Tools – Wrench – screwdriver – or driver therefor – Handle clutched to head
Reexamination Certificate
2000-06-20
2001-10-16
Smith, James G. (Department: 3723)
Tools
Wrench, screwdriver, or driver therefor
Handle clutched to head
C081S063000
Reexamination Certificate
active
06301999
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a ratchet wrench for selectively applying torque to a fastener.
BACKGROUND OF THE INVENTION
Many types of ratchet wrenches are known in the art. One known type includes a wrench body, a ratchet gear having a plurality of gear teeth radially arranged on an outer peripheral surface thereof, and a spring loaded pawl having a set of gear engaging teeth. The pawl is generally received in a slot of the wrench body with the pawl being slidable within the slot. The spring urges the pawl into engagement with the ratchet gear such that the teeth thereof engage the ratchet gear teeth. As the wrench body is manually moved in a direction to apply torque to a fastener, the pawl teeth engage the gear teeth so that movement of the wrench body is applied as torque to the ratchet gear, which in turn is transmitted to the fastener As the wrench body is moved in the opposite direction, the pawl teeth disengage from and ride over the gear teeth against the biasing of the spring in a ratcheting manner. Examples of such wrenches are disclosed in U.S. Pat. Nos. 3,186,265 and 3,838,614.
One shortcoming of these types of wrenches is that when applying torque, the engagement between the gear engagement teeth of the pawl and the ratchet gear teeth results in significant shearing forces being transmitted through the pawl. For example, in the '265 patent when torque is being applied to a fastener, a substantial amount of shear stress is generated within the pawl. Specifically, the forces applied between the pawl and the gear are at an angle with respect to the direction in which the pawl is supported, thereby tending to cantilever the pawl against its supporting surface and generating the shear stress. It is known that yielding occurs under shear at a lower value than under tension/compression. The maximum shear stress criterion says that the amount of stress required for yielding under shear is half the value required for yielding under tension/compression. As a result, the pawl must be made more robust to prevent such yield. Further, in the wrench of the '265 patent when torque is applied most of the force applied to the gear is applied to only one gear tooth. As a result, because the gear is a ring-type gear, the gear wall thickness must be increased to withstand having the force localized in one area in such a manner.
Consequently, there is a need for providing a ratchet wrench wherein the transferal of forces from the pawl to the gear is handled in a more effective manner so as to reduce the stresses in one or both of those components.
SUMMARY OF THE INVENTION
It is an object of the present invention to meet the above-described need. This objective is achieved by providing a ratchet wrench for selectively applying torque to a fastener constructed in accordance with the principles of the present invention. The wrench comprises a wrench body having a handle portion configured to be manually grasped and a pawl engaging surface. A ratchet gear is constructed and arranged to be removably engaged with the fastener such that torque applied to the gear is transmitted to the fastener to effect rotation thereof The ratchet gear is mounted to the wrench body such that the gear and the body are rotatable relative to one another about a gear axis. The ratchet gear has a plurality of gear teeth arranged on a radially outer peripheral surface thereof in circumferential relation with respect to the gear axis. Each of the teeth has opposing tooth surfaces.
The wrench comprises a pawl having first and second spaced apart tooth engaging surfaces and a load receiving surface opposite the first and second tooth engaging surfaces. The pawl is mounted to the wrench body for pivotal movement about a pawl axis with the load receiving surface thereof engaging the pawl engaging surface of the wrench body. The pawl is movable to a gear driving position wherein the first and second tooth engaging surfaces of the pawl is positioned for driving engagement with respective tooth surfaces of a pair of the gear teeth. A manual force applied in a torque applying direction to the handle portion of the wrench body is transmitted from the wrench body to the pawl via the engagement between the pawl engaging surface and the load receiving surface and from the pawl to the ratchet gear via the engagement between the tooth engaging surfaces and the aforesaid tooth surfaces of the pair of the gear teeth so as to apply torque to the gear.
The pawl is constructed and arranged with respect to the gear teeth and the pawl engaging surface such that in the gear driving position thereof a first portion of the manual force is transmitted through the pawl from the load receiving surface thereof to the first tooth engaging surface thereof for application to one of the gear teeth. A second portion of the manual force is transmitted through the pawl from the load receiving surface to the second tooth engaging surface thereof for application to the other of the gear teeth. The first and second portions of the manual force are transmitted through the pawl being in a balanced relation with respect to the pawl axis so that the first and second portions of the manual force offset each other about the pawl axis and the pawl is compressed between the pawl engaging surface and the first and second tooth engaging surfaces.
The wrench also comprises a biasing element engaged with the pawl and biasing the pawl to the gear driving position. The pawl is constructed and arranged with respect to the gear teeth such that a manual force applied in a ratcheting direction to the handle portion opposite the torque applying direction causes rotation of the wrench body relative to the ratchet gear with the pawl repeatedly ratcheting over the gear teeth against the biasing of the biasing element.
Because the first and second portions of the manual force offset one another, there is no tendency for the pawl to pivot (if it is unsupported) or bend (if it is supported) and thus the pawl is in compression with no significant shearing forces within the pawl. As a result, the pawl can be made with a smaller cross-section thus requiring less space within the wrench to be dedicated to accompanying the pawl.
In a more specific aspect of the invention, the gear has a ring-shaped wall providing the outer peripheral surface with the gear teeth. The ring-shaped wall has a fastener receiving opening defined by a plurality of fastener engaging surfaces engageable with a fastener receivable in the fastener receiving opening. Because the manual force is applied by the pawl to the pair of the gear teeth in balanced relation and not localized on one tooth, the ring-shaped wall can be made thinner than in the type of wrench disclosed in the '265 patent due to better distribution of forces.
These and other objects, features, and advantages of this invention will become apparent from the following detailed description when taken into conjunction with the accompanying drawings, which are a part of this disclosure and which illustrate, by way of example, the principles of this invention.
REFERENCES:
patent: 207117 (1878-08-01), Hammond
patent: D. 322203 (1991-12-01), Kanyuck, Sr.
patent: 1029271 (1912-06-01), Bosserman
patent: 1426127 (1922-08-01), Tuttle
patent: 1453607 (1923-05-01), Saucier
patent: 1868840 (1932-07-01), McNaught et al.
patent: 1883618 (1932-10-01), Dodge
patent: 2294510 (1942-09-01), Nakano
patent: 3186265 (1965-06-01), Wenturine et al.
patent: 3349653 (1967-10-01), Kaufman et al.
patent: 3838614 (1974-10-01), O'Donnell
patent: 4327611 (1982-05-01), Catanese et al.
patent: 4463632 (1984-08-01), Parke
patent: 4515044 (1985-05-01), Harstad
patent: 4622870 (1986-11-01), Shirley
patent: 4993288 (1991-02-01), Anderson et al.
patent: 5218891 (1993-06-01), Olson et al.
patent: 5230263 (1993-07-01), Kwaka
patent: 5280740 (1994-01-01), Ernst
patent: 5331869 (1994-07-01), Webb
patent: 5392672 (1995-02-01), Larson et al.
patent: 5454283 (1995-10-01), Stefano
patent: 5636557 (1997-06-01), Ma
patent: 5694818 (1997-12-01
Pillsbury & Winthrop LLP
Smith James G.
The Stanley Works
Thomas David B.
LandOfFree
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