Known wrenches can be divided into two categories, closed-end wrenches and open-end wrenches. As the terms are used herein, closed-end wrenches are those which must be applied axially to a nut, bolt head, or other torque receiving surface, while open-end wrenches are those which can be applied either axially or radially to a torque receiving surface.
Torque receiving surfaces themselves also generally break down into two categories, those having relatively smooth exteriors such as pipes or dowels, and those having defined sides and corners, such as nuts or bolt heads. With respect to torque receiving surfaces having defined sides and comers, the surfaces may or may not protrude from the body of the component, but in all cases the defined sides and comers would cooperate to form what is referred to herein as a nub. It will also be appreciated that the comers of a nub may be square or have some other angle, depending in general on whether the nub has four or more sides. As the term is used herein, a corner includes "rounded" or "non-sharp" comers as well as typical "sharp" corners.
Closed-end wrenches typically have four to eight contact faces, and are usually designed to contact all torque receiving surfaces at the same time. Such wrenches are typified by common box or socket type wrenches. Closed-end wrenches are often coupled to a ratcheting mechanism, which permits turning of a nub through more than 360.degree. without removing the wrench from the nub and without moving the wrench handle through more than 360.degree..
Open-end wrenches typically have only about three to five contact surfaces. This allows the wrench to engage an object from the side, but also generally precludes the wrench from engaging all the torque receiving surfaces or comers at the same time. Thus, for example, a typical open-end wrench never engages more than one half the corners of a nub at any given time, even though the wrench may engage two thirds of the sides of the nub (as in a hexagonal nub) or even three fifths of the sides (as in a pentagonal nub).
This limited-surface engagement problem has been addressed with respect to smooth torque receiving surfaces by increasing the number of contacting faces on the wrench, and by providing mechanisms that partially enwrap the torque receiving surfaces during torquing. Examples include U.S. Pat. No. 1,364,582 to Reed, U.S. Pat. No. 716,914 to Mahlen, U.S. Pat. No. 1,675,748 to Bunker, and U.S. Pat. No. 2,784,628 to Meredeth. Significantly, this approach is inapplicable to nub-type torque receiving surfaces because operation of the wrenches include slipping of the contacting surfaces over the torque receiving surfaces, and such slipping would tend to round off the comers of the nubs.
The need to retain the integrity of the comers of nubs generally requires repeated engagement and disengagement of an open-end wrench from a nub to achieve large nub rotation. This engagement/disengagement problem has been addressed to some extent by carrying nub engaging teeth or faces on a moving chain or a plurality of rotating gears (see U.S. Pat. No. 2,353, 642 to Buice, U.S. Pat. No. 5,249,487 to Armfield respectively). The problem has also been addressed by employing teeth that pivot or reciprocate within a narrow range. Examples are U.S. Pat. No. 4,644,830 to Balley et al., U.S. Pat. No. 3,906,822 to Hertelendy et al., and U.S. Pat. No. 4,327,610 to Chiarenza. None of these solutions, however, has been completely satisfactory because they cannot also address the limited-surface engagement problem. Thus, there remains a need to provide an open-end wrench which is capable of engaging more than half of the torque receiving comers of a nub while still providing a ratcheting feature.