The present invention relates to a ratchet wrench suitable for rotating a mechanical joint used in gas pipings, water supply pipings, hot water supply pipings, hydraulic pipings and the like.
A ratchet wrench is a tool in which a pair of fixed and movable jaws having opposed V-shaped nut gripping portions are mounted on a body, and a nut is tightened by fitting the nut between the laws and by rotating the body downwardly, and, when the body is returned upwardly, the movable jaw is automatically opened to idly rotate the wrench itself with respect to the nut.
In such a ratchet wrench, the nut is securely held only when the fixed jaw and the movable jaw are completely closed relative to each other. Thus, in the past, various ratchet wrenches for respective sizes of nuts have been required. To obviate the need for such plural wrenches, the inventors have proposed a ratchet wrench in which a movable jaw is steppingly advanced and retracted by utilizing an eccentric pin so that the single ratchet wrench can cope with nuts of various sizes, as disclosed in Japanese Utility Model Publication No. 2-36700 (1990).
However, the conventional ratchet wrenches including those designed for a nut of a particular size and those which can be steppingly advanced and retracted have a disadvantage that during tightening the nut may be damaged. That is to say, in a ratchet wrench, a space (mouth width) for gripping the nut is set to have a positive tolerance with respect to a reference size of the nut, or oppositely the nut is set to have a negative tolerance. Thus, when the ratchet wrench is rotated while gripping the nut, a gap corresponding to the tolerance is created in the nut gripping portions, with the result that the nut gripping portions are line contacted with edge lines of the nut, thereby damaging the nut.
To avoid such drawbacks of conventional ratchet wrenches stated above, a ratchet wrench which is capable of steplessly or continuously adjusting a space between a movable jaw and a fixed jaw has been proposed which is, for example as shown in U.S. Pat. No. 2,800,045.
FIG. 7 shows an example of such a proposed ratchet wrench. In the figure, a handle 9 is provided with an enlarged hub portion 10 which is integral with an enlarged bearing portion 11, the bearing portion 11 is slotted at 12 in order to rotatably support a knurled threaded nut 13 therein, and a threaded support 31 is threaded into the knurled threaded nut 13. An outer jaw or a movable jaw 20 is pivoted at 23 to the threaded support 31 and an inner jaw or a fixed jaw 15 is pivoted at 17 to the forward end portion of the body 10. By rotating the knurled nut 13 in one direction or the other, the threaded support 31 and the movable jaw 20 connected thereto are advanced or retracted whereby the gap between the movable jaw 20 and the fixed jaw 15 can be steplessly adjusted to be fitted on a nut N to be tightened.
In this conventional ratchet wrench, however, as shown, the pivot point 23 between the movable jaw 20 and the threaded support 31 is out of a horizontal axial line L2 passing through the apexes of both V-shaped nut gripping portions 21, 19 of the movable jaw 20 and the fixed jaw 15, and a straight line L1 connecting between the pivot point 23 and the apex of V-shaped nut gripping portion 21 of the movable jaw forms an angle .theta. relative to the horizontal axial line L2.
Thus, when the nut is tightened by the wrench, as shown, a reaction force R from the nut N is applied to the movable jaw 20 and this reaction force R is dissolved into two component forces R1 and R2, wherein R1 is a component force which is parallel to the line L1, and R2 a component force which is perpendicular to the line L1. However, since this component force R2 contributes to rotation of the movable jaw 20 in a clockwise direction about the pivot point 23, it tends to open the movable jaw 20 relative to the fixed jaw 15. Thus, the conventional ratchet wrench as shown has a drawback in that the movable jaw 20 tends to become disengaged from the nut N during a tightening operation thereof. In addition, since a fraction of a moment applied to the handle 9 for tightening the nut is wasted as a component force for disengaging the wrench from the nut, the moment applied to the handle can not be effectively used for a tightening operation.
These disadvantages are enhanced by the fact that the pivot point 17 between the fixed jaw 15 and the forward end portion of the handle 9 is out of the line L2. Namely, due to the same reasons as stated above, the reaction force R' applied to the fixed jaw 15 from the nut 4 is dissolved into two component forces R1' and R2' and the component force R2' tends to rotate the fixed jaw 15 clockwisely about the pivot point 17, which pushes the movable jaw 20 upwardly. Therefore, the movable jaw 20 is further forced to disengage from the nut being tightened.
In addition, in the conventional ratchet wrench shown in FIG. 7, since the threaded support 31 is bulky and projects out of the body 10, the overall size of the wrench is large and there is a danger of the threaded support 31 being damaged by rough use of the wrench. Further, since the springs 25 and 33 for urging the movable jaw 20 and the fixed jaw 15 to close toward each other are leaf springs and are provided outside the body of the ratchet wrench, the size of the springs is relatively large and not only is damage to the springs possible when the wrench is handled roughly, but also the appearance of the wrench is spoiled.
The present invention was made to solve the above-mentioned conventional drawbacks, and an object of the present invention is to provide a ratchet wrench which is capable of rotating nuts having a variety of sizes while maintaining face-contact with the nut, and without damaging the nut.
Another object of the present invention is to provide a ratchet wrench which presents no danger of disengaging the ratchet wrench from the nut during a tightening operation, thereby, enabling a tightening operation to be effected safely and securely.
A further object of the present invention is to provide a ratchet wrench wherein the moment applied to the handle is effectively used for tightening a nut.
A still further object of the present invention is to provide a ratchet wrench wherein the overall size is compact.