Tool driving or impacting – Impacting devices – With anvil arranged to transmit torsional impact to tool
Reexamination Certificate
2000-08-04
2001-05-08
Smith, Scott A. (Department: 3721)
Tool driving or impacting
Impacting devices
With anvil arranged to transmit torsional impact to tool
C173S093500, C173S093600, C173S109000, C173S211000
Reexamination Certificate
active
06227308
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to power hand tools, in particular to impact tools, such as impact wrenches.
2. Description of the Prior Art
Impact wrenches for applying intermittent torque impulses to tighten or loosen a fastener are well known. These prior mechanisms include a rotatable drive shaft connected to a motor, a hammer disposed about and coupled to the shaft, and an anvil engageable with a load, either directly or by means of a coupling tool, such as a socket. The anvil has a pair of ears engageable with corresponding ears on the hammer. These impact mechanisms also include a spring for biasing the hammer toward the anvil to engage the hammer ears with the anvil ears and a cam mechanism to allow the hammer to rotate with respect to the shaft and to move axially along the shaft away from the anvil when resistance torque builds up at the workpiece. In a reversible impact wrench, the cam mechanism commonly includes a pair of V-shaped cam ramps or grooves on the exterior of the drive shaft and a corresponding pair of cam ramps or grooves on the interior surface of the hammer and two balls respectively disposed in the grooves. Each leg of each V-shaped groove defines a portion of a helix. When the drive shaft rotates clockwise and enough resistance torque is built up, the cam mechanism causes the hammer to move axially away from the anvil as the balls travel along one respective leg of the V of each groove. When the shaft rotates counterclockwise, the ball travels along the other respective leg of the V of each groove as the hammer retracts axially. Depending on the torque build up, the hammer can retract axially a great enough distance such that the ball bottoms out at the end of the groove of the drive shaft. This can cause the end surfaces of the grooves and the balls to be worn and roughened, making it more difficult for the motor to rotate the shaft, and may require the replacement of either the balls or shaft.
SUMMARY OF THE INVENTION
It is a general object of the invention to provide an improved impact mechanism which avoids the disadvantages of prior impact mechanisms while affording additional structural and operating advantages.
An important feature of the invention is the provision of a reversible impact mechanism which is of relatively simple and economical construction.
Another feature of the invention is the provision of an impact mechanism of the type set forth, which can provide high torque impulses to a load without damage to the shaft or the balls of the impact mechanism.
A further feature of the invention is the provision of an impact mechanism of the type set forth, which does not cause undue stress to a motor after extended use.
Certain ones of these and other features of the invention may be attained by providing an impact mechanism including a motor, a shaft rotatable about an axis and coupled to the motor and having a first shaft groove with first and second axial ends, and a hammer disposed about the shaft and having a first hammer groove. A ball, disposed in the first hammer groove and in the first shaft groove couples the hammer to the shaft for relative axial and rotatable movement with the ball moveable along the grooves. The mechanism also includes a rotatable anvil for coupling to a load, a bias member resiliently biasing the hammer axially into engagement with the anvil and stop structure disposed along the shaft for engagement with the hammer to limit axial movement of the hammer away from the anvil so as to prevent the ball from contacting the second axial end of the first shaft groove.
The invention consists of certain novel features and a combination of parts hereinafter fully described, illustrated in the accompanying drawings, and particularly pointed out in the appended claims, it being understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention.
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DeRome Raymond D.
Ghode Anil P.
Griffin Paul W.
Shaw Seyfarth
Smith Scott A.
Snap-on Tools Company
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