Patent Application
20150202750
This invention relates generally to power driven tools, and more specifically, it relates to a power driven tool for tightening or loosening fasteners having an impact drive with a twin hammer clutch.
Power driven tools for tightening or loosening fasteners (e.g., nuts and bolts) are known, and power driven tools incorporating impact drives that can intermittently provide an increased amount of torque for tightening or loosening fasteners are common.
An impact wrench incorporating a ratchet head is disclosed in co-owned U.S. Pat. No. 4,821,611 (Izumisawa). A pneumatic motor rotates a clutch case that coaxially houses an impact drive. Under normal operation, a cam ball fixed within the clutch case engages a finger of an impact clutch and rotates the clutch simultaneously with an output shaft for tightening or loosening the fastener. But when frictional resistance of the fastener exceeds the normal torque output of the tool, the cam ball slides under the impact clutch finger and pushes the clutch axially forward along the output shaft. This simultaneously moves a pair of hammers forward into registration with a corresponding pair of anvils of the output shaft. The hammers instantaneously impact the anvils and produce an increased amount of torque in the output shaft for overcoming the frictional resistance of the fastener. Immediately following the impact, the hammers retreat axially rearward and when the cam ball makes one full rotation with the clutch case, the impact process repeats.
However, the clutch case and cam ball generally move at a rate equal to the output speed of the motor, which is very high for pneumatic motors. Therefore when the output shaft is unable to turn the fastener, the cam ball repeatedly pushes the impact clutch and hammers axially forward at a similar rate. This often occurs so rapidly that the hammers impact the anvils before corresponding surfaces fully register, or alternatively the hammers completely miss the anvils and fail to produce any additional torque. Moreover, when the frictional resistance of the fastener exceeds the additional torque produced by the hammers, the cam ball, and impact clutch may unnecessarily push the hammers into repeated registration with the anvils before an operator can disengage the motor. This can be hard on components of the impact drive (e.g., the cam ball and impact clutch) and may damage them or prematurely wear them out before other components of the wrench.
Co-owned U.S. Pat. No. 7,080,578 (Izumisawa) incorporates a speed reducing mechanism in the power driven impact wrench. This particular design reduces the speed of the motor output and controls the impact rate of the hammers of the impact drive. While the components of the impact drive are less prone to damage and wear, the speed reducing mechanism requires the use of additional components which add complexity to the tool.
Accordingly, there is a need for a power driven ratchet tool having an impact drive capable of providing adequate damage and wear protection without using a speed reducing mechanism.
This invention relates generally to a power driven tool for rotating a mechanical element. In one aspect, the tool comprises a housing and a motor positioned in the housing having an output shaft extending therefrom. The shaft rotates relative to the housing during motor operation. In addition, the tool has an impact drive axially fixed within the housing and operatively connected to the motor output shaft. The impact drive includes a base, an anvil shaft having an anvil extending therefrom rotatably mounted on the base, and a plurality of annular hammers. Each hammer has opposite impact lands pivotally mounted on the base for movement between three positions, including a forward position in which the respective hammer is positioned so one of said impact lands engages the anvil, a reverse position in which the respective hammer is positioned so another of said impact lands engages the anvil, and a disengaged position in which neither of the impact lands engages the anvil. The tool also includes a ratchet mechanism operatively connected to the anvil shaft of the impact mechanism. The ratchet mechanism includes an output drive mounted for rotation relative to the housing for rotating a mechanical element in a selected direction.
In another aspect of the invention, the tool comprises a housing having first and second ends and a longitudinal axis extending between the first and second ends. Further, the tool has an output drive rotatably mounted on the housing for operatively engaging the mechanical fastener and a motor positioned in the housing having an output shaft. The tool also has an impact drive positioned in the housing and functionally connecting the motor and the output drive. The impact drive includes a base, an anvil shaft having an anvil extending therefrom rotatably mounted on the base, and a plurality of annular hammers. Each hammer has opposite impact lands pivotally mounted on the base for movement between three positions. The three positions include a forward position in which the respective hammer is positioned so one of said impact lands engages the anvil, a reverse position in which the respective hammer is positions so another of said impact lands engages the anvil, and a disengaged position in which neither of the impact lands engages the anvil.
In yet another aspect of the invention, the tool comprises an elongate tubular housing sized for being held in one hand and a pneumatic motor in the housing having an output shaft adapted for rotation. The tool also has an impact drive axially fixed within the housing and operatively connected to the motor output shaft. The impact drive includes a base, an anvil shaft having an anvil extending therefrom rotatably mounted on the base, and a plurality of annular hammers, each hammer having opposite impact lands pivotally mounted on the base for movement between three positions, including a forward position in which the respective hammer is positioned so one of said impact lands engages the anvil, and a reverse position in which the respective hammer is positioned so another of said impact lands engages the anvil. The respective hammer impacts the anvil on the shaft in response to loading on the impact drive exceeding a predetermined torque to instantaneously increase torque provided to the anvil shaft. Moreover, the tool has a ratchet mechanism operatively connected to the anvil shaft of the impact mechanism. The ratchet mechanism includes an output drive mounted for rotation relative to the housing for rotating a mechanical element in a selected direction.
Other objects and features will be in part apparent and in part pointed out hereinafter.
Corresponding reference characters indicate corresponding parts throughout the drawings.
Referring now to the drawings, and particularly to
Referring to
As illustrated in
The anvil shaft 54 extends through the central openings 68, 70 of the bushing plates 60, 62 and the lobed central openings 80a, 80b of the hammers 52a, 52b. The shaft 54 also has spaced journals 88, 90 corresponding to the central openings 68, 70 in the plates 60, 62. The journals 88, 90 engage the central openings 68, 70 for supporting the shaft 54 and permitting the shaft to rotate in the base 50. Anvils 92a, 92b are provided on the shaft 54 between the journals 86, 88 so lands 94a, 94b, 96a, 96b in the lobed openings 80a, 80b of the hammers 52a, 52b (respectively) can intermittently engage the anvils to provide increased torque as will be explained in greater detail below. In addition, the shaft 54 includes a crank 98 at its forward end for driving the ratchet mechanism 22.
In general operation of the wrench 10, air enters through the air inlet fitting 30 at the rearward end of the grip 12 when the lever 32 is squeezed toward the grip. The air enters the motor 18 where it rotates the rotor 36 including the output shaft 40. The motor shaft 36 rotates the clutch base 50. When required torque is low, the clutch base 50 turns the hammers 52a, 52b which engage the anvils 92a, 92b to turn the shaft 54. The crank 98 orbits the wrench centerline 38, oscillating the ring gear 100. As the ring gear 100 oscillates in one direction, the dog 120 pivots into the dog carrier 114 so the output drive 112 does not turn. As the gear 100 oscillates in another direction, the dog 120 engages the gear so the output drive 112 turns with the gear. When the required torque exceeds some preselected value, the hammers 52a, 52b pivot about the respective pin 74, 76, respectively, disengaging each engaged hammer land 94a and 96b, or 94b and 96a from the anvils 92a, 92b on the shaft 54 and temporarily preventing the crank 98 from driving the ratchet mechanism 22. After the anvils 92a, 92b pass the hammer lands 94a and 96b, or 94b and 96a, the respective hammer 52a, 52b pivots back to a position in which the land engages the anvils 92a, 92b on the next revolution. When the combined spinning mass of the motor rotor 36, base 60, and hammers 52a, 52b act through the hammers to impact the anvils 92a, 92b on the next revolution, an instantaneous torque increase occurs. The torque increase acts to overcome the friction in the mechanical fastener. If the torque exceeds the preselected value on the next revolution the sequence repeats. Otherwise, the impact drive 20 delivers continuous toque.
It is envisioned that the wrench of the present invention can operate at relatively high pressures thus producing relatively high rotational speeds with the motor shaft of the motor. It is therefore a benefit of this wrench 10 that the impact drive 20 is capable of handling high pressures without a speed reducing mechanism or excessively wearing components.
It is further envisioned that the wrench may have other anvil and hammer configurations without departing from the scope of the present invention. For example, it is envisioned the anvil shaft may have one anvil orbiting the shaft. In this embodiment, the anvil strikes a hammer during each half rotation of the shaft. Alternatively, it is envisioned the anvil shaft may have more than two anvils and/or the wrench may have greater numbers of hammers without departing from the scope of the present invention.
Components of the wrench of this invention are made of a suitable rigid material, such as metal (ex., cold-forged steel). But a wrench having components made of different materials does not depart from the scope of this invention.
When introducing elements of the present invention or the preferred embodiments(s) thereof, the articles “a”, “an”, “the”, and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including”, and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.
In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.
As various changes could be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
