1. Field of the Invention
The present invention relates to a wrench used for tightening and loosening a fastening member such as a bolt, a nut, or a fastening sleeve for a tool holder, and more particularly, to a wrench which includes a wrench body having a ring portion to be engaged with an outer circumferential surface of the fastening member, and wedge members disposed on the inner circumferential surface of the ring portion and adapted to be caught between the inner circumferential surface of the ring portion and the outer circumferential surface of the fastening member.
2. Description of the Related Art
A fastening member, such as a bolt, a nut, or a fastening sleeve for a tool holder, is configured to be rotated in a tightening direction or a loosening direction; and such a fastening member is tightened or loosened through an operation of rotating, in the tightening or loosening direction, a wrench that is engaged with the outer circumference of the fastening member.
A conventional wrench of such a type is disclosed in, for example, Japanese Patent No. 3155888.
FIGS. 1 and 2 shows such a conventional wrench. The wrench 1 shown in FIGS. 1 and 2 includes a wrench body 3 having a ring portion 3a and a handle portion 3b formed integrally with the ring portion 3a. The ring portion 3a has a diameter suitable for disengagable engagement with the outer circumference of a fastening member 2. A plurality of grooves 5 are formed on the inner circumferential surface of the ring portion 3a at predetermined intervals in the circumferential direction so as to extend in the circumferential direction. A roller-shaped wedge member 4 is movably received in each of the grooves 5.
As shown in FIG. 2, each of the grooves 5 has a free region 5a having a relatively large depth and a wedge region 5b located on either side of the free region 5a and shallower than the free region 5a. Further, spring accommodation spaces 6 are formed in the ring portion 3a at circumferential locations corresponding to those of the grooves 5. A guide hole 7 is formed in a partition wall 6a between each of the spring accommodation spaces 6 and the corresponding groove 5 at a location facing the free region 5a. A cylindrical member 8 is disposed in the guide hole 7 to be projectable toward the corresponding groove 5. Moreover, a plate spring 9 is disposed within each of the spring accommodation spaces 6 in order to urge the corresponding cylindrical member 8 to project toward the corresponding groove 5. Therefore, before the ring portion 3a of the wrench 1 is engaged with the fastening member 2, as illustrated by a solid line in FIG. 2, each wedge member 4 is located in the left-hand or right-hand wedge region 5b, because of pressing force applied from the cylindrical member 8.
The conventional wrench 1 having the above-described configuration is used as follows. When the fastening member 2 is to be tightened by use of the wrench 1, the ring portion 3a of the wrench 1 is engaged with the fastening member 2, and then the wrench 1 is rotated in a direction of arrow A in FIG. 2. As result, as indicated by a solid line in FIG. 2, each wedge member 4 is pushed into the right-hand wedge region 5b, whereby the wedge member 4 is caught between the wall surface of the wedge region 5b and the outer circumferential surface of the fastening member 2, and thus the wrench 1 and the fastening member 2 are united. Therefore, the fastening member 2 is tightened through an operation of rotating the wrench 1 in the same direction.
When the fastening member 2 is to be loosened by use of the wrench 1, the ring portion 3a of the wrench 1 is engaged with the fastening member 2, and then the wrench 1 is rotated in a direction of arrow B in FIG. 2. As result, as indicated by an imaginary line in FIG. 2, each wedge member 4 is pushed into the left-hand wedge region 5b, whereby the wedge member 4 is caught between the wall surface of the wedge region 5b and the outer circumferential surface of the fastening member 2, and thus the wrench 1 and the fastening member 2 are united. Therefore, the fastening member 2 is loosened through an operation of rotating the wrench 1 in the same direction.
In such a conventional wrench 1, in a state in which the ring portion 3a of the wrench 1 is not engaged with the fastening member 2, as shown in FIG. 2, each wedge member 4 is located in the left-hand or right-hand wedge region 5b, because of pressing force applied from the corresponding plate spring 9 via the corresponding cylindrical member 8, and a portion of the wedge member 5 projects outward from the inner circumferential surface of the ring portion 3a. Therefore, when the ring portion 3a of the wrench body 3 is engaged with the fastening member 2, the above-mentioned projecting portion of the wedge member 4 interferes with the fastening member 2 and hinders smooth engagement of the ring portion 3a with the fastening member 2.
Moreover, the conventional wrench 1 is configured in such a manner that within each groove 5 the wedge member 4 is restrained in the left-hand or right-hand wedge region 5b by means of the corresponding plate spring 9 and the corresponding cylindrical member 8. This hinders smooth movement of the wedge member 4 within the groove 5 from one wedge region 5b to the other wedge region 5b and thus renders the movement unstable. Moreover, attainment of a state where all the wedge members 4 are located in the wedge regions 5b of the same side is not guaranteed; and, in some cases, some wedge members 4 are located in the left-hand wedge regions 5b, whereas the remaining wedge members 4 are located in the right-hand wedge regions 5b. In such a case, some wedge members 4 fail to operate properly, and thus hinder the operation of tightening or loosening the fastening member 2. In order to avoid such a problem, the positions of some wedge members 4 must be corrected such that all the wedge members 4 are located in the wedge regions 5b of the same side. Such position correction operation lowers the efficiency of work for tightening or loosening the fastening member 2.