotor 5 and the anvil 10. In this way a bolt or a nut in the socket (not shown) attached to the head 10a of the anvil 10 is rotated for fastening. 
     When the bolt or the nut is rotated to the end and cannot rotate any longer, it works as a brake upon the motor torque. At this stage, so long as the hammer is engaged with the projection 7 of the rotor 5, the rotation of the anvil 10 is slowed down, almost coming to a standstill. Thus the centrifugal force gradually lessens so that the spring 18 can restore its normal state. The hammer 13 is rotated in the anticlockwise direction as shown in FIG. 6, and is caused to line up with the axis of the anvil 10, with the hammer 13 being disengaged from the projection 7 of the rotor 5. Thus, the rotor 5 continues to rotate with the top ridge 14 passing in the region of the round recess 9. At the next stage, the top ridge 14 passes the projection 7, and comes into engagement with the round groove 8a. The hammer 13 is again caused to tilt as shown in FIG. 7, in which the side ridge 13a is placed into engagement with the cylindrical inside surface 5a. 
     At this stage, if any resisting force exceeding the torque of the motor 4 occurs in the anvil 10, the hammer 13 is readily disengaged from the projection 7 of the rotor 5 by overcoming the centrifugal force acting thereon. After one rotation of the rotor 5 the hammer 13 again comes into engagement with the projection 7. As the resisting torque increases, the impact between the hammer 13 and the projection 7 becomes larger. As a result of such repeated impacts the bolt or the nut is fastened. 
     When a bolt or a nut is to be unfastened, the motor 4 is rotated in the reverse direction (the anti-clockwise direction), and the engagement and disengagement between the side ridge 13b and the recessed side 7a are carried out in the same manner as when the motor 4 is rotated in the clockwise direction. 
     Referring to FIGS. 8 and 9 a modified version of the embodiment will be explained: 
     In this embodiment a pair of compression springs 24 and 25 are employed to push the hammer 13. The compression springs 24 and 25 are accommodated in a bore 19 produced transversely through the body 10b of the anvil 10. The reference numeral 20 designates a bar transversely supported in the bore 19, the bar supporting a slider 21 having a crest 21a. The hammer 13 has a bottom recess 23 in which the crest 21a is received. In FIG. 9 the reference numeral 22 designates a lengthwise space communicating with the slot 12, the lengthwise space being adapted to allow the crest 21a of the slider 21 to play in. The compression springs 24 and 25 are respectively provided between the slider 21 and the end portion of the bar 20. 
     In this arrangement, when the hammer 13 is tilted in the clockwise direction in FIG. 9, the slider 21 is caused to move to the left, thereby compressing the left-hand compression spring 24. If the hammer 13 is tilted in the anti-clockwise direction, the right-hand compression spring 25 is compressed. In this way the hammer 13 is constantly urged to line up with the axis of the anvil 10.